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Sample records for ingan single quantum

  1. Materials challenges for devices based on single, self-assembled InGaN quantum dots

    International Nuclear Information System (INIS)

    Oliver, Rachel A; Jarjour, Anas F; Tahraoui, Abbes; Kappers, Menno J; Taylor, Robert A; Humphreys, Colin J

    2007-01-01

    Builiding on earlier studies of single InGaN quantum dots (QDs), we are considering their potential for use in blue- and green-emitting single photon sources. Envisaging a device based on a resonant cavity light emitting diode, we have studied the effect of growing QDs on an underlying AlN/GaN distributed Bragg reflector, and have shown that enhanced single QD emission may be obtained. Additionally, we have studied the effect of the growth and activation of a p-type cap on an underlying QD layer and have shown that the QDs survive the anneal process

  2. Electroluminescence from a single InGaN quantum dot in the green spectral region up to 150 K

    International Nuclear Information System (INIS)

    Kalden, J; Sebald, K; Gutowski, J; Tessarek, C; Figge, S; Kruse, C; Hommel, D

    2010-01-01

    We present electrically driven luminescence from single InGaN quantum dots embedded into a light emitting diode structure grown by metal-organic vapor-phase epitaxy. Single sharp emission lines in the green spectral region can be identified. Temperature dependent measurements demonstrate thermal stability of the emission of a single quantum dot up to 150 K. These results are an important step towards applications like electrically driven single-photon emitters, which are a basis for applications incorporating plastic optical fibers as well as for modern concepts of free space quantum cryptography.

  3. The relation between photoluminescence properties and gas pressure with [0001] InGaN single quantum well systems

    Energy Technology Data Exchange (ETDEWEB)

    Tsutsumi, Toshiaki [Department of Nanosystem Sciences, Yokohama City University, Yokohama 236-0027 (Japan); Alfieri, Giovanni; Kawakami, Yoichi [Department of Electronic Science and Engineering, Kyoto University, Kyotodaigaku-katsura, Nishikyo, Kyoto 615-8510 (Japan); Micheletto, Ruggero, E-mail: ruggero@yokohama-cu.ac.jp [Department of Nanosystem Sciences, Yokohama City University, Yokohama 236-0027 (Japan)

    2017-01-15

    Highlights: • Photoluminescence of InGaN device is variable, there is no clear explanation for this. • We perform an ad-hoc absorption procedure, found that gases on the surface reduce emission. • We found that variability is related to the pressure of the gas in which the sample is immersed. • We point out the role of oxygen as major player in the reduction of photoluminescence. • A model is proposed and explains successfully the dynamical optical processes observed. - Abstract: We show for the first time that photoluminescence of InGaN single quantum wells (SQW) devices is related to the gas pressure in which the sample is immersed, also we give a model of the phenomena to suggest a possible cause. Our model shows a direct relation between experimental behavior and molecular coverage dynamics. This strongly suggests that the driving force of photoluminescence decrease is oxygen covering the surface of the device with a time dynamics that depends on the gas pressure. This aims to contribute to the understanding of the physical mechanism of the so-called optical memory effect and blinking phenomenon observed in these devices.

  4. Ultrafast and band-selective Auger recombination in InGaN quantum wells

    International Nuclear Information System (INIS)

    Williams, Kristopher W.; Monahan, Nicholas R.; Zhu, X.-Y.; Koleske, Daniel D.; Crawford, Mary H.

    2016-01-01

    In InGaN quantum well based light-emitting diodes, Auger recombination is believed to limit the quantum efficiency at high injection currents. Here, we report the direct observation of carrier loss from Auger recombination on a sub-picosecond timescale in a single InGaN quantum well using time-resolved photoemission. Selective excitations of different valence sub-bands reveal that the Auger rate constant decreases by two orders of magnitude as the effective hole mass decreases, confirming the critical role of momentum conservation.

  5. Observations of Rabi oscillations in a non-polar InGaN quantum dot

    International Nuclear Information System (INIS)

    Reid, Benjamin P. L.; Chan, Christopher C. S.; Taylor, Robert A.; Kocher, Claudius; Zhu, Tongtong; Oehler, Fabrice; Emery, Robert; Oliver, Rachel A.

    2014-01-01

    Experimental observation of Rabi rotations between an exciton excited state and the crystal ground state in a single non-polar InGaN quantum dot is presented. The exciton excited state energy is determined by photoluminescence excitation spectroscopy using two-photon excitation from a pulsed laser. The population of the exciton excited state is seen to undergo power dependent damped Rabi oscillations.

  6. Observations of Rabi oscillations in a non-polar InGaN quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Reid, Benjamin P. L., E-mail: benjamin.reid@physics.ox.ac.uk; Chan, Christopher C. S.; Taylor, Robert A. [Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Kocher, Claudius [Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Konstanz University, Konstanz (Germany); Zhu, Tongtong; Oehler, Fabrice; Emery, Robert; Oliver, Rachel A. [Department of Materials Science and Metallurgy, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

    2014-06-30

    Experimental observation of Rabi rotations between an exciton excited state and the crystal ground state in a single non-polar InGaN quantum dot is presented. The exciton excited state energy is determined by photoluminescence excitation spectroscopy using two-photon excitation from a pulsed laser. The population of the exciton excited state is seen to undergo power dependent damped Rabi oscillations.

  7. Non-polar InGaN quantum dot emission with crystal-axis oriented linear polarization

    Energy Technology Data Exchange (ETDEWEB)

    Reid, Benjamin P. L., E-mail: benjamin.reid@physics.ox.ac.uk; Chan, Christopher C. S.; Taylor, Robert A. [Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom); Kocher, Claudius [Department of Physics, University of Konstanz, Konstanz 78457 (Germany); Zhu, Tongtong; Oehler, Fabrice; Oliver, Rachel A. [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

    2015-04-27

    Polarization sensitive photoluminescence is performed on single non-polar InGaN quantum dots. The studied InGaN quantum dots are found to have linearly polarized emission with a common polarization direction defined by the [0001] crystal axis. Around half of ∼40 studied dots have a polarization degree of 1. For those lines with a polarization degree less than 1, we can resolve fine structure splittings between −800 μeV and +800 μeV, with no clear correlation between fine structure splitting and emission energy.

  8. Design analysis of phosphor-free monolithic white light-emitting-diodes with InGaN/ InGaN multiple quantum wells on ternary InGaN substrates

    Directory of Open Access Journals (Sweden)

    Yu Kee Ooi

    2015-05-01

    Full Text Available Phosphor-free monolithic white light emitting diodes (LEDs based on InGaN/ InGaN multiple quantum wells (MQWs on ternary InGaN substrates are proposed and analyzed in this study. Simulation studies show that LED devices composed of multi-color-emitting InGaN/ InGaN quantum wells (QWs employing ternary InGaN substrate with engineered active region exhibit stable white color illumination with large output power (∼ 170 mW and high external quantum efficiency (EQE (∼ 50%. The chromaticity coordinate for the investigated monolithic white LED devices are located at (0.30, 0.28 with correlated color temperature (CCT of ∼ 8200 K at J = 50 A/cm2. A reference LED device without any nanostructure engineering exhibits green color emission shows that proper engineered structure is essential to achieve white color illumination. This proof-of-concept study demonstrates that high-efficiency and cost-effective phosphor-free monolithic white LED is feasible by the use of InGaN/ InGaN MQWs on ternary InGaN substrate combined with nanostructure engineering, which would be of great impact for solid state lighting.

  9. Design analysis of phosphor-free monolithic white light-emitting-diodes with InGaN/ InGaN multiple quantum wells on ternary InGaN substrates

    Energy Technology Data Exchange (ETDEWEB)

    Ooi, Yu Kee, E-mail: Yu.Kee.Ooi@rit.edu; Zhang, Jing, E-mail: Jing.Zhang@rit.edu [Department of Electrical and Microelectronics Engineering, Rochester Institute of Technology, Rochester, New York 14623 (United States)

    2015-05-15

    Phosphor-free monolithic white light emitting diodes (LEDs) based on InGaN/ InGaN multiple quantum wells (MQWs) on ternary InGaN substrates are proposed and analyzed in this study. Simulation studies show that LED devices composed of multi-color-emitting InGaN/ InGaN quantum wells (QWs) employing ternary InGaN substrate with engineered active region exhibit stable white color illumination with large output power (∼ 170 mW) and high external quantum efficiency (EQE) (∼ 50%). The chromaticity coordinate for the investigated monolithic white LED devices are located at (0.30, 0.28) with correlated color temperature (CCT) of ∼ 8200 K at J = 50 A/cm{sup 2}. A reference LED device without any nanostructure engineering exhibits green color emission shows that proper engineered structure is essential to achieve white color illumination. This proof-of-concept study demonstrates that high-efficiency and cost-effective phosphor-free monolithic white LED is feasible by the use of InGaN/ InGaN MQWs on ternary InGaN substrate combined with nanostructure engineering, which would be of great impact for solid state lighting.

  10. Characterization of InP and InGaN quantum dots for single photon sources and AlGaInAs quantum dots in intermediate band solar cells

    International Nuclear Information System (INIS)

    Kremling, Stefan

    2014-01-01

    This thesis describes the characterization of semiconductor quantum dots (QDs) in different material systems with potential applications as single photon emitters or intermediate band solar cells. All investigations were carried out by means of optical spectroscopy methods. First, the theoretical background regarding the physics of QDs with respect to their electronic structure and their associated statistical properties are presented. Especially peculiarities of photon statistics of light are explained. Moreover, a closer look at the physics of solar cells and the respective carrier transport is given. Then experimental methods, which were used to characterize the QD-samples, are briefly explained. First, the components and techniques of optical spectroscopy for the study of individual, isolated QDs are described. Second, different experimental technologies for the characterization of solar cells are discussed. The method for measuring the two-photon-absorption process is explained in detail. The section of experimental results begins with studies of individual and spectrally isolated InP QD. Due to the low surface density of one QD per μm 2 , it is possible to study the physical properties of individual QDs optically without additional lateral sample structuring. Based on power and polarization dependent measurements, various luminescence peaks of a single QD were associated with different exciton states. In addition, the QDs were tested subject to an external magnetic field in a Faraday configuration. Finally, the temporal photon statistics of a single QD was tested using autocorrelation measurement. Afterwards, InP QDs manufactured by cyclic material deposition with growth interruptions were investigated by means of PL spectroscopy. Based on excitation power and time-resolved measurements on the QD ensemble, a bimodal QD distribution of type-I and type-II band alignment was observed. In addition, different exciton states were identified on spectrally isolated

  11. Efficiency droop in nonpolar InGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Schade, Lukas; Schwarz, Ulrich [Fraunhofer Institut fuer Angewandte Festkoerperphysik (IAF), Freiburg im Breisgau (Germany); Institut fuer Mikrosystemtechnik (IMTEK), Universitaet Freiburg, Freiburg im Breisgau (Germany); Wernicke, Tim; Rass, Jens; Ploch, Simon [Institut fuer Festkoerperphysik, Technische Universitaet Berlin (Germany); Weyers, Markus [Ferdinand-Braun-Institut (FBH), Berlin (Germany); Kneissl, Michael [Institut fuer Festkoerperphysik, Technische Universitaet Berlin (Germany); Ferdinand-Braun-Institut (FBH), Berlin (Germany)

    2012-07-01

    InGaN quantum wells (QWs) exhibit a decline of the internal efficiency at high charge carrier excitation. This has been observed for polar as well as for semipolar and nonpolar oriented QWs. Polar stands for the (0001) growth direction with strong piezoelectric fields. Due to the vanishing fields, the orthogonal growth directions (a or m) are called nonpolar, while all directions between are merged as semipolar orientations. In contrast to the polar and many semipolar QWs, nonpolar InGaN QWs provide a special property: optical polarization of the radiative transitions, which is a result of the anisotropic strain within pseudomorphic grown nonpolar QWs. Using this property, the broadened effective emission can be resolved into two fundamental transitions. They are spectrally separated by a defined energy which corresponds to the energy distance of the valence subbands. We studied nonpolar InGaN/InGaN Multi-QWs grown on low defect density GaN substrates with a setup for confocal microscopy. To reach high excitation densities of charge carriers, we use either a combination of an UV laser and highly focusing objectives or an electric pulse generator. The emission is spectrally analysed and compared to established models.

  12. Exciton dynamics in near-surface InGaN quantum wells coupled to colloidal nanocrystals

    DEFF Research Database (Denmark)

    Kopylov, Oleksii; Shirazi, Roza; Yvind, Kresten

    2013-01-01

    We study non-radiative energy transfer between InGaN quantum wells and colloidal InP nanocrystals separated by sub-10nm distance. A significant non-radiative energy transfer between the two layers is accompanied by reduced surface recombination in InGaN.......We study non-radiative energy transfer between InGaN quantum wells and colloidal InP nanocrystals separated by sub-10nm distance. A significant non-radiative energy transfer between the two layers is accompanied by reduced surface recombination in InGaN....

  13. Linearly polarized photoluminescence of InGaN quantum disks embedded in GaN nanorods.

    Science.gov (United States)

    Park, Youngsin; Chan, Christopher C S; Nuttall, Luke; Puchtler, Tim J; Taylor, Robert A; Kim, Nammee; Jo, Yongcheol; Im, Hyunsik

    2018-05-25

    We have investigated the emission from InGaN/GaN quantum disks grown on the tip of GaN nanorods. The emission at 3.21 eV from the InGaN quantum disk doesn't show a Stark shift, and it is linearly polarized when excited perpendicular to the growth direction. The degree of linear polarization is about 39.3% due to the anisotropy of the nanostructures. In order to characterize a single nanostructure, the quantum disks were dispersed on a SiO 2 substrate patterned with a metal reference grid. By rotating the excitation polarization angle from parallel to perpendicular relative to the nanorods, the variation of overall PL for the 3.21 eV peak was recorded and it clearly showed the degree of linear polarization (DLP) of 51.5%.

  14. A Comparison of the recombination efficiency in green-emitting InGaN quantum dots and quantum wells

    International Nuclear Information System (INIS)

    Park, Il-Kyu; Kwon, Min-Ki; Park, Seong-Ju

    2012-01-01

    A comparative investigation of the recombination efficiency of green-emitting InGaN quantum dots (QDs) and quantum wells (QWs) is reported in this paper. Optical investigations using temperature dependent photoluminescence (PL) results showed that the internal quantum efficiency of InGaN QDs at room temperature was 8.7 times larger than that found for InGaN QWs because they provided dislocation-free recombination sites for the electrical charge carriers. The excitation power-dependent PL and electroluminescence results showed that the effect of the polarization induced electric field on the recombination process of electrical charge carriers in the QDs was negligibly small whereas it was dominant in the QWs. These results indicate that InGaN QDs are more beneficial than QWs in improving the luminescence efficiency of LEDs in the green spectral range.

  15. Enhancement of Radiative Efficiency with Staggered InGaN Quantum Well Light Emitting Diodes

    Energy Technology Data Exchange (ETDEWEB)

    Tansu, Nelson; Dierolf, Volkmar; Huang, Gensheng; Penn, Samson; Zhao, Hongping; Liu, Guangyu; Li, Xiaohang; Poplawsky, Jonathan

    2011-07-14

    The technology on the large overlap InGaN QWs developed in this program is currently implemented in commercial technology in enhancing the internal quantum efficiency in major LED industry in US and Asia. The scientific finding from this work supported by the DOE enabled the implementation of this step-like staggered quantum well in the commercial LEDs.

  16. Investigation of self-organized quantum dots in InGaN alloys for photovoltaic devices

    Energy Technology Data Exchange (ETDEWEB)

    Yuan, Jinshe; Wang, Mingyue [Chongqing Normal Univ. (China). Dept. of Physics

    2008-07-01

    The self-organized quantum dots in InGaN alloys grown by metal organic chemical vapor deposition for photovoltaic devices were investigated using photoluminescence spectra, x-ray diffraction and atomic force microscopy measurements. The AFM view of the alloy shows the island-like microstructure appearing to be composed of granular-crystalline in nanometer scale. By analysis of the PL, it has been found that the narrow 493nm emission peak with 490nm and 487nm shoulder peaks was originated from InGaN self-organized quantum dots, which provide a candidate for realizing high efficiencies photovoltaic devices. (orig.)

  17. Measurement of the indium segregation in InGaN based LEDs with single atom sensitivity

    International Nuclear Information System (INIS)

    Jinschek, Joerg; Kisielowski, Christian; Van Dyck, Dirk; Geuens, Philippe

    2003-01-01

    In light emitting diodes (LED) consisting of GaN/InGaN/GaN quantum wells (QWs), the exact indium distribution inside the wells of the active region affects the performance of devices. Indium segregation can take place forming small InGaN clusters of locally varying composition. In the past, we used a local strain analysis from single HRTEM lattice images to determine the In composition inside the InGaN QWs with a resolution of 0.5 nm x 0.3 nm. Truly atomic resolution can be pursued by exploitation of intensity dependencies on the atomic number (Z) of the electron exit-wave (EW). In microscopes with sufficient sensitivity, local variations of amplitude and phase are found to be discrete with sample thickness, which allows for counting the number of atoms in each individual column of ∼0.08 nm diameter. In QW s of ∼17 percent of average indium concentration it is possible to discriminate between pure Ga columns and columns containing 1, 2, 3, or more In atoms because phase changes are discrete and element specific. The preparation of samples with atomically flat surfaces is a limiting factor for the application of the procedure

  18. The atomic structure of polar and non-polar InGaN quantum wells and the green gap problem

    Energy Technology Data Exchange (ETDEWEB)

    Humphreys, C.J., E-mail: colin.humphreys@msm.cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Griffiths, J.T., E-mail: jg641@cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Tang, F., E-mail: ft274@cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Oehler, F., E-mail: fabrice.oehler@lpn.cnrs.fr [CNRS/C2N, Paris Sud University, Route de Nozay, 91460 Marcoussis (France); Findlay, S.D., E-mail: scott.findlay@monash.edu [School of Physics and Astronomy, Monash University, Victoria 3800 (Australia); Zheng, C., E-mail: changlin.zheng@monash.edu [Monash Centre for Electron Microscopy, Monash University, Victoria 3800 (Australia); Etheridge, J., E-mail: joanne.etheridge@mcem.monash.edu [Department of Materials Science and Engineering, Monash University, Victoria 3800 (Australia); Martin, T.L., E-mail: tomas.martin@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Bagot, P.A.J., E-mail: paul.bagot@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Moody, M.P., E-mail: michael.moody@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Sutherland, D., E-mail: danny.sutherland@manchester.ac.uk [School of Physics and Astronomy, Photon Science Institute, University of Manchester, Manchester M13 9PL (United Kingdom); Dawson, P., E-mail: philip.dawson@manchester.ac.uk [School of Physics and Astronomy, Photon Science Institute, University of Manchester, Manchester M13 9PL (United Kingdom); Schulz, S., E-mail: stefan.schulz@tyndall.ie [Tyndall National Institute, Lee Maltings Complex, Dyke Parade, Cork (Ireland); and others

    2017-05-15

    Highlights: • We have studied the atomic structure of polar and non-polar InGaN quantum wells. • The non-polar (11-20) InGaN quantum wells contain indium-rich clusters, unlike the polar (0001) quantum wells. • The electrons and holes in the quantum wells are localised by different mechanisms. - Abstract: We have used high resolution transmission electron microscopy (HRTEM), aberration-corrected quantitative scanning transmission electron microscopy (Q-STEM), atom probe tomography (APT) and X-ray diffraction (XRD) to study the atomic structure of (0001) polar and (11-20) non-polar InGaN quantum wells (QWs). This paper provides an overview of the results. Polar (0001) InGaN in QWs is a random alloy, with In replacing Ga randomly. The InGaN QWs have atomic height interface steps, resulting in QW width fluctuations. The electrons are localised at the top QW interface by the built-in electric field and the well-width fluctuations, with a localisation energy of typically 20 meV. The holes are localised near the bottom QW interface, by indium fluctuations in the random alloy, with a localisation energy of typically 60 meV. On the other hand, the non-polar (11-20) InGaN QWs contain nanometre-scale indium-rich clusters which we suggest localise the carriers and produce longer wavelength (lower energy) emission than from random alloy non-polar InGaN QWs of the same average composition. The reason for the indium-rich clusters in non-polar (11-20) InGaN QWs is not yet clear, but may be connected to the lower QW growth temperature for the (11-20) InGaN QWs compared to the (0001) polar InGaN QWs.

  19. Effects of InGaN barriers with low indium content on internal quantum efficiency of blue InGaN multiple quantum wells

    International Nuclear Information System (INIS)

    Lai, Wang; Jia-Xing, Wang; Wei, Zhao; Xiang, Zou; Yi, Luo

    2010-01-01

    Blue In 0.2 Ga 0.8 N multiple quantum wells (MQWs) with In x Ga 1–x N (x = 0.01–0.04) barriers are grown by metal organic vapour phase epitaxy. The internal quantum efficiencies (IQEs) of these MQWs are studied in a way of temperature-dependent photoluminescence spectra. Furthermore, a 2-channel Arrhenius model is used to analyse the nonradiative recombination centres (NRCs). It is found that by adopting the InGaN barrier beneath the lowest well, it is possible to reduce the strain hence the NRCs in InGaN MQWs. By optimizing the thickness and the indium content of the InGaN barriers, the IQEs of InGaN/InGaN MQWs can be increased by about 2.5 times compared with conventional InGaN/GaN MQWs. On the other hand, the incorporation of indium atoms into the intermediate barriers between adjacent wells does not improve IQE obviously. In addition, the indium content of the intermediate barriers should match with that of the lowest barrier to avoid relaxation. (condensed matter: structure, thermal and mechanical properties)

  20. MOVPE growth and characterization of (In,Ga)N quantum structures for laser diodes emitting at 440 nm

    Energy Technology Data Exchange (ETDEWEB)

    Hoffmann, Veit

    2011-04-18

    The presented work describes the metal organic vapor phase epitaxy and characterization of nitride-based quantum structures which are used in laser heterostructures emitting in the wavelength range between 400 nm and 440 nm. Aiming at current injection and optically pumped laser structures with low threshold current or respectively threshold power densities, the device properties were correlated with the material properties of the indium gallium nitride (InGaN) active region. Furthermore, the influence of the active region and waveguide heterostructure layout on the material gain as well as the modal gain was investigated. In order to understand the InGaN growth process and the formation of structural imperfections, 15 nm-100 nm thick InGaN single layers were deposited on gallium nitride (GaN) on sapphire substrates and analyzed subsequently. It turned out that the spiral pattern of the growth edges around screw dislocations, threading from the substrate to the growth surface, and the formation of additional V-shaped surface defects are the main cause for the deterioration of the crystal perfection of the InGaN. As a result of the transition from a layer-by-layer to a 3D growth regime stable facets with preferred indium incorporation are formed that increase the lateral variation of the indium mole fraction in the layer. The higher indium incorporation at the facets is explained by dynamical elasticity theory and proven by the growth and characterization of InGaN layers on differently oriented GaN. The material properties of the InGaN quantum wells were correlated with laser device properties using 400 nm laser structures: In the case of thin quantum wells the 3D growth results in a lateral variation of the band gap due to variations of the indium mole fraction and the well width. Systematical investigations of laser structures with different band gap fluctuations show an increase of the threshold power density as the lateral variation of the band gap increases. It

  1. Modeling of the Interminiband Absorption Coefficient in InGaN Quantum Dot Superlattices

    Directory of Open Access Journals (Sweden)

    Giovanni Giannoccaro

    2016-01-01

    Full Text Available In this paper, a model to estimate minibands and theinterminiband absorption coefficient for a wurtzite (WZ indium gallium nitride (InGaN self-assembled quantum dot superlattice (QDSL is developed. It considers a simplified cuboid shape for quantum dots (QDs. The semi-analytical investigation starts from evaluation through the three-dimensional (3D finite element method (FEM simulations of crystal mechanical deformation derived from heterostructure lattice mismatch under spontaneous and piezoelectric polarization effects. From these results, mean values in QDs and barrier regions of charge carriers’ electric potentials and effective masses for the conduction band (CB and three valence sub-bands for each direction are evaluated. For the minibands’ investigation, the single-particle time-independent Schrödinger equation in effective mass approximation is decoupled in three directions and resolved using the one-dimensional (1D Kronig–Penney model. The built-in electric field is also considered along the polar axis direction, obtaining Wannier–Stark ladders. Then, theinterminiband absorption coefficient in thermal equilibrium for transverse electric (TE and magnetic (TM incident light polarization is calculated using Fermi’s golden rule implementation based on a numerical integration into the first Brillouin zone. For more detailed results, an absorption coefficient component related to superlattice free excitons is also introduced. Finally, some simulation results, observations and comments are given.

  2. Temperature-dependent fine structure splitting in InGaN quantum dots

    Science.gov (United States)

    Wang, Tong; Puchtler, Tim J.; Zhu, Tongtong; Jarman, John C.; Kocher, Claudius C.; Oliver, Rachel A.; Taylor, Robert A.

    2017-07-01

    We report the experimental observation of temperature-dependent fine structure splitting in semiconductor quantum dots using a non-polar (11-20) a-plane InGaN system, up to the on-chip Peltier cooling threshold of 200 K. At 5 K, a statistical average splitting of 443 ± 132 μeV has been found based on 81 quantum dots. The degree of fine structure splitting stays relatively constant for temperatures less than 100 K and only increases above that temperature. At 200 K, we find that the fine structure splitting ranges between 2 and 12 meV, which is an order of magnitude higher than that at low temperatures. Our investigations also show that phonon interactions at high temperatures might have a correlation with the degree of exchange interactions. The large fine structure splitting at 200 K makes it easier to isolate the individual components of the polarized emission spectrally, increasing the effective degree of polarization for potential on-chip applications of polarized single-photon sources.

  3. Enhancement of coherent acoustic phonons in InGaN multiple quantum wells

    Science.gov (United States)

    Hafiz, Shopan D.; Zhang, Fan; Monavarian, Morteza; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit

    2015-03-01

    Enhancement of coherent zone folded longitudinal acoustic phonon (ZFLAP) oscillations at terahertz frequencies was demonstrated in InGaN multiple quantum wells (MQWs) by using wavelength degenerate time resolved differential transmission spectroscopy. Screening of the piezoelectric field in InGaN MQWs by photogenerated carriers upon femtosecond pulse excitation gave rise to terahertz ZFLAPs, which were monitored at the Brillouin zone center in the transmission geometry. MQWs composed of 10 pairs InxGa1-xN wells and In0.03Ga0.97N barriers provided coherent phonon frequencies of 0.69-0.80 THz depending on the period of MQWs. Dependences of ZFLAP amplitude on excitation density and wavelength were also investigated. Possibility of achieving phonon cavity, incorporating a MQW placed between two AlN/GaN phonon mirrors designed to exhibit large acoustic gaps at the zone center, was also explored.

  4. Near-infrared InN quantum dots on high-In composition InGaN

    Energy Technology Data Exchange (ETDEWEB)

    Soto Rodriguez, Paul E. D.; Gomez, Victor J.; Kumar, Praveen; Calleja, Enrique; Noetzel, Richard [Instituto de Sistemas Optoelectronicos y Microtecnologia (ISOM), Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain)

    2013-04-01

    We report the growth of InN quantum dots (QDs) on thick InGaN layers with high In composition (>50%) by molecular beam epitaxy. Optimized growth conditions are identified for the InGaN layers at reduced growth temperature and increased active N flux resulting in minimized phase separation and defect generation. The InN QDs grown on top of the optimized InGaN layer exhibit small size, high density, and photoluminescence up to room temperature. The InN/InGaN QDs reveal excellent potential for intermediate band solar cells with the InGaN and InN QD bandgap energies tuned to the best match of absorption to the solar spectrum.

  5. Luminescence and ultrafast phenomena in InGaN multiple quantum wells

    International Nuclear Information System (INIS)

    Viswanath, Annamraju Kasi; Lee, J.I.; Kim, S.T.; Yang, G.M.; Lee, H.J.; Kim, Dongho

    2007-01-01

    High quality In 0.13 Ga 0.87 N/GaN multiple quantum wells (MQWs) on (0001) sapphire substrate were fabricated by MOCVD method. The quantum well thickness is as thin as 10 A, and the barrier thickness is 50 A. We have investigated these ultrathin MQWs by continuous wave (cw) and time-resolved spectroscopy in the picosecond time scales in a wide temperature range from 10 to 290 K. In the luminescence spectrum at 10 K, we observed a broad peak at 3.134 eV which was attributed to the quantum wells emission of InGaN. The full width at half maximum of this peak was 129 meV at 10 K and the broadening at low temperatures which was mostly inhomogeneous was thought to be due to compositional fluctuations and interfacial disorder in the alloy. We also observed an intense and narrow peak at 3.471 eV due to the GaN barrier. The temperature dependence of the luminescence was studied and the peak positions and the intensities of the different peaks were obtained. The activation energy of the InGaN quantum well emission peak was estimated as 69 meV. From the measurements of luminescence intensities and lifetimes at various temperatures, radiative and non-radiative recombination lifetimes were deduced. The results were explained by considering only the localization of the excitons due to potential fluctuations

  6. Polarisation of the spontaneous emission from nonpolar and semipolar InGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Schade, Lukas; Schwarz, Ulrich [Department of Microsystems Engineering, University of Freiburg (IMTEK) (Germany); Fraunhofer Institute for Applied Solid State Physics (IAF) (Germany); Ploch, Simon; Wernicke, Tim [Institute of Solid State Physics, Technical University Berlin (Germany); Knauer, Arne; Hoffmann, Veit; Weyers, Markus [Ferdinand-Braun-Institute (FBH) (Germany); Kneissl, Michael [Institute of Solid State Physics, Technical University Berlin (Germany); Ferdinand-Braun-Institute (FBH) (Germany)

    2011-07-01

    Spontaneously emitted light stemming from semipolar and nonpolar InGaN quantum wells is polarized. This property is a consequence of the broken in-plane symmetry of non c-plane wurtzite quantum wells. We studied the polarized photoluminescence of semipolar and nonpolar InGaN/InGaN multi quantum wells grown on low defect density GaN substrates with a setup for confocal microscopy. For excitation of charge carriers we use a 375 nm diode laser. The photoluminescence is collected with an objective of small NA, to avoid polarisation scrambling, and analyzed with a broadband polarizer and a spectrometer. The experimental results are compared to k.p band structure calculations for semipolar and nonpolar InGaN quantum wells. These simulations provide the polarisation degree of the confined states of the valence band and their energetic splitting. Next, from the thermal occupation the polarized spectra are calculated. The comparison with experimental results allows the determination of the valence subband splitting. Our experiments show a splitting of the two topmost valence subbands in nonpolar direction which is larger than predicted.

  7. Origins of efficient green light emission in phase-separated InGaN quantum wells

    International Nuclear Information System (INIS)

    Lai, Y-L; Liu, C-P; Lin, Y-H; Hsueh, T-H; Lin, R-M; Lyu, D-Y; Peng, Z-X; Lin, T-Y

    2006-01-01

    Green-light-emitting InGaN/GaN multiple quantum wells (MQWs) with high luminescent efficiency were grown by metalorganic chemical vapour deposition (MOCVD). The microstructure of the sample was studied by high-resolution transmission electron microscopy (HRTEM) and high-resolution x-ray diffraction, while its optical behaviour was analysed in great detail by a variety of photoluminescence methods. Two InGaN-related peaks that were clearly found in the photoluminescence (PL) spectrum are assigned to quasi-quantum dots (516 nm) and the InGaN matrix (450 nm), respectively, due to a strong phase separation observed by HRTEM. Except for the strong indium aggregation regions (511 meV of Stokes shift), slight composition fluctuations were also observed in the InGaN matrix, which were speculated from an 'S-shaped' transition and a Stokes shift of 341 meV. Stronger carrier localization and an internal quantum efficiency of the dot-related emission (21.5%), higher than the InGaN-matrix related emission (7.5%), was demonstrated. Additionally, a shorter lifetime and 'two-component' PL decay were found for the low-indium-content regions (matrix). Thus, the carrier transport process within quantum wells is suggested to drift from the low-In-content matrix to the high-In-content dots, resulting in the enhanced luminescence efficiency of the green light emission

  8. Carrier redistribution between different potential sites in semipolar (202¯1) InGaN quantum wells studied by near-field photoluminescence

    KAUST Repository

    Marcinkevičius, S.; Gelžinytė, K.; Zhao, Y.; Nakamura, S.; DenBaars, S. P.; Speck, J. S.

    2014-01-01

    © 2014 AIP Publishing LLC. Scanning near-field photoluminescence (PL) spectroscopy at different excitation powers was applied to study nanoscale properties of carrier localization and recombination in semipolar (202¯1) InGaN quantum wells (QWs

  9. Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Davies, M. J.; Dawson, P.; Hammersley, S. [School of Physics and Astronomy, Photon Science Institute, University of Manchester, M13 9PL Manchester (United Kingdom); Zhu, T.; Kappers, M. J.; Humphreys, C. J.; Oliver, R. A. [Department of Material Science and Metallurgy, 27 Charles Babbage Road, University of Cambridge, Cambridge CB3 0FS (United Kingdom)

    2016-06-20

    We report on a comparative study of efficiency droop in polar and non-polar InGaN quantum well structures at T = 10 K. To ensure that the experiments were carried out with identical carrier densities for any particular excitation power density, we used laser pulses of duration ∼100 fs at a repetition rate of 400 kHz. For both types of structures, efficiency droop was observed to occur for carrier densities of above 7 × 10{sup 11 }cm{sup −2 }pulse{sup −1} per quantum well; also both structures exhibited similar spectral broadening in the droop regime. These results show that efficiency droop is intrinsic in InGaN quantum wells, whether polar or non-polar, and is a function, specifically, of carrier density.

  10. Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells

    International Nuclear Information System (INIS)

    Davies, M. J.; Dawson, P.; Hammersley, S.; Zhu, T.; Kappers, M. J.; Humphreys, C. J.; Oliver, R. A.

    2016-01-01

    We report on a comparative study of efficiency droop in polar and non-polar InGaN quantum well structures at T = 10 K. To ensure that the experiments were carried out with identical carrier densities for any particular excitation power density, we used laser pulses of duration ∼100 fs at a repetition rate of 400 kHz. For both types of structures, efficiency droop was observed to occur for carrier densities of above 7 × 10 11  cm −2  pulse −1 per quantum well; also both structures exhibited similar spectral broadening in the droop regime. These results show that efficiency droop is intrinsic in InGaN quantum wells, whether polar or non-polar, and is a function, specifically, of carrier density.

  11. Recombination dynamics and internal quantum efficiency in InGaN

    International Nuclear Information System (INIS)

    Murotani, Hideaki; Andoh, Hiroya; Tsukamoto, Takehiko; Sugiura, Toko; Yamada, Yoichi; Tabata, Takuya; Honda, Yoshio; Yamaguchi, Masahito; Amano, Hiroshi

    2014-01-01

    Recombination dynamics and internal quantum efficiency (IQE) of green luminescent InGaN nanowires with different crystalline qualities have been studied by means photoluminescence (PL) and time-resolved PL spectroscopy. Temperature- and excitation-power-density-dependent PL spectroscopy enabled to evaluate the IQE as a function of excitation power density. The shape of the efficiency curves at low temperature strongly depended on the magnitude of nonradiative recombination processes. This leads to the misestimation of the IQE in the lower quality nanowire. In addition, the PL decay curves were well described by a double exponential function both at 6 and 300 K. The PL decay time of the faster component was affected by nonradiative recombination processes even at low temperature. This indicated that the radiative recombination lifetime cannot be estimated from the PL decay time in the lower quality nanowire. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Spin relaxation in InGaN quantum disks in GaN nanowires

    KAUST Repository

    Banerjee, Animesh; Dog,; Heo, Junseok; Manchon, Aurelien; Guo, Wei; Bhattacharya, Pallab K.

    2011-01-01

    The spin relaxation time of photoinduced conduction electrons has been measured in InGaN quantum disks in GaN nanowires as a function of temperature and In composition in the disks. The relaxation times are of the order of ∼100 ps at 300 K and are weakly dependent on temperature. Theoretical considerations show that the Elliott-Yafet scattering mechanism is essentially absent in these materials and the results are interpreted in terms of the D'yakonov-Perel' relaxation mechanism in the presence of Rashba spin-orbit coupling of the wurtzite structure. The calculated spin relaxation times are in good agreement with the measured values. © 2011 American Chemical Society.

  13. Spin relaxation in InGaN quantum disks in GaN nanowires

    KAUST Repository

    Banerjee, Animesh

    2011-12-14

    The spin relaxation time of photoinduced conduction electrons has been measured in InGaN quantum disks in GaN nanowires as a function of temperature and In composition in the disks. The relaxation times are of the order of ∼100 ps at 300 K and are weakly dependent on temperature. Theoretical considerations show that the Elliott-Yafet scattering mechanism is essentially absent in these materials and the results are interpreted in terms of the D\\'yakonov-Perel\\' relaxation mechanism in the presence of Rashba spin-orbit coupling of the wurtzite structure. The calculated spin relaxation times are in good agreement with the measured values. © 2011 American Chemical Society.

  14. Optoelectronical properties of InGaN quantum well light emitting diodes on semipolar GaN

    Energy Technology Data Exchange (ETDEWEB)

    Rass, Jens; Stascheit, Marcus; Ploch, Simon; Wernicke, Tim; Vogt, Patrick; Kneissl, Michael [Technische Universitaet Berlin, Institute of Solid State Physics, Secretariat EW6-1, Hardenbergstrasse 36, 10623 Berlin (Germany)

    2011-07-01

    The performance of GaN-based light emitting diodes (LEDs) is strongly affected by polarization fields along the c-axis of the crystal. Due to the resulting quantum-confined Stark effect the radiative transition rate is reduced and the emission wavelength is blue-shifted when carriers are injected. By growing the structures on semipolar or nonpolar planes the polarization fields can be significantly reduced or even eliminated. In this work, InGaN single quantum well LEDs have been grown by metal-organic vapor phase epitaxy on different semipolar surfaces such as the (10 anti 11) and (20 anti 21) plane. The optoelectronic properties such as the light output power, the emission wavelength and its shift with injection current as well as the operating voltage have been studied. By employing capacitance-voltage- and current-voltage measurements, the size of the depletion region, the build-in potential, the saturation current and the doping concentrations have been determined. LEDs with emission wavelengths ranging from the violet to the blue and green region are presented and their performance characteristics are compared to LEDs grown on the polar c-plane surface.

  15. Influence of barrier layer indium on efficiency and wavelength of InGaN multiple quantum well (MQW) with and without semi-bulk InGaN buffer for blue to green regime emission

    Energy Technology Data Exchange (ETDEWEB)

    Alam, Saiful [School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA (United States); Georgia Tech-CNRS, UMI 2958, Metz (France); CEA-LETI, Minatec Campus, Grenoble (France); Sundaram, Suresh; Li, Xin; El Gmili, Youssef [Georgia Tech-CNRS, UMI 2958, Metz (France); Jamroz, Miryam E.; Robin, Ivan C. [CEA-LETI, Minatec Campus, Grenoble (France); Voss, Paul L.; Ougazzaden, Abdallah [School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA (United States); Georgia Tech-CNRS, UMI 2958, Metz (France); Salvestrini, Jean-Paul [Georgia Tech-CNRS, UMI 2958, Metz (France); LMOPS, University of Lorraine, EA4423, Metz (France)

    2017-08-15

    The effect of indium (In) in the barrier of InGaN/GaN multiple quantum well (MQW) has been studied for MQWs with and without semi-bulk InGaN buffer. From simulation, the optimum In content in the barrier with 3-5 nm width is 5-7% to get the optimal material quality and internal quantum efficiency (IQE) of ∝65% for 450-480 nm emission range. Simulation shows a reduction of the potential barrier due to band flattening, a more homogeneous distribution of electrons and holes in the active region and subsequently, a more radiative recombination rate with InGaN as barrier layer. Both cathodoluminescence (CL) and photoluminescence (PL) experimental results show a blue-shift of emission wavelength along with an enhancement in the emission intensity when GaN barrier is replaced with InGaN barrier, for a MQW structure both with and without the semi-bulk InGaN buffer. We attribute this blue shift to the reduced polarization mismatch and increased effective bandgap. This InGaN barrier-related improvement in IQE and efficiency droop could be useful for the realization of longer wavelength ''green-gap'' range LEDs where poor IQE and efficiency droop are more prominent due to high indium (In) in the active region. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Simulation and optimization of deep violet InGaN double quantum well laser

    Science.gov (United States)

    Alahyarizadeh, Gh.; Ghazai, A. J.; Rahmani, R.; Mahmodi, H.; Hassan, Z.

    2012-03-01

    The performance characteristics of a deep violet InGaN double quantum well laser diode (LD) such as threshold current ( Ith), external differential quantum efficiency (DQE) and output power have been investigated using the Integrated System Engineering Technical Computer Aided Design (ISE-TCAD) software. As well as its operating parameters such as internal quantum efficiency ( ηi), internal loss ( αi) and transparency threshold current density ( J0) have been studied. Since, we are interested to investigate the mentioned characteristics and parameters independent of well and barrier thickness, therefore to reach a desired output wavelength, the indium mole fraction of wells and barriers has been varied consequently. The indium mole fractions of well and barrier layers have been considered 0.08 and 0.0, respectively. Some important parameters such as Al mole fraction of the electronic blocking layer (EBL) and cavity length which affect performance characteristics were also investigated. The optimum values of the Al mole fraction and cavity length in this study are 0.15 and 400 μm, respectively. The lowest threshold current, the highest DQE and output power which obtained at the emission wavelength of 391.5 nm are 43.199 mA, 44.99% and 10.334 mW, respectively.

  17. Temperature Dependence of Emission Properties of Self-Assembled InGaN Quantum Dots

    International Nuclear Information System (INIS)

    Zhao Wan-Ru; Zhang Jiang-Yong; Zhang Bao-Ping; Weng Guo-En; Liang Ming-Ming; Li Zeng-Cheng; Liu Jian-Ping

    2014-01-01

    Emission properties of self-assembled green-emitting InGaN quantum dots (QDs) grown on sapphire substrates by using metal organic chemical vapor deposition are studied by temperature-dependent photoluminescence (PL) measurements. As temperature increases (15–300 K), the PL peak energy shows an anomalous V-shaped (redshift—blueshift) variation instead of an S-shaped (redshift—blueshift—redshift) variation, as observed typically in green-emitting InGaN/GaN multi-quantum wells (MQWs). The PL full width at half maximum (FWHM) also shows a V-shaped (decrease—increase) variation. The temperature dependence of the PL peak energy and FWHM of QDs are well explained by a model similar to MQWs, in which carriers transferring in localized states play an important role, while the confinement energy of localized states in the QDs is significantly larger than that in MQWs. By analyzing the integrated PL intensity, the larger confinement energy of localized states in the QDs is estimated to be 105.9 meV, which is well explained by taking into account the band-gap shrinkage and carrier thermalization with temperature. It is also found that the nonradiative combination centers in QD samples are much less than those in QW samples with the same In content

  18. Influence of InGaN sub-quantum-well on performance of InAlN/GaN/InAlN resonant tunneling diodes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Haoran; Yang, Lin' an, E-mail: layang@xidian.edu.cn; Hao, Yue [State Key Discipline Laboratory of Wide Bandgap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an 710071 (China)

    2014-08-21

    The resonant tunneling mechanism of the GaN based resonant tunneling diode (RTD) with an InGaN sub-quantum-well has been investigated by means of numerical simulation. At resonant-state, Electrons in the InGaN/InAlN/GaN/InAlN RTD tunnel from the emitter region through the aligned discrete energy levels in the InGaN sub-quantum-well and GaN main-quantum-well into the collector region. The implantation of the InGaN sub-quantum-well alters the dominant transport mechanism, increase the transmission coefficient and give rise to the peak current and peak-to-valley current ratio. We also demonstrate that the most pronounced negative-differential-resistance characteristic can be achieved by choosing appropriately the In composition of In{sub x}Ga{sub 1−x}N at around x = 0.06.

  19. Influence of InGaN sub-quantum-well on performance of InAlN/GaN/InAlN resonant tunneling diodes

    International Nuclear Information System (INIS)

    Chen, Haoran; Yang, Lin'an; Hao, Yue

    2014-01-01

    The resonant tunneling mechanism of the GaN based resonant tunneling diode (RTD) with an InGaN sub-quantum-well has been investigated by means of numerical simulation. At resonant-state, Electrons in the InGaN/InAlN/GaN/InAlN RTD tunnel from the emitter region through the aligned discrete energy levels in the InGaN sub-quantum-well and GaN main-quantum-well into the collector region. The implantation of the InGaN sub-quantum-well alters the dominant transport mechanism, increase the transmission coefficient and give rise to the peak current and peak-to-valley current ratio. We also demonstrate that the most pronounced negative-differential-resistance characteristic can be achieved by choosing appropriately the In composition of In x Ga 1−x N at around x = 0.06

  20. Combining surface plasmonic and light extraction enhancement on InGaN quantum-well light-emitters

    DEFF Research Database (Denmark)

    Fadil, Ahmed; Ou, Yiyu; Iida, Daisuke

    2016-01-01

    and internal quantum efficiency enhancement for InGaN/GaN quantum-well light-emitters. By fabricating dielectric nano-rod pattern on the GaN surface, an optical coating that improves the light extraction is obtained, and furthermore has a low refractive index which blue-shifts the plasmonic resonance of Ag NPs......Surface plasmon coupling with light-emitters and surface nano-patterning have widely been used separately to improve low efficiency InGaN light-emitting diodes. We demonstrate a method where dielectric nano-patterning and Ag nanoparticles (NPs) are combined to provide both light extraction...

  1. Iodine-stabilized single-frequency green InGaN diode laser.

    Science.gov (United States)

    Chen, Yi-Hsi; Lin, Wei-Chen; Shy, Jow-Tsong; Chui, Hsiang-Chen

    2018-01-01

    A 520-nm InGaN diode laser can emit a milliwatt-level, single-frequency laser beam when the applied current slightly exceeds the lasing threshold. The laser frequency was less sensitive to diode temperature and could be finely tuned by adjusting the applied current. Laser frequency was stabilized onto a hyperfine component in an iodine transition through the saturated absorption spectroscopy. The uncertainty of frequency stabilization was approximately 8×10 -9 at a 10-s integration time. This compact laser system can replace the conventional green diode-pumped solid-state laser and applied as a frequency reference. A single longitudinal mode operational region with diode temperature, current, and output power was investigated.

  2. Indium clustering in a-plane InGaN quantum wells as evidenced by atom probe tomography

    International Nuclear Information System (INIS)

    Tang, Fengzai; Zhu, Tongtong; Oehler, Fabrice; Fu, Wai Yuen; Griffiths, James T.; Massabuau, Fabien C.-P.; Kappers, Menno J.; Oliver, Rachel A.; Martin, Tomas L.; Bagot, Paul A. J.; Moody, Michael P.

    2015-01-01

    Atom probe tomography (APT) has been used to characterize the distribution of In atoms within non-polar a-plane InGaN quantum wells (QWs) grown on a GaN pseudo-substrate produced using epitaxial lateral overgrowth. Application of the focused ion beam microscope enabled APT needles to be prepared from the low defect density regions of the grown sample. A complementary analysis was also undertaken on QWs having comparable In contents grown on polar c-plane sample pseudo-substrates. Both frequency distribution and modified nearest neighbor analyses indicate a statistically non-randomized In distribution in the a-plane QWs, but a random distribution in the c-plane QWs. This work not only provides insights into the structure of non-polar a-plane QWs but also shows that APT is capable of detecting as-grown nanoscale clustering in InGaN and thus validates the reliability of earlier APT analyses of the In distribution in c-plane InGaN QWs which show no such clustering

  3. Indium clustering in a-plane InGaN quantum wells as evidenced by atom probe tomography

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Fengzai; Zhu, Tongtong; Oehler, Fabrice; Fu, Wai Yuen; Griffiths, James T.; Massabuau, Fabien C.-P.; Kappers, Menno J.; Oliver, Rachel A., E-mail: rao28@cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Martin, Tomas L.; Bagot, Paul A. J.; Moody, Michael P., E-mail: michael.moody@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom)

    2015-02-16

    Atom probe tomography (APT) has been used to characterize the distribution of In atoms within non-polar a-plane InGaN quantum wells (QWs) grown on a GaN pseudo-substrate produced using epitaxial lateral overgrowth. Application of the focused ion beam microscope enabled APT needles to be prepared from the low defect density regions of the grown sample. A complementary analysis was also undertaken on QWs having comparable In contents grown on polar c-plane sample pseudo-substrates. Both frequency distribution and modified nearest neighbor analyses indicate a statistically non-randomized In distribution in the a-plane QWs, but a random distribution in the c-plane QWs. This work not only provides insights into the structure of non-polar a-plane QWs but also shows that APT is capable of detecting as-grown nanoscale clustering in InGaN and thus validates the reliability of earlier APT analyses of the In distribution in c-plane InGaN QWs which show no such clustering.

  4. Spectral properties of polarized light from semipolar grown InGaN quantum wells at low temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Schade, L.; Schwarz, U.T. [Fraunhofer Institute for Applied Solid State Physics IAF, Freiburg (Germany); Department of Microsystems Engineering (IMTEK), University of Freiburg (Germany); Wernicke, T.; Ploch, S. [Institute of Solid State Physics, TU Berlin (Germany); Weyers, M. [Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik, Berlin (Germany); Kneissl, M. [Institute of Solid State Physics, TU Berlin (Germany); Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik, Berlin (Germany)

    2012-03-15

    The polarization dependent photoluminescence at low temperatures of strained semipolar and nonpolar InGaN quantum wells was studied as a function of the emission wavelength. We found for semipolar QWs that the maximum of the spectral resolved optical polarization is either red- or blue-shifted with respect to the maximum of the emission. In contrast, the nonpolar emission exhibits no clear maximum. We assign all effects to an inhomogeneous broadening of the emission caused by indium fluctuations and explain this behavior here in the light of the optical polarization switching. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Radiative transitions in InGaN quantum-well structures

    Energy Technology Data Exchange (ETDEWEB)

    Shapiro, Noad Asaf [Univ. of California, Berkeley, CA (United States)

    2002-01-01

    InGaN based light emitting devices demonstrate excellent luminescence properties and have great potential in lighting applications. Though these devices are already being produced on an industrial scale, the nature of their radiative transition is still not well understood. In particular, the role of the huge (>1MV/cm), built-in electric field in these transitions is still under debate. The luminescence characteristics of InGaN quantum well structures were investigated as a function of excitation power, temperature, and biaxial strain, with an intent of discerning the effects of the electric field and inhomogeneous indium distribution in the QW on the radiative transition. It was found that the luminescence energy did not scale only with the indium concentration but that the QW thickness must also be taken into account. The thickness affects the transition energy due to quantum confinement and carrier separation across a potential drop in the QW. The luminescence peak width was shown to increase with increased indium fraction, due to increased indium inhomogeneity. The carrier lifetime increased exponentially with QW thickness and luminescence wavelength, due to increased carrier separation. Measuring the luminescence energy and carrier lifetime as a function of excitation density showed that the electric field can be screened by strong excitation and, as a consequence, the carrier separation reduced. The temperature dependence of the luminescence showed evidence for bandtails in the density of states, a phenomenon that has been previously related to transition in indium-rich nano-clusters, yet could be accounted for by fluctuations in other parameters that affect the transition energy. Room temperature luminescence efficiency was shown to weakly decrease with increased QW thickness. The application of biaxial strain resulted in either a redshift or blueshift of the luminescence, depending on the sample. The direction and magnitude of the shift in luminescence

  6. Deformation potentials in AlGaN and InGaN alloys and their impact on optical polarization properties of nitride quantum wells

    DEFF Research Database (Denmark)

    Łepkowski, S. P.; Gorczyca, I.; Stefańska-Skrobas, K.

    2013-01-01

    The deformation potentials acz−D1, act−D2, D3, D4, and D5 are determined for random AlGaN and InGaN alloys using electronic band structure calculations based on the density functional theory. A sublinear composition dependence is obtained for acz−D1 and D3 in AlGaN, and D3 in InGaN, whereas...... superlinear behavior on composition is found foract−D2, D4, and D5 in AlGaN, and act−D2and D5 in InGaN. The optical polarization properties of nitride quantum wells are very well described by the k·p method when the obtained deformation potentials are included. In m-plane AlGaN/AlN and InGaN/GaN quantum wells...

  7. Quantum optics with single quantum dot devices

    International Nuclear Information System (INIS)

    Zwiller, Valery; Aichele, Thomas; Benson, Oliver

    2004-01-01

    A single radiative transition in a single-quantum emitter results in the emission of a single photon. Single quantum dots are single-quantum emitters with all the requirements to generate single photons at visible and near-infrared wavelengths. It is also possible to generate more than single photons with single quantum dots. In this paper we show that single quantum dots can be used to generate non-classical states of light, from single photons to photon triplets. Advanced solid state structures can be fabricated with single quantum dots as their active region. We also show results obtained on devices based on single quantum dots

  8. Exciton localization in (11-22)-oriented semi-polar InGaN multiple quantum wells

    Science.gov (United States)

    Monavarian, Morteza; Rosales, Daniel; Gil, Bernard; Izyumskaya, Natalia; Das, Saikat; Özgür, Ümit; Morkoç, Hadis; Avrutin, Vitaliy

    2016-02-01

    Excitonic recombination dynamics in (11-22) -oriented semipolar In0.2Ga0.8N/In0.06Ga0.94N multiquantum wells (MQWs) grown on GaN/m-sapphire templates have been investigated by temperature-dependent time-resolved photoluminescence (TRPL). The radiative and nonradiative recombination contributions to the PL intensity at different temperatures were evaluated by analysing temperature dependences of PL peak intensity and decay times. The obtained data indicate the existence of exciton localization with a localization energy of Eloc(15K) =7meV and delocalization temperature of Tdeloc = 200K in the semipolar InGaN MQWs. Presence of such exciton localization in semipolar (11-22) -oriented structures could lead to improvement of excitonic emission and internal quantum efficiency.

  9. Active region dimensionality and quantum efficiencies of InGaN LEDs from temperature dependent photoluminescence transients

    Science.gov (United States)

    Can, Nuri; Okur, Serdal; Monavarian, Morteza; Zhang, Fan; Avrutin, Vitaliy; Morkoç, Hadis; Teke, Ali; Özgür, Ümit

    2015-03-01

    Temperature dependent recombination dynamics in c-plane InGaN light emitting diodes (LEDs) with different well thicknesses, 1.5, 2, and 3 nm, were investigated to determine the active region dimensionality and its effect on the internal quantum efficiencies. It was confirmed for all LEDs that the photoluminescence (PL) transients are governed by radiative recombination at low temperatures while nonradiative recombination dominates at room temperature. At photoexcited carrier densities of 3 - 4.5 x 1016 cm-3 , the room-temperature Shockley-Read-Hall (A) and the bimolecular (B) recombination coefficients (A, B) were deduced to be (9.2x107 s-1, 8.8x10-10 cm3s-1), (8.5x107 s-1, 6.6x10-10 cm3s-1), and (6.5x107 s-1, 1.4x10-10 cm3s-1) for the six period 1.5, 2, and 3 nm well-width LEDs, respectively. From the temperature dependence of the radiative lifetimes, τrad α Tn/2, the dimensionality n of the active region was found to decrease consistently with decreasing well width. The 3 nm wide wells exhibited ~T1.5 dependence, suggesting a three-dimensional nature, whereas the 1.5 nm wells were confirmed to be two-dimensional (~T1) and the 2 nm wells close to being two-dimensional. We demonstrate that a combination of temperature dependent PL and time-resolved PL techniques can be used to evaluate the dimensionality as well as the quantum efficiencies of the LED active regions for a better understanding of the relationship between active-region design and the efficiency limiting processes in InGaN LEDs.

  10. Site controlled Red-Yellow-Green light emitting InGaN Quantum Discs on nano-tipped GaN rods

    KAUST Repository

    Conroy, Michele Ann; Li, Haoning; Kusch, Gunnar; Zhao, Chao; Ooi, Boon S.; Paul, Edwards; Martin, Robert; Holmes, Justin D.; Parbrook, Peter

    2016-01-01

    We report a method of growing site controlled InGaN multiple quantum discs (QDs) at uniform wafer scale on coalescence free ultra-high density (>80%) nanorod templates by metal organic chemical vapour deposition (MOCVD). The dislocation and coalescence free nature of the GaN space filling nanorod arrays eliminates the well-known emission problems seen in InGaN based visible light sources that these types of crystallographic defects cause. Correlative scanning transmission electron microscopy (STEM), energy-dispersive x-ray (EDX) mapping and cathodoluminescence (CL) hyperspectral imaging illustrates the controlled site selection of the red, yellow and green (RYG) emission at these nano tips. This article reveals that the nanorod tips’ broad emission in the RYG visible range is in fact achieved by manipulating the InGaN QD’s confinement dimensions, rather than significantly increasing the In%. This article details the easily controlled method of manipulating the QDs dimensions producing high crystal quality InGaN without complicated growth conditions needed for strain relaxation and alloy compositional changes seen for bulk planar GaN templates.

  11. Site controlled Red-Yellow-Green light emitting InGaN Quantum Discs on nano-tipped GaN rods

    KAUST Repository

    Conroy, Michele Ann

    2016-03-10

    We report a method of growing site controlled InGaN multiple quantum discs (QDs) at uniform wafer scale on coalescence free ultra-high density (>80%) nanorod templates by metal organic chemical vapour deposition (MOCVD). The dislocation and coalescence free nature of the GaN space filling nanorod arrays eliminates the well-known emission problems seen in InGaN based visible light sources that these types of crystallographic defects cause. Correlative scanning transmission electron microscopy (STEM), energy-dispersive x-ray (EDX) mapping and cathodoluminescence (CL) hyperspectral imaging illustrates the controlled site selection of the red, yellow and green (RYG) emission at these nano tips. This article reveals that the nanorod tips’ broad emission in the RYG visible range is in fact achieved by manipulating the InGaN QD’s confinement dimensions, rather than significantly increasing the In%. This article details the easily controlled method of manipulating the QDs dimensions producing high crystal quality InGaN without complicated growth conditions needed for strain relaxation and alloy compositional changes seen for bulk planar GaN templates.

  12. Impact of band structure and transition matrix elements on polarization properties of the photoluminescence of semipolar and nonpolar InGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Schade, L.; Schwarz, U.T. [Department of Microsystems Engineering, University of Freiburg, Georges-Koehler-Allee 103, 79108 Freiburg (Germany); Fraunhofer Institute for Applied Solid State Physics (IAF), Tullastrasse 72, 79108 Freiburg (Germany); Wernicke, T. [Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin (Germany); Weyers, M. [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Kneissl, M. [Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin (Germany); Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany)

    2011-03-15

    Partial or full linear polarization is characteristic for the spontaneous emission of light from semipolar and nonpolar InGaN quantum wells. This property is an implication of the crystalline anisotropy as a basic property of the wurtzite structure. The influence of this anisotropy on the band structure and the transition matrix elements was calculated by a k.p-method for arbitrary quantum well orientations with respect to the c-axis; results are shown here in detail. Optical polarization is a direct consequence of a broken symmetry, mainly affecting the transition matrix elements from the conduction to the valence bands. Furthermore, the strain of the InGaN quantum well strongly depends on the crystal orientation of the substrate, resulting in a valence band mixing. The composition of the eigenfunctions has emerged to be most important for the polarization dependence of strained semipolar and nonpolar InGaN QW. The matrix elements, in combination with the thermal occupation of the bands, determine the polarization of the spontaneously emitted light. Our photoluminescence measurements of nonpolar QW match well with this model. However, in contrast to calculations with standard band parameters, the two topmost subbands show a larger separation in the emitted energy. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Growth of InGaN multiple quantum wells and GaN eplilayer on GaN substrate

    International Nuclear Information System (INIS)

    Lee, Sung-Nam; Paek, H.S.; Son, J.K.; Sakong, T.; Yoon, E.; Nam, O.H.; Park, Y.

    2006-01-01

    We investigated that the surface morphology of GaN epilayers was significantly affected by the surface tilt orientation of GaN substrate. Surface morphologies of GaN epilayers on GaN substrates show three types: mirror, wavy, and hillock. These surface morphologies are dependent on the surface orientation of GaN substrates. It is found that the hillock morphology of GaN epilayer was formed on the GaN substrate with surface tilt orientation less than 0.1 o . As the surface tilt angle increased to 0.35 o , the surface morphology varied from hillock to wavy morphology. Above a surface tilt angle of 0.4 o , surface morphology changed to the mirror-like type morphology. Additionally, these three types of GaN surface morphology also affected the optical quality of GaN epilayers as well as InGaN multiple quantum wells on GaN substrates by non-uniform In incorporation on the different surface morphologies of GaN epilayers

  14. Achieving Uniform Carriers Distribution in MBE Grown Compositionally Graded InGaN Multiple-Quantum-Well LEDs

    KAUST Repository

    Mishra, Pawan; Janjua, Bilal; Ng, Tien Khee; Shen, Chao; Salhi, Abdelmajid; Alyamani, Ahmed; El-Desouki, Munir; Ooi, Boon S.

    2015-01-01

    We investigated the design and growth of compositionally-graded InGaN multiple quantum wells (MQW) based light-emitting diode (LED) without an electron-blocking layer (EBL). Numerical investigation showed uniform carrier distribution in the active region, and higher radiative recombination rate for the optimized graded-MQW design, i.e. In0→xGa1→(1-x)N / InxGa(1-x)N / Inx→0Ga(1-x)→1N, as compared to the conventional stepped-MQW-LED. The composition-grading schemes, such as linear, parabolic, and Fermi-function profiles were numerically investigated for comparison. The stepped- and graded-MQW-LED were then grown using plasma assisted molecular beam epitaxy (PAMBE) through surface-stoichiometry optimization based on reflection high-energy electron-diffraction (RHEED) in-situ observations. Stepped- and graded-MQW-LED showed efficiency roll over at 160 A/cm2 and 275 A/cm2, respectively. The extended threshold current density roll-over (droop) in graded-MQW-LED is due to the improvement in carrier uniformity and radiative recombination rate, consistent with the numerical simulation.

  15. Achieving Uniform Carriers Distribution in MBE Grown Compositionally Graded InGaN Multiple-Quantum-Well LEDs

    KAUST Repository

    Mishra, Pawan

    2015-05-06

    We investigated the design and growth of compositionally-graded InGaN multiple quantum wells (MQW) based light-emitting diode (LED) without an electron-blocking layer (EBL). Numerical investigation showed uniform carrier distribution in the active region, and higher radiative recombination rate for the optimized graded-MQW design, i.e. In0→xGa1→(1-x)N / InxGa(1-x)N / Inx→0Ga(1-x)→1N, as compared to the conventional stepped-MQW-LED. The composition-grading schemes, such as linear, parabolic, and Fermi-function profiles were numerically investigated for comparison. The stepped- and graded-MQW-LED were then grown using plasma assisted molecular beam epitaxy (PAMBE) through surface-stoichiometry optimization based on reflection high-energy electron-diffraction (RHEED) in-situ observations. Stepped- and graded-MQW-LED showed efficiency roll over at 160 A/cm2 and 275 A/cm2, respectively. The extended threshold current density roll-over (droop) in graded-MQW-LED is due to the improvement in carrier uniformity and radiative recombination rate, consistent with the numerical simulation.

  16. Reducing Threshold of Multi Quantum Wells InGaN Laser Diode by Using InGaN/GaN Waveguide

    Science.gov (United States)

    Abdullah, Rafid A.; Ibrahim, Kamarulazizi

    2010-07-01

    ISE TCAD (Integrated System Engineering Technology Computer Aided Design) software simulation program has been utilized to help study the effect of using InGaN/GaN as a waveguide instead of conventional GaN waveguide for multi quantum wells violet InGaN laser diode (LD). Simulation results indicate that the threshold of the LD has been reduced by using InGaN/GaN waveguide where InGaN/GaN waveguide increases the optical confinement factor which leads to increase the confinement carriers at the active region of the LD.

  17. Light emission ranging from blue to red from a series of Iguana/GaN single quantum wells

    International Nuclear Information System (INIS)

    Martin, R.W.; Edwards, P.R.; Pecharroman-Gallego, R.; O'Donnell, K.P.; Liu, C.; Deatcher, C.J.; Watson, I.M.

    2002-01-01

    In this paper, we describe the growth and characterization of InGaN single quantum wells with emission peaks in the blue, green, amber and red spectral regions, grown by metal-organic vapour phase epitaxy. Starting from the growth of a blue-emitting (peak ∼430 nm) InGaN quantum well at 860 deg. C the InGaN growth temperature was progressively reduced. The photoluminescence peak wavelength, measured at low temperature, shifts through the green and orange spectral regions and reaches 670 nm for an InGaN growth temperature of 760 deg. C. This corresponds to an energy lower than the currently accepted band-gap of the binary compound, InN. Spectral characteristics of the luminescence peaks will be discussed, including an analysis of the phonon-assisted contribution. Low energy secondary ion mass spectrometry analysis provides information on the indium content and thickness of the 'blue' and 'red' quantum wells. The results are combined to discuss the origin of the 'sub-band-gap' luminescence in terms of the combined influence of InN-GaN segregation and the effect of intense piezoelectric fields. (author)

  18. Light emission ranging from blue to red from a series of Iguana/GaN single quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Martin, R.W. [Department of Physics, University of Strathclyde, Glasgow (United Kingdom)]. E-mail: r.w.martin@strath.ac.uk; Edwards, P.R.; Pecharroman-Gallego, R.; O' Donnell, K.P. [Department of Physics, University of Strathclyde, Glasgow (United Kingdom); Liu, C.; Deatcher, C.J.; Watson, I.M. [Institute of Photonics, University of Strathclyde, Glasgow (United Kingdom)

    2002-04-07

    In this paper, we describe the growth and characterization of InGaN single quantum wells with emission peaks in the blue, green, amber and red spectral regions, grown by metal-organic vapour phase epitaxy. Starting from the growth of a blue-emitting (peak {approx}430 nm) InGaN quantum well at 860 deg. C the InGaN growth temperature was progressively reduced. The photoluminescence peak wavelength, measured at low temperature, shifts through the green and orange spectral regions and reaches 670 nm for an InGaN growth temperature of 760 deg. C. This corresponds to an energy lower than the currently accepted band-gap of the binary compound, InN. Spectral characteristics of the luminescence peaks will be discussed, including an analysis of the phonon-assisted contribution. Low energy secondary ion mass spectrometry analysis provides information on the indium content and thickness of the 'blue' and 'red' quantum wells. The results are combined to discuss the origin of the 'sub-band-gap' luminescence in terms of the combined influence of InN-GaN segregation and the effect of intense piezoelectric fields. (author)

  19. Direct generation of linearly polarized single photons with a deterministic axis in quantum dots

    Directory of Open Access Journals (Sweden)

    Wang Tong

    2017-07-01

    Full Text Available We report the direct generation of linearly polarized single photons with a deterministic polarization axis in self-assembled quantum dots (QDs, achieved by the use of non-polar InGaN without complex device geometry engineering. Here, we present a comprehensive investigation of the polarization properties of these QDs and their origin with statistically significant experimental data and rigorous k·p modeling. The experimental study of 180 individual QDs allows us to compute an average polarization degree of 0.90, with a standard deviation of only 0.08. When coupled with theoretical insights, we show that these QDs are highly insensitive to size differences, shape anisotropies, and material content variations. Furthermore, 91% of the studied QDs exhibit a polarization axis along the crystal [1–100] axis, with the other 9% polarized orthogonal to this direction. These features give non-polar InGaN QDs unique advantages in polarization control over other materials, such as conventional polar nitride, InAs, or CdSe QDs. Hence, the ability to generate single photons with polarization control makes non-polar InGaN QDs highly attractive for quantum cryptography protocols.

  20. Direct generation of linearly polarized single photons with a deterministic axis in quantum dots

    Science.gov (United States)

    Wang, Tong; Puchtler, Tim J.; Patra, Saroj K.; Zhu, Tongtong; Ali, Muhammad; Badcock, Tom J.; Ding, Tao; Oliver, Rachel A.; Schulz, Stefan; Taylor, Robert A.

    2017-07-01

    We report the direct generation of linearly polarized single photons with a deterministic polarization axis in self-assembled quantum dots (QDs), achieved by the use of non-polar InGaN without complex device geometry engineering. Here, we present a comprehensive investigation of the polarization properties of these QDs and their origin with statistically significant experimental data and rigorous k·p modeling. The experimental study of 180 individual QDs allows us to compute an average polarization degree of 0.90, with a standard deviation of only 0.08. When coupled with theoretical insights, we show that these QDs are highly insensitive to size differences, shape anisotropies, and material content variations. Furthermore, 91% of the studied QDs exhibit a polarization axis along the crystal [1-100] axis, with the other 9% polarized orthogonal to this direction. These features give non-polar InGaN QDs unique advantages in polarization control over other materials, such as conventional polar nitride, InAs, or CdSe QDs. Hence, the ability to generate single photons with polarization control makes non-polar InGaN QDs highly attractive for quantum cryptography protocols.

  1. Effect of the quantum well thickness on the performance of InGaN photovoltaic cells

    Energy Technology Data Exchange (ETDEWEB)

    Redaelli, L.; Mukhtarova, A.; Valdueza-Felip, S.; Ajay, A.; Durand, C.; Eymery, J.; Monroy, E. [Université Grenoble Alpes, 38000 Grenoble (France); CEA-CNRS Group «Nanophysique et semiconducteurs», CEA-Grenoble, INAC/SP2M, 17 avenue des Martyrs, 38054 Grenoble cedex 9 (France); Bougerol, C.; Himwas, C. [Université Grenoble Alpes, 38000 Grenoble (France); CEA-CNRS Group «Nanophysique et semiconducteurs», Institut Néel-CNRS, 25 avenue des Martyrs, 38042 Grenoble cedex 9 (France); Faure-Vincent, J. [Université Grenoble Alpes, 38000 Grenoble (France); CNRS, INAC-SPRAM, F-38000 Grenoble (France); CEA, INAC-SPRAM, F-38000 Grenoble (France)

    2014-09-29

    We report on the influence of the quantum well thickness on the effective band gap and conversion efficiency of In{sub 0.12}Ga{sub 0.88}N/GaN multiple quantum well solar cells. The band-to-band transition can be redshifted from 395 to 474 nm by increasing the well thickness from 1.3 to 5.4 nm, as demonstrated by cathodoluminescence measurements. However, the redshift of the absorption edge is much less pronounced in absorption: in thicker wells, transitions to higher energy levels dominate. Besides, partial strain relaxation in thicker wells leads to the formation of defects, hence degrading the overall solar cell performance.

  2. InGaN quantum well epilayers morphological evolution under a wide range of MOCVD growth parameter sets

    Energy Technology Data Exchange (ETDEWEB)

    Florescu, D.I.; Ting, S.M.; Merai, V.N.; Parekh, A.; Lee, D.S.; Armour, E.A.; Quinn, W.E. [Veeco TurboDisc Operations, 394 Elizabeth Avenue, Somerset, NJ 08873 (United States)

    2006-06-15

    This study exemplifies the use of TappingMode trademark atomic force microscopy (AFM) surface morphology imaging to investigate and optimise the metalorganic chemical vapour deposition (MOCVD) growth conditions and post-growth stability of thin (<40 Aa) InGaN layers with direct implications to the structural and optical properties of blue (460 nm) and green (520 nm) LEDs. InGaN epilayers less than 40 Aa thick of {proportional_to}20% solid phase indium were produced on thick (3-4 {mu}m) 2{sup ''} GaN templates grown on (0001) c-plane sapphire substrates. The morphological evolution of the InGaN material was studied utilising a DI3100 AFM tool. Surface morphology and its correlation with photoluminescence and X-ray diffraction results are discussed for every set of conditions employed. More specifically, the post-growth ambient exposure and thermal stability of the uncapped InGaN epilayers were investigated. In addition, the initial stage of subsequent GaN growth, which is an essential step towards the manufacture of LED active regions, was examined. Based on the above findings, a flexible MOCVD growth parameter space and improved LED constituent layer sequencing techniques have been established leading to more efficient and stable LED devices. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Polarization-dependent photoluminescence studies of semipolar and nonpolar InGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Schade, Lukas; Schwarz, Ulrich [IAF, Freiburg (Germany); Wernicke, Tim; Weyers, Markus [FBH, Berlin (Germany); Kneissl, Michael [FBH, Berlin (Germany); Institute of Solid State Physics, TU Berlin (Germany)

    2010-07-01

    Light emitted from optical devices based on semi- and nonpolar GaN quantum well (QW) structures is partially or totally polarized, as a consequence of crystal symmetry and band structure. This can be an additional advantage over polar (0001)GaN in specific applications, e.g. in LED backlighting. Fundamentally, the polarized emission stems from breaking the isotropic symmetry of the hexagonal c-plane, resulting in two discrete semi- and nonpolar directions (parallel and normal to the projection of (0001)). We use the k.p method to simulate the crystal-direction dependent emission. The resulting transition matrix elements assign a specific (partial) polarization for each subband. The thermal occupation of the subbands results in a temperature dependent effective polarization of the light emission. We study MOVPE grown homoepitactical polar, semi- and nonpolar samples, measuring the polarization properties of the resonantly excited photoluminescence from the QW. With the complete polarization of the subbands for nonpolar devices it is possible to measure the energetic difference of the first two valence band levels. In contrast to our calculations we find a higher degree of polarization also in semipolar directions. A possible explanation could be a higher energetic subband difference than computed.

  4. A comparison of the optical properties of InGaN/GaN multiple quantum well structures grown with and without Si-doped InGaN prelayers

    International Nuclear Information System (INIS)

    Davies, M. J.; Hammersley, S.; Dawson, P.; Massabuau, F. C.-P.; Oliver, R. A.; Kappers, M. J.; Humphreys, C. J.

    2016-01-01

    In this paper, we report on a detailed spectroscopic study of the optical properties of InGaN/GaN multiple quantum well structures, both with and without a Si-doped InGaN prelayer. In photoluminescence and photoluminescence excitation spectroscopy, a 2nd emission band, occurring at a higher energy, was identified in the spectrum of the multiple quantum well structure containing the InGaN prelayer, originating from the first quantum well in the stack. Band structure calculations revealed that a reduction in the resultant electric field occurred in the quantum well immediately adjacent to the InGaN prelayer, therefore leading to a reduction in the strength of the quantum confined Stark effect in this quantum well. The partial suppression of the quantum confined Stark effect in this quantum well led to a modified (higher) emission energy and increased radiative recombination rate. Therefore, we ascribed the origin of the high energy emission band to recombination from the 1st quantum well in the structure. Study of the temperature dependent recombination dynamics of both samples showed that the decay time measured across the spectrum was strongly influenced by the 1st quantum well in the stack (in the sample containing the prelayer) leading to a shorter average room temperature lifetime in this sample. The room temperature internal quantum efficiency of the prelayer containing sample was found to be higher than the reference sample (36% compared to 25%) which was thus attributed to the faster radiative recombination rate of the 1st quantum well providing a recombination pathway that is more competitive with non-radiative recombination processes

  5. A comparison of the optical properties of InGaN/GaN multiple quantum well structures grown with and without Si-doped InGaN prelayers

    Energy Technology Data Exchange (ETDEWEB)

    Davies, M. J., E-mail: Matthew.Davies-2@Manchester.ac.uk; Hammersley, S.; Dawson, P. [School of Physics and Astronomy, Photon Science Institute, University of Manchester, Manchester M13 9PL (United Kingdom); Massabuau, F. C.-P.; Oliver, R. A.; Kappers, M. J.; Humphreys, C. J. [Department of Material Science and Metallurgy, 27 Charles Babbage Road, University of Cambridge, Cambridge CB3 0FS (United Kingdom)

    2016-02-07

    In this paper, we report on a detailed spectroscopic study of the optical properties of InGaN/GaN multiple quantum well structures, both with and without a Si-doped InGaN prelayer. In photoluminescence and photoluminescence excitation spectroscopy, a 2nd emission band, occurring at a higher energy, was identified in the spectrum of the multiple quantum well structure containing the InGaN prelayer, originating from the first quantum well in the stack. Band structure calculations revealed that a reduction in the resultant electric field occurred in the quantum well immediately adjacent to the InGaN prelayer, therefore leading to a reduction in the strength of the quantum confined Stark effect in this quantum well. The partial suppression of the quantum confined Stark effect in this quantum well led to a modified (higher) emission energy and increased radiative recombination rate. Therefore, we ascribed the origin of the high energy emission band to recombination from the 1st quantum well in the structure. Study of the temperature dependent recombination dynamics of both samples showed that the decay time measured across the spectrum was strongly influenced by the 1st quantum well in the stack (in the sample containing the prelayer) leading to a shorter average room temperature lifetime in this sample. The room temperature internal quantum efficiency of the prelayer containing sample was found to be higher than the reference sample (36% compared to 25%) which was thus attributed to the faster radiative recombination rate of the 1st quantum well providing a recombination pathway that is more competitive with non-radiative recombination processes.

  6. Carrier redistribution between different potential sites in semipolar (202¯1) InGaN quantum wells studied by near-field photoluminescence

    KAUST Repository

    Marcinkevičius, S.

    2014-09-15

    © 2014 AIP Publishing LLC. Scanning near-field photoluminescence (PL) spectroscopy at different excitation powers was applied to study nanoscale properties of carrier localization and recombination in semipolar (202¯1) InGaN quantum wells (QWs) emitting in violet, blue, and green-yellow spectral regions. With increased excitation power, an untypical PL peak energy shift to lower energies was observed. The shift was attributed to carrier density dependent carrier redistribution between nm-scale sites of different potentials. Near-field PL scans showed that in (202¯1) QWs the in-plane carrier diffusion is modest, and the recombination properties are uniform, which is advantageous for photonic applications.

  7. Effect of GaN cap thickness on carrier dynamics in InGaN quantum wells

    DEFF Research Database (Denmark)

    Kopylov, Oleksii; Shirazi, Roza; Svensk, O.

    2012-01-01

    We have studied optical properties of single In0.1Ga0.9N quantum wells with GaN barriers in close proximity to the wafer surface (... thickness of 3nm for achieving highest brightness emitters. At low temperature, we observe a behaviour that suggests that some surface states act as trapping centres for carriers rather than as a non-radiative recombination channel. Temperature dependence of the photoluminescence decay curves shows...

  8. InGaN quantum well epilayers morphological evolution under a wide range of MOCVD growth parameter sets

    International Nuclear Information System (INIS)

    Florescu, D.I.; Ting, S.M.; Merai, V.N.; Parekh, A.; Lee, D.S.; Armour, E.A.; Quinn, W.E.

    2006-01-01

    This study exemplifies the use of TappingMode trademark atomic force microscopy (AFM) surface morphology imaging to investigate and optimise the metalorganic chemical vapour deposition (MOCVD) growth conditions and post-growth stability of thin ( '' GaN templates grown on (0001) c-plane sapphire substrates. The morphological evolution of the InGaN material was studied utilising a DI3100 AFM tool. Surface morphology and its correlation with photoluminescence and X-ray diffraction results are discussed for every set of conditions employed. More specifically, the post-growth ambient exposure and thermal stability of the uncapped InGaN epilayers were investigated. In addition, the initial stage of subsequent GaN growth, which is an essential step towards the manufacture of LED active regions, was examined. Based on the above findings, a flexible MOCVD growth parameter space and improved LED constituent layer sequencing techniques have been established leading to more efficient and stable LED devices. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Growth of (20 anti 21)AlGaN, GaN and InGaN by metal organic vapor phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ploch, S.; Wernicke, T.; Rass, J.; Pristovsek, M. [TU Berlin, Institut fuer Festkoerperphysik, Hardenbergstr. 36, 10623 Berlin (Germany); Weyers, M. [Ferdinand-Braun-Institut, Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany); Kneissl, M. [TU Berlin, Institut fuer Festkoerperphysik, Hardenbergstr. 36, 10623 Berlin (Germany); Ferdinand-Braun-Institut, Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany)

    2012-07-01

    Green InGaN-based laser diodes on (20 anti 21)GaN substrates have recently demonstrated performances exceeding those of conventional (0001) oriented devices. However little is known regarding the growth parameters. We have investigated growth of AlGaN, GaN and InGaN on (20 anti 21)GaN substrates by MOVPE. Smooth GaN layers with a rms roughness <0.5 nm were obtained by low growth temperatures and reactor pressures. The layers exhibit undulations along [10 anti 14] similar to the GaN substrate. AlGaN and InGaN layers exhibit an increased surface roughness. Undulation bunching was observed and attributed to reduced adatom surface mobility due to the binding energy of Al and the low growth temperature for InGaN respectively or strain relaxation. AlGaN and InGaN heterostructures on (20 anti 21)GaN relax by layer tilt accompanied by formation of misfit dislocations, due to shear strain of the unit cell. This relaxation mechanism leads to a reduced critical layer thickness of (20 anti 21)AlGaN layers and InGaN multi quantum wells (MQW) in comparison to (0001). PL spectral broadening of 230 meV of (20 anti 21)InGaN single QWs emitting at 415 nm can be reduced by increased growth temperature or increased number of QWs with reduced thickness.

  10. Temperature dependence of interband recombination energy in symmetric (In,Ga)N spherical quantum dot-quantum well

    Energy Technology Data Exchange (ETDEWEB)

    El Ghazi, Haddou, E-mail: hadghazi@gmail.com [LPS, Faculty of Science, Dhar EL Mehrez, BP 1796 Fes-Atlas (Morocco); Special Mathematics, CPGE, 267 Quartier complémentaire Ennahda 1, Rabat (Morocco); Jorio, Anouar [LPS, Faculty of Science, Dhar EL Mehrez, BP 1796 Fes-Atlas (Morocco)

    2014-01-01

    Within the framework of effective-mass approximation and finite parabolic potential barrier, single particle and ground-state interband recombination energies in Core|well|shell based on GaN|(In,Ga)N|GaN spherical QDQW are investigated as a function of the inner and the outer radii. The temperature dependency of effective-mass, band-gap energy and potential barrier is taken into account. Particle eigenvalue and band-gap energy competing effects are speculated to explain our numerical results which show that the interband recombination energy increases when the temperature increases. The results we obtained are in quite good agreement with the findings.

  11. Temperature dependence of interband recombination energy in symmetric (In,Ga)N spherical quantum dot-quantum well

    International Nuclear Information System (INIS)

    El Ghazi, Haddou; Jorio, Anouar

    2014-01-01

    Within the framework of effective-mass approximation and finite parabolic potential barrier, single particle and ground-state interband recombination energies in Core|well|shell based on GaN|(In,Ga)N|GaN spherical QDQW are investigated as a function of the inner and the outer radii. The temperature dependency of effective-mass, band-gap energy and potential barrier is taken into account. Particle eigenvalue and band-gap energy competing effects are speculated to explain our numerical results which show that the interband recombination energy increases when the temperature increases. The results we obtained are in quite good agreement with the findings

  12. Single-server blind quantum computation with quantum circuit model

    Science.gov (United States)

    Zhang, Xiaoqian; Weng, Jian; Li, Xiaochun; Luo, Weiqi; Tan, Xiaoqing; Song, Tingting

    2018-06-01

    Blind quantum computation (BQC) enables the client, who has few quantum technologies, to delegate her quantum computation to a server, who has strong quantum computabilities and learns nothing about the client's quantum inputs, outputs and algorithms. In this article, we propose a single-server BQC protocol with quantum circuit model by replacing any quantum gate with the combination of rotation operators. The trap quantum circuits are introduced, together with the combination of rotation operators, such that the server is unknown about quantum algorithms. The client only needs to perform operations X and Z, while the server honestly performs rotation operators.

  13. Continuous-flux MOVPE growth of position-controlled N-face GaN nanorods and embedded InGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Bergbauer, W; Strassburg, M; Koelper, Ch; Linder, N [Osram Opto Semiconductors GmbH, Leibnizstrasse 4, D-93055 Regensburg (Germany); Roder, C; Laehnemann, J; Trampert, A [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, D-10117 Berlin (Germany); Fuendling, S; Li, S F; Wehmann, H-H; Waag, A, E-mail: werner.bergbauer@osram-os.com [Institut fuer Halbleitertechnik, TU Braunschweig, Hans-Sommer-Strasse 66, D-38106 Braunschweig (Germany)

    2010-07-30

    We demonstrate the fabrication of N-face GaN nanorods by metal organic vapour phase epitaxy (MOVPE), using continuous-flux conditions. This is in contrast to other approaches reported so far, which have been based on growth modes far off the conventional growth regimes. For position control of nanorods an SiO{sub 2} masking layer with a dense hole pattern on a c-plane sapphire substrate was used. Nanorods with InGaN/GaN heterostructures have been grown catalyst-free. High growth rates up to 25 {mu}m h{sup -1} were observed and a well-adjusted carrier gas mixture between hydrogen and nitrogen enabled homogeneous nanorod diameters down to 220 nm with aspect ratios of approximately 8:1. The structural quality and defect progression within nanorods were determined by transmission electron microscopy (TEM). Different emission energies for InGaN quantum wells (QWs) could be assigned to different side facets by room temperature cathodoluminescence (CL) measurements.

  14. Continuous-flux MOVPE growth of position-controlled N-face GaN nanorods and embedded InGaN quantum wells

    Science.gov (United States)

    Bergbauer, W.; Strassburg, M.; Kölper, Ch; Linder, N.; Roder, C.; Lähnemann, J.; Trampert, A.; Fündling, S.; Li, S. F.; Wehmann, H.-H.; Waag, A.

    2010-07-01

    We demonstrate the fabrication of N-face GaN nanorods by metal organic vapour phase epitaxy (MOVPE), using continuous-flux conditions. This is in contrast to other approaches reported so far, which have been based on growth modes far off the conventional growth regimes. For position control of nanorods an SiO2 masking layer with a dense hole pattern on a c-plane sapphire substrate was used. Nanorods with InGaN/GaN heterostructures have been grown catalyst-free. High growth rates up to 25 µm h - 1 were observed and a well-adjusted carrier gas mixture between hydrogen and nitrogen enabled homogeneous nanorod diameters down to 220 nm with aspect ratios of approximately 8:1. The structural quality and defect progression within nanorods were determined by transmission electron microscopy (TEM). Different emission energies for InGaN quantum wells (QWs) could be assigned to different side facets by room temperature cathodoluminescence (CL) measurements.

  15. Continuous-flux MOVPE growth of position-controlled N-face GaN nanorods and embedded InGaN quantum wells

    International Nuclear Information System (INIS)

    Bergbauer, W; Strassburg, M; Koelper, Ch; Linder, N; Roder, C; Laehnemann, J; Trampert, A; Fuendling, S; Li, S F; Wehmann, H-H; Waag, A

    2010-01-01

    We demonstrate the fabrication of N-face GaN nanorods by metal organic vapour phase epitaxy (MOVPE), using continuous-flux conditions. This is in contrast to other approaches reported so far, which have been based on growth modes far off the conventional growth regimes. For position control of nanorods an SiO 2 masking layer with a dense hole pattern on a c-plane sapphire substrate was used. Nanorods with InGaN/GaN heterostructures have been grown catalyst-free. High growth rates up to 25 μm h -1 were observed and a well-adjusted carrier gas mixture between hydrogen and nitrogen enabled homogeneous nanorod diameters down to 220 nm with aspect ratios of approximately 8:1. The structural quality and defect progression within nanorods were determined by transmission electron microscopy (TEM). Different emission energies for InGaN quantum wells (QWs) could be assigned to different side facets by room temperature cathodoluminescence (CL) measurements.

  16. Growth and properties of InN, InGaN, and InN/InGaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Naoi, H.; Na, H. [Center for Promotion of the COE Program, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577 (Japan); Kurouchi, M.; Muto, D.; Takado, S.; Araki, T.; Nanishi, Y. [Dept. of Photonics, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577 (Japan); Miyajima, T. [Optoelectronics Laboratory, Materials Laboratories, Sony Corporation, 4-14-1 Asahi, Atsugi, Kanagawa 243-0014 (Japan)

    2006-01-01

    This paper describes our recent progress on InN, In-rich In{sub x}Ga{sub 1-x}N, and InN/In{sub x}Ga{sub 1-x}N quantum wells (QWs) grown by radio-frequency plasma-assisted molecular-beam epitaxy. Among the essential growth sequences to obtain high-quality InN, the nitridation process of (0001) sapphire substrates was reexamined. It was found that the lower-temperature and longer-period nitridation-process was very effective in improving crystalline quality of InN films. We succeeded in dramatically improving c -axis orientation of InN films without deteriorating their a -axis orientation by nitridating the substrates at a relatively low-temperature of 300 C for a relatively long period of 2 h. The full widths at half maximum (FWHMs) of (0002) X-ray rocking curves as narrow as 1 arcmin were obtained from only 400 nm thick InN films. These FWHMs are the narrowest value ever reported for InN and moreover approximately a twentieth part of the values obtained from our conventional InN films with a similar thickness, which were grown via the conventional nitridation process carried out at 550 C for 1 h. Furthermore interference fringes in X-ray diffraction ({omega}-2{theta} scan) were observed from these improved InN films. These high crystalline quality InN layers have been employed as a template for the growth of In-rich In{sub x}Ga{sub 1-x}N layers (0.70{<=}x{<=}0.94). The resultant In{sub x}Ga{sub 1-x}N layers have shown dramatic improvements in not only the surface morphology but also both the a- and c-axis orientations. By employing In{sub 0.8}Ga{sub 0.2}N layers of improved quality as the bottom barrier layer, InN/In{sub 0.8}Ga{sub 0.2}N multiple quantum well (MQW) and single quantum well (SQW) structures with different well widths were fabricated. Clear satellite peaks of X-ray diffraction were observed from these MQW structures. Both of these SQW and MQW structures have exhibited a blue shift of the photoluminescence peak energy with decreasing well width

  17. Single-electron quantum tomography in quantum Hall edge channels

    International Nuclear Information System (INIS)

    Grenier, Ch; Degiovanni, P; Herve, R; Bocquillon, E; Parmentier, F D; Placais, B; Berroir, J M; Feve, G

    2011-01-01

    We propose a quantum tomography protocol to measure single-electron coherence in quantum Hall edge channels, and therefore access for the first time the wavefunction of single-electron excitations propagating in ballistic quantum conductors. Its implementation would open the way to quantitative studies of single-electron decoherence and would provide a quantitative tool for analyzing single- to few-electron sources. We show how this protocol could be implemented using ultrahigh-sensitivity noise measurement schemes.

  18. Parallel quantum computing in a single ensemble quantum computer

    International Nuclear Information System (INIS)

    Long Guilu; Xiao, L.

    2004-01-01

    We propose a parallel quantum computing mode for ensemble quantum computer. In this mode, some qubits are in pure states while other qubits are in mixed states. It enables a single ensemble quantum computer to perform 'single-instruction-multidata' type of parallel computation. Parallel quantum computing can provide additional speedup in Grover's algorithm and Shor's algorithm. In addition, it also makes a fuller use of qubit resources in an ensemble quantum computer. As a result, some qubits discarded in the preparation of an effective pure state in the Schulman-Varizani and the Cleve-DiVincenzo algorithms can be reutilized

  19. A single-atom quantum memory.

    Science.gov (United States)

    Specht, Holger P; Nölleke, Christian; Reiserer, Andreas; Uphoff, Manuel; Figueroa, Eden; Ritter, Stephan; Rempe, Gerhard

    2011-05-12

    The faithful storage of a quantum bit (qubit) of light is essential for long-distance quantum communication, quantum networking and distributed quantum computing. The required optical quantum memory must be able to receive and recreate the photonic qubit; additionally, it must store an unknown quantum state of light better than any classical device. So far, these two requirements have been met only by ensembles of material particles that store the information in collective excitations. Recent developments, however, have paved the way for an approach in which the information exchange occurs between single quanta of light and matter. This single-particle approach allows the material qubit to be addressed, which has fundamental advantages for realistic implementations. First, it enables a heralding mechanism that signals the successful storage of a photon by means of state detection; this can be used to combat inevitable losses and finite efficiencies. Second, it allows for individual qubit manipulations, opening up avenues for in situ processing of the stored quantum information. Here we demonstrate the most fundamental implementation of such a quantum memory, by mapping arbitrary polarization states of light into and out of a single atom trapped inside an optical cavity. The memory performance is tested with weak coherent pulses and analysed using full quantum process tomography. The average fidelity is measured to be 93%, and low decoherence rates result in qubit coherence times exceeding 180  microseconds. This makes our system a versatile quantum node with excellent prospects for applications in optical quantum gates and quantum repeaters.

  20. Direct observation of the carrier transport process in InGaN quantum wells with a pn-junction

    Science.gov (United States)

    Wu, Haiyan; Ma, Ziguang; Jiang, Yang; Wang, Lu; Yang, Haojun; Li, Yangfeng; Zuo, Peng; Jia, Haiqiang; Wang, Wenxin; Zhou, Junming; Liu, Wuming; Chen, Hong

    2016-11-01

    A new mechanism of light-to-electricity conversion that uses InGaN/GaN QWs with a p-n junction is reported. According to the well established light-to-electricity conversion theory, quantum wells (QWs) cannot be used in solar cells and photodetectors because the photogenerated carriers in QWs usually relax to ground energy levels, owing to quantum confinement, and cannot form a photocurrent. We observe directly that more than 95% of the photoexcited carriers escape from InGaN/GaN QWs to generate a photocurrent, indicating that the thermionic emission and tunneling processes proposed previously cannot explain carriers escaping from QWs. We show that photoexcited carriers can escape directly from the QWs when the device is under working conditions. Our finding challenges the current theory and demonstrates a new prospect for developing highly efficient solar cells and photodetectors. Project supported by the National Natural Science Foundation of China (Grant Nos. 11574362, 61210014, and 11374340) and the Innovative Clean-energy Research and Application Program of Beijing Municipal Science and Technology Commission, China (Grant No. Z151100003515001).

  1. Spatially and spectrally resolved photoluminescence of InGaN MQWs grown on highly Si doped a-plane GaN buffer

    Energy Technology Data Exchange (ETDEWEB)

    Thunert, Martin; Wieneke, Matthias; Dempewolf, Anja; Bertram, Frank; Dadgar, Armin; Krost, Alois; Christen, Juergen [Institute of Experimental Physics, Otto-von-Guericke-University Magdeburg (Germany)

    2011-07-01

    A set of InGaN multi quantum well (MQW) samples grown by MOVPE on highly Si doped a-plane GaN on r-plane sapphire templates has been investigated using spatially resolved photoluminescence spectroscopy ({mu}-PL). The Si doping level of nominal about 10{sup 20} cm{sup -3} leads to three dimensionally grown crystallites mostly terminated by m-facets. The MQW thickness has been systematically varied from nominally 2.1 to 4.2 nm, as well as the InGaN growth temperature, which was varied from 760 C to 700 C. The growth of a-plane GaN based devices leads to a non-polar growth direction avoiding the polarization field affected Quantum-Confined-Stark-Effect. Spatially resolved PL studies show for all samples low near band edge (NBE) GaN emission intensity over the whole area under investigation accompanied by highly intense InGaN MQW emission for single crystallites. The MQW luminescence shows a systematic blueshift with increasing InGaN growth temperature due to lower In incorporation as well as a systematic redshift with increasing MQW thickness. Excitation power dependent spectra at 4 K as well as temperature dependent PL spectra will be presented.

  2. Semipolar InGaN quantum-well laser diode with integrated amplifier for visible light communications

    KAUST Repository

    Shen, Chao

    2018-02-14

    GaN-based semiconductor optical amplifier (SOA) and its integration with laser diode (LD) is an essential building block yet to be demonstrated for III-nitride photonic integrated circuits (PICs) at visible wavelength. This paper presents the InGaN/GaN quantum well (QW) based dual-section LD consisting of integrated amplifier and laser gain regions fabricated on a semipolar GaN substrate. The threshold current in the laser gain region was favorably reduced from 229mA to 135mA at SOA driving voltages, VSOA, of 0V and 6.25V, respectively. The amplification effect was measured based on a large gain of 5.7 dB at VSOA = 6.25V from the increased optical output power of 8.2 mW to 30.5 mW. Such integrated amplifier can be modulated to achieve Gbps data communication using on-off keying technique. The monolithically integrated amplifier-LD paves the way towards the III-nitride on-chip photonic system, providing a compact, low-cost, and multi-functional solution for applications such as smart lighting and visible light communications.

  3. Semipolar InGaN quantum-well laser diode with integrated amplifier for visible light communications

    KAUST Repository

    Shen, Chao; Ng, Tien Khee; Lee, Changmin; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.; Alyamani, Ahmed Y.; El-Desouki, Munir M.; Ooi, Boon S.

    2018-01-01

    GaN-based semiconductor optical amplifier (SOA) and its integration with laser diode (LD) is an essential building block yet to be demonstrated for III-nitride photonic integrated circuits (PICs) at visible wavelength. This paper presents the InGaN/GaN quantum well (QW) based dual-section LD consisting of integrated amplifier and laser gain regions fabricated on a semipolar GaN substrate. The threshold current in the laser gain region was favorably reduced from 229mA to 135mA at SOA driving voltages, VSOA, of 0V and 6.25V, respectively. The amplification effect was measured based on a large gain of 5.7 dB at VSOA = 6.25V from the increased optical output power of 8.2 mW to 30.5 mW. Such integrated amplifier can be modulated to achieve Gbps data communication using on-off keying technique. The monolithically integrated amplifier-LD paves the way towards the III-nitride on-chip photonic system, providing a compact, low-cost, and multi-functional solution for applications such as smart lighting and visible light communications.

  4. InGaN directional coupler made with a one-step etching technique

    Science.gov (United States)

    Gao, Xumin; Yuan, Jialei; Yang, Yongchao; Zhang, Shuai; Shi, Zheng; Li, Xin; Wang, Yongjin

    2017-06-01

    We propose, fabricate and characterize an on-chip integration of light source, InGaN waveguide, directional coupler and photodiode, in which AlGaN layers are used as top and bottom optical claddings to form an InGaN waveguide for guiding the in-plane emitted light from the InGaN/GaN multiple-quantum-well light-emitting diode (MQW-LED). The difference in etch rate caused by different exposure windows leads to an etching depth discrepancy using the one-step etching technique, which forms the InGaN directional coupler with the overlapped underlying slab. Light propagation results directly confirm effective light coupling in the InGaN directional coupler, which is achieved through high-order guided modes. The InGaN waveguide couples the modulated light from the InGaN/GaN MQW-LED and transfers part of light to the coupled waveguide via the InGaN directional coupler. The in-plane InGaN/GaN MQW-photodiode absorbs the guided light by the coupled InGaN waveguide and induces the photocurrent. The on-chip InGaN photonic integration experimentally demonstrates an in-plane light communication with a data transmission of 50 Mbps.

  5. Single photon sources with single semiconductor quantum dots

    Science.gov (United States)

    Shan, Guang-Cun; Yin, Zhang-Qi; Shek, Chan Hung; Huang, Wei

    2014-04-01

    In this contribution, we briefly recall the basic concepts of quantum optics and properties of semiconductor quantum dot (QD) which are necessary to the understanding of the physics of single-photon generation with single QDs. Firstly, we address the theory of quantum emitter-cavity system, the fluorescence and optical properties of semiconductor QDs, and the photon statistics as well as optical properties of the QDs. We then review the localization of single semiconductor QDs in quantum confined optical microcavity systems to achieve their overall optical properties and performances in terms of strong coupling regime, efficiency, directionality, and polarization control. Furthermore, we will discuss the recent progress on the fabrication of single photon sources, and various approaches for embedding single QDs into microcavities or photonic crystal nanocavities and show how to extend the wavelength range. We focus in particular on new generations of electrically driven QD single photon source leading to high repetition rates, strong coupling regime, and high collection efficiencies at elevated temperature operation. Besides, new developments of room temperature single photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for practical single-photon sources are also discussed.

  6. Distributed quantum computing with single photon sources

    International Nuclear Information System (INIS)

    Beige, A.; Kwek, L.C.

    2005-01-01

    Full text: Distributed quantum computing requires the ability to perform nonlocal gate operations between the distant nodes (stationary qubits) of a large network. To achieve this, it has been proposed to interconvert stationary qubits with flying qubits. In contrast to this, we show that distributed quantum computing only requires the ability to encode stationary qubits into flying qubits but not the conversion of flying qubits into stationary qubits. We describe a scheme for the realization of an eventually deterministic controlled phase gate by performing measurements on pairs of flying qubits. Our scheme could be implemented with a linear optics quantum computing setup including sources for the generation of single photons on demand, linear optics elements and photon detectors. In the presence of photon loss and finite detector efficiencies, the scheme could be used to build large cluster states for one way quantum computing with a high fidelity. (author)

  7. Single Photon Experiments and Quantum Complementarity

    Directory of Open Access Journals (Sweden)

    Georgiev D. D.

    2007-04-01

    Full Text Available Single photon experiments have been used as one of the most striking illustrations of the apparently nonclassical nature of the quantum world. In this review we examine the mathematical basis of the principle of complementarity and explain why the Englert-Greenberger duality relation is not violated in the configurations of Unruh and of Afshar.

  8. Demonstrating quantum random with single photons

    International Nuclear Information System (INIS)

    Bronner, Patrick; Strunz, Andreas; Meyn, Jan-Peter; Silberhorn, Christine

    2009-01-01

    We present an experiment for education which demonstrates random transmission or reflection of heralded single photons on beam splitters. With our set-up, we can realize different quantum random experiments by appropriate settings of polarization rotators. The concept of entanglement is motivated by correlated randomness. The experiments are suitable for undergraduate education and are available as interactive screen experiments.

  9. Mixed biexcitons in single quantum wells

    DEFF Research Database (Denmark)

    Wagner, Hans Peter; Langbein, Wolfgang Werner; Hvam, Jørn Märcher

    1999-01-01

    Biexcitonic complexes in a ZnSe single quantum well are investigated by spectrally resolved four-wave mixing (FWM). The formation of heavy-heavy-hole XXh and of mixed heavy-light-hole XXm biexcitons showing binding energies of Delta(h) = 4.8 meV and Delta(m)= 2.8 meV is identified by polarization...

  10. Single-charge tunneling in ambipolar silicon quantum dots

    NARCIS (Netherlands)

    Müller, Filipp

    2015-01-01

    Spin qubits in coupled quantum dots (QDs) are promising for future quantum information processing (QIP). A quantum bit (qubit) is the quantum mechanical analogon of a classical bit. In general, each quantum mechanical two-level system can represent a qubit. For the spin of a single charge carrier

  11. Spin storage in quantum dot ensembles and single quantum dots

    International Nuclear Information System (INIS)

    Heiss, Dominik

    2009-01-01

    This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T 1 =20 ms at B=4 T and T=1 K. A strong magnetic field dependence T 1 ∝B -5 has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with T 1 ∝T -1 . The characteristic dependencies on magnetic field and temperature lead to the identification of the spin relaxation mechanism, which is governed by spin-orbit coupling and mediated by single phonon scattering. This finding is qualitatively supported by the energy dependent measurements. The investigations were extended to a modified device design that enabled studying the spin relaxation dynamics of heavy holes in self-assembled quantum dots. The measurements show a polarization memory effect for holes with up to 0.1 degree of polarization. Furthermore, investigations of the time dynamics of the hole spin relaxation reveal surprisingly long lifetimes T 1 h in the microsecond range, therefore, comparable with

  12. Spin storage in quantum dot ensembles and single quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Heiss, Dominik

    2009-10-15

    This thesis deals with the investigation of spin relaxation of electrons and holes in small ensembles of self-assembled quantum dots using optical techniques. Furthermore, a method to detect the spin orientation in a single quantum dot was developed in the framework of this thesis. A spin storage device was used to optically generate oriented electron spins in small frequency selected quantum dot ensembles using circularly polarized optical excitation. The spin orientation can be determined by the polarization of the time delayed electroluminescence signal generated by the device after a continuously variable storage time. The degree of spin polarized initialization was found to be limited to 0.6 at high magnetic fields, where anisotropic effects are compensated. The spin relaxation was directly measured as a function of magnetic field, lattice temperature and s-shell transition energy of the quantum dot by varying the spin storage time up to 30 ms. Very long spin lifetimes are obtained with a lower limit of T{sub 1}=20 ms at B=4 T and T=1 K. A strong magnetic field dependence T{sub 1}{proportional_to}B{sup -5} has been observed for low temperatures of T=1 K which weakens as the temperature is increased. In addition, the temperature dependence has been determined with T{sub 1}{proportional_to}T{sup -1}. The characteristic dependencies on magnetic field and temperature lead to the identification of the spin relaxation mechanism, which is governed by spin-orbit coupling and mediated by single phonon scattering. This finding is qualitatively supported by the energy dependent measurements. The investigations were extended to a modified device design that enabled studying the spin relaxation dynamics of heavy holes in self-assembled quantum dots. The measurements show a polarization memory effect for holes with up to 0.1 degree of polarization. Furthermore, investigations of the time dynamics of the hole spin relaxation reveal surprisingly long lifetimes T{sub 1}{sup h

  13. Single Molecule Applications of Quantum Dots

    DEFF Research Database (Denmark)

    Rasmussen, Thomas Elmelund; Jauffred, Liselotte; Brewer, Jonathan R.

    2013-01-01

    Fluorescent nanocrystals composed of semiconductor materials were first introduced for biological applications in the late 1990s. The focus of this review is to give a brief survey of biological applications of quantum dots (QDs) at the single QD sensitivity level. These are described as follows: 1......) QD blinking and bleaching statistics, 2) the use of QDs in high speed single particle tracking with a special focus on how to design the biofunctional coatings of QDs which enable specific targeting to single proteins or lipids of interest, 3) a hybrid lipid-DNA analogue binding QDs which allows...... for tracking single lipids in lipid bilayers, 4) two-photon fluorescence correlation spectroscopy of QDs and 5) optical trapping and excitation of single QDs. In all of these applications, the focus is on the single particle sensitivity level of QDs. The high applicability of QDs in live cell imaging...

  14. Efficiency enhancement of InGaN amber MQWs using nanopillar structures

    DEFF Research Database (Denmark)

    Ou, Yiyu; Iida, Daisuke; Liu, Jin

    2018-01-01

    We have investigated the use of nanopillar structures on high indium content InGaN amber multiple quantum well (MQW) samples to enhance the emission efficiency. A significant emission enhancement was observed which can be attributed to the enhancement of internal quantum efficiency and light extr...

  15. Electrical control of single hole spins in nanowire quantum dots

    NARCIS (Netherlands)

    Pribiag, V.S.; Nadj-Perge, S.; Frolov, S.M.; Berg, J.W.G.; Weperen, van I.; Plissard, S.R.; Bakkers, E.P.A.M.; Kouwenhoven, L.P.

    2013-01-01

    The development of viable quantum computation devices will require the ability to preserve the coherence of quantum bits (qubits)1. Single electron spins in semiconductor quantum dots are a versatile platform for quantum information processing, but controlling decoherence remains a considerable

  16. Experimental quantum tossing of a single coin

    International Nuclear Information System (INIS)

    Nguyen, A T; Frison, J; Massar, S; Huy, K Phan

    2008-01-01

    The cryptographic protocol of coin tossing consists of two parties, Alice and Bob, who do not trust each other, but want to generate a random bit. If the parties use a classical communication channel and have unlimited computational resources, one of them can always cheat perfectly. If the parties use a quantum communication channel, there exist protocols such that neither party can cheat perfectly, although they may be able to significantly bias the coin. Here, we analyze in detail how the performance of a quantum coin tossing experiment should be compared to classical protocols, taking into account the inevitable experimental imperfections. We then report an all-optical fiber experiment in which a single coin is tossed whose randomness is higher than achievable by any classical protocol and present some easily realizable cheating strategies by Alice and Bob

  17. On single-time reduction in quantum field theory

    International Nuclear Information System (INIS)

    Arkhipov, A.A.

    1984-01-01

    It is shown, how the causality and spectrality properties in qUantum field theory may help one to carry out a single-time reduction of the Bethe-Salpeter wave fUnction. The single-time reduction technique is not based on any concrete model of the quantum field theory. Axiomatic formulations underline the quantum field theory

  18. Site-controlled InGaN/GaN single-photon-emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Lei; Deng, Hui, E-mail: dengh@umich.edu [Department of Physics, University of Michigan, 450 Church St., Ann Arbor, Michigan 48109 (United States); Teng, Chu-Hsiang; Ku, Pei-Cheng, E-mail: peicheng@umich.edu [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109 (United States)

    2016-04-11

    We report single-photon emission from electrically driven site-controlled InGaN/GaN quantum dots. The device is fabricated from a planar light-emitting diode structure containing a single InGaN quantum well, using a top-down approach. The location, dimension, and height of each single-photon-emitting diode are controlled lithographically, providing great flexibility for chip-scale integration.

  19. Process tomography via sequential measurements on a single quantum system

    CSIR Research Space (South Africa)

    Bassa, H

    2015-09-01

    Full Text Available The authors utilize a discrete (sequential) measurement protocol to investigate quantum process tomography of a single two-level quantum system, with an unknown initial state, undergoing Rabi oscillations. The ignorance of the dynamical parameters...

  20. Entanglement and quantum superposition induced by a single photon

    Science.gov (United States)

    Lü, Xin-You; Zhu, Gui-Lei; Zheng, Li-Li; Wu, Ying

    2018-03-01

    We predict the occurrence of single-photon-induced entanglement and quantum superposition in a hybrid quantum model, introducing an optomechanical coupling into the Rabi model. Originally, it comes from the photon-dependent quantum property of the ground state featured by the proposed hybrid model. It is associated with a single-photon-induced quantum phase transition, and is immune to the A2 term of the spin-field interaction. Moreover, the obtained quantum superposition state is actually a squeezed cat state, which can significantly enhance precision in quantum metrology. This work offers an approach to manipulate entanglement and quantum superposition with a single photon, which might have potential applications in the engineering of new single-photon quantum devices, and also fundamentally broaden the regime of cavity QED.

  1. The effects of Si-doped prelayers on the optical properties of InGaN/GaN single quantum well structures

    Energy Technology Data Exchange (ETDEWEB)

    Davies, M. J., E-mail: Matthew.Davies-2@Manchester.ac.uk; Dawson, P. [School of Physics and Astronomy, Photon Science Institute, University of Manchester, Manchester M13 9PL (United Kingdom); Massabuau, F. C.-P.; Oliver, R. A.; Kappers, M. J.; Humphreys, C. J. [Department of Material Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

    2014-09-01

    In this paper, we report on the effects of including Si-doped (In)GaN prelayers on the low temperature optical properties of a blue-light emitting InGaN/GaN single quantum well. We observed a large blue shift of the photoluminescence peak emission energy and significant increases in the radiative recombination rate for the quantum well structures that incorporated Si-doped prelayers. Simulations of the variation of the conduction and valence band energies show that a strong modification of the band profile occurs for the quantum wells on Si-doped prelayers due to an increase in strength of the surface polarization field. The enhanced surface polarization field opposes the built-in field across the quantum well and thus reduces this built-in electric field. This reduction of the electric field across the quantum well reduces the Quantum Confined Stark Effect and is responsible for the observed blue shift and the change in the recombination dynamics.

  2. Universal quantum gates for Single Cooper Pair Box based quantum computing

    Science.gov (United States)

    Echternach, P.; Williams, C. P.; Dultz, S. C.; Braunstein, S.; Dowling, J. P.

    2000-01-01

    We describe a method for achieving arbitrary 1-qubit gates and controlled-NOT gates within the context of the Single Cooper Pair Box (SCB) approach to quantum computing. Such gates are sufficient to support universal quantum computation.

  3. Photoluminescence studies of single InGaAs quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1999-01-01

    Semiconductor quantum dots are considered a promising material system for future optical devices and quantum computers. We have studied the low-temperature photoluminescence properties of single InGaAs quantum dots embedded in GaAs. The high spatial resolution required for resolving single dots...... to resolve luminescence lines from individual quantum dots, revealing an atomic-like spectrum of sharp transition lines. A parameter of fundamental importance is the intrinsic linewidth of these transitions. Using high-resolution spectroscopy we have determined the linewidth and investigated its dependence...... on temperature, which gives information about how the exciton confined to the quantum dot interacts with the surrounding lattice....

  4. InGaN nanoinclusions in an AlGaN matrix

    International Nuclear Information System (INIS)

    Sizov, V. S.; Tsatsul'nikov, A. F.; Lundin, V. V.

    2008-01-01

    GaN-based structures with InGaN quantum dots in the active region emitting in the near-ultraviolet region are studied. In this study, two types of structures, namely, with InGaN quantum dots in a GaN or AlGaN matrix, are compared. Photoluminescence spectra are obtained for both types of structures in a temperature range of 80-300 K and at various pumping densities, and electroluminescence spectra are obtained for light-emitting (LED) structures with various types of active region. It is shown that the structures with quantum dots in the AlGaN matrix are more stable thermally due to the larger localization energy compared with quantum dots in the GaN matrix. Due to this, the LED structures with quantum dots in an AlGaN matrix are more effective.

  5. Growth mechanisms of plasma-assisted molecular beam epitaxy of green emission InGaN/GaN single quantum wells at high growth temperatures

    International Nuclear Information System (INIS)

    Yang, W. C.; Wu, C. H.; Tseng, Y. T.; Chiu, S. Y.; Cheng, K. Y.

    2015-01-01

    The results of the growth of thin (∼3 nm) InGaN/GaN single quantum wells (SQWs) with emission wavelengths in the green region by plasma-assisted molecular beam epitaxy are present. An improved two-step growth method using a high growth temperature up to 650 °C is developed to increase the In content of the InGaN SQW to 30% while maintaining a strong luminescence intensity near a wavelength of 506 nm. The indium composition in InGaN/GaN SQW grown under group-III-rich condition increases with increasing growth temperature following the growth model of liquid phase epitaxy. Further increase in the growth temperature to 670 °C does not improve the photoluminescence property of the material due to rapid loss of indium from the surface and, under certain growth conditions, the onset of phase separation

  6. Crystallographically uniform arrays of ordered (In)GaN nanocolumns

    Energy Technology Data Exchange (ETDEWEB)

    Gačević, Ž., E-mail: gacevic@isom.upm.es; Bengoechea-Encabo, A.; Albert, S.; Calleja, E. [ETSIT-ISOM, Universidad Politécnica de Madrid, Avda. Complutense s/n, 28040 Madrid (Spain); Torres-Pardo, A.; González-Calbet, J. M. [Dept. Química Inorgánica, Universidad Complutense, 28040 Madrid (Spain); CEI Campus Moncloa, UCM-UPM, Madrid (Spain)

    2015-01-21

    In this work, through a comparative study of self-assembled (SA) and selective area grown (SAG) (In)GaN nanocolumn (NC) ensembles, we first give a detailed insight into improved crystallographic uniformity (homogeneity of crystallographic tilts and twists) of the latter ones. The study, performed making use of: reflective high energy electron diffraction, X-ray diffraction and scanning electron microscopy, reveals that unlike their SA counterparts, the ensembles of SAG NCs show single epitaxial relationship to both sapphire(0001) and Si(111) underlying substrates. In the second part of the article, making use of X-ray diffraction, we directly show that the selective area growth leads to improved compositional uniformity of InGaN NC ensembles. This further leads to improved spectral purity of their luminescence, as confirmed by comparative macro-photoluminescence measurements performed on SA and SAG InGaN NC ensembles. An improved crystallographic uniformity of NC ensembles facilitates their integration into optoelectronic devices, whereas their improved compositional uniformity allows for their employment in single-color optoelectronic applications.

  7. Improvement of carrier injection symmetry and quantum efficiency in InGaN light-emitting diodes with Mg delta-doped barriers

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, F.; Can, N.; Hafiz, S.; Monavarian, M.; Das, S.; Avrutin, V.; Özgür, Ü., E-mail: uozgur@vcu.edu; Morkoç, H. [Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, Virginia 23284 (United States)

    2015-05-04

    The effect of δ-doping of In{sub 0.06}Ga{sub 0.94}N barriers with Mg on the quantum efficiency of blue light-emitting-diodes (LEDs) with active regions composed of 6 (hex) 3-nm In{sub 0.15}Ga{sub 0.85}N is investigated. Compared to the reference sample, δ-doping of the first barrier on the n-side of the LED structure improves the peak external quantum efficiency (EQE) by 20%, owing to the increased hole concentration in the wells adjacent to the n-side, as confirmed by numerical simulations of carrier distributions across the active region. Doping the second barrier, in addition to the first one, did not further enhance the EQE, which likely indicates compensation of improved hole injection by degradation of the active region quality due to Mg doping. Both LEDs with Mg δ-doped barriers effectively suppress the drop of efficiency at high injection when compared to the reference sample, and the onset of EQE peak roll-off shifts from ∼80 A/cm{sup 2} in the reference LED to ∼120 A/cm{sup 2} in the LEDs with Mg δ-doped barriers.

  8. Improvement of carrier injection symmetry and quantum efficiency in InGaN light-emitting diodes with Mg delta-doped barriers

    International Nuclear Information System (INIS)

    Zhang, F.; Can, N.; Hafiz, S.; Monavarian, M.; Das, S.; Avrutin, V.; Özgür, Ü.; Morkoç, H.

    2015-01-01

    The effect of δ-doping of In 0.06 Ga 0.94 N barriers with Mg on the quantum efficiency of blue light-emitting-diodes (LEDs) with active regions composed of 6 (hex) 3-nm In 0.15 Ga 0.85 N is investigated. Compared to the reference sample, δ-doping of the first barrier on the n-side of the LED structure improves the peak external quantum efficiency (EQE) by 20%, owing to the increased hole concentration in the wells adjacent to the n-side, as confirmed by numerical simulations of carrier distributions across the active region. Doping the second barrier, in addition to the first one, did not further enhance the EQE, which likely indicates compensation of improved hole injection by degradation of the active region quality due to Mg doping. Both LEDs with Mg δ-doped barriers effectively suppress the drop of efficiency at high injection when compared to the reference sample, and the onset of EQE peak roll-off shifts from ∼80 A/cm 2 in the reference LED to ∼120 A/cm 2 in the LEDs with Mg δ-doped barriers

  9. Improvement of carrier injection symmetry and quantum efficiency in InGaN light-emitting diodes with Mg delta-doped barriers

    Science.gov (United States)

    Zhang, F.; Can, N.; Hafiz, S.; Monavarian, M.; Das, S.; Avrutin, V.; Özgür, Ü.; Morkoç, H.

    2015-05-01

    The effect of δ-doping of In0.06Ga0.94N barriers with Mg on the quantum efficiency of blue light-emitting-diodes (LEDs) with active regions composed of 6 (hex) 3-nm In0.15Ga0.85N is investigated. Compared to the reference sample, δ-doping of the first barrier on the n-side of the LED structure improves the peak external quantum efficiency (EQE) by 20%, owing to the increased hole concentration in the wells adjacent to the n-side, as confirmed by numerical simulations of carrier distributions across the active region. Doping the second barrier, in addition to the first one, did not further enhance the EQE, which likely indicates compensation of improved hole injection by degradation of the active region quality due to Mg doping. Both LEDs with Mg δ-doped barriers effectively suppress the drop of efficiency at high injection when compared to the reference sample, and the onset of EQE peak roll-off shifts from ˜80 A/cm2 in the reference LED to ˜120 A/cm2 in the LEDs with Mg δ-doped barriers.

  10. InGaN multiple-quantum-well epifilms on GaN-sillicon substrates for microcavities and surface-emitting lasers

    International Nuclear Information System (INIS)

    Lee, June Key; Cho, Hoon; Kim, Bok Hee; Park, Si Hyun; Gu, Erdan; Watson, Ian; Dawson, Martin

    2006-01-01

    We report the processing of InGaN/GaN epifilms on GaN-silicon substrates. High-quality InGaN/GaN multi-quantum wells (MQWs) were grown on GaN-silicon substrates, and their membranes were successfully fabricated using a selective wet etching of silicon followed by a dry etching of the AlGaN buffer layer. With atomic force microscope (AFM) measurements and photoluminescence (PL) measurements, we investigated the physical and the optical properties of the InGaN/GaN MQWs membranes. On the InGaN/GaN MQW membranes, dielectric distributed Bragg reflector (DBRs) were successfully deposited, which give, new possibilities for use in GaN microcavity and surface-emitting laser fabrication.

  11. Microstructural dependency of optical properties of m-plane InGaN multiple quantum wells grown on 2° misoriented bulk GaN substrates

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Fengzai; Barnard, Jonathan S.; Zhu, Tongtong; Oehler, Fabrice; Kappers, Menno J.; Oliver, Rachel A., E-mail: rao28@cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

    2015-08-24

    A non-polar m-plane structure consisting of five InGaN/GaN quantum wells (QWs) was grown on ammonothermal bulk GaN by metal-organic vapor phase epitaxy. Surface step bunches propagating through the QW stack were found to accommodate the 2° substrate miscut towards the -c direction. Both large steps with heights of a few tens of nanometres and small steps between one and a few atomic layers in height are observed, the former of which exhibit cathodoluminescence at longer wavelengths than the adjacent m-plane terraces. This is attributed to the formation of semi-polar facets at the steps on which the QWs are shown to be thicker and have higher Indium contents than those in the adjacent m-plane regions. Discrete basal-plane stacking faults (BSFs) were occasionally initiated from the QWs on the main m-plane terraces, but groups of BSFs were frequently observed to initiate from those on the large steps, probably related to the increased strain associated with the locally higher indium content and thickness.

  12. Microstructural dependency of optical properties of m-plane InGaN multiple quantum wells grown on 2° misoriented bulk GaN substrates

    International Nuclear Information System (INIS)

    Tang, Fengzai; Barnard, Jonathan S.; Zhu, Tongtong; Oehler, Fabrice; Kappers, Menno J.; Oliver, Rachel A.

    2015-01-01

    A non-polar m-plane structure consisting of five InGaN/GaN quantum wells (QWs) was grown on ammonothermal bulk GaN by metal-organic vapor phase epitaxy. Surface step bunches propagating through the QW stack were found to accommodate the 2° substrate miscut towards the -c direction. Both large steps with heights of a few tens of nanometres and small steps between one and a few atomic layers in height are observed, the former of which exhibit cathodoluminescence at longer wavelengths than the adjacent m-plane terraces. This is attributed to the formation of semi-polar facets at the steps on which the QWs are shown to be thicker and have higher Indium contents than those in the adjacent m-plane regions. Discrete basal-plane stacking faults (BSFs) were occasionally initiated from the QWs on the main m-plane terraces, but groups of BSFs were frequently observed to initiate from those on the large steps, probably related to the increased strain associated with the locally higher indium content and thickness

  13. Investigation of new approaches for InGaN growth with high indium content for CPV application

    Energy Technology Data Exchange (ETDEWEB)

    Arif, Muhammad; Salvestrini, Jean Paul, E-mail: salvestr@metz.supelec.fr [CNRS, UMI 2958 Georgia Tech - CNRS, 57070 Metz (France); Université de Lorraine & CentraleSupelec, LMOPS, EA4423, 57070 Metz (France); Sundaram, Suresh; Streque, Jérémy; Gmili, Youssef El [CNRS, UMI 2958 Georgia Tech - CNRS, 57070 Metz (France); Puybaret, Renaud; Voss, Paul L. [Georgia Institute of Technology, UMI 2958 Georgia Tech - CNRS, 57070 Metz (France); Belahsene, Sofiane; Ramdane, Abderahim; Martinez, Anthony; Patriarche, Gilles [CNRS, UPR LPN, Route de Nozay, 91460 Marcoussis (France); Fix, Thomas; Slaoui, Abdelillah [CNRS, ICUBE - Université de Strasbourg (France); Ougazzaden, Abdallah [CNRS, UMI 2958 Georgia Tech - CNRS, 57070 Metz (France); Georgia Institute of Technology, UMI 2958 Georgia Tech - CNRS, 57070 Metz (France)

    2015-09-28

    We propose to use two new approaches that may overcome the issues of phase separation and high dislocation density in InGaN-based PIN solar cells. The first approach consists in the growth of a thick multi-layered InGaN/GaN absorber. The periodical insertion of the thin GaN interlayers should absorb the In excess and relieve compressive strain. The InGaN layers need to be thin enough to remain fully strained and without phase separation. The second approach consists in the growth of InGaN nano-structures for the achievement of high In content thick InGaN layers. It allows the elimination of the preexisting dislocations in the underlying template. It also allows strain relaxation of InGaN layers without any dislocations, leading to higher In incorporation and reduced piezo-electric effect. The two approaches lead to structural, morphological, and luminescence properties that are significantly improved when compared to those of thick InGaN layers. Corresponding full PIN structures have been realized by growing a p-type GaN layer on the top the half PIN structures. External quantum efficiency, electro-luminescence, and photo-current characterizations have been carried out on the different structures and reveal an enhancement of the performances of the InGaN PIN PV cells when the thick InGaN layer is replaced by either InGaN/GaN multi-layered or InGaN nanorod layer.

  14. Coupling of single quantum dots to a photonic crystal waveguide

    DEFF Research Database (Denmark)

    Lund-Hansen, Toke; Stobbe, Søren; Julsgaard, Brian

    Efficient and high quality single-photon sources is a key element in quantum information processing using photons. As a consequence, much current research is focused on realizing all-solid-state nanophotonic single-photon sources. Single photons can be harvested with high efficiency if the emitter...... is coupled efficiently to a single enhanced mode. One popular approach has been to couple single quantum dots to a nanocavity but a limiting factor in this configuration is that in order to apply the photon it should subsequently be coupled out of the cavity, reducing the overall efficiency significantly...

  15. Tunable single quantum dot nanocavities for cavity QED experiments

    International Nuclear Information System (INIS)

    Kaniber, M; Laucht, A; Neumann, A; Bichler, M; Amann, M-C; Finley, J J

    2008-01-01

    We present cavity quantum electrodynamics experiments performed on single quantum dots embedded in two-dimensional photonic crystal nanocavities. We begin by describing the structural and optical properties of the quantum dot sample and the photonic crystal nanocavities and compare the experimental results with three-dimensional calculations of the photonic properties. The influence of the tailored photonic environment on the quantum dot spontaneous emission dynamics is studied using spectrally and spatially dependent time-resolved spectroscopy. In ensemble and single dot measurements we show that the photonic crystals strongly enhance the photon extraction efficiency and, therefore, are a promising concept for realizing efficient single-photon sources. Furthermore, we demonstrate single-photon emission from an individual quantum dot that is spectrally detuned from the cavity mode. The need for controlling the spectral dot-cavity detuning is discussed on the basis of shifting either the quantum dot emission via temperature tuning or the cavity mode emission via a thin film deposition technique. Finally, we discuss the recently discovered non-resonant coupling mechanism between quantum dot emission and cavity mode for large detunings which drastically lowers the purity of single-photon emission from dots that are spectrally coupled to nanocavity modes.

  16. Optical Studies of Single Quantum Dots

    National Research Council Canada - National Science Library

    Gammon, Daniel; Steel, Duncan G

    2002-01-01

    ...: the atomlike entities known as quantum dots (QDs). Measuring 1-100 nm across, QDs are semiconductor structures in which the electron wavefunction is confined in all three dimensions by the potential energy barriers that form the QD's boundaries...

  17. Non-Markovian spontaneous emission from a single quantum dot

    DEFF Research Database (Denmark)

    Madsen, Kristian Høeg; Ates, Serkan; Lund-Hansen, Toke

    2011-01-01

    We observe non-Markovian dynamics of a single quantum dot when tuned into resonance with a cavity mode. Excellent agreement between experiment and theory is observed providing the first quantitative description of such a system.......We observe non-Markovian dynamics of a single quantum dot when tuned into resonance with a cavity mode. Excellent agreement between experiment and theory is observed providing the first quantitative description of such a system....

  18. Optical levitation of microdroplet containing a single quantum dot

    OpenAIRE

    Minowa, Yosuke; Kawai, Ryoichi; Ashida, Masaaki

    2014-01-01

    We demonstrate the optical levitation or trapping in helium gas of a single quantum dot (QD) within a liquid droplet. Bright single photon emission from the levitated QD in the droplet was observed for more than 200 s. The observed photon count rates are consistent with the value theoretically estimated from the two-photon-action cross section. This paper presents the realization of an optically levitated solid-state quantum emitter. This paper was published in Optics Letters and is made avai...

  19. Quantum Logic with Cavity Photons From Single Atoms.

    Science.gov (United States)

    Holleczek, Annemarie; Barter, Oliver; Rubenok, Allison; Dilley, Jerome; Nisbet-Jones, Peter B R; Langfahl-Klabes, Gunnar; Marshall, Graham D; Sparrow, Chris; O'Brien, Jeremy L; Poulios, Konstantinos; Kuhn, Axel; Matthews, Jonathan C F

    2016-07-08

    We demonstrate quantum logic using narrow linewidth photons that are produced with an a priori nonprobabilistic scheme from a single ^{87}Rb atom strongly coupled to a high-finesse cavity. We use a controlled-not gate integrated into a photonic chip to entangle these photons, and we observe nonclassical correlations between photon detection events separated by periods exceeding the travel time across the chip by 3 orders of magnitude. This enables quantum technology that will use the properties of both narrow-band single photon sources and integrated quantum photonics.

  20. Operating single quantum emitters with a compact Stirling cryocooler.

    Science.gov (United States)

    Schlehahn, A; Krüger, L; Gschrey, M; Schulze, J-H; Rodt, S; Strittmatter, A; Heindel, T; Reitzenstein, S

    2015-01-01

    The development of an easy-to-operate light source emitting single photons has become a major driving force in the emerging field of quantum information technology. Here, we report on the application of a compact and user-friendly Stirling cryocooler in the field of nanophotonics. The Stirling cryocooler is used to operate a single quantum emitter constituted of a semiconductor quantum dot (QD) at a base temperature below 30 K. Proper vibration decoupling of the cryocooler and its surrounding enables free-space micro-photoluminescence spectroscopy to identify and analyze different charge-carrier states within a single quantum dot. As an exemplary application in quantum optics, we perform a Hanbury-Brown and Twiss experiment demonstrating a strong suppression of multi-photon emission events with g((2))(0) Stirling-cooled single quantum emitter under continuous wave excitation. Comparative experiments performed on the same quantum dot in a liquid helium (LHe)-flow cryostat show almost identical values of g((2))(0) for both configurations at a given temperature. The results of this proof of principle experiment demonstrate that low-vibration Stirling cryocoolers that have so far been considered exotic to the field of nanophotonics are an attractive alternative to expensive closed-cycle cryostats or LHe-flow cryostats, which could pave the way for the development of high-quality table-top non-classical light sources.

  1. Operating single quantum emitters with a compact Stirling cryocooler

    Energy Technology Data Exchange (ETDEWEB)

    Schlehahn, A.; Krüger, L.; Gschrey, M.; Schulze, J.-H.; Rodt, S.; Strittmatter, A.; Heindel, T., E-mail: tobias.heindel@tu-berlin.de; Reitzenstein, S. [Institute of Solid State Physics, Technische Universität Berlin, 10623 Berlin (Germany)

    2015-01-15

    The development of an easy-to-operate light source emitting single photons has become a major driving force in the emerging field of quantum information technology. Here, we report on the application of a compact and user-friendly Stirling cryocooler in the field of nanophotonics. The Stirling cryocooler is used to operate a single quantum emitter constituted of a semiconductor quantum dot (QD) at a base temperature below 30 K. Proper vibration decoupling of the cryocooler and its surrounding enables free-space micro-photoluminescence spectroscopy to identify and analyze different charge-carrier states within a single quantum dot. As an exemplary application in quantum optics, we perform a Hanbury-Brown and Twiss experiment demonstrating a strong suppression of multi-photon emission events with g{sup (2)}(0) < 0.04 from this Stirling-cooled single quantum emitter under continuous wave excitation. Comparative experiments performed on the same quantum dot in a liquid helium (LHe)-flow cryostat show almost identical values of g{sup (2)}(0) for both configurations at a given temperature. The results of this proof of principle experiment demonstrate that low-vibration Stirling cryocoolers that have so far been considered exotic to the field of nanophotonics are an attractive alternative to expensive closed-cycle cryostats or LHe-flow cryostats, which could pave the way for the development of high-quality table-top non-classical light sources.

  2. Linear optical quantum computing in a single spatial mode.

    Science.gov (United States)

    Humphreys, Peter C; Metcalf, Benjamin J; Spring, Justin B; Moore, Merritt; Jin, Xian-Min; Barbieri, Marco; Kolthammer, W Steven; Walmsley, Ian A

    2013-10-11

    We present a scheme for linear optical quantum computing using time-bin-encoded qubits in a single spatial mode. We show methods for single-qubit operations and heralded controlled-phase (cphase) gates, providing a sufficient set of operations for universal quantum computing with the Knill-Laflamme-Milburn [Nature (London) 409, 46 (2001)] scheme. Our protocol is suited to currently available photonic devices and ideally allows arbitrary numbers of qubits to be encoded in the same spatial mode, demonstrating the potential for time-frequency modes to dramatically increase the quantum information capacity of fixed spatial resources. As a test of our scheme, we demonstrate the first entirely single spatial mode implementation of a two-qubit quantum gate and show its operation with an average fidelity of 0.84±0.07.

  3. Two-Way Communication with a Single Quantum Particle

    Science.gov (United States)

    Del Santo, Flavio; Dakić, Borivoje

    2018-02-01

    In this Letter we show that communication when restricted to a single information carrier (i.e., single particle) and finite speed of propagation is fundamentally limited for classical systems. On the other hand, quantum systems can surpass this limitation. We show that communication bounded to the exchange of a single quantum particle (in superposition of different spatial locations) can result in "two-way signaling," which is impossible in classical physics. We quantify the discrepancy between classical and quantum scenarios by the probability of winning a game played by distant players. We generalize our result to an arbitrary number of parties and we show that the probability of success is asymptotically decreasing to zero as the number of parties grows, for all classical strategies. In contrast, quantum strategy allows players to win the game with certainty.

  4. Quantum Privacy Amplification for a Sequence of Single Qubits

    International Nuclear Information System (INIS)

    Deng Fuguo; Long Guilu

    2006-01-01

    We present a scheme for quantum privacy amplification (QPA) for a sequence of single qubits. The QPA procedure uses a unitary operation with two controlled-not gates and a Hadamard gate. Every two qubits are performed with the unitary gate operation, and a measurement is made on one photon and the other one is retained. The retained qubit carries the state information of the discarded one. In this way, the information leakage is reduced. The procedure can be performed repeatedly so that the information leakage is reduced to any arbitrarily low level. With this QPA scheme, the quantum secure direct communication with single qubits can be implemented with arbitrarily high security. We also exploit this scheme to do privacy amplification on the single qubits in quantum information sharing for long-distance communication with quantum repeaters.

  5. Circular polarization memory in single Quantum Dots

    International Nuclear Information System (INIS)

    Khatsevich, S.; Poem, E.; Benny, Y.; Marderfeld, I.; Gershoni, D.; Badolato, A.; Petroff, P. M.

    2010-01-01

    Under quasi-resonant circularly polarized optical excitation, charged quantum dots may emit polarized light. We measured various transitions with either positive, negative or no circular-polarization memory. We explain these observations and quantitatively calculate the polarization spectrum. Our model use the full configuration-interaction method, including the electron-hole exchange interaction, for calculating the quantum dot's confined many-carrier states, along with one assumption regarding the spin relaxation of photoexcited carriers: Electrons maintain their initial spin polarization, while holes do not.

  6. Electrical control of single hole spins in nanowire quantum dots.

    Science.gov (United States)

    Pribiag, V S; Nadj-Perge, S; Frolov, S M; van den Berg, J W G; van Weperen, I; Plissard, S R; Bakkers, E P A M; Kouwenhoven, L P

    2013-03-01

    The development of viable quantum computation devices will require the ability to preserve the coherence of quantum bits (qubits). Single electron spins in semiconductor quantum dots are a versatile platform for quantum information processing, but controlling decoherence remains a considerable challenge. Hole spins in III-V semiconductors have unique properties, such as a strong spin-orbit interaction and weak coupling to nuclear spins, and therefore, have the potential for enhanced spin control and longer coherence times. A weaker hyperfine interaction has previously been reported in self-assembled quantum dots using quantum optics techniques, but the development of hole-spin-based electronic devices in conventional III-V heterostructures has been limited by fabrication challenges. Here, we show that gate-tunable hole quantum dots can be formed in InSb nanowires and used to demonstrate Pauli spin blockade and electrical control of single hole spins. The devices are fully tunable between hole and electron quantum dots, which allows the hyperfine interaction strengths, g-factors and spin blockade anisotropies to be compared directly in the two regimes.

  7. Tuning Single Quantum Dot Emission with a Micromirror.

    Science.gov (United States)

    Yuan, Gangcheng; Gómez, Daniel; Kirkwood, Nicholas; Mulvaney, Paul

    2018-02-14

    The photoluminescence of single quantum dots fluctuates between bright (on) and dark (off) states, also termed fluorescence intermittency or blinking. This blinking limits the performance of quantum dot-based devices such as light-emitting diodes and solar cells. However, the origins of the blinking remain unresolved. Here, we use a movable gold micromirror to determine both the quantum yield of the bright state and the orientation of the excited state dipole of single quantum dots. We observe that the quantum yield of the bright state is close to unity for these single QDs. Furthermore, we also study the effect of a micromirror on blinking, and then evaluate excitation efficiency, biexciton quantum yield, and detection efficiency. The mirror does not modify the off-time statistics, but it does change the density of optical states available to the quantum dot and hence the on times. The duration of the on times can be lengthened due to an increase in the radiative recombination rate.

  8. Single trapped cold ions: a testing ground for quantum mechanics

    International Nuclear Information System (INIS)

    Maniscalco, S

    2005-01-01

    In this article I review some results obtained during my PhD work in the group of Professor Messina, at the University of Palermo. I discuss some proposals aimed at exploring fundamental issues of quantum theory, e.g. entanglement and quantum superpositions, in the context of single trapped ions. This physical context turns out to be extremely well suited both for studying fundamental features of quantum mechanics, such as the quantum-classical border, and for technological applications such as quantum logic gates and quantum registers. I focus on some procedures for engineering nonclassical states of the vibrational motion of the centre of mass of the ion. I consider both the case in which the ion interacts with classical laser beams and the case of interaction with a quantized mode of light. In particular, I discuss the generation of Schroedinger cat-like states, Bell states and Greenberger-Horn-Zeilinger states. The schemes for generating nonclassical states stem from two different quantum processes: the parity effect and the quantum state manipulation via quantum non-demolition measurement. Finally, I consider a microscopic theory of the interaction of a quantum harmonic oscillator (the centre of mass of the ion in the trapped ion context) with a bosonic thermal environment. Using an exact approach to the dynamics, I discuss a quantum theory of heating of trapped ions able to describe both the short time non-Markovian regime and the thermalization process. I conclude showing briefly how the trapped ion systems can be used as simulators of key models of open quantum systems such as the Caldeira-Leggett model. (phd tutorial)

  9. Room temperature excitation spectroscopy of single quantum dots

    Directory of Open Access Journals (Sweden)

    Christian Blum

    2011-08-01

    Full Text Available We report a single molecule detection scheme to investigate excitation spectra of single emitters at room temperature. We demonstrate the potential of single emitter photoluminescence excitation spectroscopy by recording excitation spectra of single CdSe nanocrystals over a wide spectral range of 100 nm. The spectra exhibit emission intermittency, characteristic of single emitters. We observe large variations in the spectra close to the band edge, which represent the individual heterogeneity of the observed quantum dots. We also find specific excitation wavelengths for which the single quantum dots analyzed show an increased propensity for a transition to a long-lived dark state. We expect that the additional capability of recording excitation spectra at room temperature from single emitters will enable insights into the photophysics of emitters that so far have remained inaccessible.

  10. Authenticated multi-user quantum key distribution with single particles

    Science.gov (United States)

    Lin, Song; Wang, Hui; Guo, Gong-De; Ye, Guo-Hua; Du, Hong-Zhen; Liu, Xiao-Fen

    2016-03-01

    Quantum key distribution (QKD) has been growing rapidly in recent years and becomes one of the hottest issues in quantum information science. During the implementation of QKD on a network, identity authentication has been one main problem. In this paper, an efficient authenticated multi-user quantum key distribution (MQKD) protocol with single particles is proposed. In this protocol, any two users on a quantum network can perform mutual authentication and share a secure session key with the assistance of a semi-honest center. Meanwhile, the particles, which are used as quantum information carriers, are not required to be stored, therefore the proposed protocol is feasible with current technology. Finally, security analysis shows that this protocol is secure in theory.

  11. A quantum optical transistor with a single quantum dot in a photonic crystal nanocavity.

    Science.gov (United States)

    Li, Jin-Jin; Zhu, Ka-Di

    2011-02-04

    Laser and strong coupling can coexist in a single quantum dot (QD) coupled to a photonic crystal nanocavity. This provides an important clue towards the realization of a quantum optical transistor. Using experimentally realistic parameters, in this work, theoretical analysis shows that such a quantum optical transistor can be switched on or off by turning on or off the pump laser, which corresponds to attenuation or amplification of the probe laser, respectively. Furthermore, based on this quantum optical transistor, an all-optical measurement of the vacuum Rabi splitting is also presented. The idea of associating a quantum optical transistor with this coupled QD-nanocavity system may achieve images of light controlling light in all-optical logic circuits and quantum computers.

  12. A quantum optical transistor with a single quantum dot in a photonic crystal nanocavity

    International Nuclear Information System (INIS)

    Li Jinjin; Zhu Kadi

    2011-01-01

    Laser and strong coupling can coexist in a single quantum dot (QD) coupled to a photonic crystal nanocavity. This provides an important clue towards the realization of a quantum optical transistor. Using experimentally realistic parameters, in this work, theoretical analysis shows that such a quantum optical transistor can be switched on or off by turning on or off the pump laser, which corresponds to attenuation or amplification of the probe laser, respectively. Furthermore, based on this quantum optical transistor, an all-optical measurement of the vacuum Rabi splitting is also presented. The idea of associating a quantum optical transistor with this coupled QD-nanocavity system may achieve images of light controlling light in all-optical logic circuits and quantum computers.

  13. Measurement of quantum noise in a single-electron transistor near the quantum limit

    Science.gov (United States)

    Xue, W. W.; Ji, Z.; Pan, Feng; Stettenheim, Joel; Blencowe, M. P.; Rimberg, A. J.

    2009-09-01

    Quantum measurement has challenged physicists for almost a century. Classically, there is no lower bound on the noise a measurement may add. Quantum mechanically, however, measuring a system necessarily perturbs it. When applied to electrical amplifiers, this means that improved sensitivity requires increased backaction that itself contributes noise. The result is a strict quantum limit on added amplifier noise. To approach this limit, a quantum-limited amplifier must possess an ideal balance between sensitivity and backaction; furthermore, its noise must dominate that of subsequent classical amplifiers. Here, we report the first complete and quantitative measurement of the quantum noise of a superconducting single-electron transistor (S-SET) near a double Cooper-pair resonance predicted to have the right combination of sensitivity and backaction. A simultaneous measurement of our S-SET's charge sensitivity indicates that it operates within a factor of 3.6 of the quantum limit, a fourfold improvement over the nearest comparable results.

  14. Attacking quantum key distribution with single-photon two-qubit quantum logic

    International Nuclear Information System (INIS)

    Shapiro, Jeffrey H.; Wong, Franco N. C.

    2006-01-01

    The Fuchs-Peres-Brandt (FPB) probe realizes the most powerful individual attack on Bennett-Brassard 1984 quantum key distribution (BB84 QKD) by means of a single controlled-NOT (CNOT) gate. This paper describes a complete physical simulation of the FPB-probe attack on polarization-based BB84 QKD using a deterministic CNOT constructed from single-photon two-qubit quantum logic. Adding polarization-preserving quantum nondemolition measurements of photon number to this configuration converts the physical simulation into a true deterministic realization of the FPB attack

  15. Semi-quantum Dialogue Based on Single Photons

    Science.gov (United States)

    Ye, Tian-Yu; Ye, Chong-Qiang

    2018-02-01

    In this paper, we propose two semi-quantum dialogue (SQD) protocols by using single photons as the quantum carriers, where one requires the classical party to possess the measurement capability and the other does not have this requirement. The security toward active attacks from an outside Eve in the first SQD protocol is guaranteed by the complete robustness of present semi-quantum key distribution (SQKD) protocols, the classical one-time pad encryption, the classical party's randomization operation and the decoy photon technology. The information leakage problem of the first SQD protocol is overcome by the classical party' classical basis measurements on the single photons carrying messages which makes him share their initial states with the quantum party. The security toward active attacks from Eve in the second SQD protocol is guaranteed by the classical party's randomization operation, the complete robustness of present SQKD protocol and the classical one-time pad encryption. The information leakage problem of the second SQD protocol is overcome by the quantum party' classical basis measurements on each two adjacent single photons carrying messages which makes her share their initial states with the classical party. Compared with the traditional information leakage resistant QD protocols, the advantage of the proposed SQD protocols lies in that they only require one party to have quantum capabilities. Compared with the existing SQD protocol, the advantage of the proposed SQD protocols lies in that they only employ single photons rather than two-photon entangled states as the quantum carriers. The proposed SQD protocols can be implemented with present quantum technologies.

  16. Single-temperature quantum engine without feedback control.

    Science.gov (United States)

    Yi, Juyeon; Talkner, Peter; Kim, Yong Woon

    2017-08-01

    A cyclically working quantum-mechanical engine that operates at a single temperature is proposed. Its energy input is delivered by a quantum measurement. The functioning of the engine does not require any feedback control. We analyze work, heat, and the efficiency of the engine for the case of a working substance that is governed by the laws of quantum mechanics and that can be adiabatically compressed and expanded. The obtained general expressions are exemplified for a spin in an adiabatically changing magnetic field and a particle moving in a potential with slowly changing shape.

  17. Realizing InGaN monolithic solar-photoelectrochemical cells for artificial photosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Dahal, R.; Pantha, B. N.; Li, J.; Lin, J. Y.; Jiang, H. X., E-mail: hx.jiang@ttu.edu [Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas 79409 (United States)

    2014-04-07

    InGaN alloys are very promising for solar water splitting because they have direct bandgaps that cover almost the whole solar spectrum. The demonstration of direct solar-to-fuel conversion without external bias with the sunlight being the only energy input would pave the way for realizing photoelectrochemical (PEC) production of hydrogen by using InGaN. A monolithic solar-PEC cell based on InGaN/GaN multiple quantum wells capable to directly generate hydrogen gas under zero bias via solar water splitting is reported. Under the irradiation by a simulated sunlight (1-sun with 100 mW/cm{sup 2}), a 1.5% solar-to-fuel conversion efficiency has been achieved under zero bias, setting a fresh benchmark of employing III-nitrides for artificial photosynthesis. Time dependent hydrogen gas production photocurrent measured over a prolonged period (measured for 7 days) revealed an excellent chemical stability of InGaN in aqueous solution of hydrobromic acid. The results provide insights into the architecture design of using InGaN for artificial photosynthesis to provide usable clean fuel (hydrogen gas) with the sunlight being the only energy input.

  18. Nanoselective area growth and characterization of dislocation-free InGaN nanopyramids on AlN buffered Si(111) templates

    Energy Technology Data Exchange (ETDEWEB)

    Sundaram, S.; El Gmili, Y. [CNRS, UMI 2958 Georgia Tech-CNRS, 2 Rue Marconi, 57070 Metz (France); Puybaret, R.; Li, X.; Bonanno, P. L.; Voss, P. L.; Ougazzaden, A., E-mail: abdallah.ougazzaden@georgiatech-metz.fr [CNRS, UMI 2958 Georgia Tech-CNRS, 2 Rue Marconi, 57070 Metz (France); School of Electrical and Computer Engineering, Georgia Institute of Technology, GT Lorraine, 57070 Metz (France); Pantzas, K.; Patriarche, G. [CNRS, UPR LPN, Route de Nozay, 91460 Marcoussis (France); Salvestrini, J. P. [Universite de Lorraine, Centrale Supelec, LMOPS, EA 4423, 2 rue E. Belin, 57070 Metz (France)

    2015-09-14

    We report the metal organic chemical vapor deposition growth of dislocation-free 100 nm thick hexagonal InGaN nanopyramid arrays with up to 33% of indium content by nano-selective area growth on patterned AlN/Si (111) substrates. InGaN grown on SiO{sub 2} patterned templates exhibit high selectivity. Their single crystal structure is confirmed by scanning transmission electron microscope combined with an energy dispersive X-ray analysis, which also reveals the absence of threading dislocations in the InGaN nanopyramids due to elastic strain relaxation mechanisms. Cathodoluminescence measurements on a single InGaN nanopyramid clearly show an improvement of the optical properties when compared to planar InGaN grown under the same conditions. The good structural, morphological, and optical quality of the InGaN nanostructures grown on AlN/Si indicates that the nano-selective area growth technology is attractive for the realization of site-controlled indium-rich InGaN nanostructure-based devices and can also be transferred to other highly mismatched substrates.

  19. Quantum State Transfer from a Single Photon to a Distant Quantum-Dot Electron Spin

    Science.gov (United States)

    He, Yu; He, Yu-Ming; Wei, Yu-Jia; Jiang, Xiao; Chen, Kai; Lu, Chao-Yang; Pan, Jian-Wei; Schneider, Christian; Kamp, Martin; Höfling, Sven

    2017-08-01

    Quantum state transfer from flying photons to stationary matter qubits is an important element in the realization of quantum networks. Self-assembled semiconductor quantum dots provide a promising solid-state platform hosting both single photon and spin, with an inherent light-matter interface. Here, we develop a method to coherently and actively control the single-photon frequency bins in superposition using electro-optic modulators, and measure the spin-photon entanglement with a fidelity of 0.796 ±0.020 . Further, by Greenberger-Horne-Zeilinger-type state projection on the frequency, path, and polarization degrees of freedom of a single photon, we demonstrate quantum state transfer from a single photon to a single electron spin confined in an InGaAs quantum dot, separated by 5 m. The quantum state mapping from the photon's polarization to the electron's spin is demonstrated along three different axes on the Bloch sphere, with an average fidelity of 78.5%.

  20. Radial composition of single InGaN nanowires: a combined study by EDX, Raman spectroscopy, and X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Gomez-Gomez, M.; Garro, N.; Cantarero, A. [Institut de Ciencia dels Materials, Universitat de Valencia, Paterna (Spain); Segura-Ruiz, J.; Martinez-Criado, G.; Chu, M.H. [European Synchrotron Radiation Facility, Experiments Division, Grenoble (France); Denker, C.; Malindretos, J.; Rizzi, A. [IV. Physikalisches Institut, Georg-August-Universitaet Goettingen (Germany)

    2013-10-15

    The radial alloy distribution of In{sub x} Ga{sub 1-x}N nanowires grown by plasma-assisted molecular beam epitaxy has been investigated by three different techniques with nanometric spatial resolution and capability to study single nanowires. Energy-dispersive X-ray spectroscopy radial line-scans revealed a gradient in the alloy composition of individual nanowires. Resonant Raman scattering and spatially resolved X-ray diffraction showed the existence of three distinctive regions with different alloy composition. The combination of the three techniques provides robust evidence of the spontaneous formation of a core-shell structure with a thin Ga-richer shell wrapping an In-rich core at the bottom part of the nanowires. This composition-modulated nanostructure offers an attractive way to explore new device concepts in fully epitaxial nanowire-based solar cells. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. Radial composition of single InGaN nanowires: a combined study by EDX, Raman spectroscopy, and X-ray diffraction

    International Nuclear Information System (INIS)

    Gomez-Gomez, M.; Garro, N.; Cantarero, A.; Segura-Ruiz, J.; Martinez-Criado, G.; Chu, M.H.; Denker, C.; Malindretos, J.; Rizzi, A.

    2013-01-01

    The radial alloy distribution of In x Ga 1-x N nanowires grown by plasma-assisted molecular beam epitaxy has been investigated by three different techniques with nanometric spatial resolution and capability to study single nanowires. Energy-dispersive X-ray spectroscopy radial line-scans revealed a gradient in the alloy composition of individual nanowires. Resonant Raman scattering and spatially resolved X-ray diffraction showed the existence of three distinctive regions with different alloy composition. The combination of the three techniques provides robust evidence of the spontaneous formation of a core-shell structure with a thin Ga-richer shell wrapping an In-rich core at the bottom part of the nanowires. This composition-modulated nanostructure offers an attractive way to explore new device concepts in fully epitaxial nanowire-based solar cells. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Coupling single emitters to quantum plasmonic circuits

    DEFF Research Database (Denmark)

    Huck, Alexander; Andersen, Ulrik Lund

    2016-01-01

    In recent years, the controlled coupling of single-photon emitters to propagating surface plasmons has been intensely studied, which is fueled by the prospect of a giant photonic nonlinearity on a nanoscaled platform. In this article, we will review the recent progress on coupling single emitters...

  3. Quantum design rules for single molecule logic gates.

    Science.gov (United States)

    Renaud, N; Hliwa, M; Joachim, C

    2011-08-28

    Recent publications have demonstrated how to implement a NOR logic gate with a single molecule using its interaction with two surface atoms as logical inputs [W. Soe et al., ACS Nano, 2011, 5, 1436]. We demonstrate here how this NOR logic gate belongs to the general family of quantum logic gates where the Boolean truth table results from a full control of the quantum trajectory of the electron transfer process through the molecule by very local and classical inputs practiced on the molecule. A new molecule OR gate is proposed for the logical inputs to be also single metal atoms, one per logical input.

  4. Single electron-spin memory with a semiconductor quantum dot

    International Nuclear Information System (INIS)

    Young, Robert J; Dewhurst, Samuel J; Stevenson, R Mark; Atkinson, Paola; Bennett, Anthony J; Ward, Martin B; Cooper, Ken; Ritchie, David A; Shields, Andrew J

    2007-01-01

    We show storage of the circular polarization of an optical field, transferring it to the spin-state of an individual electron confined in a single semiconductor quantum dot. The state is subsequently read out through the electronically-triggered emission of a single photon. The emitted photon shares the same polarization as the initial pulse but has a different energy, making the transfer of quantum information between different physical systems possible. With an applied magnetic field of 2 T, spin memory is preserved for at least 1000 times more than the exciton's radiative lifetime

  5. Deterministic Single-Photon Source for Distributed Quantum Networking

    International Nuclear Information System (INIS)

    Kuhn, Axel; Hennrich, Markus; Rempe, Gerhard

    2002-01-01

    A sequence of single photons is emitted on demand from a single three-level atom strongly coupled to a high-finesse optical cavity. The photons are generated by an adiabatically driven stimulated Raman transition between two atomic ground states, with the vacuum field of the cavity stimulating one branch of the transition, and laser pulses deterministically driving the other branch. This process is unitary and therefore intrinsically reversible, which is essential for quantum communication and networking, and the photons should be appropriate for all-optical quantum information processing

  6. A molecular quantum spin network controlled by a single qubit.

    Science.gov (United States)

    Schlipf, Lukas; Oeckinghaus, Thomas; Xu, Kebiao; Dasari, Durga Bhaktavatsala Rao; Zappe, Andrea; de Oliveira, Felipe Fávaro; Kern, Bastian; Azarkh, Mykhailo; Drescher, Malte; Ternes, Markus; Kern, Klaus; Wrachtrup, Jörg; Finkler, Amit

    2017-08-01

    Scalable quantum technologies require an unprecedented combination of precision and complexity for designing stable structures of well-controllable quantum systems on the nanoscale. It is a challenging task to find a suitable elementary building block, of which a quantum network can be comprised in a scalable way. We present the working principle of such a basic unit, engineered using molecular chemistry, whose collective control and readout are executed using a nitrogen vacancy (NV) center in diamond. The basic unit we investigate is a synthetic polyproline with electron spins localized on attached molecular side groups separated by a few nanometers. We demonstrate the collective readout and coherent manipulation of very few (≤ 6) of these S = 1/2 electronic spin systems and access their direct dipolar coupling tensor. Our results show that it is feasible to use spin-labeled peptides as a resource for a molecular qubit-based network, while at the same time providing simple optical readout of single quantum states through NV magnetometry. This work lays the foundation for building arbitrary quantum networks using well-established chemistry methods, which has many applications ranging from mapping distances in single molecules to quantum information processing.

  7. Enhancement of indium incorporation to InGaN MQWs on AlN/GaN periodic multilayers

    Science.gov (United States)

    Monavarian, Morteza; Hafiz, Shopan; Das, Saikat; Izyumskaya, Natalia; Özgür, Ümit; Morkoç, Hadis; Avrutin, Vitaliy

    2016-02-01

    The effect of compressive strain in buffer layer on strain relaxation and indium incorporation in InGaN multi-quantum wells (MQWs) is studied for two sets of samples grown side by side on both relaxed GaN layers and strained 10-pairs of AlN/GaN periodic multilayers. The 14-nm AlN layers were utilized in both multilayers, while GaN thickness was 4.5 and 2.5 nm in the first and the second set, respectively. The obtained results for the InGaN active layers on relaxed GaN and AlN/GaN periodic multilayers indicate enhanced indium incorporation for more relaxed InGaN active layers providing a variety of emission colors from purple to green.

  8. Multiparty quantum key agreement with single particles

    Science.gov (United States)

    Liu, Bin; Gao, Fei; Huang, Wei; Wen, Qiao-yan

    2013-04-01

    Two conditions must be satisfied in a secure quantum key agreement (QKA) protocol: (1) outside eavesdroppers cannot gain the generated key without introducing any error; (2) the generated key cannot be determined by any non-trivial subset of the participants. That is, a secure QKA protocol can not only prevent the outside attackers from stealing the key, but also resist the attack from inside participants, i.e. some dishonest participants determine the key alone by illegal means. How to resist participant attack is an aporia in the design of QKA protocols, especially the multi-party ones. In this paper we present the first secure multiparty QKA protocol against both outside and participant attacks. Further more, we have proved its security in detail.

  9. Multi-microscopy study of the influence of stacking faults and three-dimensional In distribution on the optical properties of m-plane InGaN quantum wells grown on microwire sidewalls

    Energy Technology Data Exchange (ETDEWEB)

    Mancini, L.; Lefebvre, W.; Houard, J.; Blum, I.; Vurpillot, F.; Rigutti, L., E-mail: lorenzo.rigutti@univ-rouen.fr [Groupe de Physique des Matériaux, UMR CNRS 6634, Normandie University, INSA and University of Rouen, 76800 St Etienne du Rouvray (France); Hernández-Maldonado, D. [Groupe de Physique des Matériaux, UMR CNRS 6634, Normandie University, INSA and University of Rouen, 76800 St Etienne du Rouvray (France); SuperSTEM STFC Daresbury Laboratories, Warrington WA4 4AD (United Kingdom); Eymery, J.; Durand, C. [CEA, CNRS, Université Grenoble Alpes, 38000 Grenoble (France); Tchernycheva, M. [Institut d' Electronique Fondamentale, UMR CNRS 8622, University Paris Saclay, 91405 Orsay (France)

    2016-01-25

    The optical properties of m-plane InGaN/GaN quantum wells grown on microwire sidewalls were investigated carrying out a correlative scanning transmission electron microscopy (STEM), atom probe tomography (APT), and micro-photoluminescence study applied on single nanoscale field-emission tips obtained by a focused ion beam annular milling. Instead of assuming simple rectangular composition profiles, yielding misleading predictions for the optical transition energies, we can thus take into account actual compositional distributions and the presence of stacking faults (SFs). SFs were shown to be responsible for a lowering of the recombination energies of the order of 0.1 eV with respect to those expected for defect-free quantum wells (QWs). Such energy reduction allows establishing a good correspondence between the transition energies observed by optical spectroscopy and those calculated on the basis of the QWs In measured composition and distribution assessed by STEM structural analysis and APT chemical mapping.

  10. Single-Atom Gating of Quantum State Superpositions

    Energy Technology Data Exchange (ETDEWEB)

    Moon, Christopher

    2010-04-28

    The ultimate miniaturization of electronic devices will likely require local and coherent control of single electronic wavefunctions. Wavefunctions exist within both physical real space and an abstract state space with a simple geometric interpretation: this state space - or Hilbert space - is spanned by mutually orthogonal state vectors corresponding to the quantized degrees of freedom of the real-space system. Measurement of superpositions is akin to accessing the direction of a vector in Hilbert space, determining an angle of rotation equivalent to quantum phase. Here we show that an individual atom inside a designed quantum corral1 can control this angle, producing arbitrary coherent superpositions of spatial quantum states. Using scanning tunnelling microscopy and nanostructures assembled atom-by-atom we demonstrate how single spins and quantum mirages can be harnessed to image the superposition of two electronic states. We also present a straightforward method to determine the atom path enacting phase rotations between any desired state vectors. A single atom thus becomes a real-space handle for an abstract Hilbert space, providing a simple technique for coherent quantum state manipulation at the spatial limit of condensed matter.

  11. Quantum teleportation via noisy bipartite and tripartite accelerating quantum states: beyond the single mode approximation

    Science.gov (United States)

    Zounia, M.; Shamirzaie, M.; Ashouri, A.

    2017-09-01

    In this paper quantum teleportation of an unknown quantum state via noisy maximally bipartite (Bell) and maximally tripartite (Greenberger-Horne-Zeilinger (GHZ)) entangled states are investigated. We suppose that one of the observers who would receive the sent state accelerates uniformly with respect to the sender. The interactions of the quantum system with its environment during the teleportation process impose noises. These (unital and nonunital) noises are: phase damping, phase flip, amplitude damping and bit flip. In expressing the modes of the Dirac field used as qubits, in the accelerating frame, the so-called single mode approximation is not imposed. We calculate the fidelities of teleportation, and discuss their behaviors using suitable plots. The effects of noise, acceleration and going beyond the single mode approximation are discussed. Although the Bell states bring higher fidelities than GHZ states, the global behaviors of the two quantum systems with respect to some noise types, and therefore their fidelities, are different.

  12. Single-ion quantum lock-in amplifier.

    Science.gov (United States)

    Kotler, Shlomi; Akerman, Nitzan; Glickman, Yinnon; Keselman, Anna; Ozeri, Roee

    2011-05-05

    Quantum metrology uses tools from quantum information science to improve measurement signal-to-noise ratios. The challenge is to increase sensitivity while reducing susceptibility to noise, tasks that are often in conflict. Lock-in measurement is a detection scheme designed to overcome this difficulty by spectrally separating signal from noise. Here we report on the implementation of a quantum analogue to the classical lock-in amplifier. All the lock-in operations--modulation, detection and mixing--are performed through the application of non-commuting quantum operators to the electronic spin state of a single, trapped Sr(+) ion. We significantly increase its sensitivity to external fields while extending phase coherence by three orders of magnitude, to more than one second. Using this technique, we measure frequency shifts with a sensitivity of 0.42 Hz Hz(-1/2) (corresponding to a magnetic field measurement sensitivity of 15 pT Hz(-1/2)), obtaining an uncertainty of less than 10 mHz (350 fT) after 3,720 seconds of averaging. These sensitivities are limited by quantum projection noise and improve on other single-spin probe technologies by two orders of magnitude. Our reported sensitivity is sufficient for the measurement of parity non-conservation, as well as the detection of the magnetic field of a single electronic spin one micrometre from an ion detector with nanometre resolution. As a first application, we perform light shift spectroscopy of a narrow optical quadrupole transition. Finally, we emphasize that the quantum lock-in technique is generic and can potentially enhance the sensitivity of any quantum sensor. ©2011 Macmillan Publishers Limited. All rights reserved

  13. Authenticated Quantum Key Distribution with Collective Detection using Single Photons

    Science.gov (United States)

    Huang, Wei; Xu, Bing-Jie; Duan, Ji-Tong; Liu, Bin; Su, Qi; He, Yuan-Hang; Jia, Heng-Yue

    2016-10-01

    We present two authenticated quantum key distribution (AQKD) protocols by utilizing the idea of collective (eavesdropping) detection. One is a two-party AQKD protocol, the other is a multiparty AQKD protocol with star network topology. In these protocols, the classical channels need not be assumed to be authenticated and the single photons are used as the quantum information carriers. To achieve mutual identity authentication and establish a random key in each of the proposed protocols, only one participant should be capable of preparing and measuring single photons, and the main quantum ability that the rest of the participants should have is just performing certain unitary operations. Security analysis shows that these protocols are free from various kinds of attacks, especially the impersonation attack and the man-in-the-middle (MITM) attack.

  14. Resonance fluorescence and quantum interference of a single NV center

    Science.gov (United States)

    Ma, Yong-Hong; Zhang, Xue-Feng; Wu, E.

    2017-11-01

    The detection of a single nitrogen-vacancy center in diamond has attracted much interest, since it is expected to lead to innovative applications in various domains of quantum information, including quantum metrology, information processing and communications, as well as in various nanotechnologies, such as biological and subdiffraction limit imaging, and tests of entanglement in quantum mechanics. We propose a novel scheme of a single NV center coupled with a multi-mode superconducting microwave cavity driven by coherent fields in squeezed vacuum. We numerically investigate the spectra in-phase quadrature and out-of-phase quadrature for different driving regimes with or without detunings. It shows that the maximum squeezing can be obtained for optimal Rabi fields. Moreover, with the same parameters, the maximum squeezing is greatly increased when the detunings are nonzero compared to the resonance case.

  15. Quantum delayed-choice experiment with a single neutral atom.

    Science.gov (United States)

    Li, Gang; Zhang, Pengfei; Zhang, Tiancai

    2017-10-01

    We present a proposal to implement a quantum delayed-choice (QDC) experiment with a single neutral atom, such as a rubidium or cesium atom. In our proposal, a Ramsey interferometer is adopted to observe the wave-like or particle-like behaviors of a single atom depending on the existence or absence of the second π/2-rotation. A quantum-controlled π/2-rotation on target atom is realized through a Rydberg-Rydberg interaction by another ancilla atom. It shows that a heavy neutral atom can also have a morphing behavior between the particle and the wave. The realization of the QDC experiment with such heavy neutral atoms not only is significant to understand the Bohr's complementarity principle in matter-wave and matter-particle domains but also has great potential on the quantum information process with neutral atoms.

  16. Quantum Sensing of Mechanical Motion with a Single InAs Quantum Dot

    Science.gov (United States)

    2017-03-01

    Wenner, J. M. Martinis, and A. N. Cleland, “ Quantum ground state and single- phonon control of a mechanical resonator.,” Nature, vol. 464, no...G. Nogues, S. Seidelin, J. Poizat, O. Arcizet, and M. Richard, “Strain-mediated coupling in a quantum dot- mechanical oscillator hybrid system...Pos 4 Dep 5 School of N upling quantu ctive for funda dded a semico nical resonat vances in thi es large ch ell as the spin for quantum s antum Dots

  17. Quantum sensors based on single diamond defects

    International Nuclear Information System (INIS)

    Jelezko Fedor

    2014-01-01

    NV centers in diamond are promising sensors able to detect electric and magnetic fields at nanoscale. Here we report on the detection of biomolecules using magnetic noise induced by their electron and nuclear spins. Presented results show first steps towards establishing novel sensing technology for visualizing single proteins and study of their dynamics. (author)

  18. Rapid single flux quantum logic in high temperature superconductor technology

    NARCIS (Netherlands)

    Shunmugavel, K.

    2006-01-01

    A Josephson junction is the basic element of rapid single flux quantum logic (RSFQ) circuits. A high operating speed and low power consumption are the main advantages of RSFQ logic over semiconductor electronic circuits. To realize complex RSFQ circuits in HTS technology one needs a reproducible

  19. Waveguide superconducting single-photon autocorrelators for quantum photonic applications

    NARCIS (Netherlands)

    Sahin, D.; Gaggero, A.; Frucci, G.; Jahanmirinejad, S.; Sprengers, J.P.; Mattioli, F.; Leoni, R.; Beetz, J.; Lermer, M.; Kamp, M.; Höfling, S.; Fiore, A.; Hasan, Z.U.; Hemmer, P.R.; Lee, H.; Santori, C.M.

    2013-01-01

    We report a novel component for integrated quantum photonic applications, a waveguide single-photon autocorrelator. It is based on two superconducting nanowire detectors patterned onto the same GaAs ridge waveguide. Combining the electrical output of the two detectors in a correlation card enables

  20. Coherent excitonic nonlinearity versus inhomogeneous broadening in single quantum wells

    DEFF Research Database (Denmark)

    Langbein, Wolfgang Werner; Borri, Paola; Hvam, Jørn Märcher

    1998-01-01

    The coherent response of excitons in semiconductor nanostructures, as measured in four wave mixing (FWM) experiments, depends strongly on the inhomogeneous broadening of the exciton transition. We investigate GaAs-AlGaAs single quantum wells (SQW) of 4 nm to 25 nm well width. Two main mechanisms...

  1. Free-space quantum electrodynamics with a single Rydberg superatom

    DEFF Research Database (Denmark)

    Paris-Mandoki, Asaf; Braun, Christoph; Kumlin, Jan

    2017-01-01

    The interaction of a single photon with an individual two-level system is the textbook example of quantum electrodynamics. Achieving strong coupling in this system has so far required confinement of the light field inside resonators or waveguides. Here, we demonstrate strong coherent coupling...

  2. Single-photon generation with InAs quantum dots

    International Nuclear Information System (INIS)

    Santori, Charles; Fattal, David; Vuckovic, Jelena; Solomon, Glenn S; Yamamoto, Yoshihisa

    2004-01-01

    Single-photon generation using InAs quantum dots in pillar microcavities is described. The effects on performance of the excitation wavelength and polarization, and the collection bandwidth and polarization, are studied in detail. The efficiency and photon state purity of these devices have been measured, and issues affecting these parameters are discussed. Prospects for improved devices are also discussed

  3. Low temperature p-type doping of (Al)GaN layers using ammonia molecular beam epitaxy for InGaN laser diodes

    Science.gov (United States)

    Malinverni, M.; Lamy, J.-M.; Martin, D.; Feltin, E.; Dorsaz, J.; Castiglia, A.; Rossetti, M.; Duelk, M.; Vélez, C.; Grandjean, N.

    2014-12-01

    We demonstrate state-of-the-art p-type (Al)GaN layers deposited at low temperature (740 °C) by ammonia molecular beam epitaxy (NH3-MBE) to be used as top cladding of laser diodes (LDs) with the aim of further reducing the thermal budget on the InGaN quantum well active region. Typical p-type GaN resistivities and contact resistances are 0.4 Ω cm and 5 × 10-4 Ω cm2, respectively. As a test bed, we fabricated a hybrid laser structure emitting at 400 nm combining n-type AlGaN cladding and InGaN active region grown by metal-organic vapor phase epitaxy, with the p-doped waveguide and cladding layers grown by NH3-MBE. Single-mode ridge-waveguide LD exhibits a threshold voltage as low as 4.3 V for an 800 × 2 μm2 ridge dimension and a threshold current density of ˜5 kA cm-2 in continuous wave operation. The series resistance of the device is 6 Ω and the resistivity is 1.5 Ω cm, confirming thereby the excellent electrical properties of p-type Al0.06Ga0.94N:Mg despite the low growth temperature.

  4. A Single Molecule Investigation of the Photostability of Quantum Dots

    DEFF Research Database (Denmark)

    Christensen, Eva Arnspang; Kulatunga, Pasad; Lagerholm, B. Christoffer

    2012-01-01

    Quantum dots (QDs) are very attractive probes for multi-color fluorescence applications. We report here however that single QDs that are subject to continuous blue excitation from a 100W mercury arc lamp will undergo a continuous blue-switching of the emission wavelength eventually reaching a per...... is especially detrimental for multi-color single molecule applications, as we regularly observe spectral blue-shifts of 50 nm, or more even after only ten seconds of illumination....

  5. Single-passage read-out of atomic quantum memory

    DEFF Research Database (Denmark)

    Fiurasek, J; Sherson, J; Opatrny, T

    2005-01-01

    Retrieving quantum information, collective atomic spin systems, quantum memory Udgivelsesdato: 17 Feb.......Retrieving quantum information, collective atomic spin systems, quantum memory Udgivelsesdato: 17 Feb....

  6. Single-cell atomic quantum memory for light

    International Nuclear Information System (INIS)

    Opatrny, Tomas

    2006-01-01

    Recent experiments demonstrating atomic quantum memory for light [B. Julsgaard et al., Nature 432, 482 (2004)] involve two macroscopic samples of atoms, each with opposite spin polarization. It is shown here that a single atomic cell is enough for the memory function if the atoms are optically pumped with suitable linearly polarized light, and quadratic Zeeman shift and/or ac Stark shift are used to manipulate rotations of the quadratures. This should enhance the performance of our quantum memory devices since less resources are needed and losses of light in crossing different media boundaries are avoided

  7. Theoretical Modeling of Intensity Noise in InGaN Semiconductor Lasers

    Directory of Open Access Journals (Sweden)

    Moustafa Ahmed

    2014-01-01

    Full Text Available This paper introduces modeling and simulation of the noise properties of the blue-violet InGaN laser diodes. The noise is described in terms of the spectral properties of the relative intensity noise (RIN. We examine the validity of the present noise modeling by comparing the simulated results with the experimental measurements available in literature. We also compare the obtained noise results with those of AlGaAs lasers. Also, we examine the influence of gain suppression on the quantum RIN. In addition, we examine the changes in the RIN level when describing the gain suppression by the case of inhomogeneous spectral broadening. The results show that RIN of the InGaN laser is nearly 9 dB higher than that of the AlGaAs laser.

  8. Resonance fluorescence and quantum jumps in single atoms: Testing the randomness of quantum mechanics

    International Nuclear Information System (INIS)

    Erber, T.; Hammerling, P.; Hockney, G.; Porrati, M.; Putterman, S.; La Jolla Institute, La Jolla, California 92037; Department of Physics, University of California, Los Angeles, California 90024)

    1989-01-01

    When a single trapped 198 Hg + ion is illuminated by two lasers, each tuned to an approximate transition, the resulting fluorescence switches on and off in a series of pulses resembling a bistable telegraph. This intermittent fluorescence can also be obtained by optical pumping with a single laser. Quantum jumps between successive atomic levels may be traced directly with multiple-resonance fluorescence. Atomic transition rates and photon antibunching distributions can be inferred from the pulse statistics and compared with quantum theory. Stochastic tests also indicate that the quantum telegraphs are good random number generators. During periods when the fluorescence is switched off, the radiationless atomic currents that generate the telegraph signals can be adjusted by varying the laser illumination: if this coherent evolution of the wave functions is sustained over sufficiently long time intervals, novel interactive precision measurements, near the limits of the time-energy uncertainty relations, are possible. Copyright 1989 Academic Press, Inc

  9. Real-time single-molecule imaging of quantum interference.

    Science.gov (United States)

    Juffmann, Thomas; Milic, Adriana; Müllneritsch, Michael; Asenbaum, Peter; Tsukernik, Alexander; Tüxen, Jens; Mayor, Marcel; Cheshnovsky, Ori; Arndt, Markus

    2012-03-25

    The observation of interference patterns in double-slit experiments with massive particles is generally regarded as the ultimate demonstration of the quantum nature of these objects. Such matter-wave interference has been observed for electrons, neutrons, atoms and molecules and, in contrast to classical physics, quantum interference can be observed when single particles arrive at the detector one by one. The build-up of such patterns in experiments with electrons has been described as the "most beautiful experiment in physics". Here, we show how a combination of nanofabrication and nano-imaging allows us to record the full two-dimensional build-up of quantum interference patterns in real time for phthalocyanine molecules and for derivatives of phthalocyanine molecules, which have masses of 514 AMU and 1,298 AMU respectively. A laser-controlled micro-evaporation source was used to produce a beam of molecules with the required intensity and coherence, and the gratings were machined in 10-nm-thick silicon nitride membranes to reduce the effect of van der Waals forces. Wide-field fluorescence microscopy detected the position of each molecule with an accuracy of 10 nm and revealed the build-up of a deterministic ensemble interference pattern from single molecules that arrived stochastically at the detector. In addition to providing this particularly clear demonstration of wave-particle duality, our approach could also be used to study larger molecules and explore the boundary between quantum and classical physics.

  10. Multi-group dynamic quantum secret sharing with single photons

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Hongwei [School of Science and State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Ma, Haiqiang, E-mail: hqma@bupt.edu.cn [School of Science and State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Wei, Kejin [School of Science and State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Yang, Xiuqing [School of Science, Beijing Jiaotong University, Beijing 100044 (China); Qu, Wenxiu; Dou, Tianqi; Chen, Yitian; Li, Ruixue; Zhu, Wu [School of Science and State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China)

    2016-07-15

    In this letter, we propose a novel scheme for the realization of single-photon dynamic quantum secret sharing between a boss and three dynamic agent groups. In our system, the boss can not only choose one of these three groups to share the secret with, but also can share two sets of independent keys with two groups without redistribution. Furthermore, the security of communication is enhanced by using a control mode. Compared with previous schemes, our scheme is more flexible and will contribute to a practical application. - Highlights: • A multi-group dynamic quantum secret sharing with single photons scheme is proposed. • Any one of the groups can be chosen to share secret through controlling the polarization of photons. • Two sets of keys can be shared simultaneously without redistribution.

  11. Optical levitation of a microdroplet containing a single quantum dot

    Science.gov (United States)

    Minowa, Yosuke; Kawai, Ryoichi; Ashida, Masaaki

    2015-03-01

    We demonstrate the optical levitation or trapping in helium gas of a single quantum dot (QD) within a liquid droplet. Bright single photon emission from the levitated QD in the droplet was observed for more than 200 s. The observed photon count rates are consistent with the value theoretically estimated from the two-photon-action cross section. This paper presents the realization of an optically levitated solid-state quantum emitter. This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: https://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-40-6-906. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.

  12. Single-copy entanglement in critical quantum spin chains

    International Nuclear Information System (INIS)

    Eisert, J.; Cramer, M.

    2005-01-01

    We consider the single-copy entanglement as a quantity to assess quantum correlations in the ground state in quantum many-body systems. We show for a large class of models that already on the level of single specimens of spin chains, criticality is accompanied with the possibility of distilling a maximally entangled state of arbitrary dimension from a sufficiently large block deterministically, with local operations and classical communication. These analytical results--which refine previous results on the divergence of block entropy as the rate at which maximally entangled pairs can be distilled from many identically prepared chains--are made quantitative for general isotropic translationally invariant spin chains that can be mapped onto a quasifree fermionic system, and for the anisotropic XY model. For the XX model, we provide the asymptotic scaling of ∼(1/6)log 2 (L), and contrast it with the block entropy

  13. Single-cell magnetic imaging using a quantum diamond microscope.

    Science.gov (United States)

    Glenn, D R; Lee, K; Park, H; Weissleder, R; Yacoby, A; Lukin, M D; Lee, H; Walsworth, R L; Connolly, C B

    2015-08-01

    We apply a quantum diamond microscope for detection and imaging of immunomagnetically labeled cells. This instrument uses nitrogen-vacancy (NV) centers in diamond for correlated magnetic and fluorescence imaging. Our device provides single-cell resolution and a field of view (∼1 mm(2)) two orders of magnitude larger than that of previous NV imaging technologies, enabling practical applications. To illustrate, we quantified cancer biomarkers expressed by rare tumor cells in a large population of healthy cells.

  14. Quantum-classical interface based on single flux quantum digital logic

    Science.gov (United States)

    McDermott, R.; Vavilov, M. G.; Plourde, B. L. T.; Wilhelm, F. K.; Liebermann, P. J.; Mukhanov, O. A.; Ohki, T. A.

    2018-04-01

    We describe an approach to the integrated control and measurement of a large-scale superconducting multiqubit array comprising up to 108 physical qubits using a proximal coprocessor based on the Single Flux Quantum (SFQ) digital logic family. Coherent control is realized by irradiating the qubits directly with classical bitstreams derived from optimal control theory. Qubit measurement is performed by a Josephson photon counter, which provides access to the classical result of projective quantum measurement at the millikelvin stage. We analyze the power budget and physical footprint of the SFQ coprocessor and discuss challenges and opportunities associated with this approach.

  15. Quantum optics with single nanodiamonds flying over gold films: Towards a Robust quantum plasmonics

    Energy Technology Data Exchange (ETDEWEB)

    Mollet, O.; Drezet, A.; Huant, S. [Institut Néel, CNRS and Université Joseph Fourier, BP 166, F-38042 Grenoble (France)

    2013-12-04

    A nanodiamond (ND) hosting nitrogen-vacancy (NV) color centers is attached on the apex of an optical tip for near-field microscopy. Its fluorescence is used to launch surface plasmon-polaritons (SPPs) in a thin polycrystalline gold film. It is shown that the quantum nature of the initial source of light is preserved after conversion to SPPs. This opens the way to a deterministic quantum plasmonics, where single SPPs can be injected at well-defined positions in a plasmonic device produced by top-down approaches.

  16. Study of excess carrier dynamics in polar, semi-polar, and non-polar (In,Ga)N epilayers and QWs

    Energy Technology Data Exchange (ETDEWEB)

    Aleksiejunas, R. [Institute of Applied Research, Vilnius University, Sauletekio Ave. 9-III, 10222 Vilnius (Lithuania); Laser Research Center, Vilnius University, Sauletekio Ave. 10, 10222 Vilnius (Lithuania); Lubys, L.; Jarasiunas, K. [Institute of Applied Research, Vilnius University, Sauletekio Ave. 9-III, 10222 Vilnius (Lithuania); Vengris, M. [Laser Research Center, Vilnius University, Sauletekio Ave. 10, 10222 Vilnius (Lithuania); Wernicke, T.; Hoffmann, V.; Netzel, C.; Knauer, A.; Weyers, M. [Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12498 Berlin (Germany); Kneissl, M. [Ferdinand-Braun-Institut, Leibniz-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12498 Berlin (Germany); Institute of Solid State Physics, Technische Universitaet Berlin, Hardenbergstr. 36, 10623 Berlin (Germany)

    2011-07-15

    We studied carrier recombination and diffusion in GaN/sapphire templates, (In,Ga)N layers, and (In,Ga)N quantum well structures oriented along the polar [0001], semi-polar [11-22], and non-polar [11-20] orientations by means of light induced transient grating, differential transmission, and photoluminescence optical techniques. We show that the lifetime of excess carriers drops by orders of magnitude when changing the orientation from polar to non-polar, both in GaN templates and (In,Ga)N layers. We attribute the shorter lifetime to carrier trapping by extended structural defects that are more abundant in non-polar grown samples. In addition, we observe pronounced carrier localization effects in the semi- and non-polar layers. We show that thick (In,Ga)N layers inherit the properties of the GaN templates. However, the thin quantum well structures show a lower carrier trapping activity. So, a better electrical quality can be assumed as compared to the thick (In,Ga)N layers. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Single photon emission and quantum ring-cavity coupling in InAs/GaAs quantum rings

    International Nuclear Information System (INIS)

    Gallardo, E; Nowak, A K; Sanvitto, D; Meulen, H P van der; Calleja, J M; MartInez, L J; Prieto, I; Alija, A R; Granados, D; Taboada, A G; GarcIa, J M; Postigo, P A; Sarkar, D

    2010-01-01

    Different InAs/GaAs quantum rings embedded in a photonic crystal microcavity are studied by quantum correlation measurements. Single photon emission, with g (2) (0) values around 0.3, is demonstrated for a quantum ring not coupled to the microcavity. Characteristic rise-times are found to be longer for excitons than for biexcitons, resulting in the time asymmetry of the exciton-biexciton cross-correlation. No antibunching is observed in another quantum ring weakly coupled to the microcavity.

  18. Multi-Color Single Particle Tracking with Quantum Dots

    DEFF Research Database (Denmark)

    Christensen, Eva Arnspang; Brewer, J. R.; Lagerholm, B. C.

    2012-01-01

    . multiplex single molecule sensitivity applications such as single particle tracking (SPT). In order to fully optimize single molecule multiplex application with QDs, we have in this work performed a comprehensive quantitative investigation of the fluorescence intensities, fluorescence intensity fluctuations......Quantum dots (QDs) have long promised to revolutionize fluorescence detection to include even applications requiring simultaneous multi-species detection at single molecule sensitivity. Despite the early promise, the unique optical properties of QDs have not yet been fully exploited in e. g...... further show that there is only a small size advantage in using blue-shifted QDs in biological applications because of the additional size of the water-stabilizing surface coat. Extending previous work, we finally also show that parallel four color multicolor (MC)-SPT with QDs is possible at an image...

  19. Coupling single-molecule magnets to quantum circuits

    International Nuclear Information System (INIS)

    Jenkins, Mark; Martínez-Pérez, María José; Zueco, David; Luis, Fernando; Hümmer, Thomas; García-Ripoll, Juanjo

    2013-01-01

    In this work we study theoretically the coupling of single-molecule magnets (SMMs) to a variety of quantum circuits, including microwave resonators with and without constrictions and flux qubits. The main result of this study is that it is possible to achieve strong and ultrastrong coupling regimes between SMM crystals and the superconducting circuit, with strong hints that such a coupling could also be reached for individual molecules close to constrictions. Building on the resulting coupling strengths and the typical coherence times of these molecules (∼ μs), we conclude that SMMs can be used for coherent storage and manipulation of quantum information, either in the context of quantum computing or in quantum simulations. Throughout the work we also discuss in detail the family of molecules that are most suitable for such operations, based not only on the coupling strength, but also on the typical energy gaps and the simplicity with which they can be tuned and oriented. Finally, we also discuss practical advantages of SMMs, such as the possibility to fabricate the SMMs ensembles on the chip through the deposition of small droplets. (paper)

  20. Dynamical sensitivity control of a single-spin quantum sensor.

    Science.gov (United States)

    Lazariev, Andrii; Arroyo-Camejo, Silvia; Rahane, Ganesh; Kavatamane, Vinaya Kumar; Balasubramanian, Gopalakrishnan

    2017-07-26

    The Nitrogen-Vacancy (NV) defect in diamond is a unique quantum system that offers precision sensing of nanoscale physical quantities at room temperature beyond the current state-of-the-art. The benchmark parameters for nanoscale magnetometry applications are sensitivity, spectral resolution, and dynamic range. Under realistic conditions the NV sensors controlled by conventional sensing schemes suffer from limitations of these parameters. Here we experimentally show a new method called dynamical sensitivity control (DYSCO) that boost the benchmark parameters and thus extends the practical applicability of the NV spin for nanoscale sensing. In contrast to conventional dynamical decoupling schemes, where π pulse trains toggle the spin precession abruptly, the DYSCO method allows for a smooth, analog modulation of the quantum probe's sensitivity. Our method decouples frequency selectivity and spectral resolution unconstrained over the bandwidth (1.85 MHz-392 Hz in our experiments). Using DYSCO we demonstrate high-accuracy NV magnetometry without |2π| ambiguities, an enhancement of the dynamic range by a factor of 4 · 10 3 , and interrogation times exceeding 2 ms in off-the-shelf diamond. In a broader perspective the DYSCO method provides a handle on the inherent dynamics of quantum systems offering decisive advantages for NV centre based applications notably in quantum information and single molecule NMR/MRI.

  1. On-Chip Single-Plasmon Nanocircuit Driven by a Self-Assembled Quantum Dot.

    Science.gov (United States)

    Wu, Xiaofei; Jiang, Ping; Razinskas, Gary; Huo, Yongheng; Zhang, Hongyi; Kamp, Martin; Rastelli, Armando; Schmidt, Oliver G; Hecht, Bert; Lindfors, Klas; Lippitz, Markus

    2017-07-12

    Quantum photonics holds great promise for future technologies such as secure communication, quantum computation, quantum simulation, and quantum metrology. An outstanding challenge for quantum photonics is to develop scalable miniature circuits that integrate single-photon sources, linear optical components, and detectors on a chip. Plasmonic nanocircuits will play essential roles in such developments. However, for quantum plasmonic circuits, integration of stable, bright, and narrow-band single photon sources in the structure has so far not been reported. Here we present a plasmonic nanocircuit driven by a self-assembled GaAs quantum dot. Through a planar dielectric-plasmonic hybrid waveguide, the quantum dot efficiently excites narrow-band single plasmons that are guided in a two-wire transmission line until they are converted into single photons by an optical antenna. Our work demonstrates the feasibility of fully on-chip plasmonic nanocircuits for quantum optical applications.

  2. Universal quantum gates on electron-spin qubits with quantum dots inside single-side optical microcavities.

    Science.gov (United States)

    Wei, Hai-Rui; Deng, Fu-Guo

    2014-01-13

    We present some compact quantum circuits for a deterministic quantum computing on electron-spin qubits assisted by quantum dots inside single-side optical microcavities, including the CNOT, Toffoli, and Fredkin gates. They are constructed by exploiting the giant optical Faraday rotation induced by a single-electron spin in a quantum dot inside a single-side optical microcavity as a result of cavity quantum electrodynamics. Our universal quantum gates have some advantages. First, all the gates are accomplished with a success probability of 100% in principle. Second, our schemes require no additional electron-spin qubits and they are achieved by some input-output processes of a single photon. Third, our circuits for these gates are simple and economic. Moreover, our devices for these gates work in both the weak coupling and the strong coupling regimes, and they are feasible in experiment.

  3. A novel high-efficiency single-mode quantum dot single photon source

    DEFF Research Database (Denmark)

    Gerard, J.M.; Gregersen, Niels; Nielsen, Torben Roland

    2008-01-01

    We present a novel single-mode single photon source exploiting the emission of a semiconductor quantum dot (QD) located inside a photonic wire. Besides an excellent coupling (>95%) of QD spontaneous emission to the fundamental guided mode [1], we show that a single photon collection efficiency...... above 80% within a 0.5 numerical aperture can be achieved using a bottom Bragg mirror and a tapering of the nanowire tip. Because this photon collection strategy does not exploit the Purcell effect, it could also be efficiently applied to broadband single photon emitters such as F-centers in diamond....

  4. Probing quantum coherence in single-atom electron spin resonance

    Science.gov (United States)

    Willke, Philip; Paul, William; Natterer, Fabian D.; Yang, Kai; Bae, Yujeong; Choi, Taeyoung; Fernández-Rossier, Joaquin; Heinrich, Andreas J.; Lutz, Christoper P.

    2018-01-01

    Spin resonance of individual spin centers allows applications ranging from quantum information technology to atomic-scale magnetometry. To protect the quantum properties of a spin, control over its local environment, including energy relaxation and decoherence processes, is crucial. However, in most existing architectures, the environment remains fixed by the crystal structure and electrical contacts. Recently, spin-polarized scanning tunneling microscopy (STM), in combination with electron spin resonance (ESR), allowed the study of single adatoms and inter-atomic coupling with an unprecedented combination of spatial and energy resolution. We elucidate and control the interplay of an Fe single spin with its atomic-scale environment by precisely tuning the phase coherence time T2 using the STM tip as a variable electrode. We find that the decoherence rate is the sum of two main contributions. The first scales linearly with tunnel current and shows that, on average, every tunneling electron causes one dephasing event. The second, effective even without current, arises from thermally activated spin-flip processes of tip spins. Understanding these interactions allows us to maximize T2 and improve the energy resolution. It also allows us to maximize the amplitude of the ESR signal, which supports measurements even at elevated temperatures as high as 4 K. Thus, ESR-STM allows control of quantum coherence in individual, electrically accessible spins. PMID:29464211

  5. Quantum contextual phenomena observed in single-neutron interferometer experiments

    International Nuclear Information System (INIS)

    Hasegawa, Yuji; Rauch, Helmut

    2006-01-01

    Neutron optical experiments are presented, which exhibit quantum contextual phenomena. Entanglement is achieved not between particles, but between degrees of freedom, in this case, for a single-particle. Appropriate combinations of the direction of spin analysis and the position of the phase shifter allow an experimental verification of the violation of a Bell-like inequality. Our experiments manifest the fact that manipulation of the wavefunction in one Hilbert space influences the result of the measurement in the other Hilbert space: manipulation without touch! Next, we report another experiment which exhibits other peculiarity of quantum contextuality, e.g., originally intended to show a Kochen-Specker-like phenomenon. We have introduced inequalities for quantitative analysis of the experiments. The value obtained in the experiments clearly showed violations of prediction by non-contextual theory. Finally, we have accomplished a tomographic determination of entangled quantum state in single-neutrons. There, characteristics of the Bell-sate are confirmed: four poles for the real part of the density matrix are clearly seen

  6. Demonstration of quantum entanglement between a single electron spin confined to an InAs quantum dot and a photon.

    Science.gov (United States)

    Schaibley, J R; Burgers, A P; McCracken, G A; Duan, L-M; Berman, P R; Steel, D G; Bracker, A S; Gammon, D; Sham, L J

    2013-04-19

    The electron spin state of a singly charged semiconductor quantum dot has been shown to form a suitable single qubit for quantum computing architectures with fast gate times. A key challenge in realizing a useful quantum dot quantum computing architecture lies in demonstrating the ability to scale the system to many qubits. In this Letter, we report an all optical experimental demonstration of quantum entanglement between a single electron spin confined to a single charged semiconductor quantum dot and the polarization state of a photon spontaneously emitted from the quantum dot's excited state. We obtain a lower bound on the fidelity of entanglement of 0.59±0.04, which is 84% of the maximum achievable given the timing resolution of available single photon detectors. In future applications, such as measurement-based spin-spin entanglement which does not require sub-nanosecond timing resolution, we estimate that this system would enable near ideal performance. The inferred (usable) entanglement generation rate is 3×10(3) s(-1). This spin-photon entanglement is the first step to a scalable quantum dot quantum computing architecture relying on photon (flying) qubits to mediate entanglement between distant nodes of a quantum dot network.

  7. Sequential Quantum Secret Sharing Using a Single Qudit

    Science.gov (United States)

    Bai, Chen-Ming; Li, Zhi-Hui; Li, Yong-Ming

    2018-05-01

    In this paper we propose a novel and efficient quantum secret sharing protocol using d-level single particle, which it can realize a general access structure via the thought of concatenation. In addition, Our scheme includes all advantages of Tavakoli’s scheme [Phys. Rev. A 92 (2015) 030302(R)]. In contrast to Tavakoli’s scheme, the efficiency of our scheme is 1 for the same situation, and the access structure is more general and has advantages in practical significance. Furthermore, we also analyze the security of our scheme in the primary quantum attacks. Sponsored by the National Natural Science Foundation of China under Grant Nos. 61373150 and 61602291, and Industrial Research and Development Project of Science and Technology of Shaanxi Province under Grant No. 2013k0611

  8. Threshold quantum secret sharing based on single qubit

    Science.gov (United States)

    Lu, Changbin; Miao, Fuyou; Meng, Keju; Yu, Yue

    2018-03-01

    Based on unitary phase shift operation on single qubit in association with Shamir's ( t, n) secret sharing, a ( t, n) threshold quantum secret sharing scheme (or ( t, n)-QSS) is proposed to share both classical information and quantum states. The scheme uses decoy photons to prevent eavesdropping and employs the secret in Shamir's scheme as the private value to guarantee the correctness of secret reconstruction. Analyses show it is resistant to typical intercept-and-resend attack, entangle-and-measure attack and participant attacks such as entanglement swapping attack. Moreover, it is easier to realize in physic and more practical in applications when compared with related ones. By the method in our scheme, new ( t, n)-QSS schemes can be easily constructed using other classical ( t, n) secret sharing.

  9. Quantum turnstile operation of single-molecule magnets

    International Nuclear Information System (INIS)

    Moldoveanu, V; Dinu, I V; Tanatar, B; Moca, C P

    2015-01-01

    The time-dependent transport through single-molecule magnets coupled to magnetic or non-magnetic electrodes is studied in the framework of the generalized master equation method. We investigate the transient regime induced by the periodic switching of the source and drain contacts. If the electrodes have opposite magnetizations the quantum turnstile operation allows the stepwise writing of intermediate excited states. In turn, the transient currents provide a way to read these states. Within our approach we take into account both the uniaxial and transverse anisotropy. The latter may induce additional quantum tunneling processes which affect the efficiency of the proposed read-and-write scheme. An equally weighted mixture of molecular spin states can be prepared if one of the electrodes is ferromagnetic. (paper)

  10. A triple quantum dot in a single-wall carbon nanotube

    DEFF Research Database (Denmark)

    Grove-Rasmussen, Kasper; Jørgensen, Henrik Ingerslev; Hayashi, T.

    2008-01-01

    A top-gated single-wall carbon nanotube is used to define three coupled quantum dots in series between two electrodes. The additional electron number on each quantum dot is controlled by top-gate voltages allowing for current measurements of single, double, and triple quantum dot stability diagrams...

  11. Quantum Dot Platform for Single-Cell Molecular Profiling

    Science.gov (United States)

    Zrazhevskiy, Pavel S.

    In-depth understanding of the nature of cell physiology and ability to diagnose and control the progression of pathological processes heavily rely on untangling the complexity of intracellular molecular mechanisms and pathways. Therefore, comprehensive molecular profiling of individual cells within the context of their natural tissue or cell culture microenvironment is essential. In principle, this goal can be achieved by tagging each molecular target with a unique reporter probe and detecting its localization with high sensitivity at sub-cellular resolution, primarily via microscopy-based imaging. Yet, neither widely used conventional methods nor more advanced nanoparticle-based techniques have been able to address this task up to date. High multiplexing potential of fluorescent probes is heavily restrained by the inability to uniquely match probes with corresponding molecular targets. This issue is especially relevant for quantum dot probes---while simultaneous spectral imaging of up to 10 different probes is possible, only few can be used concurrently for staining with existing methods. To fully utilize multiplexing potential of quantum dots, it is necessary to design a new staining platform featuring unique assignment of each target to a corresponding quantum dot probe. This dissertation presents two complementary versatile approaches towards achieving comprehensive single-cell molecular profiling and describes engineering of quantum dot probes specifically tailored for each staining method. Analysis of expanded molecular profiles is achieved through augmenting parallel multiplexing capacity with performing several staining cycles on the same specimen in sequential manner. In contrast to other methods utilizing quantum dots or other nanoparticles, which often involve sophisticated probe synthesis, the platform technology presented here takes advantage of simple covalent bioconjugation and non-covalent self-assembly mechanisms for straightforward probe

  12. Quantum-Sequencing: Fast electronic single DNA molecule sequencing

    Science.gov (United States)

    Casamada Ribot, Josep; Chatterjee, Anushree; Nagpal, Prashant

    2014-03-01

    A major goal of third-generation sequencing technologies is to develop a fast, reliable, enzyme-free, high-throughput and cost-effective, single-molecule sequencing method. Here, we present the first demonstration of unique ``electronic fingerprint'' of all nucleotides (A, G, T, C), with single-molecule DNA sequencing, using Quantum-tunneling Sequencing (Q-Seq) at room temperature. We show that the electronic state of the nucleobases shift depending on the pH, with most distinct states identified at acidic pH. We also demonstrate identification of single nucleotide modifications (methylation here). Using these unique electronic fingerprints (or tunneling data), we report a partial sequence of beta lactamase (bla) gene, which encodes resistance to beta-lactam antibiotics, with over 95% success rate. These results highlight the potential of Q-Seq as a robust technique for next-generation sequencing.

  13. Investigating and Improving Student Understanding of Quantum Mechanics in the Context of Single Photon Interference

    Science.gov (United States)

    Marshman, Emily; Singh, Chandralekha

    2017-01-01

    Single photon experiments involving a Mach-Zehnder interferometer can illustrate the fundamental principles of quantum mechanics, e.g., the wave-particle duality of a single photon, single photon interference, and the probabilistic nature of quantum measurement involving single photons. These experiments explicitly make the connection between the…

  14. Can a quantum state over time resemble a quantum state at a single time?

    Science.gov (United States)

    Horsman, Dominic; Heunen, Chris; Pusey, Matthew F; Barrett, Jonathan; Spekkens, Robert W

    2017-09-01

    The standard formalism of quantum theory treats space and time in fundamentally different ways. In particular, a composite system at a given time is represented by a joint state, but the formalism does not prescribe a joint state for a composite of systems at different times. If there were a way of defining such a joint state, this would potentially permit a more even-handed treatment of space and time, and would strengthen the existing analogy between quantum states and classical probability distributions. Under the assumption that the joint state over time is an operator on the tensor product of single-time Hilbert spaces, we analyse various proposals for such a joint state, including one due to Leifer and Spekkens, one due to Fitzsimons, Jones and Vedral, and another based on discrete Wigner functions. Finding various problems with each, we identify five criteria for a quantum joint state over time to satisfy if it is to play a role similar to the standard joint state for a composite system: that it is a Hermitian operator on the tensor product of the single-time Hilbert spaces; that it represents probabilistic mixing appropriately; that it has the appropriate classical limit; that it has the appropriate single-time marginals; that composing over multiple time steps is associative. We show that no construction satisfies all these requirements. If Hermiticity is dropped, then there is an essentially unique construction that satisfies the remaining four criteria.

  15. Simple Atomic Quantum Memory Suitable for Semiconductor Quantum Dot Single Photons

    Science.gov (United States)

    Wolters, Janik; Buser, Gianni; Horsley, Andrew; Béguin, Lucas; Jöckel, Andreas; Jahn, Jan-Philipp; Warburton, Richard J.; Treutlein, Philipp

    2017-08-01

    Quantum memories matched to single photon sources will form an important cornerstone of future quantum network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. With an acceptance bandwidth of δ f =0.66 GHz , the memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. Operation of the memory is demonstrated using attenuated laser pulses on the single photon level. For a 50 ns storage time, we measure ηe2 e 50 ns=3.4 (3 )% end-to-end efficiency of the fiber-coupled memory, with a total intrinsic efficiency ηint=17 (3 )%. Straightforward technological improvements can boost the end-to-end-efficiency to ηe 2 e≈35 %; beyond that, increasing the optical depth and exploiting the Zeeman substructure of the atoms will allow such a memory to approach near unity efficiency. In the present memory, the unconditional read-out noise level of 9 ×10-3 photons is dominated by atomic fluorescence, and for input pulses containing on average μ1=0.27 (4 ) photons, the signal to noise level would be unity.

  16. Analysis of dominant carrier recombination mechanisms depending on injection current in InGaN green light emitting diodes

    International Nuclear Information System (INIS)

    Kim, Kyu-Sang; Han, Dong-Pyo; Kim, Hyun-Sung; Shim, Jong-In

    2014-01-01

    Two kinds of green InGaN light emitting diodes (LEDs) have been investigated in order to understand the different slopes in logarithmic light output power-current (L-I) curves. Through the analysis of the carrier rate equation and by considering the carrier density-dependent the injection efficiency into quantum wells, the slopes of the logarithmic L-I curves can be more rigorously understood. The low current level, two as the tunneling current is initially dominant. The high current level beyond the peak of the external quantum efficiency (EQE) diminishes below one as the carrier overflow becomes dominant. In addition, the normalized carrier injection efficiency can be obtained by analyzing the slopes of the logarithmic L-I curves. The carrier injection efficiency decreases after the EQE peak of the InGaN LEDs, determined from the analysis of the slopes of the logarithmic L-I curves

  17. Quantum-field theories as representations of a single $^\\ast$-algebra

    OpenAIRE

    Raab, Andreas

    2013-01-01

    We show that many well-known quantum field theories emerge as representations of a single $^\\ast$-algebra. These include free quantum field theories in flat and curved space-times, lattice quantum field theories, Wightman quantum field theories, and string theories. We prove that such theories can be approximated on lattices, and we give a rigorous definition of the continuum limit of lattice quantum field theories.

  18. Optimised quantum hacking of superconducting nanowire single-photon detectors.

    Science.gov (United States)

    Tanner, Michael G; Makarov, Vadim; Hadfield, Robert H

    2014-03-24

    We explore bright-light control of superconducting nanowire single-photon detectors (SNSPDs) in the shunted configuration (a practical measure to avoid latching). In an experiment, we simulate an illumination pattern the SNSPD would receive in a typical quantum key distribution system under hacking attack. We show that it effectively blinds and controls the SNSPD. The transient blinding illumination lasts for a fraction of a microsecond and produces several deterministic fake clicks during this time. This attack does not lead to elevated timing jitter in the spoofed output pulse, and hence does not introduce significant errors. Five different SNSPD chip designs were tested. We consider possible countermeasures to this attack.

  19. Optimised quantum hacking of superconducting nanowire single-photon detectors

    Science.gov (United States)

    Tanner, Michael G.; Makarov, Vadim; Hadfield, Robert H.

    2014-03-01

    We explore bright-light control of superconducting nanowire single-photon detectors (SNSPDs) in the shunted configuration (a practical measure to avoid latching). In an experiment, we simulate an illumination pattern the SNSPD would receive in a typical quantum key distribution system under hacking attack. We show that it effectively blinds and controls the SNSPD. The transient blinding illumination lasts for a fraction of a microsecond and produces several deterministic fake clicks during this time. This attack does not lead to elevated timing jitter in the spoofed output pulse, and hence does not introduce significant errors. Five different SNSPD chip designs were tested. We consider possible countermeasures to this attack.

  20. Quantum Secure Direct Communication with Authentication Expansion Using Single Photons

    International Nuclear Information System (INIS)

    Yang Jing; Wang Chuan; Zhang Ru

    2010-01-01

    In this paper we propose two quantum secure direct communication (QSDC) protocols with authentication. The authentication key expansion method is introduced to improve the life of the keys with security. In the first scheme, the third party, called Trent is introduced to authenticate the users that participate in the communication. He sends the polarized photons in blocks to authenticate communication parties Alice and Bob using the authentication keys. In the communication process, polarized single photons are used to serve as the carriers, which transmit the secret messages directly. The second QSDC process with authentication between two parties is also discussed.

  1. Single-flux-quantum circuit technology for superconducting radiation detectors

    International Nuclear Information System (INIS)

    Fujimaki, Akira; Onogi, Masashi; Matsumoto, Tomohiro; Tanaka, Masamitsu; Sekiya, Akito; Hayakawa, Hisao; Yorozu, Shinichi; Terai, Hirotaka; Yoshikawa, Nobuyuki

    2003-01-01

    We discuss the application of the single-flux-quantum (SFQ) logic circuits to multi superconducting radiation detectors system. The SFQ-based analog-to-digital converters (ADCs) have the advantage in current sensitivity, which can reach less than 10 nA in a well-tuned ADC. We have also developed the design technology of the SFQ circuits. We demonstrate high-speed operation of large-scale integrated circuits such as a 2x2 cross/bar switch, arithmetic logic unit, indicating that our present SFQ technology is applicable to the multi radiation detectors system. (author)

  2. Spiking neuron devices consisting of single-flux-quantum circuits

    International Nuclear Information System (INIS)

    Hirose, Tetsuya; Asai, Tetsuya; Amemiya, Yoshihito

    2006-01-01

    Single-flux-quantum (SFQ) circuits can be used for making spiking neuron devices, which are useful elements for constructing intelligent, brain-like computers. The device we propose is based on the leaky integrate-and-fire neuron (IFN) model and uses a SFQ pulse as an action signal or a spike of neurons. The operation of the neuron device is confirmed by computer simulator. It can operate with a short delay of 100 ps or less and is the highest-speed neuron device ever reported

  3. Computer-automated tuning of semiconductor double quantum dots into the single-electron regime

    Energy Technology Data Exchange (ETDEWEB)

    Baart, T. A.; Vandersypen, L. M. K. [QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Eendebak, P. T. [QuTech, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Netherlands Organisation for Applied Scientific Research (TNO), P.O. Box 155, 2600 AD Delft (Netherlands); Reichl, C.; Wegscheider, W. [Solid State Physics Laboratory, ETH Zürich, 8093 Zürich (Switzerland)

    2016-05-23

    We report the computer-automated tuning of gate-defined semiconductor double quantum dots in GaAs heterostructures. We benchmark the algorithm by creating three double quantum dots inside a linear array of four quantum dots. The algorithm sets the correct gate voltages for all the gates to tune the double quantum dots into the single-electron regime. The algorithm only requires (1) prior knowledge of the gate design and (2) the pinch-off value of the single gate T that is shared by all the quantum dots. This work significantly alleviates the user effort required to tune multiple quantum dot devices.

  4. Realization of electrically tunable single quantum dot nanocavities

    Energy Technology Data Exchange (ETDEWEB)

    Hofbauer, Felix Florian Georg

    2009-03-15

    We investigated the design, fabrication and optical investigation of electrically tunable single quantum dot-photonic crystal defect nanocavities operating in both the weak and strong coupling regimes of the light matter interaction. We demonstrate that the quantum confined Stark effect can be employed to quickly and reversibly switch the dot-cavity coupling, simply by varying a gate voltage. Our results show that exciton transitions from individual dots can be tuned by up to {proportional_to}4 meV relative to the nanocavity mode, before the emission quenches due to carrier tunneling escape from the dots. We directly probe spontaneous emission, irreversible polariton decay and the statistics of the emitted photons from a single-dot nanocavity in the weak and strong coupling regimes. New information is obtained on the nature of the dot-cavity coupling in the weak coupling regime and electrical control of zero dimensional polaritons is demonstrated for the first time. The structures investigated are p-i-n photodiodes consisting of an 180nm thick free-standing GaAs membrane into which a two dimensional photonic crystal is formed by etching a triangular lattice of air holes. Low mode volume nanocavities (V{sub mode}<1.6 ({lambda}/n){sup 3}) are realized by omitting 3 holes in a line to form L3 cavities and a single layer of InGaAs self-assembled quantum dots is embedded into the midpoint of the membrane. The nanocavities are electrically contacted via 35 nm thick p- and n-doped contact layers in the GaAs membrane. In the weak coupling regime, time resolved spectroscopy reveals a {proportional_to}7 x shortening of the spontaneous emission lifetime as the dot is tuned through the nanocavity mode, due to the Purcell effect. Upon strongly detuning the same quantum dot transition from the nanocavity mode we observe an additional {proportional_to}8 x lengthening of the spontaneous emission lifetime. These observations unequivocally highlight two regimes of dot

  5. Single-atom gating and magnetic interactions in quantum corrals

    Energy Technology Data Exchange (ETDEWEB)

    Ngo, Anh T.; Kim, Eugene H.; Ulloa, Sergio E.

    2017-04-01

    Single-atom gating, achieved by manipulation of adatoms on a surface, has been shown in experiments to allow precise control over superposition of electronic states in quantum corrals. Using a Green's function approach, we demonstrate theoretically that such atom gating can also be used to control the coupling between magnetic degrees of freedom in these systems. Atomic gating enables control not only on the direct interaction between magnetic adatoms, but also over superpositions of many-body states which can then control long distance interactions. We illustrate this effect by considering the competition between direct exchange between magnetic impurities and the Kondo screening mediated by the host electrons, and how this is affected by gating. These results suggest that both magnetic and nonmagnetic single-atom gating may be used to investigate magnetic impurity systems with tailored interactions, and may allow the control of entanglement of different spin states.

  6. Single Nucleobase Identification Using Biophysical Signatures from Nanoelectronic Quantum Tunneling.

    Science.gov (United States)

    Korshoj, Lee E; Afsari, Sepideh; Khan, Sajida; Chatterjee, Anushree; Nagpal, Prashant

    2017-03-01

    Nanoelectronic DNA sequencing can provide an important alternative to sequencing-by-synthesis by reducing sample preparation time, cost, and complexity as a high-throughput next-generation technique with accurate single-molecule identification. However, sample noise and signature overlap continue to prevent high-resolution and accurate sequencing results. Probing the molecular orbitals of chemically distinct DNA nucleobases offers a path for facile sequence identification, but molecular entropy (from nucleotide conformations) makes such identification difficult when relying only on the energies of lowest-unoccupied and highest-occupied molecular orbitals (LUMO and HOMO). Here, nine biophysical parameters are developed to better characterize molecular orbitals of individual nucleobases, intended for single-molecule DNA sequencing using quantum tunneling of charges. For this analysis, theoretical models for quantum tunneling are combined with transition voltage spectroscopy to obtain measurable parameters unique to the molecule within an electronic junction. Scanning tunneling spectroscopy is then used to measure these nine biophysical parameters for DNA nucleotides, and a modified machine learning algorithm identified nucleobases. The new parameters significantly improve base calling over merely using LUMO and HOMO frontier orbital energies. Furthermore, high accuracies for identifying DNA nucleobases were observed at different pH conditions. These results have significant implications for developing a robust and accurate high-throughput nanoelectronic DNA sequencing technique. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Construction of a single atom trap for quantum information protocols

    Science.gov (United States)

    Shea, Margaret E.; Baker, Paul M.; Gauthier, Daniel J.; Duke Physics Department Team

    2016-05-01

    The field of quantum information science addresses outstanding problems such as achieving fundamentally secure communication and solving computationally hard problems. Great progress has been made in the field, particularly using photons coupled to ions and super conducting qubits. Neutral atoms are also interesting for these applications and though the technology for control of neutrals lags behind that of trapped ions, they offer some key advantages: primarily coupling to optical frequencies closer to the telecom band than trapped ions or superconducting qubits. Here we report progress on constructing a single atom trap for 87 Rb. This system is a promising platform for studying the technical problems facing neutral atom quantum computing. For example, most protocols destroy the trap when reading out the neutral atom's state; we will investigate an alternative non-destructive state detection scheme. We detail the experimental systems involved and the challenges addressed in trapping a single atom. All of our hardware components are off the shelf and relatively inexpensive. Unlike many other systems, we place a high numerical aperture lens inside our vacuum system to increase photon collection efficiency. We gratefully acknowledge the financial support of the ARO through Grant # W911NF1520047.

  8. Simulation study of InGaN intermediate-band solar cells

    International Nuclear Information System (INIS)

    Chen, Kuo-Feng; Hung, Chien-Lun; Tsai, Yao-Lung

    2016-01-01

    The performances of single-junction InGaN solar cells with various intermediate bands (IBs) have been simulated using the lifetime model of a 1D simulation program called Analysis of Microelectronic and Photonic Structures (AMPS-1D). It has been observed that the maximum efficiencies of the InGaN solar cells with one, two and three intermediate bands are 47.72%, 55.10% and 58.20%, respectively, which outperform the 25.96% efficiency of the conventional single-junction structure by far. This is primarily attributed to the outstanding capability of the light harvesting from the sub-bandgap absorption. At the optimized bandgap of 2.41 eV, two-IB InGaN solar cells with the IB positions located at 0.95–1.1 eV and 0.3–0.75 eV, respectively, may have an opportunity to realize over 50% efficiency. (paper)

  9. Quantum ground state and single-phonon control of a mechanical resonator.

    Science.gov (United States)

    O'Connell, A D; Hofheinz, M; Ansmann, M; Bialczak, Radoslaw C; Lenander, M; Lucero, Erik; Neeley, M; Sank, D; Wang, H; Weides, M; Wenner, J; Martinis, John M; Cleland, A N

    2010-04-01

    Quantum mechanics provides a highly accurate description of a wide variety of physical systems. However, a demonstration that quantum mechanics applies equally to macroscopic mechanical systems has been a long-standing challenge, hindered by the difficulty of cooling a mechanical mode to its quantum ground state. The temperatures required are typically far below those attainable with standard cryogenic methods, so significant effort has been devoted to developing alternative cooling techniques. Once in the ground state, quantum-limited measurements must then be demonstrated. Here, using conventional cryogenic refrigeration, we show that we can cool a mechanical mode to its quantum ground state by using a microwave-frequency mechanical oscillator-a 'quantum drum'-coupled to a quantum bit, which is used to measure the quantum state of the resonator. We further show that we can controllably create single quantum excitations (phonons) in the resonator, thus taking the first steps to complete quantum control of a mechanical system.

  10. Multi-color single particle tracking with quantum dots.

    Directory of Open Access Journals (Sweden)

    Eva C Arnspang

    Full Text Available Quantum dots (QDs have long promised to revolutionize fluorescence detection to include even applications requiring simultaneous multi-species detection at single molecule sensitivity. Despite the early promise, the unique optical properties of QDs have not yet been fully exploited in e. g. multiplex single molecule sensitivity applications such as single particle tracking (SPT. In order to fully optimize single molecule multiplex application with QDs, we have in this work performed a comprehensive quantitative investigation of the fluorescence intensities, fluorescence intensity fluctuations, and hydrodynamic radii of eight types of commercially available water soluble QDs. In this study, we show that the fluorescence intensity of CdSe core QDs increases as the emission of the QDs shifts towards the red but that hybrid CdSe/CdTe core QDs are less bright than the furthest red-shifted CdSe QDs. We further show that there is only a small size advantage in using blue-shifted QDs in biological applications because of the additional size of the water-stabilizing surface coat. Extending previous work, we finally also show that parallel four color multicolor (MC-SPT with QDs is possible at an image acquisition rate of at least 25 Hz. We demonstrate the technique by measuring the lateral dynamics of a lipid, biotin-cap-DPPE, in the cellular plasma membrane of live cells using four different colors of QDs; QD565, QD605, QD655, and QD705 as labels.

  11. Statistical Characterization of Dispersed Single-Wall Carbon Nanotube Quantum Dots

    International Nuclear Information System (INIS)

    Shimizu, M; Moriyama, S; Suzuki, M; Fuse, T; Homma, Y; Ishibashi, K

    2006-01-01

    Quantum dots have been fabricated in single-wall carbon nanotubes (SWCNTs) simply by depositing metallic contacts on top of them. The fabricated quantum dots show different characteristics from sample to sample, which are even different in samples fabricated in the same chip. In this report, we study the statistical variations of the quantum dots fabricated with our method, and suggest their possible origin

  12. Efficient controlled-phase gate for single-spin qubits in quantum dots

    NARCIS (Netherlands)

    Meunier, T.; Calado, V.E.; Vandersypen, L.M.K.

    2011-01-01

    Two-qubit interactions are at the heart of quantum information processing. For single-spin qubits in semiconductor quantum dots, the exchange gate has always been considered the natural two-qubit gate. The recent integration of a magnetic field or g-factor gradients in coupled quantum dot systems

  13. Deterministic and Storable Single-Photon Source Based on a Quantum Memory

    International Nuclear Information System (INIS)

    Chen Shuai; Chen, Y.-A.; Strassel, Thorsten; Zhao Bo; Yuan Zhensheng; Pan Jianwei; Schmiedmayer, Joerg

    2006-01-01

    A single-photon source is realized with a cold atomic ensemble ( 87 Rb atoms). A single excitation, written in an atomic quantum memory by Raman scattering of a laser pulse, is retrieved deterministically as a single photon at a predetermined time. It is shown that the production rate of single photons can be enhanced considerably by a feedback circuit while the single-photon quality is conserved. Such a single-photon source is well suited for future large-scale realization of quantum communication and linear optical quantum computation

  14. Quantum interference of electrically generated single photons from a quantum dot.

    Science.gov (United States)

    Patel, Raj B; Bennett, Anthony J; Cooper, Ken; Atkinson, Paola; Nicoll, Christine A; Ritchie, David A; Shields, Andrew J

    2010-07-09

    Quantum interference lies at the foundation of many protocols for scalable quantum computing and communication with linear optics. To observe these effects the light source must emit photons that are indistinguishable. From a technological standpoint, it would be beneficial to have electrical control over the emission. Here we report of an electrically driven single-photon source emitting indistinguishable photons. The device consists of a layer of InAs quantum dots embedded in the intrinsic region of a p-i-n diode. Indistinguishability of consecutive photons is tested in a two-photon interference experiment under two modes of operation, continuous and pulsed current injection. We also present a complete theory based on the interference of photons with a Lorentzian spectrum which we compare to both our continuous wave and pulsed experiments. In the former case, a visibility was measured limited only by the timing resolution of our detection system. In the case of pulsed injection, we employ a two-pulse voltage sequence which suppresses multi-photon emission and allows us to carry out temporal filtering of photons which have undergone dephasing. The characteristic Hong-Ou-Mandel 'dip' is measured, resulting in a visibility of 64 +/- 4%.

  15. Poly-silicon quantum-dot single-electron transistors

    International Nuclear Information System (INIS)

    Kang, Kwon-Chil; Lee, Joung-Eob; Lee, Jung-Han; Lee, Jong-Ho; Shin, Hyung-Cheol; Park, Byung-Gook

    2012-01-01

    For operation of a single-electron transistors (SETs) at room temperature, we proposed a fabrication method for a SET with a self-aligned quantum dot by using polycrystalline silicon (poly-Si). The self-aligned quantum dot is formed by the selective etching of a silicon nanowire on a planarized surface and the subsequent deposition and etch-back of poly-silicon or chemical mechanical polishing (CMP). The two tunneling barriers of the SET are fabricated by thermal oxidation. Also, to decrease the leakage current and control the gate capacitance, we deposit a hard oxide mask layer. The control gate is formed by using an electron beam and photolithography on chemical vapor deposition (CVD). Owing to the small capacitance of the narrow control gate due to the tetraethyl orthosilicate (TEOS) hard mask, we observe clear Coulomb oscillation peaks and differential trans-conductance curves at room temperature. The clear oscillation period of the fabricated SET is 2.0 V.

  16. A highly efficient single-photon source based on a quantum dot in a photonic nanowire

    DEFF Research Database (Denmark)

    Claudon, Julien; Bleuse, Joel; Malik, Nitin Singh

    2010-01-01

    –4 or a semiconductor quantum dot5–7. Achieving a high extraction efficiency has long been recognized as a major issue, and both classical solutions8 and cavity quantum electrodynamics effects have been applied1,9–12. We adopt a different approach, based on an InAs quantum dot embedded in a GaAs photonic nanowire......The development of efficient solid-state sources of single photons is a major challenge in the context of quantum communication,optical quantum information processing and metrology1. Such a source must enable the implementation of a stable, single-photon emitter, like a colour centre in diamond2...

  17. Proposal of unilateral single-flux-quantum logic gate

    International Nuclear Information System (INIS)

    Mikaye, H.; Fukaya, N.; Okabe, Y.; Sugamo, T.

    1985-01-01

    A new type of single flux quantum logic gate is proposed, which can perform unilateral propagation of signal without using three-phase clock. This gate is designed to be built with bridge-type Josephson junctions. A basic logic gate consists of two one-junction interferometers coupled by superconducting interconnecting lines, and the logical states are represented by zero or one quantized fluxoid in one of one-junction interferometers. The bias current of the unequal magnitude to each of the two one-junction interferometers results in unilateral signal flow. By adjusting design parameters such as the ratio of the critical current of Josephson junctions and the inductances, circuits with the noise immunity of greater than 50% with respect to the bias current have been designed. Three cascaded gates were modeled and simulated on a computer, and the unilateral signal flow was confirmed. The simulation also shows that a switching delay about 2 picoseconds is feasible

  18. Magneto-exciton dephasing in a single quantum dot

    Science.gov (United States)

    Rodriguez, F. J.; Reyes, A.; Olaya-Castro, A.; Quiroga, L.

    2001-03-01

    Ultrafast spectroscopy experiments on single quantum dot (SQD) in magnetic fields provide a variety of unexpected results, one of them being the recently reported entanglement of exciton states. In order to explore the entanglement robustness, dephasing mechanisms must be considered. By calculating the non-linear time resolved optical spectrum of a SQD, we present a theoretical study on the exciton-exciton scattering contribution to the magneto-exciton dephasing time. Our results show that the time evolution of \\chi^(3) presents, under non-steady-state condition, a beating between the bound biexciton and the first unbound biexciton state in the strong confinement regime. The contribution coming from both left and right polarized emitted photons allows us to predict the creation of exciton entanglement, in agreement with recent experimental results. Previous theoretical works have only addressed the stationary optical response. By contrast, our results based on a full time dependent calculation show new features specially for the fast dephasing case.

  19. Quantum Tunneling of Magnetization in Trigonal Single-Molecule Magnets

    Science.gov (United States)

    Liu, Junjie; Del Barco, Enrique; Hill, Stephen

    2012-02-01

    We perform a numerical analysis of the quantum tunneling of magnetization (QTM) that occurs in a spin S = 6 single-molecule magnet (SMM) with idealized C3 symmetry. The deconstructive points in the QTM are located by following the Berry-phase interference (BPI) oscillations. We find that the O4^3 (=12[Sz,S+^3 +S-^3 ]) operator unfreezes odd-k QTM resonances and generates three-fold patterns of BPI minima in all resonances, including k = 0! This behavior cannot be reproduced with operators that possess even rotational symmetry about the quantization axis. We find also that the k = 0 BPI minima shift away from zero longitudinal field. The wider implications of these results will be discussed in terms of the QTM behavior observed in other SMMs.

  20. Universal quantum computation with the orbital angular momentum of a single photon

    International Nuclear Information System (INIS)

    García-Escartín, Juan Carlos; Chamorro-Posada, Pedro

    2011-01-01

    We prove that a single photon with quantum data encoded in its orbital angular momentum can be manipulated with simple optical elements to provide any desired quantum computation. We will show how to build any quantum unitary operator using beamsplitters, phase shifters, holograms and an extraction gate based on quantum interrogation. The advantages and challenges of these approach are then discussed, in particular the problem of the readout of the results

  1. Compact quantum dots for single-molecule imaging.

    Science.gov (United States)

    Smith, Andrew M; Nie, Shuming

    2012-10-09

    Single-molecule imaging is an important tool for understanding the mechanisms of biomolecular function and for visualizing the spatial and temporal heterogeneity of molecular behaviors that underlie cellular biology (1-4). To image an individual molecule of interest, it is typically conjugated to a fluorescent tag (dye, protein, bead, or quantum dot) and observed with epifluorescence or total internal reflection fluorescence (TIRF) microscopy. While dyes and fluorescent proteins have been the mainstay of fluorescence imaging for decades, their fluorescence is unstable under high photon fluxes necessary to observe individual molecules, yielding only a few seconds of observation before complete loss of signal. Latex beads and dye-labeled beads provide improved signal stability but at the expense of drastically larger hydrodynamic size, which can deleteriously alter the diffusion and behavior of the molecule under study. Quantum dots (QDs) offer a balance between these two problematic regimes. These nanoparticles are composed of semiconductor materials and can be engineered with a hydrodynamically compact size with exceptional resistance to photodegradation (5). Thus in recent years QDs have been instrumental in enabling long-term observation of complex macromolecular behavior on the single molecule level. However these particles have still been found to exhibit impaired diffusion in crowded molecular environments such as the cellular cytoplasm and the neuronal synaptic cleft, where their sizes are still too large (4,6,7). Recently we have engineered the cores and surface coatings of QDs for minimized hydrodynamic size, while balancing offsets to colloidal stability, photostability, brightness, and nonspecific binding that have hindered the utility of compact QDs in the past (8,9). The goal of this article is to demonstrate the synthesis, modification, and characterization of these optimized nanocrystals, composed of an alloyed HgxCd1-xSe core coated with an

  2. Low temperature p-type doping of (Al)GaN layers using ammonia molecular beam epitaxy for InGaN laser diodes

    Energy Technology Data Exchange (ETDEWEB)

    Malinverni, M., E-mail: marco.malinverni@epfl.ch; Lamy, J.-M.; Martin, D.; Grandjean, N. [ICMP, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Feltin, E.; Dorsaz, J. [NOVAGAN AG, CH-1015 Lausanne (Switzerland); Castiglia, A.; Rossetti, M.; Duelk, M.; Vélez, C. [EXALOS AG, CH-8952 Schlieren (Switzerland)

    2014-12-15

    We demonstrate state-of-the-art p-type (Al)GaN layers deposited at low temperature (740 °C) by ammonia molecular beam epitaxy (NH{sub 3}-MBE) to be used as top cladding of laser diodes (LDs) with the aim of further reducing the thermal budget on the InGaN quantum well active region. Typical p-type GaN resistivities and contact resistances are 0.4 Ω cm and 5 × 10{sup −4} Ω cm{sup 2}, respectively. As a test bed, we fabricated a hybrid laser structure emitting at 400 nm combining n-type AlGaN cladding and InGaN active region grown by metal-organic vapor phase epitaxy, with the p-doped waveguide and cladding layers grown by NH{sub 3}-MBE. Single-mode ridge-waveguide LD exhibits a threshold voltage as low as 4.3 V for an 800 × 2 μm{sup 2} ridge dimension and a threshold current density of ∼5 kA cm{sup −2} in continuous wave operation. The series resistance of the device is 6 Ω and the resistivity is 1.5 Ω cm, confirming thereby the excellent electrical properties of p-type Al{sub 0.06}Ga{sub 0.94}N:Mg despite the low growth temperature.

  3. Investigation of the radiative efficiency and threshold in InGaN laser diodes under the influence of efficiency droop

    International Nuclear Information System (INIS)

    Ryu, Han-Youl

    2012-01-01

    Based on the rate equation model of semiconductor lasers, the radiative efficiency and threshold current density of InGaN-based blue laser diodes (LDs) are theoretically investigated, including the effect of efficiency droop in the InGaN quantum wells. The peak point of the radiative efficiency versus current density relation is used as the parameter of the rate equation analysis. The threshold current density of InGaN blue LDs is found to depend strongly on the maximum radiative efficiency at low current density, implying that improving the maximum efficiency is important to maintain a high radiative efficiency at a large current density and to achieve a low-threshold lasing action under the influence of efficiency droop.

  4. Single-Photon Source for Quantum Information Based on Single Dye Molecule Fluorescence in Liquid Crystal Host

    International Nuclear Information System (INIS)

    Lukishova, S.G.; Knox, R.P.; Freivald, P.; McNamara, A.; Boyd, R.W.; Stroud, Jr. C.R.; Schmid, A.W.; Marshall, K.L.

    2006-01-01

    This paper describes a new application for liquid crystals: quantum information technology. A deterministically polarized single-photon source that efficiently produces photons exhibiting antibunching is a pivotal hardware element in absolutely secure quantum communication. Planar-aligned nematic liquid crystal hosts deterministically align the single dye molecules which produce deterministically polarized single (antibunched) photons. In addition, 1-D photonic bandgap cholesteric liquid crystals will increase single-photon source efficiency. The experiments and challenges in the observation of deterministically polarized fluorescence from single dye molecules in planar-aligned glassy nematic-liquid-crystal oligomer as well as photon antibunching in glassy cholesteric oligomer are described for the first time

  5. Studies of quantum levels in GaInNAs single quantum wells

    International Nuclear Information System (INIS)

    Shirakata, Sho; Kondow, Masahiko; Kitatani, Takeshi

    2006-01-01

    Spectroscopic studies have been carried out on the quantum levels in GaInNAs/GaAs single quantum wells (SQWs). Photoluminescence (PL), PL excitation (PLE), photoreflectance (PR), and high-density-excited PL (HDE-PL) were measured on high quality GaInNAs SQWs, Ga 0.65 In 0.35 N 0.01 As 0.99 /GaAs (well thickness: l z =10 nm) and Ga 0.65 In 0.35 N 0.005 As 0.995 /GaAs (l z =3∝10 nm), grown by molecular-beam epitaxy. For Ga 0.65 In 0.35 N 0.01 As 0.99 /GaAs (l z =10 nm), PL at 8 K exhibited a peak at 1.07 eV due to the exciton-related transition between quantum levels of ground states (e1-hh1). Both PR and PLE exhibited three transitions (1.17, 1.20 and 1.32 eV), and the former two transitions were assigned to as either of e1-lh1 and e2-hh2 transitions, while the transition at 1.32 eV was assigned to as the e2-lh2 transition. For HDE-PL, a new PL peak was observed at about 1.2 eV, and it was assigned to the unresolved e1-lh1 and e2-hh2 transitions. Similar optical measurements have been done on the Ga 0.65 In 0.35 N 0.005 As 0.995 /GaAs with various l z (3∝10 nm). Dependence of optical spectra and energies of quantum levels on l z have been studied. It has been found that HDE-PL in combination with PLE is a good tool for the study of the quantum level of GaInNAs SQW. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2006], Wiley Periodicals, Inc.)

  6. InGaN High Temperature Photovoltaic Cells, Phase II

    Data.gov (United States)

    National Aeronautics and Space Administration — The objectives of this Phase II project are to develop InGaN photovoltaic cells for high temperature and/or high radiation environments to TRL 4 and to define the...

  7. Spectral decomposition of single-tone-driven quantum phase modulation

    International Nuclear Information System (INIS)

    Capmany, Jose; Fernandez-Pousa, Carlos R

    2011-01-01

    Electro-optic phase modulators driven by a single radio-frequency tone Ω can be described at the quantum level as scattering devices where input single-mode radiation undergoes energy changes in multiples of ℎΩ. In this paper, we study the spectral representation of the unitary, multimode scattering operator describing these devices. The eigenvalue equation, phase modulation being a process preserving the photon number, is solved at each subspace with definite number of photons. In the one-photon subspace F 1 , the problem is equivalent to the computation of the continuous spectrum of the Susskind-Glogower cosine operator of the harmonic oscillator. Using this analogy, the spectral decomposition in F 1 is constructed and shown to be equivalent to the usual Fock-space representation. The result is then generalized to arbitrary N-photon subspaces, where eigenvectors are symmetrized combinations of N one-photon eigenvectors and the continuous spectrum spans the entire unit circle. Approximate normalizable one-photon eigenstates are constructed in terms of London phase states truncated to optical bands. Finally, we show that synchronous ultrashort pulse trains represent classical field configurations with the same structure as these approximate eigenstates, and that they can be considered as approximate eigenvectors of the classical formulation of phase modulation.

  8. Spectral decomposition of single-tone-driven quantum phase modulation

    Energy Technology Data Exchange (ETDEWEB)

    Capmany, Jose [ITEAM Research Institute, Univ. Politecnica de Valencia, 46022 Valencia (Spain); Fernandez-Pousa, Carlos R, E-mail: c.pousa@umh.es [Signal Theory and Communications, Department of Physics and Computer Science, Univ. Miguel Hernandez, 03202 Elche (Spain)

    2011-02-14

    Electro-optic phase modulators driven by a single radio-frequency tone {Omega} can be described at the quantum level as scattering devices where input single-mode radiation undergoes energy changes in multiples of {h_bar}{Omega}. In this paper, we study the spectral representation of the unitary, multimode scattering operator describing these devices. The eigenvalue equation, phase modulation being a process preserving the photon number, is solved at each subspace with definite number of photons. In the one-photon subspace F{sub 1}, the problem is equivalent to the computation of the continuous spectrum of the Susskind-Glogower cosine operator of the harmonic oscillator. Using this analogy, the spectral decomposition in F{sub 1} is constructed and shown to be equivalent to the usual Fock-space representation. The result is then generalized to arbitrary N-photon subspaces, where eigenvectors are symmetrized combinations of N one-photon eigenvectors and the continuous spectrum spans the entire unit circle. Approximate normalizable one-photon eigenstates are constructed in terms of London phase states truncated to optical bands. Finally, we show that synchronous ultrashort pulse trains represent classical field configurations with the same structure as these approximate eigenstates, and that they can be considered as approximate eigenvectors of the classical formulation of phase modulation.

  9. Vision for single flux quantum very large scale integrated technology

    International Nuclear Information System (INIS)

    Silver, Arnold; Bunyk, Paul; Kleinsasser, Alan; Spargo, John

    2006-01-01

    Single flux quantum (SFQ) electronics is extremely fast and has very low on-chip power dissipation. SFQ VLSI is an excellent candidate for high-performance computing and other applications requiring extremely high-speed signal processing. Despite this, SFQ technology has generally not been accepted for system implementation. We argue that this is due, at least in part, to the use of outdated tools to produce SFQ circuits and chips. Assuming the use of tools equivalent to those employed in the semiconductor industry, we estimate the density of Josephson junctions, circuit speed, and power dissipation that could be achieved with SFQ technology. Today, CMOS lithography is at 90-65 nm with about 20 layers. Assuming equivalent technology, aggressively increasing the current density above 100 kA cm -2 to achieve junction speeds approximately 1000 GHz, and reducing device footprints by converting device profiles from planar to vertical, one could expect to integrate about 250 M Josephson junctions cm -2 into SFQ digital circuits. This should enable circuit operation with clock frequencies above 200 GHz and place approximately 20 K gates within a radius of one clock period. As a result, complete microprocessors, including integrated memory registers, could be fabricated on a single chip

  10. Vision for single flux quantum very large scale integrated technology

    Energy Technology Data Exchange (ETDEWEB)

    Silver, Arnold [Northrop Grumman Space Technology, One Space Park, Redondo Beach, CA 90278 (United States); Bunyk, Paul [Northrop Grumman Space Technology, One Space Park, Redondo Beach, CA 90278 (United States); Kleinsasser, Alan [Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 (United States); Spargo, John [Northrop Grumman Space Technology, One Space Park, Redondo Beach, CA 90278 (United States)

    2006-05-15

    Single flux quantum (SFQ) electronics is extremely fast and has very low on-chip power dissipation. SFQ VLSI is an excellent candidate for high-performance computing and other applications requiring extremely high-speed signal processing. Despite this, SFQ technology has generally not been accepted for system implementation. We argue that this is due, at least in part, to the use of outdated tools to produce SFQ circuits and chips. Assuming the use of tools equivalent to those employed in the semiconductor industry, we estimate the density of Josephson junctions, circuit speed, and power dissipation that could be achieved with SFQ technology. Today, CMOS lithography is at 90-65 nm with about 20 layers. Assuming equivalent technology, aggressively increasing the current density above 100 kA cm{sup -2} to achieve junction speeds approximately 1000 GHz, and reducing device footprints by converting device profiles from planar to vertical, one could expect to integrate about 250 M Josephson junctions cm{sup -2} into SFQ digital circuits. This should enable circuit operation with clock frequencies above 200 GHz and place approximately 20 K gates within a radius of one clock period. As a result, complete microprocessors, including integrated memory registers, could be fabricated on a single chip.

  11. Single-Ion Implantation for the Development of Si-Based MOSFET Devices with Quantum Functionalities

    Directory of Open Access Journals (Sweden)

    Jeffrey C. McCallum

    2012-01-01

    Full Text Available Interest in single-ion implantation is driven in part by research into development of solid-state devices that exhibit quantum behaviour in their electronic or optical characteristics. Here, we provide an overview of international research work on single ion implantation and single ion detection for development of electronic devices for quantum computing. The scope of international research into single ion implantation is presented in the context of our own research in the Centre for Quantum Computation and Communication Technology in Australia. Various single ion detection schemes are presented, and limitations on dopant placement accuracy due to ion straggling are discussed together with pathways for scale-up to multiple quantum devices on the one chip. Possible future directions for ion implantation in quantum computing and communications are also discussed.

  12. Properties of a GaAs Single Electron Path Switching Node Device Using a Single Quantum Dot for Hexagonal BDD Quantum Circuits

    International Nuclear Information System (INIS)

    Nakamura, Tatsuya; Abe, Yuji; Kasai, Seiya; Hasegawa, Hideki; Hashizume, Tamotsu

    2006-01-01

    A new single electron (SE) binary-decision diagram (BDD) node device having a single quantum dot connected to three nanowire branches through tunnel barriers was fabricated using etched AlGaAs/GaAs nanowires and nanometer-sized Schottky wrap gates (WPGs), and their operation was characterized experimentally, for the hexagonal BDD quantum circuit. Fabricated devices showed clear and steep single electron pass switching by applying only an input voltage signal, which was completely different from switching properties in the previous SE BDD node devices composed of two single electron switches. As the possible switching mechanism, the correlation between the probabilities of tunnelling thorough a single quantum dot in exit branches was discussed

  13. Sub-Poissonian statistics of quantum jumps in single molecule or atomic ion

    International Nuclear Information System (INIS)

    Osad'ko, I.S.; Gus'kov, D.N.

    2007-01-01

    A theory for statistics of quantum jumps in single molecule or ion driven by continues wave laser field is developed. These quantum jumps can relate to nonradiative singlet-triplet transitions in a molecule or to on → off jumps in a single ion with shelving processes. Distribution function w N (T) of quantum jumps in time interval T is found. Computer simulation of quantum jumps is realized. Statistical treatment of simulated jumps reveals sub-Poissonian statistics of quantum jumps. The theoretical distribution function w N (T) fits well the distribution of jumps found from simulated data. Experimental data on quantum jumps found in experiments with single Hg + ion are described by the function w N (T) well

  14. Digital growth of thick N-polar InGaN films on relaxed InGaN pseudosubstrates

    Science.gov (United States)

    Lund, Cory; Hestroffer, Karine; Hatui, Nirupam; Nakamura, Shuji; DenBaars, Steven P.; Mishra, Umesh K.; Keller, Stacia

    2017-11-01

    Smooth relaxed N-polar InGaN films were grown by metal-organic CVD (MOCVD) on N-polar InGaN pseudosubstrates (PSs) using a novel digital approach consisting of a constant In precursor flow with the pulsed injection of H2 carrier gas. InGaN layers grown on PSs exhibited an In composition of about 50% higher than those of the layers grown on N-polar GaN templates, assuming the in-plane lattice constant of the relaxed PSs, corresponding to In0.11Ga0.89N. Additionally, the luminescence recorded from InGaN layers grown on PSs at 490 nm was twice as intense as that obtained from the layers deposited on coloaded GaN-on-sapphire templates, which emitted at 430 nm.

  15. Quantum Tunneling Symmetry of Single Molecule Magnet Mn_12-acetate

    Science.gov (United States)

    del Barco, E.; Kent, A. D.; Rumberger, E.; Hendrikson, D. N.; Christou, G.

    2003-03-01

    We have studied the symmetry of magnetic quantum tunneling (MQT) in single crystals of single molecular magnet (SMM) Mn_12-acetate. A superconducting high field vector magnet was used to apply magnetic fields in arbitrary directions respect to the axes of the crystal. The MQT probability is extracted from the change in magnetization measured on sweeping the field through a MQT resonance. This is related to the quantum splitting of the molecules relaxing in the time window of the experiment [1]. The dependence of the MQT probability on the angle between the applied transverse field and the crystallographic axes shows a four-fold rotation pattern, with maxima at angles separated by 90 degrees. By selecting a part of the splitting distribution of the sample by applying an initial transverse field in the direction of one of the observed maxima the situation changes completely. The resulting behavior of the MQT probability shows a two-fold rotation pattern with maxima separated by 180 degrees. Moreover, if the selection is made by applying the initial transverse field in the direction of a complementary four-fold maximum the behavior shows again two-fold symmetry. However, the maxima are found to be shifted by 90 degrees respect to the first selection. The fact that we observe two-fold symmetry for different selections is a clear evidence of the existence of different molecules with lower anisotropy than the imposed by the tetragonal crystallographic site symmetry. The general four-fold symmetry observed is thus due in large part to equal populations of molecules with opposite signs of the second order anisotropy, as suggested by Cornia et al. and appears to be a consequence of to the existence of a discrete set of lower symmetry isomers in a Mn_12-acetate crystal [2]. [1] E. del Barco, A. D. Kent, E. Rumberger, D. N. Hendrikson and G. Christou, Europhys. Lett. 60, 768 (2002) [2] A. Cornia, R. Sessoli, L. Sorace, D. Gatteschi, A. L. Barra and C. Daiguebonne, Phys. Rev

  16. A new approach of quantum mechanics for neutron single-slit diffraction

    International Nuclear Information System (INIS)

    Wu Xiangyao; Yang Jinghai; Liu Xiaojing; Wang Li; Liu Bing; Fan Xihui; Guo Yiqing

    2007-01-01

    Phenomena of electron, neutron, atomic and molecular diffraction have been studied in many experiments, and these experiments are explained by many theoretical works. We study neutron single-slit diffraction with a quantum mechanical approach. It is found that the obvious diffraction patterns can be obtained when the single slit width a is in the range of 3λ-60λ. We also find a new quantum effect of the thickness of single-slit which can make a large impact on the diffraction pattern. The new quantum effect predicted in our work can be tested by the neutron single-slit diffraction experiment. (authors)

  17. Electrically pumped single-photon emission at room temperature from a single InGaN/GaN quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Deshpande, Saniya; Frost, Thomas; Hazari, Arnab; Bhattacharya, Pallab, E-mail: pkb@eecs.umich.edu [Center for Photonics and Multiscale Nanomaterials, Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, Michigan 48109 (United States)

    2014-10-06

    We demonstrate a semiconductor quantum dot based electrically pumped single-photon source operating at room temperature. Single photons emitted in the red spectral range from single In{sub 0.4}Ga{sub 0.6}N/GaN quantum dots exhibit a second-order correlation value g{sup (2)}(0) of 0.29, and fast recombination lifetime ∼1.3 ±0.3 ns at room temperature. The single-photon source can be driven at an excitation repetition rate of 200 MHz.

  18. Online evolution reconstruction from a single measurement record with random time intervals for quantum communication

    Science.gov (United States)

    Zhou, Hua; Su, Yang; Wang, Rong; Zhu, Yong; Shen, Huiping; Pu, Tao; Wu, Chuanxin; Zhao, Jiyong; Zhang, Baofu; Xu, Zhiyong

    2017-10-01

    Online reconstruction of a time-variant quantum state from the encoding/decoding results of quantum communication is addressed by developing a method of evolution reconstruction from a single measurement record with random time intervals. A time-variant two-dimensional state is reconstructed on the basis of recovering its expectation value functions of three nonorthogonal projectors from a random single measurement record, which is composed from the discarded qubits of the six-state protocol. The simulated results prove that our method is robust to typical metro quantum channels. Our work extends the Fourier-based method of evolution reconstruction from the version for a regular single measurement record with equal time intervals to a unified one, which can be applied to arbitrary single measurement records. The proposed protocol of evolution reconstruction runs concurrently with the one of quantum communication, which can facilitate the online quantum tomography.

  19. High-Fidelity Single-Shot Toffoli Gate via Quantum Control.

    Science.gov (United States)

    Zahedinejad, Ehsan; Ghosh, Joydip; Sanders, Barry C

    2015-05-22

    A single-shot Toffoli, or controlled-controlled-not, gate is desirable for classical and quantum information processing. The Toffoli gate alone is universal for reversible computing and, accompanied by the Hadamard gate, forms a universal gate set for quantum computing. The Toffoli gate is also a key ingredient for (nontopological) quantum error correction. Currently Toffoli gates are achieved by decomposing into sequentially implemented single- and two-qubit gates, which require much longer times and yields lower overall fidelities compared to a single-shot implementation. We develop a quantum-control procedure to construct a single-shot Toffoli gate for three nearest-neighbor-coupled superconducting transmon systems such that the fidelity is 99.9% and is as fast as an entangling two-qubit gate under the same realistic conditions. The gate is achieved by a nongreedy quantum control procedure using our enhanced version of the differential evolution algorithm.

  20. Near-field strong coupling of single quantum dots.

    Science.gov (United States)

    Groß, Heiko; Hamm, Joachim M; Tufarelli, Tommaso; Hess, Ortwin; Hecht, Bert

    2018-03-01

    Strong coupling and the resultant mixing of light and matter states is an important asset for future quantum technologies. We demonstrate deterministic room temperature strong coupling of a mesoscopic colloidal quantum dot to a plasmonic nanoresonator at the apex of a scanning probe. Enormous Rabi splittings of up to 110 meV are accomplished by nanometer-precise positioning of the quantum dot with respect to the nanoresonator probe. We find that, in addition to a small mode volume of the nanoresonator, collective coherent coupling of quantum dot band-edge states and near-field proximity interaction are vital ingredients for the realization of near-field strong coupling of mesoscopic quantum dots. The broadband nature of the interaction paves the road toward ultrafast coherent manipulation of the coupled quantum dot-plasmon system under ambient conditions.

  1. Quantum optics. All-optical routing of single photons by a one-atom switch controlled by a single photon.

    Science.gov (United States)

    Shomroni, Itay; Rosenblum, Serge; Lovsky, Yulia; Bechler, Orel; Guendelman, Gabriel; Dayan, Barak

    2014-08-22

    The prospect of quantum networks, in which quantum information is carried by single photons in photonic circuits, has long been the driving force behind the effort to achieve all-optical routing of single photons. We realized a single-photon-activated switch capable of routing a photon from any of its two inputs to any of its two outputs. Our device is based on a single atom coupled to a fiber-coupled, chip-based microresonator. A single reflected control photon toggles the switch from high reflection (R ~ 65%) to high transmission (T ~ 90%), with an average of ~1.5 control photons per switching event (~3, including linear losses). No additional control fields are required. The control and target photons are both in-fiber and practically identical, making this scheme compatible with scalable architectures for quantum information processing. Copyright © 2014, American Association for the Advancement of Science.

  2. Storage of multiple single-photon pulses emitted from a quantum dot in a solid-state quantum memory

    Science.gov (United States)

    Tang, Jian-Shun; Zhou, Zong-Quan; Wang, Yi-Tao; Li, Yu-Long; Liu, Xiao; Hua, Yi-Lin; Zou, Yang; Wang, Shuang; He, De-Yong; Chen, Geng; Sun, Yong-Nan; Yu, Ying; Li, Mi-Feng; Zha, Guo-Wei; Ni, Hai-Qiao; Niu, Zhi-Chuan; Li, Chuan-Feng; Guo, Guang-Can

    2015-01-01

    Quantum repeaters are critical components for distributing entanglement over long distances in presence of unavoidable optical losses during transmission. Stimulated by the Duan–Lukin–Cirac–Zoller protocol, many improved quantum repeater protocols based on quantum memories have been proposed, which commonly focus on the entanglement-distribution rate. Among these protocols, the elimination of multiple photons (or multiple photon-pairs) and the use of multimode quantum memory are demonstrated to have the ability to greatly improve the entanglement-distribution rate. Here, we demonstrate the storage of deterministic single photons emitted from a quantum dot in a polarization-maintaining solid-state quantum memory; in addition, multi-temporal-mode memory with 1, 20 and 100 narrow single-photon pulses is also demonstrated. Multi-photons are eliminated, and only one photon at most is contained in each pulse. Moreover, the solid-state properties of both sub-systems make this configuration more stable and easier to be scalable. Our work will be helpful in the construction of efficient quantum repeaters based on all-solid-state devices. PMID:26468996

  3. Magnetic Quantum Tunneling and Symmetry in Single Molecule Magnets

    Science.gov (United States)

    Kent, Andrew D.

    2003-03-01

    We have studied the symmetry of magnetic quantum tunneling (MQT) in single molecule magnets (SMMs) using a micro-Hall effect magnetometer and high field vector superconducting magnet system. In the most widely studied SMM, Mn12-acetate, an average crystal 4-fold symmetry in the magnetic response is shown to be due to local molecular environments of 2-fold symmetry that are rotated by 90 degrees with respect to one another. We attribute this to ligand disorder that leads to local rhombic distortions, a model first proposed by Cornia et al. based on x-ray diffraction data [1]. We have magnetically distilled a Mn12-acetate crystal to study a subset of these lower (2-fold) site symmetry molecules and present evidence for a spin-parity effect consistent with a local 2-fold symmetry [2]. These results highlight the importance of subtle changes in molecule environment in modulating magnetic anisotropy and MQT. [1] Cornia et al. Phys. Rev. Lett. 89, 257201 (2002) [2] E. del Barco, A. D. Kent, E. Rumberger, D. H. Hendrickson, G. Christou, submitted for publication (2002) and Europhys. Lett. 60, 768 (2002)

  4. Efficiency enhancement of InGaN amber MQWs using nanopillar structures

    KAUST Repository

    Ou, Yiyu

    2017-09-09

    We have investigated the use of nanopillar structures on high indium content InGaN amber multiple quantum well (MQW) samples to enhance the emission efficiency. A significant emission enhancement was observed which can be attributed to the enhancement of internal quantum efficiency and light extraction efficiency. The size-dependent strain relaxation effect was characterized by photoluminescence, Raman spectroscopy and time-resolved photoluminescence measurements. In addition, the light extraction efficiency of different MQW samples was studied by finite-different time-domain simulations. Compared to the as-grown sample, the nanopillar amber MQW sample with a diameter of 300 nm has demonstrated an emission enhancement by a factor of 23.8.

  5. Efficiency enhancement of InGaN amber MQWs using nanopillar structures

    Directory of Open Access Journals (Sweden)

    Ou Yiyu

    2018-01-01

    Full Text Available We have investigated the use of nanopillar structures on high indium content InGaN amber multiple quantum well (MQW samples to enhance the emission efficiency. A significant emission enhancement was observed which can be attributed to the enhancement of internal quantum efficiency and light extraction efficiency. The size-dependent strain relaxation effect was characterized by photoluminescence, Raman spectroscopy and time-resolved photoluminescence measurements. In addition, the light extraction efficiency of different MQW samples was studied by finite-different time-domain simulations. Compared to the as-grown sample, the nanopillar amber MQW sample with a diameter of 300 nm has demonstrated an emission enhancement by a factor of 23.8.

  6. Efficiency enhancement of InGaN amber MQWs using nanopillar structures

    KAUST Repository

    Ou, Yiyu; Iida, Daisuke; Liu, Jin; Wu, Kaiyu; Ohkawa, Kazuhiro; Boisen, Anja; Petersen, Paul Michael; Ou, Haiyan

    2017-01-01

    We have investigated the use of nanopillar structures on high indium content InGaN amber multiple quantum well (MQW) samples to enhance the emission efficiency. A significant emission enhancement was observed which can be attributed to the enhancement of internal quantum efficiency and light extraction efficiency. The size-dependent strain relaxation effect was characterized by photoluminescence, Raman spectroscopy and time-resolved photoluminescence measurements. In addition, the light extraction efficiency of different MQW samples was studied by finite-different time-domain simulations. Compared to the as-grown sample, the nanopillar amber MQW sample with a diameter of 300 nm has demonstrated an emission enhancement by a factor of 23.8.

  7. Single electron probes of fractional quantum hall states

    Science.gov (United States)

    Venkatachalam, Vivek

    When electrons are confined to a two dimensional layer with a perpendicular applied magnetic field, such that the ratio of electrons to flux quanta (nu) is a small integer or simple rational value, these electrons condense into remarkable new phases of matter that are strikingly different from the metallic electron gas that exists in the absence of a magnetic field. These phases, called integer or fractional quantum Hall (IQH or FQH) states, appear to be conventional insulators in their bulk, but behave as a dissipationless metal along their edge. Furthermore, electrical measurements of such a system are largely insensitive to the detailed geometry of how the system is contacted or even how large the system is... only the order in which contacts are made appears to matter. This insensitivity to local geometry has since appeared in a number of other two and three dimensional systems, earning them the classification of "topological insulators" and prompting an enormous experimental and theoretical effort to understand their properties and perhaps manipulate these properties to create robust quantum information processors. The focus of this thesis will be two experiments designed to elucidate remarkable properties of the metallic edge and insulating bulk of certain FQH systems. To study such systems, we can use mesoscopic devices known as single electron transistors (SETs). These devices operate by watching single electrons hop into and out of a confining box and into a nearby wire (for measurement). If it is initially unfavorable for an electron to leave the box, it can be made favorable by bringing another charge nearby, modifying the energy of the confined electron and pushing it out of the box and into the nearby wire. In this way, the SET can measure nearby charges. Alternatively, we can heat up the nearby wire to make it easier for electrons to enter and leave the box. In this way, the SET is a sensitive thermometer. First, by operating the SET as an

  8. Hierarchical structures consisting of SiO2 nanorods and p-GaN microdomes for efficiently harvesting solar energy for InGaN quantum well photovoltaic cells.

    Science.gov (United States)

    Ho, Cheng-Han; Lien, Der-Hsien; Chang, Hung-Chih; Lin, Chin-An; Kang, Chen-Fang; Hsing, Meng-Kai; Lai, Kun-Yu; He, Jr-Hau

    2012-12-07

    We experimentally and theoretically demonstrated the hierarchical structure of SiO(2) nanorod arrays/p-GaN microdomes as a light harvesting scheme for InGaN-based multiple quantum well solar cells. The combination of nano- and micro-structures leads to increased internal multiple reflection and provides an intermediate refractive index between air and GaN. Cells with the hierarchical structure exhibit improved short-circuit current densities and fill factors, rendering a 1.47 fold efficiency enhancement as compared to planar cells.

  9. High-resolution photoluminescence studies of single semiconductor quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Østergaard, John Erland; Jensen, Jacob Riis

    2000-01-01

    Semiconductor quantum dots, especially those formed by self-organized growth, are considered a promising material system for future optical devices [1] and the optical properties of quantum dot ensembles have been investigated in detail over the past years. Recently, considerable interest has...

  10. Single-quadrature continuous-variable quantum key distribution

    DEFF Research Database (Denmark)

    Gehring, Tobias; Jacobsen, Christian Scheffmann; Andersen, Ulrik Lund

    2016-01-01

    Most continuous-variable quantum key distribution schemes are based on the Gaussian modulation of coherent states followed by continuous quadrature detection using homodyne detectors. In all previous schemes, the Gaussian modulation has been carried out in conjugate quadratures thus requiring two...... commercialization of continuous-variable quantum key distribution, provided that the low noise requirement can be achieved....

  11. Zero-phonon-line emission of single molecules for applications in quantum information processing

    Science.gov (United States)

    Kiraz, Alper; Ehrl, M.; Mustecaplioglu, O. E.; Hellerer, T.; Brauchle, C.; Zumbusch, A.

    2005-07-01

    A single photon source which generates transform limited single photons is highly desirable for applications in quantum optics. Transform limited emission guarantees the indistinguishability of the emitted single photons. This, in turn brings groundbreaking applications in linear optics quantum information processing within an experimental reach. Recently, self-assembled InAs quantum dots and trapped atoms have successfully been demonstrated as such sources for highly indistinguishable single photons. Here, we demonstrate that nearly transform limited zero-phonon-line (ZPL) emission from single molecules can be obtained by using vibronic excitation. Furthermore we report the results of coincidence detection experiments at the output of a Michelson-type interferometer. These experiments reveal Hong-Ou-Mandel correlations as a proof of the indistinguishability of the single photons emitted consecutively from a single molecule. Therefore, single molecules constitute an attractive alternative to single InAs quantum dots and trapped atoms for applications in linear optics quantum information processing. Experiments were performed with a home-built confocal microscope keeping the sample in a superfluid liquid Helium bath at 1.4K. We investigated terrylenediimide (TDI) molecules highly diluted in hexadecane (Shpol'skii matrix). A continuous wave single mode dye laser was used for excitation of vibronic transitions of individual molecules. From the integral fluorescence, the ZPL of single molecules was selected with a spectrally narrow interference filter. The ZPL emission was then sent to a scanning Fabry-Perot interferometer for linewidth measurements or a Michelson-type interferometer for coincidence detection.

  12. Thermoelectric properties of In-rich InGaN and InN/InGaN superlattices

    Directory of Open Access Journals (Sweden)

    James (Zi-Jian Ju

    2016-04-01

    Full Text Available The thermoelectric properties of n-type InGaN alloys with high In-content and InN/InGaN thin film superlattices (SL grown by molecular beam epitaxy are investigated. Room-temperature measurements of the thermoelectric properties reveal that an increasing Ga-content in ternary InGaN alloys (0 < x(Ga < 0.2 yields a more than 10-fold reduction in thermal conductivity (κ without deteriorating electrical conductivity (σ, while the Seebeck coefficient (S increases slightly due to a widening band gap compared to binary InN. Employing InN/InGaN SLs (x(Ga = 0.1 with different periods, we demonstrate that confinement effects strongly enhance electron mobility with values as high as ∼820 cm2/V s at an electron density ne of ∼5×1019 cm−3, leading to an exceptionally high σ of ∼5400 (Ωcm−1. Simultaneously, in very short-period SL structures S becomes decoupled from ne, κ is further reduced below the alloy limit (κ < 9 W/m-K, and the power factor increases to 2.5×10−4 W/m-K2 by more than a factor of 5 as compared to In-rich InGaN alloys. These findings demonstrate that quantum confinement in group-III nitride-based superlattices facilitates improvements of thermoelectric properties over bulk-like ternary nitride alloys.

  13. Efficiency Drop in Green InGaN /GaN Light Emitting Diodes: The Role of Random Alloy Fluctuations

    Science.gov (United States)

    Auf der Maur, Matthias; Pecchia, Alessandro; Penazzi, Gabriele; Rodrigues, Walter; Di Carlo, Aldo

    2016-01-01

    White light emitting diodes (LEDs) based on III-nitride InGaN /GaN quantum wells currently offer the highest overall efficiency for solid state lighting applications. Although current phosphor-converted white LEDs have high electricity-to-light conversion efficiencies, it has been recently pointed out that the full potential of solid state lighting could be exploited only by color mixing approaches without employing phosphor-based wavelength conversion. Such an approach requires direct emitting LEDs of different colors, including, in particular, the green-yellow range of the visible spectrum. This range, however, suffers from a systematic drop in efficiency, known as the "green gap," whose physical origin has not been understood completely so far. In this work, we show by atomistic simulations that a consistent part of the green gap in c -plane InGaN /GaN -based light emitting diodes may be attributed to a decrease in the radiative recombination coefficient with increasing indium content due to random fluctuations of the indium concentration naturally present in any InGaN alloy.

  14. Quantum Interference between Autonomous Single-Photon Sources from Doppler-Broadened Atomic Ensemble

    OpenAIRE

    Jeong, Teak; Lee, Yoon-Seok; Park, Jiho; Kim, Heonoh; Moon, Han Seb

    2017-01-01

    To realize a quantum network based on quantum entanglement swapping, bright and completely autonomous sources are essentially required. Here, we experimentally demonstrate Hong-Ou-Mandel (HOM) quantum interference between two independent bright photon pairs generated via the spontaneous four-wave mixing in Doppler-broadened ladder-type 87Rb atoms. Bright autonomous heralded single photons are operated in a continuous-wave (CW) mode with no synchronization or supplemental filters. The four-fol...

  15. Experimental realization of highly efficient broadband coupling of single quantum dots to a photonic crystal waveguide

    DEFF Research Database (Denmark)

    Lund-Hansen, Toke; Stobbe, Søren; Julsgaard, Brian

    2008-01-01

    We present time-resolved spontaneous emission measurements of single quantum dots embedded in photonic crystal waveguides. Quantum dots that couple to a photonic crystal waveguide are found to decay up to 27 times faster than uncoupled quantum dots. From these measurements -factors of up to 0.89 ...... taking into account that the light-matter coupling is strongly enhanced due to the significant slow-down of light in the photonic crystal waveguides....

  16. Theory of single quantum dot lasers: Pauli-blocking-enhanced anti-bunching

    International Nuclear Information System (INIS)

    Su, Yumian; Bimberg, Dieter; Carmele, Alexander; Richter, Marten; Knorr, Andreas; Lüdge, Kathy; Schöll, Eckehard

    2011-01-01

    We present a theoretical model to describe the dynamics of a single semiconductor quantum dot interacting with a microcavity system. The confined quantum dot levels are pumped electrically via a carrier reservoir. The investigated dynamics includes semiconductor-specific, reservoir-induced Pauli-blocking terms in the equations of the photon probability functions. This enables a direct study of the photon statistics of the quantum light emission in dependence on the different pumping rates

  17. Deterministic and robust generation of single photons from a single quantum dot with 99.5% indistinguishability using adiabatic rapid passage.

    Science.gov (United States)

    Wei, Yu-Jia; He, Yu-Ming; Chen, Ming-Cheng; Hu, Yi-Nan; He, Yu; Wu, Dian; Schneider, Christian; Kamp, Martin; Höfling, Sven; Lu, Chao-Yang; Pan, Jian-Wei

    2014-11-12

    Single photons are attractive candidates of quantum bits (qubits) for quantum computation and are the best messengers in quantum networks. Future scalable, fault-tolerant photonic quantum technologies demand both stringently high levels of photon indistinguishability and generation efficiency. Here, we demonstrate deterministic and robust generation of pulsed resonance fluorescence single photons from a single semiconductor quantum dot using adiabatic rapid passage, a method robust against fluctuation of driving pulse area and dipole moments of solid-state emitters. The emitted photons are background-free, have a vanishing two-photon emission probability of 0.3% and a raw (corrected) two-photon Hong-Ou-Mandel interference visibility of 97.9% (99.5%), reaching a precision that places single photons at the threshold for fault-tolerant surface-code quantum computing. This single-photon source can be readily scaled up to multiphoton entanglement and used for quantum metrology, boson sampling, and linear optical quantum computing.

  18. Spontaneous formation of {1 1-bar 0 1} InGaN quantum wells on a (1 1 2-bar 2) GaN template and their electroluminescence characteristics

    International Nuclear Information System (INIS)

    Masui, Hisashi; Kamber, Derrick S; Brinkley, Stuart E; Wu, Feng; Baker, Troy J; Zhong, Hong; Iza, Michael; Speck, James S; Nakamura, Shuji; DenBaars, Steven P

    2010-01-01

    Discrete dies of the light-emitting diode (LED) fabricated on a (1 1 2-bar 2)-oriented GaN template exhibited electroluminescence peaked at 467 nm and optical output power was greater than 200 µW at 20 mA. The LED was found to have quantum well structure grown on spontaneously formed {1 1-bar 0 1} facets, confirmed via transmission electron microscopy. Polarization switching was observed in luminescence perpendicular to the device surface: the dominant polarization was parallel to [1-bar 1-bar 2 3]. The device structure was shown to be advantageous for photovoltaic cell applications by evaluating photo-induced current, although piezoelectric effects on photocurrent were not explicitly determined. The filling rate of band-edge states was estimated to be 0.025 eV per decade of current via low-temperature electroluminescence measurements

  19. Electric field induced removal of the biexciton binding energy in a single quantum dot

    NARCIS (Netherlands)

    Reimer, M.E.; Kouwen, Van M.P.; Hidma, A.W.; Weert, van M.H.M.; Bakkers, E.P.A.M.; Kouwenhoven, L.P.; Zwiller, V.

    2011-01-01

    We control the electrostatic environment of a single InAsP quantum dot in an InP nanowire with two contacts and two lateral gates positioned to an individual nanowire. We empty the quantum dot of excess charges and apply an electric field across its radial dimension. A large tuning range for the

  20. Quantum dot-micropillars: a bright source of coherent single photons

    DEFF Research Database (Denmark)

    Unsleber, Sebastian; He, Yu-Ming; Maier, Sebastian

    2016-01-01

    We present the efficient generation of coherent single photons based on quantum dots in micropillars. We utilize a scalable lithography scheme leading to quantum dot-micropillar devices with 74% extraction efficiency. Via pulsed strict resonant pumping, we show an indistinguishability of consecut...

  1. Simulation of a quantum NOT gate for a single qutrit system

    Indian Academy of Sciences (India)

    In order to achieve a quantum NOT gate for a single qutrit, the respective Schrödinger equation is solved numerically within a two-photon rotating wave approximation. For small values of one-photon detuning, there appear decoherence effects. Meanwhile, for large values of onephoton detuning, an ideal quantum NOT gate ...

  2. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces

    International Nuclear Information System (INIS)

    Krueger, David

    2009-01-01

    Optelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1 anti 100)- and especially the (anti 2110)-plane are quite corrugated. For the first time, the (anti 2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STMmeasurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping. (orig.)

  3. InGaN stress compensation layers in InGaN/GaN blue LEDs with step graded electron injectors

    Science.gov (United States)

    Sheremet, V.; Gheshlaghi, N.; Sözen, M.; Elçi, M.; Sheremet, N.; Aydınlı, A.; Altuntaş, I.; Ding, K.; Avrutin, V.; Özgür, Ü.; Morkoç, H.

    2018-04-01

    We investigate the effect of InGaN stress compensation layer on the properties of light emitting diodes based on InGaN/GaN multiple quantum well (MQW) structures with step-graded electron injectors. Insertion of an InGaN stress compensation layer between n-GaN and the step graded electron injector provides, among others, strain reduction in the MQW region and as a result improves epitaxial quality that can be observed by 15-fold decrease of V-pit density. We observed more uniform distribution of In between quantum wells in MQW region from results of electro- and photoluminescence measurement. These structural improvements lead to increasing of radiant intensity by a factor of 1.7-2.0 and enhancement of LED efficiency by 40%.

  4. Exciton dephasing in single InGaAs quantum dots

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Østergaard, John Erland; Jensen, Jacob Riis

    2000-01-01

    The homogeneous linewidth of excitonic transitions is a parameter of fundamental physical importance. In self-assembled quantum dot systems, a strong inhomogeneous broadening due to dot size fluctuations masks the homogeneous linewidth associated with transitions between individual states....... The homogeneous and inhomogeneous broadening of InGaAs quantum dot luminescence is of central importance for the potential application of this material system in optoelectronic devices. Recent measurements of MOCVD-grown InAs/InGaAs quantum dots indicate a large homogeneous broadening at room temperature due...... to fast dephasing. We present an investigation of the low-temperature homogeneous linewidth of individual PL lines from MBE-grown In0.5Ga0.5As/GaAs quantum dots....

  5. Quantum cascade laser infrared spectroscopy of single cancer cells

    KAUST Repository

    Patel, Imran

    2017-03-27

    Quantum cascade laser infrared spectroscopy is a next generation novel imaging technique allowing high resolution spectral imaging of cells. We show after spectral pre-processing, identification of different cancer cell populations within minutes.

  6. Quantum cascade laser infrared spectroscopy of single cancer cells

    KAUST Repository

    Patel, Imran; Rajamanickam, Vijayakumar Palanisamy; Bertoncini, Andrea; Pagliari, Francesca; Tirinato, Luca; Laptenok, Sergey P.; Liberale, Carlo

    2017-01-01

    Quantum cascade laser infrared spectroscopy is a next generation novel imaging technique allowing high resolution spectral imaging of cells. We show after spectral pre-processing, identification of different cancer cell populations within minutes.

  7. Nuclear magnetic resonance on a single quantum dot and a quantum dot in a nanowire system: quantum photonics and opto-mechanical coupling

    OpenAIRE

    Wüst, Gunter Johannes

    2015-01-01

    Self-assembled semiconductor quantum dots (QD) are excellent single photon sources and possible hosts for electron spin qubits, which can be initialized, manipulated and read-out optically. The nuclear spins in nano-structured semiconductors play a central role in quantum applications. The nuclear spins represent a useful resource for generating local magnetic fields but nuclear spin noise represents a major source of dephasing for spin qubits. Controlling the nuclear spins enhances the resou...

  8. Hybrid confocal Raman fluorescence microscopy on single cells using semiconductor quantum dots

    NARCIS (Netherlands)

    van Manen, H.J.; Otto, Cornelis

    2007-01-01

    We have overcome the traditional incompatibility of Raman microscopy with fluorescence microscopy by exploiting the optical properties of semiconductor fluorescent quantum dots (QDs). Here we present a hybrid Raman fluorescence spectral imaging approach for single-cell microscopy applications. We

  9. Observation of quasiperiodic dynamics in a one-dimensional quantum walk of single photons in space

    Science.gov (United States)

    Xue, Peng; Qin, Hao; Tang, Bao; Sanders, Barry C.

    2014-05-01

    We realize the quasi-periodic dynamics of a quantum walker over 2.5 quasi-periods by realizing the walker as a single photon passing through a quantum-walk optical-interferometer network. We introduce fully controllable polarization-independent phase shifters in each optical path to realize arbitrary site-dependent phase shifts, and employ large clear-aperture beam displacers, while maintaining high-visibility interference, to enable 10 quantum-walk steps to be reached. By varying the half-wave-plate setting, we control the quantum-coin bias thereby observing a transition from quasi-periodic dynamics to ballistic diffusion.

  10. Interference with a quantum dot single-photon source and a laser at telecom wavelength

    Energy Technology Data Exchange (ETDEWEB)

    Felle, M. [Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ (United Kingdom); Centre for Advanced Photonics and Electronics, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0FA (United Kingdom); Huwer, J., E-mail: jan.huwer@crl.toshiba.co.uk; Stevenson, R. M.; Skiba-Szymanska, J.; Ward, M. B.; Shields, A. J. [Toshiba Research Europe Limited, Cambridge Research Laboratory, 208 Cambridge Science Park, Milton Road, Cambridge CB4 0GZ (United Kingdom); Farrer, I.; Ritchie, D. A. [Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Penty, R. V. [Centre for Advanced Photonics and Electronics, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0FA (United Kingdom)

    2015-09-28

    The interference of photons emitted by dissimilar sources is an essential requirement for a wide range of photonic quantum information applications. Many of these applications are in quantum communications and need to operate at standard telecommunication wavelengths to minimize the impact of photon losses and be compatible with existing infrastructure. Here, we demonstrate for the first time the quantum interference of telecom-wavelength photons from an InAs/GaAs quantum dot single-photon source and a laser; an important step towards such applications. The results are in good agreement with a theoretical model, indicating a high degree of indistinguishability for the interfering photons.

  11. Mode locking of electron spin coherences in singly charged quantum dots.

    Science.gov (United States)

    Greilich, A; Yakovlev, D R; Shabaev, A; Efros, Al L; Yugova, I A; Oulton, R; Stavarache, V; Reuter, D; Wieck, A; Bayer, M

    2006-07-21

    The fast dephasing of electron spins in an ensemble of quantum dots is detrimental for applications in quantum information processing. We show here that dephasing can be overcome by using a periodic train of light pulses to synchronize the phases of the precessing spins, and we demonstrate this effect in an ensemble of singly charged (In,Ga)As/GaAs quantum dots. This mode locking leads to constructive interference of contributions to Faraday rotation and presents potential applications based on robust quantum coherence within an ensemble of dots.

  12. Injection of a single electron from static to moving quantum dots.

    Science.gov (United States)

    Bertrand, Benoit; Hermelin, Sylvain; Mortemousque, Pierre-André; Takada, Shintaro; Yamamoto, Michihisa; Tarucha, Seigo; Ludwig, Arne; Wieck, Andreas D; Bäuerle, Christopher; Meunier, Tristan

    2016-05-27

    We study the injection mechanism of a single electron from a static quantum dot into a moving quantum dot. The moving quantum dots are created with surface acoustic waves (SAWs) in a long depleted channel. We demonstrate that the injection process is characterized by an activation law with a threshold that depends on the SAW amplitude and on the dot-channel potential gradient. By sufficiently increasing the SAW modulation amplitude, we can reach a regime where the transfer has unity probability and is potentially adiabatic. This study points to the relevant regime to use moving dots in quantum information protocols.

  13. Interference with a quantum dot single-photon source and a laser at telecom wavelength

    International Nuclear Information System (INIS)

    Felle, M.; Huwer, J.; Stevenson, R. M.; Skiba-Szymanska, J.; Ward, M. B.; Shields, A. J.; Farrer, I.; Ritchie, D. A.; Penty, R. V.

    2015-01-01

    The interference of photons emitted by dissimilar sources is an essential requirement for a wide range of photonic quantum information applications. Many of these applications are in quantum communications and need to operate at standard telecommunication wavelengths to minimize the impact of photon losses and be compatible with existing infrastructure. Here, we demonstrate for the first time the quantum interference of telecom-wavelength photons from an InAs/GaAs quantum dot single-photon source and a laser; an important step towards such applications. The results are in good agreement with a theoretical model, indicating a high degree of indistinguishability for the interfering photons

  14. Single-shot secure quantum network coding on butterfly network with free public communication

    Science.gov (United States)

    Owari, Masaki; Kato, Go; Hayashi, Masahito

    2018-01-01

    Quantum network coding on the butterfly network has been studied as a typical example of quantum multiple cast network. We propose a secure quantum network code for the butterfly network with free public classical communication in the multiple unicast setting under restricted eavesdropper’s power. This protocol certainly transmits quantum states when there is no attack. We also show the secrecy with shared randomness as additional resource when the eavesdropper wiretaps one of the channels in the butterfly network and also derives the information sending through public classical communication. Our protocol does not require verification process, which ensures single-shot security.

  15. Ultra-Low Power Optical Transistor Using a Single Quantum Dot Embedded in a Photonic Wire

    DEFF Research Database (Denmark)

    Nguyen, H.A.; Grange, T.; Malik, N.S.

    2017-01-01

    Using a single InAs quantum dot embedded in a GaAs photonic wire, we realize a giant non-linearity between two optical modes to experimentally demonstrate an all-optical transistor triggered by 10 photons.......Using a single InAs quantum dot embedded in a GaAs photonic wire, we realize a giant non-linearity between two optical modes to experimentally demonstrate an all-optical transistor triggered by 10 photons....

  16. Security of a single-state semi-quantum key distribution protocol

    Science.gov (United States)

    Zhang, Wei; Qiu, Daowen; Mateus, Paulo

    2018-06-01

    Semi-quantum key distribution protocols are allowed to set up a secure secret key between two users. Compared with their full quantum counterparts, one of the two users is restricted to perform some "classical" or "semi-quantum" operations, which potentially makes them easily realizable by using less quantum resource. However, the semi-quantum key distribution protocols mainly rely on a two-way quantum channel. The eavesdropper has two opportunities to intercept the quantum states transmitted in the quantum communication stage. It may allow the eavesdropper to get more information and make the security analysis more complicated. In the past ten years, many semi-quantum key distribution protocols have been proposed and proved to be robust. However, there are few works concerning their unconditional security. It is doubted that how secure the semi-quantum ones are and how much noise they can tolerate to establish a secure secret key. In this paper, we prove the unconditional security of a single-state semi-quantum key distribution protocol proposed by Zou et al. (Phys Rev A 79:052312, 2009). We present a complete proof from information theory aspect by deriving a lower bound of the protocol's key rate in the asymptotic scenario. Using this bound, we figure out an error threshold value such that for all error rates that are less than this threshold value, the secure secret key can be established between the legitimate users definitely. Otherwise, the users should abort the protocol. We make an illustration of the protocol under the circumstance that the reverse quantum channel is a depolarizing one with parameter q. Additionally, we compare the error threshold value with some full quantum protocols and several existing semi-quantum ones whose unconditional security proofs have been provided recently.

  17. On-chip single photon filtering and multiplexing in hybrid quantum photonic circuits.

    Science.gov (United States)

    Elshaari, Ali W; Zadeh, Iman Esmaeil; Fognini, Andreas; Reimer, Michael E; Dalacu, Dan; Poole, Philip J; Zwiller, Val; Jöns, Klaus D

    2017-08-30

    Quantum light plays a pivotal role in modern science and future photonic applications. Since the advent of integrated quantum nanophotonics different material platforms based on III-V nanostructures-, colour centers-, and nonlinear waveguides as on-chip light sources have been investigated. Each platform has unique advantages and limitations; however, all implementations face major challenges with filtering of individual quantum states, scalable integration, deterministic multiplexing of selected quantum emitters, and on-chip excitation suppression. Here we overcome all of these challenges with a hybrid and scalable approach, where single III-V quantum emitters are positioned and deterministically integrated in a complementary metal-oxide-semiconductor-compatible photonic circuit. We demonstrate reconfigurable on-chip single-photon filtering and wavelength division multiplexing with a foot print one million times smaller than similar table-top approaches, while offering excitation suppression of more than 95 dB and efficient routing of single photons over a bandwidth of 40 nm. Our work marks an important step to harvest quantum optical technologies' full potential.Combining different integration platforms on the same chip is currently one of the main challenges for quantum technologies. Here, Elshaari et al. show III-V Quantum Dots embedded in nanowires operating in a CMOS compatible circuit, with controlled on-chip filtering and tunable routing.

  18. Combined atomic force microscopy and photoluminescence imaging to select single InAs/GaAs quantum dots for quantum photonic devices.

    Science.gov (United States)

    Sapienza, Luca; Liu, Jin; Song, Jin Dong; Fält, Stefan; Wegscheider, Werner; Badolato, Antonio; Srinivasan, Kartik

    2017-07-24

    We report on a combined photoluminescence imaging and atomic force microscopy study of single, isolated self-assembled InAs quantum dots. The motivation of this work is to determine an approach that allows to assess single quantum dots as candidates for quantum nanophotonic devices. By combining optical and scanning probe characterization techniques, we find that single quantum dots often appear in the vicinity of comparatively large topographic features. Despite this, the quantum dots generally do not exhibit significant differences in their non-resonantly pumped emission spectra in comparison to quantum dots appearing in defect-free regions, and this behavior is observed across multiple wafers produced in different growth chambers. Such large surface features are nevertheless a detriment to applications in which single quantum dots are embedded within nanofabricated photonic devices: they are likely to cause large spectral shifts in the wavelength of cavity modes designed to resonantly enhance the quantum dot emission, thereby resulting in a nominally perfectly-fabricated single quantum dot device failing to behave in accordance with design. We anticipate that the approach of screening quantum dots not only based on their optical properties, but also their surrounding surface topographies, will be necessary to improve the yield of single quantum dot nanophotonic devices.

  19. Characterizing multi-photon quantum interference with practical light sources and threshold single-photon detectors

    Science.gov (United States)

    Navarrete, Álvaro; Wang, Wenyuan; Xu, Feihu; Curty, Marcos

    2018-04-01

    The experimental characterization of multi-photon quantum interference effects in optical networks is essential in many applications of photonic quantum technologies, which include quantum computing and quantum communication as two prominent examples. However, such characterization often requires technologies which are beyond our current experimental capabilities, and today's methods suffer from errors due to the use of imperfect sources and photodetectors. In this paper, we introduce a simple experimental technique to characterize multi-photon quantum interference by means of practical laser sources and threshold single-photon detectors. Our technique is based on well-known methods in quantum cryptography which use decoy settings to tightly estimate the statistics provided by perfect devices. As an illustration of its practicality, we use this technique to obtain a tight estimation of both the generalized Hong‑Ou‑Mandel dip in a beamsplitter with six input photons and the three-photon coincidence probability at the output of a tritter.

  20. Quantum discord dynamics of two qubits in single-mode cavities

    International Nuclear Information System (INIS)

    Wang Chen; Chen Qing-Hu

    2013-01-01

    The dynamics of quantum discord for two identical qubits in two independent single-mode cavities and a common single-mode cavity are discussed. For the initial Bell state with correlated spins, while the entanglement sudden death can occur, the quantum discord vanishes only at discrete moments in the independent cavities and never vanishes in the common cavity. Interestingly, quantum discord and entanglement show opposite behavior in the common cavity, unlike in the independent cavities. For the initial Bell state with anti-correlated spins, quantum discord and entanglement behave in the same way for both independent cavities and a common cavity. It is found that the detunings always stabilize the quantum discord. (general)

  1. A Quantum Field Approach for Advancing Optical Coherence Tomography Part I: First Order Correlations, Single Photon Interference, and Quantum Noise.

    Science.gov (United States)

    Brezinski, M E

    2018-01-01

    Optical coherence tomography has become an important imaging technology in cardiology and ophthalmology, with other applications under investigations. Major advances in optical coherence tomography (OCT) imaging are likely to occur through a quantum field approach to the technology. In this paper, which is the first part in a series on the topic, the quantum basis of OCT first order correlations is expressed in terms of full field quantization. Specifically first order correlations are treated as the linear sum of single photon interferences along indistinguishable paths. Photons and the electromagnetic (EM) field are described in terms of quantum harmonic oscillators. While the author feels the study of quantum second order correlations will lead to greater paradigm shifts in the field, addressed in part II, advances from the study of quantum first order correlations are given. In particular, ranging errors are discussed (with remedies) from vacuum fluctuations through the detector port, photon counting errors, and position probability amplitude uncertainty. In addition, the principles of quantum field theory and first order correlations are needed for studying second order correlations in part II.

  2. A Quantum Field Approach for Advancing Optical Coherence Tomography Part I: First Order Correlations, Single Photon Interference, and Quantum Noise

    Science.gov (United States)

    Brezinski, ME

    2018-01-01

    Optical coherence tomography has become an important imaging technology in cardiology and ophthalmology, with other applications under investigations. Major advances in optical coherence tomography (OCT) imaging are likely to occur through a quantum field approach to the technology. In this paper, which is the first part in a series on the topic, the quantum basis of OCT first order correlations is expressed in terms of full field quantization. Specifically first order correlations are treated as the linear sum of single photon interferences along indistinguishable paths. Photons and the electromagnetic (EM) field are described in terms of quantum harmonic oscillators. While the author feels the study of quantum second order correlations will lead to greater paradigm shifts in the field, addressed in part II, advances from the study of quantum first order correlations are given. In particular, ranging errors are discussed (with remedies) from vacuum fluctuations through the detector port, photon counting errors, and position probability amplitude uncertainty. In addition, the principles of quantum field theory and first order correlations are needed for studying second order correlations in part II.

  3. Optical properties of InGaN thin films in the entire composition range

    Science.gov (United States)

    Kazazis, S. A.; Papadomanolaki, E.; Androulidaki, M.; Kayambaki, M.; Iliopoulos, E.

    2018-03-01

    The optical properties of thick InGaN epilayers, with compositions spanning the entire ternary range, are studied in detail. High structural quality, single phase InxGa1-xN (0001) films were grown heteroepitaxially by radio-frequency plasma assisted molecular-beam epitaxy on freestanding GaN substrates. Their emission characteristics were investigated by low temperature photoluminescence spectroscopy, whereas variable angle spectroscopic ellipsometry was applied to determine the complex dielectric function of the films, in the 0.55-4.0 eV photon range. Photoluminescence lines were intense and narrow, in the range of 100 meV for Ga-rich InGaN films (x 0.6). The composition dependence of the strain-free emission energy was expressed by a bowing parameter of b = 2.70 ± 0.12 eV. The films' optical dielectric function dispersion was obtained by the analysis of the ellipsometric data employing a Kramers-Kronig consistent parameterized optical model. The refractive index dispersion was obtained for alloys in the entire composition range, and the corresponding values at the band edge show a parabolic dependence on the InN mole fraction expressed by a bowing parameter of b = 0.81 ± 0.04. The bowing parameter describing the fundamental energy bandgap was deduced to be equal to 1.66 ± 0.07 eV, consistent with the ab initio calculations for statistically random (non-clustered) InGaN alloys.

  4. Single-Atom Demonstration of the Quantum Landauer Principle

    Science.gov (United States)

    Yan, L. L.; Xiong, T. P.; Rehan, K.; Zhou, F.; Liang, D. F.; Chen, L.; Zhang, J. Q.; Yang, W. L.; Ma, Z. H.; Feng, M.

    2018-05-01

    One of the outstanding challenges to information processing is the eloquent suppression of energy consumption in the execution of logic operations. The Landauer principle sets an energy constraint in deletion of a classical bit of information. Although some attempts have been made to experimentally approach the fundamental limit restricted by this principle, exploring the Landauer principle in a purely quantum mechanical fashion is still an open question. Employing a trapped ultracold ion, we experimentally demonstrate a quantum version of the Landauer principle, i.e., an equality associated with the energy cost of information erasure in conjunction with the entropy change of the associated quantized environment. Our experimental investigation substantiates an intimate link between information thermodynamics and quantum candidate systems for information processing.

  5. Electrical Initialization of Electron and Nuclear Spins in a Single Quantum Dot at Zero Magnetic Field.

    Science.gov (United States)

    Cadiz, Fabian; Djeffal, Abdelhak; Lagarde, Delphine; Balocchi, Andrea; Tao, Bingshan; Xu, Bo; Liang, Shiheng; Stoffel, Mathieu; Devaux, Xavier; Jaffres, Henri; George, Jean-Marie; Hehn, Michel; Mangin, Stephane; Carrere, Helene; Marie, Xavier; Amand, Thierry; Han, Xiufeng; Wang, Zhanguo; Urbaszek, Bernhard; Lu, Yuan; Renucci, Pierre

    2018-04-11

    The emission of circularly polarized light from a single quantum dot relies on the injection of carriers with well-defined spin polarization. Here we demonstrate single dot electroluminescence (EL) with a circular polarization degree up to 35% at zero applied magnetic field. The injection of spin-polarized electrons is achieved by combining ultrathin CoFeB electrodes on top of a spin-LED device with p-type InGaAs quantum dots in the active region. We measure an Overhauser shift of several microelectronvolts at zero magnetic field for the positively charged exciton (trion X + ) EL emission, which changes sign as we reverse the injected electron spin orientation. This is a signature of dynamic polarization of the nuclear spins in the quantum dot induced by the hyperfine interaction with the electrically injected electron spin. This study paves the way for electrical control of nuclear spin polarization in a single quantum dot without any external magnetic field.

  6. Quantum routing of single optical photons with a superconducting flux qubit

    Science.gov (United States)

    Xia, Keyu; Jelezko, Fedor; Twamley, Jason

    2018-05-01

    Interconnecting optical photons with superconducting circuits is a challenging problem but essential for building long-range superconducting quantum networks. We propose a hybrid quantum interface between the microwave and optical domains where the propagation of a single-photon pulse along a nanowaveguide is controlled in a coherent way by tuning the electromagnetically induced transparency window with the quantum state of a flux qubit mediated by the spin in a nanodiamond. The qubit can route a single-photon pulse using the nanodiamond into a quantum superposition of paths without the aid of an optical cavity—simplifying the setup. By preparing the flux qubit in a superposition state our cavityless scheme creates a hybrid state-path entanglement between a flying single optical photon and a static superconducting qubit.

  7. Repetitive readout of a single electronic spin via quantum logic with nuclear spin ancillae.

    Science.gov (United States)

    Jiang, L; Hodges, J S; Maze, J R; Maurer, P; Taylor, J M; Cory, D G; Hemmer, P R; Walsworth, R L; Yacoby, A; Zibrov, A S; Lukin, M D

    2009-10-09

    Robust measurement of single quantum bits plays a key role in the realization of quantum computation and communication as well as in quantum metrology and sensing. We have implemented a method for the improved readout of single electronic spin qubits in solid-state systems. The method makes use of quantum logic operations on a system consisting of a single electronic spin and several proximal nuclear spin ancillae in order to repetitively readout the state of the electronic spin. Using coherent manipulation of a single nitrogen vacancy center in room-temperature diamond, full quantum control of an electronic-nuclear system consisting of up to three spins was achieved. We took advantage of a single nuclear-spin memory in order to obtain a 10-fold enhancement in the signal amplitude of the electronic spin readout. We also present a two-level, concatenated procedure to improve the readout by use of a pair of nuclear spin ancillae, an important step toward the realization of robust quantum information processors using electronic- and nuclear-spin qubits. Our technique can be used to improve the sensitivity and speed of spin-based nanoscale diamond magnetometers.

  8. Single-photon three-qubit quantum logic using spatial light modulators.

    Science.gov (United States)

    Kagalwala, Kumel H; Di Giuseppe, Giovanni; Abouraddy, Ayman F; Saleh, Bahaa E A

    2017-09-29

    The information-carrying capacity of a single photon can be vastly expanded by exploiting its multiple degrees of freedom: spatial, temporal, and polarization. Although multiple qubits can be encoded per photon, to date only two-qubit single-photon quantum operations have been realized. Here, we report an experimental demonstration of three-qubit single-photon, linear, deterministic quantum gates that exploit photon polarization and the two-dimensional spatial-parity-symmetry of the transverse single-photon field. These gates are implemented using a polarization-sensitive spatial light modulator that provides a robust, non-interferometric, versatile platform for implementing controlled unitary gates. Polarization here represents the control qubit for either separable or entangling unitary operations on the two spatial-parity target qubits. Such gates help generate maximally entangled three-qubit Greenberger-Horne-Zeilinger and W states, which is confirmed by tomographical reconstruction of single-photon density matrices. This strategy provides access to a wide range of three-qubit states and operations for use in few-qubit quantum information processing protocols.Photons are essential for quantum information processing, but to date only two-qubit single-photon operations have been realized. Here the authors demonstrate experimentally a three-qubit single-photon linear deterministic quantum gate by exploiting polarization along with spatial-parity symmetry.

  9. Heralded linear optical quantum Fredkin gate based on one auxiliary qubit and one single photon detector

    International Nuclear Information System (INIS)

    Zhu Chang-Hua; Cao Xin; Quan Dong-Xiao; Pei Chang-Xing

    2014-01-01

    Linear optical quantum Fredkin gate can be applied to quantum computing and quantum multi-user communication networks. In the existing linear optical scheme, two single photon detectors (SPDs) are used to herald the success of the quantum Fredkin gate while they have no photon count. But analysis results show that for non-perfect SPD, the lower the detector efficiency, the higher the heralded success rate by this scheme is. We propose an improved linear optical quantum Fredkin gate by designing a new heralding scheme with an auxiliary qubit and only one SPD, in which the higher the detection efficiency of the heralding detector, the higher the success rate of the gate is. The new heralding scheme can also work efficiently under a non-ideal single photon source. Based on this quantum Fredkin gate, large-scale quantum switching networks can be built. As an example, a quantum Beneš network is shown in which only one SPD is used. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  10. Single-hidden-layer feed-forward quantum neural network based on Grover learning.

    Science.gov (United States)

    Liu, Cheng-Yi; Chen, Chein; Chang, Ching-Ter; Shih, Lun-Min

    2013-09-01

    In this paper, a novel single-hidden-layer feed-forward quantum neural network model is proposed based on some concepts and principles in the quantum theory. By combining the quantum mechanism with the feed-forward neural network, we defined quantum hidden neurons and connected quantum weights, and used them as the fundamental information processing unit in a single-hidden-layer feed-forward neural network. The quantum neurons make a wide range of nonlinear functions serve as the activation functions in the hidden layer of the network, and the Grover searching algorithm outstands the optimal parameter setting iteratively and thus makes very efficient neural network learning possible. The quantum neuron and weights, along with a Grover searching algorithm based learning, result in a novel and efficient neural network characteristic of reduced network, high efficient training and prospect application in future. Some simulations are taken to investigate the performance of the proposed quantum network and the result show that it can achieve accurate learning. Copyright © 2013 Elsevier Ltd. All rights reserved.

  11. Two-color single-photon emission from InAs quantum dots: toward logic information management using quantum light.

    Science.gov (United States)

    Rivas, David; Muñoz-Matutano, Guillermo; Canet-Ferrer, Josep; García-Calzada, Raúl; Trevisi, Giovanna; Seravalli, Luca; Frigeri, Paola; Martínez-Pastor, Juan P

    2014-02-12

    In this work, we propose the use of the Hanbury-Brown and Twiss interferometric technique and a switchable two-color excitation method for evaluating the exciton and noncorrelated electron-hole dynamics associated with single photon emission from indium arsenide (InAs) self-assembled quantum dots (QDs). Using a microstate master equation model we demonstrate that our single QDs are described by nonlinear exciton dynamics. The simultaneous detection of two-color, single photon emission from InAs QDs using these nonlinear dynamics was used to design a NOT AND logic transference function. This computational functionality combines the advantages of working with light/photons as input/output device parameters (all-optical system) and that of a nanodevice (QD size of ∼ 20 nm) while also providing high optical sensitivity (ultralow optical power operational requirements). These system features represent an important and interesting step toward the development of new prototypes for the incoming quantum information technologies.

  12. Design and Simulation of InGaN p-n Junction Solar Cell

    Directory of Open Access Journals (Sweden)

    A. Mesrane

    2015-01-01

    Full Text Available The tunability of the InGaN band gap energy over a wide range provides a good spectral match to sunlight, making it a suitable material for photovoltaic solar cells. The main objective of this work is to design and simulate the optimal InGaN single-junction solar cell. For more accurate results and best configuration, the optical properties and the physical models such as the Fermi-Dirac statistics, Auger and Shockley-Read-Hall recombination, and the doping and temperature-dependent mobility model were taken into account in simulations. The single-junction In0.622Ga0.378N (Eg = 1.39 eV solar cell is the optimal structure found. It exhibits, under normalized conditions (AM1.5G, 0.1 W/cm2, and 300 K, the following electrical parameters: Jsc=32.6791 mA/cm2, Voc=0.94091 volts, FF = 86.2343%, and η=26.5056%. It was noticed that the minority carrier lifetime and the surface recombination velocity have an important effect on the solar cell performance. Furthermore, the investigation results show that the In0.622Ga0.378N solar cell efficiency was inversely proportional with the temperature.

  13. Novel single photon sources for new generation of quantum communications

    Science.gov (United States)

    2017-06-13

    including the time for reviewing instructions, searching existing    data sources, gathering and maintaining the data needed, and completing and...and enable absolutely secured information transfer between distant nodes – key prerequisite for quantum cryptography. Experiment : the experimental... format showing authors, title, journal, issue, pages, and date, for each category list the following: a) papers published in peer-reviewed journals

  14. Photon Cascade from a Single Crystal Phase Nanowire Quantum Dot

    DEFF Research Database (Denmark)

    Bouwes Bavinck, Maaike; Jöns, Klaus D; Zieliński, Michal

    2016-01-01

    . We notice that the emission spectra consist often of two peaks close in energy, which we explain with a comprehensive theory showing that the symmetry of the system plays a crucial role for the hole levels forming hybridized orbitals. Our results state that crystal phase quantum dots have promising...

  15. Self-organization of dislocation-free, high-density, vertically aligned GaN nanocolumns involving InGaN quantum wells on graphene/SiO2 covered with a thin AlN buffer layer

    International Nuclear Information System (INIS)

    Hayashi, Hiroaki; Konno, Yuta; Kishino, Katsumi

    2016-01-01

    We demonstrated the self-organization of high-density GaN nanocolumns on multilayer graphene (MLG)/SiO 2 covered with a thin AlN buffer layer by RF-plasma-assisted molecular beam epitaxy. MLG/SiO 2 substrates were prepared by the transfer of CVD graphene onto thermally oxidized SiO 2 /Si [100] substrates. Employing the MLG with an AlN buffer layer enabled the self-organization of high-density and vertically aligned nanocolumns. Transmission electron microscopy observation revealed that no threading dislocations, stacking faults, or twinning defects were included in the self-organized nanocolumns. The photoluminescence (PL) peak intensities of the self-organized GaN nanocolumns were 2.0–2.6 times higher than those of a GaN substrate grown by hydride vapor phase epitaxy. Moreover, no yellow luminescence or ZB-phase GaN emission was observed from the nanocolumns. An InGaN/GaN MQW and p-type GaN were integrated into GaN nanocolumns grown on MLG, displaying a single-peak PL emission at a wavelength of 533 nm. Thus, high-density nitride p–i–n nanocolumns were fabricated on SiO 2 /Si using the transferred MLG interlayer, indicating the possibility of developing visible nanocolumn LEDs on graphene/SiO 2 . (paper)

  16. Elliptical quantum dots as on-demand single photons sources with deterministic polarization states

    Energy Technology Data Exchange (ETDEWEB)

    Teng, Chu-Hsiang; Demory, Brandon; Ku, Pei-Cheng, E-mail: peicheng@umich.edu [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48105 (United States); Zhang, Lei; Hill, Tyler A.; Deng, Hui [Department of Mechanical Engineering, University of Michigan, 2350 Hayward St., Ann Arbor, Michigan 48105 (United States)

    2015-11-09

    In quantum information, control of the single photon's polarization is essential. Here, we demonstrate single photon generation in a pre-programmed and deterministic polarization state, on a chip-scale platform, utilizing site-controlled elliptical quantum dots (QDs) synthesized by a top-down approach. The polarization from the QD emission is found to be linear with a high degree of linear polarization and parallel to the long axis of the ellipse. Single photon emission with orthogonal polarizations is achieved, and the dependence of the degree of linear polarization on the QD geometry is analyzed.

  17. Single-photon sources for quantum technologies - Results of the joint research project SIQUTE

    DEFF Research Database (Denmark)

    Kück, S.; López, M.; Rodiek, B.

    2017-01-01

    In this presentation, the results of the joint research project “Single-Photon Sources for Quantum Technologies” (SIQUTE) [1] will be presented. The focus will be on the development of absolutely characterized single-photon sources, on the realization of an efficient waveguide-based single-photon......-photon source at the telecom wavelengths of 1.3 µm and 1.55 µm, on the implementation of the quantum-enhanced resolution in confocal fluorescence microscopy and on the development of a detector for very low photon fluxes...

  18. Conjugation of biotin-coated luminescent quantum dots with single domain antibody-rhizavidin fusions

    Directory of Open Access Journals (Sweden)

    Jinny L. Liu

    2016-06-01

    Full Text Available Straightforward and effective methods are required for the bioconjugation of proteins to surfaces and particles. Previously we demonstrated that the fusion of a single domain antibody with the biotin binding molecule rhizavidin provided a facile method to coat biotin-modified surfaces with a highly active and oriented antibody. Here, we constructed similar single domain antibody—rhizavidin fusions as well as unfused rhizavidin with a His-tag. The unfused rhizavidin produced efficiently and its utility for assay development was demonstrated in surface plasmon resonance experiments. The single domain antibody-rhizavidin fusions were utilized to coat quantum dots that had been prepared with surface biotins. Preparation of antibody coated quantum dots by this means was found to be both easy and effective. The prepared single domain antibody-quantum dot reagent was characterized by surface plasmon resonance and applied to toxin detection in a fluoroimmunoassay sensing format.

  19. Negative quantum capacitance induced by midgap states in single-layer graphene.

    Science.gov (United States)

    Wang, Lin; Wang, Yang; Chen, Xiaolong; Zhu, Wei; Zhu, Chao; Wu, Zefei; Han, Yu; Zhang, Mingwei; Li, Wei; He, Yuheng; Xiong, Wei; Law, Kam Tuen; Su, Dangsheng; Wang, Ning

    2013-01-01

    We demonstrate that single-layer graphene (SLG) decorated with a high density of Ag adatoms displays the unconventional phenomenon of negative quantum capacitance. The Ag adatoms act as resonant impurities and form nearly dispersionless resonant impurity bands near the charge neutrality point (CNP). Resonant impurities quench the kinetic energy and drive the electrons to the Coulomb energy dominated regime with negative compressibility. In the absence of a magnetic field, negative quantum capacitance is observed near the CNP. In the quantum Hall regime, negative quantum capacitance behavior at several Landau level positions is displayed, which is associated with the quenching of kinetic energy by the formation of Landau levels. The negative quantum capacitance effect near the CNP is further enhanced in the presence of Landau levels due to the magnetic-field-enhanced Coulomb interactions.

  20. No-go theorem for passive single-rail linear optical quantum computing.

    Science.gov (United States)

    Wu, Lian-Ao; Walther, Philip; Lidar, Daniel A

    2013-01-01

    Photonic quantum systems are among the most promising architectures for quantum computers. It is well known that for dual-rail photons effective non-linearities and near-deterministic non-trivial two-qubit gates can be achieved via the measurement process and by introducing ancillary photons. While in principle this opens a legitimate path to scalable linear optical quantum computing, the technical requirements are still very challenging and thus other optical encodings are being actively investigated. One of the alternatives is to use single-rail encoded photons, where entangled states can be deterministically generated. Here we prove that even for such systems universal optical quantum computing using only passive optical elements such as beam splitters and phase shifters is not possible. This no-go theorem proves that photon bunching cannot be passively suppressed even when extra ancilla modes and arbitrary number of photons are used. Our result provides useful guidance for the design of optical quantum computers.

  1. Reduced thermal quenching in indium-rich self-organized InGaN/GaN quantum dots

    KAUST Repository

    Elafandy, Rami T.; Bhattacharya, Pallab K.; Cha, Dong Kyu; Ng, Tien Khee; Ooi, Boon S.; Zhang, Meng

    2012-01-01

    Differences in optical and structural properties of indium rich (27), indium gallium nitride (InGaN) self-organized quantum dots (QDs), with red wavelength emission, and the two dimensional underlying wetting layer (WL) are investigated. Temperature

  2. Extracting random numbers from quantum tunnelling through a single diode.

    Science.gov (United States)

    Bernardo-Gavito, Ramón; Bagci, Ibrahim Ethem; Roberts, Jonathan; Sexton, James; Astbury, Benjamin; Shokeir, Hamzah; McGrath, Thomas; Noori, Yasir J; Woodhead, Christopher S; Missous, Mohamed; Roedig, Utz; Young, Robert J

    2017-12-19

    Random number generation is crucial in many aspects of everyday life, as online security and privacy depend ultimately on the quality of random numbers. Many current implementations are based on pseudo-random number generators, but information security requires true random numbers for sensitive applications like key generation in banking, defence or even social media. True random number generators are systems whose outputs cannot be determined, even if their internal structure and response history are known. Sources of quantum noise are thus ideal for this application due to their intrinsic uncertainty. In this work, we propose using resonant tunnelling diodes as practical true random number generators based on a quantum mechanical effect. The output of the proposed devices can be directly used as a random stream of bits or can be further distilled using randomness extraction algorithms, depending on the application.

  3. Single-Particle Quantum Dynamics in a Magnetic Lattice

    Energy Technology Data Exchange (ETDEWEB)

    Venturini, Marco

    2001-02-01

    We study the quantum dynamics of a spinless charged-particle propagating through a magnetic lattice in a transport line or storage ring. Starting from the Klein-Gordon equation and by applying the paraxial approximation, we derive a Schroedinger-like equation for the betatron motion. A suitable unitary transformation reduces the problem to that of a simple harmonic oscillator. As a result we are able to find an explicit expression for the particle wavefunction.

  4. Quantum Contextuality in a Single-Neutron Optical Experiment

    International Nuclear Information System (INIS)

    Hasegawa, Yuji; Loidl, Rudolf; Baron, Matthias; Badurek, Gerald; Rauch, Helmut

    2006-01-01

    An experimental demonstration of quantum contextuality with neutrons is presented, which intended to exhibit a Kochen-Specker-like phenomenon. Since no perfect correlation is expected in practical experiments, inequalities are derived to distinguish quantitatively the obtained results from predictions by a noncontextual hidden variable theory. Experiments were accomplished with the use of a neutron interferometer combined with spinor manipulation devices. The results clearly violate the prediction of noncontextual theories

  5. Quantum Hall states of atomic Bose gases: Density profiles in single-layer and multilayer geometries

    International Nuclear Information System (INIS)

    Cooper, N. R.; Lankvelt, F. J. M. van; Reijnders, J. W.; Schoutens, K.

    2005-01-01

    We describe the density profiles of confined atomic Bose gases in the high-rotation limit, in single-layer and multilayer geometries. We show that, in a local-density approximation, the density in a single layer shows a landscape of quantized steps due to the formation of incompressible liquids, which are analogous to fractional quantum Hall liquids for a two-dimensional electron gas in a strong magnetic field. In a multilayered setup we find different phases, depending on the strength of the interlayer tunneling t. We discuss the situation where a vortex lattice in the three-dimensional condensate (at large tunneling) undergoes quantum melting at a critical tunneling t c 1 . For tunneling well below t c 1 one expects weakly coupled or isolated layers, each exhibiting a landscape of quantum Hall liquids. After expansion, this gives a radial density distribution with characteristic features (cusps) that provide experimental signatures of the quantum Hall liquids

  6. Efficient fiber-coupled single-photon sources based on quantum dots

    DEFF Research Database (Denmark)

    Daveau, Raphaël Sura

    refrigeration with coupled quantum wells. Many photonic quantum information processing applications would benet from a highbrightness, ber-coupled source of triggered single photons. This thesis presents a study of such sources based on quantum dots coupled to unidirectional photonic-crystal waveguide devices.......6 %. This latter method opens a promising future for increasing the eciency and reliability of planar chip-based single-photon sources. Refrigeration of a solid-state system with light has potential applications for cooling small-scale electronic and photonic circuits. We show theoretically that two coupled...... semiconductor quantum wells are ecient cooling media because they support long-lived indirect electron-hole pairs. These pairs can be thermally excited to distinct higher-energy states with faster radiative recombination, thereby creating an ecient escape channel to remove thermal energy from the system. From...

  7. Spin quantum tunneling via entangled states in a dimer of exchange coupled single-molecule magnets

    Science.gov (United States)

    Tiron, R.; Wernsdorfer, W.; Aliaga-Alcalde, N.; Foguet-Albiol, D.; Christou, G.

    2004-03-01

    A new family of supramolecular, antiferromagnetically exchange-coupled dimers of single-molecule magnets (SMMs) has recently been reported [W. Wernsdorfer, N. Aliaga-Alcalde, D.N. Hendrickson, and G. Christou, Nature 416, 406 (2002)]. Each SMM acts as a bias on its neighbor, shifting the quantum tunneling resonances of the individual SMMs. Hysteresis loop measurements on a single crystal of SMM-dimers have now established quantum tunneling of the magnetization via entangled states of the dimer. This shows that the dimer really does behave as a quantum-mechanically coupled dimer. The transitions are well separated, suggesting long coherence times compared to the time scale of the energy splitting. This result is of great importance if such systems are to be used for quantum computing. It also allows the measurement of the longitudinal and transverse superexchange coupling constants [Phys. Rev. Lett. 91, 227203 (2003)].

  8. Cavity Exciton-Polariton mediated, Single-Shot Quantum Non-Demolition measurement of a Quantum Dot Electron Spin

    Science.gov (United States)

    Puri, Shruti; McMahon, Peter; Yamamoto, Yoshihisa

    2014-03-01

    The quantum non-demolition (QND) measurement of a single electron spin is of great importance in measurement-based quantum computing schemes. The current single-shot readout demonstrations exhibit substantial spin-flip backaction. We propose a QND readout scheme for quantum dot (QD) electron spins in Faraday geometry, which differs from previous proposals and implementations in that it relies on a novel physical mechanism: the spin-dependent Coulomb exchange interaction between a QD spin and optically-excited quantum well (QW) microcavity exciton-polaritons. The Coulomb exchange interaction causes a spin-dependent shift in the resonance energy of the polarized polaritons, thus causing the phase and intensity response of left circularly polarized light to be different to that of the right circularly polarized light. As a result the QD electron's spin can be inferred from the response to a linearly polarized probe. We show that by a careful design of the system, any spin-flip backaction can be eliminated and a QND measurement of the QD electron spin can be performed within a few 10's of nanoseconds with fidelity 99:95%. This improves upon current optical QD spin readout techniques across multiple metrics, including fidelity, speed and scalability. National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan.

  9. Characteristics of InGaN designed for photovoltaic applications

    International Nuclear Information System (INIS)

    Trybus, E.; Jani, O.; Burnham, S.; Ferguson, I.; Doolittle, W.A.; Honsberg, C.; Steiner, M.

    2008-01-01

    This work addresses the required properties and device structures for an InGaN solar cell. Homojunction InGaN solar cells with a bandgap greater than 2.0 eV are specifically targeted due to material limitations. These devices are attractive because over half the available power in the solar spectrum is above 2.0 eV. Using high growth rates, InGaN films with indium compositions ranging from 1 to 32% have been grown by Molecular Beam Epitaxy with negligible phase separation according to X-ray diffraction analysis, and better than 190 arc-sec ω-2θ FWHM for ∝0.6 μm thick In 0.32 Ga 0.68 N film. Using measured transmission data, the absorption coefficient of InGaN at 2.4 eV was calculated as α≅2 x 10 5 cm -1 near the band edge. This results in the optimal solar cell thickness of less than a micron and may lead to high open circuit voltage while reducing the constraints on limited minority carrier lifetimes. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Characteristics of InGaN designed for photovoltaic applications

    Energy Technology Data Exchange (ETDEWEB)

    Trybus, E.; Jani, O.; Burnham, S.; Ferguson, I.; Doolittle, W.A. [Georgia Institute of Technology, School of Electrical and Computer Engineering, Atlanta, GA (United States); Honsberg, C. [University of Delaware, Department of Electrical and Computer Engineering, Newark, DE (United States); Steiner, M. [National Renewable Energy Laboratory, Golden, CO (United States)

    2008-07-01

    This work addresses the required properties and device structures for an InGaN solar cell. Homojunction InGaN solar cells with a bandgap greater than 2.0 eV are specifically targeted due to material limitations. These devices are attractive because over half the available power in the solar spectrum is above 2.0 eV. Using high growth rates, InGaN films with indium compositions ranging from 1 to 32% have been grown by Molecular Beam Epitaxy with negligible phase separation according to X-ray diffraction analysis, and better than 190 arc-sec {omega}-2{theta} FWHM for {proportional_to}0.6 {mu}m thick In{sub 0.32}Ga{sub 0.68}N film. Using measured transmission data, the absorption coefficient of InGaN at 2.4 eV was calculated as {alpha}{approx_equal}2 x 10{sup 5} cm{sup -1} near the band edge. This results in the optimal solar cell thickness of less than a micron and may lead to high open circuit voltage while reducing the constraints on limited minority carrier lifetimes. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Detection of single quantum dots in model organisms with sheet illumination microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Friedrich, Mike; Nozadze, Revaz; Gan, Qiang; Zelman-Femiak, Monika; Ermolayev, Vladimir [Molecular Microscopy Group, Rudolf Virchow Center, University of Wuerzburg, Versbacher Str. 9, D-97078 Wuerzburg (Germany); Wagner, Toni U. [Institute of Physiological Chemistry I, Biocenter, University of Wuerzburg, Am Hubland, D-97074 Wuerzburg (Germany); Harms, Gregory S., E-mail: gregory.harms@virchow.uni-wuerzburg.de [Molecular Microscopy Group, Rudolf Virchow Center, University of Wuerzburg, Versbacher Str. 9, D-97078 Wuerzburg (Germany)

    2009-12-18

    Single-molecule detection and tracking is important for observing biomolecule interactions in the microenvironment. Here we report selective plane illumination microscopy (SPIM) with single-molecule detection in living organisms, which enables fast imaging and single-molecule tracking and optical penetration beyond 300 {mu}m. We detected single nanocrystals in Drosophila larvae and zebrafish embryo. We also report our first tracking of single quantum dots during zebrafish development, which displays a transition from flow to confined motion prior to the blastula stage. The new SPIM setup represents a new technique, which enables fast single-molecule imaging and tracking in living systems.

  12. Detection of single quantum dots in model organisms with sheet illumination microscopy

    International Nuclear Information System (INIS)

    Friedrich, Mike; Nozadze, Revaz; Gan, Qiang; Zelman-Femiak, Monika; Ermolayev, Vladimir; Wagner, Toni U.; Harms, Gregory S.

    2009-01-01

    Single-molecule detection and tracking is important for observing biomolecule interactions in the microenvironment. Here we report selective plane illumination microscopy (SPIM) with single-molecule detection in living organisms, which enables fast imaging and single-molecule tracking and optical penetration beyond 300 μm. We detected single nanocrystals in Drosophila larvae and zebrafish embryo. We also report our first tracking of single quantum dots during zebrafish development, which displays a transition from flow to confined motion prior to the blastula stage. The new SPIM setup represents a new technique, which enables fast single-molecule imaging and tracking in living systems.

  13. High performance mode locking characteristics of single section quantum dash lasers.

    Science.gov (United States)

    Rosales, Ricardo; Murdoch, S G; Watts, R T; Merghem, K; Martinez, Anthony; Lelarge, Francois; Accard, Alain; Barry, L P; Ramdane, Abderrahim

    2012-04-09

    Mode locking features of single section quantum dash based lasers are investigated. Particular interest is given to the static spectral phase profile determining the shape of the mode locked pulses. The phase profile dependence on cavity length and injection current is experimentally evaluated, demonstrating the possibility of efficiently using the wide spectral bandwidth exhibited by these quantum dash structures for the generation of high peak power sub-picosecond pulses with low radio frequency linewidths.

  14. Quantum resonances in a single plaquette of Josephson junctions: excitations of Rabi oscillations

    OpenAIRE

    Fistul, M. V.

    2001-01-01

    We present a theoretical study of a quantum regime of the resistive (whirling) state of dc driven anisotropic single plaquette containing three small Josephson junctions. The current-voltage characteristics of such a system display resonant steps that are due to the resonant interaction between the time dependent Josephson current and the excited electromagnetic oscillations (EOs). The voltage positions of the resonances are determined by the quantum interband transitions of EOs. We show that...

  15. Quantum Tunneling of Magnetization in Single Molecular Magnets Coupled to Ferromagnetic Reservoirs

    OpenAIRE

    Misiorny, Maciej; Barnas, Józef

    2006-01-01

    The role of spin polarized reservoirs in quantum tunneling of magnetization and relaxation processes in a single molecular magnet (SMM) is investigated theoretically. The SMM is exchange-coupled to the reservoirs and also subjected to a magnetic field varying in time, which enables the quantum tunneling of magnetization (QTM). The spin relaxation times are calculated from the Fermi golden rule. The exchange interaction with tunneling electrons is shown to affect the spin reversal due to QTM. ...

  16. Manifestation of Spin Selection Rules on the Quantum Tunneling of Magnetization in a Single Molecule Magnet

    OpenAIRE

    Henderson, J. J.; Koo, C.; Feng, P. L.; del Barco, E.; Hill, S.; Tupitsyn, I. S.; Stamp, P. C. E.; Hendrickson, D. N.

    2009-01-01

    We present low temperature magnetometry measurements on a new Mn3 single-molecule magnet (SMM) in which the quantum tunneling of magnetization (QTM) displays clear evidence for quantum mechanical selection rules. A QTM resonance appearing only at elevated temperatures demonstrates tunneling between excited states with spin projections differing by a multiple of three: this is dictated by the C3 symmetry of the molecule, which forbids pure tunneling from the lowest metastable state. Resonances...

  17. A feasible quantum optical experiment capable of refuting noncontextuality for single photons

    International Nuclear Information System (INIS)

    Cereceda, Jose L

    2002-01-01

    Elaborating on a previous work by Simon et al (2000 Phys. Rev. Lett. 85 1783) we propose a realizable quantum optical single-photon experiment using standard present day technology, capable of discriminating maximally between the predictions of quantum mechanics (QM) and noncontextual hidden variable theories (NCHV). Quantum mechanics predicts a gross violation (up to a factor of 2) of the noncontextual Bell-like inequality associated with the proposed experiment. An actual maximal violation of this inequality would demonstrate (modulo fair sampling) an all-or-nothing type contradiction between QM and NCHV

  18. Quantum tunneling of magnetization in single molecular magnets coupled to ferromagnetic reservoirs

    Science.gov (United States)

    Misiorny, M.; Barnas, J.

    2007-04-01

    The role of spin polarized reservoirs in quantum tunneling of magnetization and relaxation processes in a single molecular magnet (SMM) is investigated theoretically. The SMM is exchange-coupled to the reservoirs and also subjected to a magnetic field varying in time, which enables the quantum tunneling of magnetization. The spin relaxation times are calculated from the Fermi golden rule. The exchange interaction of SMM and electrons in the leads is shown to affect the spin reversal due to quantum tunneling of magnetization. It is shown that the switching is associated with transfer of a certain charge between the leads.

  19. Quantum dot single-photon switches of resonant tunneling current for discriminating-photon-number detection.

    Science.gov (United States)

    Weng, Qianchun; An, Zhenghua; Zhang, Bo; Chen, Pingping; Chen, Xiaoshuang; Zhu, Ziqiang; Lu, Wei

    2015-03-23

    Low-noise single-photon detectors that can resolve photon numbers are used to monitor the operation of quantum gates in linear-optical quantum computation. Exactly 0, 1 or 2 photons registered in a detector should be distinguished especially in long-distance quantum communication and quantum computation. Here we demonstrate a photon-number-resolving detector based on quantum dot coupled resonant tunneling diodes (QD-cRTD). Individual quantum-dots (QDs) coupled closely with adjacent quantum well (QW) of resonant tunneling diode operate as photon-gated switches- which turn on (off) the RTD tunneling current when they trap photon-generated holes (recombine with injected electrons). Proposed electron-injecting operation fills electrons into coupled QDs which turn "photon-switches" to "OFF" state and make the detector ready for multiple-photons detection. With proper decision regions defined, 1-photon and 2-photon states are resolved in 4.2 K with excellent propabilities of accuracy of 90% and 98% respectively. Further, by identifying step-like photon responses, the photon-number-resolving capability is sustained to 77 K, making the detector a promising candidate for advanced quantum information applications where photon-number-states should be accurately distinguished.

  20. High-Dimensional Single-Photon Quantum Gates: Concepts and Experiments.

    Science.gov (United States)

    Babazadeh, Amin; Erhard, Manuel; Wang, Feiran; Malik, Mehul; Nouroozi, Rahman; Krenn, Mario; Zeilinger, Anton

    2017-11-03

    Transformations on quantum states form a basic building block of every quantum information system. From photonic polarization to two-level atoms, complete sets of quantum gates for a variety of qubit systems are well known. For multilevel quantum systems beyond qubits, the situation is more challenging. The orbital angular momentum modes of photons comprise one such high-dimensional system for which generation and measurement techniques are well studied. However, arbitrary transformations for such quantum states are not known. Here we experimentally demonstrate a four-dimensional generalization of the Pauli X gate and all of its integer powers on single photons carrying orbital angular momentum. Together with the well-known Z gate, this forms the first complete set of high-dimensional quantum gates implemented experimentally. The concept of the X gate is based on independent access to quantum states with different parities and can thus be generalized to other photonic degrees of freedom and potentially also to other quantum systems.

  1. Electro-optic routing of photons from a single quantum dot in photonic integrated circuits

    Science.gov (United States)

    Midolo, Leonardo; Hansen, Sofie L.; Zhang, Weili; Papon, Camille; Schott, Rüdiger; Ludwig, Arne; Wieck, Andreas D.; Lodahl, Peter; Stobbe, Søren

    2017-12-01

    Recent breakthroughs in solid-state photonic quantum technologies enable generating and detecting single photons with near-unity efficiency as required for a range of photonic quantum technologies. The lack of methods to simultaneously generate and control photons within the same chip, however, has formed a main obstacle to achieving efficient multi-qubit gates and to harness the advantages of chip-scale quantum photonics. Here we propose and demonstrate an integrated voltage-controlled phase shifter based on the electro-optic effect in suspended photonic waveguides with embedded quantum emitters. The phase control allows building a compact Mach-Zehnder interferometer with two orthogonal arms, taking advantage of the anisotropic electro-optic response in gallium arsenide. Photons emitted by single self-assembled quantum dots can be actively routed into the two outputs of the interferometer. These results, together with the observed sub-microsecond response time, constitute a significant step towards chip-scale single-photon-source de-multiplexing, fiber-loop boson sampling, and linear optical quantum computing.

  2. Electronic properties of excited states in single InAs quantum dots

    International Nuclear Information System (INIS)

    Warming, Till

    2009-01-01

    The application of quantum-mechanical effects in semiconductor nanostructures enables the realization of novel opto-electronic devices. Examples are given by single-photon emitters and emitters of entangled photon pairs, both being essential for quantum cryptography, or for qubit systems as needed for quantum computing. InAs/GaAs quantum dots are one of the most promising candidates for such applications. A detailed knowledge of the electronic properties of quantum dots is a prerequisite for this development. The aim of this work is an experimental access to the detailed electronic structure of the excited states in single InAs/GaAs quantum dots including few-particle effects and in particular exchange interaction. The experimental approach is micro photoluminescence excitation spectroscopy (μPLE). One of the main difficulties using μPLE to probe single QDs is the unambiguous assignment of the observed resonances in the spectrum to specific transitions. By comparing micro photoluminescence (μPL) and μPLE spectra, the identification of the main resonances becomes possible. The key is given by the fine structure of the hot trion. Excitation spectroscopy on single charged QDs enables for the first time the complete observation of a non-trivial fine structure of an excitonic complex in a QD, the hot trion. Modelling based on eight-band k.p theory in combination with a configuration interaction scheme is in excellent agreement. Therewith the simulation also enables realistic predictions on the fine structure of the ground-state exciton which is of large importance for single quantum dot devices. Theory concludes from the observed transitions that the structural symmetry of the QDs is broken. Micro photoluminescence excitation spectroscopy combined with resonantly excited micro photoluminescence enables an optical access to the single particle states of the hole without the influence of few-particle coulomb interactions. Based on this knowledge the exciton binding

  3. QUANTUM NETWORKS WITH SINGLE ATOMS, PHOTONS AND PHONONS

    Science.gov (United States)

    2016-10-04

    there is interference between two different transport channels. For instance, in a cavity far from resonance, there is interference arising from all...recovers the well-known form of a Beer -Lambert law, reading T (∆A)/T0(∆A) = exp [ −N ln ∆ 2 A + (Γ′ + Γ1D)2/4 ∆2A + Γ′2/4 ] ’ exp [ − OD1 + (2∆A/Γ′)2...Elements of Quantum Optics. Springer-Verlag, Berlin, 2007. [39] J.-T. Shen and S. Fan. Coherent photon transport from spontaneous emission in one

  4. Single-Shot Quantum Nondemolition Detection of Individual Itinerant Microwave Photons

    Science.gov (United States)

    Besse, Jean-Claude; Gasparinetti, Simone; Collodo, Michele C.; Walter, Theo; Kurpiers, Philipp; Pechal, Marek; Eichler, Christopher; Wallraff, Andreas

    2018-04-01

    Single-photon detection is an essential component in many experiments in quantum optics, but it remains challenging in the microwave domain. We realize a quantum nondemolition detector for propagating microwave photons and characterize its performance using a single-photon source. To this aim, we implement a cavity-assisted conditional phase gate between the incoming photon and a superconducting artificial atom. By reading out the state of this atom in a single shot, we reach an external (internal) photon-detection fidelity of 50% (71%), limited by transmission efficiency between the source and the detector (75%) and the coherence properties of the qubit. By characterizing the coherence and average number of photons in the field reflected off the detector, we demonstrate its quantum nondemolition nature. We envisage applications in generating heralded remote entanglement between qubits and for realizing logic gates between propagating microwave photons.

  5. Double-slit experiment with single wave-driven particles and its relation to quantum mechanics

    DEFF Research Database (Denmark)

    Andersen, Anders Peter; Madsen, Jacob; Reichelt, Christian Günther

    2015-01-01

    even though it is possible to determine unambiguously which slit the walking droplet passes. Here we argue, however, that the single-particle statistics in such an experiment will be fundamentally different from the single-particle statistics of quantum mechanics. Quantum mechanical interference takes...... place between different classical paths with precise amplitude and phase relations. In the double-slit experiment with walking droplets, these relations are lost since one of the paths is singled out by the droplet. To support our conclusions, we have carried out our own double-slit experiment, and our...... results, in particular the long and variable slit passage times of the droplets, cast strong doubt on the feasibility of the interference claimed by Couder and Fort. To understand theoretically the limitations of wave-driven particle systems as analogs to quantum mechanics, we introduce a Schro...

  6. Longitudinal wave function control in single quantum dots with an applied magnetic field

    Science.gov (United States)

    Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A.; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai

    2015-01-01

    Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots. PMID:25624018

  7. Longitudinal wave function control in single quantum dots with an applied magnetic field.

    Science.gov (United States)

    Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai

    2015-01-27

    Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots.

  8. Applications of quantum measurement in single and many body systems

    International Nuclear Information System (INIS)

    Steixner, V.

    2010-01-01

    This thesis contains a study about the influence of the back action of a signal emitted by a trapped ion onto itself. The continuous measurement signal is used to alter the motional state of the ion, corresponding to classical friction, in order to cool the ion. The quantum mechanical evolution of the ion with the help of stochastic Schroedinger- and master equations is explored, as well as experimental results. A second method of feedback to obtain the momentum necessary for cooling by means of electromagnetically induced transparency is discussed next. This method allows for a theoretical cooling down to the motional ground state. In a second part of the thesis, the measurement of particle currents in optical lattices is discussed. The usual method of measuring spatial correlations in a cold gas, the time-of-flight method, disadvantageously destroys the measured sample. Here a measurement scheme for atoms with an internal Lambda level structure, coupled with lasers as a Raman transition, is used instead. The measured photons are transformed with the help of homodyne detection into a continuous photon current proportional to the particle current. This thesis contains numerical and analytical calculations for this measurement process and the back action on the measured system. As an application example, the measurement of superfluid currents in a ring optical lattice is described, as well as the entanglement of two of these macroscopic quantum objects. (author) [de

  9. Microwave testing of high-Tc based direct current to a single flux quantum converter

    DEFF Research Database (Denmark)

    Kaplunenko, V. K.; Fischer, Gerd Michael; Ivanov, Z. G.

    1994-01-01

    Design, simulation, and experimental investigations of a direct current to a single flux quantum converter loaded with a Josephson transmission line and driven by an external 70 GHz microwave oscillator are reported. The test circuit includes nine YBaCuO Josephson junctions aligned on the grain...... boundary of a 0°–32° asymmetric Y-ZrO2 bicrystal substrate. The performance of such converters is important for the development of the fast Josephson samplers required for testing of high-Tc rapid single flux quantum circuits in high-speed digital superconducting electronics. Journal of Applied Physics...

  10. Superconducting Qubit with Integrated Single Flux Quantum Controller Part II: Experimental Characterization

    Science.gov (United States)

    Leonard, Edward, Jr.; Beck, Matthew; Thorbeck, Ted; Zhu, Shaojiang; Howington, Caleb; Nelson, Jj; Plourde, Britton; McDermott, Robert

    We describe the characterization of a single flux quantum (SFQ) pulse generator cofabricated with a superconducting quantum circuit on a single chip. Resonant trains of SFQ pulses are used to induce coherent qubit rotations on the Bloch sphere. We describe the SFQ drive characteristics of the qubit at the fundamental transition frequency and at subharmonics (ω01 / n , n = 2 , 3 , 4 , ⋯). We address the issue of quasiparticle poisoning due to the proximal SFQ pulse generator, and we characterize the fidelity of SFQ-based rotations using randomized benchmarking. Present address: IBM T.J. Watson Research Center.

  11. Superconducting Qubit with Integrated Single Flux Quantum Controller Part I: Theory and Fabrication

    Science.gov (United States)

    Beck, Matthew; Leonard, Edward, Jr.; Thorbeck, Ted; Zhu, Shaojiang; Howington, Caleb; Nelson, Jj; Plourde, Britton; McDermott, Robert

    As the size of quantum processors grow, so do the classical control requirements. The single flux quantum (SFQ) Josephson digital logic family offers an attractive route to proximal classical control of multi-qubit processors. Here we describe coherent control of qubits via trains of SFQ pulses. We discuss the fabrication of an SFQ-based pulse generator and a superconducting transmon qubit on a single chip. Sources of excess microwave loss stemming from the complex multilayer fabrication of the SFQ circuit are discussed. We show how to mitigate this loss through judicious choice of process workflow and appropriate use of sacrificial protection layers. Present address: IBM T.J. Watson Research Center.

  12. Copenhagen's single system premise prevents a unified view of integer and fractional quantum Hall effect

    CERN Document Server

    Post, E J

    1999-01-01

    This essay presents conclusive evidence of the impermissibility of Copenhagen's single system interpretation of the Schroedinger process. The latter needs to be viewed as a tool exclusively describing phase and orientation randomized ensembles and is not be used for isolated single systems. Asymptotic closeness of single system and ensemble behavior and the rare nature of true single system manifestations have prevented a definitive identification of this Copenhagen deficiency over the past three quarter century. Quantum uncertainty so becomes a basic trade mark of phase and orientation disordered ensembles. The ensuing void of usable single system tools opens a new inquiry for tools without statistical connotations. Three, in part already known, period integrals here identified as flux, charge and action counters emerge as diffeo-4 invariant tools fully compatible with the demands of the general theory of relativity. The discovery of the quantum Hall effect has been instrumental in forcing a distinction betw...

  13. Double-slit experiment with single wave-driven particles and its relation to quantum mechanics.

    Science.gov (United States)

    Andersen, Anders; Madsen, Jacob; Reichelt, Christian; Rosenlund Ahl, Sonja; Lautrup, Benny; Ellegaard, Clive; Levinsen, Mogens T; Bohr, Tomas

    2015-07-01

    In a thought-provoking paper, Couder and Fort [Phys. Rev. Lett. 97, 154101 (2006)] describe a version of the famous double-slit experiment performed with droplets bouncing on a vertically vibrated fluid surface. In the experiment, an interference pattern in the single-particle statistics is found even though it is possible to determine unambiguously which slit the walking droplet passes. Here we argue, however, that the single-particle statistics in such an experiment will be fundamentally different from the single-particle statistics of quantum mechanics. Quantum mechanical interference takes place between different classical paths with precise amplitude and phase relations. In the double-slit experiment with walking droplets, these relations are lost since one of the paths is singled out by the droplet. To support our conclusions, we have carried out our own double-slit experiment, and our results, in particular the long and variable slit passage times of the droplets, cast strong doubt on the feasibility of the interference claimed by Couder and Fort. To understand theoretically the limitations of wave-driven particle systems as analogs to quantum mechanics, we introduce a Schrödinger equation with a source term originating from a localized particle that generates a wave while being simultaneously guided by it. We show that the ensuing particle-wave dynamics can capture some characteristics of quantum mechanics such as orbital quantization. However, the particle-wave dynamics can not reproduce quantum mechanics in general, and we show that the single-particle statistics for our model in a double-slit experiment with an additional splitter plate differs qualitatively from that of quantum mechanics.

  14. Double-slit experiment with single wave-driven particles and its relation to quantum mechanics

    Science.gov (United States)

    Andersen, Anders; Madsen, Jacob; Reichelt, Christian; Rosenlund Ahl, Sonja; Lautrup, Benny; Ellegaard, Clive; Levinsen, Mogens T.; Bohr, Tomas

    2015-07-01

    In a thought-provoking paper, Couder and Fort [Phys. Rev. Lett. 97, 154101 (2006), 10.1103/PhysRevLett.97.154101] describe a version of the famous double-slit experiment performed with droplets bouncing on a vertically vibrated fluid surface. In the experiment, an interference pattern in the single-particle statistics is found even though it is possible to determine unambiguously which slit the walking droplet passes. Here we argue, however, that the single-particle statistics in such an experiment will be fundamentally different from the single-particle statistics of quantum mechanics. Quantum mechanical interference takes place between different classical paths with precise amplitude and phase relations. In the double-slit experiment with walking droplets, these relations are lost since one of the paths is singled out by the droplet. To support our conclusions, we have carried out our own double-slit experiment, and our results, in particular the long and variable slit passage times of the droplets, cast strong doubt on the feasibility of the interference claimed by Couder and Fort. To understand theoretically the limitations of wave-driven particle systems as analogs to quantum mechanics, we introduce a Schrödinger equation with a source term originating from a localized particle that generates a wave while being simultaneously guided by it. We show that the ensuing particle-wave dynamics can capture some characteristics of quantum mechanics such as orbital quantization. However, the particle-wave dynamics can not reproduce quantum mechanics in general, and we show that the single-particle statistics for our model in a double-slit experiment with an additional splitter plate differs qualitatively from that of quantum mechanics.

  15. Long-Distance Single Photon Transmission from a Trapped Ion via Quantum Frequency Conversion

    Science.gov (United States)

    Walker, Thomas; Miyanishi, Koichiro; Ikuta, Rikizo; Takahashi, Hiroki; Vartabi Kashanian, Samir; Tsujimoto, Yoshiaki; Hayasaka, Kazuhiro; Yamamoto, Takashi; Imoto, Nobuyuki; Keller, Matthias

    2018-05-01

    Trapped atomic ions are ideal single photon emitters with long-lived internal states which can be entangled with emitted photons. Coupling the ion to an optical cavity enables the efficient emission of single photons into a single spatial mode and grants control over their temporal shape. These features are key for quantum information processing and quantum communication. However, the photons emitted by these systems are unsuitable for long-distance transmission due to their wavelengths. Here we report the transmission of single photons from a single 40Ca+ ion coupled to an optical cavity over a 10 km optical fiber via frequency conversion from 866 nm to the telecom C band at 1530 nm. We observe nonclassical photon statistics of the direct cavity emission, the converted photons, and the 10 km transmitted photons, as well as the preservation of the photons' temporal shape throughout. This telecommunication-ready system can be a key component for long-distance quantum communication as well as future cloud quantum computation.

  16. Highly efficient photonic nanowire single-photon sources for quantum information applications

    DEFF Research Database (Denmark)

    Gregersen, Niels; Claudon, J.; Munsch, M.

    2013-01-01

    to a collection efficiency of only 1-2 %, and efficient light extraction thus poses a major challenge in SPS engineering. Initial efforts to improve the efficiency have exploited cavity quantum electrodynamics (cQED) to efficiently couple the emitted photons to the optical cavity mode. An alternative approach......Within the emerging field of optical quantum information processing, the current challenge is to construct the basic building blocks for the quantum computing and communication systems. A key component is the singlephoton source (SPS) capable of emitting single photons on demand. Ideally, the SPS...... must feature near-unity efficiency, where the efficiency is defined as the number of detected photons per trigger, the probability g(2)(τ=0) of multi-photon emission events should be 0 and the emitted photons are required to be indistinguishable. An optically or electrically triggered quantum light...

  17. Fundamental limits to single-photon detection determined by quantum coherence and backaction

    Science.gov (United States)

    Young, Steve M.; Sarovar, Mohan; Léonard, François

    2018-03-01

    Single-photon detectors have achieved impressive performance and have led to a number of new scientific discoveries and technological applications. Existing models of photodetectors are semiclassical in that the field-matter interaction is treated perturbatively and time-separated from physical processes in the absorbing matter. An open question is whether a fully quantum detector, whereby the optical field, the optical absorption, and the amplification are considered as one quantum system, could have improved performance. Here we develop a theoretical model of such photodetectors and employ simulations to reveal the critical role played by quantum coherence and amplification backaction in dictating the performance. We show that coherence and backaction lead to trade-offs between detector metrics and also determine optimal system designs through control of the quantum-classical interface. Importantly, we establish the design parameters that result in a ideal photodetector with 100% efficiency, no dark counts, and minimal jitter, thus paving the route for next-generation detectors.

  18. Quantum resonances in a single plaquette of Josephson junctions: excitations of Rabi oscillations

    Science.gov (United States)

    Fistul, M. V.

    2002-03-01

    We present a theoretical study of a quantum regime of the resistive (whirling) state of dc driven anisotropic single plaquette containing small Josephson junctions. The current-voltage characteristics of such systems display resonant steps that are due to the resonant interaction between the time dependent Josephson current and the excited electromagnetic oscillations (EOs). The voltage positions of the resonances are determined by the quantum interband transitions of EOs. We show that in the quantum regime as the system is driven on the resonance, coherent Rabi oscillations between the quantum levels of EOs occur. At variance with the classical regime the magnitude and the width of resonances are determined by the frequency of Rabi oscillations that in turn, depends in a peculiar manner on an externally applied magnetic field and the parameters of the system.

  19. A Novel Deterministic Secure Quantum Communication Scheme with Einstein—Podolsky—Rosen Pairs and Single Photons

    International Nuclear Information System (INIS)

    Wang Chao; Liu Jian-Wei; Liu Xiao; Shang Tao

    2013-01-01

    A novel deterministic secure quantum communication (DSQC) scheme is presented based on Einstein-Podolsky-Rosen (EPR) pairs and single photons in this study. In this scheme, the secret message can be encoded directly on the first particles of the prepared Bell states by simple unitary operations and decoded by performing the Bell-basis measurement after the additional classic information is exchanged. In addition, the strategy with two-step transmission of quantum data blocks and the technique of decoy-particle checking both are exploited to guarantee the security of the communication. Compared with some previous DSQC schemes, this scheme not only has a higher resource capacity, intrinsic efficiency and total efficiency, but also is more realizable in practical applications. Security analysis shows that the proposed scheme is unconditionally secure against various attacks over an ideal quantum channel and still conditionally robust over a noisy and lossy quantum channel. (general)

  20. Quantum phase transitions in spin-1 X X Z chains with rhombic single-ion anisotropy

    Science.gov (United States)

    Ren, Jie; Wang, Yimin; You, Wen-Long

    2018-04-01

    We explore numerically the inverse participation ratios in the ground state of one-dimensional spin-1 X X Z chains with the rhombic single-ion anisotropy. By employing the techniques of density-matrix renormalization group, effects of the rhombic single-ion anisotropy on various information theoretical measures are investigated, such as the fidelity susceptibility, the quantum coherence, and the entanglement entropy. Their relations with the quantum phase transitions are also analyzed. The phase transitions from the Y -Néel phase to the large-Ex or the Haldane phase can be well characterized by the fidelity susceptibility. The second-order derivative of the ground-state energy indicates all the transitions are of second order. We also find that the quantum coherence, the entanglement entropy, the Schmidt gap, and the inverse participation ratios can be used to detect the critical points of quantum phase transitions. Results drawn from these quantum information observables agree well with each other. Finally we provide a ground-state phase diagram as functions of the exchange anisotropy Δ and the rhombic single-ion anisotropy E .

  1. Quantum Stirling heat engine and refrigerator with single and coupled spin systems

    Science.gov (United States)

    Huang, Xiao-Li; Niu, Xin-Ya; Xiu, Xiao-Ming; Yi, Xue-Xi

    2014-02-01

    We study the reversible quantum Stirling cycle with a single spin or two coupled spins as the working substance. With the single spin as the working substance, we find that under certain conditions the reversed cycle of a heat engine is NOT a refrigerator, this feature holds true for a Stirling heat engine with an ion trapped in a shallow potential as its working substance. The efficiency of quantum Stirling heat engine can be higher than the efficiency of the Carnot engine, but the performance coefficient of the quantum Stirling refrigerator is always lower than its classical counterpart. With two coupled spins as the working substance, we find that a heat engine can turn to a refrigerator due to the increasing of the coupling constant, this can be explained by the properties of the isothermal line in the magnetic field-entropy plane.

  2. Single-step fabrication of quantum funnels via centrifugal colloidal casting of nanoparticle films.

    KAUST Repository

    Kim, Jin Young; Adinolfi, Valerio; Sutherland, Brandon R; Voznyy, Oleksandr; Kwon, S Joon; Kim, Tae Wu; Kim, Jeongho; Ihee, Hyotcherl; Kemp, Kyle; Adachi, Michael; Yuan, Mingjian; Kramer, Illan; Zhitomirsky, David; Hoogland, Sjoerd; Sargent, Edward H

    2015-01-01

    Centrifugal casting of composites and ceramics has been widely employed to improve the mechanical and thermal properties of functional materials. This powerful method has yet to be deployed in the context of nanoparticles--yet size-effect tuning of quantum dots is among their most distinctive and application-relevant features. Here we report the first gradient nanoparticle films to be constructed in a single step. By creating a stable colloid of nanoparticles that are capped with electronic-conduction-compatible ligands we were able to leverage centrifugal casting for thin-films devices. This new method, termed centrifugal colloidal casting, is demonstrated to form films in a bandgap-ordered manner with efficient carrier funnelling towards the lowest energy layer. We constructed the first quantum-gradient photodiode to be formed in a single deposition step and, as a result of the gradient-enhanced electric field, experimentally measured the highest normalized detectivity of any colloidal quantum dot photodetector.

  3. Quantum key distribution with a single photon from a squeezed coherent state

    International Nuclear Information System (INIS)

    Matsuoka, Masahiro; Hirano, Takuya

    2003-01-01

    Squeezing of the coherent state by optical parametric amplifier is shown to efficiently produce single-photon states with reduced multiphoton probabilities compared with the weak coherent light. It can be a better source for a longer-distance quantum key distribution and also for other quantum optical experiments. The necessary condition for a secure quantum key distribution given by Brassard et al. is analyzed as functions of the coherent-state amplitude and squeeze parameter. Similarly, the rate of the gained secure bits G after error correction and privacy amplification given by Luetkenhaus is calculated. Compared with the weak coherent light, it is found that G is about ten times larger and its high level continues on about two times longer distance. By improvement of the detector efficiency it is shown that the distance extends further. Measurement of the intensity correlation function and the relation to photon antibunching are discussed for the experimental verification of the single-photon generation

  4. Single-step fabrication of quantum funnels via centrifugal colloidal casting of nanoparticle films

    Science.gov (United States)

    Kim, Jin Young; Adinolfi, Valerio; Sutherland, Brandon R.; Voznyy, Oleksandr; Kwon, S. Joon; Kim, Tae Wu; Kim, Jeongho; Ihee, Hyotcherl; Kemp, Kyle; Adachi, Michael; Yuan, Mingjian; Kramer, Illan; Zhitomirsky, David; Hoogland, Sjoerd; Sargent, Edward H.

    2015-01-01

    Centrifugal casting of composites and ceramics has been widely employed to improve the mechanical and thermal properties of functional materials. This powerful method has yet to be deployed in the context of nanoparticles—yet size–effect tuning of quantum dots is among their most distinctive and application-relevant features. Here we report the first gradient nanoparticle films to be constructed in a single step. By creating a stable colloid of nanoparticles that are capped with electronic-conduction-compatible ligands we were able to leverage centrifugal casting for thin-films devices. This new method, termed centrifugal colloidal casting, is demonstrated to form films in a bandgap-ordered manner with efficient carrier funnelling towards the lowest energy layer. We constructed the first quantum-gradient photodiode to be formed in a single deposition step and, as a result of the gradient-enhanced electric field, experimentally measured the highest normalized detectivity of any colloidal quantum dot photodetector. PMID:26165185

  5. Bright single photon source based on self-aligned quantum dot–cavity systems

    DEFF Research Database (Denmark)

    Maier, Sebastian; Gold, Peter; Forchel, Alfred

    2014-01-01

    We report on a quasi-planar quantum-dot-based single-photon source that shows an unprecedented high extraction efficiency of 42% without complex photonic resonator geometries or post-growth nanofabrication. This very high efficiency originates from the coupling of the photons emitted by a quantum...... dot to a Gaussian shaped nanohill defect that naturally arises during epitaxial growth in a self-aligned manner. We investigate the morphology of these defects and characterize the photonic operation mechanism. Our results show that these naturally arising coupled quantum dot-defects provide a new...... avenue for efficient (up to 42% demonstrated) and pure (g2(0) value of 0.023) single-photon emission....

  6. Simple and efficient absorption filter for single photons from a cold atom quantum memory.

    Science.gov (United States)

    Stack, Daniel T; Lee, Patricia J; Quraishi, Qudsia

    2015-03-09

    The ability to filter unwanted light signals is critical to the operation of quantum memories based on neutral atom ensembles. Here we demonstrate an efficient frequency filter which uses a vapor cell filled with (85)Rb and a buffer gas to attenuate both residual laser light and noise photons by nearly two orders of magnitude with little loss to the single photons associated with our cold (87)Rb quantum memory. This simple, passive filter provides an additional 18 dB attenuation of our pump laser and erroneous spontaneous emissions for every 1 dB loss of the single photon signal. We show that the addition of a frequency filter increases the non-classical correlations and the retrieval efficiency of our quantum memory by ≈ 35%.

  7. Single-step fabrication of quantum funnels via centrifugal colloidal casting of nanoparticle films.

    KAUST Repository

    Kim, Jin Young

    2015-07-13

    Centrifugal casting of composites and ceramics has been widely employed to improve the mechanical and thermal properties of functional materials. This powerful method has yet to be deployed in the context of nanoparticles--yet size-effect tuning of quantum dots is among their most distinctive and application-relevant features. Here we report the first gradient nanoparticle films to be constructed in a single step. By creating a stable colloid of nanoparticles that are capped with electronic-conduction-compatible ligands we were able to leverage centrifugal casting for thin-films devices. This new method, termed centrifugal colloidal casting, is demonstrated to form films in a bandgap-ordered manner with efficient carrier funnelling towards the lowest energy layer. We constructed the first quantum-gradient photodiode to be formed in a single deposition step and, as a result of the gradient-enhanced electric field, experimentally measured the highest normalized detectivity of any colloidal quantum dot photodetector.

  8. Single quantum dot tracking reveals the impact of nanoparticle surface on intracellular state.

    Science.gov (United States)

    Zahid, Mohammad U; Ma, Liang; Lim, Sung Jun; Smith, Andrew M

    2018-05-08

    Inefficient delivery of macromolecules and nanoparticles to intracellular targets is a major bottleneck in drug delivery, genetic engineering, and molecular imaging. Here we apply live-cell single-quantum-dot imaging and tracking to analyze and classify nanoparticle states after intracellular delivery. By merging trajectory diffusion parameters with brightness measurements, multidimensional analysis reveals distinct and heterogeneous populations that are indistinguishable using single parameters alone. We derive new quantitative metrics of particle loading, cluster distribution, and vesicular release in single cells, and evaluate intracellular nanoparticles with diverse surfaces following osmotic delivery. Surface properties have a major impact on cell uptake, but little impact on the absolute cytoplasmic numbers. A key outcome is that stable zwitterionic surfaces yield uniform cytosolic behavior, ideal for imaging agents. We anticipate that this combination of quantum dots and single-particle tracking can be widely applied to design and optimize next-generation imaging probes, nanoparticle therapeutics, and biologics.

  9. Multiparameter estimation with single photons—linearly-optically generated quantum entanglement beats the shotnoise limit

    Science.gov (United States)

    You, Chenglong; Adhikari, Sushovit; Chi, Yuxi; LaBorde, Margarite L.; Matyas, Corey T.; Zhang, Chenyu; Su, Zuen; Byrnes, Tim; Lu, Chaoyang; Dowling, Jonathan P.; Olson, Jonathan P.

    2017-12-01

    It was suggested in (Motes et al 2015 Phys. Rev. Lett. 114 170802) that optical networks with relatively inexpensive overheads—single photon Fock states, passive optical elements, and single photon detection—can show significant improvements over classical strategies for single-parameter estimation, when the number of modes in the network is small (ncompute the quantum Cramér-Rao bound to show these networks can have a constant-factor quantum advantage in multi-parameter estimation for even large number of modes. Additionally, we provide a simplified measurement scheme using only single-photon (on-off) detectors that is capable of approximately obtaining this sensitivity for a small number of modes.

  10. Nanostructured current-confined single quantum dot light-emitting diode at 1300 nm

    NARCIS (Netherlands)

    Monat, C.; Alloing, B.; Zinoni, C.; Li, L.; Fiore, A.

    2006-01-01

    A novel light-emitting-diode structure is demonstrated, which relies on nanoscale current injection through an oxide aperture to achieve selective excitation of single InAs/GaAs quantum dots. Low-temp. electroluminescence spectra evidence discrete narrow lines around 1300 nm (line width ~ 75 micro

  11. The exact solution of the Ising quantum chain with alternating single and sector defects

    International Nuclear Information System (INIS)

    Zhang Degang; Li Bozang; Li Yun

    1992-10-01

    The Ising quantum chain with alternating single and sector defects is solved exactly by using the technique of Lieb, Schultz and Mattis. The energy spectrum of this model is shown to have a tower structure if and only if these defects constitute a commensurate configuration. This means that conformal invariance is preserved under these circumstances. (author). 13 refs

  12. Fiber-coupled NbN superconducting single-photon detectors for quantum correlation measurements

    NARCIS (Netherlands)

    Slysz, W.; Wegrzecki, M.; Bar, J.; Grabiec, P.; Gorska, M.; Reiger, E.; Dorenbos, S.; Zwiller, V.; Milostnaya, I.; Minaeva, O.

    2007-01-01

    We have fabricated fiber-coupled superconducting single-photon detectors (SSPDs), designed for quantum-correlationtype experiments. The SSPDs are nanostructured (~100-nm wide and 4-nm thick) NbN superconducting meandering stripes, operated in the 2 to 4.2 K temperature range, and known for ultrafast

  13. Room-temperature near-field reflection spectroscopy of single quantum wells

    DEFF Research Database (Denmark)

    Langbein, Wolfgang Werner; Hvam, Jørn Marcher; Madsen, Steen

    1997-01-01

    . This technique suppresses efficiently the otherwise dominating far-field background and reduces topographic artifacts. We demonstrate its performance on a thin, strained near-surface CdS/ZnS single quantum well at room temperature. The optical structure of these topographically flat samples is due to Cd...

  14. Hybrid GaAs/AlGaAs Nanowire—Quantum dot System for Single Photon Sources

    DEFF Research Database (Denmark)

    Cirlin, G.; Reznik, R.; Shtrom, I.

    2018-01-01

    III–V nanowires, or a combination of the nanowires with quantum dots, are promising building blocks for future optoelectronic devices, in particular, single-photon emitters, lasers and photodetectors. In this work we present results of molecular beam epitaxial growth of combined nanostructures...

  15. Generating single-photon catalyzed coherent states with quantum-optical catalysis

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Xue-xiang, E-mail: xuxuexiang@jxnu.edu.cn [Center for Quantum Science and Technology, Jiangxi Normal University, Nanchang 330022 (China); Yuan, Hong-chun [College of Electrical and Optoelectronic Engineering, Changzhou Institute of Technology, Changzhou 213002 (China)

    2016-07-15

    We theoretically generate single-photon catalyzed coherent states (SPCCSs) by means of quantum-optical catalysis based on the beam splitter (BS) or the parametric amplifier (PA). These states are obtained in one of the BS (or PA) output channels if a coherent state and a single-photon Fock state are present in two input ports and a single photon is registered in the other output port. The success probabilities of the detection (also the normalization factors) are discussed, which is different for BS and PA catalysis. In addition, we prove that the generated states catalyzed by BS and PA devices are actually the same quantum states after analyzing photon number distribution of the SPCCSs. The quantum properties of the SPCCSs, such as sub-Poissonian distribution, anti-bunching effect, quadrature squeezing effect, and the negativity of the Wigner function are investigated in detail. The results show that the SPCCSs are non-Gaussian states with an abundance of nonclassicality. - Highlights: • We generate single-photon catalyzed coherent states with quantum-optical catalysis. • We prove the equivalent effects of the lossless beam splitter and the non-degenerate parametric amplifier. • Some nonclassical properties of the generated states are investigated in detail.

  16. Single atom doping for quantum device development in diamond and silicon

    NARCIS (Netherlands)

    Weis, C.D.; Schuh, A.; Batra, A.; Persaud, A.; Rangelow, I.W.; Bokor, J.; Lo, C.C.; Cabrini, S.; Sideras-Haddad, E.; Fuchs, G.D.; Hanson, R.; Awschalom, D.D.; Schenkel, T.

    2008-01-01

    The ability to inject dopant atoms with high spatial resolution, flexibility in dopant species, and high single ion detection fidelity opens opportunities for the study of dopant fluctuation effects and the development of devices in which function is based on the manipulation of quantum states in

  17. Multiparty Quantum English Auction Scheme Using Single Photons as Message Carrier

    Science.gov (United States)

    Liu, Ge; Zhang, Jian-Zhong; Xie, Shu-Cui

    2018-03-01

    In this paper, a secure and economic multiparty english auction protocol using the single photons as message carrier of bids is proposed. In order to achieve unconditional security, fairness, undeniability and so on, we adopt the decoy photon checking technique and quantum encryption algorithm. Analysis result shows that our protocol satisfies all the characteristics of traditional english auction, meanwhile, it can resist malicious attacks.

  18. Experimental demonstration of highly anisotropic decay rates of single quantum dots inside photonic crystals

    DEFF Research Database (Denmark)

    Wang, Qin; Stobbe, Søren; Nielsen, Henri Thyrrestrup

    We have systematically measured the variation of the spontaneous emission rate with polarization for self-assembled single quantum dots in two-dimensional photonic crystal membranes and obtained a maximum anisotropy factor of 6 between the decay rates of the two nondegenerate bright exciton states....

  19. Quantum dot resonant tunneling diode single photon detector with aluminum oxide aperture defined tunneling area

    DEFF Research Database (Denmark)

    Li, H.W.; Kardynal, Beata; Ellis, D.J.P.

    2008-01-01

    Quantum dot resonant tunneling diode single photon detector with independently defined absorption and sensing areas is demonstrated. The device, in which the tunneling is constricted to an aperture in an insulating layer in the emitter, shows electrical characteristics typical of high quality res...

  20. Cross correlations of quantum key distribution based on single-photon sources

    International Nuclear Information System (INIS)

    Dong Shuangli; Wang Xiaobo; Zhang Guofeng; Sun Jianhu; Zhang Fang; Xiao Liantuan; Jia Suotang

    2009-01-01

    We theoretically analyze the second-order correlation function in a quantum key distribution system with real single-photon sources. Based on single-event photon statistics, the influence of the modification caused by an eavesdropper's intervention and the effects of background signals on the cross correlations between authorized partners are presented. On this basis, we have shown a secure range of correlation against the intercept-resend attacks.

  1. Electrical control of spontaneous emission and strong coupling for a single quantum dot

    DEFF Research Database (Denmark)

    Laucht, A.; Hofbauer, F.; Hauke, N.

    2009-01-01

    We report the design, fabrication and optical investigation of electrically tunable single quantum dots—photonic crystal defect nanocavities operating in both the weak and strong coupling regimes of the light–matter interaction. Unlike previous studies where the dot–cavity spectral detuning...... switchable optical nonlinearity at the single photon level, paving the way towards on-chip dot-based nano-photonic devices that can be integrated with passive optical components....

  2. Influence of quantum dot labels on single molecule movement in the plasma membrane

    DEFF Research Database (Denmark)

    Clausen, Mathias P.; Lagerholm, B. Christoffer

    2011-01-01

    Single particle tracking results are very dependent on the probe that is used. In this study we have investigated the influence that functionalized quantum dots (QDs) have on the recorded movement in single molecule tracking experiments of plasma membrane species in live cells. Potential issues...... for simultaneous investigations of different plasma membrane species in order to discriminate the effect of the label from differences in movement of the target molecules....

  3. Simple models for InGaN alloys

    International Nuclear Information System (INIS)

    Elfituri, Fathi; Hourahine, Ben

    2012-01-01

    The properties of InGaN alloys are important for many applications in optoelectronics, since their fundamental gap spans the visible range. Calculating properties, particularly for InN, is theoretically challenging, especially to obtain accurate values for the band gap. We have developed a semi-empirical parametrisation of (In,Ga) N using the density functional based tight binding method (DFTB), where the band gaps of InN and GaN have been empirically corrected to experiment. We demonstrate the performance of this method by calculating a range of properties for the two materials, including elastic constants and carrier effective masses. There are several methods to model alloys of these material, one of the simplest being the virtual crystal approximation, which we apply to derive electronic properties over the whole composition range for InGaN. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Copenhagen's single system premise prevents a unified view of integer and fractional quantum hall effect

    Science.gov (United States)

    Post, Evert Jan

    1999-05-01

    This essay presents conclusive evidence of the impermissibility of Copenhagen's single system interpretation of the Schroedinger process. The latter needs to be viewed as a tool exclusively describing phase and orientation randomized ensembles and is not be used for isolated single systems. Asymptotic closeness of single system and ensemble behavior and the rare nature of true single system manifestations have prevented a definitive identification of this Copenhagen deficiency over the past three quarter century. Quantum uncertainty so becomes a basic trade mark of phase and orientation disordered ensembles. The ensuing void of usable single system tools opens a new inquiry for tools without statistical connotations. Three, in part already known, period integrals here identified as flux, charge and action counters emerge as diffeo-4 invariant tools fully compatible with the demands of the general theory of relativity. The discovery of the quantum Hall effect has been instrumental in forcing a distinction between ensemble disorder as in the normal Hall effect versus ensemble order in the plateau states. Since the order of the latter permits a view of the plateau states as a macro- or meso-scopic single system, the period integral description applies, yielding a straightforward unified description of integer and fractional quantum Hall effects.

  5. Experimentally measuring a quantum state by the Heisenberg exchange interaction in a single apparatus

    International Nuclear Information System (INIS)

    Peng Xinhua; Du Jiangfeng; Suter, D.

    2005-01-01

    Full text: Quantum information processing requires the effective measurement of quantum states. An important method, called quantum state tomography, needs measuring a complete set of observables on the measured system to determine its unknown quantum state ρ. The measurement involves certain noncommuting observables as a result of Bohr's complementarity. Very recently, Allahverdyan et al. proposed a new method in which the unknown quantum state r is determined by measuring a set of commuting observables in the price of a controlled interaction with an auxiliary system. If both systems S and A are spins, their z components (σ z ) can be chosen to measure after some specific Heisenberg exchange interaction. We study in detail a general Heisenberg XYZ model for a two-qubit system and present two classes of special Heisenberg interactions which can serve as the controlled interaction in Allahverdyan's scheme when the state of the auxiliary system A is initially completely disordered. Using the nuclear magnetic resonance techniques, the measurement scheme in a single apparatus has been experimentally demonstrated by designing the quantum circuit to simulate the Heisenberg exchange interaction. (author)

  6. Sustained State-Independent Quantum Contextual Correlations from a Single Ion

    Science.gov (United States)

    Leupold, F. M.; Malinowski, M.; Zhang, C.; Negnevitsky, V.; Alonso, J.; Home, J. P.; Cabello, A.

    2018-05-01

    We use a single trapped-ion qutrit to demonstrate the quantum-state-independent violation of noncontextuality inequalities using a sequence of randomly chosen quantum nondemolition projective measurements. We concatenate 53 ×106 sequential measurements of 13 observables, and unambiguously violate an optimal noncontextual bound. We use the same data set to characterize imperfections including signaling and repeatability of the measurements. The experimental sequence was generated in real time with a quantum random number generator integrated into our control system to select the subsequent observable with a latency below 50 μ s , which can be used to constrain contextual hidden-variable models that might describe our results. The state-recycling experimental procedure is resilient to noise and independent of the qutrit state, substantiating the fact that the contextual nature of quantum physics is connected to measurements and not necessarily to designated states. The use of extended sequences of quantum nondemolition measurements finds applications in the fields of sensing and quantum information.

  7. Preparation and coherent manipulation of pure quantum states of a single molecular ion

    Science.gov (United States)

    Chou, Chin-Wen; Kurz, Christoph; Hume, David B.; Plessow, Philipp N.; Leibrandt, David R.; Leibfried, Dietrich

    2017-05-01

    Laser cooling and trapping of atoms and atomic ions has led to advances including the observation of exotic phases of matter, the development of precision sensors and state-of-the-art atomic clocks. The same level of control in molecules could also lead to important developments such as controlled chemical reactions and sensitive probes of fundamental theories, but the vibrational and rotational degrees of freedom in molecules pose a challenge for controlling their quantum mechanical states. Here we use quantum-logic spectroscopy, which maps quantum information between two ion species, to prepare and non-destructively detect quantum mechanical states in molecular ions. We develop a general technique for optical pumping and preparation of the molecule into a pure initial state. This enables us to observe high-resolution spectra in a single ion (CaH+) and coherent phenomena such as Rabi flopping and Ramsey fringes. The protocol requires a single, far-off-resonant laser that is not specific to the molecule, so many other molecular ions, including polyatomic species, could be treated using the same methods in the same apparatus by changing the molecular source. Combined with the long interrogation times afforded by ion traps, a broad range of molecular ions could be studied with unprecedented control and precision. Our technique thus represents a critical step towards applications such as precision molecular spectroscopy, stringent tests of fundamental physics, quantum computing and precision control of molecular dynamics.

  8. Complete Quantum Control of a Single Silicon-Vacancy Center in a Diamond Nanopillar

    Science.gov (United States)

    Zhang, Jingyuan Linda; Lagoudakis, Konstantinos G.; Tzeng, Yan-Kai; Dory, Constantin; Radulaski, Marina; Kelaita, Yousif; Shen, Zhi-Xun; Melosh, Nicholas A.; Chu, Steven; Vuckovic, Jelena

    Coherent quantum control of a quantum bit (qubit) is an important step towards its use in a quantum network. SiV- center in diamond offers excellent physical qualities such as low inhomogeneous broadening, fast photon emission, and a large Debye-Waller factor, while the fast spin manipulation and techniques to extend the spin coherence time are under active investigation. Here, we demonstrate full coherent control over the state of a single SiV- center in a diamond nanopillar using ultrafast optical pulses. The high quality of the chemical vapor deposition grown SiV- centers allows us to coherently manipulate and quasi-resonantly read out the state of the single SiV- center. Moreover, the SiV- centers being coherently controlled are integrated into diamond nanopillar arrays in a site-controlled, individually addressable manner with high yield, low strain, and high spectral stability, which paves the way for scalable on chip optically accessible quantum system in a quantum photonic network. Financial support is provided by the DOE Office of Basic Energy Sciences, Division of Materials Sciences through Stanford Institute for Materials and Energy Sciences (SIMES) under contract DE-AC02-76SF00515.

  9. Superconducting single electron transistor for charge sensing in Si/SiGe-based quantum dots

    Science.gov (United States)

    Yang, Zhen

    Si-based quantum devices, including Si/SiGe quantum dots (QD), are promising candidates for spin-based quantum bits (quits), which are a potential platform for quantum information processing. Meanwhile, qubit readout remains a challenging task related to semiconductor-based quantum computation. This thesis describes two readout devices for Si/SiGe QDs and the techniques for developing them from a traditional single electron transistor (SET). By embedding an SET in a tank circuit and operating it in the radio-frequency (RF) regime, a superconducting RF-SET has quick response as well as ultra high charge sensitivity and can be an excellent charge sensor for the QDs. We demonstrate such RF-SETs for QDs in a Si/SiGe heterostructure. Characterization of the SET in magnetic fields is studied for future exploration of advanced techniques such as spin detection and spin state manipulation. By replacing the tank circuit with a high-quality-factor microwave cavity, the embedded SET will be operated in the supercurrent regime as a single Cooper pair transistor (CPT) to further increase the charge sensitivity and reduce any dissipation. The operating principle and implementation of the cavity-embedded CPT (cCPT) will be introduced.

  10. Constructions of secure entanglement channels assisted by quantum dots inside single-sided optical cavities

    Science.gov (United States)

    Heo, Jino; Kang, Min-Sung; Hong, Chang-Ho; Choi, Seong-Gon; Hong, Jong-Phil

    2017-08-01

    We propose quantum information processing schemes to generate and swap entangled states based on the interactions between flying photons and quantum dots (QDs) confined within optical cavities for quantum communication. To produce and distribute entangled states (Bell and Greenberger-Horne-Zeilinger [GHZ] states) between the photonic qubits of flying photons of consumers (Alice and Bob) and electron-spin qubits of a provider (trust center, or TC), the TC employs the interactions of the QD-cavity system, which is composed of a charged QD (negatively charged exciton) inside a single-sided cavity. Subsequently, the TC constructs an entanglement channel (Bell state and 4-qubit GHZ state) to link one consumer with another through entanglement swapping, which can be realized to exploit a probe photon with interactions of the QD-cavity systems and single-qubit measurements without Bell state measurement, for quantum communication between consumers. Consequently, the TC, which has quantum nodes (QD-cavity systems), can accomplish constructing the entanglement channel (authenticated channel) between two separated consumers from the distributions of entangled states and entanglement swapping. Furthermore, our schemes using QD-cavity systems, which are feasible with a certain probability of success and high fidelity, can be experimentally implemented with technology currently in use.

  11. Statistical analysis of error rate of large-scale single flux quantum logic circuit by considering fluctuation of timing parameters

    International Nuclear Information System (INIS)

    Yamanashi, Yuki; Masubuchi, Kota; Yoshikawa, Nobuyuki

    2016-01-01

    The relationship between the timing margin and the error rate of the large-scale single flux quantum logic circuits is quantitatively investigated to establish a timing design guideline. We observed that the fluctuation in the set-up/hold time of single flux quantum logic gates caused by thermal noises is the most probable origin of the logical error of the large-scale single flux quantum circuit. The appropriate timing margin for stable operation of the large-scale logic circuit is discussed by taking the fluctuation of setup/hold time and the timing jitter in the single flux quantum circuits. As a case study, the dependence of the error rate of the 1-million-bit single flux quantum shift register on the timing margin is statistically analyzed. The result indicates that adjustment of timing margin and the bias voltage is important for stable operation of a large-scale SFQ logic circuit.

  12. Statistical analysis of error rate of large-scale single flux quantum logic circuit by considering fluctuation of timing parameters

    Energy Technology Data Exchange (ETDEWEB)

    Yamanashi, Yuki, E-mail: yamanasi@ynu.ac.jp [Department of Electrical and Computer Engineering, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama 240-8501 (Japan); Masubuchi, Kota; Yoshikawa, Nobuyuki [Department of Electrical and Computer Engineering, Yokohama National University, Tokiwadai 79-5, Hodogaya-ku, Yokohama 240-8501 (Japan)

    2016-11-15

    The relationship between the timing margin and the error rate of the large-scale single flux quantum logic circuits is quantitatively investigated to establish a timing design guideline. We observed that the fluctuation in the set-up/hold time of single flux quantum logic gates caused by thermal noises is the most probable origin of the logical error of the large-scale single flux quantum circuit. The appropriate timing margin for stable operation of the large-scale logic circuit is discussed by taking the fluctuation of setup/hold time and the timing jitter in the single flux quantum circuits. As a case study, the dependence of the error rate of the 1-million-bit single flux quantum shift register on the timing margin is statistically analyzed. The result indicates that adjustment of timing margin and the bias voltage is important for stable operation of a large-scale SFQ logic circuit.

  13. InGaN High-Temperature Photovoltaic Cells

    Science.gov (United States)

    Starikov, David

    2015-01-01

    This Phase II project developed Indium-Gallium-Nitride (InGaN) photovoltaic cells for high-temperature and high-radiation environments. The project included theoretical and experimental refinement of device structures produced in Phase I as well as modeling and optimization of solar cell device processing. The devices have been tested under concentrated air mass zero (AM0) sunlight, at temperatures from 100 degC to 250 degC, and after exposure to ionizing radiation. The results are expected to further verify that InGaN can be used for high-temperature and high-radiation solar cells. The large commercial solar cell market could benefit from the hybridization of InGaN materials to existing solar cell technology, which would significantly increase cell efficiency without relying on highly toxic compounds. In addition, further development of this technology to even lower bandgap materials for space applications would extend lifetimes of satellite solar cell arrays due to increased radiation hardness. This could be of importance to the Departmentof Defense (DoD) and commercial satellite manufacturers.

  14. Single-shot quantum nondemolition measurement of a quantum-dot electron spin using cavity exciton-polaritons

    Science.gov (United States)

    Puri, Shruti; McMahon, Peter L.; Yamamoto, Yoshihisa

    2014-10-01

    We propose a scheme to perform single-shot quantum nondemolition (QND) readout of the spin of an electron trapped in a semiconductor quantum dot (QD). Our proposal relies on the interaction of the QD electron spin with optically excited, quantum well (QW) microcavity exciton-polaritons. The spin-dependent Coulomb exchange interaction between the QD electron and cavity polaritons causes the phase and intensity response of left circularly polarized light to be different than that of right circularly polarized light, in such a way that the QD electron's spin can be inferred from the response to a linearly polarized probe reflected or transmitted from the cavity. We show that with careful device design it is possible to essentially eliminate spin-flip Raman transitions. Thus a QND measurement of the QD electron spin can be performed within a few tens of nanoseconds with fidelity ˜99.95%. This improves upon current optical QD spin readout techniques across multiple metrics, including speed and scalability.

  15. Carrier transfer and magneto-transport in single modulation-doped V-grooved quantum wire modified by ion implantation

    International Nuclear Information System (INIS)

    Huang, S.H.; Chen Zhanghai; Wang, F.Z.; Shen, S.C.; Tan, H.H.; Fu, L.; Fraser, M.; Jagadish, C.

    2006-01-01

    A single Al 0.5 Ga 0.5 As/GaAs V-grooved quantum wire modified by selective ion implantation and rapid thermal annealing was investigated by using spatially resolved micro-photoluminescence spectroscopy and magneto-resistance measurements. The results of spatially resolved photoluminescence indicate that the ion-implantation-induced quantum well intermixing significantly raises the electronic sub-band energies in the side quantum wells (SQWs) and vertical quantum wells, and a more efficient accumulation of electrons in the quantum wires is achieved. Processes of real space carrier transfer from the SQW to the quantum wire was experimentally observed, and showed the blocking effect of carrier transfer due to the existence of the necking quantum well region. Furthermore, magneto-transport investigation on the ion-implanted quantum wire samples shows the quasi-one-dimensional intrinsic motion of electrons, which is important for the design and the optimization of one-dimensional electronic devices

  16. Quantum computers based on electron spins controlled by ultrafast off-resonant single optical pulses.

    Science.gov (United States)

    Clark, Susan M; Fu, Kai-Mei C; Ladd, Thaddeus D; Yamamoto, Yoshihisa

    2007-07-27

    We describe a fast quantum computer based on optically controlled electron spins in charged quantum dots that are coupled to microcavities. This scheme uses broadband optical pulses to rotate electron spins and provide the clock signal to the system. Nonlocal two-qubit gates are performed by phase shifts induced by electron spins on laser pulses propagating along a shared waveguide. Numerical simulations of this scheme demonstrate high-fidelity single-qubit and two-qubit gates with operation times comparable to the inverse Zeeman frequency.

  17. Entangling quantum-logic gate operated with an ultrabright semiconductor single-photon source.

    Science.gov (United States)

    Gazzano, O; Almeida, M P; Nowak, A K; Portalupi, S L; Lemaître, A; Sagnes, I; White, A G; Senellart, P

    2013-06-21

    We demonstrate the unambiguous entangling operation of a photonic quantum-logic gate driven by an ultrabright solid-state single-photon source. Indistinguishable single photons emitted by a single semiconductor quantum dot in a micropillar optical cavity are used as target and control qubits. For a source brightness of 0.56 photons per pulse, the measured truth table has an overlap with the ideal case of 68.4±0.5%, increasing to 73.0±1.6% for a source brightness of 0.17 photons per pulse. The gate is entangling: At a source brightness of 0.48, the Bell-state fidelity is above the entangling threshold of 50% and reaches 71.0±3.6% for a source brightness of 0.15.

  18. Stopping single photons in one-dimensional circuit quantum electrodynamics systems

    International Nuclear Information System (INIS)

    Shen, J.-T.; Povinelli, M. L.; Sandhu, Sunil; Fan Shanhui

    2007-01-01

    We propose a mechanism to stop and time reverse single photons in one-dimensional circuit quantum electrodynamics systems. As a concrete example, we exploit the large tunability of the superconducting charge quantum bit (charge qubit) to predict one-photon transport properties in multiple-qubit systems with dynamically controlled transition frequencies. In particular, two qubits coupled to a waveguide give rise to a single-photon transmission line shape that is analogous to electromagnetically induced transparency in atomic systems. Furthermore, by cascading double-qubit structures to form an array and dynamically controlling the qubit transition frequencies, a single photon can be stopped, stored, and time reversed. With a properly designed array, two photons can be stopped and stored in the system at the same time. Moreover, the unit cell of the array can be designed to be of deep subwavelength scale, miniaturizing the circuit

  19. Quantum nernst effect in a bismuth single crystal

    International Nuclear Information System (INIS)

    Matsuo, M.; Endo, A.; Hatano, N.; Nakamura, H.; Shirasaki, R.; Sugihara, K.

    2009-07-01

    We calculate the phonon-drag contribution to the transverse (Nernst) thermoelectric power S yx in a bismuth single crystal subjected to a quantizing magnetic field. The calculated heights of the Nernst peaks originating from the hole Landau levels and their temperature dependence reproduce the right order of magnitude for those of the pronounced magneto-oscillations recently reported by Behnia et al. A striking experimental finding that S yx is much larger than the longitudinal (Seebeck) thermoelectric power S xx can be naturally explained as the effect of the phonon drag, combined with the well-known relation between the longitudinal and the Hall resistivity ρ xx >> |ρ yx | in a semi-metal bismuth. The calculation that includes the contribution of both holes and electrons suggests that some of the hitherto unexplained minor peaks located roughly at the fractional filling of the hole Landau levels are attributable to the electron Landau levels. (author)

  20. Single-photon counting in the 1550-nm wavelength region for quantum cryptography

    International Nuclear Information System (INIS)

    Park, Chul-Woo; Park, Jun-Bum; Park, Young-Soo; Lee, Seung-Hun; Shin, Hyun-Jun; Bae, Byung-Seong; Moon, Sung; Han, Sang-Kook

    2006-01-01

    In this paper, we report the measured performance of an InGaAs avalanche photodiode (APD) Module fabricated for single-photon counting. We measured the dark current noise, the after-pulse noise, and the quantum efficiency of the single- photon detector for different temperatures. We then examined our single-photon source and detection system by measuring the coincident probability. From our measurement, we observed that the after-pulse effect of the APD at temperatures below 105 .deg. C caused cascade noise build-up on the succeeding electrical signals.

  1. Molecular Beam Epitaxy-Grown InGaN Nanowires and Nanomushrooms for Solid State Lighting

    KAUST Repository

    Gasim, Anwar A.

    2012-01-01

    InGaN is a promising semiconductor for solid state lighting thanks to its bandgap which spans the entire visible regime of the electromagnetic spectrum. InGaN is grown heteroepitaxially due to the absence of a native substrate; however, this results

  2. Molecular Beam Epitaxy-Grown InGaN Nanowires and Nanomushrooms for Solid State Lighting

    KAUST Repository

    Gasim, Anwar A.

    2012-05-01

    InGaN is a promising semiconductor for solid state lighting thanks to its bandgap which spans the entire visible regime of the electromagnetic spectrum. InGaN is grown heteroepitaxially due to the absence of a native substrate; however, this results in a strained film and a high dislocation density—two effects that have been associated with efficiency droop, which is the disastrous drop in efficiency of a light-emitting diode (LED) as the input current increases. Heteroepitaxially grown nanowires have recently attracted great interest due to their property of eliminating the detrimental effects of the lattice mismatch and the corollary efficiency droop. In this study, InGaN nanowires were grown on a low-cost Si (111) substrate via molecular beam epitaxy. Unique nanostructures, taking the form of mushrooms, have been observed in localized regions on the samples. These nanomushrooms consist of a nanowire body with a wide cap on top. Photoluminescence characterization revealed that the nanowires emit violet-blue, whilst the nanomushrooms emit a broad yellow-orange-red luminescence. The simultaneous emission from the nanowires and nanomushrooms forms white light. Structural characterization of a single nanomushroom via transmission electron microscopy revealed a simultaneous increase in indium and decrease in gallium at the interface between the body and the cap. Furthermore, the cap itself was found to be indium-rich, confirming it as the source of the longer wavelength yellow-orange-red luminescence. It is believed that the nanomushroom cap formed as a consequence of the saturation of growth on the c-plane of the nanowire. It is proposed that the formation of an indium droplet on the tip of the nanowire saturated growth on the c-plane, forcing the indium and gallium adatoms to incorporate on the sidewall m-planes instead, but only at the nanowire tip. This resulted in the formation of a mushroom-like cap on the tip. How and why the indium droplets formed is not

  3. Quantum and classical control of single photon states via a mechanical resonator

    International Nuclear Information System (INIS)

    Basiri-Esfahani, Sahar; Myers, Casey R; Combes, Joshua; Milburn, G J

    2016-01-01

    Optomechanical systems typically use light to control the quantum state of a mechanical resonator. In this paper, we propose a scheme for controlling the quantum state of light using the mechanical degree of freedom as a controlled beam splitter. Preparing the mechanical resonator in non-classical states enables an optomechanical Stern–Gerlach interferometer. When the mechanical resonator has a small coherent amplitude it acts as a quantum control, entangling the optical and mechanical degrees of freedom. As the coherent amplitude of the resonator increases, we recover single photon and two-photon interference via a classically controlled beam splitter. The visibility of the two-photon interference is particularly sensitive to coherent excitations in the mechanical resonator and this could form the basis of an optically transduced weak-force sensor. (paper)

  4. Deterministic Generation of Quantum State Transfer Between Spatially Separated Single Molecule Magnets

    International Nuclear Information System (INIS)

    Song Peijun; Lue Xinyou; Huang Pei; Hao Xiangying; Yang Xiaoxue

    2010-01-01

    We propose a new scheme for realizing deterministic quantum state transfer (QST) between two spatially separated single molecule magnets (SMMs) with the framework of cavity quantum electrodynamics (QED). In the present scheme, two SMMs are trapped in two spatially separated optical cavities coupled by an optical fiber. Through strictly numerically simulating, we demonstrate that our scheme is robust with respect to the SMMs' spontaneous decay and fiber loss under the conditions of dispersive SMMs-field interaction and strong coupling of cavity fiber. In addition, we also discuss the influence of photon leakage out of cavities and show that our proposal is good enough to demonstrate the generation of QST with high fidelity utilizing the current experimental technology. The present investigation provides research opportunities for realizing QST between solid-state qubits and may result in a substantial impact on the progress of solid-state-based quantum communications network. (general)

  5. Quantum sensing of the phase-space-displacement parameters using a single trapped ion

    Science.gov (United States)

    Ivanov, Peter A.; Vitanov, Nikolay V.

    2018-03-01

    We introduce a quantum sensing protocol for detecting the parameters characterizing the phase-space displacement by using a single trapped ion as a quantum probe. We show that, thanks to the laser-induced coupling between the ion's internal states and the motion mode, the estimation of the two conjugated parameters describing the displacement can be efficiently performed by a set of measurements of the atomic state populations. Furthermore, we introduce a three-parameter protocol capable of detecting the magnitude, the transverse direction, and the phase of the displacement. We characterize the uncertainty of the two- and three-parameter problems in terms of the Fisher information and show that state projective measurement saturates the fundamental quantum Cramér-Rao bound.

  6. Self-assembly of single "square" quantum rings in gold-free GaAs nanowires.

    Science.gov (United States)

    Zha, Guowei; Shang, Xiangjun; Su, Dan; Yu, Ying; Wei, Bin; Wang, Li; Li, Mifeng; Wang, Lijuan; Xu, Jianxing; Ni, Haiqiao; Ji, Yuan; Sun, Baoquan; Niu, Zhichuan

    2014-03-21

    Single nanostructures embedded within nanowires (NWs) represent one of the most promising technologies for applications in quantum photonics. However, fabrication imperfections and etching-induced defects are inevitable for top-down fabrications, whereas self-assembly bottom-up approaches cannot avoid the difficulties of its stochastic nature and are limited to restricted heterogeneous material systems. Here we demonstrate the versatile self-assembly of single "square" quantum rings (QR) on the sidewalls of gold-free GaAs NWs for the first time. By tuning the deposition temperature, As overpressure and amount of gallium-droplets, we were able to control the density and morphology of the structure, yielding novel single quantum dots, QR, coupled QRs, and nano-antidots. A proposed model based on a strain-driven, transport-dependent nucleation of gallium droplets at high temperature accounts for the formation mechanism of these structures. We achieved a single-QR-in-NW structure, of which the optical properties were analyzed using micro-photoluminescence at 10 K and a spatially resolved cathodoluminescence technique at 77 K. The spectra show sharp discrete peaks; of these peaks, the narrowest linewidth (separation) was 578 μeV (1-3 meV), reflecting the quantized nature of the ring-type electronic states.

  7. Fidelity of Quantum Teleportation for Single-Mode Squeezed State Light

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jun-Xiang; XIE Chang-De; PENG Kun-Chi

    2005-01-01

    @@ The fidelity of quantum teleportation of a single-mode squeezed state of light is calculated based on the general theory of quantum-mechanical measurement in the Schrodinger picture. It is shown that the criterion for the nonclassical state teleportation is different from that for coherent state. F = 1/2 is no longer the rigorous boundary between classical and quantum teleportation for a squeezed state of light. When the quantum entanglement of an Einstein-Podolsky-Rosen (EPR) beam used for teleportation and the parameters of the system are given,the fidelity depends on the squeezing of the input squeezed state. The higher the squeezing is, the smaller the fidelity is, and the lower the classical limitation of fidelity is. The dependence of the optimum gain for teleporting a squeezed vacuum state upon the EPR entanglement is also calculated. The results obtained provide important references for designing experimental systems of teleporting a non-classical state and judging the quality of the teleported quantum state.

  8. Single ion impact detection and scanning probe aligned ion implantation for quantum bit formation

    International Nuclear Information System (INIS)

    Weis, Christoph D.

    2011-01-01

    Quantum computing and quantum information processing is a promising path to replace classical information processing via conventional computers which are approaching fundamental physical limits. Instead of classical bits, quantum bits (qubits) are utilized for computing operations. Due to quantum mechanical phenomena such as superposition and entanglement, a completely different way of information processing is achieved, enabling enhanced performance for certain problem sets. Various proposals exist on how to realize a quantum bit. Among them are electron or nuclear spins of defect centers in solid state systems. Two such candidates with spin degree of freedom are single donor atoms in silicon and nitrogen vacancy (NV) defect centers in diamond. Both qubit candidates possess extraordinary qualities which makes them promising building blocks. Besides certain advantages, the qubits share the necessity to be placed precisely in their host materials and device structures. A commonly used method is to introduce the donor atoms into the substrate materials via ion implantation. For this, focused ion beam systems can be used, or collimation techniques as in this work. A broad ion beam hits the back of a scanning probe microscope (SPM) cantilever with incorporated apertures. The high resolution imaging capabilities of the SPM allows the non destructive location of device areas and the alignment of the cantilever and thus collimated ion beam spot to the desired implant locations. In this work, this technique is explored, applied and pushed forward to meet necessary precision requirements. The alignment of the ion beam to surface features, which are sensitive to ion impacts and thus act as detectors, is demonstrated. The technique is also used to create NV center arrays in diamond substrates. Further, single ion impacts into silicon device structures are detected which enables deliberate single ion doping.

  9. Single ion impact detection and scanning probe aligned ion implantation for quantum bit formation

    Energy Technology Data Exchange (ETDEWEB)

    Weis, Christoph D.

    2011-10-04

    Quantum computing and quantum information processing is a promising path to replace classical information processing via conventional computers which are approaching fundamental physical limits. Instead of classical bits, quantum bits (qubits) are utilized for computing operations. Due to quantum mechanical phenomena such as superposition and entanglement, a completely different way of information processing is achieved, enabling enhanced performance for certain problem sets. Various proposals exist on how to realize a quantum bit. Among them are electron or nuclear spins of defect centers in solid state systems. Two such candidates with spin degree of freedom are single donor atoms in silicon and nitrogen vacancy (NV) defect centers in diamond. Both qubit candidates possess extraordinary qualities which makes them promising building blocks. Besides certain advantages, the qubits share the necessity to be placed precisely in their host materials and device structures. A commonly used method is to introduce the donor atoms into the substrate materials via ion implantation. For this, focused ion beam systems can be used, or collimation techniques as in this work. A broad ion beam hits the back of a scanning probe microscope (SPM) cantilever with incorporated apertures. The high resolution imaging capabilities of the SPM allows the non destructive location of device areas and the alignment of the cantilever and thus collimated ion beam spot to the desired implant locations. In this work, this technique is explored, applied and pushed forward to meet necessary precision requirements. The alignment of the ion beam to surface features, which are sensitive to ion impacts and thus act as detectors, is demonstrated. The technique is also used to create NV center arrays in diamond substrates. Further, single ion impacts into silicon device structures are detected which enables deliberate single ion doping.

  10. Intrinsic errors in transporting a single-spin qubit through a double quantum dot

    Science.gov (United States)

    Li, Xiao; Barnes, Edwin; Kestner, J. P.; Das Sarma, S.

    2017-07-01

    Coherent spatial transport or shuttling of a single electron spin through semiconductor nanostructures is an important ingredient in many spintronic and quantum computing applications. In this work we analyze the possible errors in solid-state quantum computation due to leakage in transporting a single-spin qubit through a semiconductor double quantum dot. In particular, we consider three possible sources of leakage errors associated with such transport: finite ramping times, spin-dependent tunneling rates between quantum dots induced by finite spin-orbit couplings, and the presence of multiple valley states. In each case we present quantitative estimates of the leakage errors, and discuss how they can be minimized. The emphasis of this work is on how to deal with the errors intrinsic to the ideal semiconductor structure, such as leakage due to spin-orbit couplings, rather than on errors due to defects or noise sources. In particular, we show that in order to minimize leakage errors induced by spin-dependent tunnelings, it is necessary to apply pulses to perform certain carefully designed spin rotations. We further develop a formalism that allows one to systematically derive constraints on the pulse shapes and present a few examples to highlight the advantage of such an approach.

  11. Probing correlated quantum many-body systems at the single-particle level

    International Nuclear Information System (INIS)

    Endres, Manuel

    2013-01-01

    The detection of correlation and response functions plays a crucial role in the experimental characterization of quantum many-body systems. In this thesis, we present novel techniques for the measurement of such functions at the single-particle level. Specifically, we show the single-atom- and single-site-resolved detection of an ultracold quantum gas in an optical lattice. The quantum gas is described by the Bose-Hubbard model, which features a zero temperature phase transition from a superfluid to a Mott-insulating state, a paradigm example of a quantum phase transition. We used the aforementioned detection techniques to study correlation and response properties across the superfluid-Mott-insulator transition. The single-atom sensitivity of our method is achieved by fluorescence detection of individual atoms with a high signal-to-noise ratio. A high-resolution objective collects the fluorescence light and yields in situ 'snapshots' of the quantum gas that allow for a single-site-resolved reconstruction of the atomic distribution. This allowed us to measure two-site and non-local correlation-functions across the superfluid-Mott-insulator transition. Non-local correlation functions are based on the information of an extended region of the system and play an important role for the characterization of low-dimensional quantum phases. While non-local correlation functions were so far only theoretical tools, our results show that they are actually experimentally accessible. Furthermore, we used a new thermometry scheme, based on the counting of individual thermal excitations, to measure the response of the system to lattice modulation. Using this method, we studied the excitation spectrum of the system across the two-dimensional superfluid-Mott-insulator transition. In particular, we detected a 'Higgs' amplitude mode in the strongly-interacting superfluid close to the transition point where the system is described by an effectively Lorentz-invariant low-energy theory

  12. Probing correlated quantum many-body systems at the single-particle level

    Energy Technology Data Exchange (ETDEWEB)

    Endres, Manuel

    2013-02-27

    The detection of correlation and response functions plays a crucial role in the experimental characterization of quantum many-body systems. In this thesis, we present novel techniques for the measurement of such functions at the single-particle level. Specifically, we show the single-atom- and single-site-resolved detection of an ultracold quantum gas in an optical lattice. The quantum gas is described by the Bose-Hubbard model, which features a zero temperature phase transition from a superfluid to a Mott-insulating state, a paradigm example of a quantum phase transition. We used the aforementioned detection techniques to study correlation and response properties across the superfluid-Mott-insulator transition. The single-atom sensitivity of our method is achieved by fluorescence detection of individual atoms with a high signal-to-noise ratio. A high-resolution objective collects the fluorescence light and yields in situ 'snapshots' of the quantum gas that allow for a single-site-resolved reconstruction of the atomic distribution. This allowed us to measure two-site and non-local correlation-functions across the superfluid-Mott-insulator transition. Non-local correlation functions are based on the information of an extended region of the system and play an important role for the characterization of low-dimensional quantum phases. While non-local correlation functions were so far only theoretical tools, our results show that they are actually experimentally accessible. Furthermore, we used a new thermometry scheme, based on the counting of individual thermal excitations, to measure the response of the system to lattice modulation. Using this method, we studied the excitation spectrum of the system across the two-dimensional superfluid-Mott-insulator transition. In particular, we detected a 'Higgs' amplitude mode in the strongly-interacting superfluid close to the transition point where the system is described by an effectively Lorentz

  13. Epitaxial growth of In-rich InGaN on yttria-stabilized zirconia and its application to metal–insulator–semiconductor field-effect transistors

    Energy Technology Data Exchange (ETDEWEB)

    Kobayashi, Atsushi; Lye, Khe Shin; Ueno, Kohei [Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505 (Japan); Ohta, Jitsuo [Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505 (Japan); PRESTO, Japan Science and Technology Agency, Saitama 332-0012 (Japan); Fujioka, Hiroshi, E-mail: hfujioka@iis.u-tokyo.ac.jp [Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505 (Japan); ACCEL, Japan Science and Technology Agency, Tokyo 102-0076 (Japan)

    2016-08-28

    We grew In-rich In{sub x}Ga{sub 1-x}N films on yttria-stabilized zirconia (YSZ) substrates at low temperatures by pulsed sputtering deposition. It was found that single-crystal In{sub x}Ga{sub 1-x}N (0.63 ≤ x ≤ 0.82) films can be prepared without significant compositional fluctuations at growth temperatures below 500 °C. It was also found that the electrical properties of InGaN are strongly dependent on In composition, growth temperature, and film polarity. N-channel operation of the metal–insulator–semiconductor field-effect transistor (MISFET) with an ultrathin InGaN channel on the YSZ substrates was successfully demonstrated. These results indicate that an InGaN-based MISFET is a promising device for next-generation high-speed electronics.

  14. Real-time monitoring of Lévy flights in a single quantum system

    Science.gov (United States)

    Issler, M.; Höller, J.; Imamoǧlu, A.

    2016-02-01

    Lévy flights are random walks where the dynamics is dominated by rare events. Even though they have been studied in vastly different physical systems, their observation in a single quantum system has remained elusive. Here we analyze a periodically driven open central spin system and demonstrate theoretically that the dynamics of the spin environment exhibits Lévy flights. For the particular realization in a single-electron charged quantum dot driven by periodic resonant laser pulses, we use Monte Carlo simulations to confirm that the long waiting times between successive nuclear spin-flip events are governed by a power-law distribution; the corresponding exponent η =-3 /2 can be directly measured in real time by observing the waiting time distribution of successive photon emission events. Remarkably, the dominant intrinsic limitation of the scheme arising from nuclear quadrupole coupling can be minimized by adjusting the magnetic field or by implementing spin echo.

  15. Anisotropic Exciton Rabi Oscillation in Single Telecommunication-Band Quantum Dot

    Science.gov (United States)

    Toshiyuki Miyazawa,; Toshihiro Nakaoka,; Katsuyuki Watanabe,; Naoto Kumagai,; Naoki Yokoyama,; Yasuhiko Arakawa,

    2010-06-01

    Anisotropic Rabi oscillation in the exciton state in a single InAs/GaAs quantum dot (QD) was demonstrated in the telecommunication-band by selecting two orthogonal polarization angles of the excitation laser. Our InAs QDs were embedded in an intrinsic layer of an n-i-Schottky diode, which provides an electric field to extract photoexcited carriers from QDs. Owing to the potential anisotropy of QDs, the fine structure splitting (FSS) energy in the exciton state in single InAs QDs was ˜110 μeV, measured by polarization-resolved photocurrent spectroscopy. The ratio between two different Rabi frequencies, which reflect anisotropic dipole moments of two orthogonal exciton states, was estimated to be ˜1.2. This demonstrates that the selective control of two orthogonal polarized exciton states is a promising technique for exciton-based-quantum information devices compatible with fiber optics.

  16. In-plane nuclear field formation investigated in single self-assembled quantum dots

    Science.gov (United States)

    Yamamoto, S.; Matsusaki, R.; Kaji, R.; Adachi, S.

    2018-02-01

    We studied the formation mechanism of the in-plane nuclear field in single self-assembled In0.75Al0.25As /Al0.3Ga0.7As quantum dots. The Hanle curves with an anomalously large width and hysteretic behavior at the critical transverse magnetic field were observed in many single quantum dots grown in the same sample. In order to explain the anomalies in the Hanle curve indicating the formation of a large nuclear field perpendicular to the photo-injected electron spin polarization, we propose a new model based on the current phenomenological model for dynamic nuclear spin polarization. The model includes the effects of the nuclear quadrupole interaction and the sign inversion between in-plane and out-of-plane components of nuclear g factors, and the model calculations reproduce successfully the characteristics of the observed anomalies in the Hanle curves.

  17. MBE-growth, characterization and properties of InN and InGaN

    International Nuclear Information System (INIS)

    Nanishi, Y.; Saito, Y.; Yamaguchi, T.; Hori, M.; Matsuda, F.; Araki, T.; Suzuki, A.; Miyajima, T.

    2003-01-01

    Recent developments on RF-MBE growth of InN and InGaN and their structural and property characterizations are reviewed. For successful growth of high quality InN, (1) nitridation of the sapphire substrates, (2) two-step growth, (3) precise control of V/III ratio and (4) selection of optimum growth temperature are found to be essential. Characterization using XRD, TEM, EXAFS and Raman scattering have clearly demonstrated that InN films have ideal hexagonal wurtzite structure. It is also found that the film has N-polarity. Studies on optimum growth condition dependence on substrate polarity using C and Si face SiC substrates and Ga and N face free-standing GaN substrates are also demonstrated. The result explains why high-quality InN grown by RF-MBE has N-polarity. PL and CL studies on these well-characterized high-quality InN have shown luminescence peaks at approximately 0.75 eV at 77 K. These values, however, change slightly depending on measurement temperatures and probably on the residual carrier concentrations. InGaN with full compositional range are also successfully grown on sapphire substrates and band gap energies of these alloys are also studied using PL and CL. Based on these results, true band gap energies of InN are discussed. This paper also includes latest study on single crystalline InN growth on Si (111) substrates. (copyright 2003 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. MBE-growth, characterization and properties of InN and InGaN

    Energy Technology Data Exchange (ETDEWEB)

    Nanishi, Y.; Saito, Y.; Yamaguchi, T.; Hori, M.; Matsuda, F.; Araki, T. [Dept. of Photonics, Ritsumeikan Univ., 1-1-1 Noji-higashi, Kusatsu (Japan); Suzuki, A. [Res. Org. of Sci. and Eng., Ritsumeikan Univ., 1-1-1 Noji-higashi, Kusatsu (Japan); Miyajima, T. [Sony Corp. Core Technology and Network Company, 4-14-1 Asahi, Atsugi, Kanagawa 243-0014 (Japan)

    2003-11-01

    Recent developments on RF-MBE growth of InN and InGaN and their structural and property characterizations are reviewed. For successful growth of high quality InN, (1) nitridation of the sapphire substrates, (2) two-step growth, (3) precise control of V/III ratio and (4) selection of optimum growth temperature are found to be essential. Characterization using XRD, TEM, EXAFS and Raman scattering have clearly demonstrated that InN films have ideal hexagonal wurtzite structure. It is also found that the film has N-polarity. Studies on optimum growth condition dependence on substrate polarity using C and Si face SiC substrates and Ga and N face free-standing GaN substrates are also demonstrated. The result explains why high-quality InN grown by RF-MBE has N-polarity. PL and CL studies on these well-characterized high-quality InN have shown luminescence peaks at approximately 0.75 eV at 77 K. These values, however, change slightly depending on measurement temperatures and probably on the residual carrier concentrations. InGaN with full compositional range are also successfully grown on sapphire substrates and band gap energies of these alloys are also studied using PL and CL. Based on these results, true band gap energies of InN are discussed. This paper also includes latest study on single crystalline InN growth on Si (111) substrates. (copyright 2003 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Determinant method and quantum simulations of many-body effects in a single impurity Anderson model

    International Nuclear Information System (INIS)

    Gubernatis, J.E.; Olson, T.; Scalapino, D.J.; Sugar, R.L.

    1985-01-01

    A short description is presented of a quantum Monte Carlo technique, often referred to as the determinant method, that has proved useful for simulating many-body effects in systems of interacting fermions at finite temperatures. Preliminary results using this technique on a single impurity Anderson model are reported. Examples of such many-body effects as local moment formation, Kondo behavior, and mixed valence phenomena found in the simulations are shown. 10 refs., 3 figs

  20. Optical bistability in a single-sided cavity coupled to a quantum channel

    Science.gov (United States)

    Payravi, M.; Solookinejad, Gh; Jabbari, M.; Nafar, M.; Ahmadi Sangachin, E.

    2018-06-01

    In this paper, we discuss the long wavelength optical reflection and bistable behavior of an InGaN/GaN quantum dot nanostructure coupled to a single-sided cavity. It is found that due to the presence of a strong coupling field, the reflection coefficient can be controlled at long wavelength, which is essential for adjusting the threshold of reflected optical bistability. Moreover, the phase shift features of the reflection pulse inside an electromagnetically induced transparency window are also discussed.

  1. Pulsed neural networks consisting of single-flux-quantum spiking neurons

    International Nuclear Information System (INIS)

    Hirose, T.; Asai, T.; Amemiya, Y.

    2007-01-01

    An inhibitory pulsed neural network was developed for brain-like information processing, by using single-flux-quantum (SFQ) circuits. It consists of spiking neuron devices that are coupled to each other through all-to-all inhibitory connections. The network selects neural activity. The operation of the neural network was confirmed by computer simulation. SFQ neuron devices can imitate the operation of the inhibition phenomenon of neural networks

  2. Quantum private comparison with d-level single-particle states

    International Nuclear Information System (INIS)

    Yu, Chao-Hua; Guo, Gong-De; Lin, Song

    2013-01-01

    In this paper, a quantum private comparison protocol with d-level single-particle states is proposed. In the protocol, a semi-honest third party is introduced to help two participants compare the size relationship of their secrets without revealing them to any other people. It is shown that the protocol is secure in theory. Moreover, the security of the protocol in real circumstance is also discussed. (paper)

  3. Effects of Mg Doping on the Performance of InGaN Films Made by Reactive Sputtering

    Science.gov (United States)

    Kuo, Dong-Hau; Li, Cheng-Che; Tuan, Thi Tran Anh; Yen, Wei-Chun

    2015-01-01

    Mg-doped InGaN (Mg-InGaN) films have been deposited directly on Si (100) substrates by radio-frequency reactive sputtering technique with single cermet targets in an Ar/N2 atmosphere. The cermet targets with a constant 5% indium content were made by hot pressing the mixture of metallic In, Ga, and Mg powders and ceramic GaN powder. The Mg-InGaN films had a wurtzite structure with a preferential () growth plane. The SEM images showed that Mg-InGaN films were smooth, continuous, free from cracks and holes, and composed of nanometer-sized grains. As the Mg dopant content in Mg-InGaN increased to 7.7 at.%, the film was directly transformed into p-type conduction without a post-annealing process. It had high hole concentration of 5.53 × 1018 cm-3 and electrical mobility of 15.7 ± 4.2 cm2 V-1 s-1. The over-doping of Mg in InGaN degraded the electrical properties. The bandgap of Mg-InGaN films decreased from 2.92 eV to 2.84 eV, as the Mg content increased from 7.7% to 18.2%. The constructed p-type Mg-InGaN/ n-type GaN diode was used to confirm the realization of the p-type InGaN by sputtering technique.

  4. Quickest single-step one pot mechanosynthesis and characterization of ZnTe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Patra, S. [Dept of Physics, University of Burdwan, Golapbag, Burdwan, West Bengal 713104 (India); Pradhan, S.K., E-mail: skp_bu@yahoo.com [Dept of Physics, University of Burdwan, Golapbag, Burdwan, West Bengal 713104 (India)

    2011-05-05

    Research highlights: > First time quickest mechanosynthesis of ZnTe QDs starting from Zn and Te powders. > Cubic ZnTe are formed in a single pot at RT in a single step within 1 h of milling. > The existence of stacking faults and twin faults are evident from HRTEM images. > Distinct blue shift has been observed in UV-vis absorption spectra. > First time report that ZnTe QDs with faults can also show the quantum size effect. - Abstract: ZnTe quantum dots (QDs) are synthesized at room temperature in a single step by mechanical alloying the stoichiometric equimolar mixture (1:1 mol) of Zn and Te powders under Ar within 1 h of milling. Both XRD and HRTEM characterizations reveal that these QDs having size {approx}5 nm contain stacking faults of different kinds. A distinct blue-shift in absorption spectra with decreasing particle size of QDs confirms the quantum size confinement effect (QSCE). It is observed for first time that the QDs with considerable amount of faults can also show the QSCE. Optical band gaps of these QDs increase with increasing milling time and their band gaps can be fine-tuned easily by varying milling time of QDs.

  5. Thermal vibration of a rectangular single-layered graphene sheet with quantum effects

    International Nuclear Information System (INIS)

    Wang, Lifeng; Hu, Haiyan

    2014-01-01

    The thermal vibration of a rectangular single-layered graphene sheet is investigated by using a rectangular nonlocal elastic plate model with quantum effects taken into account when the law of energy equipartition is unreliable. The relation between the temperature and the Root of Mean Squared (RMS) amplitude of vibration at any point of the rectangular single-layered graphene sheet in simply supported case is derived first from the rectangular nonlocal elastic plate model with the strain gradient of the second order taken into consideration so as to characterize the effect of microstructure of the graphene sheet. Then, the RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet simply supported on an elastic foundation is derived. The study shows that the RMS amplitude of the rectangular single-layered graphene sheet predicted from the quantum theory is lower than that predicted from the law of energy equipartition. The maximal relative difference of RMS amplitude of thermal vibration appears at the sheet corners. The microstructure of the graphene sheet has a little effect on the thermal vibrations of lower modes, but exhibits an obvious effect on the thermal vibrations of higher modes. The quantum effect is more important for the thermal vibration of higher modes in the case of smaller sides and lower temperature. The relative difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet decreases monotonically with an increase of temperature. The absolute difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet increases slowly with the rising of Winkler foundation modulus.

  6. Achievement report for fiscal 1998 on the research and development of quantum function device. Research on technological trend; 1998 nendo ryoshika kino soshi no kenkyu kaihatsu seika hokokusho. Gijutsu doko chosa kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1999-03-01

    To effectively promote the research and development of quantum function devices, the advancement of the research and development concerned is surveyed and problems in the course of research and development are isolated, analyzed, and discussed, and a survey is conducted on technological trends. Researches are conducted through research committee meetings, on-the-spot surveys of overseas activities, and international conferences. As the result, reports are compiled on the integration of multi-value logic devices using tunnelling control function devices, integration of logic memory devices based on quantum levels, integration of quantum interband coupled multifunction devices, silicon insulation film tunnel memory device, mass dot function memory, quantum wave switching function device, integration of single electron logic devices, integration of CMOS coupled type single electron devices, basic technology of single electron device, etc. As for common basic technology, an integrated device in which a quantum function element and CMOS are merged, superspeed quantum device using light, spontaneous formation of InGaN quantum dot and GaSb/GaAs quantum dot, electron moderation mechanism in quantum dot, etc., are compiled into reports. (NEDO)

  7. Single, double, and triple quantum dots in the transport; Einzel-, Doppel- und Dreifachquantenpunkte im Transport

    Energy Technology Data Exchange (ETDEWEB)

    Rogge, Maximilian Christoph

    2008-12-03

    This thesis describes the fabrication of different lateral single, double and triple quantum dots as well as the investigation of these devices with electronic transport. Based on GaAs/AlGaAs heterostructures, the fabrication was carried out using optical lithography and lithography with a scanning electron microscope and an atomic force microscope. The latter ones were also used in combination. Aside from basic effects like Coulomb blockade the analysis of single quantum dots particularly yielded results by charge detection and magneto transport. With charge detection using quantum point contacts conclusions were attained concerning tunneling rates and the extension of wave functions. In a magnetic field the influence of the electronic spin is important aside from aspects concerning the Fock-Darwin spectrum. Analyses were performed on Zeeman effect, spin pairing, spin blockade and Kondo effect. The combination of spin blockade and Kondo effect allows statements concerning the spin configuration, which depends on the electron number. With double quantum dots of different geometries the two mechanisms of capacitive coupling and tunnel coupling were analyzed. They were found in spectra of ground and excited states. With gate voltage and magnetic field it was possible to freely vary character and strength of coupling. With capacitive coupling, spin blockade was investigated again. The analysis of coupling effects was performed using transport and charge measurements. Aside from results on tunneling rates the latter one allows to detect molecular states. Concerning triple quantum dots the three dimensional stability diagram was analyzed. The free variation of energies of all three dots was achieved. The evolution of resonances was observed with transport and charge detection. With a starlike device geometry it was possible to perform two-path measurements. They provide a new measurand, the distinguishability of double and triple dot physics. (orig.)

  8. An efficient single-step scheme for manipulating quantum information of two trapped ions beyond the Lamb-Dicke limit

    International Nuclear Information System (INIS)

    Wei, L.F.; Nori, Franco

    2003-01-01

    Based on the exact conditional quantum dynamics for a two-ion system, we propose an efficient single-step scheme for coherently manipulating quantum information of two trapped cold ions by using a pair of synchronous laser pulses. Neither the auxiliary atomic level nor the Lamb-Dicke approximation are needed

  9. Quantum interference effects at room temperature in OPV-based single-molecule junctions

    DEFF Research Database (Denmark)

    Arroyo, Carlos R.; Frisenda, Riccardo; Moth-Poulsen, Kasper

    2013-01-01

    Interference effects on charge transport through an individual molecule can lead to a notable modulation and suppression on its conductance. In this letter, we report the observation of quantum interference effects occurring at room temperature in single-molecule junctions based on oligo(3......)-phenylenevinylene (OPV3) derivatives, in which the central benzene ring is coupled to either para- or meta-positions. Using the break-junction technique, we find that the conductance for a single meta-OPV3 molecule wired between gold electrodes is one order of magnitude smaller than that of a para-OPV3 molecule...

  10. Super-Resolution Definition of Coordinates of Single Semiconductor Nanocrystal (Quantum Dot: Luminescence Intensity Dependence

    Directory of Open Access Journals (Sweden)

    Eremchev M. Yu.

    2015-01-01

    Full Text Available In this research a relation between the accuracy of restoration of the single quantum dots (QD CdSe/CdS/ZnS cross-cut coordinates and luminescence intensity was investigated. It was shown that the limit of the accuracy of determining the coordinates of a single QD for a considerable total amount of registered photons approaches its limiting value that is comparable to the size of the QD. It also means that the installation used in the research is mechanically stable enough to reach the limiting values of determination accuracy of point emitters coordinates.

  11. A surface-gated InSb quantum well single electron transistor

    International Nuclear Information System (INIS)

    Orr, J M S; Buckle, P D; Fearn, M; Storey, C J; Buckle, L; Ashley, T

    2007-01-01

    Single electron charging effects in a surface-gated InSb/AlInSb QW structure are reported. This material, due to its large g-factor and light effective mass, offers considerable advantages over more commonly used materials, such as GaAs, for quantum information processing devices. However, differences in material and device technology result in significant processing challenges. Simple Coulomb blockade and quantized confinement models are considered to explain the observation of conductance oscillations in these structures. The charging energy (e 2 /C) is found to be comparable with the energy spectrum for single particle states (ΔE)

  12. Experimental Evidence for Quantum Interference and Vibrationally Induced Decoherence in Single-Molecule Junctions

    Science.gov (United States)

    Ballmann, Stefan; Härtle, Rainer; Coto, Pedro B.; Elbing, Mark; Mayor, Marcel; Bryce, Martin R.; Thoss, Michael; Weber, Heiko B.

    2012-08-01

    We analyze quantum interference and decoherence effects in single-molecule junctions both experimentally and theoretically by means of the mechanically controlled break junction technique and density-functional theory. We consider the case where interference is provided by overlapping quasidegenerate states. Decoherence mechanisms arising from electronic-vibrational coupling strongly affect the electrical current flowing through a single-molecule contact and can be controlled by temperature variation. Our findings underline the universal relevance of vibrations for understanding charge transport through molecular junctions.

  13. Quantum state detection and state preparation based on cavity-enhanced nonlinear interaction of atoms with single photon

    Science.gov (United States)

    Hosseini, Mahdi

    Our ability to engineer quantum states of light and matter has significantly advanced over the past two decades, resulting in the production of both Gaussian and non-Gaussian optical states. The resulting tailored quantum states enable quantum technologies such as quantum optical communication, quantum sensing as well as quantum photonic computation. The strong nonlinear light-atom interaction is the key to deterministic quantum state preparation and quantum photonic processing. One route to enhancing the usually weak nonlinear light-atom interactions is to approach the regime of cavity quantum electrodynamics (cQED) interaction by means of high finesse optical resonators. I present results from the MIT experiment of large conditional cross-phase modulation between a signal photon, stored inside an atomic quantum memory, and a control photon that traverses a high-finesse optical cavity containing the atomic memory. I also present a scheme to probabilistically change the amplitude and phase of a signal photon qubit to, in principle, arbitrary values by postselection on a control photon that has interacted with that state. Notably, small changes of the control photon polarization measurement basis by few degrees can substantially change the amplitude and phase of the signal state. Finally, I present our ongoing effort at Purdue to realize similar peculiar quantum phenomena at the single photon level on chip scale photonic systems.

  14. Physics colloquium: Single-electron counting in quantum metrology and in statistical mechanics

    CERN Multimedia

    Geneva University

    2011-01-01

    GENEVA UNIVERSITY Ecole de physique Département de physique nucléaire et corspusculaire 24, quai Ernest-Ansermet 1211 Genève 4 Tél.: (022) 379 62 73 Fax: (022) 379 69 92olé   Lundi 17 octobre 2011 17h00 - Ecole de Physique, Auditoire Stueckelberg PHYSICS COLLOQUIUM « Single-electron counting in quantum metrology and in statistical mechanics » Prof. Jukka Pekola Low Temperature Laboratory, Aalto University Helsinki, Finland   First I discuss the basics of single-electron tunneling and its potential applications in metrology. My main focus is in developing an accurate source of single-electron current for the realization of the unit ampere. I discuss the principle and the present status of the so-called single- electron turnstile. Investigation of errors in transporting electrons one by one has revealed a wealth of observations on fundamental phenomena in mesoscopic superconductivity, including individual Andreev...

  15. Fabrication of a novel silicon single electron transistor for Si:P quantum computer devices

    International Nuclear Information System (INIS)

    Angus, S.J.; Smith, C.E.A.; Gauja, E.; Dzurak, A.S.; Clark, R.G.; Snider, G.L.

    2004-01-01

    Full text: Quantum computation relies on the successful measurement of quantum states. Single electron transistors (SETs) are known to be able to perform fast and sensitive charge measurements of solid state qubits. However, due to their sensitivity, SETs are also very susceptible to random charge fluctuations in a solid-state materials environment. In previous dc transport measurements, silicon-based SETs have demonstrated greater charge stability than A1/A1 2 O 3 SETs. We have designed and fabricated a novel silicon SET architecture for a comparison of the noise characteristics of silicon and aluminium based devices. The silicon SET described here is designed for controllable and reproducible low temperature operation. It is fabricated using a novel dual gate structure on a silicon-on-insulator substrate. A silicon quantum wire is formed in a 100nm thick high-resistivity superficial silicon layer using reactive ion etching. Carriers are induced in the silicon wire by a back gate in the silicon substrate. The tunnel barriers are created electrostatically, using lithographically defined metallic electrodes (∼40nm width). These tunnel barriers surround the surface of the quantum wire, thus producing excellent electrostatic confinement. This architecture provides independent control of tunnel barrier height and island occupancy, thus promising better control of Coulomb blockade oscillations than in previously investigated silicon SETs. The use of a near intrinsic silicon substrate offers compatibility with Si:P qubits in the longer term

  16. Quasi-one-dimensional density of states in a single quantum ring.

    Science.gov (United States)

    Kim, Heedae; Lee, Woojin; Park, Seongho; Kyhm, Kwangseuk; Je, Koochul; Taylor, Robert A; Nogues, Gilles; Dang, Le Si; Song, Jin Dong

    2017-01-05

    Generally confinement size is considered to determine the dimensionality of nanostructures. While the exciton Bohr radius is used as a criterion to define either weak or strong confinement in optical experiments, the binding energy of confined excitons is difficult to measure experimentally. One alternative is to use the temperature dependence of the radiative recombination time, which has been employed previously in quantum wells and quantum wires. A one-dimensional loop structure is often assumed to model quantum rings, but this approximation ceases to be valid when the rim width becomes comparable to the ring radius. We have evaluated the density of states in a single quantum ring by measuring the temperature dependence of the radiative recombination of excitons, where the photoluminescence decay time as a function of temperature was calibrated by using the low temperature integrated intensity and linewidth. We conclude that the quasi-continuous finely-spaced levels arising from the rotation energy give rise to a quasi-one-dimensional density of states, as long as the confined exciton is allowed to rotate around the opening of the anisotropic ring structure, which has a finite rim width.

  17. Quantum confined Stark effects of single dopant in polarized hemispherical quantum dot: Two-dimensional finite difference approach and Ritz-Hassé variation method

    Science.gov (United States)

    El Harouny, El Hassan; Nakra Mohajer, Soukaina; Ibral, Asmaa; El Khamkhami, Jamal; Assaid, El Mahdi

    2018-05-01

    Eigenvalues equation of hydrogen-like off-center single donor impurity confined in polarized homogeneous hemispherical quantum dot deposited on a wetting layer, capped by insulated matrix and submitted to external uniform electric field is solved in the framework of the effective mass approximation. An infinitely deep potential is used to describe effects of quantum confinement due to conduction band offsets at surfaces where quantum dot and surrounding materials meet. Single donor ground state total and binding energies in presence of electric field are determined via two-dimensional finite difference approach and Ritz-Hassé variation principle. For the latter method, attractive coulomb correlation between electron and ionized single donor is taken into account in the expression of trial wave function. It appears that off-center single dopant binding energy, spatial extension and radial probability density are strongly dependent on hemisphere radius and single dopant position inside quantum dot. Influence of a uniform electric field is also investigated. It shows that Stark effect appears even for very small size dots and that single dopant energy shift is more significant when the single donor is near hemispherical surface.

  18. Coherent properties of single quantum dot transitions and single photon emission

    Energy Technology Data Exchange (ETDEWEB)

    Ester, Patrick

    2008-04-23

    In this work, the properties and the different dephasing mechanisms of single QD transitions are analyzed. In addition, some applications are presented which arise due to the properties of the confined exciton. The isolation of a single QD out of the ensemble is achieved via near field shadow masks, which restricts excitation and QD luminescence to a single QD. The integration of a QD-layer into a diode structure allows for an analysis of various dephasing mechanisms of a confined electron hole pair. The single QD is characterized regarding the energy of nearly all possible transitions, e.g. the ground state, excited states, charged states, multiple occupations, and phonon assisted absorptions. A very important issue in this content is the voltage dependence of the transition energy and thereby the ability of tunneling processes of charge carriers in and out of the QD. The QD-states, which are subject of investigation here, are the single exciton ground state, the first excited state (p-shell), and the (GaAs-) LO (longitudinal optical) phonon assisted absorption. By applying a suitable voltage, the resonantly excited ground state exciton is able to decay by a tunneling process, which reflects the transition energy in the photocurrent spectra. The p-shell transition decays by a relaxation process into the ground state, followed by an optical recombination process. The phonon assisted absorption differs from the p-shell transition. The resonant excitation energy fits to the exciton ground state energy plus the energy of a GaAs LO phonon. In this case, the single exciton (ground state) is generated as well as a GaAs LO phonon. These three states are investigated in different respects, such as different applied voltages, excitation polarizations, excitation intensities, and coherent properties. The LO-assisted absorption shows also a saturation behavior. The exciton in the QD is able to interfere with the second laser pulse due to the storage of the phase information

  19. Coherent properties of single quantum dot transitions and single photon emission

    International Nuclear Information System (INIS)

    Ester, Patrick

    2008-01-01

    In this work, the properties and the different dephasing mechanisms of single QD transitions are analyzed. In addition, some applications are presented which arise due to the properties of the confined exciton. The isolation of a single QD out of the ensemble is achieved via near field shadow masks, which restricts excitation and QD luminescence to a single QD. The integration of a QD-layer into a diode structure allows for an analysis of various dephasing mechanisms of a confined electron hole pair. The single QD is characterized regarding the energy of nearly all possible transitions, e.g. the ground state, excited states, charged states, multiple occupations, and phonon assisted absorptions. A very important issue in this content is the voltage dependence of the transition energy and thereby the ability of tunneling processes of charge carriers in and out of the QD. The QD-states, which are subject of investigation here, are the single exciton ground state, the first excited state (p-shell), and the (GaAs-) LO (longitudinal optical) phonon assisted absorption. By applying a suitable voltage, the resonantly excited ground state exciton is able to decay by a tunneling process, which reflects the transition energy in the photocurrent spectra. The p-shell transition decays by a relaxation process into the ground state, followed by an optical recombination process. The phonon assisted absorption differs from the p-shell transition. The resonant excitation energy fits to the exciton ground state energy plus the energy of a GaAs LO phonon. In this case, the single exciton (ground state) is generated as well as a GaAs LO phonon. These three states are investigated in different respects, such as different applied voltages, excitation polarizations, excitation intensities, and coherent properties. The LO-assisted absorption shows also a saturation behavior. The exciton in the QD is able to interfere with the second laser pulse due to the storage of the phase information

  20. Manipulating molecular quantum states with classical metal atom inputs: demonstration of a single molecule NOR logic gate.

    Science.gov (United States)

    Soe, We-Hyo; Manzano, Carlos; Renaud, Nicolas; de Mendoza, Paula; De Sarkar, Abir; Ample, Francisco; Hliwa, Mohamed; Echavarren, Antonio M; Chandrasekhar, Natarajan; Joachim, Christian

    2011-02-22

    Quantum states of a trinaphthylene molecule were manipulated by putting its naphthyl branches in contact with single Au atoms. One Au atom carries 1-bit of classical information input that is converted into quantum information throughout the molecule. The Au-trinaphthylene electronic interactions give rise to measurable energy shifts of the molecular electronic states demonstrating a NOR logic gate functionality. The NOR truth table of the single molecule logic gate was characterized by means of scanning tunnelling spectroscopy.

  1. Method for preparation and readout of polyatomic molecules in single quantum states

    Science.gov (United States)

    Patterson, David

    2018-03-01

    Polyatomic molecular ions contain many desirable attributes of a useful quantum system, including rich internal degrees of freedom and highly controllable coupling to the environment. To date, the vast majority of state-specific experimental work on molecular ions has concentrated on diatomic species. The ability to prepare and read out polyatomic molecules in single quantum states would enable diverse experimental avenues not available with diatomics, including new applications in precision measurement, sensitive chemical and chiral analysis at the single-molecule level, and precise studies of Hz-level molecular tunneling dynamics. While cooling the motional state of a polyatomic ion via sympathetic cooling with a laser-cooled atomic ion is straightforward, coupling this motional state to the internal state of the molecule has proven challenging. Here we propose a method for readout and projective measurement of the internal state of a trapped polyatomic ion. The method exploits the rich manifold of technically accessible rotational states in the molecule to realize robust state preparation and readout with far less stringent engineering than quantum logic methods recently demonstrated on diatomic molecules. The method can be applied to any reasonably small (≲10 atoms) polyatomic ion with an anisotropic polarizability.

  2. Observation of single quantum dots in GaAs/AlAs micropillar cavities

    Energy Technology Data Exchange (ETDEWEB)

    Burger, Philipp; Karl, Matthias; Hu, Dongzhi; Schaadt, Daniel M.; Kalt, Heinz; Hetterich, Michael [Institut fuer Angewandte Physik, Universitaet Karlsruhe (Germany); DFG Center for Functional Nanostructures (CFN), Karlsruhe (Germany)

    2009-07-01

    In our contribution we present the fabrication steps of micropillar cavities and their optical properties. The layer structure consisting of a GaAs-based lambda-cavity sandwiched between two GaAs/AlAs distributed Bragg reflectors is grown by molecular-beam epitaxy. In(Ga)As quantum dots, emitting at around 950 nm, are embedded as optically active medium in the middle of the cavity. The pillars are milled out of this structure with a focused ion-beam. A confocal micro-photoluminescence set-up allows to measure optical cavity modes as well as single quantum dots in the pillars when using low excitation intensity. This enables us to observe a (thermal) shift of the single quantum dot peaks relative to the cavity mode. In addition, we increased the numerical aperture of the set-up (originally 0.4) with a solid immersion lens up to 0.8. Thus we are able to detect the fundamental mode of pillars with very small diameters. Furthermore, the collection efficiency increases substantially.

  3. Mode Engineering of Single Photons from Cavity Spontaneous Parametric Down-Conversion Source and Quantum Dots

    Science.gov (United States)

    Paudel, Uttam

    Over the past decade, much effort has been made in identifying and characterizing systems that can form a building block of quantum networks, among which semiconductor quantum dots (QD) and spontaneous parametric down-conversion (SPDC) source are two of the most promising candidates. The work presented in this thesis will be centered on investigating and engineering the mentioned systems for generating customizable single photons. A type-II SPDC source can generate a highly flexible pair of entangled photons that can be used to interface disparate quantum systems. In this thesis, we have successfully implemented a cavity-SPDC source that emits polarization correlated photons at 942 nm with a lifetime of 950-1050ps that mode matches closely with InAs/GaAs QD photons. The source emits 80 photon pairs per second per mW pump power within the 150MHz bandwidth. Though the detection of idler photons, the source is capable of emitting heralded photons with g2?0.5 for up to 40 mW pump power. For a low pump power of 5 mW, the heralded g2 is 0.06, indicating that the system is an excellent heralded single photon source. By directly exciting a single QD with cavity-SPDC photons, we have demonstrated a heralded-absorption of SPDC photons by QD, resulting in the coupling of the two systems. Due to the large pump bandwidth, the emitted source is highly multimode in nature, requiring us to post-filter the downconverted field, resulting in a lower photon pair emission rate. We propose placing an intra-cavity etalon to suppress the multi-mode emissions and increase the photon count rate. Understanding and experimentally implementing two-photon interference (HOM) measurements will be crucial for building a scalable quantum network. A detailed theoretical description of HOM measurements is given and is experimentally demonstrated using photons emitted by QD. Through HOM measurements we demonstrated that the QD sample in the study is capable of emitting indistinguishable photons, with

  4. Efficient amplitude-modulated pulses for triple- to single-quantum coherence conversion in MQMAS NMR.

    Science.gov (United States)

    Colaux, Henri; Dawson, Daniel M; Ashbrook, Sharon E

    2014-08-07

    The conversion between multiple- and single-quantum coherences is integral to many nuclear magnetic resonance (NMR) experiments of quadrupolar nuclei. This conversion is relatively inefficient when effected by a single pulse, and many composite pulse schemes have been developed to improve this efficiency. To provide the maximum improvement, such schemes typically require time-consuming experimental optimization. Here, we demonstrate an approach for generating amplitude-modulated pulses to enhance the efficiency of the triple- to single-quantum conversion. The optimization is performed using the SIMPSON and MATLAB packages and results in efficient pulses that can be used without experimental reoptimisation. Most significant signal enhancements are obtained when good estimates of the inherent radio-frequency nutation rate and the magnitude of the quadrupolar coupling are used as input to the optimization, but the pulses appear robust to reasonable variations in either parameter, producing significant enhancements compared to a single-pulse conversion, and also comparable or improved efficiency over other commonly used approaches. In all cases, the ease of implementation of our method is advantageous, particularly for cases with low sensitivity, where the improvement is most needed (e.g., low gyromagnetic ratio or high quadrupolar coupling). Our approach offers the potential to routinely improve the sensitivity of high-resolution NMR spectra of nuclei and systems that would, perhaps, otherwise be deemed "too challenging".

  5. Spin Quantum Tunneling via Entangled States in a Dimer of Exchange-Coupled Single-Molecule Magnets

    Science.gov (United States)

    Tiron, R.; Wernsdorfer, W.; Foguet-Albiol, D.; Aliaga-Alcalde, N.; Christou, G.

    2003-11-01

    A new family of supramolecular, antiferromagnetically exchange-coupled dimers of single-molecule magnets (SMMs) has recently been reported. Each SMM acts as a bias on its neighbor, shifting the quantum tunneling resonances of the individual SMMs. Hysteresis loop measurements on a single crystal of SMM dimers have now established quantum tunneling of the magnetization via entangled states of the dimer. This shows that the dimer really does behave as a quantum mechanically coupled dimer, and also allows the measurement of the longitudinal and transverse superexchange coupling constants.

  6. Electrically injected GaAsBi/GaAs single quantum well laser diodes

    Directory of Open Access Journals (Sweden)

    Juanjuan Liu

    2017-11-01

    Full Text Available We present electrically injected GaAs/GaAsBi single quantum well laser diodes (LDs emitting at a record long wavelength of 1141 nm at room temperature grown by molecular beam epitaxy. The LDs have excellent device performances with internal quantum efficiency of 86%, internal loss of 10 cm-1 and transparency current density of 196 A/cm2. The LDs can operate under continuous-wave mode up to 273 K. The characteristic temperature are extracted to be 125 K in the temperature range of 77∼150 K, and reduced to 90 K in the range of 150∼273 K. The temperature coefficient of 0.3 nm/K is extracted in the temperature range of 77∼273 K.

  7. Electronic properties of single Ge/Si quantum dot grown by ion beam sputtering deposition.

    Science.gov (United States)

    Wang, C; Ke, S Y; Yang, J; Hu, W D; Qiu, F; Wang, R F; Yang, Y

    2015-03-13

    The dependence of the electronic properties of a single Ge/Si quantum dot (QD) grown by the ion-beam sputtering deposition technique on growth temperature and QD diameter is investigated by conductive atomic force microscopy (CAFM). The Si-Ge intermixing effect is demonstrated to be important for the current distribution of single QDs. The current staircase induced by the Coulomb blockade effect is observed at higher growth temperatures (>700 °C) due to the formation of an additional barrier between dislocated QDs and Si substrate for the resonant tunneling of holes. According to the proposed single-hole-tunneling model, the fact that the intermixing effect is observed to increase as the incoherent QD size decreases may explain the increase in the starting voltage of the current staircase and the decrease in the current step width.

  8. Single-electron-occupation metal-oxide-semiconductor quantum dots formed from efficient poly-silicon gate layout

    Energy Technology Data Exchange (ETDEWEB)

    Carroll, Malcolm S.; rochette, sophie; Rudolph, Martin; Roy, A. -M.; Curry, Matthew Jon; Ten Eyck, Gregory A.; Manginell, Ronald P.; Wendt, Joel R.; Pluym, Tammy; Carr, Stephen M; Ward, Daniel Robert; Lilly, Michael; pioro-ladriere, michel

    2017-07-01

    We introduce a silicon metal-oxide-semiconductor quantum dot structure that achieves dot-reservoir tunnel coupling control without a dedicated barrier gate. The elementary structure consists of two accumulation gates separated spatially by a gap, one gate accumulating a reservoir and the other a quantum dot. Control of the tunnel rate between the dot and the reservoir across the gap is demonstrated in the single electron regime by varying the reservoir accumulation gate voltage while compensating with the dot accumulation gate voltage. The method is then applied to a quantum dot connected in series to source and drain reservoirs, enabling transport down to the single electron regime. Finally, tuning of the valley splitting with the dot accumulation gate voltage is observed. This split accumulation gate structure creates silicon quantum dots of similar characteristics to other realizations but with less electrodes, in a single gate stack subtractive fabrication process that is fully compatible with silicon foundry manufacturing.

  9. High-dimensional quantum key distribution with the entangled single-photon-added coherent state

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yang [Zhengzhou Information Science and Technology Institute, Zhengzhou, 450001 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Bao, Wan-Su, E-mail: 2010thzz@sina.com [Zhengzhou Information Science and Technology Institute, Zhengzhou, 450001 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Bao, Hai-Ze; Zhou, Chun; Jiang, Mu-Sheng; Li, Hong-Wei [Zhengzhou Information Science and Technology Institute, Zhengzhou, 450001 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2017-04-25

    High-dimensional quantum key distribution (HD-QKD) can generate more secure bits for one detection event so that it can achieve long distance key distribution with a high secret key capacity. In this Letter, we present a decoy state HD-QKD scheme with the entangled single-photon-added coherent state (ESPACS) source. We present two tight formulas to estimate the single-photon fraction of postselected events and Eve's Holevo information and derive lower bounds on the secret key capacity and the secret key rate of our protocol. We also present finite-key analysis for our protocol by using the Chernoff bound. Our numerical results show that our protocol using one decoy state can perform better than that of previous HD-QKD protocol with the spontaneous parametric down conversion (SPDC) using two decoy states. Moreover, when considering finite resources, the advantage is more obvious. - Highlights: • Implement the single-photon-added coherent state source into the high-dimensional quantum key distribution. • Enhance both the secret key capacity and the secret key rate compared with previous schemes. • Show an excellent performance in view of statistical fluctuations.

  10. Ultraclean single, double, and triple carbon nanotube quantum dots with recessed Re bottom gates

    Science.gov (United States)

    Jung, Minkyung; Schindele, Jens; Nau, Stefan; Weiss, Markus; Baumgartner, Andreas; Schoenenberger, Christian

    2014-03-01

    Ultraclean carbon nanotubes (CNTs) that are free from disorder provide a promising platform to manipulate single electron or hole spins for quantum information. Here, we demonstrate that ultraclean single, double, and triple quantum dots (QDs) can be formed reliably in a CNT by a straightforward fabrication technique. The QDs are electrostatically defined in the CNT by closely spaced metallic bottom gates deposited in trenches in Silicon dioxide by sputter deposition of Re. The carbon nanotubes are then grown by chemical vapor deposition (CVD) across the trenches and contacted using conventional electron beam lithography. The devices exhibit reproducibly the characteristics of ultraclean QDs behavior even after the subsequent electron beam lithography and chemical processing steps. We demonstrate the high quality using CNT devices with two narrow bottom gates and one global back gate. Tunable by the gate voltages, the device can be operated in four different regimes: i) fully p-type with ballistic transport between the outermost contacts (over a length of 700 nm), ii) clean n-type single QD behavior where a QD can be induced by either the left or the right bottom gate, iii) n-type double QD and iv) triple bipolar QD where the middle QD has opposite doping (p-type). Research at Basel is supported by the NCCR-Nano, NCCR-QIST, ERC project QUEST, and FP7 project SE2ND.

  11. High-dimensional quantum key distribution with the entangled single-photon-added coherent state

    International Nuclear Information System (INIS)

    Wang, Yang; Bao, Wan-Su; Bao, Hai-Ze; Zhou, Chun; Jiang, Mu-Sheng; Li, Hong-Wei

    2017-01-01

    High-dimensional quantum key distribution (HD-QKD) can generate more secure bits for one detection event so that it can achieve long distance key distribution with a high secret key capacity. In this Letter, we present a decoy state HD-QKD scheme with the entangled single-photon-added coherent state (ESPACS) source. We present two tight formulas to estimate the single-photon fraction of postselected events and Eve's Holevo information and derive lower bounds on the secret key capacity and the secret key rate of our protocol. We also present finite-key analysis for our protocol by using the Chernoff bound. Our numerical results show that our protocol using one decoy state can perform better than that of previous HD-QKD protocol with the spontaneous parametric down conversion (SPDC) using two decoy states. Moreover, when considering finite resources, the advantage is more obvious. - Highlights: • Implement the single-photon-added coherent state source into the high-dimensional quantum key distribution. • Enhance both the secret key capacity and the secret key rate compared with previous schemes. • Show an excellent performance in view of statistical fluctuations.

  12. Microscopic theory of indistinguishable single-photon emission from a quantum dot coupled to a cavity: The role of non-Markovian phonon-induced decoherence

    DEFF Research Database (Denmark)

    Nielsen, Per Kær; Lodahl, Peter; Jauho, Antti-Pekka

    2013-01-01

    We study the fundamental limit on single-photon indistinguishability imposed by decoherence due to phonon interactions in semiconductor quantum dot-cavity quantum electrodynamics systems. Employing an exact diagonalization approach we find large differences compared to standard methods...

  13. Linewidth statistics of single InGaAs quantum dot photolumincescence lines

    DEFF Research Database (Denmark)

    Leosson, Kristjan; Jensen, Jacob Riis; Hvam, Jørn Märcher

    2000-01-01

    We have used photoluminescence spectroscopy with high spatial and spectral resolution to measure the linewidths of single emission lines from In0.5Ga0.5As/GaAs self-assembled quantum dots. At 10 K, we find a broad, asymmetric distribution of linewidths with a maximum at 50 mu eV. The distribution......-dot luminescence lines depends only weakly on temperature up to 50 K, showing a broadening of 0.4 mu eV/K. Above 50 K, a thermally activated behavior of the linewidth is observed. This temperature dependence is consistent with the discrete energy level structure of the dots....

  14. Mapping the Local Density of Optical States of a Photonic Crystal with Single Quantum Dots

    DEFF Research Database (Denmark)

    Wang, Qin; Stobbe, Søren; Lodahl, Peter

    2011-01-01

    We use single self-assembled InGaAs quantum dots as internal probes to map the local density of optical states of photonic crystal membranes. The employed technique separates contributions from nonradiative recombination and spin-flip processes by properly accounting for the role of the exciton...... fine structure. We observe inhibition factors as high as 70 and compare our results to local density of optical states calculations available from the literature, thereby establishing a quantitative understanding of photon emission in photonic crystal membranes. © 2011 American Physical Society....

  15. Single-flux-quantum logic circuits exploiting collision-based fusion gates

    International Nuclear Information System (INIS)

    Asai, T.; Yamada, K.; Amemiya, Y.

    2008-01-01

    We propose a single-flux-quantum (SFQ) logic circuit based on the fusion computing systems--collision-based and reaction-diffusion fusion computers. A fusion computing system consists of regularly arrayed unit cells (fusion gates), where each unit has two input arms and two output arms and is connected to its neighboring cells with the arms. We designed functional SFQ circuits that implemented the fusion computation. The unit cell was able to be made with ten Josephson junctions. Circuit simulation with standard Nb/Al-AlOx/Nb 2.5-kA/cm 2 process parameters showed that the SFQ fusion computing systems could operate at 10 GHz clock

  16. The Relation between Structure and Quantum Interference in Single Molecule Junctions

    DEFF Research Database (Denmark)

    Markussen, Troels; Stadler, Robert; Thygesen, Kristian Sommer

    2010-01-01

    Quantum interference (QI) of electron pathways has recently attracted increased interest as an enabling tool for single-molecule electronic devices. Although various molecular systems have been shown to exhibit QI effects and a number of methods have been proposed for its analysis, simple...... guidelines linking the molecular structure to QI effects in the phase-coherent transport regime have until now been lacking. In the present work we demonstrate that QI in aromatic molecules is intimately related to the topology of the molecule’s π system and establish a simple graphical scheme to predict...

  17. Quantum theory of single events: Localized de Broglie-wavelets, Schroedinger waves and classical trajectories

    International Nuclear Information System (INIS)

    Barut, A.O.

    1990-06-01

    For an arbitrary potential V with classical trajectories x-vector=g-vector(t) we construct localized oscillating three-dimensional wave lumps ψ(x-vector,t,g-vector) representing a single quantum particle. The crest of the envelope of the ripple follows the classical orbit g-vector(t) slightly modified due to potential V and ψ(x-vector,t;g-vector) satisfies the Schroedinger equation. The field energy, momentum and angular momentum calculated as integrals over all space are equal to particle energy, momentum and angular momentum. The relation to coherent states and to Schroedinger waves are also discussed. (author). 6 refs

  18. Universal holonomic single quantum gates over a geometric spin with phase-modulated polarized light.

    Science.gov (United States)

    Ishida, Naoki; Nakamura, Takaaki; Tanaka, Touta; Mishima, Shota; Kano, Hiroki; Kuroiwa, Ryota; Sekiguchi, Yuhei; Kosaka, Hideo

    2018-05-15

    We demonstrate universal non-adiabatic non-abelian holonomic single quantum gates over a geometric electron spin with phase-modulated polarized light and 93% average fidelity. This allows purely geometric rotation around an arbitrary axis by any angle defined by light polarization and phase using a degenerate three-level Λ-type system in a negatively charged nitrogen-vacancy center in diamond. Since the control light is completely resonant to the ancillary excited state, the demonstrated holonomic gate not only is fast with low power, but also is precise without the dynamical phase being subject to control error and environmental noise. It thus allows pulse shaping for further fidelity.

  19. Hybrid single quantum well InP/Si nanobeam lasers for silicon photonics.

    Science.gov (United States)

    Fegadolli, William S; Kim, Se-Heon; Postigo, Pablo Aitor; Scherer, Axel

    2013-11-15

    We report on a hybrid InP/Si photonic crystal nanobeam laser emitting at 1578 nm with a low threshold power of ~14.7 μW. Laser gain is provided from a single InAsP quantum well embedded in a 155 nm InP layer bonded on a standard silicon-on-insulator wafer. This miniaturized nanolaser, with an extremely small modal volume of 0.375(λ/n)(3), is a promising and efficient light source for silicon photonics.

  20. Quantum Heisenberg antiferromagnetic chains with exchange and single-ion anisotropies

    International Nuclear Information System (INIS)

    Peters, D; Selke, W; McCulloch, I P

    2010-01-01

    Using density matrix renormalization group calculations, ground state properties of the spin-1 Heisenberg chain with exchange and quadratic single-ion anisotropies in an external field are studied, for special choices of the two kinds of anisotropies. In particular, the phase diagram includes antiferromagnetic, spin-liquid (or spin-flop), IS2, and supersolid (or biconical) phases. Especially, new features of the spin-liquid and supersolid phases are discussed. Properties of the quantum chains are compared to those of corresponding classical spin chains.

  1. Computation of Quantum Bound States on a Singly Punctured Two-Torus

    International Nuclear Information System (INIS)

    Kar-Tim Chan; Zainuddin Hishamuddin; Molladavoudi Saeid

    2013-01-01

    We study a quantum mechanical system on a singly punctured two-torus with bound states described by the Maass waveforms which are eigenfunctions of the hyperbolic Laplace—Beltrami operator. Since the discrete eigenvalues of the Maass cusp form are not known analytically, they are solved numerically using an adapted algorithm of Hejhal and Then to compute Maass cusp forms on the punctured two-torus. We report on the computational results of the lower lying eigenvalues for the punctured two-torus and find that they are doubly-degenerate. We also visualize the eigenstates of selected eigenvalues using GridMathematica

  2. Flexible InGaN nanowire membranes for enhanced solar water splitting

    KAUST Repository

    Elafandy, Rami T.; Elafandy, Rami T.; Min, Jung-Wook; Zhao, Chao; Ng, Tien Khee; Ooi, Boon S.

    2018-01-01

    III-Nitride nanowires (NWs) have recently emerged as potential photoelectrodes for efficient solar hydrogen generation. While InGaN NWs epitaxy over silicon is required for high crystalline quality and economic production, it leads to the formation

  3. Blinking effect and the use of quantum dots in single molecule spectroscopy

    International Nuclear Information System (INIS)

    Rombach-Riegraf, Verena; Oswald, Peter; Bienert, Roland; Petersen, Jan; Domingo, M.P.; Pardo, Julian; Gräber, P.; Galvez, E.M.

    2013-01-01

    Highlights: ► It is possible to eliminate the blinking effect of a water-soluble QD. ► We provide a direct method to study protein function and dynamics at the single level. ► QD, potent tool for single molecule studies of biochemical and biological processes. -- Abstract: Luminescent semiconductor nanocrystals (quantum dots, QD) have unique photo-physical properties: high photostability, brightness and narrow size-tunable fluorescence spectra. Due to their unique properties, QD-based single molecule studies have become increasingly more popular during the last years. However QDs show a strong blinking effect (random and intermittent light emission), which may limit their use in single molecule fluorescence studies. QD blinking has been widely studied and some hypotheses have been done to explain this effect. Here we summarise what is known about the blinking effect in QDs, how this phenomenon may affect single molecule studies and, on the other hand, how the “on”/“off” states can be exploited in diverse experimental settings. In addition, we present results showing that site-directed binding of QD to cysteine residues of proteins reduces the blinking effect. This option opens a new possibility of using QDs to study protein–protein interactions and dynamics by single molecule fluorescence without modifying the chemical composition of the solution or the QD surface.

  4. Blinking effect and the use of quantum dots in single molecule spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Rombach-Riegraf, Verena; Oswald, Peter; Bienert, Roland; Petersen, Jan [Albert-Ludwigs-Universitaet Freiburg, Institut fuer Physikalische Chemie, Albertstrasse 23a, 79104 Freiburg (Germany); Domingo, M.P. [Instituto de Carboquimica (CSIC), Miguel Luesma 4, 50018 Zaragoza (Spain); Pardo, Julian [Grupo Apoptosis, Inmunidad y Cancer, Departamento Bioquimica y Biologia Molecular y Celular, Fac. Ciencias, Universidad de Zaragoza, Zaragoza (Spain); Fundacion Aragon I-D (ARAID), Gobierno de Aragon, Zaragoza (Spain); Immune Effector Cells Group, Aragon Health Research Institute (IIS Aragon), Biomedical Research Centre of Aragon (CIBA) Fundacion Aragon I-D - ARAID, Gobierno de Aragon, Zaragoza (Spain); Graeber, P. [Albert-Ludwigs-Universitaet Freiburg, Institut fuer Physikalische Chemie, Albertstrasse 23a, 79104 Freiburg (Germany); Galvez, E.M., E-mail: eva@icb.csic.es [Instituto de Carboquimica (CSIC), Miguel Luesma 4, 50018 Zaragoza (Spain); Immune Effector Cells Group, Aragon Health Research Institute (IIS Aragon), Biomedical Research Centre of Aragon (CIBA) Fundacion Aragon I-D - ARAID, Gobierno de Aragon, Zaragoza (Spain)

    2013-01-04

    Highlights: Black-Right-Pointing-Pointer It is possible to eliminate the blinking effect of a water-soluble QD. Black-Right-Pointing-Pointer We provide a direct method to study protein function and dynamics at the single level. Black-Right-Pointing-Pointer QD, potent tool for single molecule studies of biochemical and biological processes. -- Abstract: Luminescent semiconductor nanocrystals (quantum dots, QD) have unique photo-physical properties: high photostability, brightness and narrow size-tunable fluorescence spectra. Due to their unique properties, QD-based single molecule studies have become increasingly more popular during the last years. However QDs show a strong blinking effect (random and intermittent light emission), which may limit their use in single molecule fluorescence studies. QD blinking has been widely studied and some hypotheses have been done to explain this effect. Here we summarise what is known about the blinking effect in QDs, how this phenomenon may affect single molecule studies and, on the other hand, how the 'on'/'off' states can be exploited in diverse experimental settings. In addition, we present results showing that site-directed binding of QD to cysteine residues of proteins reduces the blinking effect. This option opens a new possibility of using QDs to study protein-protein interactions and dynamics by single molecule fluorescence without modifying the chemical composition of the solution or the QD surface.

  5. Single-nitrogen-vacancy-center quantum memory for a superconducting flux qubit mediated by a ferromagnet

    Science.gov (United States)

    Lai, Yen-Yu; Lin, Guin-Dar; Twamley, Jason; Goan, Hsi-Sheng

    2018-05-01

    We propose a quantum memory scheme to transfer and store the quantum state of a superconducting flux qubit (FQ) into the electron spin of a single nitrogen-vacancy (NV) center in diamond via yttrium iron garnet (YIG), a ferromagnet. Unlike an ensemble of NV centers, the YIG moderator can enhance the effective FQ-NV-center coupling strength without introducing additional appreciable decoherence. We derive the effective interaction between the FQ and the NV center by tracing out the degrees of freedom of the collective mode of the YIG spins. We demonstrate the transfer, storage, and retrieval procedures, taking into account the effects of spontaneous decay and pure dephasing. Using realistic experimental parameters for the FQ, NV center and YIG, we find that a combined transfer, storage, and retrieval fidelity higher than 0.9, with a long storage time of 10 ms, can be achieved. This hybrid system not only acts as a promising quantum memory, but also provides an example of enhanced coupling between various systems through collective degrees of freedom.

  6. From single-shot towards general work extraction in a quantum thermodynamic framework

    International Nuclear Information System (INIS)

    Gemmer, Jochen; Anders, Janet

    2015-01-01

    This paper considers work extraction from a quantum system to a work storage system (or weight) following Horodecki and Oppenheim (2013 Nat. Commun. 4 2059). An alternative approach is here developed that relies on the comparison of subspace dimensions without a need to introduce thermo-majorization used previously. Optimal single shot work for processes where a weight transfers from (a) a single energy level to another single energy level is then re-derived. In addition we discuss the final state of the system after work extraction and show that the system typically ends in its thermal state, while there are cases where the system is only close to it. The work of formation in the single level transfer setting is also re-derived. The approach presented now allows the extension of the single shot work concept to work extraction (b) involving multiple final levels of the weight. A key conclusion here is that the single shot work for case (a) is appropriate only when a resonance of a particular energy is required. When wishing to identify ‘work extraction’ with finding the weight in a specific available energy or any higher energy a broadening of the single shot work concept is required. As a final contribution we consider transformations of the system that (c) result in general weight state transfers. Introducing a transfer-quantity allows us to formulate minimum requirements for transformations to be at all possible in a thermodynamic framework. We show that choosing the free energy difference of the weight as the transfer-quantity one recovers various single shot results including single level transitions (a), multiple final level transitions (b), and recent results on restricted sets of multi-level to multi-level weight transfers. (paper)

  7. Growth mechanism of InGaN nanodots on three-dimensional GaN structures

    Energy Technology Data Exchange (ETDEWEB)

    Park, Donghwy; Min, Daehong; Nam, Okhyun [Department of Nano-Optical Engineering, Convergence Center for Advanced Nano-Semiconductor (CANS), Korea Polytechnic University (KPU), Siheung-si, Gyeonggi-do (Korea, Republic of)

    2017-07-15

    In this study, we investigated the growth mechanism of indium gallium nitride (InGaN) nanodots (NDs) and an InGaN layer, which were simultaneously formed on a three-dimensional (3D) gallium nitride (GaN) structure, having (0001) polar, (11-22) semi-polar, and (11-20) nonpolar facets. We observed the difference in the morphological and compositional properties of the InGaN structures. From the high resolution transmission electron microscopy (HR-TEM) images, it can be seen that the InGaN NDs were formed only on the polar and nonpolar facets, whereas an InGaN layer was formed on the semi-polar facet. The indium composition variation in all the InGaN structures was observed using scanning transmission electron microscopy (STEM) and the energy dispersive X-ray spectroscopy (EDS). The different growth mechanism can be explained by two reasons: (i) The difference in the diffusivities of indium and gallium adatoms at each facet of 3D GaN structure; and (ii) the difference in the kinetic Wulff plots of polar, semi-polar, and nonpolar GaN planes. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. 10-bit rapid single flux quantum digital-to-analog converter for ac voltage standard

    International Nuclear Information System (INIS)

    Maezawa, M; Hirayama, F

    2008-01-01

    Digital-to-analog (D/A) converters based on rapid single flux quantum (RSFQ) technology are under development for ac voltage standard applications. We present design and test results on a prototype 10-bit version integrated on a single chip. The 10-bit chip includes over 6000 Josephson junctions and consumes a bias current exceeding 1 A. To reduce the effects of the high bias current on circuit operation, a custom design method was employed in part and large circuit blocks were divided into smaller ones. The 10-bit chips were fabricated and tested at low speed. The test results suggested that our design approach could manage large bias currents on the order of 1 A per chip

  9. Quantum dash based single section mode locked lasers for photonic integrated circuits.

    Science.gov (United States)

    Joshi, Siddharth; Calò, Cosimo; Chimot, Nicolas; Radziunas, Mindaugas; Arkhipov, Rostislav; Barbet, Sophie; Accard, Alain; Ramdane, Abderrahim; Lelarge, Francois

    2014-05-05

    We present the first demonstration of an InAs/InP Quantum Dash based single-section frequency comb generator designed for use in photonic integrated circuits (PICs). The laser cavity is closed using a specifically designed Bragg reflector without compromising the mode-locking performance of the self pulsating laser. This enables the integration of single-section mode-locked laser in photonic integrated circuits as on-chip frequency comb generators. We also investigate the relations between cavity modes in such a device and demonstrate how the dispersion of the complex mode frequencies induced by the Bragg grating implies a violation of the equi-distance between the adjacent mode frequencies and, therefore, forbids the locking of the modes in a classical Bragg Device. Finally we integrate such a Bragg Mirror based laser with Semiconductor Optical Amplifier (SOA) to demonstrate the monolithic integration of QDash based low phase noise sources in PICs.

  10. Optical spectroscopy of single, planar, self-assembled InAs/InP quantum dots

    International Nuclear Information System (INIS)

    Kim, D.; Williams, R.L.; Lefebvre, J.; Lapointe, J.; Reimer, M.E.; Mckee, J.; Poole, P.J.

    2006-01-01

    We present optical spectra from numerous, single, self-assembled InAs/InP quantum dots. More than 50 individual dots are studied that emit in the 1.1-1.6 mm wavelength range. The dots are of high optical quality as judged by the clean, single exciton emission line at low power, the resolution limited linewidth, and the brightness. Each dot exhibits similar trends in the power evolution spectra, despite large variations in height and diameter. The level splittings in the p -shell increase with decreasing height, which we interpret to be from dot elongation along the [01 anti 1] direction. The evolution of the spectra with increasing power agrees well with predictions from effective bond orbital calculations. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Noncovalent Attachment of PbS Quantum Dots to Single- and Multiwalled Carbon Nanotubes

    Directory of Open Access Journals (Sweden)

    Anirban Das

    2014-01-01

    Full Text Available Attachment of PbS quantum dots (QD to single-walled carbon nanotubes (SWNT and multiwalled carbon nanotubes (MWCNT is described; wherein commercially obtained PbS-QD of size 2.7 nm, stabilized by oleic acid, are added to a suspension of single- or multiwalled carbon nanotubes (CNT prefunctionalized noncovalently with 1,2-benzenedimethanethiol (1,2-BDMT in ethanol. The aromatic part of 1,2-BDMT attaches to the CNT by π-π stacking interactions, noncovalently functionalizing the CNT. The thiol part of the 1,2-BDMT on the functionalized CNT replaces oleic acid on the surface of the QD facilitating the noncovalent attachment of the QD to the CNT. The composites were characterized by TEM and FTIR spectroscopy. Quenching of NIR fluorescence of the PbS-QD on attachment to the carbon nanotubes (CNT was observed, indicating FRET from the QD to the CNT.

  12. Probing quantum entanglement in the Schwarzschild space-time beyond the single-mode approximation

    Science.gov (United States)

    He, Juan; Ding, Zhi-Yong; Ye, Liu

    2018-05-01

    In this paper, we deduce the vacuum structure for Dirac fields in the background of Schwarzschild space-time beyond the single-mode approximation and discuss the performance of quantum entanglement between particle and antiparticle modes of a Dirac field with Hawking effect. It is shown that Hawking radiation does not always destroy the physically accessible entanglement, and entanglement amplification may happen in some cases. This striking result is different from that of the single-mode approximation, which holds that the Hawking radiation can only destroy entanglement. Lastly, we analyze the physically accessible entanglement relation outside the event horizon and demonstrate that the monogamy inequality is constantly established regardless of the choice of given parameters.

  13. Single-particle model of a strongly driven, dense, nanoscale quantum ensemble

    Science.gov (United States)

    DiLoreto, C. S.; Rangan, C.

    2018-01-01

    We study the effects of interatomic interactions on the quantum dynamics of a dense, nanoscale, atomic ensemble driven by a strong electromagnetic field. We use a self-consistent, mean-field technique based on the pseudospectral time-domain method and a full, three-directional basis to solve the coupled Maxwell-Liouville equations. We find that interatomic interactions generate a decoherence in the state of an ensemble on a much faster time scale than the excited-state lifetime of individual atoms. We present a single-particle model of the driven, dense ensemble by incorporating interactions into a dephasing rate. This single-particle model reproduces the essential physics of the full simulation and is an efficient way of rapidly estimating the collective dynamics of a dense ensemble.

  14. Assessing the Nonequilibrium Thermodynamics in a Quenched Quantum Many-Body System via Single Projective Measurements

    Directory of Open Access Journals (Sweden)

    L. Fusco

    2014-08-01

    Full Text Available We analyze the nature of the statistics of the work done on or by a quantum many-body system brought out of equilibrium. We show that, for the sudden quench and for an initial state that commutes with the initial Hamiltonian, it is possible to retrieve the whole nonequilibrium thermodynamics via single projective measurements of observables. We highlight, in a physically clear way, the qualitative implications for the statistics of work coming from considering processes described by operators that either commute or do not commute with the unperturbed Hamiltonian of a given system. We consider a quantum many-body system and derive an expression that allows us to give a physical interpretation, for a thermal initial state, to all of the cumulants of the work in the case of quenched operators commuting with the unperturbed Hamiltonian. In the commuting case, the observables that we need to measure have an intuitive physical meaning. Conversely, in the noncommuting case, we show that, although it is possible to operate fully within the single-measurement framework irrespectively of the size of the quench, some difficulties are faced in providing a clear-cut physical interpretation to the cumulants. This circumstance makes the study of the physics of the system nontrivial and highlights the nonintuitive phenomenology of the emergence of thermodynamics from the fully quantum microscopic description. We illustrate our ideas with the example of the Ising model in a transverse field showing the interesting behavior of the high-order statistical moments of the work distribution for a generic thermal state and linking them to the critical nature of the model itself.

  15. Heralded quantum repeater based on the scattering of photons off single emitters in one-dimensional waveguides

    Energy Technology Data Exchange (ETDEWEB)

    Song, Guo-Zhu; Zhang, Mei; Ai, Qing; Yang, Guo-Jian [Department of Physics, Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875 (China); Alsaedi, Ahmed; Hobiny, Aatef [NAAM-Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589 (Saudi Arabia); Deng, Fu-Guo, E-mail: fgdeng@bnu.edu.cn [Department of Physics, Applied Optics Beijing Area Major Laboratory, Beijing Normal University, Beijing 100875 (China); NAAM-Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589 (Saudi Arabia)

    2017-03-15

    We propose a heralded quantum repeater based on the scattering of photons off single emitters in one-dimensional waveguides. We show the details by implementing nonlocal entanglement generation, entanglement swapping, and entanglement purification modules with atoms in waveguides, and discuss the feasibility of the repeater with currently achievable technology. In our scheme, the faulty events can be discarded by detecting the polarization of the photons. That is, our protocols are accomplished with a fidelity of 100% in principle, which is advantageous for implementing realistic long-distance quantum communication. Moreover, additional atomic qubits are not required, but only a single-photon medium. Our scheme is scalable and attractive since it can be realized in solid-state quantum systems. With the great progress on controlling atom-waveguide systems, the repeater may be very useful in quantum information processing in the future.

  16. Quantum Point Contact Single-Nucleotide Conductance for DNA and RNA Sequence Identification.

    Science.gov (United States)

    Afsari, Sepideh; Korshoj, Lee E; Abel, Gary R; Khan, Sajida; Chatterjee, Anushree; Nagpal, Prashant

    2017-11-28

    Several nanoscale electronic methods have been proposed for high-throughput single-molecule nucleic acid sequence identification. While many studies display a large ensemble of measurements as "electronic fingerprints" with some promise for distinguishing the DNA and RNA nucleobases (adenine, guanine, cytosine, thymine, and uracil), important metrics such as accuracy and confidence of base calling fall well below the current genomic methods. Issues such as unreliable metal-molecule junction formation, variation of nucleotide conformations, insufficient differences between the molecular orbitals responsible for single-nucleotide conduction, and lack of rigorous base calling algorithms lead to overlapping nanoelectronic measurements and poor nucleotide discrimination, especially at low coverage on single molecules. Here, we demonstrate a technique for reproducible conductance measurements on conformation-constrained single nucleotides and an advanced algorithmic approach for distinguishing the nucleobases. Our quantum point contact single-nucleotide conductance sequencing (QPICS) method uses combed and electrostatically bound single DNA and RNA nucleotides on a self-assembled monolayer of cysteamine molecules. We demonstrate that by varying the applied bias and pH conditions, molecular conductance can be switched ON and OFF, leading to reversible nucleotide perturbation for electronic recognition (NPER). We utilize NPER as a method to achieve >99.7% accuracy for DNA and RNA base calling at low molecular coverage (∼12×) using unbiased single measurements on DNA/RNA nucleotides, which represents a significant advance compared to existing sequencing methods. These results demonstrate the potential for utilizing simple surface modifications and existing biochemical moieties in individual nucleobases for a reliable, direct, single-molecule, nanoelectronic DNA and RNA nucleotide identification method for sequencing.

  17. Inside Perovskites: Quantum Luminescence from Bulk Cs4PbBr6 Single Crystals

    KAUST Repository

    de Bastiani, Michele

    2017-08-01

    Zero-dimensional perovskite-related structures (0D-PRS) are a new frontier of perovskite-based materials. 0D-PRS, commonly synthesized in powder form, manifest distinctive optical properties such as strong photoluminescence (PL), narrow emission linewidth, and high exciton binding energy. These properties make 0D-PRS compelling for several types of optoelectronic applications, including phosphor screens and electroluminescent devices. However, it would not be possible to rationally design the chemistry and structure of these materials, without revealing the origins of their optical behaviour, which is contradictory to the well-studied APbX3 perovskites. In this work, we synthesize single crystals of Cs4PbBr6 0D-PRS, and investigated the origins of their unique optical and electronic properties. The crystals exhibit a PL quantum yield higher than 40%, the highest reported for perovskite-based single crystals. Time-resolved and temperature dependent PL studies, supported by DFT calculations, and structural analysis, elucidate an emissive behaviour reminiscent of a quantum confined structure rather than a typical bulk perovskite material.

  18. Microwave-Controlled Generation of Shaped Single Photons in Circuit Quantum Electrodynamics

    Directory of Open Access Journals (Sweden)

    M. Pechal

    2014-10-01

    Full Text Available Large-scale quantum information processors or quantum communication networks will require reliable exchange of information between spatially separated nodes. The links connecting these nodes can be established using traveling photons that need to be absorbed at the receiving node with high efficiency. This is achievable by shaping the temporal profile of the photons and absorbing them at the receiver by time reversing the emission process. Here, we demonstrate a scheme for creating shaped microwave photons using a superconducting transmon-type three-level system coupled to a transmission line resonator. In a second-order process induced by a modulated microwave drive, we controllably transfer a single excitation from the third level of the transmon to the resonator and shape the emitted photon. We reconstruct the density matrices of the created single-photon states and show that the photons are antibunched. We also create multipeaked photons with a controlled amplitude and phase. In contrast to similar existing schemes, the one we present here is based solely on microwave drives, enabling operation with fixed frequency transmons.

  19. Non-linear effects and thermoelectric efficiency of quantum dot-based single-electron transistors.

    Science.gov (United States)

    Talbo, Vincent; Saint-Martin, Jérôme; Retailleau, Sylvie; Dollfus, Philippe

    2017-11-01

    By means of advanced numerical simulation, the thermoelectric properties of a Si-quantum dot-based single-electron transistor operating in sequential tunneling regime are investigated in terms of figure of merit, efficiency and power. By taking into account the phonon-induced collisional broadening of energy levels in the quantum dot, both heat and electrical currents are computed in a voltage range beyond the linear response. Using our homemade code consisting in a 3D Poisson-Schrödinger solver and the resolution of the Master equation, the Seebeck coefficient at low bias voltage appears to be material independent and nearly independent on the level broadening, which makes this device promising for metrology applications as a nanoscale standard of Seebeck coefficient. Besides, at higher voltage bias, the non-linear characteristics of the heat current are shown to be related to the multi-level effects. Finally, when considering only the electronic contribution to the thermal conductance, the single-electron transistor operating in generator regime is shown to exhibit very good efficiency at maximum power.

  20. Single-step colloidal quantum dot films for infrared solar harvesting

    KAUST Repository

    Kiani, Amirreza

    2016-11-01

    Semiconductors with bandgaps in the near- to mid-infrared can harvest solar light that is otherwise wasted by conventional single-junction solar cell architectures. In particular, colloidal quantum dots (CQDs) are promising materials since they are cost-effective, processed from solution, and have a bandgap that can be tuned into the infrared (IR) via the quantum size effect. These characteristics enable them to harvest the infrared portion of the solar spectrum to which silicon is transparent. To date, IR CQD solar cells have been made using a wasteful and complex sequential layer-by-layer process. Here, we demonstrate ∼1 eV bandgap solar-harvesting CQD films deposited in a single step. By engineering a fast-drying solvent mixture for metal iodide-capped CQDs, we deposited active layers greater than 200 nm in thickness having a mean roughness less than 1 nm. We integrated these films into infrared solar cells that are stable in air and exhibit power conversion efficiencies of 3.5% under illumination by the full solar spectrum, and 0.4% through a simulated silicon solar cell filter.

  1. Quantum

    CERN Document Server

    Al-Khalili, Jim

    2003-01-01

    In this lively look at quantum science, a physicist takes you on an entertaining and enlightening journey through the basics of subatomic physics. Along the way, he examines the paradox of quantum mechanics--beautifully mathematical in theory but confoundingly unpredictable in the real world. Marvel at the Dual Slit experiment as a tiny atom passes through two separate openings at the same time. Ponder the peculiar communication of quantum particles, which can remain in touch no matter how far apart. Join the genius jewel thief as he carries out a quantum measurement on a diamond without ever touching the object in question. Baffle yourself with the bizzareness of quantum tunneling, the equivalent of traveling partway up a hill, only to disappear then reappear traveling down the opposite side. With its clean, colorful layout and conversational tone, this text will hook you into the conundrum that is quantum mechanics.

  2. Quantum dot tailored to single wall carbon nanotubes: a multifunctional hybrid nanoconstruct for cellular imaging and targeted photothermal therapy.

    Science.gov (United States)

    Nair, Lakshmi V; Nagaoka, Yutaka; Maekawa, Toru; Sakthikumar, D; Jayasree, Ramapurath S

    2014-07-23

    Hybrid nanomaterial based on quantum dots and SWCNTs is used for cellular imaging and photothermal therapy. Furthermore, the ligand conjugated hybrid system (FaQd@CNT) enables selective targeting in cancer cells. The imaging capability of quantum dots and the therapeutic potential of SWCNT are available in a single system with cancer targeting property. Heat generated by the system is found to be high enough to destroy cancer cells. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Nanoscale quantum gyroscope using a single 13C nuclear spin coupled with a nearby NV center in diamond

    Science.gov (United States)

    Song, Xuerui; Wang, Liujun; Feng, Fupan; Lou, Liren; Diao, Wenting; Duan, Chongdi

    2018-03-01

    Developing gyroscopes based on quantum systems are important for inertial sensing applications, and its underlying physics is of fundamental interest. In this paper, we proposed a new type of gyroscope based on the Berry phase generated during rotation of the quantum system by using a single 13C nuclear spin coupled with a nearby nitrogen-vacancy center in diamond. Due to the atom-scale size of the quantum system, rotation information can be obtained with high spatial resolution. The gyroscope can be manipulated at room temperature and without the need for a strong magnetic field, which is also beneficial to its further applications.

  4. Operation of a quantum dot in the finite-state machine mode: Single-electron dynamic memory

    Energy Technology Data Exchange (ETDEWEB)

    Klymenko, M. V. [Department of Chemistry, University of Liège, B4000 Liège (Belgium); Klein, M. [The Fritz Haber Center for Molecular Dynamics and the Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Levine, R. D. [The Fritz Haber Center for Molecular Dynamics and the Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904 (Israel); Crump Institute for Molecular Imaging and Department of Molecular and Medical Pharmacology, David Geffen School of Medicine and Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095 (United States); Remacle, F., E-mail: fremacle@ulg.ac.be [Department of Chemistry, University of Liège, B4000 Liège (Belgium); The Fritz Haber Center for Molecular Dynamics and the Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904 (Israel)

    2016-07-14

    A single electron dynamic memory is designed based on the non-equilibrium dynamics of charge states in electrostatically defined metallic quantum dots. Using the orthodox theory for computing the transfer rates and a master equation, we model the dynamical response of devices consisting of a charge sensor coupled to either a single and or a double quantum dot subjected to a pulsed gate voltage. We show that transition rates between charge states in metallic quantum dots are characterized by an asymmetry that can be controlled by the gate voltage. This effect is more pronounced when the switching between charge states corresponds to a Markovian process involving electron transport through a chain of several quantum dots. By simulating the dynamics of electron transport we demonstrate that the quantum box operates as a finite-state machine that can be addressed by choosing suitable shapes and switching rates of the gate pulses. We further show that writing times in the ns range and retention memory times six orders of magnitude longer, in the ms range, can be achieved on the double quantum dot system using experimentally feasible parameters, thereby demonstrating that the device can operate as a dynamic single electron memory.

  5. Operation of a quantum dot in the finite-state machine mode: Single-electron dynamic memory

    International Nuclear Information System (INIS)

    Klymenko, M. V.; Klein, M.; Levine, R. D.; Remacle, F.

    2016-01-01

    A single electron dynamic memory is designed based on the non-equilibrium dynamics of charge states in electrostatically defined metallic quantum dots. Using the orthodox theory for computing the transfer rates and a master equation, we model the dynamical response of devices consisting of a charge sensor coupled to either a single and or a double quantum dot subjected to a pulsed gate voltage. We show that transition rates between charge states in metallic quantum dots are characterized by an asymmetry that can be controlled by the gate voltage. This effect is more pronounced when the switching between charge states corresponds to a Markovian process involving electron transport through a chain of several quantum dots. By simulating the dynamics of electron transport we demonstrate that the quantum box operates as a finite-state machine that can be addressed by choosing suitable shapes and switching rates of the gate pulses. We further show that writing times in the ns range and retention memory times six orders of magnitude longer, in the ms range, can be achieved on the double quantum dot system using experimentally feasible parameters, thereby demonstrating that the device can operate as a dynamic single electron memory.

  6. Effects of underlying InGaN/GaN superlattice structures on the structural and optical properties of InGaN LEDs

    Energy Technology Data Exchange (ETDEWEB)

    Tsai, Chia-Lung, E-mail: cltsai@mail.cgu.edu.tw

    2016-06-15

    This study proposes the use of InGaN/GaN superlattices grown beneath InGaN multiple quantum wells (MQWs) and designed with different well widths to act as an electron emitter layer (EEL). Cross-sectional transmission electron microscopy reveals strong indium segregation in the underlying superlattices with a 5-nm-thick In{sub 0.1}Ga{sub 0.9}N well, thus corrupting the crystalline perfection of the resulting LEDs, and also increasing their leakage current. It was also found that the depth of the localized states increases with the well width of the underlying superlattices. In the proposed LEDs, variation in the biaxial strains of the superlattice EELs with different well widths results in an increase in indium incorporation of InGaN MQWs, thus obtaining a redshifted photoluminescence emission with respect to that of normal LED. Furthermore, the presence of relatively strong carrier localization and the alleviation of electron leakage from the InGaN MQWs results in improved light output performance from the proposed LEDs grown with a narrow In{sub 0.1}Ga{sub 0.9}N well in the underlying superlattices. Although growth in a wide In{sub 0.1}Ga{sub 0.9}N well (~3.5 nm) containing underlying superlattices suffers from poor crystalline quality due to partial strain relaxation, it resulted in improved roll-off behavior in terms of light intensity. This may be due to the improved hot electron cooling capacity mitigating the extent of carrier leakage. - Highlights: • In{sub 0.1}Ga{sub 0.9}N/GaN superlattices are used as an electron emitter layer. • Improved LED performance can be achieved using a narrow In{sub 0.1}Ga{sub 0.9}N well. • A wider well can further reduce carrier leakage despite poor quality is presented.

  7. Spectroscopy of size dependent many-particle effects in single self-assembled semiconductor quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Dal Savio, C.

    2006-02-20

    Single InAs quantum dots (QDs) grown with the Stranski-Krastanov method in a In{sub 0.12}Ga{sub 0.88}As quantum well embedded in GaAs and emitting in the near infrared have been optically investigated. To perform QD spectroscopy at low temperatures a very stable micro-photoluminescence ({mu}-PL) microscope set-up fully integrated in a liquid helium (LHe) cryostate has been successfully developed. The system is based on the cold finger technique and a Fourier Transform (FT) spectrometer combined with a nitrogen cooled Ge detector. Photoluminescence of the QDs was excited non resonantly with a He-Ne laser and single dot spectroscopy was carried out at temperatures below 60 K. The experimental set-up allows mapping of the optical emission by recording spectra for every point of a scan grid. This mapping mode is used to acquire optical images and to locate a particular dot for investigation. Series of measurement on a single QD were normally performed over a long time (from a few days to a week), with the need of daily adjustment in the sub-micrometer range. At low excitation power a single sharp line (E{sub x}) arising from recombination of a single exciton in the dot is observed. Varying the excitation density the spectra become more complex, with appearance of the biexciton emission line (E{sub xx}) on the lower energies side of the E{sub x} line, followed by emission from excitons occupying higher shells in the dot. Measured biexciton binding energies and power dependence are in good agreement with values reported in the literature. The temperature dependence of the optical emission was investigated. The energy shows the characteristic decrease related to the shrinking of the semiconductor band gap, while the linewidth evolution is compatible with broadening due to coupling with acoustic and optical phonons. A statistics of biexciton binding energies over a dozen of dots was acquired and the results compared with single QD spectroscopy data available in the

  8. Solid-phase single molecule biosensing using dual-color colocalization of fluorescent quantum dot nanoprobes

    Science.gov (United States)

    Liu, Jianbo; Yang, Xiaohai; Wang, Kemin; Wang, Qing; Liu, Wei; Wang, Dong

    2013-10-01

    The development of solid-phase surface-based single molecule imaging technology has attracted significant interest during the past decades. Here we demonstrate a sandwich hybridization method for highly sensitive detection of a single thrombin protein at a solid-phase surface based on the use of dual-color colocalization of fluorescent quantum dot (QD) nanoprobes. Green QD560-modified thrombin binding aptamer I (QD560-TBA I) were deposited on a positive poly(l-lysine) assembled layer, followed by bovine serum albumin blocking. It allowed the thrombin protein to mediate the binding of the easily detectable red QD650-modified thrombin binding aptamer II (QD650-TBA II) to the QD560-TBA I substrate. Thus, the presence of the target thrombin can be determined based on fluorescent colocalization measurements of the nanoassemblies, without target amplification or probe separation. The detection limit of this assay reached 0.8 pM. This fluorescent colocalization assay has enabled single molecule recognition in a separation-free detection format, and can serve as a sensitive biosensing platform that greatly suppresses the nonspecific adsorption false-positive signal. This method can be extended to other areas such as multiplexed immunoassay, single cell analysis, and real time biomolecule interaction studies.The development of solid-phase surface-based single molecule imaging technology has attracted significant interest during the past decades. Here we demonstrate a sandwich hybridization method for highly sensitive detection of a single thrombin protein at a solid-phase surface based on the use of dual-color colocalization of fluorescent quantum dot (QD) nanoprobes. Green QD560-modified thrombin binding aptamer I (QD560-TBA I) were deposited on a positive poly(l-lysine) assembled layer, followed by bovine serum albumin blocking. It allowed the thrombin protein to mediate the binding of the easily detectable red QD650-modified thrombin binding aptamer II (QD650-TBA II) to

  9. IBIC characterisation of novel detectors for single atom doping of quantum computer devices

    International Nuclear Information System (INIS)

    Yang Changyi; Jamieson, David N.; Pakes, Chris I.; George, Damien P.; Hearne, Sean M.; Dzurak, Andrew S.; Gauja, Eric; Stanley, F.; Clark, R.G.

    2003-01-01

    Single ion implantation and online detection is highly desirable for the emerging application, in which single 31 P ions need to be inserted in prefabricated silicon cells to construct solid-state quantum bits (qubits). In order to fabricate qubit arrays, we have developed novel detectors that employ detector electrodes adjacent to the prefabricated cells that can detect single keV ion strikes appropriate for the fabrication of shallow phosphorus arrays. The method utilises a high purity silicon substrate with very high resistivity, a thin SiO 2 surface layer, nanometer masks for the lateral positioning single phosphorus implantation, biased electrodes applied to the surface of the silicon and sensitive electronics that can detect the charge transient from single keV ion strikes. A TCAD (Technology Computer Aided Design) software package was applied in the optimisation of the device design and simulation of the detector performance. Here we show the characterisation of these detectors using ion beam induced charge (IBIC) with a focused 2 MeV He ions in a nuclear microprobe. The IBIC imaging method in a nuclear microprobe allowed us to measure the dead-layer thickness of the detector structure (required to be very thin for successful detection of keV ions), and the spatial distribution of the charge collection efficiency around the entire region of the detector. We show that our detectors have near 100% charge collection efficiency for MeV ions, extremely thin dead-layer thickness (about 7 nm) and a wide active region extending laterally from the electrodes (10-20 μm) where qubit arrays can be constructed. We demonstrate that the device can be successfully applied in the detection of keV ionisation energy from single events of keV X-rays and keV 31 P ions

  10. IBIC characterisation of novel detectors for single atom doping of quantum computer devices

    Energy Technology Data Exchange (ETDEWEB)

    Yang Changyi E-mail: cjy@physics.unimelb.edu.auc.yang@physics.unimelb.edu.au; Jamieson, David N.; Pakes, Chris I.; George, Damien P.; Hearne, Sean M.; Dzurak, Andrew S.; Gauja, Eric; Stanley, F.; Clark, R.G

    2003-09-01

    Single ion implantation and online detection is highly desirable for the emerging application, in which single {sup 31}P ions need to be inserted in prefabricated silicon cells to construct solid-state quantum bits (qubits). In order to fabricate qubit arrays, we have developed novel detectors that employ detector electrodes adjacent to the prefabricated cells that can detect single keV ion strikes appropriate for the fabrication of shallow phosphorus arrays. The method utilises a high purity silicon substrate with very high resistivity, a thin SiO{sub 2} surface layer, nanometer masks for the lateral positioning single phosphorus implantation, biased electrodes applied to the surface of the silicon and sensitive electronics that can detect the charge transient from single keV ion strikes. A TCAD (Technology Computer Aided Design) software package was applied in the optimisation of the device design and simulation of the detector performance. Here we show the characterisation of these detectors using ion beam induced charge (IBIC) with a focused 2 MeV He ions in a nuclear microprobe. The IBIC imaging method in a nuclear microprobe allowed us to measure the dead-layer thickness of the detector structure (required to be very thin for successful detection of keV ions), and the spatial distribution of the charge collection efficiency around the entire region of the detector. We show that our detectors have near 100% charge collection efficiency for MeV ions, extremely thin dead-layer thickness (about 7 nm) and a wide active region extending laterally from the electrodes (10-20 {mu}m) where qubit arrays can be constructed. We demonstrate that the device can be successfully applied in the detection of keV ionisation energy from single events of keV X-rays and keV {sup 31}P ions.

  11. High spin cycles: topping the spin record for a single molecule verging on quantum criticality

    Science.gov (United States)

    Baniodeh, Amer; Magnani, Nicola; Lan, Yanhua; Buth, Gernot; Anson, Christopher E.; Richter, Johannes; Affronte, Marco; Schnack, Jürgen; Powell, Annie K.

    2018-03-01

    The cyclisation of a short chain into a ring provides fascinating scenarios in terms of transforming a finite array of spins into a quasi-infinite structure. If frustration is present, theory predicts interesting quantum critical points, where the ground state and thus low-temperature properties of a material change drastically upon even a small variation of appropriate external parameters. This can be visualised as achieving a very high and pointed summit where the way down has an infinity of possibilities, which by any parameter change will be rapidly chosen, in order to reach the final ground state. Here we report a mixed 3d/4f cyclic coordination cluster that turns out to be very near or even at such a quantum critical point. It has a ground state spin of S = 60, the largest ever observed for a molecule (120 times that of a single electron). [Fe10Gd10(Me-tea)10(Me-teaH)10(NO3)10].20MeCN forms a nano-torus with alternating gadolinium and iron ions with a nearest neighbour Fe-Gd coupling and a frustrating next-nearest neighbour Fe-Fe coupling. Such a spin arrangement corresponds to a cyclic delta or saw-tooth chain, which can exhibit unusual frustration effects. In the present case, the quantum critical point bears a `flatland' of tens of thousands of energetically degenerate states between which transitions are possible at no energy costs with profound caloric consequences. Entropy-wise the energy flatland translates into the pointed summit overlooking the entropy landscape. Going downhill several target states can be reached depending on the applied physical procedure which offers new prospects for addressability.

  12. Macroscopic quantum tunneling in Josephson tunnel junctions and Coulomb blockade in single small tunnel junctions

    International Nuclear Information System (INIS)

    Cleland, A.N.

    1991-04-01

    Experiments investigating the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very small capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters; the tunneling rate in the moderately damped (Q ∼ 1) junction is seen to be reduced by a factor of 300 from that predicted for an undamped junction. The phase is seen to be a good quantum-mechanical variable. The experiments on small capacitance tunnel junctions extend the measurements on the larger-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wavefunction has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias. I present the first clear observation of the Coulomb blockade in single junctions. The electrical environment of the tunnel junction, however, strongly affects the behavior of the junction: higher resistance leads are observed to greatly sharpen the Coulomb blockade over that seen with lower resistance leads. I present theoretical descriptions of how the environment influences the junctions; comparisons with the experimental results are in reasonable agreement

  13. Manifestation of spin selection rules on the quantum tunneling of magnetization in a single-molecule magnet.

    Science.gov (United States)

    Henderson, J J; Koo, C; Feng, P L; del Barco, E; Hill, S; Tupitsyn, I S; Stamp, P C E; Hendrickson, D N

    2009-07-03

    We present low temperature magnetometry measurements on a new Mn3 single-molecule magnet in which the quantum tunneling of magnetization (QTM) displays clear evidence for quantum mechanical selection rules. A QTM resonance appearing only at high temperatures demonstrates tunneling between excited states with spin projections differing by a multiple of three. This is dictated by the C3 molecular symmetry, which forbids pure tunneling from the lowest metastable state. Transverse field resonances are understood by correctly orienting the Jahn-Teller axes of the individual manganese ions and including transverse dipolar fields. These factors are likely to be important for QTM in all single-molecule magnets.

  14. The photonic nanowire: an emerging platform for highly efficient single-photon sources for quantum information applications

    DEFF Research Database (Denmark)

    Gregersen, Niels; Munsch, Mathieu; Malik, Nitin S.

    2013-01-01

    Efficient coupling between a localized quantum emitter and a well defined optical channel represents a powerful route to realize single-photon sources and spin-photon interfaces. The tailored fiber-like photonic nanowire embedding a single quantum dot has recently demonstrated an appealing...... potential. However, the device requires a delicate, sharp needle-like taper with performance sensitive to minute geometrical details. To overcome this limitation we demonstrate the photonic trumpet, exploiting an opposite tapering strategy. The trumpet features a strongly Gaussian far-field emission...

  15. Suppression of Magnetic Quantum Tunneling in a Chiral Single-Molecule Magnet by Ferromagnetic Interactions.

    Science.gov (United States)

    Lippert, Kai-Alexander; Mukherjee, Chandan; Broschinski, Jan-Philipp; Lippert, Yvonne; Walleck, Stephan; Stammler, Anja; Bögge, Hartmut; Schnack, Jürgen; Glaser, Thorsten

    2017-12-18

    Single-molecule magnets (SMMs) retain a magnetization without applied magnetic field for a decent time due to an energy barrier U for spin-reversal. Despite the success to increase U, the difficult to control magnetic quantum tunneling often leads to a decreased effective barrier U eff and a fast relaxation. Here, we demonstrate the influence of the exchange coupling on the tunneling probability in two heptanuclear SMMs hosting the same spin-system with the same high spin ground state S t = 21/2. A chirality-induced symmetry reduction leads to a switch of the Mn III -Mn III exchange from antiferromagnetic in the achiral SMM [Mn III 6 Cr III ] 3+ to ferromagnetic in the new chiral SMM RR [Mn III 6 Cr III ] 3+ . Multispin Hamiltonian analysis by full-matrix diagonalization demonstrates that the ferromagnetic interactions in RR [Mn III 6 Cr III ] 3+ enforce a well-defined S t = 21/2 ground state with substantially less mixing of M S substates in contrast to [Mn III 6 Cr III ] 3+ and no tunneling pathways below the top of the energy barrier. This is experimentally verified as U eff is smaller than the calculated energy barrier U in [Mn III 6 Cr III ] 3+ due to tunneling pathways, whereas U eff equals U in RR [Mn III 6 Cr III ] 3+ demonstrating the absence of quantum tunneling.

  16. Inelastic tunneling of electrons through a quantum dot with an embedded single molecular magnet

    Science.gov (United States)

    Chang, Bo; Liang, J.-Q.

    2010-06-01

    We report a theoretical analysis of electron transport through a quantum dot with an embedded biaxial single-molecule magnet (SMM) based on mapping of the many-body interaction-system onto a one-body problem by means of the non-equilibrium Green function technique. It is found that the conducting current exhibits a stepwise behavior and the nonlinear differential conductance displays additional peaks with variation of the sweeping speed and the magnitude of magnetic field. This observation can be interpreted by the interaction of electron-spin with the SMM and the quantum tunneling of magnetization. The inelastic conductance and the corresponding tunneling processes are investigated with normal as well as ferromagnetic electrodes. In the case of ferromagnetic configuration, the coupling to the SMM leads to an asymmetric tunneling magnetoresistance (TMR), which can be enhanced or suppressed greatly in certain regions. Moreover, a sudden TMR-switch with the variation of magnetic field is observed, which is seen to be caused by the inelastic tunneling.

  17. Inelastic tunneling of electrons through a quantum dot with an embedded single molecular magnet

    Energy Technology Data Exchange (ETDEWEB)

    Chang Bo [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan, Shanxi 030006 (China); Liang, J.-Q., E-mail: jqliang@sxu.edu.c [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan, Shanxi 030006 (China)

    2010-06-28

    We report a theoretical analysis of electron transport through a quantum dot with an embedded biaxial single-molecule magnet (SMM) based on mapping of the many-body interaction-system onto a one-body problem by means of the non-equilibrium Green function technique. It is found that the conducting current exhibits a stepwise behavior and the nonlinear differential conductance displays additional peaks with variation of the sweeping speed and the magnitude of magnetic field. This observation can be interpreted by the interaction of electron-spin with the SMM and the quantum tunneling of magnetization. The inelastic conductance and the corresponding tunneling processes are investigated with normal as well as ferromagnetic electrodes. In the case of ferromagnetic configuration, the coupling to the SMM leads to an asymmetric tunneling magnetoresistance (TMR), which can be enhanced or suppressed greatly in certain regions. Moreover, a sudden TMR-switch with the variation of magnetic field is observed, which is seen to be caused by the inelastic tunneling.

  18. Modeling satellite-Earth quantum channel downlinks with adaptive-optics coupling to single-mode fibers

    Science.gov (United States)

    Gruneisen, Mark T.; Flanagan, Michael B.; Sickmiller, Brett A.

    2017-12-01

    The efficient coupling of photons from a free-space quantum channel into a single-mode optical fiber (SMF) has important implications for quantum network concepts involving SMF interfaces to quantum detectors, atomic systems, integrated photonics, and direct coupling to a fiber network. Propagation through atmospheric turbulence, however, leads to wavefront errors that degrade mode matching with SMFs. In a free-space quantum channel, this leads to photon losses in proportion to the severity of the aberration. This is particularly problematic for satellite-Earth quantum channels, where atmospheric turbulence can lead to significant wavefront errors. This report considers propagation from low-Earth orbit to a terrestrial ground station and evaluates the efficiency with which photons couple either through a circular field stop or into an SMF situated in the focal plane of the optical receiver. The effects of atmospheric turbulence on the quantum channel are calculated numerically and quantified through the quantum bit error rate and secure key generation rates in a decoy-state BB84 protocol. Numerical simulations include the statistical nature of Kolmogorov turbulence, sky radiance, and an adaptive-optics system under closed-loop control.

  19. Quantum discord and classical correlation signatures of mobility edges in one-dimensional aperiodic single-electron systems

    International Nuclear Information System (INIS)

    Gong, Longyan; Zhu, Hao; Zhao, Shengmei; Cheng, Weiwen; Sheng, Yubo

    2012-01-01

    We investigate numerically the quantum discord and the classical correlation in a one-dimensional slowly varying potential model and a one-dimensional Soukoulis–Economou ones, respectively. There are well-defined mobility edges in the slowly varying potential model, while there are discrepancies on mobility edges in the Soukoulis–Economou ones. In the slowly varying potential model, we find that extended and localized states can be distinguished by both the quantum discord and the classical correlation. There are sharp transitions in the quantum discord and the classical correlation at mobility edges. Based on these, we study “mobility edges” in the Soukoulis–Economou model using the quantum discord and the classical correlation, which gives another perspectives for these “mobility edges”. All these provide us good quantities, i.e., the quantum discord and the classical correlation, to reflect mobility edges in these one-dimensional aperiodic single-electron systems. Moreover, our studies propose a consistent interpretation of the discrepancies between previous numerical results about the Soukoulis–Economou model. -- Highlights: ► Quantum discord and classical correlation can signal mobility edges in two models. ► An interpretation for mobility edges in the Soukoulis–Economou model is proposed. ► Quantum discord and classical correlation can reflect well localization properties.

  20. A high frequency test bench for rapid single-flux-quantum circuits

    International Nuclear Information System (INIS)

    Engseth, H; Intiso, S; Rafique, M R; Tolkacheva, E; Kidiyarova-Shevchenko, A

    2006-01-01

    We have designed and experimentally verified a test bench for high frequency testing of rapid single-flux-quantum (RSFQ) circuits. This test bench uses an external tunable clock signal that is stable in amplitude, phase and frequency. The high frequency external clock reads out the clock pattern stored in a long shift register. The clock pattern is consequently shifted out at high speed and split to feed both the circuit under test and an additional shift register in the test bench for later verification at low speed. This method can be employed for reliable high speed verification of RSFQ circuit operation, with use of only low speed read-out electronics. The test bench consists of 158 Josephson junctions and the occupied area is 3300 x 660 μm 2 . It was experimentally verified up to 33 GHz with ± 21.7% margins on the global bias supply current

  1. Field emission of carbon quantum dots synthesized from a single organic solvent.

    Science.gov (United States)

    Liu, Xiahui; Yang, Bingjun; Yang, Juan; Yu, Shengxue; Chen, Jiangtao

    2016-11-04

    In this paper, a facile synthesis of carbon quantum dots (CQDs) and its field emission performance are reported. The CQDs are prepared from a single N, N-dimethylformamide acting as carbon and nitrogen-doping sources simultaneously. The CQDs are investigated by photoluminescence, transmission electron microscopy and x-ray photoelectron spectroscopy. The CQDs have an average size of 3 nm and are doped with N atoms. CQD dispersion shows strong fluorescence under UV illumination. For the first time, the field emission behavior of CQDs coated on Si substrate is studied. As a candidate of cold cathode, the CQDs display good field emission performance. The CQD emitter reaches the current density of 1.1 mA cm(-2) at 7.0 V μm(-1) and exhibits good long-term emission stability, suggesting promising application in field emission devices.

  2. Thermally Assisted Macroscopic Quantum Resonance on a Single-Crystal of Mn12-ac

    Science.gov (United States)

    Lionti, F.; Thomas, L.; Ballou, R.; Wernsdorfer, W.; Barbara, B.; Sulpice, A.; Sessoli, R.; Gatteschi, D.

    1997-03-01

    Magnetization measurements have been performed on a single mono-crystal of the molecule Mn12-acetate (L. Thomas, F. Lionti, R. Ballou, R. Sessoli, D. Gatteschi and B. Barbara, Nature, 383, 145 (1996).). Steps were observed in the hysteresis loop for values of the applied field at which level crossings of the collective spin states of each manganese clusters take place. The influence of quartic terms is taken into account. At these fields, the magnetization relaxes at short time scales, being otherwise essentially blocked. This novel behavior is interpreted in terms of resonant quantum tunneling of the magnetization from thermally activated energy levels. Hysteresis loop measurements performed for different field orientations and ac-susceptibility experiments, confirm general trends of this picture.

  3. Phase locking of a semiconductor double-quantum-dot single-atom maser

    Science.gov (United States)

    Liu, Y.-Y.; Hartke, T. R.; Stehlik, J.; Petta, J. R.

    2017-11-01

    We experimentally study the phase stabilization of a semiconductor double-quantum-dot (DQD) single-atom maser by injection locking. A voltage-biased DQD serves as an electrically tunable microwave frequency gain medium. The statistics of the maser output field demonstrate that the maser can be phase locked to an external cavity drive, with a resulting phase noise L =-99 dBc/Hz at a frequency offset of 1.3 MHz. The injection locking range, and the phase of the maser output relative to the injection locking input tone are in good agreement with Adler's theory. Furthermore, the electrically tunable DQD energy level structure allows us to rapidly switch the gain medium on and off, resulting in an emission spectrum that resembles a frequency comb. The free running frequency comb linewidth is ≈8 kHz and can be improved to less than 1 Hz by operating the comb in the injection locked regime.

  4. Reference-Frame-Independent and Measurement-Device-Independent Quantum Key Distribution Using One Single Source

    Science.gov (United States)

    Li, Qian; Zhu, Changhua; Ma, Shuquan; Wei, Kejin; Pei, Changxing

    2018-04-01

    Measurement-device-independent quantum key distribution (MDI-QKD) is immune to all detector side-channel attacks. However, practical implementations of MDI-QKD, which require two-photon interferences from separated independent single-photon sources and a nontrivial reference alignment procedure, are still challenging with current technologies. Here, we propose a scheme that significantly reduces the experimental complexity of two-photon interferences and eliminates reference frame alignment by the combination of plug-and-play and reference frame independent MDI-QKD. Simulation results show that the secure communication distance can be up to 219 km in the finite-data case and the scheme has good potential for practical MDI-QKD systems.

  5. Single-Molecule Electronics with Cross- Conjugated Molecules: Quantum Interference, IETS and Non-Equilibrium "Temperatures"

    DEFF Research Database (Denmark)

    Jørgensen, Jacob Lykkebo

    Abstract The idea of using single-molecules as components in electronic devices is fas- cinating. For this idea to come into fruition, a number of technical and theo- retical challenges must be overcome. In this PhD thesis, the electron-phonon interaction is studied for a special class of molecules......, which is characterised by destructive quantum interference. The molecules are cross-conjugated, which means that the two parts of the molecules are conjugated to a third part, but not to each other. This gives rise to an anti-resonance in the trans- mission. In the low bias and low temperature regime......-conjugated molecules. We nd that the vibrational modes that would be expected to dominate, following the propensity, rules are very weak. Instead, other modes are found to be the dominant ones. We study this phenomenon for a number of cross-conjugated molecules, and link these ndings to the anti...

  6. Electronic fine structure and recombination dynamics in single InAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Seguin, R.

    2008-01-28

    In the work at hand single InAs/GaAs quantum dots (QDs) are examined via cathodoluminescence spectroscopy. A thorough analysis of the spectra leads to an unambiguous assignment of the lines to the decay of specific excitonic complexes. A special aspect of the Coulomb interaction, the exchange interaction, gives rise to a fine structure in the initial and final states of an excitonic decay. This leads to a fine structure in the emission spectra that again is unique for every excitonic complex. The exchange interaction is discussed in great detail in this work.QDs of different sizes are investigated and the influence on the electronic properties is monitored. Additionally, the structure is modified ex situ by a thermal annealing process. The changes of the spectra under different annealing temperatures are traced. Finally, recombination dynamics of different excitonic complexes are examined by performing time-resolved cathodoluminescence spectroscopy. (orig.)

  7. 3 ns single-shot read-out in a quantum dot-based memory structure

    International Nuclear Information System (INIS)

    Nowozin, T.; Bimberg, D.; Beckel, A.; Lorke, A.; Geller, M.

    2014-01-01

    Fast read-out of two to six charges per dot from the ground and first excited state in a quantum dot (QD)-based memory is demonstrated using a two-dimensional electron gas. Single-shot measurements on modulation-doped field-effect transistor structures with embedded InAs/GaAs QDs show read-out times as short as 3 ns. At low temperature (T = 4.2 K) this read-out time is still limited by the parasitics of the setup and the device structure. Faster read-out times and a larger read-out signal are expected for an improved setup and device structure

  8. Seniority in quantum many-body systems. I. Identical particles in a single shell

    Energy Technology Data Exchange (ETDEWEB)

    Van Isacker, P., E-mail: isacker@ganil.fr [Grand Accélérateur National d’Ions Lourds, CEA/DSM–CNRS/IN2P3, BP 55027, F-14076 Caen Cedex 5 (France); Heinze, S. [Institut für Kernphysik der Universität zu Köln, 50937 Köln (Germany)

    2014-10-15

    A discussion of the seniority quantum number in many-body systems is presented. The analysis is carried out for bosons and fermions simultaneously but is restricted to identical particles occupying a single shell. The emphasis of the paper is on the possibility of partial conservation of seniority which turns out to be a peculiar property of spin-9/2 fermions but prevalent in systems of interacting bosons of any spin. Partial conservation of seniority is at the basis of the existence of seniority isomers, frequently observed in semi-magic nuclei, and also gives rise to peculiar selection rules in one-nucleon transfer reactions. - Highlights: • Unified derivation of conditions for the total and partial conservation of seniority. • General analysis of the partial conservation of seniority in boson systems. • Why partial conservation of seniority is crucial for seniority isomers in nuclei. • The effect of partial conservation of seniority on one-nucleon transfer intensities.

  9. Stable Single-Mode Operation of Distributed Feedback Quantum Cascade Laser by Optimized Reflectivity Facet Coatings

    Science.gov (United States)

    Wang, Dong-Bo; Zhang, Jin-Chuan; Cheng, Feng-Min; Zhao, Yue; Zhuo, Ning; Zhai, Shen-Qiang; Wang, Li-Jun; Liu, Jun-Qi; Liu, Shu-Man; Liu, Feng-Qi; Wang, Zhan-Guo

    2018-02-01

    In this work, quantum cascade lasers (QCLs) based on strain compensation combined with two-phonon resonance design are presented. Distributed feedback (DFB) laser emitting at 4.76 μm was fabricated through a standard buried first-order grating and buried heterostructure (BH) processing. Stable single-mode emission is achieved under all injection currents and temperature conditions without any mode hop by the optimized antireflection (AR) coating on the front facet. The AR coating consists of a double layer dielectric of Al2O3 and Ge. For a 2-mm laser cavity, the maximum output power of the AR-coated DFB-QCL was more than 170 mW at 20 °C with a high wall-plug efficiency (WPE) of 4.7% in a continuous-wave (CW) mode.

  10. Photoluminescence of a single InAs/AlAs quantum dot

    International Nuclear Information System (INIS)

    Shamirzaev, T.S.; Zhuravlev, K.S.; Larsson, M.; Holtz, P.O.

    2008-01-01

    Micro-photoluminescence (μ-PL) of a simple InAs/AlAs quantum dot (QD) has been studied. It has been found that the μ-PL emission related to the recombination in a single QD is strongly broadened probably due to spectral diffusion. Emissions related to the recombination of biexcitons and excitons occupying excited levels of the QD are observed in μ-PL spectra at high excitation power densities. A red shift of the μ-PL emissions related to recombination of excitons in the ground and excited levels of the QD with increasing excitation power gives clear evidence for type I alignment of the InAs/AlAs QD. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Electronic fine structure and recombination dynamics in single InAs quantum dots

    International Nuclear Information System (INIS)

    Seguin, R.

    2008-01-01

    In the work at hand single InAs/GaAs quantum dots (QDs) are examined via cathodoluminescence spectroscopy. A thorough analysis of the spectra leads to an unambiguous assignment of the lines to the decay of specific excitonic complexes. A special aspect of the Coulomb interaction, the exchange interaction, gives rise to a fine structure in the initial and final states of an excitonic decay. This leads to a fine structure in the emission spectra that again is unique for every excitonic complex. The exchange interaction is discussed in great detail in this work.QDs of different sizes are investigated and the influence on the electronic properties is monitored. Additionally, the structure is modified ex situ by a thermal annealing process. The changes of the spectra under different annealing temperatures are traced. Finally, recombination dynamics of different excitonic complexes are examined by performing time-resolved cathodoluminescence spectroscopy. (orig.)

  12. Single-quantum annihilation of positrons with shell-bound atomic electrons

    International Nuclear Information System (INIS)

    Palathingal, J.C.; Asoka-Kumar, P.; Lynn, K.G.; Posada, Y.; Wu, X.Y.

    1991-01-01

    The single-quantum annihilation of positrons has been studied experimentally with a positron beam and a thin lead target, at energies 1 MeV and higher. Spectral peaks corresponding to the K, L, and M shells have been resolved and observed distinctly for the first time. The shell ratios L/K and M/K have been determined. An analysis of the L peak has yielded the (LII+LIII)/L ratio. The first measurements of the directional distributions of the annihilation quanta of the three individual electron shells are also reported. The results are in agreement with theory. They also point out the potential for applying the phenomena to the development of a tunable, highly directional gamma-ray source

  13. Detection of single electron spin resonance in a double quantum dota)

    Science.gov (United States)

    Koppens, F. H. L.; Buizert, C.; Vink, I. T.; Nowack, K. C.; Meunier, T.; Kouwenhoven, L. P.; Vandersypen, L. M. K.

    2007-04-01

    Spin-dependent transport measurements through a double quantum dot are a valuable tool for detecting both the coherent evolution of the spin state of a single electron, as well as the hybridization of two-electron spin states. In this article, we discuss a model that describes the transport cycle in this regime, including the effects of an oscillating magnetic field (causing electron spin resonance) and the effective nuclear fields on the spin states in the two dots. We numerically calculate the current flow due to the induced spin flips via electron spin resonance, and we study the detector efficiency for a range of parameters. The experimental data are compared with the model and we find a reasonable agreement.

  14. From quantum physics to digital communication: Single sideband continuous phase modulation

    Science.gov (United States)

    Farès, Haïfa; Christian Glattli, D.; Louët, Yves; Palicot, Jacques; Moy, Christophe; Roulleau, Preden

    2018-01-01

    In the present paper, we propose a new frequency-shift keying continuous phase modulation (FSK-CPM) scheme having, by essence, the interesting feature of single-sideband (SSB) spectrum providing a very compact frequency occupation. First, the original principle, inspired from quantum physics (levitons), is presented. Besides, we address the problem of low-complexity coherent detection of this new waveform, based on orthonormal wave functions used to perform matched filtering for efficient demodulation. Consequently, this shows that the proposed modulation can operate using existing digital communication technology, since only well-known operations are performed (e.g., filtering, integration). This SSB property can be exploited to allow large bit rates transmissions at low carrier frequency without caring about image frequency degradation effects typical of ordinary double-sideband signals. xml:lang="fr"

  15. Seniority in quantum many-body systems. I. Identical particles in a single shell

    International Nuclear Information System (INIS)

    Van Isacker, P.; Heinze, S.

    2014-01-01

    A discussion of the seniority quantum number in many-body systems is presented. The analysis is carried out for bosons and fermions simultaneously but is restricted to identical particles occupying a single shell. The emphasis of the paper is on the possibility of partial conservation of seniority which turns out to be a peculiar property of spin-9/2 fermions but prevalent in systems of interacting bosons of any spin. Partial conservation of seniority is at the basis of the existence of seniority isomers, frequently observed in semi-magic nuclei, and also gives rise to peculiar selection rules in one-nucleon transfer reactions. - Highlights: • Unified derivation of conditions for the total and partial conservation of seniority. • General analysis of the partial conservation of seniority in boson systems. • Why partial conservation of seniority is crucial for seniority isomers in nuclei. • The effect of partial conservation of seniority on one-nucleon transfer intensities

  16. Two-photon interference at telecom wavelengths for time-bin-encoded single photons from quantum-dot spin qubits.

    Science.gov (United States)

    Yu, Leo; Natarajan, Chandra M; Horikiri, Tomoyuki; Langrock, Carsten; Pelc, Jason S; Tanner, Michael G; Abe, Eisuke; Maier, Sebastian; Schneider, Christian; Höfling, Sven; Kamp, Martin; Hadfield, Robert H; Fejer, Martin M; Yamamoto, Yoshihisa

    2015-11-24

    Practical quantum communication between remote quantum memories rely on single photons at telecom wavelengths. Although spin-photon entanglement has been demonstrated in atomic and solid-state qubit systems, the produced single photons at short wavelengths and with polarization encoding are not suitable for long-distance communication, because they suffer from high propagation loss and depolarization in optical fibres. Establishing entanglement between remote quantum nodes would further require the photons generated from separate nodes to be indistinguishable. Here, we report the observation of correlations between a quantum-dot spin and a telecom single photon across a 2-km fibre channel based on time-bin encoding and background-free frequency downconversion. The downconverted photon at telecom wavelengths exhibits two-photon interference with another photon from an independent source, achieving a mean wavepacket overlap of greater than 0.89 despite their original wavelength mismatch (900 and 911 nm). The quantum-networking operations that we demonstrate will enable practical communication between solid-state spin qubits across long distances.

  17. Simplifying the complex 1H NMR spectra of fluorine-substituted benzamides by spin system filtering and spin-state selection: multiple-quantum-single-quantum correlation.

    Science.gov (United States)

    Baishya, Bikash; Reddy, G N Manjunatha; Prabhu, Uday Ramesh; Row, T N Guru; Suryaprakash, N

    2008-10-23

    The proton NMR spectra of fluorine-substituted benzamides are very complex (Figure 1) due to severe overlap of (1)H resonances from the two aromatic rings, in addition to several short and long-range scalar couplings experienced by each proton. With no detectable scalar couplings between the inter-ring spins, the (1)H NMR spectra can be construed as an overlap of spectra from two independent phenyl rings. In the present study we demonstrate that it is possible to separate the individual spectrum for each aromatic ring by spin system filtering employing the multiple-quantum-single-quantum correlation methodology. Furthermore, the two spin states of fluorine are utilized to simplify the spectrum corresponding to each phenyl ring by the spin-state selection. The demonstrated technique reduces spectral complexity by a factor of 4, in addition to permitting the determination of long-range couplings of less than 0.2 Hz and the relative signs of heteronuclear couplings. The technique also aids the judicious choice of the spin-selective double-quantum-single-quantum J-resolved experiment to determine the long-range homonuclear couplings of smaller magnitudes.

  18. In(1-x)Ga(x)N@ZnO: a rationally designed and quantum dot integrated material for water splitting and solar harvesting applications.

    Science.gov (United States)

    Rajaambal, Sivaraman; Mapa, Maitri; Gopinath, Chinnakonda S

    2014-09-07

    The highly desirable combination of the visible light absorption properties of In1-xGaxN Quantum dots (QD) along with the multifunctionality of ZnO into a single integrated material was prepared for solar harvesting. This is the first report on InGaN QD integrated with ZnO (InGaN@ZnO), synthesized by a highly reproducible, simple combustion method in 15 min. Structural, microstructural and electronic integration of the nitride and oxide components of InGaN@ZnO was demonstrated by appropriate characterization methods. Self-assembly of InGaN QD is induced in growing nascent zinc oxo nanoclusters taking advantage of the common wurtzite structure and nitrogen incorporation at the expense of oxygen vacancies. Direct integration brings about a single phase structure exhibiting extensive visible light absorption and high photostability. InGaN@ZnO suggests synergistic operation of light harvesting and charge conducting components for solar H2 generation without using any co-catalyst or sacrificial agent, and a promising photocurrent generation at 0 V under visible light illumination. The present study suggests a direct integration of QD with the host matrix and is a potential method to realize the advantages of QDs.

  19. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces; Rastertunnelmikroskopie und -spektroskopie an GaN- und InGaN-Oberflaechen

    Energy Technology Data Exchange (ETDEWEB)

    Krueger, David

    2009-12-02

    Optelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1 anti 100)- and especially the (anti 2110)-plane are quite corrugated. For the first time, the (anti 2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STMmeasurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping. (orig.)

  20. Metal-organic chemical vapor deposition of high quality, high indium composition N-polar InGaN layers for tunnel devices

    Science.gov (United States)

    Lund, Cory; Romanczyk, Brian; Catalano, Massimo; Wang, Qingxiao; Li, Wenjun; DiGiovanni, Domenic; Kim, Moon J.; Fay, Patrick; Nakamura, Shuji; DenBaars, Steven P.; Mishra, Umesh K.; Keller, Stacia

    2017-05-01

    In this study, the growth of high quality N-polar InGaN films by metalorganic chemical vapor deposition is presented with a focus on growth process optimization for high indium compositions and the structural and tunneling properties of such films. Uniform InGaN/GaN multiple quantum well stacks with indium compositions up to 0.46 were grown with local compositional analysis performed by energy-dispersive X-ray spectroscopy within a scanning transmission electron microscope. Bright room-temperature photoluminescence up to 600 nm was observed for films with indium compositions up to 0.35. To study the tunneling behavior of the InGaN layers, N-polar GaN/In0.35Ga0.65N/GaN tunnel diodes were fabricated which reached a maximum current density of 1.7 kA/cm2 at 5 V reverse bias. Temperature-dependent measurements are presented and confirm tunneling behavior under reverse bias.