Efficient quantum walk on a quantum processor

Science.gov (United States)

Qiang, Xiaogang; Loke, Thomas; Montanaro, Ashley; Aungskunsiri, Kanin; Zhou, Xiaoqi; O'Brien, Jeremy L.; Wang, Jingbo B.; Matthews, Jonathan C. F.

2016-01-01

The random walk formalism is used across a wide range of applications, from modelling share prices to predicting population genetics. Likewise, quantum walks have shown much potential as a framework for developing new quantum algorithms. Here we present explicit efficient quantum circuits for implementing continuous-time quantum walks on the circulant class of graphs. These circuits allow us to sample from the output probability distributions of quantum walks on circulant graphs efficiently. We also show that solving the same sampling problem for arbitrary circulant quantum circuits is intractable for a classical computer, assuming conjectures from computational complexity theory. This is a new link between continuous-time quantum walks and computational complexity theory and it indicates a family of tasks that could ultimately demonstrate quantum supremacy over classical computers. As a proof of principle, we experimentally implement the proposed quantum circuit on an example circulant graph using a two-qubit photonics quantum processor. PMID:27146471

High-efficiency red electroluminescent device based on multishelled InP quantum dots.

Science.gov (United States)

Jo, Jung-Ho; Kim, Jong-Hoon; Lee, Ki-Heon; Han, Chang-Yeol; Jang, Eun-Pyo; Do, Young Rag; Yang, Heesun

2016-09-01

We report on the synthesis of highly fluorescent red-emitting InP quantum dots (QDs) and their application to the fabrication of a high-efficiency QD-light-emitting diode (QLED). The core/shell heterostructure of the QDs is elaborately tailored toward a multishelled structure with a composition-gradient ZnSeS intermediate shell and an outer ZnS shell. Using the resulting InP/ZnSeS/ZnS QDs as an emitting layer, all-solution-processible red InP QLEDs are fabricated with a hybrid multilayered device structure having an organic hole transport layer (HTL) and an inorganic ZnO nanoparticle electron transport layer. Two HTLs of poly(9-vinlycarbazole) or poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenyl-amine), whose hole mobilities are different by at least three orders of magnitude, are individually applied for QLED fabrication and such HTL-dependent device performances are compared. Our best red device displays exceptional figures of merit such as a maximum luminance of 2849  cd/m2, a current efficiency of 4.2  cd/A, and an external quantum efficiency of 2.5%.

High-Efficiency Colloidal Quantum Dot Photovoltaics via Robust Self-Assembled Monolayers

KAUST Repository

Kim, Gi-Hwan

2015-11-11

© 2015 American Chemical Society. The optoelectronic tunability offered by colloidal quantum dots (CQDs) is attractive for photovoltaic applications but demands proper band alignment at electrodes for efficient charge extraction at minimal cost to voltage. With this goal in mind, self-assembled monolayers (SAMs) can be used to modify interface energy levels locally. However, to be effective SAMs must be made robust to treatment using the various solvents and ligands required for to fabricate high quality CQD solids. We report robust self-assembled monolayers (R-SAMs) that enable us to increase the efficiency of CQD photovoltaics. Only by developing a process for secure anchoring of aromatic SAMs, aided by deposition of the SAMs in a water-free deposition environment, were we able to provide an interface modification that was robust against the ensuing chemical treatments needed in the fabrication of CQD solids. The energy alignment at the rectifying interface was tailored by tuning the R-SAM for optimal alignment relative to the CQD quantum-confined electron energy levels. This resulted in a CQD PV record power conversion efficiency (PCE) of 10.7% with enhanced reproducibility relative to controls.

High Quantum Efficiency 1024x1024 Longwave Infrared SLS FPA and Camera, Phase II

Data.gov (United States)

National Aeronautics and Space Administration — We propose a high quantum efficiency (QE) 1024x1024 longwave infrared focal plane array (LWIR FPA) and CAMERA with ~ 12 micron cutoff wavelength made from...

High Efficiency Quantum Dot III-V Multijunction Solar Cell for Space Power, Phase II

Data.gov (United States)

National Aeronautics and Space Administration — We are proposing to utilize quantum dots to develop a super high-efficiency multijunction III-V solar cell for space. In metamorphic triple junction space solar...

Efficient experimental design of high-fidelity three-qubit quantum gates via genetic programming

Science.gov (United States)

Devra, Amit; Prabhu, Prithviraj; Singh, Harpreet; Arvind; Dorai, Kavita

2018-03-01

We have designed efficient quantum circuits for the three-qubit Toffoli (controlled-controlled-NOT) and the Fredkin (controlled-SWAP) gate, optimized via genetic programming methods. The gates thus obtained were experimentally implemented on a three-qubit NMR quantum information processor, with a high fidelity. Toffoli and Fredkin gates in conjunction with the single-qubit Hadamard gates form a universal gate set for quantum computing and are an essential component of several quantum algorithms. Genetic algorithms are stochastic search algorithms based on the logic of natural selection and biological genetics and have been widely used for quantum information processing applications. We devised a new selection mechanism within the genetic algorithm framework to select individuals from a population. We call this mechanism the "Luck-Choose" mechanism and were able to achieve faster convergence to a solution using this mechanism, as compared to existing selection mechanisms. The optimization was performed under the constraint that the experimentally implemented pulses are of short duration and can be implemented with high fidelity. We demonstrate the advantage of our pulse sequences by comparing our results with existing experimental schemes and other numerical optimization methods.

Structural Investigation of Cesium Lead Halide Perovskites for High-Efficiency Quantum Dot Light-Emitting Diodes

Energy Technology Data Exchange (ETDEWEB)

Le, Quyet Van [School; Kim, Jong Beom [Department; Kim, Soo Young [School; Lee, Byeongdu [X-ray; Lee, Dong Ryeol [Department

2017-08-15

We have investigated the effect of reaction temperature of hot-injection method on the structural properties of CsPbX3 (X: Br, I, Cl) perovskite nanocrystals (NCs) using the small- and wide-angle X-ray scattering. It is confirmed that the size of the NCs decreased as the reaction temperature decreased, resulting stronger quantum confinement. The cubic-phase perovskite NCs were formed despite the reaction temperatures increased from 140 to 180 °C. However, monodispersive NC cubes which are required for densely packing self-assembly film were only formed at lower temperatures. From the X-ray scattering measurements, the spin-coated film from more monodispersive perovskite nanocubes synthesized at lower temperatures resulted in more preferred orientation. This dense-packing perovskite film with preferred orientation yielded efficient light-emitting diode (LED) performance. Thus, the dense-packing structure of NC assemblies formed after spin-coating should be considered for high-efficient LEDs based on perovskite quantum dots in addition to quantum confinement effect of the quantum dots.

Highly Efficient Red and White Organic Light-Emitting Diodes with External Quantum Efficiency beyond 20% by Employing Pyridylimidazole-Based Metallophosphors.

Science.gov (United States)

Miao, Yanqin; Tao, Peng; Wang, Kexiang; Li, Hongxin; Zhao, Bo; Gao, Long; Wang, Hua; Xu, Bingshe; Zhao, Qiang

2017-11-01

Two highly efficient red neutral iridium(III) complexes, Ir1 and Ir2, were rationally designed and synthesized by selecting two pyridylimidazole derivatives as the ancillary ligands. Both Ir1 and Ir2 show nearly the same photoluminescence emission with the maximum peak at 595 nm (shoulder band at about 638 nm) and achieve high solution quantum yields of up to 0.47 for Ir1 and 0.57 for Ir2. Employing Ir1 and Ir2 as emitters, the fabricated red organic light-emitting diodes (OLEDs) show outstanding performance with the maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 20.98%, 33.04 cd/A, and 33.08 lm/W for the Ir1-based device and 22.15%, 36.89 cd/A, and 35.85 lm/W for the Ir2-based device, respectively. Furthermore, using Ir2 as red emitter, a trichromatic hybrid white OLED, showing good warm white emission with low correlated color temperature of white device also realizes excellent device efficiencies with the maximum EQE, CE, and PE reaching 22.74%, 44.77 cd/A, and 46.89 lm/W, respectively. Such high electroluminescence performance for red and white OLEDs indicates that Ir1 and Ir2 as efficient red phosphors have great potential for future OLED displays and lightings applications.

Femtosecond laser direct writing of gratings and waveguides in high quantum efficiency erbium-doped Baccarat glass

International Nuclear Information System (INIS)

Vishnubhatla, K C; Kumar, R Sai Santosh; Rao, D Narayana; Rao, S Venugopal; Osellame, R; Ramponi, R; Bhaktha, S N B; Mattarelli, M; Montagna, M; Turrell, S; Chiappini, A; Chiasera, A; Ferrari, M; Righini, G C

2009-01-01

The femtosecond laser direct writing technique was employed to inscribe gratings and waveguides in high quantum efficiency erbium-doped Baccarat glass. Using the butt coupling technique, a systematic study of waveguide loss with respect to input pulse energy and writing speed was performed to achieve the best waveguide with low propagation loss (PL). By pumping at 980 nm, we observed signal enhancement in these active waveguides in the telecom spectral region. The refractive index change was smooth and we estimated it to be ∼10 -3 . The high quantum efficiency (∼80%) and a best PL of ∼0.9 dB cm -1 combined with signal enhancement makes Baccarat glass a potential candidate for application in photonics.

High Quantum Efficiency Back-Illuminated AlGaN-Based Solar-Blind Ultraviolet p—i—n Photodetectors

International Nuclear Information System (INIS)

Wang Guo-Sheng; Lu Hai; Xie Feng; Chen Dun-Jun; Ren Fang-Fang; Zhang Rong; Zheng You-Dou

2012-01-01

AlGaN-based back-illuminated solar-blind ultraviolet (UV) p—i—n photodetectors (PDs) with high quantum efficiency are fabricated on sapphire substrates. To improve the overall performance of the PD, a series of structural design considerations and growth procedures are implemented in the epitaxy process. A distinct wavelength-selective photo-response peak of the PD is obtained in the solar-blind region. When operating in photovoltaic mode, the PD exhibits a solar-blind/UV rejection ratio of up to 4 orders of magnitude and a peak responsivity of ∼113.5 mA/W at 270 nm, which corresponds to an external quantum efficiency of ∼52%. Under a reverse bias of −5 V, the PD shows a low dark current of ∼1.8 pA and an enhanced peak quantum efficiency of ∼64%. The thermal noise limited detectivity is estimated to be ∼ 3.3 × 10 13 cm·Hz 1/2 W −1

Quantum autoencoders for efficient compression of quantum data

Science.gov (United States)

Romero, Jonathan; Olson, Jonathan P.; Aspuru-Guzik, Alan

2017-12-01

Classical autoencoders are neural networks that can learn efficient low-dimensional representations of data in higher-dimensional space. The task of an autoencoder is, given an input x, to map x to a lower dimensional point y such that x can likely be recovered from y. The structure of the underlying autoencoder network can be chosen to represent the data on a smaller dimension, effectively compressing the input. Inspired by this idea, we introduce the model of a quantum autoencoder to perform similar tasks on quantum data. The quantum autoencoder is trained to compress a particular data set of quantum states, where a classical compression algorithm cannot be employed. The parameters of the quantum autoencoder are trained using classical optimization algorithms. We show an example of a simple programmable circuit that can be trained as an efficient autoencoder. We apply our model in the context of quantum simulation to compress ground states of the Hubbard model and molecular Hamiltonians.

High Efficiency Quantum Well Waveguide Solar Cells and Methods for Constructing the Same

Science.gov (United States)

Welser, Roger E. (Inventor); Sood, Ashok K. (Inventor)

2014-01-01

Photon absorption, and thus current generation, is hindered in conventional thin-film solar cell designs, including quantum well structures, by the limited path length of incident light passing vertically through the device. Optical scattering into lateral waveguide structures provides a physical mechanism to increase photocurrent generation through in-plane light trapping. However, the insertion of wells of high refractive index material with lower energy gap into the device structure often results in lower voltage operation, and hence lower photovoltaic power conversion efficiency. The voltage output of an InGaAs quantum well waveguide photovoltaic device can be increased by employing a III-V material structure with an extended wide band gap emitter heterojunction. Analysis of the light IV characteristics reveals that non-radiative recombination components of the underlying dark diode current have been reduced, exposing the limiting radiative recombination component and providing a pathway for realizing solar-electric conversion efficiency of 30% or more in single junction cells.

Spectrometric performances of high quantum efficiency multi and single anode PMTs coupled to LaBr3(Ce) crystal

Energy Technology Data Exchange (ETDEWEB)

Cinti, Maria Nerina, E-mail: marianerina.cinti@uniroma1.it [Department of Molecular Medicine, Sapienza University of Rome, Rome 00161 (Italy); INFN Rome 1 Section, Rome (Italy); Pani, Roberto; Pellegrini, Rosanna [Department of Molecular Medicine, Sapienza University of Rome, Rome 00161 (Italy); INFN Rome 1 Section, Rome (Italy); Bennati, Paolo [Department of Molecular Medicine, Sapienza University of Rome, Rome 00161 (Italy); Orlandi, Chiara [Medical Physics Post Graduate School, Sapienza University of Rome, Rome 00161 (Italy); Fabbri, Andrea [Department of Physics, Roma Tre University, Rome (Italy); INFN Rome 3 Section, Rome (Italy); Ridolfi, Stefano; Scafè, Raffaele [Department of Molecular Medicine, Sapienza University of Rome, Rome 00161 (Italy)

2013-10-01

High quantum efficiency semiconductor photodetectors have recently drawn the attention of the scientific community for their potential in the realization of a new class of scintillation imagers with very high energy and spatial resolution performance. However, this goal does not seem within easy reach, due to various technological issues such as, for example, the difficulty to scale the characteristics of a single detector to an imager with suitable dimensions. Lately a definite technical improvement in increasing quantum efficiency up to 42% for position sensitive photomultipliers was achieved. The aim of this work is thus to test this new technological progress and to study the possible implications in imaging applications. Four Hamamatsu PMTs were tested: two multi anode photomultipliers, one with a bialkali (27% quantum efficiency) and the other one with a super-bialkali photocathode (38% quantum efficiency), and two 1×1 in. PMTs, both equipped with an ultra bialkali photocathode (42% quantum efficiency). In particular one of the ultra bialkali PMT has also an increased efficiency of first dynode charge collection. The results were compared with the ones obtained with a reference PMT (Hamamatsu R6231), mainly used in spectroscopy. The PMTs were coupled to LaBr3(Ce), NaI(Tl) and LSO(Ce) continuous scintillation crystals. The tests were done using two independent electronic chains: one dedicated for spectroscopic application and a second one, using a multi wire 64 channel readout, for imaging applications. The super-bialkali MA-PMTs have shown high energy resolution, both with spectroscopic and imaging setup, highlighting the appropriateness of these devices for the development of imaging devices with high spectroscopic performance. -- Highlights: • A study of energy resolution results coming from position sensitive photomultipliers are proposed. • The study is also extended on mono- anode photomultiplier. • The selected scintillation crystal is LeBr3(Ce

High-efficiency wavefunction updates for large scale Quantum Monte Carlo

Science.gov (United States)

Kent, Paul; McDaniel, Tyler; Li, Ying Wai; D'Azevedo, Ed

Within ab intio Quantum Monte Carlo (QMC) simulations, the leading numerical cost for large systems is the computation of the values of the Slater determinants in the trial wavefunctions. The evaluation of each Monte Carlo move requires finding the determinant of a dense matrix, which is traditionally iteratively evaluated using a rank-1 Sherman-Morrison updating scheme to avoid repeated explicit calculation of the inverse. For calculations with thousands of electrons, this operation dominates the execution profile. We propose a novel rank- k delayed update scheme. This strategy enables probability evaluation for multiple successive Monte Carlo moves, with application of accepted moves to the matrices delayed until after a predetermined number of moves, k. Accepted events grouped in this manner are then applied to the matrices en bloc with enhanced arithmetic intensity and computational efficiency. This procedure does not change the underlying Monte Carlo sampling or the sampling efficiency. For large systems and algorithms such as diffusion Monte Carlo where the acceptance ratio is high, order of magnitude speedups can be obtained on both multi-core CPU and on GPUs, making this algorithm highly advantageous for current petascale and future exascale computations.

High Efficiency Multijunction Solar Cells with Finely-Tuned Quantum Wells

Science.gov (United States)

Varonides, Argyrios C.

The field of high efficiency (inorganic) photovoltaics (PV) is rapidly maturing in both efficiency goals and cover all cost reduction of fabrication. On one hand, know-how from space industry in new solar cell design configurations and on the other, fabrication cost reduction challenges for terrestrial uses of solar energy, have paved the way to a new generation of PV devices, capable of capturing most of the solar spectrum. For quite a while now, the goal of inorganic solar cell design has been the total (if possible) capture-absorption of the solar spectrum from a single solar cell, designed in such a way that a multiple of incident wavelengths could be simultaneously absorbed. Multi-absorption in device physics indicates parallel existence of different materials that absorb solar photons of different energies. Bulk solid state devices absorb at specific energy thresholds, depending on their respective energy gap (EG). More than one energy gaps would on principle offer new ways of photon absorption: if such a structure could be fabricated, two or more groups of photons could be absorbed simultaneously. The point became then what lattice-matched semiconductor materials could offer such multiple levels of absorption without much recombination losses. It was soon realized that such layer multiplicity combined with quantum size effects could lead to higher efficiency collection of photo-excited carriers. At the moment, the main reason that slows down quantum effect solar cell production is high fabrication cost, since it involves primarily expensive methods of multilayer growth. Existing multi-layer cells are fabricated in the bulk, with three (mostly) layers of lattice-matched and non-lattice-matched (pseudo-morphic) semiconductor materials (GaInP/InGaN etc), where photo-carrier collection occurs in the bulk of the base (coming from the emitter which lies right under the window layer). These carriers are given excess to conduction via tunnel junction (grown between

Time Dependent Quantum Efficiency and Dark Current Measurements in an RF Photocathode Injector with a High Quantum Efficiency Cathode

CERN Document Server

Fliller, Raymond P; Hartung, Walter

2005-01-01

A system was developed at INFN Milano for preparing cesium telluride photo-cathodes and transferring them into an RF gun under ultra-high vacuum. This system has been in use at the Fermilab NICADD Photo-Injector Laboratory (FNPL) since 1997. A similar load-lock system is used at the TeSLA Test Facility at DESY-Hamburg. Two 1.625-cell high duty cycle RF guns have been fabricated for the project. Studies of the photo-emission and field emission ("dark current") behavior of both RF guns have been carried out. Unexpected phenomena were observed in one of the RF guns. In situ changes in the cathode's quantum efficiency and dark current with time were seen during operation of the photo-injector. These changes were correlated with the magnetostatic field at the cathode.* In addition, multipacting is observed in the RF guns under certain conditions. Recent measurements indicate a correlation between multipacting, anomalous photo-emission behavior, and anomalous field emission behavior. Results will be presented.

High-efficiency optical pumping of nuclear polarization in a GaAs quantum well

Science.gov (United States)

Mocek, R. W.; Korenev, V. L.; Bayer, M.; Kotur, M.; Dzhioev, R. I.; Tolmachev, D. O.; Cascio, G.; Kavokin, K. V.; Suter, D.

2017-11-01

The dynamic polarization of nuclear spins by photoexcited electrons is studied in a high quality GaAs/AlGaAs quantum well. We find a surprisingly high efficiency of the spin transfer from the electrons to the nuclei as reflected by a maximum nuclear field of 0.9 T in a tilted external magnetic field of 1 T strength only. This high efficiency is due to a low leakage of spin out of the polarized nuclear system, because mechanisms of spin relaxation other than the hyperfine interaction are strongly suppressed, leading to a long nuclear relaxation time of up to 1000 s. A key ingredient to that end is the low impurity concentration inside the heterostructure, while the electrostatic potential from charged impurities in the surrounding barriers becomes screened through illumination by which the spin relaxation time is increased compared to keeping the system in the dark. This finding indicates a strategy for obtaining high nuclear spin polarization as required for long-lasting carrier spin coherence.

An efficient quantum algorithm for spectral estimation

Science.gov (United States)

Steffens, Adrian; Rebentrost, Patrick; Marvian, Iman; Eisert, Jens; Lloyd, Seth

2017-03-01

We develop an efficient quantum implementation of an important signal processing algorithm for line spectral estimation: the matrix pencil method, which determines the frequencies and damping factors of signals consisting of finite sums of exponentially damped sinusoids. Our algorithm provides a quantum speedup in a natural regime where the sampling rate is much higher than the number of sinusoid components. Along the way, we develop techniques that are expected to be useful for other quantum algorithms as well—consecutive phase estimations to efficiently make products of asymmetric low rank matrices classically accessible and an alternative method to efficiently exponentiate non-Hermitian matrices. Our algorithm features an efficient quantum-classical division of labor: the time-critical steps are implemented in quantum superposition, while an interjacent step, requiring much fewer parameters, can operate classically. We show that frequencies and damping factors can be obtained in time logarithmic in the number of sampling points, exponentially faster than known classical algorithms.

Turbocharged molecular discovery of OLED emitters: from high-throughput quantum simulation to highly efficient TADF devices

Science.gov (United States)

Gómez-Bombarelli, Rafael; Aguilera-Iparraguirre, Jorge; Hirzel, Timothy D.; Ha, Dong-Gwang; Einzinger, Markus; Wu, Tony; Baldo, Marc A.; Aspuru-Guzik, Alán.

2016-09-01

Discovering new OLED emitters requires many experiments to synthesize candidates and test performance in devices. Large scale computer simulation can greatly speed this search process but the problem remains challenging enough that brute force application of massive computing power is not enough to successfully identify novel structures. We report a successful High Throughput Virtual Screening study that leveraged a range of methods to optimize the search process. The generation of candidate structures was constrained to contain combinatorial explosion. Simulations were tuned to the specific problem and calibrated with experimental results. Experimentalists and theorists actively collaborated such that experimental feedback was regularly utilized to update and shape the computational search. Supervised machine learning methods prioritized candidate structures prior to quantum chemistry simulation to prevent wasting compute on likely poor performers. With this combination of techniques, each multiplying the strength of the search, this effort managed to navigate an area of molecular space and identify hundreds of promising OLED candidate structures. An experimentally validated selection of this set shows emitters with external quantum efficiencies as high as 22%.

Conditional efficient multiuser quantum cryptography network

International Nuclear Information System (INIS)

Xue Peng; Li Chuanfeng; Guo Guangcan

2002-01-01

We propose a conditional quantum key distribution scheme with three nonorthogonal states. Combined with the idea presented by Lo et al. (H.-K. Lo, H. F. Chau, and M. Ardehali, e-print arXiv: quant-ph/0011056), the efficiency of this scheme is increased to tend to 100%. Also, such a refined data analysis guarantees the security of our scheme against the most general eavesdropping strategy. Then, based on the scheme, we present a quantum cryptography network with the addition of a device called ''space optical switch.'' Moreover, we give out a realization of a quantum random number generator. Thus, a feasible experimental scheme of this efficient quantum cryptography network is completely given

Quantum interferences reconstruction with low homodyne detection efficiency

Energy Technology Data Exchange (ETDEWEB)

Esposito, Martina; Randi, Francesco [Universita degli studi di Trieste, Dipartimento di Fisica, Trieste (Italy); Titimbo, Kelvin; Zimmermann, Klaus; Benatti, Fabio [Universita degli studi di Trieste, Dipartimento di Fisica, Trieste (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Trieste (Italy); Kourousias, Georgios; Curri, Alessio [Sincrotrone Trieste S.C.p.A., Trieste (Italy); Floreanini, Roberto [Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Trieste (Italy); Parmigiani, Fulvio [Universita degli studi di Trieste, Dipartimento di Fisica, Trieste (Italy); Sincrotrone Trieste S.C.p.A., Trieste (Italy); University of Cologne, Institute of Physics II, Cologne (Germany); Fausti, Daniele [Universita degli studi di Trieste, Dipartimento di Fisica, Trieste (Italy); Sincrotrone Trieste S.C.p.A., Trieste (Italy)

2016-12-15

Optical homodyne tomography consists in reconstructing the quantum state of an optical field from repeated measurements of its amplitude at different field phases (homodyne data). The experimental noise, which unavoidably affects the homodyne data, leads to a detection efficiency η<1. The problem of reconstructing quantum states from noisy homodyne data sets prompted an intense scientific debate about the presence or absence of a lower homodyne efficiency bound (η>0.5) below which quantum features, like quantum interferences, cannot be retrieved. Here, by numerical experiments, we demonstrate that quantum interferences can be effectively reconstructed also for low homodyne detection efficiency. In particular, we address the challenging case of a Schroedinger cat state and test the minimax and adaptive Wigner function reconstruction technique by processing homodyne data distributed according to the chosen state but with an efficiency η>0.5. By numerically reproducing the Schroedinger's cat interference pattern, we give evidence that quantum state reconstruction is actually possible in these conditions, and provide a guideline for handling optical tomography based on homodyne data collected by low efficiency detectors. (orig.)

Extremely high absolute internal quantum efficiency of photoluminescence in co-doped GaN:Zn,Si

Science.gov (United States)

Reshchikov, M. A.; Willyard, A. G.; Behrends, A.; Bakin, A.; Waag, A.

2011-10-01

We report on the fabrication of GaN co-doped with silicon and zinc by metalorganic vapor phase epitaxy and a detailed study of photoluminescence in this material. We observe an exceptionally high absolute internal quantum efficiency of blue photoluminescence in GaN:Zn,Si. The value of 0.93±0.04 has been obtained from several approaches based on rate equations.

Highly Efficient Flexible Quantum Dot Solar Cells with Improved Electron Extraction Using MgZnO Nanocrystals.

Science.gov (United States)

Zhang, Xiaoliang; Santra, Pralay Kanti; Tian, Lei; Johansson, Malin B; Rensmo, Håkan; Johansson, Erik M J

2017-08-22

Colloidal quantum dot (CQD) solar cells have high potential for realizing an efficient and lightweight energy supply for flexible or wearable electronic devices. To achieve highly efficient and flexible CQD solar cells, the electron transport layer (ETL), extracting electrons from the CQD solid layer, needs to be processed at a low-temperature and should also suppress interfacial recombination. Herein, a highly stable MgZnO nanocrystal (MZO-NC) layer is reported for efficient flexible PbS CQD solar cells. Solar cells fabricated with MZO-NC ETL give a high power conversion efficiency (PCE) of 10.4% and 9.4%, on glass and flexible plastic substrates, respectively. The reported flexible CQD solar cell has the record efficiency to date of flexible CQD solar cells. Detailed theoretical simulations and extensive characterizations reveal that the MZO-NCs significantly enhance charge extraction from CQD solids and diminish the charge accumulation at the ETL/CQD interface, suppressing charge interfacial recombination. These important results suggest that the low-temperature processed MZO-NCs are very promising for use in efficient flexible solar cells or other flexible optoelectronic devices.

Maximally efficient protocols for direct secure quantum communication

Energy Technology Data Exchange (ETDEWEB)

Banerjee, Anindita [Department of Physics and Materials Science Engineering, Jaypee Institute of Information Technology, A-10, Sector-62, Noida, UP-201307 (India); Department of Physics and Center for Astroparticle Physics and Space Science, Bose Institute, Block EN, Sector V, Kolkata 700091 (India); Pathak, Anirban, E-mail: anirban.pathak@jiit.ac.in [Department of Physics and Materials Science Engineering, Jaypee Institute of Information Technology, A-10, Sector-62, Noida, UP-201307 (India); RCPTM, Joint Laboratory of Optics of Palacky University and Institute of Physics of Academy of Science of the Czech Republic, Faculty of Science, Palacky University, 17. Listopadu 12, 77146 Olomouc (Czech Republic)

2012-10-01

Two protocols for deterministic secure quantum communication (DSQC) using GHZ-like states have been proposed. It is shown that one of these protocols is maximally efficient and that can be modified to an equivalent protocol of quantum secure direct communication (QSDC). Security and efficiency of the proposed protocols are analyzed and compared. It is shown that dense coding is sufficient but not essential for DSQC and QSDC protocols. Maximally efficient QSDC protocols are shown to be more efficient than their DSQC counterparts. This additional efficiency arises at the cost of message transmission rate. -- Highlights: ► Two protocols for deterministic secure quantum communication (DSQC) are proposed. ► One of the above protocols is maximally efficient. ► It is modified to an equivalent protocol of quantum secure direct communication (QSDC). ► It is shown that dense coding is sufficient but not essential for DSQC and QSDC protocols. ► Efficient QSDC protocols are always more efficient than their DSQC counterparts.

Efficient decoding of random errors for quantum expander codes

OpenAIRE

Fawzi , Omar; Grospellier , Antoine; Leverrier , Anthony

2017-01-01

We show that quantum expander codes, a constant-rate family of quantum LDPC codes, with the quasi-linear time decoding algorithm of Leverrier, Tillich and Z\\'emor can correct a constant fraction of random errors with very high probability. This is the first construction of a constant-rate quantum LDPC code with an efficient decoding algorithm that can correct a linear number of random errors with a negligible failure probability. Finding codes with these properties is also motivated by Gottes...

High-Efficiency InGaN/GaN Quantum Well-Based Vertical Light-Emitting Diodes Fabricated on β-Ga2O3 Substrate

KAUST Repository

Muhammed, Mufasila

2017-09-11

We demonstrate a state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (-201)-oriented (β-Ga2O3) substrate, obtained using a straightforward growth process that does not require a high cost lift-off technique or complex fabrication process. The high-resolution scanning transmission electron microscopy (STEM) images confirm that we produced high quality upper layers, including a multi-quantum well (MQW) grown on the masked β-Ga2O3 substrate. STEM imaging also shows a well-defined MQW without InN diffusion into the barrier. Electroluminescence (EL) measurements at room temperature indicate that we achieved a very high internal quantum efficiency (IQE) of 78%; at lower temperatures, IQE reaches ~ 86%. The photoluminescence (PL) and time-resolved PL analysis indicate that, at a high carrier injection density, the emission is dominated by radiative recombination with a negligible Auger effect; no quantum-confined Stark effect is observed. At low temperatures, no efficiency droop is observed at a high carrier injection density, indicating the superior VLED structure obtained without lift-off processing, which is cost-effective for large-scale devices.

High-Efficiency InGaN/GaN Quantum Well-Based Vertical Light-Emitting Diodes Fabricated on β-Ga2O3 Substrate

KAUST Repository

Muhammed, Mufasila; Alwadai, Norah Mohammed Mosfer; Lopatin, Sergei; Kuramata, Akito; Roqan, Iman S.

2017-01-01

We demonstrate a state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (-201)-oriented (β-Ga2O3) substrate, obtained using a straightforward growth process that does not require a high cost lift-off technique or complex fabrication process. The high-resolution scanning transmission electron microscopy (STEM) images confirm that we produced high quality upper layers, including a multi-quantum well (MQW) grown on the masked β-Ga2O3 substrate. STEM imaging also shows a well-defined MQW without InN diffusion into the barrier. Electroluminescence (EL) measurements at room temperature indicate that we achieved a very high internal quantum efficiency (IQE) of 78%; at lower temperatures, IQE reaches ~ 86%. The photoluminescence (PL) and time-resolved PL analysis indicate that, at a high carrier injection density, the emission is dominated by radiative recombination with a negligible Auger effect; no quantum-confined Stark effect is observed. At low temperatures, no efficiency droop is observed at a high carrier injection density, indicating the superior VLED structure obtained without lift-off processing, which is cost-effective for large-scale devices.

Delayed Slater determinant update algorithms for high efficiency quantum Monte Carlo

Science.gov (United States)

McDaniel, T.; D'Azevedo, E. F.; Li, Y. W.; Wong, K.; Kent, P. R. C.

2017-11-01

Within ab initio Quantum Monte Carlo simulations, the leading numerical cost for large systems is the computation of the values of the Slater determinants in the trial wavefunction. Each Monte Carlo step requires finding the determinant of a dense matrix. This is most commonly iteratively evaluated using a rank-1 Sherman-Morrison updating scheme to avoid repeated explicit calculation of the inverse. The overall computational cost is, therefore, formally cubic in the number of electrons or matrix size. To improve the numerical efficiency of this procedure, we propose a novel multiple rank delayed update scheme. This strategy enables probability evaluation with an application of accepted moves to the matrices delayed until after a predetermined number of moves, K. The accepted events are then applied to the matrices en bloc with enhanced arithmetic intensity and computational efficiency via matrix-matrix operations instead of matrix-vector operations. This procedure does not change the underlying Monte Carlo sampling or its statistical efficiency. For calculations on large systems and algorithms such as diffusion Monte Carlo, where the acceptance ratio is high, order of magnitude improvements in the update time can be obtained on both multi-core central processing units and graphical processing units.

Highly Efficient Coherent Optical Memory Based on Electromagnetically Induced Transparency

Science.gov (United States)

Hsiao, Ya-Fen; Tsai, Pin-Ju; Chen, Hung-Shiue; Lin, Sheng-Xiang; Hung, Chih-Chiao; Lee, Chih-Hsi; Chen, Yi-Hsin; Chen, Yong-Fan; Yu, Ite A.; Chen, Ying-Cheng

2018-05-01

Quantum memory is an important component in the long-distance quantum communication based on the quantum repeater protocol. To outperform the direct transmission of photons with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and a long storage time. Here, we achieve a storage efficiency of 92.0 (1.5)% for a coherent optical memory based on the electromagnetically induced transparency scheme in optically dense cold atomic media. We also obtain a useful time-bandwidth product of 1200, considering only storage where the retrieval efficiency remains above 50%. Both are the best record to date in all kinds of schemes for the realization of optical memory. Our work significantly advances the pursuit of a high-performance optical memory and should have important applications in quantum information science.

Energy resolution measurements of LaBr3:Ce scintillating crystals with an ultra-high quantum efficiency photomultiplier tube

International Nuclear Information System (INIS)

Pani, R.; Cinti, M.N.; Scafe, R.; Pellegrini, R.; Vittorini, F.; Bennati, P.; Ridolfi, S.; Lo Meo, S.; Mattioli, M.; Baldazzi, G.; Pisacane, F.; Navarria, F.; Moschini, G.; Boccaccio, P.; Orsolini Cencelli, V.; Sacco, D.

2009-01-01

The performance of the new prototype of high quantum efficiency PMT (43% at 380 nm), Hamamatsu R7600U-200, was studied coupled to a LaBr 3 :Ce crystal with the size of o12.5 mmx12.5 mm. The energy resolution results were compared with ones from two PMTs, Hamamatsu R7600U and R6231MOD, with 22% and 30% quantum efficiency (QE), respectively. Moreover, the photodetectors were equipped with tapered and un-tapered voltage dividers to study the non-linearity effects on pulse height distribution, due to very high peak currents induced in the PMT by the fast and intense light pulse of LaBr 3 :Ce. The results show an energy resolution improvement with UBA PMT of about 20%, in the energy range of 80-662 keV, with respect to the BA one.

Efficient multiparty quantum-secret-sharing schemes

International Nuclear Information System (INIS)

Xiao Li; Deng Fuguo; Long Guilu; Pan Jianwei

2004-01-01

In this work, we generalize the quantum-secret-sharing scheme of Hillery, Buzek, and Berthiaume [Phys. Rev. A 59, 1829 (1999)] into arbitrary multiparties. Explicit expressions for the shared secret bit is given. It is shown that in the Hillery-Buzek-Berthiaume quantum-secret-sharing scheme the secret information is shared in the parity of binary strings formed by the measured outcomes of the participants. In addition, we have increased the efficiency of the quantum-secret-sharing scheme by generalizing two techniques from quantum key distribution. The favored-measuring-basis quantum-secret-sharing scheme is developed from the Lo-Chau-Ardehali technique [H. K. Lo, H. F. Chau, and M. Ardehali, e-print quant-ph/0011056] where all the participants choose their measuring-basis asymmetrically, and the measuring-basis-encrypted quantum-secret-sharing scheme is developed from the Hwang-Koh-Han technique [W. Y. Hwang, I. G. Koh, and Y. D. Han, Phys. Lett. A 244, 489 (1998)] where all participants choose their measuring basis according to a control key. Both schemes are asymptotically 100% in efficiency, hence nearly all the Greenberger-Horne-Zeilinger states in a quantum-secret-sharing process are used to generate shared secret information

Efficient quantum computation in a network with probabilistic gates and logical encoding

DEFF Research Database (Denmark)

Borregaard, J.; Sørensen, A. S.; Cirac, J. I.

2017-01-01

An approach to efficient quantum computation with probabilistic gates is proposed and analyzed in both a local and nonlocal setting. It combines heralded gates previously studied for atom or atomlike qubits with logical encoding from linear optical quantum computation in order to perform high......-fidelity quantum gates across a quantum network. The error-detecting properties of the heralded operations ensure high fidelity while the encoding makes it possible to correct for failed attempts such that deterministic and high-quality gates can be achieved. Importantly, this is robust to photon loss, which...... is typically the main obstacle to photonic-based quantum information processing. Overall this approach opens a path toward quantum networks with atomic nodes and photonic links....

Long-term stable stacked CsPbBr3 quantum dot films for highly efficient white light generation in LEDs.

Science.gov (United States)

Song, Young Hyun; Yoo, Jin Sun; Kang, Bong Kyun; Choi, Seung Hee; Ji, Eun Kyung; Jung, Hyun Suk; Yoon, Dae Ho

2016-12-01

We report highly efficient ethyl cellulose with CsPbBr 3 perovskite QD films for white light generation in LED application. Ethyl cellulose with CsPbBr 3 quantum dots is applied with Sr 2 Si 5 N 8  : Eu 2+ red phosphor on an InGaN blue chip, achieving a highly efficient luminous efficacy of 67.93 lm W -1 under 20 mA current.

Development of III-Sb Quantum Dot Systems for High Efficiency Intermediate Band Solar Cells

Energy Technology Data Exchange (ETDEWEB)

Huffaker, Diana [Univ. of California, Los Angeles, CA (United States); Hubbard, Seth [Rochester Inst. of Technology, NY (United States); Norman, Andrew [National Renewable Energy Lab. (NREL), Golden, CO (United States)

2015-07-31

This project aimed to develop solar cells that can help reduce cost per watt. This work focused on developing solar cells that utilize quantum dot (QD) nanomaterials to provide multijunction solar cell efficiency at the cost of single junction solar cell. We focused on a novel concept known as intermediate band solar cells (IBSC) where an additional energy band is inserted in a single solar cell to accommodate sub-bandgap photons absorption which otherwise are lost through transmission. The additional energy band can be achieved by growing QDs within a solar cell p-n junction. Though numerous studies have been conducted to develop such QD systems, very small improvements in solar energy conversion efficiency have been reported. This is mainly due to non-optimal material parameters such as band gap, band offset etc. In this work, we identified and developed a novel QD material system that meets the requirements of IBSC more closely than the current state-of-the-art technology. To achieve these goals, we focused on three important areas of solar cell design: band structure calculations of new materials, efficient device design for high efficiency, and development of new semiconductor materials. In this project, we focused on III-Sb materials as they possess a wide range of energy bandgaps from 0.2 eV to 2eV. Despite the difficulty involved in realizing these materials, we were successfully developed these materials through a systematic approach. Materials studied in this work are AlAsSb (Aluminum Arsenide Antimonide), InAlAs (Indium Aluminum Arsenide) and InAs (Indium Arsenide). InAs was used to develop QD layers within AlAsSb and InAlAs p-n junctions. As the QDs have very small volume, up to 30 QD layers been inserted into the p-n junction to enhance light absorption. These QD multi-stack devices helped in understanding the challenges associated with the development of quantum dot solar cells. The results from this work show that the quantum dot solar cells indeed

Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles

DEFF Research Database (Denmark)

Iida, Daisuke; Fadil, Ahmed; Chen, Yuntian

2015-01-01

We report internal quantum efficiency enhancement of thin p-GaN green quantumwell structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhance......We report internal quantum efficiency enhancement of thin p-GaN green quantumwell structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density...

High Efficiency Quantum Well Waveguide Solar Cells, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — The long-term objective of this program is to develop flexible, lightweight, single-junction solar cells using quantum structured designs that can achieve ultra-high...

Quantum efficiency and oscillator strength of site-controlled InAs quantum dots

DEFF Research Database (Denmark)

Albert, F.; Stobbe, Søren; Schneider, C.

2010-01-01

We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled InAs quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD...

Ultra-high efficiency photovoltaic cells for large scale solar power generation.

Science.gov (United States)

Nakano, Yoshiaki

2012-01-01

The primary targets of our project are to drastically improve the photovoltaic conversion efficiency and to develop new energy storage and delivery technologies. Our approach to obtain an efficiency over 40% starts from the improvement of III-V multi-junction solar cells by introducing a novel material for each cell realizing an ideal combination of bandgaps and lattice-matching. Further improvement incorporates quantum structures such as stacked quantum wells and quantum dots, which allow higher degree of freedom in the design of the bandgap and the lattice strain. Highly controlled arrangement of either quantum dots or quantum wells permits the coupling of the wavefunctions, and thus forms intermediate bands in the bandgap of a host material, which allows multiple photon absorption theoretically leading to a conversion efficiency exceeding 50%. In addition to such improvements, microfabrication technology for the integrated high-efficiency cells and the development of novel material systems that realizes high efficiency and low cost at the same time are investigated.

High Throughput, High Yield Fabrication of High Quantum Efficiency Back-Illuminated Photon Counting, Far UV, UV, and Visible Detector Arrays

Science.gov (United States)

Nikzad, Shouleh; Hoenk, M. E.; Carver, A. G.; Jones, T. J.; Greer, F.; Hamden, E.; Goodsall, T.

2013-01-01

In this paper we discuss the high throughput end-to-end post fabrication processing of high performance delta-doped and superlattice-doped silicon imagers for UV, visible, and NIR applications. As an example, we present our results on far ultraviolet and ultraviolet quantum efficiency (QE) in a photon counting, detector array. We have improved the QE by nearly an order of magnitude over microchannel plates (MCPs) that are the state-of-the-art UV detectors for many NASA space missions as well as defense applications. These achievements are made possible by precision interface band engineering of Molecular Beam Epitaxy (MBE) and Atomic Layer Deposition (ALD).

Highly efficient luminescent solar concentrators based on earth-abundant indirect-bandgap silicon quantum dots

Science.gov (United States)

Meinardi, Francesco; Ehrenberg, Samantha; Dhamo, Lorena; Carulli, Francesco; Mauri, Michele; Bruni, Francesco; Simonutti, Roberto; Kortshagen, Uwe; Brovelli, Sergio

2017-02-01

Building-integrated photovoltaics is gaining consensus as a renewable energy technology for producing electricity at the point of use. Luminescent solar concentrators (LSCs) could extend architectural integration to the urban environment by realizing electrode-less photovoltaic windows. Crucial for large-area LSCs is the suppression of reabsorption losses, which requires emitters with negligible overlap between their absorption and emission spectra. Here, we demonstrate the use of indirect-bandgap semiconductor nanostructures such as highly emissive silicon quantum dots. Silicon is non-toxic, low-cost and ultra-earth-abundant, which avoids the limitations to the industrial scaling of quantum dots composed of low-abundance elements. Suppressed reabsorption and scattering losses lead to nearly ideal LSCs with an optical efficiency of η = 2.85%, matching state-of-the-art semi-transparent LSCs. Monte Carlo simulations indicate that optimized silicon quantum dot LSCs have a clear path to η > 5% for 1 m2 devices. We are finally able to realize flexible LSCs with performances comparable to those of flat concentrators, which opens the way to a new design freedom for building-integrated photovoltaics elements.

Quantum efficiency and thermal emittance of metal photocathodes

Directory of Open Access Journals (Sweden)

David H. Dowell

2009-07-01

Full Text Available Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths with major advances occurring since the invention of the photocathode gun and the realization of emittance compensation. These state-of-the-art electron beams are now becoming limited by the intrinsic thermal emittance of the cathode. In both dc and rf photocathode guns details of the cathode emission physics strongly influence the quantum efficiency and the thermal emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal emittance. This paper investigates the relationship between the quantum efficiency and the thermal emittance for metal cathodes using the Fermi-Dirac model for the electron distribution. We use a consistent theory to derive the quantum efficiency and thermal emittance, and compare our results to those of others.

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....

Efficient quantum circuits for one-way quantum computing.

Science.gov (United States)

Tanamoto, Tetsufumi; Liu, Yu-Xi; Hu, Xuedong; Nori, Franco

2009-03-13

While Ising-type interactions are ideal for implementing controlled phase flip gates in one-way quantum computing, natural interactions between solid-state qubits are most often described by either the XY or the Heisenberg models. We show an efficient way of generating cluster states directly using either the imaginary SWAP (iSWAP) gate for the XY model, or the sqrt[SWAP] gate for the Heisenberg model. Our approach thus makes one-way quantum computing more feasible for solid-state devices.

Efficient quantum computing using coherent photon conversion.

Science.gov (United States)

Langford, N K; Ramelow, S; Prevedel, R; Munro, W J; Milburn, G J; Zeilinger, A

2011-10-12

Single photons are excellent quantum information carriers: they were used in the earliest demonstrations of entanglement and in the production of the highest-quality entanglement reported so far. However, current schemes for preparing, processing and measuring them are inefficient. For example, down-conversion provides heralded, but randomly timed, single photons, and linear optics gates are inherently probabilistic. Here we introduce a deterministic process--coherent photon conversion (CPC)--that provides a new way to generate and process complex, multiquanta states for photonic quantum information applications. The technique uses classically pumped nonlinearities to induce coherent oscillations between orthogonal states of multiple quantum excitations. One example of CPC, based on a pumped four-wave-mixing interaction, is shown to yield a single, versatile process that provides a full set of photonic quantum processing tools. This set satisfies the DiVincenzo criteria for a scalable quantum computing architecture, including deterministic multiqubit entanglement gates (based on a novel form of photon-photon interaction), high-quality heralded single- and multiphoton states free from higher-order imperfections, and robust, high-efficiency detection. It can also be used to produce heralded multiphoton entanglement, create optically switchable quantum circuits and implement an improved form of down-conversion with reduced higher-order effects. Such tools are valuable building blocks for many quantum-enabled technologies. Finally, using photonic crystal fibres we experimentally demonstrate quantum correlations arising from a four-colour nonlinear process suitable for CPC and use these measurements to study the feasibility of reaching the deterministic regime with current technology. Our scheme, which is based on interacting bosonic fields, is not restricted to optical systems but could also be implemented in optomechanical, electromechanical and superconducting

Construction of 3-dimensional ZnO-nanoflower structures for high quantum and photocurrent efficiency in dye sensitized solar cell

Energy Technology Data Exchange (ETDEWEB)

Kilic, Bayram, E-mail: bkilic@yalova.edu.tr [Yalova University, Department of Energy Systems Engineering, Faculty of Engineering, 77100 Yalova (Turkey); Günes, Taylan; Besirli, Ilknur; Sezginer, Merve [Yalova University, Department of Energy Systems Engineering, Faculty of Engineering, 77100 Yalova (Turkey); Tuzemen, Sebahattin [Department of Physics, Faculty of Science, Atatürk University, Erzurum 25240 (Turkey)

2014-11-01

Graphical abstract: - Highlights: • The structural and optical characterizations of ZnO nanoflowers were carried out on ITO by hydrothermal method. • Dye sensitized solar cell based ZnO nanoflowers were constructed on substrate. • The surface morphology effect on quantum efficiency and solar conversion efficiency were investigated. - Abstract: 3-dimensional ZnO nanoflower were obtained on FTO (F:SnO{sub 2}) substrate by hydrothermal method in order to produce high efficiency dye sensitized solar cells (DSSCs). We showed that nanoflowers structures have nanoscale branches that stretch to fill gaps on the substrate and these branches of nano-leaves provide both a larger surface area and a direct pathway for electron transport along the channels. It was found that the solar conversion efficiency and quantum efficiency (QE) or incident photon to current conversion efficiencies (IPCE) is highly dependent on nanoflower surface due to high electron injection process. The highest solar conversion efficiency of 5.119 and QE of 60% was obtained using ZnO nanoflowers/N719 dye/I{sup −}/I{sup −}{sub 3} electrolyte. In this study, three dimensional (3D)-nanoflower and one dimensional (1D)-nanowires ZnO nanostructures were also compared against each other in respect to solar conversion efficiency and QE measurements. In the case of the 1D-ZnO nanowire conversion efficiency (η) of 2.222% and IPCE 47% were obtained under an illumination of 100 mW/cm{sup 2}. It was confirmed that the performance of the 3D-nanoflowers was better than about 50% that of the 1D-nanowire dye-sensitized solar cells.

Erbium-implanted silica colloids with 80% luminescence quantum efficiency

Science.gov (United States)

Slooff, L. H.; de Dood, M. J. A.; van Blaaderen, A.; Polman, A.

2000-06-01

Silica colloids with a diameter of 240-360 nm, grown by wet chemical synthesis using ethanol, ammonia, water, and tetraethoxysilane, were implanted with 350 keV Er ions, to peak concentrations of 0.2-1.1 at. % and put onto a silicon or glass substrate. After annealing at 700-900 °C the colloids show clear room-temperature photoluminescence at 1.53 μm, with lifetimes as high as 17 ms. By comparing data of different Er concentrations, the purely radiative lifetime is estimated to be 20-22 ms, indicating a high quantum efficiency of about 80%. This high quantum efficiency indicates that, after annealing, the silica colloids are almost free of OH impurities. Spinning a layer of polymethylmethacrylate over the silica spheres results in an optically transparent nanocomposite layer, that can be used as a planar optical waveguide amplifier at 1.5 μm that is fully compatible with polymer technology.

Quantum efficiency and oscillator strength of site-controlled InGaAs quantum dots

DEFF Research Database (Denmark)

Albert, F.; Schneider, C.; Stobbe, Søren

2010-01-01

We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled In(Ga)As quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD...

Formation of CdS/Cd{sub 1−x}Zn{sub x}S sandwich-structured quantum dots with high quantum efficiency in silicate glasses

Energy Technology Data Exchange (ETDEWEB)

Xia, Mengling; Liu, Chao, E-mail: hite@whut.edu.cn; Han, Jianjun; Zhao, Xiujian

2017-06-15

CdS/Cd{sub 1−x}Zn{sub x}S sandwich-structured quantum dots (QDs) were precipitated in silicate glasses with high quantum efficiency up to 53%. The QDs were composed by a CdS core with a Cd{sub 1−x}Zn{sub x}S shell of about 1–3 nm in thickness through heat-treatment at 550 °C for 10 h. With the increased heat-treatment temperature, the intensity ratio between the intrinsic emission and the defects emission increased and the Stokes shift decreased from 84 to 4 meV, which was caused by both the increased size and passivated surface defects of the QDs.

Exceeding Conventional Photovoltaic Efficiency Limits Using Colloidal Quantum Dots

Science.gov (United States)

Pach, Gregory F.

Colloidal quantum dots (QDs) are a widely investigated field of research due to their highly tunable nature in which the optical and electronic properties of the nanocrystal can be manipulated by merely changing the nanocrystal's size. Specifically, colloidal quantum dot solar cells (QDSCs) have become a promising candidate for future generation photovoltaic technology. Quantum dots exhibit multiple exciton generation (MEG) in which multiple electron-hole pairs are generated from a single high-energy photon. This process is not observed in bulk-like semiconductors and allows for QDSCs to achieve theoretical efficiency limits above the standard single-junction Shockley-Queisser limit. However, the fast expanding field of QDSC research has lacked standardization of synthetic techniques and device design. Therefore, we sought to detail methodology for synthesizing PbS and PbSe QDs as well as photovoltaic device fabrication techniques as a fast track toward constructing high-performance solar cells. We show that these protocols lead toward consistently achieving efficiencies above 8% for PbS QDSCs. Using the same methodology for building single-junction photovoltaic devices, we incorporated PbS QDs as a bottom cell into a monolithic tandem architecture along with solution-processed CdTe nanocrystals. Modeling shows that near-peak tandem device efficiencies can be achieved across a wide range of bottom cell band gaps, and therefore the highly tunable band gap of lead-chalcogenide QDs lends well towards a bottom cell in a tandem architecture. A fully functioning monolithic tandem device is realized through the development of a ZnTe/ZnO recombination layer that appropriately combines the two subcells in series. Multiple recent reports have shown nanocrystalline heterostructures to undergo the MEG process more efficiency than several other nanostrucutres, namely lead-chalcogenide QDs. The final section of my thesis expands upon a recent publication by Zhang et. al., which

Quantum entanglement helps in improving economic efficiency

International Nuclear Information System (INIS)

Du Jiangfeng; Ju Chenyong; Li Hui

2005-01-01

We propose an economic regulation approach based on quantum game theory for the government to reduce the abuses of oligopolistic competition. Theoretical analysis shows that this approach can help government improve the economic efficiency of the oligopolistic market, and help prevent monopoly due to incorrect information. These advantages are completely attributed to the quantum entanglement, a unique quantum mechanical character

Quantum entanglement helps in improving economic efficiency

Science.gov (United States)

Du, Jiangfeng; Ju, Chenyong; Li, Hui

2005-02-01

We propose an economic regulation approach based on quantum game theory for the government to reduce the abuses of oligopolistic competition. Theoretical analysis shows that this approach can help government improve the economic efficiency of the oligopolistic market, and help prevent monopoly due to incorrect information. These advantages are completely attributed to the quantum entanglement, a unique quantum mechanical character.

The Quantum Efficiency and Thermal Emittance of Metal Photocathodes

International Nuclear Information System (INIS)

Dowell, D.

2009-01-01

Modern electron beams have demonstrated the brilliance needed to drive free electron lasers at x-ray wavelengths, with the principle improvements occurring since the invention of the photocathode gun. The state-of-the-art normalized emittance electron beams are now becoming limited by the thermal emittance of the cathode. In both DC and RF photocathode guns, details of the cathode emission physics strongly influence the quantum efficiency and the thermal emittance. Therefore improving cathode performance is essential to increasing the brightness of beams. It is especially important to understand the fundamentals of cathode quantum efficiency and thermal emittance. This paper investigates the relationship between the quantum efficiency and the thermal emittance of metal cathodes using the Fermi-Dirac model for the electron distribution. We derive the thermal emittance and its relationship to the quantum efficiency, and compare our results to those of others

The photonic nanowire: A highly efficient single-photon source

DEFF Research Database (Denmark)

Gregersen, Niels

2014-01-01

The photonic nanowire represents an attractive platform for a quantum light emitter. However, careful optical engineering using the modal method, which elegantly allows access to all relevant physical parameters, is crucial to ensure high efficiency.......The photonic nanowire represents an attractive platform for a quantum light emitter. However, careful optical engineering using the modal method, which elegantly allows access to all relevant physical parameters, is crucial to ensure high efficiency....

High-Efficiency InGaN/GaN Quantum Well-Based Vertical Light-Emitting Diodes Fabricated on β-Ga2O3 Substrate.

Science.gov (United States)

Muhammed, Mufasila M; Alwadai, Norah; Lopatin, Sergei; Kuramata, Akito; Roqan, Iman S

2017-10-04

We demonstrate a state-of-the-art high-efficiency GaN-based vertical light-emitting diode (VLED) grown on a transparent and conductive (-201)-oriented (β-Ga 2 O 3 ) substrate, obtained using a straightforward growth process that does not require a high-cost lift-off technique or complex fabrication process. The high-resolution scanning transmission electron microscopy (STEM) images confirm that we produced high quality upper layers, including a multiquantum well (MQW) grown on the masked β-Ga 2 O 3 substrate. STEM imaging also shows a well-defined MQW without InN diffusion into the barrier. Electroluminescence (EL) measurements at room temperature indicate that we achieved a very high internal quantum efficiency (IQE) of 78%; at lower temperatures, IQE reaches ∼86%. The photoluminescence (PL) and time-resolved PL analysis indicate that, at a high carrier injection density, the emission is dominated by radiative recombination with a negligible Auger effect; no quantum-confined Stark effect is observed. At low temperatures, no efficiency droop is observed at a high carrier injection density, indicating the superior VLED structure obtained without lift-off processing, which is cost-effective for large-scale devices.

Pure sources and efficient detectors for optical quantum information processing

Science.gov (United States)

Zielnicki, Kevin

Over the last sixty years, classical information theory has revolutionized the understanding of the nature of information, and how it can be quantified and manipulated. Quantum information processing extends these lessons to quantum systems, where the properties of intrinsic uncertainty and entanglement fundamentally defy classical explanation. This growing field has many potential applications, including computing, cryptography, communication, and metrology. As inherently mobile quantum particles, photons are likely to play an important role in any mature large-scale quantum information processing system. However, the available methods for producing and detecting complex multi-photon states place practical limits on the feasibility of sophisticated optical quantum information processing experiments. In a typical quantum information protocol, a source first produces an interesting or useful quantum state (or set of states), perhaps involving superposition or entanglement. Then, some manipulations are performed on this state, perhaps involving quantum logic gates which further manipulate or entangle the intial state. Finally, the state must be detected, obtaining some desired measurement result, e.g., for secure communication or computationally efficient factoring. The work presented here concerns the first and last stages of this process as they relate to photons: sources and detectors. Our work on sources is based on the need for optimized non-classical states of light delivered at high rates, particularly of single photons in a pure quantum state. We seek to better understand the properties of spontaneous parameteric downconversion (SPDC) sources of photon pairs, and in doing so, produce such an optimized source. We report an SPDC source which produces pure heralded single photons with little or no spectral filtering, allowing a significant rate enhancement. Our work on detectors is based on the need to reliably measure single-photon states. We have focused on

Efficiency of fermionic quantum distillation

Energy Technology Data Exchange (ETDEWEB)

Herbrych, Jacek W. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Feiguin, Adrian E. [Northeastern Univ., Boston, MA (United States); Dagotto, Elbio R. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Heidrich-Meisner, F. [Ludwig-Maximilians-Univ. Munchen, Munchen (Germany)

2017-09-13

Here, we present a time-dependent density-matrix renormalization group investigation of the quantum distillation process within the Fermi-Hubbard model on a quasi-one-dimensional ladder geometry. The term distillation refers to the dynamical, spatial separation of singlons and doublons in the sudden expansion of interacting particles in an optical lattice, i.e., the release of a cloud of atoms from a trapping potential. Remarkably, quantum distillation can lead to a contraction of the doublon cloud, resulting in an increased density of the doublons in the core region compared to the initial state. As a main result, we show that this phenomenon is not limited to chains that were previously studied. Interestingly, there are additional dynamical processes on the two-leg ladder such as density oscillations and self-trapping of defects that lead to a less efficient distillation process. An investigation of the time evolution starting from product states provides an explanation for this behavior. Initial product states are also considered since in optical lattice experiments, such states are often used as the initial setup. We propose configurations that lead to a fast and efficient quantum distillation.

Fast, efficient error reconciliation for quantum cryptography

International Nuclear Information System (INIS)

Buttler, W.T.; Lamoreaux, S.K.; Torgerson, J.R.; Nickel, G.H.; Donahue, C.H.; Peterson, C.G.

2003-01-01

We describe an error-reconciliation protocol, which we call Winnow, based on the exchange of parity and Hamming's 'syndrome' for N-bit subunits of a large dataset. The Winnow protocol was developed in the context of quantum-key distribution and offers significant advantages and net higher efficiency compared to other widely used protocols within the quantum cryptography community. A detailed mathematical analysis of the Winnow protocol is presented in the context of practical implementations of quantum-key distribution; in particular, the information overhead required for secure implementation is one of the most important criteria in the evaluation of a particular error-reconciliation protocol. The increase in efficiency for the Winnow protocol is largely due to the reduction in authenticated public communication required for its implementation

Strongly coupled CdS/graphene quantum dots nanohybrids for highly efficient photocatalytic hydrogen evolution: unraveling the essential roles of graphene quantum dots

KAUST Repository

Lei, Yonggang

2017-05-23

It have been recognized that the coupling of graphene quantum dots (GQDs) with semiconductor photocatalysts endow the resulting nanocomposites with enhanced photocatalytic performances, however, the essential roles of GQDs have not been clearly revealed yet. Herein, we report that a high efficiency of the photocatalytic H2 evolution was achieved using strongly coupled nanohybrids of CdS with GQDs (CdS/GQDs) as visible-light-driven photocatalysts. CdS/GQDs nanohybrids were synthesized by a facile hydrothermal method in which the crystallization of CdS precursor and coupling of GQDs could be accomplished in one-step. GQDs are firmly decorated on the surface of CdS nanoparticles, forming “dot-on-particle” heterodimer structures. GQDs have no significant influence on the crystallite structure of CdS but render the nanohybrids with strong light absorption at the wavelength beyond the band edge of CdS. Under visible light irradiation (≥420nm), CdS/GQDs nanohybrids reach the highest H2 production rate of 95.4μmol·h−1, about 2.7 times higher than that of pure CdS nanoparticles, at GQDs content of 1.0wt %, and the apparent quantum efficiency (AQE) was determined to be 4.2% at 420nm. Incident light-wavelength dependent experiments reveal that the light absorption of CdS dominated the performance of nanohybrids, and the excess light absorption coming from GQDs hardly contributes to the observed higher activity. Photocurrent response, steady-state and time-resolved PL, and EIS measurements suggest that the high activity of CdS/GQDs is attributed predominantly to the graphene-like nature of GQDs, which can act as an efficient electron acceptor to induce an efficient charge separation. This work clearly reveals that GQDs mainly played a role of electron acceptor instead of a photosensitizer in enhancing the photocatalytic H2 evolution performances of CdS/GQDs nanohybrids, which offers a new insight to understand the essential roles of GQDs in semiconductor

On-Demand Single Photons with High Extraction Efficiency and Near-Unity Indistinguishability from a Resonantly Driven Quantum Dot in a Micropillar

DEFF Research Database (Denmark)

Ding, Xing; He, Yu; Duan, Z.-C.

2016-01-01

Scalable photonic quantum technologies require on-demand single-photon sources with simultaneously high levels of purity, indistinguishability, and efficiency. These key features, however, have only been demonstrated separately in previous experiments. Here, by s-shell pulsed resonant excitation ...

Direct determination of quantum efficiency of semiconducting films

Science.gov (United States)

Faughnan, B.W.; Hanak, J.J.

Photovoltaic quantum efficiency of semiconductor samples is determined directly, without requiring that a built-in photovoltage be generated by the sample. Electrodes are attached to the sample so as to form at least one Schottky barrier therewith. When illuminated, the generated photocurrent carriers are collected by an external bias voltage impressed across the electrodes. The generated photocurrent is measured, and photovoltaic quantum efficiency is calculated therefrom.

Development of a System for Absolute Quantum Efficiency Determination of Hybrid Photo Diodes

CERN Document Server

Hammarstedt, P

2001-01-01

At CERN, the European Laboratory for Particle Physics, a new particle accelerator, the Large Hadron Collider (LHC), is under development. The detectors at LHC require development of highly sophisticated technologies, including Hybrid Photo Diodes (HPD) for high efficiency, high resolution single photon detection with a large area coverage. During the HPD development phase, one of the crucial parameters in the optimization of the photocathode creation process is the quantum efficiency. The aim of this Master Thesis has been to design and implement a system for high precision, high resolution quantum efficiency determination over a large, 200-700 nm photon wavelength range. Commercially available components have been obtained, an optomechanical system has been designed and built, and all the necessary data acquisition, control and analysis software has been implemented. The relative precision of the measurement system has been determined to 2%, with additional possible systematic errors less than 2%. Various qu...

Ultra-bright and highly efficient inorganic based perovskite light-emitting diodes

Science.gov (United States)

Zhang, Liuqi; Yang, Xiaolei; Jiang, Qi; Wang, Pengyang; Yin, Zhigang; Zhang, Xingwang; Tan, Hairen; Yang, Yang (Michael); Wei, Mingyang; Sutherland, Brandon R.; Sargent, Edward H.; You, Jingbi

2017-06-01

Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m-2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date.

Efficient quantum secure communication with a publicly known key

International Nuclear Information System (INIS)

Li Chunyan; Li Xihan; Deng Fuguo; Zhou Hongyu

2008-01-01

This paper presents a simple way for an eavesdropper to eavesdrop freely the secret message in the experimental realization of quantum communication protocol proposed by Beige et al (2002 Acta Phys. Pol. A 101 357). Moreover, it introduces an efficient quantum secure communication protocol based on a publicly known key with decoy photons and two biased bases by modifying the original protocol. The total efficiency of this new protocol is double that of the original one. With a low noise quantum channel, this protocol can be used for transmitting a secret message. At present, this protocol is good for generating a private key efficiently. (general)

High Quantum Efficiency OLED Lighting Systems

Energy Technology Data Exchange (ETDEWEB)

Shiang, Joseph [General Electric (GE) Global Research, Fairfield, CT (United States)

2011-09-30

The overall goal of the program was to apply improvements in light outcoupling technology to a practical large area plastic luminaire, and thus enable the product vision of an extremely thin form factor high efficiency large area light source. The target substrate was plastic and the baseline device was operating at 35 LPW at the start of the program. The target LPW of the program was a >2x improvement in the LPW efficacy and the overall amount of light to be delivered was relatively high 900 lumens. Despite the extremely difficult challenges associated with scaling up a wet solution process on plastic substrates, the program was able to make substantial progress. A small molecule wet solution process was successfully implemented on plastic substrates with almost no loss in efficiency in transitioning from the laboratory scale glass to large area plastic substrates. By transitioning to a small molecule based process, the LPW entitlement increased from 35 LPW to 60 LPW. A further 10% improvement in outcoupling efficiency was demonstrated via the use of a highly reflecting cathode, which reduced absorptive loss in the OLED device. The calculated potential improvement in some cases is even larger, ~30%, and thus there is considerable room for optimism in improving the net light coupling efficacy, provided absorptive loss mechanisms are eliminated. Further improvements are possible if scattering schemes such as the silver nanowire based hard coat structure are fully developed. The wet coating processes were successfully scaled to large area plastic substrate and resulted in the construction of a 900 lumens luminaire device.

Efficient multiuser quantum cryptography network based on entanglement.

Science.gov (United States)

Xue, Peng; Wang, Kunkun; Wang, Xiaoping

2017-04-04

We present an efficient quantum key distribution protocol with a certain entangled state to solve a special cryptographic task. Also, we provide a proof of security of this protocol by generalizing the proof of modified of Lo-Chau scheme. Based on this two-user scheme, a quantum cryptography network protocol is proposed without any quantum memory.

An Efficient Quantum Somewhat Homomorphic Symmetric Searchable Encryption

Science.gov (United States)

Sun, Xiaoqiang; Wang, Ting; Sun, Zhiwei; Wang, Ping; Yu, Jianping; Xie, Weixin

2017-04-01

In 2009, Gentry first introduced an ideal lattices fully homomorphic encryption (FHE) scheme. Later, based on the approximate greatest common divisor problem, learning with errors problem or learning with errors over rings problem, FHE has developed rapidly, along with the low efficiency and computational security. Combined with quantum mechanics, Liang proposed a symmetric quantum somewhat homomorphic encryption (QSHE) scheme based on quantum one-time pad, which is unconditional security. And it was converted to a quantum fully homomorphic encryption scheme, whose evaluation algorithm is based on the secret key. Compared with Liang's QSHE scheme, we propose a more efficient QSHE scheme for classical input states with perfect security, which is used to encrypt the classical message, and the secret key is not required in the evaluation algorithm. Furthermore, an efficient symmetric searchable encryption (SSE) scheme is constructed based on our QSHE scheme. SSE is important in the cloud storage, which allows users to offload search queries to the untrusted cloud. Then the cloud is responsible for returning encrypted files that match search queries (also encrypted), which protects users' privacy.

Efficient Computation of Transition State Resonances and Reaction Rates from a Quantum Normal Form

NARCIS (Netherlands)

Schubert, Roman; Waalkens, Holger; Wiggins, Stephen

2006-01-01

A quantum version of a recent formulation of transition state theory in phase space is presented. The theory developed provides an algorithm to compute quantum reaction rates and the associated Gamov-Siegert resonances with very high accuracy. The algorithm is especially efficient for

High-fidelity quantum gates on quantum-dot-confined electron spins in low-Q optical microcavities

Science.gov (United States)

Li, Tao; Gao, Jian-Cun; Deng, Fu-Guo; Long, Gui-Lu

2018-04-01

We propose some high-fidelity quantum circuits for quantum computing on electron spins of quantum dots (QD) embedded in low-Q optical microcavities, including the two-qubit controlled-NOT gate and the multiple-target-qubit controlled-NOT gate. The fidelities of both quantum gates can, in principle, be robust to imperfections involved in a practical input-output process of a single photon by converting the infidelity into a heralded error. Furthermore, the influence of two different decay channels is detailed. By decreasing the quality factor of the present microcavity, we can largely increase the efficiencies of these quantum gates while their high fidelities remain unaffected. This proposal also has another advantage regarding its experimental feasibility, in that both quantum gates can work faithfully even when the QD-cavity systems are non-identical, which is of particular importance in current semiconductor QD technology.

Highly efficient quantum dot-based photoconductive THz materials and devices

Science.gov (United States)

Rafailov, E. U.; Leyman, R.; Carnegie, D.; Bazieva, N.

2013-09-01

We demonstrate Terahertz (THz) signal sources based on photoconductive (PC) antenna devices comprising active layers of InAs semiconductor quantum dots (QDs) on GaAs. Antenna structures comprised of multiple active layers of InAs:GaAs PC materials are optically pumped using ultrashort pulses generated by a Ti:Sapphire laser and CW dualwavelength laser diodes. We also characterised THz output signals using a two-antenna coherent detection system. We discuss preliminary performance data from such InAs:GaAs THz devices which exhibit efficient emission of both pulsed and continuous wave (CW) THz signals and significant optical-to-THz conversion at both absorption wavelength ranges, <=850 nm and <=1300 nm.

A novel 3D detector configuration enabling high quantum efficiency, low crosstalk, and low output capacitance

International Nuclear Information System (INIS)

Aurola, A.; Marochkin, V.; Tuuva, T.

2016-01-01

The benefits of pixelated planar direct conversion semiconductor radiation detectors comprising a thick fully depleted substrate are that they offer low crosstalk, small output capacitance, and that the planar configuration simplifies manufacturing. In order to provide high quantum efficiency for high energy X-rays and Gamma-rays such a radiation detector should be as thick as possible. The maximum thickness and thus the maximum quantum efficiency has been limited by the substrate doping concentration: the lower the substrate doping the thicker the detector can be before reaching the semiconductor material's electric breakdown field. Thick direct conversion semiconductor detectors comprising vertical three-dimensional electrodes protruding through the substrate have been previously proposed by Sherwood Parker in order to promote rapid detection of radiation. An additional advantage of these detectors is that their thickness is not limited by the substrate doping, i.e., the size of the maximum electric field value in the detector does not depend on detector thickness. However, the thicker the substrate of such three dimensional detectors is the larger the output capacitance is and thus the larger the output noise is. In the novel direct conversion pixelated radiation detector utilizing a novel three dimensional semiconductor architecture, which is proposed in this work, the detector thickness is not limited by the substrate doping and the output capacitance is small and does not depend on the detector thickness. In addition, by incorporating an additional node to the novel three-dimensional semiconductor architecture it can be utilized as a high voltage transistor that can deliver current across high voltages. Furthermore, it is possible to connect a voltage difference of any size to the proposed novel three dimensional semiconductor architecture provided that it is thick enough—this is a novel feature that has not been previously possible for semiconductor

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

A quantum-chemical perspective into low optical-gap polymers for highly-efficient organic solar cells

KAUST Repository

Risko, Chad

2011-03-15

The recent and rapid enhancement in power conversion efficiencies of organic-based, bulk heterojunction solar cells has been a consequence of both improved materials design and better understanding of the underlying physical processes involved in photocurrent generation. In this Perspective, we first present an overview of the application of quantum-chemical techniques to study the intrinsic material properties and molecular- and nano-scale processes involved in device operation. In the second part, these quantum-chemical tools are applied to an oligomer-based study on a collection of donor-acceptor copolymers that have been used in the highest-efficiency solar cell devices reported to date. The quantum-chemical results are found to be in good agreement with the empirical data related to the electronic and optical properties. In particular, they provide insight into the natures of the electronic excitations responsible for the near-infrared/visible absorption profiles, as well as into the energetics of the low-lying singlet and triplet states. These results lead to a better understanding of the inherent differences among the materials, and highlight the usefulness of quantum chemistry as an instrument for material design. Importantly, the results also point to the need to continue the development of integrated, multi scale modeling approaches to provide a thorough understanding of the materials properties. © The Royal Society of Chemistry 2011.

High-speed noise-free optical quantum memory

Science.gov (United States)

Kaczmarek, K. T.; Ledingham, P. M.; Brecht, B.; Thomas, S. E.; Thekkadath, G. S.; Lazo-Arjona, O.; Munns, J. H. D.; Poem, E.; Feizpour, A.; Saunders, D. J.; Nunn, J.; Walmsley, I. A.

2018-04-01

Optical quantum memories are devices that store and recall quantum light and are vital to the realization of future photonic quantum networks. To date, much effort has been put into improving storage times and efficiencies of such devices to enable long-distance communications. However, less attention has been devoted to building quantum memories which add zero noise to the output. Even small additional noise can render the memory classical by destroying the fragile quantum signatures of the stored light. Therefore, noise performance is a critical parameter for all quantum memories. Here we introduce an intrinsically noise-free quantum memory protocol based on two-photon off-resonant cascaded absorption (ORCA). We demonstrate successful storage of GHz-bandwidth heralded single photons in a warm atomic vapor with no added noise, confirmed by the unaltered photon-number statistics upon recall. Our ORCA memory meets the stringent noise requirements for quantum memories while combining high-speed and room-temperature operation with technical simplicity, and therefore is immediately applicable to low-latency quantum networks.

Efficient Raman generation in a waveguide: A route to ultrafast quantum random number generation

Energy Technology Data Exchange (ETDEWEB)

England, D. G.; Bustard, P. J.; Moffatt, D. J.; Nunn, J.; Lausten, R.; Sussman, B. J., E-mail: ben.sussman@nrc.ca [National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada)

2014-02-03

The inherent uncertainty in quantum mechanics offers a source of true randomness which can be used to produce unbreakable cryptographic keys. We discuss the development of a high-speed random number generator based on the quantum phase fluctuations in spontaneously initiated stimulated Raman scattering (SISRS). We utilize the tight confinement and long interaction length available in a Potassium Titanyl Phosphate waveguide to generate highly efficient SISRS using nanojoule pulse energies, reducing the high pump power requirements of the previous approaches. We measure the random phase of the Stokes output using a simple interferometric setup to yield quantum random numbers at 145 Mbps.

Enhancing the photon-extraction efficiency of site-controlled quantum dots by deterministically fabricated microlenses

Science.gov (United States)

Kaganskiy, Arsenty; Fischbach, Sarah; Strittmatter, André; Rodt, Sven; Heindel, Tobias; Reitzenstein, Stephan

2018-04-01

We report on the realization of scalable single-photon sources (SPSs) based on single site-controlled quantum dots (SCQDs) and deterministically fabricated microlenses. The fabrication process comprises the buried-stressor growth technique complemented with low-temperature in-situ electron-beam lithography for the integration of SCQDs into microlens structures with high yield and high alignment accuracy. The microlens-approach leads to a broadband enhancement of the photon-extraction efficiency of up to (21 ± 2)% and a high suppression of multi-photon events with g (2)(τ = 0) SPSs which, can be applied in photonic quantum circuits and advanced quantum computation schemes.

Analysis of the external and internal quantum efficiency of multi-emitter, white organic light emitting diodes

Science.gov (United States)

Furno, Mauro; Rosenow, Thomas C.; Gather, Malte C.; Lüssem, Björn; Leo, Karl

2012-10-01

We report on a theoretical framework for the efficiency analysis of complex, multi-emitter organic light emitting diodes (OLEDs). The calculation approach makes use of electromagnetic modeling to quantify the overall OLED photon outcoupling efficiency and a phenomenological description for electrical and excitonic processes. From the comparison of optical modeling results and measurements of the total external quantum efficiency, we obtain reliable estimates of internal quantum yield. As application of the model, we analyze high-efficiency stacked white OLEDs and comment on the various efficiency loss channels present in the devices.

High-efficiency cavity-dumped micro-chip Yb:YAG laser

Science.gov (United States)

Nishio, M.; Maruko, A.; Inoue, M.; Takama, M.; Matsubara, S.; Okunishi, H.; Kato, K.; Kyomoto, K.; Yoshida, T.; Shimabayashi, K.; Morioka, M.; Inayoshi, S.; Yamagata, S.; Kawato, S.

2014-09-01

High-efficiency cavity-dumped ytterbium-doped yttrium aluminum garnet (Yb:YAG) laser was developed. Although the high quantum efficiency of ytterbium-doped laser materials is appropriate for high-efficiency laser oscillation, the efficiency is decreased by their quasi-three/four laser natures. High gain operation by high intensity pumping is suitable for high efficiency oscillation on the quasi-three/four lasers without extremely low temperature cooling. In our group, highest efficiency oscillations for continuous wave, nanosecond to picosecond pulse lasers were achieved at room temperature by the high gain operation in which pump intensities were beyond 100 kW/cm2.

High-order quantum algorithm for solving linear differential equations

International Nuclear Information System (INIS)

Berry, Dominic W

2014-01-01

Linear differential equations are ubiquitous in science and engineering. Quantum computers can simulate quantum systems, which are described by a restricted type of linear differential equations. Here we extend quantum simulation algorithms to general inhomogeneous sparse linear differential equations, which describe many classical physical systems. We examine the use of high-order methods (where the error over a time step is a high power of the size of the time step) to improve the efficiency. These provide scaling close to Δt 2 in the evolution time Δt. As with other algorithms of this type, the solution is encoded in amplitudes of the quantum state, and it is possible to extract global features of the solution. (paper)

Efficient Multiphoton Generation in Waveguide Quantum Electrodynamics

Science.gov (United States)

González-Tudela, A.; Paulisch, V.; Kimble, H. J.; Cirac, J. I.

2017-05-01

Engineering quantum states of light is at the basis of many quantum technologies such as quantum cryptography, teleportation, or metrology among others. Though, single photons can be generated in many scenarios, the efficient and reliable generation of complex single-mode multiphoton states is still a long-standing goal in the field, as current methods either suffer from low fidelities or small probabilities. Here we discuss several protocols which harness the strong and long-range atomic interactions induced by waveguide QED to efficiently load excitations in a collection of atoms, which can then be triggered to produce the desired multiphoton state. In order to boost the success probability and fidelity of each excitation process, atoms are used to both generate the excitations in the rest, as well as to herald the successful generation. Furthermore, to overcome the exponential scaling of the probability of success with the number of excitations, we design a protocol to merge excitations that are present in different internal atomic levels with a polynomial scaling.

High efficient OLED displays prepared with the air-gapped bridges on quantum dot patterns for optical recycling

OpenAIRE

Hyo-Jun Kim; Min-Ho Shin; Joo-Suc Kim; Se-Eun Kim; Young-Joo Kim

2017-01-01

An optically efficient structure was proposed and fabricated to realize high brightness organic light emitting diode (OLED) displays based on a white OLED prepared with the air-gapped bridges on the quantum dot (QD) patterns. Compared with a conventional white OLED display, in our experiments, the optical intensity of the proposed OLED display shows the enhancement of 58.2% in the red color and 16.8% in the green color after applying the air-gapped bridge structure on QD patterns of 20?wt% co...

Design of Efficient Mirror Adder in Quantum- Dot Cellular Automata

Science.gov (United States)

Mishra, Prashant Kumar; Chattopadhyay, Manju K.

2018-03-01

Lower power consumption is an essential demand for portable multimedia system using digital signal processing algorithms and architectures. Quantum dot cellular automata (QCA) is a rising nano technology for the development of high performance ultra-dense low power digital circuits. QCA based several efficient binary and decimal arithmetic circuits are implemented, however important improvements are still possible. This paper demonstrate Mirror Adder circuit design in QCA. We present comparative study of mirror adder cells designed using conventional CMOS technique and mirror adder cells designed using quantum-dot cellular automata. QCA based mirror adders are better in terms of area by order of three.

An Efficient and Secure Arbitrary N-Party Quantum Key Agreement Protocol Using Bell States

Science.gov (United States)

Liu, Wen-Jie; Xu, Yong; Yang, Ching-Nung; Gao, Pei-Pei; Yu, Wen-Bin

2018-01-01

Two quantum key agreement protocols using Bell states and Bell measurement were recently proposed by Shukla et al. (Quantum Inf. Process. 13(11), 2391-2405, 2014). However, Zhu et al. pointed out that there are some security flaws and proposed an improved version (Quantum Inf. Process. 14(11), 4245-4254, 2015). In this study, we will show Zhu et al.'s improvement still exists some security problems, and its efficiency is not high enough. For solving these problems, we utilize four Pauli operations { I, Z, X, Y} to encode two bits instead of the original two operations { I, X} to encode one bit, and then propose an efficient and secure arbitrary N-party quantum key agreement protocol. In the protocol, the channel checking with decoy single photons is introduced to avoid the eavesdropper's flip attack, and a post-measurement mechanism is used to prevent against the collusion attack. The security analysis shows the present protocol can guarantee the correctness, security, privacy and fairness of quantum key agreement.

Enhanced life time and suppressed efficiency roll-off in phosphorescent organic light-emitting diodes with multiple quantum well structures

Directory of Open Access Journals (Sweden)

Ja-Ryong Koo

2012-03-01

Full Text Available We demonstrate red phosphorescent organic light-emitting diodes (OLEDs with multiple quantum well structures which confine triplet exciton inside an emitting layer (EML region. Five types of OLEDs, from a single to five quantum wells, are fabricated with charge control layers to produce high efficiencies, and the performance of the devices is investigated. The improved quantum efficiency and lifetime of the OLED with four quantum wells, and its suppressed quantum efficiency roll-off of 17.6%, can be described by the increased electron–hole charge balance owing to the bipolar property as well as the efficient triplet exciton confinement within each EML, and by prevention of serious triplet–triplet and/or triplet–polaron annihilation as well as the Förster self-quenching due to charge control layers.

High-dimensional quantum key distribution based on multicore fiber using silicon photonic integrated circuits

DEFF Research Database (Denmark)

Ding, Yunhong; Bacco, Davide; Dalgaard, Kjeld

2017-01-01

is intrinsically limited to 1 bit/photon. Here we propose and experimentally demonstrate, for the first time, a high-dimensional quantum key distribution protocol based on space division multiplexing in multicore fiber using silicon photonic integrated lightwave circuits. We successfully realized three mutually......-dimensional quantum states, and enables breaking the information efficiency limit of traditional quantum key distribution protocols. In addition, the silicon photonic circuits used in our work integrate variable optical attenuators, highly efficient multicore fiber couplers, and Mach-Zehnder interferometers, enabling...

Efficiently characterizing the total error in quantum circuits

Science.gov (United States)

Carignan-Dugas, Arnaud; Wallman, Joel J.; Emerson, Joseph

A promising technological advancement meant to enlarge our computational means is the quantum computer. Such a device would harvest the quantum complexity of the physical world in order to unfold concrete mathematical problems more efficiently. However, the errors emerging from the implementation of quantum operations are likewise quantum, and hence share a similar level of intricacy. Fortunately, randomized benchmarking protocols provide an efficient way to characterize the operational noise within quantum devices. The resulting figures of merit, like the fidelity and the unitarity, are typically attached to a set of circuit components. While important, this doesn't fulfill the main goal: determining if the error rate of the total circuit is small enough in order to trust its outcome. In this work, we fill the gap by providing an optimal bound on the total fidelity of a circuit in terms of component-wise figures of merit. Our bound smoothly interpolates between the classical regime, in which the error rate grows linearly in the circuit's length, and the quantum regime, which can naturally allow quadratic growth. Conversely, our analysis substantially improves the bounds on single circuit element fidelities obtained through techniques such as interleaved randomized benchmarking. This research was supported by the U.S. Army Research Office through Grant W911NF- 14-1-0103, CIFAR, the Government of Ontario, and the Government of Canada through NSERC and Industry Canada.

On the effect of ballistic overflow on the temperature dependence of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Prudaev, I. A., E-mail: funcelab@gmail.com; Kopyev, V. V.; Romanov, I. S.; Oleynik, V. L. [National Research Tomsk State University (Russian Federation)

2017-02-15

The dependences of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes on the temperature and excitation level are studied. The experiment is performed for two luminescence excitation modes. A comparison of the results obtained during photo- and electroluminescence shows an additional (to the loss associated with Auger recombination) low-temperature loss in the high-density current region. This causes inversion of the temperature dependence of the quantum efficiency at temperatures lower than 220–300 K. Analysis shows that the loss is associated with electron leakage from the light-emitting-diode active region. The experimental data are explained using the ballistic-overflow model. The simulation results are in qualitative agreement with the experimental dependences of the quantum efficiency on temperature and current density.

On-chip generation of high-dimensional entangled quantum states and their coherent control.

Science.gov (United States)

Kues, Michael; Reimer, Christian; Roztocki, Piotr; Cortés, Luis Romero; Sciara, Stefania; Wetzel, Benjamin; Zhang, Yanbing; Cino, Alfonso; Chu, Sai T; Little, Brent E; Moss, David J; Caspani, Lucia; Azaña, José; Morandotti, Roberto

2017-06-28

Optical quantum states based on entangled photons are essential for solving questions in fundamental physics and are at the heart of quantum information science. Specifically, the realization of high-dimensional states (D-level quantum systems, that is, qudits, with D > 2) and their control are necessary for fundamental investigations of quantum mechanics, for increasing the sensitivity of quantum imaging schemes, for improving the robustness and key rate of quantum communication protocols, for enabling a richer variety of quantum simulations, and for achieving more efficient and error-tolerant quantum computation. Integrated photonics has recently become a leading platform for the compact, cost-efficient, and stable generation and processing of non-classical optical states. However, so far, integrated entangled quantum sources have been limited to qubits (D = 2). Here we demonstrate on-chip generation of entangled qudit states, where the photons are created in a coherent superposition of multiple high-purity frequency modes. In particular, we confirm the realization of a quantum system with at least one hundred dimensions, formed by two entangled qudits with D = 10. Furthermore, using state-of-the-art, yet off-the-shelf telecommunications components, we introduce a coherent manipulation platform with which to control frequency-entangled states, capable of performing deterministic high-dimensional gate operations. We validate this platform by measuring Bell inequality violations and performing quantum state tomography. Our work enables the generation and processing of high-dimensional quantum states in a single spatial mode.

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...

Quantum engine efficiency bound beyond the second law of thermodynamics.

Science.gov (United States)

Niedenzu, Wolfgang; Mukherjee, Victor; Ghosh, Arnab; Kofman, Abraham G; Kurizki, Gershon

2018-01-11

According to the second law, the efficiency of cyclic heat engines is limited by the Carnot bound that is attained by engines that operate between two thermal baths under the reversibility condition whereby the total entropy does not increase. Quantum engines operating between a thermal and a squeezed-thermal bath have been shown to surpass this bound. Yet, their maximum efficiency cannot be determined by the reversibility condition, which may yield an unachievable efficiency bound above unity. Here we identify the fraction of the exchanged energy between a quantum system and a bath that necessarily causes an entropy change and derive an inequality for this change. This inequality reveals an efficiency bound for quantum engines energised by a non-thermal bath. This bound does not imply reversibility, unless the two baths are thermal. It cannot be solely deduced from the laws of thermodynamics.

Enhanced carrier collection efficiency and reduced quantum state absorption by electron doping in self-assembled quantum dot solar cells

Energy Technology Data Exchange (ETDEWEB)

Li, Tian, E-mail: tianlee@umd.edu, E-mail: dage@ece.umd.edu; Dagenais, Mario, E-mail: tianlee@umd.edu, E-mail: dage@ece.umd.edu [Department of Electrical Engineering, University of Maryland, College Park, Maryland 20742 (United States); Lu, Haofeng; Fu, Lan; Tan, Hark Hoe; Jagadish, Chennupati [Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra ACT 0200 (Australia)

2015-02-02

Reduced quantum dot (QD) absorption due to state filling effects and enhanced electron transport in doped QDs are demonstrated to play a key role in solar energy conversion. Reduced QD state absorption with increased n-doping is observed in the self-assembled In{sub 0.5}Ga{sub 0.5}As/GaAs QDs from high resolution below-bandgap external quantum efficiency (EQE) measurement, which is a direct consequence of the Pauli exclusion principle. We also show that besides partial filling of the quantum states, electron-doping produces negatively charged QDs that exert a repulsive Coulomb force on the mobile electrons, thus altering the electron trajectory and reducing the probability of electron capture, leading to an improved collection efficiency of photo-generated carriers, as indicated by an absolute above-bandgap EQE measurement. The resulting redistribution of the mobile electron in the planar direction is further validated by the observed photoluminescence intensity dependence on doping.

Dextran based highly conductive hydrogel polysulfide electrolyte for efficient quasi-solid-state quantum dot-sensitized solar cells

International Nuclear Information System (INIS)

Chen, Hong-Yan; Lin, Ling; Yu, Xiao-Yun; Qiu, Kang-Qiang; Lü, Xian-Yong; Kuang, Dai-Bin; Su, Cheng-Yong

2013-01-01

Highlights: ► Dextran based hydrogel is first used to prepare quasi-solid-state polysulfide electrolyte for quantum dot-sensitized solar cells. ► The ion conductivity of hydrogel electrolyte shows almost the same value as the liquid electrolyte. ► The liquid state at elevated temperature of hydrogel electrolyte allows for a good contact between electrolyte and CdS/CdSe co-sensitized TiO 2 photoanode. ► The hydrogel electrolyte based cell exhibits slightly lower power conversion efficiency than that of liquid electrolyte based cell. ► The dynamic electron transfer mechanism in hydrogel electrolyte based cell is examined in detail by EIS and CIMPS/IMVS. -- Abstract: Highly conductive hydrogel polysulfide electrolyte is first fabricated using dextran as gelator and used as quasi-solid-state electrolyte for quantum dot-sensitized solar cells (QDSSCs). The hydrogel electrolyte with gelator concentration of 15 wt% shows almost the same conductivity as the liquid one. Moreover, its liquid state at elevated temperature allow for the well penetration into the pores in electrodeposited CdS/CdSe co-sensitized TiO 2 photoanode. This gel electrolyte based QDSSC exhibits power conversion efficiency (η) of 3.23% under AG 1.5 G one sun (100 mW cm −2 ) illumination, slightly lower than that of liquid electrolyte based cell (3.69%). The dynamic electron transfer mechanism of the gel and liquid electrolyte based QDSSC are examined by electrochemical impedance spectroscopy (EIS) and controlled intensity modulated photocurrent/photovoltage spectroscopy (CIMPS/IMVS). It is found that the electron transport in gel electrolyte based cell is much faster than the liquid electrolyte based cell but it tends to recombine more easily than the latter. However, these differences fade away with increasing the light intensity, showing declining electron collection efficiency at higher light intensity illumination. As a result, a conversion efficiency of 4.58% is obtained for the gel

Enhanced quantum efficiency for CsI grown on a graphite-based substrate coating

CERN Document Server

Friese, J; Homolka, J; Kastenmüller, A; Maier-Komor, P; Peter, M; Zeitelhack, K; Kienle, P; Körner, H J

1999-01-01

Quantum efficiencies (QE) in the vacuum ultraviolet (VUV) wavelength region have been measured for solid CsI layers on various substrates. The CsI films were deposited applying electron beam evaporation. The QE measurements were performed utilizing synchrotron radiation as well as light from a deuterium lamp. A GaAsP diode with a sensitivity calibration traceable to a primary radiation standard was used for normalization. For CsI layers grown on resin-stabilized graphite films a significant enhancement of QE was observed. Substrates suitable for gas detector applications and aging properties were investigated. The procedures to prepare and reproduce high quantum efficient CsI layers are described.

Efficient tomography of a quantum many-body system

Science.gov (United States)

Lanyon, B. P.; Maier, C.; Holzäpfel, M.; Baumgratz, T.; Hempel, C.; Jurcevic, P.; Dhand, I.; Buyskikh, A. S.; Daley, A. J.; Cramer, M.; Plenio, M. B.; Blatt, R.; Roos, C. F.

2017-12-01

Quantum state tomography is the standard technique for estimating the quantum state of small systems. But its application to larger systems soon becomes impractical as the required resources scale exponentially with the size. Therefore, considerable effort is dedicated to the development of new characterization tools for quantum many-body states. Here we demonstrate matrix product state tomography, which is theoretically proven to allow for the efficient and accurate estimation of a broad class of quantum states. We use this technique to reconstruct the dynamical state of a trapped-ion quantum simulator comprising up to 14 entangled and individually controlled spins: a size far beyond the practical limits of quantum state tomography. Our results reveal the dynamical growth of entanglement and describe its complexity as correlations spread out during a quench: a necessary condition for future demonstrations of better-than-classical performance. Matrix product state tomography should therefore find widespread use in the study of large quantum many-body systems and the benchmarking and verification of quantum simulators and computers.

InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells

International Nuclear Information System (INIS)

Alonso-Álvarez, D.; Thomas, T.; Führer, M.; Hylton, N. P.; Ekins-Daukes, N. J.; Lackner, D.; Philipps, S. P.; Bett, A. W.; Sodabanlu, H.; Fujii, H.; Watanabe, K.; Sugiyama, M.; Nasi, L.; Campanini, M.

2014-01-01

Quantum wires (QWRs) form naturally when growing strain balanced InGaAs/GaAsP multi-quantum wells (MQW) on GaAs [100] 6° misoriented substrates under the usual growth conditions. The presence of wires instead of wells could have several unexpected consequences for the performance of the MQW solar cells, both positive and negative, that need to be assessed to achieve high conversion efficiencies. In this letter, we study QWR properties from the point of view of their performance as solar cells by means of transmission electron microscopy, time resolved photoluminescence and external quantum efficiency (EQE) using polarised light. We find that these QWRs have longer lifetimes than nominally identical QWs grown on exact [100] GaAs substrates, of up to 1 μs, at any level of illumination. We attribute this effect to an asymmetric carrier escape from the nanostructures leading to a strong 1D-photo-charging, keeping electrons confined along the wire and holes in the barriers. In principle, these extended lifetimes could be exploited to enhance carrier collection and reduce dark current losses. Light absorption by these QWRs is 1.6 times weaker than QWs, as revealed by EQE measurements, which emphasises the need for more layers of nanostructures or the use light trapping techniques. Contrary to what we expected, QWR show very low absorption anisotropy, only 3.5%, which was the main drawback a priori of this nanostructure. We attribute this to a reduced lateral confinement inside the wires. These results encourage further study and optimization of QWRs for high efficiency solar cells.

Equivalent Method of Solving Quantum Efficiency of Reflection-Mode Exponential Doping GaAs Photocathode

International Nuclear Information System (INIS)

Jun, Niu; Zhi, Yang; Ben-Kang, Chang

2009-01-01

The mathematical expression of the electron diffusion and drift length L DE of exponential doping photocathode is deduced. In the quantum efficiency equation of the reffection-mode uniform doping cathode, substituting L DE for L D , the equivalent quantum efficiency equation of the reffection-mode exponential doping cathode is obtained. By using the equivalent equation, theoretical simulation and experimental analysis shows that the equivalent index formula and formula-doped cathode quantum efficiency results in line. The equivalent equation avoids complicated calculation, thereby simplifies the process of solving the quantum efficiency of exponential doping photocathode

Scaling-Up Quantum Heat Engines Efficiently via Shortcuts to Adiabaticity

Directory of Open Access Journals (Sweden)

Mathieu Beau

2016-04-01

Full Text Available The finite-time operation of a quantum heat engine that uses a single particle as a working medium generally increases the output power at the expense of inducing friction that lowers the cycle efficiency. We propose to scale up a quantum heat engine utilizing a many-particle working medium in combination with the use of shortcuts to adiabaticity to boost the nonadiabatic performance by eliminating quantum friction and reducing the cycle time. To this end, we first analyze the finite-time thermodynamics of a quantum Otto cycle implemented with a quantum fluid confined in a time-dependent harmonic trap. We show that nonadiabatic effects can be controlled and tailored to match the adiabatic performance using a variety of shortcuts to adiabaticity. As a result, the nonadiabatic dynamics of the scaled-up many-particle quantum heat engine exhibits no friction, and the cycle can be run at maximum efficiency with a tunable output power. We demonstrate our results with a working medium consisting of particles with inverse-square pairwise interactions that includes non-interacting and hard-core bosons as limiting cases.

Origin of low quantum efficiency of photoluminescence of InP/ZnS nanocrystals

International Nuclear Information System (INIS)

Shirazi, Roza; Kovacs, Andras; Dan Corell, Dennis; Gritti, Claudia; Thorseth, Anders; Dam-Hansen, Carsten; Michael Petersen, Paul; Kardynal, Beata

2014-01-01

In this paper, we study the origin of a strong wavelength dependence of the quantum efficiency of InP/ZnS nanocrystals. We find that while the average size of the nanocrystals increased by 50%, resulting in longer emission wavelength, the quantum efficiency drops more than one order of magnitude compared to the quantum efficiency of the small nanocrystals. By correlating this result with the time-resolved photoluminescence we find that the reduced photoluminescence efficiency is caused by a fast growing fraction of non-emissive nanocrystals while the quality of the nanocrystals that emit light is similar for all samples. Transmission electron microscopy reveals the polycrystalline nature of many of the large nanocrystals, pointing to the grain boundaries as one possible site for the photoluminescence quenching defects. -- Highlights: • We investigate drop of quantum efficiency of InP/ZnS nanocrystals emitting at longer wavelengths. • We correlate quantum efficiency measurements with time-resolved carrier dynamics. • We find that only a small fraction of larger nanocrystals is optically active

Origin of low quantum efficiency of photoluminescence of InP/ZnS nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Shirazi, Roza, E-mail: rozas@fotonik.dtu.dk [Department of Photonics Engineering, Technical University of Denmark, Oersted Plads 343, 2800 Kgs Lyngby (Denmark); Kovacs, Andras [Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grunberg Institute, Forschungszentrum Julich, 52425 Julich (Germany); Dan Corell, Dennis [Department of Photonics Engineering, Technical University of Denmark, Riso, Frederiksborgvej 399, 4000 Roskilde (Denmark); Gritti, Claudia [Department of Photonics Engineering, Technical University of Denmark, Oersted Plads 343, 2800 Kgs Lyngby (Denmark); Thorseth, Anders; Dam-Hansen, Carsten; Michael Petersen, Paul [Department of Photonics Engineering, Technical University of Denmark, Riso, Frederiksborgvej 399, 4000 Roskilde (Denmark); Kardynal, Beata [Department of Photonics Engineering, Technical University of Denmark, Oersted Plads 343, 2800 Kgs Lyngby (Denmark); PGI-9, Forschungszentrum Julich, JARA FIT, 52425 Julich (Germany)

2014-01-15

In this paper, we study the origin of a strong wavelength dependence of the quantum efficiency of InP/ZnS nanocrystals. We find that while the average size of the nanocrystals increased by 50%, resulting in longer emission wavelength, the quantum efficiency drops more than one order of magnitude compared to the quantum efficiency of the small nanocrystals. By correlating this result with the time-resolved photoluminescence we find that the reduced photoluminescence efficiency is caused by a fast growing fraction of non-emissive nanocrystals while the quality of the nanocrystals that emit light is similar for all samples. Transmission electron microscopy reveals the polycrystalline nature of many of the large nanocrystals, pointing to the grain boundaries as one possible site for the photoluminescence quenching defects. -- Highlights: • We investigate drop of quantum efficiency of InP/ZnS nanocrystals emitting at longer wavelengths. • We correlate quantum efficiency measurements with time-resolved carrier dynamics. • We find that only a small fraction of larger nanocrystals is optically active.

Measurement of the quantum efficiency of TMAE and TEA from threshold to 120 nm

International Nuclear Information System (INIS)

Holroyd, R.A.; Preses, J.M.; Woody, C.L.; Johnson, R.A.

1986-01-01

Several existing and planned high energy physics experiments incorporate detectors which use either TMAE (tetrakis-dimethylaminoethylene) or TEA (triethylamine) as their photosensitive agent. Understanding the operation of these devices requires knowledge of the absolute photoionization quantum efficiencies and absorption lengths of TMAE and TEA. In an experiment performed at the National Synchrotron Light source at Brookhaven National Laboratory, we have measured these parameters from 120 nm to 280 nm. The quantum efficiencies were normalized to the known photoionization yields of benzene and cis-2-butene. The results of these measurements and details of the experiment are presented in this paper

Study of silicon microstrips detector quantum efficiency using mathematical simulation

International Nuclear Information System (INIS)

Leyva Pernia, Diana; Cabal Rodriguez, Ana Ester; Pinnera Hernandez, Ibrahin; Fabelo, Antonio Leyva; Abreu Alfonso, Yamiel; Cruz Inclan, Carlos M.

2011-01-01

The paper shows the results from the application of mathematical simulation to study the quantum efficiency of a microstrips crystalline silicon detector, intended for medical imaging and the development of other applications such as authentication and dating of cultural heritage. The effects on the quantum efficiency of some parameters of the system, such as the detector-source geometry, X rays energy and detector dead zone thickness, were evaluated. The simulation results were compared with the theoretical prediction and experimental available data, resulting in a proper correspondence. It was concluded that the use of frontal configuration for incident energies lower than 17 keV is more efficient, however the use of the edge-on configuration for applications requiring the detection of energy above this value is recommended. It was also found that the reduction of the detector dead zone led to a considerable increase in quantum efficiency for any energy value in the interval from 5 to 100 keV.(author)

Prediction and design of efficient exciplex emitters for high-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes.

Science.gov (United States)

Liu, Xiao-Ke; Chen, Zhan; Zheng, Cai-Jun; Liu, Chuan-Lin; Lee, Chun-Sing; Li, Fan; Ou, Xue-Mei; Zhang, Xiao-Hong

2015-04-08

High-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes based on exciplex emitters are demonstrated. The best device, based on a TAPC:DPTPCz emitter, shows a high external quantum efficiency of 15.4%. Strategies for predicting and designing efficient exciplex emitters are also provided. This approach allow prediction and design of efficient exciplex emitters for achieving high-efficiency organic light-emitting diodes, for future use in displays and lighting applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

2 W high efficiency PbS mid-infrared surface emitting laser

Science.gov (United States)

Ishida, A.; Sugiyama, Y.; Isaji, Y.; Kodama, K.; Takano, Y.; Sakata, H.; Rahim, M.; Khiar, A.; Fill, M.; Felder, F.; Zogg, H.

2011-09-01

High efficiency laser operation with output power exceeding 2 W was obtained for vertical external-cavity PbS based IV-VI compound surface emitting quantum-well structures. The laser showed external quantum efficiency as high as 16%. Generally, mid-infrared III-V or II-VI semiconductor laser operation utilizing interband electron transitions are restricted by Auger recombination and free carrier absorption. Auger recombination is much lower in the IV-VI semiconductors, and the free-carrier absorption is significantly reduced by an optically pumped laser structure including multi-step optical excitation layers.

Quantum Phenomena in High Energy Density Plasmas

Energy Technology Data Exchange (ETDEWEB)

Murnane, Margaret [Univ. of Colorado, Boulder, CO (United States); Kapteyn, Henry [Univ. of Colorado, Boulder, CO (United States)

2017-05-10

The possibility of implementing efficient (phase matched) HHG upconversion of deep- UV lasers in multiply-ionized plasmas, with potentially unprecedented conversion efficiency is a fascinating prospect. HHG results from the extreme nonlinear response of matter to intense laser light:high harmonics are radiated as a result of a quantum coherent electron recollision process that occurs during laser field ionization of an atom. Under current support from this grant in work published in Science in 2015, we discovered a new regime of bright HHG in highly-ionized plasmas driven by intense UV lasers, that generates bright harmonics to photon energies >280eV

High Efficiency Nanostructured III-V Photovoltaics for Solar Concentrator Application

Energy Technology Data Exchange (ETDEWEB)

Hubbard, Seth

2012-09-12

The High Efficiency Nanostructured III-V Photovoltaics for Solar Concentrators project seeks to provide new photovoltaic cells for Concentrator Photovoltaics (CPV) Systems with higher cell efficiency, more favorable temperature coefficients and less sensitivity to changes in spectral distribution. The main objective of this project is to provide high efficiency III-V solar cells that will reduce the overall cost per Watt for power generation using CPV systems.This work is focused both on a potential near term application, namely the use of indium arsenide (InAs) QDs to spectrally "tune" the middle (GaAs) cell of a SOA triple junction device to a more favorable effective bandgap, as well as the long term goal of demonstrating intermediate band solar cell effects. The QDs are confined within a high electric field i-region of a standard GaAs solar cell. The extended absorption spectrum (and thus enhanced short circuit current) of the QD solar cell results from the increase in the sub GaAs bandgap spectral response that is achievable as quantum dot layers are introduced into the i-region. We have grown InAs quantum dots by OMVPE technique and optimized the QD growth conditions. Arrays of up to 40 layers of strain balanced quantum dots have been experimentally demonstrated with good material quality, low residual stain and high PL intensity. Quantum dot enhanced solar cells were grown and tested under simulated one sun AM1.5 conditions. Concentrator solar cells have been grown and fabricated with 5-40 layers of QDs. Testing of these devices show the QD cells have improved efficiency compared to baseline devices without QDs. Device modeling and measurement of thermal properties were performed using Crosslight APSYS. Improvements in a triple junction solar cell with the insertion of QDs into the middle current limiting junction was shown to be as high as 29% under one sun illumination for a 10 layer stack QD enhanced triple junction solar cell. QD devices have strong

High-efficiency single-photon source: The photonic wire geometry

DEFF Research Database (Denmark)

Claudon, J.; Bazin, Maela; Malik, Nitin S.

2009-01-01

We present a single-photon-source design based on the emission of a quantum dot embedded in a semiconductor (GaAs) nanowire. The nanowire ends are engineered (efficient metallic mirror and tip taper) to reach a predicted record-high collection efficiency of 90% with a realistic design. Preliminar...

A novel quantum information hiding protocol based on entanglement swapping of high-level Bell states

International Nuclear Information System (INIS)

Xu Shu-Jiang; Wang Lian-Hai; Chen Xiu-Bo; Niu Xin-Xin; Yang Yi-Xian

2015-01-01

Using entanglement swapping of high-level Bell states, we first derive a covert layer between the secret message and the possible output results of the entanglement swapping between any two generalized Bell states, and then propose a novel high-efficiency quantum information hiding protocol based on the covert layer. In the proposed scheme, a covert channel can be built up under the cover of a high-level quantum secure direct communication (QSDC) channel for securely transmitting secret messages without consuming any auxiliary quantum state or any extra communication resource. It is shown that this protocol not only has a high embedding efficiency but also achieves a good imperceptibility as well as a high security. (paper)

High-resolution hard x-ray spectroscopy of high-temperature plasmas using an array of quantum microcalorimeters.

Science.gov (United States)

Thorn, Daniel B; Gu, Ming F; Brown, Greg V; Beiersdorfer, Peter; Porter, F Scott; Kilbourne, Caroline A; Kelley, Richard L

2008-10-01

Quantum microcalorimeters show promise in being able to fully resolve x-ray spectra from heavy highly charged ions, such as would be found in hot plasmas with temperatures in excess of 50 keV. Quantum microcalorimeter arrays are able to achieve this as they have a high-resolving power and good effective quantum efficiency for hard x-ray photons up to 60 keV. To demonstrate this, we present a measurement using an array of thin HgTe quantum microcalorimeters to measure the K-shell spectrum of hydrogenlike through carbonlike praseodymium (Z=57). With this device we are able to attain a resolving power, E/DeltaE, of 1000 at a photon energy of 37 keV.

The Efficiency of Quantum Identity Testing of Multiple States

OpenAIRE

Kada, Masaru; Nishimura, Harumichi; Yamakami, Tomoyuki

2008-01-01

We examine two quantum operations, the Permutation Test and the Circle Test, which test the identity of n quantum states. These operations naturally extend the well-studied Swap Test on two quantum states. We first show the optimality of the Permutation Test for any input size n as well as the optimality of the Circle Test for three input states. In particular, when n=3, we present a semi-classical protocol, incorporated with the Swap Test, which approximates the Circle Test efficiently. Furt...

Electrostatics and quantum efficiency simulations of asymmetrically contacted carbon nanotube photodetector

Directory of Open Access Journals (Sweden)

Xiao Guo

2017-10-01

Full Text Available Electrostatic properties of asymmetrically contacted carbon nanotube barrier-free bipolar diode photodetector are studied by solving the Poisson equation self-consistently with equilibrium carrier statistics. For electric field parallel to tube’s axis, the maximum electric field occurs near contact but decays rapidly in a few nanometers, followed by a slowly increasing trend when it extends to the center of channel. By considering the field ionization and the diffusion effect of exciton, a model of estimation on quantum efficiency for the device is made. We find that the quantum efficiency increases with increasing exciton lifetime, decreasing diffusion constant and channel length. For devices with a channel length shorter than 50 nm, the contribution of field ionization to the quantum efficiency can reach 60%.

High-efficiency and low-loss gallium nitride dielectric metasurfaces for nanophotonics at visible wavelengths

Science.gov (United States)

Emani, Naresh Kumar; Khaidarov, Egor; Paniagua-Domínguez, Ramón; Fu, Yuan Hsing; Valuckas, Vytautas; Lu, Shunpeng; Zhang, Xueliang; Tan, Swee Tiam; Demir, Hilmi Volkan; Kuznetsov, Arseniy I.

2017-11-01

The dielectric nanophotonics research community is currently exploring transparent material platforms (e.g., TiO2, Si3N4, and GaP) to realize compact high efficiency optical devices at visible wavelengths. Efficient visible-light operation is key to integrating atomic quantum systems for future quantum computing. Gallium nitride (GaN), a III-V semiconductor which is highly transparent at visible wavelengths, is a promising material choice for active, nonlinear, and quantum nanophotonic applications. Here, we present the design and experimental realization of high efficiency beam deflecting and polarization beam splitting metasurfaces consisting of GaN nanostructures etched on the GaN epitaxial substrate itself. We demonstrate a polarization insensitive beam deflecting metasurface with 64% and 90% absolute and relative efficiencies. Further, a polarization beam splitter with an extinction ratio of 8.6/1 (6.2/1) and a transmission of 73% (67%) for p-polarization (s-polarization) is implemented to demonstrate the broad functionality that can be realized on this platform. The metasurfaces in our work exhibit a broadband response in the blue wavelength range of 430-470 nm. This nanophotonic platform of GaN shows the way to off- and on-chip nonlinear and quantum photonic devices working efficiently at blue emission wavelengths common to many atomic quantum emitters such as Ca+ and Sr+ ions.

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.

High efficiency detection technology on quantum action using radiation excitation

International Nuclear Information System (INIS)

Okubo, Masataka; Ukibe, Masahiro; Sakamoto, Isao; Hayashi, Nobuyuki; Shoji, Akira; Kobayashi, Naoto

2000-01-01

In 1998 fiscal year, as a local quasi particle loss process, it was elucidated that there was a quasi particle loss induced with magnetic flux quantum trapped by a detector on its cooling. Hitherto, it was reported that action of a tunnel junction detector was different by its magnetic history. That is, the detector had unstability such as variation of its action on its cooling. Therefore, the quasi particle loss induced by magnetic flux quantum forming cause of the unstability was quantitatively evaluated. As a result, it was elucidated that output of the detector was reduced half only by trapping the magnetic flux quantum with numbers corresponding to weak magnetic field like geomagnetism. And, this phenomenon was also described by using a model concept with quasi particle trapping due to the magnetic flux quantum. (G.K.)

Double quantum dots decorated 3D graphene flowers for highly efficient photoelectrocatalytic hydrogen production

Science.gov (United States)

Cheng, Qifa; Xu, Jing; Wang, Tao; Fan, Ling; Ma, Ruifang; Yu, Xinzhi; Zhu, Jian; Xu, Zhi; Lu, Bingan

2017-11-01

Photoelectrocatalysis (PEC) has been demonstrated as a promising technique for hydrogen production. However, the high over-potential and high recombination rate of photo-induced electron-hole pairs lead to poor hydrogen production efficiency. In order to overcome these problems, TiO2 and Au dual quantum dots (QDs) on three-dimensional graphene flowers (Au@TiO2@3DGFs) was synthesized by an electro-deposition strategy. The combination of Au and TiO2 modulates the band gap of TiO2, shifts the absorption to visible lights and improves the utilization efficiency of solar light. Simultaneously, the size-quantization TiO2 on 3DGFs not only achieves a larger specific surface area over conventional nanomaterials, but also promotes the separation of the photo-induced electron-hole pairs. Besides, the 3DGFs as a scaffold for QDs can provide more active sites and stable structure. Thus, the newly-developed Au@TiO2@3DGFs composite exhibited an impressive PEC activity and excellent durability. Under -240 mV potential (vs. RHE), the photoelectric current density involved visible light illumination (100 mW cm-2) reached 90 mA cm-2, which was about 3.6 times of the natural current density (without light, only 25 mA cm-2). It worth noting that the photoelectric current density did not degrade and even increased to 95 mA cm-2 over 90 h irradiation, indicating an amazing chemical stability.

Efficient steady-state solver for hierarchical quantum master equations

Science.gov (United States)

Zhang, Hou-Dao; Qiao, Qin; Xu, Rui-Xue; Zheng, Xiao; Yan, YiJing

2017-07-01

Steady states play pivotal roles in many equilibrium and non-equilibrium open system studies. Their accurate evaluations call for exact theories with rigorous treatment of system-bath interactions. Therein, the hierarchical equations-of-motion (HEOM) formalism is a nonperturbative and non-Markovian quantum dissipation theory, which can faithfully describe the dissipative dynamics and nonlinear response of open systems. Nevertheless, solving the steady states of open quantum systems via HEOM is often a challenging task, due to the vast number of dynamical quantities involved. In this work, we propose a self-consistent iteration approach that quickly solves the HEOM steady states. We demonstrate its high efficiency with accurate and fast evaluations of low-temperature thermal equilibrium of a model Fenna-Matthews-Olson pigment-protein complex. Numerically exact evaluation of thermal equilibrium Rényi entropies and stationary emission line shapes is presented with detailed discussion.

Positive Wigner functions render classical simulation of quantum computation efficient.

Science.gov (United States)

Mari, A; Eisert, J

2012-12-07

We show that quantum circuits where the initial state and all the following quantum operations can be represented by positive Wigner functions can be classically efficiently simulated. This is true both for continuous-variable as well as discrete variable systems in odd prime dimensions, two cases which will be treated on entirely the same footing. Noting the fact that Clifford and Gaussian operations preserve the positivity of the Wigner function, our result generalizes the Gottesman-Knill theorem. Our algorithm provides a way of sampling from the output distribution of a computation or a simulation, including the efficient sampling from an approximate output distribution in the case of sampling imperfections for initial states, gates, or measurements. In this sense, this work highlights the role of the positive Wigner function as separating classically efficiently simulable systems from those that are potentially universal for quantum computing and simulation, and it emphasizes the role of negativity of the Wigner function as a computational resource.

MoS2 quantum dots@TiO2 nanotube composites with enhanced photoexcited charge separation and high-efficiency visible-light driven photocatalysis

Science.gov (United States)

Zhao, Fenfen; Rong, Yuefei; Wan, Junmin; Hu, Zhiwen; Peng, Zhiqin; Wang, Bing

2018-03-01

MoS2 quantum dots (QDs) that are 5 nm in size were deposited on the surface of ultrathin TiO2 nanotubes (TNTs) with 5 nm wall thickness by using an improved hydrothermal method to form a MoS2 QDs@TNT visible-light photocatalyst. The ultrathin TNTs with high percentage of photocatalytic reactive facets were fabricated by the commercially available TiO2 nanoparticles (P25) through an improved hydrothermal method, and the MoS2 QDs were acquired by using a surfactant-assisted technique. The novel MoS2 QDs@TNT photocatalysts showed excellent photocatalytic activity with a decolorization rate of 92% or approximately 3.5 times more than that of pure TNTs for the high initial concentration of methylene blue solution (20 mg l-1) within 40 min under visible-light irradiation. MoS2 as the co-catalysts favored the broadening of TNTs into the visible-light absorption scope. The quantum confinement and edge effects of the MoS2 QDs and the heterojunction formed between the MoS2 QDs and TNTs efficiently extended the lifetime of photoinduced charges, impeded the recombination of photoexcited electron-hole pairs, and improved the visible-light-driven high-efficiency photocatalysis.

Highly efficient red electrophosphorescent devices at high current densities

International Nuclear Information System (INIS)

Wu Youzhi; Zhu Wenqing; Zheng Xinyou; Sun, Runguang; Jiang Xueyin; Zhang Zhilin; Xu Shaohong

2007-01-01

Efficiency decrease at high current densities in red electrophosphorescent devices is drastically restrained compared with that from conventional electrophosphorescent devices by using bis(2-methyl-8-quinolinato)4-phenylphenolate aluminum (BAlq) as a hole and exciton blocker. Ir complex, bis(2-(2'-benzo[4,5-α]thienyl) pyridinato-N,C 3' ) iridium (acetyl-acetonate) is used as an emitter, maximum external quantum efficiency (QE) of 7.0% and luminance of 10000cd/m 2 are obtained. The QE is still as high as 4.1% at higher current density J=100mA/cm 2 . CIE-1931 co-ordinates are 0.672, 0.321. A carrier trapping mechanism is revealed to dominate in the process of electroluminescence

High-dimensional quantum cloning and applications to quantum hacking.

Science.gov (United States)

Bouchard, Frédéric; Fickler, Robert; Boyd, Robert W; Karimi, Ebrahim

2017-02-01

Attempts at cloning a quantum system result in the introduction of imperfections in the state of the copies. This is a consequence of the no-cloning theorem, which is a fundamental law of quantum physics and the backbone of security for quantum communications. Although perfect copies are prohibited, a quantum state may be copied with maximal accuracy via various optimal cloning schemes. Optimal quantum cloning, which lies at the border of the physical limit imposed by the no-signaling theorem and the Heisenberg uncertainty principle, has been experimentally realized for low-dimensional photonic states. However, an increase in the dimensionality of quantum systems is greatly beneficial to quantum computation and communication protocols. Nonetheless, no experimental demonstration of optimal cloning machines has hitherto been shown for high-dimensional quantum systems. We perform optimal cloning of high-dimensional photonic states by means of the symmetrization method. We show the universality of our technique by conducting cloning of numerous arbitrary input states and fully characterize our cloning machine by performing quantum state tomography on cloned photons. In addition, a cloning attack on a Bennett and Brassard (BB84) quantum key distribution protocol is experimentally demonstrated to reveal the robustness of high-dimensional states in quantum cryptography.

Highly Efficient Moisture-Triggered Nanogenerator Based on Graphene Quantum Dots.

Science.gov (United States)

Huang, Yaxin; Cheng, Huhu; Shi, Gaoquan; Qu, Liangti

2017-11-08

A high-performance moisture triggered nanogenerator is fabricated by using graphene quantum dots (GQDs) as the active material. GQDs are prepared by direct oxidation and etching of natural graphite powder, which have small sizes of 2-5 nm and abundant oxygen-containing functional groups. After the treatment by electrochemical polarization, the GQDs-based moisture triggered nanogenerator can deliver a high voltage up to 0.27 V under 70% relative humidity variation, and a power density of 1.86 mW cm -2 with an optimized load resistor. The latter value is much higher than the moisture-electric power generators reported previously. The GQD moisture triggered nanogenerator is promising for self-power electronics and miniature sensors.

Efficient construction of two-dimensional cluster states with probabilistic quantum gates

International Nuclear Information System (INIS)

Chen Qing; Cheng Jianhua; Wang Kelin; Du Jiangfeng

2006-01-01

We propose an efficient scheme for constructing arbitrary two-dimensional (2D) cluster states using probabilistic entangling quantum gates. In our scheme, the 2D cluster state is constructed with starlike basic units generated from 1D cluster chains. By applying parallel operations, the process of generating 2D (or higher-dimensional) cluster states is significantly accelerated, which provides an efficient way to implement realistic one-way quantum computers

Detective quantum efficiency gains compared with speed gains for hypersensitized astronomical plates

International Nuclear Information System (INIS)

Kaye, A.L.

1977-01-01

It is reasonable to assume that gains in detective quantum efficiency (DQE) are far better criteria for assessing the performance of hypersensitizing techniques than gains in speed. It is shown here that gains in speed can be misleading, for some methods of hypersensitization give plates of increased speed but reduced detective quantum efficiency. (author)

High-Dimensional Quantum Information Processing with Linear Optics

Science.gov (United States)

Fitzpatrick, Casey A.

Quantum information processing (QIP) is an interdisciplinary field concerned with the development of computers and information processing systems that utilize quantum mechanical properties of nature to carry out their function. QIP systems have become vastly more practical since the turn of the century. Today, QIP applications span imaging, cryptographic security, computation, and simulation (quantum systems that mimic other quantum systems). Many important strategies improve quantum versions of classical information system hardware, such as single photon detectors and quantum repeaters. Another more abstract strategy engineers high-dimensional quantum state spaces, so that each successful event carries more information than traditional two-level systems allow. Photonic states in particular bring the added advantages of weak environmental coupling and data transmission near the speed of light, allowing for simpler control and lower system design complexity. In this dissertation, numerous novel, scalable designs for practical high-dimensional linear-optical QIP systems are presented. First, a correlated photon imaging scheme using orbital angular momentum (OAM) states to detect rotational symmetries in objects using measurements, as well as building images out of those interactions is reported. Then, a statistical detection method using chains of OAM superpositions distributed according to the Fibonacci sequence is established and expanded upon. It is shown that the approach gives rise to schemes for sorting, detecting, and generating the recursively defined high-dimensional states on which some quantum cryptographic protocols depend. Finally, an ongoing study based on a generalization of the standard optical multiport for applications in quantum computation and simulation is reported upon. The architecture allows photons to reverse momentum inside the device. This in turn enables realistic implementation of controllable linear-optical scattering vertices for

Comparative study on stained InGaAs quantum wells for high-speed optical-interconnect VCSELs

Science.gov (United States)

Li, Hui; Jia, Xiaowei

2018-05-01

The gain-carrier characteristics of InGaAs quantum well for 980 nm high-speed, energy-efficient vertical-cavity surface-emitting lasers are investigated. We specially studied the potentially InGaAs quantum well designs can be used for the active region of energy-efficient, temperature-stable 980-nm VCSEL, which introduced a quantum well gain peak wavelength-to-cavity resonance wavelength offset to improve the dynamic performance at high operation temperature. Several candidate quantum wells are being compared in theory and measurement. We found that ∼5 nm InGaAs QW with ∼6 nm barrier thickness is suitable for the active region of high-speed optical interconnect 980 nm VCSELs, and no significant improvement in the 20% range of In content of InGaAs QWs. The results are useful for next generation green photonic device design.

Proposal for efficient mode converter based on cavity quantum electrodynamics dark mode in a semiconductor quantum dot coupled to a bimodal microcavity

Energy Technology Data Exchange (ETDEWEB)

Li, Jiahua [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Key Laboratory of Fundamental Physical Quantities Measurement of Ministry of Education, Wuhan 430074 (China); Yu, Rong, E-mail: yurong321@126.com [School of Science, Hubei Province Key Laboratory of Intelligent Robot, Wuhan Institute of Technology, Wuhan 430073 (China); Ma, Jinyong; Wu, Ying, E-mail: yingwu2@163.com [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

2014-10-28

The ability to engineer and convert photons between different modes in a solid-state approach has extensive technological implications not only for classical communication systems but also for future quantum networks. In this paper, we put forward a scheme for coherent mode conversion of optical photons by utilizing the intermediate coupling between a single quantum dot and a bimodal photonic crystal microcavity via a waveguide. Here, one mode of the photonic crystal microcavity is coherently driven by an external single-frequency continuous-wave laser field and the two cavity modes are not coupled to each other due to their orthogonal polarizations. The undriven cavity mode is thus not directly coupled to the input driving laser and the only way it can get light is via the quantum dot. The influences of the system parameters on the photon-conversion efficiency are analyzed in detail in the limit of weak probe field and it is found that high photon-conversion efficiency can be achieved under appropriate conditions. It is shown that the cavity dark mode, which is a superposition of the two optical modes and is decoupled from the quantum dot, can appear in such a hybrid optical system. We discuss the properties of the dark mode and indicate that the formation of the dark mode enables the efficient transfer of optical fields between the two cavity modes.

Size-dependent oscillator strength and quantum efficiency of CdSe quantum dots controlled via the local density of states

DEFF Research Database (Denmark)

Leistikow, M.D.; Johansen, Jeppe; Kettelarij, A.J.

2009-01-01

We study experimentally time-resolved emission of colloidal CdSe quantum dots in an environment with a controlled local density of states LDOS. The decay rate is measured versus frequency and as a function of distance to a mirror. We observe a linear relation between the decay rate and the LDOS, ...... with the measured radiative rates. Our results are relevant for applications of CdSe quantum dots in spontaneous emission control and cavity quantum electrodynamics.......We study experimentally time-resolved emission of colloidal CdSe quantum dots in an environment with a controlled local density of states LDOS. The decay rate is measured versus frequency and as a function of distance to a mirror. We observe a linear relation between the decay rate and the LDOS......, allowing us to determine the size-dependent quantum efficiency and oscillator strength. We find that the quantum efficiency decreases with increasing emission energy mostly due to an increase in nonradiative decay. We manage to obtain the oscillator strength of the important class of CdSe quantum dots...

Quantum Efficiency of Hybrid Photon Detectors for the LHCb RICH

CERN Document Server

Lambert, R W

2008-01-01

The production of Hybrid Photon Detectors to be used as the single-photon sensors for the RICH detectors of the LHCb experiment has recently finished. We present the quantum efficiency measurements of the entire sample of 550 tubes. The manufacturer has succeeded in consistently improving the quantum efficiency of the employed S20-type multi-alkali photocathode above our expectations, by a relative 27 % integrated over the energy spectrum. We also report measurements of the vacuum quality using the photocurrent of the device as a monitor for possible vacuum degradation.

High efficient OLED displays prepared with the air-gapped bridges on quantum dot patterns for optical recycling

Science.gov (United States)

Kim, Hyo-Jun; Shin, Min-Ho; Kim, Joo-Suc; Kim, Se-Eun; Kim, Young-Joo

2017-02-01

An optically efficient structure was proposed and fabricated to realize high brightness organic light emitting diode (OLED) displays based on a white OLED prepared with the air-gapped bridges on the quantum dot (QD) patterns. Compared with a conventional white OLED display, in our experiments, the optical intensity of the proposed OLED display shows the enhancement of 58.2% in the red color and 16.8% in the green color after applying the air-gapped bridge structure on QD patterns of 20 wt% concentration. This enhancement comes from the two facts that the QD patterns downconvert unnecessary blue or blue/green light to the required green or red light and the air-gapped bridges increase the color conversion efficiency of QDs by optical recycling using total internal reflection (TIR) at the interface. In addition, the color gamut of the proposed OLED display increases from 65.5 to 75.9% (NTSC x, y ratio) due to the narrow emission spectra of QDs.

Improved quantum efficiency models of CZTSe: GE nanolayer solar cells with a linear electric field.

Science.gov (United States)

Lee, Sanghyun; Price, Kent J; Saucedo, Edgardo; Giraldo, Sergio

2018-02-08

We fabricated and characterized CZTSe:Ge nanolayer (quantum efficiency for Ge doped CZTSe devices. The linear electric field model is developed with the incomplete gamma function of the quantum efficiency as compared to the empirical data at forward bias conditions. This model is characterized with a consistent set of parameters from a series of measurements and the literature. Using the analytical modelling method, the carrier collection profile in the absorber is calculated and closely fitted by the developed mathematical expressions to identify the carrier dynamics during the quantum efficiency measurement of the device. The analytical calculation is compared with the measured quantum efficiency data at various bias conditions.

Computationally Efficient Nonlinear Bell Inequalities for Quantum Networks

Science.gov (United States)

Luo, Ming-Xing

2018-04-01

The correlations in quantum networks have attracted strong interest with new types of violations of the locality. The standard Bell inequalities cannot characterize the multipartite correlations that are generated by multiple sources. The main problem is that no computationally efficient method is available for constructing useful Bell inequalities for general quantum networks. In this work, we show a significant improvement by presenting new, explicit Bell-type inequalities for general networks including cyclic networks. These nonlinear inequalities are related to the matching problem of an equivalent unweighted bipartite graph that allows constructing a polynomial-time algorithm. For the quantum resources consisting of bipartite entangled pure states and generalized Greenberger-Horne-Zeilinger (GHZ) states, we prove the generic nonmultilocality of quantum networks with multiple independent observers using new Bell inequalities. The violations are maximal with respect to the presented Tsirelson's bound for Einstein-Podolsky-Rosen states and GHZ states. Moreover, these violations hold for Werner states or some general noisy states. Our results suggest that the presented Bell inequalities can be used to characterize experimental quantum networks.

Highly efficient electroluminescence from a solution-processable thermally activated delayed fluorescence emitter

Energy Technology Data Exchange (ETDEWEB)

Wada, Yoshimasa; Kubo, Shosei; Suzuki, Katsuaki; Kaji, Hironori, E-mail: kaji@scl.kyoto-u.ac.jp [Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011 (Japan); Shizu, Katsuyuki [Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011 (Japan); Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Tanaka, Hiroyuki [Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Adachi, Chihaya [Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Japan Science and Technology Agency (JST), ERATO, Adachi Molecular Exciton Engineering Project, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan)

2015-11-02

We developed a thermally activated delayed fluorescence (TADF) emitter, 2,4,6-tris(4-(9,9-dimethylacridan-10-yl)phenyl)-1,3,5-triazine (3ACR-TRZ), suitable for use in solution-processed organic light-emitting diodes (OLEDs). When doped into 4,4′-bis(carbazol-9-yl)biphenyl (CBP) host at 16 wt. %, 3ACR-TRZ showed a high photoluminescence quantum yield of 98%. Transient photoluminescence decay measurements of the 16 wt. % 3ACR-TRZ:CBP film confirmed that 3ACR-TRZ exhibits efficient TADF with a triplet-to-light conversion efficiency of 96%. This high conversion efficiency makes 3ACR-TRZ attractive as an emitting dopant in OLEDs. Using 3ACR-TRZ as an emitter, we fabricated a solution-processed OLED exhibiting a maximum external quantum efficiency of 18.6%.

Laser diode bars based on AlGaAs/GaAs quantum-well heterostructures with an efficiency up to 70%

Science.gov (United States)

Ladugin, M. A.; Marmalyuk, A. A.; Padalitsa, A. A.; Bagaev, T. A.; Andreev, A. Yu.; Telegin, K. Yu.; Lobintsov, A. V.; Davydova, E. I.; Sapozhnikov, S. M.; Danilov, A. I.; Podkopaev, A. V.; Ivanova, E. B.; Simakov, V. A.

2017-05-01

The results of the development and fabrication of laser diode bars (λ = 800 - 810 nm) based on AlGaAs/GaAs quantum-well heterostructures with a high efficiency are presented. An increase in the internal quantum and external differential efficiencies together with a decrease in the working voltage and the series resistance allowed us to improve the output parameters of the semiconductor laser under quasi-cw pumping. The output power of the laser diode bars with a 5-mm transverse length reached 210 W, and the efficiency was ~70%.

Origin of low quantum efficiency of photoluminescence of InP/ZnS nanocrystals

DEFF Research Database (Denmark)

Shirazi, Roza; Kovacs, Andras; Corell, Dennis Dan

2013-01-01

In this paper, we study the origin of a strong wavelength dependence of the quantum efficiency of InP/ZnS nanocrystals. We find that while the average size of the nanocrystals increased by 50%, resulting in longer emission wavelength, the quantum efficiency drops more than one order of magnitude...

Duality quantum algorithm efficiently simulates open quantum systems

Science.gov (United States)

Wei, Shi-Jie; Ruan, Dong; Long, Gui-Lu

2016-01-01

Because of inevitable coupling with the environment, nearly all practical quantum systems are open system, where the evolution is not necessarily unitary. In this paper, we propose a duality quantum algorithm for simulating Hamiltonian evolution of an open quantum system. In contrast to unitary evolution in a usual quantum computer, the evolution operator in a duality quantum computer is a linear combination of unitary operators. In this duality quantum algorithm, the time evolution of the open quantum system is realized by using Kraus operators which is naturally implemented in duality quantum computer. This duality quantum algorithm has two distinct advantages compared to existing quantum simulation algorithms with unitary evolution operations. Firstly, the query complexity of the algorithm is O(d3) in contrast to O(d4) in existing unitary simulation algorithm, where d is the dimension of the open quantum system. Secondly, By using a truncated Taylor series of the evolution operators, this duality quantum algorithm provides an exponential improvement in precision compared with previous unitary simulation algorithm. PMID:27464855

High-efficiency organic glass scintillators

Science.gov (United States)

Feng, Patrick L.; Carlson, Joseph S.

2017-12-19

A new family of neutron/gamma discriminating scintillators is disclosed that comprises stable organic glasses that may be melt-cast into transparent monoliths. These materials have been shown to provide light yields greater than solution-grown trans-stilbene crystals and efficient PSD capabilities when combined with 0.01 to 0.05% by weight of the total composition of a wavelength-shifting fluorophore. Photoluminescence measurements reveal fluorescence quantum yields that are 2 to 5 times greater than conventional plastic or liquid scintillator matrices, which accounts for the superior light yield of these glasses. The unique combination of high scintillation light-yields, efficient neutron/gamma PSD, and straightforward scale-up via melt-casting distinguishes the developed organic glasses from existing scintillators.

Highly Enhanced Photoelectrochemical Water Oxidation Efficiency Based on Triadic Quantum Dot/Layered Double Hydroxide/BiVO ₄ Photoanodes

Energy Technology Data Exchange (ETDEWEB)

Tang, Yanqun; Wang, Ruirui; Yang, Ye; Yan, Dongpeng; Xiang, Xu

2016-08-03

The water oxidation half-reaction is considered to be a bottleneck for achieving highly efficient solar-driven water splitting due to its multiproton-coupled four-electron process and sluggish kinetics. Herein, a triadic photoanode consisting of dual-sized CdTe quantum dots (QDs), Co-based layered double hydroxide (LDH) nanosheets, and BiVO4 particles, that is, QD@LDH@BiVO4, was designed. Two sets of consecutive Type-II band alignments were constructed to improve photogenerated electron-hole separation in the triadic structure. The efficient charge separation resulted in a 2-fold enhancement of the photocurrent of the QD@LDH@BiVO4 photoanode. A significantly enhanced oxidation efficiency reaching above 90% in the low bias region (i.e., E < 0.8 V vs RHE) could be critical in determining the overall performance of a complete photoelectrochemical cell. The faradaic efficiency for water oxidation was almost 90%. The conduction band energy of QDs is -1.0 V more negative than that of LDH, favorable for the electron injection to LDH and enabling a more efficient hole separation. The enhanced photon-to-current conversion efficiency and improved water oxidation efficiency of the triadic structure may result from the non-negligible contribution of hot electrons or holes generated in QDs. Such a band-matching and multidimensional triadic architecture could be a promising strategy for achieving high-efficiency photoanodes by sufficiently utilizing and maximizing the functionalities of QDs.

High efficiency electrophosphorescence from bilayer organic light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Li Minghang; Lin, Ming-Te; Shepherd, Nigel D [Department of Material Science and Engineering, University of North Texas, Denton, TX (United States); Chen, Wei-Hsuan; Oswald, Iain; Omary, Mohammad [Department of Chemeistry, University of North Texas, Denton, TX (United States)

2011-09-14

An electron mobility of 2.7 x 10{sup -5} cm{sup 2} V{sup -1} s{sup -1} was measured for the phosphorescent emitter bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II)(Pt(ptp)2), which prompted its evaluation as both the emissive layer and electron transport layer in organic light emitting diodes with a simple bilayer structure. Power and external quantum efficiencies of 54.0 {+-} 0.2 lm W{sup -1} and 15.9% were obtained, which as far as we could ascertain are amongst the highest reported values for bilayer devices. We ascribe the high device efficiency to the combination of the high electron mobility, short excited-state lifetime (117 ns) and high luminescence quantum yield (60%) of the bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II). The colour temperature of the devices was 2855 K at 5 V, which places the emission in the 'warm' light spectral region.

High-fidelity quantum driving

DEFF Research Database (Denmark)

Bason, Mark George; Viteau, Matthieu; Malossi, Nicola

2011-01-01

Accurately controlling a quantum system is a fundamental requirement in quantum information processing and the coherent manipulation of molecular systems. The ultimate goal in quantum control is to prepare a desired state with the highest fidelity allowed by the available resources...... and the experimental constraints. Here we experimentally implement two optimal high-fidelity control protocols using a two-level quantum system comprising Bose–Einstein condensates in optical lattices. The first is a short-cut protocol that reaches the maximum quantum-transformation speed compatible...

Microstructure, electrical, and optical properties of evaporated PtSi/p-Si(100) Schottky barriers as high quantum efficient infrared detectors

International Nuclear Information System (INIS)

Wu Jihhuah; Chang Rongsen; Horng Gwoji

2004-01-01

The effects of the microstructure and the electrical and optical properties on the formation at highly efficient infrared PtSi Schottky barrier detectors (SBD) have been studied in detail. Two- to twelve-nanometer-thick PtSi films were grown by evaporation at temperature ranging from 350 to 550 deg. C. The electron diffraction patterns indicate the existence of both the (11-bar0) and (12-bar1) orientations when PtSi films formed at 350 deg. C. However, the diffraction patterns show only the (12-bar1) orientation when the PtSi films are formed at 450 deg. C or above. The electrical barrier height of the Schottky barrier detector that formed at 350 deg. C was about 20 meV higher than that formed at 450 deg. C or above. The grain size and the film thickness had a negligible effect on the electrical barrier height. However, the optical performance was strongly dependent on the film thickness and the growth conditions. The 350 deg. C PtSi film showed increased quantum efficiency as the film thickness decreased. The optimal thickness that provided the highest responsivity was 2 nm. On the other hand, the optimal thickness shifted to 8 nm for PtSi film formed at 450 deg. C or above. These results indicate that the quantum efficiency of a detector can be improved if the PtSi film has an orientation at (12-bar1), a larger grain size, and an optimal film thickness

Flexible deep-ultraviolet light-emitting diodes for significant improvement of quantum efficiencies by external bending

KAUST Repository

Shervin, Shahab

2018-01-26

Deep ultraviolet (DUV) light at the wavelength range of 250‒280 nm (UVC spectrum) is essential for numerous applications such as sterilization, purification, sensing, and communication. III-nitride-based DUV light-emitting diodes (DUV LEDs), like other solid-state lighting sources, offer a great potential to replace the conventional gas-discharged lamps with short lifetimes and toxic-element-bearing nature. However, unlike visible LEDs, the DUV LEDs are still suffering from low quantum efficiencies (QEs) and low optical output powers. In this work, reported is a new route to improve QEs of AlGaN-based DUV LEDs using mechanical flexibility of recently developed bendable thin-film structures. Numerical studies show that electronic band structures of AlGaN heterostructures and resulting optical and electrical characteristics of the devices can be significantly modified by external bending through active control of piezoelectric polarization. Internal quantum efficiency (IQE) is enhanced higher than three times, when the DUV LEDs are moderately bent to induce in-plane compressive strain in the heterostructure. Furthermore, efficiency droop at high injection currents is mitigated and turn-on voltage of diodes decreases with the same bending condition. The concept of bendable DUV LEDs with a controlled external strain can provide a new path for high-output-power and high-efficiency devices.

Flexible deep-ultraviolet light-emitting diodes for significant improvement of quantum efficiencies by external bending

KAUST Repository

Shervin, Shahab; Oh, Seung Kyu; Park, Hyun Jung; Lee, Keon Hwa; Asadirad, Mojtaba; Kim, Seung Hwan; Kim, Jeomoh; Pouladi, Sara; Lee, Sung-Nam; Li, Xiaohang; Kwak, Joon-Seop; Ryou, Jae-Hyun

2018-01-01

Deep ultraviolet (DUV) light at the wavelength range of 250‒280 nm (UVC spectrum) is essential for numerous applications such as sterilization, purification, sensing, and communication. III-nitride-based DUV light-emitting diodes (DUV LEDs), like other solid-state lighting sources, offer a great potential to replace the conventional gas-discharged lamps with short lifetimes and toxic-element-bearing nature. However, unlike visible LEDs, the DUV LEDs are still suffering from low quantum efficiencies (QEs) and low optical output powers. In this work, reported is a new route to improve QEs of AlGaN-based DUV LEDs using mechanical flexibility of recently developed bendable thin-film structures. Numerical studies show that electronic band structures of AlGaN heterostructures and resulting optical and electrical characteristics of the devices can be significantly modified by external bending through active control of piezoelectric polarization. Internal quantum efficiency (IQE) is enhanced higher than three times, when the DUV LEDs are moderately bent to induce in-plane compressive strain in the heterostructure. Furthermore, efficiency droop at high injection currents is mitigated and turn-on voltage of diodes decreases with the same bending condition. The concept of bendable DUV LEDs with a controlled external strain can provide a new path for high-output-power and high-efficiency devices.

Time–energy high-dimensional one-side device-independent quantum key distribution

International Nuclear Information System (INIS)

Bao Hai-Ze; Bao Wan-Su; Wang Yang; Chen Rui-Ke; Ma Hong-Xin; Zhou Chun; Li Hong-Wei

2017-01-01

Compared with full device-independent quantum key distribution (DI-QKD), one-side device-independent QKD (1sDI-QKD) needs fewer requirements, which is much easier to meet. In this paper, by applying recently developed novel time–energy entropic uncertainty relations, we present a time–energy high-dimensional one-side device-independent quantum key distribution (HD-QKD) and provide the security proof against coherent attacks. Besides, we connect the security with the quantum steering. By numerical simulation, we obtain the secret key rate for Alice’s different detection efficiencies. The results show that our protocol can performance much better than the original 1sDI-QKD. Furthermore, we clarify the relation among the secret key rate, Alice’s detection efficiency, and the dispersion coefficient. Finally, we simply analyze its performance in the optical fiber channel. (paper)

The Influences of Quantum Coherence on the Positive Work and the Efficiency of Quantum Heat Engine with Working Substance of Two-Qubit Heisenberg XXX Model

Science.gov (United States)

Peng, Hu-Ping; Fang, Mao-Fa; Yu, Min; Zou, Hong-Mei

2018-03-01

We study the influences of quantum coherence on the positive work and the efficiency of quantum heat engine (QHE) based on working substance of two-qubit Heisenberg model under a constant external magnetic field. By using analytical and numerical solution, we give the relation expressions for both the positive work and the efficiency with quantum coherence, and in detail discuss the effects of the quantum coherence on the positive work and the efficiency of QHE in the absence or presence of external magnetic field, respectively.

The Influences of Quantum Coherence on the Positive Work and the Efficiency of Quantum Heat Engine with Working Substance of Two-Qubit Heisenberg XXX Model

Science.gov (United States)

Peng, Hu-Ping; Fang, Mao-Fa; Yu, Min; Zou, Hong-Mei

2018-06-01

We study the influences of quantum coherence on the positive work and the efficiency of quantum heat engine (QHE) based on working substance of two-qubit Heisenberg model under a constant external magnetic field. By using analytical and numerical solution, we give the relation expressions for both the positive work and the efficiency with quantum coherence, and in detail discuss the effects of the quantum coherence on the positive work and the efficiency of QHE in the absence or presence of external magnetic field, respectively.

Emulsion Synthesis of Size-Tunable CH3NH3PbBr3 Quantum Dots: An Alternative Route toward Efficient Light-Emitting Diodes.

Science.gov (United States)

Huang, Hailong; Zhao, Fangchao; Liu, Lige; Zhang, Feng; Wu, Xian-gang; Shi, Lijie; Zou, Bingsuo; Pei, Qibing; Zhong, Haizheng

2015-12-30

We report a facile nonaqueous emulsion synthesis of colloidal halide perovskite quantum dots by controlled addition of a demulsifier into an emulsion of precursors. The size of resulting CH3NH3PbBr3 quantum dots can be tuned from 2 to 8 nm by varying the amount of demulsifier. Moreover, this emulsion synthesis also allows the purification of these quantum dots by precipitation from the colloidal solution and obtains solid-state powder which can be redissolved for thin film coating and device fabrication. The photoluminescence quantum yields of the quantum dots is generally in the range of 80-92%, and can be well-preserved after purification (∼80%). Green light-emitting diodes fabricated comprising a spin-cast layer of the colloidal CH3NH3PbBr3 quantum dots exhibited maximum current efficiency of 4.5 cd/A, power efficiency of 3.5 lm/W, and external quantum efficiency of 1.1%. This provides an alternative route toward high efficient solution-processed perovskite-based light-emitting diodes. In addition, the emulsion synthesis is versatile and can be extended for the fabrication of inorganic halide perovskite colloidal CsPbBr3 nanocrystals.

Quasi-Resonant Absorption for Quantum Efficiency Improvement in Detectors

Data.gov (United States)

National Aeronautics and Space Administration — Quasi-resonant absorption has been demonstrated to enhance the quantum efficiency of devices across the spectrum, but specifically it is a challenge in the UV...

Heterogeneous photocatalysis for air and water treatment: Fundamental needs for quantum efficiency enhancement

Energy Technology Data Exchange (ETDEWEB)

Ollis, D.F. [North Carolina State Univ., Raleigh, NC (United States)

1996-09-01

In the remediation industries, a useful treatment technology must be {open_quotes}general, robust, and cheap{close_quotes}. Among oxidation processes, heterogeneous photocatalysis is now broadly demonstrated to destroy common water and air contaminants. The potential process uses of highly stable titania, long lived lamps (one year), and room temperature operation, indicating a simple and robust process. We are left to address the third criterion: Can photocatalysis be {open_quotes}cheap{close_quotes}? In both liquid phase and gas phase treatment and purification by photocatalysis, it is established that the primary barrier to commercialization is often cost. Cost in return is dominated by the efficiency with which solar or lamp photons are harvested for productive light, and subsequent dark, reactions. This paper therefore defines fundamental needs in photocatalysis for pollution control in terms of activities which could lead to quantum efficiency enhancement. We first recall three related definitions. The quantum yield (QY) is the ratio of molecules of reactant converted per photon absorbed, a fundamental quantity. A less fundamental, but more easily measured variable is the quantum efficiency (QE), the ratio of molecules converted per photon entering the reactor. A third variable is the energy required per order of magnitude pollutant reduction, or EEO, a definition which provides for easy energy cost comparisons among different technologies. Each measure cited here reflects the photon, and thus the electrical, cost of this photochemistry.

High Quantum Yield Blue Emission from Lead-Free Inorganic Antimony Halide Perovskite Colloidal Quantum Dots.

Science.gov (United States)

Zhang, Jian; Yang, Ying; Deng, Hui; Farooq, Umar; Yang, Xiaokun; Khan, Jahangeer; Tang, Jiang; Song, Haisheng

2017-09-26

Colloidal quantum dots (QDs) of lead halide perovskite have recently received great attention owing to their remarkable performances in optoelectronic applications. However, their wide applications are hindered from toxic lead element, which is not environment- and consumer-friendly. Herein, we utilized heterovalent substitution of divalent lead (Pb 2+ ) with trivalent antimony (Sb 3+ ) to synthesize stable and brightly luminescent Cs 3 Sb 2 Br 9 QDs. The lead-free, full-inorganic QDs were fabricated by a modified ligand-assisted reprecipitation strategy. A photoluminescence quantum yield (PLQY) was determined to be 46% at 410 nm, which was superior to that of other reported halide perovskite QDs. The PL enhancement mechanism was unraveled by surface composition derived quantum-well band structure and their large exciton binding energy. The Br-rich surface and the observed 530 meV exciton binding energy were proposed to guarantee the efficient radiative recombination. In addition, we can also tune the inorganic perovskite QD (Cs 3 Sb 2 X 9 ) emission wavelength from 370 to 560 nm via anion exchange reactions. The developed full-inorganic lead-free Sb-perovskite QDs with high PLQY and stable emission promise great potential for efficient emission candidates.

Optoelectronic engineering of colloidal quantum-dot solar cells beyond the efficiency black hole: a modeling approach

Science.gov (United States)

Mahpeykar, Seyed Milad; Wang, Xihua

2017-02-01

Colloidal quantum dot (CQD) solar cells have been under the spotlight in recent years mainly due to their potential for low-cost solution-processed fabrication and efficient light harvesting through multiple exciton generation (MEG) and tunable absorption spectrum via the quantum size effect. Despite the impressive advances achieved in charge carrier mobility of quantum dot solids and the cells' light trapping capabilities, the recent progress in CQD solar cell efficiencies has been slow, leaving them behind other competing solar cell technologies. In this work, using comprehensive optoelectronic modeling and simulation, we demonstrate the presence of a strong efficiency loss mechanism, here called the "efficiency black hole", that can significantly hold back the improvements achieved by any efficiency enhancement strategy. We prove that this efficiency black hole is the result of sole focus on enhancement of either light absorption or charge extraction capabilities of CQD solar cells. This means that for a given thickness of CQD layer, improvements accomplished exclusively in optic or electronic aspect of CQD solar cells do not necessarily translate into tangible enhancement in their efficiency. The results suggest that in order for CQD solar cells to come out of the mentioned black hole, incorporation of an effective light trapping strategy and a high quality CQD film at the same time is an essential necessity. Using the developed optoelectronic model, the requirements for this incorporation approach and the expected efficiencies after its implementation are predicted as a roadmap for CQD solar cell research community.

Quantum efficiency measurement system for large area CsI photodetectors

CERN Document Server

Cusanno, F; Colilli, S; Crateri, R; Fratoni, R; Frullani, S; Garibaldi, F; Giuliani, F; Gricia, M; Lucentini, M; Mostarda, A; Santavenere, F; Veneroni, P; Breuer, H; Iodice, M; Urciuoli, G M; De Cataldo, G; De Leo, R; Lagamba, L; Braem, André

2003-01-01

A proximity focusing freon/CsI RICH detector has been built for kaon physics at Thomas Jefferson National Accelerator Facility (TJNAF or Jefferson Lab), Hall A. The Cherenkov photons are detected by a UV photosensitive CsI film which has been obtained by vacuum evaporation. A dedicated evaporation facility for large area photocathodes has been built for this task. A measuring system has been built to allow the evaluation of the absolute quantum efficiency (QE) just after the evaporation. The evaporation facility is described here, as well as the quantum efficiency measurement device. Results of the QE on-line measurements, for the first time on large area photocathodes, are reported.

An energy and cost efficient majority-based RAM cell in quantum-dot cellular automata

Directory of Open Access Journals (Sweden)

Milad Bagherian Khosroshahy

Full Text Available Nanotechnologies, notably quantum-dot cellular automata, have achieved major attentions for their prominent features as compared to the conventional CMOS circuitry. Quantum-dot cellular automata, particularly owning to its considerable reduction in size, high switching speed and ultra-low energy consumption, is considered as a potential alternative for the CMOS technology. As the memory unit is one of the most essential components in a digital system, designing a well-optimized QCA random access memory (RAM cell is an important area of research. In this paper, a new five-input majority gate is presented which is suitable for implementing efficient single-layer QCA circuits. In addition, a new RAM cell with set and reset capabilities is designed based on the proposed majority gate, which has an efficient and low-energy structure. The functionality, performance and energy consumption of the proposed designs are evaluated based on the QCADesigner and QCAPro tools. According to the simulation results, the proposed RAM design leads to on average 38% lower total energy dissipation, 25% smaller area, 20% lower cell count, 28% lower delay and 60% lower QCA cost as compared to its previous counterparts. Keywords: Quantum-dot cellular automata (QCA, Majority gate, Random access memory (RAM, Energy efficiency

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.

Quantum efficiency of silica-coated rare-earth doped yttrium silicate

International Nuclear Information System (INIS)

Cervantes-Vásquez, D.; Contreras, O.E.; Hirata, G.A.

2013-01-01

The photoluminescent properties of rare earth-activated white-emitting Y 2 SiO 5 :Ce,Tb nanocrystalline phosphor prepared by two different methods, pressure-assisted combustion synthesis and sol–gel, were studied. The synthesized phosphor samples were post-annealed at 1373 K and 1623 K in order to obtain the X1-Y 2 SiO 5 and X2-Y 2 SiO 5 phases, respectively, which were confirmed by X-ray diffraction measurements. Photoluminescence analysis showed the contribution of two blue-emission bands within the 380–450 nm region originating from 5d–4f transitions in Ce 3+ ions and a well-defined green emission of Tb 3+ ions located at 545 nm corresponding to 5 D 4 → 7 F 5 electronic transitions. Thereafter, Y 2 SiO 5 :Ce,Tb powders were coated with colloidal silica in order to investigate the effect of silica coatings on their luminescent properties. Absolute fluorescence quantum efficiency measurements were carefully performed, which revealed an increase of 12% of efficiency in coated compared with bare-Y 2 SiO 5 :Ce,Tb phosphor. -- Highlights: • Y 2 SiO 5 :Ce,Tb phosphor powders were successfully coated with colloidal silica. • Post-annealing treatments improved the quantum efficiency of silica-coated Y 2 SiO 5 :Ce,Tb phosphors. • Absolute fluorescence quantum efficiency measurements showed an increase of 12%

Parallel state transfer and efficient quantum routing on quantum networks.

Science.gov (United States)

Chudzicki, Christopher; Strauch, Frederick W

2010-12-31

We study the routing of quantum information in parallel on multidimensional networks of tunable qubits and oscillators. These theoretical models are inspired by recent experiments in superconducting circuits. We show that perfect parallel state transfer is possible for certain networks of harmonic oscillator modes. We extend this to the distribution of entanglement between every pair of nodes in the network, finding that the routing efficiency of hypercube networks is optimal and robust in the presence of dissipation and finite bandwidth.

High-efficiency white organic light-emitting diodes using thermally activated delayed fluorescence

International Nuclear Information System (INIS)

Nishide, Jun-ichi; Hiraga, Yasuhide; Nakanotani, Hajime; Adachi, Chihaya

2014-01-01

White organic light-emitting diodes (WOLEDs) have attracted much attention recently, aimed for next-generation lighting sources because of their high potential to realize high electroluminescence efficiency, flexibility, and low-cost manufacture. Here, we demonstrate high-efficiency WOLED using red, green, and blue thermally activated delayed fluorescence materials as emissive dopants to generate white electroluminescence. The WOLED has a maximum external quantum efficiency of over 17% with Commission Internationale de l'Eclairage coordinates of (0.30, 0.38).

Effects of low charge carrier wave function overlap on internal quantum efficiency in GaInN quantum wells

Energy Technology Data Exchange (ETDEWEB)

Netzel, Carsten; Hoffmann, Veit; Wernicke, Tim; Knauer, Arne; Weyers, Markus [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Kneissl, Michael [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)

2010-07-15

To determine relevant processes affecting the internal quantum efficiency in GaInN quantum well structures, we have studied the temperature and excitation power dependent photoluminescence intensity for quantum wells with different well widths on (0001) c-plane GaN and for quantum wells on nonpolar (11-20) a-plane GaN. In thick polar quantum wells, the quantum confined Stark effect (QCSE) causes a stronger intensity decrease with increasing temperature as long as the radiative recombination dominates. At higher temperatures, when the nonradiative recombination becomes more important, thick polar quantum wells feature a lower relative intensity decrease than thinner polar or nonpolar quantum wells. Excitation power dependent photoluminescence points to a transition from a recombination of excitons to a bimolecular recombination of uncorrelated charge carriers for thick polar quantum wells in the same temperature range. This transition might contribute to the limitation of nonradiative recombination by a reduced diffusivity of charge carriers. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Structural Control of InP/ZnS Core/Shell Quantum Dots Enables High-quality White LEDs.

Science.gov (United States)

Ganesh Kumar, Baskaran; Sadeghi, Sadra; Melikov, Rustamzhon; Mohammadi Aria, Mohammed; Bahmani Jalali, Houman; Ow-Yang, Cleva; Nizamoglu, Sedat

2018-05-30

Herein, we demonstrate that the structural and optical control of InP-based quantum dots can lead to high-performance LEDs. Zinc sulphide (ZnS) shells passivate the InP quantum dot core and increase the quantum yield in green-emitting quantum dots by 13-fold and red-emitting quantum dots by 8-fold. The optimised quantum dots are integrated in the liquid-state to eliminate aggregation induced emission quenching and we fabricated white LEDs with warm, neutral, and cool white appearance by the down-conversion mechanism. The quantum dot-functionalized white LEDs achieve luminous efficiency up to 14.7 lm/W and colour-rendering index up to 80. The structural and optical control of InP/ZnS core/shell quantum dots enable 23-fold enhancement in luminous efficiency of white LEDs compared to ones containing only QDs of InP core. © 2018 IOP Publishing Ltd.

Exciplex-triplet energy transfer: A new method to achieve extremely efficient organic light-emitting diode with external quantum efficiency over 30% and drive voltage below 3 V

Science.gov (United States)

Seo, Satoshi; Shitagaki, Satoko; Ohsawa, Nobuharu; Inoue, Hideko; Suzuki, Kunihiko; Nowatari, Hiromi; Yamazaki, Shunpei

2014-04-01

A novel approach to enhance the power efficiency of an organic light-emitting diode (OLED) by employing energy transfer from an exciplex to a phosphorescent emitter is reported. It was found that excitation energy of an exciplex formed between an electron-transporting material with a π-deficient quinoxaline moiety and a hole-transporting material with aromatic amine structure can be effectively transferred to a phosphorescent iridium complex in an emission layer of a phosphorescent OLED. Moreover, such an exciplex formation increases quantum efficiency and reduces drive voltage. A highly efficient, low-voltage, and long-life OLED based on this energy transfer is also demonstrated. This OLED device exhibited extremely high external quantum efficiency of 31% even without any attempt to enhance light outcoupling and also achieved a low drive voltage of 2.8 V and a long lifetime of approximately 1,000,000 h at a luminance of 1,000 cd/m2.

Efficient method for transport simulations in quantum cascade lasers

Directory of Open Access Journals (Sweden)

Maczka Mariusz

2017-01-01

Full Text Available An efficient method for simulating quantum transport in quantum cascade lasers is presented. The calculations are performed within a simple approximation inspired by Büttiker probes and based on a finite model for semiconductor superlattices. The formalism of non-equilibrium Green’s functions is applied to determine the selected transport parameters in a typical structure of a terahertz laser. Results were compared with those obtained for a infinite model as well as other methods described in literature.

Quantum secure direct communication with high-dimension quantum superdense coding

International Nuclear Information System (INIS)

Wang Chuan; Li Yansong; Liu Xiaoshu; Deng Fuguo; Long Guilu

2005-01-01

A protocol for quantum secure direct communication with quantum superdense coding is proposed. It combines the ideas of block transmission, the ping-pong quantum secure direct communication protocol, and quantum superdense coding. It has the advantage of being secure and of high source capacity

Efficient quantum state transfer in an engineered chain of quantum bits

Science.gov (United States)

Sandberg, Martin; Knill, Emanuel; Kapit, Eliot; Vissers, Michael R.; Pappas, David P.

2016-03-01

We present a method of performing quantum state transfer in a chain of superconducting quantum bits. Our protocol is based on engineering the energy levels of the qubits in the chain and tuning them all simultaneously with an external flux bias. The system is designed to allow sequential adiabatic state transfers, resulting in on-demand quantum state transfer from one end of the chain to the other. Numerical simulations of the master equation using realistic parameters for capacitive nearest-neighbor coupling, energy relaxation, and dephasing show that fast, high-fidelity state transfer should be feasible using this method.

Improve photocurrent quantum efficiency of carbon nanotube by chemical treatment

International Nuclear Information System (INIS)

Wang Hongguang; Wei Jinquan; Jia Yi; Li Zhen; Zhu Hongwei; Wang Kunlin; Wu Dehai

2012-01-01

Highlights: ► The QE of photocurrent for the H 2 O 2 -treated CNTs reaches to 5.28% at U bias = 0.1 V. ► Moderate chemical treatment can enhance the QE of photocurrent of CNTs. ► Excessive chemical treatment decreases the photocurrent quantum efficiency of CNTs. - Abstract: High photocurrent quantum efficiency (QE) of carbon nanotubes (CNTs) is important to their photovoltaic applications. The ability of photocurrent generation of CNTs depends on their band structure and surface state. For given CNTs, it is possible to improve the QE of photocurrent by chemical modification. Here, we study the effects of simple chemical treatment on the QE of CNTs by measuring the photocurrent of macroscopic CNT bundles. The QE of the H 2 O 2 -treated CNT bundle reaches 5.28% at 0.1 V bias voltage at a laser (λ = 473 nm) illumination, which is 85% higher than that of the pristine sample. But the QE of the CNTs treated in concentrated HNO 3 is lower than that of the pristine sample. It shows that moderate chemical treatment can enhance the photocurrent QE and excessive chemical treatment will decrease the QE because of introducing lots of structural defects.

Significant internal quantum efficiency enhancement of GaN/AlGaN multiple quantum wells emitting at ~350 nm via step quantum well structure design

KAUST Repository

Wu, Feng; Sun, Haiding; Ajia, Idris A.; Roqan, Iman S.; Zhang, Daliang; Dai, Jiangnan; Chen, Changqing; Feng, Zhe Chuan; Li, Xiaohang

2017-01-01

Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at similar to 350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.

Significant internal quantum efficiency enhancement of GaN/AlGaN multiple quantum wells emitting at ~350 nm via step quantum well structure design

KAUST Repository

Wu, Feng

2017-05-03

Significant internal quantum efficiency (IQE) enhancement of GaN/AlGaN multiple quantum wells (MQWs) emitting at similar to 350 nm was achieved via a step quantum well (QW) structure design. The MQW structures were grown on AlGaN/AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). High resolution x-ray diffraction (HR-XRD) and scanning transmission electron microscopy (STEM) were performed, showing sharp interface of the MQWs. Weak beam dark field imaging was conducted, indicating a similar dislocation density of the investigated MQWs samples. The IQE of GaN/AlGaN MQWs was estimated by temperature dependent photoluminescence (TDPL). An IQE enhancement of about two times was observed for the GaN/AlGaN step QW structure, compared with conventional QW structure. Based on the theoretical calculation, this IQE enhancement was attributed to the suppressed polarization-induced field, and thus the improved electron-hole wave-function overlap in the step QW.

Efficient quantum algorithm for computing n-time correlation functions.

Science.gov (United States)

Pedernales, J S; Di Candia, R; Egusquiza, I L; Casanova, J; Solano, E

2014-07-11

We propose a method for computing n-time correlation functions of arbitrary spinorial, fermionic, and bosonic operators, consisting of an efficient quantum algorithm that encodes these correlations in an initially added ancillary qubit for probe and control tasks. For spinorial and fermionic systems, the reconstruction of arbitrary n-time correlation functions requires the measurement of two ancilla observables, while for bosonic variables time derivatives of the same observables are needed. Finally, we provide examples applicable to different quantum platforms in the frame of the linear response theory.

Numerical simulation of quantum efficiency and surface recombination in HgCdTe IR photon-trapping structures

Science.gov (United States)

Schuster, Jonathan; Bellotti, Enrico

2013-06-01

We have investigated the quantum effiency in HgCdTe photovoltaic pixel arrays employing a photon-trapping structure realized with a periodic array of pillars intended to provide broadband operation. We have found that the quantum efficiency depends heavily on the passivation of the pillar surface. Pillars passivated with anodicoxide have a large fixed positive charge on the pillar surface. We use our three-dimensional numerical simulation model to study the effect of surface charge and surface recombination velocity on the exterior of the pillars. We then evaluate the quantum efficiency of this structure subject to different surface conditions. We have found that by themselves, the surface charge and surface recombination are detrimental to the quantum efficiency but the quantum efficiency is recovered when both phenomena are present. We will discuss the effects of these phenomena and the trade offs that exist between the two.

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".

Non-Markovian quantum processes: Complete framework and efficient characterization

Science.gov (United States)

Pollock, Felix A.; Rodríguez-Rosario, César; Frauenheim, Thomas; Paternostro, Mauro; Modi, Kavan

2018-01-01

Currently, there is no systematic way to describe a quantum process with memory solely in terms of experimentally accessible quantities. However, recent technological advances mean we have control over systems at scales where memory effects are non-negligible. The lack of such an operational description has hindered advances in understanding physical, chemical, and biological processes, where often unjustified theoretical assumptions are made to render a dynamical description tractable. This has led to theories plagued with unphysical results and no consensus on what a quantum Markov (memoryless) process is. Here, we develop a universal framework to characterize arbitrary non-Markovian quantum processes. We show how a multitime non-Markovian process can be reconstructed experimentally, and that it has a natural representation as a many-body quantum state, where temporal correlations are mapped to spatial ones. Moreover, this state is expected to have an efficient matrix-product-operator form in many cases. Our framework constitutes a systematic tool for the effective description of memory-bearing open-system evolutions.

Highly efficient greenish-blue platinum-based phosphorescent organic light-emitting diodes on a high triplet energy platform

Energy Technology Data Exchange (ETDEWEB)

Chang, Y. L., E-mail: yilu.chang@mail.utoronto.ca; Gong, S., E-mail: sgong@chem.utoronto.ca; White, R.; Lu, Z. H., E-mail: zhenghong.lu@utoronto.ca [Department of Materials Science and Engineering, University of Toronto, 184 College St., Toronto, Ontario M5S 3E4 (Canada); Wang, X.; Wang, S., E-mail: wangs@chem.queensu.ca [Department of Chemistry, Queen' s University, 90 Bader Lane, Kingston, Ontario K7L 3N6 (Canada); Yang, C. [Department of Chemistry, Wuhan University, Wuhan 430072 (China)

2014-04-28

We have demonstrated high-efficiency greenish-blue phosphorescent organic light-emitting diodes (PHOLEDs) based on a dimesitylboryl-functionalized C^N chelate Pt(II) phosphor, Pt(m-Bptrz)(t-Bu-pytrz-Me). Using a high triplet energy platform and optimized double emissive zone device architecture results in greenish-blue PHOLEDs that exhibit an external quantum efficiency of 24.0% and a power efficiency of 55.8 lm/W. This record high performance is comparable with that of the state-of-the-art Ir-based sky-blue organic light-emitting diodes.

Efficiency versus speed in quantum heat engines: Rigorous constraint from Lieb-Robinson bound

Science.gov (United States)

Shiraishi, Naoto; Tajima, Hiroyasu

2017-08-01

A long-standing open problem whether a heat engine with finite power achieves the Carnot efficiency is investgated. We rigorously prove a general trade-off inequality on thermodynamic efficiency and time interval of a cyclic process with quantum heat engines. In a first step, employing the Lieb-Robinson bound we establish an inequality on the change in a local observable caused by an operation far from support of the local observable. This inequality provides a rigorous characterization of the following intuitive picture that most of the energy emitted from the engine to the cold bath remains near the engine when the cyclic process is finished. Using this description, we prove an upper bound on efficiency with the aid of quantum information geometry. Our result generally excludes the possibility of a process with finite speed at the Carnot efficiency in quantum heat engines. In particular, the obtained constraint covers engines evolving with non-Markovian dynamics, which almost all previous studies on this topic fail to address.

All-photonic quantum repeaters

Science.gov (United States)

Azuma, Koji; Tamaki, Kiyoshi; Lo, Hoi-Kwong

2015-01-01

Quantum communication holds promise for unconditionally secure transmission of secret messages and faithful transfer of unknown quantum states. Photons appear to be the medium of choice for quantum communication. Owing to photon losses, robust quantum communication over long lossy channels requires quantum repeaters. It is widely believed that a necessary and highly demanding requirement for quantum repeaters is the existence of matter quantum memories. Here we show that such a requirement is, in fact, unnecessary by introducing the concept of all-photonic quantum repeaters based on flying qubits. In particular, we present a protocol based on photonic cluster-state machine guns and a loss-tolerant measurement equipped with local high-speed active feedforwards. We show that, with such all-photonic quantum repeaters, the communication efficiency scales polynomially with the channel distance. Our result paves a new route towards quantum repeaters with efficient single-photon sources rather than matter quantum memories. PMID:25873153

Luminescence quantum efficiency determination in LiYF4:Nd3+ using photoacoustic spectroscopy

International Nuclear Information System (INIS)

Franca, E.J.

1989-01-01

Optical properties of LiYF 4 :Nd 3+ were studied using absorption, emission, excitation and photo acoustic spectroscopies. The Nd 3+ transitions were identified and the Stark sublevels were determined for the 4 I 9/2 , 4 I 11/2 and 4 F 3/2 levels. It is also presented and analysed three methods for the luminescence quantum efficiency determination, based on parameters from the spectra mentioned above. These methods were applied to four groups centered on 517, 577, 743 and 792nm. The first method provided values too high due to its assumption that the material has only one luminescent channel. The values obtained from the second one are still somewhat high but closer to the expected ones. The superestimation can be atributed to the imprecision in the existing branching ratios values, needed in this method. The third one, developed from the other two, provided values closer to the expected ones, but also affected by experimental conditions limitations, mainly related to the spectral resolution of the photoacustic spectra. The obtained results show that this method, once improved and associated to better experimental conditions, will lead to more accurate luminescence quantum efficiency values. (author) [pt

Efficiency droop suppression of distance-engineered surface plasmon-coupled photoluminescence in GaN-based quantum well LEDs

Directory of Open Access Journals (Sweden)

Yufeng Li

2017-11-01

Full Text Available Ag coated microgroove with extreme large aspect-ratio of 500:1 was fabricated on p-GaN capping layer to investigate the coupling behavior between quantum wells and surface plasmon in highly spatial resolution. Significant photoluminescence enhancement was observed when the distance between Ag film and QWs was reduced from 220 nm to about 20 nm. A maximum enhancement ratio of 18-fold was achieved at the groove bottom where the surface plasmonic coupling was considered the strongest. Such enhancement ratio was found highly affected by the excitation power density. It also shows high correlation to the internal quantum efficiency as a function of coupling effect and a maximum Purcell Factor of 1.75 was estimated at maximum coupling effect, which matches number calculated independently from the time-resolved photoluminescence measurement. With such Purcell Factor, the efficiency was greatly enhanced and the droop was significantly suppressed.

High Efficiency of Two Efficient QSDC with Authentication Is at the Cost of Their Security

International Nuclear Information System (INIS)

Su-Juan, Qin; Qiao-Yan, Wen; Luo-Ming, Meng; Fu-Chen, Zhu

2009-01-01

Two efficient protocols of quantum secure direct communication with authentication [Chin. Phys. Lett. 25 (2008) 2354] were recently proposed by Liu et al. to improve the efficiency of two protocols presented in [Phys. Rev. A 75 (2007) 026301] by four Pauli operations. We show that the high efficiency of the two protocols is at the expense of their security. The authenticator Trent can reach half the secret by a particular attack strategy in the first protocol. In the second protocol, not only Trent but also an eavesdropper outside can elicit half-information about the secret from the public declaration

Band-structure tailoring and surface passivation for highly efficient near-infrared responsive PbS quantum dot photovoltaics

Science.gov (United States)

Zhou, Ru; Niu, Haihong; Ji, Fengwei; Wan, Lei; Mao, Xiaoli; Guo, Huier; Xu, Jinzhang; Cao, Guozhong

2016-11-01

PbS is a promising light harvester for near-infrared (NIR) responsive quantum dot (QD) photovoltaics due to its narrow bulk band gap (0.41 eV) and large exciton Bohr radius (18 nm). However, the relatively low conduction band (CB) and high-density surface defects of PbS as two major drawbacks for its use in solar cells severely hamper the photovoltaic performance enhancement. In this work, a modified solution-based successive ionic layer adsorption and reaction (SILAR) utilizing mixed cationic precursors of Pb2+ and Cd2+ is explored, and such a scheme offers two benefits, band-structure tailoring and surface passivation. In-situ deposited CdS suppresses the excessive growth of PbS in the mesopores, thereby facilitating the favorable electron injection from PbS to TiO2 in view of the up-shifted CB level of QDs; the intimate interpenetration of two sulfides with each other leads to superior passivation of trap state defects on PbS, which suppresses the interfacial charge recombination. With the construction of photovoltaics based on such a hybrid (Pb,Cd)S/CdS configuration, impressive power conversion efficiency up to 4.08% has been reached, outperforming that of the conventional PbS/CdS pattern (2.95%). This work highlights the great importance of band-structure tailoring and surface passivation for constructing highly efficient PbS QD photovoltaics.

Quantum efficiency harmonic analysis of exciton annihilation in organic light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Price, J. S.; Giebink, N. C., E-mail: ncg2@psu.edu [Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

2015-06-29

Various exciton annihilation processes are known to impact the efficiency roll-off of organic light emitting diodes (OLEDs); however, isolating and quantifying their contribution in the presence of other factors such as changing charge balance continue to be a challenge for routine device characterization. Here, we analyze OLED electroluminescence resulting from a sinusoidal dither superimposed on the device bias and show that nonlinearity between recombination current and light output arising from annihilation mixes the quantum efficiency measured at different dither harmonics in a manner that depends uniquely on the type and magnitude of the annihilation process. We derive a series of analytical relations involving the DC and first harmonic external quantum efficiency that enable annihilation rates to be quantified through linear regression independent of changing charge balance and evaluate them for prototypical fluorescent and phosphorescent OLEDs based on the emitters 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran and platinum octaethylporphyrin, respectively. We go on to show that, in most cases, it is sufficient to calculate the needed quantum efficiency harmonics directly from derivatives of the DC light versus current curve, thus enabling this analysis to be conducted solely from standard light-current-voltage measurement data.

Noise-free high-efficiency photon-number-resolving detectors

International Nuclear Information System (INIS)

Rosenberg, Danna; Lita, Adriana E.; Miller, Aaron J.; Nam, Sae Woo

2005-01-01

High-efficiency optical detectors that can determine the number of photons in a pulse of monochromatic light have applications in a variety of physics studies, including post-selection-based entanglement protocols for linear optics quantum computing and experiments that simultaneously close the detection and communication loopholes of Bell's inequalities. Here we report on our demonstration of fiber-coupled, noise-free, photon-number-resolving transition-edge sensors with 88% efficiency at 1550 nm. The efficiency of these sensors could be made even higher at any wavelength in the visible and near-infrared spectrum without resulting in a higher dark-count rate or degraded photon-number resolution

Observation of infrared absorption of InAs quantum dot structures in AlGaAs matrix toward high-efficiency solar cells

Science.gov (United States)

Yoshikawa, Hirofumi; Watanabe, Katsuyuki; Kotani, Teruhisa; Izumi, Makoto; Iwamoto, Satoshi; Arakawa, Yasuhiko

2018-06-01

In accordance with the detailed balance limit model of single-intermediate-band solar cells (IBSCs), the optimum matrix bandgap and IB–conduction band (CB) energy gap are ∼1.9 and 0.7 eV, respectively. We present the room-temperature polarized infrared absorption of 20 stacked InAs quantum dot (QD) structures in the Al0.32Ga0.68As matrix with a bandgap of ∼1.9 eV for the design of high-efficiency IBSCs by using a multipass waveguide geometry. We find that the IB–CB absorption is almost independent of the light polarization, and estimate the magnitude of the absorption per QD layer to be ∼0.01%. We also find that the IB–CB absorption edge of QD structures with a wide-gap matrix is ∼0.41 eV. These results indicate that both the significant increase in the magnitude of IB–CB absorption and the lower energy of the IB state for the higher IB–CB energy gap are necessary toward the realization of high-efficiency IBSCs.

Absolute determination of photoluminescence quantum efficiency using an integrating sphere setup

International Nuclear Information System (INIS)

Leyre, S.; Coutino-Gonzalez, E.; Hofkens, J.; Joos, J. J.; Poelman, D.; Smet, P. F.; Ryckaert, J.; Meuret, Y.; Durinck, G.; Hanselaer, P.; Deconinck, G.

2014-01-01

An integrating sphere-based setup to obtain a quick and reliable determination of the internal quantum efficiency of strongly scattering luminescent materials is presented. In literature, two distinct but similar measurement procedures are frequently mentioned: a “two measurement” and a “three measurement” approach. Both methods are evaluated by applying the rigorous integrating sphere theory. It was found that both measurement procedures are valid. Additionally, the two methods are compared with respect to the uncertainty budget of the obtained values of the quantum efficiency. An inter-laboratory validation using the two distinct procedures was performed. The conclusions from the theoretical study were confirmed by the experimental data

Quantum efficiency of silica-coated rare-earth doped yttrium silicate

Energy Technology Data Exchange (ETDEWEB)

Cervantes-Vásquez, D., E-mail: dcervant@cnyn.unam.mx [Centro de Investigación Científica y de Educación Superior de Ensenada, Carretera Ensenada-Tijuana No. 3918, Zona Playitas, C.P. 22860 Ensenada, B.C., México (Mexico); Contreras, O.E.; Hirata, G.A. [Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Km. 107 Carretera Tijuana-Ensenada, C.P. 22800 Ensenada, B.C., México (Mexico)

2013-11-15

The photoluminescent properties of rare earth-activated white-emitting Y{sub 2}SiO{sub 5}:Ce,Tb nanocrystalline phosphor prepared by two different methods, pressure-assisted combustion synthesis and sol–gel, were studied. The synthesized phosphor samples were post-annealed at 1373 K and 1623 K in order to obtain the X1-Y{sub 2}SiO{sub 5} and X2-Y{sub 2}SiO{sub 5} phases, respectively, which were confirmed by X-ray diffraction measurements. Photoluminescence analysis showed the contribution of two blue-emission bands within the 380–450 nm region originating from 5d–4f transitions in Ce{sup 3+} ions and a well-defined green emission of Tb{sup 3+} ions located at 545 nm corresponding to {sup 5}D{sub 4}→{sup 7}F{sub 5} electronic transitions. Thereafter, Y{sub 2}SiO{sub 5}:Ce,Tb powders were coated with colloidal silica in order to investigate the effect of silica coatings on their luminescent properties. Absolute fluorescence quantum efficiency measurements were carefully performed, which revealed an increase of 12% of efficiency in coated compared with bare-Y{sub 2}SiO{sub 5}:Ce,Tb phosphor. -- Highlights: • Y{sub 2}SiO{sub 5}:Ce,Tb phosphor powders were successfully coated with colloidal silica. • Post-annealing treatments improved the quantum efficiency of silica-coated Y{sub 2}SiO{sub 5}:Ce,Tb phosphors. • Absolute fluorescence quantum efficiency measurements showed an increase of 12%.

High-speed quantum networking by ship

Science.gov (United States)

Devitt, Simon J.; Greentree, Andrew D.; Stephens, Ashley M.; van Meter, Rodney

2016-11-01

Networked entanglement is an essential component for a plethora of quantum computation and communication protocols. Direct transmission of quantum signals over long distances is prevented by fibre attenuation and the no-cloning theorem, motivating the development of quantum repeaters, designed to purify entanglement, extending its range. Quantum repeaters have been demonstrated over short distances, but error-corrected, global repeater networks with high bandwidth require new technology. Here we show that error corrected quantum memories installed in cargo containers and carried by ship can provide a exible connection between local networks, enabling low-latency, high-fidelity quantum communication across global distances at higher bandwidths than previously proposed. With demonstrations of technology with sufficient fidelity to enable topological error-correction, implementation of the quantum memories is within reach, and bandwidth increases with improvements in fabrication. Our approach to quantum networking avoids technological restrictions of repeater deployment, providing an alternate path to a worldwide Quantum Internet.

Efficient eco-friendly inverted quantum dot sensitized solar cells

NARCIS (Netherlands)

Park, Jinhyung; Sajjad, Muhammad T.; Jouneau, Pierre-Henri; Ruseckas, Arvydas; Faure-Vincent, Jérôme; Samuel, Ifor D. W.; Reiss, Peter; Aldakov, Dmitry

2016-01-01

Recent progress in quantum dot (QD) sensitized solar cells has demonstrated the possibility of low-cost and efficient photovoltaics. However, the standard device structure based on n-type materials often suffers from slow hole injection rate, which may lead to unbalanced charge transport. We have

Tools for Multimode Quantum Information: Modulation, Detection, and Spatial Quantum Correlations

DEFF Research Database (Denmark)

Lassen, Mikael Østergaard; Delaubert, Vincent; Janousek, Jirí

2007-01-01

We present here all the tools required for continuous variable parallel quantum information protocols based on spatial multi-mode quantum correlations and entanglement. We describe techniques for encoding and detecting this quantum information with high efficiency in the individual modes. We use ...

Scales of Time Where the Quantum Discord Allows an Efficient Execution of the DQC1 Algorithm

Directory of Open Access Journals (Sweden)

M. Ávila

2014-01-01

Full Text Available The power of one qubit deterministic quantum processor (DQC1 (Knill and Laflamme (1998 generates a nonclassical correlation known as quantum discord. The DQC1 algorithm executes in an efficient way with a characteristic time given by τ=Tr[Un]/2n, where Un is an n qubit unitary gate. For pure states, quantum discord means entanglement while for mixed states such a quantity is more than entanglement. Quantum discord can be thought of as the mutual information between two systems. Within the quantum discord approach the role of time in an efficient evaluation of τ is discussed. It is found that the smaller the value of t/T is, where t is the time of execution of the DQC1 algorithm and T is the scale of time where the nonclassical correlations prevail, the more efficient the calculation of τ is. A Mösbauer nucleus might be a good processor of the DQC1 algorithm while a nuclear spin chain would not be efficient for the calculation of τ.

Nanocrystal Size-Dependent Efficiency of Quantum Dot Sensitized Solar Cells in the Strongly Coupled CdSe Nanocrystals/TiO2 System.

Science.gov (United States)

Yun, Hyeong Jin; Paik, Taejong; Diroll, Benjamin; Edley, Michael E; Baxter, Jason B; Murray, Christopher B

2016-06-15

Light absorption and electron injection are important criteria determining solar energy conversion efficiency. In this research, monodisperse CdSe quantum dots (QDs) are synthesized with five different diameters, and the size-dependent solar energy conversion efficiency of CdSe quantum dot sensitized solar cell (QDSSCs) is investigated by employing the atomic inorganic ligand, S(2-). Absorbance measurements and transmission electron microscopy show that the diameters of the uniform CdSe QDs are 2.5, 3.2, 4.2, 6.4, and 7.8 nm. Larger CdSe QDs generate a larger amount of charge under the irradiation of long wavelength photons, as verified by the absorbance results and the measurements of the external quantum efficiencies. However, the smaller QDs exhibit faster electron injection kinetics from CdSe QDs to TiO2 because of the high energy level of CBCdSe, as verified by time-resolved photoluminescence and internal quantum efficiency results. Importantly, the S(2-) ligand significantly enhances the electronic coupling between the CdSe QDs and TiO2, yielding an enhancement of the charge transfer rate at the interfacial region. As a result, the S(2-) ligand helps improve the new size-dependent solar energy conversion efficiency, showing best performance with 4.2-nm CdSe QDs, whereas conventional ligand, mercaptopropionic acid, does not show any differences in efficiency according to the size of the CdSe QDs. The findings reported herein suggest that the atomic inorganic ligand reinforces the influence of quantum confinement on the solar energy conversion efficiency of QDSSCs.

Highly Efficient Visible Colloidal Lead-Halide Perovskite Nanocrystal Light-Emitting Diodes

Science.gov (United States)

Yan, Fei; Xing, Jun; Xing, Guichuan; Quan, Lina; Tan, Swee Tiam; Zhao, Jiaxin; Su, Rui; Zhang, Lulu; Chen, Shi; Zhao, Yawen; Huan, Alfred; Sargent, Edward H.; Xiong, Qihua; Demir, Hilmi Volkan

2018-05-01

Lead-halide perovskites have been attracting attention for potential use in solid-state lighting. Following the footsteps of solar cells, the field of perovskite light-emitting diodes (PeLEDs) has been growing rapidly. Their application prospects in lighting, however, remain still uncertain due to a variety of shortcomings in device performance including their limited levels of luminous efficiency achievable thus far. Here we show high-efficiency PeLEDs based on colloidal perovskite nanocrystals (PeNCs) synthesized at room temperature possessing dominant first-order excitonic radiation (enabling a photoluminescence quantum yield of 71% in solid film), unlike in the case of bulk perovskites with slow electron-hole bimolecular radiative recombination (a second-order process). In these PeLEDs, by reaching charge balance in the recombination zone, we find that the Auger nonradiative recombination, with its significant role in emission quenching, is effectively suppressed in low driving current density range. In consequence, these devices reach a record high maximum external quantum efficiency of 12.9% reported to date and an unprecedentedly high power efficiency of 30.3 lm W-1 at luminance levels above 1000 cd m-2 as required for various applications. These findings suggest that, with feasible levels of device performance, the PeNCs hold great promise for their use in LED lighting and displays.

Efficiency Enhancement of Silicon Heterojunction Solar Cells via Photon Management Using Graphene Quantum Dot as Downconverters

KAUST Repository

Tsai, Meng-Lin

2015-12-16

By employing graphene quantum dots (GQDs), we have achieved a high efficiency of 16.55% in n-type Si heterojunction solar cells. The efficiency enhancement is based on the photon downconversion phenomenon of GQDs to make more photons absorbed in the depletion region for effective carrier separation, leading to the enhanced photovoltaic effect. The short circuit current and the fill factor are increased from 35.31 to 37.47 mA/cm2 and 70.29% to 72.51%, respectively. The work demonstrated here holds the promise for incorporating graphene-based materials in commercially available solar devices for developing ultra-high efficiency photovoltaic cells in the future.

Efficiency Enhancement of Silicon Heterojunction Solar Cells via Photon Management Using Graphene Quantum Dot as Downconverters

KAUST Repository

Tsai, Meng-Lin; Tu, Wei-Chen; Tang, Libin; Wei, Tzu-Chiao; Wei, Wan-Rou; Lau, Shu Ping; Chen, Lih-Juann; He, Jr-Hau

2015-01-01

By employing graphene quantum dots (GQDs), we have achieved a high efficiency of 16.55% in n-type Si heterojunction solar cells. The efficiency enhancement is based on the photon downconversion phenomenon of GQDs to make more photons absorbed in the depletion region for effective carrier separation, leading to the enhanced photovoltaic effect. The short circuit current and the fill factor are increased from 35.31 to 37.47 mA/cm2 and 70.29% to 72.51%, respectively. The work demonstrated here holds the promise for incorporating graphene-based materials in commercially available solar devices for developing ultra-high efficiency photovoltaic cells in the future.

Quantum Monte Carlo tunneling from quantum chemistry to quantum annealing

Science.gov (United States)

Mazzola, Guglielmo; Smelyanskiy, Vadim N.; Troyer, Matthias

2017-10-01

Quantum tunneling is ubiquitous across different fields, from quantum chemical reactions and magnetic materials to quantum simulators and quantum computers. While simulating the real-time quantum dynamics of tunneling is infeasible for high-dimensional systems, quantum tunneling also shows up in quantum Monte Carlo (QMC) simulations, which aim to simulate quantum statistics with resources growing only polynomially with the system size. Here we extend the recent results obtained for quantum spin models [Phys. Rev. Lett. 117, 180402 (2016), 10.1103/PhysRevLett.117.180402], and we study continuous-variable models for proton transfer reactions. We demonstrate that QMC simulations efficiently recover the scaling of ground-state tunneling rates due to the existence of an instanton path, which always connects the reactant state with the product. We discuss the implications of our results in the context of quantum chemical reactions and quantum annealing, where quantum tunneling is expected to be a valuable resource for solving combinatorial optimization problems.

Quantum efficiency of InAs/InP nanowire heterostructures grown on silicon substrates

International Nuclear Information System (INIS)

Anufriev, Roman; Chauvin, Nicolas; Bru-Chevallier, Catherine; Khmissi, Hammadi; Naji, Khalid; Gendry, Michel; Patriarche, Gilles

2013-01-01

Photoluminescence (PL) quantum efficiency (QE) is experimentally investigated, using an integrating sphere, as a function of excitation power on both InAs/InP quantum rod nanowires (QRod-NWs) and radial quantum well nanowires (QWell-NWs) grown on silicon substrates. The measured values of the QE are compared with those of the planar analogues such as quantum dash and quantum well samples, and found to be comparable for the quantum well structures at relatively low power density. Further studies reveal that the values of QE of the QRod-NWs and QWell-NWs are limited by the low quality of the InP NW structure and the quality of radial quantum well, respectively. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Highly efficient exciplex organic light-emitting diodes using thermally activated delayed fluorescent emitters as donor and acceptor materials

Science.gov (United States)

Jeon, Sang Kyu; Yook, Kyoung Soo; Lee, Jun Yeob

2016-06-01

Highly efficient exciplex type organic light-emitting diodes were developed using thermally activated delayed fluorescent emitters as donors and acceptors of an exciplex. Blue emitting bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) was a donor and 9,9‧-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9H-carbazole) (DDCzTrz) and 9,9‧,9″-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzene-1,2,3-triyl)tris(9H-carbazole) (TCzTrz) were acceptor materials. The exciplexes of DMAC-DPS:TCzTrz and DMAC-DPS:DDCzTrz resulted in high photoluminescence quantum yield and high quantum efficiency in the green exciplex organic light-emitting diodes. High quantum efficiencies of 13.4% and 15.3% were obtained in the DMAC-DPS:DDCzTrz and DMAC-DPS:TCzTrz exciplex devices.

An efficient numerical progressive diagonalization scheme for the quantum Rabi model revisited

International Nuclear Information System (INIS)

Pan, Feng; Bao, Lina; Dai, Lianrong; Draayer, Jerry P

2017-01-01

An efficient numerical progressive diagonalization scheme for the quantum Rabi model is revisited. The advantage of the scheme lies in the fact that the quantum Rabi model can be solved almost exactly by using the scheme that only involves a finite set of one variable polynomial equations. The scheme is especially efficient for a specified eigenstate of the model, for example, the ground state. Some low-lying level energies of the model for several sets of parameters are calculated, of which one set of the results is compared to that obtained from the Braak’s exact solution proposed recently. It is shown that the derivative of the entanglement measure defined in terms of the reduced von Neumann entropy with respect to the coupling parameter does reach the maximum near the critical point deduced from the classical limit of the Dicke model, which may provide a probe of the critical point of the crossover in finite quantum many-body systems, such as that in the quantum Rabi model. (paper)

Highly Efficient Spectrally Stable Red Perovskite Light-Emitting Diodes.

Science.gov (United States)

Tian, Yu; Zhou, Chenkun; Worku, Michael; Wang, Xi; Ling, Yichuan; Gao, Hanwei; Zhou, Yan; Miao, Yu; Guan, Jingjiao; Ma, Biwu

2018-05-01

Perovskite light-emitting diodes (LEDs) have recently attracted great research interest for their narrow emissions and solution processability. Remarkable progress has been achieved in green perovskite LEDs in recent years, but not blue or red ones. Here, highly efficient and spectrally stable red perovskite LEDs with quasi-2D perovskite/poly(ethylene oxide) (PEO) composite thin films as the light-emitting layer are reported. By controlling the molar ratios of organic salt (benzylammonium iodide) to inorganic salts (cesium iodide and lead iodide), luminescent quasi-2D perovskite thin films are obtained with tunable emission colors from red to deep red. The perovskite/polymer composite approach enables quasi-2D perovskite/PEO composite thin films to possess much higher photoluminescence quantum efficiencies and smoothness than their neat quasi-2D perovskite counterparts. Electrically driven LEDs with emissions peaked at 638, 664, 680, and 690 nm have been fabricated to exhibit high brightness and external quantum efficiencies (EQEs). For instance, the perovskite LED with an emission peaked at 680 nm exhibits a brightness of 1392 cd m -2 and an EQE of 6.23%. Moreover, exceptional electroluminescence spectral stability under continuous device operation has been achieved for these red perovskite LEDs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Layer-by-layer assembly of multicolored semiconductor quantum dots towards efficient blue, green, red and full color optical films

International Nuclear Information System (INIS)

Zhang Jun; Li Qian; Di Xiaowei; Liu Zhiliang; Xu Gang

2008-01-01

Multicolored semiconductor quantum dots have shown great promise for construction of miniaturized light-emitting diodes with compact size, low weight and cost, and high luminescent efficiency. The unique size-dependent luminescent property of quantum dots offers the feasibility of constructing single-color or full-color output light-emitting diodes with one type of material. In this paper, we have demonstrated the facile fabrication of blue-, green-, red- and full-color-emitting semiconductor quantum dot optical films via a layer-by-layer assembly technique. The optical films were constructed by alternative deposition of different colored quantum dots with a series of oppositely charged species, in particular, the new use of cationic starch on glass substrates. Semiconductor ZnSe quantum dots exhibiting blue emission were deposited for fabrication of blue-emitting optical films, while semiconductor CdTe quantum dots with green and red emission were utilized for construction of green- and red-emitting optical films. The assembly of integrated blue, green and red semiconductor quantum dots resulted in full-color-emitting optical films. The luminescent optical films showed very bright emitting colors under UV irradiation, and displayed dense, smooth and efficient luminous features, showing brighter luminescence in comparison with their corresponding quantum dot aqueous colloid solutions. The assembled optical films provide the prospect of miniaturized light-emitting-diode applications.

Intrinsic retrieval efficiency for quantum memories: A three-dimensional theory of light interaction with an atomic ensemble

Science.gov (United States)

Gujarati, Tanvi P.; Wu, Yukai; Duan, Luming

2018-03-01

Duan-Lukin-Cirac-Zoller quantum repeater protocol, which was proposed to realize long distance quantum communication, requires usage of quantum memories. Atomic ensembles interacting with optical beams based on off-resonant Raman scattering serve as convenient on-demand quantum memories. Here, a complete free space, three-dimensional theory of the associated read and write process for this quantum memory is worked out with the aim of understanding intrinsic retrieval efficiency. We develop a formalism to calculate the transverse mode structure for the signal and the idler photons and use the formalism to study the intrinsic retrieval efficiency under various configurations. The effects of atomic density fluctuations and atomic motion are incorporated by numerically simulating this system for a range of realistic experimental parameters. We obtain results that describe the variation in the intrinsic retrieval efficiency as a function of the memory storage time for skewed beam configuration at a finite temperature, which provides valuable information for optimization of the retrieval efficiency in experiments.

Quantum efficiency and excited-state relaxation dynamics in neodymium-doped phosphate laser glasses

International Nuclear Information System (INIS)

Caird, J.A.; Ramponi, A.J.; Staver, P.R.

1991-01-01

Radiometrically calibrated spectroscopic techniques employing an integrating-sphere detection system have been used to determine the fluorescence quantum efficiencies for two commercially available Nd 3+ -doped phosphate laser glasses, LG-750 and LG-760. Quantum efficiencies and fluorescence lifetimes were measured for samples with various neodymium concentrations. It is shown that the effects of concentration quenching are accurately described when both resonant nonradiative excitation hopping (the Burshtein model) and annihilation by cross relaxation are accounted for by Foerster--Dexter dipole--dipole energy-transfer theory. The Foerster--Dexter critical range for nonradiative excitation hopping was found to be R DD =11 A, while the critical range for cross relaxation was close to R DA =4 A in these glasses. The quantum efficiency at low Nd 3+ concentrations was (92±5)%, implying a nonradiative relaxation rate of 210±150 s -1 for isolated ions. Improved values for the radiative lifetimes and the stimulated emission cross sections for these glasses were also deduced from the measurements

InP/ZnSe/ZnS core-multishell quantum dots for improved luminescence efficiency

Science.gov (United States)

Greco, Tonino; Ippen, Christian; Wedel, Armin

2012-04-01

Semiconductor quantum dots (QDs) exhibit unique optical properties like size-tunable emission color, narrow emission peak, and high luminescence efficiency. QDs are therefore investigated towards their application in light-emitting devices (QLEDs), solar cells, and for bio-imaging purposes. In most cases QDs made from cadmium compounds like CdS, CdSe or CdTe are studied because of their facile and reliable synthesis. However, due to the toxicity of Cd compounds and the corresponding regulation (e.g. RoHS directive in Europe) these materials are not feasible for customer applications. Indium phosphide is considered to be the most promising alternative because of the similar band gap (InP 1.35 eV, CdSe 1.73 eV). InP QDs do not yet reach the quality of CdSe QDs, especially in terms of photoluminescence quantum yield and peak width. Typically, QDs are coated with another semiconductor material of wider band gap, often ZnS, to passivate surface defects and thus improve luminescence efficiency. Concerning CdSe QDs, multishell coatings like CdSe/CdS/ZnS or CdSe/ZnSe/ZnS have been shown to be advantageous due to the improved compatibility of lattice constants. Here we present a method to improve the luminescence efficiency of InP QDs by coating a ZnSe/ZnS multishell instead of a ZnS single shell. ZnSe exhibits an intermediate lattice constant of 5.67 Å between those of InP (5.87 Å) and ZnS (5.41 Å) and thus acts as a wetting layer. As a result, InP/ZnSe/ZnS is introduced as a new core-shell quantum dot material which shows improved photoluminescence quantum yield (up to 75 %) compared to the conventional InP/ZnS system.

High resolution STEM of quantum dots and quantum wires

DEFF Research Database (Denmark)

Kadkhodazadeh, Shima

2013-01-01

This article reviews the application of high resolution scanning transmission electron microscopy (STEM) to semiconductor quantum dots (QDs) and quantum wires (QWRs). Different imaging and analytical techniques in STEM are introduced and key examples of their application to QDs and QWRs...

High performance 5.6μm quantum cascade lasers

Science.gov (United States)

Suttinger, M.; Go, R.; Figueiredo, P.; Todi, A.; Shu, Hong; Lyakh, A.

2017-02-01

5.6 μm quantum cascade lasers based on Al 0.78 In 0.22 As/In 0.69 Ga 0.31 As active region composition with measured pulsed room temperature wall plug efficiency of 28.3% are reported. Injection efficiency for the upper laser level of 75% was measured for the new design by testing devices with variable cavity length. Threshold current density of 1.7kA/cm2 and slope efficiency of 4.9W/A were measured for uncoated 3.15mm × 9μm lasers. Threshold current density and slope efficiency dependence on temperature in the range from 288K to 348K for the new structure can be described by characteristic temperatures T0 140K and T1 710K, respectively. Experimental data for inverse slope efficiency dependence on cavity length for 15-stage quantum cascade lasers with the same design are also presented. When combined with the 40-stage device data, the new data allowed for separate evaluation of the losses originating from the active region and from the cladding layers of the laser structure. Specifically, the active region losses for the studied design were found to be 0.77 cm-1, while cladding region losses - 0.33 cm-1. The data demonstrate that active region losses in mid wave infrared quantum cascade lasers largely define total waveguide losses and that their reduction should be one of the main priorities in the quantum cascade laser design.

An efficient deterministic secure quantum communication scheme based on cluster states and identity authentication

International Nuclear Information System (INIS)

Wen-Jie, Liu; Han-Wu, Chen; Zhi-Qiang, Li; Zhi-Hao, Liu; Wen-Bo, Hu; Ting-Huai, Ma

2009-01-01

A novel efficient deterministic secure quantum communication scheme based on four-qubit cluster states and single-photon identity authentication is proposed. In this scheme, the two authenticated users can transmit two bits of classical information per cluster state, and its efficiency of the quantum communication is 1/3, which is approximately 1.67 times that of the previous protocol presented by Wang et al [Chin. Phys. Lett. 23 (2006) 2658]. Security analysis shows the present scheme is secure against intercept-resend attack and the impersonator's attack. Furthermore, it is more economic with present-day techniques and easily processed by a one-way quantum computer. (general)

Efficient Luminescence from Perovskite Quantum Dot Solids

KAUST Repository

Kim, Younghoon; Yassitepe, Emre; Voznyy, Oleksandr; Comin, Riccardo; Walters, Grant; Gong, Xiwen; Kanjanaboos, Pongsakorn; Nogueira, Ana F.; Sargent, Edward H.

2015-01-01

© 2015 American Chemical Society. Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids.

Efficient Luminescence from Perovskite Quantum Dot Solids

KAUST Repository

Kim, Younghoon

2015-11-18

© 2015 American Chemical Society. Nanocrystals of CsPbX3 perovskites are promising materials for light-emitting optoelectronics because of their colloidal stability, optically tunable bandgap, bright photoluminescence, and excellent photoluminescence quantum yield. Despite their promise, nanocrystal-only films of CsPbX3 perovskites have not yet been fabricated; instead, highly insulating polymers have been relied upon to compensate for nanocrystals\\' unstable surfaces. We develop solution chemistry that enables single-step casting of perovskite nanocrystal films and overcomes problems in both perovskite quantum dot purification and film fabrication. Centrifugally cast films retain bright photoluminescence and achieve dense and homogeneous morphologies. The new materials offer a platform for optoelectronic applications of perovskite quantum dot solids.

Modeling the irradiance dependency of the quantum efficiency of potosynthesis

NARCIS (Netherlands)

Silsbe, G.M.; Kromkamp, J.C.

2012-01-01

Measures of the quantum efficiency of photosynthesis (phi(PSII)) across an irradiance (E) gradient are an increasingly common physiological assay and alternative to traditional photosynthetic-irradiance (PE) assays. Routinely, the analysis and interpretation of these data are analogous to PE

Improvement of quantum efficiency in green light-emitting diodes with pre-TMIn flow treatment

International Nuclear Information System (INIS)

Lee, Ya-Ju; Chen, Yi-Ching; Lu, Tien-Chang

2011-01-01

The effects of pre-trimethlyindium (TMIn) flow on the improved electrical characteristics and highly stable temperature properties of InGaN green light-emitting diodes (LEDs) are discussed. For the LED sample with a pre-TMIn flow treatment, the tunnelling of injected carriers associated with threading defects is significantly reduced, which promotes the diffusion-recombination of injected carriers, as well as the overall emission efficiency of the LED. In addition, the pre-TMIn flow treatment evidently reduces the dependence of external quantum efficiency on temperature and efficiency droop of green LEDs. As a result, we conclude that the pre-TMIn flow treatment is a promising scheme for the improvement of output performance of InGaN-based green LEDs.

Efficient quantum entanglement distribution over an arbitrary collective-noise channel

Science.gov (United States)

Sheng, Yu-Bo; Deng, Fu-Guo

2010-04-01

We present an efficient quantum entanglement distribution over an arbitrary collective-noise channel. The basic idea in the present scheme is that two parties in quantum communication first transmit the entangled states in the frequency degree of freedom which suffers little from the noise in an optical fiber. After the two parties share the photon pairs, they add some operations and equipments to transfer the frequency entanglement of pairs into the polarization entanglement with the success probability of 100%. Finally, they can get maximally entangled polarization states with polarization independent wavelength division multiplexers and quantum frequency up-conversion which can erase distinguishability for frequency. Compared with conventional entanglement purification protocols, the present scheme works in a deterministic way in principle. Surprisingly, the collective noise leads to an additional advantage.

Core/shell colloidal quantum dot exciplex states for the development of highly efficient quantum-dot-sensitized solar cells.

Science.gov (United States)

Wang, Jin; Mora-Seró, Iván; Pan, Zhenxiao; Zhao, Ke; Zhang, Hua; Feng, Yaoyu; Yang, Guang; Zhong, Xinhua; Bisquert, Juan

2013-10-23

Searching suitable panchromatic QD sensitizers for expanding the light-harvesting range, accelerating charge separation, and retarding charge recombination is an effective way to improve power conversion efficiency (PCE) of quantum-dot-sensitized solar cells (QDSCs). One possible way to obtain a wide absorption range is to use the exciplex state of a type-II core/shell-structured QDs. In addition, this system could also provide a fast charge separation and low charge-recombination rate. Herein, we report on using a CdTe/CdSe type-II core/shell QD sensitizer with an absorption range extending into the infrared region because of its exciplex state, which is covalently linked to TiO2 mesoporous electrodes by dropping a bifunctional linker molecule mercaptopropionic acid (MPA)-capped QD aqueous solution onto the film electrode. High loading and a uniform distribution of QD sensitizer throughout the film electrode thickness have been confirmed by energy dispersive X-ray (EDX) elemental mapping. The accelerated electron injection and retarded charge-recombination pathway in the built CdTe/CdSe QD cells in comparison with reference CdSe QD-based cells have been confirmed by impedance spectroscopy, fluorescence decay, and intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) analysis. With the combination of the high QD loading and intrinsically superior optoelectronic properties of type-II core/shell QD (wide absorption range, fast charge separation, and slow charge recombination), the resulting CdTe/CdSe QD-based regenerative sandwich solar cells exhibit a record PCE of 6.76% (J(sc) = 19.59 mA cm(-2), V(oc) = 0.606 V, and FF = 0.569) with a mask around the active film under a full 1 sun illumination (simulated AM 1.5), which is the highest reported to date for liquid-junction QDSCs.

Efficiency enhancement of solid-state PbS quantum dot-sensitized solar cells with Al2O3 barrier layer

KAUST Repository

Brennan, Thomas P.; Trejo, Orlando; Roelofs, Katherine E.; Xu, John; Prinz, Fritz B.; Bent, Stacey F.

2013-01-01

Atomic layer deposition (ALD) was used to grow both PbS quantum dots and Al2O3 barrier layers in a solid-state quantum dot-sensitized solar cell (QDSSC). Barrier layers grown prior to quantum dots resulted in a near-doubling of device efficiency (0.30% to 0.57%) whereas barrier layers grown after quantum dots did not improve efficiency, indicating the importance of quantum dots in recombination processes. © 2013 The Royal Society of Chemistry.

Experimental demonstration of selective quantum process tomography on an NMR quantum information processor

Science.gov (United States)

Gaikwad, Akshay; Rehal, Diksha; Singh, Amandeep; Arvind, Dorai, Kavita

2018-02-01

We present the NMR implementation of a scheme for selective and efficient quantum process tomography without ancilla. We generalize this scheme such that it can be implemented efficiently using only a set of measurements involving product operators. The method allows us to estimate any element of the quantum process matrix to a desired precision, provided a set of quantum states can be prepared efficiently. Our modified technique requires fewer experimental resources as compared to the standard implementation of selective and efficient quantum process tomography, as it exploits the special nature of NMR measurements to allow us to compute specific elements of the process matrix by a restrictive set of subsystem measurements. To demonstrate the efficacy of our scheme, we experimentally tomograph the processes corresponding to "no operation," a controlled-NOT (CNOT), and a controlled-Hadamard gate on a two-qubit NMR quantum information processor, with high fidelities.

Efficient universal quantum channel simulation in IBM's cloud quantum computer

Science.gov (United States)

Wei, Shi-Jie; Xin, Tao; Long, Gui-Lu

2018-07-01

The study of quantum channels is an important field and promises a wide range of applications, because any physical process can be represented as a quantum channel that transforms an initial state into a final state. Inspired by the method of performing non-unitary operators by the linear combination of unitary operations, we proposed a quantum algorithm for the simulation of the universal single-qubit channel, described by a convex combination of "quasi-extreme" channels corresponding to four Kraus operators, and is scalable to arbitrary higher dimension. We demonstrated the whole algorithm experimentally using the universal IBM cloud-based quantum computer and studied the properties of different qubit quantum channels. We illustrated the quantum capacity of the general qubit quantum channels, which quantifies the amount of quantum information that can be protected. The behavior of quantum capacity in different channels revealed which types of noise processes can support information transmission, and which types are too destructive to protect information. There was a general agreement between the theoretical predictions and the experiments, which strongly supports our method. By realizing the arbitrary qubit channel, this work provides a universally- accepted way to explore various properties of quantum channels and novel prospect for quantum communication.

Green synthesis of highly fluorescent carbon quantum dots from sugarcane bagasse pulp

Energy Technology Data Exchange (ETDEWEB)

Thambiraj, S. [Nano-Bio Materials and Sensors Laboratory, PSG Institute of Advanced Studies, Coimbatore, 641 004, Tamil Nadu (India); Ravi Shankaran, D., E-mail: dravishankaran@hotmail.com [Nano-Bio Materials and Sensors Laboratory, PSG Institute of Advanced Studies, Coimbatore, 641 004, Tamil Nadu (India); National Centre for Nanoscience and Nanotechnology, University of Madras, Guindy Campus, Chennai, 600 025, Tamil Nadu (India)

2016-12-30

Graphical abstract: Schematic representation of CQDs from sugarcane bagasse carbon. - Highlights: • CQDs were synthesised from sugarcane bagasse waste with top down approaches. • Synthesis method is green, simple and efficient process. • CQDs possess high quantum yield, good stability and highly fluorescent in nature. • The morphological and topographical study of CQDs was done by HR-TEM and AFM and was observed that the average size is 4.1 ± 0.17 nm and surface thickness is 5 nm. - Abstract: Carbon quantum dots (CQDs) have great potential due to its advantageous characteristics of highly fluorescent nature and good stability. In this study, we aimed to develop a simple and efficient method for the green synthesis of fluorescent CQDs from sugarcane bagasse, a renewable and sustainable resource. The process involves the top down approach of chemical oxidation followed by exfoliation of sugarcane carbon. The synthesized CQDs was characterized by UV–vis absorption spectroscopy, Spectrofluorophotometry, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, X-ray photon spectroscopy (XPS), Atomic force microscopy (AFM) and High-resolution transmission electron microscopy (HR-TEM). The synthesized CQDs possess stable fluorescent properties, good bio-compatibility and high quantum yield. The CQDs are highly crystalline with longitudinal dimensions of 4.1 ± 0.17 nm with an average roughness of around 5 nm. The XRD and TEM analysis indicates that the synthesized CQDs possess face centred cubic crystal structure. The results suggest that the proposed CQDs could be utilized for bio-sensor, bio-imaging and drug delivery applications.

Efficient one-way quantum computations for quantum error correction

International Nuclear Information System (INIS)

Huang Wei; Wei Zhaohui

2009-01-01

We show how to explicitly construct an O(nd) size and constant quantum depth circuit which encodes any given n-qubit stabilizer code with d generators. Our construction is derived using the graphic description for stabilizer codes and the one-way quantum computation model. Our result demonstrates how to use cluster states as scalable resources for many multi-qubit entangled states and how to use the one-way quantum computation model to improve the design of quantum algorithms.

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.

Efficiency dip observed with InGaN-based multiple quantum well solar cells

KAUST Repository

Lai, Kunyu; Lin, G. J.; Wu, Yuhrenn; Tsai, Menglun; He, Jr-Hau

2014-01-01

The dip of external quantum efficiency (EQE) is observed on In0.15Ga0.85N/GaN multiple quantum well (MQW) solar cells upon the increase of incident optical power density. With indium composition increased to 25%, the EQE dip becomes much less noticeable. The composition dependence of EQE dip is ascribed to the competition between radiative recombination and photocurrent generation in the active region, which are dictated by quantum-confined Stark effect (QCSE) and composition fluctuation in the MQWs.

External quantum efficiency enhancement by photon recycling with backscatter evasion.

Science.gov (United States)

Nagano, Koji; Perreca, Antonio; Arai, Koji; Adhikari, Rana X

2018-05-01

The nonunity quantum efficiency (QE) in photodiodes (PD) causes deterioration of signal quality in quantum optical experiments due to photocurrent loss as well as the introduction of vacuum fluctuations into the measurement. In this paper, we report that the external QE enhancement of a PD was demonstrated by recycling the reflected photons. The external QE for an InGaAs PD was increased by 0.01-0.06 from 0.86-0.92 over a wide range of incident angles. Moreover, we confirmed that this technique does not increase backscattered light when the recycled beam is properly misaligned.

Increasing the quantum efficiency of GaAs solar cells by embedding InAs quantum dots

Science.gov (United States)

Salii, R. A.; Mintairov, S. A.; Nadtochiy, A. M.; Payusov, A. S.; Brunkov, P. N.; Shvarts, M. Z.; Kalyuzhnyy, N. A.

2016-11-01

Development of Metalorganic Vapor Phase Epitaxy (MOVPE) technology of InAs quantum dots (QDs) in GaAs for photovoltaic applications is presented. The growth peculiarities in InAs-GaAs lattice-mismatched system were considered. The photoluminescence (PL) intensity dependences on different growth parameters were obtained. The multimodal distribution of QDs by sizes was found using AFM and PL methods. GaAs solar cell nanoheterostructures with imbedded QD arrays were designed and obtained. Ones have been demonstrated a significant increase of quantum efficiency and photogenerated current of QD solar cells due to photo effect in InAs QD array (0.59 mA/cm2 for AM1.5D and 82 mA/cm2 for AM0).

Effects of quantum well growth temperature on the recombination efficiency of InGaN/GaN multiple quantum wells that emit in the green and blue spectral regions

Energy Technology Data Exchange (ETDEWEB)

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

2015-09-28

InGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, in general, lower internal quantum efficiencies than their blue-emitting counter parts, a phenomenon referred to as the “green gap.” One of the main differences between green-emitting and blue-emitting samples is that the quantum well growth temperature is lower for structures designed to emit at longer wavelengths, in order to reduce the effects of In desorption. In this paper, we report on the impact of the quantum well growth temperature on the optical properties of InGaN/GaN multiple quantum wells designed to emit at 460 nm and 530 nm. It was found that for both sets of samples increasing the temperature at which the InGaN quantum well was grown, while maintaining the same indium composition, led to an increase in the internal quantum efficiency measured at 300 K. These increases in internal quantum efficiency are shown to be due reductions in the non-radiative recombination rate which we attribute to reductions in point defect incorporation.

Effects of quantum well growth temperature on the recombination efficiency of InGaN/GaN multiple quantum wells that emit in the green and blue spectral regions

International Nuclear Information System (INIS)

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

2015-01-01

InGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, in general, lower internal quantum efficiencies than their blue-emitting counter parts, a phenomenon referred to as the “green gap.” One of the main differences between green-emitting and blue-emitting samples is that the quantum well growth temperature is lower for structures designed to emit at longer wavelengths, in order to reduce the effects of In desorption. In this paper, we report on the impact of the quantum well growth temperature on the optical properties of InGaN/GaN multiple quantum wells designed to emit at 460 nm and 530 nm. It was found that for both sets of samples increasing the temperature at which the InGaN quantum well was grown, while maintaining the same indium composition, led to an increase in the internal quantum efficiency measured at 300 K. These increases in internal quantum efficiency are shown to be due reductions in the non-radiative recombination rate which we attribute to reductions in point defect incorporation

Tuning charge balance in PHOLEDs with ambipolar host materials to achieve high efficiency

International Nuclear Information System (INIS)

Padmaperuma, Asanga B.; Koech, Phillip K.; Cosimbescu, Lelia; Polikarpov, Evgueni; Swensen, James S.; Chopra, Neetu; So, Franky; Sapochak, Linda S.; Gaspar, Daniel J.

2009-01-01

The efficiency and stability of blue organic light emitting devices (OLEDs) continue to be a primary roadblock to developing organic solid state white lighting. For OLEDs to meet the high power conversion efficiency goal, they will require both close to 100% internal quantum efficiency and low operating voltage in a white light emitting device. It is generally accepted that such high quantum efficiency, can only be achieved with the use of organometallic phosphor doped OLEDs. Blue OLEDs are particularly important for solid state lighting. The simplest (and therefore likely the lowest cost) method of generating white light is to down convert part of the emission from a blue light source with a system of external phosphors. A second method of generating white light requires the superposition of the light from red, green and blue OLEDs in the correct ratio. Either of these two methods (and indeed any method of generating white light with a high color rendering index) critically depends on a high efficiency blue light component. A simple OLED generally consists of a hole-injecting anode, a preferentially hole transporting organic layer (HTL), an emissive layer that contains the recombination zone and ideally transports both holes and electrons, a preferentially electron-transporting layer (ETL) and an electron-injecting cathode. Color in state-of-the-art OLEDs is generated by an organometallic phosphor incorporated by co-sublimation into the emissive layer (EML). New materials functioning as hosts, emitters, charge transporting, and charge blocking layers have been developed along with device architectures leading to electrophosphorescent based OLEDs with high quantum efficiencies near the theoretical limit. However, the layers added to the device architecture to enable high quantum efficiencies lead to higher operating voltages and correspondingly lower power efficiencies. Achievement of target luminance power efficiencies will require new strategies for lowering

Quantum Accelerators for High-performance Computing Systems

Energy Technology Data Exchange (ETDEWEB)

Humble, Travis S. [ORNL; Britt, Keith A. [ORNL; Mohiyaddin, Fahd A. [ORNL

2017-11-01

We define some of the programming and system-level challenges facing the application of quantum processing to high-performance computing. Alongside barriers to physical integration, prominent differences in the execution of quantum and conventional programs challenges the intersection of these computational models. Following a brief overview of the state of the art, we discuss recent advances in programming and execution models for hybrid quantum-classical computing. We discuss a novel quantum-accelerator framework that uses specialized kernels to offload select workloads while integrating with existing computing infrastructure. We elaborate on the role of the host operating system to manage these unique accelerator resources, the prospects for deploying quantum modules, and the requirements placed on the language hierarchy connecting these different system components. We draw on recent advances in the modeling and simulation of quantum computing systems with the development of architectures for hybrid high-performance computing systems and the realization of software stacks for controlling quantum devices. Finally, we present simulation results that describe the expected system-level behavior of high-performance computing systems composed from compute nodes with quantum processing units. We describe performance for these hybrid systems in terms of time-to-solution, accuracy, and energy consumption, and we use simple application examples to estimate the performance advantage of quantum acceleration.

Quantum Junction Solar Cells

KAUST Repository

Tang, Jiang

2012-09-12

Colloidal quantum dot solids combine convenient solution-processing with quantum size effect tuning, offering avenues to high-efficiency multijunction cells based on a single materials synthesis and processing platform. The highest-performing colloidal quantum dot rectifying devices reported to date have relied on a junction between a quantum-tuned absorber and a bulk material (e.g., TiO 2); however, quantum tuning of the absorber then requires complete redesign of the bulk acceptor, compromising the benefits of facile quantum tuning. Here we report rectifying junctions constructed entirely using inherently band-aligned quantum-tuned materials. Realizing these quantum junction diodes relied upon the creation of an n-type quantum dot solid having a clean bandgap. We combine stable, chemically compatible, high-performance n-type and p-type materials to create the first quantum junction solar cells. We present a family of photovoltaic devices having widely tuned bandgaps of 0.6-1.6 eV that excel where conventional quantum-to-bulk devices fail to perform. Devices having optimal single-junction bandgaps exhibit certified AM1.5 solar power conversion efficiencies of 5.4%. Control over doping in quantum solids, and the successful integration of these materials to form stable quantum junctions, offers a powerful new degree of freedom to colloidal quantum dot optoelectronics. © 2012 American Chemical Society.

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%.

High Momentum Particle Identification Detector The Study of Cesium Iodide Quantum Efficiency Dependency on Substrate Material, Temperature and Quartz Window

CERN Document Server

Wisna, Gde Bimananda M

2014-01-01

The Cesium Iodide (CsI) is used as a material for detecting Cherenkov radiation produced by high momentum particle in High Momentum Particle Identification Detector (HMPID) at ALICE Experiment at CERN. This work provides investigation and analysis of The Quantum Efficiency (QE) result of CsI which is deposited on five samples substrates such as copper passivated red, copper passivated yellow, aluminium, copper coated with nickel and copper coated with nickel then coated with gold. The measurement of five samples is held under temperature $60^{0}$ C and $25^{0}$ C (room temperature) and also with optical quartz window which can be adjusted to limit the wavelength range which reach the CsI. The result shows there are dependency of substrate, temperature due to enhancement effect and also quartz windows usage on QE of CsI. The results of five samples is then compared and analyzed.

Quantum Electrodynamics with Semiconductor Quantum Dots Coupled to Anderson‐localized Random Cavities

DEFF Research Database (Denmark)

Sapienza, Luca; Nielsen, Henri Thyrrestrup; Stobbe, Søren

2011-01-01

of the spontaneous emission decay rate by up to a factor 15 and an efficiency of channeling single photons into Anderson-localized modes reaching values as high as 94%. These results prove that disordered photonic media provide an efficient platform for quantum electrodynamics, offering a novel route to quantum......We demonstrate that the spontaneous emission decay rate of semiconductor quantum dots can be strongly modified by the coupling to disorder-induced Anderson-localized photonic modes. We experimentally measure, by means of time-resolved photoluminescence spectroscopy, the enhancement...

Finite Correlation Length Implies Efficient Preparation of Quantum Thermal States

Science.gov (United States)

Brandão, Fernando G. S. L.; Kastoryano, Michael J.

2018-05-01

Preparing quantum thermal states on a quantum computer is in general a difficult task. We provide a procedure to prepare a thermal state on a quantum computer with a logarithmic depth circuit of local quantum channels assuming that the thermal state correlations satisfy the following two properties: (i) the correlations between two regions are exponentially decaying in the distance between the regions, and (ii) the thermal state is an approximate Markov state for shielded regions. We require both properties to hold for the thermal state of the Hamiltonian on any induced subgraph of the original lattice. Assumption (ii) is satisfied for all commuting Gibbs states, while assumption (i) is satisfied for every model above a critical temperature. Both assumptions are satisfied in one spatial dimension. Moreover, both assumptions are expected to hold above the thermal phase transition for models without any topological order at finite temperature. As a building block, we show that exponential decay of correlation (for thermal states of Hamiltonians on all induced subgraphs) is sufficient to efficiently estimate the expectation value of a local observable. Our proof uses quantum belief propagation, a recent strengthening of strong sub-additivity, and naturally breaks down for states with topological order.

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.

Improving quantum efficiency and spectral resolution of a CCD through direct manipulation of the depletion region

Science.gov (United States)

Brown, Craig; Ambrosi, Richard M.; Abbey, Tony; Godet, Olivier; O'Brien, R.; Turner, M. J. L.; Holland, Andrew; Pool, Peter J.; Burt, David; Vernon, David

2008-07-01

Future generations of X-ray astronomy instruments will require position sensitive detectors in the form of charge-coupled devices (CCDs) for X-ray spectroscopy and imaging with the ability to probe the X-ray universe with greater efficiency. This will require the development of CCDs with structures that will improve their quantum efficiency over the current state of the art. The quantum efficiency improvements would have to span a broad energy range (0.2 keV to >15 keV). These devices will also have to be designed to withstand the harsh radiation environments associated with orbits that extend beyond the Earth's magnetosphere. This study outlines the most recent work carried out at the University of Leicester focused on improving the quantum efficiency of an X-ray sensitive CCD through direct manipulation of the device depletion region. It is also shown that increased spectral resolution is achieved using this method due to a decrease in the number of multi-pixel events. A Monte Carlo and analytical models of the CCD have been developed and used to determine the depletion depths achieved through variation of the device substrate voltage, Vss. The models are also used to investigate multi-pixel event distributions and quantum efficiency as a function of depletion depth.

Internal quantum efficiency in yellow-amber light emitting AlGaN-InGaN-GaN heterostructures

Energy Technology Data Exchange (ETDEWEB)

Ngo, Thi Huong; Gil, Bernard; Valvin, Pierre [Laboratoire Charles Coulomb – UMR 5221, CNRS and University Montpellier, Case courier 074, 34095 Montpellier Cedex 5 (France); Damilano, Benjamin; Lekhal, Kaddour; De Mierry, Philippe [CRHEA-CNRS Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, rue Bernard Gregory, 06560 Valbonne (France)

2015-09-21

We determine the internal quantum efficiency of strain-balanced AlGaN-InGaN-GaN hetero-structures designed for yellow-amber light emission, by using a recent model based on the kinetics of the photoluminescence decay initiated by Iwata et al. [J. Appl. Phys. 117, 075701 (2015)]. Our results indicate that low temperature internal quantum efficiencies sit in the 50% range and we measure that adding an AlGaN layer increases the internal quantum efficiency from 50% up to 57% with respect to the GaN-InGaN case. More dramatic, it almost doubles from 2.5% up to 4.3% at room temperature.

Optimal power and efficiency of quantum Stirling heat engines

Science.gov (United States)

Yin, Yong; Chen, Lingen; Wu, Feng

2017-01-01

A quantum Stirling heat engine model is established in this paper in which imperfect regeneration and heat leakage are considered. A single particle which contained in a one-dimensional infinite potential well is studied, and the system consists of countless replicas. Each particle is confined in its own potential well, whose occupation probabilities can be expressed by the thermal equilibrium Gibbs distributions. Based on the Schrödinger equation, the expressions of power output and efficiency for the engine are obtained. Effects of imperfect regeneration and heat leakage on the optimal performance are discussed. The optimal performance region and the optimal values of important parameters of the engine cycle are obtained. The results obtained can provide some guidelines for the design of a quantum Stirling heat engine.

Efficient spin filter using multi-terminal quantum dot with spin-orbit interaction

Directory of Open Access Journals (Sweden)

Yokoyama Tomohiro

2011-01-01

Full Text Available Abstract We propose a multi-terminal spin filter using a quantum dot with spin-orbit interaction. First, we formulate the spin Hall effect (SHE in a quantum dot connected to three leads. We show that the SHE is significantly enhanced by the resonant tunneling if the level spacing in the quantum dot is smaller than the level broadening. We stress that the SHE is tunable by changing the tunnel coupling to the third lead. Next, we perform a numerical simulation for a multi-terminal spin filter using a quantum dot fabricated on semiconductor heterostructures. The spin filter shows an efficiency of more than 50% when the conditions for the enhanced SHE are satisfied. PACS numbers: 72.25.Dc,71.70.Ej,73.63.Kv,85.75.-d

Experimental quantum computing without entanglement.

Science.gov (United States)

Lanyon, B P; Barbieri, M; Almeida, M P; White, A G

2008-11-14

Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of computation that uses highly mixed states. Unlike pure-state models, its power is not derived from the generation of a large amount of entanglement. Instead it has been proposed that other nonclassical correlations are responsible for the computational speedup, and that these can be captured by the quantum discord. In this Letter we implement DQC1 in an all-optical architecture, and experimentally observe the generated correlations. We find no entanglement, but large amounts of quantum discord-except in three cases where an efficient classical simulation is always possible. Our results show that even fully separable, highly mixed, states can contain intrinsically quantum mechanical correlations and that these could offer a valuable resource for quantum information technologies.

Biomolecular Structure Information from High-Speed Quantum Mechanical Electronic Spectra Calculation.

Science.gov (United States)

Seibert, Jakob; Bannwarth, Christoph; Grimme, Stefan

2017-08-30

A fully quantum mechanical (QM) treatment to calculate electronic absorption (UV-vis) and circular dichroism (CD) spectra of typical biomolecules with thousands of atoms is presented. With our highly efficient sTDA-xTB method, spectra averaged along structures from molecular dynamics (MD) simulations can be computed in a reasonable time frame on standard desktop computers. This way, nonequilibrium structure and conformational, as well as purely quantum mechanical effects like charge-transfer or exciton-coupling, are included. Different from other contemporary approaches, the entire system is treated quantum mechanically and neither fragmentation nor system-specific adjustment is necessary. Among the systems considered are a large DNA fragment, oligopeptides, and even entire proteins in an implicit solvent. We propose the method in tandem with experimental spectroscopy or X-ray studies for the elucidation of complex (bio)molecular structures including metallo-proteins like myoglobin.

Highly efficient single-layer dendrimer light-emitting diodes with balanced charge transport

Science.gov (United States)

Anthopoulos, Thomas D.; Markham, Jonathan P. J.; Namdas, Ebinazar B.; Samuel, Ifor D. W.; Lo, Shih-Chun; Burn, Paul L.

2003-06-01

High-efficiency single-layer-solution-processed green light-emitting diodes based on a phosphorescent dendrimer are demonstrated. A peak external quantum efficiency of 10.4% (35 cd/A) was measured for a first generation fac-tris(2-phenylpyridine) iridium cored dendrimer when blended with 4,4'-bis(N-carbazolyl)biphenyl and electron transporting 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene at 8.1 V. A maximum power efficiency of 12.8 lm/W was measured also at 8.1 V and 550 cd/m2. These results indicate that, by simple blending of bipolar and electron-transporting molecules, highly efficient light-emitting diodes can be made employing a very simple device structure.

Study of the photo-detection efficiency of FBK High-Density silicon photomultipliers

International Nuclear Information System (INIS)

Zappalà, G.; Regazzoni, V.; Acerbi, F.; Ferri, A.; Gola, A.; Paternoster, G.; Zorzi, N.; Piemonte, C.

2016-01-01

This work presents a study of the factors contributing to the Photo-Detection Efficiency of Silicon Photomultipliers (SiPMs): Quantum Efficiency, Triggering Probability and Fill Factor. Two different SiPM High-Density technologies are tested, NUV-HD, based on n-on-p junction, and RGB-HD, based on p-on-n junction, developed at FBK, Trento. The quantum efficiency was measured on photodiodes produced along with the SiPMs. The triggering probability, as a function of wavelength and bias voltage, was measured on circular Single Photon Avalanche Diodes (SPADs) with 100% fill factor. Square SPADs, having the same layout of single SiPM cells, were studied to measure the effective fill factor and compare it to the nominal value. The comparison of the circular and square SPADs allows to get the transition region size between the effective active area of the cell and the one defined by the layout.

The quantum Hall effect in quantum dot systems

International Nuclear Information System (INIS)

Beltukov, Y M; Greshnov, A A

2014-01-01

It is proposed to use quantum dots in order to increase the temperatures suitable for observation of the integer quantum Hall effect. A simple estimation using Fock-Darwin spectrum of a quantum dot shows that good part of carriers localized in quantum dots generate the intervals of plateaus robust against elevated temperatures. Numerical calculations employing local trigonometric basis and highly efficient kernel polynomial method adopted for computing the Hall conductivity reveal that quantum dots may enhance peak temperature for the effect by an order of magnitude, possibly above 77 K. Requirements to potentials, quality and arrangement of the quantum dots essential for practical realization of such enhancement are indicated. Comparison of our theoretical results with the quantum Hall measurements in InAs quantum dot systems from two experimental groups is also given

High-resolution photocurrent microscopy using near-field cathodoluminescence of quantum dots

Directory of Open Access Journals (Sweden)

Heayoung P. Yoon

2013-06-01

Full Text Available We report a fast, versatile photocurrent imaging technique to visualize the local photo response of solar energy devices and optoelectronics using near-field cathodoluminescence (CL from a homogeneous quantum dot layer. This approach is quantitatively compared with direct measurements of high-resolution Electron Beam Induced Current (EBIC using a thin film solar cell (n-CdS / p-CdTe. Qualitatively, the observed image contrast is similar, showing strong enhancement of the carrier collection efficiency at the p-n junction and near the grain boundaries. The spatial resolution of the new technique, termed Q-EBIC (EBIC using quantum dots, is determined by the absorption depth of photons. The results demonstrate a new method for high-resolution, sub-wavelength photocurrent imaging measurement relevant for a wide range of applications.

Quantum Chemistry on Quantum Computers: A Polynomial-Time Quantum Algorithm for Constructing the Wave Functions of Open-Shell Molecules.

Science.gov (United States)

Sugisaki, Kenji; Yamamoto, Satoru; Nakazawa, Shigeaki; Toyota, Kazuo; Sato, Kazunobu; Shiomi, Daisuke; Takui, Takeji

2016-08-18

Quantum computers are capable to efficiently perform full configuration interaction (FCI) calculations of atoms and molecules by using the quantum phase estimation (QPE) algorithm. Because the success probability of the QPE depends on the overlap between approximate and exact wave functions, efficient methods to prepare accurate initial guess wave functions enough to have sufficiently large overlap with the exact ones are highly desired. Here, we propose a quantum algorithm to construct the wave function consisting of one configuration state function, which is suitable for the initial guess wave function in QPE-based FCI calculations of open-shell molecules, based on the addition theorem of angular momentum. The proposed quantum algorithm enables us to prepare the wave function consisting of an exponential number of Slater determinants only by a polynomial number of quantum operations.

Efficiency studies on semipolar GaInN-GaN quantum well structures

Energy Technology Data Exchange (ETDEWEB)

Scholz, Ferdinand; Meisch, Tobias; Elkhouly, Karim [Institute of Optoelectronics, Ulm University (Germany)

2016-12-15

In order to clarify the reasons for the fairly poor electroluminescence (EL) performance of semipolar LED structures grown on patterned sapphire wafers, we have analyzed both, pure photoluminescence (PL) test structures without doping only containing 5 GaInN quantum wells and full EL test structures, all emitting at a wavelength of about 510 nm. Evaluating the PL intensity over a wide range of temperatures and excitation powers, we conclude that such quantum wells possess a fairly large internal quantum efficiency of about 20%. However, on EL test structures containing nominally the same quantum wells, we obtained an optical output power of only about 150μW at an applied current of 20 mA. This may be due partly to some thermal destruction of the quantum wells by the overgrowth with p-GaN. Even more important seems to be the not yet finally optimized p-doping of these structures. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Quantum Key Distribution with High Order Fibonacci-like Orbital Angular Momentum States

Science.gov (United States)

Pan, Ziwen; Cai, Jiarui; Wang, Chuan

2017-08-01

The coding space in quantum communication could be expanded to high-dimensional space by using orbital angular momentum (OAM) states of photons, as both the capacity of the channel and security are enhanced. Here we present a novel approach to realize high-capacity quantum key distribution (QKD) by exploiting OAM states. The innovation of the proposed approach relies on a unique type of entangled-photon source which produces entangled photons with OAM randomly distributed among high order Fiboncci-like numbers and a new physical mechanism for efficiently sharing keys. This combination of entanglement with mathematical properties of high order Fibonacci sequences provides the QKD protocol immunity to photon-number-splitting attacks and allows secure generation of long keys from few photons. Unlike other protocols, reference frame alignment and active modulation of production and detection bases are unnecessary.

Functional Basis for Efficient Physical Layer Classical Control in Quantum Processors

Science.gov (United States)

Ball, Harrison; Nguyen, Trung; Leong, Philip H. W.; Biercuk, Michael J.

2016-12-01

The rapid progress seen in the development of quantum-coherent devices for information processing has motivated serious consideration of quantum computer architecture and organization. One topic which remains open for investigation and optimization relates to the design of the classical-quantum interface, where control operations on individual qubits are applied according to higher-level algorithms; accommodating competing demands on performance and scalability remains a major outstanding challenge. In this work, we present a resource-efficient, scalable framework for the implementation of embedded physical layer classical controllers for quantum-information systems. Design drivers and key functionalities are introduced, leading to the selection of Walsh functions as an effective functional basis for both programing and controller hardware implementation. This approach leverages the simplicity of real-time Walsh-function generation in classical digital hardware, and the fact that a wide variety of physical layer controls, such as dynamic error suppression, are known to fall within the Walsh family. We experimentally implement a real-time field-programmable-gate-array-based Walsh controller producing Walsh timing signals and Walsh-synthesized analog waveforms appropriate for critical tasks in error-resistant quantum control and noise characterization. These demonstrations represent the first step towards a unified framework for the realization of physical layer controls compatible with large-scale quantum-information processing.

Nearly Efficiency-Droop-Free AlGaN-Based Ultraviolet Light-Emitting Diodes with a Specifically Designed Superlattice p-Type Electron Blocking Layer for High Mg Doping Efficiency

Science.gov (United States)

Zhang, Zi-Hui; Huang Chen, Sung-Wen; Chu, Chunshuang; Tian, Kangkai; Fang, Mengqian; Zhang, Yonghui; Bi, Wengang; Kuo, Hao-Chung

2018-04-01

This work reports a nearly efficiency-droop-free AlGaN-based deep ultraviolet light-emitting diode (DUV LED) emitting in the peak wavelength of 270 nm. The DUV LED utilizes a specifically designed superlattice p-type electron blocking layer (p-EBL). The superlattice p-EBL enables a high hole concentration in the p-EBL which correspondingly increases the hole injection efficiency into the multiple quantum wells (MQWs). The enhanced hole concentration within the MQW region can more efficiently recombine with electrons in the way of favoring the radiative recombination, leading to a reduced electron leakage current level. As a result, the external quantum efficiency for the proposed DUV LED structure is increased by 100% and the nearly efficiency-droop-free DUV LED structure is obtained experimentally.

The quantum walk search algorithm: Factors affecting efficiency

OpenAIRE

Lovett, Neil B.; Everitt, Matthew; Heath, Robert M.; Kendon, Viv

2011-01-01

We numerically study the quantum walk search algorithm of Shenvi, Kempe and Whaley [PRA \\textbf{67} 052307] and the factors which affect its efficiency in finding an individual state from an unsorted set. Previous work has focused purely on the effects of the dimensionality of the dataset to be searched. Here, we consider the effects of interpolating between dimensions, connectivity of the dataset, and the possibility of disorder in the underlying substrate: all these factors affect the effic...

Anisotropic behavior of quantum transport in graphene superlattices

DEFF Research Database (Denmark)

Pedersen, Jesper Goor; Cummings, Aron W.; Roche, Stephan

2014-01-01

We report on the possibility to generate highly anisotropic quantum conductivity in disordered graphene-based superlattices. Our quantum simulations, based on an efficient real-space implementation of the Kubo-Greenwood formula, show that in disordered graphene superlattices the strength of multi......We report on the possibility to generate highly anisotropic quantum conductivity in disordered graphene-based superlattices. Our quantum simulations, based on an efficient real-space implementation of the Kubo-Greenwood formula, show that in disordered graphene superlattices the strength...

Quantum entanglement of high angular momenta.

Science.gov (United States)

Fickler, Robert; Lapkiewicz, Radek; Plick, William N; Krenn, Mario; Schaeff, Christoph; Ramelow, Sven; Zeilinger, Anton

2012-11-02

Single photons with helical phase structures may carry a quantized amount of orbital angular momentum (OAM), and their entanglement is important for quantum information science and fundamental tests of quantum theory. Because there is no theoretical upper limit on how many quanta of OAM a single photon can carry, it is possible to create entanglement between two particles with an arbitrarily high difference in quantum number. By transferring polarization entanglement to OAM with an interferometric scheme, we generate and verify entanglement between two photons differing by 600 in quantum number. The only restrictive factors toward higher numbers are current technical limitations. We also experimentally demonstrate that the entanglement of very high OAM can improve the sensitivity of angular resolution in remote sensing.

Highly efficient exciplex organic light-emitting diodes incorporating a heptazine derivative as an electron acceptor.

Science.gov (United States)

Li, Jie; Nomura, Hiroko; Miyazaki, Hiroshi; Adachi, Chihaya

2014-06-11

Highly efficient exciplex systems incorporating a heptazine derivative () as an electron acceptor and 1,3-di(9H-carbazol-9-yl)benzene () as an electron donor are developed. An organic light-emitting diode containing 8 wt% : as an emitting layer exhibits a maximum external quantum efficiency of 11.3%.

Role of the substrate reflectance and surface-bulk treatments in CsI quantum efficiency

CERN Document Server

Singh, B K; Nitti, M A; Valentini, A

2003-01-01

We have experimentally investigated the following aspects related to the quantum efficiency of CsI photocathodes: the type of substrate, the film thickness and the effect of a 'bulk treatment' during the film growth. We discovered that, using a high reflectivity aluminium substrate, the photoemission of very thin CsI film is enhanced. Our study also revealed that photocathodes become less sensitive to moisture when a negative bias voltage is applied to the substrate during the film deposition process.

Fast and simple high-capacity quantum cryptography with error detection.

Science.gov (United States)

Lai, Hong; Luo, Ming-Xing; Pieprzyk, Josef; Zhang, Jun; Pan, Lei; Li, Shudong; Orgun, Mehmet A

2017-04-13

Quantum cryptography is commonly used to generate fresh secure keys with quantum signal transmission for instant use between two parties. However, research shows that the relatively low key generation rate hinders its practical use where a symmetric cryptography component consumes the shared key. That is, the security of the symmetric cryptography demands frequent rate of key updates, which leads to a higher consumption of the internal one-time-pad communication bandwidth, since it requires the length of the key to be as long as that of the secret. In order to alleviate these issues, we develop a matrix algorithm for fast and simple high-capacity quantum cryptography. Our scheme can achieve secure private communication with fresh keys generated from Fibonacci- and Lucas- valued orbital angular momentum (OAM) states for the seed to construct recursive Fibonacci and Lucas matrices. Moreover, the proposed matrix algorithm for quantum cryptography can ultimately be simplified to matrix multiplication, which is implemented and optimized in modern computers. Most importantly, considerably information capacity can be improved effectively and efficiently by the recursive property of Fibonacci and Lucas matrices, thereby avoiding the restriction of physical conditions, such as the communication bandwidth.

Fast and simple high-capacity quantum cryptography with error detection

Science.gov (United States)

Lai, Hong; Luo, Ming-Xing; Pieprzyk, Josef; Zhang, Jun; Pan, Lei; Li, Shudong; Orgun, Mehmet A.

2017-04-01

Quantum cryptography is commonly used to generate fresh secure keys with quantum signal transmission for instant use between two parties. However, research shows that the relatively low key generation rate hinders its practical use where a symmetric cryptography component consumes the shared key. That is, the security of the symmetric cryptography demands frequent rate of key updates, which leads to a higher consumption of the internal one-time-pad communication bandwidth, since it requires the length of the key to be as long as that of the secret. In order to alleviate these issues, we develop a matrix algorithm for fast and simple high-capacity quantum cryptography. Our scheme can achieve secure private communication with fresh keys generated from Fibonacci- and Lucas- valued orbital angular momentum (OAM) states for the seed to construct recursive Fibonacci and Lucas matrices. Moreover, the proposed matrix algorithm for quantum cryptography can ultimately be simplified to matrix multiplication, which is implemented and optimized in modern computers. Most importantly, considerably information capacity can be improved effectively and efficiently by the recursive property of Fibonacci and Lucas matrices, thereby avoiding the restriction of physical conditions, such as the communication bandwidth.

Thermally Activated Delayed Fluorescence in Polymers: A New Route toward Highly Efficient Solution Processable OLEDs.

Science.gov (United States)

Nikolaenko, Andrey E; Cass, Michael; Bourcet, Florence; Mohamad, David; Roberts, Matthew

2015-11-25

Efficient intermonomer thermally activated delayed fluorescence is demonstrated for the first time, opening a new route to achieving high-efficiency solution processable polymer light-emitting device materials. External quantum efficiency (EQE) of up to 10% is achieved in a simple fully solution-processed device structure, and routes for further EQE improvement identified. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Quantum optics with quantum dots in photonic nanowires

DEFF Research Database (Denmark)

Claudon, Julien; Munsch, Matthieu; Bleuse, Joel

2012-01-01

Besides microcavities and photonic crystals, photonic nanowires have recently emerged as a novel resource for solidstate quantum optics. We will review recent studies which demonstrate an excellent control over the spontaneous emission of InAs quantum dots (QDs) embedded in single-mode Ga...... quantum optoelectronic devices. Quite amazingly, this approach has for instance permitted (unlike microcavity-based approaches) to combine for the first time a record-high efficiency (72%) and a negligible g(2) in a QD single photon source....

Efficient interfacing of light and surface plasmon polaritons for quantum optics applications

DEFF Research Database (Denmark)

Eran, Kot

interaction are the window to the underlying quantum world. It is no surprise then that there has always been push to find more, and gain better control over systems in which this interaction can be studied. In the past two decades, this end was further motivated as applications were envisioned to coherent...... control of matter. These include applications such as efficient photon collection, single-photon switching and transistors, and long-range optical coupling of quantum bits for quantum communications. However, generating and controlling strong coherent interaction between otherwise very weakly interacting...... light and quantum emitters proves a difficult task. Current days solutions range from cavities, atomic ensembles, photonic band gaps structures, ion traps and optical latices are all being improved and studied but none has yet to emerge as superior. Recently, another proposal for such a strong coupling...

Highly efficient photochemical HCOOH production from CO2 and water using an inorganic system

Directory of Open Access Journals (Sweden)

Satoshi Yotsuhashi

2012-12-01

Full Text Available We have constructed a system that uses solar energy to react CO2 with water to generate formic acid (HCOOH at an energy conversion efficiency of 0.15%. It consists of an AlGaN/GaN anode photoelectrode and indium (In cathode that are electrically connected outside of the reactor cell. High energy conversion efficiency is realized due to a high quantum efficiency of 28% at 300 nm, attributable to efficient electron-hole separation in the semiconductor's heterostructure. The efficiency is close to that of natural photosynthesis in plants, and what is more, the reaction product (HCOOH can be used as a renewable energy source.

Highly efficient red phosphorescent organic light-emitting diodes based on solution processed emissive layer

International Nuclear Information System (INIS)

Liu, Baiquan; Xu, Miao; Tao, Hong; Ying, Lei; Zou, Jianhua; Wu, Hongbin; Peng, Junbiao

2013-01-01

Highly efficient red phosphorescent organic polymer light-emitting diodes (PhOLEDs) were fabricated based on a solution-processed small-molecule host 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) by doping an iridium complex, tris(1-(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine)iridium (III) (Ir(MPCPPZ) 3 ). A hole blocking layer 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBI) with a function of electron transport was thermally deposited onto the top of CBP layer. The diode with the structure of ITO/PEDOT:PSS (50 nm)/CBP:Ir(MPCPPZ) 3 (55 nm)/TPBI (30 nm)/Ba (4 nm)/Al (120 nm) showed an external quantum efficiency (QE ext ) of 19.3% and luminous efficiency (LE) of 18.3 cd/A at a current density of 0.16 mA/cm 2 , and Commission International de I'Eclairage (CIE) coordinates of (0.607, 0.375). It was suggested that the diodes using TPBI layer exhibited nearly 100% internal quantum efficiency and one order magnitude enhanced LE or QE ext efficiencies. -- Highlights: • Efficient red PhOLEDs based on a solution-processed small-molecule host were fabricated. • By altering volume ratio of chloroform/chlorobenzene solvent, we got best film quality of CBP. • EQE of the diode was 19.3%, indicating nearly 100% internal quantum yield was achieved

PsiQuaSP-A library for efficient computation of symmetric open quantum systems.

Science.gov (United States)

Gegg, Michael; Richter, Marten

2017-11-24

In a recent publication we showed that permutation symmetry reduces the numerical complexity of Lindblad quantum master equations for identical multi-level systems from exponential to polynomial scaling. This is important for open system dynamics including realistic system bath interactions and dephasing in, for instance, the Dicke model, multi-Λ system setups etc. Here we present an object-oriented C++ library that allows to setup and solve arbitrary quantum optical Lindblad master equations, especially those that are permutationally symmetric in the multi-level systems. PsiQuaSP (Permutation symmetry for identical Quantum Systems Package) uses the PETSc package for sparse linear algebra methods and differential equations as basis. The aim of PsiQuaSP is to provide flexible, storage efficient and scalable code while being as user friendly as possible. It is easily applied to many quantum optical or quantum information systems with more than one multi-level system. We first review the basics of the permutation symmetry for multi-level systems in quantum master equations. The application of PsiQuaSP to quantum dynamical problems is illustrated with several typical, simple examples of open quantum optical systems.

Efficient calculation of dissipative quantum transport properties in semiconductor nanostructures

Energy Technology Data Exchange (ETDEWEB)

Greck, Peter

2012-11-26

We present a novel quantum transport method that follows the non-equilibrium Green's function (NEGF) framework but side steps any self-consistent calculation of lesser self-energies by replacing them by a quasi-equilibrium expression. We termed this method the multi-scattering Buettiker-Probe (MSB) method. It generalizes the so-called Buettiker-Probe model but takes into account all relevant individual scattering mechanisms. It is orders of magnitude more efficient than a fully selfconsistent non-equilibrium Green's function calculation for realistic devices, yet accurately reproduces the results of the latter method as well as experimental data. This method is fairly easy to implement and opens the path towards realistic three-dimensional quantum transport calculations. In this work, we review the fundamentals of the non-equilibrium Green's function formalism for quantum transport calculations. Then, we introduce our novel MSB method after briefly reviewing the original Buettiker-Probe model. Finally, we compare the results of the MSB method to NEGF calculations as well as to experimental data. In particular, we calculate quantum transport properties of quantum cascade lasers in the terahertz (THz) and the mid-infrared (MIR) spectral domain. With a device optimization algorithm based upon the MSB method, we propose a novel THz quantum cascade laser design. It uses a two-well period with alternating barrier heights and complete carrier thermalization for the majority of the carriers within each period. We predict THz laser operation for temperatures up to 250 K implying a new temperature record.

Self-assembled quantum dot structures in a hexagonal nanowire for quantum photonics.

Science.gov (United States)

Yu, Ying; Dou, Xiu-Ming; Wei, Bin; Zha, Guo-Wei; Shang, Xiang-Jun; Wang, Li; Su, Dan; Xu, Jian-Xing; Wang, Hai-Yan; Ni, Hai-Qiao; Sun, Bao-Quan; Ji, Yuan; Han, Xiao-Dong; Niu, Zhi-Chuan

2014-05-01

Two types of quantum nanostructures based on self-assembled GaAs quantumdots embedded into GaAs/AlGaAs hexagonal nanowire systems are reported, opening a new avenue to the fabrication of highly efficient single-photon sources, as well as the design of novel quantum optics experiments and robust quantum optoelectronic devices operating at higher temperature, which are required for practical quantum photonics applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Efficient networks for quantum factoring

International Nuclear Information System (INIS)

Beckman, D.; Chari, A.N.; Devabhaktuni, S.; Preskill, J.

1996-01-01

We consider how to optimize memory use and computation time in operating a quantum computer. In particular, we estimate the number of memory quantum bits (qubits) and the number of operations required to perform factorization, using the algorithm suggested by Shor [in Proceedings of the 35th Annual Symposium on Foundations of Computer Science, edited by S. Goldwasser (IEEE Computer Society, Los Alamitos, CA, 1994), p. 124]. A K-bit number can be factored in time of order K 3 using a machine capable of storing 5K+1 qubits. Evaluation of the modular exponential function (the bottleneck of Shor close-quote s algorithm) could be achieved with about 72K 3 elementary quantum gates; implementation using a linear ion trap would require about 396K 3 laser pulses. A proof-of-principle demonstration of quantum factoring (factorization of 15) could be performed with only 6 trapped ions and 38 laser pulses. Though the ion trap may never be a useful computer, it will be a powerful device for exploring experimentally the properties of entangled quantum states. copyright 1996 The American Physical Society

Optical efficiency enhancement in white organic light-emitting diode display with high color gamut using patterned quantum dot film and long pass filter

Science.gov (United States)

Kim, Hyo-Jun; Shin, Min-Ho; Kim, Young-Joo

2016-08-01

A new structure for white organic light-emitting diode (OLED) displays with a patterned quantum dot (QD) film and a long pass filter (LPF) was proposed and evaluated to realize both a high color gamut and high optical efficiency. Since optical efficiency is a critical parameter in white OLED displays with a high color gamut, a red or green QD film as a color-converting component and an LPF as a light-recycling component are introduced to be adjusted via the characteristics of a color filter (CF). Compared with a conventional white OLED without both a QD film and the LPF, it was confirmed experimentally that the optical powers of red and green light in a new white OLED display were increased by 54.1 and 24.7% using a 30 wt % red QD film and a 20 wt % green QD film with the LPF, respectively. In addition, the white OLED with both a QD film and the LPF resulted in an increase in the color gamut from 98 to 107% (NTSC x,y ratio) due to the narrow emission linewidth of the QDs.

An energy and cost efficient majority-based RAM cell in quantum-dot cellular automata

Science.gov (United States)

Khosroshahy, Milad Bagherian; Moaiyeri, Mohammad Hossein; Navi, Keivan; Bagherzadeh, Nader

Nanotechnologies, notably quantum-dot cellular automata, have achieved major attentions for their prominent features as compared to the conventional CMOS circuitry. Quantum-dot cellular automata, particularly owning to its considerable reduction in size, high switching speed and ultra-low energy consumption, is considered as a potential alternative for the CMOS technology. As the memory unit is one of the most essential components in a digital system, designing a well-optimized QCA random access memory (RAM) cell is an important area of research. In this paper, a new five-input majority gate is presented which is suitable for implementing efficient single-layer QCA circuits. In addition, a new RAM cell with set and reset capabilities is designed based on the proposed majority gate, which has an efficient and low-energy structure. The functionality, performance and energy consumption of the proposed designs are evaluated based on the QCADesigner and QCAPro tools. According to the simulation results, the proposed RAM design leads to on average 38% lower total energy dissipation, 25% smaller area, 20% lower cell count, 28% lower delay and 60% lower QCA cost as compared to its previous counterparts.

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.

Quantum efficiencies of near-infrared emission from Ni2+-doped glass-ceramics

International Nuclear Information System (INIS)

Suzuki, Takenobu; Arai, Yusuke; Ohishi, Yasutake

2008-01-01

A systematic method to evaluate potentials of Ni 2+ -doped transparent glass-ceramics as a new broadband optical gain media is presented. At first, near-infrared emission of various ceramics were investigated to explore the suitable crystalline phase to be grown in the glass-ceramics. The quantum efficiency of Ni 2+ near-infrared emission estimated by the Struck-Fonger analysis was higher than 95% for spinel-type structure gallate crystals MgGa 2 O 4 and LiGa 5 O 8 at room temperature. Transparent glass-ceramics containing Ni 2+ :LiGa 5 O 8 could be prepared and the quantum efficiency for the glass-ceramics was measured to be about 10%. This value shows a potential of Ni-doped transparent glass-ceramics as a broadband gain media

Quantum computation with nuclear spins in quantum dots

International Nuclear Information System (INIS)

Christ, H.

2008-01-01

The role of nuclear spins for quantum information processing in quantum dots is theoretically investigated in this thesis. Building on the established fact that the most strongly coupled environment for the potential electron spin quantum bit are the surrounding lattice nuclear spins interacting via the hyperfine interaction, we turn this vice into a virtue by designing schemes for harnessing this strong coupling. In this perspective, the ensemble of nuclear spins can be considered an asset, suitable for an active role in quantum information processing due to its intrinsic long coherence times. We present experimentally feasible protocols for the polarization, i.e. initialization, of the nuclear spins and a quantitative solution to our derived master equation. The polarization limiting destructive interference effects, caused by the collective nature of the nuclear coupling to the electron spin, are studied in detail. Efficient ways of mitigating these constraints are presented, demonstrating that highly polarized nuclear ensembles in quantum dots are feasible. At high, but not perfect, polarization of the nuclei the evolution of an electron spin in contact with the spin bath can be efficiently studied by means of a truncation of the Hilbert space. It is shown that the electron spin can function as a mediator of universal quantum gates for collective nuclear spin qubits, yielding a promising architecture for quantum information processing. Furthermore, we show that at high polarization the hyperfine interaction of electron and nuclear spins resembles the celebrated Jaynes-Cummings model of quantum optics. This result opens the door for transfer of knowledge from the mature field of quantum computation with atoms and photons. Additionally, tailored specifically for the quantum dot environment, we propose a novel scheme for the generation of highly squeezed collective nuclear states. Finally we demonstrate that even an unprepared completely mixed nuclear spin

Quantum computation with nuclear spins in quantum dots

Energy Technology Data Exchange (ETDEWEB)

Christ, H.

2008-01-24

The role of nuclear spins for quantum information processing in quantum dots is theoretically investigated in this thesis. Building on the established fact that the most strongly coupled environment for the potential electron spin quantum bit are the surrounding lattice nuclear spins interacting via the hyperfine interaction, we turn this vice into a virtue by designing schemes for harnessing this strong coupling. In this perspective, the ensemble of nuclear spins can be considered an asset, suitable for an active role in quantum information processing due to its intrinsic long coherence times. We present experimentally feasible protocols for the polarization, i.e. initialization, of the nuclear spins and a quantitative solution to our derived master equation. The polarization limiting destructive interference effects, caused by the collective nature of the nuclear coupling to the electron spin, are studied in detail. Efficient ways of mitigating these constraints are presented, demonstrating that highly polarized nuclear ensembles in quantum dots are feasible. At high, but not perfect, polarization of the nuclei the evolution of an electron spin in contact with the spin bath can be efficiently studied by means of a truncation of the Hilbert space. It is shown that the electron spin can function as a mediator of universal quantum gates for collective nuclear spin qubits, yielding a promising architecture for quantum information processing. Furthermore, we show that at high polarization the hyperfine interaction of electron and nuclear spins resembles the celebrated Jaynes-Cummings model of quantum optics. This result opens the door for transfer of knowledge from the mature field of quantum computation with atoms and photons. Additionally, tailored specifically for the quantum dot environment, we propose a novel scheme for the generation of highly squeezed collective nuclear states. Finally we demonstrate that even an unprepared completely mixed nuclear spin

Engineering two-photon high-dimensional states through quantum interference

Science.gov (United States)

Zhang, Yingwen; Roux, Filippus S.; Konrad, Thomas; Agnew, Megan; Leach, Jonathan; Forbes, Andrew

2016-01-01

Many protocols in quantum science, for example, linear optical quantum computing, require access to large-scale entangled quantum states. Such systems can be realized through many-particle qubits, but this approach often suffers from scalability problems. An alternative strategy is to consider a lesser number of particles that exist in high-dimensional states. The spatial modes of light are one such candidate that provides access to high-dimensional quantum states, and thus they increase the storage and processing potential of quantum information systems. We demonstrate the controlled engineering of two-photon high-dimensional states entangled in their orbital angular momentum through Hong-Ou-Mandel interference. We prepare a large range of high-dimensional entangled states and implement precise quantum state filtering. We characterize the full quantum state before and after the filter, and are thus able to determine that only the antisymmetric component of the initial state remains. This work paves the way for high-dimensional processing and communication of multiphoton quantum states, for example, in teleportation beyond qubits. PMID:26933685

Limits to solar power conversion efficiency with applications to quantum and thermal systems

Science.gov (United States)

Byvik, C. E.; Buoncristiani, A. M.; Smith, B. T.

1983-01-01

An analytical framework is presented that permits examination of the limit to the efficiency of various solar power conversion devices. Thermodynamic limits to solar power efficiency are determined for both quantum and thermal systems, and the results are applied to a variety of devices currently considered for use in space systems. The power conversion efficiency for single-threshold energy quantum systems receiving unconcentrated air mass zero solar radiation is limited to 31 percent. This limit applies to photovoltaic cells directly converting solar radiation, or indirectly, as in the case of a thermophotovoltaic system. Photoelectrochemical cells rely on an additional chemical reaction at the semiconductor-electrolyte interface, which introduces additional second-law demands and a reduction of the solar conversion efficiency. Photochemical systems exhibit even lower possible efficiencies because of their relatively narrow absorption bands. Solar-powered thermal engines in contact with an ambient reservoir at 300 K and operating at maximum power have a peak conversion efficiency of 64 percent, and this occurs for a thermal reservoir at a temperature of 2900 K. The power conversion efficiency of a solar-powered liquid metal magnetohydrodydnamic generator, a solar-powered steam turbine electric generator, and an alkali metal thermoelectric converter is discussed.

Toward efficient fiber-based quantum interface (Conference Presentation)

Science.gov (United States)

Soshenko, Vladimir; Vorobyov, Vadim V.; Bolshedvorsky, Stepan; Lebedev, Nikolay; Akimov, Alexey V.; Sorokin, Vadim; Smolyaninov, Andrey

2016-04-01

NV center in diamond is attracting a lot of attention in quantum information processing community [1]. Been spin system in clean and well-controlled environment of diamond it shows outstanding performance as quantum memory even at room temperature, spin control with single shot optical readout and possibility to build up quantum registers even on single NV center. Moreover, NV centers could be used as high-resolution sensitive elements of detectors of magnetic or electric field, temperature, tension, force or rotation. For all of these applications collection of the light emitted by NV center is crucial point. There were number of approaches suggested to address this issue, proposing use of surface plasmoms [2], manufacturing structures in diamond [3] etc. One of the key feature of any practically important interface is compatibility with the fiber technology. Several groups attacking this problem using various approaches. One of them is placing of nanodiamonds in the holes of photonic crystal fiber [4], another is utilization of AFM to pick and place nanodiamond on the tapered fiber[5]. We have developed a novel technique of placing a nanodiamond with single NV center on the tapered fiber by controlled transfer of a nanodiamond from one "donor" tapered fiber to the "target" clean tapered fiber. We verify our ability to transfer only single color centers by means of measurement of second order correlation function. With this technique, we were able to double collection efficiency of confocal microscope. The majority of the factors limiting the collection of photons via optical fiber are technical and may be removed allowing order of magnitude improved in collection. We also discuss number of extensions of this technique to all fiber excitation and integration with nanostructures. References: [1] Marcus W. Doherty, Neil B. Manson, Paul Delaney, Fedor Jelezko, Jörg Wrachtrup, Lloyd C.L. Hollenberg , " The nitrogen-vacancy colour centre in diamond," Physics Reports

Carbon-doped SnS2 nanostructure as a high-efficiency solar fuel catalyst under visible light.

Science.gov (United States)

Shown, Indrajit; Samireddi, Satyanarayana; Chang, Yu-Chung; Putikam, Raghunath; Chang, Po-Han; Sabbah, Amr; Fu, Fang-Yu; Chen, Wei-Fu; Wu, Chih-I; Yu, Tsyr-Yan; Chung, Po-Wen; Lin, M C; Chen, Li-Chyong; Chen, Kuei-Hsien

2018-01-12

Photocatalytic formation of hydrocarbons using solar energy via artificial photosynthesis is a highly desirable renewable-energy source for replacing conventional fossil fuels. Using an L-cysteine-based hydrothermal process, here we synthesize a carbon-doped SnS 2 (SnS 2 -C) metal dichalcogenide nanostructure, which exhibits a highly active and selective photocatalytic conversion of CO 2 to hydrocarbons under visible-light. The interstitial carbon doping induced microstrain in the SnS 2 lattice, resulting in different photophysical properties as compared with undoped SnS 2 . This SnS 2 -C photocatalyst significantly enhances the CO 2 reduction activity under visible light, attaining a photochemical quantum efficiency of above 0.7%. The SnS 2 -C photocatalyst represents an important contribution towards high quantum efficiency artificial photosynthesis based on gas phase photocatalytic CO 2 reduction under visible light, where the in situ carbon-doped SnS 2 nanostructure improves the stability and the light harvesting and charge separation efficiency, and significantly enhances the photocatalytic activity.

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.

LHCb: Quantum Efficiency of Hybrid Photon Detectors for the LHCb RICH

CERN Multimedia

Lambert, Robert W

2007-01-01

The production of 550 hybrid photon detectors to be used within the LHCb RICH detectors has recently finished. Photonis-DEP have succeeded in consistently improving the tube quantum efficiency, by a relative 27,% with respect to preseries and prototype tubes, when integrated over the energy spectrum.

The effect of nonadiabaticity on the efficiency of quantum memory based on an optical cavity

Science.gov (United States)

Veselkova, N. G.; Sokolov, I. V.

2017-07-01

Quantum efficiency is an important characteristic of quantum memory devices that are aimed at recording the quantum state of light signals and its storing and reading. In the case of memory based on an ensemble of cold atoms placed in an optical cavity, the efficiency is restricted, in particular, by relaxation processes in the system of active atomic levels. We show how the effect of the relaxation on the quantum efficiency can be determined in a regime of the memory usage in which the evolution of signals in time is not arbitrarily slow on the scale of the field lifetime in the cavity and when the frequently used approximation of the adiabatic elimination of the quantized cavity mode field cannot be applied. Taking into account the effect of the nonadiabaticity on the memory quality is of interest in view of the fact that, in order to increase the field-medium coupling parameter, a higher cavity quality factor is required, whereas storing and processing of sequences of many signals in the memory implies that their duration is reduced. We consider the applicability of the well-known efficiency estimates via the system cooperativity parameter and estimate a more general form. In connection with the theoretical description of the memory of the given type, we also discuss qualitative differences in the behavior of a random source introduced into the Heisenberg-Langevin equations for atomic variables in the cases of a large and a small number of atoms.

High-efficiency green phosphorescent organic light-emitting diodes with double-emission layer and thick N-doped electron transport layer

Energy Technology Data Exchange (ETDEWEB)

Nobuki, Shunichiro, E-mail: shunichiro.nobuki.nb@hitachi.com [Hitachi Research Laboratory, Hitachi Ltd., 7-1-1 Omika-cho, Hitachi-city, Ibaraki 319-1292 (Japan); Wakana, Hironori; Ishihara, Shingo [Hitachi Research Laboratory, Hitachi Ltd., 7-1-1 Omika-cho, Hitachi-city, Ibaraki 319-1292 (Japan); Mikami, Akiyoshi [Dept. of Electrical Engineering, Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichimachi, Ishikawa 921-8501 (Japan)

2014-03-03

We have developed green phosphorescent organic light-emitting diodes (OLEDs) with high external quantum efficiency of 59.7% and power efficiency of 243 lm/W at 2.73 V at 0.053 mA/cm{sup 2}. A double emission layer and a thick n-doped electron transport layer were adopted to improve the exciton recombination factor. A high refractive index hemispherical lens was attached to a high refractive index substrate for extracting light trapped inside the substrate and the multiple-layers of OLEDs to air. Additionally, we analyzed an energy loss mechanism to clarify room for the improvement of our OLEDs including the charge balance factor. - Highlights: • We developed high efficiency green phosphorescent organic light-emitting diode (OLED). • Our OLED had external quantum efficiency of 59.7% and power efficiency of 243 lm/W. • A double emission layer and thick n-doped electron transport layer were adopted. • High refractive index media (hemispherical lens and substrate) were also used. • We analyzed an energy loss mechanism to clarify the charge balance factor of our OLED.

Nanometer-scale monitoring of quantum-confined Stark effect and emission efficiency droop in multiple GaN/AlN quantum disks in nanowires

Science.gov (United States)

Zagonel, L. F.; Tizei, L. H. G.; Vitiello, G. Z.; Jacopin, G.; Rigutti, L.; Tchernycheva, M.; Julien, F. H.; Songmuang, R.; Ostasevicius, T.; de la Peña, F.; Ducati, C.; Midgley, P. A.; Kociak, M.

2016-05-01

We report on a detailed study of the intensity dependent optical properties of individual GaN/AlN quantum disks (QDisks) embedded into GaN nanowires (NW). The structural and optical properties of the QDisks were probed by high spatial resolution cathodoluminescence (CL) in a scanning transmission electron microscope (STEM). By exciting the QDisks with a nanometric electron beam at currents spanning over three orders of magnitude, strong nonlinearities (energy shifts) in the light emission are observed. In particular, we find that the amount of energy shift depends on the emission rate and on the QDisk morphology (size, position along the NW and shell thickness). For thick QDisks (>4 nm), the QDisk emission energy is observed to blueshift with the increase of the emission intensity. This is interpreted as a consequence of the increase of carriers density excited by the incident electron beam inside the QDisks, which screens the internal electric field and thus reduces the quantum confined Stark effect (QCSE) present in these QDisks. For thinner QDisks (energy shifts, marking the transition from unscreened to partially screened QCSE. From the threshold value we estimate the lifetime in the unscreened regime. These observations suggest that, counterintuitively, electrons of high energy can behave ultimately as single electron-hole pair generators. In addition, when we increase the current from 1 to 10 pA the light emission efficiency drops by more than one order of magnitude. This reduction of the emission efficiency is a manifestation of the "efficiency droop" as observed in nitride-based 2D light emitting diodes, a phenomenon tentatively attributed to the Auger effect.

High-Capacity Quantum Secure Direct Communication Based on Quantum Hyperdense Coding with Hyperentanglement

International Nuclear Information System (INIS)

Wang Tie-Jun; Li Tao; Du Fang-Fang; Deng Fu-Guo

2011-01-01

We present a quantum hyperdense coding protocol with hyperentanglement in polarization and spatial-mode degrees of freedom of photons first and then give the details for a quantum secure direct communication (QSDC) protocol based on this quantum hyperdense coding protocol. This QSDC protocol has the advantage of having a higher capacity than the quantum communication protocols with a qubit system. Compared with the QSDC protocol based on superdense coding with d-dimensional systems, this QSDC protocol is more feasible as the preparation of a high-dimension quantum system is more difficult than that of a two-level quantum system at present. (general)

Design of Efficient Full Adder in Quantum-Dot Cellular Automata

Directory of Open Access Journals (Sweden)

Bibhash Sen

2013-01-01

Full Text Available Further downscaling of CMOS technology becomes challenging as it faces limitation of feature size reduction. Quantum-dot cellular automata (QCA, a potential alternative to CMOS, promises efficient digital design at nanoscale. Investigations on the reduction of QCA primitives (majority gates and inverters for various adders are limited, and very few designs exist for reference. As a result, design of adders under QCA framework is gaining its importance in recent research. This work targets developing multi-layered full adder architecture in QCA framework based on five-input majority gate proposed here. A minimum clock zone (2 clock with high compaction (0.01 μm2 for a full adder around QCA is achieved. Further, the usefulness of such design is established with the synthesis of high-level logic. Experimental results illustrate the significant improvements in design level in terms of circuit area, cell count, and clock compared to that of conventional design approaches.

High performance reconciliation for continuous-variable quantum key distribution with LDPC code

Science.gov (United States)

Lin, Dakai; Huang, Duan; Huang, Peng; Peng, Jinye; Zeng, Guihua

2015-03-01

Reconciliation is a significant procedure in a continuous-variable quantum key distribution (CV-QKD) system. It is employed to extract secure secret key from the resulted string through quantum channel between two users. However, the efficiency and the speed of previous reconciliation algorithms are low. These problems limit the secure communication distance and the secure key rate of CV-QKD systems. In this paper, we proposed a high-speed reconciliation algorithm through employing a well-structured decoding scheme based on low density parity-check (LDPC) code. The complexity of the proposed algorithm is reduced obviously. By using a graphics processing unit (GPU) device, our method may reach a reconciliation speed of 25 Mb/s for a CV-QKD system, which is currently the highest level and paves the way to high-speed CV-QKD.

High-Efficiency Iron Photosensitizer Explained with Quantum Wavepacket Dynamics

DEFF Research Database (Denmark)

Pápai, Mátyás Imre; Vankó, György; Rozgonyi, Tamas

2016-01-01

designed to destabilize the MC states. Using first-principles quantum nuclear wavepacket simulations we achieve a detailed understanding of the photoexcited decay mechanism, demonstrating that it is dominated by an ultrafast intersystem crossing from 1MLCT–3MLCT proceeded by slower kinetics associated...... with the conversion into the 3MC states. The slowest component of the 3MLCT decay, important in the context of photosensitizers, is much longer than related Fe(II) complexes because the population transfer to the 3MC states occurs in a region of the potential where the energy gap between the 3MLCT and 3MC states...

Data-driven gradient algorithm for high-precision quantum control

Science.gov (United States)

Wu, Re-Bing; Chu, Bing; Owens, David H.; Rabitz, Herschel

2018-04-01

In the quest to achieve scalable quantum information processing technologies, gradient-based optimal control algorithms (e.g., grape) are broadly used for implementing high-precision quantum gates, but their performance is often hindered by deterministic or random errors in the system model and the control electronics. In this paper, we show that grape can be taught to be more effective by jointly learning from the design model and the experimental data obtained from process tomography. The resulting data-driven gradient optimization algorithm (d-grape) can in principle correct all deterministic gate errors, with a mild efficiency loss. The d-grape algorithm may become more powerful with broadband controls that involve a large number of control parameters, while other algorithms usually slow down due to the increased size of the search space. These advantages are demonstrated by simulating the implementation of a two-qubit controlled-not gate.

Towards realising high-speed large-bandwidth quantum memory

Institute of Scientific and Technical Information of China (English)

SHI BaoSen; DING DongSheng

2016-01-01

Indispensable for quantum communication and quantum computation,quantum memory executes on demand storage and retrieval of quantum states such as those of a single photon,an entangled pair or squeezed states.Among the various forms of quantum memory,Raman quantum memory has advantages forits broadband and high-speed characteristics,which results in a huge potential for applications in quantum networks and quantum computation.However,realising Raman quantum memory with true single photons and photonic entanglementis challenging.In this review,after briefly introducing the main benchmarks in the development of quantum memory and describing the state of the art,we focus on our recent experimental progress inquantum memorystorage of quantum states using the Raman scheme.

Optimizing the internal quantum efficiency of GaInN SQW structures for green light emitters

International Nuclear Information System (INIS)

Fuhrmann, D.; Rossow, U.; Netzel, C.; Bremers, H.; Hangleiter, A.; Ade, G.; Hinze, P.

2006-01-01

Ga x In 1-x N/GaN single quantum well (QW) structures emitting in the range of 450 nm to 620 nm have been grown by MOVPE. Temperature and excitation power dependent photoluminescence (PL) was used to determine the internal quantum efficiency (IQE) for these structures. For the blue emitting QWs high IQE values on the order of 60% were achieved. Due to a reduced growth temperature, reduced growth rate and increased V/III ratio we obtained QWs with good morphology and high In content above 25%. Thinner QWs with high In content showed a clear improvement of IQE compared to QW-structures with larger thickness but smaller In-content emitting at the same wavelength. Between λ peak =460 nm and 530 nm we observed a slight reduction in IQE with values of 58% at 490 nm and 40% at 525 nm. But towards λ peak =620 nm IQE decreased due to the electric field induced separation of the electron and hole wavefunction down to 1%. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Highly Luminescent Phase-Stable CsPbI3 Perovskite Quantum Dots Achieving Near 100% Absolute Photoluminescence Quantum Yield.

Science.gov (United States)

Liu, Feng; Zhang, Yaohong; Ding, Chao; Kobayashi, Syuusuke; Izuishi, Takuya; Nakazawa, Naoki; Toyoda, Taro; Ohta, Tsuyoshi; Hayase, Shuzi; Minemoto, Takashi; Yoshino, Kenji; Dai, Songyuan; Shen, Qing

2017-10-24

Perovskite quantum dots (QDs) as a new type of colloidal nanocrystals have gained significant attention for both fundamental research and commercial applications owing to their appealing optoelectronic properties and excellent chemical processability. For their wide range of potential applications, synthesizing colloidal QDs with high crystal quality is of crucial importance. However, like most common QD systems such as CdSe and PbS, those reported perovskite QDs still suffer from a certain density of trapping defects, giving rise to detrimental nonradiative recombination centers and thus quenching luminescence. In this paper, we show that a high room-temperature photoluminescence quantum yield of up to 100% can be obtained in CsPbI 3 perovskite QDs, signifying the achievement of almost complete elimination of the trapping defects. This is realized with our improved synthetic protocol that involves introducing organolead compound trioctylphosphine-PbI 2 (TOP-PbI 2 ) as the reactive precursor, which also leads to a significantly improved stability for the resulting CsPbI 3 QD solutions. Ultrafast kinetic analysis with time-resolved transient absorption spectroscopy evidence the negligible electron or hole-trapping pathways in our QDs, which explains such a high quantum efficiency. We expect the successful synthesis of the "ideal" perovskite QDs will exert profound influence on their applications to both QD-based light-harvesting and -emitting devices.

Refined hyperentanglement purification of two-photon systems for high-capacity quantum communication with cavity-assisted interaction

Energy Technology Data Exchange (ETDEWEB)

Du, Fang-Fang; Li, Tao; Long, Gui-Lu, E-mail: gllong@tsinghua.edu.cn

2016-12-15

Hyperentanglement, defined as the entanglement in multiple degrees of freedom (DOFs) of a photonic quantum system, has attracted much attention recently as it can improve the channel capacity of quantum communication largely. Here we present a refined hyperentanglement purification protocol (hyper-EPP) for two-photon systems in mixed hyperentangled states in both the spatial-mode and polarization DOFs, assisted by cavity quantum electrodynamics. By means of the spatial (polarization) quantum state transfer process, the quantum states that are discarded in the previous hyper-EPPs can be preserved. That is, the spatial (polarization) state of a four-photon system with high fidelity can be transformed into another four-photon system with low fidelity, not disturbing its polarization (spatial) state, which makes this hyper-EPP take the advantage of possessing a higher efficiency.

Jefferson Lab IR demo FEL photocathode quantum efficiency scanner

CERN Document Server

Gubeli, J; Grippo, A; Jordan, K; Shinn, M; Siggins, T

2001-01-01

Jefferson Laboratory's Free Electron Laser (FEL) incorporates a cesiated gallium arsenide (GaAs) DC photocathode gun as its electron source. By using a set of scanning mirrors, the surface of the GaAs wafer is illuminated with a 543.5nm helium-neon laser. Measuring the current flow across the biased photocathode generates a quantum efficiency (QE) map of the 1-in. diameter wafer surface. The resulting QE map provides a very detailed picture of the efficiency of the wafer surface. By generating a QE map in a matter of minutes, the photocathode scanner has proven to be an exceptional tool in quickly determining sensitivity and availability of the photocathode for operation.

Synthesis of Won-WX2 (n=2.7, 2.9; X=S, Se) Heterostructures for Highly Efficient Green Quantum Dot Light-Emitting Diodes

KAUST Repository

Han, Shikui

2017-07-04

Preparation of two-dimensional (2D) heterostructures is important not only fundamentally, but also technologically for applications in electronics and optoelectronics. Herein, we report a facile colloidal method for the synthesis of WOn -WX2 (n=2.7, 2.9; X=S, Se) heterostructures by sulfurization or selenization of WOn nanomaterials. The WOn -WX2 heterostructures are composed of WO2.9 nanoparticles (NPs) or WO2.7 nanowires (NWs) grown together with single- or few-layer WX2 nanosheets (NSs). As a proof-of-concept application, the WOn -WX2 heterostructures are used as the anode interfacial buffer layer for green quantum dot light-emitting diodes (QLEDs). The QLED prepared with WO2.9 NP-WSe2 NS heterostructures achieves external quantum efficiency (EQE) of 8.53 %. To our knowledge, this is the highest efficiency in the reported green QLEDs using inorganic materials as the hole injection layer.

High quantum yield graphene quantum dots decorated TiO_2 nanotubes for enhancing photocatalytic activity

International Nuclear Information System (INIS)

Qu, Ailan; Xie, Haolong; Xu, Xinmei; Zhang, Yangyu; Wen, Shengwu; Cui, Yifan

2016-01-01

Highlights: • High concentration yellow GQDs and TiO_2 nanotubes were achieved by a simple and green method. • High quantum yield GQDs enhanced the photodegradation capacity of TiO_2 nanotube. • The catalytic performance of GQDs/TiO_2 depends on the GQDs loading. • The improved photocatalytic activity of GQDs/TiO_2 was attributed to three aspects. - Abstract: Graphene quantum dots (GQDs) with high quantum yield (about 23.6% at an excitation wavelength of 320 nm) and GQDs/TiO_2 nanotubes (GQDs/TiO_2 NTs) composites were achieved by a simple hydrothermal method at low temperature. Photoluminescence characterization showed that the GQDs exhibited the down-conversion PL features at excitation from 300 to 420 nm and up-conversion photoluminescence in the range of 600–800 nm. The photocatalytic activity of prepared GQDs/TiO_2 NTs composites on the degradation of methyl orange (MO) was significantly enhanced compared with that of pure TiO_2 nanotubes (TiO_2 NTs). For the composites coupling with 1.5%, 2.5% and 3.5% GQDs, the degradation of MO after 20 min irradiation under UV–vis light irradiation (λ = 380–780 nm) were 80.52%, 94.64% and 51.91%, respectively, which are much higher than that of pure TiO_2 NTs (35.41%). It was inferred from the results of characterization that the improved photocatalytic activity of the GQDs/TiO_2 NTs composites was attributed to the synergetic effect of up-conversion properties of the GQDs, enhanced visible light absorption and efficient separation of photogenerated electron-holes of the GQDs/TiO_2 composite.

Practical expressions describing detective quantum efficiency in flat-panel detectors

Science.gov (United States)

Kim, H. K.

2011-11-01

In radiology, image quality excellence is a balance between system performance and patient dose, hence x-ray systems must be designed to ensure the maximum image quality is obtained for the lowest consistent dose. The concept of detective quantum efficiency (DQE) is widely used to quantify, understand, measure, and predict the performance of x-ray detectors and imaging systems. Cascaded linear-systems theory can be used to estimate DQE based on the system design parameters and this theoretical DQE can be utilized for determining the impact of various physical processes, such as secondary quantum sinks, noise aliasing, reabsorption noise, and others. However, the prediction of DQE usually requires tremendous efforts to determine each parameter consisting of the cascaded linear-systems model. In this paper, practical DQE formalisms assessing both the photoconductor- and scintillator-based flat-panel detectors under quantum-noise-limited operation are described. The developed formalisms are experimentally validated and discussed for their limits. The formalisms described in this paper would be helpful for the rapid prediction of the DQE performances of developing systems as well as the optimal design of systems.

Highly efficient deep-blue organic light emitting diode with a carbazole based fluorescent emitter

Science.gov (United States)

Sahoo, Snehasis; Dubey, Deepak Kumar; Singh, Meenu; Joseph, Vellaichamy; Thomas, K. R. Justin; Jou, Jwo-Huei

2018-04-01

High efficiency deep-blue emission is essential to realize energy-saving, high-quality display and lighting applications. We demonstrate here a deep-blue organic light emitting diode using a novel carbazole based fluorescent emitter 7-[4-(diphenylamino)phenyl]-9-(2-ethylhexyl)-9H-carbazole-2-carbonitrile (JV234). The solution processed resultant device shows a maximum luminance above 1,750 cd m-2 and CIE coordinates (0.15,0.06) with a 1.3 lm W-1 power efficiency, 2.0 cd A-1 current efficiency, and 4.1% external quantum efficiency at 100 cd m-2. The resulting deep-blue emission enables a greater than 100% color saturation. The high efficiency may be attributed to the effective host-to-guest energy transfer, suitable device architecture facilitating balanced carrier injection and low doping concentration preventing efficiency roll-off caused by concentration quenching.

Li4SrCa(SiO4)2:Ce3+, a highly efficient near-UV and blue emitting orthosilicate phosphor

International Nuclear Information System (INIS)

Zhang, Jilin; Zhang, Weilu; Qiu, Zhongxian; Zhou, Wenli; Yu, Liping; Li, Zhiqiang; Lian, Shixun

2015-01-01

High quantum efficiency is a vital parameter of phosphors for practical application. An efficient near-UV and blue emitting phosphor Li 4 SrCa(SiO 4 ) 2 :Ce 3+ was synthesized by a traditional solid-state reaction, and luminescent properties were studied in detail. The Ce 3+ -activated phosphor can emit both a near-UV light centred at 345 nm and a blue light peaking at 420 nm when Ce 3+ occupies the Sr and Ca site, respectively. The internal quantum efficiency (IQE) of Li 4 SrCa(SiO 4 ) 2 :0.03Ce 3+ is as high as 97% under the excitation at 288 nm, while the external quantum efficiency (EQE) is 66%. The IQE and EQE values of Li 4 SrCa(SiO 4 ) 2 :0.03Ce 3+ under the excitation at 360 nm are 82% and 31%, respectively. - Highlights: • Phosphor Li 4 SrCa(SiO 4 ) 2 :Ce 3+ emits a near-UV (345 nm) and a blue light (420 nm). • Emission band at 345 nm originates from Ce 3+ on Sr site. • Emission band at 420 nm belongs to Ce 3+ on Ca site. • Internal quantum efficiency is 97% for Li 4 SrCa(SiO 4 ) 2 :0.03Ce 3+ excited at 288 nm

Effect of AlSb quantum dots on efficiency of GaAs solar cell (Conference Presentation)

Science.gov (United States)

Mansoori, Ahmad; Addamane, Sadhvikas J.; Renteria, Emma J.; Shima, Darryl M.; Hains, Christopher P.; Balakrishnan, Ganesh

2016-09-01

Quantum Dots (QDs) have a broad applications in science and specifically in solar cell. Many research groups show that by adding QDs with lower bandgap respect to host material, the overall absorption of sun spectrum coverage will increase. Here, we propose using QDs with higher band gap respect to host material to improve efficiency of solar cell by improving quantum efficiency. GaAs solar cells have the highest efficiency in single junction solar cells. However, the absorption of GaAs is not good enough in wavelength lower than 550nm. AlSb can absorb shorter wavelength with higher absorption coefficient and also recombination rate should be lower because of higher bandgap of AlSb respect to GaAs. We embed AlSb QDs in GaAs solar cells and results show slight improvement in quantum efficiency and also in overall efficiency. Coverage of AlSb QDs has a direct impact on quality of AlSb QDs and efficiency of cell. In the higher coverage, intermixing between GaAs and AlSb causes to shift bandgap to lower value (having AlGaSb QDs instead of pure AlSb QDs). This intermixing decrease the Voc and overall efficiency of cell. In lower coverage, AlSb can survive from intermixing and overall performance of cell improves. Optimizing growth condition of AlSb QDs is a key point for this work. By using AlSb QDs, we can decrease the thickness of active layer of GaAs solar cells and have a thinner solar cell.

Quantum dot solar cells

CERN Document Server

Wu, Jiang

2013-01-01

The third generation of solar cells includes those based on semiconductor quantum dots. This sophisticated technology applies nanotechnology and quantum mechanics theory to enhance the performance of ordinary solar cells. Although a practical application of quantum dot solar cells has yet to be achieved, a large number of theoretical calculations and experimental studies have confirmed the potential for meeting the requirement for ultra-high conversion efficiency. In this book, high-profile scientists have contributed tutorial chapters that outline the methods used in and the results of variou

Robust nonfullerene solar cells approaching unity external quantum efficiency enabled by suppression of geminate recombination.

Science.gov (United States)

Baran, Derya; Gasparini, Nicola; Wadsworth, Andrew; Tan, Ching Hong; Wehbe, Nimer; Song, Xin; Hamid, Zeinab; Zhang, Weimin; Neophytou, Marios; Kirchartz, Thomas; Brabec, Christoph J; Durrant, James R; McCulloch, Iain

2018-05-25

Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm -2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells.

Robust nonfullerene solar cells approaching unity external quantum efficiency enabled by suppression of geminate recombination

KAUST Repository

Baran, Derya

2018-05-21

Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm-2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells.

Robust nonfullerene solar cells approaching unity external quantum efficiency enabled by suppression of geminate recombination

KAUST Repository

Baran, Derya; Gasparini, Nicola; Wadsworth, Andrew; Tan, Ching Hong; Wehbe, Nimer; Song, Xin; Hamid, Zeinab; Zhang, Weimin; Neophytou, Marios; Kirchartz, Thomas; Brabec, Christoph J.; Durrant, James R.; McCulloch, Iain

2018-01-01

Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm-2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells.

Low-Cost, High Efficiency, Silicon Based Photovoltaic Devices

Science.gov (United States)

2015-08-27

for photovoltaic applications. Figure 14: (a) Absorption and scattering efficiencies versus sizes of Au nanoparticle at 550 nm, (b) scattering...efficiency as a function of wavelength for different Au nanoparticles sizes . 32 Review of plasmonics light trapping for photovoltaic application...ensure that the irradiation variation was within 3%. The external quantum efficiency (EQE) system used a 300W Xenon light source with a spot size of 1mm

Efficient charge carrier injection into sub-250 nm AlGaN multiple quantum well light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Mehnke, Frank, E-mail: mehnke@physik.tu-berlin.de; Kuhn, Christian; Guttmann, Martin; Reich, Christoph; Kolbe, Tim; Rass, Jens; Wernicke, Tim [Technische Universität Berlin, Institut für Festkörperphysik, Hardenbergstr. 36, EW 6-1, 10623 Berlin (Germany); Kueller, Viola; Knauer, Arne; Lapeyrade, Mickael; Einfeldt, Sven; Weyers, Markus [Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany); Kneissl, Michael [Technische Universität Berlin, Institut für Festkörperphysik, Hardenbergstr. 36, EW 6-1, 10623 Berlin (Germany); Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany)

2014-08-04

The design and Mg-doping profile of AlN/Al{sub 0.7}Ga{sub 0.3}N electron blocking heterostructures (EBH) for AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) emitting below 250 nm was investigated. By inserting an AlN electron blocking layer (EBL) into the EBH, we were able to increase the quantum well emission power and significantly reduce long wavelength parasitic luminescence. Furthermore, electron leakage was suppressed by optimizing the thickness of the AlN EBL while still maintaining sufficient hole injection. Ultraviolet (UV)-C LEDs with very low parasitic luminescence (7% of total emission power) and external quantum efficiencies of 0.19% at 246 nm have been realized. This concept was applied to AlGaN MQW LEDs emitting between 235 nm and 263 nm with external quantum efficiencies ranging from 0.002% to 0.93%. After processing, we were able to demonstrate an UV-C LED emitting at 234 nm with 14.5 μW integrated optical output power and an external quantum efficiency of 0.012% at 18.2 A/cm{sup 2}.

Efficient charge carrier injection into sub-250 nm AlGaN multiple quantum well light emitting diodes

International Nuclear Information System (INIS)

Mehnke, Frank; Kuhn, Christian; Guttmann, Martin; Reich, Christoph; Kolbe, Tim; Rass, Jens; Wernicke, Tim; Kueller, Viola; Knauer, Arne; Lapeyrade, Mickael; Einfeldt, Sven; Weyers, Markus; Kneissl, Michael

2014-01-01

The design and Mg-doping profile of AlN/Al 0.7 Ga 0.3 N electron blocking heterostructures (EBH) for AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) emitting below 250 nm was investigated. By inserting an AlN electron blocking layer (EBL) into the EBH, we were able to increase the quantum well emission power and significantly reduce long wavelength parasitic luminescence. Furthermore, electron leakage was suppressed by optimizing the thickness of the AlN EBL while still maintaining sufficient hole injection. Ultraviolet (UV)-C LEDs with very low parasitic luminescence (7% of total emission power) and external quantum efficiencies of 0.19% at 246 nm have been realized. This concept was applied to AlGaN MQW LEDs emitting between 235 nm and 263 nm with external quantum efficiencies ranging from 0.002% to 0.93%. After processing, we were able to demonstrate an UV-C LED emitting at 234 nm with 14.5 μW integrated optical output power and an external quantum efficiency of 0.012% at 18.2 A/cm 2

High-efficiency frequency doubling of continuous-wave laser light.

Science.gov (United States)

Ast, Stefan; Nia, Ramon Moghadas; Schönbeck, Axel; Lastzka, Nico; Steinlechner, Jessica; Eberle, Tobias; Mehmet, Moritz; Steinlechner, Sebastian; Schnabel, Roman

2011-09-01

We report on the observation of high-efficiency frequency doubling of 1550 nm continuous-wave laser light in a nonlinear cavity containing a periodically poled potassium titanyl phosphate crystal (PPKTP). The fundamental field had a power of 1.10 W and was converted into 1.05 W at 775 nm, yielding a total external conversion efficiency of 95±1%. The latter value is based on the measured depletion of the fundamental field being consistent with the absolute values derived from numerical simulations. According to our model, the conversion efficiency achieved was limited by the nonperfect mode matching into the nonlinear cavity and by the nonperfect impedance matching for the maximum input power available. Our result shows that cavity-assisted frequency conversion based on PPKTP is well suited for low-decoherence frequency conversion of quantum states of light.

Thermal effect of multi-quantum barriers within InGaN/GaN multi-quantum well light-emitting diodes

International Nuclear Information System (INIS)

Lee, Jiunn-Chyi; Wu, Ya-Fen

2010-01-01

We introduce the InGaN/GaN multi-quantum barriers (MQBs) into InGaN/GaN multi-quantum well (MQW) heterostructures to improve the performance of light-emitting diodes. The temperature and injection current dependent electroluminescence were carried out to study the thermal effect of InGaN/GaN MQWs. We observe the enhancement of carrier confinement in the active layer and the inhibited carrier leakage over the barrier for the sample with MQBs. In addition, the external quantum efficiency of the samples is obtained. It is found that the radiative efficiency of the sample possessing MQBs exhibits less sensitive temperature dependence and leads to an improved efficiency in the high temperature and high injection current range.

Highly photoluminescent and photostable CdSe quantum dot-nylon hybrid composites for efficient light conversion applications

Energy Technology Data Exchange (ETDEWEB)

Yuan Ying; Riehle, Frank-Stefan [Freiburg Materials Research Centre (FMF), University of Freiburg, Stefan-Meier-Str. 21, D-79104 Freiburg (Germany); Department of Microsystems Engineering (IMTEK), Georg Koehler Allee 103, University of Freiburg, D-79110 Freiburg (Germany); Nitschke, Roland [Life Imaging Center, Centre of Systems Biology, University of Freiburg Habsburgerstr. 49, D-79104 Freiburg (Germany); Centre for Biological Signalling Studies (BIOSS), University of Freiburg (Germany); Krueger, Michael, E-mail: michael.krueger@fmf.uni-freiburg.de [Freiburg Materials Research Centre (FMF), University of Freiburg, Stefan-Meier-Str. 21, D-79104 Freiburg (Germany); Department of Microsystems Engineering (IMTEK), Georg Koehler Allee 103, University of Freiburg, D-79110 Freiburg (Germany)

2012-02-15

Highlights: Black-Right-Pointing-Pointer A novel in situ synthesis approach for highly luminescent CdSe core QDs-nylon hybrid materials. Black-Right-Pointing-Pointer Potential applications for light and energy conversion are demonstrated. Black-Right-Pointing-Pointer Three dimensional structures out of this hybrid material are available. - Abstract: Highly photoluminescent hexadecylamine (HDA) capped core CdSe quantum dots (QDs) with fluorescent quantum yields (QYs) up to 60% were synthesized using a hot injection method and directly incorporated into nylon polymer. For the incorporation of crude CdSe QDs into nylon a simple reproducible and upscalable one pot approach was developed without the need of further purification steps. The photoluminescence (PL) properties of the core QDs and the resulting QD-polymer hybrid composites were investigated and compared. Red emitting hybrid materials exhibit a QY of 60% with a high potential for applications in direct light and energy conversion. The hybrid materials could be successfully utilized as LED conversion layers. By avoiding exposure to oxygen the hybrid films can be kept for a month without detecting a significant decrease in luminescence. Various three dimensional structures are easily available opening doors for further applications such as novel materials for fluorescence standard development in laser scanning microscopy (LSM).

Hardware-efficient bosonic quantum error-correcting codes based on symmetry operators

Science.gov (United States)

Niu, Murphy Yuezhen; Chuang, Isaac L.; Shapiro, Jeffrey H.

2018-03-01

We establish a symmetry-operator framework for designing quantum error-correcting (QEC) codes based on fundamental properties of the underlying system dynamics. Based on this framework, we propose three hardware-efficient bosonic QEC codes that are suitable for χ(2 )-interaction based quantum computation in multimode Fock bases: the χ(2 ) parity-check code, the χ(2 ) embedded error-correcting code, and the χ(2 ) binomial code. All of these QEC codes detect photon-loss or photon-gain errors by means of photon-number parity measurements, and then correct them via χ(2 ) Hamiltonian evolutions and linear-optics transformations. Our symmetry-operator framework provides a systematic procedure for finding QEC codes that are not stabilizer codes, and it enables convenient extension of a given encoding to higher-dimensional qudit bases. The χ(2 ) binomial code is of special interest because, with m ≤N identified from channel monitoring, it can correct m -photon-loss errors, or m -photon-gain errors, or (m -1 )th -order dephasing errors using logical qudits that are encoded in O (N ) photons. In comparison, other bosonic QEC codes require O (N2) photons to correct the same degree of bosonic errors. Such improved photon efficiency underscores the additional error-correction power that can be provided by channel monitoring. We develop quantum Hamming bounds for photon-loss errors in the code subspaces associated with the χ(2 ) parity-check code and the χ(2 ) embedded error-correcting code, and we prove that these codes saturate their respective bounds. Our χ(2 ) QEC codes exhibit hardware efficiency in that they address the principal error mechanisms and exploit the available physical interactions of the underlying hardware, thus reducing the physical resources required for implementing their encoding, decoding, and error-correction operations, and their universal encoded-basis gate sets.

Software Systems for High-performance Quantum Computing

Energy Technology Data Exchange (ETDEWEB)

Humble, Travis S [ORNL; Britt, Keith A [ORNL

2016-01-01

Quantum computing promises new opportunities for solving hard computational problems, but harnessing this novelty requires breakthrough concepts in the design, operation, and application of computing systems. We define some of the challenges facing the development of quantum computing systems as well as software-based approaches that can be used to overcome these challenges. Following a brief overview of the state of the art, we present models for the quantum programming and execution models, the development of architectures for hybrid high-performance computing systems, and the realization of software stacks for quantum networking. This leads to a discussion of the role that conventional computing plays in the quantum paradigm and how some of the current challenges for exascale computing overlap with those facing quantum computing.

Cavity quantum electrodynamics studies with site-controlled InGaAs quantum dots integrated into high quality microcavities

DEFF Research Database (Denmark)

Reitzenstein, S.; Schneider, C.; Albert, F.

2011-01-01

Semiconductor quantum dots (QDs) are fascinating nanoscopic structures for photonics and future quantum information technology. However, the random position of self-organized QDs inhibits a deterministic coupling in devices relying on cavity quantum electrodynamics (cQED) effects which complicates......, e.g., the large scale fabrication of quantum light sources. As a result, large efforts focus on the growth and the device integration of site-controlled QDs. We present the growth of low density arrays of site-controlled In(Ga)As QDs where shallow etched nanoholes act as nucleation sites...... linewidth, the oscillator strength and the quantum efficiency. A stacked growth of strain coupled SCQDs forming on wet chemically etched nanoholes provide the smallest linewidth with an average value of 210 μeV. Using time resolved photoluminescence studies on samples with a varying thickness of the capping...

Colored ultra-thin hybrid photovoltaics with high quantum efficiency for decorative PV applications (Presentation Recording)

Science.gov (United States)

Guo, L. Jay

2015-10-01

adopted by other material systems as well. Based on these understandings, we have also developed colored perovskite PV by integrating an optical cavity with the perovskite semiconductors [4]. The principle and experimental results will be presented. 1. J. Y. Lee, K. T. Lee, S.Y. Seo, L. J. Guo, "Decorative power generating panels creating angle insensitive transmissive colors," Sci. Rep. 4, 4192, 2014. 2. K. T. Lee, J.Y. Lee, S.-Y. Seo, and L. J. Guo, "Colored ultra-thin hybrid photovoltaics with high quantum efficiency," Light: Science and Applications, 3, e215, 2014. 3. K. T. Lee, S.-Y. Seo, J.Y. Lee, and L. J. Guo, "Ultrathin metal-semiconductor-metal resonator for angle invariant visible band transmission filters," Appl. Phys. Lett. 104, 231112, (2014); and "Strong resonance effect in a lossy medium-based optical cavity for angle robust spectrum filters," Adv. Mater, 26, 6324-6328, 2014. 4. K. T. Lee, M. Fukuda, L. J. Guo, "Colored, see-through perovskite solar cells employing an optical cavity," Submitted, 2015

In silico evaluation of highly efficient organic light-emitting materials

Science.gov (United States)

Kwak, H. Shaun; Giesen, David J.; Hughes, Thomas F.; Goldberg, Alexander; Cao, Yixiang; Gavartin, Jacob; Dixon, Steve; Halls, Mathew D.

2016-09-01

Design and development of highly efficient organic and organometallic dopants is one of the central challenges in the organic light-emitting diodes (OLEDs) technology. Recent advances in the computational materials science have made it possible to apply computer-aided evaluation and screening framework directly to the design space of organic lightemitting diodes (OLEDs). In this work, we will showcase two major components of the latest in silico framework for development of organometallic phosphorescent dopants - (1) rapid screening of dopants by machine-learned quantum mechanical models and (2) phosphorescence lifetime predictions with spin-orbit coupled calculations (SOC-TDDFT). The combined work of virtual screening and evaluation would significantly widen the design space for highly efficient phosphorescent dopants with unbiased measures to evaluate performance of the materials from first principles.

Quantum-path control in high-order harmonic generation at high photon energies

International Nuclear Information System (INIS)

Zhang Xiaoshi; Lytle, Amy L; Cohen, Oren; Murnane, Margaret M; Kapteyn, Henry C

2008-01-01

We show through experiment and calculations how all-optical quasi-phase-matching of high-order harmonic generation can be used to selectively enhance emission from distinct quantum trajectories at high photon energies. Electrons rescattered in a strong field can traverse short and long quantum trajectories that exhibit differing coherence lengths as a result of variations in intensity of the driving laser along the direction of propagation. By varying the separation of the pulses in a counterpropagating pulse train, we selectively enhance either the long or the short quantum trajectory, and observe distinct spectral signatures in each case. This demonstrates a new type of coupling between the coherence of high-order harmonic beams and the attosecond time-scale quantum dynamics inherent in the process

Internal quantum efficiency and tunable colour temperature in monolithic white InGaN/GaN LED

Science.gov (United States)

Titkov, Ilya E.; Yadav, Amit; Zerova, Vera L.; Zulonas, Modestas; Tsatsulnikov, Andrey F.; Lundin, Wsevolod V.; Sakharov, Alexey V.; Rafailov, Edik U.

2014-03-01

Internal Quantum Efficiency (IQE) of two-colour monolithic white light emitting diode (LED) was measured by temperature dependant electro-luminescence (TDEL) and analysed with modified rate equation based on ABC model. External, internal and injection efficiencies of blue and green quantum wells were analysed separately. Monolithic white LED contained one green InGaN QW and two blue QWs being separated by GaN barrier. This paper reports also the tunable behaviour of correlated colour temperature (CCT) in pulsed operation mode and effect of self-heating on device performance.

Photonic engineering of highly linearly polarized quantum dot emission at telecommunication wavelengths

Science.gov (United States)

Mrowiński, P.; Emmerling, M.; Schneider, C.; Reithmaier, J. P.; Misiewicz, J.; Höfling, S.; Sek, G.

2018-04-01

In this work, we discuss a method to control the polarization anisotropy of spontaneous emission from neutral excitons confined in quantum-dot-like nanostructures, namely single epitaxial InAs quantum dashes emitting at telecom wavelengths. The nanostructures are embedded inside lithographically defined, in-plane asymmetric photonic mesa structures, which generate polarization-dependent photonic confinement. First, we study the influence of the photonic confinement on the polarization anisotropy of the emission by photoluminescence spectroscopy, and we find evidence of different contributions to a degree of linear polarization (DOLP), i.e., from the quantum dash and the photonic mesa, in total giving rise to DOLP =0.85 . Then, we perform finite-difference time-domain simulations of photonic confinement, and we calculate the DOLP in a dipole approximation showing well-matched results for the established model. Furthermore, by using numerical calculations, we demonstrate several types of photonic confinements where highly linearly polarized emission with DOLP of about 0.9 is possible by controlling the position of a quantum emitter inside the photonic structure. Then, we elaborate on anisotropic quantum emitters allowing for exceeding DOLP =0.95 in an optimized case, and we discuss the ways towards efficient linearly polarized single photon source at telecom bands.

Achieving the classical Carnot efficiency in a strongly coupled quantum heat engine

Science.gov (United States)

Xu, Y. Y.; Chen, B.; Liu, J.

2018-02-01

Generally, the efficiency of a heat engine strongly coupled with a heat bath is less than the classical Carnot efficiency. Through a model-independent method, we show that the classical Carnot efficiency is achieved in a strongly coupled quantum heat engine. First, we present the first law of quantum thermodynamics in strong coupling. Then, we show how to achieve the Carnot cycle and the classical Carnot efficiency at strong coupling. We find that this classical Carnot efficiency stems from the fact that the heat released in a nonequilibrium process is balanced by the absorbed heat. We also analyze the restrictions in the achievement of the Carnot cycle. The first restriction is that there must be two corresponding intervals of the controllable parameter in which the corresponding entropies of the work substance at the hot and cold temperatures are equal, and the second is that the entropy of the initial and final states in a nonequilibrium process must be equal. Through these restrictions, we obtain the positive work conditions, including the usual one in which the hot temperature should be higher than the cold, and a new one in which there must be an entropy interval at the hot temperature overlapping that at the cold. We demonstrate our result through a paradigmatic model—a two-level system in which a work substance strongly interacts with a heat bath. In this model, we find that the efficiency may abruptly decrease to zero due to the first restriction, and that the second restriction results in the control scheme becoming complex.

PHOTO-ELECTROCHEMICAL QUANTUM EFFICIENCY OF TiO2 THIN FILMS : EFFECT OF CRISTAL STRUCTURE, PLASMA HYDROGENATION AND SURFACE PHOTOETCHING

Directory of Open Access Journals (Sweden)

E TEYAR

2007-12-01

Full Text Available The use of semi-conducting materials in the photoelectrochemical detoxification of water became a very important research field. For this purpose, TiO2 nanostructures thin films with size of 18 nm to 45nm have been synthesized at low temperature. It is found by means of cyclic voltametry and coulometry measurements that the best photoelectrochemical quantum efficiency under UV monochromatic light with a wavelength of 365 nm and a solution of NaOH 0.1N is obtained in the case of thermal oxidation deposition method which can reach 28% compared to ultrasonic spray and dip coating methods of which the quantum is less than 20%. The crystal structure has an influence on the photo-degradation of methanol. The crystal structure which is recommended for this task is the anatase one, especially in the dipping case when the quantum increases after addition of methanol more than twice compared to the solution of NaOH without methanol. The photoelectrochemical quantum efficiency of these films is related to the number of dips and annealing under air at 550°C during one hour. The annealing has no effect on the quantum efficiency of the films, but decreases there photocatalytic activity as showed by the measure of the photocurrent related to methanol photodegradation. The annealing has no effect on the crystal structure of the material. The impedance spectroscopy of six dips deposited films with and without methanol shows that the annealing increases the doping and weakly decreases the film quantum efficiency. This implies, the importance of surface morphology which the rough is decreasing as showed by scanning electron microscopy. The effect of the precursor concentration in ethanol have been investigated by using films, synthesized at T=550°C. The quantum efficiency increases weakly according the precursor concentration. It tends towards a saturation at great concentrations of precursor. In Na OH with methanol added, it passes by a maximum at

Highly efficient bilayer interface exciplex for yellow organic light-emitting diode.

Science.gov (United States)

Hung, Wen-Yi; Fang, Guan-Cheng; Chang, Yuh-Chia; Kuo, Ting-Yi; Chou, Pi-Tai; Lin, Shih-Wei; Wong, Ken-Tsung

2013-08-14

A simple three-layer interfacial-type yellow emission exciplex device with an external quantum efficiency as high as 7.7% has been successfully achieved by combining conformation compatible C3-symmetric hole-transporting TCTA and electron-transporting 3P-T2T. The excellent and balanced charge-transporting properties of TCTA and 3P-T2T and the large energy-levels offset (0.8 eV) of TCTA/3P-T2T interface play important roles for the efficient exciplexes formation, which are effectively confined around the interfacial region due to the high triplet energies (2.85 eV) of TCTA and 3P-T2T. The high-performance OLED was believed to be from the effective harvest of exciplex triplet excitons via reverse intersystem crossing process.

Accurate reconstruction of the jV-characteristic of organic solar cells from measurements of the external quantum efficiency

Science.gov (United States)

Meyer, Toni; Körner, Christian; Vandewal, Koen; Leo, Karl

2018-04-01

In two terminal tandem solar cells, the current density - voltage (jV) characteristic of the individual subcells is typically not directly measurable, but often required for a rigorous device characterization. In this work, we reconstruct the jV-characteristic of organic solar cells from measurements of the external quantum efficiency under applied bias voltages and illumination. We show that it is necessary to perform a bias irradiance variation at each voltage and subsequently conduct a mathematical correction of the differential to the absolute external quantum efficiency to obtain an accurate jV-characteristic. Furthermore, we show that measuring the external quantum efficiency as a function of voltage for a single bias irradiance of 0.36 AM1.5g equivalent sun provides a good approximation of the photocurrent density over voltage curve. The method is tested on a selection of efficient, common single-junctions. The obtained conclusions can easily be transferred to multi-junction devices with serially connected subcells.

Broadband Epsilon-near-Zero Reflectors Enhance the Quantum Efficiency of Thin Solar Cells at Visible and Infrared Wavelengths

KAUST Repository

Labelle, A. J.; Bonifazi, Marcella; Tian, Y.; Wong, C.; Hoogland, S.; Favraud, Gael; Walters, G.; Sutherland, B.; Liu, M.; Li, Jun; Zhang, Xixiang; Kelley, Shana O.; Sargent, E. H.; Fratalocchi, Andrea

2017-01-01

The engineering of broadband absorbers to harvest white light in thin-film semiconductors is a major challenge in developing renewable materials for energy harvesting. Many solution-processed materials with high manufacturability and low cost, such as semiconductor quantum dots, require the use of film structures with thicknesses on the order of 1 μm to absorb incoming photons completely. The electron transport lengths in these media, however, are 1 order of magnitude smaller than this length, hampering further progress with this platform. Herein, we show that, by engineering suitably disordered nanoplasmonic structures, we have created a new class of dispersionless epsilon-near-zero composite materials that efficiently harness white light. Our nanostructures localize light in the dielectric region outside the epsilon-near-zero material with characteristic lengths of 10-100 nm, resulting in an efficient system for harvesting broadband light when a thin absorptive film is deposited on top of the structure. By using a combination of theory and experiments, we demonstrate that ultrathin layers down to 50 nm of colloidal quantum dots deposited atop the epsilon-near-zero material show an increase in broadband absorption ranging from 200% to 500% compared to a planar structure of the same colloidal quantum-dot-absorber average thickness. When the epsilon-near-zero nanostructures were used in an energy-harvesting module, we observed a spectrally averaged 170% broadband increase in the external quantum efficiency of the device, measured at wavelengths between 400 and 1200 nm. Atomic force microscopy and photoluminescence excitation measurements demonstrate that the properties of these epsilon-near-zero structures apply to general metals and could be used to enhance the near-field absorption of semiconductor structures more widely. We have developed an inexpensive electrochemical deposition process that enables scaled-up production of this nanomaterial for large

Broadband Epsilon-near-Zero Reflectors Enhance the Quantum Efficiency of Thin Solar Cells at Visible and Infrared Wavelengths

KAUST Repository

Labelle, A. J.

2017-02-03

The engineering of broadband absorbers to harvest white light in thin-film semiconductors is a major challenge in developing renewable materials for energy harvesting. Many solution-processed materials with high manufacturability and low cost, such as semiconductor quantum dots, require the use of film structures with thicknesses on the order of 1 μm to absorb incoming photons completely. The electron transport lengths in these media, however, are 1 order of magnitude smaller than this length, hampering further progress with this platform. Herein, we show that, by engineering suitably disordered nanoplasmonic structures, we have created a new class of dispersionless epsilon-near-zero composite materials that efficiently harness white light. Our nanostructures localize light in the dielectric region outside the epsilon-near-zero material with characteristic lengths of 10-100 nm, resulting in an efficient system for harvesting broadband light when a thin absorptive film is deposited on top of the structure. By using a combination of theory and experiments, we demonstrate that ultrathin layers down to 50 nm of colloidal quantum dots deposited atop the epsilon-near-zero material show an increase in broadband absorption ranging from 200% to 500% compared to a planar structure of the same colloidal quantum-dot-absorber average thickness. When the epsilon-near-zero nanostructures were used in an energy-harvesting module, we observed a spectrally averaged 170% broadband increase in the external quantum efficiency of the device, measured at wavelengths between 400 and 1200 nm. Atomic force microscopy and photoluminescence excitation measurements demonstrate that the properties of these epsilon-near-zero structures apply to general metals and could be used to enhance the near-field absorption of semiconductor structures more widely. We have developed an inexpensive electrochemical deposition process that enables scaled-up production of this nanomaterial for large

Dispersion compensated mid-infrared quantum cascade laser frequency comb with high power output

Directory of Open Access Journals (Sweden)

Q. Y. Lu

2017-04-01

Full Text Available Chromatic dispersion control plays an underlying role in optoelectronics and spectroscopy owing to its enhancement to nonlinear interactions by reducing the phase mismatching. This is particularly important to optical frequency combs based on quantum cascade lasers which require negligible dispersions for efficient mode locking of the dispersed modes into equally spaced comb modes. Here, we demonstrated a dispersion compensated mid-IR quantum cascade laser frequency comb with high power output at room temperature. A low-loss dispersive mirror has been engineered to compensate the device’s dispersion residue for frequency comb generation. Narrow intermode beating linewidths of 40 Hz in the comb-working currents were identified with a high power output of 460 mW and a broad spectral coverage of 80 cm-1. This dispersion compensation technique will enable fast spectroscopy and high-resolution metrology based on QCL combs with controlled dispersion and suppressed noise.

Deterministic and efficient quantum cryptography based on Bell's theorem

International Nuclear Information System (INIS)

Chen, Z.-B.; Zhang, Q.; Bao, X.-H.; Schmiedmayer, J.; Pan, J.-W.

2005-01-01

Full text: We propose a novel double-entanglement-based quantum cryptography protocol that is both efficient and deterministic. The proposal uses photon pairs with entanglement both in polarization and in time degrees of freedom; each measurement in which both of the two communicating parties register a photon can establish a key bit with the help of classical communications. Eavesdropping can be detected by checking the violation of local realism for the detected events. We also show that our protocol allows a robust implementation under current technology. (author)

Quantum Accelerators for High-Performance Computing Systems

OpenAIRE

Britt, Keith A.; Mohiyaddin, Fahd A.; Humble, Travis S.

2017-01-01

We define some of the programming and system-level challenges facing the application of quantum processing to high-performance computing. Alongside barriers to physical integration, prominent differences in the execution of quantum and conventional programs challenges the intersection of these computational models. Following a brief overview of the state of the art, we discuss recent advances in programming and execution models for hybrid quantum-classical computing. We discuss a novel quantu...

Laser diode arrays based on AlGaAs/GaAs quantum-well heterostructures with an efficiency up to 62%

Science.gov (United States)

Ladugin, M. A.; Marmalyuk, A. A.; Padalitsa, A. A.; Telegin, K. Yu; Lobintsov, A. V.; Sapozhnikov, S. M.; Danilov, A. I.; Podkopaev, A. V.; Simakov, V. A.

2017-08-01

The results of development of quasi-cw laser diode arrays operating at a wavelength of 808 nm with a high efficiency are demonstrated. The laser diodes are based on semiconductor AlGaAs/GaAs quantum-well heterostructures grown by MOCVD. The measured spectral, spatial, electric and power characteristics are presented. The output optical power of the array with an emitting area of 5 × 10 mm is 2.7 kW at a pump current of 100 A, and the maximum efficiency reaches 62%.

A quantum computer only needs one universe

OpenAIRE

Steane, A. M.

2000-01-01

The nature of quantum computation is discussed. It is argued that, in terms of the amount of information manipulated in a given time, quantum and classical computation are equally efficient. Quantum superposition does not permit quantum computers to ``perform many computations simultaneously'' except in a highly qualified and to some extent misleading sense. Quantum computation is therefore not well described by interpretations of quantum mechanics which invoke the concept of vast numbers of ...

Combination of short-length TiO_2 nanorod arrays and compact PbS quantum-dot thin films for efficient solid-state quantum-dot-sensitized solar cells

International Nuclear Information System (INIS)

Zhang, Zhengguo; Shi, Chengwu; Chen, Junjun; Xiao, Guannan; Li, Long

2017-01-01

Graphical abstract: The TiO_2 nanorod array with the length of 600 nm, the diameter of 20 nm, the areal density of 500 μm"−"2 was successfully prepared. The compact PbS quantum-dot thin film was firstly obtained on the TiO_2 nanorod array by spin-coating-assisted successive ionic layer absorption and reaction with using 1,2-ethanedithiol. The photoelectric conversion efficiency (PCE) of the compact PbS quantum-dot thin film sensitized solar cells achieved 4.10% using spiro-OMeTAD as a hole transporting layer, while the PCE of the PbS quantum-dot sensitized solar cells was only 0.54%. - Highlights: • Preparation of TiO_2 nanorod arrays with the length of 600 nm, diameter of 20 nm. • The compact PbS QD thin film and short-length TiO_2 nanorod array were combined. • EDT addition improved PbS nanoparticle coverage and photovoltaic performance. • The compact PbS QD thin film sensitized solar cell achieved the PCE of 4.10%. - Abstract: Considering the balance of the hole diffusion length and the loading quantity of quantum-dots, the rutile TiO_2 nanorod array with the length of 600 nm, the diameter of 20 nm, and the areal density of 500 μm"−"2 is successfully prepared by the hydrothermal method using the aqueous grown solution of 38 mM titanium isopropoxide and 6 M hydrochloric acid at 170 °C for 105 min. The compact PbS quantum-dot thin film on the TiO_2 nanorod array is firstly obtained by the spin-coating-assisted successive ionic layer absorption and reaction with using 1,2-ethanedithiol (EDT). The result reveals that the strong interaction between lead and EDT is very important to control the crystallite size of PbS quantum-dots and obtain the compact PbS quantum-dot thin film on the TiO_2 nanorod array. The all solid-state sensitized solar cell with the combination of the short-length, high-density TiO_2 nanorod array and the compact PbS quantum-dot thin film achieves the photoelectric conversion efficiency of 4.10%, along with an open

Feshbach shape resonance for high Tc pairing in superlattices of quantum stripes and quantum wells

Directory of Open Access Journals (Sweden)

A Bianconi

2006-09-01

Full Text Available   The Feshbach shape resonances in the interband pairing in superconducting superlattices of quantum wells or quantum stripes is shown to provide the mechanism for high Tc superconductivity. This mechanism provides the Tc amplification driven by the architecture of material: superlattices of quantum wells (intercalated graphite or diborides and superlattices of quantum stripes (doped high Tc cuprate perovskites where the chemical potential is tuned to a Van Hove-Lifshitz singularity (vHs in the electronic energy spectrum of the superlattice associated with the change of the Fermi surface dimensionality in one of the subbands.

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.

Quantum data locking for high-rate private communication

International Nuclear Information System (INIS)

Lupo, Cosmo; Lloyd, Seth

2015-01-01

We show that, if the accessible information is used as a security quantifier, quantum channels with a certain symmetry can convey private messages at a tremendously high rate, as high as less than one bit below the rate of non-private classical communication. This result is obtained by exploiting the quantum data locking effect. The price to pay to achieve such a high private communication rate is that accessible information security is in general not composable. However, composable security holds against an eavesdropper who is forced to measure her share of the quantum system within a finite time after she gets it. (paper)

High-harmonic generation in a quantum electron gas trapped in a nonparabolic and anisotropic well

Science.gov (United States)

Hurst, Jérôme; Lévêque-Simon, Kévin; Hervieux, Paul-Antoine; Manfredi, Giovanni; Haas, Fernando

2016-05-01

An effective self-consistent model is derived and used to study the dynamics of an electron gas confined in a nonparabolic and anisotropic quantum well. This approach is based on the equations of quantum hydrodynamics, which incorporate quantum and nonlinear effects in an approximate fashion. The effective model consists of a set of six coupled differential equations (dynamical system) for the electric dipole and the size of the electron gas. Using this model we show that: (i) high harmonic generation is related to the appearance of chaos in the phase space, as attested to by related Poincaré sections; (ii) higher order harmonics can be excited efficiently and with relatively weak driving fields by making use of chirped electromagnetic waves.

Research Progress of Photoanodes for Quantum Dot Sensitized Solar Cells

Directory of Open Access Journals (Sweden)

LI Zhi-min

2017-08-01

Full Text Available This paper presents the development status and tendency of quantum dot sensitized solar cells. Photoanode research progress and its related technologies are analyzed in detail from the three ways of semiconductor thin films, quantum dot co-sensitization and quantum dot doping, deriving from the approach that the conversion efficiency can be improved by photoanode modification for quantum dot sensitized solar cells. According to the key factors which restrict the cell efficiency, the promising future development of quantum dot sensitized solar cells is proposed,for example,optimizing further the compositions and structures of semiconductor thin films for the photoanodes, exploring new quantum dots with broadband absorption and developing high efficient techniques of interface modification.

Reliable quantum communication over a quantum relay channel

Energy Technology Data Exchange (ETDEWEB)

Gyongyosi, Laszlo, E-mail: gyongyosi@hit.bme.hu [Quantum Technologies Laboratory, Department of Telecommunications, Budapest University of Technology and Economics, 2 Magyar tudosok krt, Budapest, H-1117, Hungary and Information Systems Research Group, Mathematics and Natural Sciences, Hungarian Ac (Hungary); Imre, Sandor [Quantum Technologies Laboratory, Department of Telecommunications, Budapest University of Technology and Economics, 2 Magyar tudosok krt, Budapest, H-1117 (Hungary)

2014-12-04

We show that reliable quantum communication over an unreliable quantum relay channels is possible. The coding scheme combines the results on the superadditivity of quantum channels and the efficient quantum coding approaches.

Solvothermal synthesis of InP quantum dots and their enhanced luminescent efficiency by post-synthetic treatments.

Science.gov (United States)

Byun, Ho-June; Lee, Ju Chul; Yang, Heesun

2011-03-01

InP quantum dots (QDs) were solvothermally synthesized by using a greener phosphorus source of P(N(CH(3))(2))(3) instead of highly toxic P(TMS)(3) widely used, and subsequently subjected to a size-sorting processing. While as-grown QDs showed an undetectably low emission intensity, post-synthetic treatments such as photo-etching, photo-radiation, and photo-assisted ZnS shell coating gave rise to a substantial increase in emission efficiency due to the effective removal and passivation of surface states. The emission efficiency of the photo-etched QDs was further enhanced by a consecutive UV photo-radiation, attributable to the photo-oxidation at QD surface. Furthermore, a relatively thick ZnS shell on the surface of InP QDs that were surface-modified with hydrophilic ligands beforehand was photochemically generated in an aqueous solution at room temperature. The resulting InP/ZnS core/shell QDs, emitting from blue to red wavelengths, were more efficient than the above photo-treated InP QDs, and their luminescent properties (emission bandwidth and quantum yield) were comparable to those of InP QDs synthesized with P(TMS)(3). Structural, size, and compositional analyses on InP/ZnS QDs were also conducted to elucidate their core/shell structure. Copyright © 2010 Elsevier Inc. All rights reserved.

Trade-off between bandwidth and efficiency in semipolar (20 2 ¯ 1 ¯) InGaN/GaN single- and multiple-quantum-well light-emitting diodes

Science.gov (United States)

Monavarian, M.; Rashidi, A.; Aragon, A. A.; Nami, M.; Oh, S. H.; DenBaars, S. P.; Feezell, D.

2018-05-01

InGaN/GaN light-emitting diodes (LEDs) with large modulation bandwidths are desirable for visible-light communication. Along with modulation speed, the consideration of the internal quantum efficiency (IQE) under operating conditions is also important. Here, we report the modulation characteristics of semipolar (20 2 ¯ 1 ¯ ) InGaN/GaN (LEDs) with single-quantum well (SQW) and multiple-quantum-well (MQW) active regions grown on free-standing semipolar GaN substrates with peak internal quantum efficiencies (IQEs) of 0.93 and 0.73, respectively. The MQW LEDs exhibit on average about 40-80% higher modulation bandwidth, reaching 1.5 GHz at 13 kA/cm2, but about 27% lower peak IQE than the SQW LEDs. We extract the differential carrier lifetimes (DLTs), RC parasitics, and carrier escape lifetimes and discuss their role in the bandwidth and IQE characteristics. A coulomb-enhanced capture process is shown to rapidly reduce the DLT of the MQW LED at high current densities. Auger recombination is also shown to play little role in increasing the speed of the LEDs. Finally, we investigate the trade-offs between the bandwidth and efficiency and introduce the bandwidth-IQE product as a potential figure of merit for optimizing speed and efficiency in InGaN/GaN LEDs.

Photocurrent extraction efficiency in colloidal quantum dot photovoltaics

KAUST Repository

Kemp, K. W.; Wong, C. T. O.; Hoogland, S. H.; Sargent, E. H.

2013-01-01

The efficiency of photocurrent extraction was studied directly inside operating Colloidal Quantum Dot (CQD) photovoltaic devices. A model was derived from first principles for a thin film p-n junction with a linearly spatially dependent electric field. Using this model, we were able to clarify the origins of recent improvement in CQD solar cell performance. From current-voltage diode characteristics under 1 sun conditions, we extracted transport lengths ranging from 39 nm to 86 nm for these materials. Characterization of the intensity dependence of photocurrent extraction revealed that the dominant loss mechanism limiting the transport length is trap-mediated recombination. © 2013 AIP Publishing LLC.

Holography as a highly efficient RG flow I: Rephrasing gravity

OpenAIRE

Behr, Nicolas; Kuperstein, Stanislav; Mukhopadhyay, Ayan

2015-01-01

We investigate how the holographic correspondence can be reformulated as a generalisation of Wilsonian RG flow in a strongly interacting large $N$ quantum field theory. We firstly define a \\textit{highly efficient RG flow} as one in which the Ward identities related to local conservation of energy, momentum and charges preserve the same form at each scale -- to achieve this it is necessary to redefine the background metric and external sources at each scale as functionals of the effective sin...

Simple formalism for efficient derivatives and multi-determinant expansions in quantum Monte Carlo

NARCIS (Netherlands)

Filippi, Claudia; Assaraf, R.; Moroni, S.

2016-01-01

We present a simple and general formalism to compute efficiently the derivatives of a multi-determinant Jastrow-Slater wave function, the local energy, the interatomic forces, and similar quantities needed in quantum Monte Carlo. Through a straightforward manipulation of matrices evaluated on the

Rapid Optimization of External Quantum Efficiency of Thin Film Solar Cells Using Surrogate Modeling of Absorptivity.

Science.gov (United States)

Kaya, Mine; Hajimirza, Shima

2018-05-25

This paper uses surrogate modeling for very fast design of thin film solar cells with improved solar-to-electricity conversion efficiency. We demonstrate that the wavelength-specific optical absorptivity of a thin film multi-layered amorphous-silicon-based solar cell can be modeled accurately with Neural Networks and can be efficiently approximated as a function of cell geometry and wavelength. Consequently, the external quantum efficiency can be computed by averaging surrogate absorption and carrier recombination contributions over the entire irradiance spectrum in an efficient way. Using this framework, we optimize a multi-layer structure consisting of ITO front coating, metallic back-reflector and oxide layers for achieving maximum efficiency. Our required computation time for an entire model fitting and optimization is 5 to 20 times less than the best previous optimization results based on direct Finite Difference Time Domain (FDTD) simulations, therefore proving the value of surrogate modeling. The resulting optimization solution suggests at least 50% improvement in the external quantum efficiency compared to bare silicon, and 25% improvement compared to a random design.

High-fidelity polarization storage in a gigahertz bandwidth quantum memory

International Nuclear Information System (INIS)

England, D G; Michelberger, P S; Champion, T F M; Reim, K F; Lee, K C; Sprague, M R; Jin, X-M; Langford, N K; Kolthammer, W S; Nunn, J; Walmsley, I A

2012-01-01

We demonstrate a dual-rail optical Raman memory inside a polarization interferometer; this enables us to store polarization-encoded information at GHz bandwidths in a room-temperature atomic ensemble. By performing full process tomography on the system, we measure up to 97 ± 1% process fidelity for the storage and retrieval process. At longer storage times, the process fidelity remains high, despite a loss of efficiency. The fidelity is 86 ± 4% for 1.5 μs storage time, which is 5000 times the pulse duration. Hence, high fidelity is combined with a large time-bandwidth product. This high performance, with an experimentally simple setup, demonstrates the suitability of the Raman memory for integration into large-scale quantum networks. (paper)

Selectively Modulating Triplet Exciton Formation in Host Materials for Highly Efficient Blue Electrophosphorescence.

Science.gov (United States)

Li, Huanhuan; Bi, Ran; Chen, Ting; Yuan, Kai; Chen, Runfeng; Tao, Ye; Zhang, Hongmei; Zheng, Chao; Huang, Wei

2016-03-23

The concept of limiting the triplet exciton formation to fundamentally alleviate triplet-involved quenching effects is introduced to construct host materials for highly efficient and stable blue phosphorescent organic light-emitting diodes (PhOLEDs). The low triplet exciton formation is realized by small triplet exciton formation fraction and rate with high binding energy and high reorganization energy of triplet exciton. Demonstrated in two analogue molecules in conventional donor-acceptor molecule structure for bipolar charge injection and transport with nearly the same frontier orbital energy levels and triplet excited energies, the new concept host material shows significantly suppressed triplet exciton formation in the host to avoid quenching effects, leading to much improved device efficiencies and stabilities. The low-voltage-driving blue PhOLED devices exhibit maximum efficiencies of 43.7 cd A(-1) for current efficiency, 32.7 lm W(-1) for power efficiency, and 20.7% for external quantum efficiency with low roll-off and remarkable relative quenching effect reduction ratio up to 41%. Our fundamental solution for preventing quenching effects of long-lived triplet excitons provides exciting opportunities for fabricating high-performance devices using the advanced host materials with intrinsically small triplet exciton formation cross section.

Quantum memory Quantum memory

Science.gov (United States)

Le Gouët, Jean-Louis; Moiseev, Sergey

2012-06-01

quest for higher efficiency, better fidelity, broader bandwidth, multimode capacity and longer storage lifetime is pursued in all those approaches, as shown in this special issue. The improvement of quantum memory operation specifically requires in-depth study and control of numerous physical processes leading to atomic decoherence. The present issue reflects the development of rare earth ion doped matrices offering long lifetime superposition states, either as bulk crystals or as optical waveguides. The need for quantum sources and high efficiency detectors at the single photon level is also illustrated. Several papers address the networking of quantum memories either in long-haul cryptography or in the prospect of quantum processing. In this context, much attention has been paid recently to interfacing quantum light with superconducting qubits and with nitrogen-vacancy centers in diamond. Finally, the quantum interfacing of light with matter raises questions on entanglement. The last two papers are devoted to the generation of entanglement by dissipative processes. It is shown that long lifetime entanglement may be built in this way. We hope this special issue will help readers to become familiar with the exciting field of ensemble-based quantum memories and will stimulate them to bring deeper insights and new ideas to this area.

Self-organized InGaAs/GaAs quantum dot arrays for use in high-efficiency intermediate-band solar cells

International Nuclear Information System (INIS)

Shoji, Yasushi; Okada, Yoshitaka; Akimoto, Katsuhiro

2013-01-01

We have investigated the material properties of multi-layer stacked InGaAs/GaAs quantum dots (QDs) grown on GaAs (311)B substrates. Symmetrical lens-shaped QDs were observed along [01-1], while their shape was asymmetric along the [-233] azimuth surrounded by two different dominant facets. Further, QDs were vertically aligned in the [311] direction when viewed along [01-1], while the alignment was inclined with respect to the growth direction when viewed along [-233]. The inclination angle of vertical alignment QDs became monotonically smaller from 22° to 2° with decreasing spacer layer thickness from 40 to 20 nm. Time-resolved photoluminescence measurements showed that multi-stacked QDs with thinner spacer layers resulted in increased PL decay times. We believe that an electronically coupled QD state or an intermediate band was formed, if the spacer layer thickness was reduced below 20 nm in this material system. For an InGaAs/GaAs QD solar cell grown on a GaAs (311)B substrate, the external quantum efficiency showed a clear increase in the longer wavelength range due to an additive contribution from the QD layers. Furthermore, photocurrent production due to two-step absorption of sub-bandgap photons, which is a key element that is necessary to be demonstrated for an increase in the efficiency of a single-junction solar cell beyond the Shockley-Queisser, was observed at room temperature under one sun condition. This photocurrent production increased under a forward-bias regime as the QDs were partially filled with carriers under the bias.

Resource-efficient linear-optical quantum router

Czech Academy of Sciences Publication Activity Database

Lemr, K.; Bartkiewicz, K.; Černoch, A.; Soubusta, Jan

2013-01-01

Roč. 87, č. 6 (2013), "062333-1"-"062333-7" ISSN 1050-2947 Institutional research plan: CEZ:AV0Z10100522 Keywords : quantum router * signal qubit * quantum communications Subject RIV: BH - Optics, Masers, Lasers Impact factor: 2.991, year: 2013

High quantum yield graphene quantum dots decorated TiO{sub 2} nanotubes for enhancing photocatalytic activity

Energy Technology Data Exchange (ETDEWEB)

Qu, Ailan, E-mail: qal67@163.com; Xie, Haolong; Xu, Xinmei; Zhang, Yangyu; Wen, Shengwu; Cui, Yifan

2016-07-01

Highlights: • High concentration yellow GQDs and TiO{sub 2} nanotubes were achieved by a simple and green method. • High quantum yield GQDs enhanced the photodegradation capacity of TiO{sub 2} nanotube. • The catalytic performance of GQDs/TiO{sub 2} depends on the GQDs loading. • The improved photocatalytic activity of GQDs/TiO{sub 2} was attributed to three aspects. - Abstract: Graphene quantum dots (GQDs) with high quantum yield (about 23.6% at an excitation wavelength of 320 nm) and GQDs/TiO{sub 2} nanotubes (GQDs/TiO{sub 2} NTs) composites were achieved by a simple hydrothermal method at low temperature. Photoluminescence characterization showed that the GQDs exhibited the down-conversion PL features at excitation from 300 to 420 nm and up-conversion photoluminescence in the range of 600–800 nm. The photocatalytic activity of prepared GQDs/TiO{sub 2} NTs composites on the degradation of methyl orange (MO) was significantly enhanced compared with that of pure TiO{sub 2} nanotubes (TiO{sub 2} NTs). For the composites coupling with 1.5%, 2.5% and 3.5% GQDs, the degradation of MO after 20 min irradiation under UV–vis light irradiation (λ = 380–780 nm) were 80.52%, 94.64% and 51.91%, respectively, which are much higher than that of pure TiO{sub 2} NTs (35.41%). It was inferred from the results of characterization that the improved photocatalytic activity of the GQDs/TiO{sub 2} NTs composites was attributed to the synergetic effect of up-conversion properties of the GQDs, enhanced visible light absorption and efficient separation of photogenerated electron-holes of the GQDs/TiO{sub 2} composite.

Highly Transparent, Visible-Light Photodetector Based on Oxide Semiconductors and Quantum Dots.

Science.gov (United States)

Shin, Seung Won; Lee, Kwang-Ho; Park, Jin-Seong; Kang, Seong Jun

2015-09-09

Highly transparent phototransistors that can detect visible light have been fabricated by combining indium-gallium-zinc oxide (IGZO) and quantum dots (QDs). A wide-band-gap IGZO film was used as a transparent semiconducting channel, while small-band-gap QDs were adopted to absorb and convert visible light to an electrical signal. Typical IGZO thin-film transistors (TFTs) did not show a photocurrent with illumination of visible light. However, IGZO TFTs decorated with QDs showed enhanced photocurrent upon exposure to visible light. The device showed a responsivity of 1.35×10(4) A/W and an external quantum efficiency of 2.59×10(4) under illumination by a 635 nm laser. The origin of the increased photocurrent in the visible light was the small band gap of the QDs combined with the transparent IGZO films. Therefore, transparent phototransistors based on IGZO and QDs were fabricated and characterized in detail. The result is relevant for the development of highly transparent photodetectors that can detect visible light.

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....

Development of high quantum efficiency, flat panel, thick detectors for megavoltage x-ray imaging: An experimental study of a single-pixel prototype

International Nuclear Information System (INIS)

Mei, X.; Pang, G.

2005-01-01

Our overall goal is to develop a new generation of electronic portal imaging devices (EPIDs) with a quantum efficiency (QE) more than an order of magnitude higher and a spatial resolution equivalent to that of EPIDs currently used for portal imaging. A novel design of such a high QE flat-panel based EPID was introduced recently and its feasibility was investigated theoretically [see Pang and Rowlands, Med. Phys. 31, 3004 (2004)]. In this work, we constructed a prototype single-pixel detector based on the novel design. Some fundamental imaging properties including the QE, spatial resolution, and sensitivity of the prototype detector were measured with a 6 MV beam. It has been shown that the experimental results agree well with theoretical predictions and further development based on the novel design including the construction of a prototype area detector is warranted

Device-independent quantum reading and noise-assisted quantum transmitters

International Nuclear Information System (INIS)

Roga, W; Buono, D; Illuminati, F

2015-01-01

In quantum reading, a quantum state of light (transmitter) is applied to read classical information. In the presence of noise or for sufficiently weak signals, quantum reading can outperform classical reading by reason of enhanced state distinguishability. Here we show that enhanced quantum efficiency depends on the presence in the transmitter of a particular type of quantum correlations, the discord of response. Different encodings and transmitters give rise to different levels of efficiency. Considering noisy quantum probes, we show that squeezed thermal transmitters with non-symmetrically distributed noise among the field modes yield higher quantum efficiency compared with coherent thermal quantum states. The noise-enhanced quantum advantage is a consequence of the discord of response being a non-decreasing function of increasing thermal noise under constant squeezing, a behavior that leads to increased state distinguishability. We finally show that, for non-symmetric squeezed thermal states, the probability of error, as measured by the quantum Chernoff bound, vanishes asymptotically with increasing local thermal noise with finite global squeezing. Therefore, with fixed finite squeezing, noisy but strongly discordant quantum states with a large noise imbalance between the field modes can outperform noisy classical resources as well as pure entangled transmitters with the same finite level of squeezing. (paper)

Combination of short-length TiO{sub 2} nanorod arrays and compact PbS quantum-dot thin films for efficient solid-state quantum-dot-sensitized solar cells

Energy Technology Data Exchange (ETDEWEB)

Zhang, Zhengguo [School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009 (China); School of Chemistry and Chemical Engineering, Beifang University of Nationalities, Yinchuan 750021 (China); Shi, Chengwu, E-mail: shicw506@foxmail.com [School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009 (China); Chen, Junjun; Xiao, Guannan; Li, Long [School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009 (China)

2017-07-15

Graphical abstract: The TiO{sub 2} nanorod array with the length of 600 nm, the diameter of 20 nm, the areal density of 500 μm{sup −2} was successfully prepared. The compact PbS quantum-dot thin film was firstly obtained on the TiO{sub 2} nanorod array by spin-coating-assisted successive ionic layer absorption and reaction with using 1,2-ethanedithiol. The photoelectric conversion efficiency (PCE) of the compact PbS quantum-dot thin film sensitized solar cells achieved 4.10% using spiro-OMeTAD as a hole transporting layer, while the PCE of the PbS quantum-dot sensitized solar cells was only 0.54%. - Highlights: • Preparation of TiO{sub 2} nanorod arrays with the length of 600 nm, diameter of 20 nm. • The compact PbS QD thin film and short-length TiO{sub 2} nanorod array were combined. • EDT addition improved PbS nanoparticle coverage and photovoltaic performance. • The compact PbS QD thin film sensitized solar cell achieved the PCE of 4.10%. - Abstract: Considering the balance of the hole diffusion length and the loading quantity of quantum-dots, the rutile TiO{sub 2} nanorod array with the length of 600 nm, the diameter of 20 nm, and the areal density of 500 μm{sup −2} is successfully prepared by the hydrothermal method using the aqueous grown solution of 38 mM titanium isopropoxide and 6 M hydrochloric acid at 170 °C for 105 min. The compact PbS quantum-dot thin film on the TiO{sub 2} nanorod array is firstly obtained by the spin-coating-assisted successive ionic layer absorption and reaction with using 1,2-ethanedithiol (EDT). The result reveals that the strong interaction between lead and EDT is very important to control the crystallite size of PbS quantum-dots and obtain the compact PbS quantum-dot thin film on the TiO{sub 2} nanorod array. The all solid-state sensitized solar cell with the combination of the short-length, high-density TiO{sub 2} nanorod array and the compact PbS quantum-dot thin film achieves the photoelectric conversion

Quantum optics with quantum dots in photonic wires

DEFF Research Database (Denmark)

Munsch, Mathieu; Cadeddu, Davide; Teissier, Jean

2016-01-01

We present an exploration of the spectroscopy of a single quantum dot in a photonic wire. The device presents a high photon extraction efficiency, and strong hybrid coupling to mechanical modes. We use resonance fluorescence to probe the emitter's properties with the highest sensitivity, allowing...

Quantum photonics with quantum dots in photonic wires

DEFF Research Database (Denmark)

Munsch, Mathieu; Kuhlmann, Andreas; Cadeddu, Davide

2016-01-01

We present results from the spectroscopy of a single quantum dot in a photonic wire. The device presents a high photon extraction efficiency, and strong hybrid coupling to mechanical modes. We use resonance fluorescence to probe the emitter’s properties with the highest sensitivity. Weperform...

Efficient one-out-of-two quantum oblivious transfer based on four-coherent-state postselection protocol

International Nuclear Information System (INIS)

Chen, I-C; Hwang Tzonelih; Li C-M

2008-01-01

On the basis of the modified four-coherent-state post-selection quantum key distribution protocol (Namiki and Hirano 2006 Preprint quant-ph/0608144v1), two 1-out-of-2 quantum oblivious transfer (QOT 2 1 ) protocols are proposed. The first proposed protocol (called the receiver-based QOT 2 1 protocol) requires the coherent states to be prepared by the receiver, whereas the second protocol (called the sender-based QOT 2 1 protocol) allows the coherent states to be generated by the sender. The main advantages of the proposed protocols are that (i) no quantum bit commitment schemes and the assumption of quantum memory are needed; (ii) less communication cost between participants is required, i.e. the receiver-based QOT 2 1 protocol requires only one quantum communication and one classical communication and the sender-based QOT 2 1 protocol requires only one quantum communication between participants during protocol execution; and (iii) the utilization of quantum states is very efficient, wherein the receiver-based and the sender-based QOT 2 1 protocols use only two coherent pulses and one coherent pulse respectively for sending the sender's two messages

Aqueous synthesis of high bright Ag{sub 2}Se−ZnSe quantum dots with tunable near-infrared emission

Energy Technology Data Exchange (ETDEWEB)

Che, Dongchen; Ding, Di [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201602 (China); Wang, Hongzhi, E-mail: wanghz@dhu.edu.cn [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201602 (China); Zhang, Qinghong [State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201602 (China); Li, Yaogang, E-mail: yaogang_li@dhu.edu.cn [Engineering Research Center of Advanced Glass Manufacturing Technology, Ministry of Education, Donghua University, Shanghai 201602 (China)

2016-09-05

Efficient aqueous synthetic methods for near-infrared quantum dots as bioimaging agents are urgently required. In this work, a simple and fast synthesis of highly luminescent, near-infrared Ag{sub 2}Se quantum dots (QDs) in aqueous media is reported. The method avoids high temperature, pressure and organic solvents to directly generate water-dispersible Ag{sub 2}Se QDs. The photoluminescence emission of Ag{sub 2}Se QDs ranges from 835 to 940 nm by different Ag:Se molar ratio. Using the ZnSe as a shell, the quantum yield reaches up to 42%. The Ag{sub 2}Se−ZnSe QDs with high quantum yield, near-infrared and low cytotoxic could be used as good cell labels, showing great potential applications in bio-imaging. - Highlights: • Ag{sub 2}Se−ZnSe nanocrystals are prepared directly in aqueous media at low temperature. • Ag{sub 2}Se−ZnSe nanocrystals show excellent water solubility and colloidal stability. • Ag{sub 2}Se nanocrystals exhibit tunable near-infrared emission with ultrasmall size. • Ag{sub 2}Se−ZnSe nanocrystals show high quantum yield with low cytotoxicity. • Ag{sub 2}Se−ZnSe nanocrystals are stable over a month at room temperature in the air.

Blue phosphorescent organic light-emitting diodes using an exciplex forming co-host with the external quantum efficiency of theoretical limit.

Science.gov (United States)

Shin, Hyun; Lee, Sunghun; Kim, Kwon-Hyeon; Moon, Chang-Ki; Yoo, Seung-Jun; Lee, Jeong-Hwan; Kim, Jang-Joo

2014-07-16

A high-efficiency blue-emitting organic light-emitting diode (OLED) approaching theoretical efficiency using an exciplex-forming co-host composed of N,N'-dicarbazolyl-3,5-benzene (mCP) and bis-4,6-(3,5-di-3-pyridylphenyl)- 2-methylpyrimidine (B3PYMPM) is fabricated. Iridium(III)bis[(4,6-difluorophenyl)- pyridinato-N,C2']picolinate (FIrpic) is used as the emitter, which turns out to have a preferred horizontal dipole orientation in the emitting layer. The OLED shows a maximum external quantum efficiency of 29.5% (a maximum current efficiency of 62.2 cd A(-1) ), which is in perfect agreement with the theoretical prediction. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Minimum detection efficiency for the loophole-free confirmation of quantum contextuality

International Nuclear Information System (INIS)

Xiang Yang; Hong Fang-Yu

2013-01-01

Klyachko—Can—Binicioğlu—Shumovsky (KCBS) inequality is a Bell-like inequality, the violation of which can be used to confirm the existence of quantum contextuality. However, the imperfection of detection efficiency may cause the so-called loophole in actual KCBS's experiments. We derive an alternative KCBS inequality to deal with the loophole in actual KCBS's experiments. We prove that if the experimental data violate this KCBS inequality, the loophole-free violation of the original KCBS inequality will occur. We show that the minimum detection efficiency needed for a loophole-free violation of the KCBS inequality is about 0.9738

High-efficiency power transfer for silicon-based photonic devices

Science.gov (United States)

Son, Gyeongho; Yu, Kyoungsik

2018-02-01

We demonstrate an efficient coupling of guided light of 1550 nm from a standard single-mode optical fiber to a silicon waveguide using the finite-difference time-domain method and propose a fabrication method of tapered optical fibers for efficient power transfer to silicon-based photonic integrated circuits. Adiabatically-varying fiber core diameters with a small tapering angle can be obtained using the tube etching method with hydrofluoric acid and standard single-mode fibers covered by plastic jackets. The optical power transmission of the fundamental HE11 and TE-like modes between the fiber tapers and the inversely-tapered silicon waveguides was calculated with the finite-difference time-domain method to be more than 99% at a wavelength of 1550 nm. The proposed method for adiabatic fiber tapering can be applied in quantum optics, silicon-based photonic integrated circuits, and nanophotonics. Furthermore, efficient coupling within the telecommunication C-band is a promising approach for quantum networks in the future.

Suppression of external quantum efficiency roll-off of nanopatterned organic-light emitting diodes at high current densities

Energy Technology Data Exchange (ETDEWEB)

Kuwae, Hiroyuki; Kasahara, Takashi [Nano-Science and Nano-Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan); JST, ERATO, Adachi Molecular Exciton Engineering Project, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Nitta, Atsushi; Yoshida, Kou; Inoue, Munetomo [Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Matsushima, Toshinori; Adachi, Chihaya, E-mail: adachi@cstf.kyushu-u.ac.jp [JST, ERATO, Adachi Molecular Exciton Engineering Project, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Shoji, Shuichi [Nano-Science and Nano-Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan); Mizuno, Jun [JST, ERATO, Adachi Molecular Exciton Engineering Project, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Research Organization for Nano and Life Innovation, Waseda University, 513 Waseda Tsurumaki-cho, Shinjuku, Tokyo 162-0041 (Japan)

2015-10-21

We developed organic light-emitting diodes (OLEDs) with nanopatterned current flow regions using electron-beam lithography with the aim of suppressing singlet–polaron annihilation (SPA). Nanopatterns composed of lines and circles were used in the current flow regions of nano-line and nano-dot OLEDs, respectively. Excitons partially escape from the current flow regions where SPA takes place. As such, current densities where external quantum efficiencies were half of their initial values (J{sub 0}) increased as line width and circle diameter were decreased to close to the exciton diffusion length. Circles were more efficient at enhancing exciton escape and increasing J{sub 0} than lines. The J{sub 0} increase in the nano-dot OLEDs containing nanopatterned circles with a diameter of 50 nm was approximately 41-fold that of a conventional OLED with a current flow region of 4 mm{sup 2}. The dependence of J{sub 0} on the size and shape of the nanopatterns was well explained by an SPA model that considered exciton diffusion. Nanopatterning of OLEDs is a feasible method of obtaining large J{sub 0}.

High-modulation-efficiency, integrated waveguide modulator-laser diode at 448 nm

KAUST Repository

Shen, Chao

2016-01-25

To date, solid-state lighting (SSL), visible light communication (VLC) and optical clock generation functionalities in the blue-green color regime have been demonstrated based on discrete devices, including light-emitting diodes, laser diodes, and transverse-transmission modulators. This work presents the first integrated waveguide modulator-laser diode (IWM-LD) at 448 nm, offering the advantages of small-footprint, high-speed, and low power-consumption. A high modulation efficiency of 2.68 dB/V, deriving from a large extinction ratio of 9.4 dB and a low operating voltage range of 3.5 V, was measured. The electroabsorption characteristics revealed that the modulation effect, as observed from the red-shifting of the absorption edge, was resulted from the external-field-induced quantum-confined-Stark-effect (QCSE). A comparative analysis of the photocurrent versus wavelength spectra in semipolar- and polar-plane InGaN/GaN quantum wells (QWs) confirmed that the IWM-LD based on semipolar (20¯2 ¯1) QWs was able to operate in a manner similar to other III-V materials typically used in optical telecommunications, due to the reduced piezoelectric field. Utilizing the integrated modulator, a -3dB bandwidth of ~1 GHz was measured, and a data rate of 1 Gbit/s was demonstrated using on-off keying (OOK) modulation. Our experimental investigation highlighted the advantage of implementing the IWM-LD on the same semipolar QW epitaxy in enabling a high-efficiency platform for SSL-VLC dual-functionalities.

High-modulation-efficiency, integrated waveguide modulator-laser diode at 448 nm

KAUST Repository

Shen, Chao; Ng, Tien Khee; Leonard, John T.; Pourhashemi, Arash; Oubei, Hassan M.; Alias, Mohd Sharizal; Nakamura, Shuji; DenBaars, Steven P.; Speck, James S.; Alyamani, Ahmed Y.; Eldesouki, Munir M.; Ooi, Boon S.

2016-01-01

To date, solid-state lighting (SSL), visible light communication (VLC) and optical clock generation functionalities in the blue-green color regime have been demonstrated based on discrete devices, including light-emitting diodes, laser diodes, and transverse-transmission modulators. This work presents the first integrated waveguide modulator-laser diode (IWM-LD) at 448 nm, offering the advantages of small-footprint, high-speed, and low power-consumption. A high modulation efficiency of 2.68 dB/V, deriving from a large extinction ratio of 9.4 dB and a low operating voltage range of 3.5 V, was measured. The electroabsorption characteristics revealed that the modulation effect, as observed from the red-shifting of the absorption edge, was resulted from the external-field-induced quantum-confined-Stark-effect (QCSE). A comparative analysis of the photocurrent versus wavelength spectra in semipolar- and polar-plane InGaN/GaN quantum wells (QWs) confirmed that the IWM-LD based on semipolar (20¯2 ¯1) QWs was able to operate in a manner similar to other III-V materials typically used in optical telecommunications, due to the reduced piezoelectric field. Utilizing the integrated modulator, a -3dB bandwidth of ~1 GHz was measured, and a data rate of 1 Gbit/s was demonstrated using on-off keying (OOK) modulation. Our experimental investigation highlighted the advantage of implementing the IWM-LD on the same semipolar QW epitaxy in enabling a high-efficiency platform for SSL-VLC dual-functionalities.

High Efficiency Quantum Dot III-V Thermophotovoltaic Cell for Space Power, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — Quantum dots are nanoscale materials that have already improved the performance of optical sensors, lasers, light emitting diodes and solar cells. The unique...

Quantum Sensing for High Energy Physics

Energy Technology Data Exchange (ETDEWEB)

Ahmed, Zeeshan; et al.

2018-03-29

Report of the first workshop to identify approaches and techniques in the domain of quantum sensing that can be utilized by future High Energy Physics applications to further the scientific goals of High Energy Physics.

Hybrid Integration of Solid-State Quantum Emitters on a Silicon Photonic Chip.

Science.gov (United States)

Kim, Je-Hyung; Aghaeimeibodi, Shahriar; Richardson, Christopher J K; Leavitt, Richard P; Englund, Dirk; Waks, Edo

2017-12-13

Scalable quantum photonic systems require efficient single photon sources coupled to integrated photonic devices. Solid-state quantum emitters can generate single photons with high efficiency, while silicon photonic circuits can manipulate them in an integrated device structure. Combining these two material platforms could, therefore, significantly increase the complexity of integrated quantum photonic devices. Here, we demonstrate hybrid integration of solid-state quantum emitters to a silicon photonic device. We develop a pick-and-place technique that can position epitaxially grown InAs/InP quantum dots emitting at telecom wavelengths on a silicon photonic chip deterministically with nanoscale precision. We employ an adiabatic tapering approach to transfer the emission from the quantum dots to the waveguide with high efficiency. We also incorporate an on-chip silicon-photonic beamsplitter to perform a Hanbury-Brown and Twiss measurement. Our approach could enable integration of precharacterized III-V quantum photonic devices into large-scale photonic structures to enable complex devices composed of many emitters and photons.

Quantum jumps are more quantum than quantum diffusion

International Nuclear Information System (INIS)

Daryanoosh, Shakib; M Wiseman, Howard

2014-01-01

It was recently argued (Wiseman and Gambetta 2012 Phys. Rev. Lett. 108 220402) that the stochastic dynamics (jumps or diffusion) of an open quantum system are not inherent to the system, but rather depend on the existence and nature of a distant detector. The proposed experimental tests involved homodyne detection, giving rise to quantum diffusion, and required efficiencies η of well over 50%. Here we prove that this requirement (η>0.5) is universal for diffusive-type detection, even if the system is coupled to multiple baths. However, this no-go theorem does not apply to quantum jumps, and we propose a test involving a qubit with jump-type detectors, with a threshold efficiency of only 37%. That is, quantum jumps are ‘more quantum’, and open the way to practical experimental tests. Our scheme involves a novel sort of adaptive monitoring scheme on a system coupled to two baths. (paper)

High Efficiency, Illumination Quality OLEDs for Lighting

Energy Technology Data Exchange (ETDEWEB)

Joseph Shiang; James Cella; Kelly Chichak; Anil Duggal; Kevin Janora; Chris Heller; Gautam Parthasarathy; Jeffery Youmans; Joseph Shiang

2008-03-31

. In 2003, a large area, OLED based illumination source was demonstrated that could provide light with a quality, quantity, and efficiency on par with what can be achieved with traditional light sources. The demonstration source was made by tiling together 16 separate 6-inch x 6-inch blue-emitting OLEDs. The efficiency, total lumen output, and lifetime of the OLED based illumination source were the same as what would be achieved with an 80 watt incandescent bulb. The devices had an average efficacy of 15 LPW and used solution-processed OLEDs. The individual 6-inch x 6-inch devices incorporated three technology strategies developed specifically for OLED lighting -- downconversion for white light generation, scattering for outcoupling efficiency enhancement, and a scalable monolithic series architecture to enable large area devices. The downconversion approach consists of optically coupling a blue-emitting OLED to a set of luminescent layers. The layers are chosen to absorb the blue OLED emission and then luminescence with high efficiency at longer wavelengths. The composition and number of layers are chosen so that the unabsorbed blue emission and the longer wavelength re-emission combine to make white light. A downconversion approach has the advantage of allowing a wide variety of colors to be made from a limited set of blue emitters. In addition, one does not have to carefully tune the emission wavelength of the individual electro-luminescent species within the OLED device in order to achieve white light. The downconversion architecture used to develop the 15LPW large area light source consisted of a polymer-based blue-emitting OLED and three downconversion layers. Two of the layers utilized perylene based dyes from BASF AG of Germany with high quantum efficiency (>98%) and one of the layers consisted of inorganic phosphor particles (Y(Gd)AG:Ce) with a quantum efficiency of {approx}85%. By independently varying the optical density of the downconversion layers, the

Deterministic and efficient quantum cryptography based on Bell's theorem

International Nuclear Information System (INIS)

Chen Zengbing; Pan Jianwei; Zhang Qiang; Bao Xiaohui; Schmiedmayer, Joerg

2006-01-01

We propose a double-entanglement-based quantum cryptography protocol that is both efficient and deterministic. The proposal uses photon pairs with entanglement both in polarization and in time degrees of freedom; each measurement in which both of the two communicating parties register a photon can establish one and only one perfect correlation, and thus deterministically create a key bit. Eavesdropping can be detected by violation of local realism. A variation of the protocol shows a higher security, similar to the six-state protocol, under individual attacks. Our scheme allows a robust implementation under the current technology

Efficient generation of photonic entanglement and multiparty quantum communication

Energy Technology Data Exchange (ETDEWEB)

Trojek, Pavel

2007-09-15

This thesis deals largely with the problem of efficient generation of photonic entanglement with the principal aim of developing a bright source of polarization-entangled photon pairs, which meets the requirements for reliable and economic operation of quantum communication prototypes and demonstrators. Our approach uses a cor-related photon-pair emission in nonlinear process of spontaneous parametric downconversion pumped by light coming from a compact and cheap blue laser diode. Two alternative source configurations are examined within the thesis. The first makes use of a well established concept of degenerate non-collinear emission from a single type-II nonlinear crystal and the second relies on a novel method where the emissions from two adjacent type-I phase-matched nonlinear crystals operated in collinear non-degenerate regime are coherently overlapped. The latter approach showed to be more effective, yielding a total detected rate of almost 10{sup 6} pairs/s at >98% quantum interference visibility of polarization correlations. The second issue addressed within the thesis is the simplification and practical implementation of quantum-assisted solutions to multiparty communication tasks. We show that entanglement is not the only non-classical resource endowing the quantum multiparty information processing its power. Instead, only the sequential communication and transformation of a single qubit can be sufficient to accomplish certain tasks. This we prove for two distinct communication tasks, secret sharing and communication complexity. Whereas the goal of the first is to split a cryptographic key among several parties in a way that its reconstruction requires their collaboration, the latter aims at reducing the amount of communication during distributed computational tasks. Importantly, our qubitassisted solutions to the problems are feasible with state-of-the-art technology. This we clearly demonstrate in the laboratory implementation for 6 and 5 parties

Efficient generation of photonic entanglement and multiparty quantum communication

International Nuclear Information System (INIS)

Trojek, Pavel

2007-09-01

This thesis deals largely with the problem of efficient generation of photonic entanglement with the principal aim of developing a bright source of polarization-entangled photon pairs, which meets the requirements for reliable and economic operation of quantum communication prototypes and demonstrators. Our approach uses a cor-related photon-pair emission in nonlinear process of spontaneous parametric downconversion pumped by light coming from a compact and cheap blue laser diode. Two alternative source configurations are examined within the thesis. The first makes use of a well established concept of degenerate non-collinear emission from a single type-II nonlinear crystal and the second relies on a novel method where the emissions from two adjacent type-I phase-matched nonlinear crystals operated in collinear non-degenerate regime are coherently overlapped. The latter approach showed to be more effective, yielding a total detected rate of almost 10 6 pairs/s at >98% quantum interference visibility of polarization correlations. The second issue addressed within the thesis is the simplification and practical implementation of quantum-assisted solutions to multiparty communication tasks. We show that entanglement is not the only non-classical resource endowing the quantum multiparty information processing its power. Instead, only the sequential communication and transformation of a single qubit can be sufficient to accomplish certain tasks. This we prove for two distinct communication tasks, secret sharing and communication complexity. Whereas the goal of the first is to split a cryptographic key among several parties in a way that its reconstruction requires their collaboration, the latter aims at reducing the amount of communication during distributed computational tasks. Importantly, our qubitassisted solutions to the problems are feasible with state-of-the-art technology. This we clearly demonstrate in the laboratory implementation for 6 and 5 parties

Quantum Illumination-Based Target Detection and Discrimination

Science.gov (United States)

2014-06-30

photodiode with an estimated quantum efficiency of 85% and an ultralow-noise transimpedance amplifier . Compared with to our initial QI measurements...demonstrated high signal-to-noise ratio (SNR) quantum-illumination target detection in a lossy, noisy environment using an optical parametric amplifier ...Research Triangle Park, NC 27709-2211 quantum communication, target detection, entanglement, parametric downconversion, optical parametric amplifiers

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...

Relativistic quantum chemistry on quantum computers

DEFF Research Database (Denmark)

Veis, L.; Visnak, J.; Fleig, T.

2012-01-01

The past few years have witnessed a remarkable interest in the application of quantum computing for solving problems in quantum chemistry more efficiently than classical computers allow. Very recently, proof-of-principle experimental realizations have been reported. However, so far only...... the nonrelativistic regime (i.e., the Schrodinger equation) has been explored, while it is well known that relativistic effects can be very important in chemistry. We present a quantum algorithm for relativistic computations of molecular energies. We show how to efficiently solve the eigenproblem of the Dirac......-Coulomb Hamiltonian on a quantum computer and demonstrate the functionality of the proposed procedure by numerical simulations of computations of the spin-orbit splitting in the SbH molecule. Finally, we propose quantum circuits with three qubits and nine or ten controlled-NOT (CNOT) gates, which implement a proof...

Quantum Transport Simulation of High-Power 4.6-μm Quantum Cascade Lasers

Directory of Open Access Journals (Sweden)

Olafur Jonasson

2016-06-01

Full Text Available We present a quantum transport simulation of a 4.6- μ m quantum cascade laser (QCL operating at high power near room temperature. The simulation is based on a rigorous density-matrix-based formalism, in which the evolution of the single-electron density matrix follows a Markovian master equation in the presence of applied electric field and relevant scattering mechanisms. We show that it is important to allow for both position-dependent effective mass and for effective lowering of very thin barriers in order to obtain the band structure and the current-field characteristics comparable to experiment. Our calculations agree well with experiments over a wide range of temperatures. We predict a room-temperature threshold field of 62 . 5 kV/cm and a characteristic temperature for threshold-current-density variation of T 0 = 199 K . We also calculate electronic in-plane distributions, which are far from thermal, and show that subband electron temperatures can be hundreds to thousands of degrees higher than the heat sink. Finally, we emphasize the role of coherent tunneling current by looking at the size of coherences, the off-diagonal elements of the density matrix. At the design lasing field, efficient injection manifests itself in a large injector/upper lasing level coherence, which underscores the insufficiency of semiclassical techniques to address injection in QCLs.

Synthesis of quantum dots

Science.gov (United States)

McDaniel, Hunter

2017-10-17

Common approaches to synthesizing alloyed quantum dots employ high-cost, air-sensitive phosphine complexes as the selenium precursor. Disclosed quantum dot synthesis embodiments avoid these hazardous and air-sensitive selenium precursors. Certain embodiments utilize a combination comprising a thiol and an amine that together reduce and complex the elemental selenium to form a highly reactive selenium precursor at room temperature. The same combination of thiol and amine acts as the reaction solvent, stabilizing ligand, and sulfur source in the synthesis of quantum dot cores. A non-injection approach may also be used. The optical properties of the quantum dots synthesized by this new approach can be finely tuned for a variety of applications by controlling size and/or composition of size and composition. Further, using the same approach, a shell can be grown around a quantum dot core that improves stability, luminescence efficiency, and may reduce toxicity.

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

Quantum Coherent Three-Terminal Thermoelectrics: Maximum Efficiency at Given Power Output

Directory of Open Access Journals (Sweden)

Robert S. Whitney

2016-05-01

Full Text Available This work considers the nonlinear scattering theory for three-terminal thermoelectric devices used for power generation or refrigeration. Such systems are quantum phase-coherent versions of a thermocouple, and the theory applies to systems in which interactions can be treated at a mean-field level. It considers an arbitrary three-terminal system in any external magnetic field, including systems with broken time-reversal symmetry, such as chiral thermoelectrics, as well as systems in which the magnetic field plays no role. It is shown that the upper bound on efficiency at given power output is of quantum origin and is stricter than Carnot’s bound. The bound is exactly the same as previously found for two-terminal devices and can be achieved by three-terminal systems with or without broken time-reversal symmetry, i.e., chiral and non-chiral thermoelectrics.

Scalable quantum computing based on stationary spin qubits in coupled quantum dots inside double-sided optical microcavities.

Science.gov (United States)

Wei, Hai-Rui; Deng, Fu-Guo

2014-12-18

Quantum logic gates are the key elements in quantum computing. Here we investigate the possibility of achieving a scalable and compact quantum computing based on stationary electron-spin qubits, by using the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics. We design the compact quantum circuits for implementing universal and deterministic quantum gates for electron-spin systems, including the two-qubit CNOT gate and the three-qubit Toffoli gate. They are compact and economic, and they do not require additional electron-spin qubits. Moreover, our devices have good scalability and are attractive as they both are based on solid-state quantum systems and the qubits are stationary. They are feasible with the current experimental technology, and both high fidelity and high efficiency can be achieved when the ratio of the side leakage to the cavity decay is low.

Quantum data locking for high-rate private communication

OpenAIRE

Lupo, Cosmo; Lloyd, Seth

2015-01-01

We show that, if the accessible information is used as a security quantifier, quantum channels with a certain symmetry can convey private messages at a tremendously high rate, as high as less than one bit below the rate of non-private classical communication. This result is obtained by exploiting the quantum data locking effect. The price to pay to achieve such a high private communication rate is that accessible information security is in general not composable. However, composable security ...

Quantum transport in the FMO photosynthetic light-harvesting complex.

Science.gov (United States)

Karafyllidis, Ioannis G

2017-06-01

The very high light-harvesting efficiency of natural photosynthetic systems in conjunction with recent experiments, which showed quantum-coherent energy transfer in photosynthetic complexes, raised questions regarding the presence of non-trivial quantum effects in photosynthesis. Grover quantum search, quantum walks, and entanglement have been investigated as possible effects that lead to this efficiency. Here we explain the near-unit photosynthetic efficiency without invoking non-trivial quantum effects. Instead, we use non-equilibrium Green's functions, a mesoscopic method used to study transport in nano-conductors to compute the transmission function of the Fenna-Matthews-Olson (FMO) complex using an experimentally derived exciton Hamiltonian. The chlorosome antenna and the reaction center play the role of input and output contacts, connected to the FMO complex. We show that there are two channels for which the transmission is almost unity. Our analysis also revealed a dephasing-driven regulation mechanism that maintains the efficiency in the presence of varying dephasing potentials.

Splitting efficiency and interference effects in a Cooper pair splitter based on a triple quantum dot with ferromagnetic contacts

Science.gov (United States)

Bocian, Kacper; Rudziński, Wojciech; Weymann, Ireneusz

2018-05-01

We theoretically study the spin-resolved subgap transport properties of a Cooper pair splitter based on a triple quantum dot attached to superconducting and ferromagnetic leads. Using the Keldysh Green's function formalism, we analyze the dependence of the Andreev conductance, Cooper pair splitting efficiency, and tunnel magnetoresistance on the gate and bias voltages applied to the system. We show that the system's transport properties are strongly affected by spin dependence of tunneling processes and quantum interference between different local and nonlocal Andreev reflections. We also study the effects of finite hopping between the side quantum dots on the Andreev current. This allows for identifying the optimal conditions for enhancing the Cooper pair splitting efficiency of the device. We find that the splitting efficiency exhibits a nonmonotonic dependence on the degree of spin polarization of the leads and the magnitude and type of hopping between the dots. An almost perfect splitting efficiency is predicted in the nonlinear response regime when the energies of the side quantum dots are tuned to the energies of the corresponding Andreev bound states. In addition, we analyzed features of the tunnel magnetoresistance (TMR) for a wide range of the gate and bias voltages, as well as for different model parameters, finding the corresponding sign changes of the TMR in certain transport regimes. The mechanisms leading to these effects are thoroughly discussed.

Go Pink! The Effect of Secondary Quanta on Detective Quantum Efficiency

Energy Technology Data Exchange (ETDEWEB)

Watson, Scott [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-09-05

Photons are never directly observable. Consequently, we often use photoelectric detectors (eg CCDs) to record associated photoelectrons statistically. Nonetheless, it is an implicit goal of radiographic detector designers to achieve the maximum possible detector efficiency1. In part the desire for ever higher efficiency has been due to the fact that detectors are far less expensive than associated accelerator facilities (e.g. DARHT and PHERMEX2). In addition, higher efficiency detectors often have better spatial resolution. Consequently, the optimization of the detector, not the accelerator, is the system component with the highest leverage per dollar. In recent years, imaging scientists have adopted the so-called Detective Quantum Efficiency, or DQE as a summary measure of detector performance. Unfortunately, owing to the complex nature of the trade-space associated with detector components, and the natural desire for simplicity and low(er) cost, there has been a recent trend in Los Alamos to focus only on the zerofrequency efficiency, or DQE(0), when designing such systems. This narrow focus leads to system designs that neglect or even ignore the importance of high-spatial-frequency image components. In this paper we demonstrate the significant negative impact of these design choices on the Noise Power Spectrum1 (NPS) and recommend a more holistic approach to detector design. Here we present a statistical argument which indicates that a very large number (>20) of secondary quanta (typically visible light and/or recorded photo-electrons) are needed to take maximum advantage of the primary quanta (typically x-rays or protons) which are available to form an image. Since secondary particles come in bursts, they are not independent. In short, we want to maximize the pink nature of detector noise at DARHT.

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.

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

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.

Fast and efficient wireless power transfer via transitionless quantum driving.

Science.gov (United States)

Paul, Koushik; Sarma, Amarendra K

2018-03-07

Shortcut to adiabaticity (STA) techniques have the potential to drive a system beyond the adiabatic limits. Here, we present a robust and efficient method for wireless power transfer (WPT) between two coils based on the so-called transitionless quantum driving (TQD) algorithm. We show that it is possible to transfer power between the coils significantly fast compared to its adiabatic counterpart. The scheme is fairly robust against the variations in the coupling strength and the coupling distance between the coils. Also, the scheme is found to be reasonably immune to intrinsic losses in the coils.

Efficiency enhancement of InGaN/GaN light-emitting diodes with pin-doped GaN quantum barrier

International Nuclear Information System (INIS)

Sirkeli, Vadim P; Al-Daffaie, Shihab; Oprea, Ion; Küppers, Franko; Hartnagel, Hans L; Yilmazoglu, Oktay; Ong, Duu Sheng

2017-01-01

Blue InGaN/GaN light-emitting diodes with undoped, heavily Si-doped, Si delta-doped, heavily Mg-doped, Mg delta-doped, and Mg–Si pin-doped GaN barrier are investigated numerically. The simulation results demonstrate that the Mg–Si pin-doping in the GaN barrier effectively reduces the polarization-induced electric field between the InGaN well and the GaN barrier in the multiple quantum well, suppresses the quantum-confined Stark effect, and enhances the hole injection and electron confinement in the active region. For this light-emitting diode (LED) device structure, we found that the turn-on voltage is 2.8 V, peak light emission is at 415.3 nm, and internal quantum efficiency is 85.9% at 100 A cm −2 . It is established that the LED device with Mg–Si pin-doping in the GaN barrier has significantly improved efficiency and optical output power performance, and lower efficiency droop up to 400 A cm −2 compared with LED device structures with undoped or Si(Mg)-doped GaN barrier. (paper)

Luminescence of highly excited nonpolar a-plane GaN and AlGaN/GaN multiple quantum wells

International Nuclear Information System (INIS)

Jursenas, S.; Kuokstis, E.; Miasojedovas, S.; Kurilcik, G.; Zukauskas, A.; Chen, C.Q.; Yang, J.W.; Adivarahan, V.; Asif Khan, M.

2004-01-01

Carrier recombination dynamics in polar and nonpolar GaN epilayers and GaN/AlGaN multiple quantum wells grown over sapphire substrates with a various crystallographic orientation were studied under high photoexcitation by 20 ps laser pulses. The transient luminescence featured a significant enhancement on nonradiative recombination of free carriers for nonpolar a-plane GaN epilayers compared to conventional c-plane samples. The epitaxial layer overgrowth technique was demonstrated to significantly improve the quality of nonpolar a-plane films. This was proved by more than 40-fold increase in luminescence decay time (430 ps compared to ≤ 10 ps in the ordinary a-plane epilayer). Under high-excitation regime, a complete screening of built-in electric field by free carriers in multiple quantum wells grown on c-plane and r-plane sapphire substrates was achieved. Under such high excitation, luminescence efficiency and carrier lifetime of multiple quantum wells were shown to be determined by the substrate quality. (author)

Quantum communication for satellite-to-ground networks with partially entangled states

International Nuclear Information System (INIS)

Chen Na; Quan Dong-Xiao; Pei Chang-Xing; Yang-Hong

2015-01-01

To realize practical wide-area quantum communication, a satellite-to-ground network with partially entangled states is developed in this paper. For efficiency and security reasons, the existing method of quantum communication in distributed wireless quantum networks with partially entangled states cannot be applied directly to the proposed quantum network. Based on this point, an efficient and secure quantum communication scheme with partially entangled states is presented. In our scheme, the source node performs teleportation only after an end-to-end entangled state has been established by entanglement swapping with partially entangled states. Thus, the security of quantum communication is guaranteed. The destination node recovers the transmitted quantum bit with the help of an auxiliary quantum bit and specially defined unitary matrices. Detailed calculations and simulation analyses show that the probability of successfully transferring a quantum bit in the presented scheme is high. In addition, the auxiliary quantum bit provides a heralded mechanism for successful communication. Based on the critical components that are presented in this article an efficient, secure, and practical wide-area quantum communication can be achieved. (paper)

Micro-structure Engineering of InGaN/GaN Quantum Wells for High Brightness Light Emitting Devices

KAUST Repository

Shen, Chao

2013-01-01

diameter (D) micro-LED-pillar was achieved, compared to that of a 200 μm diameter LED (20 A/cm2), both at 10 V bias voltage. In addition, an increase in sustained quantum efficiency from 70.2% to 83.7% at high injection current density (200 A/cm2

Phase-locked, high power, mid-infrared quantum cascade laser arrays

Science.gov (United States)

Zhou, W.; Slivken, S.; Razeghi, M.

2018-04-01

We demonstrate phase-locked, high power quantum cascade laser arrays, which are combined using a monolithic, tree array multimode interferometer, with emission wavelengths around 4.8 μm. A maximum output power of 15 W was achieved from an eight-element laser array, which has only a slightly higher threshold current density and a similar slope efficiency compared to a Fabry-Perot laser of the same length. Calculated multimode interferometer splitting loss is on the order of 0.27 dB for the in-phase supermode. In-phase supermode operation with nearly ideal behavior is demonstrated over the working current range of the array.

Entanglement growth and simulation efficiency in one-dimensional quantum lattice systems

OpenAIRE

Perales, Alvaro; Vidal, Guifre

2007-01-01

We study the evolution of one-dimensional quantum lattice systems when the ground state is perturbed by altering one site in the middle of the chain. For a large class of models, we observe a similar pattern of entanglement growth during the evolution, characterized by a moderate increase of significant Schmidt coefficients in all relevant bipartite decompositions of the state. As a result, the evolution can be accurately described by a matrix product state and efficiently simulated using the...

Using an ultra-thin non-doped orange emission layer to realize high efficiency white organic light-emitting diodes with low efficiency roll-off

Energy Technology Data Exchange (ETDEWEB)

Zhu, Liping; Chen, Jiangshan; Ma, Dongge, E-mail: mdg1014@ciac.ac.cn [State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Graduate University of the Chinese Academy of Sciences, Changchun 130022 (China); Zhao, Yongbiao [Luminous Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, Singapore 639798 (Singapore); Zhang, Hongmei [Department of Materials Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China)

2014-06-28

By adopting an ultra-thin non-doped orange emission layer sandwiched between two blue emission layers, high efficiency white organic light-emitting diodes (WOLEDs) with reduced efficiency roll-off were fabricated. The optimized devices show a balanced white emission with Internationale de L'Eclairage of (0.41, 0.44) at the luminance of 1000 cd/m{sup 2}, and the maximum power efficiency, current efficiency (CE), and external quantum efficiency reach 63.2 lm/W, 59.3 cd/A, and 23.1%, which slightly shift to 53.4 lm/W, 57.1 cd/A, and 22.2% at 1000 cd/m{sup 2}, respectively, showing low efficiency roll-off. Detailed investigations on the recombination zone and the transient electroluminescence (EL) clearly reveal the EL processes of the ultra-thin non-doped orange emission layer in WOLEDs.