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Sample records for 1h multiple quantum

  1. Thermal degradation in a trimodal PDMS network by 1H Multiple Quantum NMR

    Giuliani, J R; Gjersing, E L; Chinn, S C; Jones, T V; Wilson, T S; Alviso, C T; Herberg, J L; Pearson, M A; Maxwell, R S

    2007-06-06

    Thermal degradation of a filled, crosslinked siloxane material synthesized from PDMS chains of three different average molecular weights and with two different crosslinking species has been studied by {sup 1}H Multiple Quantum (MQ) NMR methods. Multiple domains of polymer chains were detected by MQ NMR exhibiting Residual Dipolar Coupling (<{Omega}{sub d}>) values of 200 Hz and 600 Hz, corresponding to chains with high average molecular weight between crosslinks and chains with low average molecular weight between crosslinks or near the multifunctional crosslinking sites. Characterization of the <{Omega}{sub d}> values and changes in <{Omega}{sub d}> distributions present in the material were studied as a function of time at 250 C and indicates significant time dependent degradation. For the domains with low <{Omega}{sub d}>, a broadening in the distribution was observed with aging time. For the domain with high <{Omega}{sub d}>, increases in both the mean <{Omega}{sub d}> and the width in <{Omega}{sub d}> were observed with increasing aging time. Isothermal Thermal Gravimetric Analysis (TGA) reveals a 3% decrease in weight over 20 hours of aging at 250 C. Degraded samples also were analyzed by traditional solid state {sup 1}H NMR techniques and offgassing products were identified by Solid Phase MicroExtraction followed by Gas Chromatography-Mass Spectrometry (SPME GC-MS). The results, which will be discussed here, suggest that thermal degradation proceeds by complex competition between oxidative chain scissioning and post-curing crosslinking that both contribute to embrittlement.

  2. Investigation of network heterogeneities in filled, trimodal, highly functional PDMS networks by 1H Multiple Quantum NMR

    Gjersing, E; Chinn, S; Maxwell, R S; Herberg, J; Eastwood, E; Bowen, D; Stephens, T

    2006-09-06

    The segmental order and dynamics of polymer network chains in a filled, tri-modal silicone network have been studied by static 1H Multiple Quantum (MQ) NMR methods to gain insight into the structure property relationships. The materials were synthesized with two different types of crosslinks, with functionalities of 4 and near 60. The network chains were composed of distributions of high, low, and medium molecular weight chains. Crosslinking was accomplished by standard acid catalyzed reactions. MQ NMR methods have detected domains with residual dipolar couplings (<{Omega}{sub d}>) of near 4 kRad/s and 1 kRad/s assigned to (a) the shorter polymer chains and chains near the multifunctional ({phi}=60) crosslinking sites and to (b) the longer polymer chains far from these sites. Three structural variables were systematically varied and the mechanical properties and distributions of residual dipolar couplings measured in order to gain insight in to the network structural motifs that contribute significantly to the composite properties. The partitioning of and the average values of the residual dipolar couplings for the two domains were observed to be dependent on formulation variable and provided increased insight into the mechanical properties of these materials which are unavailable from swelling and spin-echo methods. The results of this study suggest that the domains with high crosslink density contribute significantly to the high strain modulus, while the low crosslink density domains do not. This is in agreement with theories and experimental studies on silicone bimodal networks over the last 20 years. In-situ MQ-NMR of swollen sample suggests that the networks deform non-affinely, in agreement with theory. The NMR experiments shown here provide increased ability to characterize multimodal networks of typical engineering silicone materials and to gain significant insight into structure-property relationships.

  3. Investigation of network heterogeneities in filled, trimodal, highly functional PDMS networks by 1H Multiple Quantum NMR

    Maxwell, R; Gjersing, E; Chinn, S; Giuliani, J; Herberg, J; Eastwood, E; Bowen, D; Stephens, T

    2007-03-20

    The segmental order and dynamics of polymer network chains in a filled, tri-modal silicone foam network have been studied by static 1H Multiple Quantum (MQ) NMR methods to gain insight into the structure property relationships. The foam materials were synthesized with two different types of crosslinks, with functionalities, {phi}, of 4 and near 60. The network chains were composed of distributions of high, low, and medium molecular weight chains. Crosslinking was accomplished by standard acid catalyzed reactions. MQ NMR methods have detected domains with residual dipolar couplings (<{Omega}{sub d}>) of near 4 kRad/s and 1 kRad/s assigned to (a) the shorter polymer chains and chains near the multifunctional (f=60) crosslinking sites and to (b) the longer polymer chains far from these sites. Three structural variables were systematically varied and the mechanical properties via compression and distributions of residual dipolar couplings measured in order to gain insight in to the network structural motifs that contribute significantly to the composite properties. The partitioning of and the average values of the residual dipolar couplings for the two domains were observed to be dependent on formulation variable and provided increased insight into the network structure of these materials which are unavailable from swelling and spin-echo methods. The results of this study suggest that the domains with high crosslink density contribute significantly to the high strain modulus, while the low crosslink density domains do not. This is in agreement with theories and experimental studies on silicone bimodal networks over the last 20 years. In-situ MQ-NMR of swollen sample suggests that the networks deform heterogeneously and non-affinely. The heterogeneity of the deformation process was observed to depend on the amount of the high functionality crosslinking site PMHS. The NMR experiments shown here provide increased ability to characterize multimodal networks of typical

  4. Nitrogen-15 labeled 5S RNA. Identification of uridine base pairs in Escherichia coli 5S RNA by 1H-15N multiple quantum NMR

    Escherichia coli 5S RNA labeled with 15N at N3 of the uridines was isolated from the Sφ-187 uracil auxotroph grown on a minimal medium supplemented with [3-15N]uracil. 1H-15N multiple quantum filtered and 2D chemical shift correlated spectra gave resonances for the uridine imino 1H-15N units whose protons were exchanging slowly with solvent. Peaks with 1H/15N shifts at 11.6/154.8, 11.7/155.0, 11.8/155.5, 12.1/155.0, and 12.2/155.0 ppm were assigned to GU interactions. Two labile high-field AU resonances at 12.6/156.8 and 12.8/157.3 ppm typical of Au pairs in a shielded environment at the end of a helix were seen. Intense AU signals were also found at 13.4/158.5 and 13.6/159.2 ppm where 1H-15N units in normal Watson-Crick pairs resonate. 1H resonances at 10.6 and 13.8 ppm were too weak, presumably because of exchange with water, to give peaks in chemical shift correlated spectra. 1H chemical shifts suggest that the resonance at 13.8 ppm represents a labile AU pair, while the resonance at 10.6 ppm is typical of a tertiary interaction between U and a tightly bound water or a phosphate residue. The NMR data are consistent with proposed secondary structures for 5S RNA

  5. Localized double-quantum-filtered 1H NMR spectroscopy

    Thomas, M. A.; Hetherington, H. P.; Meyerhoff, D. J.; Twieg, D. B.

    The image-guided in vivo spectroscopic (ISIS) pulse sequence has been combined with a double-quantum-filter scheme in order to obtain localized and water-suppressed 1H NMR spectra of J-coupled metabolites. The coherence-transfer efficiency associated with the DQ filter for AX and A 3X spin systems is described. Phantom results of carnosine, alanine, and ethanol in aqueous solution are presented. For comparison, the 1H NMR spectrum of alanine in aqueous solution with the binomial (1331, 2662) spin-echo sequence is also shown.

  6. Quantum Optical Multiple Scattering

    Ott, Johan Raunkjær

    for the dipoles while treating them as quantum two-level systems and using the Born–Markov and rotating-wave approximations. Postponing the rotating-wave approximation to the very end of the formal calculations allows us to identify the different physical parameters of the dipole evolution in terms of...... first part we use a scattering-matrix formalism combined with results from random-matrix theory to investigate the interference of quantum optical states on a multiple scattering medium. We investigate a single realization of a scattering medium thereby showing that it is possible to create entangled...... states by interference of squeezed beams. Mixing photon states on the single realization also shows that quantum interference naturally arises by interfering quantum states. We further investigate the ensemble averaged transmission properties of the quantized light and see that the induced quantum...

  7. Probabilities of multiple quantum teleportation

    Woesler, Richard

    2002-01-01

    Using quantum teleportation a quantum state can be teleported with a certain probability. Here the probabilities for multiple teleportation are derived, i. e. for the case that a teleported quantum state is teleported again or even more than two times, for the two-dimensional case, e. g., for the two orthogonal direcations of the polarization of photons. It is shown that the probability for an exact teleportation, except for an irrelevant phase factor, is 25 %, i. e., surprisingly, this resul...

  8. Quantum Multiple Access Channel

    侯广; 黄民信; 张永德

    2002-01-01

    We consider the transmission of classical information over a quantum channel by many senders, which is a generalization of the two-sender case. The channel capacity region is shown to be a convex hull bound by the yon Neumann entropy and the conditional yon Neumann entropies. The result allows a reasonable distribution of channel capacity over the senders.

  9. Quantum Interference of Multiple Beams Induced by Multiple Scattering

    Ott, Johan Raunkjær; Mortensen, N. Asger; Lodahl, Peter

    2011-01-01

    We report on quantum interference induced by the transmission of quantized light through a multiple-scattering medium. We show that entangled states can be created by multiple-scattering and that quantum interference survives disorder averaging.......We report on quantum interference induced by the transmission of quantized light through a multiple-scattering medium. We show that entangled states can be created by multiple-scattering and that quantum interference survives disorder averaging....

  10. Scattering Induced Quantum Interference of Multiple Quantum Optical States

    Ott, Johan Raunkjær; Wubs, Martijn; Mortensen, N. Asger;

    2011-01-01

    Using a discrete mode theory for propagation of quantum optical states, we investigate the consequences of multiple scattering on the degree of quadrature entanglement and quantum interference. We report that entangled states can be created by multiple-scattering. We furthermore show that quantum...

  11. Quantum internet using code division multiple access

    Zhang, Jing; Liu, Yu-Xi; Özdemir, Şahin Kaya; Wu, Re-Bing; Gao, Feifei; Wang, Xiang-Bin; Yang, Lan; Nori, Franco

    2013-07-01

    A crucial open problem inS large-scale quantum networks is how to efficiently transmit quantum data among many pairs of users via a common data-transmission medium. We propose a solution by developing a quantum code division multiple access (q-CDMA) approach in which quantum information is chaotically encoded to spread its spectral content, and then decoded via chaos synchronization to separate different sender-receiver pairs. In comparison to other existing approaches, such as frequency division multiple access (FDMA), the proposed q-CDMA can greatly increase the information rates per channel used, especially for very noisy quantum channels.

  12. Longitudinal monitoring of metabolic alterations in cuprizone mouse model of multiple sclerosis using 1H-magnetic resonance spectroscopy.

    Orije, Jasmien; Kara, Firat; Guglielmetti, Caroline; Praet, Jelle; Linden, van der, M.; Ponsaerts, Peter; Verhoye, Marleen

    2015-01-01

    Non-invasive measures of well-known pathological hallmarks of multiple sclerosis (MS) such as demyelination, inflammation and axonal injury would serve as useful markers to monitor disease progression and evaluate potential therapies. To this end, in vivo localized proton magnetic resonance spectroscopy ((1)H-MRS) provides a powerful means to monitor metabolic changes in the brain and may be sensitive to these pathological hallmarks. In our study, we used the cuprizone mouse model to study pa...

  13. Multiple-Access Quantum-Classical Networks

    Razavi, Mohsen

    2011-10-01

    A multi-user network that supports both classical and quantum communication is proposed. By relying on optical code-division multiple access techniques, this system offers simultaneous key exchange between multiple pairs of network users. A lower bound on the secure key generation rate will be derived for decoy-state quantum key distribution protocols.

  14. 1H MR spectroscopy of the lumbar spine in bone demineralization of patients suffering from diffuse multiple myeloma or osteoporosis

    Purpose: To evaluate the role of in vivo 1H MR spectroscopic determination of relaxation times and of fat and water content to differentiate between infiltration of multiple myeloma or osteoporosis in patients with roentgenologic nuclear demineralization of the lumbar spine. Results: There were highly significant differences in T2 values and fat content between patients with osteoporosis and multiple myeloma. T2 values were decreased in osteoporosis (37 ms and 59 ms vs. 44 ms and 70 ms in plasmocytoma) and fat content was decreased in multiple myeloma (20% vs 31% and 34% in volunteers and osteoporosis). Between volunteers and patients with osteoporosis the differences in the T2 of the fat component was significantly different. Conclusions: In our preliminary experience MRS is helpful in the differential diagnosis of bony demineralization. It enables a differentiation between osteoporosis and diffuse multiple myeloma. T2 value measurements may be helpful in the diagnostic trial of osteoporosis. (orig./AJ)

  15. Electronic structure of (1e,1h) states of carbon nanotube quantum dots

    Osika, E. N.; B. Szafran

    2016-01-01

    We provide an atomistic tight-binding description of a few carriers confined in ambipolar (n-p) double quantum dots defined in a semiconducting carbon nanotube. We focus our attention on the charge state of the system in which Pauli blockade of the current flow is observed [F. Pei et al., Nat. Nanotechnol. 7, 630 (2012); E. A. Laird et al., ibid 8, 565 (2013)] with a single excess electron in the n-dot and a single hole in the p-dot. We use the configuration interaction approach to determine ...

  16. Quantum teleportation of multiple properties of a single quantum particle

    Wang, Xi-Lin; Su, Zu-En; Chen, Ming-Cheng; Wu, Dian; Li, Li; Liu, Nai-Le; Lu, Chao-Yang; Pan, Jian-Wei

    2014-01-01

    Quantum teleportation provides a "disembodied" way to transfer quantum states of an object over arbitrarily long distance, without physical travelling of the object itself. A single quantum particle can possess various degrees of freedom-internal and external-and with coherent coupling among them. Yet, all the previous experiments were limited to teleportation of a single degree of freedom only. A fundamental open challenge is to simultaneously teleport multiple degrees of freedom which is necessary to fully describe an object, thereby truly teleporting it intactly. Here, we demonstrate the first quantum teleportation of both spin and orbital angular momentum of a single photon, in the form of spin-orbit hybrid entangled states. We use spin-orbit hyper-entangled photon pairs as quantum channel, and develop a new technique to discriminate hyper-entangled Bell state exploiting quantum non-demolition measurement. This work demonstrates an enhanced capability for quantum communications, and moves a step toward co...

  17. (1)H NMR z-spectra of acetate methyl in stretched hydrogels: quantum-mechanical description and Markov chain Monte Carlo relaxation-parameter estimation.

    Shishmarev, Dmitry; Chapman, Bogdan E; Naumann, Christoph; Mamone, Salvatore; Kuchel, Philip W

    2015-01-01

    The (1)H NMR signal of the methyl group of sodium acetate is shown to be a triplet in the anisotropic environment of stretched gelatin gel. The multiplet structure of the signal is due to the intra-methyl residual dipolar couplings. The relaxation properties of the spin system were probed by recording steady-state irradiation envelopes ('z-spectra'). A quantum-mechanical model based on irreducible spherical tensors formed by the three magnetically equivalent spins of the methyl group was used to simulate and fit experimental z-spectra. The multiple parameter values of the relaxation model were estimated by using a Bayesian-based Markov chain Monte Carlo algorithm. PMID:25486634

  18. Electronic structure of (1e,1h) states of carbon nanotube quantum dots

    Osika, E. N.; Szafran, B.

    2016-04-01

    We provide an atomistic tight-binding description of a few carriers confined in ambipolar (n -p ) double quantum dots defined in a semiconducting carbon nanotube. We focus our attention on the charge configuration in which Pauli blockade of the current flow is observed [F. Pei et al., Nat. Nanotechnol. 7, 630 (2012), 10.1038/nnano.2012.160; E. A. Laird et al., Nat. Nanotechnol. 8, 565 (2013), 10.1038/nnano.2013.140] with a single excess electron in the n dot and a single hole in the p dot. We use the configuration interaction approach to determine the spin-valley structure of the states near the neutrality point and discuss its consequences for the interdot exchange interaction, the degeneracy of the energy spectrum, and the symmetry of the confined states. We calculate the transition energies lifting the Pauli blockade and analyze their dependence on the magnetic field vector. Furthermore, we introduce bending of the nanotube and demonstrate its influence on the transition energy spectra. The best qualitative agreement with the experimental data is observed for nanotubes deflected in the gated areas in which the carrier confinement is induced.

  19. Time-domain multiple-quantum NMR

    The development of time-domain multiple-quantum nuclear magnetic resonance is reviewed through mid 1982 and some prospects for future development are indicated. Particular attention is given to the problem of obtaining resolved, interpretable, many-quantum spectra for anisotropic magnetically isolated systems of coupled spins. New results are presented on a number of topics including the optimization of multiple-quantum-line intensities, analysis of noise in two-dimensional spectroscopy, and the use of order-selective excitation for cross polarization between nuclear-spin species

  20. Quantum hyperparallel algorithm for matrix multiplication.

    Zhang, Xin-Ding; Zhang, Xiao-Ming; Xue, Zheng-Yuan

    2016-01-01

    Hyperentangled states, entangled states with more than one degree of freedom, are considered as promising resource in quantum computation. Here we present a hyperparallel quantum algorithm for matrix multiplication with time complexity O(N(2)), which is better than the best known classical algorithm. In our scheme, an N dimensional vector is mapped to the state of a single source, which is separated to N paths. With the assistance of hyperentangled states, the inner product of two vectors can be calculated with a time complexity independent of dimension N. Our algorithm shows that hyperparallel quantum computation may provide a useful tool in quantum machine learning and "big data" analysis. PMID:27125586

  1. 15N and 1H NMR evidence for multiple conformations of the complex of dihydrofolate reductase with its substrate, folate

    The binding of folate to Lactobacillus casei dihydrofolate reductase in the presence and absence of NADP+ has been studied by 15N NMR, using [5-15N]folate. In the presence of NADP+, three separate signals were observed for the single 15N atom, in agreement with our earlier evidence from 1H and 13C NMR for multiple conformations of this complex. The 15N spectra of the binary enzyme-folate complex provide evidence for the first time that this complex also exists in at least two conformational states. This is confirmed by the observation of two separate resonances for the 7-proton of bound folate, located by two-dimensional exchange spectroscopy. 15 refs.; 3 figs.; 1 table

  2. Quantum internet using code division multiple access

    Zhang, Jing; Ozdemir, Sahin Kaya; Wu, Re-Bing; Wang, Xiang-Bin; Nori, Franco

    2012-01-01

    Code division multiple access (CDMA) is a spread-spectrum technology, in which a code is used to spread the spectral content of information to achieve larger network capacity. It has been widely used in classical communication and wireless networks. Here, we extend CDMA to the quantum case, where many pairs of nodes can transmit quantum information through a shared channel. This can be achieved by chaotic encoding of quantum information to spread its spectral content and by chaos synchronization, to separate different sender-receiver pairs. The proposed method is robust to low-frequency noise, and achieves faithful transmission with fidelities of up to 0.99.

  3. Quantum hyperparallel algorithm for matrix multiplication

    Zhang, Xin-Ding; Zhang, Xiao-Ming; Xue, Zheng-Yuan

    2016-01-01

    Hyperentangled states, entangled states with more than one degree of freedom, are considered as promising resource in quantum computation. Here we present a hyperparallel quantum algorithm for matrix multiplication with time complexity O(N2), which is better than the best known classical algorithm. In our scheme, an N dimensional vector is mapped to the state of a single source, which is separated to N paths. With the assistance of hyperentangled states, the inner product of two vectors can be calculated with a time complexity independent of dimension N. Our algorithm shows that hyperparallel quantum computation may provide a useful tool in quantum machine learning and “big data” analysis. PMID:27125586

  4. Multiple exciton generation effect in quantum dots

    Full text: Recently among various investigations in the field of nanophysics a great intensification in studying of multiple exciton generation (MEG) effect in quantum dots at absorption of photons with the energy several times higher than the gap in electronic spectra (hν>>Eg) has been made [1-2]. There have been proposed four theoretical approaches to explain the MEG effect. However, the statistic approach basing on the Fermi theory of multiple pi-mesons generation (1950) is the most adequate related to others. In this work: 1. the results of statistic approach have been generalized; 2. the microscopic mechanism basing on theory of electronic 'shaking' has been proposed; 3. the problem of deviation of mean multiplicity of MEG effect from the Poisson law of fluctuations has been investigated that is a evidence of strong non-linear and non-equilibrium character of exciton generation process; 4. the role of interface electronic states of quantum dot and ligand has been considered by means of perturbation theory of closed states related to surface Tamm electronic states of quantum dot and legend; 5. the problem of size optimization of quantum dot to receive the maximum multiplicity has been studied; 6. the efficiency of MEG effect for the third generation of solar cells has been calculated on the basis of proposed theory. (authors)

  5. Selectivity in multiple quantum nuclear magnetic resonance

    The observation of multiple-quantum nuclear magnetic resonance transitions in isotropic or anisotropic liquids is shown to give readily interpretable information on molecular configurations, rates of motional processes, and intramolecular interactions. However, the observed intensity of high multiple-quantum transitions falls off dramatically as the number of coupled spins increases. The theory of multiple-quantum NMR is developed through the density matrix formalism, and exact intensities are derived for several cases (isotropic first-order systems and anisotropic systems with high symmetry) to shown that this intensity decrease is expected if standard multiple-quantum pulse sequences are used. New pulse sequences are developed which excite coherences and produce population inversions only between selected states, even though other transitions are simultaneously resonant. One type of selective excitation presented only allows molecules to absorb and emit photons in groups of n. Coherent averaging theory is extended to describe these selective sequences, and to design sequences which are selective to arbitrarily high order in the Magnus expansion. This theory and computer calculations both show that extremely good selectivity and large signal enhancements are possible

  6. Organocatalytic asymmetric Henry reaction of 1H-pyrrole-2,3-diones with bifunctional amine-thiourea catalysts bearing multiple hydrogen-bond donors.

    Zhang, Ming-Liang; Yue, Deng-Feng; Wang, Zhen-Hua; Luo, Yuan; Xu, Xiao-Ying; Zhang, Xiao-Mei; Yuan, Wei-Cheng

    2016-01-01

    For the first time, a catalytic asymmetric Henry reaction of 1H-pyrrole-2,3-diones was achieved with a chiral bifunctional amine-thiourea as a catalyst possessing multiple hydrogen-bond donors. With this developed method, a range of 3-hydroxy-3-nitromethyl-1H-pyrrol-2(3H)-ones bearing quaternary stereocenters were obtained in acceptable yield (up to 75%) and enantioselectivity (up to 73% ee). PMID:26977188

  7. Spatial Quantum Correlations Induced by Multiple Scattering of Light

    Lodahl, Peter; Lagendijk, Ad

    2006-01-01

    It is experimentally demonstrated how quantum noise of light is transported through a multiple scattering random medium. We predict the existence of novel spatial quantum correlations that are induced by multiple scattering.......It is experimentally demonstrated how quantum noise of light is transported through a multiple scattering random medium. We predict the existence of novel spatial quantum correlations that are induced by multiple scattering....

  8. Spin-orbit interaction in multiple quantum wells

    Hao, Ya-Fei, E-mail: haoyafei@zjnu.cn [Physics Department, Zhejiang Normal University, Zhejiang 321004 (China)

    2015-01-07

    In this paper, we investigate how the structure of multiple quantum wells affects spin-orbit interactions. To increase the interface-related Rashba spin splitting and the strength of the interface-related Rashba spin-orbit interaction, we designed three kinds of multiple quantum wells. We demonstrate that the structure of the multiple quantum wells strongly affected the interface-related Rashba spin-orbit interaction, increasing the interface-related Rashba spin splitting to up to 26% larger in multiple quantum wells than in a stepped quantum well. We also show that the cubic Dresselhaus spin-orbit interaction similarly influenced the spin relaxation time of multiple quantum wells and that of a stepped quantum well. The increase in the interface-related Rashba spin splitting originates from the relationship between interface-related Rashba spin splitting and electron probability density. Our results suggest that multiple quantum wells can be good candidates for spintronic devices.

  9. Multiple-Access Quantum Key Distribution Networks

    Razavi, Mohsen

    2011-01-01

    This paper addresses multi-user quantum key distribution networks, in which any two users can mutually exchange a secret key without trusting any other nodes. The same network also supports conventional classical communications by assigning two different wavelength bands to quantum and classical signals. Time and code division multiple access (CDMA) techniques, within a passive star network, are considered. In the case of CDMA, it turns out that the optimal performance is achieved at a unity code weight. A listen-before-send protocol is then proposed to improve secret key generation rates in this case. Finally, a hybrid setup with wavelength routers and passive optical networks, which can support a large number of users, is considered and analyzed.

  10. Quantum optics in multiple scattering random media

    Lodahl, Peter

    Quantum Optics in Multiple Scattering Random Media Peter Lodahl Research Center COM, Technical University of Denmark, Dk-2800 Lyngby, Denmark. Coherent transport of light in a disordered random medium has attracted enormous attention both from a fundamental and application point of view. Coherent...... correla-tions that should be readily attainable experimentally is devised. Figure 1. Inverse total transmission of shot noise (left) and technical noise (right) as a function of the thickness of the ran-dom medium. The experimental data are well explained by theory (curves). [1] J. Tworzydlo and C...

  11. Quantum Interference and Entanglement Induced by Multiple Scattering of Light

    Ott, Johan Raunkjær; Mortensen, Asger; Lodahl, Peter

    2010-01-01

    We report on the effects of quantum interference induced by the transmission of an arbitrary number of optical quantum states through a multiple-scattering medium. We identify the role of quantum interference on the photon correlations and the degree of continuous variable entanglement between two...... output modes. It is shown that quantum interference survives averaging over all ensembles of disorder and manifests itself as increased photon correlations due to photon antibunching. Furthermore, the existence of continuous variable entanglement correlations in a volume speckle pattern is predicted. Our...... results suggest that multiple scattering provides a promising way of coherently interfering many independent quantum states of light of potential use in quantum information processing....

  12. Nonadditivity of quantum capacities of quantum multiple-access channels and the butterfly network

    Multipartite quantum information transmission without additional classical resources is investigated. We show purely quantum superadditivity of quantum capacity regions of quantum memoryless multiple-access (MA) channels, which are not entanglement breaking. Also, we find that the superadditivity holds when the MA channel extends to the quantum butterfly network, which can achieve quantum network coding. The present widespread effects for the channels which enable entanglement distribution have not been revealed for multipartite scenarios.

  13. Quantum Cosmological Perturbations of Multiple Fluids

    Peter, Patrick; Vitenti, Sandro Dias Pinto

    2015-01-01

    The formalism to treat quantization and evolution of cosmological perturbations of multiple fluids is described. We first construct the Lagrangian for both the gravitational and matter parts, providing the necessary relevant variables and momenta leading to the quadratic Hamiltonian describing linear perturbations. The final Hamiltonian is obtained without assuming any equations of motions for the background variables. This general formalism is applied to the special case of two fluids, having in mind the usual radiation and matter mix which made most of our current Universe history. Quantization is achieved using an adiabatic expansion of the basis functions. This allows for an unambiguous definition of a vacuum state up to the given adiabatic order. Using this basis, we show that particle creation is well defined for a suitable choice of vacuum and canonical variables, so that the time evolution of the corresponding quantum fields is unitary. This provides constraints for setting initial conditions for an a...

  14. On Multiplicative Linear Logic, Modality and Quantum Circuits

    Ugo Dal Lago

    2012-10-01

    Full Text Available A logical system derived from linear logic and called QMLL is introduced and shown able to capture all unitary quantum circuits. Conversely, any proof is shown to compute, through a concrete GoI interpretation, some quantum circuits. The system QMLL, which enjoys cut-elimination, is obtained by endowing multiplicative linear logic with a quantum modality.

  15. Experimental demonstration of spatial quantum correlations in multiple scattering media

    Smolka, Stephan; Huck, Alexander; Andersen, Ulrik Lund; Lagendijk, Ad; Lodahl, Peter

    We demonstrate that spatial quantum correlations are induced by multiple scattering of squeezed light. The correlation relates multiple scattered photons at different spatial positions, and is tunable by varying photon fluctuations of the illuminating beam.......We demonstrate that spatial quantum correlations are induced by multiple scattering of squeezed light. The correlation relates multiple scattered photons at different spatial positions, and is tunable by varying photon fluctuations of the illuminating beam....

  16. Study of correlations in molecular motion by multiple quantum NMR

    Nuclear magnetic resonance is a very useful tool for characterizing molecular configurations through the measurement of transition frequencies and dipolar couplings. The measurement of spectral lineshapes, spin-lattice relaxation times, and transverse relaxation times also provide us with valuable information about correlations in molecular motion. The new technique of multiple quantum nuclear magnetic resonance has numerous advantages over the conventional single quantum NMR techniques in obtaining information about static and dynamic interactions of coupled spin systems. In the first two chapters, the theoretical background of spin Hamiltonians and the density matrix formalism of multiple quantum NMR is discussed. The creation and detection of multiple quantum coherence by multiple pulse sequence are discussed. Prototype multiple quantum spectra of oriented benzene are presented. Redfield relaxation theory and the application of multiple quantum NMR to the study of correlations in fluctuations are presented. A specific example of an oriented methyl group relaxed by paramagnetic impurities is studied in detail. The study of possible correlated motion between two coupled methyl groups by multiple quantum NMR is presented. For a six spin system it is shown that the four-quantum spectrum is sensitive to two-body correlations, and serves a ready test of correlated motion. The study of the spin-lattice dynamics of orienting or tunneling methyl groups (CH3 and CD3) at low temperatures is presented. The anisotropic spin-lattice relaxation of deuterated hexamethylbenzene, caused by the sixfold reorientation of the molecules, is investigated, and the NMR spectrometers and other experimental details are discussed

  17. Quantum broadcasting multiple blind signature with constant size

    Xiao, Min; Li, Zhenli

    2016-06-01

    Using quantum homomorphic signature in quantum network, we propose a quantum broadcasting multiple blind signature scheme. Different from classical signature and current quantum signature schemes, the multi-signature proposed in our scheme is not generated by simply putting the individual signatures together, but by aggregating the individual signatures based on homomorphic property. Therefore, the size of the multi-signature is constant. Furthermore, based on a wide range of investigation for the security of existing quantum signature protocols, our protocol is designed to resist possible forgery attacks against signature and message from the various attack sources and disavowal attacks from participants.

  18. Multiple Quantum NMR Investigations of Structure- Property Relationships in Synthetic and Aged Silicone Elastomers

    Maxwell, R; Gjersing, E; Chinn, S; Herberg, J; Eastwood, E; Bowen, D; Stephens, T

    2006-09-27

    Complex engineering elastomeric materials are often characterized by a complex network structure obtained by crosslinking network chains with multiple chain lengths. Further, these networks are commonly filled with thixotropic reinforcing agents such as SiO{sub 2} or carbon black. Degradation of such materials often occurs via mechanisms that alter the fundamental network structure. In order to understand the effects of modifications of network structure and filler-polymer interaction on component performance, a series of model compounds have been studied by {sup 1}H multiple quantum NMR analysis and traditional mechanical property assessments. The {sup 1}H NMR data provides insight into the distribution of segmental dynamics that reveals insight into the changes in mechanical properties.

  19. Secure Multiparty Quantum Computation for Summation and Multiplication.

    Shi, Run-hua; Mu, Yi; Zhong, Hong; Cui, Jie; Zhang, Shun

    2016-01-01

    As a fundamental primitive, Secure Multiparty Summation and Multiplication can be used to build complex secure protocols for other multiparty computations, specially, numerical computations. However, there is still lack of systematical and efficient quantum methods to compute Secure Multiparty Summation and Multiplication. In this paper, we present a novel and efficient quantum approach to securely compute the summation and multiplication of multiparty private inputs, respectively. Compared to classical solutions, our proposed approach can ensure the unconditional security and the perfect privacy protection based on the physical principle of quantum mechanics. PMID:26792197

  20. Quantum filtering for multiple diffusive and Poissonian measurements

    We provide a rigorous derivation of a quantum filter for the case of multiple measurements being made on a quantum system. We consider a class of measurement processes which are functions of bosonic field operators, including combinations of diffusive and Poissonian processes. This covers the standard cases from quantum optics, where homodyne detection may be described as a diffusive process and photon counting may be described as a Poissonian process. We obtain a necessary and sufficient condition for any pair of such measurements taken at different output channels to satisfy a commutation relationship. Then, we derive a general, multiple-measurement quantum filter as an extension of a single-measurement quantum filter. As an application we explicitly obtain the quantum filter corresponding to homodyne detection and photon counting at the output ports of a beam splitter. (paper)

  1. Multiplicity-free Quantum 6 j-Symbols for

    Nawata, Satoshi; Pichai, Ramadevi; Zodinmawia

    2013-12-01

    We conjecture a closed form expression for the simplest class of multiplicity-free quantum 6 j-symbols for . The expression is a natural generalization of the quantum 6 j-symbols for obtained by Kirillov and Reshetikhin. Our conjectured form enables computation of colored HOMFLY polynomials for various knots and links carrying arbitrary symmetric representations.

  2. Multiple-server Flexible Blind Quantum Computation in Networks

    Kong, Xiaoqin; Li, Qin; Wu, Chunhui; Yu, Fang; He, Jinjun; Sun, Zhiyuan

    2016-06-01

    Blind quantum computation (BQC) can allow a client with limited quantum power to delegate his quantum computation to a powerful server and still keep his own data private. In this paper, we present a multiple-server flexible BQC protocol, where a client who only needs the ability of accessing qua ntum channels can delegate the computational task to a number of servers. Especially, the client's quantum computation also can be achieved even when one or more delegated quantum servers break down in networks. In other words, when connections to certain quantum servers are lost, clients can adjust flexibly and delegate their quantum computation to other servers. Obviously it is trivial that the computation will be unsuccessful if all servers are interrupted.

  3. Study of correlations in molecular motion by multiple quantum NMR

    Tang, J.H.

    1981-11-01

    Nuclear magnetic resonance is a very useful tool for characterizing molecular configurations through the measurement of transition frequencies and dipolar couplings. The measurement of spectral lineshapes, spin-lattice relaxation times, and transverse relaxation times also provide us with valuable information about correlations in molecular motion. The new technique of multiple quantum nuclear magnetic resonance has numerous advantages over the conventional single quantum NMR techniques in obtaining information about static and dynamic interactions of coupled spin systems. In the first two chapters, the theoretical background of spin Hamiltonians and the density matrix formalism of multiple quantum NMR is discussed. The creation and detection of multiple quantum coherence by multiple pulse sequence are discussed. Prototype multiple quantum spectra of oriented benzene are presented. Redfield relaxation theory and the application of multiple quantum NMR to the study of correlations in fluctuations are presented. A specific example of an oriented methyl group relaxed by paramagnetic impurities is studied in detail. The study of possible correlated motion between two coupled methyl groups by multiple quantum NMR is presented. For a six spin system it is shown that the four-quantum spectrum is sensitive to two-body correlations, and serves a ready test of correlated motion. The study of the spin-lattice dynamics of orienting or tunneling methyl groups (CH/sub 3/ and CD/sub 3/) at low temperatures is presented. The anisotropic spin-lattice relaxation of deuterated hexamethylbenzene, caused by the sixfold reorientation of the molecules, is investigated, and the NMR spectrometers and other experimental details are discussed.

  4. Frequency domain quantum optimal control under multiple constraints

    Shu, Chuan-Cun; Ho, Tak-San; Xing, Xi; Rabitz, Herschel

    2016-03-01

    Optimal control of quantum systems with complex constrained external fields is one of the longstanding theoretical and numerical challenges at the frontier of quantum control research. Here, we present a theoretical method that can be utilized to optimize the control fields subject to multiple constraints while guaranteeing monotonic convergence towards desired physical objectives. This optimization method is formulated in the frequency domain in line with the current ultrafast pulse shaping technique, providing the possibility for performing quantum optimal control simulations and experiments in a unified fashion. For illustrations, this method is successfully employed to perform multiple constraint spectral-phase-only optimization for maximizing resonant multiphoton transitions with desired pulses.

  5. Computer studies of multiple-quantum spin dynamics

    Murdoch, J.B.

    1982-11-01

    The excitation and detection of multiple-quantum (MQ) transitions in Fourier transform NMR spectroscopy is an interesting problem in the quantum mechanical dynamics of spin systems as well as an important new technique for investigation of molecular structure. In particular, multiple-quantum spectroscopy can be used to simplify overly complex spectra or to separate the various interactions between a nucleus and its environment. The emphasis of this work is on computer simulation of spin-system evolution to better relate theory and experiment.

  6. Computer studies of multiple-quantum spin dynamics

    The excitation and detection of multiple-quantum (MQ) transitions in Fourier transform NMR spectroscopy is an interesting problem in the quantum mechanical dynamics of spin systems as well as an important new technique for investigation of molecular structure. In particular, multiple-quantum spectroscopy can be used to simplify overly complex spectra or to separate the various interactions between a nucleus and its environment. The emphasis of this work is on computer simulation of spin-system evolution to better relate theory and experiment

  7. Transferring Quantum Information through the Quantum Channel using Synchronous Multiplexing for Multiple users

    H.R.Sumathi

    2015-03-01

    Full Text Available Transmission of information in the form of qubits much faster than the speed of light is the important aspects of quantum information theory. Quantum information processing exploits the quantum nature of information that needs to be stored, encoded, transmit, receive and decode the information in the form of qubits. Bosonic channels appear to be very attractive for the physical implementation of quantum communication. This paper does the study of quantum channels and how best it can be implemented with the existing infrastructure that is the classical communication. Multiple access to the quantum network is the requirement where multiple users want to transmit their quantum information simultaneously without interfering with each others.

  8. 31 P and two-dimensional 31 P-1 H NMR analysis of brain extracts in animal models of multiple sclerosis

    We report here the study of the brain phospholipid content of normal and myelin deficient (md) rats, which develop a physiological impairment at about 15-20 days, and die at 20-25 days of age. The aim is to gain insights into the lipid composition of developing brain, and also to reveal of there exist some early event in the phospholipid metabolism that produces a pathological condition similar to the formation of demyelination plaques in multiple sclerosis. 31 P NMR allows one to detect phospholipids selectively out of a complex lipid mixture in crude extracts. Two-dimensional (2D) 31 P-1H NMR with isotropic proton mixing seems to be a superior technique for assignment of phospholipid 31 P resonances. (author)

  9. Multiple choices of time in quantum cosmology

    Malkiewicz, Przemyslaw

    2014-01-01

    It is often conjectured that a choice of time function merely sets up a frame for the quantum evolution of gravitational field, meaning that all choices should be in some sense compatible. In order to explore this conjecture (and the meaning of compatibility), we develop suitable tools for determining the relation between quantum theories based on different time functions. First, we discuss how a time function fixes a canonical structure on the constraint surface. The presentation includes both the kinematical and the reduced perspective, and the relation between them. Second, we formulate twin theorems about the existence of two inequivalent maps between any two deparameterizations, a {\\it formal canonical} and a {\\it coordinate} one. They are used to separate the effect of choice of clock from other effects. We show, in an example, how the spectra of quantum observables are transformed under the change of clock and prove, via a general argument, the existence of choice-of-time-induced semiclassical effects....

  10. On Quantum Algorithm for Multiple Alignment of Amino Acid Sequences

    Iriyama, Satoshi; Ohya, Masanori

    2009-02-01

    The alignment of genome sequences or amino acid sequences is one of fundamental operations for the study of life. Usual computational complexity for the multiple alignment of N sequences with common length L by dynamic programming is O(LN). This alignment is considered as one of the NP problems, so that it is desirable to find a nice algorithm of the multiple alignment. Thus in this paper we propose the quantum algorithm for the multiple alignment based on the works12,1,2 in which the NP complete problem was shown to be the P problem by means of quantum algorithm and chaos information dynamics.

  11. A Hybrid Quantum Search Engine: A Fast Quantum Algorithm for Multiple Matches

    Younes, A; Miller, J; Younes, Ahmed; Rowe, Jon; Miller, Julian

    2003-01-01

    In this paper we will present a quantum algorithm which works very efficiently in case of multiple matches within the search space and in the case of few matches, the algorithm performs classically. This allows us to propose a hybrid quantum search engine that integrates Grover's algorithm and the proposed algorithm here to have general performance better that any pure classical or quantum search algorithm.

  12. Multiplicity-free Quantum 6j-Symbols for

    Nawata, Satoshi; Ramadevi, P.; Zodinmawia

    2013-01-01

    We conjecture a closed form expression for the simplest class of multiplicity-free quantum 6j-symbols for U_q(sl_N). The expression is a natural generalization of the quantum 6j-symbols for U_q(sl_2) obtained by Kirillov and Reshetikhin. Our conjectured form enables computation of colored HOMFLY polynomials for various knots and links carrying arbitrary symmetric representations.

  13. Quantum correlations induced by multiple scattering of quadrature squeezed light

    Lodahl, Peter

    2006-01-01

    Propagating quadrature squeezed light through a multiple scattering random medium is found to induce pronounced spatial quantum correlations that have no classical analogue. The correlations are revealed in the number of photons transported through the sample that can be measured from the intensity...... fluctuations of the total transmission or reflection. In contrast, no pronounced spatial quantum correlations appear in the quadrature amplitudes where excess noise above the shot noise level is found....

  14. Multiple Scattering of Quantum Optical States

    Ott, Johan Raunkjær; Mortensen, N. Asger; Lodahl, Peter

    2011-01-01

    Wave propagation through multiple scattering media has been an active research field since the discovery of Anderson localization [1]. This interest has amongst other resulted in the discovery of classical wave phenomena such as enhanced coherent back scattering [2] and universal conductance...

  15. Perfect transfer of multiple excitations in quantum networks

    Brougham, T; Jex, I; 10.1103/PhysRevA.83.022323

    2011-01-01

    We present a general formalism to the problem of perfect state-transfer (PST), where the state involves multiple excitations of the quantum network. A key feature of our formalism is that it allows for inclusion of nontrivial interactions between the excitations. Hence, it is perfectly suited to addressing the problem of PST in the context of various types of physical realizations. The general formalism is also flexible enough to account for situations where multiple excitations are "focused" onto the same site.

  16. Optimum testing of multiple hypotheses in quantum detection theory

    Yuen, H. P.; Kennedy, R. S.; Lax, M.

    1975-01-01

    The problem of specifying the optimum quantum detector in multiple hypotheses testing is considered for application to optical communications. The quantum digital detection problem is formulated as a linear programming problem on an infinite-dimensional space. A necessary and sufficient condition is derived by the application of a general duality theorem specifying the optimum detector in terms of a set of linear operator equations and inequalities. Existence of the optimum quantum detector is also established. The optimality of commuting detection operators is discussed in some examples. The structure and performance of the optimal receiver are derived for the quantum detection of narrow-band coherent orthogonal and simplex signals. It is shown that modal photon counting is asymptotically optimum in the limit of a large signaling alphabet and that the capacity goes to infinity in the absence of a bandwidth limitation.

  17. Multiple Nuclear Polarization States in a Double Quantum Dot

    Danon, J.; Vink, I.T.; Koppens, F.H.L.; Nowack, K.C.; Vandersypen, L.M.K.; Nazarov, Y.V.

    2009-01-01

    We observe multiple stable states of nuclear polarization and nuclear self-tuning over a large range of fields in a double quantum dot under conditions of electron spin resonance. The observations can be understood within an elaborated theoretical rate equation model for the polarization in each of

  18. Detection of electromagnetic radiation using micromechanical multiple quantum wells structures

    Datskos, Panagiotis G [Knoxville, TN; Rajic, Slobodan [Knoxville, TN; Datskou, Irene [Knoxville, TN

    2007-07-17

    An apparatus and method for detecting electromagnetic radiation employs a deflectable micromechanical apparatus incorporating multiple quantum wells structures. When photons strike the quantum-well structure, physical stresses are created within the sensor, similar to a "bimetallic effect." The stresses cause the sensor to bend. The extent of deflection of the sensor can be measured through any of a variety of conventional means to provide a measurement of the photons striking the sensor. A large number of such sensors can be arranged in a two-dimensional array to provide imaging capability.

  19. Quantum critical matter. Quantum phase transitions with multiple dynamics and Weyl superconductors

    In this PhD thesis, the physics of quantum critical matter and exotic quantum state close to quantum phase transitions is investigated. We will focus on three different examples that highlight some of the interesting phenomena related to quantum phase transitions. Firstly, we discuss the physics of quantum phase transitions in quantum wires as a function of an external gate voltage when new subbands are activated. We find that at these transitions, strong correlations lead to the formation of an impenetrable gas of polarons, and identify criteria for possible instabilities in the spin- and charge sectors of the model. Our analysis is based on the combination of exact resummations, renormalization group techniques and Luttinger liquid approaches. Secondly, we turn to the physics of multiple divergent time scales close to a quantum critical point. Using an appropriately generalized renormalization group approach, we identify that the presence of multiple dynamics at a quantum phase transition can lead to the emergence of new critical scaling exponents and thus to the breakdown of the usual scaling schemes. We calculate the critical behavior of various thermodynamic properties and detail how unusual physics can arise. It is hoped that these results might be helpful for the interpretation of experimental scaling puzzles close to quantum critical points. Thirdly, we turn to the physics of topological transitions, and more precisely the physics of Weyl superconductors. The latter are the superconducting variant of the topologically non-trivial Weyl semimetals, and emerge at the quantum phase transition between a topological superconductor and a normal insulator upon perturbing the transition with a time reversal symmetry breaking perturbation, such as magnetism. We characterize the topological properties of Weyl superconductors and establish a topological phase diagram for a particular realization in heterostructures. We discuss the physics of vortices in Weyl

  20. Formal power series arising from multiplication of quantum integers

    Nathanson, Melvyn B.

    2003-01-01

    For the quantum integer [n]_q = 1+q+q^2+... + q^{n-1} there is a natural polynomial multiplication such that [mn]_q = [m]_q \\otimes_q [n]_q. This multiplication is given by the functional equation f_{mn}(q) = f_m(q) f_n(q^m), defined on a sequence {f_n(q)} of polynomials such that f_n(0)=1 for all n. It is proved that if {f_n(q)} is a solution of this functional equation, then the sequence {f_n(q)} converges to a formal power series F(q). Quantum mulitplication also leads to the functional eq...

  1. Quantum teleportation scheme by selecting one of multiple output ports

    Ishizaka, Satoshi; Hiroshima, Tohya

    2009-01-01

    The scheme of quantum teleportation, where Bob has multiple (N) output ports and obtains the teleported state by simply selecting one of the N ports, is thoroughly studied. We consider both deterministic version and probabilistic version of the teleportation scheme aiming to teleport an unknown state of a qubit. Moreover, we consider two cases for each version: (i) the state employed for the teleportation is fixed to a maximally entangled state, and (ii) the state is also optimized as well as...

  2. Multiple Quantum Well AlGaAs Nanowires

    Chen, C.; Braidy, N.; Couteau, C.; Fradin, C.; Weihs, G.; LaPierre, R.

    2008-01-01

    This letter reports on the growth, structure and luminescent properties of individual multiple quantum well (MQW) AlGaAs nanowires (NWs). The composition modulations (MQWs) are obtained by alternating the elemental flux of Al and Ga during the molecular beam epitaxy growth of the AlGaAs wire on GaAs (111)B substrates. Transmission electron microscopy and energy dispersive X-ray spectroscopy performed on individual NWs are consistent with a configuration composed of conical segments stacked al...

  3. Lecture notes on Gaussian multiplicative chaos and Liouville Quantum Gravity

    Rhodes, Rémi; Vargas, Vincent

    2016-01-01

    The purpose of these notes, based on a course given by the second author at Les Houches summer school, is to explain the probabilistic construction of Polyakov's Liouville quantum gravity using the theory of Gaussian multiplicative chaos. In particular, these notes contain a detailed description of the so-called Liouville measures of the theory and their conjectured relation to the scaling limit of large planar maps properly embedded in the sphere. These notes are rather short and require no ...

  4. Quantum superposition of multiple clones and the novel cloning machine

    Pati, Arun Kumar

    1999-01-01

    we envisage a novel quantum cloning machine, which takes an input state and produces an output state whose success branch can exist in a linear superposition of multiple copies of the input state and the failure branch exist in a superposition of composite state independent of the input state. We prove that unknown non-orthogonal states chosen from a set $\\cal S$ can evolve into a linear superposition of multiple clones by a unitary process if and only if the states are linearly independent. ...

  5. A functional equation arising from multiplication of quantum integers

    Nathanson, Melvyn B.

    2002-01-01

    For the quantum integer $[n]_q = 1+q+...+q^{n-1}$ there is a natural polynomial multiplication $*_q$ such that $[m]_q *_q [n]_q = [mn]_q$. This multiplication leads to the functional equation $f_{mn}(q) = f_m(q)f_n(q^m),$ defined on a given sequence $\\mathcal(F)=\\{f_n(q)\\}_{n=1}^{\\infty}$ of polynomials. This paper contains various results concerning the classification and construction of polynomial sequences that satisfy the functional equation, as well as a list of open problems that arise ...

  6. Controllable multiple-quantum transitions in a T-shaped small quantum dot-ring system

    Chen, Xiongwen; Chen, Baoju; Song, Kehui; Zhou, Guanghui

    2016-05-01

    Based on the tight-binding model and the slave boson mean field approximation, we investigate the electron transport properties in a small quantum dot (QD)-ring system. Namely, a strongly correlated QD not only attaches directly to two normal metallic electrodes, but also forms a magnetic control Aharonov-Bohm quantum ring with a few noninteracting QDs. We show that the parity effect, the Kondo effect, and the multiple Fano effects coexist in our system. Moreover, the parities, defined by the odd- and even-numbered energy levels in this system, can be switched by adjusting magnetic flux phase ϕ located at the center of the quantum ring, which induces multiple controllable Fano-interference energy pathways. Therefore, the constructive and destructive multi-Fano interference transition, the Kondo and Fano resonance transition at the Fermi level, the Fano resonance and ani-resonance transition are realized in the even parity system. They can also be observed in the odd parity system when one adjusts the phase ϕ and the gate voltage Vg applied to the noninteracting QDs. The multi-quantum transitions determine some interesting transport properties such as the current switch and its multi-flatsteps, the differential conductance switch at zero bias voltage and its oscillation or quantization at the low bias voltage. These results may be useful for the observation of multiple quantum effect interplays experimentally and the design of controllable QD-based device.

  7. Improvement of a quantum broadcasting multiple blind signature scheme based on quantum teleportation

    Zhang, Wei; Qiu, Daowen; Zou, Xiangfu

    2016-06-01

    Recently, a broadcasting multiple blind signature scheme based on quantum teleportation has been proposed for the first time. It is claimed to have unconditional security and properties of quantum multiple signature and quantum blind signature. In this paper, we analyze the security of the protocol and show that each signatory can learn the signed message by a single-particle measurement and the signed message can be modified at random by any attacker according to the scheme. Furthermore, there are some participant attacks and external attacks existing in the scheme. Finally, we present an improved scheme and show that it can resist all of the mentioned attacks. Additionally, the secret keys can be used again and again, making it more efficient and practical.

  8. Improvement of a quantum broadcasting multiple blind signature scheme based on quantum teleportation

    Zhang, Wei; Qiu, Daowen; Zou, Xiangfu

    2016-03-01

    Recently, a broadcasting multiple blind signature scheme based on quantum teleportation has been proposed for the first time. It is claimed to have unconditional security and properties of quantum multiple signature and quantum blind signature. In this paper, we analyze the security of the protocol and show that each signatory can learn the signed message by a single-particle measurement and the signed message can be modified at random by any attacker according to the scheme. Furthermore, there are some participant attacks and external attacks existing in the scheme. Finally, we present an improved scheme and show that it can resist all of the mentioned attacks. Additionally, the secret keys can be used again and again, making it more efficient and practical.

  9. Mixed-time parallel evolution in multiple quantum NMR experiments: sensitivity and resolution enhancement in heteronuclear NMR

    A new strategy is demonstrated that simultaneously enhances sensitivity and resolution in three- or higher-dimensional heteronuclear multiple quantum NMR experiments. The approach, referred to as mixed-time parallel evolution (MT-PARE), utilizes evolution of chemical shifts of the spins participating in the multiple quantum coherence in parallel, thereby reducing signal losses relative to sequential evolution. The signal in a given PARE dimension, t1, is of a non-decaying constant-time nature for a duration that depends on the length of t2, and vice versa, prior to the onset of conventional exponential decay. Line shape simulations for the 1H-15N PARE indicate that this strategy significantly enhances both sensitivity and resolution in the indirect 1H dimension, and that the unusual signal decay profile results in acceptable line shapes. Incorporation of the MT-PARE approach into a 3D HMQC-NOESY experiment for measurement of HN-HN NOEs in KcsA in SDS micelles at 50oC was found to increase the experimental sensitivity by a factor of 1.7±0.3 with a concomitant resolution increase in the indirectly detected 1H dimension. The method is also demonstrated for a situation in which homonuclear 13C-13C decoupling is required while measuring weak H3'-2'OH NOEs in an RNA oligomer

  10. A QUANTUM MULTIPLE ACCESS COMMUNICATIONS SCHEME USING ORBITAL ANGULAR MOMENTUM

    Dong Xiaoliang; Zhao Shengmei; Zheng Baoyu

    2013-01-01

    We propose a quantum multiple access communications scheme using Orbital Angular Momentum (OAM) sector states in the paper.In the scheme,each user has an individual modified Poincare Bloch sphere and encodes his information with his own corresponding sector OAM states.A prepared entangled photon pairs are separated at transmitter and receiver.At the transmitter,each user encodes his information with the sector OAM states on the photons and the superposition of the different sector OAM states is carried by the photons.Then the photons are transmitted through quantum noiseless channel to the receiver.At the receiver,each user could retrieve his information by coincidently measuring the transmitted photons with the receiver side photons which are modulated by a special prepared measurement basis.The theoretical analysis and the numerical simulations show that each user could get his information from the superposition state without error.It seems that this scheme provides a novel method for quantum multiple users communications.

  11. Robust Multiple-Range Coherent Quantum State Transfer

    Chen, Bing; Peng, Yan-Dong; Li, Yong; Qian, Xiao-Feng

    2016-07-01

    We propose a multiple-range quantum communication channel to realize coherent two-way quantum state transport with high fidelity. In our scheme, an information carrier (a qubit) and its remote partner are both adiabatically coupled to the same data bus, i.e., an N-site tight-binding chain that has a single defect at the center. At the weak interaction regime, our system is effectively equivalent to a three level system of which a coherent superposition of the two carrier states constitutes a dark state. The adiabatic coupling allows a well controllable information exchange timing via the dark state between the two carriers. Numerical results show that our scheme is robust and efficient under practically inevitable perturbative defects of the data bus as well as environmental dephasing noise.

  12. Thermodynamics of quantum systems with multiple conserved quantities.

    Guryanova, Yelena; Popescu, Sandu; Short, Anthony J; Silva, Ralph; Skrzypczyk, Paul

    2016-01-01

    Recently, there has been much progress in understanding the thermodynamics of quantum systems, even for small individual systems. Most of this work has focused on the standard case where energy is the only conserved quantity. Here we consider a generalization of this work to deal with multiple conserved quantities. Each conserved quantity, which, importantly, need not commute with the rest, can be extracted and stored in its own battery. Unlike the standard case, in which the amount of extractable energy is constrained, here there is no limit on how much of any individual conserved quantity can be extracted. However, other conserved quantities must be supplied, and the second law constrains the combination of extractable quantities and the trade-offs between them. We present explicit protocols that allow us to perform arbitrarily good trade-offs and extract arbitrarily good combinations of conserved quantities from individual quantum systems. PMID:27384384

  13. Multiple Energy Exciton Shelves in Quantum-Dot-DNA Nanobioelectronics.

    Goodman, Samuel M; Singh, Vivek; Ribot, Josep Casamada; Chatterjee, Anushree; Nagpal, Prashant

    2014-11-01

    Quantum dots (QDs) are semiconductor nanocrystallites with multiple size-dependent quantum-confined states that are being explored for utilizing broadband radiation. While DNA has been used for the self-assembly of nanocrystals, it has not been investigated for the formation of simultaneous conduction pathways for transporting multiple energy charges or excitons. These exciton shelves can be formed by coupling the conduction band, valence band, and hot-carrier states in QDs with different HOMO-LUMO levels of DNA nucleobases, resulting from varying degrees of conjugation in the nucleobases. Here we present studies on the electronic density of states in four naturally occurring nucleobases (guanine, thymine, cytosine, and adenine), which energetically couple to quantized states in semiconductor QDs. Using scanning tunneling spectroscopy of single nanoparticle-DNA constructs, we demonstrate composite DOS of chemically coupled DNA oligonucleotides and cadmium chalcogenide QDs (CdS, CdSe, CdTe). While perfectly aligned CdTe QD-DNA states lead to exciton shelves for multiple energy charge transport, mismatched energy levels in CdSe QD-DNA introduce intrabandgap states that can lead to charge trapping and recombination. Although further investigations are required to study the rates of charge transfer, recombination, and back-electron transfer, these results can have important implications for the development of a new class of nanobioelectronics and biological transducers. PMID:26278768

  14. Hydrogen-bond interactions in organically-modified polysiloxane networks studied by 1D and 2D CRAMPS and double-quantum 1H MAS NMR

    Brus, Jiří; Dybal, Jiří

    2002-01-01

    Roč. 35, č. 27 (2002), s. 10038-10047. ISSN 0024-9297 R&D Projects: GA ČR GA203/98/P290; GA AV ČR KSK4050111 Institutional research plan: CEZ:AV0Z4050913 Keywords : Hydrogen bonding * polysiloxane * 1H MAS NMR Subject RIV: CD - Macromolecular Chemistry Impact factor: 3.751, year: 2002

  15. HgCdTe/CdTe multiple quantum wells

    This paper reports on HgCdTe/CdTe multiple quantum wells by molecular beam epitaxy which show room temperature photoluminescence and sharp absorption steps at mid-infrared wavelengths. Quantitative chemical mapping, performed by transmission electron microscopy, indicates minimal interdiffusion during growth. Annealing experiments performed at higher temperatures show that the interdiffusion coefficient is a strong function of the depth of the interface below the surface. Absorption spectra have been accurately modeled with a square well/envelope function approach. The films have been used to passively mode lock color center lasers and produce pulses as short as 120 fsec near 2.7 μm

  16. Multiple quantum well AlGaAs nanowires.

    Chen, Chen; Braidy, Nadi; Couteau, Christophe; Fradin, Cécile; Weihs, Gregor; LaPierre, Ray

    2008-02-01

    This letter reports on the growth, structure, and luminescent properties of individual multiple quantum well (MQW) AlGaAs nanowires (NWs). The composition modulations (MQWs) are obtained by alternating the elemental flux of Al and Ga during the molecular beam epitaxy growth of the AlGaAs wire on GaAs (111)B substrates. Transmission electron microscopy and energy dispersive X-ray spectroscopy performed on individual NWs are consistent with a configuration composed of conical segments stacked along the NW axis. Microphotoluminescence measurements and confocal microscopy showed enhanced light emission from the MQW NWs as compared to nonsegmented NWs due to carrier confinement and sidewall passivation. PMID:18184023

  17. Extraction of multiple pure component 1H and 13C NMR spectra from two mixtures: Novel solution obtained by sparse component analysis-based blind decomposition

    Sparse component analysis (SCA) is demonstrated for blind extraction of three pure component spectra from only two measured mixed spectra in 13C and 1H nuclear magnetic resonance (NMR) spectroscopy. This appears to be the first time to report such results and that is the first novelty of the paper. Presented concept is general and directly applicable to experimental scenarios that possibly would require use of more than two mixtures. However, it is important to emphasize that number of required mixtures is always less than number of components present in these mixtures. The second novelty is formulation of blind NMR spectra decomposition exploiting sparseness of the pure components in the wavelet basis defined by either Morlet or Mexican hat wavelet. This enabled accurate estimation of the concentration matrix and number of pure components by means of data clustering algorithm and pure components spectra by means of linear programming with constraints from both 1H and 13C NMR experimental data. The third novelty is capability of proposed method to estimate number of pure components in demanding underdetermined blind source separation (uBSS) scenario. This is in contrast to majority of the BSS algorithms that assume this information to be known in advance. Presented results are important for the NMR spectroscopy-associated data analysis in pharmaceutical industry, medicine diagnostics and natural products research.

  18. Synthesis, structural, and spectroscopic (FT-IR, NMR, and UV) Characterization of 1-(Cyclohexylmethyl)-2-(pyridin-2-yl)-1 H-benzo[ d]imidazole by experimental techniques and quantum chemical calculations

    Özdemir, Namık; Dayan, Osman; Demirmen, Selin

    2016-05-01

    The title compound ( II), 1-(cyclohexylmethyl)-2-(pyridin-2-yl)-1 H-benzo[ d]imidazole (C19H21N3), was synthesized via N-alkylation of 2-(pyridin-2-yl)-1 H-benzo[ d]imidazole ( I). Both compounds I and II were characterized by IR, NMR and UV-vis spectroscopy. Solid-state structure of compound II was determined by single-crystal X-ray diffraction technique. Furthermore, quantum chemical calculations employing density functional theory (DFT/B3LYP) method with the 6-311++ G( d, p) basis set were performed for the theoretical characterization of the molecular and spectroscopic features of the compounds. Using the TD-DFT method, electronic absorption spectra of the compounds have been predicted at same level. When the obtained results were compared with the experimental findings, it is seen that theoretical results support the experimental data and a good agreement exists between them.

  19. 1-Vinyl-5-amino-1 H-tetrazole: X-ray molecular and crystal structures and quantum-chemical DFT calculations

    Lyakhov, Alexander S.; Matulis, Vadim E.; Gaponik, Pavel N.; Voitekhovich, Sergei V.; Ivashkevich, Oleg A.

    2008-03-01

    The crystal and molecular structures of 1-vinyl-5-amino-1 H-tetrazole (VAT) were determined by single crystal X-ray diffraction. The amino group lies in the plane of the tetrazole ring and valence angles around the N atom are close to 120°, the exocyclic C sbnd N amino bond being substantially shorter in comparison with "normal" C sbnd N bond. Natural bond orbital analysis was performed, using density functional theory B3LYP method, to explain the structural peculiarities of crystalline VAT. By using MO calculations, relative stability of all possible tautomeric forms of protonated VAT molecule was investigated.

  20. Observation of spatial quantum correlations induced by multiple scattering of nonclassical light

    Smolka, Stephan; Huck, Alexander; Andersen, Ulrik Lund;

    2009-01-01

    negative spatial quantum correlations are observed when varying the quantum state incident to the multiple scattering medium, and the strength of the correlations is controlled by the number of photons. The experimental results are in excellent agreement with recent theoretical proposals by implementing......We present the experimental realization of spatial quantum correlations of photons that are induced by multiple scattering of squeezed light. The quantum correlation relates photons propagating along two different light paths through the random medium and is infinite in range. Both positive and...... the full quantum model of multiple scattering....

  1. Quantum-chemical insight into structure-reactivity relationship in 4,5,6,7-tetrahalogeno-1H-benzimidazoles: a combined X-ray, DSC, DFT/QTAIM, Hirshfeld surface-based, and molecular docking approach.

    Latosińska, Jolanta Natalia; Latosińska, Magdalena; Maurin, Jan Krzysztof; Orzeszko, Andrzej; Kazimierczuk, Zygmunt

    2014-03-20

    The weak interaction patterns in 4,5,6,7-tetrahalogeno-1H-benzimidazoles, protein kinase CK2 inhibitors, in solid state are studied by the X-ray method and quantum chemistry calculations. The crystal structures of 4,5,6,7-tetrachloro- and 4,5,6,7-tetrabromo-1H-benzimidazole are determined by X-ray diffraction and refined to a final R-factor of 3.07 and 3.03%, respectively, at room temperature. The compound 4,5,6,7-tetrabromo-1H-benzimidazole, which crystallizes in the I41/a space group, is found to be isostructural with previously studied 4,5,6,7-tetraiodo-1H-benzimidazole in contrast to 4,5,6,7-tetrachloro-1H-benzimidazole, which crystallizes as triclinic P1̅ with 4 molecules in elementary unit. For 4,5,6,7-tetrachloro-1H-benzimidazole, differential scanning calorimetry (DSC) revealed a second order glassy phase transition at Tg = 95°/106° (heating/cooling), an indication of frozen disorder. The lack of 3D isostructurality found in all 4,5,6,7-tetrahalogeno-1H-benzimidazoles is elucidated on the basis of the intra- and intermolecular interactions (hydrogen bonding, van der Waals contacts, and C-H···π interactions). The topological Bader's Quantum Theory of Atoms in Molecules (QTAIM) and Spackman's Hirshfeld surface-based approaches reveal equilibration of electrostatic matching and dispersion van der Waals interactions between molecules consistent with the crystal site-symmetry. The weakening of van der Waals forces accompanied by increasing strength of the hydrogen bond (N-H···N) result in a decrease in the crystal site-symmetry and a change in molecular packing in the crystalline state. Crystal packing motifs were investigated with the aid of Hirshfeld surface fingerprint plots. The ordering 4,5,6,7-tetraiodo > 4,5,6,7-tetrabromo > 4,5,6,7-tetrachloro > 4,5,6,7-tetrafluoro reflects not only a decrease in crystal symmetry but also increase in chemical reactivity (electronic activation), which could explain some changes in biological activity of

  2. Spatial quantum correlations induced by random multiple scattering of quadrature squeezed light

    Lodahl, Peter

    The authors demonstrates that spatial quantum correlations are induced by multiple scattering of quadrature squeezed light through a random medium. As a consequence, light scattered along two different directions by the random medium will not be independent, but be correlated to an extent that can...... only be described by a quantum mechanical theory for multiple scattering. The spatial quantum correlation is revealed in the fluctuations of the total intensity transmission or reflection through the multiple scattering medium....

  3. Primidone - An antiepileptic drug - characterisation by quantum chemical and spectroscopic (FTIR, FT-Raman, 1H, 13C NMR and UV-Visible) investigations

    Arjunan, V.; Santhanam, R.; Subramanian, S.; Mohan, S.

    2013-05-01

    The solid phase FTIR and FT-Raman spectra of primidone were recorded in the regions 4000-400 cm-1 and 4000-100 cm-1, respectively. The vibrational spectra were analysed and the observed fundamentals were assigned and analysed. The experimental wavenumbers were compared with the theoretical scaled vibrational wavenumbers determined by DFT methods. The Raman intensities were also determined with B3LYP/6-31G(d,p) method. The total electron density and molecular electrostatic potential surface of the molecule were constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron + nuclei) distribution. The HOMO and LUMO energies were measured. Natural bond orbital analysis of primidone has been performed to indicate the presence of intramolecular charge transfer. The 1H and 13C NMR spectra were recorded and the chemical shifts of the molecule were calculated.

  4. Rank-based model selection for multiple ions quantum tomography

    The statistical analysis of measurement data has become a key component of many quantum engineering experiments. As standard full state tomography becomes unfeasible for large dimensional quantum systems, one needs to exploit prior information and the ‘sparsity’ properties of the experimental state in order to reduce the dimensionality of the estimation problem. In this paper we propose model selection as a general principle for finding the simplest, or most parsimonious explanation of the data, by fitting different models and choosing the estimator with the best trade-off between likelihood fit and model complexity. We apply two well established model selection methods—the Akaike information criterion (AIC) and the Bayesian information criterion (BIC)—two models consisting of states of fixed rank and datasets such as are currently produced in multiple ions experiments. We test the performance of AIC and BIC on randomly chosen low rank states of four ions, and study the dependence of the selected rank with the number of measurement repetitions for one ion states. We then apply the methods to real data from a four ions experiment aimed at creating a Smolin state of rank 4. By applying the two methods together with the Pearson χ2 test we conclude that the data can be suitably described with a model whose rank is between 7 and 9. Additionally we find that the mean square error of the maximum likelihood estimator for pure states is close to that of the optimal over all possible measurements. (paper)

  5. Quantum teleportation scheme by selecting one of multiple output ports

    Ishizaka, Satoshi; Hiroshima, Tohya

    2009-04-01

    The scheme of quantum teleportation, where Bob has multiple (N) output ports and obtains the teleported state by simply selecting one of the N ports, is thoroughly studied. We consider both the deterministic version and probabilistic version of the teleportation scheme aiming to teleport an unknown state of a qubit. Moreover, we consider two cases for each version: (i) the state employed for the teleportation is fixed to a maximally entangled state and (ii) the state is also optimized as well as Alice’s measurement. We analytically determine the optimal protocols for all the four cases and show the corresponding optimal fidelity or optimal success probability. All these protocols can achieve the perfect teleportation in the asymptotic limit of N→∞ . The entanglement properties of the teleportation scheme are also discussed.

  6. Multiple quantum wells for passive ultra short laser pulse generation

    Quintero-Torres, R; Rodriguez-Rodriguez, E; Stintz, Andreas; Diels, Jean-Claude

    2007-01-01

    Solid state lasers are demanding independent control in the gain media and cavity loss to achieve ultra short laser pulses using passive mode-locking. Recently, laser mode-locking is achieved with a MBE structure with multiple quantum wells, designed to achieve two functions; Bragg mirror and changes in absorption to control the cavity dynamics. The use of an AlGaAs/AlAs Bragg mirror with a 15 nm GaAs saturable absorber used in a Cr:LiSAF tuneable laser proved to be effective to produce femtosecond pulses. The use of saturable absorbers thus far is a trial and error procedure that is changing due to the correlation with more predictive procedures.

  7. Quantum mechanical investigation of 2,3-dihydro-1-methyl-2-thioxopyrimidin-4(1H-one tautomers and their complexes with iodine.

    T. Hadadi

    2015-03-01

    Full Text Available DFT and AB initio theoretical methods were used to calculate the relative stability of tautomers and complexes with iodine in the 2,3-dihydro-1-methyl-2-thioxopyrimidin-4(1H-one. This compound can be used to treat hyper thyroidism due to their ability to make complexes with iodine.All tautomers and complexes are optimized using the B3LYP Method with two different energies, the relative energies shows that in all tautomers and complexes. Thione forms are more stable than thieolforms.The NBO calculation is carried out for tautomers and complexes to obtain atomic charges and accept donor interactions. These result confirm the ability ofT tautomers to form complexes and show that the planar complexes has more effective interaction than the perpendicular complex.The atom in molecule (AIM analysis show that the charge density and its laplacian at the S-I bond critical point of the planar complex is greater than the perpendicular complex.

  8. Comprehensive quantum chemical and spectroscopic (FTIR, FT-Raman, 1H, 13C NMR) investigations of O-desmethyltramadol hydrochloride an active metabolite in tramadol - An analgesic drug

    Arjunan, V.; Santhanam, R.; Marchewka, M. K.; Mohan, S.

    2014-03-01

    O-desmethyltramadol is one of the main metabolites of tramadol widely used clinically and has analgesic activity. The FTIR and FT-Raman spectra of O-desmethyl tramadol hydrochloride are recorded in the solid phase in the regions 4000-400 cm-1 and 4000-100 cm-1, respectively. The observed fundamentals are assigned to different normal modes of vibration. Theoretical studies have been performed as its hydrochloride salt. The structure of the compound has been optimised with B3LYP method using 6-31G** and cc-pVDZ basis sets. The optimised bond length and bond angles are correlated with the X-ray data. The experimental wavenumbers were compared with the scaled vibrational frequencies determined by DFT methods. The IR and Raman intensities are determined with B3LYP method using cc-pVDZ and 6-31G(d,p) basic sets. The total electron density and molecular electrostatic potential surfaces of the molecule are constructed by using B3LYP/cc-pVDZ method to display electrostatic potential (electron + nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. Natural bond orbital analysis of O-desmethyltramadol hydrochloride has been performed to indicate the presence of intramolecular charge transfer. The 1H and 13C NMR chemical shifts of the molecule have been anlysed.

  9. MR Imaging with Intermolecular Multiple quantum Coherences (iMQCs):Fundamental Questions and Potentials

    2002-01-01

    @@ Pursuit of new contrast in imaging has been the driving force behind many innovative applications of physics in medical MRI. Even though the use of intramolecular multiple quantum coherence in NMR spectroscopy has a long history, intermolecular multiple quantum coherence (iMQC) among spins on different molecules, such as protonproton iMQC in water, was considered impossible for many years.

  10. Ab initio multiple cloning algorithm for quantum nonadiabatic molecular dynamics

    We present a new algorithm for ab initio quantum nonadiabatic molecular dynamics that combines the best features of ab initio Multiple Spawning (AIMS) and Multiconfigurational Ehrenfest (MCE) methods. In this new method, ab initio multiple cloning (AIMC), the individual trajectory basis functions (TBFs) follow Ehrenfest equations of motion (as in MCE). However, the basis set is expanded (as in AIMS) when these TBFs become sufficiently mixed, preventing prolonged evolution on an averaged potential energy surface. We refer to the expansion of the basis set as “cloning,” in analogy to the “spawning” procedure in AIMS. This synthesis of AIMS and MCE allows us to leverage the benefits of mean-field evolution during periods of strong nonadiabatic coupling while simultaneously avoiding mean-field artifacts in Ehrenfest dynamics. We explore the use of time-displaced basis sets, “trains,” as a means of expanding the basis set for little cost. We also introduce a new bra-ket averaged Taylor expansion (BAT) to approximate the necessary potential energy and nonadiabatic coupling matrix elements. The BAT approximation avoids the necessity of computing electronic structure information at intermediate points between TBFs, as is usually done in saddle-point approximations used in AIMS. The efficiency of AIMC is demonstrated on the nonradiative decay of the first excited state of ethylene. The AIMC method has been implemented within the AIMS-MOLPRO package, which was extended to include Ehrenfest basis functions

  11. Ab initio multiple cloning algorithm for quantum nonadiabatic molecular dynamics

    Makhov, Dmitry V.; Glover, William J.; Martinez, Todd J.; Shalashilin, Dmitrii V.

    2014-08-01

    We present a new algorithm for ab initio quantum nonadiabatic molecular dynamics that combines the best features of ab initio Multiple Spawning (AIMS) and Multiconfigurational Ehrenfest (MCE) methods. In this new method, ab initio multiple cloning (AIMC), the individual trajectory basis functions (TBFs) follow Ehrenfest equations of motion (as in MCE). However, the basis set is expanded (as in AIMS) when these TBFs become sufficiently mixed, preventing prolonged evolution on an averaged potential energy surface. We refer to the expansion of the basis set as "cloning," in analogy to the "spawning" procedure in AIMS. This synthesis of AIMS and MCE allows us to leverage the benefits of mean-field evolution during periods of strong nonadiabatic coupling while simultaneously avoiding mean-field artifacts in Ehrenfest dynamics. We explore the use of time-displaced basis sets, "trains," as a means of expanding the basis set for little cost. We also introduce a new bra-ket averaged Taylor expansion (BAT) to approximate the necessary potential energy and nonadiabatic coupling matrix elements. The BAT approximation avoids the necessity of computing electronic structure information at intermediate points between TBFs, as is usually done in saddle-point approximations used in AIMS. The efficiency of AIMC is demonstrated on the nonradiative decay of the first excited state of ethylene. The AIMC method has been implemented within the AIMS-MOLPRO package, which was extended to include Ehrenfest basis functions.

  12. Ab initio multiple cloning algorithm for quantum nonadiabatic molecular dynamics

    Makhov, Dmitry V.; Shalashilin, Dmitrii V. [Department of Chemistry, University of Leeds, Leeds LS2 9JT (United Kingdom); Glover, William J.; Martinez, Todd J. [Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, USA and SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States)

    2014-08-07

    We present a new algorithm for ab initio quantum nonadiabatic molecular dynamics that combines the best features of ab initio Multiple Spawning (AIMS) and Multiconfigurational Ehrenfest (MCE) methods. In this new method, ab initio multiple cloning (AIMC), the individual trajectory basis functions (TBFs) follow Ehrenfest equations of motion (as in MCE). However, the basis set is expanded (as in AIMS) when these TBFs become sufficiently mixed, preventing prolonged evolution on an averaged potential energy surface. We refer to the expansion of the basis set as “cloning,” in analogy to the “spawning” procedure in AIMS. This synthesis of AIMS and MCE allows us to leverage the benefits of mean-field evolution during periods of strong nonadiabatic coupling while simultaneously avoiding mean-field artifacts in Ehrenfest dynamics. We explore the use of time-displaced basis sets, “trains,” as a means of expanding the basis set for little cost. We also introduce a new bra-ket averaged Taylor expansion (BAT) to approximate the necessary potential energy and nonadiabatic coupling matrix elements. The BAT approximation avoids the necessity of computing electronic structure information at intermediate points between TBFs, as is usually done in saddle-point approximations used in AIMS. The efficiency of AIMC is demonstrated on the nonradiative decay of the first excited state of ethylene. The AIMC method has been implemented within the AIMS-MOLPRO package, which was extended to include Ehrenfest basis functions.

  13. Quantum correlation approach to criticality in the XX spin chain with multiple interaction

    We investigate the quantum critical behavior in the XX spin chain with a XZY-YZX type multiple interaction by means of quantum correlation (Concurrence C, quantum discord DQ and geometric discord DG). Around the critical point, the values of these quantum correlations and corresponding derivatives are investigated numerically and analytically. The results show that the non-analyticity property of the concurrence cannot signal well the quantum phase transition, but both the quantum discord and geometric discord can characterize the critical behavior in such model exactly.

  14. Continuous-wave spatial quantum correlations of light induced by multiple scattering

    Smolka, Stephan; Ott, Johan Raunkjær; Huck, Alexander;

    2012-01-01

    We present theoretical and experimental results on spatial quantum correlations induced by multiple scattering of nonclassical light. A continuous-mode quantum theory is derived that enables determining the spatial quantum correlation function from the fluctuations of the total transmittance...... and reflectance. Utilizing frequency-resolved quantum noise measurements, we observe that the strength of the spatial quantum correlation function can be controlled by changing the quantum state of an incident bright squeezed-light source. Our results are found to be in excellent agreement with the developed...

  15. Equations of Motion with Multiple Proper Time: A New Interpretation of Basic Quantum Physics

    Chen, Xiaodong

    2005-01-01

    Equations of motion for single particle under two proper time model and three proper time model have been proposed and analyzed. The motions of particle are derived from pure classical method but they exhibit the same properties of quantum physics: the quantum wave equation, de Broglie equations, uncertainty relation, statistical result of quantum wave-function. This shows us a possible new way to interpret quantum physics. We will also prove that physics with multiple proper time does not ca...

  16. Stochastic Integral Representations of Quantum Martingales on Multiple Fock Space

    Un Cig Ji

    2006-11-01

    In this paper a quantum stochastic integral representation theorem is obtained for unbounded regular martingales with respect to multidimensional quantum noise. This simultaneously extends results of Parthasarathy and Sinha to unbounded martingales and those of the author to multidimensions.

  17. Comment on "Quantum Superimposing Multiple Anti-Cloning Machine"

    Chang, Da-Wei

    2015-03-01

    Recently, Li et al. (Int. J. Theor. Phys. 46, 2599, 2007) has constructed the quantum superimposing multiple anti-cloning machine, moreover established the sufficient and necessary condition of this machine exists. In the proofs given by Li et al. (Int. J. Theor. Phys. 46, 2599, 2007), claimed that the following key fact to hold : Fact For an arbitrary unknown state | ψ> belongs to n-dimensional Hilbert space, there exists an antiunitary operator K such that K| ψ>=| ψ ⊥> here the state | ψ ⊥> is an orthogonal complement state of | ψ>, that is, it satisfies the following two conditions ==0 and ==1 In this Comment, we would like to point out that (a). In 1-dimensional Hilbert space, for an arbitrary unknown state | ψ>, the antiunitary operator K and the orthogonal complement state both do not exist in general. (b). In 3-dimensional Hilbert space, for an arbitrary unknown state | ψ>, the antiunitary operator K do not exist in general, there are uncountably many orthogonal complement states that can be constructed through the skew-symmetric operator, but is not unitary one. Which shows that above Fact given by Li et al. [1] is incorrect in general for both 1 and 3-dimensional Hilbert space

  18. Single-photon quantum router with multiple output ports.

    Yan, Wei-Bin; Fan, Heng

    2014-01-01

    The routing capability is a requisite in quantum network. Although the quantum routing of signals has been investigated in various systems both in theory and experiment, the general form of quantum routing with many output terminals still needs to be explored. Here we propose a scheme to achieve the multi-channel quantum routing of the single photons in a waveguide-emitter system. The channels are composed by the waveguides and are connected by intermediate two-level emitters. By adjusting the intermediate emitters, the output channels of the input single photons can be controlled. This is demonstrated in the cases of one output channel, two output channels and the generic N output channels. The results show that the multi-channel quantum routing of single photons can be well achieved in the proposed system. This offers a scheme for the experimental realization of general quantum routing of single photons. PMID:24769619

  19. Implementation of non-local quantum controlled-NOT gate with multiple targets

    Libing Chen(陈立冰); Hong Lu(路洪)

    2004-01-01

    We show how a non-local quantum controlled-NOT (CNOT) gate with multiple targets can be implemented with unit fidelity and unit probability. The explicit quantum circuit for implementing the operation is presented. Two schemes for probabilistic implementing the operation via partially entangled quantum channels with unit fidelity are put forward. The overall physical resources required for accomplishing these schemes are different, and the successful implementation probabilities are also different.

  20. Skyrmion Burst and Multiple Quantum Walk in Thin Ferromagnetic Films

    Ezawa, Motohiko

    2011-01-01

    A giant Skyrmion collapses to a singular point by emitting spin waves in a thin ferromagnetic film, when external magnetic field is increased beyond the critical one. The remnant is a single-spin flipped (SSF) point. The SSF point has a quantum diffusion dynamics governed by the Heisenberg model. We determine its time evolution and show the diffusion process is a continuous-time quantum walk. We also analyze an interference of two SSF points after two Skyrmion bursts. Quantum walks for $S=1/2...

  1. Statistics, synergy, and mechanism of multiple photogeneration of excitons in quantum dots: Fundamental and applied aspects

    The effect of multiple exciton generation is analyzed based on statistical physics, quantum mechanics, and synergetics. Statistical problems of the effect of multiple exciton generation (MEG) are broadened and take into account not only exciton generation, but also background excitation. The study of the role of surface states of quantum dots is based on the synergy of self-catalyzed electronic reactions. An analysis of the MEG mechanism is based on the idea of electronic shaking using the sudden perturbation method in quantum mechanics. All of the above-mentioned results are applied to the problem of calculating the limiting efficiency to transform solar energy into electric energy. (authors)

  2. Multiple surface plasmons in an unbounded quantum plasma half-space

    Palade, D. I.

    2016-07-01

    The propagation of surface plasmons on a quantum plasma half-space in the absence of any external confinement is investigated. By means of the Quantum Hydrodynamic Model in the electrostatic limit, it is found that the equilibrium density profile is a smooth continuous function which, in the linear regime, supports multiple non-normal surface modes. Defining a spectrum function and using a cutting condition, the dispersion relations of these modes and their relevance for realistic dynamics are computed. It is found that the multiple surface plasmons present a significant red-shift with respect to the case of fully bounded quantum plasmas.

  3. Multiple surface plasmons on an unbounded quantum plasma half-space

    Palade, D I

    2016-01-01

    The propagation of surface plasmons on a quantum plasma half-space in the absence of any external confinement is investigated. By means of Quantum Hydrodynamic Model in the electrostatic limit it is found that the equilibrium density profile is a smooth continuous function which, in the linear regime, supports multiple non-normal surface modes. Defining a spectrum function and using a cutting condition, the dispersion relations of these modes and their relevance for realistic dynamics are computed. It is found that the multiple surface plasmons present a significant red-shift with respect to the case of fully bounded quantum plasmas.

  4. Time Dependent Study of Multiple Exciton Generation in Nanocrystal Quantum Dots

    Damtie, Fikeraddis A.; Wacker, Andreas

    2016-03-01

    We study the exciton dynamics in an optically excited nanocrystal quantum dot. Multiple exciton formation is more efficient in nanocrystal quantum dots compared to bulk semiconductors due to enhanced Coulomb interactions and the absence of conservation of momentum. The formation of multiple excitons is dependent on different excitation parameters and the dissipation. We study this process within a Lindblad quantum rate equation using the full many-particle states. We optically excite the system by creating a single high energy exciton ESX in resonance to a double exciton EDX. With Coulomb electron-electron interaction, the population can be transferred from the single exciton to the double exciton state by impact ionisation (inverse Auger process). The ratio between the recombination processes and the absorbed photons provide the yield of the structure. We observe a quantum yield of comparable value to experiment assuming typical experimental conditions for a 4 nm PbS quantum dot.

  5. Multiple quantum filtered nuclear magnetic resonance spectroscopy of spin 7/2 nuclei in solution

    Tsoref, L.; Eliav, U.; Navon, G.

    1996-03-01

    Multiple quantum dynamics of spin I=7/2 are presented considering modulation of quadrupolar interaction as the relaxation mechanism. The equation of motion of the spin system is calculated in Liouville space using irreducible spherical tensor operators as the orthonormal basis. Relaxation matrices are given explicitly for coherences one to seven. Experiments for measuring the creation of multiple rank tensors and multiple quantum relaxation for spin 7/2 are described and analyzed. Results of double quantum and triple quantum filtered spectra of Cs+ bound to the crown ether 18-crown-6, dissolved in glycerol, were analyzed in terms of the microscopic parameters of the system, the reorientation correlation time and the quadrupolar coupling constant. Numerical calculations indicated that the expected MQF signal intensities decrease in the order TQF≳DQF≫5QF≳4QF≫7QF≳6QF.

  6. Radiation induced crosslinking in a silica-filled silicone elastomer as investigated by multiple quantum H NMR

    Maxwell, R S; Chinn, S C; Solyom, D; Cohenour, R

    2005-05-24

    DC745 is a commercially available silicone elastomer consisting of dimethyl, methylphenyl, and vinyl-methyl siloxane monomers crosslinked with a peroxide vinyl specific curing agent. It is generally considered to age gracefully and to be resistant to chemical and thermally harsh environments. However, little data exists on the radiation resistance of this commonly used silicone elastomer. We report static {sup 1}H NMR studies of residual dipolar couplings in DC745 solid elastomers subject to exposure to ionizing gamma radiation. {sup 1}H spin-echo NMR data shows that with increasing dose, the segmental dynamics decrease is consistent with radiatively induced crosslinking. {sup 1}H multiple quantum NMR was used to assess changes in the network structure and observed the presence of a bimodal distribution of residual dipolar couplings, <{Omega}{sub d}>, that were dose dependent. The domain with the lower <{Omega}{sub d}> has been assigned to the polymer network while the domain with the higher <{Omega}{sub d}> has been assigned to polymer chains interacting with the inorganic filler surfaces. In samples exposed to radiation, the residual dipolar couplings in both reservoirs were observed to increase and the populations were observed to be dose dependent. The NMR results are compared to Differential Scanning Calorimetry (DSC) and a two-step solvent swelling technique. The solvent swelling data lend support to the interpretation of the NMR results and the DSC data show both a decrease in the melt temperature and the heat of fusion with cumulative dose, consistent with radiative crosslinking. In addition, DSC thermograms obtained following a 3 hr isothermal soak at -40 C showed the presence of a second melt feature at T{sub m} {approx} -70 C consistent with a network domain with significantly reduced segmental motion.

  7. Quantum teleportation of multiple degrees of freedom of a single photon.

    Wang, Xi-Lin; Cai, Xin-Dong; Su, Zu-En; Chen, Ming-Cheng; Wu, Dian; Li, Li; Liu, Nai-Le; Lu, Chao-Yang; Pan, Jian-Wei

    2015-02-26

    Quantum teleportation provides a 'disembodied' way to transfer quantum states from one object to another at a distant location, assisted by previously shared entangled states and a classical communication channel. As well as being of fundamental interest, teleportation has been recognized as an important element in long-distance quantum communication, distributed quantum networks and measurement-based quantum computation. There have been numerous demonstrations of teleportation in different physical systems such as photons, atoms, ions, electrons and superconducting circuits. All the previous experiments were limited to the teleportation of one degree of freedom only. However, a single quantum particle can naturally possess various degrees of freedom--internal and external--and with coherent coupling among them. A fundamental open challenge is to teleport multiple degrees of freedom simultaneously, which is necessary to describe a quantum particle fully and, therefore, to teleport it intact. Here we demonstrate quantum teleportation of the composite quantum states of a single photon encoded in both spin and orbital angular momentum. We use photon pairs entangled in both degrees of freedom (that is, hyper-entangled) as the quantum channel for teleportation, and develop a method to project and discriminate hyper-entangled Bell states by exploiting probabilistic quantum non-demolition measurement, which can be extended to more degrees of freedom. We verify the teleportation for both spin-orbit product states and hybrid entangled states, and achieve a teleportation fidelity ranging from 0.57 to 0.68, above the classical limit. Our work is a step towards the teleportation of more complex quantum systems, and demonstrates an increase in our technical control of scalable quantum technologies. PMID:25719668

  8. Quantum teleportation of multiple degrees of freedom of a single photon

    Wang, Xi-Lin; Cai, Xin-Dong; Su, Zu-En; Chen, Ming-Cheng; Wu, Dian; Li, Li; Liu, Nai-Le; Lu, Chao-Yang; Pan, Jian-Wei

    2015-02-01

    Quantum teleportation provides a `disembodied' way to transfer quantum states from one object to another at a distant location, assisted by previously shared entangled states and a classical communication channel. As well as being of fundamental interest, teleportation has been recognized as an important element in long-distance quantum communication, distributed quantum networks and measurement-based quantum computation. There have been numerous demonstrations of teleportation in different physical systems such as photons, atoms, ions, electrons and superconducting circuits. All the previous experiments were limited to the teleportation of one degree of freedom only. However, a single quantum particle can naturally possess various degrees of freedom--internal and external--and with coherent coupling among them. A fundamental open challenge is to teleport multiple degrees of freedom simultaneously, which is necessary to describe a quantum particle fully and, therefore, to teleport it intact. Here we demonstrate quantum teleportation of the composite quantum states of a single photon encoded in both spin and orbital angular momentum. We use photon pairs entangled in both degrees of freedom (that is, hyper-entangled) as the quantum channel for teleportation, and develop a method to project and discriminate hyper-entangled Bell states by exploiting probabilistic quantum non-demolition measurement, which can be extended to more degrees of freedom. We verify the teleportation for both spin-orbit product states and hybrid entangled states, and achieve a teleportation fidelity ranging from 0.57 to 0.68, above the classical limit. Our work is a step towards the teleportation of more complex quantum systems, and demonstrates an increase in our technical control of scalable quantum technologies.

  9. Optimized In composition and quantum well thickness for yellow-emitting (Ga,In)N/GaN multiple quantum wells

    Lekhal, Kaddour; Hussain, Sakhawat; De Mierry, Philippe; Vennéguès, Philippe; Nemoz, Maud; Chauveau, Jean-Michel; Damilano, Benjamin

    2016-01-01

    Yellow-emitting InxGa1-xN/GaN multiple quantum wells (MQWs) with different pairs of In composition and QW thickness have been grown by metal-organic chemical vapor deposition on sapphire substrates. We show that a trade-off between the MQW crystalline quality and the quantum confined Stark effect has to be found to maximize the room temperature photoluminescence efficiency. With our growth conditions, an optimum design of the MQW is obtained for x=0.21 and a QW thickness of 3.6 nm.

  10. Nonadditivity of quantum and classical capacities for entanglement breaking multiple-access channels and the butterfly network

    We analyze quantum network primitives which are entanglement breaking. We show superadditivity of quantum and classical capacity regions for quantum multiple-access channels and the quantum butterfly network. Since the effects are especially visible at high noise they suggest that quantum information effects may be particularly helpful in the case of the networks with occasional high noise rates. The present effects provide a qualitative borderline between superadditivities of bipartite and multipartite systems.

  11. Hopping mixed hybrid excitations in multiple composite quantum wire structures

    A structure consisting of N pairs of inorganic semiconductor and organic quantum wires is considered theoretically. In such an isolated pair of wires, while the intrawire coupling forms Wannier-Mott exciton in an inorganic semiconductor quantum wire and Frenkel exciton in an organic one, the interwire coupling gives rise to hybrid excitons residing within the pair. When N pairs of wires are packed together 2N new mixed hybrid modes appear that are the true elementary excitations and can hop throughout the whole structure. Energies and wave functions of such hopping mixed hybrid excitations are derived analytically in detail accounting for the global interwire coupling and the different polarization configurations. (author). 19 refs

  12. Quantum superadditivity in linear optics networks: Sending bits via multiple-access Gaussian channels

    Superadditivity effects of communication capacities are known in the case of discrete variable quantum channels. We describe the continuous variable analog of one of these effects in the framework of Gaussian multiple access channels (MACs). Classically, superadditivity-type effects are strongly restricted: For example, adding resources to one sender is never advantageous to other senders in sending their respective information to the receiver. We show that this rule can be surpassed using quantum resources, giving rise to a type of truly quantum superadditivity. This is illustrated here for two examples of experimentally feasible Gaussian MACs.

  13. Multiplicative properties of a quantum Caldero-Chapoton map associated to valued quivers

    Ding, Ming

    2011-01-01

    We prove a multiplication theorem of a quantum Caldero-Chapoton map associated to valued quivers which extends the results in \\cite{DX}\\cite{D}. As an application, when $Q$ is a valued quiver of finite type or rank 2, we obtain that the algebra $\\mathcal{AH}_{|k|}(Q)$ generated by all cluster characters (see Definition \\ref{def}) is exactly the quantum cluster algebra $\\mathcal{EH}_{|k|}(Q)$ and various bases of the quantum cluster algebras of rank 2 can naturally be deduced.

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

    Lai, Kunyu

    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.

  15. Controlled quantum perfect teleportation of multiple arbitrary multi-qubit states

    Shi, Runhua; Huang, Liusheng; Yang, Wei; Zhong, Hong

    2011-12-01

    We present an efficient controlled quantum perfect teleportation scheme. In our scheme, multiple senders can teleport multiple arbitrary unknown multi-qubit states to a single receiver via a previously shared entanglement state with the help of one or more controllers. Furthermore, our scheme has a very good performance in the measurement and operation complexity, since it only needs to perform Bell state and single-particle measurements and to apply Controlled-Not gate and other single-particle unitary operations. In addition, compared with traditional schemes, our scheme needs less qubits as the quantum resources and exchanges less classical information, and thus obtains higher communication efficiency.

  16. Entanglement distribution over quantum code-division multiple-access networks

    Zhu, Chang-long; Yang, Nan; Liu, Yu-xi; Nori, Franco; Zhang, Jing

    2015-10-01

    We present a method for quantum entanglement distribution over a so-called code-division multiple-access network, in which two pairs of users share the same quantum channel to transmit information. The main idea of this method is to use different broadband chaotic phase shifts, generated by electro-optic modulators and chaotic Colpitts circuits, to encode the information-bearing quantum signals coming from different users and then recover the masked quantum signals at the receiver side by imposing opposite chaotic phase shifts. The chaotic phase shifts given to different pairs of users are almost uncorrelated due to the randomness of chaos and thus the quantum signals from different pair of users can be distinguished even when they are sent via the same quantum channel. It is shown that two maximally entangled states can be generated between two pairs of users by our method mediated by bright coherent lights, which can be more easily implemented in experiments compared with single-photon lights. Our method is robust under the channel noises if only the decay rates of the information-bearing fields induced by the channel noises are not quite high. Our study opens up new perspectives for addressing and transmitting quantum information in future quantum networks.

  17. Generation of multiple excitons in Ag2S quantum dots: Single high-energy versus multiple-photon excitation

    Sun, Jingya

    2014-02-20

    We explored biexciton generation via carrier multiplication (or multiple-exciton generation) by high-energy photons and by multiple-photon absorption in Ag2S quantum dots (QDs) using femtosecond broad-band transient absorption spectroscopy. Irrespective of the size of the QDs and how the multiple excitons are generated in the Ag2S QDs, two distinct characteristic time constants of 9.6-10.2 and 135-175 ps are obtained for the nonradiative Auger recombination of the multiple excitons, indicating the existence of two binding excitons, namely, tightly bound and weakly bound excitons. More importantly, the lifetimes of multiple excitons in Ag 2S QDs were about 1 and 2 orders of magnitude longer than those of comparable size PbS QDs and single-walled carbon nanotubes, respectively. This result is significant because it suggests that by utilizing an appropriate electron acceptor, there is a higher possibility to extract multiple electron-hole pairs in Ag2S QDs, which should improve the performance of QD-based solar cell devices. © 2014 American Chemical Society.

  18. Solution behavior and complete 1H and 13C NMR assignments of the coenzyme B12 derivative (5'-deoxyadenosyl)cobinamide using modern 2D NMR experiments, including 600-MHz 1H NMR data

    Two-dimensional (2D) NMR methods have been used to assign completely the 1H and 13C NMR spectra of the (5'-deoxyadenosyl)cobinamide cation (AdoCbi+) in D2O. Most of the 1H spectral assignments were made by using 2D homonuclear shift correlation spectroscopy (COSY), homonuclear Hartmann-Hahn spectroscopy (HOHAHA), absorption-mode (phase sensitive) 2D nuclear Overhauser effect (NOE) spectroscopy, and spin-locked NOE spectroscopy (also called ROESY, for rotating-frame Overhauser enhancement spectroscopy). Most of the protonated carbon resonances were assigned by using 1H-detected heteronuclear multiple-quantum coherence (HMQC) spectroscopy. The nonprotonated carbon resonances, as well as the remaining unassigned 1H and 13C NMR signals, were assigned from long-range 1H-13C connectivities determined from 1H-detected multiple-bond heteronuclear multiple-quantum coherence spectroscopy (HMBC). Comparison of the 13C chemical shifts and 1H NOEs of AdoCbi+ with those of coenzyme B12 ((5'-deoxyadenosyl)cobalamin) and its benzimidazole-protonated, base-off form indicates that the electronic properties and structure of AdoCbi+ are similar to that of coenzyme B12 in the protonated, base-off form. The 13C chemical shifts of most of the carbons of AdoCbi+ do not vary significantly from those of base-off, benzimidazole-protonated coenzyme B12, indicating that the electronic environment of the corrin ring is also similar in both compounds. However, significant differences in the chemical shifts of some of the corresponding carbons of the b, d, e, and f corrin side chains in AdoCbi+ and in base-off, benzimidazole-protonated coenzyme B12 indicate that the positions of these side chains may be different in AdoCbi+ compared to base-off coenzyme B12

  19. Multi-bands photoconductive response in AlGaN/GaN multiple quantum wells

    Chen, G.; Rong, X.; Xu, F. J.; Tang, N. [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Wang, X. Q., E-mail: wangshi@pku.edu.cn; Shen, B., E-mail: bshen@pku.edu.cn [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Fu, K.; Zhang, B. S. [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Ruoshui Road 398, 215123 Suzhou (China); Hashimoto, H.; Yoshikawa, A. [Center for SMART Green Innovation Research, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Ge, W. K. [Department of Physics, Tsinghua University, Beijing 100871 (China)

    2014-04-28

    Based on the optical transitions among the quantum-confined electronic states in the conduction band, we have fabricated multi-bands AlGaN/GaN quantum well infrared photodetectors. Crack-free AlGaN/GaN multiple quantum wells (MQWs) with atomically sharp interfaces have been achieved by inserting an AlN interlayer, which releases most of the tensile strain in the MQWs grown on the GaN underlayer. With significant reduction of dark current by using thick AlGaN barriers, photoconductive responses are demonstrated due to intersubband transition in multiple regions with center wavelengths of 1.3, 2.3, and 4 μm, which shows potential applications on near infrared detection.

  20. Multi-bands photoconductive response in AlGaN/GaN multiple quantum wells

    Based on the optical transitions among the quantum-confined electronic states in the conduction band, we have fabricated multi-bands AlGaN/GaN quantum well infrared photodetectors. Crack-free AlGaN/GaN multiple quantum wells (MQWs) with atomically sharp interfaces have been achieved by inserting an AlN interlayer, which releases most of the tensile strain in the MQWs grown on the GaN underlayer. With significant reduction of dark current by using thick AlGaN barriers, photoconductive responses are demonstrated due to intersubband transition in multiple regions with center wavelengths of 1.3, 2.3, and 4 μm, which shows potential applications on near infrared detection

  1. Resonant Rayleigh scattering of exciton-polaritons in multiple quantum wells

    Malpuech, Guillaume; Kavokin, Alexey; Langbein, Wolfgang Werner;

    2000-01-01

    A theoretical concept of resonant Rayleigh scattering (RRS) of exciton-polaritons in multiple quantum wells (QWs) is presented. The optical coupling between excitons in different QWs can strongly affect the RRS dynamics, giving rise to characteristic temporal oscillations on a picosecond scale. B...

  2. Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David;

    We studied the THz conductivity of InGaN/GaN multiple quantum wells (MQWs)by time-resolved terahertz spectroscopy. A nonexponential carrier density decay is observed due to the restoration of a built-in piezoelectric field. Terahertz conductivity spectra show a nonmetallic behavior of the carriers....

  3. Terahertz study of ultrafast carrier dynamics in InGa/GaN multiple quantum wells

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David;

    2009-01-01

    Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells is measured by time-resolved terahertz spectroscopy. The built-in piezoelectric field is initially screened by photoexcited, polarized carriers, and is gradullay restored as the carriers recombine. We observe a nonexponential decay of...

  4. Electrical and optical properties of multiple quantum well structures and their applications to infrared detectors

    In this work the author investigate the subband nature of multiple quantum well structures by photoconductance spectroscopy, optical absorption measurements and tunneling experiments. Both interband and intraband transitions have been studied. The work is aimed at making an infrared detector using wide band gap semiconductors. 14 refs

  5. Dislocation Behavior in AlGaN/GaN Multiple Quantum-Well Films Grown with Different Interlayers

    Dislocation behaviors are analyzed in AlGaN/GaN multiple-quantum-well films grown with different strain-modified interlayers. In the case of multiple-quantum-well layers grown on a GaN buffer layer without the interlayer, many threading dislocations interact and annihilate within about 100 nm below the multiple quantum well layer. For multiple-quantum-well layers grown with the AlGaN interlayer, misfit dislocations between the GaN buffer layer and the AlGaN interlayer enter multiple-quantum-well layers and result in an increase of threading dislocation density. Besides misfit dislocations, the edge-type dislocation is another dislocation origin attributed to the dissociation of Shockley partials bounding the stacking fault in AlN/GaN superlattices below the interlayer interface

  6. Excitonic transitions in Be-doped GaAs/AlAs multiple quantum well

    Wei-Min, Zheng; Su-Mei, Li; Wei-Yan, Cong; Ai-Fang, Wang; Bin, Li; Hai-Bei, Huang

    2016-04-01

    A series of GaAs/AlAs multiple-quantum wells doped with Be is grown by molecular beam epitaxy. The photoluminescence spectra are measured at 4, 20, 40, 80, 120, and 200 K, respectively. The recombination transition emission of heavy-hole and light-hole free excitons is clearly observed and the transition energies are measured with different quantum well widths. In addition, a theoretical model of excitonic states in the quantum wells is used, in which the symmetry of the component of the exciton wave function representing the relative motion is allowed to vary between the two- and three-dimensional limits. Then, within the effective mass and envelope function approximation, the recombination transition energies of the heavy- and light-hole excitons in GaAs/AlAs multiple-quantum wells are calculated each as a function of quantum well width by the shooting method and variational principle with two variational parameters. The results show that the excitons are neither 2D nor 3D like, but are in between in character and that the theoretical calculation is in good agreement with the experimental results. Project supported by the National Natural Science Foundation of China (Grant No. 61178039) and the Natural Science Foundation of Shandong Province, China (Grant No. ZR2012FM028).

  7. High-Efficiency White Organic Light-Emitting Devices Based on Multiple Quantum-Well Structure

    DUAN Yu; HOU Jing-Ying; WU Zhi-Jun; CHENG Gang; ZHAO Yi; LIU Shi-Yong

    2004-01-01

    @@ We report the white organic-light devices (WOLEDs) employing a multiple quantum-well (MQW) structure,which consist of alternate layers of 4,48-bis(2,28-diphenylvinyl)-1,18-biphenyl (DPVBi) and (DPVBi:Rubrene) as the potential barrier and the potential well, respectively. The results demonstrate that the MQW structure can prominently increase the performance of WOLEDs, the double quantum well device exhibits the efficiency up to 5.4 cd/A, and yields a peak luminance of 14206 cd/m2. It is also interesting to find that the MQW structure can enhance the colour stability of WOLEDs at different voltages.

  8. Synthesis of cadmium chalcogenide based quantum dots for enhanced multiple exciton generation

    Page, Robert Christopher

    2014-01-01

    Quantum dots (QDs) have the potential to produce more than one exciton per incident photon, if the photon energy is greater than twice the band gap energy. This process of multiple exciton generation (MEG) has the potential to lead to a step change in the efficiency of solar panels, by utilising energy commonly wasted as heat in conventional solar cells. A wide range of CdSe/CdTe and CdTe/CdSe quantum dots with and without a CdS shell were synthesised with varying core sizes and shell thickne...

  9. Motional Quantum-State Engineering and Implementation of a Quantum Phase-Gate for Multiple Trapped Ions

    YANG Wen-Xing

    2006-01-01

    We propose a scheme to generate a superposition of motional coherent states with arbitrary coefficients on a line in phase space and implement a quantum controlled phase-gate for multiple trapped ions with a single standing-wave laser pulse whose carrier frequency is tuned to the ions transition. In the scheme each ion does not need to be exactly positioned at the node of the standing wave, which is very important from viewpoint of experiment. Furthermore, our scheme may allow the generation of a superposition of coherent states with large mean phonon number for a large number of trapped ions in a fast way by choosing suitable laser intensity. We show that it can also be used to generate maximally entangled states of multiple trapped ions.

  10. Highly efficient multiple-layer CdS quantum dot sensitized III-V solar cells.

    Lin, Chien-Chung; Han, Hau-Vei; Chen, Hsin-Chu; Chen, Kuo-Ju; Tsai, Yu-Lin; Lin, Wein-Yi; Kuo, Hao-Chung; Yu, Peichen

    2014-02-01

    In this review, the concept of utilization of solar spectrum in order to increase the solar cell efficiency is discussed. Among the three mechanisms, down-shifting effect is investigated in detail. Organic dye, rare-earth minerals and quantum dots are three most popular down-shift materials. While the enhancement of solar cell efficiency was not clearly observed in the past, the advances in quantum dot fabrication have brought strong response out of the hybrid platform of a quantum dot solar cell. A multiple layer structure, including PDMS as the isolation layer, is proposed and demonstrated. With the help of pulse spray system, precise control can be achieved and the optimized concentration can be found. PMID:24749412

  11. Multiple-photon spectrum of CdS semiconductor quantum dot for bioimaging

    We study the dynamic processes of multiple-photon absorption and emission in a semiconductor quantum dot. By the non-perturbative time-dependent Schroedinger equation, it is shown that electrons in the quantum dot can be optically excited from the valence band to the conduction band via multiphoton processes, leaving holes in the valence band. The radiative recombination of the conduction-band electrons with the valence-band holes results in optical emission of a single photon having an energy which is larger than the input photon energy, resulting in the high-photon-energy luminescence from the quantum dot activated by low-energy photons to emit radiation in the visible optical regime for bioimaging application

  12. Effective one-body dynamics in multiple-quantum NMR experiments

    Rufeil-Fiori, E.; Sánchez, C. M.; Oliva, F. Y.; Pastawski, H. M.; Levstein, P. R.

    2009-03-01

    A suitable NMR experiment in a one-dimensional dipolar coupled spin system allows one to reduce the natural many-body dynamics into effective one-body dynamics. We verify this in a polycrystalline sample of hydroxyapatite (HAp) by monitoring the excitation of NMR many-body superposition states: the multiple-quantum coherences. The observed effective one-dimensionality of HAp relies on the quasi-one-dimensional structure of the dipolar coupled network that, as we show here, is dynamically enhanced by the quantum Zeno effect. Decoherence is also probed through a Loschmidt echo experiment, where the time reversal is implemented on the double-quantum Hamiltonian, HDQ∝Ii+Ij++Ii-Ij- . We contrast the decoherence of adamantane, a standard three-dimensional system, with that of HAp. While the first shows an abrupt Fermi-type decay, HAp presents a smooth exponential law.

  13. Defect structures in InGaN/GaN multiple quantum wells on Si(111 substrates

    G.M. Wu

    2006-08-01

    Full Text Available Purpose: Nitrides are compound semiconductor nanomaterials that are suitable for use in light-emitting diodes.It has been desired to grow high quality gallium nitride crystal thin film on silicon substrates because siliconsubstrates have the advantages of low cost, large wafer size, and good electrical and thermal conductivity.However, the higher defect density can limit the industrial applications due to lower quantum efficiency. Thepurpose of this study has been to investigate the crystal defect structure within InGaN/GaN multiple quantumwells on Si(111 substrates. In addition, the variation in quantum well thickness was also explained by theselective area growth model.Design/methodology/approach: InGaN/GaN nano-structures were prepared by metal-organic chemicalvapor phase epitaxy (MOVPE using composite buffer layers. The crystal defect structures in the buriedmultiple quantum wells on both (0001 and {10-11} sidewalls were carefully studied by transmission electronmicroscopy. Previous studies on sapphire substrates have been compared and discussed.Findings: The V defect structures have been found in InGaN/GaN multiple quantum wells on Si(111 substrates.A simplified structural model with increasing barrier thickness has been reported. The barrier thickness increasedon both (0001 and {10-11} facets along thin film growth. A decreased fill factor based on the selective areagrowth model was proposed. In addition, the average thin film growth rate was found to be four times higheralong (0001 than that along {10-11} facet. As the number of multiple quantum wells increased, the barrierthickness increasing was also intensified.Research limitations/implications: The understanding in defect structure could help to modify the processingand design parameters.Originality/value: The V-defect structure and model were reported for the first time using silicon substrates.The different growth rates along defect structures were quantified. High quality gallium

  14. Suppression of decoherence in gallium arsenide multiple quantum wells by means of bang-bang control

    Takasago, K. [Department of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan)], E-mail: takasago.k.aa@m.titech.ac.jp; Ogawa, Y.; Minami, F. [Department of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan)

    2008-05-15

    We performed a three-pulse six-wave mixing (SWM) measurement on a gallium arsenide (GaAs) multiple quantum well and observed the time-resolved SWM signal using the heterodyne detection technique. The second pulse acts as a {pi} pulse that reverses the time evolution of the non-Markovian dynamics. By changing the pulse interval conditions, we confirmed the suppression of exciton decoherence by {pi} pulse irradiation (bang-bang control)

  15. One-dimensional multiple-well oscillators: A time-dependent quantum mechanical approach

    Neetu Gupta; Amlan K Roy; B M Deb

    2002-10-01

    Time-dependent Schrödinger equation (TDSE) is solved numerically to calculate the ground- and first three excited-state energies, expectation values $\\langle x^{2j}\\rangle$, $j=1,2,\\ldots,6$ and probability densities of quantum mechanical multiple-well oscillators. An imaginary-time evolution technique, coupled with the minimization of energy expectation value to reach a global minimum, subject to orthogonality constraint (for excited states) has been employed. Pseudodegeneracy in symmetric, deep multiple-well potentials, probability densities and the effect of an asymmetry parameter on pseudodegeneracy are discussed.

  16. Impact of biexcitons on the relaxation mechanisms of polaritons in III-nitride based multiple quantum well microcavities

    Corfdir, P.; Levrat, J.; Rossbach, G; Butte, R.; Feltin, E.; Carlin, J.-F.; Christmann, G.; Lefebvre, P.; Ganiere, J. -D.; Grandjean, N.; Deveaud-Pledran, B.

    2012-01-01

    We report on the direct observation of biexcitons in a III-nitride based multiple quantum well microcavity operating in the strong light-matter coupling regime by means of nonresonant continuous wave and time-resolved photoluminescence at low temperature. First, the biexciton dynamics is investigated for the bare active medium (multiple quantum wells alone) evidencing localization on potential fluctuations due to alloy disorder and thermalization between both localized and free excitonic and ...

  17. Study of optical non-linear properties of a constant total effective length multiple quantum wells system

    Solaimani, M.; Morteza, Izadifard [Faculty of Physics, Shahrood University of technology, Shahrood (Iran, Islamic Republic of); Arabshahi, H., E-mail: arabshahi@um.ac.ir [Department of Physics, Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of); Physics Department, Payame Noor University, P.O. Box 19395-3697, Tehran (Iran, Islamic Republic of); Reza, Sarkardehi Mohammad [Physics Department, Al-Zahra University, Vanak, Tehran (Iran, Islamic Republic of)

    2013-02-15

    In this work, we have studied the effect of the number of the wells, in a multiple quantum wells structure with constant total effective length, on the optical properties of multiple quantum wells like the absorption coefficient and the refractive index by means of compact density matrix approach. GaAs/Al{sub x}Ga{sub (1-x)}As multiple quantum wells systems was selected as an example. Besides, the effect of varying number of wells on the subband energies, wave functions, number of bound states, and the Fermi energy have been also investigated. Our calculation revealed that the number of wells in a multiple quantum well is a criterion with which we can control the amount of nonlinearity. This study showed that for the third order refractive index change there is two regimes of variations and the critical well number was six. In our calculations, we have used the same wells and barrier thicknesses to construct the multiple quantum wells system. - Highlights: Black-Right-Pointing-Pointer OptiOptical Non-Linear. Black-Right-Pointing-Pointer Total Effective Length. Black-Right-Pointing-Pointer Multiple Quantum Wells System - genetic algorithm Black-Right-Pointing-Pointer Schroedinger equation solution. Black-Right-Pointing-Pointer Nanostructure.

  18. Direction Tracking of Multiple Moving Targets Using Quantum Particle Swarm Optimization

    Gao Hongyuan

    2016-01-01

    Full Text Available Based on weighted signal covariance (WSC matrix and maximum likelihood (ML estimation, a directionof-arrival (DOA estimation method of multiple moving targets is designed and named as WSC-ML in the presence of impulse noise. In order to overcome the shortcoming of the multidimensional search cost of maximum likelihood estimation, a novel continuous quantum particle swarm optimization (QPSO is proposed for this continuous optimization problem. And a tracking method of multiple moving targets in impulsive noise environment is proposed and named as QPSO-WSC-ML. Later, we make use of rank-one updating to update the weighted signal covariance matrix of WSC-ML. Simulation results illustrate the proposed QPSO-WSC-ML method is efficient and robust for the direction tracking of multiple moving targets in the presence of impulse noise.

  19. Electric field dependent Electroreflectance of GaAs/AlGaAs multiple quantum well Bragg structure at second quantum state

    Nakarmi, Mim; Shakya, Naresh; Chaldyshev, Vladimir

    Electroreflectance Spectroscopy was employed to study the effect of electric field on the excitonic transitions in a GaAs/AlGaAs multiple quantum well (MQW) Bragg structure. The sample used in this experiment consists of 60 periods of quantum well structures with GaAs well layer (~13 nm) and AlGaAs barrier layer (~94 nm), grown by molecular beam expitaxy on a semi-insulating GaAs substrate. The sample structure was designed to coincide the Bragg resonance peak with the x(e2-hh2) exciton transitions. We observed a significant enhancement of excitonic feature around the x(e2-hh2) exciton transition due to the double resonance along with the sharp features of x(e1-hh1) and x(e1-lh1) ground state exciton transitions by tuning the angle of incidence of the light. We will present the results on electric field dependent electroreflectance measurements of this structure and discuss the effect of electric field on the first and second energy states.

  20. Polarizabilities of Impurity Doped Quantum Dots Under Pulsed Field: Role of Multiplicative White Noise

    Saha, Surajit; Ghosh, Manas

    2016-02-01

    We perform a rigorous analysis of the profiles of a few diagonal and off-diagonal components of linear ( α xx , α yy , α xy , and α yx ), first nonlinear ( β xxx , β yyy , β xyy , and β yxx ), and second nonlinear ( γ xxxx , γ yyyy , γ xxyy , and γ yyxx ) polarizabilities of quantum dots exposed to an external pulsed field. Simultaneous presence of multiplicative white noise has also been taken into account. The quantum dot contains a dopant represented by a Gaussian potential. The number of pulse and the dopant location have been found to fabricate the said profiles through their interplay. Moreover, a variation in the noise strength also contributes evidently in designing the profiles of above polarizability components. In general, the off-diagonal components have been found to be somewhat more responsive to a variation of noise strength. However, we have found some exception to the above fact for the off-diagonal β yxx component. The study projects some pathways of achieving stable, enhanced, and often maximized output of linear and nonlinear polarizabilities of doped quantum dots driven by multiplicative noise.

  1. GaN/AlGaN Multiple-Quantum-Well Ultraviolet Schottky Photodetectors

    We report on characterization and operation principle of a set of GaN/AlGaN multiple-quantum-well (MQW) photovoltaic detectors. The structures were grown by molecular beam epitaxy (MBE) on c-plane sapphire substrates and fabricated in the back illuminated vertical Schottky geometry. Introduction of MQWs into the active region of devices is expected to enhance the quantum efficiency due to the high absorption coefficient. A nearly flat spectral responsivity between 325nm and 350nm with 0.054 A/W peak responsivity was achieved from the single-side polished backside (rough) illuminated GaN/AlGaN multiple quantum well devices. The cutoff wavelength MQWs photodetector can be tuned by adjusting the well width, well compasition, and barrier height. A model has also been developed to gauge the performance and gain insight into the operation principles of MQWs photodiodes. We observed that the peak responsivity was device parameter dependent and increased with decreasing barrier thickness due to enhanced tunneling of photo generated carriers

  2. Luminescence and ultrafast phenomena in InGaN multiple quantum wells

    High quality In0.13Ga0.87N/GaN multiple quantum wells (MQWs) on (0001) sapphire substrate were fabricated by MOCVD method. The quantum well thickness is as thin as 10 A, and the barrier thickness is 50 A. We have investigated these ultrathin MQWs by continuous wave (cw) and time-resolved spectroscopy in the picosecond time scales in a wide temperature range from 10 to 290 K. In the luminescence spectrum at 10 K, we observed a broad peak at 3.134 eV which was attributed to the quantum wells emission of InGaN. The full width at half maximum of this peak was 129 meV at 10 K and the broadening at low temperatures which was mostly inhomogeneous was thought to be due to compositional fluctuations and interfacial disorder in the alloy. We also observed an intense and narrow peak at 3.471 eV due to the GaN barrier. The temperature dependence of the luminescence was studied and the peak positions and the intensities of the different peaks were obtained. The activation energy of the InGaN quantum well emission peak was estimated as 69 meV. From the measurements of luminescence intensities and lifetimes at various temperatures, radiative and non-radiative recombination lifetimes were deduced. The results were explained by considering only the localization of the excitons due to potential fluctuations

  3. Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions

    Weng, Z. F.; Smidman, M.; Jiao, L.; Lu, Xin; Yuan, H. Q.

    2016-09-01

    Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.

  4. Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions.

    Weng, Z F; Smidman, M; Jiao, L; Lu, Xin; Yuan, H Q

    2016-09-01

    Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology. PMID:27533524

  5. Tunable Symmetries of Integer and Fractional Quantum Hall Phases in Heterostructures with Multiple Dirac Bands

    Stepanov, Petr; Barlas, Yafis; Espiritu, Tim; Che, Shi; Watanabe, Kenji; Taniguchi, Takashi; Smirnov, Dmitry; Lau, Chun Ning

    2016-08-01

    The copresence of multiple Dirac bands in few-layer graphene leads to a rich phase diagram in the quantum Hall regime. Using transport measurements, we map the phase diagram of BN-encapsulated A B A -stacked trilayer graphene as a function charge density n , magnetic field B , and interlayer displacement field D , and observe transitions among states with different spin, valley, orbital, and parity polarizations. Such a rich pattern arises from crossings between Landau levels from different subbands, which reflect the evolving symmetries that are tunable in situ. At D =0 , we observe fractional quantum Hall (FQH) states at filling factors 2 /3 and -11 /3 . Unlike those in bilayer graphene, these FQH states are destabilized by a small interlayer potential that hybridizes the different Dirac bands.

  6. Growth and structural characterization of GaAsBi/GaAs multiple quantum wells

    GaAsBi/GaAs multiple quantum well (MQW) p–i–n diodes are grown by molecular beam epitaxy. Transmission electron microscope images of the diodes show good agreement between the intended and measured MQW periods, but poor agreement between the intended and measured GaAsBi quantum well thicknesses. This is likely due to the incorporation of Bi from a physisorbed surface layer that takes a finite time to accumulate during growth. The diodes with more than 40 wells show dislocations that indicate strain relaxation. This is supported by x-ray diffraction analysis, which also suggests that the i-region of the 54 well diode is tilted with respect to the substrate. (paper)

  7. Protected quantum computation with multiple resonators in ultrastrong coupling circuit QED

    Nataf, Pierre

    2011-01-01

    We investigate theoretically the dynamical behavior of a qubit obtained with the two ground eigenstates of an ultrastrong coupling circuit-QED system consisting of a finite number of Josephson fluxonium atoms inductively coupled to a transmission line resonator. We show an universal set of quantum gates by using multiple transmission line resonators (each resonator represents a single qubit). We discuss the intrinsic 'anisotropic' nature of noise sources for fluxonium artificial atoms. Through a master equation treatment with colored noise and manylevel dynamics, we prove that, for a general class of anisotropic noise sources, the coherence time of the qubit and the fidelity of the quantum operations can be dramatically improved in an optimal regime of ultrastrong coupling, where the ground state is an entangled photonic 'cat' state.

  8. The role of the fano resonance in multiple exciton generation in quantum dots

    Oksengendler, B. L.; Marasulov, M. B.; Nikiforov, V. N.

    2016-02-01

    The phenomenon of interference between two pathways of electron transfer from the valence to the conduction band at a quantum dot is considered. The first way is the conventional "valence band-conduction band" transition, while the second is the transition via a virtual two-electron state on the Tamm level in a quantum dot (QD) followed by the Auger effect, which ejects one electron from the Tamm level to the conduction band. In the case of a coherent addition of these ionization pathways, the Fano resonance can take place, this leading to an increase in the coefficient of photon absorption. This results in increasing internal efficiency of light conversion and can provide a basis for increasing the efficiency of solar cells due to the phenomenon of multiple exciton generation.

  9. Scale-estimation of quantum coherent energy transport in multiple-minima systems.

    Farrow, Tristan; Vedral, Vlatko

    2014-01-01

    A generic and intuitive model for coherent energy transport in multiple minima systems coupled to a quantum mechanical bath is shown. Using a simple spin-boson system, we illustrate how a generic donor-acceptor system can be brought into resonance using a narrow band of vibrational modes, such that the transfer efficiency of an electron-hole pair (exciton) is made arbitrarily high. Coherent transport phenomena in nature are of renewed interest since the discovery that a photon captured by the light-harvesting complex (LHC) in photosynthetic organisms can be conveyed to a chemical reaction centre with near-perfect efficiency. Classical explanations of the transfer use stochastic diffusion to model the hopping motion of a photo-excited exciton. This accounts inadequately for the speed and efficiency of the energy transfer measured in a series of recent landmark experiments. Taking a quantum mechanical perspective can help capture the salient features of the efficient part of that transfer. To show the versatility of the model, we extend it to a multiple minima system comprising seven-sites, reminiscent of the widely studied Fenna-Matthews-Olson (FMO) light-harvesting complex. We show that an idealised transport model for multiple minima coupled to a narrow-band phonon can transport energy with arbitrarily high efficiency. PMID:24980547

  10. Design and Realization of InP/AlGaInAs Multiple Quantum Well Ring Laser

    谢生; 郭婧; 管坤; 毛陆虹; 郭维廉; 齐利芳; 李献杰

    2014-01-01

    Using beam propagation method (BPM), key optical design parameters of InP/AlGaInAs multiple quan-tum well (MQW) ring laser were numerically analyzed. The influences of waveguide dimensions, curvature radius and gap size on the coupling efficiency were discussed. An InP/AlGaInAs MQW ring laser with radius of 350μm was designed and realized. The experimental results show that the designed device, lasing at 1 563.2 nm with side mode suppression ratio higher than 20 dB, exhibited unidirectional bistability between the clockwise and counterclockwise modes.

  11. Polariton Resonances for Ultrastrong Coupling Cavity Optomechanics in GaAs/AlAs Multiple Quantum Wells.

    Jusserand, B; Poddubny, A N; Poshakinskiy, A V; Fainstein, A; Lemaitre, A

    2015-12-31

    Polariton-mediated light-sound interaction is investigated through resonant Brillouin scattering experiments in GaAs/AlAs multiple-quantum wells. Photoelastic coupling enhancement at exciton-polariton resonance reaches 10(5) at 30 K as compared to a typical bulk solid room temperature transparency value. When applied to GaAs based cavity optomechanical nanodevices, this result opens the path to huge displacement sensitivities and to ultrastrong coupling regimes in cavity optomechanics with couplings g(0) in the range of 100 GHz. PMID:26765028

  12. Dynamic analysis of multiple-photon optical processes in semiconductor quantum dots

    Semiconductor quantum dots (QDs) have been gaining much attention because of their outstanding properties for multiple-photon microscopy applications. By solving nonperturbatively the time-dependent Schroedinger equation, it has been shown that the large number of energy states densely compacted in both the conduction and valence bands of the QD greatly enhance the inter-band and intra-band optical couplings between two energy states induced by multiple photons from ultra-fast and ultra-intense lasers. The multiphoton absorption processes are further enhanced by many energy relaxation processes in commonly used semiconductors, which are generally represented by the relaxation energy in the order of tens of meV. Numerical calculation of multiphoton processes in QDs agrees with experimental demonstration. After proper designing, QDs can be activated by infrared radiation to emit radiation in the visible optical regime (up-conversion) for bioimaging applications

  13. Quantum Query Complexity for Searching Multiple Marked States from an Unsorted Database

    2007-01-01

    An important and usual sort of search problems is to find all marked states from an unsorted database with a large number of states. Grover's original quantum search algorithm is for finding single marked state with uncertainty, and it has been generalized to the case of multiple marked states, as well as been modified to find single marked state with certainty. However, the query complexity for finding all multiple marked states has not been addressed. We use a generalized Long's algorithm with high precision to solve such a problem. We calculate the approximate query complexity, which increases with the number of marked states and with the precision that we demand. In the end we introduce an algorithm for the problem on a "duality computer" and show its advantage over other algorithms.

  14. Dynamic light-matter coupling across multiple spatial dimensions in a quantum dots-in-a-well heterostructure

    Prasankumar, Rohit P [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory; Chow, W W [SNL; Attaluri, R S [UNM; Shenoi, R [UNM

    2009-01-01

    Semiconductor heterostructures incorporating multiple degrees of spatial confinement have recently attracted substantial interest for photonic applications. One example is the quantum dots-in-a-well (DWELL) heterostructure, consisting of zero-dimensional quantum dots embedded in a two-dimensional quantum well and surrounded by three-dimensional bulk material. This structure offers several advantages over conventional photonic devices while providing a model system for the study of light-matter interactions across multiple spatial dimensions. Here, we use ultrafast differential transmission spectroscopy2 to temporally and spectrally resolve density-dependent carrier dynamics in a DWELL heterostructure. We observe excitation-dependent shifts of the quantum dot energy levels at low densities, while at high densities we observe an anomalous induced absorption at the quantum dot excited state that is correlated to quantum well population dynamics. These studies of density-dependent light-matter interactions across multiple coupled spatial dimensions provide clues to the underlying physics governing quantum dot properties, with important implications for DWELL-based photonic devices.

  15. Multiple quantum collapse of the inflaton field and its implications on the birth of cosmic structure

    Leon, Gabriel [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Mexico DF 04510 (Mexico); De Unanue, Adolfo [C3 Centro de Ciencias de la Complejidad, Universidad Nacional Autonoma de Mexico, Torre de IngenierIa, Circuito Exterior S/N Ciudad Universitaria, Mexico DF 04510 (Mexico); Sudarsky, Daniel, E-mail: gabriel.leon@nucleares.unam.mx, E-mail: adolfo@nucleares.unam.mx, E-mail: sudarsky@nucleares.unam.mx [Instituto de AstronomIa y Fisica del Espacio (UBA-CONICET), Casilla de Correos 67, Sucursal 28, 1428 Buenos Aires (Argentina)

    2011-08-07

    The standard inflationary account for the origin of cosmic structure is, without a doubt, extremely successful. However, it is not fully satisfactory as has been argued in Perez et al (2006 Class. Quantum Grav. 23 2317). The central point is that, in the standard accounts, the inhomogeneity and anisotropy of our universe seem to emerge, unexplained, from an exactly homogeneous and isotropic initial state through processes that do not break those symmetries. The proposal made there to address this shortcoming calls for a dynamical and self-induced quantum collapse of the original homogeneous and isotropic state of the inflaton. In this paper, we consider the possibility of a multiplicity of collapses in each one of the modes of the quantum field. As we will see, the results are sensitive to a more detailed characterization of the collapse than those studied in the previous works, and in this regard two simple options will be studied. We find important constraints on the model, most remarkably on the number of possible collapses for each mode.

  16. Main: 1H82 [RPSD[Archive

    Full Text Available 1H82 トウモロコシ Corn Zea mays L. Polyamine Oxidase Precursor Name=Pao; Zea Mays Molecul...PEGKGREFFLYASSRRGYYGVWQEFEKQYPDANVLLVTVTDEESRRIEQQSDEQTKAEIMQVLRKMFPGKDVPDATDILVPRWWSDRFYKGTFSNWPVGVNRYEYDQLRAPVGRVYFTGEHTSEHYNGYVHGAYLSGIDSAEILINCAQKKMCKYHVQGKYD corn_1H82.jpg ...

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    Full Text Available 1H84 トウモロコシ Corn Zea mays L. Polyamine Oxidase Precursor Name=Pao; Zea Mays Molecul...GYYGVWQEFEKQYPDANVLLVTVTDEESRRIEQQSDEQTKAEIMQVLRKMFPGKDVPDATDILVPRWWSDRFYKGTFSNWPVGVNRYEYDQLRAPVGRVYFTGEHTSEHYNGYVHGAYLSGIDSAEILINCAQKKMCKYHVQGKYD corn_1H84.jpg ...

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    Full Text Available 1H86 トウモロコシ Corn Zea mays L. Polyamine Oxidase Precursor Name=Pao; Zea Mays Molecul...PEGKGREFFLYASSRRGYYGVWQEFEKQYPDANVLLVTVTDEESRRIEQQSDEQTKAEIMQVLRKMFPGKDVPDATDILVPRWWSDRFYKGTFSNWPVGVNRYEYDQLRAPVGRVYFTGEHTSEHYNGYVHGAYLSGIDSAEILINCAQKKMCKYHVQGKYD corn_1H86.jpg ...

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    Full Text Available 1H83 トウモロコシ Corn Zea mays L. Polyamine Oxidase Precursor Name=Pao; Zea Mays Molecul...GYYGVWQEFEKQYPDANVLLVTVTDEESRRIEQQSDEQTKAEIMQVLRKMFPGKDVPDATDILVPRWWSDRFYKGTFSNWPVGVNRYEYDQLRAPVGRVYFTGEHTSEHYNGYVHGAYLSGIDSAEILINCAQKKMCKYHVQGKYD corn_1H83.jpg ...

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    Full Text Available 1H81 トウモロコシ Corn Zea mays L. Polyamine Oxidase Precursor Name=Pao; Zea Mays Molecul...PEGKGREFFLYASSRRGYYGVWQEFEKQYPDANVLLVTVTDEESRRIEQQSDEQTKAEIMQVLRKMFPGKDVPDATDILVPRWWSDRFYKGTFSNWPVGVNRYEYDQLRAPVGRVYFTGEHTSEHYNGYVHGAYLSGIDSAEILINCAQKKMCKYHVQGKYD corn_1H81.jpg ...

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    Full Text Available 1H49 トウモロコシ Corn Zea mays L. Beta-Glucosidase, Chloroplast Precursor Name=Glu1; Zea...NPWIYMYPEGLKDLLMIMKNKYGNPPIYITENGIGDVDTKETPLPMEAALNDYKRLDYIQRHIATLKESIDLGSNVQGYFAWSLLDNFEWFAGFTERYGIVYVDRNNNCTRYMKESAKWLKEFNTAKKPSKKILTPA corn_1H49.jpg ...

  2. Entanglement Entropy Signature of Quantum Phase Transitions in a Multiple Spin Interactions Model

    HUANG Hai-Lin

    2011-01-01

    Through the Jordan-Wigner transformation, the entanglement entropy and ground state phase diagrams of exactly solvable spin model with alternating and multiple spin exchange interactions are investigated by means of Green's function theory.In the absence of four-spin interactions, the ground state presents plentiful quantum phases due to the multiple spin interactions and magnetic fields.It is shown that the two-site entanglement entropy is a good indicator of quantum phase transition (QPT).In addition, the alternating interactions can destroy the magnetization plateau and wash out the spin-gap of low-lying excitations.However, in the presence of four-spin interactions, apart from the second order QPTs, the system manifests the first order QPT at the tricritical point and an additional new phase called "spin waves", which is due to the collapse of the continuous tower-like low-lying excitations modulated by the four-spin interactions for large three-spin couplings.

  3. Theoretical model of optical fiber secure communication system with chaotic multiple-quantum-well lasers

    2007-01-01

    Chaotic synchronization of injected multiple-quantum-well lasers of optical fiber system and a theoretical model of optical fiber chaotic secure communication system are presented by coupling a chaotic multiple-quantum-well laser synchronization system and a fiber channel. A new chaotic encoding method of chaos phase shift keying On/Off is proposed for optical fiber secure communications. Chaotic synchronization is achieved numerically in long-haul fiber system at wavelength 1.55μm. The effect of the nonlinear-phase of fiber is analyzed on chaotic signal and synchronization. A sinusoidal signal of 0.2 GHz frequency is simulated numerically with chaos masking in long-haul fiber analog communication at wavelength 1.55μm while a digital signal of 0.5 Gbit/s bit rate is simulated numerically with c1 haos masking and a rate of 0.05 Gbit/s are also simulated numerically with chaos shift keying and chaos phase shift keying On/Off in long-haul fiber digital communications at wavelength 1.55μm

  4. Theory of multiple quantum dot formation in strained-layer heteroepitaxy

    Du, Lin; Maroudas, Dimitrios

    2016-07-01

    We develop a theory for the experimentally observed formation of multiple quantum dots (QDs) in strained-layer heteroepitaxy based on surface morphological stability analysis of a coherently strained epitaxial thin film on a crystalline substrate. Using a fully nonlinear model of surface morphological evolution that accounts for a wetting potential contribution to the epitaxial film's free energy as well as surface diffusional anisotropy, we demonstrate the formation of multiple QD patterns in self-consistent dynamical simulations of the evolution of the epitaxial film surface perturbed from its planar state. The simulation predictions are supported by weakly nonlinear analysis of the epitaxial film surface morphological stability. We find that, in addition to the Stranski-Krastanow instability, long-wavelength perturbations from the planar film surface morphology can trigger a nonlinear instability, resulting in the splitting of a single QD into multiple QDs of smaller sizes, and predict the critical wavelength of the film surface perturbation for the onset of the nonlinear tip-splitting instability. The theory provides a fundamental interpretation for the observations of "QD pairs" or "double QDs" and other multiple QDs reported in experimental studies of epitaxial growth of semiconductor strained layers and sets the stage for precise engineering of tunable-size nanoscale surface features in strained-layer heteroepitaxy by exploiting film surface nonlinear, pattern forming phenomena.

  5. Molecular structures and conformations of 1-benzenesulphonyl-2-oxo-5-alkoxypyrrolidines with anti-amnesic activity. X-ray, 1H-NMR and quantum mechanical (PM3) studies

    Amato, Maria E.; Bandoli, Giuliano; Dolmella, Alessandro; Grassi, Antonio; Pappalardo, Giuseppe C.; Toja, Emilio

    1991-04-01

    The crystal and molecular structures of the nootropic agents RU-47001 ((±) 1-(4-nitrobenzenesulphonyl)-2-oxo-5-ethoxypyrrolidine) and RU-47064 ((±) 1-(4-nitrobenzenesulphonyl)-2-oxo-5-isopropyloxypyrrolidine) have been determined by X-ray analysis and their solution conformation has been investigated using 1H NMR spectroscopy. The conformations of these molecules together with those of their analogues RU-35929 ((±) 1-benzenesulphonyl-2-oxo-5-ethoxypyrrolidine), RU-47010 ((±) 1-(3-pyridinylsulphonyl)-2-oxo-5-ethoxypyrrolidine) and RU-35965 ((±) 1-benzenesulphonyl-2-oxo-5-isopropyloxypyrrolidine) have been deduced from semi-quantitative PM3 type theoretical calculations. The main feature of all compounds consists of a common envelope conformation with C (4) at the flap of the pyrrolidinone ring in the solid, that in solution changes into the analogous, but opposite, possible puckered conformational isomer. The 5-alkoxy groups were found rather flexible in solution. Theoretical preferred conformations about NS and SC bonds were in acceptable agreement with those of the solid state. The calculated torsional energetics suggested that 1- 5 do not undergo conformational interconversion.

  6. Comprehensive quantum chemical and spectroscopic (FTIR, FT-Raman, 1H, 13C NMR) investigations of (1,2-epoxyethyl)benzene and (1,2-epoxy-2-phenyl)propane

    Arjunan, V.; Anitha, R.; Devi, L.; Mohan, S.; Yang, Haifeng

    2015-01-01

    Aromatic epoxides are causative factors for mutagenic and carcinogenic activity of polycyclic arenes. The 1,2- or 2,3-epoxy compounds are widely used to a considerable extent in the textile, plastics, pharmaceutical, cosmetics, detergent and photochemical industries. The FTIR and FT-Raman spectra of (1,2-epoxyethyl)benzene and (1,2-epoxy-2-phenyl)propane are recorded in the regions 4000-400 cm-1 and 4000-100 cm-1, respectively. The observed fundamentals are assigned to different normal modes of vibration. The structure of the compound has been optimised with B3LYP method using 6-311++G** and cc-pVTZ basis sets. The IR and Raman intensities are determined. The total electron density and molecular electrostatic potential surfaces of the molecule are constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron + nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. Natural bond orbital analysis of the compounds has been performed to indicate the presence of intramolecular charge transfer. The 1H and 13C NMR chemical shifts of the molecules have been analysed.

  7. Measuring out-of-time-order correlations and multiple quantum spectra in a trapped ion quantum magnet

    Gärttner, Martin; Safavi-Naini, Arghavan; Wall, Michael L; Bollinger, John J; Rey, Ana Maria

    2016-01-01

    Highly controllable arrays of ions and ultra-cold atoms are providing exciting opportunities for realizing quantum simulators of complex many-body phenomena that can provide insights into unsolved problems in modern science. A fundamental step towards this goal is the development of protocols that can quantify how a quantum simulator builds up quantum correlations and stores quantum information starting from easily prepared uncorrelated states. Out-of-time-order correlation functions have been recently suggested as ideal probes to accomplish this task, because they can quantify the spreading, or "scrambling", of quantum information and set speed limits for thermalization. They might also enable experimental tests of the holographic duality between quantum and gravitational systems. Here we report experimental measurements of dynamics of out-of-time-order correlations in a quantum simulator of more than 100 ions in a Penning trap by using the many-body echo sequence developed in the context of nuclear magnetic...

  8. Multiple functional UV devices based on III-Nitride quantum wells for biological warfare agent detection

    Wang, Qin; Savage, Susan; Persson, Sirpa; Noharet, Bertrand; Junique, Stéphane; Andersson, Jan Y.; Liuolia, Vytautas; Marcinkevicius, Saulius

    2009-02-01

    We have demonstrated surface normal detecting/filtering/emitting multiple functional ultraviolet (UV) optoelectronic devices based on InGaN/GaN, InGaN/AlGaN and AlxGa1-xN/AlyGa1-yN multiple quantum well (MQW) structures with operation wavelengths ranging from 270 nm to 450 nm. Utilizing MQW structure as device active layer offers a flexibility to tune its long cut-off wavelength in a wide UV range from solar-blind to visible by adjusting the well width, well composition and barrier height. Similarly, its short cut-off wavelength can be adjusted by using a GaN or AlGaN block layer on a sapphire substrate when the device is illuminated from its backside, which further provides an optical filtering effect. When a current injects into the device under forward bias the device acts as an UV light emitter, whereas the device performs as a typical photodetector under reverse biases. With applying an alternating external bias the device might be used as electroabsorption modulator due to quantum confined Stark effect. In present work fabricated devices have been characterized by transmission/absorption spectra, photoresponsivity, electroluminescence, and photoluminescence measurements under various forward and reverse biases. The piezoelectric effect, alloy broadening and Stokes shift between the emission and absorption spectra in different InGaN- and AlGaN-based QW structures have been investigated and compared. Possibilities of monolithic or hybrid integration using such multiple functional devices for biological warfare agents sensing application have also be discussed.

  9. Structural and optical characteristics of InN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition

    The structural and electrical properties of InN/GaN multiple quantum wells, which were grown by metalorganic chemical vapor deposition, were characterized by transmission electron microscopy (TEM) and electroluminescence measurements. From the TEM micrographs, it was shown that the well layer was grown like a quantum dot. The well layer is expected to be the nano-size structures in the InN multiple quantum well layers. The multi-photon confocal laser scanning microscopy was used to investigate the optical properties of the light emitting diode (LED) structures with InN active layers. It was found that the two-photon excitation was possible in InN system. The pit density was measured by using the far-field optical technique. In the varied current conditions, the blue LED with the InN multiple quantum well structures did not have the wavelength shift. With this result, we can expect that the white LEDs with the InN multiple quantum well structures do not show the color temperature changes with the variations of applied currents

  10. Multiple quantum and dipolar correlation effect NMR studies of cross-linking in elastomer systems

    Physical and chemical aging of filled polydimethylsiloxane-polydimphylsiloxane (PDMS-PDPS) copolymer foams is currently being studied to assess engineering performance degradation and to provide fundamental understanding of aging mechanisms for predictive modeling. Nuclear Magnetic Resonance (NMR) spectroscopy has been shown to be a powerful method for the characterization of polymer aging mechanisms. NMR offers the ability to assess speciation changes and changes in motional properties caused by chemical and physical aging mechanisms. In fact, the measurement of 1H transverse relaxation times (T2) of aged silica filled PDMS/PDPS copolymers have been shown to be sensitive to bulk changes in motional processes caused by aging mechanisms such as radiation exposure. However, more subtle aging mechanisms cause only small changes in bulk relaxation times and conclusive interpretation of the NMR data can be difficult. 1H T2 studies of surveillance return samples, for example, have suffered from such an insensitivity to age and no direct correlation between age and relaxation time have been detected, mirroring solvent swelling results. Close examination of the echo decay functions for surveillance return elastomers sample shows that the main difference between samples are (a) the degree of non-exponential decay behavior at early times between samples, and (b) the amount of material that can be characterized by a long T2. Local and long range structure have important implications on the motional properties of the polymer chains. In PDMS based polymers the couplings between protons within methyl groups are attenuated by rapid spinning about the C3 axis and by the more complex translational and rotational motion of the polymer chains. Crosslinks and entanglements reduce the amplitude and frequency of such long-range segmental motions. The result is that dipolar couplings between protons are not completely averaged to zero. The non-exponential decay is a direct consequence of

  11. Multiple exciton generation and ultrafast exciton dynamics in HgTe colloidal quantum dots.

    Al-Otaify, Ali; Kershaw, Stephen V; Gupta, Shuchi; Rogach, Andrey L; Allan, Guy; Delerue, Christophe; Binks, David J

    2013-10-21

    The investigation of sub-nanosecond exciton dynamics in HgTe colloidal quantum dots using ultrafast transient absorption spectroscopy is reported. The transmittance change spectrum acquired immediately after pumping is dominated by a bleach blue-shifted by ~200-300 nm from the photoluminescent emission band. Comparison with a tight-binding model of the electronic structure allows this feature to be attributed to the filling of band edge states. The form of the pump-induced transmittance transients is dependent on the excitation rate and the rate of sample stirring. For moderate pumping of stirred samples, the transmittance transients are well-described by a mono-exponential decay associated with biexciton recombination, with a lifetime of 49 ± 2 ps. For samples that are strongly-pumped or unstirred, the decay becomes bi-exponential in form, indicating that trap-related recombination has become significant. We also present a new analysis that enables fractional transmittance changes to be related to band edge occupation for samples with arbitrary optical density at the pump wavelength. This allows us to identify the occurrence of multiple exciton generation, which results in a quantum yield of 1.36 ± 0.04 for a photon energy equivalent to 3.1 times the band gap, in good agreement with the results of the model. PMID:23999734

  12. Scale-estimation of quantum coherent energy transport in multiple-minima systems

    Farrow, Tristan

    2014-01-01

    A generic and intuitive model for coherent energy transport in multiple minima systems coupled to a quantum mechanical bath is shown. Using a simple spin-boson system, we illustrate how a generic donor-acceptor system can be brought into resonance using a narrow band of vibrational modes, such that the transfer efficiency of an electron-hole pair (exciton) is made arbitrarily high. Coherent transport phenomena in nature are of renewed interest since the discovery that a photon captured by the light-harvesting complex (LHC) in photosynthetic organisms can be conveyed to a chemical reaction centre with near-perfect efficiency. Classical explanations of the transfer use stochastic diffusion to model the hopping motion of a photo-excited exciton. This accounts inadequately for the speed and efficiency of the energy transfer measured in a series of recent landmark experiments. Taking a quantum mechanical perspective can help capture the salient features of the efficient part of that transfer. To show the versatili...

  13. The multiple quantum NMR dynamics in systems of equivalent spins with the dipolar ordered initial state

    Doronin, S I; Zenchuk, A I

    2011-01-01

    The multiple quantum (MQ) NMR dynamics in the system of equivalent spins with the dipolar ordered initial state is considered. The high symmetry of the MQ Hamiltonian is used in order to develop the analytical and numerical methods for an investigation of the MQ NMR dynamics in the systems consisting of hundreds of spins from "the first principles". We obtain the dependence of the intensities of the MQ NMR coherences on their orders (profiles of the MQ NMR coherences) for the systems of $200 - 600$ spins. It is shown that these profiles may be well approximated by the exponential distribution functions. We also compare the MQ NMR dynamics in the systems of equivalent spins having two different initial states, namely the dipolar ordered state and the thermal equilibrium state in the strong external magnetic field.

  14. Harsh photovoltaics using InGaN/GaN multiple quantum well schemes

    Lien, Derhsien

    2015-01-01

    Harvesting solar energy at extremely harsh environments is of practical interest for building a self-powered harsh electronic system. However, working at high temperature and radiative environments adversely affects the performance of conventional solar cells. To improve the performance, GaN-based multiple quantum wells (MQWs) are introduced into the solar cells. The implementation of MQWs enables improved efficiency (+0.52%/K) and fill factor (+0.35%/K) with elevated temperature and shows excellent reliability under high-temperature operation. In addition, the GaN-based solar cell exhibits superior radiation robustness (lifetime >30 years under solar storm proton irradiation) due to their strong atomic bonding and direct-bandgap characteristics. This solar cell employing MQW nanostructures provides valuable routes for future developments in self-powered harsh electronics.

  15. Dynamics of quantum Fisher information in a two-level system coupled to multiple bosonic reservoirs

    Wang, Guo-You; Guo, You-Neng; Zeng, Ke

    2015-11-01

    We consider the optimal parameter estimation for a two-level system coupled to multiple bosonic reservoirs. By using quantum Fisher information (QFI), we investigate the effect of the Markovian reservoirs’ number N on QFI in both weak and strong coupling regimes for a two-level system surrounded by N zero-temperature reservoirs of field modes initially in the vacua. The results show that the dynamics of QFI non-monotonically decays to zero with revival oscillations at some time in the weak coupling regime depending on the reservoirs’ parameters. Furthermore, we also present the relations between the QFI flow, the flows of energy and information, and the sign of the decay rate to gain insight into the physical processes characterizing the dynamics. Project supported by the Hunan Provincial Innovation Foundation for Postgraduate, China (Grant No. CX2014B194) and the Scientific Research Foundation of Hunan Provincial Education Department, China (Grant No. 13C039).

  16. Bound states for multiple Dirac-δ wells in space-fractional quantum mechanics

    Tare, Jeffrey D., E-mail: jeffreytare@gmail.com; Esguerra, Jose Perico H., E-mail: pesguerra@nip.upd.edu.ph [National Institute of Physics, University of the Philippines, Diliman, Quezon City 1101 (Philippines)

    2014-01-15

    Using the momentum-space approach, we obtain bound states for multiple Dirac-δ wells in the framework of space-fractional quantum mechanics. Introducing first an attractive Dirac-comb potential, i.e., Dirac comb with strength −g (g > 0), in the space-fractional Schrödinger equation we show that the problem of obtaining eigenenergies of a system with N Dirac-δ wells can be reduced to a problem of obtaining the eigenvalues of an N × N matrix. As an illustration we use the present matrix formulation to derive expressions satisfied by the bound-state energies of N = 1, 2, 3 delta wells. We also obtain the corresponding wave functions and express them in terms of Fox's H-function.

  17. Germanium-tin multiple quantum well on silicon avalanche photodiode for photodetection at two micron wavelength

    Dong, Yuan; Wang, Wei; Lee, Shuh Ying; Lei, Dian; Gong, Xiao; Khai Loke, Wan; Yoon, Soon-Fatt; Liang, Gengchiau; Yeo, Yee-Chia

    2016-09-01

    We report the demonstration of a germanium-tin multiple quantum well (Ge0.9Sn0.1 MQW)-on-Si avalanche photodiode (APD) for light detection near the 2 μm wavelength range. The measured spectral response covers wavelengths from 1510 to 2003 nm. An optical responsivity of 0.33 A W‑1 is achieved at 2003 nm due to the internal avalanche gain. In addition, a thermal coefficient of breakdown voltage is extracted to be 0.053% K‑1 based on the temperature-dependent dark current measurement. As compared to the traditional 2 μm wavelength APDs, the Si-based APD is promising for its small excess noise factor, less stringent demand on temperature stability, and its compatibility with silicon technology.

  18. Stimulated emission in InGaN/GaN multiple quantum wells with different indium content

    We report on high-excitation luminescence spectroscopy of InxGa1-xN/GaN multiple quantum wells with a high indium content (x = 0.22 - 0.30). High excitation conditions enabled to achieve screening of built-in field by free carriers. This allowed for the evaluation of the influence of the band potential fluctuations due to variation in In-content on optical properties. Enhanced spontaneous emission was found for x ≥ 0.22 due to carrier localization within the chaotic band potential. Meanwhile the stimulated emission was found to be the highest for structures with x ∼ 0.25 - 0.27. We attribute the In-content dependence of the stimulated emission intensity to a trade-off between an increased carrier density and a decrease of the density of states. (author)

  19. Microcavity effect on the pump-probe intersubband response of multiple-quantum-well structures

    We study theoretically the coherent pump-probe intersubband response of a multiple quantum well (MQW) embedded in a semiconductor microcavity. An n-type doped MQW structure with two subbands in the conduction band is considered. Self-consistent numerical calculations are performed for realistic systems employing a semiclassical approach based on the transfer matrix formalism and the so-called sheet model. They show that in the strong coupling limit the pumping of the system leads to evolution of the intersubband cavity polariton doublet into a Mollow-type spectrum. By using appropriate angles, both the pump and the probe light can be tuned into resonance with the cavity mode. In this double-resonance case, simultaneously with a dramatic enhancement of the Rabi flopping frequency, a strong selective enhancement of distinct parts of the Rabi sidebands is possible. (paper)

  20. Infrared Supercontinuum Generation in Multiple Quantum Well Nanostructures under Electromagnetically Induced Transparency

    Borgohain, Nitu; Konar, S

    2015-01-01

    Mid-infrared spectral broadening is of great scientific and technological interest, which till date is mainly achieved using non-silica glass fibers, primarily made of tellurite, fluoride and chalcogenide glasses. We investigate broadband mid-infrared supercontinuum generation at very low power in semiconductor multiple quantum well (MQW) systems facilitated by electromagnetically induced transparency. 100 femto-seconds pulses of peak power close to a Watt have been launched in the electromagnetically induced transparency window of a 30 period 1.374 {\\mu}m long MQW system. Broadband supercontinuum spectra, attributed to self phase modulation and modulation instability, is achievable at the end of the MQW system. The central part of the spectra is dominated by several dips and the far infra-red part of the spectra is more broadened in comparison to the infra-red portion. Key advantage of the proposed scheme is that the supercontinuum source could be easily integrated with other semiconductor devices.

  1. A multiple quantum NMR (MQNMR) study of hydrogen microstructure in boron doped a-Si:H

    In this paper, an IR and multiple quantum NMR (MQNMR) study of hydrogen microstructure in three boron doped a-Si:H is discussed. The total Si-bonded H content of all films was 6.5 ± 1.0 at. % as determined by the 640 cm-1 IR wagging mode, but their boron content, which was determined by secondary ion mass spectrometry, ranged from 0.02 to 0.3 at %. The number of correlated hydrogen, as measured at a preparation time of 600 μs, was found to be more weakly dependent on the boron content than previously observed in phosphorous-doped glow-discharge films. Upon annealing at 220 degrees C the MQNMR spectrum show a moderate increase in the number of correlated hydrogen in all three samples

  2. Optical Properties of GaN Nanorods Containing a Single or Multiple InGaN Quantum Wells

    Zhuang, Yi D.; Lis, Szymon; Bruckbauer, Jochen; O'Kane, Simon E. J.; Shields, Philip A.; Edwards, Paul R.; Sarma, Jayanta; Martin, Robert W.; Allsopp, Duncan W. E.

    2013-08-01

    Measurements of light emission from GaN nanorods of diameter between 80 and 350 nm, containing either a three-well multiple InGaN quantum well or a single quantum well, have been performed by photoluminescence (PL) and cathodoluminescence (CL) hyperspectral imaging. The PL underwent a Stark shift to the blue as the nanorod diameter was reduced, indicating substantial relaxation of the compressive strain in the quantum wells. The intensity of the nanorod emission per unit area can exceed that of the planar starting material. The CL measurements revealed that the wavelength of the quantum well emission varied with radial position in the nanorod. Simulations by a modal expansion method revealed that the light extraction efficiency varies with radial position and the variation is dependent on nanorod diameter. Finite difference time domain simulations showed that Bloch mode formation in the buffer layer below the nanorods impacts on the light extraction.

  3. Use of external cavity quantum cascade laser compliance voltage in real-time trace gas sensing of multiple chemicals

    Phillips, Mark C.; Taubman, Matthew S.; Kriesel, Jason M.

    2015-02-08

    We describe a prototype trace gas sensor designed for real-time detection of multiple chemicals. The sensor uses an external cavity quantum cascade laser (ECQCL) swept over its tuning range of 940-1075 cm-1 (9.30-10.7 µm) at a 10 Hz repetition rate.

  4. Nanoroughness localization of excitons in GaAs multiple quantum wells studied by transient four-wave mixing

    Birkedal, Dan; Vadim, Lyssenko; Pantke, Karl-Heinz;

    1995-01-01

    The interface roughness on a nanometer scale plays a decisive role in dephasing of excitons in GaAs multiple quantum wells. The excitonic four-wave mixing signal shows a free polarization decay and a corresponding homogeneously broadened line from areas with interface roughness on a scale larger...... mechanisms by spectrally resolving the transient four-wave-mixing signal....

  5. Ultrafast conductivity dynamics in optically excited InGaN/GaN multiple quantum wells, observed by transient THz spectroscopy

    Turchinovich, Dmitry; Porte, Henrik; Cooke, David;

    2010-01-01

    We investigate ultrafast carrier dynamics in photoexcited InGaN/GaN multiple quantum wells by time-resolved terahertz spectroscopy. The initially very strong built-in piezoelectric field is screened upon photoexcitation by the polarized carriers, and is gradually restored as the carriers recombine...

  6. The two-mode quantum Fresnel operator and the multiplication rule of 2D Collins diffraction formula

    Xie, Chuan-Mei; Fan, Hong-Yi

    2012-04-01

    By using the two-mode Fresnel operator we derive a multiplication rule of two-dimensional (2D) Collins diffraction formula, the inverse of 2D Collins diffraction integration can also be conveniently derived in this way in the context of quantum optics theory.

  7. The two-mode quantum Fresnel operator and the multiplication rule of 2D Collins diffraction formula

    By using the two-mode Fresnel operator we derive a multiplication rule of two-dimensional (2D) Collins diffraction formula, the inverse of 2D Collins diffraction integration can also be conveniently derived in this way in the context of quantum optics theory. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  8. {sup 1}H MR spectroscopy in epilepsy

    Hajek, Milan [MR Unit, Department of Diagnostic and Interventional Radiology, Institute for Clinical and Experimental Medicine, Videnska 1958/9, 140 21 Prague (Czech Republic)], E-mail: miha@medicon.cz; Dezortova, Monika [MR Unit, Department of Diagnostic and Interventional Radiology, Institute for Clinical and Experimental Medicine, Videnska 1958/9, 140 21 Prague (Czech Republic)], E-mail: mode@medicon.cz; Krsek, Pavel [Department of Pediatric Neurology, Charles University, Second Medical School, Motol Hospital, V Uvalu 84, 150 06 Prague 5 (Czech Republic)], E-mail: pavel.krsek@post.cz

    2008-08-15

    The introduction to the application of {sup 1}H MR spectroscopy for clinical and research studies of mesial temporal and extratemporal epilepsies is done. The techniques of single voxel and spectroscopic imaging are discussed and the analysis of {sup 1}H MR spectra together with basic metabolic descriptions is presented.

  9. 1H MR spectroscopy in epilepsy

    The introduction to the application of 1H MR spectroscopy for clinical and research studies of mesial temporal and extratemporal epilepsies is done. The techniques of single voxel and spectroscopic imaging are discussed and the analysis of 1H MR spectra together with basic metabolic descriptions is presented

  10. Influence of Dry Etching Damage on the Internal Quantum Efficiency of Nanorod InGaN/GaN Multiple Quantum Wells

    The influence of dry etching damage on the internal quantum efficiency of InGaN/GaN nanorod multiple quantum wells (MQWs) is studied. The samples were etched by inductively coupled plasma (ICP) etching via a self-assembled nickel nanomask, and examined by room-temperature photoluminescence measurement. The key parameters in the etching process are rf power and ICP power. The internal quantum efficiency of nanorod MQWs shows a 5.6 times decrease substantially with the rf power increasing from 3 W to 100 W. However, it is slightly influenced by the ICP power, which shows 30% variation over a wide ICP power range between 30 W and 600 W. Under the optimized etching condition, the internal quantum efficiency of nanorod MQWs can be 40% that of the as-grown MQW sample, and the external quantum efficiency of nanorod MQWs can be about 4 times that of the as-grown one. (cross-disciplinary physics and related areas of science and technology)

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

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

    2015-01-01

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

  12. Study of multiple InAs/GaAs quantum-well structures by electroreflectance spectroscopy

    Bolshakov, A. S., E-mail: bolsh-as@mail.ioffe.ru; Chaldyshev, V. V., E-mail: chald.gvg@mail.ioffe.ru; Babichev, A. V. [Russian Academy of Sciences, Ioffe Institute (Russian Federation); Kudryashov, D. A.; Gudovskikh, A. S.; Morozov, I. A.; Sobolev, M. S.; Nikitina, E. V. [Russian Academy of Sciences, Saint Petersburg Academic University—Nanotechnology Research and Education Center (Russian Federation)

    2015-11-15

    A periodic Bragg heterostructure with three ultrathin InAs/GaAs quantum wells in a period is fabricated and studied. The splitting energy of exciton transitions in quantum wells is determined by the electroreflectance- spectroscopy method and numerical quantum-mechanical calculation. The significant influence of interference effects on individual peak areas in the electroreflectance spectrum is detected.

  13. Effect of exciton oscillator strength on upconversion photoluminescence in GaAs/AlAs multiple quantum wells

    Kojima, Osamu, E-mail: kojima@phoenix.kobe-u.ac.jp; Okumura, Shouhei; Kita, Takashi [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan); Akahane, Kouichi [National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei, Tokyo 184-8795 (Japan)

    2014-11-03

    We report upconversion photoluminescence (UCPL) in GaAs/AlAs multiple quantum wells. UCPL from the AlAs barrier is caused by the resonant excitation of the excitons in the GaAs well. When the quantum well has sufficient miniband width, UCPL is hardly observed because of the small exciton oscillator strength. The excitation-energy and excitation-density dependences of UCPL intensity show the exciton resonant profile and a linear increase, respectively. These results demonstrate that the observed UCPL caused by the saturated two-step excitation process requires a large number of excitons.

  14. Continuous-variable quantum teleportation with non-Gaussian entangled states generated via multiple-photon subtraction and addition

    Wang, Shuai; Chen, Xian-Feng; Xu, Xue-Fen

    2014-01-01

    We investigate the Einstein-Podolsky-Rosen correlation (EPR), the quadrature squeezing and the continuous variable quantum teleportation when considering non-Gaussian entangled states generated by applying multiple-photon addition and multiple-photon subtraction to a two-mode squeezed vacuum state (TMSVs). Our results indicate that, in the case of symmetric multiple-photon-subtracted TMSVs, the corresponding EPR correlation, the two-mode squeezing, the sum squeezing and the fidelity of teleporting a coherent state and a squeezed vacuum state can be enhanced for any squeezing parameter $r$, and these enhancements increase with the number of the operations in small-squeezing regime. While asymmetric multiple-photon subtractions will generally reduce these quantities. For the multiple-photon added TMSVs, although it holds stronger entanglement, its EPR correlation, two-mode squeezing, sum squeezing and the fidelity of a coherent state are always smaller than that of the TMSVs. Only when considering teleporting a...

  15. Multiple-Resonance Local Wave Functions for Accurate Excited States in Quantum Monte Carlo.

    Zulfikri, Habiburrahman; Amovilli, Claudio; Filippi, Claudia

    2016-03-01

    We introduce a novel class of local multideterminant Jastrow-Slater wave functions for the efficient and accurate treatment of excited states in quantum Monte Carlo. The wave function is expanded as a linear combination of excitations built from multiple sets of localized orbitals that correspond to the bonding patterns of the different Lewis resonance structures of the molecule. We capitalize on the concept of orbital domains of local coupled-cluster methods, which is here applied to the active space to select the orbitals to correlate and construct the important transitions. The excitations are further grouped into classes, which are ordered in importance and can be systematically included in the Jastrow-Slater wave function to ensure a balanced description of all states of interest. We assess the performance of the proposed wave function in the calculation of vertical excitation energies and excited-state geometry optimization of retinal models whose π → π* state has a strong intramolecular charge-transfer character. We find that our multiresonance wave functions recover the reference values of the total energies of the ground and excited states with only a small number of excitations and that the same expansion can be flexibly used at very different geometries. Furthermore, significant computational saving can also be gained in the orbital optimization step by selectively mixing occupied and virtual orbitals based on spatial considerations without loss of accuracy on the excitation energy. Our multiresonance wave functions are therefore compact, accurate, and very promising for the calculation of multiple excited states of different character in large molecules. PMID:26761421

  16. Aptamer/quantum dot-based simultaneous electrochemical detection of multiple small molecules

    Zhang Haixia [Key Laboratory on Luminescence and Real-Time Analysis, Ministry of Education, School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715 (China); Jiang Bingying [School of Chemistry and Chemical Engineering, Chongqing University of Technology, Chongqing 400040 (China); Xiang Yun, E-mail: yunatswu@swu.edu.cn [Key Laboratory on Luminescence and Real-Time Analysis, Ministry of Education, School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715 (China); Zhang Yuyong; Chai Yaqin [Key Laboratory on Luminescence and Real-Time Analysis, Ministry of Education, School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715 (China); Yuan Ruo, E-mail: yuanruo@swu.edu.cn [Key Laboratory on Luminescence and Real-Time Analysis, Ministry of Education, School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715 (China)

    2011-03-04

    A novel strategy for 'signal on' and sensitive one-spot simultaneous detection of multiple small molecular analytes based on electrochemically encoded barcode quantum dot (QD) tags is described. The target analytes, adenosine triphosphate (ATP) and cocaine, respectively, are sandwiched between the corresponding set of surface-immobilized primary binding aptamers and the secondary binding aptamer/QD bioconjugates. The captured QDs yield distinct electrochemical signatures after acid dissolution, whose position and size reflect the identity and level, respectively, of the corresponding target analytes. Due to the inherent amplification feature of the QD labels and the 'signal on' detection scheme, as well as the sensitive monitoring of the metal ions released upon acid dissolution of the QD labels, low detection limits of 30 nM and 50 nM were obtained for ATP and cocaine, respectively, in our assays. Our multi-analyte sensing system also shows high specificity to target analytes and promising applicability to complex sample matrix, which makes the proposed assay protocol an attractive route for screening of small molecules in clinical diagnosis.

  17. Anomalous disorder-related phenomena in InGaN/GaN multiple quantum well heterosystems

    Hu, Y.-J. [Department of Electrical Engineering, Technology and Science Institute of Northern Taiwan, Taipei 112, Taiwan (China); Huang, Y.-W.; Fang, C.-H.; Wang, J.-C.; Chen, Y.-F. [Group of Abel and Lie Operations In Sciences and Quantum Electro-optical Science and Technology Laboratory (GALOIS-Quest-Lab), Department of Electronic Engineering, Chang Gung University, Kwei-Shan, Tao-Yuan 333, Taiwan (China); Nee, T.-E., E-mail: neete@mail.cgu.edu.t [Group of Abel and Lie Operations In Sciences and Quantum Electro-optical Science and Technology Laboratory (GALOIS-Quest-Lab), Department of Electronic Engineering, Chang Gung University, Kwei-Shan, Tao-Yuan 333, Taiwan (China)

    2010-06-15

    The influences of InGaN/GaN multiple quantum well (MQW) heterostructures with InGaN/GaN and GaN barriers on carrier confinement were investigated. The degree of disordering over a broad range of temperatures from 20 to 300 K was considered. The optical and electrical properties were strongly influenced by structural and compositional disordering of the InGaN/GaN MQW heterostructures. To compare the degree of disordering we examined the temperature dependence of the luminescence spectra and electrical conductance contingent on the Berthelot-type mechanisms in the InGaN/GaN MQW heterostructures. We further considered carrier transport in the InGaN/GaN disordered systems, probability of carrier tunneling, and activation energy of the transport mechanism for devices with InGaN/GaN and GaN barriers. The optical properties of InGaN/GaN disordered heterosystems can be interpreted from the features of the absorption spectra. The anomalous temperature-dependent characteristics of the disordered InGaN/GaN MQW structures were attributable to the enhancement of the exciton confinement.

  18. Carrier localization effect in polarized InGaN multiple quantum wells

    Carrier localization effects in polarized InGaN/GaN multiple quantum wells (MQWs) were investigated as a function of well width, d, and In content, x. Using photoreflectance (PR), photoluminescence (PL), PL excitation (PLE), selective excitation of PL, PL excitation power, and time-resolved PL spectroscopy, the dominance of the localization effect against the built-in field effect on carrier recombination dynamics in InxGa1-xN MQWs of different well width (d = 2.0-4.0 nm, x ∼ 0.15) and In content (x ∼ 0.22-0.27, d = 2.5 nm) was revealed. Based on the modeling of the PL spectra by Monte Carlo simulation of exciton hopping and the spectroscopic reference provided by PR, increased In content and well width were found to increase the band potential fluctuations and carrier localization depth. The density of localized states deduced from the simulation was found to be in a fair agreement with the PLE data. The built-in field strength in InGaN QWs containing 15% of In was estimated to be of 0.5 MV/cm. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Carrier localization effect in polarized InGaN multiple quantum wells

    Zukauskas, A.; Kazlauskas, K.; Tamulaitis, G.; Mickevicius, J.; Jursenas, S.; Kurilcik, G.; Miasojedovas, S. [Institute of Materials Science and Applied Research, Vilnius University, Sauletekio al. 9, Build. III, 10222 Vilnius (Lithuania); Springis, M.; Tale, I. [Institute of Solid State Physics, University of Latvia, Kengaraga iela 8, Riga 1063 (Latvia); Cheng, Yung-Chen; Wang, Hsiang-Chen; Huang, Chi-Feng; Yang, C.C. [Graduate Institute of Electro-Optical Engineering, National Taiwan University, 1 Roosevelt Road, Sec. 4, Taipei (Taiwan)

    2005-05-01

    Carrier localization effects in polarized InGaN/GaN multiple quantum wells (MQWs) were investigated as a function of well width, d, and In content, x. Using photoreflectance (PR), photoluminescence (PL), PL excitation (PLE), selective excitation of PL, PL excitation power, and time-resolved PL spectroscopy, the dominance of the localization effect against the built-in field effect on carrier recombination dynamics in In{sub x}Ga{sub 1-x}N MQWs of different well width (d = 2.0-4.0 nm, x {approx} 0.15) and In content (x {approx} 0.22-0.27, d = 2.5 nm) was revealed. Based on the modeling of the PL spectra by Monte Carlo simulation of exciton hopping and the spectroscopic reference provided by PR, increased In content and well width were found to increase the band potential fluctuations and carrier localization depth. The density of localized states deduced from the simulation was found to be in a fair agreement with the PLE data. The built-in field strength in InGaN QWs containing 15% of In was estimated to be of 0.5 MV/cm. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Anisotropy mapping in rat brains using Intermolecular Multiple Quantum Coherence Effects

    Han, Yi

    2014-01-01

    This document reports an unconventional and rapidly developing approach to magnetic resonance imaging (MRI) using intermolecular multiple-quantum coherences (iMQCs). Rat brain images are acquired using iMQCs. We detect iMQCs between spins that are 10 {\\mu}m to 500 {\\mu}m apart. The interaction between spins is dependent on different directions. We can choose the directions on physical Z, Y and X axis by choosing correlation gradients along those directions. As an important application, iMQCs can be used for anisotropy mapping. In the rat brains, we investigate tissue microstructure. We simulated images expected from rat brains without microstructure. We compare those with experimental results to prove that the dipolar field from the overall shape only has small contributions to the experimental iMQC signal. Because of the underlying low signal to noise ratio (SNR) in iMQCs, this anisotropy mapping method still has comparatively large potentials to grow. The ultimate goal of my project is to develop creative a...

  1. Vertical coupling in multiple stacks quantum-dot semiconductor optical amplifiers

    The characteristics of vertically coupled multiple stacks quantum-dot (QD) semiconductor optical amplifiers (SOAs) are studied taking into account the effect of carrier coupling between adjacent stacks. We find that QD-SOAs that consist of a few numbers of stacks provide higher optical gain at lower applied current. Our analysis shows that the optical gain of the amplifier can be considerably enhanced due to short tunnelling lifetimes between adjacent stacks. Also, our analysis reveals that short coupling lifetimes can significantly reduce the transparency current and improve the uniformity of the active region since the net coupling rate is a linear function of the injection rate. Long coupling lifetime, on the other hand, produces non-linear and non-uniform coupling rates, which reduce the optical gain and increase the transparency current of the amplifier. We also find that the degradation in the unsaturated optical gain due to long coupling lifetimes is more severe in p-type doped QD-SOA compared with un-doped QD-SOA.

  2. Analytical and numerical study of GaAs/AlGaAs based multiple quantum wells heigh electron mobility transistors (HEMTs)

    Nawaz, M.; Jensen, G.U.

    1995-02-01

    The authors have developed an analytical charge control model for GaAs/AlGaAs multiple quantum wells based Highly Electron Mobility Transistors (HEMTs). The validity of the developed model was tested with a separate numerical calculation based on self consistent solution of Poisson and Schroedinger equations. The analytical expressions for dependence of sheet charge density on the gate bias for different quantum well structures developed in this model, provides excellent agreement with numerical results as well as experimental data. Furthermore, simple expressions are developed for location of sheet charge density from the top and bottom interfaces inside the GaAs quantum well. This model provides a good tool for the design and optimization of microwave circuit design. 12 refs., 7 figs.

  3. The influence of quasi-quantum dots on the physical properties of blue InGaN/GaN multiple quantum wells

    Lai, Y-L [Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan (China); Liu, C-P [Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan (China); Hsueh, T-H [Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan, Taiwan (China); Lin, Y-H [Department of Electronic Engineering, Chang Gung University, KweiShan, TaoYuan, Taiwan (China); Chung, H-C [Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan (China); Lin, R-M [Department of Electronic Engineering, Chang Gung University, KweiShan, TaoYuan, Taiwan (China); Chen, Z-Q [Genesis Photonics Inc, Hsien, Tainan, Taiwan (China)

    2006-09-14

    The effect of barrier growth temperatures on blue InGaN (2 nm)/GaN (12 nm) multiple quantum wells was studied with samples grown by metallorganic chemical vapour deposition. It was found that InGaN active layers composed of InGaN quasi-dots of 2 {+-} 0.2 nm in diameter, changing from their homogeneous nature, could be obtained by elevating the barrier growth temperature from 700 to 800 deg. C based on the results of energy-filtered high resolution transmission electron microscopy. These dots may have formed during the ramping process by in situ annealing. Strong piezoelectric field, 'S-shape-like' carrier transition and high internal quantum efficiency of 71.3% were observed in the sample with a higher barrier growth temperature closely related to the dot formation. Furthermore, the forward voltage and the light output power at 20 mA of light emitting diodes from the sample with dots were 0.3 V lower and 11% higher than that from the homogeneous multiple quantum wells.

  4. The influence of quasi-quantum dots on the physical properties of blue InGaN/GaN multiple quantum wells

    The effect of barrier growth temperatures on blue InGaN (2 nm)/GaN (12 nm) multiple quantum wells was studied with samples grown by metallorganic chemical vapour deposition. It was found that InGaN active layers composed of InGaN quasi-dots of 2 ± 0.2 nm in diameter, changing from their homogeneous nature, could be obtained by elevating the barrier growth temperature from 700 to 800 deg. C based on the results of energy-filtered high resolution transmission electron microscopy. These dots may have formed during the ramping process by in situ annealing. Strong piezoelectric field, 'S-shape-like' carrier transition and high internal quantum efficiency of 71.3% were observed in the sample with a higher barrier growth temperature closely related to the dot formation. Furthermore, the forward voltage and the light output power at 20 mA of light emitting diodes from the sample with dots were 0.3 V lower and 11% higher than that from the homogeneous multiple quantum wells

  5. Dynamic stereochemistry of erigeroside by measurement of 1H- 1H and 13C- 1H coupling constants

    Tafazzoli, Mohsen; Ghiasi, Mina; Moridi, Mahdi

    2008-07-01

    Erigeroside was extracted from Satureja khuzistanica Jamzad (Marzeh Khuzistani in Persian, family of lamiaceae), and 1H, 13C, 13C{ 1H}, 1H- 1H COSY, HMQC and J-HMBC were obtained to identify this compound and determine a complete set of J-coupling constants ( 1JC-H, 2JC-H, 3JC-H and 3JH-H) values within the exocyclic hydroxymethyl group (CH 2OH) and anomeric center. In parallel, density functional theory (DFT) using B3LYP functional and split-valance 6-311++G** basis set has been used to optimized the structures and conformers of erigeroside. In all calculations solvent effects were considered using a polarized continuum (overlapping spheres) model (PCM). The dependencies of 1J, 2J and 3J involving 1H and 13C on the C 5'-C 6' ( ω), C 6'-O 6' ( θ) and C 1'-O 1' ( φ) torsion angles in erigeroside were computed using DFT method. Complete hyper surfaces for 1JC1',H1', 2JC5',H6'R, 2JC5',H6'S, 2JC6',H5', 3JC4',H6'R, 3JC4',H6'S and 2JH6'R-H5'S as well as 3JH5',H6'R were obtained and used to derive Karplus equations to correlate these couplings to ω, θ and φ. These calculated J-couplings are in agreement with experimental values. These results confirm the reliability of DFT calculated coupling constants in aqueous solution.

  6. Correlation between dark current RTS noise and defects for AlGaInP multiple-quantum-well laser diode

    The correlation model between dark current RTS noise and defects for AlGaInP multiple-quantum-well laser diode is derived. Experimental results show that dark current RTS noise caused carrier number fluctuations at the interface of the heterojunction in the active region. According to this correlation model, the defect types are determined, and the defects' energy levels are quantitatively determined. The corner frequency of RTS noise power spectral density is analyzed. The experimental results are in good agreement with the theoretical. This result provided an effective method for estimating the deep-level traps in the active region of AlGaInP multiple quantum well laser diode. (semiconductor devices)

  7. Demonstration of optically controlled data routing with the use of multiple-quantum-well bistable and electro-optical devices

    Koppa, Pàl; Chavel, Pierre; Oudar, Jean-Louis; Kuszelewicz, Robert; Schnell, Jean-Philippe; Pocholle, Jean-Paul

    1997-01-01

    We present experimental results on a 1-to-64-channel free-space photonic switching demonstration system based on GaAs/GaAlAs multiple-quantum-well active device arrays. Two control schemes are demonstrated: data transparent optical self-routing usable in a packet-switching environment and direct optical control with potential signal amplification for circuit switching. The self-routing operation relies on the optical recognition of the binary destination address coded in each packet header. A...

  8. Photoexcited electron and hole dynamics in semiconductor quantum dots: phonon-induced relaxation, dephasing, multiple exciton generation and recombination.

    Kim, Hyeon-Deuk; Prezhdo, Oleg V.

    2012-01-01

    Photoexcited dynamics of electrons and holes in semiconductor quantum dots (QD), including phonon-induced relaxation, multiple exciton generation, fission and recombination (MEG, MEF and MER), were simulated by combining ab initio time-dependent density functional theory and non-adiabatic molecular dynamics. These nonequilibrium phenomena govern the optical properties and photoexcited dynamics of QDs, determining the branching between electronic processes and thermal energy losses. Our approa...

  9. Multiple quantum NMR of spin-carrying molecules in nanopores: high order corrections to the two-spin/two-quantum Hamiltonian

    Doronina, Sergei I; Fel’dmana, Edward B; Zenchuka, Alexander I

    2010-01-01

    This paper is devoted to the multiple-quantum (MQ) NMR spectroscopy in nanopores filled by a gas of spin-carrying molecules (s=1/2) in the strong external magnetic field. It turned out that the high symmetry of the spin system in nanopores yields a possibility to overcome the problem of the exponential growth of the Hilbert space dimension with an increase in a number of spins and to investigate MQ NMR dynamics in systems consisting of several hundreds of spins. We investigate the dependence of the MQ coherence intensities on their order (the profile of the MQ coherence intensities) for the spin system governed by the standard MQ NMR Hamiltonian (the nonsecular two-quantum/two-spin Hamiltonian) together with the second order correction of the average Hamiltonian theory. It is shown that the profile depends on the value of this correction and varies from the exponential to the logarithmic one.

  10. Multiple-path Quantum Interference Effects in a Double-Aharonov-Bohm Interferometer

    Yang XF

    2010-01-01

    Full Text Available Abstract We investigate quantum interference effects in a double-Aharonov-Bohm (AB interferometer consisting of five quantum dots sandwiched between two metallic electrodes in the case of symmetric dot-electrode couplings by the use of the Green’s function equation of motion method. The analytical expression for the linear conductance at zero temperature is derived to interpret numerical results. A three-peak structure in the linear conductance spectrum may evolve into a double-peak structure, and two Fano dips (zero conductance points may appear in the quantum system when the energy levels of quantum dots in arms are not aligned with one another. The AB oscillation for the magnetic flux threading the double-AB interferometer is also investigated in this paper. Our results show the period of AB oscillation can be converted from 2π to π by controlling the difference of the magnetic fluxes threading the two quantum rings.

  11. Quantum

    Al-Khalili, Jim

    2003-01-01

    In this lively look at quantum science, a physicist takes you on an entertaining and enlightening journey through the basics of subatomic physics. Along the way, he examines the paradox of quantum mechanics--beautifully mathematical in theory but confoundingly unpredictable in the real world. Marvel at the Dual Slit experiment as a tiny atom passes through two separate openings at the same time. Ponder the peculiar communication of quantum particles, which can remain in touch no matter how far apart. Join the genius jewel thief as he carries out a quantum measurement on a diamond without ever touching the object in question. Baffle yourself with the bizzareness of quantum tunneling, the equivalent of traveling partway up a hill, only to disappear then reappear traveling down the opposite side. With its clean, colorful layout and conversational tone, this text will hook you into the conundrum that is quantum mechanics.

  12. Role of thermal stress on the magnetophonon peak structure in the parallel transport of the GaAs/AlGaAs multiple quantum wells

    The magnetophonon resonance in parallel transport of two types multiple quantum wells was studied. The transverse magnetresonance was measured in pulsed magnetic fields up to 30 T (within temperature region from 77 to 340 K). A fine structure of magnetophonon resonance peaks which depends on temperature and does not depend on the type of multiple quantum wells, was observed. This effect could be attributed to two phenomena: contribution of barrier phonons and influence of thermostresses. (author)

  13. Correlation between the structural and cathodoluminescence properties in InGaN/GaN multiple quantum wells with large number of quantum wells

    Yang, Jing; Zhao, Degang, E-mail: dgzhao@red.semi.ac.cn; Jiang, Desheng; Chen, Ping; Zhu, Jianjun; Liu, Zongshun; Le, Lingcong; He, Xiaoguang; Li, Xiaojing [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Wang, Hui; Yang, Hui [Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Jahn, Uwe [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5–7, 10117 Berlin (Germany)

    2014-09-01

    Cathodoluminescence (CL) characteristics on 30-period InGaN/GaN multiple quantum well (MQW) solar cell structures are investigated, revealing the relationship between optical and structural properties of the MQW structures with a large number of quantum wells. In the bottom MQW layers, a blueshift of CL peak along the growth direction is found and attributed to the decrease of indium content due to the compositional pulling effect. An obvious split of emission peak and a redshift of the main emission energy are found in the top MQW layers when the MQW grows above the critical layer thickness. They are attributed to the segregation of In-rich InGaN clusters rather than the increase of indium content in quantum well layer. The MQW structure is identified to consist of two regions: a strained one in the bottom, where the indium content is gradually decreased, and a partly relaxed one in the top with segregated In-rich InGaN clusters.

  14. Correlation between the structural and cathodoluminescence properties in InGaN/GaN multiple quantum wells with large number of quantum wells

    Cathodoluminescence (CL) characteristics on 30-period InGaN/GaN multiple quantum well (MQW) solar cell structures are investigated, revealing the relationship between optical and structural properties of the MQW structures with a large number of quantum wells. In the bottom MQW layers, a blueshift of CL peak along the growth direction is found and attributed to the decrease of indium content due to the compositional pulling effect. An obvious split of emission peak and a redshift of the main emission energy are found in the top MQW layers when the MQW grows above the critical layer thickness. They are attributed to the segregation of In-rich InGaN clusters rather than the increase of indium content in quantum well layer. The MQW structure is identified to consist of two regions: a strained one in the bottom, where the indium content is gradually decreased, and a partly relaxed one in the top with segregated In-rich InGaN clusters

  15. Effect of barrier height and indium composition on the internal quantum efficiency of (In)AlGaN multiple quantum well structures

    Ledentsov, Nikolay Jr.; Reich, Christoph; Mehnke, Frank; Kuhn, Christian; Wernicke, Tim; Kolbe, Tim; Lobo Ploch, Neysha; Rass, Jens [Institute of Solid State Physics, Technische Universitaet Berlin (Germany); Kueller, Viola [Ferdinand-Braun-Institut, Berlin (Germany); Kneissl, Michael [Institute of Solid State Physics, Technische Universitaet Berlin (Germany); Ferdinand-Braun-Institut, Berlin (Germany)

    2013-07-01

    We studied (In)AlGaN multiple quantum wells (MQWs) emitting in the UV-B spectral region with photoluminescence and electroluminescence spectroscopy. The internal quantum efficiency (IQE) was determined by temperature dependent measurements (5 K-300 K). The quantum confined Stark effect (QCSE) was investigated by studying the shift of the emission energy with increasing excitation power density. In the first series, Al{sub 0.27}Ga{sub 0.73}N MQWs with different Al{sub x}Ga{sub 1-x}N barriers (0.32

  16. Multiple Metamagnetic Quantum Criticality in Sr_{3}Ru_{2}O_{7}.

    Tokiwa, Y; Mchalwat, M; Perry, R S; Gegenwart, P

    2016-06-01

    Bilayer strontium ruthenate Sr_{3}Ru_{2}O_{7} displays pronounced non-Fermi liquid behavior at magnetic fields around 8 T, applied perpendicular to the ruthenate planes, which previously has been associated with an itinerant metamagnetic quantum critical end point (QCEP). We focus on the magnetic Grüneisen parameter Γ_{H}, which is the most direct probe to characterize field-induced quantum criticality. We confirm quantum critical scaling due to a putative two-dimensional QCEP near 7.845(5) T, which is masked by two ordered phases A and B, identified previously by neutron scattering. In addition, we find evidence for a QCEP at 7.53(2) T and determine the quantum critical regimes of both instabilities and the effect of their superposition. PMID:27314732

  17. Multiple Metamagnetic Quantum Criticality in Sr3 Ru2 O7

    Tokiwa, Y.; Mchalwat, M.; Perry, R. S.; Gegenwart, P.

    2016-06-01

    Bilayer strontium ruthenate Sr3 Ru2 O7 displays pronounced non-Fermi liquid behavior at magnetic fields around 8 T, applied perpendicular to the ruthenate planes, which previously has been associated with an itinerant metamagnetic quantum critical end point (QCEP). We focus on the magnetic Grüneisen parameter ΓH, which is the most direct probe to characterize field-induced quantum criticality. We confirm quantum critical scaling due to a putative two-dimensional QCEP near 7.845(5) T, which is masked by two ordered phases A and B , identified previously by neutron scattering. In addition, we find evidence for a QCEP at 7.53(2) T and determine the quantum critical regimes of both instabilities and the effect of their superposition.

  18. Simultaneous SU(2) rotations on multiple quantum dot exciton qubits using a single shaped pulse

    Mathew, Reuble; Yang, Hong Yi Shi; Hall, Kimberley C.

    2015-10-01

    Recent experimental demonstration of a parallel (π ,2 π ) single qubit rotation on excitons in two distant quantum dots [Nano Lett. 13, 4666 (2013), 10.1021/nl4018176] is extended in numerical simulations to the design of pulses for more general quantum state control, demonstrating the feasibility of full SU(2) rotations of each exciton qubit. Our results show that simultaneous high-fidelity quantum control is achievable within the experimentally accessible parameter space for commercial Fourier-domain pulse shaping systems. The identification of a threshold of distinguishability for the two quantum dots (QDs) for achieving high-fidelity parallel rotations, corresponding to a difference in transition energies of ˜0.25 meV , points to the possibility of controlling more than 10 QDs with a single shaped optical pulse.

  19. Decoherence-Free Subspaces for Multiple-Qubit Errors (II) Universal, Fault-Tolerant Quantum Computation

    Lidar, D A; Kempe, J; Whaley, K B; Lidar, Daniel A.; Bacon, David; Kempe, Julia

    2001-01-01

    Decoherence-free subspaces (DFSs) shield quantum information from errors induced by the interaction with an uncontrollable environment. Here we study a model of correlated errors forming an Abelian subgroup (stabilizer) of the Pauli group (the group of tensor products of Pauli matrices). Unlike previous studies of DFSs, this type of errors does not involve any spatial symmetry assumptions on the system-environment interaction. We solve the problem of universal, fault-tolerant quantum computation on the associated class of DFSs.

  20. Constructing a Multiple-Choice Assessment For Upper-Division Quantum Physics From An Open-Ended Tool

    Sadaghiani, Homeyra; Pollock, Steven; Rehn, Daniel

    2013-01-01

    As part of an ongoing investigation of student learning in upper-division quantum mechanics, we needed a high-quality conceptual assessment instrument for comparing outcomes of different curricular approaches. The 14 item open-ended Quantum Mechanics Assessment Tool (QMAT) was previously developed for this purpose. However, open-ended tests require complex scoring rubrics, are difficult to score consistently, and demand substantial investment of faculty time to grade. Here, we present the process of converting open-ended questions to multiple-choice (MC) format. We highlight the construction of effective distractors and the use of student interviews to revise and validate questions and distractors. We examine other elements of the process, including results of a preliminary implementation of the MC assessment given at Cal Poly Pomona and CU Boulder.

  1. Enhanced performance of InGaN/GaN multiple quantum well solar cells with double indium content

    Zhao Bi-Jun; Chen Xin; Ren Zhi-Wei; Tong Jin-Hui; Wang Xing-Fu; Li Dan-Wei; Zhuo Xiang-Jing

    2013-01-01

    The performance of a multiple quantum well (MQW) InGaN solar cell with double indium content is investigated.It is found that the adoption of a double indium structure can effectively broaden the spectral response of the external quantum efficiencies and optimize the overall performance of the solar cell.Under AM1.5G illumination,the short-circuit current density (Jsc) and conversion efficiency of the solar cell are enhanced by 65% and 13% compared with those of a normal single-indium-content MQW solar cell.These improvements are mainly attributed to the expansion of the absorption spectrum and better extraction efficiency of the photon-generated carriers induced by higher polarization.

  2. Storage and retrieval of vector beams of light in a multiple-degree-of-freedom quantum memory

    Parigi, V; Arnold, C; Marrucci, L; Sciarrino, F; Laurat, J

    2015-01-01

    The full structuration of light in the transverse plane, including intensity, phase and polarization, holds the promise of unprecedented capabilities for applications in classical optics as well as in quantum optics and information sciences. Harnessing special topologies can lead to enhanced focusing, data multiplexing or advanced sensing and metrology. Here we experimentally demonstrate the storage of such spatio-polarization-patterned beams into an optical memory. A set of vectorial vortex modes is generated via liquid crystal cell with topological charge in the optic axis distribution, and preservation of the phase and polarization singularities is demonstrated after retrieval, at the single-photon level. The realized multiple-degree-of-freedom memory can find applications in classical data processing but also in quantum network scenarios where structured states have been shown to provide promising attributes, such as rotational invariance.

  3. Efficient Multiple Exciton Generation Observed in Colloidal PbSe Quantum Dots with Temporally and Spectrally Resolved Intraband Excitation

    Ji, Minbiao

    2009-03-11

    We have spectrally resolved the intraband transient absorption of photogenerated excitons to quantify the exciton population dynamics in colloidal PbSe quantum dots (QDs). These measurements demonstrate that the spectral distribution, as well as the amplitude, of the transient spectrum depends on the number of excitons excited in a QD. To accurately quantify the average number of excitons per QD, the transient spectrum must be spectrally integrated. With spectral integration, we observe efficient multiple exciton generation In colloidal PbSe QDs. © 2009 American Chemical Society.

  4. Quantum Path Interference and Multiple Electron Scattering in Soft X-Ray High-Order Harmonic Generation

    Jozsef Seres

    2015-01-01

    Full Text Available High-order harmonic generation is an important mechanism to generate coherent radiation in the few–100-eV spectral range with ultrashort laser pulses. Moreover, a closer inspection of the measured spectra provides unique information about the underlying physics and allows deriving guidelines for improvements. The long-range modulation of the spectral envelope is linked to phase matching, and we will show how to improve it with a double-pulse excitation scheme. Additionally, the spectrum contains only every fourth harmonic, which can be well explained by the quantum interference of multiple scattered electrons, and two dominant electron trajectories were selected by X-ray parametric interaction.

  5. Multiple-quantum magic-angle spinning: high-resolution solid state NMR spectroscopy of half-integer quadrupolar nuclei

    Experimental and theoretical aspects of the multiple-quantum magic-angle spinning experiment (MQMAS) are discussed in this review. The significance of this experiment, introduced by Frydman and Harwood, is in its ability to provide high-resolution NMR spectra of half-integer quadrupolar nuclei (I /geq 3/2). This technique has proved to be useful in various systems ranging from inorganic materials to biological samples. This review addresses the development of various pulse schemes aimed at improving the signal-to-noise ratio and anisotropic lineshapes. Representative spectra are shown to underscore the importance and applications of the MQMAS experiment. Refs. 97 (author)

  6. Spatial search by continuous-time quantum walk with multiple marked vertices

    Wong, Thomas G.

    2016-04-01

    In the typical spatial search problems solved by continuous-time quantum walk, changing the location of the marked vertices does not alter the search problem. In this paper, we consider search when this is no longer true. In particular, we analytically solve search on the "simplex of K_M complete graphs" with all configurations of two marked vertices, two configurations of M+1 marked vertices, and two configurations of 2(M+1) marked vertices, showing that the location of the marked vertices can dramatically influence the required jumping rate of the quantum walk, such that using the wrong configuration's value can cause the search to fail. This sensitivity to the jumping rate is an issue unique to continuous-time quantum walks that does not affect discrete-time ones.

  7. Generating free charges by carrier multiplication in quantum dots for highly efficient photovoltaics.

    Ten Cate, Sybren; Sandeep, C S Suchand; Liu, Yao; Law, Matt; Kinge, Sachin; Houtepen, Arjan J; Schins, Juleon M; Siebbeles, Laurens D A

    2015-02-17

    CONSPECTUS: In a conventional photovoltaic device (solar cell or photodiode) photons are absorbed in a bulk semiconductor layer, leading to excitation of an electron from a valence band to a conduction band. Directly after photoexcitation, the hole in the valence band and the electron in the conduction band have excess energy given by the difference between the photon energy and the semiconductor band gap. In a bulk semiconductor, the initially hot charges rapidly lose their excess energy as heat. This heat loss is the main reason that the theoretical efficiency of a conventional solar cell is limited to the Shockley-Queisser limit of ∼33%. The efficiency of a photovoltaic device can be increased if the excess energy is utilized to excite additional electrons across the band gap. A sufficiently hot charge can produce an electron-hole pair by Coulomb scattering on a valence electron. This process of carrier multiplication (CM) leads to formation of two or more electron-hole pairs for the absorption of one photon. In bulk semiconductors such as silicon, the energetic threshold for CM is too high to be of practical use. However, CM in nanometer sized semiconductor quantum dots (QDs) offers prospects for exploitation in photovoltaics. CM leads to formation of two or more electron-hole pairs that are initially in close proximity. For photovoltaic applications, these charges must escape from recombination. This Account outlines our recent progress in the generation of free mobile charges that result from CM in QDs. Studies of charge carrier photogeneration and mobility were carried out using (ultrafast) time-resolved laser techniques with optical or ac conductivity detection. We found that charges can be extracted from photoexcited PbS QDs by bringing them into contact with organic electron and hole accepting materials. However, charge localization on the QD produces a strong Coulomb attraction to its counter charge in the organic material. This limits the production

  8. 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

    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

  9. Photoluminescence temperature behavior and Monte Carlo simulation of exciton hopping in InGaN multiple quantum wells

    Kazlauskas, K.; Tamulatis, G.; Pobedinskas, P.; Zukauskas, A. [Institute of Materials Science and Applied Research, Vilnius University, Sauletekio 9, Build. III, 10222 Vilnius (Lithuania); Huang, Chi-Feng; Cheng, Yung-Chen; Wang, Hsiang-Chen; Yang, C.C. [Graduate Institute of Electro-Optical Engineering, National Taiwan University, 1 Roosevelt Road, Sec. 4, Taipei (Taiwan)

    2005-05-01

    Application of Monte Carlo simulation of exciton (carrier) hopping for the analysis of the photoluminescence (PL) temperature behavior in In{sub 0.2}Ga{sub 0.8}N/GaN multiple quantum wells is reported. The PL linewidth and peak position measured in the 10-300 K range exhibited a W-shaped and S-shaped temperature behavior, respectively. The W-shaped linewidth dependence was fitted with the results of Monte Carlo simulation, which involved phonon-assisted exciton hopping through energy states confined in the band potential fluctuation minima. The simulation yielded the values of the standard deviation for potential fluctuations within In-rich regions (31 meV), dispersion of the average exciton energy in different regions (29 meV), and the temperature dependence of the band gap, which was found to be in a fair agreement with the photoreflectance data. Our results, which infer in-plane motion of localized excitons within the wells, are consistent with the model of large In-rich regions (''segmented quantum wells'' or ''quantum discs'') with band potential fluctuations inside these regions. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Real-Time Observation of Ultrafast Intraband Relaxation and Exciton Multiplication in PbS Quantum Dots

    El-Ballouli, Ala’a O.

    2014-03-19

    We examine ultrafast intraconduction band relaxation and multiple-exciton generation (MEG) in PbS quantum dots (QDs) using transient absorption spectroscopy with 120 fs temporal resolution. The intraconduction band relaxation can be directly and excellently resolved spectrally and temporally by applying broadband pump-probe spectroscopy to excite and detect the wavelengths around the exciton absorption peak, which is located in the near-infrared region. The time-resolved data unambiguously demonstrate that the intraband relaxation time progressively increases as the pump-photon energy increases. Moreover, the relaxation time becomes much shorter as the size of the QDs decreases, indicating the crucial role of spatial confinement in the intraband relaxation process. Additionally, our results reveal the systematic scaling of the intraband relaxation time with both excess energy above the effective energy band gap and QD size. We also assess MEG in different sizes of the QDs. Under the condition of high-energy photon excitation, which is well above the MEG energy threshold, ultrafast bleach recovery due to the nonradiative Auger recombination of the multiple electron-hole pairs provides conclusive experimental evidence for the presence of MEG. For instance, we achieved quantum efficiencies of 159, 129 and 106% per single-absorbed photon at pump photoexcition of three times the band gap for QDs with band gaps of 880 nm (1.41 eV), 1000 nm (1.24 eV) and 1210 nm (1.0 eV), respectively. These findings demonstrate clearly that the efficiency of transferring excess photon energy to carrier multiplication is significantly increased in smaller QDs compared with larger ones. Finally, we discuss the Auger recombination dynamics of the multiple electron-hole pairs as a function of QD size.

  11. Highly efficient flexible organic light-emitting devices utilizing F4-TCNQ/m-MTDATA multiple quantum well structures

    Wu Xiaoming, E-mail: wxm@mail.nankai.edu.cn [School of Materials Science and Engineering, Tianjin University of Technology, Key Laboratory of Display Materials and Photoelectric devices, Ministry of Education, Tianjin Key Laboratory of Photoelectric Materials and Devices, Tianjin 300384 (China); Shen Liying; Hua Yulin; Dong Musen; Su Yueju; Jiao Zhiqiang; Yang Xiaoyan; Yin Shougen [School of Materials Science and Engineering, Tianjin University of Technology, Key Laboratory of Display Materials and Photoelectric devices, Ministry of Education, Tianjin Key Laboratory of Photoelectric Materials and Devices, Tianjin 300384 (China)

    2012-05-15

    Flexible organic light-emitting devices (FOLEDs) based on multiple quantum well (MQW) structures, which consist of alternate layers of 2,3,5,6-Tetrafluoro-7,7,8,8,-tetracyano-quinodimethane (F4-TCNQ) and 4,4 Prime ,4 Double-Prime -tris-(3-methylphenylphe-nylamino)tripheny-lamine (m-MTDATA) have been fabricated. The Alq{sub 3}-based device with double quantum well (DQW) structure exhibits the remarkable electroluminescent (EL) performances for the brightness of 23,500 cd/m{sup 2} at 14 V and the maximum current efficiency of 7.0 cd/A at 300.3 mA/cm{sup 2}, respectively, which are greatly improved by 114% and 56% compared with the brightness of 10,958 cd/m{sup 2} at 14 V and the maximum current efficiency of 4.5 cd/A at 174.0 mA/cm{sup 2} for the conventional device without MQW structures. These results demonstrate that the EL performances of FOLEDs could be greatly improved by utilizing the novel MQW structures, and the reason for this improvement has also been explained by the effect of interfacial dipole and interfacial doping between F4-TCNQ and m-MTDATA in this article. - Highlights: Black-Right-Pointing-Pointer We introduce multiple-quantum-well structures in flexible OLEDs for the first time. Black-Right-Pointing-Pointer The MQW structures consist of alternate layers of F4-TCNQ and m-MTDATA. Black-Right-Pointing-Pointer The EL performances of FOLEDs are greatly improved by utilizing these MQW structures.

  12. Optical polarisation anisotropy in a-plane GaN/AlGaN multiple quantum well structures

    Badcock, Tom J.; Dawson, Philip [School of Physics and Astronomy, Photon Science Institute, Alan Turing Building, University of Manchester, Manchester, M13 9PL (United Kingdom); Kappers, Menno J.; McAleese, Clifford; Hollander, Jonathan L.; Johnston, Carol F.; Sridhara Rao, Duggi V.; Sanchez, Ana M.; Humphreys, Colin J. [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ (United Kingdom)

    2009-06-15

    In this paper we report on the optical properties of a series of a-plane GaN/AlGaN multiple quantum well structures of varying well width. The low temperature photoluminescence spectrum of each structure is characterised by two distinct emission bands, both of which shift to higher energy with decreasing well thickness. The origin of the lower energy emission band is attributed to the recombination of carriers trapped in regions of the quantum wells intersected by basal plane stacking faults. The higher energy feature is assigned to localised exciton recombination at well width fluctuations. We have used photoluminescence excitation spectroscopy to reveal details of the bandstructure of the quantum wells. Excitation with unpolarised light resulted in the observation of exciton transitions associated with the n = 1 and n = 2 electron sub-bands. For linearly polarised (E perpendicular to c and E parallel c) excitation, both the transitions observed with unpolarised light were shown to consist of overlapping transitions involving heavy and light hole like valence subbands. Their observed polarisation anisotropy was attributed to anisotropic biaxial compressive strain in the GaN film. As well as the exciton transitions we were also able to resolve well defined continuum edges in some of the excitation spectra. This enabled us to estimate the exciton binding energy of the n=1 heavy and light hole states for quantum wells of differing width. Values were found to lie in the range of 38 to 76 {+-}5 meV. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Quantum Darwinism

    Zurek, Wojciech H [Los Alamos National Laboratory

    2008-01-01

    Quantum Darwinism - proliferation, in the environment, of multiple records of selected states of the system (its information-theoretic progeny) - explains how quantum fragility of individual state can lead to classical robustness of their multitude.

  14. Ultrafast Supercontinuum Spectroscopy of Carrier Multiplication and Biexcitonic Effects in Excited States of PbS Quantum Dots

    Sfeir M. Y.; Gesuele, F.; Koh, W.-K.; Murray, C.B.; Heinz, T.F.; Wong, C.W.

    2012-06-01

    We examine the population dynamics of multiple excitons in PbS quantum dots using spectrally resolved ultrafast supercontinuum transient absorption (SC-TA) measurements. We simultaneously probe the first three excitonic transitions. The transient spectra show the presence of bleaching of absorption for the 1S{sub h}-1S{sub e} transition, as well as transients associated with the 1P{sub h}-1P{sub e} transition. We examine signatures of carrier multiplication (multiple excitons arising from a single absorbed photon) from analysis of the bleaching features in the limit of low absorbed photon numbers (multiple-exciton generation is discussed both in terms of the ratio between early- to long-time transient absorption signals and of a broadband global fit to the data. Analysis of the population dynamics shows that bleaching associated with biexciton population is red shifted with respect to the single exciton feature, which is in accordance with a positive binding energy for the biexciton.

  15. On-chip photonic system using suspended p-n junction InGaN/GaN multiple quantum wells device and multiple waveguides

    Wang, Yongjin; Zhu, Guixia; Cai, Wei; Gao, Xumin; Yang, Yongchao; Yuan, Jialei; Shi, Zheng; Zhu, Hongbo

    2016-04-01

    We propose, fabricate, and characterize the on-chip integration of suspended p-n junction InGaN/GaN multiple quantum wells (MQWs) device and multiple waveguides on the same GaN-on-silicon platform. The integrated devices are fabricated via a wafer-level process and exhibit selectable functionalities for diverse applications. As the suspended p-n junction InGaN/GaN MQWs device operates under a light emitting diode (LED) mode, part of the light emission is confined and guided by the suspended waveguides. The in-plane propagation along the suspended waveguides is measured by a micro-transmittance setup. The on-chip data transmission is demonstrated for the proof-of-concept photonic integration. As the suspended p-n junction InGaN/GaN MQWs device operates under photodiode mode, the light is illuminated on the suspended waveguides with the aid of the micro-transmittance setup and, thus, coupled into the suspended waveguides. The guided light is finally sensed by the photodiode, and the induced photocurrent trace shows a distinct on/off switching performance. These experimental results indicate that the on-chip photonic integration is promising for the development of sophisticated integrated photonic circuits in the visible wavelength region.

  16. Very high efficiency photovoltaic cells based on fully organic multiple quantum wells. Quarterly technical progress report, 15 February 1995--15 May 1995

    Forrest, S R [Princeton Univ., NJ (United States)

    1997-03-01

    The principal project objective is to demonstrate relatively high solar conversion efficiency using extremely low-cost, thin-film technology based on crystalline organic multiple quantum well (MQW) photovoltaic cells. The authors base their work on recent observations both in the laboratory and elsewhere that have indicated the quantum efficiency of organic photoconductors based on vacuum-deposited thin films can be increased by at least two orders of magnitude (to at least 10%) if the organic films are grown in a highly ordered manner, and if organic multiple quantum wells are used in the absorption region. The authors are investigating the physical origin of this phenomenon, and they are growing thin-film MQW cells that demonstrate relatively high quantum efficiencies to determine the practicality of crystalline organic thin-film cells for solar power applications. The investigations are based on a unique, ultrahigh-vacuum organic molecular beam deposition system in the laboratory.

  17. Quantum gauge confinement of multiple quarks based on the homogeneous 5D projection theory

    Wong, K W; Jungner, H

    2015-01-01

    A quick and simplified review of the 5D quantum field theory is presented. The role of topological mapping, which must preserve gauge invariance, is done in two ways, leading to the realization of the gauge transformation in the 5D space-time becoming two separate gauge constraints, one for the multi-quark state quark constituents, while the other is the quantum confinement imposed on the gluon potentials, formed from products of vector potentials generated by products of the fractional charged quark currents. The procedure presented clearly shows multi-quark states can be designed and that they can be verified by experiments, such as the penta-quark state reported. Based on these gauge constraints we propose the existence of 4, 5 and 6 quark states.

  18. Quantum spin chains of Temperley-Lieb type: periodic boundary conditions, spectral multiplicities and finite temperature

    Aufgebauer, Britta; Kluemper, Andreas

    2010-01-01

    We determine the spectra of a class of quantum spin chains of Temperley-Lieb type by utilizing the concept of Temperley-Lieb equivalence with the S=1/2 XXZ chain as a reference system. We consider open boundary conditions and in particular periodic boundary conditions. For both types of boundaries the identification with XXZ spectra is performed within isomorphic representations of the underlying Temperley-Lieb algebra. For open boundaries the spectra of these models differ from the spectrum ...

  19. A numerical study of the quantum oscillations in multiple dangling rings

    We present the quantum mechanical calculations on magnetoconductance of the quantum waveguide topology containing multiply connected dangling mesoscopic rings with the transfer matrix approach. The profiles of the conductance as functions of the Fermi wave number of electrons and of the magnetic flux depend on the number of rings as also on the geometric configuration of the system. The conductance spectrum of this system for disordered lengths in the ring circumferences, dangling links, ballistic leads connecting consecutive dangling rings and disordered magnetic flux is examined in details. We find that there exist two kinds of mini-bands, one originating from the eigenstates of the rings, i.e. the intrinsic mini-bands, and the extra mini-bands. Some of these extra minibands are associated with the dangling links connecting the rings to the main quantum wire, while others are from the standing wave modes associated with the ballistic leads connecting adjacent dangling rings. These different kinds of mini-bands have completely different properties and responds differently to the geometric parameter fluctuations. Unlike the system of potential scatterers, this system of geometric scatterers shows complete band formations at all energies even for finite number of scatterers present. There is a preferential decay of the energy states, depending upon the type of disorder introduced. By controlling the geometric parameters, the conductance band structure of such a model can be artificially tailored and thus may guide the design of better mesoscopic switching devices. (author). 19 refs, 7 figs

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

    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.

  1. 1H NMR in a-Si

    Carlos, W. E.; Taylor, P. C.

    1982-10-01

    Results of pulsed NMR studies of hydrogen in a-Si: H prepared at several laboratories by glow discharge of silane are presented. The origins of the two 1H NMR lines seen in almost all samples of a-Si: H are discussed. Solid-echo measurements are presented which indicate that these two components are due to spatially isolated groups of protons. We attribute the narrow line to protons slightly clustered in the bulk of the material and the broad line to protons distributed on internal surfaces. The spin-lattice relaxation time shows a minimum at T~30 K which is interpreted as due to relaxation via spin diffusion to a small number of H2 molecules acting as relaxation centers. Annealing results suggest that all the hydrogen molecules are trapped in very similar sites.

  2. Picture this: The value of multiple visual representations for student learning of quantum concepts in general chemistry

    Allen, Emily Christine

    Mental models for scientific learning are often defined as, "cognitive tools situated between experiments and theories" (Duschl & Grandy, 2012). In learning, these cognitive tools are used to not only take in new information, but to help problem solve in new contexts. Nancy Nersessian (2008) describes a mental model as being "[loosely] characterized as a representation of a system with interactive parts with representations of those interactions. Models can be qualitative, quantitative, and/or simulative (mental, physical, computational)" (p. 63). If conceptual parts used by the students in science education are inaccurate, then the resulting model will not be useful. Students in college general chemistry courses are presented with multiple abstract topics and often struggle to fit these parts into complete models. This is especially true for topics that are founded on quantum concepts, such as atomic structure and molecular bonding taught in college general chemistry. The objectives of this study were focused on how students use visual tools introduced during instruction to reason with atomic and molecular structure, what misconceptions may be associated with these visual tools, and how visual modeling skills may be taught to support students' use of visual tools for reasoning. The research questions for this study follow from Gilbert's (2008) theory that experts use multiple representations when reasoning and modeling a system, and Kozma and Russell's (2005) theory of representational competence levels. This study finds that as students developed greater command of their understanding of abstract quantum concepts, they spontaneously provided additional representations to describe their more sophisticated models of atomic and molecular structure during interviews. This suggests that when visual modeling with multiple representations is taught, along with the limitations of the representations, it can assist students in the development of models for reasoning about

  3. Optical Study of Exciton Localization Phenomena in Semimagnetic Semiconductors and Their Multiple Quantum Wells.

    Zhang, Xi-Cheng

    1986-12-01

    The results of picosecond photomodulation and photoluminescence spectroscopies in novel II-VI semimagnetic semiconductors Cd(,1-x)Mn(,x)Te (x CdTe/Cd(,1 -x)Mn(,x)Te MQW samples at low temperature shows intense excitonic emission where their radiative quantum efficiencies are two or three orders of magnitude larger than that of the high quality CdTe bulk samples. Time-resolved photoluminescence shows that the excitons have relatively short lifetime (500 picosecond). High quantum efficiency and short exciton lifetime suggest that the radiative recombination is a dominating factor in the excitonic-decay processes in the MQW samples. In general, excitonic emission energies in CdMnTe MQW samples are lower than the free exciton energies (typically 20-40 meV lower as noted from the reflectance spectra). The behavior of these emissions under an external magnetic field (up to 36 tesla) shows that excitons prefer to be localized at the heterointerfaces rather than at the center of the wells in MQW samples. The kinetics of the free and the heterointerface localized excitons in the Cd(,1-x)Mn(,x)Te/Cd(,1-y)Mn(,y)Te MQW samples have been studied by using a transient photoluminescence technique. Exciton lifetimes have been measured in several samples with various quantum well widths. The trapping time of the free exciton localized at the interface has been observed in the wide quantum well samples. The average energy loss rate of localized excitons has been calculated. The resonance excitation spectra of steady-state and transient luminescence show that the exciton spectra are spatially inhomogeneously broadened. An external magnetic field accelerates the localized exciton recombination processes. The dynamics of the excitons in CdMnTe MQW samples suggests that quasi-2D bound magnetic polarons (BMP) exist. A discussion of this quasi-2D BMP and the influence of an external magnetic field on exciton lifetime and exciton dynamics in Cd(,1 -x)Mn(,x)Te MQW is included.

  4. Localization effect in green light emitting InGaN/GaN multiple quantum wells with varying well thickness

    Liu, W. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); School of Electronic and Electrical Engineering, Chongqing University of Arts and Sciences, Chongqing 402160 (China); Zhao, D.G., E-mail: dgzhao@red.semi.ac.cn [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Jiang, D.S.; Chen, P.; Liu, Z.S.; Zhu, J.J.; Shi, M.; Zhao, D.M.; Li, X. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Liu, J.P.; Zhang, S.M.; Wang, H. [Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215125 (China); Yang, H. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215125 (China)

    2015-03-15

    Highlights: • A macroscopic method is used to investigate the microscopic localization effect. • Two origins of localization states in InGaN quantum wells are distinguished. • The composition-related deep localization states dominate luminescence in thin wells. • The shallow localization states dominate luminescence in thick wells. - Abstract: Green light emitting InGaN/GaN multiple-quantum-well (MQW) structures with varying well thickness are grown via metal-organic chemical vapor deposition (MOCVD). The localization effect in these samples is studied by means of temperature-dependent photoluminescence (PL) measurements. The S-shape shift of PL peak energy with increasing temperature is observed, from which the extent of localization effect is determined quantitatively by using a band-tail model. It is found that the composition-related deep localization states dominate the light emission in thin-well MQWs, while in thick-well MQWs the shallow localization states induced by the fluctuations of InGaN well thickness dominate the luminescence efficiency. It is considered that in the thinner wells the improved emitting efficiency may partially originate from the stronger localization effect.

  5. Intra-acceptor hole relaxation in Be 5-doped GaAs/A1As multiple quantum wells

    Li Su-Mei; Zheng Wei-Min; Song Ying-Xin; Liu Jing; Chu Ning-Ning

    2009-01-01

    This paper studies the dynamics of intra-acceptor hole relaxation in Be 5-doped GaAs/AlAs multiple quantum wells (MQW) with doping at the centre by time-resolved pump-probe spectroscopy using a picosecond free electron laser for infrared experiments. Low temperature far-infrared absorption measurements clearly show three principal absorption lines due to transitions of the Be acceptor from the ground state to the first three odd-parity excited states respectively.The pump-probe experiments are performed at different temperatures and different pump pulse wavelengths. The hole relaxation time from 2p excited state to ls ground state in MQW is found to be much shorter than that in bulk GaAs,and shown to be independent of temperature but strongly dependent on wavelength. The zone-folded acoustic phonon emission and slower decay of the wavefunctions of impurity states are suggested to account for the reduction of the 2p excited state lifetime in MQW. The wavelength dependence of the 2p lifetime is attributed to the diffusion of the Be atom 5-layer in quantum wells.

  6. Localization effect in green light emitting InGaN/GaN multiple quantum wells with varying well thickness

    Highlights: • A macroscopic method is used to investigate the microscopic localization effect. • Two origins of localization states in InGaN quantum wells are distinguished. • The composition-related deep localization states dominate luminescence in thin wells. • The shallow localization states dominate luminescence in thick wells. - Abstract: Green light emitting InGaN/GaN multiple-quantum-well (MQW) structures with varying well thickness are grown via metal-organic chemical vapor deposition (MOCVD). The localization effect in these samples is studied by means of temperature-dependent photoluminescence (PL) measurements. The S-shape shift of PL peak energy with increasing temperature is observed, from which the extent of localization effect is determined quantitatively by using a band-tail model. It is found that the composition-related deep localization states dominate the light emission in thin-well MQWs, while in thick-well MQWs the shallow localization states induced by the fluctuations of InGaN well thickness dominate the luminescence efficiency. It is considered that in the thinner wells the improved emitting efficiency may partially originate from the stronger localization effect

  7. Infrared photoluminescence of high In-content InN/InGaN multiple-quantum-wells

    Valdueza-Felip, Sirona; Naranjo, Fernando B.; Gonzalez-Herraez, Miguel [Electronics Department, University of Alcala, Alcala de Henares (Spain); Rigutti, Lorenzo; Julien, Francois H. [Institut d' Electronique Fondamentale, University of Paris Sud XI, UMR 8622 CNRS, Orsay (France); Lacroix, Bertrand; Ruterana, Pierre [Centre de Recherche sur les Ions les Materiaux et la Photonique (CIMAP), UMR 6252, CNRS, ENSICAEN, CEA, UCBN, Caen (France); Fernandez, Susana [Departamento de Energias Renovables, Energia Solar Fotovoltaica, CIEMAT, Madrid (Spain); Monroy, Eva [CEA Grenoble, INAC/SP2M, Grenoble (France)

    2012-01-15

    We report on the thermal evolution of the photoluminescence (PL) from high In-content InN/In{sub 0.9}Ga{sub 0.1}N multiple-quantum wells (MQWs) synthesized by plasma-assisted molecular-beam epitaxy on GaN-on-sapphire templates. The structural quality and the well/barrier thickness uniformity in the MQW structure are assessed by X-ray diffraction and transmission electron microscopy measurements. PL results are compared with the luminescence from a 1-{mu}m-thick InN reference sample. In both cases, the dominant low-temperature (5 K) PL emission peaks at {proportional_to}0.73 eV with a full width at half maximum of {proportional_to}86 meV. The InN layer displays an S-shape evolution of the emission peak energy with temperaure, explained in terms of carrier localization. A carrier localization energy of {proportional_to}12 meV is estimated for the InN layer, in good agreement with the expected carrier concentration. In the case of the MQW structure, an enhancement of the carrier localization associated to the piezoelectric field results in an improved thermal stability of the PL intensity, reaching an internal quantum efficiency of {proportional_to}16%. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. CdTe-Cd1 - xMnxTe multiple quantum well structures grown by pulsed laser evaporation and epitaxy

    Dubowski, J. J.; Roth, A. P.; Wasilewski, Z. R.; Rolfe, S. J.

    1991-09-01

    Structural and optical properties of (001) CdTe-Cd1-xMnxTe (x=0.10) multiple quantum well structures grown by pulsed laser evaporation and epitaxy (PLEE) are investigated. The layers are grown on (001) CdZnTe wafers held at a temperature in the range of 210-230 °C. Secondary-ion mass spectroscopy in-depth profiles reveal that highly uniform structures are grown. Numerical analysis of double crystal x-ray diffraction results demonstrates high structural quality of the layers and indicates partial relaxation of the strain in these structures. Low-temperature photoluminescence exhibits excitonic recombinations in the CdTe wells whereas photoluminescence from the Cd1-xMnxTe barriers is not observed. The chemical composition of the barriers deduced from photoluminescence is in excellent agreement with the intended chemical composition set during growth.

  9. Growth of GaNAs/GaAs multiple quantum well by molecular beam epitaxy using modulated N radical beam source

    GaNAs/GaAs multiple quantum well (MQW) structures have been grown on GaAs(001) substrates by molecular beam epitaxy (MBE) using modulated N radical beam source under optimized conditions, wherein the amount of N2 gas flow, RF-power and shutter sequence are systematically controlled. Clear and flat GaNAs/GaAs interfaces were observed in the cross-sectional transmission electron microscopy (TEM) measurements. Fine MQW structures originating from the precise control of the modulated N radical beam have been demonstrated as clear satellite peaks from the X-ray diffraction (XRD) measurements and sharp photoluminescence (PL) peaks. The step-like behaviors in the absorption spectra which reflect the density of state in two-dimensional systems, were clearly observed for all MQW samples. (authors)

  10. Intensity dependent absorption bleaching of high subband excitons in GaAs/AlGaAs multiple quantum wells

    Shin, S H; Lee, E H; Chae, K M; Park, S H; Kim, U

    1998-01-01

    We have investigated the influence of carrier generation on the absorption bleaching of the n=2 and n=3 excitons in GaAs/AlGaAs multiple quantum wells (MQWs). With the excitation near the resonance of the n=1 exciton absorption, the long range coulomb screening and collision broadening had significant effects on the exciton bleaching. At low excitation intensity, the absorption bleaching of the n=2 exciton in 75 A-thick MQWs and that of the n=3 exciton in 150 A-thick MQWs were due to linewidth broadening by the collision broadening effect only. At high excitation intensity, however, the reduction of oscillator strength due to the long range coulomb screening contributed dominantly to absorption bleaching.