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Sample records for 1h multiple quantum

  1. Probing degradation in complex engineering silicones by 1H multiple quantum NMR

    SciTech Connect

    Maxwell, R S; Chinn, S C; Giuliani, J; Herberg, J L

    2007-09-05

    Static {sup 1}H Multiple Quantum Nuclear Magnetic Resonance (MQ NMR) has recently been shown to provide detailed insight into the network structure of pristine silicon based polymer systems. The MQ NMR method characterizes the residual dipolar couplings of the silicon chains that depend on the average molecular weight between physical or chemical constraints. Recently, we have employed MQ NMR methods to characterize the changes in network structure in a series of complex silicone materials subject to numerous degradation mechanisms, including thermal, radiative, and desiccative. For thermal degradation, MQ NMR shows that a combination of crosslinking due to post-curing reactions as well as random chain scissioning reactions occurs. For radiative degradation, the primary mechanisms are via crosslinking both in the network and at the interface between the polymer and the inorganic filler. For samples stored in highly desiccating environments, MQ NMR shows that the average segmental dynamics are slowed due to increased interactions between the filler and the network polymer chains.

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

    SciTech Connect

    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.

  3. Thermal degradation in a trimodal poly(dimethylsiloxane) network studied by (1)H multiple quantum NMR.

    PubMed

    Giuliani, Jason R; Gjersing, Erica L; Chinn, Sarah C; Jones, Ticora V; Wilson, Thomas S; Alviso, Cynthia T; Herberg, Julie L; Pearson, Mark A; Maxwell, Robert S

    2007-11-15

    Thermal degradation of a filled, cross-linked siloxane material synthesized from poly(dimethylsiloxane) chains of three different average molecular weights and with two different cross-linking species has been studied by (1)H multiple quantum (MQ) NMR methods. Multiple domains of polymer chains were detected by MQ NMR exhibiting residual dipolar coupling () values of 200 and 600 Hz, corresponding to chains with high average molecular weight between cross-links and chains with low average molecular weight between cross-links or near the multifunctional cross-linking sites. Characterization of the values and changes in distributions present in the material were studied as a function of time at 250 degrees C and indicate significant time-dependent degradation. For the domains with low , a broadening in the distribution was observed with aging time. For the domain with high , increases in both the mean and the width in were observed with increasing aging time. Isothermal thermal gravimetric analysis reveals a 3% decrease in weight over 20 h of aging at 250 degrees C. Degraded samples also were analyzed by traditional solid-state (1)H NMR techniques, and off-gassing products were identified by solid-phase microextraction followed by gas chromatography-mass spectrometry. The results, which will be discussed here, suggest that thermal degradation proceeds by complex competition between oxidative chain scissioning and postcuring cross-linking that both contribute to embrittlement.

  4. Hydrogen cluster/network in tobermorite as studied by multiple-quantum spin counting {sup 1}H NMR

    SciTech Connect

    Mogami, Yuuki; Yamazaki, Satoru; Matsuno, Shinya; Matsui, Kunio; Noda, Yasuto; Takegoshi, K.

    2014-12-15

    Proton multiple-quantum (MQ) spin-counting experiment has been employed to study arrangement of hydrogen atoms in 9 Å/11 Å natural/synthetic tobermorites. Even though all tobermorite samples give similar characterless, broad static-powder {sup 1}H NMR spectra, their MQ spin-counting spectra are markedly different; higher quanta in 11 Å tobermorite do not grow with the MQ excitation time, while those in 9 Å one do. A statistical analysis of the MQ results recently proposed [26] is applied to show that hydrogens align in 9 Å tobermorite one dimensionally, while in 11 Å tobermorite they exist as a cluster of 5–8 hydrogen atoms.

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

    SciTech Connect

    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

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

    SciTech Connect

    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.

  7. A study of dipolar interactions and dynamic processes of water molecules in tendon by 1H and 2H homonuclear and heteronuclear multiple-quantum-filtered NMR spectroscopy.

    PubMed

    Eliav, U; Navon, G

    1999-04-01

    The effect of proton exchange on the measurement of 1H-1H, 1H-2H, and 2H-2H residual dipolar interactions in water molecules in bovine Achilles tendons was investigated using double-quantum-filtered (DQF) NMR and new pulse sequences based on heteronuclear and homonuclear multiple-quantum filtering (MQF). Derivation of theoretical expressions for these techniques allowed evaluation of the 1H-1H and 1H-2H residual dipolar interactions and the proton exchange rate at a temperature of 24 degrees C and above, where no dipolar splitting is evident. The values obtained for these parameters at 24 degrees C were 300 and 50 Hz and 3000 s-1, respectively. The results for the residual dipolar interactions were verified by repeating the above measurements at a temperature of 1.5 degrees C, where the spectra of the H2O molecules were well resolved, so that the 1H-1H dipolar interaction could be determined directly from the observed splitting. Analysis of the MQF experiments at 1.5 degrees C, where the proton exchange was in the intermediate regime for the 1H-2H dipolar interaction, confirmed the result obtained at 24 degrees C for this interaction. A strong dependence of the intensities of the MQF signals on the proton exchange rate, in the intermediate and the fast exchange regimes, was observed and theoretically interpreted. This leads to the conclusion that the MQF techniques are mostly useful for tissues where the residual dipolar interaction is not significantly smaller than the proton exchange rate. Dependence of the relaxation times and signal intensities of the MQF experiments on the orientation of the tendon with respect to the magnetic field was observed and analyzed. One of the results of the theoretical analysis is that, in the fast exchange regime, the signal decay rates in the MQF experiments as well as in the spin echo or CPMG pulse sequences (T2) depend on the orientation as the square of the second-rank Legendre polynomial.

  8. Identification and localization of bound internal water in the solution structure of interleukin 1. beta. by heteronuclear three-dimensional sup 1 H rotating-frame Overhauser sup 15 N- sup 1 H multiple quantum coherence NMR spectroscopy

    SciTech Connect

    Clore, G.M.; Bax, A.; Wingfield, P.T.; Gronenborn, A.M. )

    1990-06-19

    The presence and location of bound internal water molecules in the solution structure of interleukin 1{beta} have been investigated by means of three-dimensional {sup 1}H rotating-frame Overhauser {sup 1}H-{sup 15}N multiple quantum coherence spectroscopy (ROESY-HMQC). In this experiment through-space rotating-frame Overhauser (ROE) interactions between NH protons and bound water separated by {le}3.5{angstrom} are clearly distinguished from chemical exchange effects, as the cross-peaks for these two processes are of opposite sign. The identification of ROEs between NH protons and water is rendered simple by spreading out the spectrum into a third dimensional according to the {sup 15}N chemical shift of the directly bonded nitrogen atoms. By this means, the problems that prevent, in all but a very few limited cases, the interpretation, identification, and assignment of ROE peaks between NH protons and water in a 2D {sup 1}H-{sup 1}H ROESY spectrum of a large protein such as interleukin 1{beta}, namely, extensive NH chemical shift degeneracy and ROE peaks obscured by much stronger chemical exchange peaks, are completely circumvented. We demonstrate the existence of 15 NH protons that are close to bound water molecules. From an examination of the crystal structure of interleukin, the results can be attributed to 11 water molecules that are involved in interactions bridging hydrogen-bonding interactions with backbone amide and carbonyl groups which stabilize the 3-fold pseudosymmetric topology of interleukin 1{beta} and thus constitute an integral part of the protein structure in solution.

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

    SciTech Connect

    Davis, D.R.; Yamaizumi, Z.; Nishimura, S.; Poulter, C.D. )

    1989-05-02

    Escherichia coli 5S RNA labeled with {sup 15}N at N3 of the uridines was isolated from the S{phi}-187 uracil auxotroph grown on a minimal medium supplemented with (3-{sup 15}N)uracil. {sup 1}H-{sup 15}N multiple quantum filtered and 2D chemical shift correlated spectra gave resonances for the uridine imino {sup 1}H-{sup 15}N units whose protons were exchanging slowly with solvent. Peaks with {sup 1}H/{sup 15}N 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 {sup 1}H-{sup 15}N units in normal Watson-Crick pairs resonate. {sup 1}H 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. {sup 1}H 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.

  10. Overcoming the overlap problem in the assignment of sup 1 H NMR spectra of larger proteins by use of three-dimensional heteronuclear sup 1 H- sup 15 N Hartmann-Hahn-multiple quantum coherence and nuclear Overhauser-multiple quantum coherence spectroscopy: Application to interleukin 1. beta

    SciTech Connect

    Marion, D.; Driscoll, P.C.; Kay, L.E.; Wingfield, P.T.; Bax, A.; Gronenborn, A.M.; Clore, G.M. )

    1989-07-25

    The application of three-dimensional (3D) heteronuclear NMR spectroscopy to the sequential assignment of the {sup 1}H NMR spectra of larger proteins is presented, using uniformly labeled ({sup 15}N)interleukin 1{beta}, a protein of 153 residues and molecular mass of 17.4 kDa, as an example. The two-dimensional (2D) 600-MHz spectra of interleukin 1{beta} are too complex for complete analysis, owing to extensive cross-peak overlap and chemical shift degeneracy. The authors show that the combined use of 3D {sup 1}H-{sup 15}N Hartmann-Hahn-multiple quantum coherence (HOHAHA-HMQC) and nuclear Overhauser-multiple quantum coherence (NOESY-HMQC) spectroscopy, designed to provide the necessary through-bond and through-space correlations for sequential assignment, provides a practical general-purpose method for resolving ambiguities which severely limit the analysis of conventional 2D NMR spectra. The problem of amide NH chemical shift degeneracy in the {sup 1}H NMR spectrum is therefore effectively removed, and the assignment procedure simply involves inspecting a series of 2D {sup 1}H-{sup 1}H slices edited by the chemical shift of the directly bonded {sup 15}N atom. It is envisaged that the intrinsic simplicity of the 3D heteronuclear spectra, even for proteins of 150-200 residues, will permit the development of efficient computer-assisted or automated sequential assignment methods.

  11. Synthesis, multiple interactions and spectroscopy analysis of ethyl-4-[(benzoyl)-hydrazonomethyl]-3,5-dimethyl-1H-pyrrole-2-carboxylate: Through experimental and quantum chemical approaches

    NASA Astrophysics Data System (ADS)

    Singh, R. N.; Kumar, Amit; Tiwari, R. K.; Rawat, Poonam

    2013-03-01

    The carboxaldehydes of pyrrole form important class of precursors for synthesis of acid hydrazide-hydrazones and their derivatives which show the various applications. A novel hydrazide-hydrazone of pyrrole: Ethyl-4-[(benzoyl)-hydrazonomethyl]-3,5-dimethyl-1H-pyrrole-2-carboxylate (3) has been synthesized by condensation of ethyl-4-formyl-3,5-dimetyl-1H-pyrrole-2-carboxylate and benzohydrazide. The product was characterized by spectroscopy methods (FT-IR, 1H NMR, UV-Vis and DART Mass) and quantum chemical calculations. The calculated thermodynamic parameters show that the formation of (3) is exothermic and spontaneous at room temperature. The local electronic descriptors analysis and molecular electrostatic potential surface were used to predict the sites and nature of interactions which indicate the dimer formation through multiple interaction through Nsbnd H⋯O and C-H⋯O. The vibrational analysis shows red shifts in vNsbnd H and vCdbnd O as result of dimer formation. Topological and energetic parameters generated by AIM show the nature of interactions in dimer. The interaction energies of dimer formation using DFT and AIM calculations are found to be 14.19 and 15.19 kcal/mol respectively. Ellipticity analysis confirms the presence of resonance assisted heteronuclear H-bonding in dimer.

  12. High-resolution 1H NMR spectroscopy of fish muscle, eggs and small whole fish via Hadamard-encoded intermolecular multiple-quantum coherence.

    PubMed

    Cai, Honghao; Chen, Yushan; Cui, Xiaohong; Cai, Shuhui; Chen, Zhong

    2014-01-01

    Nuclear magnetic resonance (NMR) spectroscopy has become an important technique for tissue studies. Since tissues are in semisolid-state, their high-resolution (HR) spectra cannot be obtained by conventional NMR spectroscopy. Because of this restriction, extraction and high-resolution magic angle spinning (HR MAS) are widely applied for HR NMR spectra of tissues. However, both of the methods are subject to limitations. In this study, the feasibility of HR (1)H NMR spectroscopy based on intermolecular multiple-quantum coherence (iMQC) technique is explored using fish muscle, fish eggs, and a whole fish as examples. Intact salmon muscle tissues, intact eggs from shishamo smelt and a whole fish (Siamese algae eater) are studied by using conventional 1D one-pulse sequence, Hadamard-encoded iMQC sequence, and HR MAS. When we use the conventional 1D one-pulse sequence, hardly any useful spectral information can be obtained due to the severe field inhomogeneity. By contrast, HR NMR spectra can be obtained in a short period of time by using the Hadamard-encoded iMQC method without shimming. Most signals from fatty acids and small metabolites can be observed. Compared to HR MAS, the iMQC method is non-invasive, but the resolution and the sensitivity of resulting spectra are not as high as those of HR MAS spectra. Due to the immunity to field inhomogeneity, the iMQC technique can be a proper supplement to HR MAS, and it provides an alternative for the investigation in cases with field distortions and with samples unsuitable for spinning. The acquisition time of the proposed method is greatly reduced by introduction of the Hadamard-encoded technique, in comparison with that of conventional iMQC method.

  13. Multiple quantum correlated spectroscopy revamped by asymmetric z-gradient echo detection signal intensity as a function of the read pulse flip angle as verified by heteronuclear 1H/31P experiments.

    PubMed

    Jiang, Bin; Liu, Huili; Liu, Maili; Ye, Chaohui; Mao, Xi-an

    2007-02-07

    Heteronuclear multiple quantum (n=+/-0 and n=+/-2) correlated spectroscopy revamped by asymmetric z-gradient echo detection (CRAZED) experiments were performed on the spins 31P and 1H in a H3PO4 solution in order to determine the optimum flip angle for the read pulse. It has been shown that for the negative quantum signals, the maximum signals appear at beta=0, and for the positive quantum signals, the maximum signals appear at beta=pi. The CRAZED signals were compared to the single quantum signals in two-pulse two-gradient experiments. It is found that the CRAZED signals can also be distinguished into gradient echoes and spin echoes. The gradient-echo-type CRAZED signal requires beta=0 and the spin-echo-type CRAZED signal requires beta=pi for maximum echo intensities, in the same way as in single quantum experiments.

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

    NASA Astrophysics Data System (ADS)

    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.

  15. Nuclear receptor NR1H3 in familial multiple sclerosis

    PubMed Central

    Wang, Zhe; Sadovnick, A. Dessa; Traboulsee, Anthony L.; Ross, Jay P.; Bernales, Cecily Q.; Encarnacion, Mary; Yee, Irene M.; de Lemos, Madonna; Greenwood, Talitha; Lee, Joshua D.; Wright, Galen; Ross, Colin J.; Zhang, Si; Song, Weihong; Vilariño-Güell, Carles

    2016-01-01

    SUMMARY Multiple sclerosis (MS) is an inflammatory disease characterized by myelin loss and neuronal dysfunction. Despite the aggregation observed in some families, pathogenic mutations have remained elusive. In this study we describe the identification of NR1H3 p.Arg415Gln in seven MS patients from two multi-incident families presenting severe and progressive disease, with an average age at onset of 34 years. Additionally, association analysis of common variants in NR1H3 identified rs2279238 conferring a 1.35-fold increased risk of developing progressive MS. The p.Arg415Gln position is highly conserved in orthologs and paralogs, and disrupts NR1H3 heterodimerization and transcriptional activation of target genes. Protein expression analysis revealed that mutant NR1H3 (LXRA) alters gene expression profiles, suggesting a disruption in transcriptional regulation as one of the mechanisms underlying MS pathogenesis. Our study indicates that pharmacological activation of LXRA or its targets may lead to effective treatments for the highly debilitating and currently untreatable progressive phase of MS. PMID:27253448

  16. Multiplicative properties of quantum channels

    NASA Astrophysics Data System (ADS)

    Rahaman, Mizanur

    2017-08-01

    In this paper, we study the multiplicative behaviour of quantum channels, mathematically described by trace preserving, completely positive maps on matrix algebras. It turns out that the multiplicative domain of a unital quantum channel has a close connection to its spectral properties. A structure theorem (theorem 2.5), which reveals the automorphic property of an arbitrary unital quantum channel on a subalgebra, is presented. Various classes of quantum channels (irreducible, primitive, etc) are then analysed in terms of this stabilising subalgebra. The notion of the multiplicative index of a unital quantum channel is introduced, which measures the number of times a unital channel needs to be composed with itself for the multiplicative algebra to stabilise. We show that the maps that have trivial multiplicative domains are dense in completely bounded norm topology in the set of all unital completely positive maps. Some applications in quantum information theory are discussed.

  17. Efficient dipolar double quantum filtering under magic angle spinning without a 1H decoupling field

    NASA Astrophysics Data System (ADS)

    Courtney, Joseph M.; Rienstra, Chad M.

    2016-08-01

    We present a systematic study of dipolar double quantum (DQ) filtering in 13C-labeled organic solids over a range of magic-angle spinning rates, using the SPC-n recoupling sequence element with a range of n symmetry values from 3 to 11. We find that efficient recoupling can be achieved for values n ⩾ 7, provided that the 13C nutation frequency is on the order of 100 kHz or greater. The decoupling-field dependence was investigated and explicit heteronuclear decoupling interference conditions identified. The major determinant of DQ filtering efficiency is the decoupling interference between 13C and 1H fields. For 13C nutation frequencies greater than 75 kHz, optimal performance is observed without an applied 1H field. At spinning rates exceeding 20 kHz, symmetry conditions as low as n = 3 were found to perform adequately.

  18. Efficient dipolar double quantum filtering under magic angle spinning without a (1)H decoupling field.

    PubMed

    Courtney, Joseph M; Rienstra, Chad M

    2016-08-01

    We present a systematic study of dipolar double quantum (DQ) filtering in (13)C-labeled organic solids over a range of magic-angle spinning rates, using the SPC-n recoupling sequence element with a range of n symmetry values from 3 to 11. We find that efficient recoupling can be achieved for values n⩾7, provided that the (13)C nutation frequency is on the order of 100kHz or greater. The decoupling-field dependence was investigated and explicit heteronuclear decoupling interference conditions identified. The major determinant of DQ filtering efficiency is the decoupling interference between (13)C and (1)H fields. For (13)C nutation frequencies greater than 75kHz, optimal performance is observed without an applied (1)H field. At spinning rates exceeding 20kHz, symmetry conditions as low as n=3 were found to perform adequately.

  19. Selective Detection of 1H NMR Resonances of CH n Groups Using a Heteronuclear Maximum-Quantum Filter and Pulsed Field Gradients

    NASA Astrophysics Data System (ADS)

    Liu, M.; Farrant, R. D.; Nicholson, J. K.; Lindon, J. C.

    A number of approaches are described for the provision of separate one-dimensional 1H NMR spectra of CH, CH 2, and CH 3 groups utilizing the natural-abundance 13C spins and based upon the selection of the maximum multiple-quantum coherences of the various groups, This sequence is termed edited maximum-quantum proton spectroscop y (MAXY) spectroscopy, The replacement of phase cycling with the application of z magnetic field gradient pulses is also demonstrated, The editing approach is demonstrated using the 1H NMR spectrum of dexamethasone in DMSO- d6 solution, Extension to a complex mixture biofluid is exemplified by the CH 3-only 1H NMR spectrum of human seminal plasma. This aid to the assignment of endogenous metabolite resonances is demonstrated to result in dramatic spectral simplification.

  20. Single-Quantum Coherence Filter for Strongly Coupled Spin Systems for Localized 1H NMR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Trabesinger, Andreas H.; Mueller, D. Christoph; Boesiger, Peter

    2000-08-01

    A pulse sequence for localized in vivo1H NMR spectroscopy is presented, which selectively filters single-quantum coherence built up by strongly coupled spin systems. Uncoupled and weakly coupled spin systems do not contribute to the signal output. Analytical calculations using a product operator description of the strongly coupled AB spin system as well as in vitro tests demonstrate that the proposed filter produces a signal output for a strongly coupled AB spin system, whereas the resonances of a weakly coupled AX spin system and of uncoupled spins are widely suppressed. As a potential application, the detection of the strongly coupled AA‧BB‧ spin system of taurine at 1.5 T is discussed.

  1. Assessing Heterogeneity of Osteolytic Lesions in Multiple Myeloma by 1H HR-MAS NMR Metabolomics

    PubMed Central

    Tavel, Laurette; Fontana, Francesca; Garcia Manteiga, Josè Manuel; Mari, Silvia; Mariani, Elisabetta; Caneva, Enrico; Sitia, Roberto; Camnasio, Francesco; Marcatti, Magda; Cenci, Simone; Musco, Giovanna

    2016-01-01

    Multiple myeloma (MM) is a malignancy of plasma cells characterized by multifocal osteolytic bone lesions. Macroscopic and genetic heterogeneity has been documented within MM lesions. Understanding the bases of such heterogeneity may unveil relevant features of MM pathobiology. To this aim, we deployed unbiased 1H high-resolution magic-angle spinning (HR-MAS) nuclear magnetic resonance (NMR) metabolomics to analyze multiple biopsy specimens of osteolytic lesions from one case of pathological fracture caused by MM. Multivariate analyses on normalized metabolite peak integrals allowed clusterization of samples in accordance with a posteriori histological findings. We investigated the relationship between morphological and NMR features by merging morphological data and metabolite profiling into a single correlation matrix. Data-merging addressed tissue heterogeneity, and greatly facilitated the mapping of lesions and nearby healthy tissues. Our proof-of-principle study reveals integrated metabolomics and histomorphology as a promising approach for the targeted study of osteolytic lesions. PMID:27809247

  2. Multiple-Quantum-Well Intersubband Infrared Detector

    NASA Technical Reports Server (NTRS)

    Borenstain, Shmuel I.

    1991-01-01

    Proposed multiple-quantum-well intersubband semiconductor device detects photons over broader range of wavelengths. Device is stack of substacks, each of which contains quantum-well layers sensitive to different narrow band of wavelengths. Bandwidth and detectivity increased.

  3. 1H NMR z-spectra of acetate methyl in stretched hydrogels: Quantum-mechanical description and Markov chain Monte Carlo relaxation-parameter estimation

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    The 1H 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.

  4. MULTIPLE-QUANTUM NMR IN SOLIDS

    SciTech Connect

    Yen, Y-S.

    1982-11-01

    Time domain multiple-quantum (MQ) nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for spectral simplification and for providing new information on molecular dynamics. In this thesis, applications of MQ NMR are presented and show distinctly the advantages of this method over the conventional single-quantum NMR. Chapter 1 introduces the spin Hamiltonians, the density matrix formalism and some basic concepts of MQ NMR spectroscopy. In chapter 2, {sup 14}N double-quantum coherence is observed with high sensitivity in isotropic solution, using only the magnetization of bound protons. Spin echoes are used to obtain the homogeneous double-quantum spectrum and to suppress a large H{sub 2}O solvent signal. Chapter 3 resolves the main difficulty in observing high MQ transitions in solids. Due to the profusion of spin transitions in a solid, individual lines are unresolved. Excitation and detection of high quantum transitions by normal schemes are thus difficult. To ensure that overlapping lines add constructively and thereby to enhance sensitivity, time-reversal pulse sequences are used to generate all lines in phase. Up to 22-quantum {sup 1}H absorption in solid adamantane is observed. A time dependence study shows an increase in spin correlations as the excitation time increased. In chapter 4, a statistical theory of MQ second moments is developed for coupled spins of spin I = 1/2. The model reveals that the ratio of the average dipolar coupling to the rms value largely determines the dependence of second moments on the number of quanta. The results of this model are checked against computer-calculated and experimental second moments, and show good agreement. A simple scheme is proposed in chapter 5 for sensitivity improvement in a MQ experiment. The scheme involves acquiring all of the signal energy available in the detection period by applying pulsed spinlocking and sampling between pulses. Using this technique on polycrystalline adamantane, a large

  5. 1H-NMR analysis provides a metabolomic profile of patients with multiple sclerosis

    PubMed Central

    Cocco, Eleonora; Murgia, Federica; Lorefice, Lorena; Barberini, Luigi; Poddighe, Simone; Frau, Jessica; Fenu, Giuseppe; Coghe, Giancarlo; Murru, Maria Rita; Murru, Raffaele; Del Carratore, Francesco; Atzori, Luigi

    2015-01-01

    Objective: To investigate the metabolomic profiles of patients with multiple sclerosis (MS) and to define the metabolic pathways potentially related to MS pathogenesis. Methods: Plasma samples from 73 patients with MS (therapy-free for at least 90 days) and 88 healthy controls (HC) were analyzed by 1H-NMR spectroscopy. Data analysis was conducted with principal components analysis followed by a supervised analysis (orthogonal partial least squares discriminant analysis [OPLS-DA]). The metabolites were identified and quantified using Chenomx software, and the receiver operating characteristic (ROC) curves were calculated. Results: The model obtained with the OPLS-DA identified predictive metabolic differences between the patients with MS and HC (R2X = 0.615, R2Y = 0.619, Q2 = 0.476; p < 0.001). The differential metabolites included glucose, 5-OH-tryptophan, and tryptophan, which were lower in the MS group, and 3-OH-butyrate, acetoacetate, acetone, alanine, and choline, which were higher in the MS group. The suitability of the model was evaluated using an external set of samples. The values returned by the model were used to build the corresponding ROC curve (area under the curve of 0.98). Conclusion: NMR metabolomic analysis was able to discriminate different metabolic profiles in patients with MS compared with HC. With the exception of choline, the main metabolic changes could be connected to 2 different metabolic pathways: tryptophan metabolism and energy metabolism. Metabolomics appears to represent a promising noninvasive approach for the study of MS. PMID:26740964

  6. Combined (1)H and (31)P spectroscopy provides new insights into the pathobiochemistry of brain damage in multiple sclerosis.

    PubMed

    Hattingen, Elke; Magerkurth, Jörg; Pilatus, Ulrich; Hübers, Annemarie; Wahl, Mathias; Ziemann, Ulf

    2011-06-01

    (1)H MRSI has evolved as an important tool to study the onset and progression of brain damage in multiple sclerosis. Abnormal increases in total creatine, total choline and myoinositol have been noted in multiple sclerosis. However, the pathobiochemical mechanisms related to these changes are still largely unclear. The combination of (1)H MRSI and (1)H-decoupled (31)P MRSI can specify to what extent phosphorylated components of total creatine and total choline contribute to this increase. Combined (1)H and (31)P MRSI data were obtained at 3 T in 22 patients with multiple sclerosis and in 23 healthy controls, and aligned with structural MRI to allow for correction for partial volume effects caused by cerebrospinal fluid and lesion load. A significant increase in total creatine was found in multiple sclerosis, and this was attributed to equal changes in the phosphorylated and unphosphorylated components. The concentrations of the putative glial markers total creatine and myoinositol in lesion-free (1)H MRSI voxels correlated with the global lesion load. We conclude that changes in total creatine are not related to altered energy metabolism, but rather indicate gliosis. Together with the increase in myoinositol, total creatine can be considered as a biomarker for disease severity. A significant total choline increase was mainly a result of choline components not visible by (31)P MRS. The origin of this residual choline fraction remains to be investigated. Copyright © 2010 John Wiley & Sons, Ltd.

  7. Quantum internet using code division multiple access.

    PubMed

    Zhang, Jing; Liu, Yu-xi; Ozdemir, Sahin Kaya; Wu, Re-Bing; Gao, Feifei; Wang, Xiang-Bin; Yang, Lan; Nori, Franco

    2013-01-01

    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.

  8. Quantum internet using code division multiple access

    NASA Astrophysics Data System (ADS)

    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.

  9. Quantum internet using code division multiple access

    PubMed Central

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

    2013-01-01

    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. PMID:23860488

  10. Multiple Multi-Qubit Quantum States Sharing

    NASA Astrophysics Data System (ADS)

    Qin, Hua-Wang; Dai, Yue-Wei

    2016-04-01

    A multiple multi-qubit quantum states sharing scheme is proposed, in which the dealer can share multiple multi-qubit quantum states among the participants through only one distribution and one recovery. The dealer encodes the secret quantum states into a special entangled state, and then distributes the particles of the entangled state to the participants. The participants perform the single-particle measurements on their particles, and can cooperate to recover the multiple multi-qubit quantum states. Compared to the existing schemes, our scheme is more efficient and more flexible in practice.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. Quantum hyperparallel algorithm for matrix multiplication

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  13. Quantum hyperparallel algorithm for matrix multiplication.

    PubMed

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

    2016-04-29

    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.

  14. Valence Photoisomerization of 1-Ethoxycarbonyl-1H-Azepine: Excited State Energetics and Multiplicity

    DTIC Science & Technology

    1976-12-01

    Photochemistry Department of Chemistry Boston University Boston, Massachusetts 02215 December 1, 1976 D D C" EISEDDJE ’rA j/W 10 1977 ^ A...of Photochemistry 19. KEY WORDS (Contlnua on raveraa alda II nacaisary and Idantlty by block numbar) Valence photoisomerization, excited state...configuration and photochemistry or heterocycles. multiplicity. 20. ABSTRACT (Contlnua on ravaraa alda II nacaaaary and Idantlty by block numbar

  15. Time-domain multiple-quantum NMR

    SciTech Connect

    Weitekamp, Daniel P.

    1982-11-01

    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.

  16. Analysis of a zebrafish dync1h1 mutant reveals multiple functions for cytoplasmic dynein 1 during retinal photoreceptor development

    PubMed Central

    2010-01-01

    Background Photoreceptors of the retina are highly compartmentalized cells that function as the primary sensory neurons for receiving and initiating transmission of visual information. Proper morphogenesis of photoreceptor neurons is essential for their normal function and survival. We have characterized a zebrafish mutation, cannonball, that completely disrupts photoreceptor morphogenesis. Results Analysis revealed a non-sense mutation in cytoplasmic dynein heavy chain 1 (dync1h1), a critical subunit in Dynein1, to underlie the cannonball phenotypes. Dynein1 is a large minus-end directed, microtubule motor protein complex that has been implicated in multiple, essential cellular processes. In photoreceptors, Dynein1 is thought to mediate post-Golgi vesicle trafficking, while Dynein2 is thought to be responsible for outer segment maintenance. Surprisingly, cannonball embryos survive until larval stages, owing to wild-type maternal protein stores. Retinal photoreceptor neurons, however, are significantly affected by loss of Dync1h1, as transmission electron microscopy and marker analyses demonstrated defects in organelle positioning and outer segment morphogenesis and suggested defects in post-Golgi vesicle trafficking. Furthermore, dosage-dependent antisense oligonucleotide knock-down of dync1h1 revealed outer segment abnormalities in the absence of overt inner segment polarity and trafficking defects. Consistent with a specific function of Dync1h1 within the outer segment, immunolocalization showed that this protein and other subunits of Dynein1 and Dynactin localized to the ciliary axoneme of the outer segment, in addition to their predicted inner segment localization. However, knock-down of Dynactin subunits suggested that this protein complex, which is known to augment many Dynein1 activities, is only essential for inner segment processes as outer segment morphogenesis was normal. Conclusions Our results indicate that Dynein1 is required for multiple cellular

  17. Quantitative Quantum Mechanical Spectral Analysis (qQMSA) of (1)H NMR spectra of complex mixtures and biofluids.

    PubMed

    Tiainen, Mika; Soininen, Pasi; Laatikainen, Reino

    2014-05-01

    The quantitative interpretation of (1)H NMR spectra of mixtures like the biofluids is a demanding task due to spectral complexity and overlap. Complications may arise also from water suppression, T2-editing, protein interactions, relaxation differences of the species, experimental artifacts and, furthermore, the spectra may contain unknown components and macromolecular background which cannot be easily separated from baseline. In this work, tools and strategies for quantitative Quantum Mechanical Spectral Analysis (qQMSA) of (1)H NMR spectra from complex mixtures were developed and systematically assessed. In the present approach, the signals of well-defined, stoichiometric components are described by a QM model, while the background is described by a multiterm baseline function and the unknown signals using optimizable and adjustable lines, regular multiplets or any spectral structures which can be composed from spectral lines. Any prior knowledge available from the spectrum can also be added to the model. Fitting strategies for weak and strongly overlapping spectral systems were developed and assessed using two basic model systems, the metabolite mixtures without and with macromolecular (serum) background. The analyses show that if the spectra are measured in high-throughput manner, the consistent absolute quantification demands some calibration to compensate the different response factors of the protons and compounds. On the other hand, the results show that also the T2-edited spectra can be measured so that they obey well the QM rules. In general, qQMSA exploits and interprets the spectral information in maximal way taking full advantage from the QM properties of the spectra and, at the same time, offers chemical confidence which means that individual components can be identified with high confidence on the basis of their accurate spectral parameters. Copyright © 2014 Elsevier Inc. All rights reserved.

  18. Quantitative Quantum Mechanical Spectral Analysis (qQMSA) of 1H NMR spectra of complex mixtures and biofluids

    NASA Astrophysics Data System (ADS)

    Tiainen, Mika; Soininen, Pasi; Laatikainen, Reino

    2014-05-01

    The quantitative interpretation of 1H NMR spectra of mixtures like the biofluids is a demanding task due to spectral complexity and overlap. Complications may arise also from water suppression, T2-editing, protein interactions, relaxation differences of the species, experimental artifacts and, furthermore, the spectra may contain unknown components and macromolecular background which cannot be easily separated from baseline. In this work, tools and strategies for quantitative Quantum Mechanical Spectral Analysis (qQMSA) of 1H NMR spectra from complex mixtures were developed and systematically assessed. In the present approach, the signals of well-defined, stoichiometric components are described by a QM model, while the background is described by a multiterm baseline function and the unknown signals using optimizable and adjustable lines, regular multiplets or any spectral structures which can be composed from spectral lines. Any prior knowledge available from the spectrum can also be added to the model. Fitting strategies for weak and strongly overlapping spectral systems were developed and assessed using two basic model systems, the metabolite mixtures without and with macromolecular (serum) background. The analyses show that if the spectra are measured in high-throughput manner, the consistent absolute quantification demands some calibration to compensate the different response factors of the protons and compounds. On the other hand, the results show that also the T2-edited spectra can be measured so that they obey well the QM rules. In general, qQMSA exploits and interprets the spectral information in maximal way taking full advantage from the QM properties of the spectra and, at the same time, offers chemical confidence which means that individual components can be identified with high confidence on the basis of their accurate spectral parameters.

  19. Multiple phase estimation in quantum cloning machines

    NASA Astrophysics Data System (ADS)

    Yao, Yao; Ge, Li; Xiao, Xing; Wang, Xiao-guang; Sun, Chang-pu

    2014-08-01

    Since the initial discovery of the Wootters-Zurek no-cloning theorem, a wide variety of quantum cloning machines have been proposed aiming at imperfect but optimal cloning of quantum states within its own context. Remarkably, most previous studies have employed the Bures fidelity or the Hilbert-Schmidt norm as the figure of merit to characterize the quality of the corresponding cloning scenarios. However, in many situations, what we truly care about is the relevant information about certain parameters encoded in quantum states. In this work, we investigate the multiple phase estimation problem in the framework of quantum cloning machines, from the perspective of quantum Fisher information matrix (QFIM). Focusing on the generalized d-dimensional equatorial states, we obtain the analytical formulas of QFIM for both universal quantum cloning machine (UQCM) and phase-covariant quantum cloning machine (PQCM), and prove that PQCM indeed performs better than UQCM in terms of QFIM. We highlight that our method can be generalized to arbitrary cloning schemes where the fidelity between the single-copy input and output states is input-state independent. Furthermore, the attainability of the quantum Cramér-Rao bound is also explicitly discussed.

  20. Homo- and Heteronuclear Multiple-Quantum Filters for Measurement of NMR Isotope Shifts

    NASA Astrophysics Data System (ADS)

    Wooten, E. W.; Dua, R. K.; Dotson, G. D.; Woodard, R. W.

    The measurement of NMR isotope shifts as mechanistic probes can be complicated by mixtures of isotopomers. Homo- and heteronuclear NMR techniques based on multiple-quantum filtration are presented and shown to be a useful aid in measuring such shifts. The effects of 1H/ 2H substitution and 16O/ 18O substitution on the nuclear shielding of 1H, 13C, and 31P in a multiply labeled phosphoenolpyruvate are measured and interpreted qualitatively in terms of their rovibrational origins.

  1. Quantum decoherence and quasi-equilibrium in open quantum systems with few degrees of freedom: application to 1H NMR of nematic liquid crystals.

    PubMed

    Segnorile, Héctor H; Zamar, Ricardo C

    2011-12-28

    Explanation of decoherence and quasi-equilibrium in systems with few degrees of freedom demands a deep theoretical analysis that considers the observed system as an open quantum system. In this work, we study the problem of decoherence of an observed system of quantum interacting particles, coupled to a quantum lattice. Our strategy is based on treating the environment and the system-environment Hamiltonians fully quantum mechanically, which yields a representation of the time evolution operator useful for disentangling the different time scales underlying in the observed system dynamics. To describe the possible different stages of the dynamics of the observed system, we introduce quantum mechanical definitions of essentially isolated, essentially adiabatic, and thermal-contact system-environment interactions. This general approach is then applied to the study of decoherence and quasi-equilibrium in proton nuclear magnetic resonance ((1)H NMR) of nematic liquid crystals. A summary of the original results of this work is as follows. We calculate the decoherence function and apply it to describe the evolution of a coherent spin state, induced by the coupling with the molecular environment, in absence of spin-lattice relaxation. By assuming quantum energy conserving or non-demolition interactions, we identify an intermediate time scale, between those controlled by self-interactions and thermalization, where coherence decays irreversibly. This treatment is also adequate for explaining the buildup of quasi-equilibrium of the proton spin system, via the process we called eigen-selectivity. By analyzing a hypothetical time reversal experiment, we identify two sources of coherence loss which are of a very different nature and give rise to distinct time scales of the spin dynamics: (a) reversible or adiabatic quantum decoherence and (b) irreversible or essentially adiabatic quantum decoherence. Local irreversibility arises as a consequence of the uncertainty introduced by

  2. Selectivity in multiple quantum nuclear magnetic resonance

    SciTech Connect

    Warren, W.S.

    1980-11-01

    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.

  3. Infrared Multiple-Quantum-Well Phototransistor

    NASA Technical Reports Server (NTRS)

    Borenstain, Shmuel I.

    1992-01-01

    Proposed npn AlxGa1-xAs phototransistor incorporates multiple-quantum-well (MQW) infrared photodetector. Has n-doped contacts and is embedded between p-doped base region and n-doped collector region of transistor. Photocurrent amplified, and dark current suppressed.

  4. Subcarrier multiplexing multiple-input multiple-output quantum key distribution scheme with orthogonal quantum states

    NASA Astrophysics Data System (ADS)

    Xiao, Hailin; Zhang, Zhongshan

    2017-01-01

    Quantum key distribution (QKD) system is presently being developed for providing high-security transmission in future free-space optical communication links. However, current QKD technique restricts quantum secure communication to a low bit rate. To improve the QKD bit rate, we propose a subcarrier multiplexing multiple-input multiple-output quantum key distribution (SCM-MQKD) scheme with orthogonal quantum states. Specifically, we firstly present SCM-MQKD system model and drive symmetrical SCM-MQKD system into decoherence-free subspaces. We then utilize bipartite Werner and isotropic states to construct multiple parallel single photon with orthogonal quantum states that are invariant for unitary operations. Finally, we derive the density matrix and the capacity of SCM-MQKD system, respectively. Theoretical analysis and numerical results show that the capacity of SCM-MQKD system will increase {log _2}(N^2+1) times than that of single-photon QKD system.

  5. Accurate Measurements of Multiple-Bond 13C- 1H Coupling Constants from Phase-Sensitive 2D INEPT Spectra

    NASA Astrophysics Data System (ADS)

    Ding, Keyang

    1999-10-01

    Measurements of multiple-bond 13C-1H coupling constants are of great interest for the assignment of nonprotonated 13C resonances and the elucidation of molecular conformation in solution. Usually, the heteronuclear multiple-bond coupling constants were measured either by the JCH splittings mostly in selective 2D spectra or in 3D spectra, which are time consuming, or by the cross peak intensity analysis in 2D quantitative heteronuclear J correlation spectra (1994, G. Zhu, A. Renwick, and A. Bax, J. Magn. Reson. A 110, 257; 1994, A. Bax, G. W. Vuister, S. Grzesiek, F. Delaglio, A. C. Wang, R. Tschudin, and G. Zhu, Methods Enzymol. 239, 79.), which suffer from the accuracy problem caused by the signal-to-noise ratio and the nonpure absorptive peak patterns. Concerted incrementation of the duration for developing proton antiphase magnetization with respect to carbon-13 and the evolution time for proton chemical shift in different steps in a modified INEPT pulse sequence provides a new method for accurate measurements of heteronuclear multiple-bond coupling constants in a single 2D experiment.

  6. Multiple quantum phase transitions of plutonium compounds

    SciTech Connect

    Matsumoto, Munehisa; Yin, Quan; Otsuki, Junya; Savrasov, Sergey Y.

    2011-07-22

    We show by quantum Monte Carlo simulations of realistic Kondo lattice models derived from electronicstructure calculations that multiple quantum critical points can be realized in plutonium-based materials. We place representative systems, including PuCoGa5, on a realistic Doniach phase diagram and identify the regions where the magnetically mediated superconductivity could occur. The solution of an inverse problem to restore the quasiparticle renormalization factor for f electrons is shown to be sufficiently good to predict the trends among Sommerfeld coefficients and magnetism. A suggestion on the possible experimental verification for this scenario is given for PuAs.

  7. IL-21 drives secondary autoimmunity in patients with multiple sclerosis, following therapeutic lymphocyte depletion with alemtuzumab (Campath-1H)

    PubMed Central

    Jones, Joanne L.; Phuah, Chia-Ling; Cox, Amanda L.; Thompson, Sara A.; Ban, Maria; Shawcross, Jacqueline; Walton, Amie; Sawcer, Stephen J.; Compston, Alastair; Coles, Alasdair J.

    2009-01-01

    Phase II clinical trials revealed that the lymphocyte-depleting humanized monoclonal antibody alemtuzumab (Campath-1H) is highly effective in the treatment of early relapsing-remitting multiple sclerosis. However, 30% of patients develop autoimmunity months to years after pulsed exposure to alemtuzumab, usually targeting the thyroid gland and, more rarely, blood components. In this study, we show that autoimmunity arose in those patients with greater T cell apoptosis and cell cycling in response to alemtuzumab-induced lymphocyte depletion, a phenomenon that is driven by higher levels of IL-21. Before treatment, patients who went on to develop secondary autoimmunity had more than 2-fold greater levels of serum IL-21 than the nonautoimmune group. We suggest that serum IL-21 may, therefore, serve as a biomarker for the risk of developing autoimmunity months to years after alemtuzumab treatment. This has implications for counseling those patients with multiple sclerosis who are considering lymphocyte-depleting therapy with alemtuzumab. Finally, we demonstrate through genotyping that IL-21 expression is genetically predetermined. We propose that, by driving cycles of T cell expansion and apoptosis to excess, IL-21 increases the stochastic opportunities for T cells to encounter self antigen and, hence, for autoimmunity. PMID:19546505

  8. Quantum key distribution network for multiple applications

    NASA Astrophysics Data System (ADS)

    Tajima, A.; Kondoh, T.; Ochi, T.; Fujiwara, M.; Yoshino, K.; Iizuka, H.; Sakamoto, T.; Tomita, A.; Shimamura, E.; Asami, S.; Sasaki, M.

    2017-09-01

    The fundamental architecture and functions of secure key management in a quantum key distribution (QKD) network with enhanced universal interfaces for smooth key sharing between arbitrary two nodes and enabling multiple secure communication applications are proposed. The proposed architecture consists of three layers: a quantum layer, key management layer and key supply layer. We explain the functions of each layer, the key formats in each layer and the key lifecycle for enabling a practical QKD network. A quantum key distribution-advanced encryption standard (QKD-AES) hybrid system and an encrypted smartphone system were developed as secure communication applications on our QKD network. The validity and usefulness of these systems were demonstrated on the Tokyo QKD Network testbed.

  9. Gene mutation profiling of primary glioblastoma through multiple tumor biopsy guided by 1H-magnetic resonance spectroscopy.

    PubMed

    Tang, Chao; Guo, Jun; Chen, Hong; Yao, Cheng-Jun; Zhuang, Dong-Xiao; Wang, Yin; Tang, Wei-Jun; Ren, Guang; Yao, Yu; Wu, Jin-Song; Mao, Ying; Zhou, Liang-Fu

    2015-01-01

    Genetic mutation has served as the biomarkers for the diagnosis and treatment of glioblastoma multiforme (GBM). However, intra-tumor heterogeneity may interfere with personalized treatment strategies based on mutation analysis. This study aimed to characterize somatic mutation profiling of GBM. We collected 33 samples from 7 patients with the primary GBM associated with different Choline (Cho) to N-acetylaspartate (NAA) index (CNI) through the frameless proton magnetic resonance spectroscopy (1H-MRS) guided biopsies and investigated multiple somatic mutations profiling using the AmpliSeq cancer hotspot panel V2. We identified 53 missense or nonsense mutations in 27 genes including some novel mutations such as APC and IDH2. The mutations in EGFR, TP53, PTEN, PIK3CA genes were presented with different frequency and the majority of the mutated gene was only shared by 1-2 samples from one patient. Moreover, we found the association of CNI with histological grade, but there was no significant change of CNI in the presence of TP53, EGFR and PTEN mutations. These data suggest that gene mutations constitute a heterogeneous marker for primary GBM which may be independent of intra-tumor morphological phenotypes of GBM; therefore, gene mutation markers could not be determined from a small number of needle biopsies or only confined to the high-grade region.

  10. Gene mutation profiling of primary glioblastoma through multiple tumor biopsy guided by 1H-magnetic resonance spectroscopy

    PubMed Central

    Tang, Chao; Guo, Jun; Chen, Hong; Yao, Cheng-Jun; Zhuang, Dong-Xiao; Wang, Yin; Tang, Wei-Jun; Ren, Guang; Yao, Yu; Wu, Jin-Song; Mao, Ying; Zhou, Liang-Fu

    2015-01-01

    Genetic mutation has served as the biomarkers for the diagnosis and treatment of glioblastoma multiforme (GBM). However, intra-tumor heterogeneity may interfere with personalized treatment strategies based on mutation analysis. This study aimed to characterize somatic mutation profiling of GBM. We collected 33 samples from 7 patients with the primary GBM associated with different Choline (Cho) to N-acetylaspartate (NAA) index (CNI) through the frameless proton magnetic resonance spectroscopy (1H-MRS) guided biopsies and investigated multiple somatic mutations profi ling using the AmpliSeq cancer hotspot panel V2. We identifi ed 53 missense or nonsense mutations in 27 genes including some novel mutations such as APC and IDH2. The mutations in EGFR, TP53, PTEN, PIK3CA genes were presented with different frequency and the majority of the mutated gene was only shared by 1-2 samples from one patient. Moreover, we found the association of CNI with histological grade, but there was no signifi cant change of CNI in the presence of TP53, EGFR and PTEN mutations. These data suggest that gene mutations constitute a heterogeneous marker for primary GBM which may be independent of intra-tumor morphological phenotypes of GBM; therefore, gene mutation markers could not be determined from a small number of needle biopsies or only confi ned to the high-grade region. PMID:26191234

  11. Spin-orbit interaction in multiple quantum wells

    SciTech Connect

    Hao, Ya-Fei

    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.

  12. Multiple Exciton Generation in Semiconductor Quantum Dots.

    PubMed

    Beard, Matthew C

    2011-06-02

    Multiple exciton generation in quantum dots (QDs) has been intensively studied as a way to enhance solar energy conversion by utilizing the excess energy in the absorbed photons. Among other useful properties, quantum confinement can both increase Coulomb interactions that drive the MEG process and decrease the electron-phonon coupling that cools hot excitons in bulk semiconductors. However, variations in the reported enhanced quantum yields (QYs) have led to disagreements over the role that quantum confinement plays. The enhanced yield of excitons per absorbed photon is deduced from a dynamical signature in the transient absorption or transient photoluminescence and is ascribed to the creation of biexcitons. Extraneous effects such as photocharging are partially responsible for the observed variations. When these extraneous effects are reduced, the MEG efficiency, defined in terms of the number of additional electron-hole pairs produced per additional band gap of photon excitation, is about two times better in PbSe QDs than that in bulk PbSe. Thin films of electronically coupled QDs have shown promise in simple photon-to-electron conversion architectures. If the MEG efficiency can be further enhanced and charge separation and transport can be optimized within QD films, then QD solar cells can lead to third-generation solar energy conversion technologies.

  13. Semidirect Products of C*-Quantum Groups: Multiplicative Unitaries Approach

    NASA Astrophysics Data System (ADS)

    Meyer, Ralf; Roy, Sutanu; Woronowicz, Stanisław Lech

    2017-04-01

    C*-quantum groups with projection are the noncommutative analogues of semidirect products of groups. Radford's Theorem about Hopf algebras with projection suggests that any C*-quantum group with projection decomposes uniquely into an ordinary C*-quantum group and a "braided" C*-quantum group. We establish this on the level of manageable multiplicative unitaries.

  14. Selective Detection of 1H NMR Resonances of 13CH n Groups Using Two-Dimensional Maximum-Quantum Correlation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, M.; Farrant, R. D.; Nicholson, J. K.; Lindon, J. C.

    Methods for editing spectra based upon maximum-quantum filtering in two-dimensional 1H NMR are presented (MAXY NMR). Separation of 1H resonances from 13CH, 13CH 2, and 13CH 3 groups is demonstrated, using the coherence of the attached natural-abundance 13C spin. Two-dimensional correlation pulse sequences based on J connectivity (MAXY-COSY), total J connectivity (MAXY-TOCSY), and NOE and exchange processes (MAXY-NOESY) are given and exemplified using dexamethasone as a model compound. In addition, an improved form of a 13CH 2 only COSY spectrum (gem-COSY) is shown, and the application of z magnetic-field gradients is demonstrated as an alternative to phase cycling. The approach should have utility in the assignment of complex 1H NMR spectra which arise from peptides or complex mixtures such as biofluids.

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

    PubMed Central

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

    2016-01-01

    Summary 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

  16. Multiple network alignment on quantum computers

    NASA Astrophysics Data System (ADS)

    Daskin, Anmer; Grama, Ananth; Kais, Sabre

    2014-12-01

    Comparative analyses of graph-structured datasets underly diverse problems. Examples of these problems include identification of conserved functional components (biochemical interactions) across species, structural similarity of large biomolecules, and recurring patterns of interactions in social networks. A large class of such analyses methods quantify the topological similarity of nodes across networks. The resulting correspondence of nodes across networks, also called node alignment, can be used to identify invariant subgraphs across the input graphs. Given graphs as input, alignment algorithms use topological information to assign a similarity score to each -tuple of nodes, with elements (nodes) drawn from each of the input graphs. Nodes are considered similar if their neighbors are also similar. An alternate, equivalent view of these network alignment algorithms is to consider the Kronecker product of the input graphs and to identify high-ranked nodes in the Kronecker product graph. Conventional methods such as PageRank and HITS (Hypertext-Induced Topic Selection) can be used for this purpose. These methods typically require computation of the principal eigenvector of a suitably modified Kronecker product matrix of the input graphs. We adopt this alternate view of the problem to address the problem of multiple network alignment. Using the phase estimation algorithm, we show that the multiple network alignment problem can be efficiently solved on quantum computers. We characterize the accuracy and performance of our method and show that it can deliver exponential speedups over conventional (non-quantum) methods.

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

    NASA Astrophysics Data System (ADS)

    Tang, J. H.

    1981-11-01

    The theoretical background of spin Hamiltonians, the density matrix formalism of multiple quantum NMR are discussed as well as creation and detection of multiple quantum coherence by multiple pulse sequence. 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 considered. An oriented methyl group relaxed by paramagnetic impurities is examined and possible correlated motion between two coupled methyl groups is investigated by multiple quantum NMR. 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 spin lattice dynamics of orienting or tunneling methyl groups (CH3 and CD3) at low temperatures and the anisotropic spin lattice relaxation of deuterated hexamethylbenzene, caused by the sixfold reorientation of the molecules are described as well as NMR spectrometers.

  18. Assessing the Detection Limit of a Minority Solid-State Form of a Pharmaceutical by (1)H Double-Quantum Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy.

    PubMed

    Maruyoshi, Keisuke; Iuga, Dinu; Watts, Abigail E; Hughes, Colan E; Harris, Kenneth D M; Brown, Steven P

    2017-07-25

    The lower detection limit for 2 distinct crystalline phases by (1)H magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) is investigated for a minority amount of cimetidine (anhydrous polymorph A) in a physical mixture with the anhydrous HCl salt of cimetidine. Specifically, 2-dimensional (1)H double-quantum (DQ) MAS NMR spectra of polymorph A and the anhydrous HCl salt constitute fingerprints for the presence of each of these solid forms. For solid-state NMR data recorded at a (1)H Larmor frequency of 850 MHz and a MAS frequency of 30 kHz on ∼10 mg of sample, it is shown that, by following the pair of cross-peaks at a (1)H DQ frequency of 7.4 + 11.6 = 19.0 ppm that are unique to polymorph A, the level of detection for polymorph A in a physical mixture with the anhydrous HCl salt is a concentration of 1% w/w. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

  19. Orally bioavailable 6-chloro-7-methoxy-4(1H)-quinolones efficacious against multiple stages of Plasmodium.

    PubMed

    Cross, R Matthew; Flanigan, David L; Monastyrskyi, Andrii; LaCrue, Alexis N; Sáenz, Fabián E; Maignan, Jordany R; Mutka, Tina S; White, Karen L; Shackleford, David M; Bathurst, Ian; Fronczek, Frank R; Wojtas, Lukasz; Guida, Wayne C; Charman, Susan A; Burrows, Jeremy N; Kyle, Dennis E; Manetsch, Roman

    2014-11-13

    The continued proliferation of malaria throughout temperate and tropical regions of the world has promoted a push for more efficacious treatments to combat the disease. Unfortunately, more recent remedies such as artemisinin combination therapies have been rendered less effective due to developing parasite resistance, and new drugs are required that target the parasite in the liver to support the disease elimination efforts. Research was initiated to revisit antimalarials developed in the 1940s and 1960s that were deemed unsuitable for use as therapeutic agents as a result of poor understanding of both physicochemical properties and parasitology. Structure-activity and structure-property relationship studies were conducted to generate a set of compounds with the general 6-chloro-7-methoxy-2-methyl-4(1H)-quinolone scaffold which were substituted at the 3-position with a variety of phenyl moieties possessing various properties. Extensive physicochemical evaluation of the quinolone series was carried out to downselect the most promising 4(1H)-quinolones, 7, 62, 66, and 67, which possessed low-nanomolar EC50 values against W2 and TM90-C2B as well as improved microsomal stability. Additionally, in vivo Thompson test results using Plasmodium berghei in mice showed that these 4(1H)-quinolones were efficacious for the reduction of parasitemia at >99% after 6 days.

  20. Orally Bioavailable 6-Chloro-7-methoxy-4(1H)-quinolones Efficacious against Multiple Stages of Plasmodium

    PubMed Central

    2015-01-01

    The continued proliferation of malaria throughout temperate and tropical regions of the world has promoted a push for more efficacious treatments to combat the disease. Unfortunately, more recent remedies such as artemisinin combination therapies have been rendered less effective due to developing parasite resistance, and new drugs are required that target the parasite in the liver to support the disease elimination efforts. Research was initiated to revisit antimalarials developed in the 1940s and 1960s that were deemed unsuitable for use as therapeutic agents as a result of poor understanding of both physicochemical properties and parasitology. Structure–activity and structure–property relationship studies were conducted to generate a set of compounds with the general 6-chloro-7-methoxy-2-methyl-4(1H)-quinolone scaffold which were substituted at the 3-position with a variety of phenyl moieties possessing various properties. Extensive physicochemical evaluation of the quinolone series was carried out to downselect the most promising 4(1H)-quinolones, 7, 62, 66, and 67, which possessed low-nanomolar EC50 values against W2 and TM90-C2B as well as improved microsomal stability. Additionally, in vivo Thompson test results using Plasmodium berghei in mice showed that these 4(1H)-quinolones were efficacious for the reduction of parasitemia at >99% after 6 days. PMID:25148516

  1. Multiple-state quantum Otto engine, 1D box system

    SciTech Connect

    Latifah, E.; Purwanto, A.

    2014-03-24

    Quantum heat engines produce work using quantum matter as their working substance. We studied adiabatic and isochoric processes and defined the general force according to quantum system. The processes and general force are used to evaluate a quantum Otto engine based on multiple-state of one dimensional box system and calculate the efficiency. As a result, the efficiency depends on the ratio of initial and final width of system under adiabatic processes.

  2. Multiple-state quantum Otto engine, 1D box system

    NASA Astrophysics Data System (ADS)

    Latifah, E.; Purwanto, A.

    2014-03-01

    Quantum heat engines produce work using quantum matter as their working substance. We studied adiabatic and isochoric processes and defined the general force according to quantum system. The processes and general force are used to evaluate a quantum Otto engine based on multiple-state of one dimensional box system and calculate the efficiency. As a result, the efficiency depends on the ratio of initial and final width of system under adiabatic processes.

  3. Multiple-quantum cross-polarization in MAS NMR of quadrupolar nuclei

    NASA Astrophysics Data System (ADS)

    Ashbrook, Sharon E.; Brown, Steven P.; Wimperis, Stephen

    1998-05-01

    Using 27Al ( I=5/2) NMR of aluminium acetylacetonate, we show that it is possible to cross-polarize from a spin I=1/2 nucleus ( 1H) directly to the central triple-quantum transition of a half-integer quadrupolar nucleus ( 27Al) in a powdered sample under MAS conditions. The optimum conditions for this multiple-quantum cross-polarization (MQCP) are investigated experimentally and compared with existing theoretical results. The new technique is applied to the recently introduced two-dimensional MQMAS experiment for recording high-resolution NMR spectra of half-integer quadrupolar nuclei.

  4. Multiple-Particle Interference and Quantum Error Correction

    NASA Astrophysics Data System (ADS)

    Steane, Andrew

    1996-11-01

    The concept of multiple-particle interference is discussed, using insights provided by the classical theory of error correcting codes. This leads to a discussion of error correction in a quantum communication channel or a quantum computer. Methods of error correction in the quantum regime are presented, and their limitations assessed. A quantum channel can recover from arbitrary decoherence of x qubits if K bits of quantum information are encoded using n quantum bits, where K/n can be greater than 1 - 2H (2x/n), but must be less than 1 - 2H (x/n). This implies exponential reduction of decoherence with only a polynomial increase in the computing resources required. Therefore quantum computation can be made free of errors in the presence of physically realistic levels of decoherence. The methods also allow isolation of quantum communication from noise and evesdropping (quantum privacy amplification).

  5. Synthesis, conformational, spectroscopic and chemical reactivity analysis of 2-cyano-3-(1H-pyrrol-2-yl)acrylohydrazide using experimental and quantum chemical approaches

    NASA Astrophysics Data System (ADS)

    Rawat, Poonam; Singh, R. N.

    2015-02-01

    This paper describes the synthesis, spectroscopic (1H and 13C NMR, UV-Visible, FT-IR and ESI Mass), conformational analysis, chemical reactivity and non-linear optical (NLO) properties of newly synthesized pyrrole derivative 2-cyano-3-(1H-pyrrol-2-yl)acrylohydrazide (2CPA) C8H8N4O using experimental and quantum chemical techniques. The presence of signal at δ 8.010 ppm due to vinyl proton as well as NH and NH2 protons signals at 11.054 and 2.499 ppm in experimental 1H NMR spectrum indicate that 2CPA contain sbnd CHdbnd CCNsbnd and sbnd NHsbnd NH2 frame. The combined experimental and theoretical symmetric (3194 cm-1) and asymmetric (3221 cm-1) stretching wavenumber analysis confirms free NH2 group in the solid phase FT-IR spectrum of the synthesized compound. The interaction energies of dimer formation using density functional theory (DFT) and Quantum theory of Atoms in Molecules (QTAIM) calculations are found to be 20.210, 19.683 kcal/mol, respectively. The maximum values of the electrophilic reactivity descriptors at C6 indicate that this site is more prone to nucleophilic attack and favoring the formation of heterocyclic derivatives. A natural bond orbital (NBOs) analysis has been carried out to investigate intramolecular charge transfer, conjugative and hyperconjugative interactions within molecule. The calculated first hyperpolarizability (β0) of 2CPA, indicates that investigated molecule will show non-linear optical response and might be used as non-linear optical (NLO) material.

  6. Efficient quantum transmission in multiple-source networks.

    PubMed

    Luo, Ming-Xing; Xu, Gang; Chen, Xiu-Bo; Yang, Yi-Xian; Wang, Xiaojun

    2014-04-02

    A difficult problem in quantum network communications is how to efficiently transmit quantum information over large-scale networks with common channels. We propose a solution by developing a quantum encoding approach. Different quantum states are encoded into a coherent superposition state using quantum linear optics. The transmission congestion in the common channel may be avoided by transmitting the superposition state. For further decoding and continued transmission, special phase transformations are applied to incoming quantum states using phase shifters such that decoders can distinguish outgoing quantum states. These phase shifters may be precisely controlled using classical chaos synchronization via additional classical channels. Based on this design and the reduction of multiple-source network under the assumption of restricted maximum-flow, the optimal scheme is proposed for specially quantized multiple-source network. In comparison with previous schemes, our scheme can greatly increase the transmission efficiency.

  7. Efficient Quantum Transmission in Multiple-Source Networks

    PubMed Central

    Luo, Ming-Xing; Xu, Gang; Chen, Xiu-Bo; Yang, Yi-Xian; Wang, Xiaojun

    2014-01-01

    A difficult problem in quantum network communications is how to efficiently transmit quantum information over large-scale networks with common channels. We propose a solution by developing a quantum encoding approach. Different quantum states are encoded into a coherent superposition state using quantum linear optics. The transmission congestion in the common channel may be avoided by transmitting the superposition state. For further decoding and continued transmission, special phase transformations are applied to incoming quantum states using phase shifters such that decoders can distinguish outgoing quantum states. These phase shifters may be precisely controlled using classical chaos synchronization via additional classical channels. Based on this design and the reduction of multiple-source network under the assumption of restricted maximum-flow, the optimal scheme is proposed for specially quantized multiple-source network. In comparison with previous schemes, our scheme can greatly increase the transmission efficiency. PMID:24691590

  8. Quantum broadcasting multiple blind signature with constant size

    NASA Astrophysics Data System (ADS)

    Xiao, Min; Li, Zhenli

    2016-09-01

    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.

  9. Quantum cosmological perturbations of multiple fluids

    NASA Astrophysics Data System (ADS)

    Peter, Patrick; Pinto-Neto, N.; Vitenti, Sandro D. P.

    2016-01-01

    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 arbitrary number of fluids and background time evolution. We also show that the common choice of variables for quantization can lead to an ill-defined vacuum definition. Our formalism is not restricted to the case where the coupling between fields is small, but is only required to vary adiabatically with respect to the ultraviolet modes, thus paving the way to consistent descriptions of general models not restricted to single-field (or fluid).

  10. Multiple hydrogen-bonded complexes based on 2-ureido-4[1H]-pyrimidinone: a theoretical study.

    PubMed

    Sun, Hao; Lee, Hui Hui; Blakey, Idriss; Dargaville, Bronwin; Chirila, Traian V; Whittaker, Andrew K; Smith, Sean C

    2011-09-29

    In the present work, the electronic structures and properties of a series of 2-ureido-4[1H]-pyrimidinone(UPy)-based monomers and dimers in various environments (vacuum, chloroform, and water) are studied by density functional theoretical methods. Most dimers prefer to form a DDAA-AADD (D, H-bond donor; A, H-bond acceptor) array in both vacuum and solvents. Topological analysis proved that intramolecular and intermolecular hydrogen bonds coexist in the dimers. Frequency and NBO calculations show that all the hydrogen bonds exhibit an obvious red shift in their stretching vibrational frequencies. Larger substituents at position 6 of the pyrimidinone ring with stronger electron-donating ability favor the total binding energy and free energy of dimerization. Calculations on the solvent effect show that dimerization is discouraged by the stronger polarity of the solvent. Further computations show that Dimer-1 may be formed in chloroform, but water molecules may interact with the donor or acceptor sites and hence disrupt the hydrogen bonds of Dimer-1.

  11. Secure Multiparty Quantum Computation for Summation and Multiplication

    NASA Astrophysics Data System (ADS)

    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.

  12. Secure Multiparty Quantum Computation for Summation and Multiplication

    PubMed Central

    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

  13. Quantum filtering for multiple diffusive and Poissonian measurements

    NASA Astrophysics Data System (ADS)

    Emzir, Muhammad F.; Woolley, Matthew J.; Petersen, Ian R.

    2015-09-01

    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.

  14. Imaging Quantum Confinement in Multiple Graphene Quantum Dots

    NASA Astrophysics Data System (ADS)

    Wong, Dillon; Velasco, Jairo; Lee, Juwon; Rodriguez-Nieva, Joaquin; Kahn, Salman; Vo, Phong; Tsai, Hsinzon; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Levitov, Leonid; Crommie, Michael

    Quantum dots provide a useful means for controlling the electronic and spin degrees of freedom of mesoscale and nanoscale materials. Here we demonstrate a new method for fabricating interacting graphene quantum dots that is compatible with electrostatic gating and visualization by way of scanning tunneling microscopy (STM). Using this new technique we have created and spatially characterized systems of two or more interacting quantum dots. Our results show that it is possible to engineer electronic wave functions in graphene with a high degree of spatial control.

  15. Polarization quantum beat spectroscopy of HCF(A1A"). I. 19F and 1H hyperfine structure and Zeeman effect.

    PubMed

    Fan, Haiyan; Ionescu, Ionela; Xin, Ju; Reid, Scott A

    2004-11-08

    To further investigate the (19)F and (1)H nuclear hyperfine structure and Zeeman effect in the simplest singlet carbene, HCF, we recorded polarization quantum beat spectra (QBS) of the pure bending levels 2(0) (n) with n = 0-7 and combination bands 1(0) (1)2(0) (n) with n = 1-6 and 2(0) (n)3(0) (1) with n = 0-3 in the HCF A(1)A(")<--X(1)A(') system. The spectra were measured under jet-cooled conditions using a pulsed discharge source, both at zero field and under application of a weak magnetic field (<30 G). Analysis yielded the nuclear spin-rotation constants C(aa) and weak field Lande g(aa) factors. Consistent with a two-state model, the majority of observed vibrational levels exhibit a linear correlation of C(aa) and g(aa), and our analysis yielded effective (a) hyperfine constants for the (19)F and (1)H nuclei (in MHz) of 728(23) and 55(2), respectively. The latter was determined here owing to the high resolving power of QBS. The vibrational state selectivity of the (19)F hyperfine constants is discussed, and we suggest that the underlying Renner-Teller interaction may play an important role. Copyright 2004 American Institute of Physics.

  16. Quantum irreversible decoherence behaviour in open quantum systems with few degrees of freedom: application to 1H NMR reversion experiments in nematic liquid crystals.

    PubMed

    Segnorile, H H; Zamar, R C

    2013-10-21

    An experimental study of NMR spin decoherence in nematic liquid crystals is presented. Decoherence dynamics can be put in evidence by means of refocusing experiments of the dipolar interactions. The experimental technique used in this work is based on the MREV8 pulse sequence. The aim of the work is to detect the main features of the irreversible quantum decoherence in liquid crystals, on the basis of the theory presented by the authors recently. The focus is laid on experimentally probing the eigen-selection process in the intermediate time scale, between quantum interference of a closed system and thermalization, as a signature of the quantum spin decoherence of the open quantum system, as well as on quantifying the effects of non-idealities as possible sources of signal decays which could mask the intrinsic decoherence. In order to contrast experiment and theory, the theory was adapted to obtain the decoherence function corresponding to the MREV8 reversion experiments. Non-idealities of the experimental setting, like external field inhomogeneity, pulse misadjustments, and the presence of non-reverted spin interaction terms are analysed in detail within this framework, and their effects on the observed signal decay are numerically estimated. It is found that though all these non-idealities could in principle affect the evolution of the spin dynamics, their influence can be mitigated and they do not present the characteristic behaviour of the irreversible spin decoherence. As unique characteristic of decoherence, the experimental results clearly show the occurrence of eigen-selectivity in the intermediate timescale, in complete agreement with the theoretical predictions. We conclude that the eigen-selection effect is the fingerprint of decoherence associated with a quantum open spin system in liquid crystals. Besides, these features of the results account for the quasi-equilibrium states of the spin system, which were observed previously in these mesophases, and

  17. Photoluminescence of 1,3-Diphenyl-1 H-pyrazolo[3,4- b]quinoline and its derivatives: Experiment and quantum chemical simulations

    NASA Astrophysics Data System (ADS)

    Całus, S.; Gondek, E.; Danel, A.; Jarosz, B.; Kityk, A. V.

    2007-03-01

    The optical absorption and photoluminescent spectra are studied in recently synthesized diphenyl pyrazoloquinolines (DPPQ): 1,3-diphenyl-1H-pyrazolo[3,4-b] quinoline and its 6-vinyl, 6-N,N-diphenyl, 6-methyl, 6-fluoro, 6-bromo and 6-chloro derivatives. The photoemission spectra are recorded in organic solvents of different polarity and found to be highly solvatochromic. The measured spectra are compared with the quantum chemical calculations performed by means of the semiempirical methods (AM1 or PM3) in combination with the equilibrium molecular conformation (EMC) in vacuo (T = 0 K, Γ = 0.12 eV) or MD simulations (T = 300 K). The broadening of absorption and emission bands and their red-shift with increasing of temperature may be well reproduced by MD simulations. The Stokes shift of the photoluminescent spectra is obtained by including vibrational modes into the emission equation. The quantum chemical method AM1 in combination with MD simulations gives in most cases the best agreement with the experimental data. By comparing the emission spectra of 6-N,N-diphenyl-DPPQ with other DPPQ-derivatives one concludes that the molecular fragment diphenyl-amin [(C6H5)2N-] is likely subjected to strong conformational changes in solvents. The large difference between the excited- and state-dipole moments indicates on a strong electron transfer effect being common for all DPPQ derivatives.

  18. Effect of Multiple Scattering in a Quantum Well

    NASA Astrophysics Data System (ADS)

    Sheng, Hanyu; Chua, Soo-Jin; Sinkkonen, Juha

    This paper gives a potentially useful application to quantum well of the theory of scattering in the Born approximation. The simple formulae for multiple scattering in a quantum well of double barrier structure are derived. The multiple scattering parameter is the complex mean free path. We show that the amplitude of the coherent wave will be exponentially attenuated and the phase of the wave will be delayed because of the scattering.

  19. Implementation of an absolute brain 1H-MRS quantification method to assess different tissue alterations in multiple sclerosis.

    PubMed

    Bagory, Matthieu; Durand-Dubief, Françoise; Ibarrola, Danielle; Comte, Jean-Christophe; Cotton, François; Confavreux, Christian; Sappey-Marinier, Dominique

    2012-10-01

    Magnetic resonance spectroscopy has emerged as a sensitive modality to detect early and diffuse alterations in multiple sclerosis. Recently, the hypothesis of neurodegenerative pathogenesis has highlightened the interest for measurement of metabolites concentrations, to gain specificity, in a large brain volume encompassing different tissue alterations. Therefore, we proposed in this paper the implementation of an absolute quantification method based on localized spectroscopy at short (30 ms) and long (135 ms) echo time of a volume including normal appearing white matter, cortical gray matter, and lesions. First, methodological developments were implemented including external calibration, and corrections of phased-array coil sensitivity and cerebrospinal fluid volume contribution. Second, these improvements were validated and optimized using an original methodology based on simulations of brain images with lesions. Finally, metabolic alterations were assessed in 65 patients including 26 relapsing-remitting, 17 primary-progressive (PP), 22 secondary-progressive (SP) patients, and in 23 normal subjects. Results showed increases of choline, creatine, and myo-inositol concentrations in PP and SP patients compared to controls, whereas the concentration of N-acetyl compounds remained constant. The major finding of this study was the identification of Cho concentration and Cho/tNA ratio as putative markers of progressive onset, suggesting interesting perspectives in detection and followup of neurodegenerative processes.

  20. 1H, 13C NMR spectral and single crystal structural studies of toxaphene congeners. Quantum chemical calculations for preferred conformers of 2,5- endo,6- exo,8,9,9,10,10-octachloro-2-bornene and their DFT/GIAO 13C chemical shifts

    NASA Astrophysics Data System (ADS)

    Laihia, K.; Valkonen, A.; Kolehmainen, E.; Suontamo, R.; Nissinen, M.; Nikiforov, V.; Selivanov, S.

    2005-11-01

    The 1H and 13C NMR chemical shifts for six toxaphene congeners: 2- exo,3- endo,6- exo,8,9,10-hexachloro- ( 1), 2- exo,3- endo,5- exo,9,9,10,10-heptachloro- ( 2), 2- exo,3- endo,6- exo,8,9,10,10-heptachloro- ( 3), 2- exo,3- endo,5- exo,6- endo,8,9,10-heptachloro- ( 4), 2- exo,3- endo,5- exo,6- endo,8,9,9,10-octachlorobornane ( 5) and 2,5- endo,6- exo,8,9,9,10,10-octachloro-2-bornene ( 6) are reported. Their chemical shift assignments have been obtained by means of Pulsed Field Gradient (PFG) Double Quantum Filtered (DQF) 1H, 1H correlation spectroscopy (COSY), PFG 1H, 13C Heteronuclear Multiple Quantum Coherence (HMQC) and PFG 1H, 13C Heteronuclear Multiple Bond Correlation (HMBC) experiments. A single crystal X-ray structural analysis was made for compounds 1, 3, 4 and 6. The prevalences of two octachlorobornene rotamers ( 6 a, 6 b) were elucidated by ab initio MO method and single point DFT/GIAO calculations for 13C chemical shifts. Theoretical calculations proved that the single crystal structure of 6 corresponds its most stable conformer in solution.

  1. Frequency domain quantum optimal control under multiple constraints

    NASA Astrophysics Data System (ADS)

    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.

  2. Computer studies of multiple-quantum spin dynamics

    SciTech Connect

    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.

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

    SciTech Connect

    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. Quantum search with multiple walk steps per oracle query

    NASA Astrophysics Data System (ADS)

    Wong, Thomas G.; Ambainis, Andris

    2015-08-01

    We identify a key difference between quantum search by discrete- and continuous-time quantum walks: a discrete-time walk typically performs one walk step per oracle query, whereas a continuous-time walk can effectively perform multiple walk steps per query while only counting query time. As a result, we show that continuous-time quantum walks can outperform their discrete-time counterparts, even though both achieve quadratic speedups over their corresponding classical random walks. To provide greater equity, we allow the discrete-time quantum walk to also take multiple walk steps per oracle query while only counting queries. Then it matches the continuous-time algorithm's runtime, but such that it is a cubic speedup over its corresponding classical random walk. This yields a greater-than-quadratic speedup for quantum search over its corresponding classical random walk.

  5. Proline isomerism leads to multiple folded conformations of calbindin D9k: direct evidence from two-dimensional 1H NMR spectroscopy.

    PubMed Central

    Chazin, W J; Kördel, J; Drakenberg, T; Thulin, E; Brodin, P; Grundström, T; Forsén, S

    1989-01-01

    A complete analysis of calbindin D9k by two-dimensional 1H nuclear magnetic resonance spectroscopy has established the existence of two conformations for the folded protein in solution. Well-resolved major and minor resonances in a ratio of 3:1 are observed throughout the 1H NMR spectrum. Two-dimensional exchange experiments show that the major and minor species are related by an equilibrium process. Analysis of short proton-proton distances along the peptide backbone, identified by two-dimensional nuclear Overhauser effect spectroscopy, provides unambiguous evidence that the two forms of the folded protein differ only in the isomerization state of the peptide bond between Gly-42 and Pro-43. Cis-trans isomerism of Pro-43 is thereby directly identified as the cause of multiple conformations for the folded protein in solution. In addition, when Pro-43 is mutated to a glycine residue there is no indication of multiple conformations. These results provide evidence for the possibility of conformational heterogeneity in the native state of globular proteins. PMID:2928325

  6. A Relativistic Quantum-Chemical Analysis of the trans Influence on (1)H NMR Hydride Shifts in Square-Planar Platinum(II) Complexes.

    PubMed

    Greif, Anja H; Hrobárik, Peter; Hrobáriková, Veronika; Arbuznikov, Alexei V; Autschbach, Jochen; Kaupp, Martin

    2015-08-03

    Empirical correlations between characteristic (1)H NMR shifts in Pt(II) hydrides with trans ligand influence series, Pt-H distances, and (195)Pt shifts are analyzed at various levels of including relativistic effects into density-functional calculations. A close examination of the trans ligand effects on hydride NMR shifts is shown to be dominated by spin-orbit shielding σ(SO). A rather complete understanding of the trends has been obtained by detailed molecular orbital (MO)-by-MO and localized MO analyses of the paramagnetic and spin-orbit (SO) contributions to the chemical shifts, noting that it is the perpendicular shift-tensor components that determine the trend of the (1)H hydride shifts. In contrast to previous assumptions, the change of the Pt-H distance in given complexes does not allow correlations between hydride shifts and metal-hydrogen bond length to be understood. Instead, variations in the polarization of metal 5d orbitals by the trans ligand affects the SO (and partly paramagnetic) shift contributions, as well as the Pt-H distances and the covalency of the metal-hydrogen bond (quantified, e.g., by natural atomic charges and delocalization indices from quantum theory atoms-in-molecules), resulting in a reasonable correlation of these structural/electronic quantities with hydride σ(SO) shieldings. Our analysis also shows that specific σ(p)- and σ(SO)-active MOs are not equally important across the entire series. This explains some outliers in the correlation for limited ranges of trans-influence ligands. Additionally, SO effects from heavy-halide ligands may further complicate trends, indicating some limitations of the simple one-parameter correlations. Strikingly, σ-donating/π-accepting ligands with a very strong trans influence are shown to invert the sign of the usually shielding σ(SO) contribution to the (1)H shifts, by a substantial reduction of the metal 5d orbital involvement in Pt-H bonding, and by involvement of metal 6p-type orbitals

  7. Thermodynamic behavior of the binaries 1-butylpyridinium tetrafluoroborate with water and alkanols: their interpretation using 1H NMR spectroscopy and quantum-chemistry calculations.

    PubMed

    Vreekamp, Remko; Castellano, Desire; Palomar, José; Ortega, Juan; Espiau, Fernando; Fernández, Luís; Penco, Eduvigis

    2011-07-14

    Here we present experimental data of different properties for a set of binary mixtures composed of water or alkanols (methanol to butanol) with an ionic liquid (IL), butylpyridinium tetrafluoroborate [bpy][BF(4)]. Solubility data (x(IL),T) are presented for each of the mixtures, including water, which is found to have a small interval of compositions in IL, x(IL), with immiscibility. In each case, the upper critical solubility temperature (UCST) is determined and a correlation was observed between the UCST and the nature of the compounds in the mixtures. Miscibility curves establish the composition and temperature intervals where thermodynamic properties of the mixtures, such as enthalpies H(m)(E) and volumes V(m)(E), can be determined. Hence, at 298.15 and 318.15 K these can only be found with the first four alkanols. All mixing properties are correlated with a suitable equation ξ (x(IL),T,Y(m)(E) = 0. An analysis on the influence of the temperature in the properties is shown, likewise a comparison between the results obtained here and those of analogous mixtures, discussing the position of the -CH(3) group in the pyridinic ring. The (1)H NMR spectra are determined to analyze the molecular interactions present, especially those due to hydrogen bonds. Additional information about the molecular interactions and their influence on the mixing properties is obtained by quantum chemistry calculations. © 2011 American Chemical Society

  8. [1H, 15N] heteronuclear single quantum coherence NMR study of the mechanism of aquation of platinum(IV) ammine complexes.

    PubMed

    Davies, Murray S; Hall, Matthew D; Berners-Price, Susan J; Hambley, Trevor W

    2008-09-01

    The aquation and hydrolysis of a series of platinum(IV) complexes of the general form cis, trans, cis-[PtCl 2(X) 2( (15)NH 3) 2] (X = Cl (-), O 2CCH 3 (-), OH (-)) have been followed by [ (1)H, (15)N] Heteronuclear Single Quantum Coherence NMR spectroscopy. Negligible aquation (<5%) is observed for the complexes where X = O 2CCH 3 (-) or OH (-) over 3-4 weeks. Aquation of cis-[PtCl 4( (15)NH 3) 2] ( 1) is observed, and the rate of aquation increases with increasing pH and upon the addition of 0.01 mol equiv of the platinum(II) complex cis-[PtCl 2( (15)NH 3) 2] (cisplatin). The first aquated species formed from cis-[PtCl 4(NH 3) 2] has one of the axial chloro groups (relative to the equatorial NH 3 ligands) replaced by an aqua/hydroxo ligand. The second observed substitution occurs in an equatorial position. Peaks that are consistent with five of the eight possible aquation species were observed in the NMR spectra.

  9. Evolution of multiple quantum coherences with scaled dipolar Hamiltonian

    NASA Astrophysics Data System (ADS)

    Sánchez, Claudia M.; Buljubasich, Lisandro; Pastawski, Horacio M.; Chattah, Ana K.

    2017-08-01

    In this article, we introduce a pulse sequence which allows the monitoring of multiple quantum coherences distribution of correlated spin states developed with scaled dipolar Hamiltonian. The pulse sequence is a modification of our previous Proportionally Refocused Loschmidt echo (PRL echo) with phase increment, in order to verify the accuracy of the weighted coherent quantum dynamics. The experiments were carried out with different scaling factors to analyze the evolution of the total magnetization, the time dependence of the multiple quantum coherence orders, and the development of correlated spins clusters. In all cases, a strong dependence between the evolution rate and the weighting factor is observed. Remarkably, all the curves appeared overlapped in a single trend when plotted against the self-time, a new time scale that includes the scaling factor into the evolution time. In other words, the spin system displayed always the same quantum evolution, slowed down as the scaling factor decreases, confirming the high performance of the new pulse sequence.

  10. Theoretical analysis of the quantum contributions to the reactions H/sub 2/(v=1)+H. -->. H + H/sub 2/(v'=0,1) and H/sub 2/(v=1) + D. -->. H + HD(v'=0,1)

    SciTech Connect

    Walker, R.B.; Hayes, E.F.

    1983-03-31

    Detailed quantum-dynamical calculations on the Siegbahn-Liu-Truhlar-Horowitz (SLTH) surface reported for a rotating linear model (RLM) approximation with and without corrections for bending zero-point energy. These dynamical results predict that there are substantial prethreshold quantum contributions to state-selected cross sections and rate constants for both of the title reactions. However, the mechanisms for these prethreshold quantum effects are not the same. For H/sub 2/(v=1)+H, a threshold resonance is responsible for the large prethreshold quantum contribution: 65% of the total rate of 300K. For H/sub 2/(v=1)+D, tunneling is found to be large, leading to a 66% prethreshold quantum contribution at 300K. These large quantum corrections are not large enough to provide an explanation for the previously identified discrepancy between the experimental and classical theoretical rate constants for these reactions.

  11. Remote Entanglement by Coherent Multiplication of Concurrent Quantum Signals.

    PubMed

    Roy, Ananda; Jiang, Liang; Stone, A Douglas; Devoret, Michel

    2015-10-09

    Concurrent remote entanglement of distant, noninteracting quantum entities is a crucial function for quantum information processing. In contrast with the existing protocols which employ the addition of signals to generate entanglement between two remote qubits, the continuous variable protocol we present is based on the multiplication of signals. This protocol can be straightforwardly implemented by a novel Josephson junction mixing circuit. Our scheme would be able to generate provable entanglement even in the presence of practical imperfections: finite quantum efficiency of detectors and undesired photon loss in current state-of-the-art devices.

  12. Optimum testing of multiple hypotheses in quantum detection theory

    NASA Technical Reports Server (NTRS)

    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.

  13. Multiple quantum magic-angle spinning using rotary resonance excitation

    NASA Astrophysics Data System (ADS)

    Vosegaard, Thomas; Florian, Pierre; Massiot, Dominique; Grandinetti, Philip J.

    2001-03-01

    We have discovered rotary resonances between rf field strength, ω1, and magic-angle spinning (MAS) frequency, ωR, which dramatically enhance the sensitivity of triple quantum preparation and mixing in the multiple-quantum MAS experiment, particularly for quadrupolar nuclei having low gyromagnetic ratios or experiencing strong quadrupole couplings. Triple quantum excitation efficiency minima occur when 2ω1=nωR, where n is an integer, with significant maxima occurring between these minima. For triple quantum mixing we observe maxima when ω1=nωR. In both preparation and mixing the pulse lengths required to reach maxima exceed one rotor period. We have combined these rotary resonance conditions into a new experiment called FASTER MQ-MAS, and have experimentally demonstrated a factor of 3 enhancement in sensitivity in comparison to conventional MQ-MAS.

  14. 1H-MRS in patients with multiple sclerosis undergoing treatment with interferon β-1a: results of a preliminary study

    PubMed Central

    Sarchielli, P; Presciutti, O; Tarducci, R; Gobbi, G; Alberti, A; Pelliccioli, G; Orlacchio, A; Gallai, V

    1998-01-01

    BACKGROUND—In vivo magnetic resonance spectroscopy (MRS) has been widely used to assess biochemical changes which occur in demyelinating lesions in white matter of patients with multiple sclerosis. It has been suggested that metabolic variations evidenced by MRS are sensitive indicators of the effects of immunomodulatory treatments in this disease.
 Given the recent finding of an increase in the disease activity in patients with multiple sclerosis treated with interferon (IFN) β-1a in the first period of treatment,1H MRS was used to investigate further the modification in brain metabolic indices, particularly in the first phase of IFN βtreatment.
METHODS—A 1H MRS study was performed on five patients with relapsing-remitting multiple sclerosis who were being treated with intramuscular IFN β-1a (6 million units/week) for six months and on five untreated patients. The mean age, duration of the disease, and expanded disability status scores (EDSS) of the two groups were similar. Patients were evaluated at the beginning of the study and in the first, third, and sixth months of treatment.
RESULTS—In the multiple sclerosis white matter lesions, N-acetylaspartate (NAA), choline (Cho), inositol (Ins), and creatine (Cr) peaks did not vary significantly over the entire period of the study in the untreated group.
 In the treated group there was a significant increase in the Cho peak area at the first month compared with the pretreatment period, and this increase continued in the third and sixth months (p<0.001). A slight but not significant rise in the Cho peak was also found in normal appearing white matter in the patient group undergoing treatment with IFN β-1a. The increase in Cho and the lack of significant changes in Cr and NAA peaks induced a significant rise in Cho/Cr and Cho/NAA ratios over the entire period of treatment compared with those at the beginning of the study (p<0.02 and p<0.005 respectively).
 In the treated group there was a slight but

  15. Multiple Quantum Wells for P T -Symmetric Phononic Crystals

    NASA Astrophysics Data System (ADS)

    Poshakinskiy, A. V.; Poddubny, A. N.; Fainstein, A.

    2016-11-01

    We demonstrate that the parity-time symmetry for sound is realized in laser-pumped multiple-quantum-well structures. Breaking of the parity-time symmetry for the phonons with wave vectors corresponding to the Bragg condition makes the structure a highly selective acoustic wave amplifier. Single-mode distributed feedback phonon lasing is predicted for structures with realistic parameters.

  16. High-field 1H-NMR study around a 1/4 plateau of quantum spin dimer system NH4CuCl3

    NASA Astrophysics Data System (ADS)

    Matsui, K.; Fujisawa, M.; Tanaka, H.; Scheuermann, R.; Goto, T.

    2017-04-01

    We have investigated high-field TF-µSR and 1H-NMR on the S = 1/2 three dimensional spin dimer system NH4CuCl3, which shows a magnetic order at TN = 1.29 K under zero field and the two-stepped plateaus in high field regions HC1 = 5.0 T - HC2 = 12.8 T and HC3 = 17.9 T - HC4 = 24.7 T. Both probes showed spectra containing multiple peaks corresponding to different hyperfine fields, demonstrating the existence of magnetically inequivalent dimers in a unit cell. In the slope-state field region H < HC1, the existence of magnetic order was confirmed by the splitting in some of the NMR peaks. The whole width of NMR and µSR spectra increased with increasing field, and no drastic change in their profile was observed at HC1. This indicates that the change in the spin state is continuous on entering the plateau state, and that no liquid-solid transition of magnons takes place at the phase boundary.

  17. Location of protons in anhydrous Keggin heteropolyacids H(3)PMo(12)O(40) and H(3)PW(12)O(40) by (1)H[(31)P]/(31)P[(1)H] REDOR NMR and DFT quantum chemical calculations.

    PubMed

    Ganapathy, S; Fournier, M; Paul, J F; Delevoye, L; Guelton, M; Amoureux, J P

    2002-07-03

    HeteroPolyAcids (HPA's) are a class of solid acids that have broad applications in many fields of science and technology, including catalysis and chemical engineering. The proton locations within the thermally stable and commonly known Keggin unit, which is the primary structure building unit/block, has remained undetermined in anhydrous HPAs, despite numerous theoretical and experimental efforts. However, Rotational Echo DOuble Resonance (REDOR) NMR and Density Functional Theory (DFT) quantum chemical calculations offer a new opportunity to determine the exact locations of protons within the Keggin unit. The crucial experimental evidence is provided for the basic and very extensively studied acidic form of H(8-n)X(n+)M(12)O(40), X = Si, P and M = Mo, W, belonging to the Keggin structure. While showing that the acidic protons are located in the bridging oxygen positions (R(P-H) = 520 +/- 20 pm) in H(3)PMo(12)O(40) and in the terminal oxygen positions (R(P-H) = 570 +/- 20 pm) in H(3)PW(12)O(40), REDOR measurements also provide for the first time the structural basis to consistently rank the acid strength for the important class of Keggin solid catalysts.

  18. Quantum theory of multiple-input-multiple-output Markovian feedback with diffusive measurements

    NASA Astrophysics Data System (ADS)

    Chia, A.; Wiseman, H. M.

    2011-07-01

    Feedback control engineers have been interested in multiple-input-multiple-output (MIMO) extensions of single-input-single-output (SISO) results of various kinds due to its rich mathematical structure and practical applications. An outstanding problem in quantum feedback control is the extension of the SISO theory of Markovian feedback by Wiseman and Milburn [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.70.548 70, 548 (1993)] to multiple inputs and multiple outputs. Here we generalize the SISO homodyne-mediated feedback theory to allow for multiple inputs, multiple outputs, and arbitrary diffusive quantum measurements. We thus obtain a MIMO framework which resembles the SISO theory and whose additional mathematical structure is highlighted by the extensive use of vector-operator algebra.

  19. A SiGe/Si multiple quantum well avalanche photodetector

    NASA Astrophysics Data System (ADS)

    Sun, Po-Hsing; Chang, Shu-Tong; Chen, Yu-Chun; Lin, Hongchin

    2010-10-01

    The present work investigates the performance of APDs with a SiGe/Si multi-quantum well (MQW) structure, which was fabricated using ultrahigh-vacuum chemical vapor deposition (UHV/CVD). Absorption of radiation and avalanche multiplication occur in both SiGe/Si MQW and the i-SiGe layer. Intense photoluminescence (PL) from strained, epitaxial SiGe alloys grown using UHV/CVD was reported with multiple SiGe/Si MQW and i-SiGe layer. It was found that the avalanche multiplication occurred at about 7 V, when exceeding 7 V, the responsiveness and quantum efficiency rapidly increased. An APD consisting of an epitaxial SiGe/Si MQW as the active absorption layer with intense response in the 800-1500 nm wavelength range is also demonstrated.

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

    DOEpatents

    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.

  1. Multiple-junction quantum cascade photodetectors for thermophotovoltaic energy conversion.

    PubMed

    Yin, Jian; Paiella, Roberto

    2010-01-18

    The use of intersubband transitions in quantum cascade structures for thermophotovoltaic energy conversion is investigated numerically. The intrinsic cascading scheme, spectral agility, and design flexibility of these structures make them ideally suited to the development of high efficiency multiple-junction thermophotovoltaic detectors. A specific implementation of this device concept is designed, based on bound-to-continuum intersubband transitions in large-conduction-band-offset In(0.7)Ga(0.3)As/AlAs(0.8)Sb(0.2) quantum wells. The device electrical characteristics in the presence of thermal radiation from a blackbody source at 1300 K are calculated, from which a maximum extracted power density of 1.4 W/cm(2) is determined. This value compares favorably with the present state-of-the-art in interband thermophotovoltaic energy conversion, indicating that quantum cascade photodetectors may provide a promising approach to improve energy extraction from thermal sources.

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Evolution of multiple quantum coherences with scaled dipolar Hamiltonian.

    PubMed

    Sánchez, Claudia M; Buljubasich, Lisandro; Pastawski, Horacio M; Chattah, Ana K

    2017-08-01

    In this article, we introduce a pulse sequence which allows the monitoring of multiple quantum coherences distribution of correlated spin states developed with scaled dipolar Hamiltonian. The pulse sequence is a modification of our previous Proportionally Refocused Loschmidt echo (PRL echo) with phase increment, in order to verify the accuracy of the weighted coherent quantum dynamics. The experiments were carried out with different scaling factors to analyze the evolution of the total magnetization, the time dependence of the multiple quantum coherence orders, and the development of correlated spins clusters. In all cases, a strong dependence between the evolution rate and the weighting factor is observed. Remarkably, all the curves appeared overlapped in a single trend when plotted against the self-time, a new time scale that includes the scaling factor into the evolution time. In other words, the spin system displayed always the same quantum evolution, slowed down as the scaling factor decreases, confirming the high performance of the new pulse sequence. Copyright © 2017 Elsevier Inc. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

    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.

  5. Multiple Potts models coupled to two-dimensional quantum gravity

    NASA Astrophysics Data System (ADS)

    Baillie, C. F.; Johnston, D. A.

    1992-07-01

    We perform Monte Carlo simulations using the Wolff cluster algorithm of multiple q=2, 3, 4 state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the c>1 region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for c>1. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for c>1.

  6. A broadcasting multiple blind signature scheme based on quantum GHZ entanglement

    NASA Astrophysics Data System (ADS)

    Tian, Yuan; Chen, Hong; Gao, Yan; Zhuang, Honglin; Lian, Haigang; Han, Zhengping; Yu, Peng; Kong, Xiangze; Wen, Xiaojun

    2014-09-01

    Using the correlation of the GHZ triplet states, a broadcasting multiple blind signature scheme is proposed. Different from classical multiple signature and current quantum signature schemes, which could only deliver either multiple signature or unconditional security, our scheme guarantees both by adopting quantum key preparation, quantum encryption algorithm and quantum entanglement. Our proposed scheme has the properties of multiple signature, blindness, non-disavowal, non-forgery and traceability. To the best of our knowledge, we are the first to propose the broadcasting multiple blind signature of quantum cryptography.

  7. Multiple Exciton Generation in PbSe Quantum Dots and Quantum Dot Solar Cells

    SciTech Connect

    Beard, M. C.; Semonin, O. E.; Nozik, A. J.; Midgett, A. G.; Luther, J. M.

    2012-01-01

    Multiple exciton generation in quantum dots (QDs) has been intensively studied as a way to enhance solar energy conversion by channeling the excess photon energy (energy greater than the bandgap) to produce multiple electron-hole pairs. Among other useful properties, quantum confinement can both increase Coulomb interactions that drive the MEG process and decrease the electron-phonon coupling that cools hot-excitons in bulk semiconductors. We have demonstrated that MEG in PbSe QDs is about two times as efficient at producing multiple electron-hole pairs than bulk PbSe. I will discuss our recent results investigating MEG in PbSe, PbS and PbSxSe1-x, which exhibits an interesting size-dependence of the MEG efficiency. Thin films of electronically coupled PbSe QDs have shown promise in simple photon-to-electron conversion architectures with power conversion efficiencies above 5%. We recently reported an enhancement in the photocurrent resulting from MEG in PbSe QD-based solar cells. We find that the external quantum efficiency (spectrally resolved ratio of collected charge carriers to incident photons) peaked at 114% in the best devices measured, with an internal quantum efficiency of 130%. These results demonstrate that MEG charge carriers can be collected in suitably designed QD solar cells. We compare our results to transient absorption measurements and find reasonable agreement.

  8. Incompatible multiple consistent sets of histories and measures of quantumness

    NASA Astrophysics Data System (ADS)

    Halliwell, J. J.

    2017-07-01

    In the consistent histories approach to quantum theory probabilities are assigned to histories subject to a consistency condition of negligible interference. The approach has the feature that a given physical situation admits multiple sets of consistent histories that cannot in general be united into a single consistent set, leading to a number of counterintuitive or contrary properties if propositions from different consistent sets are combined indiscriminately. An alternative viewpoint is proposed in which multiple consistent sets are classified according to whether or not there exists any unifying probability for combinations of incompatible sets which replicates the consistent histories result when restricted to a single consistent set. A number of examples are exhibited in which this classification can be made, in some cases with the assistance of the Bell, Clauser-Horne-Shimony-Holt, or Leggett-Garg inequalities together with Fine's theorem. When a unifying probability exists logical deductions in different consistent sets can in fact be combined, an extension of the "single framework rule." It is argued that this classification coincides with intuitive notions of the boundary between classical and quantum regimes and in particular, the absence of a unifying probability for certain combinations of consistent sets is regarded as a measure of the "quantumness" of the system. The proposed approach and results are closely related to recent work on the classification of quasiprobabilities and this connection is discussed.

  9. Thermodynamics of quantum systems with multiple conserved quantities

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    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.

  10. Thermodynamics of quantum systems with multiple conserved quantities

    PubMed Central

    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

  11. Robust Multiple-Range Coherent Quantum State Transfer

    NASA Astrophysics Data System (ADS)

    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. Robust Multiple-Range Coherent Quantum State Transfer.

    PubMed

    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.

  13. Robust Multiple-Range Coherent Quantum State Transfer

    PubMed Central

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

    2016-01-01

    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. PMID:27364891

  14. Synthesis, spectral analysis and quantum chemical studies on molecular geometry, chemical reactivity of 7-chloro-9-(2‧-chlorophenyl)-2,3-dihydroacridin-4(1H)-one and 7-chloro-9-(2‧-fluorophenyl)-2,3-dihydroacridin-4(1H)-one

    NASA Astrophysics Data System (ADS)

    Satheeshkumar, Rajendran; Sayin, Koray; Kaminsky, Werner; Rajendra Prasad, Karnam Jayarampillai

    2017-01-01

    7-Chloro-9-(2'-chlorophenyl)-2,3-dihydroacridin-4(1H)-one (3a) and 7-chloro-9-(2'-fluorophenyl)-2,3-dihydroacridin-4-(1H)-one (3b) were synthesized from 2-amino-2‧,5-dichlorobenzophenone (1a) and 2-amino-5-chloro-2'-fluorobenzophenone (1b) respectively with 1,2-cyclohexanedione (2) in the presence of 1-butyl-3-methylimidazolium tetrafluoroborate and InCl3 condition. The synthesized compounds have been recorded of FT-IR, NMR spectra and the structure was further confirmed by using single crystal X-ray diffraction. The synthesized compounds have been further checked the photo physical properties like UV, emission and fluorescent quantum yields were calculated. FT-NMR spectra and 1H and 13C NMR chemical shifts have been measured and computational calculations of compounds 3 are done by using B3LYP method with 6-311G basis set in gas phase. Similarly calculated vibrational frequencies were found in good agreement with experimental findings. The optimized geometry of molecules 3 was compared with experimental XRD values. DFT calculations of the molecular electrostatic potential (MEP) and HOMO - LUMO frontier orbitals identified chemically active sites of compounds 3 responsible for its chemical reactivity.

  15. Multiple biological activities and molecular docking studies of newly synthesized 3-(pyridin-4-yl)-1H-pyrazole-5-carboxamide chalcone hybrids.

    PubMed

    Sribalan, Rajendran; Banuppriya, Govindharasu; Kirubavathi, Maruthan; Jayachitra, A; Padmini, Vediappen

    2016-12-01

    A series of fifteen new chemical entities, 3-(pyridin-4-yl)-1H-pyrazole-5-carboxamide chalcones (6a-o), were synthesized as new hybrids with enriched biological activities compared to their parent molecules. The compounds were characterized by (1)H NMR, (13)C NMR, Mass and IR spectral studies. Their antibacterial, anti-inflammatory and antioxidant activities have been evaluated. These compounds showed moderate to good antibacterial, anti-inflammatory and antioxidant activities. The molecular docking analysis was performed with cyclooxygenase enzyme to ascertain the probable binding model. Copyright © 2016 Elsevier Ltd. All rights reserved.

  16. Quantum-chemical simulation of 1H NMR spectra. 2. Comparison of DFT-based procedures for computing proton-proton coupling constants in organic molecules.

    PubMed

    Bally, Thomas; Rablen, Paul R

    2011-06-17

    The performance of 250 different computational protocols (combinations of density functionals, basis sets and methods) was assessed on a set of 165 well-established experimental (1)H-(1)H nuclear coupling constants (J(H-H)) from 65 molecules spanning a wide range of "chemical space". Thereby we found that, if one uses core-augmented basis sets and allows for linear scaling of the raw results, calculations of only the Fermi contact term yield more accurate predictions than calculations where all four terms that contribute to J(H-H) are evaluated. It turns out that B3LYP/6-31G(d,p)u+1s is the best (and, in addition, one of the most economical) of all tested methods, yielding predictions of J(H-H) with a root-mean-square deviation from experiment of less than 0.5 Hz for our test set. Another method that does similarly well, without the need for additional 1s basis functions, is B3LYP/cc-pVTZ, which is, however, ca. 8 times more "expensive" in terms of CPU time. A selection of the better methods was tested on a probe set comprising 61 J(H-H) values from 37 molecules. In this set we also included five molecules where conformational averaging is required. The rms deviations were better than or equal to those with the training set, which indicates that the method we recommend is generally applicable for organic molecules. We give instructions on how to carry out calculations of (1)H chemical shifts and J(H-H) most economically and provide scripts to extract the relevant information from the outputs of calculations with the Gaussian program in clearly arranged form, e.g., to feed them into programs for simulating entire (1)H NMR spectra.

  17. Quantum canonical ensemble and correlation femtoscopy at fixed multiplicities

    NASA Astrophysics Data System (ADS)

    Akkelin, S. V.; Sinyukov, Yu. M.

    2016-07-01

    Identical particle correlations at fixed multiplicity are considered by means of quantum canonical ensemble of finite systems. We calculate one-particle momentum spectra and two-particle Bose-Einstein correlation functions in the ideal gas by using a recurrence relation for the partition function. Within such a model we investigate the validity of the thermal Wick's theorem and its applicability for decomposition of the two-particle distribution function. The dependence of the Bose-Einstein correlation parameters on the average momentum of the particle pair is also investigated. Specifically, we present the analytical formulas that allow one to estimate the effect of suppressing the correlation functions in a finite canonical system. The results can be used for the femtoscopy analysis of the A +A and p +p collisions with selected (fixed) multiplicity.

  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

    NASA Astrophysics Data System (ADS)

    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. Quantum transport in multiple-barrier resonant-tunneling devices

    NASA Astrophysics Data System (ADS)

    Newaz, A. K. M.

    I have studied experimentally the quantum transport in multiple-barrier resonant-tunneling devices, namely double-barrier resonant-tunneling diodes (DBRTD) and triple-barrier resonant-tunneling diodes (TBRTD), to understand the tunneling processes in multiple-barrier resonant structures. We have performed various types of transport measurements, such as current, conductance, resonant magnetotunneling spectroscopy and shot noise measurements at low temperature (T=4.2K). To test the validity of the in-plane momentum conservation rule when electrons tunnel through a multiple-barrier resonant-tunneling device, I have studied in details the current and conductance with and without magnetic field perpendicular to the interfaces. We have found conclusive evidence that though this conservation rule governs the tunneling processes in DBRTD, the conservation rule breaks down in TBRTD. In addition, I have observed profound effect of nonparabolicity in the tunneling processes. By measuring the shot noise in TBRTDs at low temperature, I have found that the shot noise in a TBRTD is reduced over the Poissonian value, 2 eI, whenever the differential conductance is positive and is enhanced over 2eI when the differential conductance is negative. This behavior, although qualitatively similar to that found in DBRTD, differs from it in important details. In TBRTDs the noise reduction is considerably greater than that predicted by a semiclassical model, and the enhancement does not correlate with the strength of the negative differential conductance. Moreover, I have not observed any signature of the effect of the coherent tunneling on the shot noise suppression in coherently coupled TBRTDs. This suggests that the phase coherence does not have any effect on the shot noise suppression. On the other hand, the failure of a semiclassical model to explain shot noise suppression suggests an incomplete understanding of the noise properties of multiple-barrier heterostructures and a need for

  20. Investigation of enzymatic C-P bond formation using multiple quantum HCP nuclear magnetic resonance spectroscopy.

    PubMed

    Hu, Kaifeng; Werner, Williard J; Allen, Kylie D; Wang, Susan C

    2015-04-01

    The biochemical mechanism for the formation of the C-P-C bond sequence found in l-phosphinothricin, a natural product with antibiotic and herbicidal activity, remains unclear. To obtain further insight into the catalytic mechanism of PhpK, the P-methyltransferase responsible for the formation of the second C-P bond in l-phosphinothricin, we utilized a combination of stable isotopes and two-dimensional nuclear magnetic resonance spectroscopy. Exploiting the newly emerged Bruker QCI probe (Bruker Corp.), we specifically designed and ran a (13) C-(31) P multiple quantum (1) H-(13) C-(31) P (HCP) experiment in (1) H-(31) P two-dimensional mode directly on a PhpK-catalyzed reaction mixture using (13) CH3 -labeled methylcobalamin as the methyl group donor. This method is particularly advantageous because minimal sample purification is needed to maximize product visualization. The observed 3:1:1:3 multiplet specifically and unequivocally illustrates direct bond formation between (13) CH3 and (31) P. Related nuclear magnetic resonance experiments based upon these principles may be designed for the study of enzymatic and/or synthetic chemical reaction mechanisms.

  1. Quantum Chemical Study of the Solvent Effect on the Anticancer Active Molecule of Iproplatin: Structural, Electronic, and Spectroscopic Properties (IR, 1H NMR, UV)

    NASA Astrophysics Data System (ADS)

    Sadeghi, N.; Ghiasi, R.; Fazaeli, R.; Jamehbozorgi, S.

    2017-01-01

    The structural, electronic, and spectroscopic properties of the anticancer active molecule of iproplatin were investigated in the gas and liquid phases. Based on the polarizable continuum model (PCM), the solvent effect on the structural parameters, frontier orbitals, and spectroscopic parameters of the complex was investigated. The results indicate that the polarity of solvents plays a significant role in the structure and pro perties of the complex. 1H and 13C NMR chemical shifts were calculated using the Gauge-invariant atomic orbital (GIAO) method. Pt-Cl and Pt-OH bonds were investigated through a vibrational analysis. Moreover, time dependent density functional theory (TD-DFT) was used to calculate the energy, oscillatory strength, and wavelength absorption maximum (λmax) of electronic transitions and its nature within the complex.

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

    PubMed

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

    2013-05-15

    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 (1)H and (13)C NMR spectra were recorded and the chemical shifts of the molecule were calculated. Copyright © 2013 Elsevier B.V. All rights reserved.

  3. Coherent nanocavity structures for enhancement in internal quantum efficiency of III-nitride multiple quantum wells

    SciTech Connect

    Kim, T.; Liu, B.; Smith, R.; Athanasiou, M.; Gong, Y.; Wang, T.

    2014-04-21

    A “coherent” nanocavity structure has been designed on two-dimensional well-ordered InGaN/GaN nanodisk arrays with an emission wavelength in the green spectral region, leading to a massive enhancement in resonance mode in the green spectra region. By means of a cost-effective nanosphere lithography technique, we have fabricated such a structure on an InGaN/GaN multiple quantum well epiwafer and have observed the “coherent” nanocavity effect, which leads to an enhanced spontaneous emission (SE) rate. The enhanced SE rate has been confirmed by time resolved photoluminescence measurements. Due to the coherent nanocavity effect, we have achieved a massive improvement in internal quantum efficiency with a factor of 88, compared with the as-grown sample, which could be significant to bridge the “green gap” in solid-state lighting.

  4. Electron-interface phonon interaction in multiple quantum well structures

    NASA Astrophysics Data System (ADS)

    Sun, J. P.; Teng, H. B.; Haddad, G. I.; Stroscio, M. A.

    1998-08-01

    Intersubband relaxation rates due to electron interactions with the interface phonons are evaluated for multiple quantum well structures designed for step quantum well lasers operating at mid-infrared to submillimetre wavelengths. The interface phonon modes and electron-phonon interaction Hamiltonians for the structures are derived using the transfer matrix method, based on the macroscopic dielectric continuum model, whereas the electron wavefunctions are obtained by solving the Schrödinger equation. Fermi's golden rule is employed to calculate the electron relaxation rates between the subbands in these structures. The relaxation rates for two different structures are examined and compared with those calculated using the bulk phonon modes and the Fröhlich interaction Hamiltonian. The sum rule for the relationship between the form factors of the various localized phonon modes and the bulk phonon modes is verified. The results obtained in this work illustrate that the transfer matrix method provides a convenient way for deriving the properties of the interface phonon modes in different structures of current interest and that, for preferential electron relaxation in intersubband laser structures, the effects of the interface phonon modes are significant and should be considered for optimal design of these laser structures.

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

    NASA Astrophysics Data System (ADS)

    Guţă, Mădălin; Kypraios, Theodore; Dryden, Ian

    2012-10-01

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  7. Spectral analysis, structural elucidation, and evaluation of both nonlinear optical properties and chemical reactivity of a newly synthesized ethyl-3,5-dimethyl-4-[(toluenesulfonyl)-hydrazonomethyl]-1H-pyrrole-2-carboxylate through experimental studies and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Singh, R. N.; Rawat, Poonam

    2013-12-01

    As part of study of hydrazide-hydrazones, we have synthesized ethyl-3,5-dimethyl-4-[(toluenesulfonyl)-hydrazonomethyl]-1H-pyrrole-2-carboxylate (EDTHMPC) and characterized by elemental analysis, FT-IR, UV-Vis, 1H, 13C NMR and Mass spectroscopy. The structure, spectral and thermodynamic parameters of EDTHMPC were quantum chemically calculated performing density functional level theory (DFT) with B3LYP functional and 6-31G (d,p) basis set. Electrophilic charge transfer (ECT) values of interacting molecules indicate that charge flows from p-toluene sulphonyl-hydrazide to ethyl-3,5-dimethyl-4-formyl-1H-pyrrole-2-carboxylate confirming the formation of product by nucleophilic attack. The calculated and experimental wavenumbers analysis confirms the formation of dimer. The calculated changes in thermodynamic quantities during dimer formation in gaseous phase have the negative values for ΔH, ΔG (kcal/mol) and ΔS (cal/mol-K) indicating that the dimer formation is exothermic and will proceed only at low temperature. The strength and nature of hydrogen bonding and weak interactions in dimer have been analyzed by 'Quantum theory of atoms in molecules' (QTAIM) and found to be five types of interactions in which three types are (C⋯N, CH⋯O and CH⋯HC) intramolecular and two types are (CO⋯HN and CH⋯OC) intermolecular. The calculated binding energy of dimer using DFT and QTAIM theory are 14.32 and 15.41 kcal/mol, respectively. The β0 value for monomer is calculated as 11.54 x 10-30 esu indicating microscopic nonlinear optical (NLO) behavior with non-zero values.

  8. 1H-detected 1H- 1H correlation spectroscopy of a stereo-array isotope labeled amino acid under fast magic-angle spinning

    NASA Astrophysics Data System (ADS)

    Takahashi, Hiroki; Kainosho, Masatsune; Akutsu, Hideo; Fujiwara, Toshimichi

    2010-04-01

    The combined use of selective deuteration, stereo-array isotope labeling (SAIL), and fast magic-angle spinning effectively suppresses the 1H-1H dipolar couplings in organic solids. This method provided the high-field 1H NMR linewidths comparable to those achieved by combined rotation and multiple-pulse spectroscopy. This technique was applied to two-dimensional 1H-detected 1H-1H polarization transfer CHH experiments of valine. The signal sensitivity for the 1H-detected CHH experiments was greater than that for the 13C-detected 1H-1H polarization transfer experiments by a factor of 2-4. We obtained the 1H-1H distances in SAIL valine by CHH experiments with an accuracy of about 0.2 Å by using a theory developed for 1H-1H polarization transfer in 13C-labeled organic compounds.

  9. FT-IR, Laser-Raman spectra and quantum chemical calculations of methyl 4-(trifluoromethyl)-1H-pyrrole-3-carboxylate-A DFT approach

    NASA Astrophysics Data System (ADS)

    Sert, Yusuf; Sreenivasa, S.; Doğan, H.; Manojkumar, K. E.; Suchetan, P. A.; Ucun, Fatih

    2014-06-01

    In this study the experimental and theoretical vibrational frequencies of a newly synthesized anti-tumor and anti-inflammatory agent namely, methyl 4-(trifluoromethyl)-1H-pyrrole-3-carboxylate have been investigated. The experimental FT-IR (4000-400 cm-1) and Laser-Raman spectra (4000-100 cm-1) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths, bond angles and torsion angles) have been calculated using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr and DFT/M06-2X: highly parameterized, empirical exchange correlation function) with 6-311++G(d,p) basis set by Gaussian 03 software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data and results in the literature. In addition, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy and the other related molecular energy values of the compound have been investigated using the same theoretical calculations.

  10. FT-IR, Laser-Raman spectra and quantum chemical calculations of methyl 4-(trifluoromethyl)-1H-pyrrole-3-carboxylate-A DFT approach.

    PubMed

    Sert, Yusuf; Sreenivasa, S; Doğan, H; Manojkumar, K E; Suchetan, P A; Ucun, Fatih

    2014-06-05

    In this study the experimental and theoretical vibrational frequencies of a newly synthesized anti-tumor and anti-inflammatory agent namely, methyl 4-(trifluoromethyl)-1H-pyrrole-3-carboxylate have been investigated. The experimental FT-IR (4000-400cm(-1)) and Laser-Raman spectra (4000-100cm(-1)) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths, bond angles and torsion angles) have been calculated using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr and DFT/M06-2X: highly parameterized, empirical exchange correlation function) with 6-311++G(d,p) basis set by Gaussian 03 software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data and results in the literature. In addition, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy and the other related molecular energy values of the compound have been investigated using the same theoretical calculations.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. Multiple particle production processes in the light'' of quantum optics

    SciTech Connect

    Friedlander, E.M.

    1990-09-01

    Ever since the observation that high-energy nuclear active'' cosmic-ray particles create bunches of penetrating particles upon hitting targets, a controversy has raged about whether these secondaries are created in a single act'' or whether many hadrons are just the result of an intra-nuclear cascade, yielding one meson in every step. I cannot escape the impression that: the latter kind of model appeals naturally as a consequence of an innate bio-morphism in our way of thinking and that in one guise or another it has tenaciously survived to this day, also for hadron-hadron collisions, via multi-peripheral models to the modern parton shower approach. Indeed, from the very beginning of theoretical consideration of multiparticle production, the possibility of many particles arising from a single hot'' system has been explored, with many fruitful results, not the least of which are the s{sup 1/4} dependence of the mean produced particle multiplicity and the thermal'' shape of the P{sub T} spectra. An important consequence of the thermodynamical-hydrodynamical models is that particle emission is treated in analogy to black-body radiation, implying for the secondaries a set of specific Quantum-Statistical properties, very similar to those observed in quantum optics. From here on I shall try to review a number of implications and applications of this QS analogy in the study of multiplicity distributions of the produced secondaries. I will touch only in passing another very important topic of this class, the Bose-Einstein two-particle correlations.

  13. Experimental Generation of Multiple Quantum Correlated Beams from Hot Rubidium Vapor

    NASA Astrophysics Data System (ADS)

    Qin, Zhongzhong; Cao, Leiming; Wang, Hailong; Marino, A. M.; Zhang, Weiping; Jing, Jietai

    2014-07-01

    Quantum correlations and entanglement shared among multiple quantum modes are important for both fundamental science and the future development of quantum technologies. This development will also require an efficient quantum interface between multimode quantum light sources and atomic ensembles, which makes it necessary to implement multimode quantum light sources that match the atomic transitions. Here, we report on such a source that provides a method for generating quantum correlated beams that can be extended to a large number of modes by using multiple four-wave mixing (FWM) processes in hot rubidium vapor. Experimentally, we show that two cascaded FWM processes produce strong quantum correlations between three bright beams but not between any two of them. In addition, the intensity-difference squeezing is enhanced with the cascaded system to -7.0±0.1 dB from the -5.5±0.1/-4.5±0.1 dB squeezing obtained with only one FWM process. One of the main advantages of our system is that as the number of quantum modes increases, so does the total degree of quantum correlations. The proposed method is also immune to phase instabilities due to its phase insensitive nature, can easily be extended to multiple modes, and has potential applications in the production of multiple quantum correlated images.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

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

    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.

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

    SciTech Connect

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

    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.

  17. Irreducible Tensor Operators and Multiple-Quantum NMR.

    NASA Astrophysics Data System (ADS)

    Hutchison, Wayne Douglas

    The aim of the work detailed in this thesis, is to provide a concise, and illuminating, mathematical description of multiple quantum nuclear magnetic resonance (MQNMR) experiments, on essentially isolated (non-coupled) nuclei. The treatment used is based on irreducible tensor operators, which form an orthonormal basis set. Such operators can be used to detail the state of the nuclear ensemble (density matrix) during every stage, preparation, evolution and detection, of a MQNMR experiment. Moreover, such operators can be also used to provide a rigorous analysis of pulsed NMR experiments, on oriented nuclei at low temperatures, where the initial density matrix is far from trivial. The specific topics dealt with in this thesis are as follows. In the first place the properties of irreducible tensor operators are discussed in some detail. In particular, symmetric and anti-symmetric combinations of tensor operators are introduced, to reflect the Hermitian nature of the nuclear Hamiltonian and density matrix. Secondly, the creation of multipolar nuclear states using hard, non-selective rf pulses, is detailed for spin I = 1, 3/2, 2 and 5/2 nuclei, subject to an axially symmetric quadrupole interaction. Results are also given for general I. Thirdly, some experimental results, verifying the production of a triple quantum NMR state, for the I = 3/2 ^{23}Na nuclei in a single crystal of NaIO_4 are presented and discussed. Fourthly, the treatment of MQNMR experiments is extended to the low temperature regime where the initial density matrix includes Fano statistical tensors other than rank one. In particular, it is argued that MQNMR techniques could be used to enhance the anisotropy of gamma-ray emission from oriented nuclei at low temperatures. Fifthly, the effect of a more general quadrupole Hamiltonian (including an asymmetry term) on MQNMR experiments is considered for spins I = 1 and 3/2. In particular, it is shown that double quantum states evolve to give longitudinal NMR

  18. Experimental realization of entanglement in multiple degrees of freedom between two quantum memories.

    PubMed

    Zhang, Wei; Ding, Dong-Sheng; Dong, Ming-Xin; Shi, Shuai; Wang, Kai; Liu, Shi-Long; Li, Yan; Zhou, Zhi-Yuan; Shi, Bao-Sen; Guo, Guang-Can

    2016-11-14

    Entanglement in multiple degrees of freedom has many benefits over entanglement in a single one. The former enables quantum communication with higher channel capacity and more efficient quantum information processing and is compatible with diverse quantum networks. Establishing multi-degree-of-freedom entangled memories is not only vital for high-capacity quantum communication and computing, but also promising for enhanced violations of nonlocality in quantum systems. However, there have been yet no reports of the experimental realization of multi-degree-of-freedom entangled memories. Here we experimentally established hyper- and hybrid entanglement in multiple degrees of freedom, including path (K-vector) and orbital angular momentum, between two separated atomic ensembles by using quantum storage. The results are promising for achieving quantum communication and computing with many degrees of freedom.

  19. Experimental realization of entanglement in multiple degrees of freedom between two quantum memories

    PubMed Central

    Zhang, Wei; Ding, Dong-Sheng; Dong, Ming-Xin; Shi, Shuai; Wang, Kai; Liu, Shi-Long; Li, Yan; Zhou, Zhi-Yuan; Shi, Bao-Sen; Guo, Guang-Can

    2016-01-01

    Entanglement in multiple degrees of freedom has many benefits over entanglement in a single one. The former enables quantum communication with higher channel capacity and more efficient quantum information processing and is compatible with diverse quantum networks. Establishing multi-degree-of-freedom entangled memories is not only vital for high-capacity quantum communication and computing, but also promising for enhanced violations of nonlocality in quantum systems. However, there have been yet no reports of the experimental realization of multi-degree-of-freedom entangled memories. Here we experimentally established hyper- and hybrid entanglement in multiple degrees of freedom, including path (K-vector) and orbital angular momentum, between two separated atomic ensembles by using quantum storage. The results are promising for achieving quantum communication and computing with many degrees of freedom. PMID:27841274

  20. Multiple-quantum spin coherence in the ground state of alkali atomic vapors

    NASA Astrophysics Data System (ADS)

    Xu, J. D.; Wäautckerle, G.; Mehring, M.

    1997-01-01

    Two-dimensional (2D) multiple-quantum coherence is reported for the hyperfine ground state of rubidium and cesium atoms by applying multiple radio-frequency pulses to the optically polarized atoms. Calculations of 1D and 2D multiple quantum coherences were performed with a general theory for an arbitrary high spin system by using irreducible tensor operators. The experimental results compare very well with the calculations.

  1. 1H NMR spectroscopic and quantum chemical studies on a poly(ester amide) model compound: Nalpha-benzoyl-L-argininate ethyl ester chloride. Structural preferences for the isolated molecule and in solution.

    PubMed

    Fonseca, A C; Jarmelo, S; Carvalho, R A; Fausto, R; Gil, M H; Simões, P N

    2010-05-13

    The molecular structure of the L-arginine derivative, N(alpha)-benzoyl-L-argininate ethyl ester chloride (BAEEH(+).Cl(-)), was characterized by combining quantum chemical methods and (1)H NMR spectroscopy. A conformational search on the potential energy surfaces of the three lowest-energy tautomers of BAEEH(+) [A: R-N(+)H=(NH(2))(2); B: R-NH-C(=NH)N(+)H(3); C: R-N(+)H(2)-C(=NH)NH(2); R = C(6)H(5)C(=O)NH-CH(COOCH(2)CH(3))CH(2)CH(2)CH(2)-] was carried out using the semiempirical PM3 method. The lowest-energy conformations obtained using this method were then optimized at the DFT(B3LYP)/6-31++G(d,p) level of theory. For all tautomers, it was found that all low-energy conformers present folded structures, in which a H-bond interaction between the guanidinium group and the amide carbonyl oxygen atom appears to be the most relevant stabilizing factor. (1)H NMR spectra of BAEEH(+).Cl(-) in DMF-D(7) were acquired in the temperature range [-55 to 75 degrees C], providing information about the rotational motions in the guanidinium group and showing that the tautomeric form of BAEEH(+) that exists in solution is tautomer A. The interpretation of the experimental findings was supported by (1)H NMR chemical shifts obtained theoretically at the DFT(B3LYP)/6-31++G(d,p) level of approximation, using both the polarized continuum model and a BAEEH(+)-water complex model.

  2. Hot carrier cooling mechanisms in multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Conibeer, Gavin; Zhang, Yi; Bremner, Stephen; Shrestha, Santosh

    2017-02-01

    The Hot Carrier solar cell has the potential to yield a very high efficiency, well over 50% under 1 sun. Multiple quantum wells have been shown to have significantly slow hot carrier cooling rates than bulk material and are thus a promising candidate for hot carrier solar cell absorbers. However, the mechanism(s) by which hot carrier cooling is restricted is not clear. In this paper is presented a systematic study of carrier cooling rates in GaAs/AlAs MQW with either varying barrier or varying well thickness. These allow an investigation as to whether the mechanisms of either a reduction in hot carrier diffusion; a localisation of phonons emitted by hot carriers; or mini-gaps in the MQW phonon dispersion are primarily responsible for reduced carrier cooling rates. With the conclusion that the interfaces between QW and barrier are primarily responsible for reducing carrier cooling rates through a mechanism of phonon confinement leading to phonon bottleneck restriction of phonon decay and hence re-heating of hot carriers. Some aspects of the consequent affect on the use of MQW as absorbers in a real hot carrier cell are discussed.

  3. Near-infrared hybrid plasmonic multiple quantum well nanowire lasers.

    PubMed

    Wang, Jiamin; Wei, Wei; Yan, Xin; Zhang, Jinnan; Zhang, Xia; Ren, Xiaomin

    2017-04-17

    The lasing characteristics of hybrid plasmonic AlGaAs/GaAs multiple quantum well (MQW) nanowire (NW) lasers beyond diffraction limit have been investigated by 3D finite-difference time-domain simulations. The results show that the hybrid plasmonic MQW NW has lower threshold gain over a broad diameter range in comparison with its photonic counterpart. Beyond the diffraction limit, the hybrid plasmonic MQW NW has a lowest threshold gain of 788 cm-1 at a diameter of 130 nm, and a cutoff diameter of 80 nm, half that of the photonic lasers. In comparison with the hybrid plasmonic core-shell NWs, the hybrid plasmonic MQW NWs exhibit significantly lower threshold gain, higher Purcell factor, and smaller cutoff diameter, which are attributed to the superior overlap between the hybrid plasmonic modes and gain medium, as well as a stronger optical confinement due to the grating-like effect of MQW structures. Moreover, the hybrid plasmonic MQW NW has a lower threshold gain than that of the core-shell NW over a broad wavelength range. The hybrid plasmonic MQW NW structure is promising for ultrasmall and low-consumption near-infrared nanolasers.

  4. Single-photon quantum router with multiple output ports

    PubMed Central

    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

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

    PubMed

    Yan, Wei-Bin; Fan, Heng

    2014-04-28

    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.

  6. Multiple energy scales at a quantum critical point.

    PubMed

    Gegenwart, P; Westerkamp, T; Krellner, C; Tokiwa, Y; Paschen, S; Geibel, C; Steglich, F; Abrahams, E; Si, Q

    2007-02-16

    We report thermodynamic measurements in a magnetic-field-driven quantum critical point of a heavy fermion metal, YbRh2Si2. The data provide evidence for an energy scale in the equilibrium excitation spectrum that is in addition to the one expected from the slow fluctuations of the order parameter. Both energy scales approach zero as the quantum critical point is reached, thereby providing evidence for a new class of quantum criticality.

  7. In vivo quantification of response to treatment in patients with multiple myeloma by 1H magnetic resonance spectroscopy of bone marrow.

    PubMed

    Oriol, Albert; Valverde, Daniel; Capellades, Jaume; Cabañas, Miquel E; Ribera, Josep-Maria; Arús, Carles

    2007-04-01

    Magnetic resonance imaging (MRI) is the gold standard non-invasive technique to detect malignant disease in the bone marrow. Proton magnetic resonance spectroscopy (MRS) can be performed as a quick adjunct to routine spinal MRI. We performed proton MRS to patients with multiple myeloma (MM) at diagnosis and after treatment to investigate the possible correlation of MRS data with response to therapy. Twenty-one patients with newly diagnosed MM underwent combined MRI/MRS explorations of a transverse center section in the fifth lumbar vertebral body. MRS was acquired with STEAM and 40 ms TE. Areas of unsuppressed water and lipid resonances were used to calculate the lipid-to-water ratio (LWR). No association was detected between initial LWRs and the clinical characteristics of patients. Post treatment MRS was available in 16 patients of whom 11 (69%) presented an LWR increase, this included all complete responders (8/8, 100%, P = 0.012). A post-treatment LWR value equal to or larger than one is proposed as a non-invasive marker of complete response to treatment. Only patients responding to treatment presented a significant increase in bone marrow LWR after therapy. MRS may provide an adequate quantification of response to chemotherapy in patients with MM.

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

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

    2015-10-15

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

  10. Experimental investigation of quantum entropic uncertainty relations for multiple measurements in pure diamond.

    PubMed

    Xing, Jian; Zhang, Yu-Ran; Liu, Shang; Chang, Yan-Chun; Yue, Jie-Dong; Fan, Heng; Pan, Xin-Yu

    2017-05-31

    One unique feature of quantum mechanics is the Heisenberg uncertainty principle, which states that the outcomes of two incompatible measurements cannot simultaneously achieve arbitrary precision. In an information-theoretic context of quantum information, the uncertainty principle can be formulated as entropic uncertainty relations with two measurements for a quantum bit (qubit) in two-dimensional system. New entropic uncertainty relations are studied for a higher-dimensional quantum state with multiple measurements, and the uncertainty bounds can be tighter than that expected from two measurements settings and cannot result from qubits system with or without a quantum memory. Here we report the first room-temperature experimental testing of the entropic uncertainty relations with three measurements in a natural three-dimensional solid-state system: the nitrogen-vacancy center in pure diamond. The experimental results confirm the entropic uncertainty relations for multiple measurements. Our result represents a more precise demonstrating of the fundamental uncertainty principle of quantum mechanics.

  11. Optimized multiple quantum MAS lineshape simulations in solid state NMR

    NASA Astrophysics Data System (ADS)

    Brouwer, William J.; Davis, Michael C.; Mueller, Karl T.

    2009-10-01

    The majority of nuclei available for study in solid state Nuclear Magnetic Resonance have half-integer spin I>1/2, with corresponding electric quadrupole moment. As such, they may couple with a surrounding electric field gradient. This effect introduces anisotropic line broadening to spectra, arising from distinct chemical species within polycrystalline solids. In Multiple Quantum Magic Angle Spinning (MQMAS) experiments, a second frequency dimension is created, devoid of quadrupolar anisotropy. As a result, the center of gravity of peaks in the high resolution dimension is a function of isotropic second order quadrupole and chemical shift alone. However, for complex materials, these parameters take on a stochastic nature due in turn to structural and chemical disorder. Lineshapes may still overlap in the isotropic dimension, complicating the task of assignment and interpretation. A distributed computational approach is presented here which permits simulation of the two-dimensional MQMAS spectrum, generated by random variates from model distributions of isotropic chemical and quadrupole shifts. Owing to the non-convex nature of the residual sum of squares (RSS) function between experimental and simulated spectra, simulated annealing is used to optimize the simulation parameters. In this manner, local chemical environments for disordered materials may be characterized, and via a re-sampling approach, error estimates for parameters produced. Program summaryProgram title: mqmasOPT Catalogue identifier: AEEC_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEEC_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 3650 No. of bytes in distributed program, including test data, etc.: 73 853 Distribution format: tar.gz Programming language: C, OCTAVE Computer: UNIX

  12. U1h Superstructure

    SciTech Connect

    Glen Sykes

    2000-11-01

    The U1H Shaft Project is a design build subcontract to supply the U. S. Department of Energy (DOE) a 1,045 ft. deep, 20 ft. diameter, concrete lined shaft for unspecified purposes. The subcontract awarded to Atkinson Construction by Bechtel Nevada to design and construct the shaft for the DOE has been split into phases with portions of the work being released as dictated by available funding. The first portion released included the design for the shaft, permanent hoist, headframe, and collar arrangement. The second release consisted of constructing the shaft collar to a depth of 110 ft., the service entry, utility trenches, and installation of the temporary sinking plant. The temporary sinking plant included the installation of the sinking headframe, the sinking hoist, two deck winches, the shaft form, the sinking work deck, and temporary utilities required to sink the shaft. Both the design and collar construction were completed on schedule. The third release consisted of excavating and lining the shaft to the station depth of approximately 950 feet. Work is currently proceeding on this production sinking phase. At a depth of approximately 600 feet, Atkinson has surpassed production expectation and is more than 3 months ahead of schedule. Atkinson has employed the use of a Bobcat 331 excavator as the primary means of excavation. the shaft is being excavated entirely in an alluvial deposit with varying degrees of calcium carbonate cementation. Several more work packages are expected to be released in the near future. The remaining work packages include, construction of the shaft station a depth of 975 ft. and construction of the shaft sump to a depth of 1,045 ft., installation of the loading pocket and station steel and equipment, installation of the shaft steel and guides, installation of the shaft utilities, and installation of the permanent headframe, hoist, collar utilities, and facilities.

  13. Natural-abundance 15N NMR studies of Turkey ovomucoid third domain. Assignment of peptide 15N resonances to the residues at the reactive site region via proton-detected multiple-quantum coherence

    NASA Astrophysics Data System (ADS)

    Ortiz-Polo, Gilberto; Krishnamoorthi, R.; Markley, John L.; Live, David H.; Davis, Donald G.; Cowburn, David

    Heteronuclear two-dimensional 1H{ 15N} multiple-quantum (MQ) spectroscopy has been applied to a protein sample at natural abundance: ovomucoid third domain from turkey ( Meleagris gallopavo), a serine proteinase inhibitor of 56 amino acid residues. Peptide amide 1H NMR assignments obtained by two-dimensional 1H{ 1H} NMR methods (R. Krishnamoorthi and J. L. Markley, unpublished data) led to identification of the corresponding 1H{ 15N} MQ coherence cross peaks. From these, 15N NMR chemical shifts were determined for several specific backbone amide groups of amino acid residues located around the reactive site region of the inhibitor. The results suggest that amide 15N chemical shifts, which are readily obtained in this way, may serve as sensitive probes for conformational studies of proteins.

  14. Multiple Quantum Well-Based Modulating Retroreflectors for Inter- and Intra-Spacecraft Communications

    DTIC Science & Technology

    2006-01-01

    Multiple quantum well-based modulating retroreflectors for inter- and intra-spacecraft communication Peter G. Goetz, William S. Rabinovich, G...is presented. Keywords: Free-space optics, modulating retroreflector , multiple quantum well, radiation tolerance, FSO, MQW, MRR 1. INTRODUCTION...RETRO-REFLECTORS (MRRS) A MRR couples a passive optical retroreflector such as a corner-cube or a cat’s eye retroreflector with an electro-optic

  15. A quantum-inspired genetic algorithm based on probabilistic coding for multiple sequence alignment.

    PubMed

    Huo, Hong-Wei; Stojkovic, Vojislav; Xie, Qiao-Luan

    2010-02-01

    Quantum parallelism arises from the ability of a quantum memory register to exist in a superposition of base states. Since the number of possible base states is 2(n), where n is the number of qubits in the quantum memory register, one operation on a quantum computer performs what an exponential number of operations on a classical computer performs. The power of quantum algorithms comes from taking advantages of quantum parallelism. Quantum algorithms are exponentially faster than classical algorithms. Genetic optimization algorithms are stochastic search algorithms which are used to search large, nonlinear spaces where expert knowledge is lacking or difficult to encode. QGMALIGN--a probabilistic coding based quantum-inspired genetic algorithm for multiple sequence alignment is presented. A quantum rotation gate as a mutation operator is used to guide the quantum state evolution. Six genetic operators are designed on the coding basis to improve the solution during the evolutionary process. The experimental results show that QGMALIGN can compete with the popular methods, such as CLUSTALX and SAGA, and performs well on the presenting biological data. Moreover, the addition of genetic operators to the quantum-inspired algorithm lowers the cost of overall running time.

  16. Simple Approaches for Estimating Vicinal 1H- 1H Coupling-Constants and for Obtaining Stereospecific Resonance Assignments in Leucine Side Chains

    NASA Astrophysics Data System (ADS)

    Constantine, K. L.; Friedrichs, M. S.; Mueller, L.

    An approach for deriving stereospecific δ-methyl assignments and χ 2 dihedral angle constraints for leucine residues, based on easily recognized patterns of 1H- 1H spin-spin coupling constants and intraresidue nuclear-Overhauser-effect spectroscopy (NOESY) cross-peak intensities, is described. The approach depends on resolved H γ and/or δ-methyl resonances and on initially obtaining stereospecific assignments for H β2 and H β3. As part of the overall strategy, a method is presented for obtaining qualitative or, in favorable cases, semiquantitative estimates of vicinal 1H- 1H coupling constants from peak intensities measured in a short-mixing-time 1H- 1H total correlation spectroscopy (TOCSY) experiment. This method of estimating 1H- 1H spin-spin coupling constants is generally applicable to all side-chain types. The approach is illustrated for several leucine residues within uniformly 15N-labeled and 15N/ 13C-double-labeled isolated light-chain variable domain of the anti-digoxin antibody 26-10. Estimates of 3Jαβ and 3Jβγ coupling constants are derived from a three-dimensional (3D) 13C-edited TOCSY-heteronuclear multiple-quantum coherence (HMQC) spectrum. These data are combined with information from 3D 15N-edited NOESY and 3D 13C-edited NOESY spectra to yield stereospecific H β2, H β3, and δ-methyl assignments, as well as constraints on χ (1) and χ 2 dihedral angles. Although the overall approach is illustrated using 3D 15N-edited and 13C-edited data, it is equally applicable to analysis of two-dimensional 1H- 1H NOESY and TOCSY spectra.

  17. Monomeric and dimeric structures analysis and spectroscopic characterization of 3,5-difluorophenylboronic acid with experimental (FT-IR, FT-Raman, 1H and 13C NMR, UV) techniques and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Karabacak, Mehmet; Kose, Etem; Atac, Ahmet; Asiri, Abdullah M.; Kurt, Mustafa

    2014-01-01

    The spectroscopic properties of 3,5-difluorophenylboronic acid (3,5-DFPBA, C6H3F2B(OH)2) were investigated by FT-IR, FT-Raman UV-Vis, 1H and 13C NMR spectroscopic techniques. FT-IR (4000-400 cm-1) and FT-Raman spectra (3500-10 cm-1) in the solid phase and 1H and 13C NMR spectra in DMSO solution were recorded. The UV spectra that dissolved in ethanol and water were recorded in the range of 200-400 nm for each solution. The structural and spectroscopic data of the molecule have been obtained for possible three conformers from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. Hydrogen-bonded dimer of title molecule, optimized by counterpoise correction, was also studied B3LYP at the 6-311++G(d,p) level and the effects of molecular association through O-H⋯O hydrogen bonding have been discussed. 1H and 13C NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, were performed by time-dependent density functional theory (TD-DFT) results complements with the experimental findings. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (OPDOS) diagrams analysis were presented. The effects due to the substitutions of boric acid group and halogen were investigated. The results of the calculations were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. Besides, frontier molecular orbitals (FMO), molecular electrostatic potential (MEP), nonlinear optical properties (NLO) and thermodynamic features were performed.

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

    SciTech Connect

    Palade, D. I.

    2016-07-15

    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.

  19. Multiple-exciton generation in lead selenide nanorod solar cells with external quantum efficiencies exceeding 120%

    PubMed Central

    Davis, Nathaniel J. L. K.; Böhm, Marcus L.; Tabachnyk, Maxim; Wisnivesky-Rocca-Rivarola, Florencia; Jellicoe, Tom C.; Ducati, Caterina; Ehrler, Bruno; Greenham, Neil C.

    2015-01-01

    Multiple-exciton generation—a process in which multiple charge-carrier pairs are generated from a single optical excitation—is a promising way to improve the photocurrent in photovoltaic devices and offers the potential to break the Shockley–Queisser limit. One-dimensional nanostructures, for example nanorods, have been shown spectroscopically to display increased multiple exciton generation efficiencies compared with their zero-dimensional analogues. Here we present solar cells fabricated from PbSe nanorods of three different bandgaps. All three devices showed external quantum efficiencies exceeding 100% and we report a maximum external quantum efficiency of 122% for cells consisting of the smallest bandgap nanorods. We estimate internal quantum efficiencies to exceed 150% at relatively low energies compared with other multiple exciton generation systems, and this demonstrates the potential for substantial improvements in device performance due to multiple exciton generation. PMID:26411283

  20. Multiple-exciton generation in lead selenide nanorod solar cells with external quantum efficiencies exceeding 120.

    PubMed

    Davis, Nathaniel J L K; Böhm, Marcus L; Tabachnyk, Maxim; Wisnivesky-Rocca-Rivarola, Florencia; Jellicoe, Tom C; Ducati, Caterina; Ehrler, Bruno; Greenham, Neil C

    2015-09-28

    Multiple-exciton generation-a process in which multiple charge-carrier pairs are generated from a single optical excitation-is a promising way to improve the photocurrent in photovoltaic devices and offers the potential to break the Shockley-Queisser limit. One-dimensional nanostructures, for example nanorods, have been shown spectroscopically to display increased multiple exciton generation efficiencies compared with their zero-dimensional analogues. Here we present solar cells fabricated from PbSe nanorods of three different bandgaps. All three devices showed external quantum efficiencies exceeding 100% and we report a maximum external quantum efficiency of 122% for cells consisting of the smallest bandgap nanorods. We estimate internal quantum efficiencies to exceed 150% at relatively low energies compared with other multiple exciton generation systems, and this demonstrates the potential for substantial improvements in device performance due to multiple exciton generation.

  1. Quantum mechanical study and spectroscopic (FT-IR, FT-Raman, (13)C, (1)H) study, first order hyperpolarizability, NBO analysis, HOMO and LUMO analysis of 2-acetoxybenzoic acid by density functional methods.

    PubMed

    Bhavani, K; Renuga, S; Muthu, S; Sankara Narayanan, K

    2015-02-05

    In this work, colorless crystals of 2-acetoxybenzoic acid were grown by slow evaporation method and the FT-IR and FT-Raman spectra of the sample were recorded in the region 4000-500cm(-1) and 4000-100cm(-1) respectively. Molecular structure is optimized with the help of density functional theory method (B3LYP) with 6-31+G(d,p), 6-311++G(d,p) basis sets. Stability of the molecule arising from hyperconjugation and charge delocalization is confirmed by the natural bond orbital analysis (NBO). The results show that electron density (ED) in the σ(∗) antibonding orbitals and E(2) energies confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis following the scaled quantum mechanical force field (SQMFF) methodology. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by GIAO method. Mulliken population analysis on atomic charges is also calculated. The calculated HOMO and LUMO energy gap shows that charge transfer occurs within the molecule. Copyright © 2014 Elsevier B.V. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

    Controllable arrays of ions and ultracold atoms can simulate complex many-body phenomena and may provide insights into unsolved problems in modern science. To this end, experimentally feasible protocols for quantifying the buildup of quantum correlations and coherence are needed, as performing full state tomography does not scale favourably with the number of particles. Here we develop and experimentally demonstrate such a protocol, which uses time reversal of the many-body dynamics to measure out-of-time-order correlation functions (OTOCs) in a long-range Ising spin quantum simulator with more than 100 ions in a Penning trap. By measuring a family of OTOCs as a function of a tunable parameter we obtain fine-grained information about the state of the system encoded in the multiple quantum coherence spectrum, extract the quantum state purity, and demonstrate the buildup of up to 8-body correlations. Future applications of this protocol could enable studies of many-body localization, quantum phase transitions, and tests of the holographic duality between quantum and gravitational systems.

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  5. Exciton multiplication and relaxation dynamics in quantum dots: applications to ultrahigh-efficiency solar photon conversion.

    PubMed

    Nozik, A J

    2005-10-03

    Huge amounts of carbon-free energy will be required during the coming decades in order to stabilize atmospheric CO2 to acceptable levels. Solar energy is the largest source of non-carbonaceous energy and can be used to produce both electricity and fuel. However, the ratio of the areal cost to the conversion efficiency for devices converting solar photons to electricity or fuel must be reduced by at least 1 order of magnitude from the present values; this requires large increases in the cell efficiency and large reductions in the cost per unit area. We have shown how semiconductor quantum dots may greatly increase photon conversion efficiencies by producing multiple excitons from a single photon. This is possible because quantization of energy levels in quantum dots slows the cooling of hot excitons, promotes multiple exciton generation, and lowers the photon energy threshold for this process. Quantum yields of 300% for exciton formation in PbSe quantum dots have been reported at photon energies 3.8 times the HOMO-LUMO transition energy, indicating the formation of three excitons/photon for all photoexcited quantum dots. Similar high quantum yields have also been reported for PbS quantum dots. A new model for this effect that is based on a coherent superposition of multiple excitonic states has been proposed.

  6. Exact non-Markovian master equations for multiple qubit systems: Quantum-trajectory approach

    NASA Astrophysics Data System (ADS)

    Chen, Yusui; You, J. Q.; Yu, Ting

    2014-11-01

    A wide class of exact master equations for a multiple qubit system can be explicitly constructed by using the corresponding exact non-Markovian quantum-state diffusion equations. These exact master equations arise naturally from the quantum decoherence dynamics of qubit system as a quantum memory coupled to a collective colored noisy source. The exact master equations are also important in optimal quantum control, quantum dissipation, and quantum thermodynamics. In this paper, we show that the exact non-Markovian master equation for a dissipative N -qubit system can be derived explicitly from the statistical average of the corresponding non-Markovian quantum trajectories. We illustrated our general formulation by an explicit construction of a three-qubit system coupled to a non-Markovian bosonic environment. This multiple qubit master equation offers an accurate time evolution of quantum systems in various domains, and paves the way to investigate the memory effect of an open system in a non-Markovian regime without any approximation.

  7. Carrier multiplication detected through transient photocurrent in device-grade films of lead selenide quantum dots

    SciTech Connect

    Gao, Jianbo; Fidler, Andrew F.; Klimov, Victor I.

    2015-09-08

    In carrier multiplication, the absorption of a single photon results in two or more electron–hole pairs. Quantum dots are promising materials for implementing carrier multiplication principles in real-life technologies. So far, however, most of research in this area has focused on optical studies of solution samples with yet to be proven relevance to practical devices. We report ultra-fast electro-optical studies of device-grade films of electronically coupled quantum dots that allow us to observe multiplication directly in the photocurrent. Our studies help rationalize previous results from both optical spectroscopy and steady-state photocurrent measurements and also provide new insights into effects of electric field and ligand treatments on multiexciton yields. Importantly, we demonstrate that using appropriate chemical treatments of the films, extra charges produced by carrier multiplication can be extracted from the quantum dots before they are lost to Auger recombination and hence can contribute to photocurrent of practical devices.

  8. Carrier multiplication detected through transient photocurrent in device-grade films of lead selenide quantum dots

    PubMed Central

    Gao, Jianbo; Fidler, Andrew F.; Klimov, Victor I.

    2015-01-01

    In carrier multiplication, the absorption of a single photon results in two or more electron–hole pairs. Quantum dots are promising materials for implementing carrier multiplication principles in real-life technologies. So far, however, most of research in this area has focused on optical studies of solution samples with yet to be proven relevance to practical devices. Here we report ultrafast electro-optical studies of device-grade films of electronically coupled quantum dots that allow us to observe multiplication directly in the photocurrent. Our studies help rationalize previous results from both optical spectroscopy and steady-state photocurrent measurements and also provide new insights into effects of electric field and ligand treatments on multiexciton yields. Importantly, we demonstrate that using appropriate chemical treatments of the films, extra charges produced by carrier multiplication can be extracted from the quantum dots before they are lost to Auger recombination and hence can contribute to photocurrent of practical devices. PMID:26345390

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

    SciTech Connect

    Grudka, Andrzej; Horodecki, Pawel

    2010-06-15

    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.

  10. Physically feasible three-level transitionless quantum driving with multiple Schrödinger dynamics

    NASA Astrophysics Data System (ADS)

    Song, Xue-Ke; Ai, Qing; Qiu, Jing; Deng, Fu-Guo

    2016-05-01

    Three-level quantum systems, which possess some unique characteristics beyond two-level ones, such as electromagnetically induced transparency, coherent trapping, and Raman scatting, play important roles in solid-state quantum information processing. Here, we introduce an approach to implement the physically feasible three-level transitionless quantum driving with multiple Schrödinger dynamics (MSDs). It can be used to control accurately population transfer and entanglement generation for three-level quantum systems in a nonadiabatic way. Moreover, we propose an experimentally realizable hybrid architecture, based on two nitrogen-vacancy-center ensembles coupled to a transmission line resonator, to realize our transitionless scheme which requires fewer physical resources and simple procedures, and it is more robust against environmental noises and control parameter variations than conventional adiabatic passage techniques. All these features inspire the further application of MSDs on robust quantum information processing in experiment.

  11. Estimating side-chain order in methyl-protonated, perdeuterated proteins via multiple-quantum relaxation violated coherence transfer NMR spectroscopy.

    PubMed

    Sun, Hechao; Godoy-Ruiz, Raquel; Tugarinov, Vitali

    2012-03-01

    Relaxation violated coherence transfer NMR spectroscopy (Tugarinov et al. in J Am Chem Soc 129:1743-1750, 2007) is an established experimental tool for quantitative estimation of the amplitudes of side-chain motions in methyl-protonated, highly deuterated proteins. Relaxation violated coherence transfer experiments monitor the buildup of methyl proton multiple-quantum coherences that can be created in magnetically equivalent spin-systems as long as their transverse magnetization components relax with substantially different rates. The rate of this build-up is a reporter of the methyl-bearing side-chain mobility. Although the build-up of multiple-quantum (1)H coherences is monitored in these experiments, the decay of the methyl signal during relaxation delays occurs when methyl proton magnetization is in a single-quantum state. We describe a relaxation violated coherence transfer approach where the relaxation of multiple-quantum (1)H-(13)C methyl coherences during the relaxation delay period is quantified. The NMR experiment and the associated fitting procedure that models the time-dependence of the signal build-up, are applicable to the characterization of side-chain order in [(13)CH(3)]-methyl-labeled, highly deuterated protein systems up to ~100 kDa in molecular weight. The feasibility of extracting reliable measures of side-chain order is experimentally verified on methyl-protonated, perdeuterated samples of an 8.5-kDa ubiquitin at 10°C and an 82-kDa Malate Synthase G at 37°C.

  12. High Efficiency Quantum Dot Solar Cells Based on Multiple Exciton Generation

    SciTech Connect

    Breeze, Alison

    2011-04-15

    The objective of this project was to demonstrate that efficient multiple exciton generation observed in quantum dot materials could be harvested in nanostructured solar cells to dramatically improve the maximum power efficiency obtainable in photovoltaic modules. This proposal aimed to develop a high efficiency solar cell through a combination of quantum dot materials, nanostructured surfaces and atomic layer deposition for fabricating conformal and ultrathin films.

  13. Band-edge absorption coefficients from photoluminescence in semiconductor multiple quantum wells

    NASA Technical Reports Server (NTRS)

    Kost, Alan; Zou, Yao; Dapkus, P. D.; Garmire, Elsa; Lee, H. C.

    1989-01-01

    A novel approach to determining absorption coefficients in thin films using luminescence is described. The technique avoids many of the difficulties typically encountered in measurements of thin samples, Fabry-Perot effects, for example, and can be applied to a variety of materials. The absorption edge for GaAs/AlGaAs multiple quantum well structures, with quantum well widths ranging from 54 to 193 A is examined. Urbach (1953) parameters and excitonic linewidths are tabulated.

  14. Photoconductivity of InGaN/GaN multiple quantum well heterostructures

    NASA Astrophysics Data System (ADS)

    Baranovskiy, M. V.; Glinskii, G. F.

    2013-08-01

    Photocurrent and photoconductivity of InGaN/GaN multiple quantum well heterostructures as a function of applied reverse bias is investigated. Optical excitation was carried out in blue and violet regions of the spectrum, and temperature was ranging from 10 to 300 K. We observed characteristic features related to consequently moving space charge boundary through the quantum wells. For each quantum well there is a range of reverse bias with negative differential conductivity when excited by blue light. Frequency and temperature measurements revealed the presence of at least two different mechanisms that determine the photoconductivity of the structures.

  15. Decoherence of multiple quantum coherences generated from a dipolar ordered state

    NASA Astrophysics Data System (ADS)

    González, C. E.; Segnorile, H. H.; Zamar, R. C.

    2011-01-01

    Starting from the hypothesis that the decay of coherent signals observed in H1 NMR experiments is driven by quantum interference, irreversible decoherence, and nonidealities in the experiment, we design an experiment to isolate and identify the irreversible attenuation of multiple-quantum coherences toward quasiequilibrium states of dipolar order in nematic liquid crystals (LCs). The experiment combines the well-known “magic sandwich” pulse sequence with preparation of dipolar ordered states and encoding of multiple-quantum coherences. The spin system composed of the dipole-coupled protons of a LC molecule provides an example of a small cluster of strongly interacting spins. We study decoherence rates under a sequence that reverses time evolution with the secular dipolar Hamiltonian to compensate coherent evolution of a closed quantum system. In this way, the time scale is made evident where irreversible decoherence takes place, providing insight into the nature of the processes responsible for the attainment of quasiequilibrium. The behavior of single- and double-quantum-coherence amplitudes with reversal time is interpreted as evidence of the quantum character (as opposed to stochastic character) of the processes that drive irreversible decoherence. The experimental method proposed is useful for probing the action of the environment on materials with quantum information processing potential.

  16. A probabilistic coding based quantum genetic algorithm for multiple sequence alignment.

    PubMed

    Huo, Hongwei; Xie, Qiaoluan; Shen, Xubang; Stojkovic, Vojislav

    2008-01-01

    This paper presents an original Quantum Genetic algorithm for Multiple sequence ALIGNment (QGMALIGN) that combines a genetic algorithm and a quantum algorithm. A quantum probabilistic coding is designed for representing the multiple sequence alignment. A quantum rotation gate as a mutation operator is used to guide the quantum state evolution. Six genetic operators are designed on the coding basis to improve the solution during the evolutionary process. The features of implicit parallelism and state superposition in quantum mechanics and the global search capability of the genetic algorithm are exploited to get efficient computation. A set of well known test cases from BAliBASE2.0 is used as reference to evaluate the efficiency of the QGMALIGN optimization. The QGMALIGN results have been compared with the most popular methods (CLUSTALX, SAGA, DIALIGN, SB_PIMA, and QGMALIGN) results. The QGMALIGN results show that QGMALIGN performs well on the presenting biological data. The addition of genetic operators to the quantum algorithm lowers the cost of overall running time.

  17. High charge-carrier mobility enables exploitation of carrier multiplication in quantum-dot films

    PubMed Central

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

    2013-01-01

    Carrier multiplication, the generation of multiple electron–hole pairs by a single photon, is of great interest for solar cells as it may enhance their photocurrent. This process has been shown to occur efficiently in colloidal quantum dots, however, harvesting of the generated multiple charges has proved difficult. Here we show that by tuning the charge-carrier mobility in quantum-dot films, carrier multiplication can be optimized and may show an efficiency as high as in colloidal dispersion. Our results are explained quantitatively by the competition between dissociation of multiple electron–hole pairs and Auger recombination. Above a mobility of ~1 cm2 V−1 s−1, all charges escape Auger recombination and are quantitatively converted to free charges, offering the prospect of cheap quantum-dot solar cells with efficiencies in excess of the Shockley–Queisser limit. In addition, we show that the threshold energy for carrier multiplication is reduced to twice the band gap of the quantum dots. PMID:23974282

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

    SciTech Connect

    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.

  19. Joint source-channel coding for a quantum multiple access channel

    NASA Astrophysics Data System (ADS)

    Wilde, Mark M.; Savov, Ivan

    2012-11-01

    Suppose that two senders each obtain one share of the output of a classical, bivariate, correlated information source. They would like to transmit the correlated source to a receiver using a quantum multiple access channel. In prior work, Cover, El Gamal and Salehi provided a combined source-channel coding strategy for a classical multiple access channel which outperforms the simpler ‘separation’ strategy where separate codebooks are used for the source coding and the channel coding tasks. In this paper, we prove that a coding strategy similar to the Cover-El Gamal-Salehi strategy and a corresponding quantum simultaneous decoder allow for the reliable transmission of a source over a quantum multiple access channel, as long as a set of information inequalities involving the Holevo quantity hold.

  20. Surface Passivation by Quantum Exclusion Using Multiple Layers

    NASA Technical Reports Server (NTRS)

    Hoenk, Michael E. (Inventor)

    2013-01-01

    A semiconductor device has a multilayer doping to provide improved passivation by quantum exclusion. The multilayer doping includes a plurality M of doped layers, where M is an integer greater than 1. The dopant sheet densities in the M doped layers need not be the same, but in principle can be selected to be the same sheet densities or to be different sheet densities. M-1 interleaved layers provided between the M doped layers are not deliberately doped (also referred to as "undoped layers"). Structures with M=2, M=3 and M=4 have been demonstrated and exhibit improved passivation.

  1. Reliability assessment of multiple quantum well avalanche photodiodes

    NASA Technical Reports Server (NTRS)

    Yun, Ilgu; Menkara, Hicham M.; Wang, Yang; Oguzman, Isamil H.; Kolnik, Jan; Brennan, Kevin F.; May, Gray S.; Wagner, Brent K.; Summers, Christopher J.

    1995-01-01

    The reliability of doped-barrier AlGaAs/GsAs multi-quantum well avalanche photodiodes fabricated by molecular beam epitaxy is investigated via accelerated life tests. Dark current and breakdown voltage were the parameters monitored. The activation energy of the degradation mechanism and median device lifetime were determined. Device failure probability as a function of time was computed using the lognormal model. Analysis using the electron beam induced current method revealed the degradation to be caused by ionic impurities or contamination in the passivation layer.

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Room-Temperature Photocurrent Spectroscopy of GaAs/GaAlAs Multiple Quantum Wells,

    DTIC Science & Technology

    1994-11-15

    Hailong , Wang Qiuning, et al. DO..... ... . .I C- DTIC ~ELECTIEE 199|11O9034 19950109 034Ditiuinnlmed NAIC- ID(RS)T-0385-94 AOSSI.O •z [ A Si8 eol1Y de...MULTIPLE QUANTUM WELLS 5y: Duan Hailong , Wang Qiuning, et al. English pages: 12 Source: Bandaoti Xuebao, Vol. 12, Nr. 7, July 1991, pp. 399-4O4...TEMPERATURE PHOTOCURRENT SPECTROSCOPY OF GaAs/GaAlAs MULTIPLE QUANTUM WELLS DUAN HAILONG , WANG QIUNING, WU RONGHAN, ZENG YIPING and KONG MEIYING

  4. Selective Inversion of Spin-Tickling Spectra in a 13C-1H Spin System

    NASA Astrophysics Data System (ADS)

    Ishiwata, Mitsumasa

    1993-10-01

    Selective spin inversion usually produces transfer of the longitudinal magnetization in a coupled spin system. Under irradiation of a stirring-field, however, transverse ones and multiple quantum coherences can also be simultaneously transferred in this process. For a coupled 13C-1H spin system under irradiation resonant with one of the 1H lines, 13C tickling spectra are observed immediately after inversion of one component of the 13C-polarizations. Spectra thus obtained are considerably different from a simple selectively-inverted pattern of the steady-state ones. These changes depend on amplitude and frequency of the rf field, frequency and phase of the inversion pulse and inhomogeneity of the static magnetic field. The most prominent change in these spectra can be explained by transfer of zero quantum coherence, which is made in the differential form into each line of the spectra.

  5. Single-loop multiple-pulse nonadiabatic holonomic quantum gates

    NASA Astrophysics Data System (ADS)

    Herterich, Emmi; Sjöqvist, Erik

    2016-11-01

    Nonadiabatic holonomic quantum computation provides the means to perform fast and robust quantum gates by utilizing the resilience of non-Abelian geometric phases to fluctuations of the path in state space. While the original scheme [E. Sjöqvist et al., New J. Phys. 14, 103035 (2012), 10.1088/1367-2630/14/10/103035] needs two loops in the Grassmann manifold (i.e., the space of computational subspaces of the full state space) to generate an arbitrary holonomic one-qubit gate, we propose single-loop one-qubit gates that constitute an efficient universal set of holonomic gates when combined with an entangling holonomic two-qubit gate. Our one-qubit gate is realized by dividing the loop into path segments, each of which is generated by a Λ -type Hamiltonian. We demonstrate that two path segments are sufficient to realize arbitrary single-loop holonomic one-qubit gates. We describe how our scheme can be implemented experimentally in a generic atomic system exhibiting a three-level Λ -coupling structure by utilizing carefully chosen laser pulses.

  6. Quantum mechanical and spectroscopic (FT-IR, FT-Raman,1H,13C NMR, UV-Vis) studies, NBO, NLO, HOMO, LUMO and Fukui function analysis of 5-Methoxy-1H-benzo[d]imidazole-2(3H)-thione by DFT studies

    NASA Astrophysics Data System (ADS)

    Pandey, Manju; Muthu, S.; Nanje Gowda, N. M.

    2017-02-01

    Theoretical analysis of the molecular structure, spectroscopic (FT-IR, FT-Raman, 1H, 13C NMR, UV-Vis) studies, and thermodynamic characteristics of 5-Methoxy-1H-benzo[d]imidazole-2(3H)-thione (5MBIT) molecule were done by DFT/B3LYP using 6-311++G(d, p) basis set. Theoretical parameters were compared with experimental data. The dipole moment (μ), polarizability (Δα) and first order hyperpolarizability (β) of the molecule were calculated. Thermodynamic properties, HOMO and LUMO energies were determined. Global reactivity parameters and Fukui function of the 5MBIT molecule were predicted.

  7. Fast and simultaneous determination of (1) H-(1) H and (1) H-(19) F scalar couplings in complex spin systems: Application of PSYCHE homonuclear broadband decoupling.

    PubMed

    Kakita, Veera Mohana Rao; Rachineni, Kavitha; Hosur, Ramakrishna V

    2017-07-21

    The present manuscript focuses on fast and simultaneous determination of (1) H-(1) H and (1) H-(19) F scalar couplings in fluorinated complex steroid molecules. Incorporation of broadband PSYCHE homonuclear decoupling in the indirect dimension of zero-quantum filtered diagonal experiments (F1-PSYCHE-DIAG) suppresses (1) H-(1) H scalar couplings; however, it retains (1) H-(19) F scalar couplings (along F1 dimension) for the (19) F coupled protons while preserving the pure-shift nature for (1) H resonances uncoupled to (19) F. In such cases, along the direct dimensions, (1) H-(1) H scalar coupling multiplets deconvolute and they appear as duplicated multiplets for the (19) F coupled protons, which facilitates unambiguous discrimination of (19) F coupled (1) H chemical sites from the others. Further, as an added advantage, data acquisition has been accelerated by invoking the known ideas of spectral aliasing in the F1-PSYCHE-DIAG scheme and experiments demand only ~10 min of spectrometer times. Copyright © 2017 John Wiley & Sons, Ltd.

  8. Simultaneous nano-tracking of multiple motor proteins via spectral discrimination of quantum dots

    PubMed Central

    Kakizuka, Taishi; Ikezaki, Keigo; Kaneshiro, Junichi; Fujita, Hideaki; Watanabe, Tomonobu M.; Ichimura, Taro

    2016-01-01

    Simultaneous nanometric tracking of multiple motor proteins was achieved by combining multicolor fluorescent labeling of target proteins and imaging spectroscopy, revealing dynamic behaviors of multiple motor proteins at the sub-diffraction-limit scale. Using quantum dot probes of distinct colors, we experimentally verified the localization precision to be a few nanometers at temporal resolution of 30 ms or faster. One-dimensional processive movement of two heads of a single myosin molecule and multiple myosin molecules was successfully traced. Furthermore, the system was modified for two-dimensional measurement and applied to tracking of multiple myosin molecules. Our approach is useful for investigating cooperative movement of proteins in supramolecular nanomachinery. PMID:27446684

  9. Characteristics of AlGaAs/GaAs multiple quantum well infrared detectors

    NASA Technical Reports Server (NTRS)

    Janousek, Bruce K.; Rosenbluth, Mary L.; Oloughlin, Michael J.; Bloss, Walter L.; Deluccia, Frank J.; Kanter, Helmut; Perry, L. Elaine; Daugherty, Michael J.

    1990-01-01

    Researchers fabricated and characterized several AlGaAs/GaAs multiple quantum well infrared detectors to evaluate the ultimate performance of these devices for low infrared background applications. The detectors were designed to have a single bound state in the quantum well and the first excited state in the continuum above the AlGaAs conduction band edge. The difference in energy between the two levels, as determined by the quantum well width and aluminum mole fraction in the barrier, was chosen such that peak absorption would occur near 8 microns. The initial structures studied comprised 50 periods with 40 A well widths and 300 A Al(0.28)Ga(0.72)As barriers. The performance of these detectors are summarized. To better interpret these results and design optimized detectors, researchers modeled both the detector noise and tunneling currents. The noise model correctly predicts that multiple quantum well detectors will, indeed, exhibit noise lower than full shot noise. The tunneling current model predicts the dark current versus bias for any choice of design parameters in a multiple quantum well detector. This model predicts a substantially reduced dark current (x 10(exp 04)) for samples with 400 A barriers. To evaluate structures with thicker barriers, researchers fabricated and characterized detectors with 400 A and 500 A barriers; a comparison of detector dark currents is shown. These results are consistent with the predictions of the dark current model.

  10. Precision Control of Multiple Quantum Cascade Lasers for Calibration Systems

    SciTech Connect

    Taubman, Matthew S.; Myers, Tanya L.; Pratt, Richard M.; Stahl, Robert D.; Cannon, Bret D.

    2014-01-15

    We present a precision, digitally interfaced current controller for quantum cascade lasers, with demonstrated DC and modulated temperature coefficients of 1- 2 ppm/ºC and 15 ppm/ºC respectively. High linearity digital to analog converters (DACs) together with an ultra-precision voltage reference, produce highly stable, precision voltages. These are in turn selected by a low charge-injection multiplexer (MUX) chip, which are then used to set output currents via a linear current regulator. The controller is operated in conjunction with a power multiplexing unit, allowing one of three lasers to be driven by the controller while ensuring protection of controller and all lasers during operation, standby and switching. Simple ASCII commands sent over a USB connection to a microprocessor located in the current controller operate both the controller (via the DACs and MUX chip) and the power multiplexer.

  11. Surface Passivation by Quantum Exclusion Using Multiple Layers

    NASA Technical Reports Server (NTRS)

    Hoenk, Michael E. (Inventor)

    2015-01-01

    A semiconductor device has a multilayer doping to provide improved passivation by quantum exclusion. The multilayer doping includes at least two doped layers fabricated using MBE methods. The dopant sheet densities in the doped layers need not be the same, but in principle can be selected to be the same sheet densities or to be different sheet densities. The electrically active dopant sheet densities are quite high, reaching more than 1.times.10.sup.14 cm.sup.-2, and locally exceeding 10.sup.22 per cubic centimeter. It has been found that silicon detector devices that have two or more such dopant layers exhibit improved resistance to degradation by UV radiation, at least at wavelengths of 193 nm, as compared to conventional silicon p-on-n devices.

  12. Precision control of multiple quantum cascade lasers for calibration systems

    SciTech Connect

    Taubman, Matthew S. Myers, Tanya L.; Pratt, Richard M.; Stahl, Robert D.; Cannon, Bret D.

    2014-01-15

    We present a precision, 1-A, digitally interfaced current controller for quantum cascade lasers, with demonstrated temperature coefficients for continuous and 40-kHz full-depth square-wave modulated operation, of 1–2 ppm/ °C and 15 ppm/ °C, respectively. High precision digital to analog converters (DACs) together with an ultra-precision voltage reference produce highly stable, precision voltages, which are selected by a multiplexer (MUX) chip to set output currents via a linear current regulator. The controller is operated in conjunction with a power multiplexing unit, allowing one of three lasers to be driven by the controller, while ensuring protection of controller and all lasers during operation, standby, and switching. Simple ASCII commands sent over a USB connection to a microprocessor located in the current controller operate both the controller (via the DACs and MUX chip) and the power multiplexer.

  13. Multiple-User Quantum Information Theory for Optical Communication Channels

    DTIC Science & Technology

    2008-06-01

    detection uses 6 spatial modes with (from top to bottom) 1 ≤ q ≤ 3. ( d ) Wideband, multiple- spatial -mode capacities (in bits per second) for the scalar...detection imply that their wideband multiple- spatial -mode capacities bear the follow- ing relationship, Chom(P ) = 1 2 Chet (4P ). (2.22) Thus, only two... spatial modes, but we have only plotted the spectra for 1 ≤ q ≤ 6. In Fig. 2-4( d ) we have plotted the heterodyne detection, homodyne detection, and

  14. Quantum circuits for -multiplication with subquadratic gate count

    NASA Astrophysics Data System (ADS)

    Kepley, Shane; Steinwandt, Rainer

    2015-07-01

    One of the most cost-critical operations when applying Shor's algorithm to binary elliptic curves is the underlying field arithmetic. Here, we consider binary fields in polynomial basis representation, targeting especially field sizes as used in elliptic curve cryptography. Building on Karatsuba's algorithm, our software implementation automatically synthesizes a multiplication circuit with the number of -gates being bounded by for any given reduction polynomial of degree . If an irreducible trinomial of degree exists, then a multiplication circuit with a total gate count of is available.

  15. Interface and photoluminescence characteristics of graphene-(GaN/InGaN){sub n} multiple quantum wells hybrid structure

    SciTech Connect

    Wang, Liancheng E-mail: lzq@semi.ac.cn; Liu, Zhiqiang E-mail: lzq@semi.ac.cn Tian, Ying Dong; Yi, Xiaoyan; Wang, Junxi; Li, Jinmin; Wang, Guohong; Zhang, Zi-Hui E-mail: lzq@semi.ac.cn

    2016-04-14

    The effects of graphene on the optical properties of active system, e.g., the InGaN/GaN multiple quantum wells, are thoroughly investigated and clarified. Here, we have investigated the mechanisms accounting for the photoluminescence reduction for the graphene covered GaN/InGaN multiple quantum wells hybrid structure. Compared to the bare multiple quantum wells, the photoluminescence intensity of graphene covered multiple quantum wells showed a 39% decrease after excluding the graphene absorption losses. The responsible mechanisms have been identified with the following factors: (1) the graphene two dimensional hole gas intensifies the polarization field in multiple quantum wells, thus steepening the quantum well band profile and causing hole-electron pairs to further separate; (2) a lower affinity of graphene compared to air leading to a weaker capability to confine the excited hot electrons in multiple quantum wells; and (3) exciton transfer through non-radiative energy transfer process. These factors are theoretically analysed based on advanced physical models of semiconductor devices calculations and experimentally verified by varying structural parameters, such as the indium fraction in multiple quantum wells and the thickness of the last GaN quantum barrier spacer layer.

  16. Interface and photoluminescence characteristics of graphene-(GaN/InGaN)n multiple quantum wells hybrid structure

    NASA Astrophysics Data System (ADS)

    Wang, Liancheng; Liu, Zhiqiang; Zhang, Zi-Hui; Tian, Ying Dong; Yi, Xiaoyan; Wang, Junxi; Li, Jinmin; Wang, Guohong

    2016-04-01

    The effects of graphene on the optical properties of active system, e.g., the InGaN/GaN multiple quantum wells, are thoroughly investigated and clarified. Here, we have investigated the mechanisms accounting for the photoluminescence reduction for the graphene covered GaN/InGaN multiple quantum wells hybrid structure. Compared to the bare multiple quantum wells, the photoluminescence intensity of graphene covered multiple quantum wells showed a 39% decrease after excluding the graphene absorption losses. The responsible mechanisms have been identified with the following factors: (1) the graphene two dimensional hole gas intensifies the polarization field in multiple quantum wells, thus steepening the quantum well band profile and causing hole-electron pairs to further separate; (2) a lower affinity of graphene compared to air leading to a weaker capability to confine the excited hot electrons in multiple quantum wells; and (3) exciton transfer through non-radiative energy transfer process. These factors are theoretically analysed based on advanced physical models of semiconductor devices calculations and experimentally verified by varying structural parameters, such as the indium fraction in multiple quantum wells and the thickness of the last GaN quantum barrier spacer layer.

  17. Impact ionization can explain carrier multiplication in PbSe quantum dots.

    PubMed

    Franceschetti, A; An, J M; Zunger, A

    2006-10-01

    The efficiency of conventional solar cells is limited because the excess energy of absorbed photons converts to heat instead of producing electron-hole pairs. Recently, efficient carrier multiplication has been observed in semiconductor quantum dots. In this process, a single, high-energy photon generates multiple electron-hole pairs. Rather exotic mechanisms have been proposed to explain the efficiency of carrier multiplication in PbSe quantum dots. Using atomistic pseudopotential calculations, we show here that the more conventional impact ionization mechanism, whereby a photogenerated electron-hole pair decays into a biexciton in a process driven by Coulomb interactions between the carriers, can explain both the rate (<1 ps) and the energy threshold ( approximately 2.2 times the band gap) of carrier multiplication, without the need to invoke alternative mechanisms.

  18. Intersubband Transition in GaN/InGaN Multiple Quantum Wells

    PubMed Central

    Chen, G.; Wang, X. Q.; Rong, X.; Wang, P.; Xu, F. J.; Tang, N.; Qin, Z. X.; Chen, Y. H.; Shen, B.

    2015-01-01

    Utilizing the growth temperature controlled epitaxy, high quality GaN/In0.15Ga0.85N multiple quantum wells designed for intersubband transition (ISBT) as novel candidates in III-nitride infrared device applications have been experimentally realized for the first time. Photo-absorption originated from the ISBT has been successfully observed at infrared regime covering the 3–5 μm atmosphere window, where the central absorption wavelength is modulated by adjusting the quantum well width. With increasing the quantum well thickness, the ISBT center wave length blue shifts at thickness less than 2.8 nm and then redshifts with further increase of the well thickness. The non-monotonic trend is most likely due to the polarization induced asymmetric shape of the quantum wells. PMID:26089133

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

    SciTech Connect

    Chen, G.; Rong, X.; Xu, F. J.; Tang, N.; Wang, X. Q. Shen, B.; Fu, K.; Zhang, B. S.; Hashimoto, H.; Yoshikawa, A.; Ge, W. K.

    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. Control of coherence transfer via tunneling in quadruple and multiple quantum dots

    NASA Astrophysics Data System (ADS)

    Tian, Si-Cong; Xing, En-Bo; Wan, Ren-Gang; Wang, Chun-Liang; Wang, Li-Jie; Shu, Shi-Li; Tong, Cun-Zhu; Wang, Li-Jun

    2016-12-01

    Transfer and manipulation of coherence among the ground state and indirect exciton states via tunneling in quadruple and multiple quantum dots is analyzed. By applying suitable amplitudes and sequences of the pump and tunneling pulses, a complete transfer of coherence or an arbitrary distribution of coherence of multiple states can be realized. The method, which is an adiabatic passage process, is different from previous works on quantum dot molecules in the way that the population can transfer from the ground state to the indirect exciton states without populating the direct exciton state, and thus no spontaneous emission occurs. This investigation can provide further insight to help the experimental development of coherence transfer in semiconductor structures, and may have potential applications in quantum information processing.

  1. Modulating retroreflector architecture using multiple quantum wells for free-space optical communications

    NASA Astrophysics Data System (ADS)

    Gilbreath, G. Charmaine; Rabinovich, William S.; Mahon, Rita; Corson, Michael R.; Kline, John F.; Resnick, Joshua H.; Merk, H. C.; Vilcheck, Michael J.

    1998-12-01

    In this paper, we describe a demonstration using a Multiple Quantum Well modulator combined with an optical retroreflector which supported a high speed free space optical data link. Video images were transmitted over an 859 nanometer link at a rate of 460 kilo bits per second, where rate of modulation was limited by demonstration hardware, not the modulator. Reflection architectures for the modulator were used although transmission architectures have also been investigated but are not discussed in this paper. The modulator was a GaAs/Al0.3Ga0.7As quantum well which was designed and fabricated for use as a shutter at the Naval Research Laboratory. We believe these are the first results reported demonstrating a high speed free space optical data link using multiple quantum well shutters combined with retroreflectors for viable free space optical communications.

  2. Quantum Optimal Multiple Assignment Scheme for Realizing General Access Structure of Secret Sharing

    NASA Astrophysics Data System (ADS)

    Matsumoto, Ryutaroh

    The multiple assignment scheme is to assign one or more shares to single participant so that any kind of access structure can be realized by classical secret sharing schemes. We propose its quantum version including ramp secret sharing schemes. Then we propose an integer optimization approach to minimize the average share size.

  3. Generation of Multiple Excitons in Ag2S Quantum Dots: Single High-Energy versus Multiple-Photon Excitation.

    PubMed

    Sun, Jingya; Yu, Weili; Usman, Anwar; Isimjan, Tayirjan T; DGobbo, Silvano; Alarousu, Erkki; Takanabe, Kazuhiro; Mohammed, Omar F

    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 Ag2S 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.

  4. An optimized quantum information splitting scheme with multiple controllers

    NASA Astrophysics Data System (ADS)

    Jiang, Min

    2016-12-01

    We propose an efficient scheme for splitting multi-qudit information with cooperative control of multiple agents. Each controller is assigned one controlling qudit, and he can monitor the state sharing of all multi-qudit information. Compared with the existing schemes, our scheme requires less resource consumption and approaches higher communication efficiency. In addition, our proposal involves only generalized Bell-state measurement, single-qudit measurement, one-qudit gates and a unitary-reduction operation, which makes it flexible and achievable for physical implementation.

  5. Coherent manipulation of valley states at multiple charge configurations of a silicon quantum dot device.

    PubMed

    Schoenfield, Joshua S; Freeman, Blake M; Jiang, HongWen

    2017-07-05

    Qubits based on silicon quantum dots are emerging as leading candidates for the solid-state implementation of quantum information processing. In silicon, valley states represent a degree of freedom in addition to spin and charge. Characterizing and controlling valley states is critical for the encoding and read-out of electrons-in-silicon-based qubits. Here, we report the coherent manipulation of a qubit, which is based on the two valley states of an electron confined in a silicon quantum dot. We carry out valley qubit operations at multiple charge configurations of the double quantum dot device. The dependence of coherent oscillations on pulse excitation level and duration allows us to map out the energy dispersion as a function of detuning as well as the phase coherence time of the valley qubit. The coherent manipulation also provides a method of measuring valley splittings that are too small to probe with conventional methods.Silicon quantum dots provide a promising platform for quantum computing based on manipulation of electron degrees of freedom in a well-characterized environment. Here, the authors demonstrate coherent control of electron valley states, yielding an accurate determination of the valley splitting.

  6. Multiplicative logarithmic corrections to quantum criticality in three-dimensional dimerized antiferromagnets

    NASA Astrophysics Data System (ADS)

    Qin, Yan Qi; Normand, B.; Sandvik, Anders W.; Meng, Zi Yang

    2015-12-01

    We investigate the quantum phase transition in an S =1 /2 dimerized Heisenberg antiferromagnet in three spatial dimensions. By performing large-scale quantum Monte Carlo simulations and detailed finite-size scaling analyses, we obtain high-precision results for the quantum critical properties at the transition from the magnetically disordered dimer-singlet phase to the antiferromagnetically ordered Néel phase. This transition breaks O(N ) symmetry with N =3 in D =3 +1 dimensions. This is the upper critical dimension, where multiplicative logarithmic corrections to the leading mean-field critical properties are expected; we extract these corrections, establishing their precise forms for both the zero-temperature staggered magnetization ms and the Néel temperature TN. We present a scaling ansatz for TN, including logarithmic corrections, which agrees with our data and indicates exact linearity with ms, implying a complete decoupling of quantum and thermal fluctuation effects even arbitrarily close to the quantum critical point. We also demonstrate the predicted N -independent leading and subleading logarithmic corrections in the size dependence of the staggered magnetic susceptibility. These logarithmic scaling forms have not previously been identified or verified by unbiased numerical methods, and we discuss their relevance to experimental studies of dimerized quantum antiferromagnets such as TlCuCl3.

  7. Multiplicative logarithmic corrections to quantum criticality in three-dimensional dimerized antiferromagnets

    NASA Astrophysics Data System (ADS)

    Qin, Yanqi; Normand, Bruce; Sandvik, Anders; Meng, Zi Yang

    We investigate the quantum phase transition in an S=1/2 dimerized Heisenberg antiferromagnet in three spatial dimensions. By means of quantum Monte Carlo simulations and finite-size scaling analyses, we get high-precision results for the quantum critical properties at the transition from the magnetically disordered dimer-singlet phase to the ordered Neel phase. This transition breaks O(N) symmetry with N=3 in D=3+1 dimensions. This is the upper critical dimension, where multiplicative logarithmic corrections to the leading mean-field critical properties are expected; we extract these corrections, establishing their precise forms for both the zero-temperature staggered magnetization, ms, and the Neel temperature, TN. We present a scaling ansatz for TN, including logarithmic corrections, which agrees with our data and indicates exact linearity with ms, implying a complete decoupling of quantum and thermal fluctuation effects close to the quantum critical point. These logarithmic scaling forms have not previously identified or verified by unbiased numerical methods and we discuss their relevance to experimental studies of dimerized quantum antiferromagnets such as TlCuCl3. Ref.: arXiv:1506.06073

  8. High performance red-emitting multiple layer InGaN/GaN quantum dot lasers

    NASA Astrophysics Data System (ADS)

    Frost, Thomas; Hazari, Arnab; Aiello, Anthony; Zunaid Baten, Md; Yan, Lifan; Mirecki-Millunchick, Joanna; Bhattacharya, Pallab

    2016-03-01

    InGaN/GaN self-organized quantum dots can provide useful advantages over quantum wells for the realization of long-wavelength visible light sources because the dots are formed by strain relaxation. A III-nitride based laser emitting in the red (λ ˜ 630 nm), which has not been demonstrated with quantum wells, would be useful for a host of applications. We have investigated the epitaxy and characteristics of self-organized InGaN/GaN multiple layer quantum dots grown by plasma-assisted molecular beam epitaxy and have optimized their properties by tuning the growth parameters. Red-emitting (λ ˜ 630 nm) quantum dots have radiative lifetime ˜2.5 ns and internal quantum efficiency greater than 50%. Edge-emitting red-lasers with multi-dot layers in the active region exhibit an extremely low threshold current density of 1.6 kA/cm2, a high temperature coefficient T0 = 240 K, and a large differential gain dg/dn = 9 × 10-17 cm2.

  9. Quadrupole-Echo Techniques in Multiple-Quantum-Filtered NMR Spectroscopy of Heterogeneous Systems

    NASA Astrophysics Data System (ADS)

    Eliav, U.; Navon, G.

    Multiple-quantum-filtered quadrupole-echo pulse sequences for spin I = 1 and I = {3}/{2} are suggested. A general condition for obtaining simultaneously Zeeman and quadrupolar echo is formulated. A theoretical analysis of the various pulse sequences was performed on the basis of second-order perturbation approximation of the Liouville equation for the density matrix. The extent of refocusing as a function of the ratio of the residual quadrupolar interaction and the relaxation rates was calculated. Experimental results are presented for 2H and 23Na in cartilage as an example of a heterogeneous system with residual quadrupolar interaction. The difference between relaxation times measured by the multiple-quantum-filtered echo techniques and those measured by conventional multiple-quantum-filtered NMR spectroscopy is a simple diagnostic of anisotropic motion that leads to a residual quadrupolar interaction. The results of the echo experiments are compared with the relaxation times computed on the basis of lineshape analysis of double-quantum-filtered spectra of a heterogeneous system.

  10. Measuring correlations of cold-atom systems using multiple quantum probes

    NASA Astrophysics Data System (ADS)

    Streif, Michael; Buchleitner, Andreas; Jaksch, Dieter; Mur-Petit, Jordi

    2016-11-01

    We present a nondestructive method to probe a complex quantum system using multiple-impurity atoms as quantum probes. Our protocol provides access to different equilibrium properties of the system by changing its coupling to the probes. In particular, we show that measurements with two probes reveal the system's nonlocal two-point density correlations, for probe-system contact interactions. We illustrate our findings with analytic and numerical calculations for the Bose-Hubbard model in the weakly and strongly interacting regimes, under conditions relevant to ongoing experiments in cold-atom systems.

  11. Excitonic localization at macrostep edges in AlGaN/AlGaN multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Hou, Mengjun; Qin, Zhixin; Zhang, Lisheng; Han, Tianyang; Wang, Mingxing; Xu, Fujun; Wang, Xinqiang; Yu, Tongjun; Fang, Zheyu; Shen, Bo

    2017-04-01

    Double peaks at wavelength of 276 and 290 nm are observed for AlGaN/AlGaN multiple quantum wells (MQWs). Cathodoluminescence (CL) mappings identify that the emission at 290 nm originates from the macrostep edges. Potential minima induced by local variation of QW thickness and Ga incorporation are found along the step edges, where quantum wires (QWRs) are formed. The lateral advance rate of macrostep (∼310 nm/h) is obtained by investigating the distribution of QWRs. Temperature-dependent CL spectrum suggest that thermal quenching for 290 nm emission is dramatically suppressed compared with that for conventional QWs emission, which shows excitonic localization characteristics of QWRs.

  12. Pulsed field gradient multiple-quantum MAS NMR spectroscopy of half-integer spin quadrupolar nuclei

    NASA Astrophysics Data System (ADS)

    Fyfe, C. A.; Skibsted, J.; Grondey, H.; Meyer zu Altenschildesche, H.

    1997-12-01

    Pulsed field gradients (PFGs) have been applied to select coherence transfer pathways in multiple-quantum (MQ) MAS NMR spectra of half-integer spin quadrupolar nuclei in rigid solids. 27Al triple-quantum (3Q) MAS NMR spectra of the aluminophosphate molecular sieves VPI-5 and AlPO 4-18 have been used to demonstrate the selection of the (0)→(3)→(-1) coherence transfer pathway using PFGs and no phase cycling. Compared to MQMAS experiments that employ phase cycling schemes, the main advantage of the PFG-MQMAS technique is its simplicity, which should facilitate the combination of MQMAS with other pulse sequences.

  13. Possibility of multiple tunnelling current peaks in a coupled quantum well system

    NASA Astrophysics Data System (ADS)

    Luis, D.; Díaz, J. P.; Capuj, N. E.; Cruz, H.

    2000-07-01

    In this work, we have numerically integrated in space and time the effective-mass nonlinear Schrödinger equation for an electron wave packet in a bilayer electron system. Considering both Hartree and exchange-correlation potentials, we have calculated the tunnelling rates between the two quantum wells when an external bias is applied in the double quantum well system. Due to the nonlinear effective-mass equation, it is found that the charge dynamically trapped in both wells produces a reaction field which modifies the system resonant condition. At different electronic sheet densities, we have shown the possibility of having multiple resonant tunnelling peaks in a bilayer electron system.

  14. A practical multiple reflection technique for improving the quantum efficiency of photomultiplier tubes.

    PubMed

    Oke, J B; Schild, R E

    1968-04-01

    A technique is described by which multiple reflection techniques can be used to increase the quantum efficiency of some end-on photomultiplier tubes in the red and near ir. The method can be used in practice for astronomical and other applications where field lens imaging on the cathode is required and where small cathodes are desirable. Tests of a group of unselected production model S-20 and S-1 photomultiplier tubes show quantum efficiency gains as high as factors of 3.8 and 1.8, respectively, at practical operating wavelengths.

  15. Singlet fission in pentacene through multiple exciton quantum states

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiyong; Zimmerman, Paul; Musgrave, Charles

    2010-03-01

    Multi-exciton generation (MEG) has been reported for several materials and may dramatically increase solar cell efficiency. Singlet fission is the molecular analogue of MEG and has been observed in various systems, including tetracene and pentacene, however, no fundamental mechanism for singlet fission has yet been described, although it may govern MEG processes in a variety of materials. Because photoexcited states have single-exciton character, singlet fission to produce a pair of triplet excitons must involve an intermediate state that: (1) exhibits multi-exciton (ME) character, (2) is accessible from S1 and satisfies the fission energy requirement, and (3) efficiently dissociates into multiple electron-hole pairs. Here, we use sophisticated ab initio calculations to show that singlet fission in pentacene proceeds through a dark state (D) of ME character that lies just below S1, satisfies the fission energy requirement (ED>2ET0), and splits into two triplets (2xT0). In tetracene, D lies just above S1, consistent with the observation that singlet fission is thermally activated in tetracene. Rational design of photovoltaic systems that exploit singlet fission will require ab initio analysis of ME states such as D.

  16. Carrier multiplication detected through transient photocurrent in device-grade films of lead selenide quantum dots

    DOE PAGES

    Gao, Jianbo; Fidler, Andrew F.; Klimov, Victor I.

    2015-09-08

    In carrier multiplication, the absorption of a single photon results in two or more electron–hole pairs. Quantum dots are promising materials for implementing carrier multiplication principles in real-life technologies. So far, however, most of research in this area has focused on optical studies of solution samples with yet to be proven relevance to practical devices. We report ultra-fast electro-optical studies of device-grade films of electronically coupled quantum dots that allow us to observe multiplication directly in the photocurrent. Our studies help rationalize previous results from both optical spectroscopy and steady-state photocurrent measurements and also provide new insights into effects ofmore » electric field and ligand treatments on multiexciton yields. Importantly, we demonstrate that using appropriate chemical treatments of the films, extra charges produced by carrier multiplication can be extracted from the quantum dots before they are lost to Auger recombination and hence can contribute to photocurrent of practical devices.« less

  17. Multiple exciton generation for photoelectrochemical hydrogen evolution reactions with quantum yields exceeding 100%

    NASA Astrophysics Data System (ADS)

    Yan, Yong; Crisp, Ryan W.; Gu, Jing; Chernomordik, Boris D.; Pach, Gregory F.; Marshall, Ashley R.; Turner, John A.; Beard, Matthew C.

    2017-04-01

    Multiple exciton generation (MEG) in quantum dots (QDs) has the potential to greatly increase the power conversion efficiency in solar cells and in solar-fuel production. During the MEG process, two electron-hole pairs (excitons) are created from the absorption of one high-energy photon, bypassing hot-carrier cooling via phonon emission. Here we demonstrate that extra carriers produced via MEG can be used to drive a chemical reaction with quantum efficiency above 100%. We developed a lead sulfide (PbS) QD photoelectrochemical cell that is able to drive hydrogen evolution from aqueous Na2S solution with a peak external quantum efficiency exceeding 100%. QD photoelectrodes that were measured all demonstrated MEG when the incident photon energy was larger than 2.7 times the bandgap energy. Our results demonstrate a new direction in exploring high-efficiency approaches to solar fuels.

  18. Multiple exciton generation for photoelectrochemical hydrogen evolution reactions with quantum yields exceeding 100%

    DOE PAGES

    Yan, Yong; Crisp, Ryan W.; Gu, Jing; ...

    2017-04-03

    Multiple exciton generation (MEG) in quantum dots (QDs) has the potential to greatly increase the power conversion efficiency in solar cells and in solar-fuel production. During the MEG process, two electron-hole pairs (excitons) are created from the absorption of one high-energy photon, bypassing hot-carrier cooling via phonon emission. Here we demonstrate that extra carriers produced via MEG can be used to drive a chemical reaction with quantum efficiency above 100%. We developed a lead sulfide (PbS) QD photoelectrochemical cell that is able to drive hydrogen evolution from aqueous Na2S solution with a peak external quantum efficiency exceeding 100%. QD photoelectrodesmore » that were measured all demonstrated MEG when the incident photon energy was larger than 2.7 times the bandgap energy. Finally, our results demonstrate a new direction in exploring high-efficiency approaches to solar fuels.« less

  19. Code-division multiple-access multiuser demodulator by using quantum fluctuations

    NASA Astrophysics Data System (ADS)

    Otsubo, Yosuke; Inoue, Jun-ichi; Nagata, Kenji; Okada, Masato

    2014-07-01

    We examine the average-case performance of a code-division multiple-access (CDMA) multiuser demodulator in which quantum fluctuations are utilized to demodulate the original message within the context of Bayesian inference. The quantum fluctuations are built into the system as a transverse field in the infinite-range Ising spin glass model. We evaluate the performance measurements by using statistical mechanics. We confirm that the CDMA multiuser modulator using quantum fluctuations achieve roughly the same performance as the conventional CDMA multiuser modulator through thermal fluctuations on average. We also find that the relationship between the quality of the original information retrieval and the amplitude of the transverse field is somehow a "universal feature" in typical probabilistic information processing, viz., in image restoration, error-correcting codes, and CDMA multiuser demodulation.

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

    PubMed

    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.

  1. Parametric Investigation of Si1-xGex/Si Multiple Quantum Well Growth

    NASA Astrophysics Data System (ADS)

    Thompson, Phillip; Godbey, David; Hobart, Karl; Glaser, Evan; Kennedy, Thomas; Twigg, Mark; Simons, David

    1994-04-01

    Si0.8Ge0.2/Si multiple quantum wells (3 nm/30 nm) have been grown by molecular beam epitaxy and have been characterized using photoluminescence (PL), secondary ion mass spectrometry, and transmission electron microscopy. A parametric investigation relating the growth conditions to the PL was carried out. The existence of phonon-resolved band-edge PL appears to be strongly related to the background impurity concentration. The connection between phonon-resolved band-edge PL and higher substrate growth temperatures is probably due to the temperature-dependent incorporation of impurities. In the as-grown samples a correlation of the broad PL with platelet density in the quantum wells was observed. The broad PL may be associated with Cr at the platelets since a high temperature ( 710° C) anneal extinguished the broad PL and caused a reduction in the Cr found in the quantum wells, but had no effect on the platelet density.

  2. Code-division multiple-access multiuser demodulator by using quantum fluctuations.

    PubMed

    Otsubo, Yosuke; Inoue, Jun-Ichi; Nagata, Kenji; Okada, Masato

    2014-07-01

    We examine the average-case performance of a code-division multiple-access (CDMA) multiuser demodulator in which quantum fluctuations are utilized to demodulate the original message within the context of Bayesian inference. The quantum fluctuations are built into the system as a transverse field in the infinite-range Ising spin glass model. We evaluate the performance measurements by using statistical mechanics. We confirm that the CDMA multiuser modulator using quantum fluctuations achieve roughly the same performance as the conventional CDMA multiuser modulator through thermal fluctuations on average. We also find that the relationship between the quality of the original information retrieval and the amplitude of the transverse field is somehow a "universal feature" in typical probabilistic information processing, viz., in image restoration, error-correcting codes, and CDMA multiuser demodulation.

  3. Polyad quantum numbers and multiple resonances in anharmonic vibrational studies of polyatomic molecules.

    PubMed

    Krasnoshchekov, Sergey V; Stepanov, Nikolay F

    2013-11-14

    In the theory of anharmonic vibrations of a polyatomic molecule, mixing the zero-order vibrational states due to cubic, quartic and higher-order terms in the potential energy expansion leads to the appearance of more-or-less isolated blocks of states (also called polyads), connected through multiple resonances. Such polyads of states can be characterized by a common secondary integer quantum number. This polyad quantum number is defined as a linear combination of the zero-order vibrational quantum numbers, attributed to normal modes, multiplied by non-negative integer polyad coefficients, which are subject to definition for any particular molecule. According to Kellman's method [J. Chem. Phys. 93, 6630 (1990)], the corresponding formalism can be conveniently described using vector algebra. In the present work, a systematic consideration of polyad quantum numbers is given in the framework of the canonical Van Vleck perturbation theory (CVPT) and its numerical-analytic operator implementation for reducing the Hamiltonian to the quasi-diagonal form, earlier developed by the authors. It is shown that CVPT provides a convenient method for the systematic identification of essential resonances and the definition of a polyad quantum number. The method presented is generally suitable for molecules of significant size and complexity, as illustrated by several examples of molecules up to six atoms. The polyad quantum number technique is very useful for assembling comprehensive basis sets for the matrix representation of the Hamiltonian after removal of all non-resonance terms by CVPT. In addition, the classification of anharmonic energy levels according to their polyad quantum numbers provides an additional means for the interpretation of observed vibrational spectra.

  4. High-resolution absorptive intermolecular multiple-quantum coherence NMR spectroscopy under inhomogeneous fields

    NASA Astrophysics Data System (ADS)

    Lin, Meijin; Lin, Yanqin; Chen, Xi; Cai, Shuhui; Chen, Zhong

    2012-01-01

    Intermolecular multiple-quantum coherence (iMQC) is capable of improving NMR spectral resolution using a 2D shearing manipulation method. A pulse sequence termed CT-iDH, which combines intermolecular double-quantum filter (iDQF) with a modified constant-time (CT) scheme, is designed to achieve fast acquisition of high-resolution intermolecular zero-quantum coherences (iZQCs) and intermolecular double-quantum coherences (iDQCs) spectra without strong coupling artifacts. Furthermore, double-absorption lineshapes are first realized in 2D intermolecular multi-quantum coherences (iMQCs) spectra under inhomogeneous fields through a combination of iZQC and iDQC signals to double the resolution without loss of sensitivity. Theoretically the spectral linewidth can be further reduced by half compared to original iMQC high-resolution spectra. Several experiments were performed to test the feasibility of the new method and the improvements are evaluated quantitatively. The study suggests potential applications for in vivo spectroscopy.

  5. Reversed polarized emission in highly strained a -plane GaN/AlN multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Mata, R.; Cros, A.; Budagosky, J. A.; Molina-Sánchez, A.; Garro, N.; García-Cristóbal, A.; Renard, J.; Founta, S.; Gayral, B.; Bellet-Amalric, E.; Bougerol, C.; Daudin, B.

    2010-09-01

    The polarization of the emission from a set of highly strained a -plane GaN/AlN multiple quantum wells of varying well widths has been studied. A single photoluminescence peak is observed that shifts to higher energies as the quantum well thickness decreases due to quantum confinement. The emitted light is linearly polarized. For the thinnest samples the preferential polarization direction is perpendicular to the wurtzite c axis with a degree of polarization that decreases with increasing well width. However, for the thickest well the preferred polarization direction is parallel to the c axis. Raman scattering, x-ray diffraction, and transmission electron microscopy studies have been performed to determine the three components of the strain tensor in the active region. Moreover, the experimental results have been compared with the strain values computed by means of a model based on the elastic continuum theory. A high anisotropic compressive in-plane strain has been found, namely, -0.6% and -2.8% along the in-plane directions [11¯00] and [0001], respectively, for the thickest quantum well. The oscillator strength of the lowest optical transition has been calculated within the framework of a multiband envelope function model for various quantum well widths and strain values. The influence of confinement and strain on the degree of polarization is discussed and compared with experiment considering various sets of material parameters.

  6. Towards an understanding of hot carrier cooling mechanisms in multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Conibeer, Gavin; Zhang, Yi; Bremner, Stephen P.; Shrestha, Santosh

    2017-09-01

    Multiple quantum wells have been shown significantly reduced hot carrier cooling rates compared to bulk material and are thus a promising candidate for hot carrier solar cell absorbers. However, the mechanism(s) by which hot carrier cooling is restricted is not clear. A systematic study of carrier cooling rates in GaAs/AlAs multiple quantum wells (MQWs) with either varying barrier thickness or varying well thickness is presented in this paper. These allow an investigation as to whether the mechanisms of either a modification in hot carrier diffusion or a localisation of phonons emitted by hot carriers are primarily responsible for reduced carrier cooling rates. With the conclusion that for the structures investigated the situation is rather more complex with both carrier mobility to modify hot carrier diffusion, different diffusion rates for electrons and holes and reflection and localisation of phonons to enhance phonon bottleneck all playing their parts in modulating phonon reabsorption and hot carrier behaviour.

  7. Entropic Uncertainty Relation and Information Exclusion Relation for multiple measurements in the presence of quantum memory.

    PubMed

    Zhang, Jun; Zhang, Yang; Yu, Chang-shui

    2015-06-29

    The Heisenberg uncertainty principle shows that no one can specify the values of the non-commuting canonically conjugated variables simultaneously. However, the uncertainty relation is usually applied to two incompatible measurements. We present tighter bounds on both entropic uncertainty relation and information exclusion relation for multiple measurements in the presence of quantum memory. As applications, three incompatible measurements on Werner state and Horodecki's bound entangled state are investigated in details.

  8. Multiple-quantum NMR studies of spin clusters in liquid crystals and zeolites

    SciTech Connect

    Pearson, J. . Dept. of Chemistry Lawrence Berkeley Lab., CA )

    1991-07-01

    This work will describe the use of MQ NMR to study spin clusters in anisotropic materials. A technique known as multiple-quantum spin counting was used to determine average spin cluster sizes liquid crystalline materials and in faujacitic zeolites containing aromatic hydrocarbons. The first half of the thesis will describe MQ NMR and the MQ spin counting technique, and the second half of the thesis will describe the actual experiments and their results.

  9. Entropic Uncertainty Relation and Information Exclusion Relation for multiple measurements in the presence of quantum memory

    NASA Astrophysics Data System (ADS)

    Zhang, Jun; Zhang, Yang; Yu, Chang-Shui

    2015-06-01

    The Heisenberg uncertainty principle shows that no one can specify the values of the non-commuting canonically conjugated variables simultaneously. However, the uncertainty relation is usually applied to two incompatible measurements. We present tighter bounds on both entropic uncertainty relation and information exclusion relation for multiple measurements in the presence of quantum memory. As applications, three incompatible measurements on Werner state and Horodecki’s bound entangled state are investigated in details.

  10. Resonant enhancement of the photocurrent in multiple-quantum-well photovoltaic devices

    SciTech Connect

    Raisky, O.Y.; Wang, W.B.; Alfano, R.R.; Reynolds, C.L. Jr.; Stampone, D.V.; Focht, M.W.

    1999-01-01

    Sequential resonant tunneling is proposed to enhance the photocurrent and reduce recombination losses in photovoltaic devices based on multiple-quantum-well (MQW) heterostructures. An InGaAsP/InP MQW {ital p{endash}i{endash}n} diode with built-in sequential resonant tunneling has been fabricated, and demonstrates an increase in the photocurrent and reduction in photoluminescence intensity. These effects are attributed to the resonance tunneling effect. {copyright} {ital 1999 American Institute of Physics.}

  11. Transmission coefficients for chemical reactions with multiple states: role of quantum decoherence.

    PubMed

    de la Lande, Aurélien; Řezáč, Jan; Lévy, Bernard; Sanders, Barry C; Salahub, Dennis R

    2011-03-23

    Transition-state theory (TST) is a widely accepted paradigm for rationalizing the kinetics of chemical reactions involving one potential energy surface (PES). Multiple PES reaction rate constants can also be estimated within semiclassical approaches provided the hopping probability between the quantum states is taken into account when determining the transmission coefficient. In the Marcus theory of electron transfer, this hopping probability was historically calculated with models such as Landau-Zener theory. Although the hopping probability is intimately related to the question of the transition from the fully quantum to the semiclassical description, this issue is not adequately handled in physicochemical models commonly in use. In particular, quantum nuclear effects such as decoherence or dephasing are not present in the rate constant expressions. Retaining the convenient semiclassical picture, we include these effects through the introduction of a phenomenological quantum decoherence function. A simple modification to the usual TST rate constant expression is proposed: in addition to the electronic coupling, a characteristic decoherence time τ(dec) now also appears as a key parameter of the rate constant. This new parameter captures the idea that molecular systems, although intrinsically obeying quantum mechanical laws, behave semiclassically after a finite but nonzero amount of time (τ(dec)). This new degree of freedom allows a fresh look at the underlying physics of chemical reactions involving more than one quantum state. The ability of the proposed formula to describe the main physical lines of the phenomenon is confirmed by comparison with results obtained from density functional theory molecular dynamics simulations for a triplet to singlet transition within a copper dioxygen adduct relevant to the question of dioxygen activation by copper monooxygenases.

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

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

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

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

    NASA Astrophysics Data System (ADS)

    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.

  14. Internal quantum efficiency improvement of InGaN/GaN multiple quantum well green light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Zhou, Q.; Xu, M.; Wang, H.

    2016-01-01

    In recent years, GaN-based light-emitting diode (LED) has been widely used in various applications, such as RGB lighting system, full-colour display and visible-light communication. However, the internal quantum efficiency (IQE) of green LEDs is significantly lower than that of other visible spectrum LED. This phenomenon is called "green gap". This paper briefly describes the physical mechanism of the low IQE for InGaN/GaN multiple quantum well (MQW) green LED at first. The IQE of green LED is limited by the defects and the internal electric field in MQW. Subsequently, we discuss the recent progress in improving the IQE of green LED in detail. These strategies can be divided into two categories. Some of these methods were proposed to enhance crystal quality of InGaN/GaN MQW with high In composition and low density of defects by modifying the growth conditions. Other methods focused on increasing electron-hole wave function overlap by eliminating the polarization effect.

  15. Third generation photovoltaics based on multiple exciton generation in quantum confined semiconductors.

    PubMed

    Beard, Matthew C; Luther, Joseph M; Semonin, Octavi E; Nozik, Arthur J

    2013-06-18

    Improving the primary photoconversion process in a photovoltaiccell by utilizing the excess energy that is otherwise lost as heat can lead to an increase in the overall power conversion efficiency (PCE). Semiconductor nanocrystals (NCs) with at least one dimension small enough to produce quantum confinement effects provide new ways of controlling energy flow not achievable in thin film or bulk semiconductors. Researchers have developed various strategies to incorporate these novel structures into suitable solar conversion systems. Some of these methods could increase the PCE past the Shockley-Queisser (SQ) limit of ∼33%, making them viable "third generation photovoltaic" (TGPV) cell architectures. Surpassing the SQ limit for single junction solar cells presents both a scientific and a technological challenge, and the use of semiconductor NCs to enhance the primary photoconversion process offers a promising potential solution. The NCs are synthesized via solution phase chemical reactions producing stable colloidal solutions, where the reaction conditions can be modified to produce a variety of shapes, compositions, and structures. The confinement of the semiconductor NC in one dimension produces quantum films, wells, or discs. Two-dimensional confinement leads to quantum wires or rods (QRs), and quantum dots (QDs) are three-dimensionally confined NCs. The process of multiple exciton generation (MEG) converts a high-energy photon into multiple electron-hole pairs. Although many studies have demonstrated that MEG is enhanced in QDs compared with bulk semiconductors, these studies have either used ultrafast spectroscopy to measure the photon-to-exciton quantum yields (QYs) or theoretical calculations. Implementing MEG in a working solar cell has been an ongoing challenge. In this Account, we discuss the status of MEG research and strategies towards implementing MEG in working solar cells. Recently we showed an external quantum efficiency for photocurrent of greater

  16. Ultrafast Optical Studies of Multiple Exciton Generation in Lead Chalcogenide Quantum Dots

    NASA Astrophysics Data System (ADS)

    Midgett, Aaron G.

    2011-12-01

    Providing affordable, clean energy is one of the major challenges facing society today, and one of the promising solutions is third generation solar energy conversion. Present day, first and second-generation solar cells can at most convert each absorbed photon into a single electron hole pair, thereby establishing a theoretical limit to the power conversion efficiency. The process of multiple exciton generation (MEG) in semiconductor quantum dots increases that theoretical efficiency from 33% to 42% by utilizing the excess energy of high energy photons that is otherwise wasted as heat to excite a second electron-hole pair, thereby boosting the potential photocurrent. This thesis explores the benefits of MEG in quantum confined systems and shows that quantum dots are more efficient at generating multiple excitons from a single photon than bulk semiconductors. The variations in optical measurements of MEG have raised skepticism and brought into question the validity of these experiments. The two important questions that this thesis attempts to address are (1) what are the enhanced QYs in isolated PbSe QDs and (2) does quantum confinement enhance MEG over bulk semiconductors. Experimental variations in the enhanced QYs are partially explained by the production of a long-lived photocharged state that increases the apparent photon-to-exciton QYs. A procedure is detailed that decreases the possibility of producing this charged state. By studying the production of these states, conditions are found that minimize their effect and produce less variation in the reported QYs. Variations in the MEG efficiency were studied in films of chemically treated PbSe quantum dots where a different mechanism was responsible for an apparent decrease of the measured QYs. Finally, for the first time, a quantum dot size-dependence in the MEG efficiency was found in colloidal PbSe, PbS, and PbSxSe1-x quantum dot solutions and is attributed to the increased Coulomb interaction in materials

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

    PubMed

    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.

  18. Analyses and improvement of a broadcasting multiple blind signature scheme based on quantum GHZ entanglement

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Qiu, Daowen; Zou, Xiangfu; Mateus, Paulo

    2017-06-01

    A broadcasting multiple blind signature scheme based on quantum GHZ entanglement has been presented recently. It is said that the scheme's unconditional security is guaranteed by adopting quantum key preparation, quantum encryption algorithm and quantum entanglement. In this paper, we prove that each signatory can get the signed message just by an intercept-resend attack. Then, we show there still exist some participant attacks and external attacks. Specifically, we verify the message sender Alice can impersonate each signatory to sign the message at will, and so is the signature collector Charlie. Also, we demonstrate that the receiver Bob can forge the signature successfully, and with respect to the external attacks, the eavesdropper Eve can modify the signature at random. Besides, we discover Eve can change the signed message at random, and Eve can impersonate Alice as the message sender without being discovered. In particular, we propose an improved scheme based on the original one and show that it is secure against not only the attacks mentioned above but also some collusion attacks.

  19. Characterization of Pairwise Correlations from Multiple Quantum Correlated Beams Generated from Cascaded Four-Wave Mixing Processes

    PubMed Central

    Wang, Hailong; Cao, Leiming; Jing, Jietai

    2017-01-01

    We theoretically characterize the performance of the pairwise correlations (PCs) from multiple quantum correlated beams based on the cascaded four-wave mixing (FWM) processes. The presence of the PCs with quantum corre- lation in these systems can be verified by calculating the degree of intensity difference squeezing for any pair of all the output fields. The quantum correlation characteristics of all the PCs under different cascaded schemes are also discussed in detail and the repulsion effect between PCs in these cascaded FWM processes is theoretically predicted. Our results open the way for the classification and application of quantum states generated from the cascaded FWM processes. PMID:28071759

  20. Influence of metalorganic precursors flow interruption timing on green InGaN multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Dmukauskas, M.; Kadys, A.; Malinauskas, T.; Grinys, T.; Reklaitis, I.; Badokas, K.; Skapas, M.; Tomašiūnas, R.; Dobrovolskas, D.; Stanionytė, S.; Pietzonka, I.; Strassburg, M.; Lugauer, H.-J.

    2016-12-01

    The paper reports on fully strained green light emitting InGaN/GaN multiple quantum wells, grown by metalorganic vapor phase epitaxy, using metal precursor multiple flow interruptions during InGaN quantum well growth. Optimization of the interruption timing (pulse t 1  =  20 s, pause t 2  =  12 s) lets us reach the integrated photoluminescence enhancement for the growth at temperature 780 ºC. The enhancement, as a function of pause duration, appeared to be pulse duration dependent: a lower enhancement can be achieved using shorter pulses with optimized relatively shorter pauses. Indium evaporation during the interruption time was interpreted as the main issue to keep the layers intact. Quantum wells revealing the highest photoluminescence enhancement were inspected for interface quality, layer thickness, growth speed, strain, surface morphology and roughness by TEM, XRD and AFM techniques, and compared with the one grown in the conventional mode.

  1. Enhancement of spectral editing efficacy of multiple quantum filters in in vivo proton magnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Kim, Hyeonjin; Thompson, Richard B.; Allen, Peter S.

    2012-10-01

    The performance of multiple quantum filters (MQFs) can be disappointing when the background signal also arises from coupled spins. Moreover, at 3.0 T and even higher fields the majority of the spin systems of key brain metabolites fall into the strong-coupling regime. In this manuscript we address comprehensively, the importance of the phase of the multiple quantum coherence-generating pulse (MQ-pulse) in the design of MQFs, using both product operator and numerical analysis, in both zero and double quantum filter designs. The theoretical analyses were experimentally validated with the examples of myo-inositol editing and the separation of glutamate from glutamine. The results demonstrate that the phase of the MQ-pulse per se provides an additional spectral discrimination mechanism based on the degree of coupling beyond the conventional level-of-coherence approach of MQFs. To obtain the best spectral discrimination of strongly-coupled spin systems, therefore, the phase of the MQ-pulse must be included in the portfolio of the sequence parameters to be optimized.

  2. Enhancement of spectral editing efficacy of multiple quantum filters in in vivo proton magnetic resonance spectroscopy.

    PubMed

    Kim, Hyeonjin; Thompson, Richard B; Allen, Peter S

    2012-10-01

    The performance of multiple quantum filters (MQFs) can be disappointing when the background signal also arises from coupled spins. Moreover, at 3.0 T and even higher fields the majority of the spin systems of key brain metabolites fall into the strong-coupling regime. In this manuscript we address comprehensively, the importance of the phase of the multiple quantum coherence-generating pulse (MQ-pulse) in the design of MQFs, using both product operator and numerical analysis, in both zero and double quantum filter designs. The theoretical analyses were experimentally validated with the examples of myo-inositol editing and the separation of glutamate from glutamine. The results demonstrate that the phase of the MQ-pulse per se provides an additional spectral discrimination mechanism based on the degree of coupling beyond the conventional level-of-coherence approach of MQFs. To obtain the best spectral discrimination of strongly-coupled spin systems, therefore, the phase of the MQ-pulse must be included in the portfolio of the sequence parameters to be optimized.

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Determination Of The Third Order Nonlinearity As A Function Of Quantum Well Width In Gaas/A1Gaas Multiple Quantum Wells

    NASA Astrophysics Data System (ADS)

    Derstine, M. W.; Grider, D. E.; Lehman, J. A.; Ruden, P. P.; Peyghambarian, Nasser

    1988-05-01

    We present a study of the dependence of the magnitude of optical nonlinearities of GaAs/AlGaAs multiple quantum wells on quantum well thickness. Using four-wave mixing and nonlinear absorption measurements the refractive nonlinearity was determined in 17 samples grown by MOCVD and MBE. We find a small variation (less tban a factor of three) in the change in refractive index per photoexcited carrier for well sizes between 50 A and 300 A. or bulk GaAs.

  5. Single-shot single-voxel lactate measurements using FOCI-LASER and a multiple-quantum filter.

    PubMed

    Payne, Geoffrey S; deSouza, Nandita M; Messiou, Christina; Leach, Martin O

    2015-04-01

    Measurement of tissue lactate using (1) H MRS is often confounded by overlap with intense lipid signals at 1.3 ppm. Single-voxel localization using PRESS is also compromised by the large chemical shift displacement between voxels for the 4.1 ppm (-CH) resonance and the 1.3 ppm -CH3 resonance, leading to subvoxels with signals of opposite phase and hence partial signal cancellation. To reduce the chemical shift displacement to negligible proportions, a modified semi-LASER sequence was written ("FOCI-LASER", abbreviated as fLASER) using FOCI pulses to permit high RF bandwidth even with the limited RF amplitude characteristic of clinical MRI scanners. A further modification, MQF-fLASER, includes a selective multiple-quantum filter to detect lactate and reject lipid signals. The sequences were implemented on a Philips 3 T Achieva TX system. In a solution of brain metabolites fLASER lactate signals were 2.7 times those of PRESS. MQF-fLASER lactate was 47% of fLASER (the theoretical maximum is 50%) but still larger than PRESS lactate. In oil, the main 1.3 ppm lipid peak was suppressed to less than 1%. Enhanced suppression was possible using increased gradient durations. The minimum detectable lactate concentration was approximately 0.5 mM. Coherence selection gradients needed to be at the magic angle to avoid large water signals derived from intermolecular multiple-quantum coherences. In pilot patient measurements, lactate peaks were often observed in brain tumours, but not in cervix tumours; lipids were effectively suppressed. In summary, compared with PRESS, the fLASER sequence yields greatly superior sensitivity for direct detection of lactate (and equivalent sensitivity for other metabolites), while the single-voxel single-shot MQF-fLASER sequence surpasses PRESS for lactate detection while eliminating substantial signals from lipids. This sequence will increase the potential for in vivo lactate measurement as a biomarker in targeted anti-cancer treatments as well as

  6. The use of a selective saturation pulse to suppress t1 noise in two-dimensional 1H fast magic angle spinning solid-state NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Robertson, Aiden J.; Pandey, Manoj Kumar; Marsh, Andrew; Nishiyama, Yusuke; Brown, Steven P.

    2015-11-01

    A selective saturation pulse at fast magic angle spinning (MAS) frequencies (60+ kHz) suppresses t1 noise in the indirect dimension of two-dimensional 1H MAS NMR spectra. The method is applied to a synthetic nucleoside with an intense methyl 1H signal due to triisopropylsilyl (TIPS) protecting groups. Enhanced performance in terms of suppressing the methyl signal while minimising the loss of signal intensity of nearby resonances of interest relies on reducing spin diffusion - this is quantified by comparing two-dimensional 1H NOESY-like spin diffusion spectra recorded at 30-70 kHz MAS. For a saturation pulse centred at the methyl resonance, the effect of changing the nutation frequency at different MAS frequencies as well as the effect of changing the pulse duration is investigated. By applying a pulse of duration 30 ms and nutation frequency 725 Hz at 70 kHz MAS, a good compromise of significant suppression of the methyl resonance combined with the signal intensity of resonances greater than 5 ppm away from the methyl resonance being largely unaffected is achieved. The effectiveness of using a selective saturation pulse is demonstrated for both homonuclear 1H-1H double quantum (DQ)/single quantum (SQ) MAS and 14N-1H heteronuclear multiple quantum coherence (HMQC) two-dimensional solid-state NMR experiments.

  7. The use of a selective saturation pulse to suppress t1 noise in two-dimensional (1)H fast magic angle spinning solid-state NMR spectroscopy.

    PubMed

    Robertson, Aiden J; Pandey, Manoj Kumar; Marsh, Andrew; Nishiyama, Yusuke; Brown, Steven P

    2015-11-01

    A selective saturation pulse at fast magic angle spinning (MAS) frequencies (60+kHz) suppresses t1 noise in the indirect dimension of two-dimensional (1)H MAS NMR spectra. The method is applied to a synthetic nucleoside with an intense methyl (1)H signal due to triisopropylsilyl (TIPS) protecting groups. Enhanced performance in terms of suppressing the methyl signal while minimising the loss of signal intensity of nearby resonances of interest relies on reducing spin diffusion--this is quantified by comparing two-dimensional (1)H NOESY-like spin diffusion spectra recorded at 30-70 kHz MAS. For a saturation pulse centred at the methyl resonance, the effect of changing the nutation frequency at different MAS frequencies as well as the effect of changing the pulse duration is investigated. By applying a pulse of duration 30 ms and nutation frequency 725 Hz at 70 kHz MAS, a good compromise of significant suppression of the methyl resonance combined with the signal intensity of resonances greater than 5 ppm away from the methyl resonance being largely unaffected is achieved. The effectiveness of using a selective saturation pulse is demonstrated for both homonuclear (1)H-(1)H double quantum (DQ)/single quantum (SQ) MAS and (14)N-(1)H heteronuclear multiple quantum coherence (HMQC) two-dimensional solid-state NMR experiments.

  8. Optimization of carrier multiplication for more effcient solar cells: the case of Sn quantum dots.

    PubMed

    Allan, Guy; Delerue, Christophe

    2011-09-27

    We present calculations of impact ionization rates, carrier multiplication yields, and solar-power conversion efficiencies in solar cells based on quantum dots (QDs) of a semimetal, α-Sn. Using these results and previous ones on PbSe and PbS QDs, we discuss a strategy to select QDs with the highest carrier multiplication rate for more efficient solar cells. We suggest using QDs of materials with a close to zero band gap and a high multiplicity of the bands in order to favor the relaxation of photoexcited carriers by impact ionization. Even in that case, the improvement of the maximum solar-power conversion efficiency appears to be a challenging task.

  9. Electroluminescence property improvement by adjusting quantum wells' position relative to p-doped region in InGaN/GaN multiple-quantum-well light emitting diodes

    NASA Astrophysics Data System (ADS)

    Chen, P.; Zhao, D. G.; Jiang, D. S.; Long, H.; Li, M.; Yang, J.; Zhu, J. J.; Liu, Z. S.; Li, X. J.; Liu, W.; Li, X.; Liang, F.; Liu, J. P.; Zhang, B. S.; Yang, H.

    2017-03-01

    The hole distribution and electroluminescence property improvement by adjusting the relative position between quantum wells and p-doped region in InGaN/GaN multiple-quantum-well structures are experimentally and theoretically investigated. Five designed samples with different barrier layer parameters of multiple-quantum-well structure are grown by MOCVD and then fabricated into devices. The electroluminescence properties of these samples are measured and compared. It is found that the output electroluminescence intensity of samples is enhanced if the position of quantum wells shifts towards p-side, while the output power is reduced if their position is shifted towards the n-side. The theoretical calculation of characteristics of these devices using the simulation program APSYS agrees well with the experimental data, illustrating that the effect of relative position between p-doped region and quantum wells on the improvement of hole distribution and electroluminescence performance is significant, especially for InGaN/GaN multiple-quantum-well devices operated under high injection condition.

  10. Multiple exciton generation in films of electronically coupled PbSe quantum dots.

    PubMed

    Luther, Joseph M; Beard, Matthew C; Song, Qing; Law, Matt; Ellingson, Randy J; Nozik, Arthur J

    2007-06-01

    We study multiple exciton generation (MEG) in electronically coupled films of PbSe quantum dots (QDs) employing ultrafast time-resolved transient absorption spectroscopy. We demonstrate that the MEG efficiency in PbSe does not decrease when the QDs are treated with hydrazine, which has been shown to greatly enhance carrier transport in PbSe QD films by decreasing the interdot distance. The quantum yield is measured and compared to previously reported values for electronically isolated QDs suspended in organic solvents at approximately 4 and 4.5 times the effective band gap. A slightly modified analysis is applied to extract the MEG efficiency and the absorption cross section of each sample at the pump wavelength. We compare the absorption cross sections of our samples to that of bulk PbSe. We find that both the biexciton lifetime and the absorption cross section increase in films relative to isolated QDs in solution.

  11. Demonstration of InGaN-based orange LEDs with hybrid multiple-quantum-wells structure

    NASA Astrophysics Data System (ADS)

    Iida, Daisuke; Niwa, Kazumasa; Kamiyama, Satoshi; Ohkawa, Kazuhiro

    2016-11-01

    We demonstrate the effectiveness of a hybrid multiple-quantum-wells (MQWs) structure in InGaN-based orange light-emitting diodes (LEDs) grown by metalorganic vapor phase epitaxy. The hybrid MQWs-LED is composed of orange InGaN double QWs and a blue-green InGaN single QW. Using the hybrid MQWs structure, the orange LEDs exhibited electroluminescence spectra with narrow full widths at half maximum of 51 nm at 20 mA. The light output power and external quantum efficiency of the InGaN-based orange LEDs were 0.23 mW and 0.6%, respectively, at 20 mA.

  12. Engineering Efficiency Droop in InGaN/GaN Multiple Quantum Well LEDs

    NASA Astrophysics Data System (ADS)

    Puttaswamy, Yashvanth; Sundaresan, Sasi; Yalavarthi, Krishna; Ahmed, Shaikh

    2012-02-01

    In this work, we address the technologically important issue of efficiency droop pronounced in InGaN/GaN multiple quantum well (QW) LEDs. A two-fold modeling approach is employed where: 1) the NEMO 3-D tool is used to compute the atomistic strain fields and associated polarization potentials in the active region, and 2) the outputs from NEMO 3-D are then coupled to the Synopsys TCAD tool to determine the terminal electrical and optical properties of the device. Next, a series of numerical experiments are performed that mainly aims to improve the efficiency droop without compromising the internal quantum efficiency (IQE) of the device. These include:1) varying the QW thickness, 2) employing different configurations of tri-material barriers, 3) varying the molar concentration of the barrier materials, and 4) varying the doping density in the barrier region.

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

    NASA Astrophysics Data System (ADS)

    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.

  14. Nonequilibrium high-frequency noise and responsivity in multiple quantum well infrared photodetectors

    SciTech Connect

    Ershov, M.

    2001-06-01

    A theory of the nonequilibrium high-frequency noise and responsivity in multiple quantum well infrared photodetectors (QWIPs) is presented. The nonequilibrium regime dominates at frequencies higher than the inverse characteristic response time of the injecting contact. The nonequilibrium generation{endash}recombination (GR) noise and responsivity are determined by the fast component of the transient current (primary current) in response to impulse excitation. The nonequilibrium GR noise power and responsivity are lower than their low-frequency values due to the cutoff of the injection from the emitter at high frequencies. Analytical formulas for the noise and responsivity are obtained. These expressions are consistent with the conventional formulas of the standard model of unipolar photoconductors if the transit time across the QWIP is longer than the capture time by the quantum wells. {copyright} 2001 American Institute of Physics.

  15. Birefringence in the transparency region of GaAs/AlAs multiple quantum wells

    SciTech Connect

    Sirenko, A.A.; Etchegoin, P.; Fainstein, A.; Eberl, K.; Cardona, M.

    1999-09-01

    Birefringence measurements for in-plane propagation of light below the absorption edge in GaAs/AlAs multiple quantum wells (MQW{close_quote}s) are reported for different well/barrier widths. A remarkable drop in the low-frequency limit of the birefringence has been observed for MQW structures with small periods and ascribed to the presence of local fields. The temperature dependence of the birefringence is also studied and complementary results in InP quantum dot structures are also presented. The latter exhibit a strong resonant birefringence, which can be explained by the reduced dimensionality in the joint density of states for optical transitions in the dots. {copyright} {ital 1999} {ital The American Physical Society}

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

    PubMed

    Nataf, Pierre; Ciuti, Cristiano

    2011-11-04

    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 a 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 many-level 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.

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

    PubMed

    Farrow, Tristan; Vedral, Vlatko

    2014-07-01

    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.

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

    PubMed Central

    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

  19. Systematic evaluation of a new organic material: 1-methyl-1H-imidazol-3-ium-2,4,6-trinitrobenzene-1,3-bis(olate) for optoelectronics through spectral, structural, electrical, optical, quantum chemical and Hirshfeld surface studies

    NASA Astrophysics Data System (ADS)

    Dhamodharan, P.; Sathya, K.; Dhandapani, M.

    2017-05-01

    A new organic material, 1-methyl-1H-imidazol-3-ium-2,4,6-trinitrobenzene-1,3-bis(olate) (MITB), was synthesized and crystallized by solution growth-slow evaporation technique at ambient temperature. The characteristic functional groups in MITB were identified from FT-IR spectrum. 1H, 13C and DEPT-135 NMR spectroscopic techniques were used to ascertain types of carbons and protons in MITB. The compound crystallizes in the monoclinic system with a space group of P21/c. The electrostatic attraction between anions and cations stabilizes the crystal lattice and the N-H…O and C-H…O hydrogen bonds linking the cations and anions supplement the stable three dimensional networks. The material was thermally stable up to 178 °C. The molecular structure was optimized by Gaussian 09 program at B3LYP/6-311++G(d,p) level of basis set. Hydrogen bonding interactions are responsible for greater hyperpolarizability value of MITB and the value was found to be 34 times greater than that of reference material, urea. HOMO-LUMO, electrostatic potential surface and Mulliken atomic charges were calculated to explore covalent and non covalent interactions present in MITB. Hirshfeld surface analysis was carried out to estimate prominent covalent and non covalent interactions. Dielectric constant and dielectric loss have been determined to find MITB's suitability for optoelectronic applications.

  20. Synthesis, crystal structure, spectroscopic and quantum chemical studies of novel 3-((2-chlorophenyl)(piperidin-1-yl)methyl)-4-hydroxy-1-phenylquinolin-2(1H)-one

    NASA Astrophysics Data System (ADS)

    Fatma, Shaheen; Bishnoi, Abha; Verma, Anil Kumar; Singh, Ramesh; Srivastava, Amrita

    2017-07-01

    A novel 3-((2-chlorophenyl)(piperidin-1-yl)methyl)-4-hydroxy-1-phenylquinolin-2(1H)-one was synthesized using Michael addition of secondary amine to the α, β-unsaturated carbonyl compound which was formed during the reaction. The crystal structure was studied by X-ray crystallography. Molecular geometry, first order hyperpolarizability, molecular electrostatic potential and vibrational analysis was carried out by using density functional theory (DFT/B3LYP) method with 6-31G (d,p) as basis set. Calculated 13C NMR and 1H NMR chemical shift values and vibrational wavenumbers showed good agreement with the experimental data. X-ray study confirmed that each molecule interacts with other molecule through Csbnd H⋯O, Csbnd C⋯Cl and Csbnd H ….C interactions. Conformational analysis of the molecule was studied by DFT/6-31G (d, p) method. Increment in wavenumber has been confirmed by AIM calculation. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital analysis. Local reactivity descriptors were calculated to explain the chemically reactive site in the molecule. Electronic absorption spectrum has been predicted and found agreement with the experimental one. Intramolecular interactions were analyzed by AIM approach. In addition, thermodynamic properties were investigated using theoretical calculations.

  1. Terahertz study of ultrafast carrier dynamics in InGaN/GaN multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Porte, H. P.; Turchinovich, D.; Cooke, D. G.; Jepsen, P. Uhd

    2009-11-01

    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 the carrier density. Time-integrated photoluminescence spectra have shown a complete screening of the built-in piezoelectric field at high excitation fluences. We also observe that the terahertz conductivity spectra differs from simple Drude conductivity, describing the response of free carriers, and are well fitted by the Drude-Smith model.

  2. Phosphor-free white light-emitting diode with laterally distributed multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Park, Il-Kyu; Kim, Ja-Yeon; Kwon, Min-Ki; Cho, Chu-Young; Lim, Jae-Hong; Park, Seong-Ju

    2008-03-01

    A phosphor-free white light-emitting diode (LED) was fabricated with laterally distributed blue and green InGaN /GaN multiple quantum wells (MQWs) grown by a selective area growth method. Photoluminescence and electroluminescence (EL) spectra of the LED showed emission peaks corresponding to the individual blue and green MQWs. The integrated EL intensity ratio of green to blue emission varied from 2.5 to 6.5 with the injection current below 300mA, but remained constant at high injection currents above 300mA. The stability of the emission color at high currents is attributed to parallel carrier injection into both MQWs.

  3. Sensitivity Enhancement in Static Solid-State NMR Experiments VIA Single and Multiple Quantum Dipolar Coherences

    PubMed Central

    Gopinath, T.; Veglia, Gianluigi

    2012-01-01

    We present a new method to enhance the sensitivity in static solid-state NMR for a gain in signal-to-noise ratio up to 40%. This sensitivity enhancement is different from the corresponding solution NMR sensitivity enhancement schemes and is achieved by combining single and multiple quantum dipolar coherences. While this new approach is demonstrated for the PISEMA (polarization inversion spin exchange at magic angle) experiment, it can be generalized to the other separated local field experiments for solid-state NMR spectroscopy. This method will have a direct impact on solid-state NMR spectroscopy of liquid crystals as well as membrane proteins aligned in lipid membranes. PMID:19351170

  4. Sensitivity Enhancement in Multiple-Quantum NMR Experiments with CPMG Detection

    NASA Astrophysics Data System (ADS)

    Lim, Kwang Hun; Nguyen, Tuan; Mazur, Tanya; Wemmer, David E.; Pines, Alexander

    2002-07-01

    We present a modified multiple-quantum (MQ) experiment, which implements the Carr-Purcell-Meiboom-Gill (CPMG) detection scheme in the static MQ NMR experiment proposed by W. S. Warren et al. (1980, J. Chem. Phys.73, 2084-2099) and exploited further by O. N. Antzutkin and R. Tycko (1999, J. Chem. Phys.110, 2749-2752). It is demonstrated that a significant enhancement in the sensitivity can be achieved by acquiring echo trains in the MQ experiments for static powder samples. The modified scheme employing the CPMG detection was superior to the original MQ experiment, in particular for the carbonyl carbon with a very large chemical shift anisotropy.

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

    SciTech Connect

    Prasankumar, Rohit P; Taylor, Antoinette J; Chow, W W; Attaluri, R S; Shenoi, R

    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.

  6. Degenerate ground states and multiple bifurcations in a two-dimensional q-state quantum Potts model.

    PubMed

    Dai, Yan-Wei; Cho, Sam Young; Batchelor, Murray T; Zhou, Huan-Qiang

    2014-06-01

    We numerically investigate the two-dimensional q-state quantum Potts model on the infinite square lattice by using the infinite projected entangled-pair state (iPEPS) algorithm. We show that the quantum fidelity, defined as an overlap measurement between an arbitrary reference state and the iPEPS ground state of the system, can detect q-fold degenerate ground states for the Z_{q} broken-symmetry phase. Accordingly, a multiple bifurcation of the quantum ground-state fidelity is shown to occur as the transverse magnetic field varies from the symmetry phase to the broken-symmetry phase, which means that a multiple-bifurcation point corresponds to a critical point. A (dis)continuous behavior of quantum fidelity at phase transition points characterizes a (dis)continuous phase transition. Similar to the characteristic behavior of the quantum fidelity, the magnetizations, as order parameters, obtained from the degenerate ground states exhibit multiple bifurcation at critical points. Each order parameter is also explicitly demonstrated to transform under the Z_{q} subgroup of the symmetry group of the Hamiltonian. We find that the q-state quantum Potts model on the square lattice undergoes a discontinuous (first-order) phase transition for q=3 and q=4 and a continuous phase transition for q=2 (the two-dimensional quantum transverse Ising model).

  7. Quantum mechanical and spectroscopic (FT-IR, 13C, 1H NMR and UV) investigations of 2-(5-(4-Chlorophenyl)-3-(pyridin-2-yl)-4,5-dihydropyrazol-1-yl)benzo[d]thiazole by DFT method

    NASA Astrophysics Data System (ADS)

    Diwaker

    2014-07-01

    The electronic, NMR, vibrational, structural properties of a new pyrazoline derivative: 2-(5-(4-Chlorophenyl)-3-(pyridine-2-yl)-4,5-dihydropyrazol-1-yl)benzo[d]thiazole has been studied using Gaussian 09 software package. Using VEDA 4 program we have reported the PED potential energy distribution of normal mode of vibrations of the title compound. We have also reported the 1H and 13C NMR chemical shifts of the title compound using B3LYP level of theory with 6-311++G(2d,2p) basis set. Using time dependent (TD-DFT) approach electronic properties such as HOMO and LUMO energies, electronic spectrum of the title compound has been studied and reported. NBO analysis and MEP surface mapping has also been calculated and reported using ab initio methods.

  8. Quantum mechanical and spectroscopic (FT-IR, 13C, 1H NMR and UV) investigations of 2-(5-(4-Chlorophenyl)-3-(pyridin-2-yl)-4,5-dihydropyrazol-1-yl)benzo[d]thiazole by DFT method.

    PubMed

    Diwaker

    2014-07-15

    The electronic, NMR, vibrational, structural properties of a new pyrazoline derivative: 2-(5-(4-Chlorophenyl)-3-(pyridine-2-yl)-4,5-dihydropyrazol-1-yl)benzo[d]thiazole has been studied using Gaussian 09 software package. Using VEDA 4 program we have reported the PED potential energy distribution of normal mode of vibrations of the title compound. We have also reported the (1)H and (13)C NMR chemical shifts of the title compound using B3LYP level of theory with 6-311++G(2d,2p) basis set. Using time dependent (TD-DFT) approach electronic properties such as HOMO and LUMO energies, electronic spectrum of the title compound has been studied and reported. NBO analysis and MEP surface mapping has also been calculated and reported using ab initio methods.

  9. Quantum confinement in semiconductor nanofilms: Optical spectra and multiple exciton generation

    NASA Astrophysics Data System (ADS)

    Khmelinskii, Igor; Makarov, Vladimir I.

    2016-04-01

    We report optical absorption and photoluminescence (PL) spectra of Si and SnO2 nanocrystalline films in the UV-vis-NIR range, featuring discrete bands resulting from transverse quantum confinement, observed in the optical spectra of nanofilms for the first time ever. The film thickness ranged from 3.9 to 12.2 nm, depending on the material. The results are interpreted within the particle-in-a-box model, with infinite walls. The calculated values of the effective electron mass are independent on the film thickness and equal to 0.17mo (Si) and 0.21mo (SnO2), with mo the mass of the free electron. The second calculated model parameter, the quantum number n of the HOMO (valence band), was also thickness-independent: 8.00 (Si) and 7.00 (SnO2). The transitions observed in absorption all start at the level n and correspond to Δn = 1, 2, 3, …. The photoluminescence bands exhibit large Stokes shifts, shifting to higher energies with increased excitation energy. In effect, nanolayers of Si, an indirect-gap semiconductor, behave as a direct-gap semiconductor, as regards the transverse-quantized level system. A prototype Si-SnO2 nanofilm photovoltaic cell demonstrated photoelectron quantum yields achieving 2.5, showing clear evidence of multiple exciton generation, for the first time ever in a working nanofilm device.

  10. Size dependence of carrier dynamics and carrier multiplication in PbS quantum dots

    NASA Astrophysics Data System (ADS)

    Nootz, Gero; Padilha, Lazaro A.; Levina, Larissa; Sukhovatkin, Vlad; Webster, Scott; Brzozowski, Lukasz; Sargent, Edward H.; Hagan, David J.; van Stryland, Eric W.

    2011-04-01

    The time dynamics of the photoexcited carriers and carrier-multiplication efficiencies in PbS quantum dots (QDs) are investigated. In particular, we report on the carrier dynamics, including carrier multiplication, as a function of QD size and compare them to the bulk value. We show that the intraband 1P→1S decay becomes faster for smaller QDs, in agreement with the absence of a phonon bottleneck. Furthermore, as the size of the QDs decreases, the energy threshold for carrier multiplication shifts from the bulk value to higher energies. However, the energy threshold shift is smaller than the band-gap shift and, therefore, for the smallest QDs, the threshold approaches 2.35 Eg, which is close to the theoretical energy conservation limit of twice the band gap. We also show that the carrier-multiplication energy efficiency increases with decreasing QD size. By comparing to theoretical models, our results suggest that impact ionization is sufficient to explain carrier multiplication in QDs.

  11. Gain properties of doped GaAs/AlGaAs multiple quantum well avalanche photodiode structures

    NASA Technical Reports Server (NTRS)

    Menkara, H. M.; Wagner, B. K.; Summers, C. J.

    1995-01-01

    A comprehensive characterization has been made of the static and dynamical response of conventional and multiple quantum well (MQW) avalanche photodiodes (APDs). Comparison of the gain characteristics at low voltages between the MQW and conventional APDs show a direct experimental confirmation of a structure-induced carrier multiplication due to interband impact ionization. Similar studies of the bias dependence of the excess noise characteristics show that the low-voltage gain is primarily due to electron ionization in the MQW-APDS, and to both electron and hole ionization in the conventional APDS. For the doped MQW APDS, the average gain per stage was calculated by comparing gain data with carrier profile measurements, and was found to vary from 1.03 at low bias to 1.09 near avalanche breakdown.

  12. Resonant optical properties of AlGaAs/GaAs multiple-quantum-well based Bragg structure at the second quantum state

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Maharjan, N.; Liu, Z.; Nakarmi, M. L.; Chaldyshev, V. V.; Kundelev, E. V.; Poddubny, A. N.; Vasil'ev, A. P.; Yagovkina, M. A.; Shakya, N. M.

    2017-03-01

    An AlGaAs/GaAs multiple-quantum-well based resonant Bragg structure was designed to match the optical Bragg resonance with the exciton-polariton resonance at the second quantum state in the GaAs quantum wells. The sample structure with 60 periods of AlGaAs/GaAs quantum wells was grown on a semi-insulating GaAs substrate by molecular beam epitaxy. Angle- and temperature-dependent photoluminescence, optical reflectance, and electro-reflectance spectroscopies were employed to study the resonant optical properties of the Bragg structure. Broad and enhanced optical and electro-reflectance features were observed when the Bragg resonance was tuned to the second quantum state of the GaAs quantum well excitons, manifesting a strong light-matter interaction. From the electro-optical experiments, we found the electro-reflectance features related to the transitions of x(e2-hh2) and x(e2-hh1) excitons. The excitonic transition x(e2-hh1), which is prohibited at zero electric field, was allowed by a DC bias due to the brake of symmetry and increased overlap of the electron and hole wave functions caused by the electric field. By tuning the Bragg resonance frequency, we have observed the electro-reflectance feature related to the second quantum state up to room temperature, which evidences a robust light-matter interaction in the resonant Bragg structure.

  13. NMR Method for Characterizing Microsecond-to-Millisecond Chemical Exchanges Utilizing Differential Multiple-Quantum Relaxation in High Molecular Weight Proteins.

    PubMed

    Toyama, Yuki; Osawa, Masanori; Yokogawa, Mariko; Shimada, Ichio

    2016-02-24

    Chemical exchange processes of proteins on the order of microseconds (μs) to milliseconds (ms) play critical roles in biological functions. Developments in methyl-transverse relaxation optimized spectroscopy (methyl-TROSY), which observes the slowly relaxing multiple quantum (MQ) coherences, have enabled the studies of biologically important large proteins. However, the analyses of μs to ms chemical exchange processes based on the methyl-TROSY principle are still challenging, because the interpretation of the chemical exchange contributions to the MQ relaxation profiles is complicated, as significant chemical shift differences occur in both (1)H and (13)C nuclei. Here, we report a new methyl-based NMR method for characterizing chemical exchanges, utilizing differential MQ relaxation rates and a heteronuclear double resonance pulse technique. The method enables quantitative evaluations of the chemical exchange processes, in which significant chemical shift differences exist in both the (1)H and (13)C nuclei. The versatility of the method is demonstrated with the application to KirBac1.1, with an apparent molecular mass of 200 kDa.

  14. Upper bounds on the error probabilities and asymptotic error exponents in quantum multiple state discrimination

    SciTech Connect

    Audenaert, Koenraad M. R.; Mosonyi, Milán

    2014-10-01

    We consider the multiple hypothesis testing problem for symmetric quantum state discrimination between r given states σ₁, …, σ{sub r}. By splitting up the overall test into multiple binary tests in various ways we obtain a number of upper bounds on the optimal error probability in terms of the binary error probabilities. These upper bounds allow us to deduce various bounds on the asymptotic error rate, for which it has been hypothesized that it is given by the multi-hypothesis quantum Chernoff bound (or Chernoff divergence) C(σ₁, …, σ{sub r}), as recently introduced by Nussbaum and Szkoła in analogy with Salikhov's classical multi-hypothesis Chernoff bound. This quantity is defined as the minimum of the pairwise binary Chernoff divergences min{sub jquantum Chernoff bound is always achieved.

  15. Investigation of Photoluminescence and Photocurrent in InGaAsP/InP Strained Multiple Quantum Well Heterostructures

    NASA Technical Reports Server (NTRS)

    Raisky, O. Y.; Wang, W. B.; Alfano, R. R.; Reynolds, C. L., Jr.; Swaminathan, V.

    1997-01-01

    Multiple quantum well InGaAsP/InP p-i-n laser heterostructures with different barrier thicknesses have been investigated using photoluminescence (PL) and photocurrent (PC) measurements. The observed PL spectrum and peak positions are in good agreement with those obtained from transfer matrix calculations. Comparing the measured quantum well PC with calculated carrier escape rates, the photocurrent changes are found to be governed by the temperature dependence of the electron escape time.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    Du, Lin; Maroudas, Dimitrios

    2016-07-11

    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.

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

    PubMed

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

    2015-01-25

    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 (1)H and (13)C NMR chemical shifts of the molecules have been analysed.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  1. Intramolecular excited proton transfer of 1-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol - A combined experimental and quantum chemical studies

    NASA Astrophysics Data System (ADS)

    Jayabharathi, J.; Thanikachalam, V.; Ramanathan, P.; Arunpandiyan, A.

    2014-03-01

    Synthesis of the 1-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol [PPIN] is reported, spectral and fluorescent properties of the title compound are investigated. The feasibility of excited state intramolecular proton transfer (ESIPT) has been argued from the changeover of relative stability of the enol and the keto forms on photoexcitation from the S0-PES to the S1-PES. Critical evaluation on the modulations of geometrical parameters other than the proton transfer reaction coordinate has also been undertaken. The intramolecular hydrogen bonding (IMHB) interaction in PPIN has been explored by calculation of the hyperconjugative charge transfer interaction from the lone electron pair of ring nitrogen atom to the σ∗ orbital of O-H bond, under the provision of Natural Bond Orbital (NBO) analysis. However, DFT calculations together with the experimental results reveal that the excited species with the intramolecular N⋯HO hydrogen bond type undergoes rapid radiationless deactivation. This leads to a conclusion that the low-intensity dual-band fluorescence of the title compound in solution originates from the traces of the conformation with the -OH bond to azomethine nitrogen atom (ESIPT).

  2. Intramolecular excited proton transfer of 1-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol--a combined experimental and quantum chemical studies.

    PubMed

    Jayabharathi, J; Thanikachalam, V; Ramanathan, P; Arunpandiyan, A

    2014-01-01

    Synthesis of the 1-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol [PPIN] is reported, spectral and fluorescent properties of the title compound are investigated. The feasibility of excited state intramolecular proton transfer (ESIPT) has been argued from the changeover of relative stability of the enol and the keto forms on photoexcitation from the S0-PES to the S1-PES. Critical evaluation on the modulations of geometrical parameters other than the proton transfer reaction coordinate has also been undertaken. The intramolecular hydrogen bonding (IMHB) interaction in PPIN has been explored by calculation of the hyperconjugative charge transfer interaction from the lone electron pair of ring nitrogen atom to the σ(∗) orbital of O-H bond, under the provision of Natural Bond Orbital (NBO) analysis. However, DFT calculations together with the experimental results reveal that the excited species with the intramolecular N⋯HO hydrogen bond type undergoes rapid radiationless deactivation. This leads to a conclusion that the low-intensity dual-band fluorescence of the title compound in solution originates from the traces of the conformation with the -OH bond to azomethine nitrogen atom (ESIPT). Copyright © 2013 Elsevier B.V. All rights reserved.

  3. Optically induced excitonic electroabsorption in a periodically delta-doped InGaAs/GaAs multiple quantum well structure

    NASA Technical Reports Server (NTRS)

    Larsson, A.; Maserjian, J.

    1991-01-01

    Large optically induced Stark shifts have been observed in a periodically delta-doped InGaAs/GaAs multiple quantum well structure. With an excitation intensity of 10 mW/sq cm, an absolute quantum well absorption change of 7000/cm was measured with a corresponding differential absorption change as high as 80 percent. The associated maximum change in the quantum well refractive index is 0.04. This material is promising for device development for all-optical computing and signal processing.

  4. Studies of heteronuclear dipolar interactions between spin-1/2 and quadrupolar nuclei by using REDOR during multiple quantum evolution

    NASA Astrophysics Data System (ADS)

    Pruski, M.; Bailly, A.; Lang, D. P.; Amoureux, J.-P.; Fernandez, C.

    1999-06-01

    A new technique for measurements of dipolar interactions in rotating solids is presented that combines the capabilities of multiple quantum magic angle spinning (MQMAS) with the rotational echo double resonance (REDOR). It employs the dipolar recoupling between spin-1/2 ( I) and quadrupolar ( S) nuclei by applying a series of π pulses to the I spins. In contrast to the previously reported MQ-REDOR method, the recoupling sequence is applied during the triple quantum, rather than single quantum evolution. As the dipolar effect is enhanced by the MQ coherence order, this new technique exhibits improved sensitivity toward weak dipolar interactions.

  5. The rigorous stochastic matrix multiplication scheme for the calculations of reduced equilibrium density matrices of open multilevel quantum systems

    NASA Astrophysics Data System (ADS)

    Chen, Xin

    2014-04-01

    Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.

  6. The rigorous stochastic matrix multiplication scheme for the calculations of reduced equilibrium density matrices of open multilevel quantum systems

    SciTech Connect

    Chen, Xin

    2014-04-21

    Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.

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

    NASA Astrophysics Data System (ADS)

    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.

  8. Improved characteristics of ultraviolet AlGaN multiple-quantum-well laser diodes with step-graded quantum barriers close to waveguide layers

    NASA Astrophysics Data System (ADS)

    Cai, Xuefen; Li, Shuping; Kang, Junyong

    2016-09-01

    Ultraviolet AlGaN multiple-quantum-well laser diodes (LDs) with step-graded quantum barriers (QBs) instead of conventional first and last QBs close to waveguide layers are proposed. The characteristics of this type of laser diodes are numerically investigated by using the software PICS3D and it is found that the performances of these LDs are greatly improved. The results indicates that the structure with step-graded QBs exhibits higher output light power, slope efficiency and emission intensity, as well as lower series resistance and threshold current density under the identical condition, compared with conventional LD structure.

  9. Roles of V-shaped pits on the improvement of quantum efficiency in InGaN/GaN multiple quantum well light-emitting diodes

    SciTech Connect

    Quan, Zhijue Wang, Li Zheng, Changda; Liu, Junlin; Jiang, Fengyi

    2014-11-14

    The roles of V-shaped pits on the improvement of quantum efficiency in InGaN/GaN multiple quantum well (MQW) light-emitting diodes are investigated by numerical simulation. The simulation results show that V-shaped pits cannot only screen dislocations, but also play an important role on promoting hole injection into the MQWs. It is revealed that the injection of holes into the MQW via the sidewalls of the V-shaped pits is easier than via the flat region, due to the lower polarization charge densities in the sidewall structure with lower In concentration and (10–11)-oriented semi-polar facets.

  10. Quantum-well intermixing for the control of second-order nonlinear effects in AlGaAs multiple-quantum-well waveguides.

    PubMed

    Street, M W; Whitbread, N D; Hutchings, D C; Arnold, J M; Marsh, J H; Aitchison, J S; Kennedy, G T; Sibbett, W

    1997-11-01

    We present experimental evidence to demonstrate the feasibility of a promising new quasi-phase-matching technique in AlGaAs multiple-quantum-well waveguides. Non-phase-matched second-harmonic-generation measurements indicate that, for sub-half-bandgap excitation near 1.5 microm , quantum-well intermixing by impurity-free vacancy disordering results in a reduction of the nonlinear susceptibility chi((2))(zxy) (~340 pm/V) by 17%. Relatively low intermixed waveguide losses, and the high spatial resolution of the impurity-free vacancy disordering process, suggest that periodic intermixing along the direction of propagation should lead to useful frequency-conversion efficiencies.

  11. Quantum Chemically Estimated Abraham Solute Parameters Using Multiple Solvent-Water Partition Coefficients and Molecular Polarizability.

    PubMed

    Liang, Yuzhen; Xiong, Ruichang; Sandler, Stanley I; Di Toro, Dominic M

    2017-09-05

    Polyparameter Linear Free Energy Relationships (pp-LFERs), also called Linear Solvation Energy Relationships (LSERs), are used to predict many environmentally significant properties of chemicals. A method is presented for computing the necessary chemical parameters, the Abraham parameters (AP), used by many pp-LFERs. It employs quantum chemical calculations and uses only the chemical's molecular structure. The method computes the Abraham E parameter using density functional theory computed molecular polarizability and the Clausius-Mossotti equation relating the index refraction to the molecular polarizability, estimates the Abraham V as the COSMO calculated molecular volume, and computes the remaining AP S, A, and B jointly with a multiple linear regression using sixty-five solvent-water partition coefficients computed using the quantum mechanical COSMO-SAC solvation model. These solute parameters, referred to as Quantum Chemically estimated Abraham Parameters (QCAP), are further adjusted by fitting to experimentally based APs using QCAP parameters as the independent variables so that they are compatible with existing Abraham pp-LFERs. QCAP and adjusted QCAP for 1827 neutral chemicals are included. For 24 solvent-water systems including octanol-water, predicted log solvent-water partition coefficients using adjusted QCAP have the smallest root-mean-square errors (RMSEs, 0.314-0.602) compared to predictions made using APs estimated using the molecular fragment based method ABSOLV (0.45-0.716). For munition and munition-like compounds, adjusted QCAP has much lower RMSE (0.860) than does ABSOLV (4.45) which essentially fails for these compounds.

  12. Multiple quantum oscillation frequencies in YBa2Cu3O6+δ and bilayer splitting

    NASA Astrophysics Data System (ADS)

    Garcia-Aldea, David; Chakravarty, Sudip

    2010-10-01

    Experiments have revealed multiple quantum oscillation frequencies in underdoped high-temperature superconductor YBa2Cu3O6+δ, corresponding to approximately 10% doping, which contains CuO bilayers in the unit cell. These unit cells are further coupled along the c-axis by a tunneling matrix element. A model of the energy dispersion that has its roots in the previously determined electronic structure, combined with twofold commensurate density waves, reveals multiple electron and hole pockets. To the extent that quasiparticles of the reconstructed Fermi surface have finite residues, however small, the formation of Landau levels is the cause of these oscillations, and the bilayer splitting and warping of the electronic dispersion along the direction perpendicular to the CuO-planes are firm consequences. The goal here is to explore this possibility from various directions and provide a better understanding of the rapidly developing experimental situation involving multiple frequencies. An important conclusion is that bilayer splitting is considerably renormalized from the value obtained from band structure calculations. It would be extremely interesting to perform these experiments for higher values of doping. We roughly expect the splitting of the frequencies to increase with doping, but the full picture may be more complex because the density wave order parameter is also expected to decrease with doping, vanishing around the middle of the superconducting dome.

  13. Auxiliary-field quantum Monte Carlo calculations with multiple-projector pseudopotentials

    NASA Astrophysics Data System (ADS)

    Ma, Fengjie; Zhang, Shiwei; Krakauer, Henry

    2017-04-01

    We have implemented recently developed multiple-projector pseudopotentials into the plane-wave-based auxiliary-field quantum Monte Carlo (pw-AFQMC) method. Multiple-projector pseudopotentials can yield smaller plane-wave cutoffs while maintaining or improving transferability. This reduces the computational cost of pw-AFQMC, increasing its reach to larger and more complicated systems. We discuss the use of nonlocal pseudopotentials in the separable Kleinman-Bylander form, and the implementation in pw-AFQMC of the multiple-projector optimized norm-conserving pseudopotential ONCVPSP of Hamann. The accuracy of the method is first demonstrated by equation-of-state calculations of the ionic insulator NaCl and more strongly correlated metal Cu. The method is then applied to calibrate the accuracy of density-functional theory (DFT) predictions of the phase stability of recently discovered high temperature and pressure superconducting sulfur hydride systems. We find that DFT results are in good agreement with pw-AFQMC, due to the near cancellation of electron-electron correlation effects between different structures.

  14. Strong multiple-capture effect in slow Ar^17+-Ar collisions: a quantum mechanical analysis

    NASA Astrophysics Data System (ADS)

    Salehzadeh, Arash; Kirchner, Tom

    2012-10-01

    A recent X-ray spectroscopy experiment on 255 keV Ar^17+-Ar collisions [1] provided evidence for strong multiple-electron capture --- a feature that is supported by classical trajectory Monte Carlo calculations for similar collision systems [2]. We have coupled a quantum-mechanical independent-electron model calculation for the Ar^17+-Ar system with (semi-) phenomenological Auger and radiative cascade models to test these findings. The capture calculations are performed using the basis generator method and include single-particle states on the projectile up to the 10th shell. The cross sections obtained for shell-specific multiple capture are fed into a stabilization scheme proposed in Ref. [3] in order to obtain n-specific cross sections for apparent single (and double) capture that in turn are fed into a radiative cascade code [1] to obtain X-ray emission intensities that can be compared with the experimental data. Good agreement is found for the Lyman series from n=3 to n=7 if the multiple-capture contributions are included, whereas calculations that ignore them are in stark conflict with the data. [4pt] [1] M. Trassinelli et al., J. Phys. B 45, 085202 (2012)[0pt] [2] S. Otranto and R. Olson, Phys. Rev. A 83, 032710 (2011)[0pt] [3] R. Ali et al., Phys. Rev A 49, 3586 (1994).

  15. Time-Resolved Photoluminescence Studies of InGaN/AlGaN Multiple Quantum Wells

    NASA Astrophysics Data System (ADS)

    Zeng, K. C.; Smith, M.; Lin, J. Y.; Jiang, H. X.; Robert, J. C.; Piner, E. L.; McIntosh, F. G.; Bahbahani, M.; Bedair, S. M.; Zavada, J.

    1997-03-01

    Picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the dynamic processes of optical transitions in InGaN/AlGaN multiple quantum wells (MQW) grown by metal-organic chemical vapor deposition (MOCVD). The dynamical behavior of the PL emission reveals that the main emission line in these MQW is the combination of the localized exciton and a band-to-impurity emission lines. The spectral lineshape and the recombination dynamics of the localized exciton and of the band-to-impurity transitions have been systematically investigated at different temperatures and excitation intensities and for MQW with different structures and growth conditions. From these studies, important parameters, including the localization energy and the recombination lifetimes of the localized excitons in InGaN/AlGaN quantum wells, the well width fluctuation, alloy compositions in the well and the barrier materials, and the band offset between InGaN and AlGaN can be deduced. Comparing with time-resolved PL results of InGaN/GaN and GaN/AlGaN MQW, important effects of interface on the optical properties of the III-nitride MQW have been evaluated. Implications of our results to device applications will be discussed.

  16. Thin-Wall GaN/InAlN Multiple Quantum Well Tubes.

    PubMed

    Durand, Christophe; Carlin, Jean-François; Bougerol, Catherine; Gayral, Bruno; Salomon, Damien; Barnes, Jean-Paul; Eymery, Joël; Butté, Raphaël; Grandjean, Nicolas

    2017-06-14

    Thin-wall tubes composed of nitride semiconductors (III-N compounds) based on GaN/InAlN multiple quantum wells (MQWs) are fabricated by metal-organic vapor-phase epitaxy in a simple and full III-N approach. The synthesis of such MQW-tubes is based on the growth of N-polar c-axis vertical GaN wires surrounded by a core-shell MQW heterostructure followed by in situ selective etching using controlled H2/NH3 annealing at 1010 °C to remove the inner GaN wire part. After this process, well-defined MQW-based tubes having nonpolar m-plane orientation exhibit UV light near 330 nm up to room temperature, consistent with the emission of GaN/InAlN MQWs. Partially etched tubes reveal a quantum-dotlike signature originating from nanosized GaN residuals present inside the tubes. The possibility to fabricate in a simple way thin-wall III-N tubes composed of an embedded MQW-based active region offering controllable optical emission properties constitutes an important step forward to develop new nitride devices such as emitters, detectors or sensors based on tubelike nanostructures.

  17. Efficient Red Perovskite Light-Emitting Diodes Based on Solution-Processed Multiple Quantum Wells.

    PubMed

    Zhang, Shuting; Yi, Chang; Wang, Nana; Sun, Yan; Zou, Wei; Wei, Yingqiang; Cao, Yu; Miao, Yanfeng; Li, Renzhi; Yin, Yao; Zhao, Ni; Wang, Jianpu; Huang, Wei

    2017-06-01

    This paper reports a facile and scalable process to achieve high performance red perovskite light-emitting diodes (LEDs) by introducing inorganic Cs into multiple quantum well (MQW) perovskites. The MQW structure facilitates the formation of cubic CsPbI3 perovskites at low temperature, enabling the Cs-based QWs to provide pure and stable red electroluminescence. The versatile synthesis of MQW perovskites provides freedom to control the crystallinity and morphology of the emission layer. It is demonstrated that the inclusion of chloride can further improve the crystallization and consequently the optical properties of the Cs-based MQW perovskites, inducing a low turn-on voltage of 2.0 V, a maximum external quantum efficiency of 3.7%, a luminance of ≈440 cd m(-2) at 4.0 V. These results suggest that the Cs-based MQW LED is among the best performing red perovskite LEDs. Moreover, the LED device demonstrates a record lifetime of over 5 h under a constant current density of 10 mA cm(-2) . This work suggests that the MQW perovskites is a promising platform for achieving high performance visible-range electroluminescence emission through high-throughput processing methods, which is attractive for low-cost lighting and display applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Perovskite light-emitting diodes based on solution-processed self-organized multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Wang, Nana; Cheng, Lu; Ge, Rui; Zhang, Shuting; Miao, Yanfeng; Zou, Wei; Yi, Chang; Sun, Yan; Cao, Yu; Yang, Rong; Wei, Yingqiang; Guo, Qiang; Ke, You; Yu, Maotao; Jin, Yizheng; Liu, Yang; Ding, Qingqing; di, Dawei; Yang, Le; Xing, Guichuan; Tian, He; Jin, Chuanhong; Gao, Feng; Friend, Richard H.; Wang, Jianpu; Huang, Wei

    2016-11-01

    Organometal halide perovskites can be processed from solutions at low temperatures to form crystalline direct-bandgap semiconductors with promising optoelectronic properties. However, the efficiency of their electroluminescence is limited by non-radiative recombination, which is associated with defects and leakage current due to incomplete surface coverage. Here we demonstrate a solution-processed perovskite light-emitting diode (LED) based on self-organized multiple quantum wells (MQWs) with excellent film morphologies. The MQW-based LED exhibits a very high external quantum efficiency of up to 11.7%, good stability and exceptional high-power performance with an energy conversion efficiency of 5.5% at a current density of 100 mA cm-2. This outstanding performance arises because the lower bandgap regions that generate electroluminescence are effectively confined by perovskite MQWs with higher energy gaps, resulting in very efficient radiative decay. Surprisingly, there is no evidence that the large interfacial areas between different bandgap regions cause luminescence quenching.

  19. Characteristics of nanoporous InGaN/GaN multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Wang, W. J.; Yang, G. F.; Chen, P.; Yu, Z. G.; Liu, B.; Xie, Z. L.; Xiu, X. Q.; Wu, Z. L.; Xu, F.; Xu, Z.; Hua, X. M.; Zhao, H.; Han, P.; Shi, Y.; Zhang, R.; Zheng, Y. D.

    2014-07-01

    The nanoporous InGaN/GaN multiple quantum wells (MQWs) has been fabricated through rapid thermal annealing (RTA) and inductively coupled plasma (ICP) dry etching process using self-assembled Ni nanoporous masks. In comparison with the as-grown planar InGaN/GaN MQWs, both internal quantum efficiency and light extraction efficiency for nanoporous InGaN/GaN MQWs are increased, which can be concluded from the photoluminescence (PL) measurements. The thermal activation energy of nanoporous structure (107.44 meV) is significantly higher than that of the as-grown sample (33.02 meV) from temperature-dependent PL measurement, indicating that carriers are well confined and the non-radiative recombination caused by the dislocations and other defects has been reduced. Besides, enhanced light scattering in the disordered nanoporous system can further increase the output emission intensity. The enhanced performance of nanoporous InGaN/GaN MQWs reveals its promising applications for high-efficiency light-emitting devices.

  20. Enhanced carrier multiplication in engineered quasi-type-II quantum dots

    PubMed Central

    Cirloganu, Claudiu M.; Padilha, Lazaro A.; Lin, Qianglu; Makarov, Nikolay S.; Velizhanin, Kirill A.; Luo, Hongmei; Robel, Istvan; Pietryga, Jeffrey M.; Klimov, Victor I.

    2014-01-01

    One process limiting the performance of solar cells is rapid cooling (thermalization) of hot carriers generated by higher-energy solar photons. In principle, the thermalization losses can be reduced by converting the kinetic energy of energetic carriers into additional electron-hole pairs via carrier multiplication (CM). While being inefficient in bulk semiconductors this process is enhanced in quantum dots, although not sufficiently high to considerably boost the power output of practical devices. Here we demonstrate that thick-shell PbSe/CdSe nanostructures can show almost a fourfold increase in the CM yield over conventional PbSe quantum dots, accompanied by a considerable reduction of the CM threshold. These structures enhance a valence-band CM channel due to effective capture of energetic holes into long-lived shell-localized states. The attainment of the regime of slowed cooling responsible for CM enhancement is indicated by the development of shell-related emission in the visible observed simultaneously with infrared emission from the core. PMID:24938462

  1. Hot exciton cooling and multiple exciton generation in PbSe quantum dots.

    PubMed

    Kumar, Manoj; Vezzoli, Stefano; Wang, Zilong; Chaudhary, Varun; Ramanujan, Raju V; Gurzadyan, Gagik G; Bruno, Annalisa; Soci, Cesare

    2016-11-16

    Multiple exciton generation (MEG) is a promising process to improve the power conversion efficiency of solar cells. PbSe quantum dots (QDs) have shown reasonably high MEG quantum yield (QY), although the photon energy threshold for this process is still under debate. One of the reasons for this inconsistency is the complicated competition of MEG and hot exciton cooling, especially at higher excited states. Here, we investigate MEG QY and the origin of the photon energy threshold for MEG in PbSe QDs of three different sizes by studying the transient absorption (TA) spectra, both at the band gap (near infrared, NIR) and far from the band gap energy (visible range). The comparison of visible TA spectra and dynamics for different pump wavelengths, below, around and above the MEG threshold, provides evidence of the role of the Σ transition in slowing down the exciton cooling process that can help MEG to take over the phonon relaxation process. The universality of this behavior is confirmed by studying QDs of three different sizes. Moreover, our results suggest that MEG QY can be determined by pump-probe experiments probed above the band gap.

  2. Influence of annealing and surfactant on InGaAsN/GaAs multiple quantum well

    NASA Astrophysics Data System (ADS)

    Kim, T. S.; Park, J. Y.; Cuong, T. V.; Kim, H. G.; Lee, H. J.; Suh, E.-K.; Hong, C.-H.

    2004-07-01

    Influence of antimony (Sb) as a surfactant and annealing on the structural and optical properties of InGaAsN/GaAs multiple quantum-well (MQW) grown by metalorganic chemical vapor deposition (MOCVD) is studied. It was found that an increase in compressive strain from an analysis of the satellite peaks in high-resolution X-ray diffraction was observed with increasing interruption time and annealing temperature. The photocurrent (PC) peak of as-grown MQW is blue-shifted with introduction time of excess Sb flux during growth interruption process. It seems to be due to the improvement of structure properties at interface by a surfactant suppressing surface diffusion phenomenon. After annealing process, the PC peak is blue-shifted with increasing annealing temperature for all samples. It seems to be related with the compressive strain and QW intermixing.

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

    SciTech Connect

    Tare, Jeffrey D. Esguerra, Jose Perico H.

    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.

  4. Exciton effects in the index of refraction of multiple quantum wells and superlattices

    NASA Technical Reports Server (NTRS)

    Kahen, K. B.; Leburton, J. P.

    1986-01-01

    Theoretical calculations of the index of refraction of multiple quantum wells and superlattices are presented. The model incorporates both the bound and continuum exciton contributions for the gamma region transitions. In addition, the electronic band structure model has both superlattice and bulk alloy properties. The results indicate that large light-hole masses, i.e., of about 0.23, produced by band mixing effects, are required to account for the experimental data. Furthermore, it is shown that superlattice effects rapidly decrease for energies greater than the confining potential barriers. Overall, the theoretical results are in very good agreement with the experimental data and show the importance of including exciton effects in the index of refraction.

  5. Phonon-Induced Dephasing of Excitons in Semiconductor Quantum Dots: Multiple Exciton Generation, Fission, and Luminescence

    NASA Astrophysics Data System (ADS)

    Madrid, Angeline; Kim, Hyeon-Deuk; Habenicht, Bradley; Prezhdo, Oleg

    2010-03-01

    Phonon-induced dephasing processes that govern optical line widths, multiple exciton (ME) generation (MEG), and ME fission (MEF) in semiconductor quantum dots (QDs) are investigated by ab initio molecular dynamics simulation. Using Si QDs as an example, we propose that MEF occurs by phonon-induced dephasing and, for the first time, estimate its time scale to be 100 fs. In contrast, luminescence and MEG dephasing times are all sub-10 fs. Generally, dephasing is faster for higher-energy and higher-order excitons and increased temperatures. MEF is slow because it is facilitated only by low-frequency acoustic modes. Luminescence and MEG couple to both acoustic and optical modes of the QD, as well as ligand vibrations. The detailed atomistic simulation of the dephasing processes advances understanding of exciton dynamics in QDs and other nanoscale materials.

  6. Effective mobility for sequential carrier transport in multiple quantum well structures

    NASA Astrophysics Data System (ADS)

    Toprasertpong, Kasidit; Goodnick, Stephen M.; Nakano, Yoshiaki; Sugiyama, Masakazu

    2017-08-01

    We investigate a theoretical model for effective carrier mobility to comprehensively describe the behavior of the perpendicular carrier transport across multiple quantum well (MQW) structures under applied electric field. The analytical expressions of effective mobilities for thermionic emission, direct tunneling, and thermally assisted tunneling are derived based on the quasithermal equilibrium approximation and the semiclassical approach. Effective electron and hole mobilities in InGaAs/GaAsP MQWs predicted from our model are in good agreement with the experimental results obtained from the carrier time-of-flight measurement near room temperature. With this concept, the complicated carrier dynamics inside MQWs can be simplified to an effective mobility, an equivalent parameter that is more straightforward to handle and can be easily incorporated in the conventional drift-diffusion model.

  7. Ultraviolet laser and photodetector of CdZnS/ZnS multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Tauchi, T.; Yamada, Y.; Ohno, T.; Mullins, J. T.; Masumoto, Y.

    1993-09-01

    Ultraviolet (UV) lasers have been constructed for the first time from multiple quantum well (MQW) heterostructures of CdxZn1-xS/ZnS (x=0.11-0.31) strained-layer superlattices. Stimulated emission can be observed either under optical pumping at RT or under pulsed injection at 30 K in the spectral range of 357-390 nm. Structures of the laser were fabricated by the gaseous low-pressure MOCVD method. A spectral narrowing in the emission spectrum with increasing current in the UV injection diode was clearly observed in the vicinity of 375 nm at 30 K. An UV photodetector has been successfully prepared from this MQW system, in which a spectral responsivity at 366 nm exhibits a high efficiency of about 60 mA/W.

  8. Ultraviolet laser and photodetector of CdZnS/ZnS multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Tauchi, T.; Yamada, Y.; Ohno, T.; Mullins, J. T.; Masumoto, Y.

    1993-09-01

    Ultraviolet (UV) lasers have been constructed for the first time from multiple quantum well (MQW) heterostructures of Cd xZn 1- xS/ZnS ( x=0.11-0.31) strained-layer superlattices. Stimulated emission can be observed either under optical pumping at RT or under pulsed injection at 30 K in the spectral range of 357-390 nm. Structures of the laser were fabricated by the gaseous low-pressure MOCVD method. A spectral narrowing in the emission spectrum with increasing current in the UV injection diode was clearly observed in the vicinity of 375 nm at 30 K. An UV photodetector has been successfully prepared from this MQW system, in which a spectral responsivity at 366 nm exhibits a high efficiency of about 60 mA/W.

  9. Order dependence of the profile of the intensities of multiple-quantum coherences

    SciTech Connect

    Lundin, A. A.; Zobov, V. E.

    2015-05-15

    A modification of the widespread phenomenological model theory of multiple-quantum (MQ) nuclear magnetic resonance spectra of a single cluster of correlated spins has been developed. In contrast to the mentioned theory, the size distribution of such clusters has been consistently taken into account. To obtain the distribution, solutions for the amplitudes of the expansion in the complete set of orthogonal operators are used. Expressions specifying the dependence of the profile of the intensities of MQ coherences on their number n (order) have been obtained. The total form of the dependence has been evaluated by means of the numerical implementation of the resulting expressions. The asymptotic expressions for large n values (wings of the spectrum) have been obtained analytically by the saddle-point method. It has been shown that the dependence under study has a Gaussian central part and exponential wings. The results obtained are in agreement with the previous calculations for some model systems and existing experimental data.

  10. Oxidation effects on cleaved multiple quantum well surfaces in air observed by scanning probe microscopy

    NASA Astrophysics Data System (ADS)

    Howells, S.; Gallagher, M. J.; Chen, T.; Pax, P.; Sarid, D.

    1992-08-01

    The paper presents the first atomic force microscopy (AFM) images of cleaved InGaAs/InP multiple quantum wells and compares them with scanning tunneling microscopy (STM) images taken of the same heterostructure. The images were stable in air for over a day. Based on these results, it is proposed that the mechanism for contrast in the images is due to an oxide layer that grows primarily on the InGaAs wells and not on the InP barriers. Both STM and AFM clearly resolve the individual wells of the heterostructure, although STM measured a larger corrugation than an AFM. STM also exhibited superior lateral resolution of about 2 nm, while AFM had a lateral resolution of approximately 6 nm.

  11. Phase separation in InGaN/GaN multiple quantum wells

    SciTech Connect

    McCluskey, M.D.; Romano, L.T.; Krusor, B.S.; Bour, D.P.; Johnson, N.M.; Brennan, S.

    1998-04-01

    Evidence is presented for phase separation in In{sub 0.27}Ga{sub 0.73}N/GaN multiple quantum wells. After annealing for 40 h at a temperature of 950{degree}C, the absorption threshold at 2.95 eV is replaced by a broad peak at 2.65 eV. This peak is attributed to the formation of In-rich InGaN phases in the active region. X-ray diffraction measurements show a shift in the diffraction peaks toward GaN, consistent with the formation of an In-poor phase. A diffraction peak corresponding to an In-rich phase is also present in the annealed material. Nanoscale In-rich InGaN precipitates are observed by transmission electron microscopy and energy dispersive x-ray chemical analysis. {copyright} {ital 1998 American Institute of Physics.}

  12. Design of a datapath for single-flux-quantum microprocessors with multiple ALUs

    NASA Astrophysics Data System (ADS)

    Tanaka, M.; Kondo, T.; Kawamoto, T.; Kamiya, Y.; Fujiwara, K.; Yamanashi, Y.; Akimoto, A.; Fujimaki, A.; Yoshikawa, N.; Terai, H.; Yorozu, S.

    2005-10-01

    We have demonstrated the components of datapath toward single-flux-quantum microprocessors based on our new architecture called the forwarding architecture. In the forwarding architecture, we improve the performance by utilizing multiple ALUs to conceal the inefficiency of bit-serial processing. The key components of the datapath are a register file and cascaded ALUs. We have designed the register file to hold four bit-serial data with two read ports and one write port. In each ALU, we have implemented six functionalities: addition, subtraction, logical AND, OR and Exclusive OR operations, and comparison with zero. We have tested the register file and the ALU using high-speed on-chip testing, and confirmed the correct operations up to 18 GHz and 23 GHz, respectively.

  13. Effects of dead zones in multiple-quantum-well binary-phase modulators on optical interconnections.

    PubMed

    Inbar, H; Taghizadeh, M R

    1998-02-10

    We investigate the effects of inactive regions [dead zones (DZ's)] in multiple-quantum-well binary-phase modulators used for free-space dynamic optical interconnection applications. Results, however, have implications for other types of pixelated spatial light modulators (SLM's). To our knowledge, the effects of DZ's in SLM's have not before been thoroughly studied in a context other than optical correlation. We investigate the DZ's (considered to be either opaque or transmissive) as a feature that may be exploited in system design, calculating light efficiency and fidelity as a function of DZ fractional width. It is shown that in particular cases an appropriate choice of DZ width would lead to an optical interconnection with substantially improved cross-talk performance.

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

    SciTech Connect

    Tare, Jeffrey D. Esguerra, Jose Perico H.

    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.

  15. Exciton effects in the index of refraction of multiple quantum wells and superlattices

    NASA Technical Reports Server (NTRS)

    Kahen, K. B.; Leburton, J. P.

    1986-01-01

    Theoretical calculations of the index of refraction of multiple quantum wells and superlattices are presented. The model incorporates both the bound and continuum exciton contributions for the gamma region transitions. In addition, the electronic band structure model has both superlattice and bulk alloy properties. The results indicate that large light-hole masses, i.e., of about 0.23, produced by band mixing effects, are required to account for the experimental data. Furthermore, it is shown that superlattice effects rapidly decrease for energies greater than the confining potential barriers. Overall, the theoretical results are in very good agreement with the experimental data and show the importance of including exciton effects in the index of refraction.

  16. Flat pancake distant dipolar fields for enhancement of intermolecular multiple-quantum coherence signals.

    PubMed

    Cai, Congbo; Lin, Yulan; Cai, Shuhui; Sun, Huijun; Zhong, Jianhui; Chen, Zhong

    2012-03-07

    Intermolecular multiple-quantum coherences (iMQCs) originated from distant dipolar field (DDF) possess some appealing unique properties for magnetic resonance imaging (MRI). DDF is usually induced with continuous wave (i.e., sine- or square-wave) magnetization modulation in the whole sample. In this article, a spatially localized and enhanced DDF was optimally tailored in a thin slice with an adiabatic inversion pulse. Evidence was provided to show that careful tailoring of the spatially localized DDF can generate highly efficient iMQC signals, with more than two-fold enhancement compared to the conventional sine-wave magnetization modulation method, and 1.5 times of that with the square-wave modulation under the similar condition. Theoretical predictions, simulation results, and experimental verifications agree well with each other. Practical implementation of this approach for efficient iMQC MRI was explored. © 2012 American Institute of Physics

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

    NASA Astrophysics Data System (ADS)

    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. Analytical modeling of the resolution of photorefractive multiple quantum well spatial light modulators

    NASA Astrophysics Data System (ADS)

    Abeeluck, A. K.; Garmire, E.; Canoglu, E.

    2000-11-01

    An analytical model that includes lateral drift of photocarriers is developed to explain the experimental resolution of photorefractive multiple quantum well (MQW) devices. The model is in excellent agreement with a phenomenological fit proposed earlier and it follows a small intensity modulation model closely. Charge distributions with and without lateral drift of carriers at the MQW interfaces are assumed in order to calculate the peak diffraction efficiency as a function of grating period. An effective mobility-lifetime product is used to account for the effect of lateral drift in the MQW region. It is shown that good agreement with experiment is obtained when lateral drift is taken into account. Moreover, the model is applied to the study of design tradeoff between resolution, sensitivity, and diffraction efficiency which are all of crucial importance in the performance of practical devices.

  19. Quantum

    NASA Astrophysics Data System (ADS)

    Elbaz, Edgard

    This book gives a new insight into the interpretation of quantum mechanics (stochastic, integral paths, decoherence), a completely new treatment of angular momentum (graphical spin algebra) and an introduction to Fermion fields (Dirac equation) and Boson fields (e.m. and Higgs) as well as an introduction to QED (quantum electrodynamics), supersymmetry and quantum cosmology.

  20. Strain-balanced InGaN/GaN multiple quantum wells

    SciTech Connect

    Van Den Broeck, D. M.; Hosalli, A. M.; Bedair, S. M.; Bharrat, D.; El-Masry, N. A.

    2014-07-21

    InGaN/GaN multiple quantum well (MQW) structures suffer from a high amount of compressive strain in the InGaN wells and the accompanied piezoelectric field resulting in both a blue shift in emission and a reduction of emission intensity. We report the growth of In{sub x}Ga{sub 1−x}N/GaN “strain-balanced” multiple quantum wells (SBMQWs) grown on thick In{sub y}Ga{sub 1−y}N templates for x > y by metal organic chemical vapor deposition. SBMQWs consist of alternating layers of In{sub x}Ga{sub 1−x}N wells and GaN barriers under compressive and tensile stress, respectively, which have been lattice matched to a thick In{sub y}Ga{sub 1−y}N template. Growth of the In{sub y}Ga{sub 1−y}N template is also detailed in order to achieve thick, relaxed In{sub y}Ga{sub 1−y}N grown on GaN without the presence of V-grooves. When compared to conventional In{sub x}Ga{sub 1−x}N/GaN MQWs grown on GaN, the SBMQW structures exhibit longer wavelength emission and higher emission intensity for the same InN mole fraction due to a reduction in the well strain and piezoelectric field. By matching the average lattice constant of the MQW active region to the lattice constant of the In{sub y}Ga{sub 1−y}N template, essentially an infinite number of periods can be grown using the SBMQW growth method without relaxation-related effects. SBMQWs can be utilized to achieve longer wavelength emission in light emitting diodes without the use of excess indium and can be advantageous in addressing the “green gap.”.

  1. Multiple excitons and the electron phonon bottleneck in semiconductor quantum dots: An ab initio perspective

    NASA Astrophysics Data System (ADS)

    Prezhdo, Oleg V.

    2008-07-01

    The article presents the current perspective on the nature of photoexcited states in semiconductor quantum dots (QDs). The focus is on multiple excitons and photo-induced electron-phonon dynamics in PbSe and CdSe QDs, and the advocated view is rooted in the results of ab initio studies in both energy and time domains. As a new type of material, semiconductor QDs represent the borderline between chemistry and physics, exhibiting both molecular and bulk-like properties. Similar to atoms and molecules, the electronic spectra of QD show discrete bands. Just as bulk semiconductors, QDs comprise multiple copies of the elementary unit cell, and are characterized by valence and conduction bands. The electron-phonon coupling in QDs is weaker than in molecules, but stronger than in bulk semiconductors. Unlike either material, the QD properties can be tuned continuously by changing QD size and shape. The molecular and bulk points of view often lead to contradicting conclusions. For example, the molecular view suggests that the excitations in QDs should exhibit strong electron-correlation (excitonic) effects, and that the electron-phonon relaxation should be slow due to the discrete nature of the optical bands and the mismatch of the electronic energy gaps with vibrational frequencies. In contrast, a finite-size limit of bulk properties indicates that the kinetic energy of quantum confinement should be significantly greater than excitonic effects and that the electron-phonon relaxation inside the quasi-continuous bands should be efficient. Such qualitative differences have generated heated discussions in the literature. The great potential of QDs for a variety of applications, including photovoltaics, spintronics, lasers, light-emitting diodes, and field-effect transistors makes it crutual to settle the debates. By synthesizing different viewpoints and presenting a unified atomistic picture of the excited state processes, our ab initio analysis clarifies the controversies

  2. Iii-V Compound Multiple Quantum Well Based Modulator and Switching Devices.

    NASA Astrophysics Data System (ADS)

    Hong, Songcheol

    A general formalism to study the absorption and photocurrent in multiple quantum well is provided with detailed consideration of quantum confined Stark shift, exciton binding energy, line broadening, tunneling, polarization, and strain effects. Results on variation of exciton size, binding energies and transition energies as a function electric field and well size have been presented. Inhomogeneous line broadening of exciton lines due to interface roughness, alloy disorder and well to well size fluctuation is calculated. The potential of material tailoring by introducing strain for specific optical response is discussed. Theoretical and experimental results on excitonic and band-to-band absorption spectra in strained multi-quantum well structures are shown. I also report on polarization dependent optical absorption for excitonic and interband transitions in lattice matched and strained multiquantum well structures in presence of transverse electric field. Photocurrent in a p-i(MQW)-n diode with monochromatic light is examined with respect to different temperatures and intensities. The negative resistance of I-V characteristic of the p-i-n diode is based on the quantum confined Stark effect of the heavy hole excitonic transition in a multiquantum well. This exciton based photocurrent characteristic allows efficient switching. A general purpose low power optical logic device using the controller-modulator concept bas been proposed and realized. The controller is a heterojunction phototransistor with multiquantum wells in the base-collector depletion region. This allows an amplified photocurrent controlled voltage feedback with low light intensity levels. Detailed analysis of the sensitivity of this device in various modes of operation is studied. Studies are also presented on the cascadability of the device as well as its integrating -thresholding properties. A multiquantum well heterojunction bipolar transistor (MHBT), which has N^+ -p^+-i(MQW)-N structure has been

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Solution behavior and complete sup 1 H and sup 13 C NMR assignments of the coenzyme B sub 12 derivative (5 prime -deoxyadenosyl)cobinamide using modern 2D NMR experiments, including 600-MHz sup 1 H NMR data

    SciTech Connect

    Pagano, T.G.; Yohannes, P.G.; Marzilli, L.G. ); Hay, B.P.; Scott, J.R.; Finke, R.G. )

    1989-02-15

    Two-dimensional (2D) NMR methods have been used to assign completely the {sup 1}H and {sup 13}C NMR spectra of the (5{prime}-deoxyadenosyl)cobinamide cation (AdoCbi{sup +}) in D{sub 2}O. Most of the {sup 1}H 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 {sup 1}H-detected heteronuclear multiple-quantum coherence (HMQC) spectroscopy. The nonprotonated carbon resonances, as well as the remaining unassigned {sup 1}H and {sup 13}C NMR signals, were assigned from long-range {sup 1}H-{sup 13}C connectivities determined from {sup 1}H-detected multiple-bond heteronuclear multiple-quantum coherence spectroscopy (HMBC). Comparison of the {sup 13}C chemical shifts and {sup 1}H NOEs of AdoCbi{sup +} with those of coenzyme B{sup 12} ((5{prime}-deoxyadenosyl)cobalamin) and its benzimidazole-protonated, base-off form indicates that the electronic properties and structure of AdoCbi{sup +} are similar to that of coenzyme B{sup 12} in the protonated, base-off form. The {sup 13}C chemical shifts of most of the carbons of AdoCbi{sup +} do not vary significantly from those of base-off, benzimidazole-protonated coenzyme B{sup 12}, 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{sup +} and in base-off, benzimidazole-protonated coenzyme B{sub 12} indicate that the positions of these side chains may be different in AdoCbi{sup +} compared to base-off coenzyme B{sup 12}.

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

    SciTech Connect

    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.

  6. Long term operation of high quantum efficiency GaAs(Cs,O) photocathodes using multiple recleaning by atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Orlov, D. A.; Krantz, C.; Wolf, A.; Jaroshevich, A. S.; Kosolobov, S. N.; Scheibler, H. E.; Terekhov, A. S.

    2009-09-01

    Atomic hydrogen, produced by thermal dissociation of H2 molecules inside a hot tungsten capillary, is shown to be an efficient tool for multiple recleaning of degraded surfaces of high quantum efficiency transmission-mode GaAs photocathodes within an ultrahigh vacuum (UHV) multichamber photoelectron gun. Ultraviolet quantum yield photoemission spectroscopy has been used to study the removal of surface pollutants and the degraded (Cs,O)-activation layer during the cleaning procedure. For photocathodes grown by the liquid-phase epitaxy technique, the quantum efficiency is found to be stable at about 20% over a large number of atomic hydrogen cleaning cycles. A slow degradation of the quantum efficiency is observed for photocathodes grown by metal-organic chemical vapor deposition, although they reached a higher initial quantum efficiency of about 30%-35%. Study of the spatial distributions of photoluminescence intensity on these photocathodes proved that this overall degradation is likely due to insertion of a dislocation network into the mechanically strained photocathode heterostructures during multiple heating cycles and is not due to the atomic hydrogen treatment itself.

  7. High Contrast Fabry-Perot Multiple Quantum Well Modulators and Systems.

    NASA Astrophysics Data System (ADS)

    Cheung, Siu Kwan

    Multiple Quantum Well (MQW) symmetric Fabry-Perot optical modulators, which utilize field-induced changes in optical absorption and index of refraction due to the Quantum Confined Stark Effect (QCSE), are presented using InGaAs/GaAs system. An on/off contrast ratio exceeding 1200:1 has been obtained using MBE-grown symmetric Fabry -Perot structure which consists of two AlAs/GaAs quarter -wavelength dielectric mirrors and an InGaAs/GaAs rectangular MQW cavity. A tuning range of about 10 nm has been observed for an applied voltage change of ~15 V. Theoretical and experimental studies, including the excitonic absorption in MQW layers, QCSE, optical characterization and device performance, and system modeling are presented. Analytic expressions have been obtained for the optimal design of the symmetric Fabry-Perot modulators. The calculations are based on the optical transfer matrix and the two effective interfaces approach under the plane wave approximation. Optical characterizations and measurements using Spectrophotometer, Variable Angle Spectroscopic Ellipsometry (VASE) and computer -controlled Argon-pumped Ti:Sapphire laser measuring setup are described. Comparisons between theoretical and experimental results indicate a 0.037% deviation of the Fabry-Perot mode for the nontunable structure with projected dynamic range of 38.7 dB and a 0.2% deviation for the tunable modulator from the calculated results. The good matchings of the experimental and calculated Fabry-Perot modes indicate the validity of the theoretical models. Related applications, including the design and performance study of Heterostructure Acoustic Charge Transport Spatial Light Modulators (HACT/SLMs), tunable narrowband optical filters and reflectivity-tunable vertical surface emitting laser structures, are also presented.

  8. Phase control of Goos-Hänchen shift via biexciton coherence in a multiple quantum well

    NASA Astrophysics Data System (ADS)

    Asadpour, Seyyed Hossein; Nasehi, Rajab; Soleimani, H. Rahimpour; Mahmoudi, M.

    2015-09-01

    The behavior of the Goos-Hänchen (GH) shifts of the reflected and transmitted probe and signal pulses through a cavity containing four-level GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5 nm GaAs wells and 15-nm Al0.3Ga0.7As barriers is theoretically discussed. The biexciton coherence set up by two coupling fields can induce the destructive interference to control the absorption and gain properties of probe field under appropriate conditions. It is realized that for the specific values of the intensities and the relative phase of applied fields, the simultaneous negative or positive GH shift in the transmitted and reflected light beam can be obtained via amplification in a probe light. It is found that by adjusting the controllable parameters, the GH shifts can be switched between the large positive and negative values in the medium. Moreover, the effect of exciton spin relaxation on the GH shift has also been discussed. We find that the exciton spin relaxation can manipulate the behavior of GH shift in the reflected and transmitted probe beam through the cavity. We show that by controlling the incident angles of probe beam and under certain conditions, the GH shifts in the reflected and transmitted probe beams can become either negative or positive corresponding to the superluminal or subluminal light propagation. Our proposed model may supply a new prospect in technological applications for the light amplification in optical sensors working on quantum coherence impacts in solid-state systems.

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

    SciTech Connect

    Bolshakov, A. S. Chaldyshev, V. V. Babichev, A. V.; Kudryashov, D. A.; Gudovskikh, A. S.; Morozov, I. A.; Sobolev, M. S.; Nikitina, E. V.

    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.

  10. Sorting photon wave packets using temporal-mode interferometry based on multiple-stage quantum frequency conversion

    NASA Astrophysics Data System (ADS)

    Reddy, D. V.; Raymer, M. G.; McKinstrie, C. J.

    2015-01-01

    All classical and quantum technologies that encode in and retrieve information from optical fields rely on the ability to selectively manipulate orthogonal field modes of light. Such manipulation can be achieved with high selectivity for polarization modes and transverse-spatial modes. For the time-frequency degree of freedom, this could efficiently be achieved for a limited choice of approximately orthogonal modes, i.e., nonoverlapping bins in time or frequency. We recently proposed a method that surmounts the selectivity barrier for sorting arbitrary orthogonal temporal modes [Opt. Lett. 39, 2924 (2014)., 10.1364/OL.39.002924] using cascaded interferometric quantum frequency conversion in nonlinear optical media. We call this method temporal-mode interferometry, as it has a close resemblance to the well-known separated-fields atomic interferometry method introduced by Ramsey. The method has important implications for quantum memories, quantum dense coding, quantum teleportation, and quantum key distribution. Here we explore the inner workings of the method in detail, and extend it to multiple stages with a concurrent asymptotic convergence of temporal-mode selectivity to unity. We also complete our analysis of pump-chirp compensation to counter pump-induced nonlinear phase modulation in four-wave mixing implementations.

  11. Controllably releasing long-lived quantum memory for photonic polarization qubit into multiple spatially-separate photonic channels

    NASA Astrophysics Data System (ADS)

    Chen, Lirong; Xu, Zhongxiao; Zeng, Weiqing; Wen, Yafei; Li, Shujing; Wang, Hai

    2016-09-01

    We report an experiment in which long-lived quantum memories for photonic polarization qubits (PPQs) are controllably released into any one of multiple spatially-separate channels. The PPQs are implemented with an arbitrarily-polarized coherent signal light pulses at the single-photon level and are stored in cold atoms by means of electromagnetic-induced-transparency scheme. Reading laser pulses propagating along the direction at a small angle relative to quantum axis are applied to release the stored PPQs into an output channel. By changing the propagating directions of the read laser beam, we controllably release the retrieved PPQs into 7 different photonic output channels, respectively. At a storage time of δt = 5 μs, the least quantum-process fidelity in 7 different output channels is ~89%. At one of the output channels, the measured maximum quantum-process fidelity for the PPQs is 94.2% at storage time of δt = 0.85 ms. At storage time of 6 ms, the quantum-process fidelity is still beyond the bound of 78% to violate the Bell’s inequality. The demonstrated controllable release of the stored PPQs may extend the capabilities of the quantum information storage technique.

  12. Controllably releasing long-lived quantum memory for photonic polarization qubit into multiple spatially-separate photonic channels

    PubMed Central

    Chen, Lirong; Xu, Zhongxiao; Zeng, Weiqing; Wen, Yafei; Li, Shujing; Wang, Hai

    2016-01-01

    We report an experiment in which long-lived quantum memories for photonic polarization qubits (PPQs) are controllably released into any one of multiple spatially-separate channels. The PPQs are implemented with an arbitrarily-polarized coherent signal light pulses at the single-photon level and are stored in cold atoms by means of electromagnetic-induced-transparency scheme. Reading laser pulses propagating along the direction at a small angle relative to quantum axis are applied to release the stored PPQs into an output channel. By changing the propagating directions of the read laser beam, we controllably release the retrieved PPQs into 7 different photonic output channels, respectively. At a storage time of δt = 5 μs, the least quantum-process fidelity in 7 different output channels is ~89%. At one of the output channels, the measured maximum quantum-process fidelity for the PPQs is 94.2% at storage time of δt = 0.85 ms. At storage time of 6 ms, the quantum-process fidelity is still beyond the bound of 78% to violate the Bell’s inequality. The demonstrated controllable release of the stored PPQs may extend the capabilities of the quantum information storage technique. PMID:27667262

  13. Optically detected magnetic resonance study of a type-II GaAs/AlAs multiple quantum well

    NASA Astrophysics Data System (ADS)

    van Kesteren, H. W.; Cosman, E. C.; Greidanus, F. J. A. M.; Dawson, P.; Moore, K. J.; Foxon, C. T.

    1988-07-01

    In a type-II GaAs/AlAs multiple quantum well three optically detected magnetic resonance lines and two level anticrossings were observed. Two of the resonance lines and the two level anticrossings are in agreement with the electronic level scheme of the heavy-hole exciton. The third resonance line is in accordance with a magnetic spin resonance of an unbound electron. These optically detected magnetic resonance measurements open up the possibility to obtain detailed information about the excitons in and the band structure of type-II quantum wells.

  14. Probing Structure Property Relationships in Complex Engineering Silicones by 1H NMR

    SciTech Connect

    Chinn, S C; Gjersing, E L; Maxwell, R S; Eastwood, E; Bowen, D; Stephens, T

    2006-07-14

    It is generally accepted that the properties of polymeric materials are controlled by the network structure and the reactions by which they have been constructed. These properties include the bulk moduli at creation, but also the properties as a function of age during use. In order to interpret mechanical properties and predict the time dependent changes in these properties, detailed knowledge of the effect of structural changes must be obtained. The degree and type of crosslinking, the molecular weight between crosslinks, the number of elastically ineffective chains (loops, dangling chain ends, sol-fraction) must be characterized. A number of theoretical and experimental efforts have been reported in the last few years on model networks prepared by endlinking reactions and the relationships of those structures with the ultimate mechanical properties. A range of experimental methods have been used to investigate structure including rheometric, scattering, infrared, {sup 29}Si MAS and CPMAS, {sup 1}H relaxation measurements, and recently {sup 1}H multiple quantum methods. Characterization of the growth of multiple quantum coherences have recently been shown to provide detailed insight into silicone network structure by the ability to selective probe the individual components of the polymer network, such as the polymer-filler interface or network chains. We have employed recently developed MQ methods to investigate the structure-property relationships in a series of complex, endlinked filled-PDMS blends. Here, a systematic study of the relationship between the molecular formulation, as dictated by the amount and type of crosslinks present and by the remaining network chains, and the segmental dynamics as observed by MQ NMR was performed.

  15. Barrier potential design criteria in multiple-quantum-well-based solar-cell structures

    NASA Technical Reports Server (NTRS)

    Mohaidat, Jihad M.; Shum, Kai; Wang, W. B.; Alfano, R. R.

    1994-01-01

    The barrier potential design criteria in multiple-quantum-well (MQW)-based solar-cell structures is reported for the purpose of achieving maximum efficiency. The time-dependent short-circuit current density at the collector side of various MQW solar-cell structures under resonant condition was numerically calculated using the time-dependent Schroedinger equation. The energy efficiency of solar cells based on the InAs/Ga(y)In(1-y)As and GaAs/Al(x)Ga(1-x)As MQW structues were compared when carriers are excited at a particular solar-energy band. Using InAs/Ga(y)In(1-y)As MQW structures it is found that a maximum energy efficiency can be achieved if the structure is designed with barrier potential of about 450 meV. The efficiency is found to decline linearly as the barrier potential increases for GaAs/Al(x)Ga(1-x)As MQW-structure-based solar cells.

  16. Strained germanium-tin multiple quantum well microdisk resonators towards a light source on silicon

    NASA Astrophysics Data System (ADS)

    Shang, Colleen K.; Chen, Robert; Gupta, Suyog; Huang, Yi-Chiau; Huo, Yijie; Sanchez, Errol; Kim, Yihwan; Kamins, Theodore I.; Saraswat, Krishna C.; Harris, James S.

    2015-02-01

    Although the development of a monolithically-integrated, silicon-compatible light source has been traditionally limited by the indirect band gaps of Group IV materials, germanium-tin (Ge1-xSnx) is predicted to exhibit direct band gap behavior. In pseudomorphic conditions with materials of smaller lattice constant, the accumulation of compressive strain in Ge1-xSnx counteracts this behavior to prevent the direct band gap transition. One possible approach to compensate for this compressive strain is to introduce tensile strain into the system, which can be achieved by applying an external stressing agent to post-fabricated devices. We describe a suspended Ge0:922Sn0:078 multiple quantum well microdisk resonator cavity strained by 140 nm of highly compressively stressed silicon nitride. Raman shifts and photoluminescence redshifts indicate that an additional 0.23-0.30% strain can be induced in these microdisks with this approach. The ability to tune the optical performance of these resonator structures by strain engineering has the potential to enable the development of low threshold Ge1-xSnx-based lasers on Si.

  17. Germanium-tin interdiffusion in strained Ge/GeSn multiple-quantum-well structure

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Dong, Yuan; Zhou, Qian; Tok, Eng Soon; Yeo, Yee-Chia

    2016-06-01

    The thermal stability and germanium-tin (Ge-Sn) interdiffusion properties were studied in epitaxial Ge/GeSn multiple-quantum-well (MQW) structure. No obvious interdiffusion was observed for annealing temperatures of 300 °C or below, while observable interdiffusion occurred for annealing temperatures of 380 °C and above. High-resolution x-ray diffraction was used to obtain the interdiffusion coefficient by analyzing the decrease rate of Ge/GeSn periodic satellite peaks. The interdiffusion coefficient is much higher, and the activation enthalpy of 1.21 eV is substantially lower in Ge/GeSn MQW structure than that previously reported in silicon-germanium (Si-Ge) systems. When the annealing temperature is increased to above 500 °C, Ge-Sn interdiffusion becomes severe. Some small pits appear on the surface, which should be related to Sn out-diffusion to the Ge cap layer, followed by Sn desorption from the top surface. This work provides insights into the Ge-Sn interdiffusion and Sn segregation behaviors in Ge/GeSn MQW structure, and the thermal budget that may be used for fabrication of devices comprising Ge/GeSn heterostructures.

  18. Barrier potential design criteria in multiple-quantum-well-based solar-cell structures

    NASA Technical Reports Server (NTRS)

    Mohaidat, Jihad M.; Shum, Kai; Wang, W. B.; Alfano, R. R.

    1994-01-01

    The barrier potential design criteria in multiple-quantum-well (MQW)-based solar-cell structures is reported for the purpose of achieving maximum efficiency. The time-dependent short-circuit current density at the collector side of various MQW solar-cell structures under resonant condition was numerically calculated using the time-dependent Schroedinger equation. The energy efficiency of solar cells based on the InAs/Ga(y)In(1-y)As and GaAs/Al(x)Ga(1-x)As MQW structues were compared when carriers are excited at a particular solar-energy band. Using InAs/Ga(y)In(1-y)As MQW structures it is found that a maximum energy efficiency can be achieved if the structure is designed with barrier potential of about 450 meV. The efficiency is found to decline linearly as the barrier potential increases for GaAs/Al(x)Ga(1-x)As MQW-structure-based solar cells.

  19. Ultrafast biexciton spectroscopy in semiconductor quantum dots: evidence for early emergence of multiple-exciton generation

    PubMed Central

    Choi, Younghwan; Sim, Sangwan; Lim, Seong Chu; Lee, Young Hee; Choi, Hyunyong

    2013-01-01

    Understanding multiple-exciton generation (MEG) in quantum dots (QDs) requires in-depth measurements of transient exciton dynamics. Because MEG typically faces competing ultrafast energy-loss intra-band relaxation, it is of central importance to investigate the emerging time-scale of the MEG kinetics. Here, we present ultrafast spectroscopic measurements of the MEG in PbS QDs via probing the ground-state biexciton transients. Specifically, we directly compare the biexciton spectra with the single-exciton ones before and after the intra-band relaxation. Early emergence of MEG is evidenced by observing transient Stark shift and quasi-instantaneous linewidth broadening, both of which take place before the intra-band relaxation. Photon-density-dependent study shows that the broadened biexciton linewidth strongly depends on the MEG-induced extra-exciton generation. Long after the intra-band relaxation, the biexciton broadening is small and the single-exciton state filling is dominant. PMID:24220495

  20. Formation mechanism of highly luminescent silica capsules incorporating multiple hydrophobic quantum dots with various emission wavelengths.

    PubMed

    Li, Chunliang; Murase, Norio

    2013-12-01

    A synthesis process was reconsidered for encapsulating hydrophobic quantum dots (QDs) into silica capsules with high photoluminescent (PL) efficiency. The process comprises three steps: silanization of QD surfaces, seed formation by assembly of the QDs, and coating of the QD seeds with a silica shell. Analysis of the encapsulation mechanism enabled this process to be adapted for application to CdSe-based core-shell QDs with various organic ligands such as oleic acid and with various emission wavelengths. Formation of the seeds is the key step in synthesizing the silica capsules, so that they have high PL efficiency. Due to the differences in QD size and in the affinity of the ligands on their surfaces, the concentration of QDs used in the synthesis must be optimized to maximize emission efficiency. Contrary to an initial assumption, several ligands remained on the QD surfaces even after the QDs were transferred from organic solution to water. This greatly affected the size and PL efficiency of the seeds. Judicious selection of the conditions for seed and silica capsule synthesis resulted in seeds with PL efficiency greater than 70% and in silica capsules encapsulating multiple CdSe/CdZnS QDs with PL efficiency as high as 41%. Silica capsules incorporating QDs with various emission peak wavelengths from green to red were also prepared. The process presented serves as a guideline for encapsulating various types of hydrophobic QDs into silica capsules for biological tagging applications.

  1. Modeling and simulation of magnetic resonance imaging based on intermolecular multiple quantum coherences

    NASA Astrophysics Data System (ADS)

    Cai, Congbo; Dong, Jiyang; Cai, Shuhui; Cheng, En; Chen, Zhong

    2006-11-01

    Intermolecular multiple quantum coherences (iMQCs) have many potential applications since they can provide interaction information between different molecules within the range of dipolar correlation distance, and can provide new contrast in magnetic resonance imaging (MRI). Because of the non-localized property of dipolar field, and the non-linear property of the Bloch equations incorporating the dipolar field term, the evolution behavior of iMQC is difficult to deduce strictly in many cases. In such cases, simulation studies are very important. Simulation results can not only give a guide to optimize experimental conditions, but also help analyze unexpected experimental results. Based on our product operator matrix and the K-space method for dipolar field calculation, the MRI simulation software was constructed, running on Windows operation system. The non-linear Bloch equations are calculated by a fifth-order Cash-Karp Runge-Kutta formulism. Computational time can be efficiently reduced by separating the effects of chemical shifts and strong gradient field. Using this software, simulation of different kinds of complex MRI sequences can be done conveniently and quickly on general personal computers. Some examples were given. The results were discussed.

  2. Optical modes within III-nitride multiple quantum well microdisk cavities

    NASA Astrophysics Data System (ADS)

    Mair, R. A.; Zeng, K. C.; Lin, J. Y.; Jiang, H. X.; Zhang, B.; Dai, L.; Botchkarev, A.; Kim, W.; Morkoç, H.; Khan, M. A.

    1998-03-01

    Optical resonance modes have been observed in optically pumped microdisk cavities fabricated from 50 Å/50 Å GaN/AlxGa1-xN(x˜0.07) and 45 Å/45 Å InxGa1-xN/GaN(x˜0.15) multiple quantum well structures. Microdisks, approximately 9 μm in diameter and regularly spaced every 50 μm, were formed by an ion beam etch process. Individual disks were pumped at 300 and 10 K with 290 nm laser pulses focused to a spot size much smaller than the disk diameter. Optical modes corresponding to (i) the radial mode type with a spacing of 49-51 meV (both TE and TM) and (ii) the Whispering Gallery mode with a spacing of 15-16 meV were observed in the GaN microdisk cavities. The spacings of these modes are consistent with those expected for modes within a resonant cavity of cylindrical symmetry, refractive index, and dimensions of the microdisks under investigation. The GaN-based microdisk cavity is compared with its GaAs counterpart and implications regarding future GaN-based microdisk lasers are discussed.

  3. Recombination Pathways in Green InGaN/GaN Multiple Quantum Wells

    NASA Astrophysics Data System (ADS)

    Lin, Tao; Kuo, Hao Chung; Jiang, Xiao Dong; Feng, Zhe Chuan

    2017-02-01

    This paper reports the transient photoluminescence (PL) properties of an InGaN/GaN multiple quantum well (MQW) light-emitting diode (LED) with green emission. Recombination of localized excitons was proved to be the main microscopic mechanism of green emission in the sample. The PL dynamics were ascribed to two pathways of the exciton recombination, corresponding to the fast decay and the slow decay, respectively. The origins of slow decay and fast decay were assigned to local compositional fluctuations of indium and thickness variations of InGaN layers, respectively. Furthermore, the contributions of two decay pathways to the green PL were found to vary at different emission photon energy. The fraction of fast decay pathway decreased with decreasing photon energy. The slow radiative PL from deep localized exciton recombination suffered less suppression from non-radiative delocalization process, for the higher requested activation energy. All these results supported a clear microscopy mechanism of excitation-emission process of the green MQW LED structure.

  4. Recombination Pathways in Green InGaN/GaN Multiple Quantum Wells.

    PubMed

    Lin, Tao; Kuo, Hao Chung; Jiang, Xiao Dong; Feng, Zhe Chuan

    2017-12-01

    This paper reports the transient photoluminescence (PL) properties of an InGaN/GaN multiple quantum well (MQW) light-emitting diode (LED) with green emission. Recombination of localized excitons was proved to be the main microscopic mechanism of green emission in the sample. The PL dynamics were ascribed to two pathways of the exciton recombination, corresponding to the fast decay and the slow decay, respectively. The origins of slow decay and fast decay were assigned to local compositional fluctuations of indium and thickness variations of InGaN layers, respectively. Furthermore, the contributions of two decay pathways to the green PL were found to vary at different emission photon energy. The fraction of fast decay pathway decreased with decreasing photon energy. The slow radiative PL from deep localized exciton recombination suffered less suppression from non-radiative delocalization process, for the higher requested activation energy. All these results supported a clear microscopy mechanism of excitation-emission process of the green MQW LED structure.

  5. Optimization of TCR and heat transport in group-IV multiple-quantum-well microbolometers

    NASA Astrophysics Data System (ADS)

    Morea, Matthew; Gu, Kevin; Savikhin, Victoria; Fenrich, Colleen S.; Pop, Eric; Harris, James S.

    2016-09-01

    Group-IV semiconductors have the opportunity to have an equivalent or better temperature coefficient of resistance (TCR) than other microbolometer thermistor materials. By using multiple-quantum-well (MQW) structures, their TCR values can be optimized due to a confinement of carriers. Through two approaches - an activation energy approximation and a custom Monte Carlo transfer matrix method - we simulated this effect for a combination of Group-IV semiconductors and their alloys (e.g., SiGe and GeSn) to find the highest possible TCR, while keeping in mind the critical thicknesses of such layers in a MQW epitaxial stack. We calculated the TCR for a critical-thickness-limited Ge0.8Sn0.2/Ge MQW device to be about -1.9 %/K. Although this TCR is lower than similar SiGe/Si MQW thermistors, GeSn offers possible advantages in terms of fabricating suspended devices with its interesting etch-stop properties shown in previous literature. Furthermore, using finite element modeling of heat transport, we looked at another key bolometer parameter: the thermal time constant. The dimensions of a suspended Ge microbolometer's supporting legs were fine-tuned for a target response time of 5 ms, incorporating estimations for the size effects of the nanowire-like legs on thermal conductivity.

  6. Electroabsorption modulators based on bulk GaN films and GaN/AlGaN multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Kao, Chen-Kai; Bhattacharyya, Anirban; Thomidis, Christos; Paiella, Roberto; Moustakas, Theodore D.

    2011-04-01

    Ultraviolet electroabsorption modulators based on bulk GaN films and on GaN/AlGaN multiple quantum wells were developed and characterized. In both types of devices, the absorption edge at room temperature is dominated by excitonic effects and can be strongly modified through the application of an external electric field. In the bulk devices, the applied voltage causes a broadening and quenching of the excitonic absorption, leading to enhanced transmission. In the quantum-well devices, the external field partially cancels the built-in polarization-induced electric fields in the well layers, thereby increasing the absorption. Unlike optical modulators based on smaller-bandgap zinc blende semiconductors, the bulk devices here are shown to provide similar performance levels as the quantum well devices, which is mainly a consequence of the uniquely large exciton binding energies of nitride semiconductors.

  7. VIS-UV ZnCdO/ZnO multiple quantum well nanowires and the quantification of Cd diffusion.

    PubMed

    Lopez-Ponce, M; Nakamura, A; Suzuki, M; Temmyo, J; Agouram, S; Martínez-Tomás, M C; Muñoz-Sanjosé, V; Lefebvre, P; Ulloa, J M; Muñoz, E; Hierro, A

    2014-06-27

    We report on the growth and microstructure analysis of high Cd content ZnCdO/ZnO multiple quantum wells (MQW) within a nanowire. Heterostructures consisting of ten wells with widths from 0.7 to 10 nm are demonstrated, and show photoluminescence emissions ranging from 3.03 to 1.97 eV. The wells with thicknesses ≦̸2 nm have high radiative efficiencies compared to the thickest ones, consistent with the presence of quantum confinement. However, a nanometric analysis of the Cd profile along the heterostructures shows the presence of Cd diffusion from the ZnCdO well to the ZnO barrier. This phenomenon modifies the band structure and the optical properties of the heterostructure, and is considered in order to correctly identify quantum effects in the ZnCdO/ZnO MQWs.

  8. Design and Synthesis of Antiblinking and Antibleaching Quantum Dots in Multiple Colors via Wave Function Confinement.

    PubMed

    Cao, Hujia; Ma, Junliang; Huang, Lin; Qin, Haiyan; Meng, Renyang; Li, Yang; Peng, Xiaogang

    2016-12-07

    Single-molecular spectroscopy reveals that photoluminescence (PL) of a single quantum dot blinks, randomly switching between bright and dim/dark states under constant photoexcitation, and quantum dots photobleach readily. These facts cast great doubts on potential applications of these promising emitters. After ∼20 years of efforts, synthesis of nonblinking quantum dots is still challenging, with nonblinking quantum dots only available in red-emitting window. Here we report synthesis of nonblinking quantum dots covering most part of the visible window using a new synthetic strategy, i.e., confining the excited-state wave functions of the core/shell quantum dots within the core quantum dot and its inner shells (≤ ∼5 monolayers). For the red-emitting ones, the new synthetic strategy yields nonblinking quantum dots with small sizes (∼8 nm in diameter) and improved nonblinking properties. These new nonblinking quantum dots are found to be antibleaching. Results further imply that the PL blinking and photobleaching of quantum dots are likely related to each other.

  9. Photoinduced Single- and Multiple- Electron Dynamics Processes Enhanced by Quantum Confinement in Lead Halide Perovskite Quantum Dots.

    PubMed

    Vogel, Dayton Jon; Kryjevski, Andrei; Inerbaev, Talgat M; Kilin, Dmitri S

    2017-03-21

    Methyl-ammonium lead iodide perovskite (MAPbI3) is a promising material for photovoltaic devices. A modification of the MAPbI3 into confined nanostructures is expected to further increase efficiency of solar energy conversion. Photo-excited dynamic processes in a MAPbI3 quantum dot (QD) have been modeled by many-body perturbation theory and nonadiabatic dynamics. A photoexcitation is followed by either exciton cooling (EC), its radiative (RR) or non-radiative recombination (NRR), or multi-exciton generation (MEG) processes. Computed times of these processes fall in the order of MEG < EC < RR < NRR, where MEG is in the order of a few femtoseconds, EC at the picosecond range while RR and NRR are in the order of nanoseconds. Computed timescales indicate which electronic transition pathways can contribute to increase in charge collection efficiency. Simulated mechanism relaxation rates show that quantum confinement promotes MEG in MAPbI3 QDs.

  10. Photoinduced Single- and Multiple-Electron Dynamics Processes Enhanced by Quantum Confinement in Lead Halide Perovskite Quantum Dots

    DOE PAGES

    Vogel, Dayton J.; Kryjevski, Andrei; Inerbaev, Talgat; ...

    2017-03-21

    Methylammonium lead iodide perovskite (MAPbI3) is a promising material for photovoltaic devices. A modification of MAPbI3 into confined nanostructures is expected to further increase efficiency of solar energy conversion. Photoexcited dynamic processes in a MAPbI3 quantum dot (QD) have been modeled by many-body perturbation theory and nonadiabatic dynamics. A photoexcitation is followed by either exciton cooling (EC), its radiative (RR) or nonradiative recombination (NRR), or multiexciton generation (MEG) processes. Computed times of these processes fall in the order of MEG < EC < RR < NRR, where MEG is on the order of a few femtoseconds, EC is in themore » picosecond range, while RR and NRR are on the order of nanoseconds. Computed time scales indicate which electronic transition pathways can contribute to increase in charge collection efficiency. Simulated mechanisms of relaxation and their rates show that quantum confinement promotes MEG in MAPbI3 QDs.« less

  11. Properties of multiple quantum wells and their use in high-speed detectors and modulators

    NASA Technical Reports Server (NTRS)

    Bhattacharya, Pallab

    1988-01-01

    Quantum well systems lattice matched to GaAs and InP have emerged as important materials for use in long wavelength optoelectronic devices. Intrinsic problems associated with the growth of these quantum wells by molecular beam epitaxy are discussed and the luminescence properties of state-of-art quantum wells, using novel growth techniques are described. Finally, the properties of detectors, modulators and integrated devices made with these heterojunction materials are described and discussed.

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

    SciTech Connect

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

    2014-08-04

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

  13. Quantum dynamics of hydrogen interacting with single-walled carbon nanotubes: multiple H-atom adsorbates.

    PubMed

    McAfee, Jason L; Poirier, Bill

    2011-02-21

    In a previous paper [J. L. McAfee and B. Poirier, J. Chem. Phys. 130, 064701 (2009)], using spin-polarized density functional theory (DFT), the authors reported a binding energy of 0.755 eV, for a single hydrogen atom adsorbed on a pristine (unrelaxed) (5,5) single-walled carbon nanotube (SWNT) substrate. A full three-dimensional (3D) potential energy surface (PES) for the SWNT-H system was also developed, and used in a quantum dynamics calculation to compute all rovibrational bound states, and associated equatorial and longitudinal adsorbate migration rates. A highly pronounced preference for the latter migration pathway at ambient temperatures was observed. In this work, we extend the aforementioned study to include multiple H-atom adsorbates. Extensive DFT calculations are performed, in order to ascertain the most relevant dynamical pathways. For two adsorbates, the SWNT-H-H system is found to exhibit highly site-specific binding, as well as long-range correlation and pronounced binding energy enhancement. The latter effect is even more pronounced in the full-hydrogenation limit, increasing the per-adsorbate binding energy to 2.6 eV. To study migration dynamics, a single-hole model is developed, for which the binding energy drops to 2.11 eV. A global 3D PES is developed for the hole migration model, using 40 radial × 18 cylindrical ab initio geometries, fit to a Fourier basis with radially dependent expansion coefficients (rms error 4.9 meV). As compared with the single-adsorbate case, the hole migration PES does not exhibit separate chemisorption and physisorption wells. The barrier to longitudinal migration is also found to be much lower. Quantum dynamics calculations for all rovibrational states are then performed (using a mixed spectral basis/phase-space optimized discrete variable representation), and used to compute longitudinal migration rates. Ramifications for the use of SWNTs as potential hydrogen storage materials are discussed.

  14. Flowing versus Static Conditions for Measuring Multiple Exciton Generation in PbSe Quantum Dots

    SciTech Connect

    Midgett, Aaron G.; Hillhouse, Hugh W.; Hughes, Barbara K.; Nozik, Arthur J.; Beard, Matthew C.

    2010-09-22

    Recent reports question the validity of pulsed fs-laser experiments for measuring the photon-to-exciton quantum yields (QYs) that result from multiple exciton generation (MEG). The repetitive nature of these experiments opens up an alternative relaxation pathway that may produce artificially high results. We present transient-absorption (TA) data for 4.6 and 6.6 nm diameter PbSe quantum dots (QDs) at a variety of pump photon energies. The data are collected under laminar flow conditions with volumetric flow rates ranging from 0 to 150 mL/min (resulting in Reynolds numbers up to 460). The results are modeled with a spatially resolved population balance of generation, recombination, convective replacement, and accumulation of long-lived excited QDs. By comparing the simulations and experiments, the steady-state population of the long-lived QD-excited states and their kinetics are determined for different experimental conditions. We also improve upon reported photon-to-exciton QYs for PbSe QDs. We find differences in the observed TA dynamics between flowing and static conditions that depend upon photon fluence, pump photon energy, and quality of the QD surfaces. For excitation energies below 2 Eg, independent of QD size or photon fluence, we observe no flow rate dependence in the TA dynamics. At excitation energies of hν > 3 Eg, we observe differences between static and flowing conditions that are most pronounced for high photon fluences. At 3.7 Eg and for 4.6 nm PbSe QDs we find a QY of 1.2 ± 0.1 and at 4.5 Eg the QY is 1.55 ± 0.05. With 6.6 nm QDs excited at 4.7 Eg we observe no difference between static and flowing conditions and find a QY of 1.61 ± 0.05. We also find that by treating the surface of QDs, we can decrease the charging probability (Pg ≈ 5 × 10-5) by a factor of 3-4. The observed variations suggest that different QD samples vary regarding their susceptibility to the

  15. Synthesis, crystal structure analysis, spectral (NMR, FT-IR, FT-Raman and UV-Vis) investigations, molecular docking studies, antimicrobial studies and quantum chemical calculations of a novel 4-chloro-8-methoxyquinoline-2(1H)-one: An effective antimicrobial agent and an inhibition of DNA gyrase and lanosterol-14α-demethylase enzymes

    NASA Astrophysics Data System (ADS)

    Murugavel, S.; Sundramoorthy, S.; Lakshmanan, D.; Subashini, R.; Pavan Kumar, P.

    2017-03-01

    The novel title compound 4-chloro-8-methoxyquinoline-2(1H)-one (4CMOQ) has been synthesized by slow evaporation solution growth technique at room temperature. The synthesized 4CMOQ molecule was characterized experimentally by FT-IR, FT-Raman, UV-Vis, NMR and single crystal diffraction (XRD) and theoretically by quantum chemical calculations. The molecular geometry was also optimized using density functional theory (DFT/B3LYP) method with the 6-311++G (d,p) basis set in ground state and compared with the experimental data. The entire vibrational assignments of wave numbers were made on the basis of potential energy distribution (PED) by VEDA 4 programme. The nuclear magnetic resonance spectra (1H and 13C NMR) are obtained by using the gauge-invariant atomic orbital (GIAO) method. The change in electron density (ED) in the antibonding orbital's and stabilization energies E(2) of the molecule have been evaluated by natural bond orbital (NBO) analysis to give clear evidence of stabilization. Moreover, electronic characteristics such as HOMO and LUMO energies, Mulliken atomic charges and molecular electrostatic potential surface are investigated. Absorption spectrum analysis, nonlinear optical properties, chemical reactivity descriptors and thermodynamic features are also outlined theoretically. Molecular docking studies were executed to understand the inhibitory activity of 4CMOQ against DNA gyrase and Lanosterol 14 α-demethylase. The antimicrobial activity of 4CMOQ was determined against bacterial strains such as Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa and fungal strains such as Aspergillus niger, Monascus purpureus and Penicillium citrinum. The obtained results show that the compound exhibited good to moderate antimicrobial activity.

  16. Ultrafast carrier capture and Auger recombination in single GaN/InGaN multiple quantum well nanowires

    DOE PAGES

    Boubanga-Tombet, Stephane; Wright, Jeremy B.; Lu, Ping; ...

    2016-11-04

    Ultrafast optical microscopy is an important tool for examining fundamental phenomena in semiconductor nanowires with high temporal and spatial resolution. In this paper, we used this technique to study carrier dynamics in single GaN/InGaN core–shell nonpolar multiple quantum well nanowires. We find that intraband carrier–carrier scattering is the main channel governing carrier capture, while subsequent carrier relaxation is dominated by three-carrier Auger recombination at higher densities and bimolecular recombination at lower densities. Finally, the Auger constants in these nanowires are approximately 2 orders of magnitude lower than in planar InGaN multiple quantum wells, highlighting their potential for future light-emitting devices.

  17. Ultrafast carrier capture and Auger recombination in single GaN/InGaN multiple quantum well nanowires

    SciTech Connect

    Boubanga-Tombet, Stephane; Wright, Jeremy B.; Lu, Ping; Williams, Michael R. C.; Li, Changyi; Wang, George T.; Prasankumar, Rohit P.

    2016-11-04

    Ultrafast optical microscopy is an important tool for examining fundamental phenomena in semiconductor nanowires with high temporal and spatial resolution. In this paper, we used this technique to study carrier dynamics in single GaN/InGaN core–shell nonpolar multiple quantum well nanowires. We find that intraband carrier–carrier scattering is the main channel governing carrier capture, while subsequent carrier relaxation is dominated by three-carrier Auger recombination at higher densities and bimolecular recombination at lower densities. Finally, the Auger constants in these nanowires are approximately 2 orders of magnitude lower than in planar InGaN multiple quantum wells, highlighting their potential for future light-emitting devices.

  18. One dimensional 1H, 2H and 3H

    NASA Astrophysics Data System (ADS)

    Vidal, A. J.; Astrakharchik, G. E.; Vranješ Markić, L.; Boronat, J.

    2016-05-01

    The ground-state properties of one-dimensional electron-spin-polarized hydrogen 1H, deuterium 2H, and tritium 3H are obtained by means of quantum Monte Carlo methods. The equations of state of the three isotopes are calculated for a wide range of linear densities. The pair correlation function and the static structure factor are obtained and interpreted within the framework of the Luttinger liquid theory. We report the density dependence of the Luttinger parameter and use it to identify different physical regimes: Bogoliubov Bose gas, super-Tonks-Girardeau gas, and quasi-crystal regimes for bosons; repulsive, attractive Fermi gas, and quasi-crystal regimes for fermions. We find that the tritium isotope is the one with the richest behavior. Our results show unambiguously the relevant role of the isotope mass in the properties of this quantum system.

  19. Monolithic strained-InGaAsP multiple-quantum-well lasers with integrated electroabsorption modulators for active mode locking

    NASA Astrophysics Data System (ADS)

    Sato, Kenji; Wakita, Koichi; Kotaka, Isamu; Kondo, Yasuhiro; Yamamoto, Mitsuo; Takada, Atsushi

    1994-07-01

    Active mode locking by monolithic lasers with integrated electroabsorption modulators using strained-InGaAsP multiple quantum wells is described. The electroabsorption modulator acts as a short optical gate when a sinusoidal voltage is driven at a deep bias point. Pulse widths as short as 2 ps have been obtained at a repetition rate of 16.3 GHz for a 2.5-mm-long monolithic laser.

  20. Plasma Heating in Highly Excited GaN/AlGaN Multiple Quantum Wells

    SciTech Connect

    Botchkarev, A; Chow, W W; Jiang, H X; Lin, J Y; Mair, R; Morkoc, H; Zeng, K C

    1998-10-09

    Plasma Heating in Highly Excited GaN/AIGaN Multiple Quantum @@lvEu Wells w f + 1998 %p, K. C. Zeng, R. Mair, J. Y. Liz and H. X. Jiang a) ` fabrication and understanding of MQW lasers [2-5]. For the design of these lasers, one on RT optical studies. Our results revealed that in the GaN/AIGaN MQWS, plasma heating strongly effects the carrier distribution between the confined and unconfined band-to-band and fke excitonic transitions [7]. In the MQW sample under low the unconfined states as determined from the band structure. sample under high Lxc, we varied the excitation intensity by one order of magnitude from 0.110 to IO. The carrier density is estimated to be about N=1012/cm2 (at UC= 0.1 Io) to 1013/cm2 (at 1=== l.). We plotted the PL spectra for four representative excitation fimction of injected carrier density N (open squares). The ratio starts at a value of about 18% for N=1012/cm2 (& = O. lb), and reaches a value over 64 `XO for N=1013/cm2 (& = regions is a loss to optical gain. The carrier density is ve~ high in our experiment and an electron-hole plasma (EHP) state is expected. Because the carrier transfer process plasma temperature. The laser pump energy is about 4.3 eV, which is far above the energy band gap of the sample studied here. This may result in a hot carrier population carrier densities and plasma temperatures. Using a phenomenological expression based The calculated ratio of carriers in the unconfked to the confined states (Ima~ kf) as a finction of carrier density at different temperatures are plotted in Fig. 3 (solid lines). The figure shows that the experiment results can only be explained by plasma heating of the injected carriers at high & ( TP > TJ. The transparency carrier densities for GaN/AIXGal.XN MQW structures with well thickness from 2 to 4 nm were calculated to be around 1x 1012/cm2 [10]. It is thus obvious from Fig. 3 that under high carrier injection density above the transparency density, the plasma temperature, TP, is no

  1. The role of phases and their interplay in molecular vibrational quantum computing with multiple qubits

    NASA Astrophysics Data System (ADS)

    Troppmann, Ulrike; Gollub, Caroline; de Vivie-Riedle, Regina

    2006-06-01

    Within the scope of molecular quantum computing with vibrational qubits, we analyse the impact of phases that are present during the quantum computation processes. While the phase relation in superposition states and its temporal evolution are crucial to any implementation of quantum computing, we elucidate the special challenge that emerges for phase control of qubits encoded in molecular vibrational eigenstates. Phase correctly prepared superposition states in general exist only for a finite time and with the inherent entanglement in molecular vibrational qubit systems their development displays a complex pattern. We show that the free relative phase evolution in such qubit systems can be utilized for the implementation of quantum phase gates. Moreover, a practical experimental realization of phase correct quantum gates acting on molecular vibrational qubits could be accomplished by a decomposition into laser-induced population transfer and free evolution phase gates. This concept adds to the flexibility in the implementation of quantum gate sequences and algorithms. A modification, where only a reduced number of selected relative phases needs to be adjusted, will make this scheme more robust and versatile. Finally, we also disclose and discuss another key feature for the implementation of phase correct quantum gates, i.e. the dependence of the quantum gate fidelity on the absolute or carrier-envelope phase of the driving femtosecond laserfield.

  2. Performance analysis of quantum access network using code division multiple access model

    NASA Astrophysics Data System (ADS)

    Hu, Linxi; Yang, Can; He, Guangqiang

    2017-06-01

    Not Available Project supported by the National Natural Science Foundation of China (Grant Nos. 61475099 and 61102053), the Program of State Key Laboratory of Quantum Optics and Quantum Optics Devices (Grant No. KF201405), the Open Fund of IPOC (BUPT) (Grant No. IPOC2015B004), and the Program of State Key Laboratory of Information Security (Grant No. 2016-MS-05).

  3. Time domain terahertz spectroscopy of semiconductor bulk and multiple quantum wells structures

    NASA Astrophysics Data System (ADS)

    Chen, Yue

    A time-domain terahertz spectroscopic system with high source power (average power > 10 nW) and high signal-to- noise ratio (>104) was developed and used to study ultrafast electronic processes in semiconductor structures. The physics of the spectroscopy, the theoretical basis of the interferometry, the model of the electron-electromagnetic field interaction, and the principle of experimental data processing are presented. The first direct measurement of the intervalley scattering time in In 0.53Ga0.47As was performed. The intervalley scattering time constants obtained were τLΓ = 35 fs and τLΓ = 450 fs. The spectroscopic data showed that at low carrier density the carrier- carrier scattering is unimportant. The intervalley deformation potential was obtained from the measured intervalley scattering time constant τ LΓ. The transient conductivity was obtained using time-domain terahertz spectroscopy. The frequency dependent terahertz spectroscopy enabled us to uniquely determine the transient mobility and density. The transient electron mobility is ~5200 cm2/Vs, which is less than the Hall mobility. For large photocarrier densities, this discrepancy is attributed to the additional momentum relaxation associated with electron-hole scattering. Using pump pulses with wavelength of 810 run, the electron trapping time in low-temperature-grown GaAs was accurately determined. The measured trapping time is slightly larger than that observed from a band-edge pump- probe measurements. We argue that the terahertz technique provides the most reliable measure of carrier lifetime due to the unique interaction. The carrier dynamics of low-temperature-grown InGaAs bulk and InGaAs/InAlAs multiple quantum wells were investigated. We were able to differentiate the two dominant mechanisms in the electron decay process, trapping and recombination. A trapping time as fast as 1.3-2.6 ps was observed for photo-excited electrons. The effects of Be-doping and growth temperature on the

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

    PubMed

    Yang, Xf; Liu, Ys

    2010-05-22

    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.

  5. Optical Control of Intersubband Absorption in a Multiple Quantum Well-Embedded Semiconductor Microcravity

    NASA Technical Reports Server (NTRS)

    Liu, Ansheng; Ning, Cun-Zheng

    2000-01-01

    Optical intersubband response of a multiple quantum well (MQW)-embedded microcavity driven by a coherent pump field is studied theoretically. The n-type doped MQW structure with three subbands in the conduction band is sandwiched between a semi-infinite medium and a distributed Bragg reflector (DBR). A strong pump field couples the two upper subbands and a weak field probes the two lower subbands. To describe the optical response of the MQW-embedded microcavity, we adopt a semi-classical nonlocal response theory. Taking into account the pump-probe interaction, we derive the probe-induced current density associated with intersubband transitions from the single-particle density-matrix formalism. By incorporating the current density into the Maxwell equation, we solve the probe local field exactly by means of Green's function technique and the transfer-matrix method. We obtain an exact expression for the probe absorption coefficient of the microcavity. For a GaAs/Al(sub x)Ga(sub 1-x)As MQW structure sandwiched between a GaAs/AlAs DBR and vacuum, we performed numerical calculations of the probe absorption spectra for different parameters such as pump intensity, pump detuning, and cavity length. We find that the probe spectrum is strongly dependent on these parameters. In particular, we find that the combination of the cavity effect and the Autler-Townes effect results in a triplet in the optical spectrum of the MQW system. The optical absorption peak value and its location can be feasibly controlled by varying the pump intensity and detuning.

  6. Multiple quantum filtered 23Na NMR in the Langendorff perfused mouse heart: Ratio of triple/double quantum filtered signals correlates with [Na]i

    PubMed Central

    Eykyn, Thomas R.; Aksentijević, Dunja; Aughton, Karen L.; Southworth, Richard; Fuller, William; Shattock, Michael J.

    2015-01-01

    We investigate the potential of multiple quantum filtered (MQF) 23Na NMR to probe intracellular [Na]i in the Langendorff perfused mouse heart. In the presence of Tm(DOTP) shift reagent the triple quantum filtered (TQF) signal originated largely from the intracellular sodium pool with a 32 ± 6% contribution of the total TQF signal arising from extracellular sodium, whilst the rank 2 double-quantum filtered signal (DQF), acquired with a 54.7° flip-angle pulse, originated exclusively from the extracellular sodium pool. Given the different cellular origins of the 23Na MQF signals we propose that the TQF/DQF ratio can be used as a semi-quantitative measure of [Na]i in the mouse heart. We demonstrate a good correlation of this ratio with [Na]i measured with shift reagent at baseline and under conditions of elevated [Na]i. We compare the measurements of [Na]i using both shift reagent and TQF/DQF ratio in a cohort of wild type mouse hearts and in a transgenic PLM3SA mouse expressing a non-phosphorylatable form of phospholemman, showing a modest but measurable elevation of baseline [Na]i. MQF filtered 23Na NMR is a potentially useful tool for studying normal and pathophysiological changes in [Na]i, particularly in transgenic mouse models with altered Na regulation. PMID:26196304

  7. Multiple quantum filtered (23)Na NMR in the Langendorff perfused mouse heart: Ratio of triple/double quantum filtered signals correlates with [Na]i.

    PubMed

    Eykyn, Thomas R; Aksentijević, Dunja; Aughton, Karen L; Southworth, Richard; Fuller, William; Shattock, Michael J

    2015-09-01

    We investigate the potential of multiple quantum filtered (MQF) (23)Na NMR to probe intracellular [Na]i in the Langendorff perfused mouse heart. In the presence of Tm(DOTP) shift reagent the triple quantum filtered (TQF) signal originated largely from the intracellular sodium pool with a 32±6% contribution of the total TQF signal arising from extracellular sodium, whilst the rank 2 double-quantum filtered signal (DQF), acquired with a 54.7° flip-angle pulse, originated exclusively from the extracellular sodium pool. Given the different cellular origins of the (23)Na MQF signals we propose that the TQF/DQF ratio can be used as a semi-quantitative measure of [Na]i in the mouse heart. We demonstrate a good correlation of this ratio with [Na]i measured with shift reagent at baseline and under conditions of elevated [Na]i. We compare the measurements of [Na]i using both shift reagent and TQF/DQF ratio in a cohort of wild type mouse hearts and in a transgenic PLM(3SA) mouse expressing a non-phosphorylatable form of phospholemman, showing a modest but measurable elevation of baseline [Na]i. MQF filtered (23)Na NMR is a potentially useful tool for studying normal and pathophysiological changes in [Na]i, particularly in transgenic mouse models with altered Na regulation.

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

    SciTech Connect

    Yang, Jing; Zhao, Degang Jiang, Desheng; Chen, Ping; Zhu, Jianjun; Liu, Zongshun; Le, Lingcong; He, Xiaoguang; Li, Xiaojing; Wang, Hui; Yang, Hui; Jahn, Uwe

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    We theoretically analyze the Einstein-Podolsky-Rosen (EPR) correlation, the quadrature squeezing, and the continuous-variable quantum teleportation when considering non-Gaussian entangled states generated by applying multiple-photon subtraction and multiple-photon addition to a two-mode squeezed vacuum state (TMSVs). Our results indicate that in the case of the multiple-photon-subtracted TMSVs with symmetric operations, the corresponding EPR correlation, the two-mode squeezing degree, the sum squeezing, and the fidelity of teleporting a coherent state or a squeezed vacuum state can be enhanced for any squeezing parameter r and these enhancements increase with the number of subtracted photons in the low-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 the case of teleporting a squeezed vacuum state does the symmetric photon addition make somewhat of an improvement in the fidelity for large-squeezing parameters. In addition, we analytically prove that a one-mode multiple-photon-subtracted TMSVs is equivalent to that of the one-mode multiple-photon-added one. And one-mode multiple-photon operations will diminish the above four quantities for any squeezing parameter r .

  10. In-plane commensurate GaN/AlN junctions: Single-layer composite structures, single and multiple quantum wells and quantum dots

    NASA Astrophysics Data System (ADS)

    Onen, A.; Kecik, D.; Durgun, E.; Ciraci, S.

    2017-04-01

    In-plane composite structures constructed of the stripes or core/shells of single-layer GaN and AlN, which are joined commensurately, display a diversity of electronic properties that can be tuned by the size of their constituents. In heterostructures, the dimensionality of the electrons changes from two dimensional (2D) to one dimensional (1D) upon their confinements in wide constituent stripes, leading to the type-I band alignment and hence multiple quantum well structure in the direct space. The δ doping of one wide stripe by another narrow stripe results in local narrowing or widening of the band gap. A single quantum well structure is acquired from the finite-size AlN-GaN-AlN junctions. In a patterned array of GaN/AlN core/shells, the dimensionality of the electronic states is reduced from two dimensional to zero dimensional, forming multiple quantum dots in large GaN cores, while 2D electrons propagate in multiply connected AlN shell as if they are in a supercrystal. A consistent and detailed discussion of the effects of confinement in momentum and direct spaces is provided. As a result of confinement, the variation of the band gap in the direct space is found to be rather different from the edges of the conduction and valence bands inferred from the band edges of constituent 2D single-layer GaN and AlN. Even if all the results in this study pertain to the free-standing single-layer composite structures, the effects of the different substrates over which these composites can grow are examined in detail. This study unveils the potential of composite structures in designing novel nanomaterials. These predictions are obtained from first-principles calculations based on density functional theory on 2D GaN and AlN compound semiconductors which were synthesized recently.

  11. 19F single-quantum and 19F-33S heteronuclear multiple-quantum coherence NMR of SF6 in thermotropic nematogens and in the gas phase.

    PubMed

    Tervonen, Henri; Saunavaara, Jani; Ingman, L Petri; Jokisaari, Jukka

    2006-08-24

    (19)F single-quantum (SQC) and (19)F-(33)S heteronuclear multiple-quantum coherence (HMQC) NMR spectroscopy of sulfur hexafluoride (SF(6)) dissolved in thermotropic liquid crystals (TLCs) were used to investigate the properties of TLCs. On one hand, environmental effects on the NMR parameters of SF(6), (19)F nuclear shielding, (19)F-(33)S spin-spin coupling, secondary isotope effects of sulfur on (19)F shielding, and the self-diffusion coefficient in the direction of the external magnetic field were studied as well. The temperature dependence of the (19)F shielding of SF(6) in TLCs was modeled with a function that takes into account the properties of both TLC and SF(6). It appears that the TLC environment deforms the electronic system of SF(6) so that the (19)F shielding tensor becomes slightly anisotropic, with the anisotropy being from -0.5 to -1.4 ppm, depending upon the TLC solvent. On the contrary, no sign of residual dipolar coupling between (19)F and (33)S was found, meaning that the so-called deformational effects, which arise from the interaction between vibrational and reorientational motions of the molecule, on the geometry of the molecule are insignificant. Diffusion activation energies, E(a), were determined from the temperature dependence of the self-diffusion coefficients. In each TLC, E(a) increases when moving from an isotropic phase to a nematic phase. The spin-spin coupling constant, J((19)F,(33)S), increases by ca. 10 Hz when moving from the gas phase to TLC solutions. The secondary isotope shifts of (19)F shielding are practically independent of TLC solvent and temperature. For the first time, (19)F-(33)S heteronuclear multiple-quantum NMR spectra were recorded for SF(6) in the gas phase and in a liquid-crystalline solution.

  12. High efficiency InGaN/GaN light emitting diodes with asymmetric triangular multiple quantum wells

    SciTech Connect

    Chang, Chiao-Yun; Li, Hen; Lu, Tien-Chang

    2014-03-03

    In this study, we demonstrated high efficiency InGaN/GaN light emitting diodes (LEDs) with asymmetric triangular multiple quantum wells (MQWs). Asymmetric triangular MQWs not only contribute to uniform carrier distribution in InGaN/GaN MQWs but also yield a low Auger recombination rate. In addition, asymmetric triangular MQWs with gallium face-oriented inclination band profiles can be immune from the polarization charge originating from typical c-plane InGaN/GaN quantum well structures. In the experiment, LEDs incorporated with asymmetric triangular MQWs with gallium face-oriented inclination band profiles exhibited a 60.0% external quantum efficiency at 20 mA and a 27.0% efficiency droop at 100 mA (corresponding to a current density of 69 A/cm{sup 2}), which accounted for an 11.7% efficiency improvement and a 31.1% droop reduction compared with symmetric square quantum well structure LEDs.

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

    PubMed

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

    2016-06-03

    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.

  14. Multiple Metamagnetic Quantum Criticality in Sr3 Ru2 O7

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Optimizing the multiple quantum well thickness of an InGaN blue light emitting diode

    NASA Astrophysics Data System (ADS)

    Xu, Bing; Zhao, Jun Liang; Wang, Shu Guo; Dai, Hai Tao; Yu, Sheng-Fu; Lin, Ray-Ming; Chu, Fu-Chuan; Huang, Chou-Hsiung; Sun, Xiao Wei

    2013-03-01

    InGaN/GaN blue light emitting diodes with varied quantum well thickness from 2.4 nm to 3.6 nm are fabricated and characterized by atmosphere pressure metalorganic chemical vapor deposition (AP-MOCVD). Experimental results show that the exciton localization effect is enhanced from 21.76 to 23.48 by increasing the quantum well thickness from 2.4 nm to 2.7 nm. However, with the further increase of quantum well thickness, the exciton localization effect becomes weaker. Meanwhile, the peak wavelength of electroluminescence redshift with the increase of well thickness due to the larger quantum confined Stark effect (QCSE). In addition, the efficiency droop can be improved by increasing the well thickness.

  17. Quantum Darwinism

    SciTech Connect

    Zurek, Wojciech H

    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.

  18. Optically controlled reflection modulator using GaAs-AlGaAs n-i-p-i/multiple-quantum-well structures

    NASA Technical Reports Server (NTRS)

    Law, K.-K.; Simes, R. J.; Coldren, L. A.; Gossard, A. C.; Maserjian, J.

    1989-01-01

    An optically controlled reflection modulator has been demonstrated that consists of a combination of a GaAs-AlGaAs n-i-p-i doping structure with a multiple-quantum-well structures on top of a distributed Bragg reflector, all grown by MBE. A modulation of approximately 60 percent is obtained on the test structure, corresponding to a differential change of absorption coefficient in the quantum wells of approximately 7500/cm. Changes in reflectance can be observed with a control beam power as low as 1.5 microW. This device structure has the potential of being developed as an optically addressed spatial light modulator for optical information processing.

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

    PubMed

    Parigi, Valentina; D'Ambrosio, Vincenzo; Arnold, Christophe; Marrucci, Lorenzo; Sciarrino, Fabio; Laurat, Julien

    2015-07-13

    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.

  20. Picosecond excitonic absorption recovery of 100 nm GaAs/AlGaAs narrow multiple quantum-well wires

    NASA Astrophysics Data System (ADS)

    Tackeuchi, Atsushi; Kitada, Hideki; Arimoto, Hiroshi; Sugiyama, Yoshihiro; Endoh, Akira; Nakata, Yoshiaki; Inata, Tsuguo; Muto, Shunichi

    1991-08-01

    We report the time-resolved absorption measurement of narrow multiple quantum-well (MQW) wires to investigate their fast recoveries from excitonic absorption bleaching. Wires down to 130 nm were fabricated from MQWs using focused ion beam lithography and electron cyclotron-resonance chlorine-plasma etching. In this structure, the photoexcited carriers diffuse toward the sidewalls and recombine on the surface of the sidewalls. We show that the strong optical nonlinearity of excitons is preserved, even in wires of 130 nm width, and having a fast recovery time in the picosecond region. We also briefly discuss the possibility of making quantum wires which have a faster recovery time and larger optical nonlinearity.

  1. Characterization of heroin samples by 1H NMR and 2D DOSY 1H NMR.

    PubMed

    Balayssac, Stéphane; Retailleau, Emmanuel; Bertrand, Geneviève; Escot, Marie-Pierre; Martino, Robert; Malet-Martino, Myriam; Gilard, Véronique

    2014-01-01

    Twenty-four samples of heroin from different illicit drug seizures were analyzed using proton Nuclear Magnetic Resonance ((1)H NMR) and two-dimensional diffusion-ordered spectroscopy (2D DOSY) (1)H NMR. A careful assignment and quantification of (1)H signals enabled a comprehensive characterization of the substances present in the samples investigated: heroin, its main related impurities (6-acetylmorphine, acetylcodeine, morphine, noscapine and papaverine) and cutting agents (caffeine and acetaminophen in nearly all samples as well as lactose, lidocaine, mannitol, piracetam in one sample only), and hence to establish their spectral signatures. The good agreement between the amounts of heroin, noscapine, caffeine and acetaminophen determined by (1)H NMR and gas chromatography, the reference method in forensic laboratories, demonstrates the validity of the (1)H NMR technique. In this paper, 2D DOSY (1)H NMR offers a new approach for a whole characterization of the various components of these complex mixtures.

  2. Multiple Exciton Generation Solar Cells Using CdSe Quantum Dots

    NASA Astrophysics Data System (ADS)

    Gebreselassie, Haftom Mesfin; Sharma, R. B.; Chander, Nikhil

    2011-10-01

    Experimental and Simulation works of Nanostructured Solar Cells Using CdSe Quantum Dots have been analyzed and investigated. CdSe quantum dots have been synthesized from non coordinating and high boiling solvent Octadecene and a series of increasing CdSe particle sizes are produced. The synthesized CdSe quantum dots are highly examined under a Transmission Electron Microscope and four images of different sizes of CdSe quantum dots (5.8 nm, 6.4 nm, 7.0 nm and 7.7 nm) have been obtained. A 1.1×1.1 cm2 TiO2 electrode is prepared using indium tin oxide conducting glass and TiO2 nanoparticles. The Oleic acid terminated CdSe quantum dots are separated from the octadecene by using 100% ethanol and centrifuge machine of spin about 4000 rpm until the shaking gave no longer suspension. The CdSe quantum dot (5.8 nm) was adsorbed on TiO2 photoelectrode and used as sensitizer. The relationship of Bandgap energy, Emission wavelength with respect to quantum dot size have been simulated and investigated. In this paper work, a sandwich type cell configuration which is made up of TiO2 photoelectrode, graphite coated counter electrode, an electrolyte of iodine and potassium iodide have been used. This sandwich type cell has been exposed to sun light and we have achieved 0.32 V and 0.2 mA cm-2 of potential difference and current respectively.

  3. Enhanced Y1H Assays for Arabidopis

    USDA-ARS?s Scientific Manuscript database

    Transcription regulation plays a key role in development and response to environment. To understand this mechanism, we need to know which transcription factor (TFs) would bind to which promoter, thus regulate their target gene expression. Yeast one-hybrid (Y1H) technique can be used to map this kind...

  4. High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates

    SciTech Connect

    Bryan, Zachary Bryan, Isaac; Sitar, Zlatko; Collazo, Ramón; Xie, Jinqiao; Mita, Seiji

    2015-04-06

    The internal quantum efficiency (IQE) of Al{sub 0.55}Ga{sub 0.45}N/AlN and Al{sub 0.55}Ga{sub 0.45}N/Al{sub 0.85}Ga{sub 0.15}N UVC MQW structures was analyzed. The use of bulk AlN substrates enabled us to undoubtedly distinguish the effect of growth conditions, such as V/III ratio, on the optical quality of AlGaN based MQWs from the influence of dislocations. At a high V/III ratio, a record high IQE of ∼80% at a carrier density of 10{sup 18 }cm{sup −3} was achieved at ∼258 nm. The high IQE was correlated with the decrease of the non-radiative coefficient A and a reduction of midgap defect luminescence, all suggesting that, in addition to dislocations, point defects are another major factor that strongly influences optical quality of AlGaN MQW structures.

  5. 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

    SciTech Connect

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

    2015-09-28

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

  6. Strong electronic interaction and multiple quantum Hall ferromagnetic phases in trilayer graphene

    NASA Astrophysics Data System (ADS)

    Datta, Biswajit; Dey, Santanu; Samanta, Abhisek; Agarwal, Hitesh; Borah, Abhinandan; Watanabe, Kenji; Taniguchi, Takashi; Sensarma, Rajdeep; Deshmukh, Mandar M.

    2017-02-01

    Quantum Hall effect provides a simple way to study the competition between single particle physics and electronic interaction. However, electronic interaction becomes important only in very clean graphene samples and so far the trilayer graphene experiments are understood within non-interacting electron picture. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism seen in Bernal-stacked trilayer graphene. Due to high mobility ~500,000 cm2 V-1 s-1 in our device compared to previous studies, we find all symmetry broken states and that Landau-level gaps are enhanced by interactions; an aspect explained by our self-consistent Hartree-Fock calculations. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of quantum Hall ferromagnetic states at low magnetic field.

  7. Strong electronic interaction and multiple quantum Hall ferromagnetic phases in trilayer graphene.

    PubMed

    Datta, Biswajit; Dey, Santanu; Samanta, Abhisek; Agarwal, Hitesh; Borah, Abhinandan; Watanabe, Kenji; Taniguchi, Takashi; Sensarma, Rajdeep; Deshmukh, Mandar M

    2017-02-20

    Quantum Hall effect provides a simple way to study the competition between single particle physics and electronic interaction. However, electronic interaction becomes important only in very clean graphene samples and so far the trilayer graphene experiments are understood within non-interacting electron picture. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism seen in Bernal-stacked trilayer graphene. Due to high mobility ∼500,000 cm(2 )V(-1 )s(-1) in our device compared to previous studies, we find all symmetry broken states and that Landau-level gaps are enhanced by interactions; an aspect explained by our self-consistent Hartree-Fock calculations. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of quantum Hall ferromagnetic states at low magnetic field.

  8. Strong electronic interaction and multiple quantum Hall ferromagnetic phases in trilayer graphene

    PubMed Central

    Datta, Biswajit; Dey, Santanu; Samanta, Abhisek; Agarwal, Hitesh; Borah, Abhinandan; Watanabe, Kenji; Taniguchi, Takashi; Sensarma, Rajdeep; Deshmukh, Mandar M.

    2017-01-01

    Quantum Hall effect provides a simple way to study the competition between single particle physics and electronic interaction. However, electronic interaction becomes important only in very clean graphene samples and so far the trilayer graphene experiments are understood within non-interacting electron picture. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism seen in Bernal-stacked trilayer graphene. Due to high mobility ∼500,000 cm2 V−1 s−1 in our device compared to previous studies, we find all symmetry broken states and that Landau-level gaps are enhanced by interactions; an aspect explained by our self-consistent Hartree–Fock calculations. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of quantum Hall ferromagnetic states at low magnetic field. PMID:28216666

  9. Efficiency enhancement of InGaN/GaN multiple quantum well solar cells using CdS quantum dots and distributed Bragg reflectors

    NASA Astrophysics Data System (ADS)

    Tsai, Yu-Lin; Lin, Chien-Chung; Han, Hau-Vei; Chen, Hsin-Chu; Chen, Kuo-Ju; Lai, Wei-Chi; Sheu, Jin-Kong; Lai, Fang-I.; Yu, Peichen; Kuo, Hao-Chung

    2013-03-01

    In recent year, InGaN-based alloy was also considered for photovoltaic devices owing to the distinctive material properties which are benefit photovoltaic performance. However, the Indium tin oxide (ITO) layer on top, which plays a role of transparent conductive oxide (TCO), can absorb UV photons without generating photocurrent. Also, the thin absorber layer in the device, which is consequent result after compromising with limited crystal quality, has caused insufficient light absorption. In this report, we propose an approach for solving these problems. A hybrid design of InGaN/GaN multiple quantum wells (MQWs) solar cells combined with colloidal CdS quantum dots (QDs) and back side distributed Bragg reflectors (DBRs) has been demonstrated. CdS QDs provide down-conversion effect at UV regime to avoid absorption of ITO. Moreover, CdS QDs also exhibit anti-reflective feature. DBRs at the back side have effectively reflected the light back into the absorber layer. CdS QDs enhance the external quantum efficiency (EQE) for light with wavelength shorter than 400 nm, while DBRs provide a broad band enhancement in EQE, especially within the region of 400 nm ~ 430 nm in wavelength. CdS QDs effectively achieved a power conversion efficiency enhancement as high as 7.2% compared to the device without assistance of CdS QDs. With the participation of DBRs, the power conversion efficiency enhancement has been further boosted to 14%. We believe that the hybrid design of InGaN/GaN MQWs solar cells with QDs and DBRs can be a method for high efficiency InGaN/GaN MQWs solar cells.

  10. A core-multiple shell nanostructure enabling concurrent upconversion and quantum cutting for photon management.

    PubMed

    Shao, Wei; Chen, Guanying; Ohulchanskyy, Tymish Y; Yang, Chunhui; Ågren, Hans; Prasad, Paras N

    2017-02-02

    Photon management enables the manipulation of the number of input photons by conversion of two or more light quanta into one (upconversion) or vice versa (quantum cutting). Simultaneous realization of both these processes in a single unit provides unique opportunities of efficient utilization of photons throughout a broad spectral range. Yet, concurrent realization of these two parallel optical processes in one single unit remains elusive, limiting its impact on many existing or possible future applications such as for panchromatic photovoltaics. Here, we describe an epitaxial active core/inert shell/active shell/inert shell fluoride nanostructure to implement upconversion and quantum cutting within spatially confined and isolated rare-earth-doped active domains. The core area transforms infrared photons through trivalent erbium (Er(3+)) ions into three- and two-photon upconverted visible and near infrared luminescence, while the second shell domain splits an excitation photon into two near infrared photons through cooperative quantum cutting from one trivalent terbium ion (Tb(3+)) to two trivalent ytterbium ions (Yb(3+)). The inert layer in between the active domains is able to effectively suppress the destructive interference between upconversion and quantum cutting, while the outermost inert shell is able to eliminate surface-related quenching. This design enables the colloidal core/multishell nanoparticles to have an upconversion quantum yield of ∼1.6%, and to have a luminescence yield of the quantum cutting process as high as ∼130%. This work constitutes a solid step for flexible photon management in a single nanostructure, and has an implication for photonic applications beyond photovoltaics.

  11. Photogalvanic effects for interband transition in p-Si0.5Ge0.5/Si multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Wei, C. M.; Cho, K. S.; Chen, Y. F.; Peng, Y. H.; Chiu, C. W.; Kuan, C. H.

    2007-12-01

    Circular photogalvanic effect (CPGE) and linear photogalvanic effect for interband transition have been observed simultaneously in Si0.5Ge0.5/Si multiple quantum wells. The signature of the CPGE is evidenced by the change of its sign upon reversing the radiation helicity. It is found that the observed CPGE photocurrent is an order of magnitude greater than that obtained for intersubband transition. The dependences of the CPGE on the angle of incidence and the excitation intensities can be well interpreted based on its characteristics. The large signal of spin generation observed here at room temperature should be very useful for the realization of practical application of spintronics.

  12. An optically detectable CO2 sensor utilizing polyethylenimine and starch functionalized InGaN/GaN multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Chen, Y. C.; Shih, H. Y.; Chen, J. Y.; Tan, W. J.; Chen, Y. F.

    2013-07-01

    An optically detectable gas sensor based on the high surface sensitivity of functionalized polyethylenimine/starch In0.15Ga0.85N/GaN strained semiconductor multiple quantum wells (MQWs) has been developed. Due to the excellent piezoelectricity of the MQWs, the change of surface charges caused by chemical interaction can introduce a strain and induce an internal field. In turn, it tilts the energy levels of the MQWs and modifies the optical properties. Through the measurement of the changes in photoluminescence as well as Raman scattering spectra under different concentrations of carbon dioxide gas, we demonstrate the feasibility and high sensitivity of the sensors derived from our methodology.

  13. Quantum-noise quenching in the correlated spontaneous-emission laser as a multiplicative noise process. I. A geometrical argument

    SciTech Connect

    Schleich, W.; Scully, M.O.

    1988-02-15

    We show, via simple geometrical arguments, the quantum-noise quenching in a correlated (spontaneous) emission laser (CEL). This noise quenching is a consequence of the correlation between noise sources which results in a multiplicative noise process. The steady-state distribution for the phase difference between the two electric fields in a CEL is compared and contrasted to that of a standard phase-locked laser. Noise quenching is shown to occur in the case of the CEL via an explicit solution of the Fokker-Planck equation.

  14. Multiple-wavelength operation of electroabsorption intensity modulator array fabricated using the one-step quantum well intermixing process

    NASA Astrophysics Data System (ADS)

    Ng, S. L.; Lim, H. S.; Lam, Y. L.; Chan, Y. C.; Ooi, B. S.; Aimez, V.; Beauvais, J.; Beerens, J.

    2002-09-01

    Multiple-wavelength selective channel electroabsorption intensity modulators have been fabricated on a single InGaAs/InGaAsP chip using a one-step quantum well intermixing process. This technique was demonstrated for tailoring the intensity modulator operating wavelength by incorporating low-energy (360 keV) phosphorus ions implantation induced disordering process with gray-mask lithography technology. A modulation depth of -15 dB has been measured from these devices with a voltage swing of -4.5 V.

  15. Two distinct carrier localization in green light-emitting diodes with InGaN/GaN multiple quantum wells

    SciTech Connect

    Li, Zhi; Kang, Junjie; Li, Hongjian; Liu, Zhiqiang Yi, Xiaoyan Wang, Guohong; Wei Wang, Bo; Chuan Feng, Zhe; Hsiang Weng, Yu; Lee, Yueh-Chien

    2014-02-28

    The effect of carrier localization in InGaN/GaN multiple quantum wells (MQWs) light-emitting diodes is investigated by photoluminescence (PL) and time-resolved PL (TRPL) measurements. PL results show that two peaks obtained by Gaussian fitting both relate to the emission from localized states. By fitting the TRPL lifetimes at various emission energies, two localization depths corresponding to the In-rich regions and quasi-MQWs regions are obtained. Using a model we proposed, we suggest that compositional fluctuations of In content and variation of well width are responsible for carrier localization in In-rich regions and quasi-MQWs regions, respectively.

  16. Time-dependent multiple scattering approach for a single finger-gate in a Rashba-type quantum channel .

    NASA Astrophysics Data System (ADS)

    Wang, Lu-Yao

    2006-03-01

    We consider a Rashba-type quantum channel (RQC) consisting of one AC-biased finger-gates (FG) that orient perpendicularly and located above the RQC. Such an AC-biased FG gives rise to a local time-modulation in the Rashba coupling parameter, and generates a dc spin current (SC). A static potential is located inside or outside the FG in the RQC and the backscattering effect is studied. We use analytical time-dependent multiple scattering approach to treat the effect of the SC suppression due to a static potential in the RQC.

  17. Long Wavelength Multiple Quantum Well Lasers for High-Speed Modulation Applications

    DTIC Science & Technology

    1992-02-01

    Laboratory Air Force Systems Command Griffiss Air Force Base , NY 13441-5700 This report has been reviewed by the Rome Laboratory Public Affairs Office (PA...this document. 3 2. Technical Report 2.1 Introduction Early work on quantum well lasers for 1.3g.m operation was almost exclusively based upon LPE, and...InGaAlAs based (graded-index separate confinement heterostructure) GRIN-SCH quantum well laser at 1.3gm was among the first of a small number of papers

  18. Effect of well layer thickness on quantum and energy conversion efficiencies for InGaN/GaN multiple quantum well solar cells

    NASA Astrophysics Data System (ADS)

    Miyoshi, Makoto; Tsutsumi, Tatsuya; Kabata, Tomoki; Mori, Takuma; Egawa, Takashi

    2017-03-01

    We investigated the effect of well layer thicknesses on the external quantum efficiency (EQE) and energy conversion efficiency (ECE) for InGaN/GaN multiple quantum well (MQW) solar cells grown on sapphire substrates by metalorganic chemical vapor deposition. The results indicated that EQE and ECE have maximum values at a specific well thickness. When the well thickness is sufficiently thin, EQE and ECE increase with an increase in the well thickness owing to an increase in light absorption. Then, once the well thickness surpasses a critical thickness, EQE and ECE begin to decrease owing to the influence of nonradiative recombination processes, which was indicated by the static and dynamic photoluminescence analyses. The critical well thickness probably depends not only on the MQW design but also on growth conditions. Further, we confirmed that the increased total thickness of the stacked well layers leads to increased light absorption and thereby contributes to the improvement of solar cell performance. A high short circuit current density of 1.34 mA/cm2 and a high ECE of 1.31% were achieved for a InGaN/GaN MQW solar cell with a 3.2-nm-thick InGaN well with total well thickness of 115 nm.

  19. Carrier Localization Effects in InGaN/GaN Multiple-Quantum-Wells LED Nanowires: Luminescence Quantum Efficiency Improvement and "Negative" Thermal Activation Energy.

    PubMed

    Bao, Wei; Su, Zhicheng; Zheng, Changcheng; Ning, Jiqiang; Xu, Shijie

    2016-09-30

    Two-dimensional InGaN/GaN multiple-quantum-wells (MQW) LED structure was nanotextured into quasi-one-dimensional nanowires (NWs) with different average diameters with a combination approach of Ni nanoislands as mask + dry etching. Such nanotexturing bring out several appealing effects including deeper localization of carriers and significant improvement in quantum efficiency (e.g., from 4.76% of the planar MQW structure to 12.5% of the 160 nm MQW NWs) of light emission in the whole interested temperature range from 4 K to 300 K. With the aid of localized-state ensemble (LSE) luminescence model, the photoluminescence spectra of the samples are quantitatively interpreted in the entire temperature range. In terms of distinctive temperature dependence of photoluminescence from these samples, a concept of "negative" thermal activation energy is tentatively proposed for the MQW NWs samples. These findings could lead to a deeper insight into the physical nature of localization and luminescence mechanism of excitons in InGaN/GaN nanowires.

  20. Carrier Localization Effects in InGaN/GaN Multiple-Quantum-Wells LED Nanowires: Luminescence Quantum Efficiency Improvement and “Negative” Thermal Activation Energy

    NASA Astrophysics Data System (ADS)

    Bao, Wei; Su, Zhicheng; Zheng, Changcheng; Ning, Jiqiang; Xu, Shijie

    2016-09-01

    Two-dimensional InGaN/GaN multiple-quantum-wells (MQW) LED structure was nanotextured into quasi-one-dimensional nanowires (NWs) with different average diameters with a combination approach of Ni nanoislands as mask + dry etching. Such nanotexturing bring out several appealing effects including deeper localization of carriers and significant improvement in quantum efficiency (e.g., from 4.76% of the planar MQW structure to 12.5% of the 160 nm MQW NWs) of light emission in the whole interested temperature range from 4 K to 300 K. With the aid of localized-state ensemble (LSE) luminescence model, the photoluminescence spectra of the samples are quantitatively interpreted in the entire temperature range. In terms of distinctive temperature dependence of photoluminescence from these samples, a concept of “negative” thermal activation energy is tentatively proposed for the MQW NWs samples. These findings could lead to a deeper insight into the physical nature of localization and luminescence mechanism of excitons in InGaN/GaN nanowires.

  1. Carrier Localization Effects in InGaN/GaN Multiple-Quantum-Wells LED Nanowires: Luminescence Quantum Efficiency Improvement and “Negative” Thermal Activation Energy

    PubMed Central

    Bao, Wei; Su, Zhicheng; Zheng, Changcheng; Ning, Jiqiang; Xu, Shijie

    2016-01-01

    Two-dimensional InGaN/GaN multiple-quantum-wells (MQW) LED structure was nanotextured into quasi-one-dimensional nanowires (NWs) with different average diameters with a combination approach of Ni nanoislands as mask + dry etching. Such nanotexturing bring out several appealing effects including deeper localization of carriers and significant improvement in quantum efficiency (e.g., from 4.76% of the planar MQW structure to 12.5% of the 160 nm MQW NWs) of light emission in the whole interested temperature range from 4 K to 300 K. With the aid of localized-state ensemble (LSE) luminescence model, the photoluminescence spectra of the samples are quantitatively interpreted in the entire temperature range. In terms of distinctive temperature dependence of photoluminescence from these samples, a concept of “negative” thermal activation energy is tentatively proposed for the MQW NWs samples. These findings could lead to a deeper insight into the physical nature of localization and luminescence mechanism of excitons in InGaN/GaN nanowires. PMID:27686154

  2. Molecularly Engineered Organic-Inorganic Hybrid Perovskite with Multiple Quantum Well Structure for Multicolored Light-Emitting Diodes

    PubMed Central

    Hu, Hongwei; Salim, Teddy; Chen, Bingbing; Lam, Yeng Ming

    2016-01-01

    Organic-inorganic hybrid perovskites have the potential to be used as a new class of emitters with tunable emission, high color purity and good ease of fabrication. Recent studies have so far been focused on three-dimensional (3D) perovskites, such as CH3NH3PbBr3 and CH3NH3PbI3 for green and infrared emission. Here, we explore a new series of hybrid perovskite emitters with a general formula of (C4H9NH3)2(CH3NH3)n−1PbnI3n+1 (where n = 1, 2, 3), which possesses a multiple quantum well structure. The quantum well thickness of these materials is adjustable through simple molecular engineering which results in a continuously tunable bandgap and emission spectra. Deep saturated red emission was obtained with a peak external quantum efficiency of 2.29% and a maximum luminance of 214 cd/m2. Green and blue LEDs were also demonstrated through halogen substitutions in these hybrid perovskites. We expect these results to open up the way towards high performance perovskite LEDs through molecular-structure engineering of these perovskite emitters. PMID:27633084

  3. Multiple Andreev reflections in s -wave superconductor-quantum dot-topological superconductor tunnel junctions and Majorana bound states

    NASA Astrophysics Data System (ADS)

    Golub, Anatoly

    2015-05-01

    We calculate the current as a function of applied voltage in a nontopological s -wave superconductor-quantum dot-topological superconductor (TS) tunnel junction. We consider the type of TS which hosts two Majorana bound states (MBSs) at the ends of a semiconductor quantum wire or of a chain of magnetic atoms in the proximity with an s -wave superconductor. We find that the I -V characteristic of such a system in the regime of big voltages has a typical two-dot shape and is ornamented by peaks of multiple Andreev reflections. We also consider the other options when the zero-energy states are created by disorder (hereby Shiba states) or by Andreev zero-energy bound states at the surface of a quantum dot and a superconductor. The later are obtained by tuning the magnetic field to a specific value. Unlike the last two cases the MBS I -V curves are robust to change the magnetic field. Therefore, the magnetic-field dependence of the tunneling current can serve as a unique signature for the presence of a MBS.

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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. The sensor was designed for operation in multiple modes, including gas sensing within a multi-pass Heriott cell and intracavity absorption sensing using the ECQCL compliance voltage. In addition, the ECQCL compliance voltage was used to reduce effects of long-term drifts in the ECQCL output power. The sensor was characterized for noise, drift, and detection of chemicals including ammonia, methanol, ethanol, isopropanol, Freon- 134a, Freon-152a, and diisopropyl methylphosphonate (DIMP). We also present use of the sensor for mobile detection of ammonia downwind of cattle facilities, in which concentrations were recorded at 1-s intervals.

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

    NASA Astrophysics Data System (ADS)

    Corfdir, P.; Levrat, J.; Rossbach, G.; Butté, R.; Feltin, E.; Carlin, J.-F.; Christmann, G.; Lefebvre, P.; Ganière, J.-D.; Grandjean, N.; Deveaud-Plédran, B.

    2012-06-01

    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 biexcitonic populations. Then, the role of biexcitons is considered for the full microcavity: in particular, we observe that for specific detunings the bottom of the lower polariton branch is directly fed by the radiative dissociation of either cavity biexcitons or excitons mediated by one LO-phonon. Accordingly, minimum polariton lasing thresholds are observed, when the bottom of the lower polariton branch corresponds in energy to the exciton or cavity biexciton first LO-phonon replica. This singular observation highlights the role of excitonic molecules in the polariton condensate formation process as being a more efficient relaxation channel when compared to the usually assumed acoustical phonon emission one.

  7. Bandgaps and band offsets in strain-compensated InGaAs/InGaAsP multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Ma, Chunsheng; Jin, Zhi; Tian, Fengshou; Yang, Ningguo; Yang, Shuren; Liu, Shiyong

    1998-08-01

    In terms of the parameter interpolation principle, calculations are performed for bandgaps and band offsets in strain-compensated InzGa1-zAs/InxGa1-xAsyP1-y multiple quantum well structures on InP. Relations between strains and material compositions in InzGa1-zAs wells and InxGa1-xAsyP1-y barriers are analyzed, and relative ranges of strains are evaluated. Bandgaps of InzGa1-zAs wells and InxGa1-xAsyP1-y barriers for heavy- and light-holes are studied, and relative ranges of bandgaps are estimated. Dependence of band offsets of conduction band and valence band for heavy- and light-holes on strain compensation between InzGa1-zAs wells and InxGa1-xAsyP1-y barriers is investigated, and variation of band offsets versus strain compensation is discussed. The computed results show that strains, bandgaps and band offsets are functions of material compositions, strain compensation changes the band offsets, and hence modifies the band structures and improves the features of strain- compensated multiple quantum well optoelectronic devices.

  8. Suppression of surface recombination in surface plasmon coupling with an InGaN/GaN multiple quantum well sample.

    PubMed

    Wang, Hsiang-Chen; Yu, Xuan-Yu; Chueh, Yu-Lun; Malinauskas, Tadas; Jarasiunas, Kestutis; Feng, Shih-Wei

    2011-09-26

    Temperature-dependent picosecond non-degenerate four-wave-mixing experiments were performed to explore the carrier dynamics in an InGaN/GaN multiple quantum well sample, in which light emission enhancement with surface plasmon (SP) coupling has been identified. In the time-resolved photoluminescence results, we can identify the faster carrier decay time of the sample with surface plasmon coupling. The faster decay time is due to this sample's ability to create additional channels for effective carrier recombination. In the four-wave-mixing results, a slower grating decay time of the sample with surface plasmon coupling was measured. The diffusion coefficients and surface recombination velocities of photo-created carriers were estimated by modeling the decay rate of transient grating signals. For the sample for which surface plasmon coupling exists, smaller diffusion coefficients and slower surface recombination velocities can be estimated when the temperatures are above 150 K. The carriers coupling with some SP modes is not the only mechanism contributing to emission enhancement. In the InGaN/GaN multiple quantum well sample, surface recombination suppressed by SP coupling is another factor for increased light emission efficiency. © 2011 Optical Society of America

  9. Split-Inteins for Simultaneous, site-specific conjugation of Quantum Dots to multiple protein targets In vivo

    PubMed Central

    2011-01-01

    Background Proteins labelled with Quantum Dots (QDs) can be imaged over long periods of time with ultrahigh spatial and temporal resolution, yielding important information on the spatiotemporal dynamics of proteins within live cells or in vivo. However one of the major problems regarding the use of QDs for biological imaging is the difficulty of targeting QDs onto proteins. We have recently developed a DnaE split intein-based method to conjugate Quantum Dots (QDs) to the C-terminus of target proteins in vivo. In this study, we expand this approach to achieve site-specific conjugation of QDs to two or more proteins simultaneously with spectrally distinguishable QDs for multiparameter imaging of cellular functions. Results Using the DnaE split intein we target QDs to the C-terminus of paxillin and show that paxillin-QD conjugates become localized at focal adhesions allowing imaging of the formation and dissolution of these complexes. We go on to utilize a different split intein, namely Ssp DnaB mini-intein, to demonstrate N-terminal protein tagging with QDs. Combination of these two intein systems allowed us to simultaneously target two distinct proteins with spectrally distinguishable QDs, in vivo, without any cross talk between the two intein systems. Conclusions Multiple target labeling is a unique feature of the intein based methodology which sets it apart from existing tagging methodologies in that, given the large number of characterized split inteins, the number of individual targets that can be simultaneously tagged is only limited by the number of QDs that can be spectrally distinguished within the cell. Therefore, the intein-mediated approach for simultaneous, in vivo, site-specific (N- and C-terminus) conjugation of Quantum Dots to multiple protein targets opens up new possibilities for bioimaging applications and offers an effective system to target QDs and other nanostructures to intracellular compartments as well as specific molecular complexes. PMID

  10. Influence of temperature on the mechanism of carrier injection in light-emitting diodes based on InGaN/GaN multiple quantum wells

    SciTech Connect

    Prudaev, I. A. Golygin, I. Yu.; Shirapov, S. B.; Romanov, I. S.; Khludkov, S. S.; Tolbanov, O. P.

    2013-10-15

    The experimental current-voltage characteristics and dependences of the external quantum yield on the current density of light-emitting diodes based on InGaN/GaN multiple quantum wells for the wide temperature range T = 10-400 K are presented. It is shown that, at low-temperatures T < 100 K, the injection of holes into the quantum wells occurs from localized acceptor states. The low-temperature injection of electrons into p-GaN occurs due to quasi-ballistic transport in the region of multiple quantum wells. An increase in temperature leads to an increase in the current which is governed by thermally activated hole and electron injection from the allowed bands of GaN.

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

    SciTech Connect

    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.

  12. Complete (1) H NMR assignment of cedranolides.

    PubMed

    Perez-Hernandez, Nury; Gordillo-Roman, Barbara; Arrieta-Baez, Daniel; Cerda-Garcia-Rojas, Carlos M; Joseph-Nathan, Pedro

    2017-03-01

    Complete and unambiguous (1) H NMR chemical shift assignment of α-cedrene (2) and cedrol (9), as well as for α-pipitzol (1), isocedrol (10), and the six related compounds 3-8 has been established by iterative full spin analysis using the PERCH NMR software (PERCH Solutions Ltd., Kuopio, Finland). The total sets of coupling constants are described and correlated with the conformational equilibria of the five-membered ring of 1-10, which were calculated using the complete basis set method. Copyright © 2015 John Wiley & Sons, Ltd.

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

    SciTech Connect

    Prasankumar, Rohit P; Taylor, Antoinette J

    2009-01-01

    Ultrafast density-dependent optical spectroscopic measurements on a quantum dots-in-a-well heterostructure reveal several distinctive phenomena, most notably a strong coupling between the quantum well population and light absorption at the quantum dot excited state.

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

    NASA Astrophysics Data System (ADS)

    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

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

    SciTech Connect

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

    2016-04-18

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Shapiro steps observed in a dc superconducting quantum interference device with multiple junctions in each arm

    NASA Astrophysics Data System (ADS)

    Chen, L.; Chen, P.; Ong, C. K.

    2002-02-01

    A high-Tc dc superconducting quantum interference device (SQUID) with three Josephson junctions (JJs) in series in each of its arms has been fabricated. Its Shapiro steps were studied using microwave (rf) radiation of 10 GHz and weak magnetic fields. The appearance of giant Shapiro steps and of some of half-integer steps was observed. Separation between the adjacent Shapiro steps could be tuned by rf magnetic fields and small external dc magnetic fields. This phenomenon was analyzed by phase locking the JJs in the SQUID.

  18. Deterministic coupling of a system of multiple quantum dots to a single photonic cavity mode

    NASA Astrophysics Data System (ADS)

    Lyasota, A.; Jarlov, C.; Gallo, P.; Rudra, A.; Dwir, B.; Kapon, E.

    2017-07-01

    We fabricated and studied a system comprising four site-controlled semiconductor quantum dots (QDs) embedded in a linear photonic crystal membrane cavity. The excellent position control and small spectral broadening permit coupling of the emission of all four QDs to the same photonic cavity modes. This is corroborated by co-polarization of the QD and cavity emission lines, as well as reduction in decay time, both with characteristic dependence on QD-cavity energy detuning. Scaling up to larger QD systems is discussed.

  19. Temperature dependent photoluminescence and micromapping of multiple stacks InAs quantum dots

    SciTech Connect

    Xu, Ming Jaffré, Alexandre Alvarez, José Kleider, Jean-Paul Boutchich, Mohamed; Jittrong, Apichat; Chokamnuai, Thitipong; Panyakeow, Somsak; Kanjanachuchai, Songphol

    2015-02-27

    We utilized temperature dependent photoluminescence (PL) techniques to investigate 1, 3 and 5 stack InGaAs quantum dots (QDs) grown on cross-hatch patterns. PL mapping can well reproduce the QDs distribution as AFM and position dependency of QD growth. It is possible to observe crystallographic dependent PL. The temperature dependent spectra exhibit the QDs energy distribution which reflects the size and shape. The inter-dot carrier coupling effect is observed and translated as a red shift of 120mV on the [1–10] direction peak is observed at 30K on 1 stack with regards to 3 stacks samples, which is assigned to lateral coupling.

  20. Nonpolar and semipolar InGaN/GaN multiple-quantum-well solar cells with improved carrier collection efficiency

    NASA Astrophysics Data System (ADS)

    Huang, Xuanqi; Fu, Houqiang; Chen, Hong; Zhang, Xiaodong; Lu, Zhijian; Montes, Jossue; Iza, Michael; DenBaars, Steven P.; Nakamura, Shuji; Zhao, Yuji

    2017-04-01

    We demonstrate the nonpolar and semipolar InGaN/GaN multiple-quantum-well (MQW) solar cells grown on the nonpolar m-plane and semipolar ( 20 2 ¯ 1 ) plane bulk GaN substrates. The optical properties and photovoltaic performance of the nonpolar and semipolar InGaN solar cells were systematically studied, and the results were compared to the conventional polar c-plane devices. The absorption spectra, current density-voltage (J-V) characteristics, external quantum efficiency (EQE), and internal quantum efficiency (IQE) were measured for nonpolar m-plane, semipolar ( 20 2 ¯ 1 ) plane, and polar c-plane InGaN/GaN MQW solar cells. Nonpolar m-plane InGaN/GaN MQW solar cells showed the best performance across all devices, with a high open-circuit voltage of 2.32 V, a low bandgap-voltage offset of 0.59 V, and the highest EQE and IQE. In contrast, the polar c-plane device showed the lowest EQE despite the highest absorption spectra. This huge difference is attributed to the better carrier transport and collection on nonpolar m-plane devices due to the reduced polarization effects, which were further confirmed by bias-dependent EQE measurements and energy band diagram simulations. This study demonstrates the high potential of nonpolar and semipolar InGaN solar cells and can serve as guidance for the future design and fabrication of high efficiency III-nitride solar cells.

  1. Anthropomorphic 1H MRS head phantom.

    PubMed

    Rice, J R; Milbrandt, R H; Madsen, E L; Frank, G R; Boote, E J; Blechinger, J C

    1998-07-01

    An anthropomorphic 1H MRS head phantom has been developed which mimics the in vivo structure, metabolite concentrations, and relaxation times (for both water and metabolites) of human brain tissue. Different brain regions and two tumor types, fluid-containing ventricles, and air-filled sinus, and subcutaneous fat are all simulated. The main tissue-mimicking materials are gelatin/agar mixtures with metabolites and several other ingredients added. Their composition and method of production are thoroughly described. T1's and T2's of water in the phantom are very close to in vivo values, and metabolite T1's and T2's are considerably more realistic than those in aqueous solutions. Spectra and relaxation times for the pig brain were also acquired and compare well with those of the phantom. The realistic properties of this phantom should be useful for testing spectral quantitation and localization.

  2. Femtosecond Pulse Distortion by Diffraction from Semi-insulating Multiple Quantum Wells

    NASA Astrophysics Data System (ADS)

    Brubaker, R. M.; Dinu, M.; Nolte, D. D.; Melloch, M. R.; Weiner, A. M.

    1996-03-01

    We have performed nondegenerate four-wave mixing of ultrafast pulses from photorefractive quantum wells.(Q. Wang, R. M. Brubaker, D. D. Nolte and M. R. Melloch, J. Opt. Soc. Am. 9), 1626 (1992) This work is a first step towards performing dynamic femtosecond pulse shaping.(A. M. Weiner, Prog. Quant. Electr. 19), 161 (1995) The pulse shape is changed by the amplitude and phase of gratings written by an above-gap laser in steady-state. We use electric field cross-correlation measurements to detect the change in pulse shape. The gratings are formed by space charge gratings trapped at deep level defects. For pulse shaping, a diffraction spectrum is desired to be flat over 10 nm to minimize pulse distortion. The spectrum depends on the distribution of oscillator strength, which is a sensitive function of the quantum well parameters. We show that diffraction of a pulse with a center wavelength displaced from the diffraction peak results in significant pulse broadening by over a factor of two.

  3. Graphene Quantum Dots Downregulate Multiple Multidrug-Resistant Genes via Interacting with Their C-Rich Promoters.

    PubMed

    Luo, Chao; Li, Yanfang; Guo, Lijuan; Zhang, Fangwei; Liu, Hui; Zhang, Jiali; Zheng, Jing; Zhang, Jingyan; Guo, Shouwu

    2017-07-27

    Multidrug resistance (MDR) is the major factor in the failure of many forms of chemotherapy, mostly due to the increased efflux of anticancer drugs that mediated by ATP-binding cassette (ABC) transporters. Therefore, inhibiting ABC transporters is one of effective methods of overcoming MDR. However, high enrichment of ABC transporters in cells and their broad substrate spectra made to circumvent MDR are almost insurmountable by a single specific ABC transporter inhibitor. Here, this study demonstrates that graphene quantum dots (GQDs) could downregulate the expressions of P-glycoprotein, multidrug resistance protein MRP1, and breast cancer resistance protein genes via interacting with C-rich regions of their promoters. This is the first example that a single reagent could suppress multiple MDR genes, suggesting that it will be possible to target multiple ABC transporters simultaneously with a single reagent. The inhibitory ability of the GQDs to these drug-resistant genes is validated further by reversing the doxorubicin resistance of MCF-7/ADR cells. Notably, GQDs have superb chemical and physical properties, unique structure, low toxicity, and high biocompatibility; hence, their capability of inhibiting multiple drug-resistant genes holds great potential in cancer therapy. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    DOE PAGES

    Valdueza-Felip, Sirona; Naranjo, Fernando B.; Gonzalez-Herraez, Miguel; ...

    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 temperature,more » 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)« less

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

    DOE PAGES

    Valdueza-Felip, Sirona; Naranjo, Fernando B.; Gonzalez-Herraez, Miguel; ...

    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{sub to}}0.73 eV with a full width at half maximum of {proportional{sub to}}86 meV. The InN layer displays an S-shape evolution of the emission peak energymore » with temperature, explained in terms of carrier localization. A carrier localization energy of {proportional{sub 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{sub to}}16%. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)« less

  6. Enhanced power conversion efficiency in InGaN-based solar cells via graded composition multiple quantum wells.

    PubMed

    Tsai, Yu-Lin; Wang, Sheng-Wen; Huang, Jhih-Kai; Hsu, Lung-Hsing; Chiu, Ching-Hsueh; Lee, Po-Tsung; Yu, Peichen; Lin, Chien-Chung; Kuo, Hao-Chung

    2015-11-30

    This work demonstrates the enhanced power conversion efficiency (PCE) in InGaN/GaN multiple quantum well (MQWs) solar cells with gradually decreasing indium composition in quantum wells (GQWs) toward p-GaN as absorber. The GQW can improve the fill factor from 42% to 62% and enhance the short current density from 0.8 mA/cm2 to 0.92 mA/cm2, as compares to the typical MQW solar cells. As a result, the PCE is boosted from 0.63% to 1.11% under AM1.5G illumination. Based on simulation and experimental results, the enhanced PCE can be attributed to the improved carrier collection in GQW caused by the reduction of potential barriers and piezoelectric polarization induced fields near the p-GaN layer. The presented concept paves a way toward highly efficient InGaN-based solar cells and other GaN-related MQW devices.

  7. Multiple environment single system quantum mechanical/molecular mechanical (MESS-QM/MM) calculations. 1. Estimation of polarization energies

    DOE PAGES

    Sodt, Alexander J.; Mei, Ye; Konig, Gerhard; ...

    2014-10-16

    In combined quantum mechanical/molecular mechanical (QM/MM) free energy calculations, it is often advantageous to have a frozen geometry for the quantum mechanical (QM) region. For such multiple-environment single-system (MESS) cases, two schemes are proposed here for estimating the polarization energy: the first scheme, termed MESS-E, involves a Roothaan step extrapolation of the self-consistent field (SCF) energy; whereas the other scheme, termed MESS-H, employs a Newton–Raphson correction using an approximate inverse electronic Hessian of the QM region (which is constructed only once). Both schemes are extremely efficient, because the expensive Fock updates and SCF iterations in standard QM/MM calculations are completelymore » avoided at each configuration. Here, they produce reasonably accurate QM/MM polarization energies: MESS-E can predict the polarization energy within 0.25 kcal/mol in terms of the mean signed error for two of our test cases, solvated methanol and solvated β-alanine, using the M06-2X or ωB97X-D functionals; MESS-H can reproduce the polarization energy within 0.2 kcal/mol for these two cases and for the oxyluciferin–luciferase complex, if the approximate inverse electronic Hessians are constructed with sufficient accuracy.« less

  8. Control of Multiple Exciton Generation and Electron-Phonon Coupling by Interior Nanospace in Hyperstructured Quantum Dot Superlattice.

    PubMed

    Chang, I-Ya; Kim, DaeGwi; Hyeon-Deuk, Kim

    2017-09-20

    The possibility of precisely manipulating interior nanospace, which can be adjusted by ligand-attaching down to the subnanometer regime, in a hyperstructured quantum dot (QD) superlattice (QDSL) induces a new kind of collective resonant coupling among QDs and opens up new opportunities for developing advanced optoelectric and photovoltaic devices. Here, we report the first real-time dynamics simulations of the multiple exciton generation (MEG) in one-, two-, and three-dimensional (1D, 2D, and 3D) hyperstructured H-passivated Si QDSLs, accounting for thermally fluctuating band energies and phonon dynamics obtained by finite-temperature ab initio molecular dynamics simulations. We computationally demonstrated that the MEG was significantly accelerated, especially in the 3D QDSL compared to the 1D and 2D QDSLs. The MEG acceleration in the 3D QDSL was almost 1.9 times the isolated QD case. The dimension-dependent MEG acceleration was attributed not only to the static density of states but also to the dynamical electron-phonon couplings depending on the dimensionality of the hyperstructured QDSL, which is effectively controlled by the interior nanospace. Such dimension-dependent modifications originated from the short-range quantum resonance among component QDs and were intrinsic to the hyperstructured QDSL. We propose that photoexcited dynamics including the MEG process can be effectively controlled by only manipulating the interior nanospace of the hyperstructured QDSL without changing component QD size, shape, compositions, ligand, etc.

  9. InGaN/GaN multiple quantum well for fast scintillation application: radioluminescence and photoluminescence study.

    PubMed

    Hospodková, Alice; Nikl, Martin; Pacherová, Oliva; Oswald, Jiří; Brůža, Petr; Pánek, Dalibor; Foltynski, Bartosz; Hulicius, Eduard; Beitlerová, Alena; Heuken, Michael

    2014-11-14

    We prepare InGaN/GaN multiple quantum well (MQW) structure by metal-organic vapour phase epitaxy and characterize it by fine XRD measurements. We demonstrate its suitability for scintillator application including a unique measurement of wavelength-resolved scintillation response under nanosecond pulse soft x-ray source in extended dynamical and time scales. The photoluminescence and radioluminescence were measured: we have shown that the ratio of the intensity of quantum well (QW) exciton luminescence to the intensity of the yellow luminescence (YL) band IQW/IYL depends strongly on the type and intensity of excitation. Slower scintillation decay measured at YL band maximum confirmed the presence of several radiative recombination centres responsible for wide YL band, which also partially overlap with the QW peak. Further improvements of the structure are suggested, but even the presently reported decay characteristics of the excitonic emission in MQW are better compared to the currently widely used single crystal YAP:Ce or YAG:Ce scintillators. Thus, such a type of a semiconductor scintillator is highly promising for fast detection of soft x-ray and related beam diagnostics.

  10. InGaN/GaN multiple quantum well for fast scintillation application: radioluminescence and photoluminescence study

    NASA Astrophysics Data System (ADS)

    Hospodková, Alice; Nikl, Martin; Pacherová, Oliva; Oswald, Jiří; Brůža, Petr; Pánek, Dalibor; Foltynski, Bartosz; Hulicius, Eduard; Beitlerová, Alena; Heuken, Michael

    2014-11-01

    We prepare InGaN/GaN multiple quantum well (MQW) structure by metal-organic vapour phase epitaxy and characterize it by fine XRD measurements. We demonstrate its suitability for scintillator application including a unique measurement of wavelength-resolved scintillation response under nanosecond pulse soft x-ray source in extended dynamical and time scales. The photoluminescence and radioluminescence were measured: we have shown that the ratio of the intensity of quantum well (QW) exciton luminescence to the intensity of the yellow luminescence (YL) band IQW/IYL depends strongly on the type and intensity of excitation. Slower scintillation decay measured at YL band maximum confirmed the presence of several radiative recombination centres responsible for wide YL band, which also partially overlap with the QW peak. Further improvements of the structure are suggested, but even the presently reported decay characteristics of the excitonic emission in MQW are better compared to the currently widely used single crystal YAP:Ce or YAG:Ce scintillators. Thus, such a type of a semiconductor scintillator is highly promising for fast detection of soft x-ray and related beam diagnostics.

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

    NASA Astrophysics Data System (ADS)

    Hyeon-Deuk, Kim; Prezhdo, Oleg V.

    2012-09-01

    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 approach accounts for QD size and shape as well as defects, core-shell distribution, surface ligands and charge trapping, which significantly influence the properties of photoexcited QDs. The method creates an explicit time-domain representation of photoinduced processes and describes various kinetic regimes owing to the non-perturbative treatment of quantum dynamics. QDs of different sizes and materials, with and without ligands, are considered. The simulations provide direct evidence that the high-frequency ligand modes on the QD surface play a pivotal role in the electron-phonon relaxation, MEG, MEF and MER. The insights reported here suggest novel routes for controlling the photoinduced processes in semiconductor QDs and lead to new design principles for increasing the efficiencies of photovoltaic devices.

  12. Three Temperature Regimes in Superconducting Photon Detectors: Quantum, Thermal and Multiple Phase-Slips as Generators of Dark Counts

    PubMed Central

    Murphy, Andrew; Semenov, Alexander; Korneev, Alexander; Korneeva, Yulia; Gol’tsman, Gregory; Bezryadin, Alexey

    2015-01-01

    We perform measurements of the switching current distributions of three w ≈ 120 nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter of the vortex cores, so they are classified as quasi-two-dimensional (quasi-2D). We discover evidence of macroscopic quantum tunneling by observing the saturation of the standard deviation of the switching distributions at temperatures around 2 K. We analyze our results using the Kurkijärvi-Garg model and find that the escape temperature also saturates at low temperatures, confirming that at sufficiently low temperatures, macroscopic quantum tunneling is possible in quasi-2D strips and can contribute to dark counts observed in single photon detectors. At the highest temperatures the system enters a multiple phase-slip regime. In this range single phase-slips are unable to produce dark counts and the fluctuations in the switching current are reduced. PMID:25988591

  13. Three temperature regimes in superconducting photon detectors: quantum, thermal and multiple phase-slips as generators of dark counts.

    PubMed

    Murphy, Andrew; Semenov, Alexander; Korneev, Alexander; Korneeva, Yulia; Gol'tsman, Gregory; Bezryadin, Alexey

    2015-05-19

    We perform measurements of the switching current distributions of three w ≈ 120 nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter of the vortex cores, so they are classified as quasi-two-dimensional (quasi-2D). We discover evidence of macroscopic quantum tunneling by observing the saturation of the standard deviation of the switching distributions at temperatures around 2 K. We analyze our results using the Kurkijärvi-Garg model and find that the escape temperature also saturates at low temperatures, confirming that at sufficiently low temperatures, macroscopic quantum tunneling is possible in quasi-2D strips and can contribute to dark counts observed in single photon detectors. At the highest temperatures the system enters a multiple phase-slip regime. In this range single phase-slips are unable to produce dark counts and the fluctuations in the switching current are reduced.

  14. Separation of isotropic chemical and second-order quadrupolar shifts by multiple-quantum double rotation NMR.

    PubMed

    Hung, Ivan; Wong, Alan; Howes, Andy P; Anupõld, Tiit; Samoson, Ago; Smith, Mark E; Holland, Diane; Brown, Steven P; Dupree, Ray

    2009-04-01

    Using a two-dimensional multiple-quantum (MQ) double rotation (DOR) experiment the contributions of the chemical shift and quadrupolar interaction to isotropic resonance shifts can be completely separated. Spectra were acquired using a three-pulse triple-quantum z-filtered pulse sequence and subsequently sheared along both the nu(1) and nu(2) dimensions. The application of this method is demonstrated for both crystalline (RbNO(3)) and amorphous samples (vitreous B(2)O(3)). The existence of the two rubidium isotopes ((85)Rb and (87)Rb) allows comparison of results for two nuclei with different spins (I=3/2 and 5/2), as well as different dipole and quadrupole moments in a single chemical compound. Being only limited by homogeneous line broadening and sample crystallinity, linewidths of approximately 0.1 and 0.2 ppm can be measured for (87)Rb in the quadrupolar and chemical shift dimensions, enabling highly accurate determination of the isotropic chemical shift and the quadrupolar product, P(Q). For vitreous B(2)O(3), the use of MQDOR allows the chemical shift and electric field gradient distributions to be directly determined-information that is difficult to obtain otherwise due to the presence of second-order quadrupolar broadening.

  15. An approach to high efficiencies using GaAs/GaInNAs multiple quantum well and superlattice solar cell

    NASA Astrophysics Data System (ADS)

    Courel, Maykel; Rimada, Julio C.; Hernández, Luis

    2012-09-01

    A new type of photovoltaic device where GaAs/GaInNAs multiple quantum wells (MQW) or superlattice (SL) are inserted in the i-region of a GaAs p-i-n solar cell (SC) is presented. The results suggest the device can reach record efficiencies for single-junction solar cells. A theoretical model is developed to study the performance of this device. The conversion efficiency as a function of wells width and depth is modeled for MQW solar cells. It is shown that the MQW solar cells reach high conversion efficiency values. A study of the SL solar cell viability is also presented. The conditions for resonant tunneling are established by the matrix transfer method for a superlattice with variable quantum wells width. The effective density of states and the absorption coefficient for SL structure are calculated in order to determinate the J-V characteristic. The influence of superlattice length on the conversion efficiency is researched, showing a better performance when width and cluster numbers are increased. The SL solar cell conversion efficiency is compared with the maximum conversion efficiency obtained for the MQW solar cell and shows an efficiency enhancement.

  16. Piezoelectric Effects on the Optical Properties of GaN/Al(x)Ga(1-x)N Multiple Quantum Wells

    SciTech Connect

    Botchkarev, A.; Chow, W.W.; Jiang, H.X.; Kim, H.S.; Lin, J.Y.; Morkoc, H.

    1998-11-10

    Piezoelectric effects on the optical properties of GaN/AlGaN multiple quantum wells (MQWS) have been investigated by picosecond time-resolved photoluminescence (PL) measurements. For MQWS with well thickness 30 and 40 the excitonic transition peak positions at 10 K in continuous wave (CW) spectra are red-shifted with respect to the GaN epilayer by 17 meV and 57 meV, respectively. The time-resolved PL spectra of the 30 and 40 well MQWS reveal that the excitonic transition is in fact blue-shifted at early delay times due to quantum confinement of carriers. The spectral peak position shifts toward lower energies as the delay time increases and becomes red-shifted at longer delay times. We have demonstrated that the results described above is due to the presence of the piezoelectric field in the GaN wells of GaN/AlGaN MQWS subject to elastic strain together with screening of the photoexcited carriers. By comparing experimental and calculation results, we conclude that the piezoelectric field strength in GaN/Al.15G~.85N MQWS has a lower limit value of about 560 kV/cm: The electron and hole wave function distributions have also been obtained. The implication of our findings on the practical applications of GaN based optoelectronic devices is also discussed.

  17. Multiple environment single system quantum mechanical/molecular mechanical (MESS-QM/MM) calculations. 1. Estimation of polarization energies

    SciTech Connect

    Sodt, Alexander J.; Mei, Ye; Konig, Gerhard; Tao, Peng; Steele, Ryan P.; Brooks, Bernard R.; Shao, Yihan

    2014-10-16

    In combined quantum mechanical/molecular mechanical (QM/MM) free energy calculations, it is often advantageous to have a frozen geometry for the quantum mechanical (QM) region. For such multiple-environment single-system (MESS) cases, two schemes are proposed here for estimating the polarization energy: the first scheme, termed MESS-E, involves a Roothaan step extrapolation of the self-consistent field (SCF) energy; whereas the other scheme, termed MESS-H, employs a Newton–Raphson correction using an approximate inverse electronic Hessian of the QM region (which is constructed only once). Both schemes are extremely efficient, because the expensive Fock updates and SCF iterations in standard QM/MM calculations are completely avoided at each configuration. Here, they produce reasonably accurate QM/MM polarization energies: MESS-E can predict the polarization energy within 0.25 kcal/mol in terms of the mean signed error for two of our test cases, solvated methanol and solvated β-alanine, using the M06-2X or ωB97X-D functionals; MESS-H can reproduce the polarization energy within 0.2 kcal/mol for these two cases and for the oxyluciferin–luciferase complex, if the approximate inverse electronic Hessians are constructed with sufficient accuracy.

  18. Nonlinear absorption properties of AlGaAs/GaAs multiple quantum wells grown by metalorganic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Lee, Hsing-Chung; Kost, A.; Kawase, M.; Hariz, A.; Dapkus, P. Daniel

    1988-01-01

    The nonlinear absorption properties of the excitonic resonances associated with multiple quantum wells (MQWs) in AlGaAs/GaAs grown by metalorganic chemical vapor deposition are reported. The dependence of the saturation properties on growth parameters, especially growth temperature, and the well width are described. The minimum measured saturation intensity for these materials is 250 W/sq cm, the lowest reported value to date. The low saturation intensities are the result of excellent minority carrier properties. A systematic study of minority carrier lifetimes in quantum wells are reported. Lifetimes range from 50-350 ns depending on growth temperature and well width. When corrected for lateral diffusion effects and the measured minority carrier lifetime, the saturation data suggest that saturation intensities as low as 2.3 W/sq cm can be achieved in this system. The first measurements of the dependence of the exciton area and the magnitude of the excitonic absorption on well width are prsented. The growth of MQW structures on transparent GaP substrates is demonstrated and the electroabsorption properties of these structures are reviewed.

  19. Nonlinear absorption properties of AlGaAs/GaAs multiple quantum wells grown by metalorganic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Lee, Hsing-Chung; Kost, A.; Kawase, M.; Hariz, A.; Dapkus, P. Daniel

    1988-01-01

    The nonlinear absorption properties of the excitonic resonances associated with multiple quantum wells (MQWs) in AlGaAs/GaAs grown by metalorganic chemical vapor deposition are reported. The dependence of the saturation properties on growth parameters, especially growth temperature, and the well width are described. The minimum measured saturation intensity for these materials is 250 W/sq cm, the lowest reported value to date. The low saturation intensities are the result of excellent minority carrier properties. A systematic study of minority carrier lifetimes in quantum wells are reported. Lifetimes range from 50-350 ns depending on growth temperature and well width. When corrected for lateral diffusion effects and the measured minority carrier lifetime, the saturation data suggest that saturation intensities as low as 2.3 W/sq cm can be achieved in this system. The first measurements of the dependence of the exciton area and the magnitude of the excitonic absorption on well width are prsented. The growth of MQW structures on transparent GaP substrates is demonstrated and the electroabsorption properties of these structures are reviewed.

  20. Carrier localization in InN/InGaN multiple-quantum wells with high In-content

    NASA Astrophysics Data System (ADS)

    Valdueza-Felip, S.; Rigutti, L.; Naranjo, F. B.; Ruterana, P.; Mangeney, J.; Julien, F. H.; González-Herráez, M.; Monroy, E.

    2012-08-01

    We study the carrier localization in InN/In0.9Ga0.1N multiple-quantum-wells (MQWs) and bulk InN by means of temperature-dependent photoluminescence and pump-probe measurements at 1.55 μm. The S-shaped thermal evolution of the emission energy of the InN film is attributed to carrier localization at structural defects with an average localization energy of ˜12 meV. Carrier localization is enhanced in the MQWs due to well/barrier thickness and ternary alloy composition fluctuations, leading to a localization energy above 35 meV and longer carrier relaxation time. As a result, the luminescence efficiency in the MQWs is improved by a factor of five over bulk InN.

  1. Atmospheric-pressure epitaxial growth technique of a multiple quantum well by mist chemical vapor deposition based on Leidenfrost droplets

    NASA Astrophysics Data System (ADS)

    Kawaharamura, Toshiyuki; Dang, Giang T.; Nitta, Noriko

    2016-10-01

    A multiple quantum well α-Fe2O3/α-Ga2O3 with parallel and coherent formation of uniform and highly single-crystalline layers on a sapphire substrate has been fabricated by open-air atmospheric-pressure solution-processed mist chemical vapor deposition (Mist CVD). This report demonstrates that complicated structures with atomic-level control can be fabricated even in non-vacuum conditions by the Mist CVD. This can be achieved via the precise control of the precursor flow and ambient temperature combined with the formation of mist droplets of the special Leidenfrost state, which increased the atomic migration length by 108 times more than that of traditional vacuum techniques. This work could be a milestone in the transformation from vacuum to non-vacuum thin film deposition techniques towards a green and sustainable industry.

  2. Optical bistability and multistability in a defect slab doped by GaAs/AlGaAs multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Seyyed, Hossein Asadpour; G, Solookinejad; M, Panahi; E Ahmadi, Sangachin

    2016-05-01

    We proposed a new model for controlling the optical bistability (OB) and optical multistability (OM) in a defect slab doped with four-level GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5 nm GaAs wells and 15-nm Al0.3 Ga0.7As barriers. The effects of biexciton energy renormalization, exciton spin relaxation, and thickness of the slab on the OB and OM properties of the defect slab were theoretically investigated. We found that the transition from OB to OM or vice versa is possible by adjusting the controllable parameters in a lab. Moreover, the transmission, reflection, and absorption properties of the weak probe light through the slab were also discussed in detail.

  3. Low-temperature pulsed sputtering growth of InGaN multiple quantum wells for photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Arakawa, Yasuaki; Ueno, Kohei; Noguchi, Hidenari; Ohta, Jitsuo; Fujioka, Hiroshi

    2017-03-01

    We investigated the potential of low-temperature pulsed sputtering deposition (PSD) for the fabrication of high-In-composition thick InGaN multiple quantum wells (MQWs). Low-temperature PSD growth allowed the growth of a 100-period 1.2-nm-thick In0.3Ga0.7N MQW on GaN bulk crystals without apparent lattice relaxation. We fabricated a nitride-based photovoltaic device using 100-period In0.3Ga0.7N MQW absorption layers and obtained a clear photovoltaic response with an open-circuit voltage of 1.24 V, a short-circuit current density of 1.76 mA·cm‑2, and a maximum output power density of 1.10 mW·cm‑2 under 1 sun with air mass 1.5 illumination.

  4. Membrane-type photonic integration of InGaN/GaN multiple-quantum-well diodes and waveguide

    NASA Astrophysics Data System (ADS)

    Gao, Xumin; Bai, Dan; Cai, Wei; Xu, Yin; Yuan, Jialei; Yang, Yongchao; Zhu, Guixia; Cao, Xun; Zhu, Hongbo; Wang, Yongjin

    2017-02-01

    We report here a membrane-type integration of InGaN/GaN multiple-quantum-well diodes (MQWDs) with a waveguide to build a highly integrated photonic system to perform functionalities on a GaN-on-silicon platform. Suspended MQWDs can be used as either for light-emitting diode (LED) or photodiode. In the fabricated photonic system, part of the LED emission is coupled into a suspended waveguide, and the guided light laterally propagates along the waveguide and is finally sensed by the photodiode. The photonic system can detect the in-plane guided light and the external incident light simultaneously. Planar optical communication experimentally demonstrates that the proof-of-concept monolithic photonic integration system can achieve the in-plane visible light communication. This work paves the way towards novel active electro-optical sensing systems and planar optical communication in the visible range.

  5. Imaging of multiple mRNA targets using quantum dot based in situ hybridization and spectral deconvolution in clinical biopsies

    SciTech Connect

    Tholouli, Eleni; Hoyland, Judith A.; Di Vizio, Dolores; O'Connell, Fionnuala; MacDermott, Sarah A.; Twomey, David; Levenson, Richard; Yin, John A. Liu; Golub, Todd R.; Loda, Massimo; Byers, Richard . E-mail: r.byers@manchester.ac.uk

    2006-09-22

    Gene expression mapping using microarray analysis has identified useful gene signatures for predicting outcome. However, little of this has been translated into clinically effective diagnostic tools as microarrays require high quality fresh-frozen tissue samples. We describe a methodology of multiplexed in situ hybridization (ISH) using a novel combination of quantum dot (QD)-labeled oligonucleotide probes and spectral imaging analysis in routinely processed, formalin-fixed paraffin embedded human biopsies. The conditions for QD-ISH were optimized using a poly d(T) oligonucleotide in decalcified bone marrow samples. Single and multiplex QD-ISH was performed in samples with acute leukemia and follicular lymphoma using oligonucleotide probes for myeloperoxidase, bcl-2, survivin, and XIAP. Spectral imaging was used for post hybridization tissue analysis, enabling separation of spatially colocalized signals. The method allows quantitative characterization of multiple gene expression using non-bleaching fluorochromes. This is expected to facilitate multiplex in situ transcript detection in routinely processed human clinical tissue.

  6. Quantum dynamical response of ultracold few-boson ensembles in finite optical lattices to multiple interaction quenches

    NASA Astrophysics Data System (ADS)

    Neuhaus-Steinmetz, J.; Mistakidis, S. I.; Schmelcher, P.

    2017-05-01

    The correlated nonequilibrium quantum dynamics following a multiple interaction quench protocol for few-bosonic ensembles confined in finite optical lattices is investigated. The quenches give rise to an interwell tunneling and excite the cradle and a breathing mode. Several tunneling pathways open during the time interval of increased interactions, while only a few occur when the system is quenched back to its original interaction strength. The cradle mode, however, persists during and in between the quenches, while the breathing mode possesses distinct frequencies. The occupation of excited bands is explored in detail revealing a monotonic behavior with increasing quench amplitude and a nonlinear dependence on the duration of the application of the quenched interaction strength. Finally, a periodic population transfer between momenta for quenches of increasing interaction is observed, with a power-law frequency dependence on the quench amplitude. Our results open the possibility to dynamically manipulate various excited modes of the bosonic system.

  7. Resonant enhancement of second order sideband generation for intraexcitonic transitions in GaAs/AlGaAs multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Wagner, M.; Schneider, H.; Winnerl, S.; Helm, M.; Roch, T.; Andrews, A. M.; Schartner, S.; Strasser, G.

    2009-06-01

    We present an experimental study on efficient second order sideband generation in symmetric undoped GaAs/AlGaAs multiple quantum wells. A near-infrared laser tuned to excitonic interband transitions is mixed with an in-plane polarized terahertz beam from a free-electron laser. The terahertz beam is tuned either to the intraexcitonic heavy-hole 1s-2p transition or to the interexcitonic heavy-hole light-hole transition. We find strong evidence that the intraexcitonic transition is of paramount influence on n =±2 sideband generation, leading to an order-of-magnitude resonant enhancement of the conversion efficiency up to 0.1% at low temperature. At room temperature, the efficiency drops only by a factor of 7 for low terahertz powers.

  8. Extended defects in InGaAs/InGaAs strain-balanced multiple quantum wells for photovoltaic applications

    NASA Astrophysics Data System (ADS)

    Nasi, Lucia; Ferrari, Claudio; Lazzarini, Laura; Salviati, Giancarlo; Tundo, Stefania; Mazzer, Massimo; Clarke, Graham; Rohr, Carsten

    2002-12-01

    Different strain-balanced InGaAs/InGaAs multiple quantum wells (MQWs) were grown on (001) InP changing the In composition in the wells/barriers in order to extend the absorption edge beyond 2 μm for thermophotovoltaic applications. The strain increase in the structures results in the formation of isolated highly defected regions taking their origin from lateral layer thickness modulations. Experimental results are consistent with the existence of a critical elastic energy density for the development of MQW waviness. An empirical model for predicting the maximum number of layers that can be grown without modulations as a function of the strain energy stored in the MQW period is presented.

  9. Sensitivity enhancement in static solid-state NMR experiments via single- and multiple-quantum dipolar coherences.

    PubMed

    Gopinath, T; Veglia, Gianluigi

    2009-04-29

    We present a new method for enhancing the sensitivity in static solid-state NMR experiments for a gain in signal-to-noise ratio of up to 40%. This sensitivity enhancement is different from the corresponding solution NMR sensitivity enhancement schemes and is achieved by combining single- and multiple-quantum dipolar coherences. While this new approach is demonstrated for the polarization inversion spin exchange at magic angle (PISEMA) experiment, it can be generalized to the other separated local field experiments for solid-state NMR spectroscopy. This method will have a direct impact on solid-state NMR spectroscopy of liquid crystals as well as of membrane proteins aligned in lipid membranes.

  10. SIMQUADNMR: a program for simulation and interpretation of multiple quantum-filtered NMR spectra of quadrupolar nuclei.

    PubMed

    D'Amelio, Nicola; Gaggelli, Elena; Molteni, Elena; Valensin, Gianni

    2005-01-01

    In this paper, we present a computer program which simulates NMR multiple quantum-filtered spectra of quadrupolar nuclei as a function of physical parameters, of the type of experiment and experimental conditions. The program works by solving relaxation theory equations for the given system, and it can be useful in order to plan the ideal conditions to set up specific experiments or to give a physical interpretation of experimental results. The program allows to independently follow the dependence of individual coherences and relaxation rates as a function of up to 50 parameters regarding the physical properties of the system under investigation, sample conditions and instrumental setup making it an helpful tool also for teaching purposes.

  11. Degenerate four-wave mixing in room-temperature GaAs/GaAlAs multiple quantum well structures

    NASA Astrophysics Data System (ADS)

    Miller, D. A. B.; Chemla, D. S.; Eilenberger, D. J.; Smith, P. W.; Gossard, A. C.; Wiegman, W.

    1983-06-01

    Degenerate four-wave mixing (DFWM) is of current interest both for practical applications (e.g., phase conjugation) and as a physical probe. DFWM makes it possible to detect very small nonlinear changes in refraction. In connection with the present investigation, the first observations of DFWM in GaAs/GaAlAs multiple quantum well structures (MQW's) at room temperature are reported. By combining DFWM and nonlinear absorption results, a direct measurement of the nonlinear refraction near the band gap of the MQW is conducted. The obtained value is compared with previous estimates. The measurements are of practical importance for possible low-power optical devices compatible with laser diodes based either on DFWM, nonlinear refraction (such as optical bistability) of nonlinear absorption. The MQW samples were grown by molecular beam epitaxy (MBE) on GaAs substrates, with the MQW layers sandwiched between GaAlAs cap layers which are transparent at the considered wavelengths.

  12. Stereospecificity of (1) H, (13) C and (15) N shielding constants in the isomers of methylglyoxal bisdimethylhydrazone: problem with configurational assignment based on (1) H chemical shifts.

    PubMed

    Afonin, Andrei V; Pavlov, Dmitry V; Ushakov, Igor A; Keiko, Natalia A

    2012-07-01

    In the (13) C NMR spectra of methylglyoxal bisdimethylhydrazone, the (13) C-5 signal is shifted to higher frequencies, while the (13) C-6 signal is shifted to lower frequencies on going from the EE to ZE isomer following the trend found previously. Surprisingly, the (1) H-6 chemical shift and (1) J(C-6,H-6) coupling constant are noticeably larger in the ZE isomer than in the EE isomer, although the configuration around the -CH═N- bond does not change. This paradox can be rationalized by the C-H⋯N intramolecular hydrogen bond in the ZE isomer, which is found from the quantum-chemical calculations including Bader's quantum theory of atoms in molecules analysis. This hydrogen bond results in the increase of δ((1) H-6) and (1) J(C-6,H-6) parameters. The effect of the C-H⋯N hydrogen bond on the (1) H shielding and one-bond (13) C-(1) H coupling complicates the configurational assignment of the considered compound because of these spectral parameters. The (1) H, (13) C and (15) N chemical shifts of the 2- and 8-(CH(3) )(2) N groups attached to the -C(CH(3) )═N- and -CH═N- moieties, respectively, reveal pronounced difference. The ab initio calculations show that the 8-(CH(3) )(2) N group conjugate effectively with the π-framework, and the 2-(CH(3) )(2) N group twisted out from the plane of the backbone and loses conjugation. As a result, the degree of charge transfer from the N-2- and N-8- nitrogen lone pairs to the π-framework varies, which affects the (1) H, (13) C and (15) N shieldings. Copyright © 2012 John Wiley & Sons, Ltd.

  13. Devices based on InGaN/GaN multiple quantum well for scintillator and detector applications

    NASA Astrophysics Data System (ADS)

    Hospodková, Alice; Pangrác, Jiří; Kuldová, Karla; Nikl, Martin; Pacherová, Oliva; Oswald, Jiří; Hubáček, Tomáš; Zíková, Markéta; Brůža, Petr; Pánek, Dalibor; Blažek, Karel; Ledoux, Gilles; Dujardin, Christophe; Heuken, Michael; Hulicius, Eduard

    2016-02-01

    Fast scintillators are necessary for electron microscopes, as well as in many other application fields like medical diagnostics and therapy and fundamental science. InGaN/GaN multiple quantum well structures (QW) are perspective candidates due to strong exciton binding energy, high quantum efficiency, short decay time in order of ns and good radiation resistance. The aim of our work is to prepare scintillator structure with fast luminescence response and high intensity of light. InGaN/GaN multiple QW structures described here were prepared by metal-organic vapour phase epitaxy and characterized by high resolution X-ray diffraction measurements. We demonstrate structure suitability for scintillator application including a unique measurement of wavelength-resolved scintillation response under nanosecond pulse soft X-ray source in extended dynamical and time scales. The photo-, radio- and cathodo-luminescence (PL, RL, CL) were measured. We observed double peak luminescence governed by different recombination mechanisms: i) exciton in QW and ii) related to defects. We have shown that for obtaining fast and intensive luminescence response proper structure design is required. The radioluminescence decay time of QW exciton maximum decreased 4 times from 16 ns to 4 ns when the QW thickness was decreased from 2.4 nm to 2 nm. We have proved suitability of InGaN/GaN structures for fast scintillator application for electron or other particle radiation detection. For x-ray detection the fast scintillation response would be hard to achieve due to the dominant slow defect luminescence maximum.

  14. Optimized selective lactate excitation with a refocused multiple-quantum filter

    NASA Astrophysics Data System (ADS)

    Holbach, Mirjam; Lambert, Jörg; Johst, Sören; Ladd, Mark E.; Suter, Dieter

    2015-06-01

    Selective detection of lactate signals in in vivo MR spectroscopy with spectral editing techniques is necessary in situations where strong lipid or signals from other molecules overlap the desired lactate resonance in the spectrum. Several pulse sequences have been proposed for this task. The double-quantum filter SSel-MQC provides very good lipid and water signal suppression in a single scan. As a major drawback, it suffers from significant signal loss due to incomplete refocussing in situations where long evolution periods are required. Here we present a refocused version of the SSel-MQC technique that uses only one additional refocussing pulse and regains the full refocused lactate signal at the end of the sequence.

  15. Frequency up-conversion in nonpolar a-plane GaN/AlGaN based multiple quantum wells optimized for applications with silicon solar cells

    SciTech Connect

    Radosavljević, S.; Radovanović, J. Milanović, V.; Tomić, S.

    2014-07-21

    We have described a method for structural parameters optimization of GaN/AlGaN multiple quantum well based up-converter for silicon solar cells. It involves a systematic tuning of individual step quantum wells by use of the genetic algorithm for global optimization. In quantum well structures, the up-conversion process can be achieved by utilizing nonlinear optical effects based on intersubband transitions. Both single and double step quantum wells have been tested in order to maximize the second order susceptibility derived from the density matrix formalism. The results obtained for single step wells proved slightly better and have been further pursued to obtain a more complex design, optimized for conversion of an entire range of incident photon energies.

  16. Synthesis, characterization, and pharmacological studies of ferrocene-1H-1,2,3-triazole hybrids

    NASA Astrophysics Data System (ADS)

    Haque, Ashanul; Hsieh, Ming-Fa; Hassan, Syed Imran; Haque Faizi, Md. Serajul; Saha, Anannya; Dege, Necmi; Rather, Jahangir Ahmad; Khan, Muhammad S.

    2017-10-01

    A series of ferrocene-1H-1,2,3-triazole hybrids namely 1-(4-nitrophenyl)-4-ferrocenyl-1H-1,2,3-triazole (1), 1-(4,4‧-dinitro-2-biphenyl)-4-ferrocenyl-1H-1,2,3-triazole (2), 1-(3-chloro-4-fluorophenyl)-4-ferrocenyl-1H-1,2,3-triazole (3), 1-(4-bromophenyl)-4-ferrocenyl-1H-1,2,3-triazole (4) and 1-(2-nitrophenyl)-4-ferrocenyl-1H-1,2,3-triazole (5) were designed and synthesized by copper-catalyzed azide alkyne cycloaddition (CuAAC) reaction. All the new hybrids were characterized by microanalyses, NMR (1H and 13C), UV-vis, IR, ESI-MS and electrochemical techniques. Crystal structure of the compound (3) was solved by single crystal X-ray diffraction method. The structural (single crystal) and spectroscopic (UV-Vis. and IR) properties of the compound 3 have been analyzed and compared by complementary quantum modeling. Hybrids 1-5 exhibited low toxicity and demonstrated neuroprotective effect.

  17. Self-powered smart window controlled by a high open-circuit voltage InGaN/GaN multiple quantum well solar cell.

    PubMed

    Wu, Chia-Ching; Liou, Jian-Chiun; Diao, Chien-Chen

    2015-08-14

    A self-powered complementary electrochromic device (CECD) driven by a high open-circuit voltage InGaN/GaN multiple quantum well (MQW) solar cell has been designed. The coloration and bleaching time of the system were 5 and 8 s, respectively.

  18. Multiple exciton generation in quantum dots versus singlet fission in molecular chromophores for solar photon conversion.

    PubMed

    Beard, Matthew C; Johnson, Justin C; Luther, Joseph M; Nozik, Arthur J

    2015-06-28

    Both multiple exciton generation (MEG) in semiconductor nanocrystals and singlet fission (SF) in molecular chromophores have the potential to greatly increase the power conversion efficiency of solar cells for the production of solar electricity (photovoltaics) and solar fuels (artificial photosynthesis) when used in solar photoconverters. MEG creates two or more excitons per absorbed photon, and SF produces two triplet states from a single singlet state. In both cases, multiple charge carriers from a single absorbed photon can be extracted from the cell and used to create higher power conversion efficiencies for a photovoltaic cell or a cell that produces solar fuels, like hydrogen from water splitting or reduced carbon fuels from carbon dioxide and water (analogous to biological photosynthesis). The similarities and differences in the mechanisms and photoconversion cell architectures between MEG and SF are discussed.

  19. Multiple exciton generation in quantum dots versus singlet fission in molecular chromophores for solar photon conversion

    SciTech Connect

    Beard, M. C.; Johnson, J. C.; Luther, J. M.; Nozik, A. J.

    2015-05-18

    Both multiple exciton generation (MEG) in semiconductor nanocrystals and singlet fission (SF) in molecular chromophores have the potential to greatly increase the power conversion efficiency of solar cells for the production of solar electricity (photovoltaics) and solar fuels (artificial photosynthesis) when used in solar photoconverters. MEG creates two or more excitons per absorbed photon, and SF produces two triplet states from a single singlet state. In both cases, multiple charge carriers from a single absorbed photon can be extracted from the cell and used to create higher power conversion efficiencies for a photovoltaic cell or a cell that produces solar fuels, like hydrogen from water splitting or reduced carbon fuels from carbon dioxide and water (analogous to biological photosynthesis). The similarities and differences in the mechanisms and photoconversion cell architectures between MEG and SF are discussed.

  20. Multicolor Quantum Dot-Based Chemical Nose for Rapid and Array-Free Differentiation of Multiple Proteins.

    PubMed

    Xu, Qinfeng; Zhang, Yihong; Tang, Bo; Zhang, Chun-yang

    2016-02-16

    Nanomaterial-based differential sensors (e.g., chemical nose) have shown great potential for identification of multiple proteins because of their modulatable recognition and transduction capability but with the limitation of array separation, single-channel read-out, and long incubation time. Here, we develop a multicolor quantum dot (QD)-based multichannel sensing platform for rapid identification of multiple proteins in an array-free format within 1 min. A protein-binding dye of bromophenol blue (BPB) is explored as an efficient reversible quencher of QDs, and the mixture of BPB with multicolor QDs may generate the quenched QD-BPB complexes. The addition of proteins will disrupt the QD-BPB complexes as a result of the competitive protein-BPB binding, inducing the separation of BPB from the QDs and the generation of distinct fluorescence patterns. The multicolor patterns may be collected at a single-wavelength excitation and differentiated by a linear discriminant analysis (LDA). This multichannel sensing platform allows for the discrimination of ten proteins and seven cell lines with the fastest response rate reported to date, holding great promise for rapid and high-throughput medical diagnostics.

  1. Injection current dependences of electroluminescence transition energy in InGaN/GaN multiple quantum wells light emitting diodes under pulsed current conditions

    SciTech Connect

    Zhang, Feng; Ikeda, Masao Liu, Jianping; Zhang, Shuming; Zhou, Kun; Yang, Hui; Liu, Zongshun

    2015-07-21

    Injection current dependences of electroluminescence transition energy in blue InGaN/GaN multiple quantum wells light emitting diodes (LEDs) with different quantum barrier thicknesses under pulsed current conditions have been analyzed taking into account the related effects including deformation caused by lattice strain, quantum confined Stark effects due to polarization field partly screened by carriers, band gap renormalization, Stokes-like shift due to compositional fluctuations which are supposed to be random alloy fluctuations in the sub-nanometer scale, band filling effect (Burstein-Moss shift), and quantum levels in finite triangular wells. The bandgap renormalization and band filling effect occurring at high concentrations oppose one another, however, the renormalization effect dominates in the concentration range studied, since the band filling effect arising from the filling in the tail states in the valence band of quantum wells is much smaller than the case in the bulk materials. In order to correlate the carrier densities with current densities, the nonradiative recombination rates were deduced experimentally by curve-fitting to the external quantum efficiencies. The transition energies in LEDs both with 15 nm quantum barriers and 5 nm quantum barriers, calculated using full strengths of theoretical macroscopic polarization given by Barnardini and Fiorentini [Phys. Status Solidi B 216, 391 (1999)] are in excellent accordance with experimental results. The LED with 5 nm barriers has been shown to exhibit a higher transition energy and a smaller blue shift than those of LED with 15 nm barriers, which is mainly caused by the smaller internal polarization field in the quantum wells.

  2. Next Generation Photovoltaics Based on Multiple Exciton Generation in Quantum Dot Solar Cells

    NASA Astrophysics Data System (ADS)

    Nozik, Arthur J.

    Next Generation solar cells based onMultiple Exciton Generation (MEG) in semiconductorquantum dots (QDs) are described. This application of QDs depends upon efficient MEG in QDs incorporated into PV cells, followed by efficient exciton splitting into free electrons and holes and their efficient separation and collection in the cell contacts to produce multiple free carriers per absorbed photon. Using time-resolved transient absorption, bleaching, photoluminescence and THz spectroscopy, MEG has been initially confirmed in several Group IV-VI, III-V, II-VI, and IV colloidal semiconductor QDs. Some controversy using these techniques have now been attributed to effects of the variable of the QD surface chemisty and under certain conditions to artifacts arising from long-lived trapping of photoinduced charge; in our opinion these controversies have been resolved and are discussed here. Furthermore, various photovoltaic cell architectures utilizing QDs have recently been constructed and the photocurrent and photovoltage characterisitics have been studied. These photocurrent measurements provide a more direct measurement of MEG since the photogenerated carriers are counted directly via the current, and they are very consistent with the QYs of MEG reported using the proper spectroscopic techniques; thus, these new photocurrent measurements confirm the existence of enhanced exciton and carrier multiplication in QDs. The past work and prognosis for QD-based Next Generation PV cells based on MEG are discussed.

  3. Quantum Darwinism

    NASA Astrophysics Data System (ADS)

    Zurek, Wojciech Hubert

    2009-03-01

    Quantum Darwinism describes the proliferation, in the environment, of multiple records of selected states of a quantum system. It explains how the quantum fragility of a state of a single quantum system can lead to the classical robustness of states in their correlated multitude; shows how effective `wave-packet collapse' arises as a result of the proliferation throughout the environment of imprints of the state of the system; and provides a framework for the derivation of Born's rule, which relates the probabilities of detecting states to their amplitudes. Taken together, these three advances mark considerable progress towards settling the quantum measurement problem.

  4. An ultrafast spectroscopic and quantum mechanical investigation of multiple emissions in push-pull pyridinium derivatives bearing different electron donors.

    PubMed

    Carlotti, B; Benassi, E; Cesaretti, A; Fortuna, C G; Spalletti, A; Barone, V; Elisei, F

    2015-08-28

    A joint experimental and theoretical approach, involving state-of-the-art femtosecond fluorescence up-conversion measurements and quantum mechanical computations including vibronic effects, was employed to get a deep insight into the excited state dynamics of two cationic dipolar chromophores (Donor-π-Acceptor(+)) where the electron deficient portion is a N-methyl pyridinium and the electron donor a trimethoxyphenyl or a pyrene, respectively. The ultrafast spectroscopic investigation, and the time resolved area normalised emission spectra in particular, revealed a peculiar multiple emissive behaviour and allowed the distinct emitting states to be remarkably distinguished from solvation dynamics, occurring in water in a similar timescale. The two and three emissions experimentally detected for the trimethoxyphenyl and pyrene derivatives, respectively, were associated with specific local emissive minima in the potential energy surface of S1 on the ground of quantum-mechanical calculations. A low polar and planar Locally Excited (LE) state together with a highly polar and Twisted Intramolecular Charge Transfer (TICT) state is identified to be responsible for the dual emission of the trimethoxyphenyl compound. Interestingly, the more complex photobehaviour of the pyrenyl derivative was explained considering the contribution to the fluorescence coming not only from the LE and TICT states but also from a nearly Planar Intramolecular Charge Transfer (PICT) state, with both the TICT and the PICT generated from LE by progressive torsion around the quasi-single bond between the methylpyridinium and the ethene bridge. These findings point to an interconversion between rotamers for the pyrene compound taking place in its excited state against the Non-equilibrated Excited Rotamers (NEER) principle.

  5. Field-Induced Multiple Reentrant Quantum Phase Transitions in Randomly Dimerized Antiferromagnetic S=1/2 Heisenberg Chains

    NASA Astrophysics Data System (ADS)

    Hida, Kazuo

    2006-07-01

    The multiple reentrant quantum phase transitions in the S=1/2 antiferromagnetic Heisenberg chains with random bond alternation in the magnetic field are investigated by the density matrix renormalization group method combined with interchain mean field approximation. It is assumed that odd numbered bonds are antiferromagnetic with strength J and even numbered bonds can take the values JS and JW (JS > J > JW > 0) randomly with the probabilities p and 1- p, respectively. The pure version ( p=0 and 1) of this model has a spin gap but exhibits a field-induced antiferromagnetism in the presence of interchain coupling if Zeeman energy due to the magnetic field exceeds the spin gap. For 0 < p < 1, antiferromagnetism is induced by randomness at the small field region where the ground state is disordered due to the spin gap in the pure version. At the same time, this model exhibits randomness-induced plateaus at several values of magnetization. The antiferromagnetism is destroyed on the plateaus. As a consequence, we find a series of reentrant quantum phase transitions between transverse antiferromagnetic phases and disordered plateau phases with the increase of magnetic field for a moderate strength of interchain coupling. Above the main plateaus, the magnetization curve consists of a series of small plateaus and jumps between them. It is also found that antiferromagnetism is induced by infinitesimal interchain coupling at the jumps between the small plateaus. We conclude that this antiferromagnetism is supported by the mixing of low-lying excited states by the staggered interchain mean field even though the spin correlation function is short ranged in the ground state of each chain.

  6. Quantum interferences induced by multiple scattering paths of the electron prior to emission in large molecules

    NASA Astrophysics Data System (ADS)

    Agueny, H.; Makhoute, A.; Tökési, K.; Dubois, A.; Hansen, J. P.

    2017-09-01

    We theoretically investigate electron emission process from a dimer generated by swift highly charged ions. The process under consideration is dealt with a non-perturbative approach by solving the time-dependent Schrödinger equation on a two-dimensional spatial grid. Numerical calculations show rich structures related to the multiple scattering paths of the electron prior to emission. This manifests by the emergence of additional oscillations with high-frequency superimposed on the Young-type oscillatory structure in the observed electron-ejected spectrum. This is not the case when calculations are performed based on the superposition principle, in which the final wave function is just a coherent sum of component wave functions described the electron emission from two-independent atoms. Within this assumption, only a direct electron emission process is taken into account. We find that contributions arising from these multiple scattering paths modify the dynamic electron emission process, and therefore, show the incorrect applicability of the above-mentioned principle, in concordance with the recent findings based on a simple three-slit interference experiment, reported in Sawant et al. (2014).

  7. Origin of Hund's multiplicity rule in quasi-two-dimensional two-electron quantum dots

    SciTech Connect

    Sako, Tokuei; Paldus, Josef; Diercksen, Geerd H. F.

    2010-02-15

    The origin of Hund's multiplicity rules has been studied for a system of two electrons confined by a quasi-two-dimensional harmonic-oscillator potential by relying on a full configuration interaction wave function and Cartesian anisotropic Gaussian basis sets. In terms of appropriate normal-mode coordinates the wave function factors into a product of the center-of-mass and the internal components. The {sup 1{Pi}}{sub u} singlet state and the {sup 3{Pi}}{sub u} triplet state represent the energetically lowest pair of states to which Hund's multiplicity rule applies. They are shown to involve excitations into different degrees of freedom, namely, into the center-of-mass angular mode and the internal angular mode for the singlet and triplet states, respectively. The presence of an angular nodal line in the internal space allows then the triplet state to avoid the singularity in the electron-electron interaction potential, leading to the energy lowering of the triplet state relative to its counterpart singlet state.

  8. The Conformations and Structures of 1H-NONAFLUOROBUTANE

    NASA Astrophysics Data System (ADS)

    Fournier, Joseph A.; Bohn, Robert K.; Montgomery, John A.; , Jr.

    2012-06-01

    The all trans conformers of perfluorocarbons, unlike hydrocarbons, are helical with C-C-C-C dihedral angles about 1640. Fluorocarbons with H substitution can replace chlorofluorocarbons as propellants and compressor fluids without the disadvantage of causing ozone depletion in the upper atmosphere. 1H-perfluorobutane, CHF_2CF_2CF_2CF_3, has been studied by pulsed-jet Fourier transform microwave spectroscopy. The spectrum is very rich. Quantum chemical calculations identify five stable conformers with relative energies up to 1.1 kcal/mol. Thus far three conformers have been characterized and many lines remain unassigned. The assigned species have CCCCanti/CCCH gauche as well as the anti/anti and gauche/anti forms. Rotational constant values are 1428.9501(2) MHz, 593.323877(6) MHz, and 546.43578(6) MHz for the anti/gauche species, 1323.664(3) MHz, 617.6051(5) MHz for the ant/anti species, and 1066.9384(4) MHz, 768.4736(4) MHz, and 671.3145(4) MHz for the gauche/anti form.

  9. Crystalline 1H-1,2,3-triazol-5-ylidenes

    SciTech Connect

    Bertrand, Guy; Gulsado-Barrios, Gregorio; Bouffard, Jean; Donnadieu, Bruno

    2016-08-02

    The present invention provides novel and stable crystalline 1H-1,2,3 triazolium carbenes and metal complexes of 1H-1,2,3 triazolium carbenes. The present invention also provides methods of making 1H-1,2,3 triazolium carbenes and metal complexes of 1H-1,2,3 triazolium carbenes. The present invention also provides methods of using 1H-1,2,3 triazolium carbenes and metal complexes of 1H-1,2,3 triazolium carbenes in catalytic reactions.

  10. Absorption enhancement through Fabry-Pérot resonant modes in a 430 nm thick InGaAs/GaAsP multiple quantum wells solar cell

    NASA Astrophysics Data System (ADS)

    Behaghel, B.; Tamaki, R.; Vandamme, N.; Watanabe, K.; Dupuis, C.; Bardou, N.; Sodabanlu, H.; Cattoni, A.; Okada, Y.; Sugiyama, M.; Collin, S.; Guillemoles, J.-F.

    2015-02-01

    We study light management in a 430 nm-thick GaAs p-i-n single junction solar cell with 10 pairs of InGaAs/GaAsP multiple quantum wells (MQWs). The epitaxial layer transfer on a gold mirror improves light absorption and increases the external quantum efficiency below GaAs bandgap by a factor of four through the excitation of Fabry-Perot resonances. We show a good agreement with optical simulation and achieve around 10% conversion efficiency. We demonstrate numerically that this promising result can be further improved by anti-reflection layers. This study paves the way to very thin MQWs solar cells.

  11. Absorption enhancement through Fabry-Pérot resonant modes in a 430 nm thick InGaAs/GaAsP multiple quantum wells solar cell

    SciTech Connect

    Behaghel, B.; Tamaki, R.; Watanabe, K.; Sodabanlu, H.; Vandamme, N.; Dupuis, C.; Bardou, N.; Cattoni, A.; Okada, Y.; Sugiyama, M.; Collin, S.; Guillemoles, J.-F.

    2015-02-23

    We study light management in a 430 nm-thick GaAs p-i-n single junction solar cell with 10 pairs of InGaAs/GaAsP multiple quantum wells (MQWs). The epitaxial layer transfer on a gold mirror improves light absorption and increases the external quantum efficiency below GaAs bandgap by a factor of four through the excitation of Fabry-Perot resonances. We show a good agreement with optical simulation and achieve around 10% conversion efficiency. We demonstrate numerically that this promising result can be further improved by anti-reflection layers. This study paves the way to very thin MQWs solar cells.

  12. Multiple logic functions from extended blockade region in a silicon quantum-dot transistor

    SciTech Connect

    Lee, Youngmin; Lee, Sejoon Im, Hyunsik; Hiramoto, Toshiro

    2015-02-14

    We demonstrate multiple logic-functions at room temperature on a unit device of the Si single electron transistor (SET). Owing to the formation of the multi-dot system, the device exhibits the enhanced Coulomb blockade characteristics (e.g., large peak-to-valley current ratio ∼200) that can improve the reliability of the SET-based logic circuits. The SET displays a unique feature useful for the logic applications; namely, the Coulomb oscillation peaks are systematically shifted by changing either of only the gate or the drain voltage. This enables the SET to act as a multi-functional one-transistor logic gate with AND, OR, NAND, and XOR functions.

  13. The impact of quantum dots magnetization on spin separation and spin current in a multiple quantum-dot ring in the presence of Rashba spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Faizabadi, Edris; Eslami, Leila

    2012-06-01

    The influence of quantum dot magnetization on electronic spin-dependent transport is investigated through a triple-quantum-dot ring structure in which one of the quantum dots is non-magnetic subjected to the Rashba spin-orbit interaction and the two other ones possess magnetic structure. Evaluated results, based on single particle Green's function formalism, indicate that the presence of magnetic moment on the quantum dots leads to additional spin-dependent phase factor which affects electronic transport through the system. For both antiferromagnetic and ferromagnetic quantum dots, the system can operate as a spin-splitter but differently; by tuning Rashba spin-orbit strength and in the presence of magnetic flux, respectively. Besides, in the absence of one of the outgoing leads, spin current in the output is calculated and demonstrated that magnetization of quantum dots leads to spin current even in the absence of Rashba spin-orbit effect. Moreover, it is shown that in the presence of Rashba spin orbit interaction, magnetic quantum dots, and magnetic flux, the two terminal system produces a completely tunable spin current.

  14. 3D 15N/15N/1H chemical shift correlation experiment utilizing an RFDR-based 1H/1H mixing period at 100 kHz MAS

    NASA Astrophysics Data System (ADS)

    Nishiyama, Yusuke; Malon, Michal; Ishii, Yuji; Ramamoorthy, Ayyalusamy

    2014-07-01

    Homonuclear correlation NMR experiments are commonly used in the high-resolution structural studies of proteins. While 13C/13C chemical shift correlation experiments utilizing dipolar recoupling techniques are fully utilized under MAS, correlation of the chemical shifts of 15N nuclei in proteins has been a challenge. Previous studies have shown that the negligible 15N-15N dipolar coupling in peptides or proteins necessitates the use of a very long mixing time (typically several seconds) for effective spin diffusion to occur and considerably slows down a 15N/15N correlation experiment. In this study, we show that the use of mixing proton magnetization, instead of 15N, via the recoupled 1H-1H dipolar couplings enable faster 15N/15N correlation. In addition, the use of proton-detection under ultrafast MAS overcomes the sensitivity loss due to multiple magnetization transfer (between 1H and 15N nuclei) steps. In fact, less than 300 nL (∼1.1 micromole quantity) sample is sufficient to acquire the 3D spectrum within 5 h. Our results also demonstrate that a 3D 15N/15N/1H experiment can render higher resolution spectra that will be useful in the structural studies of proteins at ultrafast MAS frequencies. 3D 15N/15N/1H and 2D radio frequency-driven dipolar recoupling (RFDR)-based 1H/1H experimental results obtained from a powder sample of N-acetyla-L-15N-valyl-L-15N-leucine at 70 and 100 kHz MAS frequencies are presented.

  15. Simultaneous quantitative detection of multiple tumor markers with a rapid and sensitive multicolor quantum dots based immunochromatographic test strip.

    PubMed

    Wang, Chunying; Hou, Fei; Ma, Yicai

    2015-06-15

    A novel multicolor quantum dots (QDs) based immunochromatographic test strip (ICTS) was developed for simultaneous quantitative detection of multiple tumor markers, by utilizing alpha fetoprotein (AFP) and carcinoembryonic antigen (CEA) as models. The immunosensor could realize simultaneous quantitative detection of tumor markers with only one test line and one control line on the nitrocellulose membrane (NC membrane) due to the introduction of multicolor QDs. In this method, a mixture of mouse anti-AFP McAb and mouse anti-CEA McAb was coated on NC membrane as test line and goat anti-mouse IgG antibody was coated as control line. Anti-AFP McAb-QDs546 conjugates and anti-CEA McAb-QDs620 conjugates were mixed and applied to the conjugate pad. Simultaneous quantitative detection of multiple tumor markers was achieved by detecting the fluorescence intensity of captured QDs labels on test line and control line using a test strip reader. Under the optimum conditions, AFP and CEA could be detected as low as 3 ng/mL and 2 ng/mL in 15 min with a sample volume of 80 μL, and no obvious cross-reactivity was observed. The immunosensor was validated with 130 clinical samples and in which it exhibited high sensitivity (93% for AFP and 87% for CEA) and specificity (94% for AFP and 97% for CEA). The immunosensor also demonstrated high recoveries (87.5-113% for AFP and 90-97.3% for CEA) and low relative standard deviations (RSDs) (2.8-6.2% for AFP and 4.9-9.6% for CEA) when testing spiked human serum. This novel multicolor QDs based ICTS provides an easy and rapid, simultaneous quantitative detecting strategy for point-of-care testing of tumor markers. Copyright © 2014 Elsevier B.V. All rights reserved.

  16. Aromatic derivatives of 2,3-dihydro-1H-1,5-benzodiazepine

    SciTech Connect

    Orlov, V.D.; Desenko, S.M.; Kiroga, Kh.

    1987-09-01

    The formation of 2,2,4-trisubstituted 2,3-dihydro-1H-1,5-benzodiazepines in the reactions of acetylarenes with 4-ethoxy- and 3,5-dimethyl-1,2-phenylenediamine was studied. The effect of the substituents on the individual stages of the reactions is discussed. A quantum-chemical calculation of the relative nucleophilicity of 1,2-phenylenediamine, 2,3-diaminopyridine, and 3,4-diaminofurazan was undertaken.

  17. Simultaneous dual-functioning InGaN/GaN multiple-quantum-well diode for transferrable optoelectronics

    NASA Astrophysics Data System (ADS)

    Shi, Zheng; Yuan, Jialei; Zhang, Shuai; Liu, Yuhuai; Wang, Yongjin

    2017-10-01

    We propose a wafer-level procedure for the fabrication of 1.5-mm-diameter dual functioning InGaN/GaN multiple-quantum-well (MQW) diodes on a GaN-on-silicon platform for transferrable optoelectronics. Nitride semiconductor materials are grown on (111) silicon substrates with intermediate Al-composition step-graded buffer layers, and membrane-type MQW-diode architectures are obtained by a combination of silicon removal and III-nitride film backside thinning. Suspended MQW-diodes are directly transferred from silicon to foreign substrates such as metal, glass and polyethylene terephthalate by mechanically breaking the support beams. The transferred MQW-diodes display strong electroluminescence under current injection and photodetection under light irradiation. Interestingly, they demonstrate a simultaneous light-emitting light-detecting function, endowing the 1.5-mm-diameter MQW-diode with the capability of producing transferrable optoelectronics for adjustable displays, wearable optical sensors, multifunctional energy harvesting, flexible light communication and monolithic photonic circuit.

  18. Photoluminescence from ultrathin Ge-rich multiple quantum wells observed up to room temperature: Experiments and modeling

    NASA Astrophysics Data System (ADS)

    Wendav, T.; Fischer, I. A.; Virgilio, M.; Capellini, G.; Oliveira, F.; Cerqueira, M. F.; Benedetti, A.; Chiussi, S.; Zaumseil, P.; Schwartz, B.; Busch, K.; Schulze, J.

    2016-12-01

    Employing a low-temperature growth mode, we fabricated ultrathin S i1 -xG ex /Si multiple quantum well structures with a well thickness of less than 1.5 nm and a Ge concentration above 60% directly on a Si substrate. We identified an unusual temperature-dependent blueshift of the photoluminescence (PL) and exceptionally low thermal quenching. We find that this behavior is related to the relative intensities of the no-phonon (NP) peak and a phonon-assisted replica that are the main contributors to the total PL signal. To investigate these aspects in more detail, we developed a strategy to calculate the PL spectrum employing a self-consistent multivalley effective mass model, in combination with second-order perturbation theory. Through our investigation, we find that while the phonon-assisted feature decreases with temperature, the NP feature shows a strong increase in the recombination rate. Besides leading to the observed robustness against thermal quenching, this causes the observed blueshift of the total PL signal.

  19. Passivation of multiple-quantum-well Ge0.97Sn0.03/Ge p-i-n photodetectors

    NASA Astrophysics Data System (ADS)

    Morea, Matthew; Brendel, Corinna E.; Zang, Kai; Suh, Junkyo; Fenrich, Colleen S.; Huang, Yi-Chiau; Chung, Hua; Huo, Yijie; Kamins, Theodore I.; Saraswat, Krishna C.; Harris, James S.

    2017-02-01

    We study the effect of surface passivation on pseudomorphic multiple-quantum-well Ge0.97Sn0.03/Ge p-i-n photodetectors. A combination of ozone oxidation to form GeOx and GeSnOx on the surface of the diodes followed by atomic layer deposition of Al2O3 for protection of these native oxides provides reduced dark current. With a temperature-dependent investigation of dark current, we calculate the activation energy to be 0.26 eV at a bias of -0.1 V and 0.05 eV at -1 V for the sample passivated by this ozone method. Based on these activation energy results, we find that the current is less dominated by bulk tunneling at lower reverse bias values; hence, the effect of surface passivation is more noticeable with nearly an order-of-magnitude improvement in dark current for the ozone-passivated sample compared to control devices without the ozone treatment at a voltage of -0.1 V. Passivation also results in a significant enhancement of the responsivity, particularly for shorter wavelengths, with 26% higher responsivity at 1100 nm and 16% higher performance at 1300 nm.

  20. Non-protein coding RNA-based genosensor with quantum dots as electrochemical labels for attomolar detection of multiple pathogens.

    PubMed

    Vijian, Dinesh; Chinni, Suresh V; Yin, Lee Su; Lertanantawong, Benchaporn; Surareungchai, Werasak

    2016-03-15

    The ability of a diagnostic test to detect multiple pathogens simultaneously is useful to obtain meaningful information for clinical treatment and preventive measures. We report a highly sensitive and specific electrochemical biosensor assay for simultaneous detection of three gene targets using quantum dots (QDs). The targets are novel non-protein coding RNA (npcRNA) sequences of Vibrio cholerae, Salmonella sp. and Shigella sp., which cause diarrheal diseases. QDs (PbS, CdS, ZnS) were synthesized and functionalized with DNA probes that were specific to each pathogen. Electrochemical detection of QDs was performed using square wave anodic stripping voltammetry (SWASV). The QDs gave distinct peaks at 0.5 V (PbS), 0.75 V (CdS) and 1.1 V (ZnS). There was no interference in signal response when all three QDs were mixed and detected simultaneously. The detection limits of single and multiplex assays with linear targets and PCR products were in the attomolar ranges. The high assay sensitivity, in combination with specific npcRNA sequences as novel diagnostic targets, makes it a viable tool for detecting pathogens from food, environment and clinical samples. Copyright © 2015 Elsevier B.V. All rights reserved.

  1. Onset of surface stimulated emission at 260 nm from AlGaN multiple quantum wells

    SciTech Connect

    Li, Xiaohang E-mail: dupuis@gatech.edu; Xie, Hongen; Ponce, Fernando A.; Ryou, Jae-Hyun; Detchprohm, Theeradetch; Dupuis, Russell D. E-mail: dupuis@gatech.edu

    2015-12-14

    We demonstrated onset of deep-ultraviolet (DUV) surface stimulated emission (SE) from c-plane AlGaN multiple-quantum well (MQW) heterostructures grown on a sapphire substrate by optical pumping at room temperature. The onset of SE became observable at a pumping power density of 630 kW/cm{sup 2}. Spectral deconvolution revealed superposition of a linearly amplified spontaneous emission peak at λ ∼ 257.0 nm with a full width at half maximum (FWHM) of ∼12 nm and a superlinearly amplified SE peak at λ ∼ 260 nm with a narrow FWHM of less than 2 nm. In particular, the wavelength of ∼260 nm is the shortest wavelength of surface SE from III-nitride MQW heterostructures to date. Atomic force microscopy and scanning transmission electron microscopy measurements were employed to investigate the material and structural quality of the AlGaN heterostructures, showing smooth surface and sharp layer interfaces. This study offers promising results for AlGaN heterostructures grown on sapphire substrates for the development of DUV vertical cavity surface emitting lasers (VCSELs)

  2. Suspended p-n junction InGaN/GaN multiple quantum wells device with bottom silver reflector

    NASA Astrophysics Data System (ADS)

    Gao, Xumin; Li, Xin; Yang, Yongchao; Yuan, Wei; Xu, Yin; Cai, Wei; Wang, Yongjin

    2017-07-01

    In this study, we propose, fabricate, and characterize suspended p-n junction InGaN/GaN multiple quantum wells (MQWs) device with a bottom silver reflector for diverse applications. The suspended device was achieved through a double-side process on the GaN-on-silicon platform and tested by using a micro-reflectance/transmittance setup. When the suspended device operates under the light-emitting diode mode, a fraction of the emitted light reflected by the bottom silver reflector can enter into the air through the top escape cone, leading to improved light extraction efficiency. When the suspended device operates under the photodiode mode, part of the transmitted light can be reflected back by the bottom silver reflector to enhance the photovoltaic effect. The experimental results demonstrate that such suspended device can be used as both transmitter and receiver for visible light communication. And the detecting features even when the suspended structure is under turn-on state, demonstrating a potential realization of light emission and photodetection simultaneously.

  3. Nanoscale characterization of GaN/InGaN multiple quantum wells on GaN nanorods by photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Chen, Weijian; Wen, Xiaoming; Latzel, Michael; Yang, Jianfeng; Huang, Shujuan; Shrestha, Santosh; Patterson, Robert; Christiansen, Silke; Conibeer, Gavin

    2017-02-01

    GaN/InGaN multiple quantum wells (MQW) and GaN nanorods have been widely studied as a candidate material for high-performance light emitting diodes. In this study, GaN/InGaN MQW on top of GaN nanorods are characterized in nanoscale using confocal microscopy associated with photoluminescence spectroscopy, including steady-state PL, timeresolved PL and fluorescence lifetime imaging (FLIM). Nanorods are fabricated by etching planar GaN/InGaN MQWs on top of a GaN layer on a c-plane sapphire substrate. Photoluminescence efficiency from the GaN/InGaN nanorods is evidently higher than that of the planar structure, indicating the emission improvement. Time-resolved photoluminescence (TRPL) prove that surface defects on GaN nanorod sidewalls have a strong influence on the luminescence property of the GaN/InGaN MWQs. Such surface defects can be eliminated by proper surface passivation. Moreover, densely packed nanorod array and sparsely standing nanorods have been studied for better understanding the individual property and collective effects from adjacent nanorods. The combination of the optical characterization techniques guides optoelectronic materials and device fabrication.

  4. Experimental and theoretical study of multiple cations intermixing in InP-based quantum dot-in-well structure

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Djie, Hery S.; Ooi, Boon S.

    2006-02-01

    We investigated the multiple cations intermixing in InAs/InGaAlAs quantum dot-in-well laser structure grown on InP substrate using impurity-free vacancy disordering (IFVD) technique. Selective control of the bandgap shifts has been achieved using SiO II and Si xN y annealing caps. A differential wavelength shift of 76 nm has been observed after a rapid thermal annealing step at 750 °C for 30 s. In contrast to most IFVD results in other materials, we observed a larger bandgap shift from the Si xN y capped samples than from the SiO II capped samples. Based on theoretical calculations, we attribute this to the different effective interdiffusion rates of group-III cations. The demonstrated intermixing process provides an effective method for fine tuning the bandgap of InAs QDs around 1.55 μm as an alternative to the growth manipulation, as well as for realizing photonics integrated circuits.

  5. Design and Room-Temperature Operation of GaAs/AlGaAs Multiple Quantum Well Nanowire Lasers.

    PubMed

    Saxena, Dhruv; Jiang, Nian; Yuan, Xiaoming; Mokkapati, Sudha; Guo, Yanan; Tan, Hark Hoe; Jagadish, Chennupati

    2016-08-10

    We present the design and room-temperature lasing characteristics of single nanowires containing coaxial GaAs/AlGaAs multiple quantum well (MQW) active regions. The TE01 mode, which has a doughnut-shaped intensity profile and is polarized predominantly in-plane to the MQWs, is predicted to lase in these nanowire heterostructures and is thus chosen for the cavity design. Through gain and loss calculations, we determine the nanowire dimensions required to minimize loss for the TE01 mode and determine the optimal thickness and number of QWs for minimizing the threshold sheet carrier density. In particular, we show that there is a limit to the minimum and maximum number of QWs that are required for room-temperature lasing. Based on our design, we grew nanowires of a suitable diameter containing eight uniform coaxial GaAs/AlGaAs MQWs. Lasing was observed at room temperature from optically pumped single nanowires and was verified to be from TE01 mode by polarization measurements. The GaAs MQW nanowire lasers have a threshold fluence that is a factor of 2 lower than that previously demonstrated for room-temperature GaAs nanowire lasers.

  6. Design and Performance of a Sensor System for Detection of Multiple Chemicals Using an External Cavity Quantum Cascade Laser

    SciTech Connect

    Phillips, Mark C.; Taubman, Matthew S.; Bernacki, Bruce E.; Cannon, Bret D.; Schiffern, John T.; Myers, Tanya L.

    2010-01-23

    We describe the performance of a sensor system designed for simultaneous detection of multiple chemicals with both broad and narrow absorption features. The sensor system consists of a broadly tunable external cavity quantum cascade laser (ECQCL), multi-pass Herriott cell, and custom low-noise electronics. The ECQCL features a rapid wavelength tuning rate of 2265 cm 1/s (15660 nm/s) over its tuning range of 1150-1270 cm 1 (7.87-8.70 μm), which permits detection of molecules with broad absorption features and dynamic concentrations, while the 0.2 cm-1 spectral resolution of the ECQCL system allows measurement of small molecules with atmospherically broadened absorption lines. High-speed amplitude modulation and low-noise electronics are used to improve the ECQCL performance for direct absorption measurements. We demonstrate simultaneous detection of Freon-134a (1,1,1,2-tetrafluoroethane), ammonia (NH3), and nitrous oxide (N2O) at low-ppb concentrations in field measurements of atmospheric chemical releases from a point source.

  7. Calculation of absorption spectra involving multiple excited states: approximate methods based on the mixed quantum classical Liouville equation.

    PubMed

    Bai, Shuming; Xie, Weiwei; Zhu, Lili; Shi, Qiang

    2014-02-28

    We investigate the calculation of absorption spectra based on the mixed quantum classical Liouville equation (MQCL) methods. It has been shown previously that, for a single excited state, the averaged classical dynamics approach to calculate the linear and nonlinear spectroscopy can be derived using the MQCL formalism. This work focuses on problems involving multiple coupled excited state surfaces, such as in molecular aggregates and in the cases of coupled electronic states. A new equation of motion to calculate the dipole-dipole correlation functions within the MQCL formalism is first presented. Two approximate methods are then proposed to solve the resulted equations of motion. The first approximation results in a mean field approach, where the nuclear dynamics is governed by averaged forces depending on the instantaneous electronic states. A modification to the mean field approach based on first order moment expansion is also proposed. Numerical examples including calculation of the absorption spectra of Frenkel exciton models of molecular aggregates, and the pyrazine molecule are presented.

  8. Calculation of absorption spectra involving multiple excited states: Approximate methods based on the mixed quantum classical Liouville equation

    SciTech Connect

    Bai, Shuming; Xie, Weiwei; Zhu, Lili; Shi, Qiang

    2014-02-28

    We investigate the calculation of absorption spectra based on the mixed quantum classical Liouville equation (MQCL) methods. It has been shown previously that, for a single excited state, the averaged classical dynamics approach to calculate the linear and nonlinear spectroscopy can be derived using the MQCL formalism. This work focuses on problems involving multiple coupled excited state surfaces, such as in molecular aggregates and in the cases of coupled electronic states. A new equation of motion to calculate the dipole-dipole correlation functions within the MQCL formalism is first presented. Two approximate methods are then proposed to solve the resulted equations of motion. The first approximation results in a mean field approach, where the nuclear dynamics is governed by averaged forces depending on the instantaneous electronic states. A modification to the mean field approach based on first order moment expansion is also proposed. Numerical examples including calculation of the absorption spectra of Frenkel exciton models of molecular aggregates, and the pyrazine molecule are presented.

  9. Computation of Hydration Free Energies Using the Multiple Environment Single System Quantum Mechanical/Molecular Mechanical Method.

    PubMed

    König, Gerhard; Mei, Ye; Pickard, Frank C; Simmonett, Andrew C; Miller, Benjamin T; Herbert, John M; Woodcock, H Lee; Brooks, Bernard R; Shao, Yihan

    2016-01-12

    A recently developed MESS-E-QM/MM method (multiple-environment single-system quantum mechanical molecular/mechanical calculations with a Roothaan-step extrapolation) is applied to the computation of hydration free energies for the blind SAMPL4 test set and for 12 small molecules. First, free energy simulations are performed with a classical molecular mechanics force field using fixed-geometry solute molecules and explicit TIP3P solvent, and then the non-Boltzmann-Bennett method is employed to compute the QM/MM correction (QM/MM-NBB) to the molecular mechanical hydration free energies. For the SAMPL4 set, MESS-E-QM/MM-NBB corrections to the hydration free energy can be obtained 2 or 3 orders of magnitude faster than fully converged QM/MM-NBB corrections, and, on average, the hydration free energies predicted with MESS-E-QM/MM-NBB fall within 0.10-0.20 kcal/mol of full-converged QM/MM-NBB results. Out of five density functionals (BLYP, B3LYP, PBE0, M06-2X, and ωB97X-D), the BLYP functional is found to be most compatible with the TIP3P solvent model and yields the most accurate hydration free energies against experimental values for solute molecules included in this study.

  10. Optical properties of as-grown and annealed InAs(N)/InGaAsP strained multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Chen, Guan-Ru; Lin, Hao-Hsiung; Wang, Jyh-Shyang; Shih, Ding-Kang

    2001-12-01

    Optical and structural properties of as-grown and annealed InAs(N)/InGaAsP strained multiple quantum-well (MQW) structures grown by gas source molecular-beam epitaxy are investigated by photoluminescence (PL), double crystal x-ray diffraction, and photoconductivity spectroscopies. Properties of the as-grown and annealed MQW's are studied and those of the InAs/InGaAsP MQW (C821) and the InAsN/InGaAsP MQW with the lowest nitrogen contents N=1.1% in the well (C822) are compared. For the C821 InAs/InGaAsP MQW with a very large total strain, a low energy shoulder, possibly induced by defects or impurities, can be seen in the low temperature PL spectrum, and a large density of nonradiative recombination centers is found. For nitrogen-containing MQW's, the PL full width at half maximum and PL peak evolutions with increasing annealing temperature are influenced by the alloy inhomogeneities. The initial redshift of the PL peak after rapid thermal annealing means that the luminescence is dominated by As-rich regions in these as-grown samples. Exciton localization induced by alloy disorders is also found in high-nitrogen-content samples. By comparing the experimental results of C821 and C822, adding a little nitrogen to reduce the rather large total strain in the structure is beneficial to structural and optical quality improvement.

  11. Proton and H+-ion radiation effect on intersubband transition in GaAs/AlGaAs multiple quantum wells

    NASA Astrophysics Data System (ADS)

    Berhane, Yosief; Manasreh, M. Omar; Weaver, B. D.; Tan, H. H.; Jagadish, Chennupati

    2001-11-01

    Intersubband transition in 3-Me He+-ion or 1 MeV proton irradiated GaAs/AlGaAs multiple quantum wells were studied using optical absorption technique. The intersubband transitions in 3MeV He+-ion irradiated were completely depleted in samples irradiated with doses as low as 1 X 1014 cm-2. Thermal annealing recovery of intersubband transitions was observed in samples irradiated with lower doses while in heavily irradiated samples intersubband transition show no annealing recovery which could be said irradiation induced defects are so severe that annealing temperature could not repair the damage. On the other hand, intersubband transitions in 1 MeV proton irradiated samples were completely depleted with irradiation doses as low as 4 X 1014 cm-2. More than 80 percent recovery was achieved at annealing temperature as low as 650 degrees C. The total integrated area and peak position energy of un-irradiated and irradiated samples were monitored as a function of annealing temperature. Depletion recovery here is noted to depend on the thermal annealing and irradiation dose.

  12. Hydration free energies using semiempirical quantum mechanical Hamiltonians and a continuum solvent model with multiple atomic-type parameters.

    PubMed

    Anisimov, Victor M; Cavasotto, Claudio N

    2011-06-23

    To build the foundation for accurate quantum mechanical (QM) simulation of biomacromolecules in an aqueous environment, we undertook the optimization of the COnductor-like Screening MOdel (COSMO) atomic radii and atomic surface tension coefficients for different semiempirical Hamiltonians adhering to the same computational conditions recently followed in the simulation of biomolecular systems. This optimization was achieved by reproducing experimental hydration free energies of a set consisting of 507 neutral and 99 ionic molecules. The calculated hydration free energies were significantly improved by introducing a multiple atomic-type scheme that reflects different chemical environments. The nonpolar contribution was treated according to the scaled particle Claverie-Pierotti formalism. Separate radii and surface tension coefficient sets have been developed for AM1, PM3, PM5, and RM1 semiempirical Hamiltonians, with an average unsigned error for neutral molecules of 0.64, 0.66, 0.73, and 0.71 kcal/mol, respectively. Free energy calculation of each molecule took on average 0.5 s on a single processor. The new sets of parameters will enhance the quality of semiempirical QM calculations using COSMO in biomolecular systems. Overall, these results further extend the utility of QM methods to chemical and biological systems in the condensed phase.

  13. Observation of Room Temperature Photoluminescence from Asymmetric CuGaO2/ZnO/ZnMgO Multiple Quantum Well Structures.

    PubMed

    Aneesh, P M; Jayaraj, M K; Reshmi, R; Ajimsha, R S; Kukreja, L M; Aldrin, A; Rojas, F; Bertomeu, J; López-Vidrier, J; Hernández, S

    2015-05-01

    Asymmetric (CuGaO2/ZnO/ZnMgO) and symmetric (ZnMgO/ZnO/ZnMgO) multiple quantum well (MQW) structures were successfully fabricated using pulsed laser deposition (PLD) and their comparison were made. Efficient room temperature photoluminescent (PL) emission was observed from these MQWs and temperature dependent luminescence of asymmetric and symmetric MQWs can be explained using the existing theories. A systematic blue shift was observed in both MQWs with decrease in the confinement layer thickness which could be attributed to the quantum confinement effects. The PL emission from asymmetric and symmetric MQW structures were blue shifted compared to 150 nm thick ZnO thin film grown by PLD due to quantum confinement effects.

  14. Multiplicity

    DTIC Science & Technology

    1991-04-01

    practice as a "[descent] into that inner circle of the Inferno where the damned endlessly degate multiplicity for sentencing." United States v. Barnard...select the charges to be brought in a particular case"). 19 Brown v. Ohio, 432 U.S. 161, 165 (1977). 20 Whalen v. United States, 445 U.S. at 689. 21...parte Lange, 8-5 U.S. (19 Wall.) 163 (1874). Cf. Brown v. Ohio, 432 U.S. at 165 ("once the legislature has acted courts may not impose more than one

  15. Some properties of the sum C1(h, k)

    NASA Astrophysics Data System (ADS)

    Cetin, Elif

    2017-07-01

    In [10], we have investigated properties of the sum C1(h, k). In this paper, we will give some other arithmetic properties of the sum C1(h, k). Moreover, in the light of the sum B1(h, k), which has also defined in [10], we will give specific values of the sum C1(h, k) when h + k is an odd number. Finally, we will give a relation between the sum C1(h, k) and the Hardy-Berndt sum s5(h, k) for a special case.

  16. Accurate molecular dynamics and nuclear quantum effects at low cost by multiple steps in real and imaginary time: Using density functional theory to accelerate wavefunction methods.

    PubMed

    Kapil, V; VandeVondele, J; Ceriotti, M

    2016-02-07

    The development and implementation of increasingly accurate methods for electronic structure calculations mean that, for many atomistic simulation problems, treating light nuclei as classical particles is now one of the most serious approximations. Even though recent developments have significantly reduced the overhead for modeling the quantum nature of the nuclei, the cost is still prohibitive when combined with advanced electronic structure methods. Here we present how multiple time step integrators can be combined with ring-polymer contraction techniques (effectively, multiple time stepping in imaginary time) to reduce virtually to zero the overhead of modelling nuclear quantum effects, while describing inter-atomic forces at high levels of electronic structure theory. This is demonstrated for a combination of MP2 and semi-local DFT applied to the Zundel cation. The approach can be seamlessly combined with other methods to reduce the computational cost of path integral calculations, such as high-order factorizations of the Boltzmann operator or generalized Langevin equation thermostats.

  17. High-resolution 2D NMR spectra in inhomogeneous fields based on intermolecular multiple-quantum coherences with efficient acquisition schemes

    NASA Astrophysics Data System (ADS)

    Lin, Meijin; Huang, Yuqing; Chen, Xi; Cai, Shuhui; Chen, Zhong

    2011-01-01

    High-resolution 2D NMR spectra in inhomogeneous fields can be achieved by the use of intermolecular multiple-quantum coherences and shearing reconstruction of 3D data. However, the long acquisition time of 3D spectral data is generally unbearable for invivo applications. To overcome this problem, two pulse sequences dubbed as iDH-COSY and iDH-JRES were proposed in this paper. Although 3D acquisition is still required for the new sequences, the high-resolution 2D spectra can be obtained with a relatively short scanning time utilizing the manipulation of indirect evolution period and sparse sampling. The intermolecular multiple-quantum coherence treatment combined with the raising and lowering operators was applied to derive analytical signal expressions for the new sequences. And the experimental observations agree with the theoretical predictions. Our results show that the new sequences possess bright perspective in the applications on invivo localized NMR spectroscopy.

  18. Accurate molecular dynamics and nuclear quantum effects at low cost by multiple steps in real and imaginary time: Using density functional theory to accelerate wavefunction methods

    SciTech Connect

    Kapil, V.; Ceriotti, M.; VandeVondele, J.

    2016-02-07

    The development and implementation of increasingly accurate methods for electronic structure calculations mean that, for many atomistic simulation problems, treating light nuclei as classical particles is now one of the most serious approximations. Even though recent developments have significantly reduced the overhead for modeling the quantum nature of the nuclei, the cost is still prohibitive when combined with advanced electronic structure methods. Here we present how multiple time step integrators can be combined with ring-polymer contraction techniques (effectively, multiple time stepping in imaginary time) to reduce virtually to zero the overhead of modelling nuclear quantum effects, while describing inter-atomic forces at high levels of electronic structure theory. This is demonstrated for a combination of MP2 and semi-local DFT applied to the Zundel cation. The approach can be seamlessly combined with other methods to reduce the computational cost of path integral calculations, such as high-order factorizations of the Boltzmann operator or generalized Langevin equation thermostats.

  19. Accurate molecular dynamics and nuclear quantum effects at low cost by multiple steps in real and imaginary time: Using density functional theory to accelerate wavefunction methods

    NASA Astrophysics Data System (ADS)

    Kapil, V.; VandeVondele, J.; Ceriotti, M.

    2016-02-01

    The development and implementation of increasingly accurate methods for electronic structure calculations mean that, for many atomistic simulation problems, treating light nuclei as classical particles is now one of the most serious approximations. Even though recent developments have significantly reduced the overhead for modeling the quantum nature of the nuclei, the cost is still prohibitive when combined with advanced electronic structure methods. Here we present how multiple time step integrators can be combined with ring-polymer contraction techniques (effectively, multiple time stepping in imaginary time) to reduce virtually to zero the overhead of modelling nuclear quantum effects, while describing inter-atomic forces at high levels of electronic structure theory. This is demonstrated for a combination of MP2 and semi-local DFT applied to the Zundel cation. The approach can be seamlessly combined with other methods to reduce the computational cost of path integral calculations, such as high-order factorizations of the Boltzmann operator or generalized Langevin equation thermostats.

  20. In vivo single-shot three-dimensionally localized multiple quantum spectroscopy of GABA in the human brain with improved spectral selectivity

    NASA Astrophysics Data System (ADS)

    Choi, In-Young; Lee, Sang-Pil; Shen, Jun

    2005-01-01

    A single-shot multiple quantum filtering method is developed that uses two double-band frequency selective pulses for enhanced spectral selectivity in combination with a slice-selective 90°, a slice-selective universal rotator 90°, and a spectral-spatial pulse composed of two slice-selective universal rotator 45° pulses for single-shot three-dimensional localization. The use of this selective multiple quantum filtering method for C3 and C4 methylene protons of GABA resulted in improved spectral selectivity for GABA and effective suppression of overlapping signals such as creatine and glutathione in each single scan, providing reliable measurements of the GABA doublet in all subjects. The concentration of GABA was measured to be 0.7 ± 0.2 μmol/g (means ± SD, n = 15) in the fronto-parietal region of the human brain in vivo.