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Sample records for quantum conductance steps

  1. Tunneling into a quantum confinement created by a single-step nanolithography of conducting oxide interfaces

    NASA Astrophysics Data System (ADS)

    Maniv, E.; Ron, A.; Goldstein, M.; Palevski, A.; Dagan, Y.

    2016-07-01

    A unique nanolithography technique compatible with conducting oxide interfaces, which requires a single lithographic step with no additional amorphous deposition or etching, is presented. It is demonstrated on a SrTiO3/LaAlO3 interface where a constriction is patterned in the electron liquid. We find that an additional backgating can further confine the electron liquid into an isolated island. Conductance and differential conductance measurements show resonant tunneling through the island. The data at various temperatures and magnetic fields are analyzed and the effective island size is found to be of the order of 10 nm. The magnetic field dependence suggests the absence of spin degeneracy in the island. Our method is suitable for creating superconducting and oxide-interface-based electronic devices.

  2. Fractional quantum conductance in edge channels of silicon quantum wells

    SciTech Connect

    Bagraev, Nikolay; Klyachkin, Leonid; Kudryavtsev, Andrey; Malyarenko, Anna

    2013-12-04

    We present the findings for the fractional quantum conductance of holes that is caused by the edge channels in the silicon nanosandwich prepared within frameworks of the Hall geometry. This nanosandwich represents the ultra-narrow p-type silicon quantum well (Si-QW), 2 nm, confined by the δ-barriers heavily doped with boron on the n-type Si (100) surface. The edge channels in the Si-QW plane are revealed by measuring the longitudinal quantum conductance staircase, G{sub xx}, as a function of the voltage applied to the Hall contacts, V{sub xy}, to a maximum of 4e{sup 2}/h. In addition to the standard plateau, 2e{sup 2}/h, the variations of the V{sub xy} voltage appear to exhibit the fractional form of the quantum conductance staircase with the plateaus and steps that bring into correlation respectively with the odd and even fractions.

  3. Quantum Conductance in Metal Nanowires

    NASA Astrophysics Data System (ADS)

    Ugarte, Daniel

    2004-03-01

    Quantum Conductance in Metal Nanowires D. Ugarte Brazilian National Synchrotron Light Laboratory C.P. 6192, 13084-971 Campinas SP, Brazil. Electrical transport properties of metallic nanowires (NWs) have received great attention due to their quantum conductance behavior. Atomic scale wires can be generated by stretching metal contacts; during the elongation and just before rupture, the NW conductance shows flat plateaus and abrupt jumps of approximately a conductance quantum. In this experiments, both the NW atomic arrangement and conductance change simultaneously, making difficult to discriminate electronic and structural effects. In this work, the atomic structure of NWs was studied by time-resolved in situ experiments in a high resolution transmission electron microscope, while their electrical properties using an UHV mechanically controllable break junction (MCBJ). From the analysis of numerous HRTEM images and videos, we have deduced that metal (Au, Ag, Pt, etc.) junctions generated by tensile deformation are crystalline and free of defects. The neck structure is strongly dependent on the surface properties of the analyzed metal, this was verified by comparing different metal NWs (Au, Ag, Cu), which have similar atomic structure (FCC), but show very different faceting patterns. The correlation between the observed structural and transport properties of NW points out that the quantum conductance behavior is defined by preferred atomic arrangement at the narrowest constriction. In the case of magnetic (ex. Fe,Co,Ni) or quasi-magnetic (ex. Pd) wires, we have observed that one-atom-thick structures show a conductance of half the quantum as expected for a fully spin polarized current. This phenomenon seems to occur spontaneously for magnetic suspended atom-chains in zero magnetic field and at room temperature. These results open new opportunities for spin control in nanostructures. Funded by FAPESP, LNLS and CNPq.

  4. Steps toward fault-tolerant quantum chemistry.

    SciTech Connect

    Taube, Andrew Garvin

    2010-05-01

    Developing quantum chemistry programs on the coming generation of exascale computers will be a difficult task. The programs will need to be fault-tolerant and minimize the use of global operations. This work explores the use a task-based model that uses a data-centric approach to allocate work to different processes as it applies to quantum chemistry. After introducing the key problems that appear when trying to parallelize a complicated quantum chemistry method such as coupled-cluster theory, we discuss the implications of that model as it pertains to the computational kernel of a coupled-cluster program - matrix multiplication. Also, we discuss the extensions that would required to build a full coupled-cluster program using the task-based model. Current programming models for high-performance computing are fault-intolerant and use global operations. Those properties are unsustainable as computers scale to millions of CPUs; instead one must recognize that these systems will be hierarchical in structure, prone to constant faults, and global operations will be infeasible. The FAST-OS HARE project is introducing a scale-free computing model to address these issues. This model is hierarchical and fault-tolerant by design, allows for the clean overlap of computation and communication, reducing the network load, does not require checkpointing, and avoids the complexity of many HPC runtimes. Development of an algorithm within this model requires a change in focus from imperative programming to a data-centric approach. Quantum chemistry (QC) algorithms, in particular electronic structure methods, are an ideal test bed for this computing model. These methods describe the distribution of electrons in a molecule, which determine the properties of the molecule. The computational cost of these methods is high, scaling quartically or higher in the size of the molecule, which is why QC applications are major users of HPC resources. The complexity of these algorithms means that

  5. Single-step direct fabrication of luminescent Cu-doped Zn(x)Cd(1-x)S quantum dot thin films via a molecular precursor solution approach and their application in luminescent, transparent, and conductive thin films.

    PubMed

    Chen, Yanyan; Li, Shenjie; Huang, Lijian; Pan, Daocheng

    2014-08-21

    Luminescent Cu-doped ZnxCd1-xS quantum dot thin films have been directly fabricated via a facile solution method in open air. Cu2O, ZnO, and Cd(OH)2 were used as starting materials, and 3-mercaptopropionic acid was used as the capping agent. The effects of Cu dopant concentration, sintering temperature, and sintering time on the photoluminescence properties of Cu-doped ZnxCd1-xS nanocrystal thin films have been systematically investigated. As-prepared quantum dot thin films exhibit tunable emission covering the whole visible light region and the absolute photoluminescence quantum yields can reach as high as 25.5%, which have high potential for applications in luminescent, transparent, and conductive thin films.

  6. Quantized conductance through the quantum evaporation of bosonic atoms

    NASA Astrophysics Data System (ADS)

    Papoular, D. J.; Pitaevskii, L. P.; Stringari, S.

    2016-08-01

    We analyze theoretically the quantization of conductance occurring with cold bosonic atoms trapped in two reservoirs connected by a constriction with an attractive gate potential. We focus on temperatures slightly above the condensation threshold in the reservoirs. We show that a conductance step occurs, coinciding with the appearance of a condensate in the constriction. Conductance relies on a collective process involving the quantum condensation of an atom into an elementary excitation and the subsequent quantum evaporation of an atom, in contrast with ballistic fermion transport. The value of the bosonic conductance plateau is strongly enhanced compared to fermions and explicitly depends on temperature. We highlight the role of the repulsive interactions between the bosons in preventing them from collapsing into the constriction. We also point out the differences between the bosonic and fermionic thermoelectric effects in the quantized conductance regime.

  7. Topologically induced fractional Hall steps in the integer quantum Hall regime of MoS 2

    NASA Astrophysics Data System (ADS)

    Firoz Islam, SK; Benjamin, Colin

    2016-09-01

    The quantum magnetotransport properties of a monolayer of molybdenum disulfide are derived using linear response theory. In particular, the effect of topological terms on longitudinal and Hall conductivity is analyzed. The Hall conductivity exhibits fractional steps in the integer quantum Hall regime. Further complete spin and valley polarization of the longitudinal conductivitity is seen in presence of these topological terms. Finally, the Shubnikov-de Hass oscillations are suppressed or enhanced contingent on the sign of these topological terms.

  8. Topologically induced fractional Hall steps in the integer quantum Hall regime of MoS 2.

    PubMed

    Islam, S K Firoz; Benjamin, Colin

    2016-09-23

    The quantum magnetotransport properties of a monolayer of molybdenum disulfide are derived using linear response theory. In particular, the effect of topological terms on longitudinal and Hall conductivity is analyzed. The Hall conductivity exhibits fractional steps in the integer quantum Hall regime. Further complete spin and valley polarization of the longitudinal conductivitity is seen in presence of these topological terms. Finally, the Shubnikov-de Hass oscillations are suppressed or enhanced contingent on the sign of these topological terms.

  9. Topologically induced fractional Hall steps in the integer quantum Hall regime of MoS 2.

    PubMed

    Islam, S K Firoz; Benjamin, Colin

    2016-09-23

    The quantum magnetotransport properties of a monolayer of molybdenum disulfide are derived using linear response theory. In particular, the effect of topological terms on longitudinal and Hall conductivity is analyzed. The Hall conductivity exhibits fractional steps in the integer quantum Hall regime. Further complete spin and valley polarization of the longitudinal conductivitity is seen in presence of these topological terms. Finally, the Shubnikov-de Hass oscillations are suppressed or enhanced contingent on the sign of these topological terms. PMID:27533362

  10. One Step Quantum Key Distribution Based on EPR Entanglement.

    PubMed

    Li, Jian; Li, Na; Li, Lei-Lei; Wang, Tao

    2016-01-01

    A novel quantum key distribution protocol is presented, based on entanglement and dense coding and allowing asymptotically secure key distribution. Considering the storage time limit of quantum bits, a grouping quantum key distribution protocol is proposed, which overcomes the vulnerability of first protocol and improves the maneuverability. Moreover, a security analysis is given and a simple type of eavesdropper's attack would introduce at least an error rate of 46.875%. Compared with the "Ping-pong" protocol involving two steps, the proposed protocol does not need to store the qubit and only involves one step. PMID:27357865

  11. One Step Quantum Key Distribution Based on EPR Entanglement

    PubMed Central

    Li, Jian; Li, Na; Li, Lei-Lei; Wang, Tao

    2016-01-01

    A novel quantum key distribution protocol is presented, based on entanglement and dense coding and allowing asymptotically secure key distribution. Considering the storage time limit of quantum bits, a grouping quantum key distribution protocol is proposed, which overcomes the vulnerability of first protocol and improves the maneuverability. Moreover, a security analysis is given and a simple type of eavesdropper’s attack would introduce at least an error rate of 46.875%. Compared with the “Ping-pong” protocol involving two steps, the proposed protocol does not need to store the qubit and only involves one step. PMID:27357865

  12. Quantum conductance of carbon nanotube peapods

    SciTech Connect

    Yoon, Young-Gui; Mazzoni, Mario S.C.; Louie, Steven G.

    2003-08-01

    We present a first-principles study of the quantum conductance of hybrid nanotube systems consisting of single-walled carbon nanotubes (SWCNTs) encapsulating either an isolated single C60 molecule or a chain of C60 molecules (nanotube peapods). The calculations show a rather weak bonding interaction between the fullerenes and the SWCNTs. The conductance of a (10,10) SWCNT with a single C60 molecule is virtually unaffected at the Fermi level, but exhibits quantized resonant reductions at the molecular levels. The nanotube peapod arrangement gives rise to high density of states for the fullerene highest occupied molecular orbital and lowest unoccupied molecular orbital bands.

  13. Dirac Cellular Automaton from Split-step Quantum Walk

    NASA Astrophysics Data System (ADS)

    Mallick, Arindam; Chandrashekar, C. M.

    2016-05-01

    Simulations of one quantum system by an other has an implication in realization of quantum machine that can imitate any quantum system and solve problems that are not accessible to classical computers. One of the approach to engineer quantum simulations is to discretize the space-time degree of freedom in quantum dynamics and define the quantum cellular automata (QCA), a local unitary update rule on a lattice. Different models of QCA are constructed using set of conditions which are not unique and are not always in implementable configuration on any other system. Dirac Cellular Automata (DCA) is one such model constructed for Dirac Hamiltonian (DH) in free quantum field theory. Here, starting from a split-step discrete-time quantum walk (QW) which is uniquely defined for experimental implementation, we recover the DCA along with all the fine oscillations in position space and bridge the missing connection between DH-DCA-QW. We will present the contribution of the parameters resulting in the fine oscillations on the Zitterbewegung frequency and entanglement. The tuneability of the evolution parameters demonstrated in experimental implementation of QW will establish it as an efficient tool to design quantum simulator and approach quantum field theory from principles of quantum information theory.

  14. Dirac Cellular Automaton from Split-step Quantum Walk.

    PubMed

    Mallick, Arindam; Chandrashekar, C M

    2016-05-17

    Simulations of one quantum system by an other has an implication in realization of quantum machine that can imitate any quantum system and solve problems that are not accessible to classical computers. One of the approach to engineer quantum simulations is to discretize the space-time degree of freedom in quantum dynamics and define the quantum cellular automata (QCA), a local unitary update rule on a lattice. Different models of QCA are constructed using set of conditions which are not unique and are not always in implementable configuration on any other system. Dirac Cellular Automata (DCA) is one such model constructed for Dirac Hamiltonian (DH) in free quantum field theory. Here, starting from a split-step discrete-time quantum walk (QW) which is uniquely defined for experimental implementation, we recover the DCA along with all the fine oscillations in position space and bridge the missing connection between DH-DCA-QW. We will present the contribution of the parameters resulting in the fine oscillations on the Zitterbewegung frequency and entanglement. The tuneability of the evolution parameters demonstrated in experimental implementation of QW will establish it as an efficient tool to design quantum simulator and approach quantum field theory from principles of quantum information theory.

  15. Dirac Cellular Automaton from Split-step Quantum Walk

    PubMed Central

    Mallick, Arindam; Chandrashekar, C. M.

    2016-01-01

    Simulations of one quantum system by an other has an implication in realization of quantum machine that can imitate any quantum system and solve problems that are not accessible to classical computers. One of the approach to engineer quantum simulations is to discretize the space-time degree of freedom in quantum dynamics and define the quantum cellular automata (QCA), a local unitary update rule on a lattice. Different models of QCA are constructed using set of conditions which are not unique and are not always in implementable configuration on any other system. Dirac Cellular Automata (DCA) is one such model constructed for Dirac Hamiltonian (DH) in free quantum field theory. Here, starting from a split-step discrete-time quantum walk (QW) which is uniquely defined for experimental implementation, we recover the DCA along with all the fine oscillations in position space and bridge the missing connection between DH-DCA-QW. We will present the contribution of the parameters resulting in the fine oscillations on the Zitterbewegung frequency and entanglement. The tuneability of the evolution parameters demonstrated in experimental implementation of QW will establish it as an efficient tool to design quantum simulator and approach quantum field theory from principles of quantum information theory. PMID:27184159

  16. Step-by-step magic state encoding for efficient fault-tolerant quantum computation.

    PubMed

    Goto, Hayato

    2014-12-16

    Quantum error correction allows one to make quantum computers fault-tolerant against unavoidable errors due to decoherence and imperfect physical gate operations. However, the fault-tolerant quantum computation requires impractically large computational resources for useful applications. This is a current major obstacle to the realization of a quantum computer. In particular, magic state distillation, which is a standard approach to universality, consumes the most resources in fault-tolerant quantum computation. For the resource problem, here we propose step-by-step magic state encoding for concatenated quantum codes, where magic states are encoded step by step from the physical level to the logical one. To manage errors during the encoding, we carefully use error detection. Since the sizes of intermediate codes are small, it is expected that the resource overheads will become lower than previous approaches based on the distillation at the logical level. Our simulation results suggest that the resource requirements for a logical magic state will become comparable to those for a single logical controlled-NOT gate. Thus, the present method opens a new possibility for efficient fault-tolerant quantum computation.

  17. How to Conduct Surveys: A Step-by-Step Guide. Sixth Edition

    ERIC Educational Resources Information Center

    Fink, Arlene

    2016-01-01

    Packed with new topics that reflect today's challenges, the Sixth Edition of the bestselling "How to Conduct Surveys" guides readers through the process of developing their own rigorous surveys and evaluating the credibility and transparency of surveys created by others. Offering practical, step-by-step advice and written in the same…

  18. Dynamics and conductivity near quantum criticality

    NASA Astrophysics Data System (ADS)

    Gazit, Snir; Podolsky, Daniel; Auerbach, Assa; Arovas, Daniel P.

    2013-12-01

    Relativistic O(N) field theories are studied near the quantum-critical point in two space dimensions. We compute dynamical correlations by large-scale Monte Carlo simulations and numerical analytic continuation. In the ordered side, the scalar spectral function exhibits a universal peak at the Higgs mass. For N=3 and 4, we confirm its ω3 rise at low frequency. On the disordered side, the spectral function exhibits a sharp gap. For N=2, the dynamical conductivity rises above a threshold at the Higgs mass (density gap), in the superfluid (Mott insulator) phase. For charged bosons (Josephson arrays), the power-law rise above the Higgs mass increases from two to four. Approximate charge-vortex duality is reflected in the ratio of imaginary conductivities on either side of the transition. We determine the critical conductivity to be σc*=0.3(±0.1)×4e2/h and describe a generalization of the worm algorithm to N>2. We use a singular value decomposition error analysis for the numerical analytic continuation.

  19. Five questions to consider before conducting a stepped wedge trial.

    PubMed

    Hargreaves, James R; Copas, Andrew J; Beard, Emma; Osrin, David; Lewis, James J; Davey, Calum; Thompson, Jennifer A; Baio, Gianluca; Fielding, Katherine L; Prost, Audrey

    2015-08-17

    Researchers should consider five questions before starting a stepped wedge trial. Why are you planning one? Researchers sometimes think that stepped wedge trials are useful when there is little doubt about the benefit of the intervention being tested. However, if the primary reason for an intervention is to measure its effect, without equipoise there is no ethical justification for delaying implementation in some clusters. By contrast, if you are undertaking pragmatic research, where the primary reason for rolling out the intervention is for it to exert its benefits, and if phased implementation is inevitable, a stepped wedge trial is a valid option and provides better evidence than most non-randomized evaluations. What design will you use? Two common stepped wedge designs are based on the recruitment of a closed or open cohort. In both, individuals may experience both control and intervention conditions and you should be concerned about carry-over effects. In a third, continuous-recruitment, short-exposure design, individuals are recruited as they become eligible and experience either control or intervention condition, but not both. How will you conduct the primary analysis? In stepped wedge trials, control of confounding factors through secular variation is essential. 'Vertical' approaches preserve randomization and compare outcomes between randomized groups within periods. 'Horizontal' approaches compare outcomes before and after crossover to the intervention condition. Most analysis models used in practice combine both types of comparison. The appropriate analytic strategy should be considered on a case-by-case basis. How large will your trial be? Standard sample size calculations for cluster randomized trials do not accommodate the specific features of stepped wedge trials. Methods exist for many stepped wedge designs, but simulation-based calculations provide the greatest flexibility. In some scenarios, such as when the intracluster correlation coefficient is

  20. Single-step fabrication of quantum funnels via centrifugal colloidal casting of nanoparticle films

    PubMed Central

    Kim, Jin Young; Adinolfi, Valerio; Sutherland, Brandon R.; Voznyy, Oleksandr; Kwon, S. Joon; Kim, Tae Wu; Kim, Jeongho; Ihee, Hyotcherl; Kemp, Kyle; Adachi, Michael; Yuan, Mingjian; Kramer, Illan; Zhitomirsky, David; Hoogland, Sjoerd; Sargent, Edward H.

    2015-01-01

    Centrifugal casting of composites and ceramics has been widely employed to improve the mechanical and thermal properties of functional materials. This powerful method has yet to be deployed in the context of nanoparticles—yet size–effect tuning of quantum dots is among their most distinctive and application-relevant features. Here we report the first gradient nanoparticle films to be constructed in a single step. By creating a stable colloid of nanoparticles that are capped with electronic-conduction-compatible ligands we were able to leverage centrifugal casting for thin-films devices. This new method, termed centrifugal colloidal casting, is demonstrated to form films in a bandgap-ordered manner with efficient carrier funnelling towards the lowest energy layer. We constructed the first quantum-gradient photodiode to be formed in a single deposition step and, as a result of the gradient-enhanced electric field, experimentally measured the highest normalized detectivity of any colloidal quantum dot photodetector. PMID:26165185

  1. Single-step fabrication of quantum funnels via centrifugal colloidal casting of nanoparticle films.

    PubMed

    Kim, Jin Young; Adinolfi, Valerio; Sutherland, Brandon R; Voznyy, Oleksandr; Kwon, S Joon; Kim, Tae Wu; Kim, Jeongho; Ihee, Hyotcherl; Kemp, Kyle; Adachi, Michael; Yuan, Mingjian; Kramer, Illan; Zhitomirsky, David; Hoogland, Sjoerd; Sargent, Edward H

    2015-07-13

    Centrifugal casting of composites and ceramics has been widely employed to improve the mechanical and thermal properties of functional materials. This powerful method has yet to be deployed in the context of nanoparticles--yet size-effect tuning of quantum dots is among their most distinctive and application-relevant features. Here we report the first gradient nanoparticle films to be constructed in a single step. By creating a stable colloid of nanoparticles that are capped with electronic-conduction-compatible ligands we were able to leverage centrifugal casting for thin-films devices. This new method, termed centrifugal colloidal casting, is demonstrated to form films in a bandgap-ordered manner with efficient carrier funnelling towards the lowest energy layer. We constructed the first quantum-gradient photodiode to be formed in a single deposition step and, as a result of the gradient-enhanced electric field, experimentally measured the highest normalized detectivity of any colloidal quantum dot photodetector.

  2. Quantum-limited heat conduction over macroscopic distances

    NASA Astrophysics Data System (ADS)

    Partanen, Matti; Tan, Kuan Yen; Govenius, Joonas; Lake, Russell E.; Mäkelä, Miika K.; Tanttu, Tuomo; Möttönen, Mikko

    2016-05-01

    The emerging quantum technological apparatuses, such as the quantum computer, call for extreme performance in thermal engineering. Cold distant heat sinks are needed for the quantized electric degrees of freedom owing to the increasing packaging density and heat dissipation. Importantly, quantum mechanics sets a fundamental upper limit for the flow of information and heat, which is quantified by the quantum of thermal conductance. However, the short distance between the heat-exchanging bodies in the previous experiments hinders their applicability in quantum technology. Here, we present experimental observations of quantum-limited heat conduction over macroscopic distances extending to a metre. We achieved this improvement of four orders of magnitude in the distance by utilizing microwave photons travelling in superconducting transmission lines. Thus, it seems that quantum-limited heat conduction has no fundamental distance cutoff. This work establishes the integration of normal-metal components into the framework of circuit quantum electrodynamics, which provides a basis for the superconducting quantum computer. Especially, our results facilitate remote cooling of nanoelectronic devices using faraway in situ-tunable heat sinks. Furthermore, quantum-limited heat conduction is important in contemporary thermodynamics. Here, the long distance may lead to ultimately efficient mesoscopic heat engines with promising practical applications.

  3. Quantum-limited heat conduction over macroscopic distances

    PubMed Central

    Partanen, Matti; Tan, Kuan Yen; Govenius, Joonas; Lake, Russell E.; Mäkelä, Miika K.; Tanttu, Tuomo; Möttönen, Mikko

    2016-01-01

    The emerging quantum technological apparatuses1, 2, such as the quantum computer3–6, call for extreme performance in thermal engineering7. Cold distant heat sinks are needed for the quantized electric degrees of freedom due to the increasing packaging density and heat dissipation. Importantly, quantum mechanics sets a fundamental upper limit for the flow of information and heat, which is quantified by the quantum of thermal conductance8–10. However, the short distance between the heat-exchanging bodies in the previous experiments11–14 hinders their applicability in quantum technology. Here, we present experimental observations of quantum-limited heat conduction over macroscopic distances extending to a metre. We achieved this improvement of four orders of magnitude in the distance by utilizing microwave photons travelling in superconducting transmission lines. Thus, it seems that quantum-limited heat conduction has no fundamental distance cutoff. This work establishes the integration of normal-metal components into the framework of circuit quantum electrodynamics15–17 which provides a basis for the superconducting quantum computer18–21. Especially, our results facilitate remote cooling of nanoelectronic devices using far-away in-situ-tunable heat sinks22, 23. Furthermore, quantum-limited heat conduction is important in contemporary thermodynamics24, 25. Here, the long distance may lead to ultimately efficient mesoscopic heat engines with promising practical applications26. PMID:27239219

  4. Conductance fluctuations in chaotic bilayer graphene quantum dots.

    PubMed

    Bao, Rui; Huang, Liang; Lai, Ying-Cheng; Grebogi, Celso

    2015-07-01

    Previous studies of quantum chaotic scattering established a connection between classical dynamics and quantum transport properties: Integrable or mixed classical dynamics can lead to sharp conductance fluctuations but chaos is capable of smoothing out the conductance variations. Relativistic quantum transport through single-layer graphene systems, for which the quasiparticles are massless Dirac fermions, exhibits, due to scarring, this classical-quantum correspondence, but sharp conductance fluctuations persist to a certain extent even when the classical system is fully chaotic. There is an open issue regarding the effect of finite mass on relativistic quantum transport. To address this issue, we study quantum transport in chaotic bilayer graphene quantum dots for which the quasiparticles have a finite mass. An interesting phenomenon is that, when traveling along the classical ballistic orbit, the quasiparticle tends to hop back and forth between the two layers, exhibiting a Zitterbewegung-like effect. We find signatures of abrupt conductance variations, indicating that the mass has little effect on relativistic quantum transport. In solid-state electronic devices based on Dirac materials, sharp conductance fluctuations are thus expected, regardless of whether the quasiparticle is massless or massive and whether there is chaos in the classical limit.

  5. Conductance fluctuations in chaotic bilayer graphene quantum dots.

    PubMed

    Bao, Rui; Huang, Liang; Lai, Ying-Cheng; Grebogi, Celso

    2015-07-01

    Previous studies of quantum chaotic scattering established a connection between classical dynamics and quantum transport properties: Integrable or mixed classical dynamics can lead to sharp conductance fluctuations but chaos is capable of smoothing out the conductance variations. Relativistic quantum transport through single-layer graphene systems, for which the quasiparticles are massless Dirac fermions, exhibits, due to scarring, this classical-quantum correspondence, but sharp conductance fluctuations persist to a certain extent even when the classical system is fully chaotic. There is an open issue regarding the effect of finite mass on relativistic quantum transport. To address this issue, we study quantum transport in chaotic bilayer graphene quantum dots for which the quasiparticles have a finite mass. An interesting phenomenon is that, when traveling along the classical ballistic orbit, the quasiparticle tends to hop back and forth between the two layers, exhibiting a Zitterbewegung-like effect. We find signatures of abrupt conductance variations, indicating that the mass has little effect on relativistic quantum transport. In solid-state electronic devices based on Dirac materials, sharp conductance fluctuations are thus expected, regardless of whether the quasiparticle is massless or massive and whether there is chaos in the classical limit. PMID:26274258

  6. Quantum Annealing at Google: Recent Learnings and Next Steps

    NASA Astrophysics Data System (ADS)

    Neven, Hartmut

    Recently we studied optimization problems with rugged energy landscapes that featured tall and narrow energy barriers separating energy minima. We found that for a crafted problem of this kind, called the weak-strong cluster glass, the D-Wave 2X processor achieves a significant advantage in runtime scaling relative to Simulated Annealing (SA). For instances with 945 variables this results in a time-to-99%-success-probability 109 times shorter than SA running on a single core. When comparing to the Quantum Monte Carlo (QMC) algorithm we only observe a pre-factor advantage but the pre-factor is large, about 106 for an implementation on a single core. We should note that we expect QMC to scale like physical quantum annealing only for problems for which the tunneling transitions can be described by a dominant purely imaginary instanton. We expect these findings to carry over to other problems with similar energy landscapes. A class of practical interest are k-th order binary optimization problems. We studied 4-spin problems using numerical methods and found again that simulated quantum annealing has better scaling than SA. This leaves us with a final step to achieve a wall clock speedup of practical relevance. We need to develop an annealing architecture that supports embedding of k-th order binary optimization in a manner that preserves the runtime advantage seen prior to embedding.

  7. Size distributions of quantum islands on stepped substrates.

    PubMed

    Liang, S; Zhu, H L; Wang, W

    2009-10-21

    The size distributions of self-assembled quantum islands on stepped substrates are studied using kinetic Monte Carlo simulations. It is found that the energy barrier E(SW) between the step and the terrace region is the key factor in affecting the size distribution of islands. With small E(SW) (< or = 0.1 eV), lines of uniform islands can be obtained at relative low surface coverage. As the surface coverage is increased, wirelike islands can be obtained. Scaling behavior is obeyed for the size distributions of the wirelike islands. When the size distributions are separated into their width and length components, however, scaling is only observed in the length distribution of the wirelike islands. With larger E(SW), the size distribution of islands shows a clear bimodal size distribution and anomalous growth temperature dependent island size evolutions are observed. The simulation results reproduce qualitatively the phenomena observed in the cases of InAs islands grown on stepped GaAs substrates.

  8. Observation of quantum-limited heat conduction over macroscopic distances

    NASA Astrophysics Data System (ADS)

    Mottonen, Mikko; Partanen, Matti; Tan, Kuan Yen; Govenius, Joonas; Lake, Russell; Makela, Miika; Tanttu, Tuomo

    The emerging quantum technological devices, such as the quantum computer, call for extreme performance in thermal engineering at the nanoscale. Importantly, quantum mechanics sets a fundamental upper limit for the flow of information and heat, which is quantified by the quantum of thermal conductance. We present experimental observations of quantum-limited heat conduction over macroscopic distances extending to a meter. We achieved this striking improvement of four orders of magnitude in the distance by utilizing microwave photons travelling in superconducting transmission lines. Thus it seems that quantum-limited heat conduction has no fundamental restriction in its distance. This work lays the foundation for the integration of normal-metal components into superconducting transmission lines, and hence provides an important tool for circuit quantum electrodynamics, the basis of the emerging superconducting quantum computer. In particular, our results may lead to remote cooling of nanoelectronic devices with the help of a far-away in-situ-tunable heat sink. European Research Council (ERC) is acknowledged for funding under the Grant No. 278117 (SINGLEOUT).

  9. Proton Conductivity in Phosphoric Acid: The Role of Quantum Effects

    NASA Astrophysics Data System (ADS)

    Heres, M.; Wang, Y.; Griffin, P. J.; Gainaru, C.; Sokolov, A. P.

    2016-10-01

    Phosphoric acid has one of the highest intrinsic proton conductivities of any known liquids, and the mechanism of this exceptional conductivity remains a puzzle. Our detailed experimental studies discovered a strong isotope effect in the conductivity of phosphoric acids caused by (i) a strong isotope shift of the glass transition temperature and (ii) a significant reduction of the energy barrier by zero-point quantum fluctuations. These results suggest that the high conductivity in phosphoric acids is caused by a very efficient proton transfer mechanism, which is strongly assisted by quantum effects.

  10. A variable multi-step method for transient heat conduction

    NASA Technical Reports Server (NTRS)

    Smolinski, Patrick

    1991-01-01

    A variable explicit time integration algorithm is developed for unsteady diffusion problems. The algorithm uses nodal partitioning and allows the nodal groups to be updated with different time steps. The stability of the algorithm is analyzed using energy methods and critical time steps are found in terms of element eigenvalues with no restrictions on element types. Several numerical examples are given to illustrate the accuracy of the method.

  11. Quantum conductance of carbon nanotubes with defects

    SciTech Connect

    Chico, L.; Benedict, L.X.; Louie, S.G.; Cohen, M.L. |

    1996-07-01

    We study the conductance of metallic carbon nanotubes with vacancies and pentagon-heptagon pair defects within the Landauer formalism. Using a tight-binding model and a Green{close_quote}s function technique to calculate the scattering matrix, we examine the one-dimensional to two-dimensional crossover in these systems and show the existence of metallic tube junctions in which the conductance is suppressed for symmetry reasons. {copyright} {ital 1996 The American Physical Society.}

  12. Getting the Schools You Want: A Step-by-Step Guide to Conducting Your Own Curriculum Management Audit.

    ERIC Educational Resources Information Center

    Logan, Kimberly

    The curriculum-management audit was developed to provide school districts with a tool for making districtwide improvements. The audit can be used to help districts improve quality control over their instructional programs. This book offers a step-by-step guide to school improvement with a focus on conducting an internal audit. The first four…

  13. Four Simple Steps to Conduct an Assessment of Your Practice.

    PubMed

    Gurganious, Valora S

    2016-01-01

    Medical practice management has never been more complex than it is today, with volumes of rapidly changing regulations, increasing cost pressures, and rising quality standards under the Affordable Care Act. These challenges have made it more critical for practices to assess their current position in order to determine how best to move the practice forward. A practice assessment begins with four simple steps: an evaluation of the long-term goals and motivation of the practice's owner; a review of key practice financials and how successfully the practice captures every dollar to which it is rightfully entitled; a measure of provider productivity and strategies to improve it; and an assessment of the talent and morale of the team of professionals at the practice. PMID:27443050

  14. Multisublevel Magnetoquantum Conductance in Single and Coupled Double Quantum Wires

    SciTech Connect

    Lyo, Sungkwun Ken; Huang, Danhong

    2001-09-15

    We study the ballistic and diffusive magnetoquantum transport using a typical quantum point contact geometry for single and tunnel-coupled double wires that are wide (less than or similar to1 mum) in one perpendicular direction with densely populated sublevels and extremely confined in the other perpendicular (i.e., growth) direction. A general analytic solution to the Boltzmann equation is presented for multisublevel elastic scattering at low temperatures. The solution is employed to study interesting magnetic-field dependent behavior of the conductance such as a large enhancement and quantum oscillations of the conductance for various structures and field orientations. These phenomena originate from the following field-induced properties: magnetic confinement, displacement of the initial- and final-state wave functions for scattering, variation of the Fermi velocities, mass enhancement, depopulation of the sublevels and anticrossing (in double quantum wires). The magnetoconductance is strikingly different in long diffusive (or rough. dirty) wires from the quantized conductance in short ballistic (or clean) wires. Numerical results obtained for the rectangular confinement potentials in the growth direction are satisfactorily interpreted in terms of the analytic solutions based on harmonic confinement potentials. Some of the predicted features of the field-dependent diffusive and quantized conductances are consistent with recent data from GaAs/AlxGa1-xAs double quantum wires.

  15. Derivation of the Drude conductivity from quantum kinetic equations

    NASA Astrophysics Data System (ADS)

    Kitamura, Hikaru

    2015-11-01

    The Drude formula of ac (frequency-dependent) electric conductivity has been established as a simple and practically useful model to understand the electromagnetic response of simple free-electron-like metals. In most textbooks of solid-state physics, the Drude formula is derived from either a classical equation of motion or the semiclassical Boltzmann transport equation. On the other hand, quantum-mechanical derivation of the Drude conductivity, which requires an appropriate treatment of phonon-assisted intraband transitions with small momentum transfer, has not been well documented except for the zero- or high-frequency case. Here, a lucid derivation of the Drude conductivity that covers the entire frequency range is presented by means of quantum kinetic equations in the density-matrix formalism. The derivation is straightforward so that advanced undergraduate students or early-year graduate students will be able to gain insight into the link between the microscopic Schrödinger equation and macroscopic transport.

  16. Thermal conductivity at a disordered quantum critical point

    NASA Astrophysics Data System (ADS)

    Hartnoll, Sean A.; Ramirez, David M.; Santos, Jorge E.

    2016-04-01

    Strongly disordered and strongly interacting quantum critical points are difficult to access with conventional field theoretic methods. They are, however, both experimentally important and theoretically interesting. In particular, they are expected to realize universal incoherent transport. Such disordered quantum critical theories have recently been constructed holographically by deforming a CFT by marginally relevant disorder. In this paper we find additional disordered fixed points via relevant disordered deformations of a holographic CFT. Using recently developed methods in holographic transport, we characterize the thermal conductivity in both sets of theories in 1+1 dimensions. The thermal conductivity is found to tend to a constant at low temperatures in one class of fixed points, and to scale as T 0.3 in the other. Furthermore, in all cases the thermal conductivity exhibits discrete scale invariance, with logarithmic in temperature oscillations superimposed on the low temperature scaling behavior. At no point do we use the replica trick.

  17. Quantum authencryption: one-step authenticated quantum secure direct communications for off-line communicants

    NASA Astrophysics Data System (ADS)

    Hwang, Tzonelih; Luo, Yi-Ping; Yang, Chun-Wei; Lin, Tzu-Han

    2014-04-01

    This work proposes a new direction in quantum cryptography called quantum authencryption. Quantum authencryption (QA), a new term to distinguish from authenticated quantum secure direct communications, is used to describe the technique of combining quantum encryption and quantum authentication into one process for off-line communicants. QA provides a new way of quantum communications without the presence of a receiver on line, and thus makes many applications depending on secure one-way quantum communications, such as quantum E-mail systems, possible. An example protocol using single photons and one-way hash functions is presented to realize the requirements on QA.

  18. Contactless measurement of alternating current conductance in quantum Hall structures

    NASA Astrophysics Data System (ADS)

    Drichko, I. L.; Diakonov, A. M.; Malysh, V. A.; Smirnov, I. Yu.; Galperin, Y. M.; Ilyinskaya, N. D.; Usikova, A. A.; Kummer, M.; von Känel, H.

    2014-10-01

    We report a procedure to determine the frequency-dependent conductance of quantum Hall structures in a broad frequency domain. The procedure is based on the combination of two known probeless methods—acoustic spectroscopy and microwave spectroscopy. By using the acoustic spectroscopy, we study the low-frequency attenuation and phase shift of a surface acoustic wave in a piezoelectric crystal in the vicinity of the electron (hole) layer. The electronic contribution is resolved using its dependence on a transverse magnetic field. At high frequencies, we study the attenuation of an electromagnetic wave in a coplanar waveguide. To quantitatively calibrate these data, we use the fact that in the quantum-Hall-effect regime the conductance at the maxima of its magnetic field dependence is determined by extended states. Therefore, it should be frequency independent in a broad frequency domain. The procedure is verified by studies of a well-characterized p-SiGe/Ge/SiGe heterostructure.

  19. Contactless measurement of alternating current conductance in quantum Hall structures

    SciTech Connect

    Drichko, I. L.; Diakonov, A. M.; Malysh, V. A.; Smirnov, I. Yu.; Ilyinskaya, N. D.; Usikova, A. A.; Galperin, Y. M.; Kummer, M.; Känel, H. von

    2014-10-21

    We report a procedure to determine the frequency-dependent conductance of quantum Hall structures in a broad frequency domain. The procedure is based on the combination of two known probeless methods—acoustic spectroscopy and microwave spectroscopy. By using the acoustic spectroscopy, we study the low-frequency attenuation and phase shift of a surface acoustic wave in a piezoelectric crystal in the vicinity of the electron (hole) layer. The electronic contribution is resolved using its dependence on a transverse magnetic field. At high frequencies, we study the attenuation of an electromagnetic wave in a coplanar waveguide. To quantitatively calibrate these data, we use the fact that in the quantum-Hall-effect regime the conductance at the maxima of its magnetic field dependence is determined by extended states. Therefore, it should be frequency independent in a broad frequency domain. The procedure is verified by studies of a well-characterized p-SiGe/Ge/SiGe heterostructure.

  20. Universal spin Hall conductance fluctuations in chaotic Dirac quantum dots

    NASA Astrophysics Data System (ADS)

    Vasconcelos, T. C.; Ramos, J. G. G. S.; Barbosa, A. L. R.

    2016-03-01

    We present complete analytical and numerical results that demonstrate the anomalous universal fluctuations of the spin Hall conductance in chiral materials such as graphene and topological insulators. We investigate both the corresponding fluctuations, the universal fractionated and the universal quantized, and also the open channel orbital number crossover between the two regimes. In particular, we show that the Wigner-Dyson symmetries do not properly describe such conductances and the preponderant role of the chiral classes on the Dirac quantum dots. The results are analytical and solve outstanding issues.

  1. One-step implementation of the 1->3 orbital state quantum cloning machine via quantum Zeno dynamics

    SciTech Connect

    Shao Xiaoqiang; Wang Hongfu; Zhang Shou; Chen Li; Zhao Yongfang; Yeon, Kyu-Hwang

    2009-12-15

    We present an approach for implementation of a 1->3 orbital state quantum cloning machine based on the quantum Zeno dynamics via manipulating three rf superconducting quantum interference device (SQUID) qubits to resonantly interact with a superconducting cavity assisted by classical fields. Through appropriate modulation of the coupling constants between rf SQUIDs and classical fields, the quantum cloning machine can be realized within one step. We also discuss the effects of decoherence such as spontaneous emission and the loss of cavity in virtue of master equation. The numerical simulation result reveals that the quantum cloning machine is especially robust against the cavity decay, since all qubits evolve in the decoherence-free subspace with respect to cavity decay due to the quantum Zeno dynamics.

  2. Lattice thermal conductance of quantum wires with disorder

    NASA Astrophysics Data System (ADS)

    Vyhmeister, Erik; Hershfield, Selman

    We model the lattice thermal conductance in long quantum wires connected to two large heat baths at different temperatures in the harmonic approximation. The thermal conductance is computed with the Landauer formula for phonons, where it is related to the sum over all transmission probabilities for phonons through the wire. The net transmission probability is computed using a recursive Green function technique, which allows one to study long wires efficiently. We consider several different kinds of disorder to reduce the lattice thermal conductivity: periodic rectangular holes of varying sizes and shapes, periodic triangular holes, and narrow bands, averaged over randomness to account for variance in manufacturing. Depending on the model, the thermal conductance was reduced by 80 percent or more from the perfectly ordered wire case. Funded by NSF grant DMR-1461019.

  3. A multiple step random walk Monte Carlo method for heat conduction involving distributed heat sources

    NASA Astrophysics Data System (ADS)

    Naraghi, M. H. N.; Chung, B. T. F.

    1982-06-01

    A multiple step fixed random walk Monte Carlo method for solving heat conduction in solids with distributed internal heat sources is developed. In this method, the probability that a walker reaches a point a few steps away is calculated analytically and is stored in the computer. Instead of moving to the immediate neighboring point the walker is allowed to jump several steps further. The present multiple step random walk technique can be applied to both conventional Monte Carlo and the Exodus methods. Numerical results indicate that the present method compares well with finite difference solutions while the computation speed is much faster than that of single step Exodus and conventional Monte Carlo methods.

  4. Controlling thermal conductance through quantum dot roughening at interfaces

    NASA Astrophysics Data System (ADS)

    Hopkins, Patrick E.; Duda, John C.; Petz, Christopher W.; Floro, Jerrold A.

    2011-07-01

    We examine the fundamental phonon mechanisms affecting the interfacial thermal conductance across a single layer of quantum dots (QDs) on a planar substrate. We synthesize a series of GexSi1-x QDs by heteroepitaxial self-assembly on Si surfaces and modify the growth conditions to provide QD layers with different root-mean-square (rms) roughness levels in order to quantify the effects of roughness on thermal transport. We measure the thermal boundary conductance (hK) with time-domain thermoreflectance. The trends in thermal boundary conductance show that the effect of the QDs on hK are more apparent at elevated temperatures, while at low temperatures, the QD patterning does not drastically affect hK. The functional dependence of hK with rms surface roughness reveals a trend that suggests that both vibrational mismatch and changes in the localized phonon transport near the interface contribute to the reduction in hK. We find that QD structures with rms roughnesses greater than 4 nm decrease hK at Si interfaces by a factor of 1.6. We develop an analytical model for phonon transport at rough interfaces based on a diffusive scattering assumption and phonon attenuation that describes the measured trends in hK. This indicates that the observed reduction in thermal conductivity in SiGe quantum dot superlattices is primarily due to the increased physical roughness at the interfaces, which creates additional phonon resistive processes beyond the interfacial vibrational mismatch.

  5. Anisotropic Conductance of a Surface Quantum-Wire Array

    NASA Astrophysics Data System (ADS)

    Weitering, Hanno; Yoo, Kwonjae

    2001-03-01

    The Ga/Si(112)6x1 interface consists of a self-assembled, mesoscopic array of atomic Ga wires on a high-index Si(112) surface. The structural uniformity of this atomic-wire- or quantum-wire array is far superior to those created by nano-lithography or STM atom manipulation. The details of electron transport in these quantum wires should be very interesting. Si atoms also possess dangling bonds. Since the trivalent Ga atoms are threefold coordinated, their dangling bond orbitals are empty and hence, they should not contribute significantly to the conductivity. However, quasi one-dimensional metallic transport might be possible in the silicon dangling bonds because each dangling bond contributes one electron. These dangling bonds can form a quasi one-dimensional, half-filled electronic band. One of the interesting questions is whether this surface is indeed a quasi 1D metal or whether the Si chains undergo a Jahn-Teller or buckling distortion that opens up a band gap. We have measured the conductance of this mesoscopic wire array as a function of temperature parallel and perpendicular to the Ga chains. Transport measurements reveal a strong conductance anisotropy as expected. However, the conduction channels are orthogonal to the crystallographic chains. This counterintuitive result is in excellent agreement with electronic structure calculations by Ortega and Flores. The theoretical band structure was confirmed independently with photoemission spectroscopy.

  6. Intersubband optical absorption in InSb stepped quantum wells: Effect of spin sublevels crossing

    NASA Astrophysics Data System (ADS)

    Hernández-Cabrera, A.; Aceituno, P.

    2015-06-01

    We study linear and non-linear coefficients of the intersubband absorption in InSb-based stepped quantum wells subjected to an in-plane magnetic field. We consider also a transverse electric field to achieve near resonance conditions. Taking into account the two deepest conduction levels and their corresponding Zeeman spin splitting sublevels, we calculate dispersion relations by means of an improved version of Kane model. Besides the known anti-crossing between down and up spin split sublevels, we obtain an extra spin level crossing for some determined parameters. This crossing clearly modifies the absorption spectrum for transitions among the four sublevels considered. We study a low electron density case, when only the first deepest sublevel is occupied, and a high density case with only the highest sublevel empty. We find a similar behavior of the absorption spectrum in both cases.

  7. Direct imaging of quantum wires nucleated at diatomic steps

    SciTech Connect

    Molina, S. I.; Varela, M.; Sales, D. L.; Ben, T.; Pizarro, J.; Galindo, P. L.; Fuster, D.; Gonzalez, Y.; Gonzalez, L.; Pennycook, S. J.

    2007-10-01

    Atomic steps at growth surfaces are important heterogeneous sources for nucleation of epitaxial nano-objects. In the presence of misfit strain, we show that the nucleation process takes place preferentially at the upper terrace of the step as a result of the local stress relaxation. Evidence for strain-induced nucleation comes from the direct observation by postgrowth, atomic resolution, Z-contrast imaging of an InAs-rich region in a nanowire located on the upper terrace surface of an interfacial diatomic step.

  8. Growth of Quantum Wires on Step-Bunched Substrate

    SciTech Connect

    Liu, Feng

    2005-02-01

    This proposal initiates a combined theoretical and experimental multidisciplinary research effort to explore a novel approach for growing metallic and magnetic nanowires on step-bunched semiconductor and dielectric substrates, and to lay the groundwork for understanding the growth mechanisms and the electronic, electrical, and magnetic properties of metallic and magnetic nanowires. The research will focus on four topics: (1) fundamental studies of step bunching and self-organization in a strained thin film for creating step-bunched substrates. (2) Interaction between metal adatoms (Al,Cu, and Ni) and semiconductor (Si and SiGe) and dielectric (CaF2) surface steps. (3) growth and characterization of metallic and magnetic nanowires on step-bunched templates. (4) fabrication of superlattices of nanowires by growing multilayer films. We propose to attack these problems at both a microscopic and macroscopic level, using state-of-the-art theoretical and experimental techniques. Multiscale (electronic-atomic-continuum) theories will be applied to investigate growth mechanisms of nanowires: mesoscopic modeling and simulation of step flow growth of strained thin films, in particular, step bunching and self-organization will be carried out within the framework of continuum linear elastic theory; atomistic calculation of interaction between metal adatoms and semiconductor and dielectric surface steps will be done by large-scale computations using first-principles total-energy methods. In parallel, thin films and nanowires will be grown by molecular beam epitaxy (MBE), and the resultant structure and morphology will be characterized at the atomic level up to micrometer range, using a combination of different surface/interface probes, including scanning tunneling microscopy (STM, atomic resolution), atomic force microscopy (AFM, nanometer resolution), low-energy electron microscopy (LEEM, micrometer resolution), reflectance high-energy electron diffraction (RHEED), and x

  9. Mid-infrared Photoconductive Response in AlGaN/GaN Step Quantum Wells

    PubMed Central

    Rong, X.; Wang, X. Q.; Chen, G.; Zheng, X. T.; Wang, P.; Xu, F. J.; Qin, Z. X.; Tang, N.; Chen, Y. H.; Sang, L. W.; Sumiya, M.; Ge, W. K.; Shen, B.

    2015-01-01

    AlGaN/GaN quantum structure is an excellent candidate for high speed infrared detectors based on intersubband transitions. However, fabrication of AlGaN/GaN quantum well infrared detectors suffers from polarization-induced internal electric field, which greatly limits the carrier vertical transport. In this article, a step quantum well is proposed to attempt solving this problem, in which a novel spacer barrier layer is used to balance the internal electric field. As a result, a nearly flat band potential profile is obtained in the step barrier layers of the AlGaN/GaN step quantum wells and a bound-to-quasi-continuum (B-to-QC) type intersubband prototype device with detectable photocurrent at atmosphere window (3–5 μm) is achieved in such nitride semiconductors. PMID:26395756

  10. Phonon-mediated negative differential conductance in molecular quantum dots

    NASA Astrophysics Data System (ADS)

    Zazunov, Alex; Feinberg, Denis; Martin, Thierry

    2006-03-01

    Transport through a single-molecular conductor is considered, showing negative differential conductance behavior associated with phonon-mediated electron tunneling processes. This theoretical work is motivated by a recent experiment by Leroy using a carbon nanotube contacted by a scanning tunneling microscope tip [Nature 432, 371 (2004)], where negative differential conductance of the breathing-mode phonon side peaks could be observed. A peculiarity of this system is that the tunneling couplings which inject electrons and those which collect them on the substrate are highly asymmetrical. A quantum dot model is used, coupling a single electronic level to a local phonon, forming polaron levels. A “half-shuttle” mechanism is also introduced. A quantum kinetic formulation allows us to derive rate equations. Assuming asymmetric tunneling rates and in the absence of the half-shuttle coupling, negative differential conductance (NDC) is obtained for a wide range of parameters. A detailed explanation of this phenomenon is provided, showing that NDC is maximal for intermediate electron-phonon coupling. In addition, in the absence of a gate, the “floating” level results in two distinct lengths for the current plateaus, related to the capacitive couplings at the two junctions. It is shown that the half-shuttle mechanism tends to reinforce the negative differential regions, but it cannot trigger this behavior on its own.

  11. Modeling of graphene nanoscroll conductance with quantum capacitance effect

    NASA Astrophysics Data System (ADS)

    Khaledian, Mohsen; Ismail, Razali

    2015-12-01

    Graphene nanoscrolls (GNSs) as a new category of quasi one dimensional belong to the carbon-based nanomaterials, which have recently captivated the attention of researchers. The latest discoveries of exceptional structural and electronic properties of GNSs like, high mobility, controllable band gap and tunable core size has become a new stimuli for nanotechnology researchers. Fundamental descriptions about structure and electronic properties of GNSs have been investigated in order to apply them in nanoelectronic applications like nanotransistors and nanosensors as a new semiconducting material. By utilizing a novel approach, the analytical conductance model (G) of GNSs with the effect of Hall quantum is derived. This letter introduces a geometrydependent model to analyze the conductance of GNSs. The conductance modeling of GNS in parabolic part of the band structure which displays minimum conductance near the charge neutrality point is calculated. Subsequently, the effect of temperature and physical parameters on GNS conductivity is studied. This study emphasized that the GNS is a promising candidate for new generation of nanoelectronic devices.

  12. Experimental Observation of Quantum Confinement in the Conduction Band of CdSe Quantum Dots

    SciTech Connect

    Lee, J I; Meulenberg, R W; Hanif, K M; Mattoussi, H; Klepeis, J E; Terminello, L J; van Buuren, T

    2006-12-15

    Recent theoretical descriptions as to the magnitude of effect that quantum confinement has on he conduction band (CB) of CdSe quantum dots (QD) have been conflicting. In this manuscript, we experimentally identify quantum confinement effects in the CB of CdSe QDs for the first time. Using X-ray absorption spectroscopy, we have unambiguously witnessed the CB minimum shift to higher energy with decreasing particle size and have been able to compare these results to recent theories. Our experiments have been able to identify which theories correctly describe the CB states in CdSe QDs. In particular, our experiments suggest that multiple theories describe the shifts in the CB of CdSe QDs and are not mutually exclusive.

  13. Rapid sodium channel conductance changes during voltage clamp steps in squid giant axons.

    PubMed Central

    Fohlmeister, J F; Adelman, W J

    1984-01-01

    The sodium conductance of the membrane of the giant axon of squid was isolated by the use of potassium-free solutions and voltage-clamped with pulses containing three levels of depolarization. The conductance appears to undergo rapid changes during certain repolarizing clamp steps whose voltage reach at least partially overlaps the gating range. The percentage change in conductance increases with time of depolarization from approximately 0 to approximately 25-30% at 7 ms for a potential step from +70 to -30 mV. Conductance steps were also observed for voltage steps from various depolarized levels to -70 mV. All observed shifts were in the direction of a decreased conductance. The conductance steps appear to be a weak function of the concentration of external calcium, which also acts as a voltage-dependent channel blocker for inwardly directed sodium currents. A number of possible mechanisms are suggested. One of these is discussed in some detail and postulates a voltage- and time-dependent molecular process that does not itself yield open or closed channel conformations, but that affects the magnitude of the rate constants that do connect open and closed state conformations. PMID:6324915

  14. Error correction in short time steps during the application of quantum gates

    NASA Astrophysics Data System (ADS)

    de Castro, L. A.; Napolitano, R. d. J.

    2016-04-01

    We propose a modification of the standard quantum error-correction method to enable the correction of errors that occur due to the interaction with a noisy environment during quantum gates without modifying the codification used for memory qubits. Using a perturbation treatment of the noise that allows us to separate it from the ideal evolution of the quantum gate, we demonstrate that in certain cases it is necessary to divide the logical operation in short time steps intercalated by correction procedures. A prescription of how these gates can be constructed is provided, as well as a proof that, even for the cases when the division of the quantum gate in short time steps is not necessary, this method may be advantageous for reducing the total duration of the computation.

  15. Observation of temporal quantum interference via two collision-assisted two-step excitations

    SciTech Connect

    Yang Xihua; Sun Zhenrong; Wang Zugeng

    2007-10-15

    We report the experimental observation of temporal quantum interference between two time-delayed 3S-3P-5S (or 4D) transition pathways created through two collision-assisted two-step excitation processes by using a single nanosecond laser pulse in the Na{sub 2}-Na system. It is clearly shown that the collisions offer a promising alternative to realize quantum interference in the time domain at room or higher temperatures despite the dephasing nature.

  16. 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.

  17. Quantum resonance catastrophe for conductance through a periodically driven barrier

    NASA Astrophysics Data System (ADS)

    Thuberg, Daniel; Reyes, Sebastián A.; Eggert, Sebastian

    2016-05-01

    We consider the quantum conductance in a tight-binding chain with a locally applied potential which is oscillating in time. The steady state for such a driven impurity can be calculated exactly for any energy and applied potential using the Floquet formalism. The resulting transmission has a nontrivial, nonmonotonic behavior depending on incoming momentum, driving frequency, and the strength of the applied periodic potential. Hence there is an abundance of tuning possibilities, which allows finding the resonances of total reflection for any choice of incoming momentum and periodic potential. Remarkably, this implies that even for an arbitrarily small infinitesimal impurity potential it is always possible to find a resonance frequency at which there is a catastrophic breakdown of the transmission T =0 . The points of zero transmission are closely related to the phenomenon of Fano resonances at dynamically created bound states in the continuum. The results are relevant for a variety of one-dimensional systems where local AC driving is possible, such as quantum nanodot arrays, ultracold gases in optical lattices, photonic crystals, or molecular electronics.

  18. Quantum simulation of conductivity plateaux and fractional quantum Hall effect using ultracold atoms

    NASA Astrophysics Data System (ADS)

    Barberán, Nuria; Dagnino, Daniel; García-March, Miguel Angel; Trombettoni, Andrea; Taron, Josep; Lewenstein, Maciej

    2015-12-01

    We analyze the role of impurities in the fractional quantum Hall effect using a highly controllable system of ultracold atoms. We investigate the mechanism responsible for the formation of plateaux in the resistivity/conductivity as a function of the applied magnetic field in the lowest Landau level regime. To this aim, we consider an impurity immersed in a small cloud of an ultracold quantum Bose gas subjected to an artificial magnetic field. We consider scenarios corresponding to experimentally realistic systems with gauge fields induced by rotation of the trapping parabolic potential. Systems of this kind are adequate to simulate quantum Hall effects in ultracold atom setups. We use exact diagonalization for few atoms and to emulate transport equations, we analyze the time evolution of the system under a periodic perturbation. We provide a theoretical proposal to detect the up-to-now elusive presence of strongly correlated states related to fractional filling factors in the context of ultracold atoms. We analyze the conditions under which these strongly correlated states are associated with the presence of the resistivity/conductivity plateaux. Our main result is the presence of a plateau in a region, where the transfer between localized and non-localized particles takes place, as a necessary condition to maintain a constant value of the resistivity/conductivity as the magnetic field increases.

  19. Electrical Conductivity through a Single Atomic Step Measured with the Proximity-Induced Superconducting Pair Correlation

    NASA Astrophysics Data System (ADS)

    Kim, Howon; Lin, Shi-Zeng; Graf, Matthias J.; Miyata, Yoshinori; Nagai, Yuki; Kato, Takeo; Hasegawa, Yukio

    2016-09-01

    Local disordered nanostructures in an atomically thick metallic layer on a semiconducting substrate play significant and decisive roles in transport properties of two-dimensional (2D) conductive systems. We measured the electrical conductivity through a step of monoatomic height in a truly microscopic manner by using as a signal the superconducting pair correlation induced by the proximity effect. The transport property across a step of a one-monolayer Pb surface metallic phase, formed on a Si(111) substrate, was evaluated by inducing the pair correlation around the local defect and measuring its response, i.e., the reduced density of states at the Fermi energy using scanning tunneling microscopy. We found that the step resistance has a significant contribution to the total resistance on a nominally flat surface. Our study also revealed that steps in the 2D metallic layer terminate the propagation of the pair correlation. Superconductivity is enhanced between the first surface step and the superconductor-normal-metal interface by reflectionless tunneling when the step is located within a coherence length.

  20. Electrical Conductivity through a Single Atomic Step Measured with the Proximity-Induced Superconducting Pair Correlation.

    PubMed

    Kim, Howon; Lin, Shi-Zeng; Graf, Matthias J; Miyata, Yoshinori; Nagai, Yuki; Kato, Takeo; Hasegawa, Yukio

    2016-09-01

    Local disordered nanostructures in an atomically thick metallic layer on a semiconducting substrate play significant and decisive roles in transport properties of two-dimensional (2D) conductive systems. We measured the electrical conductivity through a step of monoatomic height in a truly microscopic manner by using as a signal the superconducting pair correlation induced by the proximity effect. The transport property across a step of a one-monolayer Pb surface metallic phase, formed on a Si(111) substrate, was evaluated by inducing the pair correlation around the local defect and measuring its response, i.e., the reduced density of states at the Fermi energy using scanning tunneling microscopy. We found that the step resistance has a significant contribution to the total resistance on a nominally flat surface. Our study also revealed that steps in the 2D metallic layer terminate the propagation of the pair correlation. Superconductivity is enhanced between the first surface step and the superconductor-normal-metal interface by reflectionless tunneling when the step is located within a coherence length. PMID:27661710

  1. XANES: observation of quantum confinement in the conduction band of colloidal PbS quantum dots

    NASA Astrophysics Data System (ADS)

    Demchenko, I. N.; Chernyshova, M.; He, X.; Minikayev, R.; Syryanyy, Y.; Derkachova, A.; Derkachov, G.; Stolte, W. C.; Piskorska-Hommel, E.; Reszka, A.; Liang, H.

    2013-04-01

    The presented investigations aimed at development of inexpensive method for synthesized materials suitable for utilization of solar energy. This important issue was addressed by focusing, mainly, on electronic local structure studies with supporting x-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis of colloidal galena nano-particles (NPs) and quantum dots (QDs) synthesized using wet chemistry under microwave irradiation. Performed x-ray absorption near edge structure (XANES) analysis revealed an evidence of quantum confinement for the sample with QDs, where the bottom of the conduction band was shifted to higher energy. The QDs were found to be passivated with oxides at the surface. Existence of sulfate/sulfite and thiosulfate species in pure PbS and QDs, respectively, was identified.

  2. Observing ``quantized'' conductance steps in silver sulfide: Two parallel resistive switching mechanisms

    NASA Astrophysics Data System (ADS)

    Wagenaar, Jelmer J. T.; Morales-Masis, Monica; van Ruitenbeek, Jan M.

    2012-01-01

    We demonstrate that it is possible to distinguish two conductance switching mechanisms in silver sulfide devices at room temperature. Experiments were performed using a Ag2S thin film deposited on a wide Ag bottom electrode, which was contacted by the Pt tip of a scanning tunneling microscope. By applying a positive voltage on the silver electrode, the conductance is seen to switch to a state having three orders of magnitude higher conductance, which is related to the formation of a conductive path inside the Ag2S thin film. We argue this to be composed of a metallic silver nanowire accompanied by a modification of the surrounding lattice structure. Metallic silver nanowires decaying after applying a negative voltage allow observing conductance steps in the breaking traces characteristic for atomic-scale contacts, while the lattice structure deformation is revealed by gradual and continuously decreasing conductance traces.

  3. Single-step synthesis of graphene quantum dots by femtosecond laser ablation of graphene oxide dispersions.

    PubMed

    Russo, Paola; Liang, Robert; Jabari, Elahe; Marzbanrad, Ehsan; Toyserkani, Ehsan; Zhou, Y Norman

    2016-04-28

    In the last few years, graphene quantum dots (GQDs) have attracted the attention of many research groups for their outstanding properties, which include low toxicity, chemical stability and photoluminescence. One of the challenges of GQD synthesis is finding a single-step, cheap and sustainable approach for synthesizing these promising nanomaterials. In this study, we demonstrate that femtosecond laser ablation of graphene oxide (GO) dispersions could be employed as a facile and environmentally friendly synthesis method for GQDs. With the proper control of laser ablation parameters, such as ablation time and laser power, it is possible to produce GQDs with average sizes of 2-5 nm, emitting a blue luminescence at 410 nm. We tested the feasibility of the synthesized GQDs as materials for electronic devices by aerosol-jet printing of an ink that is a mixture of water dispersion of laser synthesized GQDs and silver nanoparticle dispersion, which resulted in lower resistivity of the final printed patterns. Preliminary results showed that femtosecond laser synthesized GQDs can be mixed with silver nanoparticle dispersion to fabricate a hybrid material, which can be employed in printing electronic devices by either printing patterns that are more conductive and/or reducing costs of the ink by decreasing the concentration of silver nanoparticles (AgNPs) in the ink. PMID:27071944

  4. Single-step propagators for calculation of time evolution in quantum systems with arbitrary interactions

    NASA Astrophysics Data System (ADS)

    Gonoskov, Ivan; Marklund, Mattias

    2016-05-01

    We propose and develop a general method of numerical calculation of the wave function time evolution in a quantum system which is described by Hamiltonian of an arbitrary dimensionality and with arbitrary interactions. For this, we obtain a general n-order single-step propagator in closed-form, which could be used for the numerical solving of the problem with any prescribed accuracy. We demonstrate the applicability of the proposed approach by considering a quantum problem with non-separable time-dependent Hamiltonian: the propagation of an electron in focused electromagnetic field with vortex electric field component.

  5. Magnetic Semiconductor Quantum Wells in High Fields to 60 Tesla: Photoluminescence Linewidth Annealing at Magnetization Steps

    SciTech Connect

    Awschalom, D.D.; Crooker, S.A.; Lyo, S.K.; Rickel, D.G.; Samarth, N.

    1999-05-24

    Magnetic semiconductors offer a unique possibility for strongly tuning the intrinsic alloy disorder potential with applied magnetic field. We report the direct observation of a series of step-like reductions in the magnetic alloy disorder potential in single ZnSe/Zn(Cd,Mn)Se quantum wells between O and 60 Tesla. This disorder, measured through the linewidth of low temperature photoluminescence spectra drops abruptly at -19, 36, and 53 Tesla, in concert with observed magnetization steps. Conventional models of alloy disorder (developed for nonmagnetic semiconductors) reproduce the general shape of the data, but markedly underestimate the size of the linewidth reduction.

  6. Single-step synthesis of graphene quantum dots by femtosecond laser ablation of graphene oxide dispersions

    NASA Astrophysics Data System (ADS)

    Russo, Paola; Liang, Robert; Jabari, Elahe; Marzbanrad, Ehsan; Toyserkani, Ehsan; Zhou, Y. Norman

    2016-04-01

    In the last few years, graphene quantum dots (GQDs) have attracted the attention of many research groups for their outstanding properties, which include low toxicity, chemical stability and photoluminescence. One of the challenges of GQD synthesis is finding a single-step, cheap and sustainable approach for synthesizing these promising nanomaterials. In this study, we demonstrate that femtosecond laser ablation of graphene oxide (GO) dispersions could be employed as a facile and environmentally friendly synthesis method for GQDs. With the proper control of laser ablation parameters, such as ablation time and laser power, it is possible to produce GQDs with average sizes of 2-5 nm, emitting a blue luminescence at 410 nm. We tested the feasibility of the synthesized GQDs as materials for electronic devices by aerosol-jet printing of an ink that is a mixture of water dispersion of laser synthesized GQDs and silver nanoparticle dispersion, which resulted in lower resistivity of the final printed patterns. Preliminary results showed that femtosecond laser synthesized GQDs can be mixed with silver nanoparticle dispersion to fabricate a hybrid material, which can be employed in printing electronic devices by either printing patterns that are more conductive and/or reducing costs of the ink by decreasing the concentration of silver nanoparticles (AgNPs) in the ink.In the last few years, graphene quantum dots (GQDs) have attracted the attention of many research groups for their outstanding properties, which include low toxicity, chemical stability and photoluminescence. One of the challenges of GQD synthesis is finding a single-step, cheap and sustainable approach for synthesizing these promising nanomaterials. In this study, we demonstrate that femtosecond laser ablation of graphene oxide (GO) dispersions could be employed as a facile and environmentally friendly synthesis method for GQDs. With the proper control of laser ablation parameters, such as ablation time and

  7. Suppressed Conductance From Spin Selection Rules in F-CNT-F Quantum Dots

    NASA Astrophysics Data System (ADS)

    Hartman, Nikolaus; Morgan-Wall, Tyler; Markovic, Nina

    Conductance through a quantum dot can be suppressed due to spin selection rules governing the hoping of an additional electron onto an already-occupied quantum dot. Measurements of this effect in a carbon nanotube quantum dot with ferromagnetic contacts will be presented. Suppressed conductance peaks are observed in the Coulomb diamond plots at zero field and explained using spin selection rules. The pattern of suppressed peaks is observed to change with applied magnetic field as the spin ground state of the occupied quantum dot changes. This work was supported by NSF DMR-1106167.

  8. Visualizing Non-abrupt Transition of Quantum Well States at Stepped Silver Surfaces

    PubMed Central

    Kumar Saha, Srijan; Manna, Sujit; Stepanyuk, Valeri S.; Kirschner, Jürgen

    2015-01-01

    We use scanning tunneling spectroscopy (STS) experiments and first-principles density functional theory (DFT) calculations to address a fundamental question of how quantum well (QW) states for electrons in a metal evolve spatially in the lateral direction when there is a surface step that changes the vertical confinement thickness. This study reveals a clear spatially dependent, nearly continuous trend in the energetic shifts of quantum well (QW) states of thin Ag(111) film grown on Cu(111) substrate, showing the strongest change near the step edge. A large energetic shift equaling up to ~200 meV with a lateral extension of the QW states of the order of ~20 Å is found, even though the step-edge is atomically sharp as evidenced by a line scan. The observed lateral extension and the nearly smooth transition of QW states are understood within the context of step-induced charge oscillation, and Smoluchowski-type charge spreading and smoothing. PMID:26243639

  9. Control of valley dynamics in silicon quantum dots in the presence of an interface step

    NASA Astrophysics Data System (ADS)

    Boross, Péter; Széchenyi, Gábor; Culcer, Dimitrie; Pályi, András

    2016-07-01

    Recent experiments on silicon nanostructures have seen breakthroughs toward scalable, long-lived quantum information processing. The valley degree of freedom plays a fundamental role in these devices, and the two lowest-energy electronic states of a silicon quantum dot can form a valley qubit. In this paper, we show that a single-atom high step at the silicon/barrier interface induces a strong interaction of the qubit and in-plane electric fields and that the strength of this interaction can be controlled by varying the relative position of the electron and the step. We analyze the consequences of this enhanced interaction on the dynamics of the qubit. The charge densities of the qubit states are deformed differently by the interface step, allowing nondemolition qubit readout via valley-to-charge conversion. A gate-induced in-plane electric field together with the interface step enables fast control of the valley qubit via electrically driven valley resonance. We calculate single- and two-qubit gate times, as well as relaxation and dephasing times, and present predictions for the parameter range where the gate times can be much shorter than the relaxation time and dephasing is reduced.

  10. Boosting the accuracy and speed of quantum Monte Carlo: Size consistency and time step

    NASA Astrophysics Data System (ADS)

    Zen, Andrea; Sorella, Sandro; Gillan, Michael J.; Michaelides, Angelos; Alfè, Dario

    2016-06-01

    Diffusion Monte Carlo (DMC) simulations for fermions are becoming the standard for providing high-quality reference data in systems that are too large to be investigated via quantum chemical approaches. DMC with the fixed-node approximation relies on modifications of the Green's function to avoid singularities near the nodal surface of the trial wave function. Here we show that these modifications affect the DMC energies in a way that is not size consistent, resulting in large time-step errors. Building on the modifications of Umrigar et al. and DePasquale et al. we propose a simple Green's function modification that restores size consistency to large values of the time step, which substantially reduces time-step errors. This algorithm also yields remarkable speedups of up to two orders of magnitude in the calculation of molecule-molecule binding energies and crystal cohesive energies, thus extending the horizons of what is possible with DMC.

  11. Measurement of the quantum conductance of germanium by an electrochemical scanning tunneling microscope break junction based on a jump-to-contact mechanism.

    PubMed

    Xie, Xufen; Yan, Jiawei; Liang, Jinghong; Li, Jijun; Zhang, Meng; Mao, Bingwei

    2013-10-01

    We present quantum conductance measurements of germanium by means of an electrochemical scanning tunneling microscope (STM) break junction based on a jump-to-contact mechanism. Germanium nanowires between a platinum/iridium tip and different substrates were constructed to measure the quantum conductance. By applying appropriate potentials to the substrate and the tip, the process of heterogeneous contact and homogeneous breakage was realized. Typical conductance traces exhibit steps at 0.025 and 0.05 G0. The conductance histogram indicates that the conductance of germanium nanowires is located between 0.02 and 0.15 G0 in the low-conductance region and is free from the influence of substrate materials. However, the distribution of conductance plateaus is too discrete to display distinct peaks in the conductance histogram of the high-conductance region. PMID:23704043

  12. Quantum transport with long-range steps on Watts-Strogatz networks

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Xu, Xin-Jian

    2016-07-01

    We study transport dynamics of quantum systems with long-range steps on the Watts-Strogatz network (WSN) which is generated by rewiring links of the regular ring. First, we probe physical systems modeled by the discrete nonlinear schrödinger (DNLS) equation. Using the localized initial condition, we compute the time-averaged occupation probability of the initial site, which is related to the nonlinearity, the long-range steps and rewiring links. Self-trapping transitions occur at large (small) nonlinear parameters for coupling ɛ=-1 (1), as long-range interactions are intensified. The structure disorder induced by random rewiring, however, has dual effects for ɛ=-1 and inhibits the self-trapping behavior for ɛ=1. Second, we investigate continuous-time quantum walks (CTQW) on the regular ring ruled by the discrete linear schrödinger (DLS) equation. It is found that only the presence of the long-range steps does not affect the efficiency of the coherent exciton transport, while only the allowance of random rewiring enhances the partial localization. If both factors are considered simultaneously, localization is greatly strengthened, and the transport becomes worse.

  13. Highly efficient hyperentanglement concentration with two steps assisted by quantum swap gates.

    PubMed

    Ren, Bao-Cang; Long, Gui Lu

    2015-01-01

    We present a two-step hyperentanglement concentration protocol (hyper-ECP) for polarization-spatial hyperentangled Bell states based on the high-capacity character of hyperentanglement resorting to the swap gates, which is used to obtain maximally hyperentangled states from partially hyperentangled pure states in long-distance quantum communication. The swap gate, which is constructed with the giant optical circular birefringence (GOCB) of a diamond nitrogen-vacancy (NV) center embedded in a photonic crystal cavity, can be used to transfer the information in one degree of freedom (DOF) between photon systems. By transferring the useful information between hyperentangled photon pairs, more photon pairs in maximally hyperentangled state can be obtained in our hyper-ECP, and the success probability of the hyper-ECP is greatly improved. Moreover, we show that the high-fidelity quantum gate operations can be achieved by mapping the infidelities to heralded losses even in the weak coupling regime. PMID:26552898

  14. Highly efficient hyperentanglement concentration with two steps assisted by quantum swap gates

    PubMed Central

    Ren, Bao-Cang; Long, Gui Lu

    2015-01-01

    We present a two-step hyperentanglement concentration protocol (hyper-ECP) for polarization-spatial hyperentangled Bell states based on the high-capacity character of hyperentanglement resorting to the swap gates, which is used to obtain maximally hyperentangled states from partially hyperentangled pure states in long-distance quantum communication. The swap gate, which is constructed with the giant optical circular birefringence (GOCB) of a diamond nitrogen-vacancy (NV) center embedded in a photonic crystal cavity, can be used to transfer the information in one degree of freedom (DOF) between photon systems. By transferring the useful information between hyperentangled photon pairs, more photon pairs in maximally hyperentangled state can be obtained in our hyper-ECP, and the success probability of the hyper-ECP is greatly improved. Moreover, we show that the high-fidelity quantum gate operations can be achieved by mapping the infidelities to heralded losses even in the weak coupling regime. PMID:26552898

  15. Quantized steps and topological nature of universal conductance fluctuation in Bi2Te2Se

    NASA Astrophysics Data System (ADS)

    Song, Fengqi

    Here we report the experimental observation of universal conductance fluctuations (UCF) in Bi2Te2Se. Four aspects were addressed to support the UCF's topological nature of the electronic state. i) The irregular fluctuations are repeatable in different temperature and reversal magnetic fields. ii) All the UCF features coincide after the field is normalized to the perpendicular direction. This points to a two-dimensional electronic state. iii) A parallel field is applied to suppress the bulk coherent paths, while the UCF features stays similar. This excludes a quasi-2D bulk state. iv). The intrinsic UCF magnitude is extracted, which is close to the predicted values of a topological surface state. v). Quantized steps of the UCF magnitudes are observed when the magnetic field is modulated. (Sci.Rep. 2012, 2,595; Appl. Phys. Expre. 2014,7,065202; arxiv 2015)

  16. Observation of conductance doubling in an Andreev quantum point contact

    NASA Astrophysics Data System (ADS)

    Kjaergaard, M.; Nichele, F.; Suominen, H.; Nowak, M.; Wimmer, M.; Akhmerov, A.; Folk, J.; Flensberg, K.; Shabani, J.; Palmstrom, C.; Marcus, C.

    One route to study the non-Abelian nature of excitations in topological superconductors is to realise gateable two dimensional (2D) semiconducting systems, with spin-orbit coupling in proximity to an s-wave superconductor. Previous work on coupling 2D electron gases (2DEG) with superconductors has been hindered by a non-ideal interface and unstable gateability. We report measurements on a gateable 2DEG coupled to superconductors through a pristine interface, and use aluminum grown in situ epitaxially on an InGaAs/InAs electron gas. We demonstrate quantization in units of 4e2 / h in a quantum point contact (QPC) in such hybrid systems. Operating the QPC as a tunnel probe, we observe a hard superconducting gap, overcoming the soft-gap problem in 2D superconductor/semiconductor systems. Our work paves way for a new and highly scalable system in which to pursue topological quantum information processing. Research supported by Microsoft Project Q and the Danish National Research Foundation.

  17. Quantum conductance in electrodeposited nanocontacts and magnetoresistance measurements

    NASA Astrophysics Data System (ADS)

    Elhoussine, F.; Encinas, A.; Mátéfi-Tempfli, S.; Piraux, L.

    2003-05-01

    We present conductance and magnetoresistance measurements in magnetic Ni-Ni and Co-Ni nanocontacts prepared by electrodeposition within the pores of a track-etched polymer membrane. At room temperature, Ni-Ni constrictions show broad quantization plateaus of conductance during their dissolution into units of e2/h, as expected for ferromagnetic ballistic nanocontacts. Additionally, positive and negative magnetoresistance has been measured in Co-Ni nanocontacts.

  18. Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry.

    PubMed

    Ma, Eric Yue; Calvo, M Reyes; Wang, Jing; Lian, Biao; Mühlbauer, Mathias; Brüne, Christoph; Cui, Yong-Tao; Lai, Keji; Kundhikanjana, Worasom; Yang, Yongliang; Baenninger, Matthias; König, Markus; Ames, Christopher; Buhmann, Hartmut; Leubner, Philipp; Molenkamp, Laurens W; Zhang, Shou-Cheng; Goldhaber-Gordon, David; Kelly, Michael A; Shen, Zhi-Xun

    2015-01-01

    The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. This indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.

  19. Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry

    DOE PAGES

    Ma, Eric Yue; Calvo, M. Reyes; Wang, Jing; Lian, Biao; Muhlbauer, Mathias; Brune, Christoph; Cui, Yong -Tao; Lai, Keji; Kundhikanjana, Worasom; Yang, Yongliang; et al

    2015-05-26

    The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy,more » and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. Finally, this indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.« less

  20. Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry

    SciTech Connect

    Ma, Eric Yue; Calvo, M. Reyes; Wang, Jing; Lian, Biao; Muhlbauer, Mathias; Brune, Christoph; Cui, Yong -Tao; Lai, Keji; Kundhikanjana, Worasom; Yang, Yongliang; Baenninger, Matthias; Konig, Markus; Ames, Christopher; Buhmann, Hartmut; Leubner, Philipp; Molenkamp, Laurens W.; Zhang, Shou -Cheng; Goldhaber-Gordon, David; Kelly, Michael A.; Shen, Zhi -Xun

    2015-05-26

    The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a non-inverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. Finally, this indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.

  1. Investigating Student Understanding of Quantum Physics: Spontaneous Models of Conductivity.

    ERIC Educational Resources Information Center

    Wittmann, Michael C.; Steinberg, Richard N.; Redish, Edward F.

    2002-01-01

    Investigates student reasoning about models of conduction. Reports that students often are unable to account for the existence of free electrons in a conductor and create models that lead to incorrect predictions and responses contradictory to expert descriptions of the physics involved. (Contains 36 references.) (Author/YDS)

  2. Terahertz single conductance quantum and topological phase transitions in topological insulator Bi₂Se₃ ultrathin films.

    PubMed

    Park, Byung Cheol; Kim, Tae-Hyeon; Sim, Kyung Ik; Kang, Boyoun; Kim, Jeong Won; Cho, Beongki; Jeong, Kwang-Ho; Cho, Mann-Ho; Kim, Jae Hoon

    2015-03-16

    Strong spin-orbit interaction and time-reversal symmetry in topological insulators generate novel quantum states called topological surface states. Their study provides unique opportunities to explore exotic phenomena such as spin Hall effects and topological phase transitions, relevant to the development of quantum devices for spintronics and quantum computation. Although ultrahigh-vacuum surface probes can identify individual topological surface states, standard electrical and optical experiments have so far been hampered by the interference of bulk and quantum well states. Here, with terahertz time-domain spectroscopy of ultrathin Bi₂Se₃ films, we give evidence for topological phase transitions, a single conductance quantum per topological surface state, and a quantized terahertz absorbance of 2.9% (four times the fine structure constant). Our experiment demonstrates the feasibility to isolate, detect and manipulate topological surface states in the ambient at room temperature for future fundamental research on the novel physics of topological insulators and their practical applications.

  3. Theory of quantum conduction of supercurrent through a constriction

    SciTech Connect

    Furusaki, A.; Takayanagi, H.; Tsukada, M. Nippon Telegraph and Telephone Corporation Basic Research Laboratories, Musashino-shi, Tokyo 180, Japan)

    1991-07-01

    The dc Josephson current through a constriction in a two-dimensional superconductor-semiconductor-superconductor junction is calculated. It is shown that when the Fermi wavelength is comparable with the width of the constriction, the critical current shows a steplike variation as a function of the width of the constriction; this is reminiscent of the quantization of the normal-state conductance of point contacts in a two-dimensional electron gas.

  4. Dynamical conductivity at the dirty superconductor-metal quantum phase transition

    NASA Astrophysics Data System (ADS)

    Hoyos, J. A.; Del Maestro, Adrian; Rosenow, Bernd; Vojta, Thomas

    2011-03-01

    We study the transport properties of ultrathin disordered nanowires in the neighborhood of the superconductor-metal quantum phase transition. To this end we combine numerical calculations with analytical strong-disorder renormalization group results. The quantum critical conductivity at zero temperature diverges logarithmically as a function of frequency. In the metallic phase, it obeys activated scaling associated with an infinite-randomness quantum critical point. We extend the scaling theory to higher dimensions and discuss implications for experiments. Financial support: Fapesp, CNPq, NSF, and Research Corporation.

  5. Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis

    NASA Astrophysics Data System (ADS)

    Tadi, Kiran Kumar; Palve, Anil M.; Pal, Shubhadeep; Sudeep, P. M.; Narayanan, Tharangattu N.

    2016-07-01

    Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here.

  6. Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis.

    PubMed

    Tadi, Kiran Kumar; Palve, Anil M; Pal, Shubhadeep; Sudeep, P M; Narayanan, Tharangattu N

    2016-07-01

    Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here.

  7. Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis.

    PubMed

    Tadi, Kiran Kumar; Palve, Anil M; Pal, Shubhadeep; Sudeep, P M; Narayanan, Tharangattu N

    2016-07-01

    Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here. PMID:27231837

  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. Conducting High Cycle Fatigue Strength Step Tests on Gamma TiAl

    NASA Technical Reports Server (NTRS)

    Lerch, Brad; Draper, Sue; Pereira, J. Mike

    2002-01-01

    High cycle fatigue strength testing of gamma TiAl by the step test method is investigated. A design of experiments was implemented to determine if the coaxing effect occurred during testing. Since coaxing was not observed, step testing was deemed a suitable method to define the fatigue strength at 106 cycles.

  10. Exact conductance through point contacts in the {nu}=1/3 fractional quantum Hall Effect

    SciTech Connect

    Fendley, P.; Ludwig, A.W.W.; Saleur, H. |

    1995-04-10

    The conductance for tunneling through an impurity in a Luttinger liquid is described by a universal scaling function. We compute this scaling function exactly, by using the thermodynamic Bethe ansatz and a kinetic (Boltzmann) equation. This model has been proposed to describe resonant tunneling through a point contact between two {nu}=1/3 quantum Hall edges. Recent experiments on quantum Hall devices agree well with our exact results. We also derive the exact conductance and {ital I}({ital V}) curve, out of equilibrium, in this fully interacting system.

  11. Quantum ring conductance sensitivity to potential perturbation in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Chwiej, T.; Szafran, B.

    2014-05-01

    We study the sensitivity of quantum ring (QR) conductance to potential perturbation introduced by an external charged probe in the context of scanning gate microscopy experiments and analyze its correspondence to the local density of states at the Fermi level for up to four subbands participating in the transport. We find that the conductance of the QR can be weakly sensitive or almost insensitive to the perturbation potential due to magnetic deflection of the wave function. The conductance becomes very sensitive to external perturbations at localized resonances for which the local density of states can be extracted by conductance mapping.

  12. Direct validation of the single step classical to quantum free energy perturbation.

    PubMed

    Cave-Ayland, Christopher; Skylaris, Chris-Kriton; Essex, Jonathan W

    2015-01-22

    The use of the Zwanzig equation in the calculation of single-step perturbations to provide first-principles (ab initio) quantum mechanics (QM) correction terms to molecular mechanics (MM) free energy cycles is well established. A rigorous test of the ability to converge such calculations would be very useful in this context. In this work, we perform a direct assessment of the convergence of the MM to QM perturbation, by attempting the reverse QM to MM perturbation. This required the generation of extensive QM molecular dynamics trajectories, using density functional theory (DFT), within the representative biological system of a DNA adenosine-thymidine dimer. Over 100 ps of dynamics with the PBE functional and 6.25 ps with the LDA functional were generated. We demonstrate that calculations with total potential energies are very poorly convergent due to a lack of overlap of phase space distributions between ensembles. While not theoretically rigorous, the use of interaction energies provides far superior convergence, despite the presence of nonclassical charge transfer effects within the DFT trajectories. The source of poor phase space overlap for total energies is diagnosed, the approximate quantification of overlaps suggesting that even for the comparatively simple system considered here convergence of total energy calculations within a reasonable simulation time is unfeasible.

  13. One-Step Deposition of Photovoltaic Layers Using Iodide Terminated PbS Quantum Dots.

    PubMed

    Kim, Sungwoo; Noh, Jaehong; Choi, Hyekyoung; Ha, Heonseok; Song, Jung Hoon; Shim, Hyung Cheoul; Jang, Jihoon; Beard, Matthew C; Jeong, Sohee

    2014-11-20

    We present a one-step layer deposition procedure employing ammonium iodide (NH4I) to achieve photovoltaic quality PbS quantum dot (QD) layers. Ammonium iodide is used to replace the long alkyl organic native ligands binding to the QD surface resulting in iodide terminated QDs that are stabilized in polar solvents such as N,N-dimethylformamide without particle aggregation. We extensively characterized the iodide terminated PbS QD via UV-vis absorption, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), FT-IR transmission spectroscopy, and X-ray photoelectron spectroscopy (XPS). Finally, we fabricated PbS QD photovoltaic cells that employ the iodide terminated PbS QDs. The resulting QD-PV devices achieved a best power conversion efficiency of 2.36% under ambient conditions that is limited by the layer thickness. The PV characteristics compare favorably to similar devices that were prepared using the standard layer-by-layer ethandithiol (EDT) treatment that had a similar layer thickness.

  14. Anisotropic behavior of quantum transport in graphene superlattices: Coexistence of ballistic conduction with Anderson insulating regime

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    We report on the possibility to generate highly anisotropic quantum conductivity in disordered graphene-based superlattices. Our quantum simulations, based on an efficient real-space implementation of the Kubo-Greenwood formula, show that in disordered graphene superlattices the strength of multiple scattering phenomena can strongly depend on the transport measurement geometry. This eventually yields the coexistence of a ballistic waveguide and a highly resistive channel (Anderson insulator) in the same two-dimensional platform, evidenced by a σyy/σxx ratio varying over several orders of magnitude, and suggesting the possibility of building graphene electronic circuits based on the unique properties of chiral massless Dirac fermions in graphene.

  15. Universal conductivity in a two-dimensional superfluid-to-insulator quantum critical system.

    PubMed

    Chen, Kun; Liu, Longxiang; Deng, Youjin; Pollet, Lode; Prokof'ev, Nikolay

    2014-01-24

    We compute the universal conductivity of the (2+1)-dimensional XY universality class, which is realized for a superfluid-to-Mott insulator quantum phase transition at constant density. Based on large-scale Monte Carlo simulations of the classical (2+1)-dimensional J-current model and the two-dimensional Bose-Hubbard model, we can precisely determine the conductivity on the quantum critical plateau, σ(∞) = 0.359(4)σQ with σQ the conductivity quantum. The universal conductivity curve is the standard example with the lowest number of components where the bottoms-up AdS/CFT correspondence from string theory can be tested and made to use [R. C. Myers, S. Sachdev, and A. Singh, Phys. Rev. D 83, 066017 (2011)]. For the first time, the shape of the σ(iω(n)) - σ(∞) function in the Matsubara representation is accurate enough for a conclusive comparison and establishes the particlelike nature of charge transport. We find that the holographic gauge-gravity duality theory for transport properties can be made compatible with the data if temperature of the horizon of the black brane is different from the temperature of the conformal field theory. The requirements for measuring the universal conductivity in a cold gas experiment are also determined by our calculation. PMID:24484123

  16. Universal conductivity in a two-dimensional superfluid-to-insulator quantum critical system.

    PubMed

    Chen, Kun; Liu, Longxiang; Deng, Youjin; Pollet, Lode; Prokof'ev, Nikolay

    2014-01-24

    We compute the universal conductivity of the (2+1)-dimensional XY universality class, which is realized for a superfluid-to-Mott insulator quantum phase transition at constant density. Based on large-scale Monte Carlo simulations of the classical (2+1)-dimensional J-current model and the two-dimensional Bose-Hubbard model, we can precisely determine the conductivity on the quantum critical plateau, σ(∞) = 0.359(4)σQ with σQ the conductivity quantum. The universal conductivity curve is the standard example with the lowest number of components where the bottoms-up AdS/CFT correspondence from string theory can be tested and made to use [R. C. Myers, S. Sachdev, and A. Singh, Phys. Rev. D 83, 066017 (2011)]. For the first time, the shape of the σ(iω(n)) - σ(∞) function in the Matsubara representation is accurate enough for a conclusive comparison and establishes the particlelike nature of charge transport. We find that the holographic gauge-gravity duality theory for transport properties can be made compatible with the data if temperature of the horizon of the black brane is different from the temperature of the conformal field theory. The requirements for measuring the universal conductivity in a cold gas experiment are also determined by our calculation.

  17. Sharp peaks in the conductance of a double quantum dot and a quantum-dot spin valve at high temperatures: A hierarchical quantum master equation approach

    NASA Astrophysics Data System (ADS)

    Wenderoth, S.; Bätge, J.; Härtle, R.

    2016-09-01

    We study sharp peaks in the conductance-voltage characteristics of a double quantum dot and a quantum dot spin valve that are located around zero bias. The peaks share similarities with a Kondo peak but can be clearly distinguished, in particular as they occur at high temperatures. The underlying physical mechanism is a strong current suppression that is quenched in bias-voltage dependent ways by exchange interactions. Our theoretical results are based on the quantum master equation methodology, including the Born-Markov approximation and a numerically exact, hierarchical scheme, which we extend here to the spin-valve case. The comparison of exact and approximate results allows us to reveal the underlying physical mechanisms, the role of first-, second- and beyond-second-order processes and the robustness of the effect.

  18. Negative differential conductivity and quantum statistical effects in a three-site Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Olsen, M. K.; Corney, J. F.

    2016-09-01

    The use of an electron beam to remove ultracold atoms from selected sites in an optical lattice has opened up new opportunities to study transport in quantum systems [R. Labouvie et al., Phys. Rev. Lett. 115, 050601 (2015), 10.1103/PhysRevLett.115.050601]. Inspired by this experimental result, we examine the effects of number difference, dephasing, and initial quantum statistics on the filling of an initially depleted middle well in the three-well inline Bose-Hubbard model. We find that the well-known phenomenon of macroscopic self-trapping is the main contributor to oscillatory negative differential conductivity in our model, with phase diffusion being a secondary effect. However, we find that phase diffusion is required for the production of direct atomic current, with the coherent process showing damped oscillatory currents. We also find that our results are highly dependent on the initial quantum states of the atoms in the system.

  19. Wave-function description of conductance mapping for a quantum Hall electron interferometer

    NASA Astrophysics Data System (ADS)

    Kolasiński, K.; Szafran, B.

    2014-04-01

    Scanning gate microscopy of quantum point contacts (QPC) in the integer quantum Hall regime is considered in terms of the scattering wave functions with a finite-difference implementation of the quantum transmitting boundary approach. Conductance (G) maps for a clean QPC as well as for a system including an antidot within the QPC constriction are evaluated. The steplike locally flat G maps for clean QPCs turn into circular resonances that are reentrant in an external magnetic field when the antidot is introduced to the constriction. The current circulation around the antidot and the spacing of the resonances at the magnetic field scale react to the probe approaching the QPC. The calculated G maps with a rigid but soft antidot potential reproduce the features detected recently in the electron interferometer [F. Martins et al., Sci. Rep. 3, 1416 (2013), 10.1038/srep01416].

  20. Conductive atomic force microscopy studies on the transformation of GeSi quantum dots to quantum rings.

    PubMed

    Zhang, S L; Xue, F; Wu, R; Cui, J; Jiang, Z M; Yang, X J

    2009-04-01

    Conductive atomic force microscopy has been employed to study the topography and conductance distribution of individual GeSi quantum dots (QDs) and quantum rings (QRs) during the transformation from QDs to QRs by depositing an Si capping layer on QDs. The current distribution changes significantly with the topographic transformation during the Si capping process. Without the capping layer, the QDs are dome-shaped and the conductance is higher at the ring region between the center and boundary than that at the center. After capping with 0.32 nm Si, the shape of the QDs changes to pyramidal and the current is higher at both the center and the arris. When the Si capping layer increases to 2 nm, QRs are formed and the current of individual QRs is higher at the rim than that at the central hole. By comparing the composition distributions obtained by scanning Auger microscopy and atomic force microscopy combined with selective chemical etching, the origin of the current distribution change is discussed.

  1. Mapping out spin and particle conductances in a quantum point contact

    NASA Astrophysics Data System (ADS)

    Krinner, Sebastian; Lebrat, Martin; Husmann, Dominik; Grenier, Charles; Brantut, Jean-Philippe; Esslinger, Tilman

    2016-07-01

    We study particle and spin transport in a single-mode quantum point contact, using a charge neutral, quantum degenerate Fermi gas with tunable, attractive interactions. This yields the spin and particle conductance of the point contact as a function of chemical potential or confinement. The measurements cover a regime from weak attraction, where quantized conductance is observed, to the resonantly interacting superfluid. Spin conductance exhibits a broad maximum when varying the chemical potential at moderate interactions, which signals the emergence of Cooper pairing. In contrast, the particle conductance is unexpectedly enhanced even before the gas is expected to turn into a superfluid, continuously rising from the plateau at 1/h1/h for weak interactions to plateau-like features at nonuniversal values as high as 4/h4/h for intermediate interactions. For strong interactions, the particle conductance plateaus disappear and the spin conductance gets suppressed, confirming the spin-insulating character of a superfluid. Our observations document the breakdown of universal conductance quantization as many-body correlations appear. The observed anomalous quantization challenges a Fermi liquid description of the normal phase, shedding new light on the nature of the strongly attractive Fermi gas.

  2. Mapping out spin and particle conductances in a quantum point contact.

    PubMed

    Krinner, Sebastian; Lebrat, Martin; Husmann, Dominik; Grenier, Charles; Brantut, Jean-Philippe; Esslinger, Tilman

    2016-07-19

    We study particle and spin transport in a single-mode quantum point contact, using a charge neutral, quantum degenerate Fermi gas with tunable, attractive interactions. This yields the spin and particle conductance of the point contact as a function of chemical potential or confinement. The measurements cover a regime from weak attraction, where quantized conductance is observed, to the resonantly interacting superfluid. Spin conductance exhibits a broad maximum when varying the chemical potential at moderate interactions, which signals the emergence of Cooper pairing. In contrast, the particle conductance is unexpectedly enhanced even before the gas is expected to turn into a superfluid, continuously rising from the plateau at [Formula: see text] for weak interactions to plateau-like features at nonuniversal values as high as [Formula: see text] for intermediate interactions. For strong interactions, the particle conductance plateaus disappear and the spin conductance gets suppressed, confirming the spin-insulating character of a superfluid. Our observations document the breakdown of universal conductance quantization as many-body correlations appear. The observed anomalous quantization challenges a Fermi liquid description of the normal phase, shedding new light on the nature of the strongly attractive Fermi gas. PMID:27357668

  3. Mapping out spin and particle conductances in a quantum point contact.

    PubMed

    Krinner, Sebastian; Lebrat, Martin; Husmann, Dominik; Grenier, Charles; Brantut, Jean-Philippe; Esslinger, Tilman

    2016-07-19

    We study particle and spin transport in a single-mode quantum point contact, using a charge neutral, quantum degenerate Fermi gas with tunable, attractive interactions. This yields the spin and particle conductance of the point contact as a function of chemical potential or confinement. The measurements cover a regime from weak attraction, where quantized conductance is observed, to the resonantly interacting superfluid. Spin conductance exhibits a broad maximum when varying the chemical potential at moderate interactions, which signals the emergence of Cooper pairing. In contrast, the particle conductance is unexpectedly enhanced even before the gas is expected to turn into a superfluid, continuously rising from the plateau at [Formula: see text] for weak interactions to plateau-like features at nonuniversal values as high as [Formula: see text] for intermediate interactions. For strong interactions, the particle conductance plateaus disappear and the spin conductance gets suppressed, confirming the spin-insulating character of a superfluid. Our observations document the breakdown of universal conductance quantization as many-body correlations appear. The observed anomalous quantization challenges a Fermi liquid description of the normal phase, shedding new light on the nature of the strongly attractive Fermi gas.

  4. Mapping out spin and particle conductances in a quantum point contact

    PubMed Central

    Krinner, Sebastian; Lebrat, Martin; Husmann, Dominik; Grenier, Charles; Brantut, Jean-Philippe; Esslinger, Tilman

    2016-01-01

    We study particle and spin transport in a single-mode quantum point contact, using a charge neutral, quantum degenerate Fermi gas with tunable, attractive interactions. This yields the spin and particle conductance of the point contact as a function of chemical potential or confinement. The measurements cover a regime from weak attraction, where quantized conductance is observed, to the resonantly interacting superfluid. Spin conductance exhibits a broad maximum when varying the chemical potential at moderate interactions, which signals the emergence of Cooper pairing. In contrast, the particle conductance is unexpectedly enhanced even before the gas is expected to turn into a superfluid, continuously rising from the plateau at 1/h for weak interactions to plateau-like features at nonuniversal values as high as 4/h for intermediate interactions. For strong interactions, the particle conductance plateaus disappear and the spin conductance gets suppressed, confirming the spin-insulating character of a superfluid. Our observations document the breakdown of universal conductance quantization as many-body correlations appear. The observed anomalous quantization challenges a Fermi liquid description of the normal phase, shedding new light on the nature of the strongly attractive Fermi gas. PMID:27357668

  5. Many-body effects on graphene conductivity: Quantum Monte Carlo calculations

    NASA Astrophysics Data System (ADS)

    Boyda, D. L.; Braguta, V. V.; Katsnelson, M. I.; Ulybyshev, M. V.

    2016-08-01

    Optical conductivity of graphene is studied using quantum Monte Carlo calculations. We start from a Euclidean current-current correlator and extract σ (ω ) from Green-Kubo relations using the Backus-Gilbert method. Calculations were performed both for long-range interactions and taking into account only the contact term. In both cases we vary interaction strength and study its influence on optical conductivity. We compare our results with previous theoretical calculations choosing ω ≈κ , thus working in the region of the plateau in σ (ω ) which corresponds to optical conductivity of Dirac quasiparticles. No dependence of optical conductivity on interaction strength is observed unless we approach the antiferromagnetic phase transition in the case of an artificially enhanced contact term. Our results strongly support previous theoretical studies that claimed very weak regularization of graphene conductivity.

  6. Photoreflectance spectroscopy of step-like GaInNAs/GaInNAs/GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Kudrawiec, R.; Andrzejewski, J.; Misiewicz, J.; Gollub, D.; Forchel, A.

    2005-05-01

    Photoreflectance (PR) spectroscopy has been applied to study of step-like GaInNAs/GaInNAs/GaAs double quantum well (DQW) structures grown by molecular beam epitaxy. PR features related to optical transitions in the active part of the step-like QW structure, i.e. GaInNAs/GaInNAs QW, as well as PR features related to transitions above the step-like barrier (SLB) have been clearly observed and analysed in this paper. The analysis of the QW transitions gives information about the number of confined states in the active part of the step-like QW structure. In addition, the analysis of the second portion of PR signal gives information about the band gap energy of the SLB and optical transitions between hole and electron levels confined above the SLB.

  7. Dielectric relaxation and ac conductivity behaviour of polyvinyl alcohol-HgSe quantum dot hybrid films

    NASA Astrophysics Data System (ADS)

    Sinha, Subhojyoti; Chatterjee, Sanat Kumar; Ghosh, Jiten; Meikap, Ajit Kumar

    2014-07-01

    Here we report a comparative study on the dielectric relaxation and ac conductivity behaviour of pure polyvinyl alcohol (PVA) and PVA-mercury selenide (HgSe) quantum dot hybrid films in the temperature range 298 K ⩽ T ⩽ 420 K and in the frequency range 100 Hz ⩽ f ⩽ 1 MHz. The prepared nanocomposite exhibits a larger dielectric constant as compared to the pure PVA. The real and imaginary parts of the dielectric constants were found to fit appreciably with the modified Cole-Cole equation, from which temperature-dependent values of the relaxation times, free charge carrier conductivity and space charge carrier conductivity were calculated. The relaxation time decreases with the quantum dot's inclusion in the PVA matrix and with an increase in temperature, whereas free charge carrier conductivity and space charge carrier conductivity increases with an increase in temperature. An increase in ac conductivity for the nanocomposites has also been observed, while the charge transport mechanism was found to follow the correlated barrier hopping model in both cases. An easy-path model with a suitable electrical equivalent circuit has been employed to analyse the temperature-dependent impedance spectra. The imaginary part of the complex electric modulus spectra exhibit an asymmetric nature and a non-Debye type of behaviour, which has been elucidated considering a generalized susceptibility function. The electric modulus spectra of the nanocomposite demonstrate a smaller amplitude and broader width, as compared to the pure PVA sample.

  8. Conductance stability in chaotic and integrable quantum dots with random impurities.

    PubMed

    Wang, Guanglei; Ying, Lei; Lai, Ying-Cheng

    2015-08-01

    For a quantum dot system of fixed geometry, in the presence of random impurities the average conductance over an appropriate range of the Fermi energy decreases as the impurity strength is increased. Can the nature of the corresponding classical dynamics in the dot region affect the rate of decrease? Utilizing graphene quantum dots with two semi-infinite, single-mode leads as a prototypical model, we address the device stability issue by investigating the combined effects of classical dynamics and impurities on the average conductance over the energy range of the first transverse mode. We find that, for chaotic dot systems, the rate of decrease in the average conductance with the impurity strength is in general characteristically smaller than that for integrable dots. We develop a semiclassical analysis for the phenomenon and also obtain an understanding based on the random matrix theory. Our results demonstrate that classical chaos can generally lead to a stronger stability in the device performance, strongly advocating exploiting chaos in the development of nanoscale quantum transport devices. PMID:26382470

  9. Simulation and experimental design of a new advanced variable step size Incremental Conductance MPPT algorithm for PV systems.

    PubMed

    Loukriz, Abdelhamid; Haddadi, Mourad; Messalti, Sabir

    2016-05-01

    Improvement of the efficiency of photovoltaic system based on new maximum power point tracking (MPPT) algorithms is the most promising solution due to its low cost and its easy implementation without equipment updating. Many MPPT methods with fixed step size have been developed. However, when atmospheric conditions change rapidly , the performance of conventional algorithms is reduced. In this paper, a new variable step size Incremental Conductance IC MPPT algorithm has been proposed. Modeling and simulation of different operational conditions of conventional Incremental Conductance IC and proposed methods are presented. The proposed method was developed and tested successfully on a photovoltaic system based on Flyback converter and control circuit using dsPIC30F4011. Both, simulation and experimental design are provided in several aspects. A comparative study between the proposed variable step size and fixed step size IC MPPT method under similar operating conditions is presented. The obtained results demonstrate the efficiency of the proposed MPPT algorithm in terms of speed in MPP tracking and accuracy. PMID:26337741

  10. The effects of doping layer location on the electronic and optical properties of GaN step quantum well

    NASA Astrophysics Data System (ADS)

    Dakhlaoui, Hassen

    2016-09-01

    In the present work, the intersubband transition and the optical absorption coefficient between the ground and the first excited states in the Si-δ-doped step AlGaN/GaN quantum well were theoretically studied by solving Schrödinger-Poisson equations self-consistently within the framework of effective mass approximation. The delta-doped layer was inserted in three different locations (middle of the quantum well, middle of the step quantum well and middle of the left barrier). The obtained results show that the energy difference between the ground and the first excited state and the optical absorption depend not only on the doping layer concentration but also on its location. The shape of the confining potential and the wavefunctions were also changed depending on the doped layer location. It was found that doping in the middle quantum well is advantageous to obtain an optical absorption with a higher energy separation; however, doping in the left barrier gives us an optical absorption with a lower energy separation. The obtained results in optical absorption give us a new degree of freedom in optoelectronic devices based on intersubband transitions.

  11. Fractional quantum conductance values in Au nanoelectrodes due to hydrogen adsorption

    NASA Astrophysics Data System (ADS)

    Díaz, M.; Martín-González, M. S.; Costa-Krämer, J. L.

    2010-08-01

    Hydrogen adsorption in gold nanocontact electrodes in electrochemical solution is experimentally discerned. This is performed with gold nanocontact conductance histograms in an electrochemical environment in which both the electrochemical potential and the electrolyte type are varied. Different salts, acids, and hydrogen peroxide electrolytes are studied. Salts and acids exhibit at negative electrochemical potentials different fractional quantum conductance histograms peaks associated to extra stable structures due to H adsorption while these peaks do not appear for H 2O 2 where electron transfer between solution and electrodes occurs without hydrogen formation or hydrogen adsorption on the gold electrode.

  12. Suppression of bulk conductivity in InAs/GaSb broken gap composite quantum wells

    SciTech Connect

    Charpentier, Christophe; Fält, Stefan; Reichl, Christian; Nichele, Fabrizio; Nath Pal, Atindra; Pietsch, Patrick; Ihn, Thomas; Ensslin, Klaus; Wegscheider, Werner

    2013-09-09

    The two-dimensional topological insulator state in InAs/GaSb quantum wells manifests itself by topologically protected helical edge channel transport relying on an insulating bulk. This work investigates a way of suppressing bulk conductivity by using gallium source materials of different degrees of impurity concentrations. While highest-purity gallium is accompanied by clear conduction through the sample bulk, intentional impurity incorporation leads to a bulk resistance over 1 MΩ, independent of applied magnetic fields. In addition, ultra high electron mobilities for GaAs/AlGaAs structures fabricated in a molecular beam epitaxy system used for the growth of Sb-based samples are reported.

  13. Two-dimensional quantum transport in highly conductive carbon nanotube fibers

    NASA Astrophysics Data System (ADS)

    Piraux, L.; Abreu Araujo, F.; Bui, T. N.; Otto, M. J.; Issi, J.-P.

    2015-08-01

    Measurements of the electrical resistivity, from 1.5 to 300 K, and of the low temperature magnetoresistance of highly conductive carbon nanotube (CNT) fibers, obtained by wet-spinning from liquid crystalline phase (LCP), are reported. At high temperature the results obtained on the raw CNT fibers show a typical metallic behavior and the resistivity levels without postdoping process were found to be only one order of magnitude higher than the best electrical conductors, with the specific conductivity (conductivity per unit weight) comparable to that of pure copper. At low temperature a logarithmic dependence of the resistivity and the temperature dependence of the negative magnetoresistance are consistent with a two-dimensional quantum charge transport—weak localization and Coulomb interaction—in the few-walled CNT fibers. The temperature dependence of the phase-breaking scattering rate has also been determined from magnetoresistance measurements. In the temperature range T <100 K , electron-electron scattering is found to be the dominant source of dephasing in these highly conductive CNT fibers. While quantum effects demonstrate the two-dimensional aspect of conduction in the fibers, the fact that it was found that their resistance is mainly determined by the intrinsic resistivity of the CNTs—and not by intertube resistances—suggests that better practical conductors could be obtained by improving the quality of the CNTs and the fiber morphology.

  14. Emergence of helical edge conduction in graphene at the ν =0 quantum Hall state

    NASA Astrophysics Data System (ADS)

    Tikhonov, Pavel; Shimshoni, Efrat; Fertig, H. A.; Murthy, Ganpathy

    2016-03-01

    The conductance of graphene subject to a strong, tilted magnetic field exhibits a dramatic change from insulating to conducting behavior with tilt angle, regarded as evidence for the transition from a canted antiferromagnetic (CAF) to a ferromagnetic (FM) ν =0 quantum Hall state. We develop a theory for the electric transport in this system based on the spin-charge connection, whereby the evolution in the nature of collective spin excitations is reflected in the charge-carrying modes. To this end, we derive an effective field-theoretical description of the low-energy excitations, associated with quantum fluctuations of the spin-valley domain-wall ground-state configuration which characterizes the two-dimensional (2D) system with an edge. This analysis yields a model describing a one-dimensional charged edge mode coupled to charge-neutral spin-wave excitations in the 2D bulk. Focusing particularly on the FM phase, naively expected to exhibit perfect conductance, we study a mechanism whereby the coupling to these bulk excitations assists in generating backscattering. Our theory yields the conductance as a function of temperature and the Zeeman energy—the parameter that tunes the transition between the FM and CAF phases—with behavior in qualitative agreement with experiment.

  15. The electrochemistry of transparent quantum size rutile nanowire thin films prepared by one-step low temperature chemical bath deposition

    NASA Astrophysics Data System (ADS)

    Berger, Thomas; Lana-Villarreal, Teresa; Monllor-Satoca, Damián; Gómez, Roberto

    2007-10-01

    We performed a spectro- and photoelectrochemical study of electrodes consisting of oriented rutile TiO 2 nanowires with a diameter of ˜2 nm prepared directly by chemical bath deposition on conducting glass. A significant increase (around 0.25 eV with respect to bulk rutile) of the band gap energy for the nanowire film is observed and attributed to quantum size effects, pointing to the presence of individual monocrystalline nanowires with no significant electronic communication among them. This allows for the investigation of morphologically well defined electrodes in the two dimensional quantum confinement regime, which are characterized by particularly good photoelectrocatalytic and electrochromic properties.

  16. Conductance phases in the quantum dots of an Aharonov-Bohm ring

    NASA Astrophysics Data System (ADS)

    Yahalom, A.; Englman, R.

    2006-09-01

    The regimes of growing phases (for electron numbers N≈0 8 ) that pass into regions of self-returning phases (for N>8 ), found recently in quantum dot conductances by Heiblum and co-workers are accounted for by an elementary Green’s function formalism, appropriate to an equi-spaced ladder structure (with at least three rungs) of electronic levels in the quantum dot. The key features of the theory are physically a dissipation rate that increases linearly with the level number (and is tentatively linked to coupling to longitudinal optical phonons) and a set of Fano-like metastable levels, which disturb the unitarity, and mathematically the changeover of the position of the complex transmission amplitude zeros from the upper half in the complex gap-voltage plane to the lower half of that plane. The two regimes are identified with (respectively) the Blaschke term and the Kramers-Kronig integral term in the theory of complex variables.

  17. Strong reduction of the lattice thermal conductivity in superlattices and quantum dot superlattices

    NASA Astrophysics Data System (ADS)

    Fomin, V. M.; Nika, D. L.; Cocemasov, A. I.; Isacova, C. I.; Schmidt, O. G.

    2012-06-01

    Thermal transport is theoretically investigated in the planar Si/Ge superlattices and Si/Ge quantum dot superlattices. The phonon states in the considered nanostructures are obtained using the Face-centered Cubic Cell model of lattice dynamics. A significant reduction of the lattice thermal conductivity is revealed in both considered structures in a wide range of temperatures from 100 K to 400 K. This effect is explained by the removal of the high-energy and high-velocity phonon modes from the heat flux due to their localization in superlattice segments and the phonon scattering on the interfaces. The obtained results show prospects of the planar superlattices and quantum-dot superlattices for thermoelectric and thermo-insulating applications.

  18. Quantum beats in conductance oscillations in graphene-based asymmetric double velocity wells and electrostatic wells

    SciTech Connect

    Liu, Lei; Li, Yu-Xian; Zhang, Ying-Tao; Liu, Jian-Jun

    2014-01-14

    The transport properties in graphene-based asymmetric double velocity well (Fermi velocity inside the well less than that outside the well) and electrostatic well structures are investigated using the transfer matrix method. The results show that quantum beats occur in the oscillations of the conductance for asymmetric double velocity wells. The beating effect can also be found in asymmetric double electrostatic wells, but only if the widths of the two wells are different. The beat frequency for the asymmetric double well is exactly equal to the frequency difference between the oscillation rates in two isolated single wells with the same structures as the individual wells in the double well structure. A qualitative interpretation is proposed based on the fact that the resonant levels depend upon the sizes of the quantum wells. The beating behavior can provide a new way to identify the symmetry of double well structures.

  19. Surface-step defect in three-dimensional topological insulators: Electric manipulation of spin and quantum spin Hall effect

    NASA Astrophysics Data System (ADS)

    Zhou, Yan-Feng; Guo, Ai-Min; Sun, Qing-Feng

    2016-08-01

    We study the influence of a step defect on surface states in three-dimensional topological insulators subject to a perpendicular magnetic field. By calculating the energy spectrum of the surface states, we find that Landau levels (LLs) can form on flat regions of the surface and are distant from the step defect, and several subbands emerge at the side surface of the step defect. The subband which connects to the two zeroth LLs is spin polarized and chiral. In particular, when the electron transports along the side surface, the electron spin direction can be manipulated arbitrarily by gate voltage. Also, no reflection occurs even if the electron spin direction is changed. This provides a fascinating avenue to control the electron spin easily and coherently. In addition, regarding the subbands with a high LL index, there exist spin-momentum locking helical states and the quantum spin Hall effect can appear.

  20. Development of Electrically Conductive Double-Network Hydrogels via One-Step Facile Strategy for Cardiac Tissue Engineering.

    PubMed

    Yang, Boguang; Yao, Fanglian; Hao, Tong; Fang, Wancai; Ye, Lei; Zhang, Yabin; Wang, Yan; Li, Junjie; Wang, Changyong

    2016-02-18

    Cardiac tissue engineering is an effective method to treat the myocardial infarction. However, the lack of electrical conductivity of biomaterials limits their applications. In this work, a homogeneous electronically conductive double network (HEDN) hydrogel via one-step facile strategy is developed, consisting of a rigid/hydrophobic/conductive network of chemical crosslinked poly(thiophene-3-acetic acid) (PTAA) and a flexible/hydrophilic/biocompatible network of photo-crosslinking methacrylated aminated gelatin (MAAG). Results suggest that the swelling, mechanical, and conductive properties of HEDN hydrogel can be modulated via adjusting the ratio of PTAA network to MAAG network. HEDN hydrogel has Young's moduli ranging from 22.7 to 493.1 kPa, and its conductivity (≈10(-4) S cm(-1)) falls in the range of reported conductivities for native myocardium tissue. To assess their biological activity, the brown adipose-derived stem cells (BADSCs) are seeded on the surface of HEDN hydrogel with or without electrical stimulation. Our data show that the HEDN hydrogel can support the survival and proliferation of BADSCs, and that it can improve the cardiac differentiation efficiency of BADSCs and upregulate the expression of connexin 43. Moreover, electrical stimulation can further improve this effect. Overall, it is concluded that the HEDN hydrogel may represent an ideal scaffold for cardiac tissue engineering.

  1. Multi-channel conduction in redox-based resistive switch modelled using quantum point contact theory

    NASA Astrophysics Data System (ADS)

    Miranda, E.; Mehonic, A.; Suñé, J.; Kenyon, A. J.

    2013-11-01

    A simple analytic model for the electron transport through filamentary-type structures in Si-rich silica (SiOx)-based resistive switches is proposed. The model is based on a mesoscopic description and is able to account for the linear and nonlinear components of conductance that arise from both fully and partially formed conductive channels spanning the dielectric film. Channels are represented by arrays of identical scatterers whose number and quantum transmission properties determine the current magnitude in the low and high resistance states. We show that the proposed model not only reproduces the experimental current-voltage (I-V) characteristics but also the normalized differential conductance (dln(I)/dln(V)-V) curves of devices under test.

  2. Effect of the tilted magnetic field on the magnetosubbands and conductance in the bilayer quantum wire

    NASA Astrophysics Data System (ADS)

    Chwiej, T.

    2016-10-01

    We theoretically study the single electron magnetotransport in GaAs and InGaAs vertically stacked bilayer nanowires. In considered geometry, the tilted magnetic field is always perpendicular to the main (transport) axis of the quantum wire and, therefore its transverse and vertical components allow separately for changing the magnitude of intralayer and interlayer subbands mixing. We study the changes introduced to energy dispersion relation E(k) by tilted magnetic field of strength up to several tesla and analyze their origins for symmetric as well as asymmetric confining potentials in the growth direction. Calculated energy dispersion relations are thereafter used to show that the value of a conductance of the bilayer nanowire may abruptly rise as well as fall by few conductance quanta when the Fermi energy in nanosystem is changed. It is also shown that such conductance oscillations, in conjunction with spin Zeeman effect, may give a moderately spin polarized current in the bilayer nanowire.

  3. Transmission zero in a quantum dot with strong electron-electron interaction: Perturbative conductance calculations

    NASA Astrophysics Data System (ADS)

    Kim, Sejoong; Lee, Hyun-Woo

    2006-05-01

    A pioneering experiment [E. Schuster, E. Buks, M. Heiblum, D. Mahalu, V. Umansky, and Hadas Shtrikman, Nature 385, 417 (1997)] reported the measurement of the transmission phase of an electron traversing a quantum dot and found the intriguing feature of a sudden phase drop in the conductance valleys. Based on the Friedel sum rule for a spinless effective one-dimensional system, it has been previously argued [H.-W. Lee, Phys. Rev. Lett. 82, 2358 (1999)] that the sudden phase drop should be accompanied by the vanishing of the transmission amplitude, or transmission zero. Here we address roles of strong electron-electron interactions on the electron transport through a two-level quantum dot where one level couples with the leads much more strongly than the other level does [P. G. Silvestrov and Y. Imry, Phys. Rev. Lett. 85, 2565 (2000)]. We perform a perturbative conductance calculation with an explicit account of large charging energy and verify that the resulting conductance exhibits transmission zero, in agreement with the analysis based on the Friedel sum rule.

  4. Hopping conductivity in the quantum Hall effect: revival of universal scaling.

    PubMed

    Hohls, F; Zeitler, U; Haug, R J

    2002-01-21

    We have measured the temperature dependence of the conductivity sigma(xx) of a two-dimensional electron system deep into the localized regime of the quantum Hall plateau transition. Using variable-range hopping theory we extract directly the localization length xi from this experiment. We use our results to study the scaling behavior of xi as a function of the filling factor distance /deltanu/ to the critical point of the transition. We find for all samples a power-law behavior xi equivalent to /deltanu/(-gamma) in agreement with the theoretically proposed universal exponent gamma = 2.35.

  5. Bound states induced giant oscillations of the conductance in the quantum Hall regime.

    PubMed

    Kadigrobov, A M; Fistul, M V

    2016-06-29

    We theoretically studied the quasiparticle transport in a 2D electron gas biased in the quantum Hall regime and in the presence of a lateral potential barrier. The lateral junction hosts the specific magnetic field dependent quasiparticle states highly localized in the transverse direction. The quantum tunnelling across the barrier provides a complex bands structure of a one-dimensional energy spectrum of these bound states, [Formula: see text], where p y is the electron momentum in the longitudinal direction y. Such a spectrum manifests itself by a large number of peaks and drops in the dependence of the magnetic edge states transmission coefficient D(E ) on the electron energy E. E.g. the high value of D occurs as soon as the electron energy E reaches gaps in the spectrum. These peaks and drops of D(E) result in giant oscillations of the transverse conductance G x with the magnetic field and/or the transport voltage. Our theoretical analysis, based on the coherent macroscopic quantum superposition of the bound states and the magnetic edge states propagating along the system boundaries, is in a good accord with the experimental observations found in Kang et al (2000 Lett. Nat. 403 59).

  6. Long-wavelength corrections to Hall conductivity in fractional quantum Hall fluids

    NASA Astrophysics Data System (ADS)

    Yang, Bo; Haldane, F. D. M.

    2013-03-01

    Recent work by Hoyos and Son, then Bradlyn et al., has investigated the relation between the long-wavelength (O (q2)) corrections to the Hall conductivity σH (q) and the Hall viscosity of quantum Hall states. These works assume the presence of Galilean and rotational invariance. However, these are not generic symmetries of electrons in condensed matter. We identify translation and (2D) inversion symmetry as the only generic symmetries of an ``ideal'' quantum Hall liquid, as these are needed to guarantee the absence of any dissipationless ground state current density; then σH (q) = σH (- q) characterizes the dissipation less current that flows in response to a spatially-non-uniform electric field. We consider the general problem for fractional quantum Hall (FQH) states without Galilean or rotational invariance, when the guiding-center contribution to the Hall viscosity becomes a non-trivial tensor property related to an emergent geometry of the FQH state, (Bo Yang et,al (PRB 85,165318). Supported by DOE DE-SC0002140 and Agency for Science Technology and Research (A*STAR, Singapore).

  7. Breaking time reversal symmetry, quantum anomalous Hall state and dissipationless chiral conduction in topological insulators

    NASA Astrophysics Data System (ADS)

    Moodera, Jagadeesh

    Breaking time reversal symmetry (TRS) in a topological insulator (TI) with ferromagnetic perturbation can lead to many exotic quantum phenomena exhibited by Dirac surface states including the quantum anomalous Hall (QAH) effect and dissipationless quantized Hall transport. The realization of the QAH effect in realistic materials requires ferromagnetic insulating materials and topologically non-trivial electronic band structures. In a TI, the ferromagnetic order and TRS breaking is achievable by conventional way, through doping with a magnetic element, or by ferromagnetic proximity coupling. Our experimental studies by both approaches will be discussed. In doped TI van Vleck ferromagnetism was observed. The proximity induced magnetism at the interface was stable, beyond the expected temperature range. We shall describe in a hard ferromagnetic TI system a robust QAH state and dissipationless edge current flow is achieved,1,2 a major step towards dissipationless electronic applications with no external fields, making such devices more amenable for metrology and spintronics applications. Our study of the gate and temperature dependences of local and nonlocal magnetoresistance, may elucidate the causes of the dissipative edge channels and the need for very low temperature to observe QAH. In close collaboration with: CuiZu Chang,2,3 Ferhat Katmis, 1 . 2 , 3 Peng Wei. 1 , 2 , 3 ; From Nuclear Eng. Dept. MIT, M. Li, J. Li; From Penn State U, W-W. Zhao, D. Y. Kim, C-x. Liu, J. K. Jain, M. H. W. Chan; From Oakridge National Lab, V. Lauter; From Northeastern U., B. A. Assaf, M. E. Jamer, D. Heiman; From Argonne Lab, J. W. Freeland; From Ruhr-Universitaet Bochum (Germany), F. S. Nogueira, I. Eremin; From Saha Institute of Nuclear Physics (India), B. Satpati. Work supported by NSF Grant DMR-1207469, the ONR Grant N00014-13-1-0301, and the STC Center for Integrated Quantum Materials under NSF Grant DMR-1231319.

  8. Quantum Femtosecond Magnetism: Phase Transition in Step with Light in a Strongly Correlated Manganese Oxide

    NASA Astrophysics Data System (ADS)

    Wang, Jigang

    2014-03-01

    Research of non-equilibrium phase transitions of strongly correlated electrons is built around addressing an outstanding challenge: how to achieve ultrafast manipulation of competing magnetic/electronic phases and reveal thermodynamically hidden orders at highly non-thermal, femtosecond timescales? Recently we reveal a new paradigm called quantum femtosecond magnetism-photoinduced femtosecond magnetic phase transitions driven by quantum spin flip fluctuations correlated with laser-excited inter-atomic coherent bonding. We demonstrate an antiferromagnetic (AFM) to ferromagnetic (FM) switching during about 100 fs laser pulses in a colossal magneto-resistive manganese oxide. Our results show a huge photoinduced femtosecond spin generation, measured by magnetic circular dichroism, with photo-excitation threshold behavior absent in the picosecond dynamics. This reveals an initial quantum coherent regime of magnetism, while the optical polarization/coherence still interacts with the spins to initiate local FM correlations that compete with the surrounding AFM matrix. Our results thus provide a framework that explores quantum non-equilibrium kinetics to drive phase transitions between exotic ground states in strongly correlated elecrons, and raise fundamental questions regarding some accepted rules, such as free energy and adiabatic potential surface. This work is in collaboration with Tianqi Li, Aaron Patz, Leonidas Mouchliadis, Jiaqiang Yan, Thomas A. Lograsso, Ilias E. Perakis. This work was supported by the National Science Foundation (contract no. DMR-1055352). Material synthesis at the Ames Laboratory was supported by the US Department of Energy-Basic Energy Sciences (contract no. DE-AC02-7CH11358).

  9. Electrostatic control of quantum Hall ferromagnetic transition: A step toward reconfigurable network of helical channels

    NASA Astrophysics Data System (ADS)

    Kazakov, Aleksandr; Simion, George; Lyanda-Geller, Yuli; Kolkovsky, Valery; Adamus, Zbigniew; Karczewski, Grzegorz; Wojtowicz, Tomasz; Rokhinson, Leonid P.

    2016-08-01

    Ferromagnetic transitions between quantum Hall states with different polarization at a fixed filling factor can be studied by varying the ratio of cyclotron and Zeeman energies in tilted magnetic field experiments. However, an ability to locally control such transitions at a fixed magnetic field would open a range of attractive applications, e.g., formation of a reconfigurable network of one-dimensional helical domain walls in a two-dimensional plane. Coupled to a superconductor, such domain walls can support non-Abelian excitations. In this paper we report development of heterostructures where quantum Hall ferromagnetic (QHFm) transition can be controlled locally by electrostatic gating. A high mobility two-dimensional electron gas is formed in CdTe quantum wells with engineered placement of paramagnetic Mn impurities. A gate-induced electrostatic field shifts the electron wave function in the growth direction and changes an overlap between electrons in the quantum well and d -shell electrons on Mn, thus controlling the s -d exchange interaction and the field of the QHFm transition. The demonstrated shift of the QHFm transition at a filling factor ν =2 is large enough to allow full control of spin polarization at a fixed magnetic field.

  10. Quantum Domains for Macroscopic Transport Effects in Nanostructures with Control Topology: Optics and e-Conductivity

    NASA Astrophysics Data System (ADS)

    Antipov, A.; Arakelian, S.; Kucherik, A.; Kutrovskaya, S.; Nogtev, D.; Osipov, A.; Vartanyan, T.; Zimin, S.

    2015-09-01

    The nanostructures with different morphology have been obtained by us by methods of both direct laser modification (from cw to fs laser radiation) of the target surface/thin films and laser evaporation of the target substance in liquid to produce the colloid systems, and then - to deposite substance on substrate from colloid, and also - by a single drop deposition technique. The analysis of induced nanostructures has been carried out by absorption spectroscopy, scanning electron microscopy and transmission electron microscopy. The island conductivity is dominant for the nanocluster semiconductor systems induced by laser ablation technique, and electroresistance can dramatically decrease due to spontaneous selected multichannel/parallel electron transportation trajectories. A tunneling quantum coherent effect takes place for electron conductivity for the case.

  11. On the quantum magnetic oscillations of electrical and thermal conductivities of graphene

    NASA Astrophysics Data System (ADS)

    Alisultanov, Z. Z.; Reis, M. S.

    2016-05-01

    Oscillating thermodynamic quantities of diamagnetic materials, specially graphene, have been attracting attention of the scientific community due to the possibility to experimentally map the Fermi surface of the material. These have been the case of the de Haas-van Alphen and Shubnikov-de Haas effects, found on the magnetization and electrical conductivity, respectively. In this direction, managing the thermodynamic oscillations is of practical purpose, since from the reconstructed Fermi surface it is possible to access, for instance, the electronic density. The present work theoretically explores the quantum oscillations of electrical and thermal conductivities of a monolayer graphene under a crossed magnetic and electric fields. We found that the longitudinal electric field can increase the amplitude of the oscillations and this result is of practical and broad interest for both, experimental and device physics.

  12. Tunnel magnetoresistance and linear conductance of double quantum dots strongly coupled to ferromagnetic leads

    SciTech Connect

    Weymann, Ireneusz

    2015-05-07

    We analyze the spin-dependent linear-response transport properties of double quantum dots strongly coupled to external ferromagnetic leads. By using the numerical renormalization group method, we determine the dependence of the linear conductance and tunnel magnetoresistance on the degree of spin polarization of the leads and the position of the double dot levels. We focus on the transport regime where the system exhibits the SU(4) Kondo effect. It is shown that the presence of ferromagnets generally leads the suppression of the linear conductance due to the presence of an exchange field. Moreover, the exchange field gives rise to a transition from the SU(4) to the orbital SU(2) Kondo effect. We also analyze the dependence of the tunnel magnetoresistance on the double dot levels' positions and show that it exhibits a very nontrivial behavior.

  13. Charge Carrier Conduction Mechanism in PbS Quantum Dot Solar Cells: Electrochemical Impedance Spectroscopy Study.

    PubMed

    Wang, Haowei; Wang, Yishan; He, Bo; Li, Weile; Sulaman, Muhammad; Xu, Junfeng; Yang, Shengyi; Tang, Yi; Zou, Bingsuo

    2016-07-20

    With its properties of bandgap tunability, low cost, and substrate compatibility, colloidal quantum dots (CQDs) are becoming promising materials for optoelectronic applications. Additionally, solution-processed organic, inorganic, and hybrid ligand-exchange technologies have been widely used in PbS CQDs solar cells, and currently the maximum certified power conversion efficiency of 9.9% has been reported by passivation treatment of molecular iodine. Presently, there are still some challenges, and the basic physical mechanism of charge carriers in CQDs-based solar cells is not clear. Electrochemical impedance spectroscopy is a monitoring technology for current by changing the frequency of applied alternating current voltage, and it provides an insight into its electrical properties that cannot be measured by direct current testing facilities. In this work, we used EIS to analyze the recombination resistance, carrier lifetime, capacitance, and conductivity of two typical PbS CQD solar cells Au/PbS-TBAl/ZnO/ITO and Au/PbS-EDT/PbS-TBAl/ZnO/ITO, in this way, to better understand the charge carriers conduction mechanism behind in PbS CQD solar cells, and it provides a guide to design high-performance quantum-dots solar cells. PMID:27176547

  14. Theory of quantum metal to superconductor transitions in highly conducting systems

    SciTech Connect

    Spivak, B.

    2010-04-06

    We derive the theory of the quantum (zero temperature) superconductor to metal transition in disordered materials when the resistance of the normal metal near criticality is small compared to the quantum of resistivity. This can occur most readily in situations in which 'Anderson's theorem' does not apply. We explicitly study the transition in superconductor-metal composites, in an swave superconducting film in the presence of a magnetic field, and in a low temperature disordered d-wave superconductor. Near the point of the transition, the distribution of the superconducting order parameter is highly inhomogeneous. To describe this situation we employ a procedure which is similar to that introduced by Mott for description of the temperature dependence of the variable range hopping conduction. As the system approaches the point of the transition from the metal to the superconductor, the conductivity of the system diverges, and the Wiedemann-Franz law is violated. In the case of d-wave (or other exotic) superconductors we predict the existence of (at least) two sequential transitions as a function of increasing disorder: a d-wave to s-wave, and then an s-wave to metal transition.

  15. Charge Carrier Conduction Mechanism in PbS Quantum Dot Solar Cells: Electrochemical Impedance Spectroscopy Study.

    PubMed

    Wang, Haowei; Wang, Yishan; He, Bo; Li, Weile; Sulaman, Muhammad; Xu, Junfeng; Yang, Shengyi; Tang, Yi; Zou, Bingsuo

    2016-07-20

    With its properties of bandgap tunability, low cost, and substrate compatibility, colloidal quantum dots (CQDs) are becoming promising materials for optoelectronic applications. Additionally, solution-processed organic, inorganic, and hybrid ligand-exchange technologies have been widely used in PbS CQDs solar cells, and currently the maximum certified power conversion efficiency of 9.9% has been reported by passivation treatment of molecular iodine. Presently, there are still some challenges, and the basic physical mechanism of charge carriers in CQDs-based solar cells is not clear. Electrochemical impedance spectroscopy is a monitoring technology for current by changing the frequency of applied alternating current voltage, and it provides an insight into its electrical properties that cannot be measured by direct current testing facilities. In this work, we used EIS to analyze the recombination resistance, carrier lifetime, capacitance, and conductivity of two typical PbS CQD solar cells Au/PbS-TBAl/ZnO/ITO and Au/PbS-EDT/PbS-TBAl/ZnO/ITO, in this way, to better understand the charge carriers conduction mechanism behind in PbS CQD solar cells, and it provides a guide to design high-performance quantum-dots solar cells.

  16. High-frequency hopping conductivity in the quantum Hall effect regime: Acoustical studies

    NASA Astrophysics Data System (ADS)

    Drichko, I. L.; Diakonov, A. M.; Smirnov, I. Yu.; Galperin, Yu. M.; Toropov, A. I.

    2000-09-01

    The high-frequency conductivity of Si δ-doped GaAs/AlGaAs heterostructures is studied in the integer quantum Hall effect (QHE) regime, using acoustic methods. Both the real and the imaginary parts of the complex conductivity are determined from the experimentally observed magnetic field and temperature dependencies of the velocity and the attenuation of a surface acoustic wave. It is demonstrated that in structures with carrier density (1.3-2.8)×1011 cm-2 and mobility (1-2)×105 cm2/V s the mechanism of low-temperature conductance near the QHE plateau centers is hopping. It is also shown that at magnetic fields corresponding to filling factors 2 and 4, the doped Si δ layer efficiently shunts the conductance in the two-dimensional electron gas (2DEG) channel. A method to separate the two contributions to the real part of the conductivity is developed, and the localization length in the 2DEG channel is estimated within the context of a nearest-neighbor hopping model.

  17. Revisiting the Valence and Conduction Band Size Dependence of PbS Quantum Dot Thin Films.

    PubMed

    Miller, Elisa M; Kroupa, Daniel M; Zhang, Jianbing; Schulz, Philip; Marshall, Ashley R; Kahn, Antoine; Lany, Stephan; Luther, Joseph M; Beard, Matthew C; Perkins, Craig L; van de Lagemaat, Jao

    2016-03-22

    We use a high signal-to-noise X-ray photoelectron spectrum of bulk PbS, GW calculations, and a model assuming parabolic bands to unravel the various X-ray and ultraviolet photoelectron spectral features of bulk PbS as well as determine how to best analyze the valence band region of PbS quantum dot (QD) films. X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) are commonly used to probe the difference between the Fermi level and valence band maximum (VBM) for crystalline and thin-film semiconductors. However, we find that when the standard XPS/UPS analysis is used for PbS, the results are often unrealistic due to the low density of states at the VBM. Instead, a parabolic band model is used to determine the VBM for the PbS QD films, which is based on the bulk PbS experimental spectrum and bulk GW calculations. Our analysis highlights the breakdown of the Brillioun zone representation of the band diagram for large band gap, highly quantum confined PbS QDs. We have also determined that in 1,2-ethanedithiol-treated PbS QD films the Fermi level position is dependent on the QD size; specifically, the smallest band gap QD films have the Fermi level near the conduction band minimum and the Fermi level moves away from the conduction band for larger band gap PbS QD films. This change in the Fermi level within the QD band gap could be due to changes in the Pb:S ratio. In addition, we use inverse photoelectron spectroscopy to measure the conduction band region, which has similar challenges in the analysis of PbS QD films due to a low density of states near the conduction band minimum. PMID:26895310

  18. Revisiting the Valence and Conduction Band Size Dependence of PbS Quantum Dot Thin Films.

    PubMed

    Miller, Elisa M; Kroupa, Daniel M; Zhang, Jianbing; Schulz, Philip; Marshall, Ashley R; Kahn, Antoine; Lany, Stephan; Luther, Joseph M; Beard, Matthew C; Perkins, Craig L; van de Lagemaat, Jao

    2016-03-22

    We use a high signal-to-noise X-ray photoelectron spectrum of bulk PbS, GW calculations, and a model assuming parabolic bands to unravel the various X-ray and ultraviolet photoelectron spectral features of bulk PbS as well as determine how to best analyze the valence band region of PbS quantum dot (QD) films. X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) are commonly used to probe the difference between the Fermi level and valence band maximum (VBM) for crystalline and thin-film semiconductors. However, we find that when the standard XPS/UPS analysis is used for PbS, the results are often unrealistic due to the low density of states at the VBM. Instead, a parabolic band model is used to determine the VBM for the PbS QD films, which is based on the bulk PbS experimental spectrum and bulk GW calculations. Our analysis highlights the breakdown of the Brillioun zone representation of the band diagram for large band gap, highly quantum confined PbS QDs. We have also determined that in 1,2-ethanedithiol-treated PbS QD films the Fermi level position is dependent on the QD size; specifically, the smallest band gap QD films have the Fermi level near the conduction band minimum and the Fermi level moves away from the conduction band for larger band gap PbS QD films. This change in the Fermi level within the QD band gap could be due to changes in the Pb:S ratio. In addition, we use inverse photoelectron spectroscopy to measure the conduction band region, which has similar challenges in the analysis of PbS QD films due to a low density of states near the conduction band minimum.

  19. Distortions of the coulomb blockade conductance line in scanning gate measurements of inas nanowire based quantum dots

    SciTech Connect

    Zhukov, A. A.; Volk, Ch.; Winden, A.; Hardtdegen, H.; Schaepers, Th.

    2013-01-15

    We performed measurements at helium temperatures of the electronic transport in the linear regime in an InAs quantum wire in the presence of a charged tip of an atomic force microscope (AFM) at low electron concentration. We show that at certain concentration of electrons, only two closely placed quantum dots, both in the Coulomb blockade regime, govern conductance of the whole wire. Under this condition, two types of peculiarities-wobbling and splitting-arise in the behavior of the lines of the conductance peaks of Coulomb blockade. These peculiarities are measured in quantum-wire-based structures for the first time. We explain both peculiarities as an interplay of the conductance of two quantum dots present in the wire. Detailed modeling of wobbling behavior made in the framework of the orthodox theory of Coulomb blockade demonstrates good agreement with the obtained experimental data.

  20. Quantum transport through disordered 1D wires: Conductance via localized and delocalized electrons

    SciTech Connect

    Gopar, Víctor A.

    2014-01-14

    Coherent electronic transport through disordered systems, like quantum wires, is a topic of fundamental and practical interest. In particular, the exponential localization of electron wave functions-Anderson localization-due to the presence of disorder has been widely studied. In fact, Anderson localization, is not an phenomenon exclusive to electrons but it has been observed in microwave and acoustic experiments, photonic materials, cold atoms, etc. Nowadays, many properties of electronic transport of quantum wires have been successfully described within a scaling approach to Anderson localization. On the other hand, anomalous localization or delocalization is, in relation to the Anderson problem, a less studied phenomenon. Although one can find signatures of anomalous localization in very different systems in nature. In the problem of electronic transport, a source of delocalization may come from symmetries present in the system and particular disorder configurations, like the so-called Lévy-type disorder. We have developed a theoretical model to describe the statistical properties of transport when electron wave functions are delocalized. In particular, we show that only two physical parameters determine the complete conductance distribution.

  1. Single step deposition of an interacting layer of a perovskite matrix with embedded quantum dots

    NASA Astrophysics Data System (ADS)

    Ngo, Thi Tuyen; Suarez, Isaac; Sanchez, Rafael S.; Martinez-Pastor, Juan P.; Mora-Sero, Ivan

    2016-07-01

    Hybrid lead halide perovskite (PS) derivatives have emerged as very promising materials for the development of optoelectronic devices in the last few years. At the same time, inorganic nanocrystals with quantum confinement (QDs) possess unique properties that make them suitable materials for the development of photovoltaics, imaging and lighting applications, among others. In this work, we report on a new methodology for the deposition of high quality, large grain size and pinhole free PS films (CH3NH3PbI3) with embedded PbS and PbS/CdS core/shell Quantum Dots (QDs). The strong interaction between both semiconductors is revealed by the formation of an exciplex state, which is monitored by photoluminescence and electroluminescence experiments. The radiative exciplex relaxation is centered in the near infrared region (NIR), ~1200 nm, which corresponds to lower energies than the corresponding band gap of both perovskite (PS) and QDs. Our approach allows the fabrication of multi-wavelength light emitting diodes (LEDs) based on a PS matrix with embedded QDs, which show considerably low turn-on potentials. The presence of the exciplex state of PS and QDs opens up a broad range of possibilities with important implications in both LEDs and solar cells.Hybrid lead halide perovskite (PS) derivatives have emerged as very promising materials for the development of optoelectronic devices in the last few years. At the same time, inorganic nanocrystals with quantum confinement (QDs) possess unique properties that make them suitable materials for the development of photovoltaics, imaging and lighting applications, among others. In this work, we report on a new methodology for the deposition of high quality, large grain size and pinhole free PS films (CH3NH3PbI3) with embedded PbS and PbS/CdS core/shell Quantum Dots (QDs). The strong interaction between both semiconductors is revealed by the formation of an exciplex state, which is monitored by photoluminescence and

  2. Multi-scale quantum point contact model for filamentary conduction in resistive random access memories devices

    SciTech Connect

    Lian, Xiaojuan Cartoixà, Xavier; Miranda, Enrique; Suñé, Jordi; Perniola, Luca; Rurali, Riccardo; Long, Shibing; Liu, Ming

    2014-06-28

    We depart from first-principle simulations of electron transport along paths of oxygen vacancies in HfO{sub 2} to reformulate the Quantum Point Contact (QPC) model in terms of a bundle of such vacancy paths. By doing this, the number of model parameters is reduced and a much clearer link between the microscopic structure of the conductive filament (CF) and its electrical properties can be provided. The new multi-scale QPC model is applied to two different HfO{sub 2}-based devices operated in the unipolar and bipolar resistive switching (RS) modes. Extraction of the QPC model parameters from a statistically significant number of CFs allows revealing significant structural differences in the CF of these two types of devices and RS modes.

  3. Random-matrix theory of thermal conduction in superconducting quantum dots

    NASA Astrophysics Data System (ADS)

    Dahlhaus, J. P.; Béri, B.; Beenakker, C. W. J.

    2010-07-01

    We calculate the probability distribution of the transmission eigenvalues Tn of Bogoliubov quasiparticles at the Fermi level in an ensemble of chaotic Andreev quantum dots. The four Altland-Zirnbauer symmetry classes (determined by the presence or absence of time-reversal and spin-rotation symmetries) give rise to four circular ensembles of scattering matrices. We determine P({Tn}) for each ensemble, characterized by two symmetry indices β and γ . For a single d -fold degenerate transmission channel we thus obtain the distribution P(g)∝g-1+β/2(1-g)γ/2 of the thermal conductance g (in units of dπ2kB2T0/6h at low temperatures T0 ). We show how this single-channel limit can be reached using a topological insulator or superconductor, without running into the problem of fermion doubling.

  4. Frequency scaling of microwave conductivity in the integer quantum Hall effect minima

    SciTech Connect

    Lewis, R. M.; Carini, J. P.

    2001-08-15

    We measure the longitudinal conductivity {sigma}{sub xx} at frequencies 1.246 GHz{<=}f{<=}10.05 GHz over a range of temperatures 235 mK{<=}T{<=}4.2 K with particular emphasis on the quantum Hall plateaus. We find that Re({sigma}{sub xx}) scales linearly with frequency for a range of magnetic field around the center of the plateaus, i.e., where {sigma}{sub xx}({omega})>>{sigma}{sub xx}{sup dc}. The width of this scaling region decreases with higher temperature and vanishes by 1.2 K altogether. Comparison between localization length determined from {sigma}{sub xx}({omega}) and dc measurements on the same wafer show good agreement.

  5. Conducting fixed points for inhomogeneous quantum wires: A conformally invariant boundary theory

    NASA Astrophysics Data System (ADS)

    Sedlmayr, N.; Morath, D.; Sirker, J.; Eggert, S.; Affleck, I.

    2014-01-01

    Inhomogeneities and junctions in wires are natural sources of scattering, and hence resistance. A conducting fixed point usually requires an adiabatically smooth system. One notable exception is "healing," which has been predicted in systems with special symmetries, where the system is driven to the homogeneous fixed point. Here we present theoretical results for a different type of conducting fixed point which occurs in inhomogeneous wires with an abrupt jump in hopping and interaction strength. We show that it is always possible to tune the system to an unstable conducting fixed point which does not correspond to translational invariance. We analyze the temperature scaling of correlation functions at and near this fixed point and show that two distinct boundary exponents appear, which correspond to different effective Luttinger liquid parameters. Even though the system consists of two separate interacting parts, the fixed point is described by a single conformally invariant boundary theory. We present details of the general effective bosonic field theory including the mode expansion and the finite size spectrum. The results are confirmed by numerical quantum Monte Carlo simulations on spinless fermions. We predict characteristic experimental signatures of the local density of states near junctions.

  6. Single step deposition of an interacting layer of a perovskite matrix with embedded quantum dots.

    PubMed

    Ngo, Thi Tuyen; Suarez, Isaac; Sanchez, Rafael S; Martinez-Pastor, Juan P; Mora-Sero, Ivan

    2016-08-14

    Hybrid lead halide perovskite (PS) derivatives have emerged as very promising materials for the development of optoelectronic devices in the last few years. At the same time, inorganic nanocrystals with quantum confinement (QDs) possess unique properties that make them suitable materials for the development of photovoltaics, imaging and lighting applications, among others. In this work, we report on a new methodology for the deposition of high quality, large grain size and pinhole free PS films (CH3NH3PbI3) with embedded PbS and PbS/CdS core/shell Quantum Dots (QDs). The strong interaction between both semiconductors is revealed by the formation of an exciplex state, which is monitored by photoluminescence and electroluminescence experiments. The radiative exciplex relaxation is centered in the near infrared region (NIR), ≈1200 nm, which corresponds to lower energies than the corresponding band gap of both perovskite (PS) and QDs. Our approach allows the fabrication of multi-wavelength light emitting diodes (LEDs) based on a PS matrix with embedded QDs, which show considerably low turn-on potentials. The presence of the exciplex state of PS and QDs opens up a broad range of possibilities with important implications in both LEDs and solar cells. PMID:27437778

  7. Single-step assembly of homogenous lipid-polymeric and lipid-quantum dot nanoparticles enabled by microfluidic rapid mixing.

    PubMed

    Valencia, Pedro M; Basto, Pamela A; Zhang, Liangfang; Rhee, Minsoung; Langer, Robert; Farokhzad, Omid C; Karnik, Rohit

    2010-03-23

    A key challenge in the synthesis of multicomponent nanoparticles (NPs) for therapy or diagnosis is obtaining reproducible monodisperse NPs with a minimum number of preparation steps. Here we report the use of microfluidic rapid mixing using hydrodynamic flow focusing in combination with passive mixing structures to realize the self-assembly of monodisperse lipid-polymer and lipid-quantum dot (QD) NPs in a single mixing step. These NPs are composed of a polymeric core for drug encapsulation or a QD core for imaging purposes, a hydrophilic polymeric shell, and a lipid monolayer at the interface of the core and the shell. In contrast to slow mixing of lipid and polymeric solutions, rapid mixing directly results in formation of homogeneous NPs with relatively narrow size distribution that obviates the need for subsequent thermal or mechanical agitation for homogenization. We identify rapid mixing conditions that result in formation of homogeneous NPs and show that self-assembly of polymeric core occurs independent of the lipid component, which only provides stability against aggregation over time and in the presence of high salt concentrations. Physicochemical properties of the NPs including size (35-180 nm) and zeta potential (-10 to +20 mV in PBS) are controlled by simply varying the composition and concentration of precursors. This method for preparation of hybrid NPs in a single mixing step may be useful for combinatorial synthesis of NPs with different properties for imaging and drug delivery applications. PMID:20166699

  8. Bias voltage dependence of two-step photocurrent in GaAs/AlGaAs quantum well solar cells

    NASA Astrophysics Data System (ADS)

    Noda, T.; Elborg, M.; Mano, T.; Kawazu, T.; Han, L.; Sakaki, H.

    2016-02-01

    We investigated photoresponses of AlGaAs solar cells in which coupled GaAs quantum wells were embedded in the i-region of p-i-n diodes; we studied how the bias voltage Vb affects the normal photocurrent I generated by the visible light and a "two-step" photocurrent ΔI generated by the absorption of visible and infrared photons. We found that as Vb exceeds -0.2 V, ΔI rises and peaks at 0.6 V, while the normal photocurrent I falls to about half of its saturated level. These findings are discussed in terms of a rate equation model to show that ΔI is mainly determined by the balance of escape and recombination of photogenerated carriers.

  9. Chiral topological superconductor and half-integer conductance plateau from quantum anomalous Hall plateau transition

    SciTech Connect

    Wang, Jing; Zhou, Quan; Lian, Biao; Zhang, Shou -Cheng

    2015-08-31

    Here, we propose to realize a two-dimensional chiral topological superconducting (TSC) state from the quantum anomalous Hall plateau transition in a magnetic topological insulator thin film through the proximity effect to a conventional s -wave superconductor. This state has a full pairing gap in the bulk and a single chiral Majorana mode at the edge. The optimal condition for realizing such chiral TSC is to have inequivalent superconducting pairing amplitudes on top and bottom surfaces of the doped magnetic topological insulator. We further propose several transport experiments to detect the chiral TSC. One unique signature is that the conductance will be quantized into a half-integer plateau at the coercive field in this hybrid system. In particular, with the point contact formed by a superconducting junction, the conductance oscillates between e2 /2h and e2 /h with the frequency determined by the voltage across the junction. We close by discussing the feasibility of these experimental proposals.

  10. Chiral topological superconductor and half-integer conductance plateau from quantum anomalous Hall plateau transition

    DOE PAGES

    Wang, Jing; Zhou, Quan; Lian, Biao; Zhang, Shou -Cheng

    2015-08-31

    Here, we propose to realize a two-dimensional chiral topological superconducting (TSC) state from the quantum anomalous Hall plateau transition in a magnetic topological insulator thin film through the proximity effect to a conventional s -wave superconductor. This state has a full pairing gap in the bulk and a single chiral Majorana mode at the edge. The optimal condition for realizing such chiral TSC is to have inequivalent superconducting pairing amplitudes on top and bottom surfaces of the doped magnetic topological insulator. We further propose several transport experiments to detect the chiral TSC. One unique signature is that the conductance willmore » be quantized into a half-integer plateau at the coercive field in this hybrid system. In particular, with the point contact formed by a superconducting junction, the conductance oscillates between e2 /2h and e2 /h with the frequency determined by the voltage across the junction. We close by discussing the feasibility of these experimental proposals.« less

  11. One-step multiplexed detection of foodborne pathogens: Combining a quantum dot-mediated reverse assaying strategy and magnetic separation.

    PubMed

    Yin, Binfeng; Wang, Yu; Dong, Mingling; Wu, Jing; Ran, Bei; Xie, Mengxia; Joo, Sang Woo; Chen, Yiping

    2016-12-15

    A rapid and multiplexed immunosensor was developed based on a quantum dot (QD)-reverse assaying strategy (RAS) and immuno-magnetic beads (IMBs) for one-step and simultaneous detection of Escherichia coli O157: H7 and Salmonella. In a conventional QD-based immunosensor, the fluorescence signal of the "IMBs-target-QD" immunoconjugate is directly used as the assaying readout. However, the fluorescence signal is affected by IMBs due to light scattering and the "IMBs-target-QD" immunoconjugate needs multiple washing and re-suspension steps. To address these problems, we use the surplus QD-antibody conjugate as signal readout in the RAS, which prevents interference from the IMBs, increases the fluorescence signal, and avoids complex operations. Compared with conventional QD-based immunosensor, the sensitivity of QD-RSA immunosensor for detection of Escherichia coli O157: H7 has been improved fifty-fold, and whole analysis procedure can be finished within 1h. Therefore, this RSA strategy is promising for improving the performance of QD-based immunosensors and could greatly broaden their applications.

  12. One-step multiplexed detection of foodborne pathogens: Combining a quantum dot-mediated reverse assaying strategy and magnetic separation.

    PubMed

    Yin, Binfeng; Wang, Yu; Dong, Mingling; Wu, Jing; Ran, Bei; Xie, Mengxia; Joo, Sang Woo; Chen, Yiping

    2016-12-15

    A rapid and multiplexed immunosensor was developed based on a quantum dot (QD)-reverse assaying strategy (RAS) and immuno-magnetic beads (IMBs) for one-step and simultaneous detection of Escherichia coli O157: H7 and Salmonella. In a conventional QD-based immunosensor, the fluorescence signal of the "IMBs-target-QD" immunoconjugate is directly used as the assaying readout. However, the fluorescence signal is affected by IMBs due to light scattering and the "IMBs-target-QD" immunoconjugate needs multiple washing and re-suspension steps. To address these problems, we use the surplus QD-antibody conjugate as signal readout in the RAS, which prevents interference from the IMBs, increases the fluorescence signal, and avoids complex operations. Compared with conventional QD-based immunosensor, the sensitivity of QD-RSA immunosensor for detection of Escherichia coli O157: H7 has been improved fifty-fold, and whole analysis procedure can be finished within 1h. Therefore, this RSA strategy is promising for improving the performance of QD-based immunosensors and could greatly broaden their applications. PMID:27498327

  13. Parallel magnetic field-induced conductance fluctuations in GaAs/AlGaAs ballistic quantum dots.

    NASA Astrophysics Data System (ADS)

    Faniel, S.; Gustin, C.; Melinte, S.; Hackens, B.; Bayot, V.; Shayegan, M.

    2004-03-01

    We present magnetotransport measurements in ballistic quantum dots under a parallel magnetic field. The dots were fabricated on two different GaAs/AlGaAs quantum wells with thicknesses of 15 and and 45 nm and with one and two subbands occupied, respectively. The samples were patterned using e-beam lithography and wet etching. A Cr/Au electrostatic top gate was used in order to tune the width of the dot openings. The measurements were performed down to 300 mK with the magnetic field applied strictly parallel to the plane of the two-dimensional electron gas. For both dots, we observe universal conductance fluctuations and, in the case of the wide quantum well, a reduction of their amplitude at large magnetic field. We discuss these conductance fluctuations in terms of orbital effect(V.I. Fal'ko and T. Jungwirth, Phys Rev B 65), 081306 (2002) and magnetic subband depopulation.

  14. Externally controlled local magnetic field in a conducting mesoscopic ring coupled to a quantum wire

    SciTech Connect

    Maiti, Santanu K.

    2015-01-14

    In the present work, the possibility of regulating local magnetic field in a quantum ring is investigated theoretically. The ring is coupled to a quantum wire and subjected to an in-plane electric field. Under a finite bias voltage across the wire a net circulating current is established in the ring which produces a strong magnetic field at its centre. This magnetic field can be tuned externally in a wide range by regulating the in-plane electric field, and thus, our present system can be utilized to control magnetic field at a specific region. The feasibility of this quantum system in designing spin-based quantum devices is also analyzed.

  15. Interference features in scanning gate conductance maps of quantum point contacts with disorder

    NASA Astrophysics Data System (ADS)

    Kolasiński, K.; Szafran, B.; Brun, B.; Sellier, H.

    2016-08-01

    We consider quantum point contact (QPC) defined within a disordered two-dimensional electron gas as studied by scanning gate microscopy. We evaluate the conductance maps in the Landauer approach with a wave-function picture of electron transport for samples with both low and high electron mobility at finite temperatures. We discuss the spatial distribution of the impurities in the context of the branched electron flow. We reproduce the surprising temperature stability of the experimental interference fringes far from the QPC. Next, we discuss funnel-shaped features that accompany splitting of the branches visible in previous experiments. Finally, we study elliptical interference fringes formed by an interplay of scattering by the pointlike impurities and by the scanning probe. We discuss the details of the elliptical features as functions of the tip voltage and the temperature, showing that the first interference fringe is very robust against the thermal widening of the Fermi level. We present a simple analytical model that allows for extraction of the impurity positions and the electron-gas depletion radius induced by the negatively charged tip of the atomic force microscope, and apply this model on experimental scanning gate images showing such elliptical fringes.

  16. Leading-order calculation of electric conductivity in hot quantum electrodynamics from diagrammatic methods

    SciTech Connect

    Gagnon, Jean-Sebastien; Jeon, Sangyong

    2007-01-15

    Using diagrammatic methods, we show how the Ward identity can be used to constrain the ladder kernel in transport coefficient calculations. More specifically, we use the Ward identity to determine the necessary diagrams that must be resummed using an integral equation. One of our main results is an equation relating the kernel of the integral equation with functional derivatives of the full self-energy; it is similar to what is obtained with two-particle irreducible (2PI) effective action methods. However, since we use the Ward identity as our starting point, gauge invariance is preserved. Using power counting arguments, we also show which self-energies must be included in the resummation at leading order, including 2 to 2 scatterings and 1 to 2 collinear scatterings with the Landau-Pomeranchuk-Migdal effect. We show that our quantum field theory result is equivalent to the one of Arnold, Moore, and Yaffe obtained using effective kinetic theory. In this paper we restrict our discussion to electrical conductivity in hot QED, but our method can in principle be generalized to other transport coefficients and other theories.

  17. Space charge limited conduction in ultrathin PbS quantum dot solid diodes

    SciTech Connect

    Kwan Kim, Jun; Hoon Song, Jung; Choi, Hyekyoung; Jeong, Sohee E-mail: sjeong@kimm.re.kr; Jae Baik, Seung E-mail: sjeong@kimm.re.kr

    2014-02-07

    As a simple and direct characterization of carrier transport in nanocrystal quantum dot (NQD) solids, current-voltage characterization of ultrathin diodes is proposed. We found the space charge limited conduction (SCLC) behavior in ultrathin PbS NQD diodes with active layer thickness half of the full depletion width; and extracted hole concentrations in the order of 10{sup 15} cm{sup −3}, hole mobilities from 10{sup −4} to 10{sup −5} cm{sup 2}/Vs, trap energy depths varying from 140 meV to 200 meV, and volume trap density around 10{sup 17} cm{sup −3} for thin films with NQDs of diameters 3.3 and 3.6 nm, respectively. We further discuss the validity of applying SCLC to the NQD solids based diodes and the implications of the extracted parameters extensively. Proposed characterization method here is a direct measure of carrier transport in solar cell structures which could provide exact directions in NQD solids based solar cell fabrication and modeling.

  18. Quantization and anomalous structures in the conductance of Si/SiGe quantum point contacts

    NASA Astrophysics Data System (ADS)

    von Pock, J. F.; Salloch, D.; Qiao, G.; Wieser, U.; Hackbarth, T.; Kunze, U.

    2016-04-01

    Quantum point contacts (QPCs) are fabricated on modulation-doped Si/SiGe heterostructures and ballistic transport is studied at low temperatures. We observe quantized conductance with subband separations up to 4 meV and anomalies in the first conductance plateau at 4e2/h. At a temperature of T = 22 mK in the linear transport regime, a weak anomalous kink structure arises close to 0.5(4e2/h), which develops into a distinct plateau-like structure as temperature is raised up to T = 4 K. Under magnetic field parallel to the wire up to B = 14 T, the anomaly evolves into the Zeeman spin-split level at 0.5(4e2/h), resembling the "0.7 anomaly" in GaAs/AlGaAs QPCs. Additionally, a zero-bias anomaly (ZBA) is observed in nonlinear transport spectroscopy. At T = 22 mK, a parallel magnetic field splits the ZBA peak up into two peaks. At B = 0, elevated temperatures lead to similar splitting, which differs from the behavior of ZBAs in GaAs/AlGaAs QPCs. Under finite dc bias, the differential resistance exhibits additional plateaus approximately at 0.8(4e2/h) and 0.2(4e2/h) known as "0.85 anomaly" and "0.25 anomaly" in GaAs/AlGaAs QPCs. Unlike the first regular plateau at 4e2/h, the 0.2(4e2/h) plateau is insensitive to dc bias voltage up to at least VDS = 80 mV, in-plane magnetic fields up to B = 15 T, and to elevated temperatures up to T = 25 K. We interpret this effect as due to pinching off one of the reservoirs close to the QPC. We do not see any indication of lifting of the valley degeneracy in our samples.

  19. Composition and conductance distributions of single GeSi quantum rings studied by conductive atomic force microscopy combined with selective chemical etching

    NASA Astrophysics Data System (ADS)

    Lv, Y.; Cui, J.; Jiang, Z. M.; Yang, X. J.

    2013-02-01

    Atomic force microscopy imaging combined with selective chemical etching is employed to quantitatively investigate three-dimensional (3D) composition distributions of single GeSi quantum rings (QRs). In addition, the 3D quantitative composition distributions and the corresponding conductance distributions are simultaneously obtained on the same single GeSi QRs by conductive atomic force microscopy combined with selective chemical etching, allowing us to investigate the correlations between the conductance and composition distributions of single QRs. The results show that the QRs’ central holes have higher Ge content, but exhibit lower conductance, indicating that the QRs’ conductance distribution is not consistent with their composition distribution. By comparing the topography, composition and conductance profiles of the same single QRs before and after different etching processes, it is found that the conductance distributions of GeSi QRs do not vary with the change of composition distribution. Instead, the QRs’ conductance distributions are found to be consistent with their topographic shapes, which can be supposed to be due to the shape determined electronic structures.

  20. Composition and conductance distributions of single GeSi quantum rings studied by conductive atomic force microscopy combined with selective chemical etching.

    PubMed

    Lv, Y; Cui, J; Jiang, Z M; Yang, X J

    2013-02-15

    Atomic force microscopy imaging combined with selective chemical etching is employed to quantitatively investigate three-dimensional (3D) composition distributions of single GeSi quantum rings (QRs). In addition, the 3D quantitative composition distributions and the corresponding conductance distributions are simultaneously obtained on the same single GeSi QRs by conductive atomic force microscopy combined with selective chemical etching, allowing us to investigate the correlations between the conductance and composition distributions of single QRs. The results show that the QRs' central holes have higher Ge content, but exhibit lower conductance, indicating that the QRs' conductance distribution is not consistent with their composition distribution. By comparing the topography, composition and conductance profiles of the same single QRs before and after different etching processes, it is found that the conductance distributions of GeSi QRs do not vary with the change of composition distribution. Instead, the QRs' conductance distributions are found to be consistent with their topographic shapes, which can be supposed to be due to the shape determined electronic structures.

  1. Direct Observation of Two-Step Photon Absorption in an InAs/GaAs Single Quantum Dot for the Operation of Intermediate-Band Solar Cells.

    PubMed

    Nozawa, Tomohiro; Takagi, Hiroyuki; Watanabe, Katsuyuki; Arakawa, Yasuhiko

    2015-07-01

    We present the first direct observation of two-step photon absorption in an InAs/GaAs single quantum dot (QD) using photocurrent spectroscopy with two lasers. The sharp peaks of the photocurrent are shifted due to the quantum confined Stark effect, indicating that the photocurrent from a single QD is obtained. In addition, the intensity of the peaks depends on the power of the secondary laser. These results reveal the direct demonstration of the two-step photon absorption in a single QD. This is an essential result for both the fundamental operation and the realization of ultrahigh solar-electricity energy conversion in quantum dot intermediate-band solar cells.

  2. Single step synthesis of ZnS quantum dots and their microstructure characterization and electrical transport below room temperature

    NASA Astrophysics Data System (ADS)

    Mukherjee, P. S.; Patra, S.; Chakraborty, G.; Pradhan, S. K.; Meikap, A. K.

    2016-09-01

    Low dimensional cubic phase ZnS quantum dots (QDs) are formed by mechanical alloying the stoichiometric mixture of Zn and S powders at room temperature. During milling process the primary mixed phase ZnS is formed at about 3.5 h of milling and strain less single phase (cubic) ZnS QDs are formed with ∼4.5 nm in size after 20 h of milling. Detailed microstructure study has been done by both Rietveld analysis of x-ray diffraction pattern and high resolution transmission electron microscope images. Dc resistivity decreases with increasing temperature which can be explained by three-dimensional hopping conduction mechanisms. Observed negative magnetoconductivity has been analyzed by wave function shrinkage model. Alternating current conductivity can be described by the correlated barrier hopping conduction mechanism. Analysis of complex impedance indicates that the grain boundary resistance is found to be dominating over the grain resistance. Relaxation behavior has been explained by the analysis of the electric modulus.

  3. Quantum restricted effects on ballistic thermal conductance associated with six types of vibration modes in nanowire superlattice

    NASA Astrophysics Data System (ADS)

    Peng, Xiao-Fang; Wang, Xin-Jun

    2011-08-01

    We study ballistic phonon transport and thermal conductance associated with six low-lying vibrational modes in a quadrate nanowire superlattice at low temperatures. The results show that the transmission rates of the six vibrational modes display periodic forbidden regions of frequencies and have different relations with geometrical details of the nanowire superlattice. The thermal conductances contributed from different vibrational modes show different characteristics. On the basis of the theoretical analysis and calculated simulation, quantum restricted effects on ballistic thermal conductance in the quadrate nanowire superlattice are revealed.

  4. One-step colloidal synthesis of biocompatible water-soluble ZnS quantum dot/chitosan nanoconjugates

    NASA Astrophysics Data System (ADS)

    Ramanery, Fábio P.; Mansur, Alexandra AP; Mansur, Herman S.

    2013-12-01

    Quantum dots (QDs) are luminescent semiconductor nanocrystals with great prospective for use in biomedical and environmental applications. Nonetheless, eliminating the potential cytotoxicity of the QDs made with heavy metals is still a challenge facing the research community. Thus, the aim of this work was to develop a novel facile route for synthesising biocompatible QDs employing carbohydrate ligands in aqueous colloidal chemistry with optical properties tuned by pH. The synthesis of ZnS QDs capped by chitosan was performed using a single-step aqueous colloidal process at room temperature. The nanobioconjugates were extensively characterised by several techniques, and the results demonstrated that the average size of ZnS nanocrystals and their fluorescent properties were influenced by the pH during the synthesis. Hence, novel 'cadmium-free' biofunctionalised systems based on ZnS QDs capped by chitosan were successfully developed exhibiting luminescent activity that may be used in a large number of possible applications, such as probes in biology, medicine and pharmacy.

  5. Quantum chemical modeling of the kinetic isotope effect of the carboxylation step in RuBisCO.

    PubMed

    Götze, Jan Philipp; Saalfrank, Peter

    2012-05-01

    Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the most important enzyme for the assimilation of carbon into biomass, features a well-known isotope effect with regards to the CO(2) carbon atom. This kinetic isotope effect α = k(12)/k(13) for the carboxylation step of the RuBisCO reaction sequence, and its microscopic origin, was investigated with the help of cluster models and quantum chemical methods [B3LYP/6-31G(d,p)]. We use a recently proposed model for the RuBisCO active site, in which a water molecule remains close to the reaction center during carboxylation of ribulose-1,5-bisphosphate [B. Kannappan, J.E. Gready, J. Am. Chem. Soc. 130 (2008), 15063]. Alternative active-site models and/or computational approaches were also tested. An isotope effect alpha for carboxylation is found, which is reasonably close to the one measured for the overall reaction, and which originates from a simple frequency shift of the bending vibration of (12)CO(2) compared to (13)CO(2). The latter is the dominant mode for the product formation at the transition state.

  6. Evidence of quantum correction to conductivity and variable range hopping conduction in nano-crystalline Cu{sub 3}N thin film

    SciTech Connect

    Sahoo, Guruprasad Jain, Mahaveer K.

    2015-10-15

    We have investigated the temperature dependent carrier transport properties of nano-crystalline copper nitride thin films synthesized by modified activated reactive evaporation. The films, prepared in a Cu-rich growth condition are found to be highly disordered and the carrier transport in these films is mainly attributed to the impurity band conduction. We have observed that no single conduction mechanism is appropriate to elucidate the carrier transport in the entire temperature range of 20 – 300 K. Therefore, we have employed different conduction mechanisms in different temperature regimes. The carrier transport of the films in the low temperature regime (20 – 150 K) has been interpreted by implementing quantum correction to the conductivity. In the high temperature regime (200 – 300 K), the conduction mechanism has been successfully analyzed on the basis of Mott’s variable range hopping mechanism. Furthermore, it can be predicted that copper ions present at the surface of the crystallites are responsible for the hopping conduction mechanism.

  7. Anomalous Conductivity Tensor and Quantum Oscillations in the Dirac Semimetal Na3Bi

    NASA Astrophysics Data System (ADS)

    Xiong, Jun; Kushwaha, Satya; Krizan, Jason; Liang, Tian; Cava, Robert J.; Ong, Nai Phuan

    2015-03-01

    Na3Bi is a 3D Dirac semimetal with protected nodes. Angle-resolved photoemission experiments have observed these massless Dirac fermions in the bulk band, but transport experiments have been hampered by the extreme air sensitivity of Na3Bi crystals. Transport experiments can potentially address interesting issues such as charge pumping between the separated Weyl nodes when the time-reversal symmetry is broken by a strong magnetic field. Here we report a transport measurement that reveals robust anomalies in both the conductivity and resistivity tensors. The resistivity ρxx is B-linear up to 35 T, while the Hall angle exhibits an unusual profile approaching a step-function. In addition, we have also observed a prominent beating pattern in the Shubnikov de Haas (SdH) oscillations indicating the existence of two nearly equal SdH frequencies when the Fermi energy falls inside the non-trivial gap-inverted regime. Supported by NSF-MRSEC (DMR 0819860), Army Research Office (ARO W911NF-11-1-0379) and MURI Grant (ARO W911NF-12-1-0461).

  8. Parity independence of the zero-bias conductance peak in a nanowire based topological superconductor-quantum dot hybrid device

    PubMed Central

    Deng, M. T.; Yu, C. L.; Huang, G. Y.; Larsson, M.; Caroff, P.; Xu, H. Q.

    2014-01-01

    We explore the signatures of Majorana fermions in a nanowire based topological superconductor-quantum dot-topological superconductor hybrid device by charge transport measurements. At zero magnetic field, well-defined Coulomb diamonds and the Kondo effect are observed. Under the application of a finite, sufficiently strong magnetic field, a zero-bias conductance peak structure is observed. It is found that the zero-bias conductance peak is present in many consecutive Coulomb diamonds, irrespective of the even-odd parity of the quasi-particle occupation number in the quantum dot. In addition, we find that the zero-bias conductance peak is in most cases accompanied by two differential conductance peaks, forming a triple-peak structure, and the separation between the two side peaks in bias voltage shows oscillations closely correlated to the background Coulomb conductance oscillations of the device. The observed zero-bias conductance peak and the associated triple-peak structure are in line with Majorana fermion physics in such a hybrid topological system. PMID:25434375

  9. Parity independence of the zero-bias conductance peak in a nanowire based topological superconductor-quantum dot hybrid device.

    PubMed

    Deng, M T; Yu, C L; Huang, G Y; Larsson, M; Caroff, P; Xu, H Q

    2014-01-01

    We explore the signatures of Majorana fermions in a nanowire based topological superconductor-quantum dot-topological superconductor hybrid device by charge transport measurements. At zero magnetic field, well-defined Coulomb diamonds and the Kondo effect are observed. Under the application of a finite, sufficiently strong magnetic field, a zero-bias conductance peak structure is observed. It is found that the zero-bias conductance peak is present in many consecutive Coulomb diamonds, irrespective of the even-odd parity of the quasi-particle occupation number in the quantum dot. In addition, we find that the zero-bias conductance peak is in most cases accompanied by two differential conductance peaks, forming a triple-peak structure, and the separation between the two side peaks in bias voltage shows oscillations closely correlated to the background Coulomb conductance oscillations of the device. The observed zero-bias conductance peak and the associated triple-peak structure are in line with Majorana fermion physics in such a hybrid topological system.

  10. Quantum Mechanics Studies of Fuel Cell Catalysts and Proton Conducting Ceramics with Validation by Experiment

    NASA Astrophysics Data System (ADS)

    Tsai, Ho-Cheng

    We carried out quantum mechanics (QM) studies aimed at improving the performance of hydrogen fuel cells. In part I, The challenge was to find a replacement for the Pt cathode that would lead to improved performance for the Oxygen Reduction Reaction (ORR) while remaining stable under operational conditions and decreasing cost. Our design strategy was to find an alloy with composition Pt3M that would lead to surface segregation such that the top layer would be pure Pt, with the second and subsequent layers richer in M. Under operating conditions we expect the surface to have significant O and/or OH chemisorbed on the surface; we searched for M that would remain segregated under these conditions. Using QM we examined surface segregation for 28 Pt3M alloys, where M is a transition metal. We found that only Pt3Os and Pt3Ir showed significant surface segregation when O and OH are chemisorbed on the catalyst surfaces. This result indicates that Pt3Os and Pt 3Ir favor formation of a Pt-skin surface layer structure that would resist the acidic electrolyte corrosion during fuel cell operation environments. We chose to focus on Os because the phase diagram for Pt-Ir indicated that Pt-Ir could not form a homogeneous alloy at lower temperature. To determine the performance for ORR, we used QM to examine intermediates, reaction pathways, and reaction barriers involved in the processes for which protons from the anode reactions react with O2 to form H2O. These QM calculations used our Poisson-Boltzmann implicit solvation model include the effects of the solvent (water with dielectric constant 78 with pH 7 at 298K). We also carried out similar QM studies followed by experimental validation for the Os/Pt core-shell catalyst fabricated by the underpotential deposition (UPD) method. The QM results indicated that the RDS for ORR is a compromise between the OOH formation step (0.37 eV for Pt, 0.23 eV for Pt2ML/Os core-shell) and H2O formation steps (0.32 eV for Pt, 0.22 eV for Pt2ML

  11. Quantum Mechanics Studies of Fuel Cell Catalysts and Proton Conducting Ceramics with Validation by Experiment

    NASA Astrophysics Data System (ADS)

    Tsai, Ho-Cheng

    We carried out quantum mechanics (QM) studies aimed at improving the performance of hydrogen fuel cells. In part I, The challenge was to find a replacement for the Pt cathode that would lead to improved performance for the Oxygen Reduction Reaction (ORR) while remaining stable under operational conditions and decreasing cost. Our design strategy was to find an alloy with composition Pt3M that would lead to surface segregation such that the top layer would be pure Pt, with the second and subsequent layers richer in M. Under operating conditions we expect the surface to have significant O and/or OH chemisorbed on the surface; we searched for M that would remain segregated under these conditions. Using QM we examined surface segregation for 28 Pt3M alloys, where M is a transition metal. We found that only Pt3Os and Pt3Ir showed significant surface segregation when O and OH are chemisorbed on the catalyst surfaces. This result indicates that Pt3Os and Pt 3Ir favor formation of a Pt-skin surface layer structure that would resist the acidic electrolyte corrosion during fuel cell operation environments. We chose to focus on Os because the phase diagram for Pt-Ir indicated that Pt-Ir could not form a homogeneous alloy at lower temperature. To determine the performance for ORR, we used QM to examine intermediates, reaction pathways, and reaction barriers involved in the processes for which protons from the anode reactions react with O2 to form H2O. These QM calculations used our Poisson-Boltzmann implicit solvation model include the effects of the solvent (water with dielectric constant 78 with pH 7 at 298K). We also carried out similar QM studies followed by experimental validation for the Os/Pt core-shell catalyst fabricated by the underpotential deposition (UPD) method. The QM results indicated that the RDS for ORR is a compromise between the OOH formation step (0.37 eV for Pt, 0.23 eV for Pt2ML/Os core-shell) and H2O formation steps (0.32 eV for Pt, 0.22 eV for Pt2ML

  12. 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

    2016-02-01

    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.

  13. 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.

  14. Thermal and Electrical Conduction of Single-crystal Bi2Te3 Nanostructures grown using a one step process

    PubMed Central

    Park, Dambi; Park, Sungjin; Jeong, Kwangsik; Jeong, Hong-Sik; Song, Jea Yong; Cho, Mann–Ho

    2016-01-01

    Single-crystal Bi2Te3 nanowires (NWs) and nanoribbons (NRs) were synthesized by a vapor-liquid-solid (VLS) method from Bi2Te3 powder. To investigate the thermal properties of the Bi2Te3 nanostructure, a nondestructive technique based on temperature dependent Raman mapping was carried out. The Raman peaks were red shifted with increasing temperature. In addition, the fraction of the laser power absorbed inside the Bi2Te3 nanostructures was estimated by optical simulation and used to calculate the thermal conductivity value (κ). The thermal conductivity value obtained for the Bi2Te3 NW and NR was 1.47 Wm−1K−1 and 1.81 Wm−1K−1 at 300 K, respectively. The electrical conductivity of the Bi2Te3 nanostructure was also measured. In particular, an excellent electrical conductivity value of 1.22 * 103 Ω−1 cm−1 was obtained for the Bi2Te3 NW at 300 K. This result can be attributed to topological insulator surface states. As a result of our study, the figure of merit (ZT) for the Bi2Te3 NW and NR can be significantly improved. PMID:26750563

  15. One-step fabrication of a highly conductive and durable copper paste and its flexible dipole tag-antenna application.

    PubMed

    Shin, Keun-Young; Lee, James S; Hong, Jin-Yong; Jang, Jyongsik

    2014-03-21

    A highly conductive and durable copper (Cu) paste was successfully fabricated via acid treatment and mechanical blending with corrosion inhibitors. A screen-printed Cu pattern was evaluated as a dipole tag-antenna with long term and thermal stability, and structural flexibility. PMID:24514876

  16. Finite shot noise and electron heating at quantized conductance in high-mobility quantum point contacts

    NASA Astrophysics Data System (ADS)

    Muro, Tatsuya; Nishihara, Yoshitaka; Norimoto, Shota; Ferrier, Meydi; Arakawa, Tomonori; Kobayashi, Kensuke; Ihn, Thomas; Rössler, Clemens; Ensslin, Klaus; Reichl, Christian; Wegscheider, Werner

    2016-05-01

    We report a precise experimental study on the shot noise of a quantum point contact (QPC) fabricated in a GaAs/AlGaAs based high-mobility two-dimensional electron gas (2DEG). The combination of unprecedented cleanliness and very high measurement accuracy has enabled us to discuss the Fano factor to characterize the shot noise with a precision of 0.01. We observed that the shot noise at zero magnetic field exhibits a slight enhancement exceeding the single particle theoretical prediction, and that it gradually decreases as a perpendicular magnetic field is applied. We also confirmed that this additional noise completely vanishes in the quantum Hall regime. These phenomena can be explained by the electron heating effect near the QPC, which is suppressed with increasing magnetic field.

  17. Peak values of the longitudinal conductivity under integer quantum Hall effect conditions for sharp and smooth chaotic potentials

    SciTech Connect

    Greshnov, A. A. Zegrya, G. G.; Kolesnikova, E. N.

    2008-09-15

    The problem of the peak values of the longitudinal conductivity under integer quantum Hall effect conditions is studied. The limiting cases of sharp and smooth chaotic potentials are considered. In the case of a sharp chaotic potential, the first longitudinal conductivity peak ({delta}{sub xx}{sup (0)}) obtained by the extrapolation of numerical data to an infinite sample size L{sup {yields}}{infinity} is (0.55{+-}0.03)e{sup 2}/h. In the case of a smooth chaotic potential, the peak values of the longitudinal conductivity are independent of the Landau level number and decrease as the chaotic-potential correlation length {lambda} increases. The results obtained for sharp and smooth chaotic potentials agree with the reported experimental and numerically calculated data.

  18. How strong is localization in the integer quantum Hall effect: Relevant quantum corrections to conductivity in non-zero magnetic field

    NASA Astrophysics Data System (ADS)

    Greshnov, A. A.; Kolesnikova, E. N.; Utesov, O. I.; Zegrya, G. G.

    2010-02-01

    The divergent at ω=0 quantum correction to conductivity δσ2(ω) of the leading order in (kFl)-1 has been calculated neglecting Cooperon-type contributions suppressed by moderate or strong magnetic field. In the so-called diffusion approximation this quantity is equal to zero up to the second order in (kFl)-1. More subtle treatment of the problem shows that δσ2(ω) is non-zero due to ballistic contributions neglected previously. Knowledge of δσ2(ω) allows to estimate value of the so-called unitary localization length as ξu≈lexp(1.6g2) where Drude conductivity is given by σ0=ge2/h. This estimation underpins the statement of the linear growth of σxx peaks with Landau level number n in the integer quantum Hall effect regime [1] (Greshnov and Zegrya, 2008; Greshnov et al., 2008) at least for n≤2 and calls Pruisken-Khmelnitskii hypothesis of universality [2] (Levine et al., 1983; Khmelnitskii, 1983) in question.

  19. Linear and total intersubband transitions in the step-like GaAs/GaAlAs asymmetric quantum well as dependent on intense laser field

    NASA Astrophysics Data System (ADS)

    Ozturk, Emine

    2015-11-01

    In this study, for a step-like GaAs- Ga_{1-x}AlxAs asymmetric quantum well (AQW) the linear and total intersubband optical absorption coefficients and the refractive index changes are calculated as dependent on the intense laser field (ILF) and the right quantum well (RQW) width. Our results show that the location and the magnitude of all absorption coefficients and refractive index changes depend on ILF and the asymmetric parameter ( d=LR/LL). Also, we showed that both ILF and d provide an important effect on the electronic and optical properties of step-like quantum well, and the changes of the energy levels, the dipole moment matrix elements and the resonant peak values of the absorption coefficients are dependent on the shape of the confinement potential. While for different asymmetric parameters the intersubband absorption spectrum shows blue shift up to the different critical ILF values, this spectrum shows red shift for ILF values greater than certain values. By considering the variation of the energy difference as dependent on the RQW width, for step-like QW the absorption spectrum shows blue or red shift. Especially, step-like QWs are used for producing terahertz radiation from intersubband transitions and they have more tunable structure parameters (the left (right) quantum well width, LL(LR), and the confinement potential in the left (right) hand side, VL (VR) with respect to other asymmetric QWs (in the present study we used LR=LL/2, LL, 3 L L/2 and V R = 2 V L/3 values). This case provides a new degree of freedom for controlling the optical properties in quantum wells (QWs). In addition, the nonlinear optics underlying the application of the ILF to asymmetric potential heterostructures becomes a subject of present-day interest. In conclusion: i) The electronic and optical properties of the step-like AQW vary by increasing ILF. ii) ILF leads to major modifications on the shape of the confining potential. iii) The position and the size of all absorption

  20. Effect of gate-driven spin resonance on the conductance through a one-dimensional quantum wire

    NASA Astrophysics Data System (ADS)

    Sadreev, Almas F.; Sherman, E. Ya.

    2013-09-01

    We consider quasiballistic electron transmission in a one-dimensional quantum wire subject to both time-independent and periodic potentials of a finger gate that results in a local time-dependent Rashba-type spin-orbit coupling. A spin-dependent conductance is calculated as a function of external constant magnetic field, the electric field frequency, and potential strength. The results demonstrate the effect of the gate-driven electric dipole spin resonance in a transport phenomenon such as spin-flip electron transmission.

  1. Ten Steps to Conducting a Large, Multi-Site, Longitudinal Investigation of Language and Reading in Young Children

    PubMed Central

    Farquharson, Kelly; Murphy, Kimberly A.

    2016-01-01

    Purpose: This paper describes methodological procedures involving execution of a large-scale, multi-site longitudinal study of language and reading comprehension in young children. Researchers in the Language and Reading Research Consortium (LARRC) developed and implemented these procedures to ensure data integrity across multiple sites, schools, and grades. Specifically, major features of our approach, as well as lessons learned, are summarized in 10 steps essential for successful completion of a large-scale longitudinal investigation in early grades. Method: Over 5 years, children in preschool through third grade were administered a battery of 35 higher- and lower-level language, listening, and reading comprehension measures (RCM). Data were collected from children, their teachers, and their parents/guardians at four sites across the United States. Substantial and rigorous effort was aimed toward maintaining consistency in processes and data management across sites for children, assessors, and staff. Conclusion: With appropriate planning, flexibility, and communication strategies in place, LARRC developed and executed a successful multi-site longitudinal research study that will meet its goal of investigating the contribution and role of language skills in the development of children's listening and reading comprehension. Through dissemination of our design strategies and lessons learned, research teams embarking on similar endeavors can be better equipped to anticipate the challenges. PMID:27064308

  2. Observation of a 0.5 conductance plateau in asymmetrically biased GaAs quantum point contact

    NASA Astrophysics Data System (ADS)

    Bhandari, N.; Das, P. P.; Cahay, M.; Newrock, R. S.; Herbert, S. T.

    2012-09-01

    We report the observation of a robust anomalous conductance plateau near G = 0.5 G0 (G0 = 2e2/h) in asymmetrically biased AlGaAs/GaAs quantum point contacts (QPCs), with in-plane side gates in the presence of lateral spin-orbit coupling. This is interpreted as evidence of spin polarization in the narrow portion of the QPC. The appearance and evolution of the conductance anomaly has been studied at T = 4.2 K as a function of the potential asymmetry between the side gates. Because GaAs is a material with established processing techniques, high mobility, and a relatively high spin coherence length, the observation of spontaneous spin polarization in a side-gated GaAs QPC could eventually lead to the realization of an all-electric spin-valve at tens of degrees Kelvin.

  3. Dynamic conductivity of the bulk states of n-type HgTe/CdTe quantum well topological insulator

    SciTech Connect

    Chen, Qinjun; Sanderson, Matthew; Cao, J. C.; Zhang, Chao

    2014-11-17

    We theoretically studied the frequency-dependent current response of the bulk state of topological insulator HgTe/CdTe quantum well. The optical conductivity is mainly due to the inter-band process at high frequencies. At low frequencies, intra-band process dominates with a dramatic drop to near zero before the inter-band contribution takes over. The conductivity decreases with temperature at low temperature and increases with temperature at high temperature. The transport scattering rate has an opposite frequency dependence in the low and high temperature regime. The different frequency dependence is due to the interplay of the carrier-impurity scattering and carrier population near the Fermi surface.

  4. Quantum theory of the effect of grain boundaries on the electrical conductivity of thin films and wires

    NASA Astrophysics Data System (ADS)

    Moraga, Luis; Henriquez, Ricardo; Solis, Basilio

    2015-08-01

    We calculate the electrical conductivity of a metallic sample under the effects of distributed impurities and a random distribution of grain boundaries by means of a quantum mechanical procedure based on Kubo formula. Grain boundaries are represented either by a one-dimensional regular array of Dirac delta potentials (Mayadas and Shatzkes model) or by its three-dimensional extension (Szczyrbowski and Schmalzbauer model). We give formulas expressing the conductivity of bulk samples, thin films and thin wires of rectangular cross-sections in the case when the samples are bounded by perfectly flat surfaces. We find that, even in the absence of surface roughness, the conductivity in thin samples is reduced from its bulk value. If there are too many grain boundaries per unit length, or their scattering strength is high enough, there is a critical value Rc of the reflectivity R of an individual boundary such that the electrical conductivity vanishes for R >Rc. Also, the conductivity of thin wires shows a stepwise dependence on R. The effect of weak random variations in the strength or separation of the grain boundaries is computed by means of the method of correlation length. Finally, the resistivity of nanometric polycrystalline tungsten films reported in Choi et al. J. Appl. Phys. (2014) 115 104308 is tentatively analyzed by means of the present formalism.

  5. Spectrally resolved intraband transitions on two-step photon absorption in InGaAs/GaAs quantum dot solar cell

    SciTech Connect

    Tamaki, Ryo Shoji, Yasushi; Okada, Yoshitaka; Miyano, Kenjiro

    2014-08-18

    Two-step photon absorption processes in a self-organized In{sub 0.4}Ga{sub 0.6}As/GaAs quantum dot (QD) solar cell have been investigated by monitoring the mid-infrared (IR) photoinduced modulation of the external quantum efficiency (ΔEQE) at low temperature. The first step interband and the second step intraband transitions were both spectrally resolved by scanning photon energies of visible to near-IR CW light and mid-IR pulse lasers, respectively. A peak centered at 0.20 eV corresponding to the transition to virtual bound states and a band above 0.42 eV probably due to photoexcitation to GaAs continuum states were observed in ΔEQE spectra, when the interband transition was above 1.4 eV, directly exciting wetting layers or GaAs spacer layers. On the other hand, resonant excitation of the ground state of QDs at 1.35 eV resulted in a reduction of EQE. The sign of ΔEQE below 1.40 eV changed from negative to positive by increasing the excitation intensity of the interband transition. We ascribe this to the filling of higher energy trap states.

  6. Quantum transport in strongly disordered crystals: Electrical conductivity with large negative vertex corrections

    NASA Astrophysics Data System (ADS)

    Janiš, Václav; Pokorný, Vladislav

    2012-12-01

    We propose a renormalization scheme of the Kubo formula for the electrical conductivity with multiple backscatterings contributing to the electron-hole irreducible vertex derived from the asymptotic limit to high spatial dimensions. We use this vertex to represent the two-particle Green function via a symmetrized Bethe-Salpeter equation in momentum space. We further utilize the dominance of a pole in the irreducible vertex to an approximate diagonalization of the Bethe-Salpeter equation and a non-perturbative representation of the electron-hole correlation function. The latter function is then used to derive a compact representation for the electrical conductivity at zero temperature without the necessity to evaluate separately the Drude term and vertex corrections. The electrical conductivity calculated in this way remains nonnegative also in the strongly disordered regime where the localization effects become significant and the negative vertex corrections in the standard Kubo formula overweight the Drude term.

  7. Two-Step Reactive Aid Sintering of BaZr0.8Y0.2O3-δ Proton-Conducting Ceramics

    DOE PAGES

    Wang, Siwei; Chen, Yan; Zhang, Lingling; Ren, Cong; Chen, Fanglin; Brinkman, Kyle S.

    2015-10-14

    Ceramic-based proton conductors enable high-temperature hydrogen economy applications such as hydrogen separation membranes, fuel cells, and steam electrolyzers. BaZr0.8Y0.2O3-δ (BZY) proton-conducting oxide possesses the highest level of proton conductivity reported to date, but poor sinterability hinders its widespread utilization. Here, we report a two-step reactive aid sintering (TRAS) method involving the introduction of BaCO3 and B2O3-Li2O for the preparation of dense BZY ceramics sintered at 1500°C. The resulting BZY samples showed a pure perovskite structure with a dramatic increase in the relative density to 91.5%. In addition, the shrinkage during sintering was improved to 19.3% by a TRAS method asmore » compared to 2.6% by the conventional solid date reaction method. Moreover, the bulk conductivity was improved due to enhanced densification, while the grain boundary conductivity decreased due to the blocking behavior of the sintering aid resulting in a decrease in the total conductivity of the samples.« less

  8. Two-Step Reactive Aid Sintering of BaZr0.8Y0.2O3- δ Proton-Conducting Ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Siwei; Chen, Yan; Zhang, Lingling; Ren, Cong; Chen, Fanglin; Brinkman, Kyle S.

    2015-12-01

    Ceramic-based proton conductors enable high-temperature hydrogen economy applications such as hydrogen separation membranes, fuel cells, and steam electrolyzers. BaZr0.8Y0.2O3- δ (BZY) proton-conducting oxide possesses the highest level of proton conductivity reported to date, but poor sinterability hinders its widespread utilization. In this paper, we report a two-step reactive aid sintering (TRAS) method involving the introduction of BaCO3 and B2O3-Li2O for the preparation of dense BZY ceramics sintered at 1500°C. The resulting BZY samples showed a pure perovskite structure with a dramatic increase in the relative density to 91.5%. In addition, the shrinkage during sintering was improved to 19.3% by a TRAS method as compared to 2.6% by the conventional solid date reaction method. The bulk conductivity was improved due to enhanced densification, while the grain boundary conductivity decreased due to the blocking behavior of the sintering aid resulting in a decrease in the total conductivity of the samples.

  9. Close relation between quantum interference in molecular conductance and diradical existence.

    PubMed

    Tsuji, Yuta; Hoffmann, Roald; Strange, Mikkel; Solomon, Gemma C

    2016-01-26

    An empirical observation of a relationship between a striking feature of electronic transmission through a π-system, destructive quantum interference (QI), on one hand, and the stability of diradicals on the other, leads to the proof of a general theorem that relates the two. Subject to a number of simplifying assumptions, in a π-electron system, QI occurs when electrodes are attached to those positions of an N-carbon atom N-electron closed-shell hydrocarbon where the matrix elements of the Green's function vanish. These zeros come in two types, which are called easy and hard. Suppose an N+2 atom, N+2 electron hydrocarbon is formed by substituting 2 CH2 groups at two atoms, where the electrodes were. Then, if a QI feature is associated with electrode attachment to the two atoms of the original N atom system, the resulting augmented N+2 molecule will be a diradical. If there is no QI feature, i.e., transmission of current is normal if electrodes are attached to the two atoms, the resulting hydrocarbon will not be a diradical but will have a classical closed-shell electronic structure. Moreover, where a diradical exists, the easy zero is associated with a nondisjoint diradical, and the hard zero is associated with a disjoint one. A related theorem is proven for deletion of two sites from a hydrocarbon. PMID:26755578

  10. Close relation between quantum interference in molecular conductance and diradical existence

    PubMed Central

    Tsuji, Yuta; Hoffmann, Roald; Strange, Mikkel; Solomon, Gemma C.

    2016-01-01

    An empirical observation of a relationship between a striking feature of electronic transmission through a π-system, destructive quantum interference (QI), on one hand, and the stability of diradicals on the other, leads to the proof of a general theorem that relates the two. Subject to a number of simplifying assumptions, in a π-electron system, QI occurs when electrodes are attached to those positions of an N-carbon atom N-electron closed-shell hydrocarbon where the matrix elements of the Green’s function vanish. These zeros come in two types, which are called easy and hard. Suppose an N+2 atom, N+2 electron hydrocarbon is formed by substituting 2 CH2 groups at two atoms, where the electrodes were. Then, if a QI feature is associated with electrode attachment to the two atoms of the original N atom system, the resulting augmented N+2 molecule will be a diradical. If there is no QI feature, i.e., transmission of current is normal if electrodes are attached to the two atoms, the resulting hydrocarbon will not be a diradical but will have a classical closed-shell electronic structure. Moreover, where a diradical exists, the easy zero is associated with a nondisjoint diradical, and the hard zero is associated with a disjoint one. A related theorem is proven for deletion of two sites from a hydrocarbon. PMID:26755578

  11. Modulation of Step Heights of Thin Pb Films by the Quantum Size Effect Observed by Non-Contact Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Mao, Han-Qing; Li, Na; Chen, Xi; Xue, Qi-Kun

    2012-06-01

    Using a home-made Q-plus sensor, simultaneous scanning tunneling microscopy (STM) and atomic force microscopy (AFM) measurements were performed on the wedge-shaped Pb islands grown on Si(111)-7 × 7. Atomic resolved AFM images were observed. The contrast of AFM topography shows no dependence on the sample bias (tip is grounded), while the simultaneously obtained tunneling current image exhibits strong bias dependence due to quantum well states (QWS). Furthermore, In the AFM mode, neighboring Pb films with one monolayer (ML) thickness difference within the same Pb island show the same apparent height, which means that the apparent step heights of Pb films oscillate with a bilayer periodicity, being consistent with previous observations by helium atom scattering, x-ray diffraction, and STM. The possible reasons underlying the oscillation of apparent step heights in AFM topography are discussed.

  12. Electrical Conductivity.

    ERIC Educational Resources Information Center

    Allen, Philip B.

    1979-01-01

    Examines Drude's classical (1900) theory of electrical conduction, details the objections to and successes of the 1900 theory, and investigates the Quantum (1928) theory of conduction, reviewing its successes and limitations. (BT)

  13. Inelastic quantum transport in a ladder model: Implications for DNA conduction and comparison to experiments on suspended DNA oligomers

    NASA Astrophysics Data System (ADS)

    Gutiérrez, R.; Mohapatra, S.; Cohen, H.; Porath, D.; Cuniberti, G.

    2006-12-01

    We investigate quantum transport characteristics of a ladder model, which effectively mimics the topology of a double-stranded DNA molecule. We consider the interaction of tunneling charges with a selected internal vibrational degree of freedom and discuss its influence on the structure of the current-voltage characteristics. Further, molecule-electrode contact effects are shown to dramatically affect the orders of magnitude of the current. Recent electrical transport measurements on suspended DNA oligomers with a complex base-pair sequence, revealing strikingly high currents, are also presented and used as a reference point for the theoretical modeling. A semiquantitative description of the measured I-V curves is achieved, suggesting that the coupling to vibrational excitations plays an important role in DNA conduction.

  14. Cluster-continuum quantum mechanical models to guide the choice of anions for Li{sup +}-conducting ionomers

    SciTech Connect

    Shiau, Huai-Suen; Janik, Michael J.; Liu, Wenjuan; Colby, Ralph H.

    2013-11-28

    A quantum-mechanical investigation on Li poly(ethylene oxide)-based ionomers was performed in the cluster-continuum solvation model (CCM) that includes specific solvation in the first shell surrounding the cation, all surrounded by a polarizable continuum. A four-state model, including a free Li cation, Li{sup +}-anion pair, triple ion, and quadrupole was used to represent the states of Li{sup +} within the ionomer in the CCM. The relative energy of each state was calculated for Li{sup +} with various anions, with dimethyl ether representing the ether oxygen solvation. The population distribution of Li{sup +} ions among states was estimated by applying Boltzmann statistics to the CCM energies. Entropy difference estimates are needed for populations to better match the true ionomer system. The total entropy change is considered to consist of four contributions: translational, rotational, electrostatic, and solvent immobilization entropies. The population of ion states is reported as a function of Bjerrum length divided by ion-pair separation with/without entropy considered to investigate the transition between states. Predicted concentrations of Li{sup +}-conducting states (free Li{sup +} and positive triple ions) are compared among a series of anions to indicate favorable features for design of an optimal Li{sup +}-conducting ionomer; the perfluorotetraphenylborate anion maximizes the conducting positive triple ion population among the series of anions considered.

  15. Conduction band mass determinations for n-type InGaAs/InAlAs single quantum wells

    SciTech Connect

    Jones, E.D.; Reno, J.L.; Kotera, Nobuo; Wang, Y.

    1998-05-01

    The authors report the measurement of the conduction band mass in n-type single 27-ML-wide InGaAs/InAlAs quantum well lattice matched to InP using two methods: (1) Magnetoluminescence spectroscopy and (2) far-infrared cyclotron resonance. The magnetoluminescence method utilizes Landau level transitions between 0 and 14 T at 1.4 K. The far infrared cyclotron resonance measurements were made at 4.2 K and to fields as large up to 18 T. The 2D-carrier density N{sub 2D} = 3 {times} 10{sup 11} cm{sup {minus}2} at low temperatures. The magnetoluminescence technique yielded an effective conduction-band mass of m{sub c} = 0.062m{sub 0} while the far infrared cyclotron resonance measurements gave m{sub c} = 0.056m{sub 0}, where m{sub 0} is the free electron mass. Both measurements show no evidence for any significant conduction-band nonparabolicity.

  16. Investigating the Composition and Conductance Distributions on Highly GeSi Mixed Quantum Dots and Inside Oxidation Problem

    NASA Astrophysics Data System (ADS)

    Ye, F. F.; Ma, Y. J.; Lv, Y.; Jiang, Z. M.; Yang, X. J.

    2015-12-01

    With the help of a nanoscale trench, the composition and conductance distributions of single GeSi quantum dots (QDs) are obtained by conductive atomic force microscopy combined with selective chemical etching. However, the obtained composition and current distributions are unwonted and inconsistent on the QDs grown at 680 °C. With a series of confirmatory experiments, it is suggested that a thick oxide layer is formed and remains on the QDs' surface after etching. Though this selective chemical etching has already been widely applied to investigate the composition distribution of GeSi nanostructures, the oxidation problem has not been concerned yet. Our results indicate that the oxidation problem could not be ignored on highly GeSi mixed QDs. After removing the oxide layer, the composition and conductance distributions as well as their correlation are obtained. The results suggest that QDs' current distribution is mainly determined by the topographic shape, while the absolute current values are influenced by the Ge/Si contents.

  17. Next Step for STEP

    SciTech Connect

    Wood, Claire; Bremner, Brenda

    2013-08-09

    The Siletz Tribal Energy Program (STEP), housed in the Tribe’s Planning Department, will hire a data entry coordinator to collect, enter, analyze and store all the current and future energy efficiency and renewable energy data pertaining to administrative structures the tribe owns and operates and for homes in which tribal members live. The proposed data entry coordinator will conduct an energy options analysis in collaboration with the rest of the Siletz Tribal Energy Program and Planning Department staff. An energy options analysis will result in a thorough understanding of tribal energy resources and consumption, if energy efficiency and conservation measures being implemented are having the desired effect, analysis of tribal energy loads (current and future energy consumption), and evaluation of local and commercial energy supply options. A literature search will also be conducted. In order to educate additional tribal members about renewable energy, we will send four tribal members to be trained to install and maintain solar panels, solar hot water heaters, wind turbines and/or micro-hydro.

  18. Core size dependent hole transfer from a photoexcited CdSe/ZnS quantum dot to a conductive polymer.

    PubMed

    Zang, Huidong; Routh, Prahlad K; Alam, Rabeka; Maye, Mathew M; Cotlet, Mircea

    2014-06-01

    Photoinduced hole transfer from a CdSe/ZnS quantum dot to a conjugated polymer is tuned by varying the quantum dot core size. Hole transfer affects the photoluminescence blinking of the quantum dot, increasing the duration of the on-states and decreasing that of the off-states.

  19. Quantum and classical magnetoresistance in ambipolar topological insulator transistors with gate-tunable bulk and surface conduction.

    PubMed

    Tian, Jifa; Chang, Cuizu; Cao, Helin; He, Ke; Ma, Xucun; Xue, Qikun; Chen, Yong P

    2014-05-07

    Weak antilocalization (WAL) and linear magnetoresistance (LMR) are two most commonly observed magnetoresistance (MR) phenomena in topological insulators (TIs) and often attributed to the Dirac topological surface states (TSS). However, ambiguities exist because these phenomena could also come from bulk states (often carrying significant conduction in many TIs) and are observable even in non-TI materials. Here, we demonstrate back-gated ambipolar TI field-effect transistors in (Bi0.04Sb0.96)2Te3 thin films grown by molecular beam epitaxy on SrTiO3(111), exhibiting a large carrier density tunability (by nearly 2 orders of magnitude) and a metal-insulator transition in the bulk (allowing switching off the bulk conduction). Tuning the Fermi level from bulk band to TSS strongly enhances both the WAL (increasing the number of quantum coherent channels from one to peak around two) and LMR (increasing its slope by up to 10 times). The SS-enhanced LMR is accompanied by a strongly nonlinear Hall effect, suggesting important roles of charge inhomogeneity (and a related classical LMR), although existing models of LMR cannot capture all aspects of our data. Our systematic gate and temperature dependent magnetotransport studies provide deeper insights into the nature of both MR phenomena and reveal differences between bulk and TSS transport in TI related materials.

  20. Decoupling Edge Versus Bulk Conductance in the Trivial Regime of an InAs/GaSb Double Quantum Well Using Corbino Ring Geometry.

    PubMed

    Nguyen, Binh-Minh; Kiselev, Andrey A; Noah, Ramsey; Yi, Wei; Qu, Fanming; Beukman, Arjan J A; de Vries, Folkert K; van Veen, Jasper; Nadj-Perge, Stevan; Kouwenhoven, Leo P; Kjaergaard, Morten; Suominen, Henri J; Nichele, Fabrizio; Marcus, Charles M; Manfra, Michael J; Sokolich, Marko

    2016-08-12

    A Corbino ring geometry is utilized to analyze edge and bulk conductance of InAs/GaSb quantum well structures. We show that edge conductance exists in the trivial regime of this theoretically predicted topological system with a temperature-insensitive linear resistivity per unit length in the range of 2  kΩ/μm. A resistor network model of the device is developed to decouple the edge conductance from the bulk conductance, providing a quantitative technique to further investigate the nature of this trivial edge conductance, conclusively identified here as being of n type.

  1. Decoupling Edge Versus Bulk Conductance in the Trivial Regime of an InAs/GaSb Double Quantum Well Using Corbino Ring Geometry.

    PubMed

    Nguyen, Binh-Minh; Kiselev, Andrey A; Noah, Ramsey; Yi, Wei; Qu, Fanming; Beukman, Arjan J A; de Vries, Folkert K; van Veen, Jasper; Nadj-Perge, Stevan; Kouwenhoven, Leo P; Kjaergaard, Morten; Suominen, Henri J; Nichele, Fabrizio; Marcus, Charles M; Manfra, Michael J; Sokolich, Marko

    2016-08-12

    A Corbino ring geometry is utilized to analyze edge and bulk conductance of InAs/GaSb quantum well structures. We show that edge conductance exists in the trivial regime of this theoretically predicted topological system with a temperature-insensitive linear resistivity per unit length in the range of 2  kΩ/μm. A resistor network model of the device is developed to decouple the edge conductance from the bulk conductance, providing a quantitative technique to further investigate the nature of this trivial edge conductance, conclusively identified here as being of n type. PMID:27563999

  2. Decoupling Edge Versus Bulk Conductance in the Trivial Regime of an InAs /GaSb Double Quantum Well Using Corbino Ring Geometry

    NASA Astrophysics Data System (ADS)

    Nguyen, Binh-Minh; Kiselev, Andrey A.; Noah, Ramsey; Yi, Wei; Qu, Fanming; Beukman, Arjan J. A.; de Vries, Folkert K.; van Veen, Jasper; Nadj-Perge, Stevan; Kouwenhoven, Leo P.; Kjaergaard, Morten; Suominen, Henri J.; Nichele, Fabrizio; Marcus, Charles M.; Manfra, Michael J.; Sokolich, Marko

    2016-08-01

    A Corbino ring geometry is utilized to analyze edge and bulk conductance of InAs /GaSb quantum well structures. We show that edge conductance exists in the trivial regime of this theoretically predicted topological system with a temperature-insensitive linear resistivity per unit length in the range of 2 k Ω /μ m . A resistor network model of the device is developed to decouple the edge conductance from the bulk conductance, providing a quantitative technique to further investigate the nature of this trivial edge conductance, conclusively identified here as being of n type.

  3. One-step synthesis of NiCo2S4 ultrathin nanosheets on conductive substrates as advanced electrodes for high-efficient energy storage

    NASA Astrophysics Data System (ADS)

    Wang, Jian-Gan; Jin, Dandan; Zhou, Rui; Shen, Chao; Xie, Keyu; Wei, Bingqing

    2016-02-01

    A simple one-step and low-temperature synthesis approach has been developed to grow hierarchical NiCo2S4 ultrathin nanosheets (2-3 nm in thickness) on Ni foam. Owing to the unique nanoarchitecture, the NiCo2S4 nanosheets not only offer abundant electro-active sites for energy storage, but also have good electrical and mechanical connections to the conductive Ni foam for enhancing reaction kinetics and improving electrode integrity. When used as anodes for Li-ion batteries, the NiCo2S4 nanosheets demonstrate exceptional energy storage performance in terms of high specific capacity, excellent rate capability, and good cycling stability. The mild-solution synthesis of NiCo2S4 nanostructures and the outstanding electrochemical performance enable the novel electrodes to hold great potential for high-efficient energy storage systems.

  4. Quantum-chemical ab initio investigation of the two-step charge transfer process of hydrogen reaction: approach of reaction pathways via hydrogen intermediate on Cu(100)

    NASA Astrophysics Data System (ADS)

    Kuznetsov, An. M.; Lorenz, W.

    1994-08-01

    Local reaction events in the course of the electrochemical two-step hydrogen evolution reaction have been investigated by means of quantum-chemical all-electron ab initio calculations on interfacial supermolecular cluster models including a hydrated hydrogen intermediate on Cu(100). Expanding on preceding study to larger hydration clusters, an approach to relevant reaction path characteristics has been pursued for two processes: (i) the transfer of hydrated hydronium ion into a chemisorbed hydrogen intermediate: (ii) the reaction of hydronium ion with the intermediate to molecular hydrogen. Computations were carried out on RHF level, using contracted (12,8,4)/[8,6,2,] and/or 6-31G * or G ** pol-O bases for the metal and adsorbate part, respectively. Destruction of the hydronium configuration in process (i) has been confirmed. Electronic partial charge transfer dut to chemical bond conversions in both steps (i) and (ii) has been displayed along relevant cuts of adiabatic potential surfaces, proving significantly different amounts of charge transfer in both steps, λ 1 > 1, λ 2≡(2-λ 1) < 1. In advance of consideration of macroscopic double layer effects, first insight has been gained into coupled nuclear motions and into the origin of reaction barriers

  5. Quantum Confinement Induced Oscillatory Electric Field on a Stepped Pb(111) Film and Its Influence on Surface Reactivity

    SciTech Connect

    Liu, Xiaojie; Wang, Cai-Zhuang; Hupalo, Myron; Lin, Hai-Quing; Ho, Kai-Ming; Tringides, Michael C.

    2014-01-06

    When the thickness of ultrathin metal films approaches the nanometer scale comparable to the coherence length of the electrons, significant effects on the structure stability and the electronic properties of the metal films emerge due to electron confinement and quantization of the allowed electronic states in the direction perpendicular to the film. Using first-principles calculations, we showed that such quantum size effects can induce oscillatory electrostatic potential and thus alternating electric field on the surface of the wedge-shaped Pb(111) films. The alternating electric field has significant influence on surface reactivity, leading to selective even- or odd-layer adsorption preference depending on the charge state of the adatoms, consistent with the odd-layer preference of higher Mg coverage on wedge-shaped Pb(111) films, as observed in experiment.

  6. Synthesis and Characterization of Eu3+-Doped CdS Quantum Dots by a Single-Step Aqueous Method.

    PubMed

    Zhou, Chunyan; Song, Jiahui; Zhang, Xinguo; Sun, Lu; Zhou, Liya; Huang, Ni; Gan, Yufei; Chen, Mengyang; Zhang, Wei

    2016-04-01

    Eu3+-doped CdS quantum dots (QDs) are successfully synthesized through a straightforward single-pot process in aqueous solution using thioglycolic acid as the capping ligand. The structure, shape, and spectral properties of the QDs are investigated. The obtained CdS:Eu3+ QDs exhibit cubic structures with good crystallinity and approximately sphere-like shapes about 4 nm in diameter. The CdS QDs manifest a broadband emission peak at 600 nm and enhanced Photoluminescence (PL) emission intensity after doping with Eu3+ ions. Given the strong PL intensity and good chromaticity of the sulfide-based QDs, they have potential use in doping rare-earth ions. PMID:27451722

  7. Adiabatic passage for one-step generation of n-qubit Greenberger-Horne-Zeilinger states of superconducting qubits via quantum Zeno dynamics

    NASA Astrophysics Data System (ADS)

    Wu, Jin-Lei; Song, Chong; Xu, Jing; Yu, Lin; Ji, Xin; Zhang, Shou

    2016-09-01

    An efficient scheme is proposed for generating n-qubit Greenberger-Horne-Zeilinger states of n superconducting qubits separated by (n-1) coplanar waveguide resonators capacitively via adiabatic passage with the help of quantum Zeno dynamics in one step. In the scheme, it is not necessary to precisely control the time of the whole operation and the Rabi frequencies of classical fields because of the introduction of adiabatic passage. The numerical simulations for three-qubit Greenberger-Horne-Zeilinger state show that the scheme is insensitive to the dissipation of the resonators and the energy relaxation of the superconducting qubits. The three-qubit Greenberger-Horne-Zeilinger state can be deterministically generated with comparatively high fidelity in the current experimental conditions, though the scheme is somewhat sensitive to the dephasing of superconducting qubits.

  8. Synthesis and Characterization of TiO2 Nanotubes Sensitized with CdS Quantum Dots Using a One-Step Method

    NASA Astrophysics Data System (ADS)

    Song, Jiahui; Zhang, Xinguo; Zhou, Chunyan; Lan, Yuwei; Pang, Qi; Zhou, Liya

    2015-01-01

    A novel one-step synthesis process was used to assemble CdS quantum dots (QDs) into TiO2 nanotube arrays (TNTAs). The sensitization time of the TiO2 nanotubes can be adjusted by controlling the CdS QD synthesis time. The absorption band of sensitized TNTAs red-shifted and broadened to the visible spectrum. The photoelectric conversion efficiency increased to 0.83%, the open-circuit voltage to 776 mV, and the short-circuit current density ( J SC) to 2.30 mA cm-2 with increased sensitization time. The conversion efficiency with this new sensitization method was five times that of nonsensitized TNTAs, providing novel ideas for study of TNTA solar cells.

  9. Step bunch assisted two dimensional ordering of In{sub 0.19}Ga{sub 0.81}As/GaAs quantum dots on vicinal GaAs(001) surfaces

    SciTech Connect

    Hanke, M.; Wang, Zh. M.; Mazur, Yu. I.; Lee, J. H.; Salamo, G. J.; Schmidbauer, M.

    2008-01-21

    We have investigated the self-organized, step bunch assisted formation of In{sub 0.19}Ga{sub 0.81}As/GaAs quantum dots in vertical superlattices consisting of one, four, eight, and ten periods. Samples were grown by molecular beam epitaxy on vicinal 2 deg. A and 2 deg. B GaAs(001) substrates. Those with miscut along the [110] (2 deg. B) exclusively show step bunches of an aspect ratio larger than 10 but without the formation of quantum dots. This highly linear pattern is improved during subsequent periods as proved by high resolution x-ray diffraction and grazing incidence diffraction. On the other hand, a miscut along the [110] (2 deg. A) initially causes a crosslike pattern of step bunches, which finally becomes a two-dimensional arrangement of individual quantum dots.

  10. Optical and electrical characterizations of a single step ion beam milling mesa devices of chloride passivated PbS colloidal quantum dots based film

    NASA Astrophysics Data System (ADS)

    Hechster, Elad; Shapiro, Arthur; Lifshitz, Efrat; Sarusi, Gabby

    2016-07-01

    Colloidal Quantum Dots (CQDs) are of increasing interest, thanks to their quantum size effect that gives rise to their usage in various applications, such as biological tagging, solar cells and as the sensitizing layer of night vision devices. Here, we analyze the optical absorbance of chloride passivated PbS CQDs as well as revealing a correlation between their photoluminescence and sizes distribution, using theoretical models and experimental results from the literature. Next, we calculate the CQDs resistivity as a film. Although resistivity can be calculated from sheet resistance measurement using four point probes, such measurement is usually carried-out on the layer's surface that in most cases has dangling bonds and surface states, which might affect the charges flow and modify the resistivity. Therefore; our approach, which was applied in this work, is to extract the actual resistivity from measurements that are performed along the film's thickness (z-direction). For this intent, we fabricated gold capped PbS mesas devices using a single step Ion Beam Milling (IBM) process where we milled the gold and the PbS film continually, and then measured the vertical resistance. Knowing the mesas' dimensions, we calculate the resistivity. To the best of our knowledge, no previous work has extracted, vertically, the resistivity of chloride passivated PbS CQDs using the above method.

  11. Observation of Rabi splitting from surface plasmon coupled conduction state transitions in electrically excited InAs quantum dots.

    PubMed

    Passmore, Brandon S; Adams, David C; Ribaudo, Troy; Wasserman, Dan; Lyon, Stephen; Davids, Paul; Chow, Weng W; Shaner, Eric A

    2011-02-01

    We demonstrate strong coupling between a surface plasmon and intersublevel transitions in self-assembled InAs quantum dots. The surface plasmon mode exists at the interface between the semiconductor emitter structure and a periodic array of holes perforating a metallic Pd/Ge/Au film that also serves as the top electrical contact for the emitters. Spectrally narrowed quantum-dot electroluminescence was observed for devices with varying subwavelength hole spacing. Devices designed for 9, 10, and 11 μm wavelength emission also exhibit a significant spectral splitting. The association of the splitting with quantum-dot Rabi oscillation is consistent with results from a calculation of spontaneous emission from an interacting plasmonic field and quantum-dot ensemble. The fact that this Rabi oscillation can be observed in an incoherently excited, highly inhomogeneously broadened system demonstrates the utility of intersublevel transitions in quantum dots for investigations of coherent transient and quantum coherence phenomena.

  12. Quantum mechanics/molecular mechanics study on the oxygen binding and substrate hydroxylation step in AlkB repair enzymes.

    PubMed

    Quesne, Matthew G; Latifi, Reza; Gonzalez-Ovalle, Luis E; Kumar, Devesh; de Visser, Sam P

    2014-01-01

    AlkB repair enzymes are important nonheme iron enzymes that catalyse the demethylation of alkylated DNA bases in humans, which is a vital reaction in the body that heals externally damaged DNA bases. Its mechanism is currently controversial and in order to resolve the catalytic mechanism of these enzymes, a quantum mechanics/molecular mechanics (QM/MM) study was performed on the demethylation of the N(1) -methyladenine fragment by AlkB repair enzymes. Firstly, the initial modelling identified the oxygen binding site of the enzyme. Secondly, the oxygen activation mechanism was investigated and a novel pathway was found, whereby the catalytically active iron(IV)-oxo intermediate in the catalytic cycle undergoes an initial isomerisation assisted by an Arg residue in the substrate binding pocket, which then brings the oxo group in close contact with the methyl group of the alkylated DNA base. This enables a subsequent rate-determining hydrogen-atom abstraction on competitive σ- and π-pathways on a quintet spin-state surface. These findings give evidence of different locations of the oxygen and substrate binding channels in the enzyme and the origin of the separation of the oxygen-bound intermediates in the catalytic cycle from substrate. Our studies are compared with small model complexes and the effect of protein and environment on the kinetics and mechanism is explained.

  13. Quantum transparency of Anderson insulator junctions: Statistics of transmission eigenvalues, shot noise, and proximity conductance

    NASA Astrophysics Data System (ADS)

    Nikolić, Branislav K.; Dragomirova, Ralitsa L.

    2005-01-01

    We investigate quantum transport through strongly disordered barriers, made of a material with exceptionally high resistivity that behaves as an Anderson insulator or a “bad metal” in the bulk, by analyzing the distribution of Landauer transmission eigenvalues for a junction where such barrier is attached to two clean metallic leads. We find that scaling of the transmission eigenvalue distribution with the junction thickness (starting from the single interface limit) always predicts a nonzero probability to find high transmission channels even in relatively thick barriers. Using this distribution, we compute the zero frequency shot noise power (as well as its sample-to-sample fluctuations) and demonstrate how it provides a single number characterization of nontrivial transmission properties of different types of disordered barriers. The appearance of open conducting channels, whose transmission eigenvalue is close to one, and corresponding violent mesoscopic fluctuations of transport quantities explain at least some of the peculiar zero-bias anomalies in the Anderson-insulator/superconductor junctions observed in recent experiments [A. Vaknin, A. Frydman, and Z. Ovadyahu, Phys. Rev. B 61, 13037 (2000)]. Our findings are also relevant for the understanding of the role of defects that can undermine quality of thin tunnel barriers made of conventional band insulators.

  14. Two-Step Nucleation and Growth of InP Quantum Dots via Magic-Sized Cluster Intermediates

    SciTech Connect

    Gary, Dylan C.; Terban, Maxwell W.; Billinge, Simon J. L.; Cossairt, Brandi M.

    2015-01-30

    We report on the role of magic-sized clusters (MSCs) as key intermediates in the synthesis of indium phosphide quantum dots (InP QDs) from molecular precursors. These observations suggest that previous efforts to control nucleation and growth by tuning precursor reactivity have been undermined by formation of these kinetically persistent MSCs prior to QD formation. The thermal stability of InP MSCs is influenced by the presence of exogenous bases as well as choice of the anionic ligand set. Addition of a primary amine, a common additive in previous InP QD syntheses, to carboxylate terminated MSCs was found to bypass the formation of MSCs, allowing for homogeneous growth of InP QDs through a continuum of isolable sizes. Substitution of the carboxylate ligand set for a phosphonate ligand set increased the thermal stability of one particular InP MSC to 400°C. The structure and optical properties of the MSCs with both carboxylate and phosphonate ligand sets were studied by UV-Vis absorption spectroscopy, powder XRD analysis, and solution ³¹P{¹H} and ¹H NMR spectroscopy. Finally, the carboxylate terminated MSCs were identified as effective single source precursors (SSPs) for the synthesis of high quality InP QDs. Employing InP MSCs as SSPs for QDs effectively decouples the formation of MSCs from the subsequent second nucleation event and growth of InP QDs. The concentration dependence of this SSP reaction, as well as the shape uniformity of particles observed by TEM suggests that the stepwise growth from MSCs directly to QDs proceeds via a second nucleation event rather than an aggregative growth mechanism.

  15. Two-Step Nucleation and Growth of InP Quantum Dots via Magic-Sized Cluster Intermediates

    DOE PAGES

    Gary, Dylan C.; Terban, Maxwell W.; Billinge, Simon J. L.; Cossairt, Brandi M.

    2015-01-30

    We report on the role of magic-sized clusters (MSCs) as key intermediates in the synthesis of indium phosphide quantum dots (InP QDs) from molecular precursors. These observations suggest that previous efforts to control nucleation and growth by tuning precursor reactivity have been undermined by formation of these kinetically persistent MSCs prior to QD formation. The thermal stability of InP MSCs is influenced by the presence of exogenous bases as well as choice of the anionic ligand set. Addition of a primary amine, a common additive in previous InP QD syntheses, to carboxylate terminated MSCs was found to bypass the formationmore » of MSCs, allowing for homogeneous growth of InP QDs through a continuum of isolable sizes. Substitution of the carboxylate ligand set for a phosphonate ligand set increased the thermal stability of one particular InP MSC to 400°C. The structure and optical properties of the MSCs with both carboxylate and phosphonate ligand sets were studied by UV-Vis absorption spectroscopy, powder XRD analysis, and solution ³¹P{¹H} and ¹H NMR spectroscopy. Finally, the carboxylate terminated MSCs were identified as effective single source precursors (SSPs) for the synthesis of high quality InP QDs. Employing InP MSCs as SSPs for QDs effectively decouples the formation of MSCs from the subsequent second nucleation event and growth of InP QDs. The concentration dependence of this SSP reaction, as well as the shape uniformity of particles observed by TEM suggests that the stepwise growth from MSCs directly to QDs proceeds via a second nucleation event rather than an aggregative growth mechanism.« less

  16. Time-resolved spectral characterization of ring cavity surface emitting and ridge-type distributed feedback quantum cascade lasers by step-scan FT-IR spectroscopy.

    PubMed

    Brandstetter, Markus; Genner, Andreas; Schwarzer, Clemens; Mujagic, Elvis; Strasser, Gottfried; Lendl, Bernhard

    2014-02-10

    We present the time-resolved comparison of pulsed 2nd order ring cavity surface emitting (RCSE) quantum cascade lasers (QCLs) and pulsed 1st order ridge-type distributed feedback (DFB) QCLs using a step-scan Fourier transform infrared (FT-IR) spectrometer. Laser devices were part of QCL arrays and fabricated from the same laser material. Required grating periods were adjusted to account for the grating order. The step-scan technique provided a spectral resolution of 0.1 cm(-1) and a time resolution of 2 ns. As a result, it was possible to gain information about the tuning behavior and potential mode-hops of the investigated lasers. Different cavity-lengths were compared, including 0.9 mm and 3.2 mm long ridge-type and 0.97 mm (circumference) ring-type cavities. RCSE QCLs were found to have improved emission properties in terms of line-stability, tuning rate and maximum emission time compared to ridge-type lasers.

  17. Optical reading of field-effect transistors by phase-space absorption quenching in a single InGaAs quantum well conducting channel

    NASA Astrophysics Data System (ADS)

    Chemla, D. S.; Bar-Joseph, I.; Klingshirn, C.; Miller, D. A. B.; Kuo, J. M.

    1987-03-01

    Absorption switching in a semiconductor quantum well by electrically varying the charge density in the quantum well conducting channel of a selectively doped heterostructure transistor is reported for the first time. The phase-space absorption quenching (PAQ) is observed at room temperature in an InGaAs/InAlAs grown on InP FET, and it shows large absorption coefficient changes with relatively broad spectral bandwidth. This PAQ is large enough to be used for direct optical determination of the logic state of the FET.

  18. Multiple-Step Humidity-Induced Single-Crystal to Single-Crystal Transformations of a Cobalt Phosphonate: Structural and Proton Conductivity Studies.

    PubMed

    Cai, Zhong-Sheng; Bao, Song-Song; Wang, Xi-Zhang; Hu, Zheng; Zheng, Li-Min

    2016-04-01

    Humidity-induced multiple-step single-crystal to single-crystal (SC-SC) transformations are observed in the cobalt phosphonate (NH4)3[Co2(bamdpH)2(HCOO)(H2O)2] (1), where bamdpH4 is (benzylazanediyl)bis(methylene)diphosphonic acid, [C6H5CH2N(CH2PO3H2)2]. Under high-humidity conditions (95% RH), compound 1 experiences hydrolysis at 60 °C which is accompanied by the transformation from a double-chain structure of compound 1 into a single-chain structure of [Co(bamdpH2)(H2O)2]·2H2O (2). When the humidity is below 10% RH, part of the lattice water in compound 2 can be released, forming a third phase, [Co(bamdpH2)(H2O)2]·H2O (3). The structural transformation processes have been monitored by infrared and proton conductivity measurements.

  19. Quantized ionic conductance in nanopores

    SciTech Connect

    Zwolak, Michael; Lagerqvist, Johan; Di Ventra, Massimilliano

    2009-01-01

    Ionic transport in nanopores is a fundamentally and technologically important problem in view of its ubiquitous occurrence in biological processes and its impact on DNA sequencing applications. Using microscopic calculations, we show that ion transport may exhibit strong non-liDearities as a function of the pore radius reminiscent of the conductance quantization steps as a function of the transverse cross section of quantum point contacts. In the present case, however, conductance steps originate from the break up of the hydration layers that form around ions in aqueous solution. Once in the pore, the water molecules form wavelike structures due to multiple scattering at the surface of the pore walls and interference with the radial waves around the ion. We discuss these effects as well as the conditions under which the step-like features in the ionic conductance should be experimentally observable.

  20. The first step of the dioxygenation reaction carried out by tryptophan dioxygenase and indoleamine 2,3-dioxygenase as revealed by quantum mechanical/molecular mechanical studies

    PubMed Central

    Capece, Luciana; Lewis-Ballester, Ariel; Batabyal, Dipanwita; Di Russo, Natali; Estrin, Dario A.

    2015-01-01

    Tryptophan dioxygenase (TDO) and indole-amine 2,3-dioxygenase (IDO) are two heme-containing enzymes which catalyze the conversion of L-tryptophan to N-formylkynurenine (NFK). In mammals, TDO is mostly expressed in liver and is involved in controlling homeostatic serum tryptophan concentrations, whereas IDO is ubiquitous and is involved in modulating immune responses. Previous studies suggested that the first step of the dioxygenase reaction involves the deprotonation of the indoleamine group of the substrate by an evolutionarily conserved distal histidine residue in TDO and the heme-bound dioxygen in IDO. Here, we used classical molecular dynamics and hybrid quantum mechanical/molecular mechanical methods to evaluate the base-catalyzed mechanism. Our data suggest that the deprotonation of the indoleamine group of the substrate by either histidine in TDO or heme-bound dioxygen in IDO is not energetically favorable. Instead, the dioxygenase reaction can be initiated by a direct attack of heme-bound dioxygen on the C2=C3 bond of the indole ring, leading to a protein-stabilized 2,3-alkylperoxide transition state and a ferryl epoxide intermediate, which subsequently recombine to generate NFK. The novel sequential two-step oxygen addition mechanism is fully supported by our recent resonance Raman data that allowed identification of the ferryl intermediate (Lewis-Ballester et al. in Proc Natl Acad Sci USA 106:17371–17376, 2009). The results reveal the subtle differences between the TDO and IDO reactions and highlight the importance of protein matrix in modulating stereoelectronic factors for oxygen activation and the stabilization of both transition and intermediate states. PMID:20361220

  1. One-step microwave synthesis of N-doped hydroxyl-functionalized carbon dots with ultra-high fluorescence quantum yields.

    PubMed

    Zhang, Yongqiang; Liu, Xingyuan; Fan, Yi; Guo, Xiaoyang; Zhou, Lei; Lv, Ying; Lin, Jie

    2016-08-18

    A one-step microwave synthesis of N-doped hydroxyl-functionalized carbon dots (CDs) with ultra-high fluorescence quantum yields (QYs) of 99% is reported. These ultra-high QY CDs were synthesized using citric acid and amino compound-containing hydroxyls like ethanolamine and tris(hydroxylmethyl)aminomethane. Amino and carboxyl moieties can form amides through dehydration condensation reactions, and these amides act as bridges between carboxyl and hydroxyl groups, and modify hydroxyl groups on the surface of the CDs. The entire reaction can be carried out within 5 min. When the molar ratio of reactants is 1 : 1, the hydroxyl and graphitic nitrogen content is the highest, and the synergy leads to a high ratio between the radiative transition rate and nonradiative transition rate as well as a high QY. The developed pathway to N-doped hydroxyl-functionalized CDs can provide unambiguous and remarkable insights into the design of highly luminescent functionalized carbon dots, and expedite the applications of CDs. PMID:27500530

  2. Ge/Si(001) heterostructures with dense arrays of Ge quantum dots: morphology, defects, photo-emf spectra and terahertz conductivity

    PubMed Central

    2012-01-01

    Issues of Ge hut cluster array formation and growth at low temperatures on the Ge/Si(001) wetting layer are discussed on the basis of explorations performed by high resolution STM and in-situ RHEED. Dynamics of the RHEED patterns in the process of Ge hut array formation is investigated at low and high temperatures of Ge deposition. Different dynamics of RHEED patterns during the deposition of Ge atoms in different growth modes is observed, which reflects the difference in adatom mobility and their ‘condensation’ fluxes from Ge 2D gas on the surface for different modes, which in turn control the nucleation rates and densities of Ge clusters. Data of HRTEM studies of multilayer Ge/Si heterostructures are presented with the focus on low-temperature formation of perfect films. Heteroepitaxial Si p–i–n-diodes with multilayer stacks of Ge/Si(001) quantum dot dense arrays built in intrinsic domains have been investigated and found to exhibit the photo-emf in a wide spectral range from 0.8 to 5 μm. An effect of wide-band irradiation by infrared light on the photo-emf spectra has been observed. Photo-emf in different spectral ranges has been found to be differently affected by the wide-band irradiation. A significant increase in photo-emf is observed in the fundamental absorption range under the wide-band irradiation. The observed phenomena are explained in terms of positive and neutral charge states of the quantum dot layers and the Coulomb potential of the quantum dot ensemble. A new design of quantum dot infrared photodetectors is proposed. By using a coherent source spectrometer, first measurements of terahertz dynamical conductivity (absorptivity) spectra of Ge/Si(001) heterostructures were performed at frequencies ranged from 0.3 to 1.2 THz in the temperature interval from 300 to 5 K. The effective dynamical conductivity of the heterostructures with Ge quantum dots has been discovered to be significantly higher than that of the structure with the same amount

  3. Security: Step by Step

    ERIC Educational Resources Information Center

    Svetcov, Eric

    2005-01-01

    This article provides a list of the essential steps to keeping a school's or district's network safe and sound. It describes how to establish a security architecture and approach that will continually evolve as the threat environment changes over time. The article discusses the methodology for implementing this approach and then discusses the…

  4. Negative differential conductance and super-Poissonian shot noise in a single quantum dot coupled to two noncollinear polarized ferromagnetic leads

    NASA Astrophysics Data System (ADS)

    Xue, Hai-Bin; Nie, Yi-Hang; Ren, Wei

    2015-03-01

    We have theoretically studied the full counting statistics of electron transport through a single quantum dot (QD) weakly coupled to two noncollinearly polarized ferromagnetic leads. We found a strong robust bias-voltage-tunable negative differential conductance (NDC) region, in which the shot noise is dramatically enhanced and reaches up to a super-Poissonian value. In particular, the formed super-Poissonian shot noise can still occur in a wide bias voltage region where only the singly-occupied electronic states entering the bias voltage window. The underlying mechanisms of the observed NDC and super-Poissonian shot noise originate from the quantum coherence between the two singly-occupied electronic states. In addition, the skewness in the NDC regime can be significantly increased up to a large positive value, which is also attributed to the quantum coherence of the QD system, and the variation of the skewness value is more sensitive to the quantum coherence than the shot noise. Our findings suggest a QD-based tunable NDC device, and the predicted properties of high-order current cumulants can provide a deeper understanding of electron transport through the single QD.

  5. Validation of a two-step quality control approach for a large-scale human urine metabolomic study conducted in seven experimental batches with LC/QTOF-MS.

    PubMed

    Demetrowitsch, Tobias J; Petersen, Beate; Keppler, Julia K; Koch, Andreas; Schreiber, Stefan; Laudes, Matthias; Schwarz, Karin

    2015-01-01

    After his study of food science at the Rheinische Friedrich-Wilhelms University of Bonn, Tobias J Demetrowitsch obtained his doctoral degree in the research field of metabolomics at the Christian-Albrechts-University of Kiel. The present paper is part of his doctoral thesis and describes an extended strategy to evaluate and verify complex or large-scale experiments and data sets. Large-scale studies result in high sample numbers, requiring the analysis of samples in different batches. So far, the verification of such LC-MS-based metabolomics studies is difficult. Common approaches have not provided a reliable validation procedure to date. This article shows a novel verification process for a large-scale human urine study (analyzed by a LC/QToF-MS system) using a two-step validation procedure. The first step comprises a targeted approach that aims to examine and exclude statistical outliers. The second step consists of a principle component analysis, with the aim of a tight cluster of all quality controls and a second for all volunteer samples. The applied study design provides a reliable two-step validation procedure for large-scale studies and additionally contains an inhouse verification procedure. PMID:25558939

  6. Microscopic origin of the 1.3 G{sub 0} conductance observed in oxygen-doped silver quantum point contacts

    SciTech Connect

    Tu, Xingchen; Wang, Minglang; Hou, Shimin; Sanvito, Stefano

    2014-11-21

    Besides the peak at one conductance quantum, G{sub 0}, two additional features at ∼0.4 G{sub 0} and ∼1.3 G{sub 0} have been observed in the conductance histograms of silver quantum point contacts at room temperature in ambient conditions. In order to understand such feature, here we investigate the electronic transport and mechanical properties of clean and oxygen-doped silver atomic contacts by employing the non-equilibrium Green's function formalism combined with density functional theory. Our calculations show that, unlike clean Ag single-atom contacts showing a conductance of 1 G{sub 0}, the low-bias conductance of oxygen-doped Ag atomic contacts depends on the number of oxygen impurities and their binding configuration. When one oxygen atom binds to an Ag monatomic chain sandwiched between two Ag electrodes, the low-bias conductance of the junction always decreases. In contrast, when the number of oxygen impurities is two and the O-O axis is perpendicular to the Ag-Ag axis, the transmission coefficients at the Fermi level are, respectively, calculated to be 1.44 for the junction with Ag(111) electrodes and 1.24 for that with Ag(100) electrodes, both in good agreement with the measured value of ∼1.3 G{sub 0}. The calculated rupture force (1.60 nN for the junction with Ag(111) electrodes) is also consistent with the experimental value (1.66 ± 0.09 nN), confirming that the measured ∼1.3 G{sub 0} conductance should originate from Ag single-atom contacts doped with two oxygen atoms in a perpendicular configuration.

  7. Improved Open- Circuit Voltage in ZnO–PbSe Quantum Dot Solar Cells by Understanding and Reducing Losses Arising from the ZnO Conduction Band Tail

    PubMed Central

    Hoye, Robert L Z; Ehrler, Bruno; Böhm, Marcus L; Muñoz-Rojas, David; Altamimi, Rashid M; Alyamani, Ahmed Y; Vaynzof, Yana; Sadhanala, Aditya; Ercolano, Giorgio; Greenham, Neil C; Friend, Richard H; MacManus-Driscoll, Judith L; Musselman, Kevin P

    2014-01-01

    Colloidal quantum dot solar cells (CQDSCs) are attracting growing attention owing to significant improvements in efficiency. However, even the best depleted-heterojunction CQDSCs currently display open-circuit voltages (VOCs) at least 0.5 V below the voltage corresponding to the bandgap. We find that the tail of states in the conduction band of the metal oxide layer can limit the achievable device efficiency. By continuously tuning the zinc oxide conduction band position via magnesium doping, we probe this critical loss pathway in ZnO–PbSe CQDSCs and optimize the energetic position of the tail of states, thereby increasing both the VOC (from 408 mV to 608 mV) and the device efficiency. PMID:26225131

  8. Hamilton-Jacobi and quantum theory formulations of thermal-wave propagation under the dual-phase lagging model of heat conduction

    SciTech Connect

    Ordonez-Miranda, J.; Alvarado-Gil, J. J.; Zambrano-Arjona, Miguel A.

    2010-02-15

    Dual-phase lagging model is one of the most promising approaches to generalize the Fourier heat conduction equation, and it can be reduced in the appropriate limits to the hyperbolic Cattaneo-Vernotte and to the parabolic equations. In this paper it is shown that the Hamilton-Jacobi and quantum theory formulations that have been developed to study the thermal-wave propagation in the Fourier framework can be extended to include the more general approach based on dual-phase lagging. It is shown that the problem of solving the heat conduction equation can be treated as a thermal harmonic oscillator. In the classical approach a formulation in canonical variables is presented. This formalism is used to introduce a quantum mechanical approach from which the expectation values of observables such as the temperature and heat flux are obtained. These formalisms permit to use a methodology that could provide a deeper insight into the phenomena of heat transport at different time scales in media with inhomogeneous thermophysical properties.

  9. Influence of surface scattering on the anomalous conductance plateaus in an asymmetrically biased InAs/In(0.52)Al(0.48)As quantum point contact.

    PubMed

    Das, Partha P; Bhandari, Nikhil K; Wan, Junjun; Charles, James; Cahay, Marc; Chetry, Krishna B; Newrock, Richard S; Herbert, Steven T

    2012-06-01

    We study of the appearance and evolution of several anomalous (i.e., G < G(0) D 2e(2)/h) conductance plateaus in an In(0.52)Al(0.48)As/InAs quantum point contact (QPC). This work was performed at T = 4:2 K as a function of the offset bias ΔV(G) between the two in-plane gates of the QPC. The number and location of the anomalous conductance plateaus strongly depend on the polarity of the offset bias. The anomalous plateaus appear only over an intermediate range of offset bias of several volts. They are quite robust, being observed over a maximum range of nearly 1 V for the common sweep voltage applied to the two gates. These results are interpreted as evidence for the sensitivity of the QPC spin polarization to defects (surface roughness and impurity (dangling bond) scattering) generated during the etching process that forms the QPC side walls. This assertion is supported by non-equilibrium Green function simulations of the conductance of a single QPC in the presence of dangling bonds on its walls. Our simulations show that a spin conductance polarization as high as 98% can be achieved despite the presence of dangling bonds. The maximum in is not necessarily reached where the conductance of the channel is equal to 0:5G(0).

  10. A 250 mV Cu/SiO2/W Memristor with Half-Integer Quantum Conductance States.

    PubMed

    Nandakumar, S R; Minvielle, Marie; Nagar, Saurabh; Dubourdieu, Catherine; Rajendran, Bipin

    2016-03-01

    Memristive devices, whose conductance depends on previous programming history, are of significant interest for building nonvolatile memory and brain-inspired computing systems. Here, we report half-integer quantized conductance transitions G = (n/2) (2e(2)/h) for n = 1, 2, 3, etc., in Cu/SiO2/W memristive devices observed below 300 mV at room temperature. This is attributed to the nanoscale filamentary nature of Cu conductance pathways formed inside SiO2. Retention measurements also show spontaneous filament decay with quantized conductance levels. Numerical simulations shed light into the dynamics underlying the data retention loss mechanisms and provide new insights into the nanoscale physics of memristive devices and trade-offs involved in engineering them for computational applications.

  11. Dissipation-induced quantum phase transition in a quantum box

    NASA Astrophysics Data System (ADS)

    Borda, László; Zaránd, Gergely; Simon, Pascal

    2005-10-01

    In a recent work, Le Hur has shown, using perturbative arguments, that dissipative coupling to gate electrodes may play an important role in a quantum box near its degeneracy point [K. Le Hur, Phys. Rev. Lett. 92, 196804 (2004)]: While quantum fluctuations of the charge of the dot tend to round Coulomb blockade charging steps of the box, strong enough dissipation suppresses these fluctuations and leads to the reappearance of sharp charging steps. In the present paper, we study this quantum phase transition in detail using bosonization and the numerical renormalization group in the limit of vanishing level spacing and map out the phase diagram using these nonperturbative methods. We also discuss the properties of the renormalized lead-dot conductance in the vicinity of the phase transition and determine the scaling properties of the dynamically generated crossover scale analytically.

  12. Optical conductivity of warm dense matter within a wide frequency range using quantum statistical and kinetic approaches

    NASA Astrophysics Data System (ADS)

    Veysman, M.; Röpke, G.; Winkel, M.; Reinholz, H.

    2016-07-01

    Fundamental properties of warm dense matter are described by the dielectric function, which gives access to the frequency-dependent electrical conductivity; absorption, emission, and scattering of radiation; charged particles stopping; and further macroscopic properties. Different approaches to the dielectric function and the related dynamical collision frequency are compared in a wide frequency range. The high-frequency limit describing inverse bremsstrahlung and the low-frequency limit of the dc conductivity are considered. Sum rules and Kramers-Kronig relation are checked for the generalized linear response theory and the standard approach following kinetic theory. The results are discussed in application to aluminum, xenon, and argon plasmas.

  13. Optical conductivity of warm dense matter within a wide frequency range using quantum statistical and kinetic approaches.

    PubMed

    Veysman, M; Röpke, G; Winkel, M; Reinholz, H

    2016-07-01

    Fundamental properties of warm dense matter are described by the dielectric function, which gives access to the frequency-dependent electrical conductivity; absorption, emission, and scattering of radiation; charged particles stopping; and further macroscopic properties. Different approaches to the dielectric function and the related dynamical collision frequency are compared in a wide frequency range. The high-frequency limit describing inverse bremsstrahlung and the low-frequency limit of the dc conductivity are considered. Sum rules and Kramers-Kronig relation are checked for the generalized linear response theory and the standard approach following kinetic theory. The results are discussed in application to aluminum, xenon, and argon plasmas. PMID:27575226

  14. Experimental study on the contribution of the quantum tunneling effect to the improvement of the conductivity and piezoresistivity of a nickel powder-filled cement-based composite

    NASA Astrophysics Data System (ADS)

    Han, B. G.; Han, B. Z.; Yu, X.

    2009-06-01

    The voltage-current characteristics of a nickel powder (NP)-filled cement-based composite (NPCC) and the variation of electrical resistivity of NPCC under compression are studied by using a four-pole method based on embedded loop electrodes. The generation of conductivity and piezoresistivity in NPCC is investigated by examining the morphology of NPCC by SEM and studying the variation of distance between NP particles under compression. Experimental results indicate that the electrical conductivity of NPCC is ohmic when the voltage is below 3.5 V. Although NP particles are dispersed in the cement matrix and they do not form a connected conductive network, NPCC has a low electrical resistivity of 2.29 × 103Ω cm without loading. A decrease of 0.042% in the fractional change in volume of NPCC under compression causes the tunneling distance to decrease 0.60-1.42 nm and the fractional change in electrical resistivity to reach 62.61%. It is therefore concluded that the improvement of conductivity and piezoresistivity of NPCC is due to the quantum tunneling effect.

  15. The quantum space race

    NASA Astrophysics Data System (ADS)

    Jennewein, Thomas; Higgins, Brendon

    2013-03-01

    Sending satellites equipped with quantum technologies into space will be the first step towards a global quantum-communication network. As Thomas Jennewein and Brendon Higgins explain, these systems will also enable physicists to test fundamental physics in new regimes.

  16. Possibility of the effect of absolute negative conductivity in quantum superlattice exposed to the high-frequency electromagnetic radiation

    NASA Astrophysics Data System (ADS)

    Kryuchkov, S. V.; Kukhar', E. I.

    2015-07-01

    Current density in superlattice placed in quantizing electric field and in high-frequency field of electromagnetic wave was calculated. The calculations were performed by taking into account an inelastic scattering of charge carriers by phonons. Possibility of the effect of absolute negative conductivity, i.e. the effect of appearance of electric current flowing in opposite direction than that of vector of quantizing electric field intensity, was shown. Such effect in graphene superlattices was discussed.

  17. Energy level alignment and quantum conductance of functionalized metal-molecule junctions: Density functional theory versus GW calculations

    SciTech Connect

    Jin, Chengjun; Markussen, Troels; Thygesen, Kristian S.; Strange, Mikkel; Solomon, Gemma C.

    2013-11-14

    We study the effect of functional groups (CH{sub 3}*4, OCH{sub 3}, CH{sub 3}, Cl, CN, F*4) on the electronic transport properties of 1,4-benzenediamine molecular junctions using the non-equilibrium Green function method. Exchange and correlation effects are included at various levels of theory, namely density functional theory (DFT), energy level-corrected DFT (DFT+Σ), Hartree-Fock and the many-body GW approximation. All methods reproduce the expected trends for the energy of the frontier orbitals according to the electron donating or withdrawing character of the substituent group. However, only the GW method predicts the correct ordering of the conductance amongst the molecules. The absolute GW (DFT) conductance is within a factor of two (three) of the experimental values. Correcting the DFT orbital energies by a simple physically motivated scissors operator, Σ, can bring the DFT conductances close to experiments, but does not improve on the relative ordering. We ascribe this to a too strong pinning of the molecular energy levels to the metal Fermi level by DFT which suppresses the variation in orbital energy with functional group.

  18. A direct investigation of photocharge transfer across monomolecular layer between C60 and CdS quantum dots by photoassisted conductive atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Jiang, Xiaohong; Liu, He; Zhang, Xingtang; Cheng, Gang; Wang, Shujie; Du, Zuliang

    2016-04-01

    The composite assembly of C60 and CdS Quantum Dots (QDs) on ITO substrate was prepared by Langmuir-Blodgett (LB) technique using arachic acid (AA), stearic acid (SA) and octadecanyl amine (OA) as additives. Photoassisted conductive atomic force microscopy was used to make point contact current-voltage (I-V) measurements on both the CdS QDs and the composite assembly of C60/CdS. The result make it clear that the CdS, C60/CdS assemblies deposited on ITO substrate showed linear characteristics and the current increased largely under illumination comparing with that in the dark. The coherent, nonresonant tunneling mechanism was used to explain the current occurrence. It is considered that the photoinduced carriers CdS QDs tunneled through alkyl chains increased the current rapidly.

  19. Electrical Bistabilities and Conduction Mechanisms of Nonvolatile Memories Based on a Polymethylsilsesquioxane Insulating Layer Containing CdSe/ZnS Quantum Dots

    NASA Astrophysics Data System (ADS)

    Ma, Zehao; Ooi, Poh Choon; Li, Fushan; Yun, Dong Yeol; Kim, Tae Whan

    2015-10-01

    Nonvolatile memory (NVM) devices based on a metal-insulator-metal structure consisting of CdSe/ZnS quantum dots embedded in polymethylsilsesquioxane dielectric layers were fabricated. The current-voltage ( I- V) curves showed a bistable current behavior and the presence of hysteresis. The current-time ( I- t) curves showed that the fabricated NVM memory devices were stable up to 1 × 104 s with a distinct ON/OFF ratio of 104 and were reprogrammable when the endurance test was performed. The extrapolation of the I- t curve to 105 s with corresponding current ON/OFF ratio 1 × 105 indicated a long performance stability of the NVM devices. Schottky emission, Poole-Frenkel emission, trapped-charge limited-current and Child-Langmuir law were proposed as the dominant conduction mechanisms for the fabricated NVM devices based on the obtained I- V characteristics.

  20. Host-Guest Chemistry between Perylene Diimide (PDI) Derivatives and 18-Crown-6: Enhancement in Luminescence Quantum Yield and Electrical Conductivity.

    PubMed

    Lasitha, P; Prasad, Edamana

    2016-07-18

    Perylene diimide (PDI) derivatives exhibit a high propensity for aggregation, which causes the aggregation-induced quenching of emission from the system. Host-guest chemistry is one of the best-known methods for preventing aggregation through the encapsulation of guest molecules. Herein we report the use of 18-crown-6 (18-C-6) as a host system to disaggregate suitably substituted PDI derivatives in methanol. 18-C-6 formed complexes with amino-substituted PDIs in methanol, which led to disaggregation and enhanced emission from the systems. Furthermore, the embedding of the PDI⋅18-C-6 complexes in poly(vinyl alcohol) (PVA) films generated remarkably high emission quantum yields (60-70 %) from the PDI derivatives. More importantly, the host-guest systems were tested for their ability to conduct electricity in PVA films. The electrical conductivities of the self-assembled systems in PVA were measured by electrochemical impedance spectroscopy (EIS) and the highest conductivity observed was 2.42×10(-5)  S cm(-1) .

  1. Quantum Interference in Graphene Nanoconstrictions.

    PubMed

    Gehring, Pascal; Sadeghi, Hatef; Sangtarash, Sara; Lau, Chit Siong; Liu, Junjie; Ardavan, Arzhang; Warner, Jamie H; Lambert, Colin J; Briggs, G Andrew D; Mol, Jan A

    2016-07-13

    We report quantum interference effects in the electrical conductance of chemical vapor deposited graphene nanoconstrictions fabricated using feedback controlled electroburning. The observed multimode Fabry-Pérot interferences can be attributed to reflections at potential steps inside the channel. Sharp antiresonance features with a Fano line shape are observed. Theoretical modeling reveals that these Fano resonances are due to localized states inside the constriction, which couple to the delocalized states that also give rise to the Fabry-Pérot interference patterns. This study provides new insight into the interplay between two fundamental forms of quantum interference in graphene nanoconstrictions.

  2. Aharonov-Bohm conductance through a single-channel quantum ring: persistent-current blockade and zero-mode dephasing.

    PubMed

    Dmitriev, A P; Gornyi, I V; Kachorovskii, V Yu; Polyakov, D G

    2010-07-16

    We study the effect of electron-electron interaction on transport through a tunnel-coupled single-channel ring. We find that the conductance as a function of magnetic flux shows a series of interaction-induced resonances that survive thermal averaging. The period of the series is given by the interaction strength α. The physics behind this behavior is the blocking of the tunneling current by the circular current. The main mechanism of dephasing is due to circular-current fluctuations. The dephasing rate is proportional to the tunneling rate and does not depend on α.

  3. PHYSICAL BASIS OF QUANTUM ELECTRONICS: Variation of the emission characteristics of an atom located near an ideally conducting conical surface

    NASA Astrophysics Data System (ADS)

    Klimov, Vasilii V.; Perventsev, Ya A.

    1999-10-01

    The line width and the emission frequency of an atom located near the vertex of an ideally conducting cone or inside a conical cavity in an ideal conductor are analysed. It is shown that the influence of the vertex diminishes with decrease in the vertex angle. On the other hand, the line width and the emission frequency of an atom located in a conical cavity may both increase and decrease greatly, depending on the position of the atom and on the vertex angle of the cavity. The results obtained may prove useful in the development of both monatomic microlasers and spectrally selective near-field nanoscopes.

  4. Conduction quantization in monolayer MoS2

    NASA Astrophysics Data System (ADS)

    Li, T. S.

    2016-10-01

    We study the ballistic conduction of a monolayer MoS2 subject to a spatially modulated magnetic field by using the Landauer-Buttiker formalism. The band structure depends sensitively on the field strength, and its change has profound influence on the electron conduction. The conductance is found to demonstrate multi-step behavior due to the discrete number of conduction channels. The sharp peak and rectangular structures of the conductance are stretched out as temperature increases, due to the thermal broadening of the derivative of the Fermi-Dirac distribution function. Finally, quantum behavior in the conductance of MoS2 can be observed at temperatures below 10 K.

  5. Suppression of thermal carrier escape and efficient photo-carrier generation by two-step photon absorption in InAs quantum dot intermediate-band solar cells using a dot-in-well structure

    SciTech Connect

    Asahi, S.; Teranishi, H.; Kasamatsu, N.; Kada, T.; Kaizu, T.; Kita, T.

    2014-08-14

    We investigated the effects of an increase in the barrier height on the enhancement of the efficiency of two-step photo-excitation in InAs quantum dot (QD) solar cells with a dot-in-well structure. Thermal carrier escape of electrons pumped in QD states was drastically reduced by sandwiching InAs/GaAs QDs with a high potential barrier of Al{sub 0.3}Ga{sub 0.7}As. The thermal activation energy increased with the introduction of the barrier. The high potential barrier caused suppression of thermal carrier escape and helped realize a high electron density in the QD states. We observed efficient two-step photon absorption as a result of the high occupancy of the QD states at room temperature.

  6. Universal quantum computation by discontinuous quantum walk

    SciTech Connect

    Underwood, Michael S.; Feder, David L.

    2010-10-15

    Quantum walks are the quantum-mechanical analog of random walks, in which a quantum ''walker'' evolves between initial and final states by traversing the edges of a graph, either in discrete steps from node to node or via continuous evolution under the Hamiltonian furnished by the adjacency matrix of the graph. We present a hybrid scheme for universal quantum computation in which a quantum walker takes discrete steps of continuous evolution. This ''discontinuous'' quantum walk employs perfect quantum-state transfer between two nodes of specific subgraphs chosen to implement a universal gate set, thereby ensuring unitary evolution without requiring the introduction of an ancillary coin space. The run time is linear in the number of simulated qubits and gates. The scheme allows multiple runs of the algorithm to be executed almost simultaneously by starting walkers one time step apart.

  7. Nonlinear refractive index change and optical rectification in a GaN-based step quantum wells with strong built-in electric field

    NASA Astrophysics Data System (ADS)

    Zhang, Li

    2015-11-01

    Based on the compact density matrix approach, the linear and nonlinear refractive index change (RIC) and optical rectification (OR) coefficients in a GaN-based step QW with strong built-in electric field (BEF) have been theoretically deduced and investigated in detail. The analytical electronic state is derived by the two airy functions. And the band nonparabolicity is taken into account by using an energy dependence effective mass (EDEM) method. Numerical calculations on a four-layer AlN/GaN/AlxGa1-xN/AlN step QW are performed, and the curves for the geometric factors, the linear, the nonlinear, the total RICs and the OR coefficients as functions of the structural parameters of the step QW are discussed. The features for these curves were specified and reasons for the features were explained reasonably. It is found that the decreasing of well width Lw, and step barrier width Lb and the doped concentration x in step barrier will result in the significant enhancement of the RICs. With the decrease of Lw, Lb and x, the resonant photon energies of RIC and OR coefficients have obvious blue-shift. Moreover, the RIC and OR coefficients behave different dependence on the structural parameters of the GaN-based step QWs. The profound physical reasons are also analyzed.

  8. Au-induced quantum chains on Ge(001)-symmetries, long-range order and the conduction path.

    PubMed

    Blumenstein, C; Meyer, S; Mietke, S; Schäfer, J; Bostwick, A; Rotenberg, E; Matzdorf, R; Claessen, R

    2013-01-01

    Atomic nanowires on the Au/Ge(001) surface are investigated for their structural and electronic properties using scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES). STM reveals two distinct symmetries: a c(8 × 2) describing the basic repeating distances, while the fine structure on top of the wires causes an additional superstructure of p(4 × 1). Both symmetries are long-range ordered as judged from low-energy electron diffraction. The Fermi surface is composed of almost perfectly straight sheets. Thus, the electronic states are one-dimensionally confined. Spatial dI/dV maps, where both topography and density of states (DOS) are probed simultaneously, reveal that the DOS at low energies, i.e. the conduction path, is oriented along the chain direction. This is fully consistent with the recently reported Tomonaga-Luttinger liquid phase of Au/Ge(001), with the density of states being suppressed by a power-law towards the Fermi energy. PMID:23220774

  9. Au-induced quantum chains on Ge(001)-symmetries, long-range order and the conduction path.

    PubMed

    Blumenstein, C; Meyer, S; Mietke, S; Schäfer, J; Bostwick, A; Rotenberg, E; Matzdorf, R; Claessen, R

    2013-01-01

    Atomic nanowires on the Au/Ge(001) surface are investigated for their structural and electronic properties using scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES). STM reveals two distinct symmetries: a c(8 × 2) describing the basic repeating distances, while the fine structure on top of the wires causes an additional superstructure of p(4 × 1). Both symmetries are long-range ordered as judged from low-energy electron diffraction. The Fermi surface is composed of almost perfectly straight sheets. Thus, the electronic states are one-dimensionally confined. Spatial dI/dV maps, where both topography and density of states (DOS) are probed simultaneously, reveal that the DOS at low energies, i.e. the conduction path, is oriented along the chain direction. This is fully consistent with the recently reported Tomonaga-Luttinger liquid phase of Au/Ge(001), with the density of states being suppressed by a power-law towards the Fermi energy.

  10. Au-induced quantum chains on Ge(001)—symmetries, long-range order and the conduction path

    NASA Astrophysics Data System (ADS)

    Blumenstein, C.; Meyer, S.; Mietke, S.; Schäfer, J.; Bostwick, A.; Rotenberg, E.; Matzdorf, R.; Claessen, R.

    2013-01-01

    Atomic nanowires on the Au/Ge(001) surface are investigated for their structural and electronic properties using scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES). STM reveals two distinct symmetries: a c(8 × 2) describing the basic repeating distances, while the fine structure on top of the wires causes an additional superstructure of p(4 × 1). Both symmetries are long-range ordered as judged from low-energy electron diffraction. The Fermi surface is composed of almost perfectly straight sheets. Thus, the electronic states are one-dimensionally confined. Spatial dI/dV maps, where both topography and density of states (DOS) are probed simultaneously, reveal that the DOS at low energies, i.e. the conduction path, is oriented along the chain direction. This is fully consistent with the recently reported Tomonaga-Luttinger liquid phase of Au/Ge(001), with the density of states being suppressed by a power-law towards the Fermi energy.

  11. Two-Step Reactive Aid Sintering of BaZr0.8Y0.2O3-δ Proton-Conducting Ceramics

    SciTech Connect

    Wang, Siwei; Chen, Yan; Zhang, Lingling; Ren, Cong; Chen, Fanglin; Brinkman, Kyle S.

    2015-10-14

    Ceramic-based proton conductors enable high-temperature hydrogen economy applications such as hydrogen separation membranes, fuel cells, and steam electrolyzers. BaZr0.8Y0.2O3-δ (BZY) proton-conducting oxide possesses the highest level of proton conductivity reported to date, but poor sinterability hinders its widespread utilization. Here, we report a two-step reactive aid sintering (TRAS) method involving the introduction of BaCO3 and B2O3-Li2O for the preparation of dense BZY ceramics sintered at 1500°C. The resulting BZY samples showed a pure perovskite structure with a dramatic increase in the relative density to 91.5%. In addition, the shrinkage during sintering was improved to 19.3% by a TRAS method as compared to 2.6% by the conventional solid date reaction method. Moreover, the bulk conductivity was improved due to enhanced densification, while the grain boundary conductivity decreased due to the blocking behavior of the sintering aid resulting in a decrease in the total conductivity of the samples.

  12. PHOEBE - step by step manual

    NASA Astrophysics Data System (ADS)

    Zasche, P.

    2016-03-01

    An easy step-by-step manual of PHOEBE is presented. It should serve as a starting point for the first time users of PHOEBE analyzing the eclipsing binary light curve. It is demonstrated on one particular detached system also with the downloadable data and the whole procedure is described easily till the final trustworthy fit is being reached.

  13. Observation of Rabi Splitting from Surface-plasmon Coupled Conduction-state Transitions in Electrically-excited InAs Quantum Dots

    SciTech Connect

    Passmore, Brian S.; Adams, David C.; Ribaudo, Troy; Wasserman, Daniel; Lyon, Stephen; Chow, Weng W.; Shaner, Eric A.

    2011-02-09

    We demonstrate strong coupling between a surface plasmon and intersublevel transitions in self-assembled InAs quantum dots. The surface plasmon mode exists at the interface between the semiconductor emitter structure and a periodic array of holes perforating a metallic Pd/Ge/Au film that also serves as the top electrical contact for the emitters. Spectrally narrowed quantum-dot electroluminescence was observed for devices with varying subwavelength hole spacing. Devices designed for 9, 10, and 11 μm wavelength emission also exhibit a significant spectral splitting. The association of the splitting with quantum-dot Rabi oscillation is consistent with results from a calculation of spontaneous emission from an interacting plasmonic field and quantum-dot ensemble. The fact that this Rabi oscillation can be observed in an incoherently excited, highly inhomogeneously broadened system demonstrates the utility of intersublevel transitions in quantum dots for investigations of coherent transient and quantum coherence phenomena.

  14. Quantum picturalism

    NASA Astrophysics Data System (ADS)

    Coecke, Bob

    2010-01-01

    Why did it take us 50 years since the birth of the quantum mechanical formalism to discover that unknown quantum states cannot be cloned? Yet, the proof of the 'no-cloning theorem' is easy, and its consequences and potential for applications are immense. Similarly, why did it take us 60 years to discover the conceptually intriguing and easily derivable physical phenomenon of 'quantum teleportation'? We claim that the quantum mechanical formalism doesn't support our intuition, nor does it elucidate the key concepts that govern the behaviour of the entities that are subject to the laws of quantum physics. The arrays of complex numbers are kin to the arrays of 0s and 1s of the early days of computer programming practice. Using a technical term from computer science, the quantum mechanical formalism is 'low-level'. In this review we present steps towards a diagrammatic 'high-level' alternative for the Hilbert space formalism, one which appeals to our intuition. The diagrammatic language as it currently stands allows for intuitive reasoning about interacting quantum systems, and trivialises many otherwise involved and tedious computations. It clearly exposes limitations such as the no-cloning theorem, and phenomena such as quantum teleportation. As a logic, it supports 'automation': it enables a (classical) computer to reason about interacting quantum systems, prove theorems, and design protocols. It allows for a wider variety of underlying theories, and can be easily modified, having the potential to provide the required step-stone towards a deeper conceptual understanding of quantum theory, as well as its unification with other physical theories. Specific applications discussed here are purely diagrammatic proofs of several quantum computational schemes, as well as an analysis of the structural origin of quantum non-locality. The underlying mathematical foundation of this high-level diagrammatic formalism relies on so-called monoidal categories, a product of a fairly

  15. Step-like increase of quantum yield of 1.5 μm Er-related emission in SiO{sub 2} doped with Si nanocrystals

    SciTech Connect

    Saeed, S.; Jong, E. M. L. D. de; Gregorkiewicz, T.

    2015-02-14

    We investigate the excitation dependence of the efficiency of the Si nanocrystals-mediated photoluminescence from Er{sup 3+} ions embedded in a SiO{sub 2} matrix. We show that the quantum yield of this emission increases in a step-like manner with excitation energy. The subsequent thresholds of this characteristic dependence are approximately given by the sum of the Si nanocrystals bandgap energy and multiples of 0.8 eV, corresponding to the energy of the first excited state of Er{sup 3+} ions. By comparing differently prepared materials, we explicitly demonstrate that the actual values of the threshold energies and the rate of the observed increase of the external quantum yield depend on sample characteristics—the size, the optical activity and the concentration of Si nanocrystals as well Er{sup 3+} ions to Si nanocrystals concentration ratio. In that way, detailed insights into the efficient excitation of Er{sup 3+} ions are obtained. In particular, the essential role of the hot-carrier-mediated Er excitation route is established, with a possible application perspective for highly efficient future-generation photovoltaics.

  16. STEP Experiment Requirements

    NASA Technical Reports Server (NTRS)

    Brumfield, M. L. (Compiler)

    1984-01-01

    A plan to develop a space technology experiments platform (STEP) was examined. NASA Langley Research Center held a STEP Experiment Requirements Workshop on June 29 and 30 and July 1, 1983, at which experiment proposers were invited to present more detailed information on their experiment concept and requirements. A feasibility and preliminary definition study was conducted and the preliminary definition of STEP capabilities and experiment concepts and expected requirements for support services are presented. The preliminary definition of STEP capabilities based on detailed review of potential experiment requirements is investigated. Topics discussed include: Shuttle on-orbit dynamics; effects of the space environment on damping materials; erectable beam experiment; technology for development of very large solar array deployers; thermal energy management process experiment; photovoltaic concentrater pointing dynamics and plasma interactions; vibration isolation technology; flight tests of a synthetic aperture radar antenna with use of STEP.

  17. Quantum dots and duplex-specific nuclease enabled ultrasensitive detection and serotyping of Dengue viruses in one step in a single tube.

    PubMed

    Shen, Wei; Gao, Zhiqiang

    2015-03-15

    Leveraging on the enzymatic processing of Dengue virus (DV) RNA hybridized quantum dot-capped DNA capture probes (QD-CPs), an ultrasensitive assay for the detection and serotyping of DVs is described in the report. Briefly, DV-specific DNA CPs are first capped by QDs and then conjugated to magnetic beads. In a sample solution, strands of DV RNA form heteroduplexes with the QD-CPs on the magnetic beads. The CPs together with the QDs in the heteroduplexes are subsequently cleaved off the magnetic beads by a duplex-specific nuclease (DSN), releasing the QDs to the solution, freeing the target RNA strands, and availing them for another around of hybridization with the remaining QD-CPs. After removing the magnetic beads along with unreacted (uncleaved) QD-CPs by using a permanent magnet, ultrasensitive fluorescent detection of DV is realized through the cleaved QDs. Serotyping of DV is accomplished by a judicious design of the QD-CPs. The assay combines excellent signal generation by the highly fluorescent QDs and the effortlessness of utilizing magnetic beads in the removal of the unreacted QD-CPs. The highly efficient DSN cleavage in conjunction with its excellent mismatch discrimination ability permits serotyping of DVs in one tube with excellent sensitivity and selectivity.

  18. Quantum Hall effect in quantum electrodynamics

    SciTech Connect

    Penin, Alexander A.

    2009-03-15

    We consider the quantum Hall effect in quantum electrodynamics and find a deviation from the quantum-mechanical prediction for the Hall conductivity due to radiative antiscreening of electric charge in an external magnetic field. A weak dependence of the universal von Klitzing constant on the magnetic field strength, which can possibly be observed in a dedicated experiment, is predicted.

  19. Characteristics of InAs/AlGaAs self-organized quantum dot modulation doped field effect transistors

    NASA Astrophysics Data System (ADS)

    Phillips, J.; Kamath, K.; Brock, T.; Bhattacharya, P.

    1998-06-01

    We have investigated the dc characteristics of InGaAs/AlGaAs modulation doped field effect transistors in which a layer of self-organized InAs quantum dots is inserted adjacent to the pseudomorphic quantum well channel. Distinct steps and a negative differential resistance are observed in the current-voltage characteristics at room temperature and lower temperatures. These are attributed to conduction through the bound states in the quantum dots.

  20. Photoconductivity of PbSe quantum-dot solids: dependence on ligand anchor group and length.

    PubMed

    Gao, Yunan; Aerts, Michiel; Sandeep, C S Suchand; Talgorn, Elise; Savenije, Tom J; Kinge, Sachin; Siebbeles, Laurens D A; Houtepen, Arjan J

    2012-11-27

    The assembly of quantum dots is an essential step toward many of their potential applications. To form conductive solids from colloidal quantum dots, ligand exchange is required. Here we study the influence of ligand replacement on the photoconductivity of PbSe quantum-dot solids, using the time-resolved microwave conductivity technique. Bifunctional replacing ligands with amine, thiol, or carboxylic acid anchor groups of various lengths are used to assemble quantum solids via a layer-by-layer dip-coating method. We find that when the ligand lengths are the same, the charge carrier mobility is higher in quantum-dot solids with amine ligands, while in quantum-dot solids with thiol ligands the charge carrier lifetime is longer. If the anchor group is the same, the charge carrier mobility is ligand length dependent. The results show that the diffusion length of charge carriers can reach several hundred nanometers.

  1. Quantum Chaos

    NASA Astrophysics Data System (ADS)

    Casati, Giulio; Chirikov, Boris

    2006-11-01

    in two-electron atoms R. Blümel and W. P. Reinhardt; Part III. Semiclassical Approximations: 20. Semiclassical theory of spectral rigidity M. V. Berry; 21. Semiclassical structure of trace formulas R. G. Littlejohn; 22. h-Expansion for quantum trace formulas P. Gaspard; 23. Pinball scattering B. Eckhardt, G. Russberg, P. Cvitanovic, P. E. Rosenqvist and P. Scherer; 24. Logarithm breaking time in quantum chaos G. P. Berman and G. M. Zaslavsky; 25. Semiclassical propagation: how long can it last? M. A. Sepulveda, S. Tomsovic and E. J. Heller; 26. The quantized Baker's transformation N. L. Balazs and A. Voros; 27. Classical structures in the quantized baker transformation M. Saraceno; 28. Quantum nodal points as fingerprints of classical chaos P. Leboeuf and A. Voros; 29. Chaology of action billiards A. M. Ozorio de Almeida and M. A. M. de Aguiar; Part IV. Level Statistics and Random Matrix Theory: 30. Characterization of chaotic quantum spectra and universality of level fluctuation laws O. Bohigas, M. J. Giannono, and C. Schmit; 31. Quantum chaos, localization and band random matrices F. M. Izrailev; 32. Structural invariance in channel space: a step toward understanding chaotic scattering in quantum mechanics T. H. Seligman; 33. Spectral properties of a Fermi accelerating disk R. Badrinarayanan and J. J. José; 34. Spectral properties of systems with dynamical localization T. Dittrich and U. Smilansky; 35. Unbound quantum diffusion and fractal spectra T. Geisel, R. Ketzmerick and G. Petschel; 36. Microwave studies in irregularly shaped billiards H.-J. Stöckmann, J. Stein and M. Kollman; Index.

  2. Quantum Chaos

    NASA Astrophysics Data System (ADS)

    Casati, Giulio; Chirikov, Boris

    1995-04-01

    in two-electron atoms R. Blümel and W. P. Reinhardt; Part III. Semiclassical Approximations: 20. Semiclassical theory of spectral rigidity M. V. Berry; 21. Semiclassical structure of trace formulas R. G. Littlejohn; 22. h-Expansion for quantum trace formulas P. Gaspard; 23. Pinball scattering B. Eckhardt, G. Russberg, P. Cvitanovic, P. E. Rosenqvist and P. Scherer; 24. Logarithm breaking time in quantum chaos G. P. Berman and G. M. Zaslavsky; 25. Semiclassical propagation: how long can it last? M. A. Sepulveda, S. Tomsovic and E. J. Heller; 26. The quantized Baker's transformation N. L. Balazs and A. Voros; 27. Classical structures in the quantized baker transformation M. Saraceno; 28. Quantum nodal points as fingerprints of classical chaos P. Leboeuf and A. Voros; 29. Chaology of action billiards A. M. Ozorio de Almeida and M. A. M. de Aguiar; Part IV. Level Statistics and Random Matrix Theory: 30. Characterization of chaotic quantum spectra and universality of level fluctuation laws O. Bohigas, M. J. Giannono, and C. Schmit; 31. Quantum chaos, localization and band random matrices F. M. Izrailev; 32. Structural invariance in channel space: a step toward understanding chaotic scattering in quantum mechanics T. H. Seligman; 33. Spectral properties of a Fermi accelerating disk R. Badrinarayanan and J. J. José; 34. Spectral properties of systems with dynamical localization T. Dittrich and U. Smilansky; 35. Unbound quantum diffusion and fractal spectra T. Geisel, R. Ketzmerick and G. Petschel; 36. Microwave studies in irregularly shaped billiards H.-J. Stöckmann, J. Stein and M. Kollman; Index.

  3. Quantum Oscillations in the Transverse Magnetoresistance (shubnikov - de Haas Effect) and Electronic Conduction in the Diluted Magnetic Semiconductor MERCURY(1-X)IRON(X)SELENIDE.

    NASA Astrophysics Data System (ADS)

    Vaziri, Mojtaba

    A study of the quantum oscillations in the transverse magneto- resistance (Shubnikov-de Haas effect) in oriented single crystals of Hg(,1-x)Fe(,x)Se with x (LESSTHEQ) 0.06 has been made as a function of tempera- ture (1.3 K (LESSTHEQ) T (LESSTHEQ) 35K) and for magnetic fields less than 5 Tesla. Significant(, )differences in the temperature dependence of the amp- litude of the oscillations for magnetic fields oriented along 110 , 111 , and 001 have been observed. The analysis of the data for (')H// 110 provide evidence for spin dependent scattering of the conduction electrons. Lineshape fits to the data allow estimates for the difference Dingle temperature (delta)T(,D) and the exchange enhanced effective g-factor as a function of temperature and magnetic field. It is concluded that some Fe ions, when incorporated in a HgSe host, exist in a magnetically active state. This result indicates the presence of Fe('+3) in addition to the Fe('+2) that might normally be expected in this material. In addition the amplitude of these oscillations as a function of the magnet angle for two different planes of rotation for x = 0.03 and x = 0.05 have been measured. The results clearly show two sets of zeros in the amplitude of the fundamental harmonic with completely different angular dependences. Low field zeros (H < 1 Tesla) have been identified that have a similar angular dependence as those reported for HgSe. The position of the zeros can not be explained by the combination of two different signals which result from lack of the inversion symmetry in the zinc-blende structure of the lattice. A distinct set of high field zeros (H > 1 Tesla) have also been observed which exhibit a different angular dependence than the zeros formed in HgSe. Finally, the variation in the carrier concentration as function of annealing conditions in HgSe, Hg(,1-x)Mn(,x)Se, and Hg(,1-x)Fe(,x)Se has been studied. Our results show that the carrier concentration in Hg(,1-x)Fe(,x)Se system with x

  4. Stepped nozzle

    DOEpatents

    Sutton, George P.

    1998-01-01

    An insert which allows a supersonic nozzle of a rocket propulsion system to operate at two or more different nozzle area ratios. This provides an improved vehicle flight performance or increased payload. The insert has significant advantages over existing devices for increasing nozzle area ratios. The insert is temporarily fastened by a simple retaining mechanism to the aft end of the diverging segment of the nozzle and provides for a multi-step variation of nozzle area ratio. When mounted in place, the insert provides the nozzle with a low nozzle area ratio. During flight, the retaining mechanism is released and the insert ejected thereby providing a high nozzle area ratio in the diverging nozzle segment.

  5. Stepped nozzle

    DOEpatents

    Sutton, G.P.

    1998-07-14

    An insert is described which allows a supersonic nozzle of a rocket propulsion system to operate at two or more different nozzle area ratios. This provides an improved vehicle flight performance or increased payload. The insert has significant advantages over existing devices for increasing nozzle area ratios. The insert is temporarily fastened by a simple retaining mechanism to the aft end of the diverging segment of the nozzle and provides for a multi-step variation of nozzle area ratio. When mounted in place, the insert provides the nozzle with a low nozzle area ratio. During flight, the retaining mechanism is released and the insert ejected thereby providing a high nozzle area ratio in the diverging nozzle segment. 5 figs.

  6. Probabilistic authenticated quantum dialogue

    NASA Astrophysics Data System (ADS)

    Hwang, Tzonelih; Luo, Yi-Ping

    2015-12-01

    This work proposes a probabilistic authenticated quantum dialogue (PAQD) based on Bell states with the following notable features. (1) In our proposed scheme, the dialogue is encoded in a probabilistic way, i.e., the same messages can be encoded into different quantum states, whereas in the state-of-the-art authenticated quantum dialogue (AQD), the dialogue is encoded in a deterministic way; (2) the pre-shared secret key between two communicants can be reused without any security loophole; (3) each dialogue in the proposed PAQD can be exchanged within only one-step quantum communication and one-step classical communication. However, in the state-of-the-art AQD protocols, both communicants have to run a QKD protocol for each dialogue and each dialogue requires multiple quantum as well as classical communicational steps; (4) nevertheless, the proposed scheme can resist the man-in-the-middle attack, the modification attack, and even other well-known attacks.

  7. One-step synthesis of vertically aligned anatase thornbush-like TiO2 nanowire arrays on transparent conducting oxides for solid-state dye-sensitized solar cells.

    PubMed

    Roh, Dong Kyu; Chi, Won Seok; Ahn, Sung Hoon; Jeon, Harim; Kim, Jong Hak

    2013-08-01

    Herein, we report a facile synthesis of high-density anatase-phase vertically aligned thornbush-like TiO2 nanowires (TBWs) on transparent conducting oxide glasses. Morphologically controllable TBW arrays of 9 μm in length are generated through a one-step hydrothermal reaction at 200 °C over 11 h using potassium titanium oxide oxalate dehydrate, diethylene glycol (DEG), and water. The TBWs consist of a large number of nanoplates or nanorods, as confirmed by SEM and TEM imaging. The morphologies of TBWs are controllable by adjusting DEG/water ratios. TBW diameters gradually decrease from 600 (TBW600) to 400 (TBW400) to 200 nm (TBW200) and morphologies change from nanoplates to nanorods with an increase in DEG content. TBWs are utilized as photoanodes for quasi-solid-state dye-sensitized solar cells (qssDSSCs) and solid-state DSSCs (ssDSSCs). The energy-conversion efficiency of qssDSSCs is in the order: TBW200 (5.2%)>TBW400 (4.5%)>TBW600 (3.4%). These results can be attributed to the different surface areas, light-scattering effects, and charge transport rates, as confirmed by dye-loading measurements, reflectance spectroscopy, and incident photon-to-electron conversion efficiency and intensity-modulated photovoltage spectroscopy/intensity-modulated photocurrent spectroscopy analyses. TBW200 is further treated with a graft-copolymer-directed organized mesoporous TiO2 to increase the surface area and interconnectivity of TBWs. As a result, the energy-conversion efficiency of the ssDSSC increases to 6.7% at 100 mW cm(-2) , which is among the highest values for N719-dye-based ssDSSCs.

  8. Relativistic Quantum Scars

    SciTech Connect

    Huang, Liang; Lai Yingcheng; Ferry, David K.; Goodnick, Stephen M.; Akis, Richard

    2009-07-31

    The concentrations of wave functions about classical periodic orbits, or quantum scars, are a fundamental phenomenon in physics. An open question is whether scarring can occur in relativistic quantum systems. To address this question, we investigate confinements made of graphene whose classical dynamics are chaotic and find unequivocal evidence of relativistic quantum scars. The scarred states can lead to strong conductance fluctuations in the corresponding open quantum dots via the mechanism of resonant transmission.

  9. Quantum exhaustive key search with simplified-DES as a case study.

    PubMed

    Almazrooie, Mishal; Samsudin, Azman; Abdullah, Rosni; Mutter, Kussay N

    2016-01-01

    To evaluate the security of a symmetric cryptosystem against any quantum attack, the symmetric algorithm must be first implemented on a quantum platform. In this study, a quantum implementation of a classical block cipher is presented. A quantum circuit for a classical block cipher of a polynomial size of quantum gates is proposed. The entire work has been tested on a quantum mechanics simulator called libquantum. First, the functionality of the proposed quantum cipher is verified and the experimental results are compared with those of the original classical version. Then, quantum attacks are conducted by using Grover's algorithm to recover the secret key. The proposed quantum cipher is used as a black box for the quantum search. The quantum oracle is then queried over the produced ciphertext to mark the quantum state, which consists of plaintext and key qubits. The experimental results show that for a key of n-bit size and key space of N such that [Formula: see text], the key can be recovered in [Formula: see text] computational steps. PMID:27652067

  10. Quantum exhaustive key search with simplified-DES as a case study.

    PubMed

    Almazrooie, Mishal; Samsudin, Azman; Abdullah, Rosni; Mutter, Kussay N

    2016-01-01

    To evaluate the security of a symmetric cryptosystem against any quantum attack, the symmetric algorithm must be first implemented on a quantum platform. In this study, a quantum implementation of a classical block cipher is presented. A quantum circuit for a classical block cipher of a polynomial size of quantum gates is proposed. The entire work has been tested on a quantum mechanics simulator called libquantum. First, the functionality of the proposed quantum cipher is verified and the experimental results are compared with those of the original classical version. Then, quantum attacks are conducted by using Grover's algorithm to recover the secret key. The proposed quantum cipher is used as a black box for the quantum search. The quantum oracle is then queried over the produced ciphertext to mark the quantum state, which consists of plaintext and key qubits. The experimental results show that for a key of n-bit size and key space of N such that [Formula: see text], the key can be recovered in [Formula: see text] computational steps.

  11. Quantum Walk Schemes for Universal Quantum Computation

    NASA Astrophysics Data System (ADS)

    Underwood, Michael S.

    Random walks are a powerful tool for the efficient implementation of algorithms in classical computation. Their quantum-mechanical analogues, called quantum walks, hold similar promise. Quantum walks provide a model of quantum computation that has recently been shown to be equivalent in power to the standard circuit model. As in the classical case, quantum walks take place on graphs and can undergo discrete or continuous evolution, though quantum evolution is unitary and therefore deterministic until a measurement is made. This thesis considers the usefulness of continuous-time quantum walks to quantum computation from the perspectives of both their fundamental power under various formulations, and their applicability in practical experiments. In one extant scheme, logical gates are effected by scattering processes. The results of an exhaustive search for single-qubit operations in this model are presented. It is shown that the number of distinct operations increases exponentially with the number of vertices in the scattering graph. A catalogue of all graphs on up to nine vertices that implement single-qubit unitaries at a specific set of momenta is included in an appendix. I develop a novel scheme for universal quantum computation called the discontinuous quantum walk, in which a continuous-time quantum walker takes discrete steps of evolution via perfect quantum state transfer through small 'widget' graphs. The discontinuous quantum-walk scheme requires an exponentially sized graph, as do prior discrete and continuous schemes. To eliminate the inefficient vertex resource requirement, a computation scheme based on multiple discontinuous walkers is presented. In this model, n interacting walkers inhabiting a graph with 2n vertices can implement an arbitrary quantum computation on an input of length n, an exponential savings over previous universal quantum walk schemes. This is the first quantum walk scheme that allows for the application of quantum error correction

  12. Quantum state transfer via Bloch oscillations.

    PubMed

    Tamascelli, Dario; Olivares, Stefano; Rossotti, Stefano; Osellame, Roberto; Paris, Matteo G A

    2016-05-18

    The realization of reliable quantum channels, able to transfer a quantum state with high fidelity, is a fundamental step in the construction of scalable quantum devices. In this paper we describe a transmission scheme based on the genuinely quantum effect known as Bloch oscillations. The proposed protocol makes it possible to carry a quantum state over different distances with a minimal engineering of the transmission medium and can be implemented and verified on current quantum technology hardware.

  13. Quantum state transfer via Bloch oscillations

    PubMed Central

    Tamascelli, Dario; Olivares, Stefano; Rossotti, Stefano; Osellame, Roberto; Paris, Matteo G. A.

    2016-01-01

    The realization of reliable quantum channels, able to transfer a quantum state with high fidelity, is a fundamental step in the construction of scalable quantum devices. In this paper we describe a transmission scheme based on the genuinely quantum effect known as Bloch oscillations. The proposed protocol makes it possible to carry a quantum state over different distances with a minimal engineering of the transmission medium and can be implemented and verified on current quantum technology hardware. PMID:27189630

  14. Quantum state transfer via Bloch oscillations

    NASA Astrophysics Data System (ADS)

    Tamascelli, Dario; Olivares, Stefano; Rossotti, Stefano; Osellame, Roberto; Paris, Matteo G. A.

    2016-05-01

    The realization of reliable quantum channels, able to transfer a quantum state with high fidelity, is a fundamental step in the construction of scalable quantum devices. In this paper we describe a transmission scheme based on the genuinely quantum effect known as Bloch oscillations. The proposed protocol makes it possible to carry a quantum state over different distances with a minimal engineering of the transmission medium and can be implemented and verified on current quantum technology hardware.

  15. Baby steps.

    PubMed

    Bader, E J; Truax, H

    1991-01-01

    The focus of the discussion of US national environmental efforts on population growth issues is on carrying capacity, the impact of the antiabortion movement, the insensitivity of some population control advocated to people of color, and congressional and presidential actions. Efforts are being made to surmount the mistrust that has characterized efforts to deal with population issues. The World Wildlife Fund, the Sierra Club, and the National Audubon Society recognize the need for population stabilization, albeit with meager budgets. Carrying capacity is the number of people the earth can sustain without rapidly depleting non-renewable resources or degrading resources necessary to sustain life. In 1970, Earth Day called for stabilization of the global population, but most celebrations of Earth Day in 1990 did not recognize this. Sensitive issues are involved, and the abortion controversy has muffled open forums on population growth. Lobbyists were successful in having the US withdraw funding for international family planning (FP) programs that had abortion components. Then Reagan eliminated all funding to the UN Fund for Population Activities, because of China's FP policies. The results for women have been disastrous. Zero Population Growth has been conducting information meetings for environmental groups. The National wildlife Federation has a new program linking population and environmental issues but will not deal with the issue of abortion. A Philadelphia editorial recommended implanted contraceptives for welfare mothers, which raised fears of the reemergence of the eugenic movement which sought involuntary sterilization or population control for the poor. Another effort was to protect the US from immigration as a way of curbing population growth. Meaningful change means education women, changing unfavorable survival conditions, and heeding the reasons women have children. Japan's FP Association criticizes population control efforts undertaken for economic and

  16. Publishing Ethical Research: A Step-by-Step Overview

    ERIC Educational Resources Information Center

    Wester, Kelly L.

    2011-01-01

    To publish ethical research, one must conduct research responsibly, making ethical choices from the inception of the research idea and throughout the research process. Conducting and publishing ethical research is important because of the impact the results will have on the counseling profession. Steps to consider are discussed.

  17. Quantum robots plus environments.

    SciTech Connect

    Benioff, P.

    1998-07-23

    A quantum robot is a mobile quantum system, including an on board quantum computer and needed ancillary systems, that interacts with an environment of quantum systems. Quantum robots carry out tasks whose goals include making specified changes in the state of the environment or carrying out measurements on the environment. The environments considered so far, oracles, data bases, and quantum registers, are seen to be special cases of environments considered here. It is also seen that a quantum robot should include a quantum computer and cannot be simply a multistate head. A model of quantum robots and their interactions is discussed in which each task, as a sequence of alternating computation and action phases,is described by a unitary single time step operator T {approx} T{sub a} + T{sub c} (discrete space and time are assumed). The overall system dynamics is described as a sum over paths of completed computation (T{sub c}) and action (T{sub a}) phases. A simple example of a task, measuring the distance between the quantum robot and a particle on a 1D lattice with quantum phase path dispersion present, is analyzed. A decision diagram for the task is presented and analyzed.

  18. Towards Quantum Plasmonic Networks

    DOE PAGES

    Holtfrerich, M.W.; Dowran, M.; Lawrie, Benjamin J; Pooser, Raphael C; Marino, Alberto

    2016-01-01

    We demonstrate the transduction of macroscopic quantum entanglement by independent, distant plasmonic structures embedded in separate thin silver films. In particular, we show that the plasmon-mediated transmission through each film conserves spatially dependent, entangled quantum images, opening the door for the implementation of parallel quantum protocols, super-resolution imaging, and quantum plasmonic sensing geometries at the nanoscale level. The conservation of quantum information by the transduction process shows that continuous variable multi-mode entanglement is momentarily transferred from entangled beams of light to the space-like separated, completely independent plasmonic structures, thus providing a first important step toward establishing a multichannel quantum networkmore » across separate solid-state substrates.« less

  19. Towards Quantum Plasmonic Networks

    SciTech Connect

    Holtfrerich, M.W.; Dowran, M.; Lawrie, Benjamin J; Pooser, Raphael C; Marino, Alberto

    2016-01-01

    We demonstrate the transduction of macroscopic quantum entanglement by independent, distant plasmonic structures embedded in separate thin silver films. In particular, we show that the plasmon-mediated transmission through each film conserves spatially dependent, entangled quantum images, opening the door for the implementation of parallel quantum protocols, super-resolution imaging, and quantum plasmonic sensing geometries at the nanoscale level. The conservation of quantum information by the transduction process shows that continuous variable multi-mode entanglement is momentarily transferred from entangled beams of light to the space-like separated, completely independent plasmonic structures, thus providing a first important step toward establishing a multichannel quantum network across separate solid-state substrates.

  20. Quantum Zeno effect

    NASA Astrophysics Data System (ADS)

    Petrosky, T.; Tasaki, S.; Prigogine, I.

    1991-01-01

    In 1977, Misra and Sudarshan showed, based on the quantum measurement theory, that an unstable particle will never be found to decay when it is continuously observed. They called it the quantum Zeno effect (or paradox). More generally the quantum Zeno effect is associated to the inhibition of transitions by frequent measurements. This possibility has attracted much interest over the last years. Recently, Itano, Heinzen, Bollinger and Wineland have reported that they succeeded in observing the quantum Zeno effect. This would indeed be an important step towards the understanding of the role of the observer in quantum mechanics. However, in the present paper, we will show that their results can be recovered through conventional quantum mechanics and do not involve a repeated reduction (or collapse) of the wave function.

  1. The use of bulk states to accelerate the band edge statecalculation of a semiconductor quantum dot

    SciTech Connect

    Vomel, Christof; Tomov, Stanimire Z.; Wang, Lin-Wang; Marques,Osni A.; Dongarra, Jack J.

    2006-05-10

    We present a new technique to accelerate the convergence of the folded spectrum method in empirical pseudopotential band edge state calculations for colloidal quantum dots. We use bulk band states of the materials constituent of the quantum dot to construct initial vectors and a preconditioner. We apply these to accelerate the convergence of the folded spectrum method for the interior states at the top of the valence and the bottom of the conduction band. For large CdSe quantum dots, the number of iteration steps until convergence decreases by about a factor of 4 compared to previous calculations.

  2. Enhanced electrocatalytic activity of the Au-electrodeposited Pt nanoparticles-coated conducting oxide for the quantum dot-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Yoon, Yeung-Pil; Kim, Jae-Hong; Kang, Soon-Hyung; Kim, Hyunsoo; Choi, Chel-Jong; Kim, Kyong-Kook; Ahn, Kwang-Soon

    2014-08-01

    Au was electrodeposited potentiostatically at 0.3 V for 5 min on nanoporous Pt nanoparticle-coated F-doped SnO2 (FTO/Pt) substrates. For comparison, Au-electrodeposited FTO (FTO/Au) and Au-uncoated FTO/Pt were prepared. FTO/Au showed large-sized Au clusters dispersed sparsely over FTO, which resulted in lower electrocatalytic activity than FTO/Pt. In contrast, FTO/Pt exhibited poor stability unlike FTO/Au due to poisoning by the adsorption of sulfur species. The Au-electrodeposited FTO/Pt (FTO/Pt/Au) consisted of small Au clusters deposited over the entire area of Pt due to the effective Au nucleation provided by nanoporous metallic Pt. FTO/Pt/Au exhibited enhanced electrocatalytic activity and excellent stability because the small Au particles well-dispersed over the nanoporous metallic Pt network provided numerous electrochemical reaction sites, and the Pt surface was not exposed to the electrolyte. When FTO/Pt/Au was used as the counter electrode (CE) of a quantum dot-sensitized solar cell, the significantly enhanced electrocatalytic activity of the FTO/Pt/Au CE facilitated the reduction reaction of Sn2- + 2e- (CE) → Sn-12- + S2- at the CE/electrolyte interface, resulting in a significantly hindered recombination reaction, Sn2- + 2e- (TiO2 in the photoanode) → Sn-12- + S2-, and significantly improved overall energy conversion efficiency.

  3. PHYSICAL BASIS OF QUANTUM ELECTRONICS: Frequency shift of radiation of an atom near a cluster of two perfectly conducting spherical nanoparticles

    NASA Astrophysics Data System (ADS)

    Guzatov, D. V.

    2005-10-01

    Expressions for the frequency shift of radiation of an atom located near a cluster of two perfectly conducting spherical nanoparticles are obtained within the framework of a classical model. The asymptotic expression is found for the radiation frequency shift of an atom located between spheres approaching each other.

  4. Enhanced electrocatalytic activity of the Au-electrodeposited Pt nanoparticles-coated conducting oxide for the quantum dot-sensitized solar cells

    SciTech Connect

    Yoon, Yeung-Pil; Kim, Jae-Hong; Ahn, Kwang-Soon; Kang, Soon-Hyung; Kim, Hyunsoo; Choi, Chel-Jong; Kim, Kyong-Kook

    2014-08-25

    Au was electrodeposited potentiostatically at 0.3 V for 5 min on nanoporous Pt nanoparticle-coated F-doped SnO{sub 2} (FTO/Pt) substrates. For comparison, Au-electrodeposited FTO (FTO/Au) and Au-uncoated FTO/Pt were prepared. FTO/Au showed large-sized Au clusters dispersed sparsely over FTO, which resulted in lower electrocatalytic activity than FTO/Pt. In contrast, FTO/Pt exhibited poor stability unlike FTO/Au due to poisoning by the adsorption of sulfur species. The Au-electrodeposited FTO/Pt (FTO/Pt/Au) consisted of small Au clusters deposited over the entire area of Pt due to the effective Au nucleation provided by nanoporous metallic Pt. FTO/Pt/Au exhibited enhanced electrocatalytic activity and excellent stability because the small Au particles well-dispersed over the nanoporous metallic Pt network provided numerous electrochemical reaction sites, and the Pt surface was not exposed to the electrolyte. When FTO/Pt/Au was used as the counter electrode (CE) of a quantum dot-sensitized solar cell, the significantly enhanced electrocatalytic activity of the FTO/Pt/Au CE facilitated the reduction reaction of S{sub n}{sup 2− }+ 2e{sup −} (CE) → S{sub n−1}{sup 2−} + S{sup 2−} at the CE/electrolyte interface, resulting in a significantly hindered recombination reaction, S{sub n}{sup 2− }+ 2e{sup −} (TiO{sub 2} in the photoanode) → S{sub n-1}{sup 2−} + S{sup 2−}, and significantly improved overall energy conversion efficiency.

  5. Quantum Hall conductance and de Haas-van Alphen oscillation in a tight-binding model with electron and hole pockets for (TMTSF) 2NO3

    NASA Astrophysics Data System (ADS)

    Kishigi, Keita; Hasegawa, Yasumasa

    2016-08-01

    Quantized Hall conductance and de Haas-van Alphen (dHvA) oscillation are studied theoretically in the tight-binding model for (TMTSF) 2NO3 , in which there are small pockets of electrons and holes due to the periodic potentials of anion ordering in the a direction. The magnetic field is treated by hoppings as complex numbers due to the phase caused by the vector potential, i.e., Peierls substitution. In realistic values of parameters and the magnetic field, the energy as a function of the magnetic field (Hofstadter butterfly diagram) is obtained. It is shown that the energy levels are broadened and the gaps are closed or almost closed periodically as a function of the inverse magnetic field, which is not seen in the semiclassical theory of the magnetic breakdown. The Hall conductance is quantized with an integer obtained by the Diophantine equation when the chemical potential lies in an energy gap. When electrons or holes are doped in this system, the Hall conductance is quantized in some regions of a magnetic field but it is not quantized in other regions of a magnetic field due to the broadening of the Landau levels. The amplitude of the dHvA oscillation at zero temperature decreases as the magnetic field increases, while it is constant in the semiclassical Lifshitz Kosevich formula.

  6. Quantum computing

    PubMed Central

    Li, Shu-Shen; Long, Gui-Lu; Bai, Feng-Shan; Feng, Song-Lin; Zheng, Hou-Zhi

    2001-01-01

    Quantum computing is a quickly growing research field. This article introduces the basic concepts of quantum computing, recent developments in quantum searching, and decoherence in a possible quantum dot realization. PMID:11562459

  7. Quantum cost for sending entanglement.

    PubMed

    Streltsov, Alexander; Kampermann, Hermann; Bruß, Dagmar

    2012-06-22

    Establishing quantum entanglement between two distant parties is an essential step of many protocols in quantum information processing. One possibility for providing long-distance entanglement is to create an entangled composite state within a lab and then physically send one subsystem to a distant lab. However, is this the "cheapest" way? Here, we investigate the minimal "cost" that is necessary for establishing a certain amount of entanglement between two distant parties. We prove that this cost is intrinsically quantum, and is specified by quantum correlations. Our results provide an optimal protocol for entanglement distribution and show that quantum correlations are the essential resource for this task.

  8. Electrically conductive composite material

    DOEpatents

    Clough, R.L.; Sylwester, A.P.

    1988-06-20

    An electrically conductive composite material is disclosed which comprises a conductive open-celled, low density, microcellular carbon foam filled with a non-conductive polymer or resin. The composite material is prepared in a two-step process consisting of first preparing the microcellular carbon foam from a carbonizable polymer or copolymer using a phase separation process, then filling the carbon foam with the desired non-conductive polymer or resin. The electrically conductive composites of the present invention has a uniform and consistent pattern of filler distribution, and as a result is superior over prior art materials when used in battery components, electrodes, and the like. 2 figs.

  9. Electrically conductive composite material

    DOEpatents

    Clough, Roger L.; Sylwester, Alan P.

    1989-01-01

    An electrically conductive composite material is disclosed which comprises a conductive open-celled, low density, microcellular carbon foam filled with a non-conductive polymer or resin. The composite material is prepared in a two-step process consisting of first preparing the microcellular carbon foam from a carbonizable polymer or copolymer using a phase separation process, then filling the carbon foam with the desired non-conductive polymer or resin. The electrically conductive composites of the present invention has a uniform and consistant pattern of filler distribution, and as a result is superior over prior art materials when used in battery components, electrodes, and the like.

  10. Towards quantum chemistry on a quantum computer.

    PubMed

    Lanyon, B P; Whitfield, J D; Gillett, G G; Goggin, M E; Almeida, M P; Kassal, I; Biamonte, J D; Mohseni, M; Powell, B J; Barbieri, M; Aspuru-Guzik, A; White, A G

    2010-02-01

    Exact first-principles calculations of molecular properties are currently intractable because their computational cost grows exponentially with both the number of atoms and basis set size. A solution is to move to a radically different model of computing by building a quantum computer, which is a device that uses quantum systems themselves to store and process data. Here we report the application of the latest photonic quantum computer technology to calculate properties of the smallest molecular system: the hydrogen molecule in a minimal basis. We calculate the complete energy spectrum to 20 bits of precision and discuss how the technique can be expanded to solve large-scale chemical problems that lie beyond the reach of modern supercomputers. These results represent an early practical step toward a powerful tool with a broad range of quantum-chemical applications. PMID:21124400

  11. Writing the Winning Dissertation: A Step-By-Step Guide.

    ERIC Educational Resources Information Center

    Glatthorn, Allan A.

    This book is a practical guide to researching and writing the doctoral dissertation or master's thesis. Part 1 offers seven chapters on preparatory steps: laying the groundwork for the thesis and dissertation; finding a research problem; conducting a focused review of the literature; making a preliminary choice of methodology; organizing and…

  12. Toward quantum plasmonic networks

    DOE PAGES

    Holtfrerich, M. W.; Dowran, M.; Davidson, R.; Lawrie, B. J.; Pooser, R. C.; Marino, A. M.

    2016-08-30

    Here, we demonstrate the transduction of macroscopic quantum entanglement by independent, distant plasmonic structures embedded in separate thin silver films. In particular, we show that the plasmon-mediated transmission through each film conserves spatially dependent, entangled quantum images, opening the door for the implementation of parallel quantum protocols, super-resolution imaging, and quantum plasmonic sensing geometries at the nanoscale level. The conservation of quantum information by the transduction process shows that continuous variable multi-mode entanglement is momentarily transferred from entangled beams of light to the space-like separated, completely independent plasmonic structures, thus providing a first important step toward establishing a multichannel quantummore » network across separate solid-state substrates.« less

  13. Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Auletta, Gennaro; Fortunato, Mauro; Parisi, Giorgio

    2014-01-01

    Introduction; Part I. Basic Features of Quantum Mechanics: 1. From classical mechanics to quantum mechanics; 2. Quantum observable and states; 3. Quantum dynamics; 4. Examples of quantum dynamics; 5. Density matrix; Part II. More Advanced Topics: 6. Angular momentum and spin; 7. Identical particles; 8. Symmetries and conservation laws; 9. The measurement problem; Part III. Matter and Light: 10. Perturbations and approximation methods; 11. Hydrogen and helium atoms; 12. Hydrogen molecular ion; 13. Quantum optics; Part IV. Quantum Information: State and Correlations: 14. Quantum theory of open systems; 15. State measurement in quantum mechanics; 16. Entanglement: non-separability; 17. Entanglement: quantum information; References; Index.

  14. Effects of some aliphatic alcohols on the conductance change caused by a quantum of acetylcholine at the toad end-plate.

    PubMed Central

    Gage, P W; McBurney, R N; Schneider, G T

    1975-01-01

    1. The post-synaptic effects of the aliphatic alcohols, ethanol to hexanol, were investigated at the neuromuscular junctions of toads, with particular emphasis on the effects of ethanol. 2. The alcohols increased the amplitude and duration of miniature end-plate potentials. It is shown that this effect was due to the prolongation of the decay phase of miniature end-plate currents (m.e.p.c.s). There was no effect of alcohols on the growth phase of m.e.p.c.s. 3. The prolonged decay of m.e.p.c.s in ethanol remained exponential and was normally sensitive to membrane potential. Prolonged m.e.p.c.s were associated with an equivalent prolongation of the mean duration of elementary events, as determined from power spectra of acetylcholine noise in 0-5 M ethanol. 4. The relationship betweeen the time constant of decay of m.e.p.c.s (tau) and the concentration of an alcohol of carbon chain length N (C-N) was exponential, conforming to the equation tau equals tau-s exp (B-N-C-N), in which tau-s is the decay time constant in standard solution and B-N is a constant, different for each alcohol. 5. There was also an exponential relationship between B-N and N, which closely followed the relationship between membrane-buffer partition coefficient and carbon chain length for the different alcohols, indicating that the alcohols are active in the lipid phase of the post-synaptic membrane. 6. It is suggested that the alcohols act by causing a change in the dielectric constant of the post-synaptic membrane which forms the environment of the rate-limiting reaction responsible for the decay of the end-plate conductance. On the assumption that this reaction involves dipoles, it is shown that the small changes in dielectric constant, calculated from the partition coefficients of the alcohols and by assuming an initial lipid dielectric constant of 3, would give an exponential relationship between the time constant of decay of m.e.p.c.s and alcohol concentration. 7. The results support the

  15. Electroluminescence of quantum-dash-based quantum cascade laser structures

    SciTech Connect

    Liverini, V.; Bismuto, A.; Nevou, L.; Beck, M.; Faist, J.

    2011-12-23

    We developed two mid-infrared quantum cascade structures based on InAs quantum dashes. The dashes were embedded either in AlInGaAs lattice-matched to InP or in tensile-strained AlInAs. The devices emit between 7 and 11 {mu}m and are a step forward in the development of quantum cascade lasers based on 3-D confined active regions.

  16. Stepping motor controller

    DOEpatents

    Bourret, S.C.; Swansen, J.E.

    1982-07-02

    A stepping motor is microprocessor controlled by digital circuitry which monitors the output of a shaft encoder adjustably secured to the stepping motor and generates a subsequent stepping pulse only after the preceding step has occurred and a fixed delay has expired. The fixed delay is variable on a real-time basis to provide for smooth and controlled deceleration.

  17. Stepping motor controller

    DOEpatents

    Bourret, Steven C.; Swansen, James E.

    1984-01-01

    A stepping motor is microprocessingly controlled by digital circuitry which monitors the output of a shaft encoder adjustably secured to the stepping motor and generates a subsequent stepping pulse only after the preceding step has occurred and a fixed delay has expired. The fixed delay is variable on a real-time basis to provide for smooth and controlled deceleration.

  18. Step-Growth Polymerization.

    ERIC Educational Resources Information Center

    Stille, J. K.

    1981-01-01

    Following a comparison of chain-growth and step-growth polymerization, focuses on the latter process by describing requirements for high molecular weight, step-growth polymerization kinetics, synthesis and molecular weight distribution of some linear step-growth polymers, and three-dimensional network step-growth polymers. (JN)

  19. Quantum cloning attacks against PUF-based quantum authentication systems

    NASA Astrophysics Data System (ADS)

    Yao, Yao; Gao, Ming; Li, Mo; Zhang, Jian

    2016-08-01

    With the advent of physical unclonable functions (PUFs), PUF-based quantum authentication systems have been proposed for security purposes, and recently, proof-of-principle experiment has been demonstrated. As a further step toward completing the security analysis, we investigate quantum cloning attacks against PUF-based quantum authentication systems and prove that quantum cloning attacks outperform the so-called challenge-estimation attacks. We present the analytical expression of the false-accept probability by use of the corresponding optimal quantum cloning machines and extend the previous results in the literature. In light of these findings, an explicit comparison is made between PUF-based quantum authentication systems and quantum key distribution protocols in the context of cloning attacks. Moreover, from an experimental perspective, a trade-off between the average photon number and the detection efficiency is discussed in detail.

  20. Quantum memory Quantum memory

    NASA Astrophysics Data System (ADS)

    Le Gouët, Jean-Louis; Moiseev, Sergey

    2012-06-01

    Interaction of quantum radiation with multi-particle ensembles has sparked off intense research efforts during the past decade. Emblematic of this field is the quantum memory scheme, where a quantum state of light is mapped onto an ensemble of atoms and then recovered in its original shape. While opening new access to the basics of light-atom interaction, quantum memory also appears as a key element for information processing applications, such as linear optics quantum computation and long-distance quantum communication via quantum repeaters. Not surprisingly, it is far from trivial to practically recover a stored quantum state of light and, although impressive progress has already been accomplished, researchers are still struggling to reach this ambitious objective. This special issue provides an account of the state-of-the-art in a fast-moving research area that makes physicists, engineers and chemists work together at the forefront of their discipline, involving quantum fields and atoms in different media, magnetic resonance techniques and material science. Various strategies have been considered to store and retrieve quantum light. The explored designs belong to three main—while still overlapping—classes. In architectures derived from photon echo, information is mapped over the spectral components of inhomogeneously broadened absorption bands, such as those encountered in rare earth ion doped crystals and atomic gases in external gradient magnetic field. Protocols based on electromagnetic induced transparency also rely on resonant excitation and are ideally suited to the homogeneous absorption lines offered by laser cooled atomic clouds or ion Coulomb crystals. Finally off-resonance approaches are illustrated by Faraday and Raman processes. Coupling with an optical cavity may enhance the storage process, even for negligibly small atom number. Multiple scattering is also proposed as a way to enlarge the quantum interaction distance of light with matter. The

  1. Quantum-enhanced absorption refrigerators

    NASA Astrophysics Data System (ADS)

    Correa, Luis A.; Palao, José P.; Alonso, Daniel; Adesso, Gerardo

    2014-02-01

    Thermodynamics is a branch of science blessed by an unparalleled combination of generality of scope and formal simplicity. Based on few natural assumptions together with the four laws, it sets the boundaries between possible and impossible in macroscopic aggregates of matter. This triggered groundbreaking achievements in physics, chemistry and engineering over the last two centuries. Close analogues of those fundamental laws are now being established at the level of individual quantum systems, thus placing limits on the operation of quantum-mechanical devices. Here we study quantum absorption refrigerators, which are driven by heat rather than external work. We establish thermodynamic performance bounds for these machines and investigate their quantum origin. We also show how those bounds may be pushed beyond what is classically achievable, by suitably tailoring the environmental fluctuations via quantum reservoir engineering techniques. Such superefficient quantum-enhanced cooling realises a promising step towards the technological exploitation of autonomous quantum refrigerators.

  2. Quantum-enhanced absorption refrigerators.

    PubMed

    Correa, Luis A; Palao, José P; Alonso, Daniel; Adesso, Gerardo

    2014-01-01

    Thermodynamics is a branch of science blessed by an unparalleled combination of generality of scope and formal simplicity. Based on few natural assumptions together with the four laws, it sets the boundaries between possible and impossible in macroscopic aggregates of matter. This triggered groundbreaking achievements in physics, chemistry and engineering over the last two centuries. Close analogues of those fundamental laws are now being established at the level of individual quantum systems, thus placing limits on the operation of quantum-mechanical devices. Here we study quantum absorption refrigerators, which are driven by heat rather than external work. We establish thermodynamic performance bounds for these machines and investigate their quantum origin. We also show how those bounds may be pushed beyond what is classically achievable, by suitably tailoring the environmental fluctuations via quantum reservoir engineering techniques. Such superefficient quantum-enhanced cooling realises a promising step towards the technological exploitation of autonomous quantum refrigerators. PMID:24492860

  3. Quantum Communication

    NASA Astrophysics Data System (ADS)

    Weinfurter, Harald; Zeilinger, Anton

    Quantum entanglement lies at the heart of the new field of quantum communication and computation. For a long time, entanglement was seen just as one of those fancy features which make quantum mechanics so counterintuitive. But recently, quantum information theory has shown the tremendous importance of quantum correlations for the formulation of new methods of information transfer and for algorithms exploiting the capabilities of quantum computers.This chapter describes the first experimental realizations of quantum communication schemes using entangled photon pairs. We show how to make communication secure against eavesdropping using entanglement-based quantum cryptography, how to increase the information capacity of a quantum channel by quantum dense coding and, finally, how to communicate quantum information itself in the process of quantum teleportation.

  4. Step by Step: Avoiding Spiritual Bypass in 12-Step Work

    ERIC Educational Resources Information Center

    Cashwell, Craig S.; Clarke, Philip B.; Graves, Elizabeth G.

    2009-01-01

    With spirituality as a cornerstone, 12-step groups serve a vital role in the recovery community. It is important for counselors to be mindful, however, of the potential for clients to be in spiritual bypass, which likely will undermine the recovery process.

  5. Phonon scattering in graphene over substrate steps

    SciTech Connect

    Sevinçli, H.; Brandbyge, M.

    2014-10-13

    We calculate the effect on phonon transport of substrate-induced bends in graphene. We consider bending induced by an abrupt kink in the substrate, and provide results for different step-heights and substrate interaction strengths. We find that individual substrate steps reduce thermal conductance in the range between 5% and 47%. We also consider the transmission across linear kinks formed by adsorption of atomic hydrogen at the bends and find that individual kinks suppress thermal conduction substantially, especially at high temperatures. Our analysis show that substrate irregularities can be detrimental for thermal conduction even for small step heights.

  6. Communications: quantum teleportation across the Danube.

    PubMed

    Ursin, Rupert; Jennewein, Thomas; Aspelmeyer, Markus; Kaltenbaek, Rainer; Lindenthal, Michael; Walther, Philip; Zeilinger, Anton

    2004-08-19

    Efficient long-distance quantum teleportation is crucial for quantum communication and quantum networking schemes. Here we describe the high-fidelity teleportation of photons over a distance of 600 metres across the River Danube in Vienna, with the optimal efficiency that can be achieved using linear optics. Our result is a step towards the implementation of a quantum repeater, which will enable pure entanglement to be shared between distant parties in a public environment and eventually on a worldwide scale.

  7. Quantum simulation

    NASA Astrophysics Data System (ADS)

    Georgescu, I. M.; Ashhab, S.; Nori, Franco

    2014-01-01

    Simulating quantum mechanics is known to be a difficult computational problem, especially when dealing with large systems. However, this difficulty may be overcome by using some controllable quantum system to study another less controllable or accessible quantum system, i.e., quantum simulation. Quantum simulation promises to have applications in the study of many problems in, e.g., condensed-matter physics, high-energy physics, atomic physics, quantum chemistry, and cosmology. Quantum simulation could be implemented using quantum computers, but also with simpler, analog devices that would require less control, and therefore, would be easier to construct. A number of quantum systems such as neutral atoms, ions, polar molecules, electrons in semiconductors, superconducting circuits, nuclear spins, and photons have been proposed as quantum simulators. This review outlines the main theoretical and experimental aspects of quantum simulation and emphasizes some of the challenges and promises of this fast-growing field.

  8. Rapid prototype extruded conductive pathways

    DOEpatents

    Bobbitt, III, John T.

    2016-06-21

    A process of producing electrically conductive pathways within additively manufactured parts and similar parts made by plastic extrusion nozzles. The process allows for a three-dimensional part having both conductive and non-conductive portions and allows for such parts to be manufactured in a single production step.

  9. Wurtzite GaAs Quantum Wires: One-Dimensional Subband Formation.

    PubMed

    Vainorius, Neimantas; Lehmann, Sebastian; Gustafsson, Anders; Samuelson, Lars; Dick, Kimberly A; Pistol, Mats-Erik

    2016-04-13

    It is of contemporary interest to fabricate nanowires having quantum confinement and one-dimensional subband formation. This is due to a host of applications, for example, in optical devices, and in quantum optics. We have here fabricated and optically investigated narrow, down to 10 nm diameter, wurtzite GaAs nanowires which show strong quantum confinement and the formation of one-dimensional subbands. The fabrication was bottom up and in one step using the vapor-liquid-solid growth mechanism. Combining photoluminescence excitation spectroscopy with transmission electron microscopy on the same individual nanowires, we were able to extract the effective masses of the electrons in the two lowest conduction bands as well as the effective masses of the holes in the two highest valence bands. Our results, combined with earlier demonstrations of thin crystal phase nanodots in GaAs, set the stage for the fabrication of crystal phase quantum dots having full three-dimensional confinement. PMID:27004550

  10. Inertial-Hall effect: the influence of rotation on the Hall conductivity

    NASA Astrophysics Data System (ADS)

    Brandão, Julio E.; Moraes, F.; Cunha, M. M.; Lima, Jonas R. F.; Filgueiras, C.

    Inertial effects play an important role in classical mechanics but have been largely overlooked in quantum mechanics. Nevertheless, the analogy between inertial forces on mass particles and electromagnetic forces on charged particles is not new. In this paper, we consider a rotating non-interacting planar two-dimensional electron gas with a perpendicular uniform magnetic field and investigate the effects of the rotation in the Hall conductivity. The rotation introduces a shift and a split in the Landau levels. As a consequence of the break of the degeneracy, the counting of the states fully occupied below the Fermi energy increases, tuning the Hall quantization steps. The rotation also changes the quantum Hall plateau widths. Additionally, we find the Hall quantization steps as a function of rotation at a fixed value of the magnetic field.

  11. Quantum spin Hall effect.

    PubMed

    Bernevig, B Andrei; Zhang, Shou-Cheng

    2006-03-17

    The quantum Hall liquid is a novel state of matter with profound emergent properties such as fractional charge and statistics. The existence of the quantum Hall effect requires breaking of the time reversal symmetry caused by an external magnetic field. In this work, we predict a quantized spin Hall effect in the absence of any magnetic field, where the intrinsic spin Hall conductance is quantized in units of 2(e/4pi). The degenerate quantum Landau levels are created by the spin-orbit coupling in conventional semiconductors in the presence of a strain gradient. This new state of matter has many profound correlated properties described by a topological field theory.

  12. Quantum Spin Hall Effect

    SciTech Connect

    Bernevig, B.Andrei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-01-15

    The quantum Hall liquid is a novel state of matter with profound emergent properties such as fractional charge and statistics. Existence of the quantum Hall effect requires breaking of the time reversal symmetry caused by an external magnetic field. In this work, we predict a quantized spin Hall effect in the absence of any magnetic field, where the intrinsic spin Hall conductance is quantized in units of 2 e/4{pi}. The degenerate quantum Landau levels are created by the spin-orbit coupling in conventional semiconductors in the presence of a strain gradient. This new state of matter has many profound correlated properties described by a topological field theory.

  13. Experimental realization of quantum zeno dynamics

    PubMed Central

    Schäfer, F.; Herrera, I.; Cherukattil, S.; Lovecchio, C.; Cataliotti, F.S.; Caruso, F.; Smerzi, A.

    2014-01-01

    It is generally impossible to probe a quantum system without disturbing it. However, it is possible to exploit the back action of quantum measurements and strong couplings to tailor and protect the coherent evolution of a quantum system. This is a profound and counterintuitive phenomenon known as quantum Zeno dynamics. Here we demonstrate quantum Zeno dynamics with a rubidium Bose–Einstein condensate in a five-level Hilbert space. We harness measurements and strong couplings to dynamically disconnect different groups of quantum states and constrain the atoms to coherently evolve inside a two-level subregion. In parallel to the foundational importance due to the realization of a dynamical superselection rule and the theory of quantum measurements, this is an important step forward in protecting and controlling quantum dynamics and, broadly speaking, quantum information processing. PMID:24476716

  14. Exploiting Symmetry for Quantum Error Suppression

    NASA Astrophysics Data System (ADS)

    Nam, Yunseong; Blümel, Reinhold

    2016-05-01

    In light of recent experimental progress in quantum computing, the time is ripe to discuss quantum computer hardware optimization. Taking the digital/analog hybrid nature of quantum computers into account, choosing a proper processor architecture for a given quantum algorithm becomes crucial in making quantum computing a practical reality. As a first step in this direction, we investigate the robustness of quantum adders with respect to naturally occurring hardware defects and errors. In particular, we compare the robustness of the ripple-carry adder to that of the quantum Fourier adder. We show that, surprisingly, when used in Shor's algorithm, the quantum Fourier adder may well be more robust than the ripple-carry adder. We present a noise suppression scheme, called symmetric noise, applicable to the quantum Fourier architecture, that, measured in terms of fidelity, results in an order-of-magnitude performance boost.

  15. Beyond the Quantum

    NASA Astrophysics Data System (ADS)

    Nieuwenhuizen, Theo M.; Mehmani, Bahar; Špička, Václav; Aghdami, Maryam J.; Khrennikov, Andrei Yu

    2007-09-01

    pt. A. Introductions. The mathematical basis for deterministic quantum mechanics / G.'t Hooft. What did we learn from quantum gravity? / A. Ashtekar. Bose-Einstein condensates and EPR quantum non-locality / F. Laloe. The quantum measurement process: lessons from an exactly solvable model / A.E. Allahverdyan, R. Balian and Th. M. Nieuwenhuizen -- pt. B. Quantum mechanics and quantum information. POVMs: a small but important step beyond standard quantum mechanics / W. M. de Muynck. State reduction by measurements with a null result / G. Nienhuis. Solving open questions in the Bose-Einstein condensation of an ideal gas via a hybrid mixture of laser and statistical physics / M. Kim, A. Svidzinsky and M.O. Scully. Twin-Photon light scattering and causality / G. Puentes, A. Aiello and J. P. Woerdman. Simultaneous measurement of non-commuting observables / G. Aquino and B. Mehmani. Quantum decoherence and gravitational waves / M.T. Jaekel ... [et al.]. Role of various entropies in the black hole information loss problem / Th. M. Nieuwenhuizen and I.V. Volovich. Quantum and super-quantum correlations / G.S. Jaeger -- pt. C. Long distance correlations and bell inequalities. Understanding long-distance quantum correlations / L. Marchildon. Connection of probability models to EPR experiments: probability spaces and Bell's theorem / K. Hess and W. Philipp. Fair sampling vs no-signalling principle in EPR experiments / G. Adenier and A. Yu. Khrennikov -- pt. D. Mathematical foundations. Where the mathematical structure of quantum mechanics comes from / G.M. D'Ariano. Phase space description of quantum mechanics and non-commutative geometry: Wigner-Moyal and Bohm in a wider context / B.J. Hiley. Quantum mechanics as simple algorithm for approximation of classical integrals / A. Yu. Khrennikov. Noncommutative quantum mechanics viewed from Feynman Formalism / J. Lages ... [et al.]. Beyond the quantum in Snyder space / J.F.S. van Huele and M. K. Transtrum -- pt. E. Stochastic

  16. Neutron Matter Wave Quantum Optics

    NASA Astrophysics Data System (ADS)

    Rauch, Helmut

    2012-06-01

    Neutron matter-wave optics provides the basis for new quantum experiments and a step towards applications of quantum phenomena. Most experiments have been performed with a perfect crystal neutron interferometer where widely separated coherent beams can be manipulated individually. Various geometric phases have been measured and their robustness against fluctuation effects has been proven, which may become a useful property for advanced quantum communication. Quantum contextuality for single particle systems shows that quantum correlations are to some extent more demanding than classical ones. In this case entanglement between external and internal degrees of freedom offers new insights into basic laws of quantum physics. Non-contextuality hidden variable theories can be rejected by arguments based on the Kochen-Specker theorem.

  17. One step, microwave assisted green synthesis of biocompatible carbon quantum dots and their composites with [α−PW{sub 12}O{sub 40}{sup 3−}] for visible light photocatalysis

    SciTech Connect

    Sahasrabudhe, Atharva Pant, Shashank Chatti, Manjunath Maiti, Binoy De, Priyadarsi Roy, Soumyajit

    2014-04-24

    We report a simple, rapid and green route for synthesis of fluorescent carbon quantum dots (CQDs) by microwave assisted pyrolysis method using polyleucine polymer (Boc-L-Leu-HEMA) as precursor and self-passivating agent. The as synthesized CQDs were found to possess low cytotoxicity, thus making them suitable candidates for bioimaging and bio-labelling. Moreover, nanocomposites of as prepared CQDs with [α−PW{sub 12}O{sub 40}{sup 3−}] polyoxometalate were synthesized and were shown to possess excellent photocatalytic properties under visible light towards degradation of organic dye pollutants. Based on the control experiments, a suitable mechanism has been proposed to explain the remarkable photoactivity of the CQD/[α−PW{sub 12}O{sub 40}{sup 3−}] composites.

  18. Cyclic steps on ice

    NASA Astrophysics Data System (ADS)

    Yokokawa, M.; Izumi, N.; Naito, K.; Parker, G.; Yamada, T.; Greve, R.

    2016-05-01

    Boundary waves often form at the interface between ice and fluid flowing adjacent to it, such as ripples under river ice covers, and steps on the bed of supraglacial meltwater channels. They may also be formed by wind, such as the megadunes on the Antarctic ice sheet. Spiral troughs on the polar ice caps of Mars have been interpreted to be cyclic steps formed by katabatic wind blowing over ice. Cyclic steps are relatives of upstream-migrating antidunes. Cyclic step formation on ice is not only a mechanical but also a thermodynamic process. There have been very few studies on the formation of either cyclic steps or upstream-migrating antidunes on ice. In this study, we performed flume experiments to reproduce cyclic steps on ice by flowing water, and found that trains of steps form when the Froude number is larger than unity. The features of those steps allow them to be identified as ice-bed analogs of cyclic steps in alluvial and bedrock rivers. We performed a linear stability analysis and obtained a physical explanation of the formation of upstream-migrating antidunes, i.e., precursors of cyclic steps. We compared the results of experiments with the predictions of the analysis and found the observed steps fall in the range where the analysis predicts interfacial instability. We also found that short antidune-like undulations formed as a precursor to the appearance of well-defined steps. This fact suggests that such antidune-like undulations correspond to the instability predicted by the analysis and are precursors of cyclic steps.

  19. Quantum ontologies

    SciTech Connect

    Stapp, H.P.

    1988-12-01

    Quantum ontologies are conceptions of the constitution of the universe that are compatible with quantum theory. The ontological orientation is contrasted to the pragmatic orientation of science, and reasons are given for considering quantum ontologies both within science, and in broader contexts. The principal quantum ontologies are described and evaluated. Invited paper at conference: Bell's Theorem, Quantum Theory, and Conceptions of the Universe, George Mason University, October 20-21, 1988. 16 refs.

  20. Quantum Computer Games: Quantum Minesweeper

    ERIC Educational Resources Information Center

    Gordon, Michal; Gordon, Goren

    2010-01-01

    The computer game of quantum minesweeper is introduced as a quantum extension of the well-known classical minesweeper. Its main objective is to teach the unique concepts of quantum mechanics in a fun way. Quantum minesweeper demonstrates the effects of superposition, entanglement and their non-local characteristics. While in the classical…

  1. Golgi-Cox Staining Step by Step

    PubMed Central

    Zaqout, Sami; Kaindl, Angela M.

    2016-01-01

    Golgi staining remains a key method to study neuronal morphology in vivo. Since most protocols delineating modifications of the original staining method lack details on critical steps, establishing this method in a laboratory can be time-consuming and frustrating. Here, we describe the Golgi-Cox staining in such detail that should turn the staining into an easily feasible method for all scientists working in the neuroscience field. PMID:27065817

  2. Quantum memristors

    PubMed Central

    Pfeiffer, P.; Egusquiza, I. L.; Di Ventra, M.; Sanz, M.; Solano, E.

    2016-01-01

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems. PMID:27381511

  3. Quantum memristors.

    PubMed

    Pfeiffer, P; Egusquiza, I L; Di Ventra, M; Sanz, M; Solano, E

    2016-01-01

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems. PMID:27381511

  4. Quantum memristors.

    PubMed

    Pfeiffer, P; Egusquiza, I L; Di Ventra, M; Sanz, M; Solano, E

    2016-07-06

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems.

  5. Quantum memristors

    NASA Astrophysics Data System (ADS)

    Pfeiffer, P.; Egusquiza, I. L.; di Ventra, M.; Sanz, M.; Solano, E.

    2016-07-01

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems.

  6. Electrical Conductivity.

    ERIC Educational Resources Information Center

    Hershey, David R.; Sand, Susan

    1993-01-01

    Explains how electrical conductivity (EC) can be used to measure ion concentration in solutions. Describes instrumentation for the measurement, temperature dependence and EC, and the EC of common substances. (PR)

  7. Quantum Teardrops

    NASA Astrophysics Data System (ADS)

    Brzeziński, Tomasz; Fairfax, Simon A.

    2012-11-01

    Algebras of functions on quantum weighted projective spaces are introduced, and the structure of quantum weighted projective lines or quantum teardrops is described in detail. In particular the presentation of the coordinate algebra of the quantum teardrop in terms of generators and relations and classification of irreducible *-representations are derived. The algebras are then analysed from the point of view of Hopf-Galois theory or the theory of quantum principal bundles. Fredholm modules and associated traces are constructed. C*-algebras of continuous functions on quantum weighted projective lines are described and their K-groups computed.

  8. High conductivity composite metal

    DOEpatents

    Zhou, R.; Smith, J.L.; Embury, J.D.

    1998-01-06

    Electrical conductors and methods of producing them are disclosed, where the conductors possess both high strength and high conductivity. Conductors are comprised of carbon steel and a material chosen from a group consisting of copper, nickel, silver, and gold. Diffusion barriers are placed between these two materials. The components of a conductor are assembled and then the assembly is subjected to heat treating and mechanical deformation steps. 10 figs.

  9. High conductivity composite metal

    DOEpatents

    Zhou, Ruoyi; Smith, James L.; Embury, John David

    1998-01-01

    Electrical conductors and methods of producing them, where the conductors possess both high strength and high conductivity. Conductors are comprised of carbon steel and a material chosen from a group consisting of copper, nickel, silver, and gold. Diffusion barriers are placed between these two materials. The components of a conductor are assembled and then the assembly is subjected to heat treating and mechanical deformation steps.

  10. Multi-step interrupted-growth MBE technology for GaAs/AlGaAs (˜9.4 μm) room temperature operating quantum-cascade lasers

    NASA Astrophysics Data System (ADS)

    Kosiel, K.; Kubacka-Traczyk, J.; Sankowska, I.; Szerling, A.; Gutowski, P.; Bugajski, M.

    2012-09-01

    In order to adjust the highly controllable and optimum growth conditions, the multi-step interrupted-growth MBE processes were performed to deposit a series of GaAs/Al0.45Ga0.55As QCL structures. The additional calibrations of MBE system were carried out during the designed growth interruptions. This solution was combined with a relatively low growth rate of active region layers, in order to suppress the negative effects of elemental flux instabilities. As a result, the fabricated QCL structures have yielded devices operating with peak optical power of ˜12 mW at room temperature. That is a better result than was obtained for comparable structures deposited with a growth rate kept constant, and with the only initial calibrations performed just before the epitaxy of the overall structure.

  11. Weak Topological Insulators with Step Edges: Subband Engineering and Its Effect on Electron Transport

    NASA Astrophysics Data System (ADS)

    Arita, Takashi; Takane, Yositake

    2016-03-01

    A three-dimensional weak topological insulator (WTI) can be regarded as stacked layers of two-dimensional quantum spin-Hall insulators, each of which accommodates a one-dimensional helical edge mode. Massless Dirac electrons emerge on a side surface of WTIs as a consequence of the hybridization of such helical edge modes. We study the energy spectrum and transport of Dirac electrons on a side surface in the presence of step edges, which significantly modify the way of hybridization. It is shown that pseudo-helical modes with a nearly gapless linear dispersion can be created by manipulating step edges in a certain manner. We numerically calculate the average conductance of weakly disordered WTIs and show that it is markedly enhanced by pseudo-helical modes.

  12. 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.

  13. Quantum memristors

    DOE PAGES

    Pfeiffer, P.; Egusquiza, I. L.; Di Ventra, M.; Sanz, M.; Solano, E.

    2016-07-06

    Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantummore » regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. As a result, the proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems.« less

  14. Conclusive identification of quantum channels via monogamy of quantum correlations

    NASA Astrophysics Data System (ADS)

    Kumar, Asutosh; Singha Roy, Sudipto; Pal, Amit Kumar; Prabhu, R.; Sen(De), Aditi; Sen, Ujjwal

    2016-10-01

    We investigate the action of global noise and local channels, namely, amplitude-damping, phase-damping, and depolarizing channels, on monogamy of quantum correlations, such as negativity and quantum discord, in three-qubit systems. We discuss the monotonic and non-monotonic variation, and robustness of the monogamy scores. By using monogamy scores, we propose a two-step protocol to conclusively identify the noise applied to the quantum system, by using generalized Greenberger-Horne-Zeilinger and generalized W states as resource states. We discuss a possible generalization of the results to higher number of parties.

  15. One-way quantum computation with circuit quantum electrodynamics

    SciTech Connect

    Wu Chunwang; Han Yang; Chen Pingxing; Li Chengzu; Zhong Xiaojun

    2010-03-15

    In this Brief Report, we propose a potential scheme to implement one-way quantum computation with circuit quantum electrodynamics (QED). Large cluster states of charge qubits can be generated in just one step with a superconducting transmission line resonator (TLR) playing the role of a dispersive coupler. A single-qubit measurement in the arbitrary basis can be implemented using a single electron transistor with the help of one-qubit gates. By examining the main decoherence sources, we show that circuit QED is a promising architecture for one-way quantum computation.

  16. Appropriate Conduct

    ERIC Educational Resources Information Center

    Di Lullo, Louis

    2004-01-01

    Many years ago when the author assumed the role of assistant principal for school climate, discipline, and attendance, he inherited many school policies and guidelines that were outdated, unfair, and without merit in the current school climate. Because the school conduct code had not been revised since the school opened in 1960, many of the…

  17. Quantum criticality

    NASA Astrophysics Data System (ADS)

    Coleman, Piers; Schofield, Andrew J.

    2005-01-01

    As we mark the centenary of Albert Einstein's seminal contribution to both quantum mechanics and special relativity, we approach another anniversary - that of Einstein's foundation of the quantum theory of solids. But 100 years on, the same experimental measurement that puzzled Einstein and his contemporaries is forcing us to question our understanding of how quantum matter transforms at ultra-low temperatures.

  18. Modern Canonical Quantum General Relativity

    NASA Astrophysics Data System (ADS)

    Thiemann, Thomas

    2008-11-01

    Preface; Notation and conventions; Introduction; Part I. Classical Foundations, Interpretation and the Canonical Quantisation Programme: 1. Classical Hamiltonian formulation of general relativity; 2. The problem of time, locality and the interpretation of quantum mechanics; 3. The programme of canonical quantisation; 4. The new canonical variables of Ashtekar for general relativity; Part II. Foundations of Modern Canonical Quantum General Relativity: 5. Introduction; 6. Step I: the holonomy-flux algebra [P]; 7. Step II: quantum-algebra; 8. Step III: representation theory of [A]; 9. Step IV: 1. Implementation and solution of the kinematical constraints; 10. Step V: 2. Implementation and solution of the Hamiltonian constraint; 11. Step VI: semiclassical analysis; Part III. Physical Applications: 12. Extension to standard matter; 13. Kinematical geometrical operators; 14. Spin foam models; 15. Quantum black hole physics; 16. Applications to particle physics and quantum cosmology; 17. Loop quantum gravity phenomenology; Part IV. Mathematical Tools and their Connection to Physics: 18. Tools from general topology; 19. Differential, Riemannian, symplectic and complex geometry; 20. Semianalytical category; 21. Elements of fibre bundle theory; 22. Holonomies on non-trivial fibre bundles; 23. Geometric quantisation; 24. The Dirac algorithm for field theories with constraints; 25. Tools from measure theory; 26. Elementary introduction to Gel'fand theory for Abelean C* algebras; 27. Bohr compactification of the real line; 28. Operatir -algebras and spectral theorem; 29. Refined algebraic quantisation (RAQ) and direct integral decomposition (DID); 30. Basics of harmonic analysis on compact Lie groups; 31. Spin network functions for SU(2); 32. + Functional analytical description of classical connection dynamics; Bibliography; Index.

  19. Modern Canonical Quantum General Relativity

    NASA Astrophysics Data System (ADS)

    Thiemann, Thomas

    2007-09-01

    Preface; Notation and conventions; Introduction; Part I. Classical Foundations, Interpretation and the Canonical Quantisation Programme: 1. Classical Hamiltonian formulation of general relativity; 2. The problem of time, locality and the interpretation of quantum mechanics; 3. The programme of canonical quantisation; 4. The new canonical variables of Ashtekar for general relativity; Part II. Foundations of Modern Canonical Quantum General Relativity: 5. Introduction; 6. Step I: the holonomy-flux algebra [P]; 7. Step II: quantum-algebra; 8. Step III: representation theory of [A]; 9. Step IV: 1. Implementation and solution of the kinematical constraints; 10. Step V: 2. Implementation and solution of the Hamiltonian constraint; 11. Step VI: semiclassical analysis; Part III. Physical Applications: 12. Extension to standard matter; 13. Kinematical geometrical operators; 14. Spin foam models; 15. Quantum black hole physics; 16. Applications to particle physics and quantum cosmology; 17. Loop quantum gravity phenomenology; Part IV. Mathematical Tools and their Connection to Physics: 18. Tools from general topology; 19. Differential, Riemannian, symplectic and complex geometry; 20. Semianalytical category; 21. Elements of fibre bundle theory; 22. Holonomies on non-trivial fibre bundles; 23. Geometric quantisation; 24. The Dirac algorithm for field theories with constraints; 25. Tools from measure theory; 26. Elementary introduction to Gel'fand theory for Abelean C* algebras; 27. Bohr compactification of the real line; 28. Operatir -algebras and spectral theorem; 29. Refined algebraic quantisation (RAQ) and direct integral decomposition (DID); 30. Basics of harmonic analysis on compact Lie groups; 31. Spin network functions for SU(2); 32. + Functional analytical description of classical connection dynamics; Bibliography; Index.

  20. The Next Giant Step

    NASA Video Gallery

    Artist Robert McCall painted "The Next Giant Step" in 1979 to commemorate the heroism and courage of spaceflight pioneers. Located in the lobby of Johnson's building 2, the mural depicts America's ...

  1. Experimental teleportation of a quantum controlled-NOT gate.

    PubMed

    Huang, Yun-Feng; Ren, Xi-Feng; Zhang, Yong-Sheng; Duan, Lu-Ming; Guo, Guang-Can

    2004-12-10

    Teleportation of quantum gates is a critical step for the implementation of quantum networking and teleportation-based models of quantum computation. We report an experimental demonstration of teleportation of the prototypical quantum controlled-NOT (CNOT) gate. Assisted with linear optical manipulations, photon entanglement produced from parametric down-conversion, and postselection from the coincidence measurements, we teleport the quantum CNOT gate from acting on local qubits to acting on remote qubits. The quality of the quantum gate teleportation is characterized through the method of quantum process tomography, with an average fidelity of 0.84 demonstrated for the teleported gate. PMID:15697787

  2. The scalable implementation of quantum walks using classical light

    NASA Astrophysics Data System (ADS)

    Goyal, Sandeep K.; Roux, F. S.; Forbes, Andrew; Konrad, Thomas

    2014-02-01

    A quantum walk is the quantum analog of the classical random walks. Despite their simple structure they form a universal platform to implement any algorithm of quantum computation. However, it is very hard to realize quantum walks with a sufficient number of iterations in quantum systems due to their sensitivity to environmental influences and subsequent loss of coherence. Here we present a scalable implementation scheme for one-dimensional quantum walks for arbitrary number of steps using the orbital angular momentum modes of classical light beams. Furthermore, we show that using the same setup with a minor adjustment we can also realize electric quantum walks.

  3. Experimental teleportation of a quantum controlled-NOT gate.

    PubMed

    Huang, Yun-Feng; Ren, Xi-Feng; Zhang, Yong-Sheng; Duan, Lu-Ming; Guo, Guang-Can

    2004-12-10

    Teleportation of quantum gates is a critical step for the implementation of quantum networking and teleportation-based models of quantum computation. We report an experimental demonstration of teleportation of the prototypical quantum controlled-NOT (CNOT) gate. Assisted with linear optical manipulations, photon entanglement produced from parametric down-conversion, and postselection from the coincidence measurements, we teleport the quantum CNOT gate from acting on local qubits to acting on remote qubits. The quality of the quantum gate teleportation is characterized through the method of quantum process tomography, with an average fidelity of 0.84 demonstrated for the teleported gate.

  4. A big first step.

    PubMed

    Jones, Howard W

    2004-11-01

    The singleton, term gestation, live birth rate per cycle initiated (BESST) endpoint proposed at the beginning of 2004 is a first big step which should be added to by the consideration of multiple pregnancy rates in relation to singleton rates, by recording of fetal reductions and of pregnancies resulting from cryopreserved material. After three or more steps we may have an accurate reporting system which helps patients to distinguish the pros and cons for singleton term delivery. PMID:15479704

  5. Quantum random walks without walking

    SciTech Connect

    Manouchehri, K.; Wang, J. B.

    2009-12-15

    Quantum random walks have received much interest due to their nonintuitive dynamics, which may hold the key to a new generation of quantum algorithms. What remains a major challenge is a physical realization that is experimentally viable and not limited to special connectivity criteria. We present a scheme for walking on arbitrarily complex graphs, which can be realized using a variety of quantum systems such as a Bose-Einstein condensate trapped inside an optical lattice. This scheme is particularly elegant since the walker is not required to physically step between the nodes; only flipping coins is sufficient.

  6. Electrodeless conductivity.

    PubMed

    Light, T S; McHale, E J; Fletcher, K S

    1989-01-01

    Electrodeless conductivity is a technique for measuring the concentration of electrolytes in solution and utilizes a probe consisting of two toroids in close proximity, both of which are immersed in the solution. In special cases, the toroids may be mounted externally on insulated pipes carrying the solution. One toroid radiates an alternating electric field in the audiofrequency range and the other acts as a receiver to pick up the small current induced by the ions moving in a conducting loop of solution. Coatings which would foul contacting electrodes, such as suspensions, precipitates or oil, have little or no effect. Applications are chiefly to continuous measurement in the chemical processing industries, including pulp and paper, mining and heavy chemical production. The principles and practical details of the method are reviewed and cell-diameter, wall, and temperature effects are discussed. PMID:18964695

  7. A Step by Step Guide for Planning a Japanese Cultural Festival.

    ERIC Educational Resources Information Center

    Murphy, Carole

    Teachers at all academic levels can adapt the design and content of the sixth grade Japanese cultural festival detailed in this learning packet. Material is divided into 2 sections. Section 1 provides a step-by-step guide to planning and conducting the festival. These instructions, based on 5 years of experience, include a detailed planning…

  8. SPSS for Windows Step by Step: A Simple Guide and Reference.

    ERIC Educational Resources Information Center

    George, Darren; Mallery, Paul

    This book is designed to give step-by-step instructions necessary to do most major types of data analysis using the Statistical Package for the Social Sciences (SPSS). SPSS is a powerful tool that is capable of conducting nearly any type of data analysis used in the social sciences. This book should enable the reader to do 95% of what the program…

  9. Efficient entanglement distillation without quantum memory.

    PubMed

    Abdelkhalek, Daniela; Syllwasschy, Mareike; Cerf, Nicolas J; Fiurášek, Jaromír; Schnabel, Roman

    2016-05-31

    Entanglement distribution between distant parties is an essential component to most quantum communication protocols. Unfortunately, decoherence effects such as phase noise in optical fibres are known to demolish entanglement. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps. Quantum memories have been contemplated to make entanglement distillation practical, but suitable quantum memories are not realised to date. Here, we present the theory for an efficient iterative entanglement distillation protocol without quantum memories and provide a proof-of-principle experimental demonstration. The scheme is applied to phase-diffused two-mode-squeezed states and proven to distil entanglement for up to three iteration steps. The data are indistinguishable from those that an efficient scheme using quantum memories would produce. Since our protocol includes the final measurement it is particularly promising for enhancing continuous-variable quantum key distribution.

  10. Efficient entanglement distillation without quantum memory

    NASA Astrophysics Data System (ADS)

    Abdelkhalek, Daniela; Syllwasschy, Mareike; Cerf, Nicolas J.; Fiurášek, Jaromír; Schnabel, Roman

    2016-05-01

    Entanglement distribution between distant parties is an essential component to most quantum communication protocols. Unfortunately, decoherence effects such as phase noise in optical fibres are known to demolish entanglement. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps. Quantum memories have been contemplated to make entanglement distillation practical, but suitable quantum memories are not realised to date. Here, we present the theory for an efficient iterative entanglement distillation protocol without quantum memories and provide a proof-of-principle experimental demonstration. The scheme is applied to phase-diffused two-mode-squeezed states and proven to distil entanglement for up to three iteration steps. The data are indistinguishable from those that an efficient scheme using quantum memories would produce. Since our protocol includes the final measurement it is particularly promising for enhancing continuous-variable quantum key distribution.

  11. Efficient entanglement distillation without quantum memory

    PubMed Central

    Abdelkhalek, Daniela; Syllwasschy, Mareike; Cerf, Nicolas J.; Fiurášek, Jaromír; Schnabel, Roman

    2016-01-01

    Entanglement distribution between distant parties is an essential component to most quantum communication protocols. Unfortunately, decoherence effects such as phase noise in optical fibres are known to demolish entanglement. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps. Quantum memories have been contemplated to make entanglement distillation practical, but suitable quantum memories are not realised to date. Here, we present the theory for an efficient iterative entanglement distillation protocol without quantum memories and provide a proof-of-principle experimental demonstration. The scheme is applied to phase-diffused two-mode-squeezed states and proven to distil entanglement for up to three iteration steps. The data are indistinguishable from those that an efficient scheme using quantum memories would produce. Since our protocol includes the final measurement it is particularly promising for enhancing continuous-variable quantum key distribution. PMID:27241946

  12. Efficient entanglement distillation without quantum memory.

    PubMed

    Abdelkhalek, Daniela; Syllwasschy, Mareike; Cerf, Nicolas J; Fiurášek, Jaromír; Schnabel, Roman

    2016-01-01

    Entanglement distribution between distant parties is an essential component to most quantum communication protocols. Unfortunately, decoherence effects such as phase noise in optical fibres are known to demolish entanglement. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps. Quantum memories have been contemplated to make entanglement distillation practical, but suitable quantum memories are not realised to date. Here, we present the theory for an efficient iterative entanglement distillation protocol without quantum memories and provide a proof-of-principle experimental demonstration. The scheme is applied to phase-diffused two-mode-squeezed states and proven to distil entanglement for up to three iteration steps. The data are indistinguishable from those that an efficient scheme using quantum memories would produce. Since our protocol includes the final measurement it is particularly promising for enhancing continuous-variable quantum key distribution. PMID:27241946

  13. Quantum frames

    NASA Astrophysics Data System (ADS)

    Brown, Matthew J.

    2014-02-01

    The framework of quantum frames can help unravel some of the interpretive difficulties i the foundation of quantum mechanics. In this paper, I begin by tracing the origins of this concept in Bohr's discussion of quantum theory and his theory of complementarity. Engaging with various interpreters and followers of Bohr, I argue that the correct account of quantum frames must be extended beyond literal space-time reference frames to frames defined by relations between a quantum system and the exosystem or external physical frame, of which measurement contexts are a particularly important example. This approach provides superior solutions to key EPR-type measurement and locality paradoxes.

  14. Quantum cheques

    NASA Astrophysics Data System (ADS)

    Moulick, Subhayan Roy; Panigrahi, Prasanta K.

    2016-06-01

    We propose the idea of a quantum cheque scheme, a cryptographic protocol in which any legitimate client of a trusted bank can issue a cheque, that cannot be counterfeited or altered in anyway, and can be verified by a bank or any of its branches. We formally define a quantum cheque and present the first unconditionally secure quantum cheque scheme and show it to be secure against any no-signalling adversary. The proposed quantum cheque scheme can been perceived as the quantum analog of Electronic Data Interchange, as an alternate for current e-Payment Gateways.

  15. 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.

  16. Conductive Polymers

    SciTech Connect

    Bohnert, G.W.

    2002-11-22

    Electroluminescent devices such as light-emitting diodes (LED) and high-energy density batteries. These new polymers offer cost savings, weight reduction, ease of processing, and inherent rugged design compared to conventional semiconductor materials. The photovoltaic industry has grown more than 30% during the past three years. Lightweight, flexible solar modules are being used by the U.S. Army and Marine Corps for field power units. LEDs historically used for indicator lights are now being investigated for general lighting to replace fluorescent and incandescent lights. These so-called solid-state lights are becoming more prevalent across the country since they produce efficient lighting with little heat generation. Conductive polymers are being sought for battery development as well. Considerable weight savings over conventional cathode materials used in secondary storage batteries make portable devices easier to carry and electric cars more efficient and nimble. Secondary battery sales represent an $8 billion industry annually. The purpose of the project was to synthesize and characterize conductive polymers. TRACE Photonics Inc. has researched critical issues which affect conductivity. Much of their work has focused on production of substituted poly(phenylenevinylene) compounds. These compounds exhibit greater solubility over the parent polyphenylenevinylene, making them easier to process. Alkoxy substituted groups evaluated during this study included: methoxy, propoxy, and heptyloxy. Synthesis routes for production of alkoxy-substituted poly phenylenevinylene were developed. Considerable emphasis was placed on final product yield and purity.

  17. Quantum technology: from research to application

    NASA Astrophysics Data System (ADS)

    Schleich, Wolfgang P.; Ranade, Kedar S.; Anton, Christian; Arndt, Markus; Aspelmeyer, Markus; Bayer, Manfred; Berg, Gunnar; Calarco, Tommaso; Fuchs, Harald; Giacobino, Elisabeth; Grassl, Markus; Hänggi, Peter; Heckl, Wolfgang M.; Hertel, Ingolf-Volker; Huelga, Susana; Jelezko, Fedor; Keimer, Bernhard; Kotthaus, Jörg P.; Leuchs, Gerd; Lütkenhaus, Norbert; Maurer, Ueli; Pfau, Tilman; Plenio, Martin B.; Rasel, Ernst Maria; Renn, Ortwin; Silberhorn, Christine; Schiedmayer, Jörg; Schmitt-Landsiedel, Doris; Schönhammer, Kurt; Ustinov, Alexey; Walther, Philip; Weinfurter, Harald; Welzl, Emo; Wiesendanger, Roland; Wolf, Stefan; Zeilinger, Anton; Zoller, Peter

    2016-05-01

    The term quantum physics refers to the phenomena and characteristics of atomic and subatomic systems which cannot be explained by classical physics. Quantum physics has had a long tradition in Germany, going back nearly 100 years. Quantum physics is the foundation of many modern technologies. The first generation of quantum technology provides the basis for key areas such as semiconductor and laser technology. The "new" quantum technology, based on influencing individual quantum systems, has been the subject of research for about the last 20 years. Quantum technology has great economic potential due to its extensive research programs conducted in specialized quantum technology centres throughout the world. To be a viable and active participant in the economic potential of this field, the research infrastructure in Germany should be improved to facilitate more investigations in quantum technology research.

  18. Quantum Cryptography

    NASA Astrophysics Data System (ADS)

    Fehr, Serge

    2010-05-01

    Quantum cryptography makes use of the quantum-mechanical behavior of nature for the design and analysis of cryptographic schemes. Optimally (but not always), quantum cryptography allows for the design of cryptographic schemes whose security is guaranteed solely by the laws of nature. This is in sharp contrast to standard cryptographic schemes, which can be broken in principle, i.e., when given sufficient computing power. From a theory point of view, quantum cryptography offers a beautiful interplay between the mathematics of adversarial behavior and quantum information theory. In this review article, we discuss the traditional application of quantum cryptography, quantum key distribution (QKD), from a modern perspective, and we discuss some recent developments in the context of quantum two-party cooperation (2PC). QKD allows two distant parties to communicate in a provably-secure way in the presence of an outside eavesdropper, whereas 2PC is concerned with protecting information against possibly malicious insiders. We show the basic idea of constructing quantum cryptographic schemes, but we also show some connections to quantum information theory as needed for the rigorous security analyses, and we discuss some of the relevant quantum-information-theoretic results.

  19. Quantum Optics

    NASA Astrophysics Data System (ADS)

    Orvil Scully, Marlan; Zubairy, Muhammad Suhail

    1997-09-01

    Quantum optics has witnessed significant theoretical and experimental developments in recent years. This book provides an in-depth and wide-ranging introduction to the subject, emphasizing throughout the basic principles and their applications. The book begins by developing the basic tools of quantum optics, and goes on to show the application of these tools in a variety of quantum optical systems, including lasing without inversion, squeezed states, and atom optics. The final four chapters discuss quantum optical tests of the foundations of quantum mechanics, and particular aspects of measurement theory. Assuming only a background of standard quantum mechanics and electromagnetic theory, and containing many problems and references, this book will be invaluable to graduate students of quantum optics, as well as to researchers in this field.

  20. Loop quantum cosmology in 2 +1 dimension

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangdong

    2014-12-01

    As a first step to generalize the structure of loop quantum cosmology to the theories with the spacetime dimension other than four, the isotropic model of loop quantum cosmology in 2 +1 dimension is studied in this paper. We find that the classical big bang singularity is again replaced by a quantum bounce in the model. The similarities and differences between the (2 +1 )-dimensional model and the (3 +1 )-dimensional one are also discussed.

  1. Quantum image matching

    NASA Astrophysics Data System (ADS)

    Jiang, Nan; Dang, Yijie; Wang, Jian

    2016-09-01

    Quantum image processing (QIP) means the quantum-based methods to speed up image processing algorithms. Many quantum image processing schemes claim that their efficiency is theoretically higher than their corresponding classical schemes. However, most of them do not consider the problem of measurement. As we all know, measurement will lead to collapse. That is to say, executing the algorithm once, users can only measure the final state one time. Therefore, if users want to regain the results (the processed images), they must execute the algorithms many times and then measure the final state many times to get all the pixels' values. If the measurement process is taken into account, whether or not the algorithms are really efficient needs to be reconsidered. In this paper, we try to solve the problem of measurement and give a quantum image matching algorithm. Unlike most of the QIP algorithms, our scheme interests only one pixel (the target pixel) instead of the whole image. It modifies the probability of pixels based on Grover's algorithm to make the target pixel to be measured with higher probability, and the measurement step is executed only once. An example is given to explain the algorithm more vividly. Complexity analysis indicates that the quantum scheme's complexity is O(2n) in contradistinction to the classical scheme's complexity O(2^{2n+2m}), where m and n are integers related to the size of images.

  2. Quantum susceptance and its effects on the high-frequency response of superconducting tunnel junctions

    SciTech Connect

    Hu, Q.; Mears, C.A.; Richards, P.L. Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA ); Lloyd, F.L. )

    1990-12-01

    We have made the first direct measurement of the quantum susceptance that arises from the nondissipative part of quasiparticle tunneling in a superconductor-insulator-superconductor tunnel junction. The junction is coupled to an antenna and a superconducting microstrip stub to form a resonator; the resonant frequency is determined from the response of the junction to broadband radiation from a Fourier-transform spectrometer. A 19% shift of the resonant frequency, from 73 to 87 GHz, is observed, which arises from the change of the quantum susceptance of the junction with dc bias voltage. This shift is in excellent agreement with calculations based on the Werthamer-Tucker theory, which includes the quantum susceptance. We also demonstrate that it is essential to include the quantum susceptance in our theoretical computation to explain the photon-assisted-tunneling steps, which have negative dynamic conductance. Such steps are observed when the junction is pumped at slightly below the resonant frequency of the capacitor and the stub. The quantum susceptance should exist in all tunnel devices whose nonlinear {ital I}-{ital V} characteristics are due to elastic tunneling.

  3. Conductivity Probe

    NASA Technical Reports Server (NTRS)

    2008-01-01

    The Thermal and Electrical Conductivity Probe (TECP) for NASA's Phoenix Mars Lander took measurements in Martian soil and in the air.

    The needles on the end of the instrument were inserted into the Martian soil, allowing TECP to measure the propagation of both thermal and electrical energy. TECP also measured the humidity in the surrounding air.

    The needles on the probe are 15 millimeters (0.6 inch) long.

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  4. Electric spaser in the extreme quantum limit.

    PubMed

    Li, Dabing; Stockman, Mark I

    2013-03-01

    We consider theoretically the spaser that is excited electrically via a nanowire with ballistic quantum conductance. We show that, in the extreme quantum regime, i.e., for a single conductance-quantum nanowire, the spaser with a core made of common plasmonic metals, such as silver and gold, is fundamentally possible. For ballistic nanowires with multiple-quanta or nonquantized conductance, the performance of the spaser is enhanced in comparison with the extreme quantum limit. The electrically pumped spaser is promising as an optical source, nanoamplifier, and digital logic device for optoelectronic information processing with a speed of ~100 GHz to ~100 THz. PMID:23521278

  5. Quantum entanglement, quantum communication and the limits of quantum computing

    NASA Astrophysics Data System (ADS)

    Ambainis, Andris

    Quantum entanglement is a term describing the quantum correlations between different parts of a quantum system. Quantum information theory has developed sophisticated techniques to quantify and study quantum entanglement. In this thesis, we show how to apply those techniques to problems in quantum algorithms, complexity theory, communication and cryptography. The main results are: (1) quantum communication protocols that are exponentially more efficient that conventional (classical) communication protocols, (2) unconditionally secure quantum protocols for cryptographic problems, (3) a new "quantum adversary" method for proving lower bounds on quantum algorithms, (4) a study of "one clean qubit computation", a model related to the experimental implementation of quantum computers using NMR (nucleo-magnetic resonance) technology.

  6. Quantum volume

    NASA Astrophysics Data System (ADS)

    Ryabov, V. A.

    2015-08-01

    Quantum systems in a mechanical embedding, the breathing mode of a small particles, optomechanical system, etc. are far not the full list of examples in which the volume exhibits quantum behavior. Traditional consideration suggests strain in small systems as a result of a collective movement of particles, rather than the dynamics of the volume as an independent variable. The aim of this work is to show that some problem here might be essentially simplified by introducing periodic boundary conditions. At this case, the volume is considered as the independent dynamical variable driven by the internal pressure. For this purpose, the concept of quantum volume based on Schrödinger’s equation in 𝕋3 manifold is proposed. It is used to explore several 1D model systems: An ensemble of free particles under external pressure, quantum manometer and a quantum breathing mode. In particular, the influence of the pressure of free particle on quantum oscillator is determined. It is shown also that correction to the spectrum of the breathing mode due to internal degrees of freedom is determined by the off-diagonal matrix elements of the quantum stress. The new treatment not using the “force” theorem is proposed for the quantum stress tensor. In the general case of flexible quantum 3D dynamics, quantum deformations of different type might be introduced similarly to monopole mode.

  7. BOOK REVIEW Quantum Measurement and Control Quantum Measurement and Control

    NASA Astrophysics Data System (ADS)

    Kiefer, Claus

    2010-12-01

    In the last two decades there has been an enormous progress in the experimental investigation of single quantum systems. This progress covers fields such as quantum optics, quantum computation, quantum cryptography, and quantum metrology, which are sometimes summarized as `quantum technologies'. A key issue there is entanglement, which can be considered as the characteristic feature of quantum theory. As disparate as these various fields maybe, they all have to deal with a quantum mechanical treatment of the measurement process and, in particular, the control process. Quantum control is, according to the authors, `control for which the design requires knowledge of quantum mechanics'. Quantum control situations in which measurements occur at important steps are called feedback (or feedforward) control of quantum systems and play a central role here. This book presents a comprehensive and accessible treatment of the theoretical tools that are needed to cope with these situations. It also provides the reader with the necessary background information about the experimental developments. The authors are both experts in this field to which they have made significant contributions. After an introduction to quantum measurement theory and a chapter on quantum parameter estimation, the central topic of open quantum systems is treated at some length. This chapter includes a derivation of master equations, the discussion of the Lindblad form, and decoherence - the irreversible emergence of classical properties through interaction with the environment. A separate chapter is devoted to the description of open systems by the method of quantum trajectories. Two chapters then deal with the central topic of quantum feedback control, while the last chapter gives a concise introduction to one of the central applications - quantum information. All sections contain a bunch of exercises which serve as a useful tool in learning the material. Especially helpful are also various separate

  8. Quantum rewinding via phase estimation

    NASA Astrophysics Data System (ADS)

    Tabia, Gelo Noel

    2015-03-01

    In cryptography, the notion of a zero-knowledge proof was introduced by Goldwasser, Micali, and Rackoff. An interactive proof system is said to be zero-knowledge if any verifier interacting with an honest prover learns nothing beyond the validity of the statement being proven. With recent advances in quantum information technologies, it has become interesting to ask if classical zero-knowledge proof systems remain secure against adversaries with quantum computers. The standard approach to show the zero-knowledge property involves constructing a simulator for a malicious verifier that can be rewinded to a previous step when the simulation fails. In the quantum setting, the simulator can be described by a quantum circuit that takes an arbitrary quantum state as auxiliary input but rewinding becomes a nontrivial issue. Watrous proposed a quantum rewinding technique in the case where the simulation's success probability is independent of the auxiliary input. Here I present a more general quantum rewinding scheme that employs the quantum phase estimation algorithm. This work was funded by institutional research grant IUT2-1 from the Estonian Research Council and by the European Union through the European Regional Development Fund.

  9. Demonstration of one-dimensional quantum random walks using orbital angular momentum of photons

    SciTech Connect

    Zhang, Pei; Ren, Xi-Feng; Zou, Xu-Bo; Liu, Bi-Heng; Huang, Yun-Feng; Guo, Guang-Can

    2007-05-15

    Quantum random walks have attracted special interest because they could lead to new quantum algorithms. Photons can carry orbital angular momentum (OAM) thereby offering a practical realization of a high-dimensional quantum information carrier. By employing OAM of photons, we experimentally realized the one-dimensional discrete-time quantum random walk. Three steps of a one-dimensional quantum random walk were implemented in our protocol showing the obvious difference between quantum and classical random walks.

  10. Quantum flywheel

    NASA Astrophysics Data System (ADS)

    Levy, Amikam; Diósi, Lajos; Kosloff, Ronnie

    2016-05-01

    In this work we present the concept of a quantum flywheel coupled to a quantum heat engine. The flywheel stores useful work in its energy levels, while additional power is extracted continuously from the device. Generally, the energy exchange between a quantum engine and a quantized work repository is accompanied by heat, which degrades the charging efficiency. Specifically when the quantum harmonic oscillator acts as a work repository, quantum and thermal fluctuations dominate the dynamics. Quantum monitoring and feedback control are applied to the flywheel in order to reach steady state and regulate its operation. To maximize the charging efficiency one needs a balance between the information gained by measuring the system and the information fed back to the system. The dynamics of the flywheel are described by a stochastic master equation that accounts for the engine, the external driving, the measurement, and the feedback operations.

  11. Stepped inlet optical panel

    DOEpatents

    Veligdan, James T.

    2001-01-01

    An optical panel includes stacked optical waveguides having stepped inlet facets collectively defining an inlet face for receiving image light, and having beveled outlet faces collectively defining a display screen for displaying the image light channeled through the waveguides by internal reflection.

  12. Quantum criticality.

    PubMed

    Coleman, Piers; Schofield, Andrew J

    2005-01-20

    As we mark the centenary of Albert Einstein's seminal contribution to both quantum mechanics and special relativity, we approach another anniversary--that of Einstein's foundation of the quantum theory of solids. But 100 years on, the same experimental measurement that puzzled Einstein and his contemporaries is forcing us to question our understanding of how quantum matter transforms at ultra-low temperatures. PMID:15662409

  13. Lanczos steps to improve variational wave functions

    NASA Astrophysics Data System (ADS)

    Becca, Federico; Hu, Wen-Jun; Iqbal, Yasir; Parola, Alberto; Poilblanc, Didier; Sorella, Sandro

    2015-09-01

    Gutzwiller-projected fermionic states can be efficiently implemented within quantum Monte Carlo calculations to define extremely accurate variational wave functions for Heisenberg models on frustrated two-dimensional lattices, not only for the ground state but also for low-energy excitations. The application of few Lanczos steps on top of these states further improves their accuracy, allowing calculations on large clusters. In addition, by computing both the energy and its variance, it is possible to obtain reliable estimations of exact results. Here, we report the cases of the frustrated Heisenberg models on square and Kagome lattices.

  14. Quantum seismography

    NASA Astrophysics Data System (ADS)

    Lanzagorta, Marco; Jitrik, Oliverio; Uhlmann, Jeffrey; Venegas, Salvador

    2016-05-01

    A major scientific thrust from recent years has been to try to harness quantum phenomena to increase the performance of a wide variety of information processing devices. In particular, quantum radar has emerged as an intriguing theoretical concept that could revolutionize electromagnetic standoff sensing. In this paper we will discuss how the techniques developed for quantum radar could also be used towards the design of novel seismographs able to detect small ground vibrations., We use a hypothetical earthquake warning system in order to compare quantum seismography with traditional seismographic techniques.

  15. Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tartakovskii, Alexander

    2012-07-01

    Part I. Nanostructure Design and Structural Properties of Epitaxially Grown Quantum Dots and Nanowires: 1. Growth of III/V semiconductor quantum dots C. Schneider, S. Hofling and A. Forchel; 2. Single semiconductor quantum dots in nanowires: growth, optics, and devices M. E. Reimer, N. Akopian, M. Barkelid, G. Bulgarini, R. Heeres, M. Hocevar, B. J. Witek, E. Bakkers and V. Zwiller; 3. Atomic scale analysis of self-assembled quantum dots by cross-sectional scanning tunneling microscopy and atom probe tomography J. G. Keizer and P. M. Koenraad; Part II. Manipulation of Individual Quantum States in Quantum Dots Using Optical Techniques: 4. Studies of the hole spin in self-assembled quantum dots using optical techniques B. D. Gerardot and R. J. Warburton; 5. Resonance fluorescence from a single quantum dot A. N. Vamivakas, C. Matthiesen, Y. Zhao, C.-Y. Lu and M. Atature; 6. Coherent control of quantum dot excitons using ultra-fast optical techniques A. J. Ramsay and A. M. Fox; 7. Optical probing of holes in quantum dot molecules: structure, symmetry, and spin M. F. Doty and J. I. Climente; Part III. Optical Properties of Quantum Dots in Photonic Cavities and Plasmon-Coupled Dots: 8. Deterministic light-matter coupling using single quantum dots P. Senellart; 9. Quantum dots in photonic crystal cavities A. Faraon, D. Englund, I. Fushman, A. Majumdar and J. Vukovic; 10. Photon statistics in quantum dot micropillar emission M. Asmann and M. Bayer; 11. Nanoplasmonics with colloidal quantum dots V. Temnov and U. Woggon; Part IV. Quantum Dot Nano-Laboratory: Magnetic Ions and Nuclear Spins in a Dot: 12. Dynamics and optical control of an individual Mn spin in a quantum dot L. Besombes, C. Le Gall, H. Boukari and H. Mariette; 13. Optical spectroscopy of InAs/GaAs quantum dots doped with a single Mn atom O. Krebs and A. Lemaitre; 14. Nuclear spin effects in quantum dot optics B. Urbaszek, B. Eble, T. Amand and X. Marie; Part V. Electron Transport in Quantum Dots Fabricated by

  16. Atomic step-and-terrace surface of polyimide sheet for advanced polymer substrate engineering

    NASA Astrophysics Data System (ADS)

    Tan, G.; Shimada, K.; Nozawa, Y.; Kaneko, S.; Urakami, T.; Koyama, K.; Komura, M.; Matsuda, A.; Yoshimoto, M.

    2016-07-01

    Typical thermostable and flexible polyimide polymers exhibit many excellent properties such as strong mechanical and chemical resistance. However, in contrast to single-crystal substrates like silicon or sapphire, polymers mostly display disordered and rough surfaces, which may result in instability and degradation of the interfaces between thin films and polymer substrates. As a step toward the development of next-generation polymer substrates, we here report single-atom-layer imprinting onto the polyimide sheets, resulting in an ultrasmooth 0.3 nm high atomic step-and-terrace surface on the polyimides. The ultrasmooth polymer substrates are expected to be applied to the fabrication of nanostructures such as superlattices, nanowires, or quantum dots in nanoscale-controlled electronic devices. We fabricate smooth and atomically stepped indium tin oxide transparent conducting oxide thin films on the imprinted polyimide sheets for future use in organic-based optoelectronic devices processed with nanoscale precision. Furthermore, toward 2D polymer substrate nanoengineering, we demonstrate nanoscale letter writing on the atomic step-and-terrace polyimide surface via atomic force microscopy probe scratching.

  17. Step-wise switching of anomalous Hall effect in a topological insulator

    NASA Astrophysics Data System (ADS)

    Zhao, Lukas; Chen, Zhiyi; Korzhovska, Inna; Zhao, Shihua; Krusin-Elbaum, Lia; Konczykowski, Marcin

    Surfaces of three-dimensional (3D) topological insulators (TIs) have emerged as one of the most remarkable states of condensed quantum matter where exotic charge and spin phases of Dirac particles could arise. The main challenge to finding these phases comes from a non-vanishing conductivity of the bulk. Recently we have demonstrated that we can access 2D surface transport and reach the charge neutrality point (CNP) by compensating intrinsically p-type TIs using high energy electron beams, and increase bulk resistivity by orders of magnitude. Here we report a discovery of anomalous Hall signal (AHE) at the CNP in Bi2Te3 of unprecedented appearance; it shows regions of plateaus on sweeping the temperature, where Hall resistivity is flat in temperature, and has sharp (nearly discontinuous) `steps' in-between the plateaus. The height of the steps increases on cooling, consistently following the ratio of 1:3 with each step. We will show by electrostatically tuning gated structures how this macroscopic switching of spins evolves in the vicinity of CNP and discuss the phenomenon of step-wise AHE in the context of charge inhomogeneities (puddles) and correlations between the localized bulk spins and Dirac spins. Supported by NSF-DMR-1420634, NSF-DMR-1312483-MWN, and DOD-W911NF-13-1-0159.

  18. Atomic step-and-terrace surface of polyimide sheet for advanced polymer substrate engineering.

    PubMed

    Tan, G; Shimada, K; Nozawa, Y; Kaneko, S; Urakami, T; Koyama, K; Komura, M; Matsuda, A; Yoshimoto, M

    2016-07-22

    Typical thermostable and flexible polyimide polymers exhibit many excellent properties such as strong mechanical and chemical resistance. However, in contrast to single-crystal substrates like silicon or sapphire, polymers mostly display disordered and rough surfaces, which may result in instability and degradation of the interfaces between thin films and polymer substrates. As a step toward the development of next-generation polymer substrates, we here report single-atom-layer imprinting onto the polyimide sheets, resulting in an ultrasmooth 0.3 nm high atomic step-and-terrace surface on the polyimides. The ultrasmooth polymer substrates are expected to be applied to the fabrication of nanostructures such as superlattices, nanowires, or quantum dots in nanoscale-controlled electronic devices. We fabricate smooth and atomically stepped indium tin oxide transparent conducting oxide thin films on the imprinted polyimide sheets for future use in organic-based optoelectronic devices processed with nanoscale precision. Furthermore, toward 2D polymer substrate nanoengineering, we demonstrate nanoscale letter writing on the atomic step-and-terrace polyimide surface via atomic force microscopy probe scratching. PMID:27284690

  19. Dissipative quantum computing with open quantum walks

    SciTech Connect

    Sinayskiy, Ilya; Petruccione, Francesco

    2014-12-04

    An open quantum walk approach to the implementation of a dissipative quantum computing scheme is presented. The formalism is demonstrated for the example of an open quantum walk implementation of a 3 qubit quantum circuit consisting of 10 gates.

  20. 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.

  1. Conducting a thermal conductivity survey

    NASA Technical Reports Server (NTRS)

    Allen, P. B.

    1985-01-01

    A physically transparent approximate theory of phonon decay rates is presented starting from a pair potential model of the interatomic forces in an insulator or semiconductor. The theory applies in the classical regime and relates the 3-phonon decay rate to the third derivative of the pair potential. Phonon dispersion relations do not need to be calculated, as sum rules relate all the needed quantities directly to the pair potential. The Brillouin zone averaged phonon lifetime turns out to involve a dimensionless measure of the anharmonicity multiplied by an effective density of states for 3-phonon decay. Results are given for rare gas and alkali halide crystals. For rare gases, the results are in good agreement with more elaborate perturbation calculations. Comparison to experimental data on phonon linewidths and thermal conductivity are made.

  2. Electrically conductive alternating copolymers

    DOEpatents

    Aldissi, M.; Jorgensen, B.S.

    1987-08-31

    Polymers which are soluble in common organic solvents and are electrically conductive, but which also may be synthesized in such a manner that they become nonconductive. Negative ions from the electrolyte used in the electrochemical synthesis of a polymer are incorporated into the polymer during the synthesis and serve as a dopant. A further electrochemical step may be utilized to cause the polymer to be conductive. The monomer repeat unit is comprised of two rings, a pyrrole molecule joined to a thienyl group, or a furyl group, or a phenyl group. The individual groups of the polymers are arranged in an alternating manner. For example, the backbone arrangement of poly(furylpyrrole) is -furan-pyrrole-furan-pyrrole- furan-pyrrole. An alkyl group or phenyl group may be substituted for either or both of the hydrogen atoms of the pyrrole ring.

  3. Micromachine Wedge Stepping Motor

    SciTech Connect

    Allen, J.J.; Schriner, H.K.

    1998-11-04

    A wedge stepping motor, which will index a mechanism, has been designed and fabricated in the surface rnicromachine SUMMiT process. This device has demonstrated the ability to index one gear tooth at a time with speeds up to 205 teeth/see. The wedge stepper motor has the following features, whi:h will be useful in a number of applications. o The ability to precisely position mechanical components. . Simple pulse signals can be used for operation. o Only 2 drive signals are requixed for operation. o Torque and precision capabilities increase with device size . The device to be indexed is restrained at all times by the wedge shaped tooth that is used for actuation. This paper will discuss the theory of operation and desi=m of the wedge stepping motor. The fabrication and testing of I he device will also be presented.

  4. The digital step edge

    NASA Technical Reports Server (NTRS)

    Haralick, R. M.

    1982-01-01

    The facet model was used to accomplish step edge detection. The essence of the facet model is that any analysis made on the basis of the pixel values in some neighborhood has its final authoritative interpretation relative to the underlying grey tone intensity surface of which the neighborhood pixel values are observed noisy samples. Pixels which are part of regions have simple grey tone intensity surfaces over their areas. Pixels which have an edge in them have complex grey tone intensity surfaces over their areas. Specially, an edge moves through a pixel only if there is some point in the pixel's area having a zero crossing of the second directional derivative taken in the direction of a non-zero gradient at the pixel's center. To determine whether or not a pixel should be marked as a step edge pixel, its underlying grey tone intensity surface was estimated on the basis of the pixels in its neighborhood.

  5. Digital quantum Rabi and Dicke models in superconducting circuits.

    PubMed

    Mezzacapo, A; Las Heras, U; Pedernales, J S; DiCarlo, L; Solano, E; Lamata, L

    2014-12-15

    We propose the analog-digital quantum simulation of the quantum Rabi and Dicke models using circuit quantum electrodynamics (QED). We find that all physical regimes, in particular those which are impossible to realize in typical cavity QED setups, can be simulated via unitary decomposition into digital steps. Furthermore, we show the emergence of the Dirac equation dynamics from the quantum Rabi model when the mode frequency vanishes. Finally, we analyze the feasibility of this proposal under realistic superconducting circuit scenarios.

  6. Digital Quantum Rabi and Dicke Models in Superconducting Circuits

    PubMed Central

    Mezzacapo, A.; Las Heras, U.; Pedernales, J. S.; DiCarlo, L.; Solano, E.; Lamata, L.

    2014-01-01

    We propose the analog-digital quantum simulation of the quantum Rabi and Dicke models using circuit quantum electrodynamics (QED). We find that all physical regimes, in particular those which are impossible to realize in typical cavity QED setups, can be simulated via unitary decomposition into digital steps. Furthermore, we show the emergence of the Dirac equation dynamics from the quantum Rabi model when the mode frequency vanishes. Finally, we analyze the feasibility of this proposal under realistic superconducting circuit scenarios. PMID:25500735

  7. QUANTUM MECHANICS: Enhanced: Schrodinger's Cat Is Out of the Hat.

    PubMed

    Tesche, C

    2000-10-27

    In 1935, Erwin Schrödinger suggested his famous gedanken experiment of the cat that is simultaneously "dead" and "alive" inside its box until the box is opened. But as Tesche explains in her Perspective, such a macroscopic manifestation of quantum mechanics has remained elusive until recently. The experiments by van der Wal et al. are an important step toward demonstrating that quantum mechanics can describe macroscopic phenomena. The approach may be exploited in quantum computing and quantum cryptography.

  8. Quantum metrology

    NASA Technical Reports Server (NTRS)

    Lee, H.; Kok, P.; Dowling, J. P.

    2002-01-01

    This paper addresses the formal equivalence between the Mach-Zehnder interferometer, the Ramsey spectroscope, and a specific quantum logical gate. Based on this equivalence we introduce the quantum Rosetta Stone, and we describe a projective measurement scheme for generating the desired correlations between the interferometric input states in order to achieve Heisenberg-limited sensitivity.

  9. Quantum microbiology.

    PubMed

    Trevors, J T; Masson, L

    2011-01-01

    During his famous 1943 lecture series at Trinity College Dublin, the reknown physicist Erwin Schrodinger discussed the failure and challenges of interpreting life by classical physics alone and that a new approach, rooted in Quantum principles, must be involved. Quantum events are simply a level of organization below the molecular level. This includes the atomic and subatomic makeup of matter in microbial metabolism and structures, as well as the organic, genetic information code of DNA and RNA. Quantum events at this time do not elucidate, for example, how specific genetic instructions were first encoded in an organic genetic code in microbial cells capable of growth and division, and its subsequent evolution over 3.6 to 4 billion years. However, due to recent technological advances, biologists and physicists are starting to demonstrate linkages between various quantum principles like quantum tunneling, entanglement and coherence in biological processes illustrating that nature has exerted some level quantum control to optimize various processes in living organisms. In this article we explore the role of quantum events in microbial processes and endeavor to show that after nearly 67 years, Schrödinger was prophetic and visionary in his view of quantum theory and its connection with some of the fundamental mechanisms of life. PMID:21368338

  10. Quantum spin Hall effect in nanostructures based on cadmium fluoride

    SciTech Connect

    Bagraev, N. T.; Guimbitskaya, O. N.; Klyachkin, L. E.; Koudryavtsev, A. A.; Malyarenko, A. M.; Romanov, V. V.; Ryskin, A. I.; Shcheulin, A. S.

    2010-10-15

    Tunneling current-voltage (I-V) characteristics and temperature dependences of static magnetic susceptibility and specific heat of the CdB{sub x}F{sub 2-x}/p-CdF{sub 2}-QW/CdB{sub x}F{sub 2-x} planar sandwich structures formed on the surface of an n-CdF{sub 2} crystal have been studied in order to identify superconducting properties of the CdB{sub x}F{sub 2-x} {delta} barriers confining the p-type CdF{sub 2} ultranarrow quantum well. Comparative analysis of current-voltage (I-V) characteristics and conductance-voltage dependences (measured at the temperatures, respectively, below and above the critical temperature of superconducting transition) indicates that there is an interrelation between quantization of supercurrent and dimensional quantization of holes in the p-CdF{sub 2} ultranarrow quantum well. It is noteworthy that detection of the Josephson peak of current in each hole subband is accompanied by the appearance of the spectrum of the multiple Andreev reflection (MAR). A high degree of spin polarization of holes in the edge channels along the perimeter of the p-CdF{sub 2} ultranarrow quantum well appears as a result of MAR and makes it possible to identify the quantum spin Hall effect I-V characteristics; this effect becomes pronounced in the case of detection of nonzero conductance at the zero voltage applied to the vertical gate in the Hall geometry of the experiment. Within the energy range of superconducting gap, the I-V characteristics of the spin transistor and quantum spin Hall effect are controlled by the MAR spectrum appearing as the voltage applied to the vertical gate is varied. Beyond the range of the superconducting gap, the observed I-V characteristic of the quantum spin Hall effect is represented by a quantum conductance staircase with a height of the steps equal to e{sub 2}/h; this height is interrelated with the Aharonov-Casher oscillations of longitudinal and depends on the voltage applied to the vertical gate.

  11. Scattering in Quantum Lattice Gases

    NASA Astrophysics Data System (ADS)

    O'Hara, Andrew; Love, Peter

    2009-03-01

    Quantum Lattice Gas Automata (QLGA) are of interest for their use in simulating quantum mechanics on both classical and quantum computers. QLGAs are an extension of classical Lattice Gas Automata where the constraint of unitary evolution is added. In the late 1990s, David A. Meyer as well as Bruce Boghosian and Washington Taylor produced similar models of QLGAs. We start by presenting a unified version of these models and study them from the point of view of the physics of wave-packet scattering. We show that the Meyer and Boghosian-Taylor models are actually the same basic model with slightly different parameterizations and limits. We then implement these models computationally using the Python programming language and show that QLGAs are able to replicate the analytic results of quantum mechanics (for example reflected and transmitted amplitudes for step potentials and the Klein paradox).

  12. Quantum Dots: An Experiment for Physical or Materials Chemistry

    ERIC Educational Resources Information Center

    Winkler, L. D.; Arceo, J. F.; Hughes, W. C.; DeGraff, B. A.; Augustine, B. H.

    2005-01-01

    An experiment is conducted for obtaining quantum dots for physical or materials chemistry. This experiment serves to both reinforce the basic concept of quantum confinement and providing a useful bridge between the molecular and solid-state world.

  13. Quantum computing with defects.

    PubMed

    Weber, J R; Koehl, W F; Varley, J B; Janotti, A; Buckley, B B; Van de Walle, C G; Awschalom, D D

    2010-05-11

    Identifying and designing physical systems for use as qubits, the basic units of quantum information, are critical steps in the development of a quantum computer. Among the possibilities in the solid state, a defect in diamond known as the nitrogen-vacancy (NV(-1)) center stands out for its robustness--its quantum state can be initialized, manipulated, and measured with high fidelity at room temperature. Here we describe how to systematically identify other deep center defects with similar quantum-mechanical properties. We present a list of physical criteria that these centers and their hosts should meet and explain how these requirements can be used in conjunction with electronic structure theory to intelligently sort through candidate defect systems. To illustrate these points in detail, we compare electronic structure calculations of the NV(-1) center in diamond with those of several deep centers in 4H silicon carbide (SiC). We then discuss the proposed criteria for similar defects in other tetrahedrally coordinated semiconductors.

  14. Quantum computing with defects

    PubMed Central

    Weber, J. R.; Koehl, W. F.; Varley, J. B.; Janotti, A.; Buckley, B. B.; Van de Walle, C. G.; Awschalom, D. D.

    2010-01-01

    Identifying and designing physical systems for use as qubits, the basic units of quantum information, are critical steps in the development of a quantum computer. Among the possibilities in the solid state, a defect in diamond known as the nitrogen-vacancy (NV-1) center stands out for its robustness—its quantum state can be initialized, manipulated, and measured with high fidelity at room temperature. Here we describe how to systematically identify other deep center defects with similar quantum-mechanical properties. We present a list of physical criteria that these centers and their hosts should meet and explain how these requirements can be used in conjunction with electronic structure theory to intelligently sort through candidate defect systems. To illustrate these points in detail, we compare electronic structure calculations of the NV-1 center in diamond with those of several deep centers in 4H silicon carbide (SiC). We then discuss the proposed criteria for similar defects in other tetrahedrally coordinated semiconductors. PMID:20404195

  15. Quantum thermal transport in stanene

    NASA Astrophysics Data System (ADS)

    Zhou, Hangbo; Cai, Yongqing; Zhang, Gang; Zhang, Yong-Wei

    2016-07-01

    By way of the nonequilibrium Green's function simulations and analytical expressions, the quantum thermal conductance of stanene is studied. We find that, due to the existence of Dirac fermion in stanene, the ratio of electron thermal conductance and electric conductance becomes a chemical-potential-dependent quantity, violating the Wiedemann-Franz law. This finding is applicable to any two-dimensional (2D) materials that possess massless Dirac fermions. In strong contrast to the negligible electronic contribution in graphene, surprisingly, the electrons and phonons in stanene carry a comparable heat current. The unusual behaviors in stanene widen our knowledge of quantum thermal transport in 2D materials.

  16. Optimal time step for incompressible SPH

    NASA Astrophysics Data System (ADS)

    Violeau, Damien; Leroy, Agnès

    2015-05-01

    A classical incompressible algorithm for Smoothed Particle Hydrodynamics (ISPH) is analyzed in terms of critical time step for numerical stability. For this purpose, a theoretical linear stability analysis is conducted for unbounded homogeneous flows, leading to an analytical formula for the maximum CFL (Courant-Friedrichs-Lewy) number as a function of the Fourier number. This gives the maximum time step as a function of the fluid viscosity, the flow velocity scale and the SPH discretization size (kernel standard deviation). Importantly, the maximum CFL number at large Reynolds number appears twice smaller than with the traditional Weakly Compressible (WCSPH) approach. As a consequence, the optimal time step for ISPH is only five times larger than with WCSPH. The theory agrees very well with numerical data for two usual kernels in a 2-D periodic flow. On the other hand, numerical experiments in a plane Poiseuille flow show that the theory overestimates the maximum allowed time step for small Reynolds numbers.

  17. Karl Popper's Quantum Ghost

    NASA Astrophysics Data System (ADS)

    Shields, William

    2004-05-01

    Karl Popper, though not trained as a physicist and embarrassed early in his career by a physics error pointed out by Einstein and Bohr, ultimately made substantial contributions to the interpretation of quantum mechanics. As was often the case, Popper initially formulated his position by criticizing the views of others - in this case Niels Bohr and Werner Heisenberg. Underlying Popper's criticism was his belief that, first, the "standard interpretation" of quantum mechanics, sometimes called the Copenhagen interpretation, abandoned scientific realism and second, the assertion that quantum theory was "complete" (an assertion rejected by Einstein among others) amounted to an unfalsifiable claim. Popper insisted that the most basic predictions of quantum mechanics should continue to be tested, with an eye towards falsification rather than mere adding of decimal places to confirmatory experiments. His persistent attacks on the Copenhagen interpretation were aimed not at the uncertainty principle itself and the formalism from which it was derived, but at the acceptance by physicists of an unclear epistemology and ontology that left critical questions unanswered. In 1999, physicists at the University of Maryland conducted a version of Popper's Experiment, re-igniting the debate over quantum predictions and the role of locality in physics.

  18. Quantum strategies of quantum measurements

    NASA Astrophysics Data System (ADS)

    Li, Chuan-Feng; Zhang, Yong-Sheng; Huang, Yun-Feng; Guo, Guang-Can

    2001-03-01

    In the classical Monty Hall problem, one player can always win with probability 2/3. We generalize the problem to the quantum domain and show that a fair two-party zero-sum game can be carried out if the other player is permitted to adopt quantum measurement strategy.

  19. New photolithography stepping machine

    SciTech Connect

    Hale, L.; Klingmann, J.; Markle, D.

    1995-03-08

    A joint development project to design a new photolithography steeping machine capable of 150 nanometer overlay accuracy was completed by Ultratech Stepper and the Lawrence Livermore National Laboratory. The principal result of the project is a next-generation product that will strengthen the US position in step-and-repeat photolithography. The significant challenges addressed and solved in the project are the subject of this report. Design methods and new devices that have broader application to precision machine design are presented in greater detail while project specific information serves primarily as background and motivation.

  20. Steps to the moon

    USGS Publications Warehouse

    ,; Dale, Alvin E.

    1976-01-01

    On July 20, 1969, man walked on the surface of the Moon and began a new chapter of his studies that will eventually disclose the geologic nature of the Earth's nearest neighbor. Although he has finally reached the Moon and sampled its substance, much work and study remain before he will know the full scientific significance of the first landing. This booklet briefly summarizes the steps man has taken to understand the Moon and what he thinks he has learned to date as a result of his centuries-long speculations and studies.

  1. Experimentation: the next step

    PubMed Central

    Marinker, Marshall

    1987-01-01

    General practice has entered a period of accelerating change, and those responsible for planning its development now put forward a variety of promising proposals. Unless provision is made for large scale experimentation and scientific evaluation, the direction of future change will be determined not by evidence but by rhetoric. A framework for creating and evaluating a substantial programme of experimentation is suggested. The programme is the logical next step in the process of change which was given impetus by the publication of the government green paper. It should be seen as a professional, moral and political priority. PMID:3681850

  2. Predictive Quantum Chemistry: A Step Toward ``Chemistry Without Test Tubes''

    NASA Astrophysics Data System (ADS)

    Perera, Ajith

    2007-12-01

    The merits of the claims made in two recent papers entitled "First generation of pentazole (HN5, pentazolic acid), the final azole, and a zinc pentazolate salt in solution: A new N-dearylation of 1-(p-methoxyphenyl) pyrazoles, a 2-(p-methoxyphenyl) tetrazole and application of the methodology to 1-(p-methoxyphenyl) pentazole" (R. N. Butler, J. C. Stephan and L. A. Burke, J. Chem. Commun. 2003, 1016-1017) and "First generation of the pentazolate anion is solution is far from over" (T. Schroer, R. Haiges, S. Schneider and K. O. Christe, Chem. Commun. 2005, 1607-1609) are verified by predictive quality theoretical methods. Knowing whether the CF3OH in HF solution undergoes protonation to form CF3[OH2]+ is critical to the success of the recently proposed synthetic route to form the prototype perfluorinated alcohol, CF3OH. Chirstie and co-workers first considered the 13C and 19F shielding constants to distinguish CF3OH and CF3[OH2]+, but it turns out that they both have similar chemical shifts. Furthermore, they noted that the computed 13C chemical shifts differ by 11 ppm from the measured ones and claimed that "These findings presented a dilemma because either experimental or the calculated shifts has to be seriously flawed and, therefore chemical shifts alone it was impossible to decide whether CF3OH in liquid HF is protonated or not". Instead of chemical shifts, they propose to use 13C-19F NMR spin-spin coupling constants and argue that the observed 20 Hz difference of 1J(13C-19F) to the increase in the covalent character upon protonation. The reported discrepancy in computed and measured chemical shifts is reexamined and the spin-spin coupling constants results are verified by the predicative-level calculations.

  3. Quantum physics without quantum philosophy

    NASA Astrophysics Data System (ADS)

    Dürr, Detlef; Goldstein, Sheldon; Zanghì, Nino

    Quantum philosophy, a peculiar twentieth-century malady, is responsible for most of the conceptual muddle plaguing the foundations of quantum physics. When this philosophy is eschewed, one naturally arrives at Bohmian mechanics, which is what emerges from Schrödinger's equation for a nonrelativistic system of particles when we merely insist that 'particles' means particles. While distinctly non-Newtonian, Bohmian mechanics is a fully deterministic theory of particles in motion, a motion choreographed by the wave function. The quantum formalism emerges when measurement situations are analyzed according to this theory. When the quantum formalism is regarded as arising in this way, the paradoxes and perplexities so often associated with quantum theory simply evaporate.

  4. Realization of reliable solid-state quantum memory for photonic polarization qubit.

    PubMed

    Zhou, Zong-Quan; Lin, Wei-Bin; Yang, Ming; Li, Chuan-Feng; Guo, Guang-Can

    2012-05-11

    Faithfully storing an unknown quantum light state is essential to advanced quantum communication and distributed quantum computation applications. The required quantum memory must have high fidelity to improve the performance of a quantum network. Here we report the reversible transfer of photonic polarization states into collective atomic excitation in a compact solid-state device. The quantum memory is based on an atomic frequency comb (AFC) in rare-earth ion-doped crystals. We obtain up to 0.999 process fidelity for the storage and retrieval process of single-photon-level coherent pulse. This reliable quantum memory is a crucial step toward quantum networks based on solid-state devices.

  5. Optimizing qubit resources for quantum chemistry simulations in second quantization on a quantum computer

    NASA Astrophysics Data System (ADS)

    Moll, Nikolaj; Fuhrer, Andreas; Staar, Peter; Tavernelli, Ivano

    2016-07-01

    Quantum chemistry simulations on a quantum computer suffer from the overhead needed for encoding the Fermionic problem in a system of qubits. By exploiting the block diagonality of a Fermionic Hamiltonian, we show that the number of required qubits can be reduced while the number of terms in the Hamiltonian will increase. All operations for this reduction can be performed in operator space. The scheme is conceived as a pre-computational step that would be performed prior to the actual quantum simulation. We apply this scheme to reduce the number of qubits necessary to simulate both the Hamiltonian of the two-site Fermi-Hubbard model and the hydrogen molecule. Both quantum systems can then be simulated with a two-qubit quantum computer. Despite the increase in the number of Hamiltonian terms, the scheme still remains a useful tool to reduce the dimensionality of specific quantum systems for quantum simulators with a limited number of resources.

  6. Optimizing qubit resources for quantum chemistry simulations in second quantization on a quantum computer

    NASA Astrophysics Data System (ADS)

    Moll, Nikolaj; Fuhrer, Andreas; Staar, Peter; Tavernelli, Ivano

    2016-07-01

    Quantum chemistry simulations on a quantum computer suffer from the overhead needed for encoding the Fermionic problem in a system of qubits. By exploiting the block diagonality of a Fermionic Hamiltonian, we show that the number of required qubits can be reduced while the number of terms in the Hamiltonian will increase. All operations for this reduction can be performed in operator space. The scheme is conceived as a pre-computational step that would be performed prior to the actual quantum simulation. We apply this scheme to reduce the number of qubits necessary to simulate both the Hamiltonian of the two-site Fermi–Hubbard model and the hydrogen molecule. Both quantum systems can then be simulated with a two-qubit quantum computer. Despite the increase in the number of Hamiltonian terms, the scheme still remains a useful tool to reduce the dimensionality of specific quantum systems for quantum simulators with a limited number of resources.

  7. SPAR-H Step-by-Step Guidance

    SciTech Connect

    W. J. Galyean; A. M. Whaley; D. L. Kelly; R. L. Boring

    2011-05-01

    This guide provides step-by-step guidance on the use of the SPAR-H method for quantifying Human Failure Events (HFEs). This guide is intended to be used with the worksheets provided in: 'The SPAR-H Human Reliability Analysis Method,' NUREG/CR-6883, dated August 2005. Each step in the process of producing a Human Error Probability (HEP) is discussed. These steps are: Step-1, Categorizing the HFE as Diagnosis and/or Action; Step-2, Rate the Performance Shaping Factors; Step-3, Calculate PSF-Modified HEP; Step-4, Accounting for Dependence, and; Step-5, Minimum Value Cutoff. The discussions on dependence are extensive and include an appendix that describes insights obtained from the psychology literature.

  8. Quantum memory with millisecond coherence in circuit QED

    NASA Astrophysics Data System (ADS)

    Reagor, Matthew; Pfaff, Wolfgang; Axline, Christopher; Heeres, Reinier W.; Ofek, Nissim; Sliwa, Katrina; Holland, Eric; Wang, Chen; Blumoff, Jacob; Chou, Kevin; Hatridge, Michael J.; Frunzio, Luigi; Devoret, Michel H.; Jiang, Liang; Schoelkopf, Robert J.

    2016-07-01

    Significant advances in coherence render superconducting quantum circuits a viable platform for fault-tolerant quantum computing. To further extend capabilities, highly coherent quantum systems could act as quantum memories for these circuits. A useful quantum memory must be rapidly addressable by Josephson-junction-based artificial atoms, while maintaining superior coherence. We demonstrate a superconducting microwave cavity architecture that is highly robust against major sources of loss that are encountered in the engineering of circuit QED systems. The architecture allows for storage of quantum superpositions in a resonator on the millisecond scale, while strong coupling between the resonator and a transmon qubit enables control, encoding, and readout at MHz rates. This extends the maximum available coherence time attainable in superconducting circuits by almost an order of magnitude compared to earlier hardware. Our design is an ideal platform for studying coherent quantum optics and marks an important step towards hardware-efficient quantum computing in Josephson-junction-based quantum circuits.

  9. Experimental quantum fingerprinting with weak coherent pulses.

    PubMed

    Xu, Feihu; Arrazola, Juan Miguel; Wei, Kejin; Wang, Wenyuan; Palacios-Avila, Pablo; Feng, Chen; Sajeed, Shihan; Lütkenhaus, Norbert; Lo, Hoi-Kwong

    2015-10-30

    Quantum communication holds the promise of creating disruptive technologies that will play an essential role in future communication networks. For example, the study of quantum communication complexity has shown that quantum communication allows exponential reductions in the information that must be transmitted to solve distributed computational tasks. Recently, protocols that realize this advantage using optical implementations have been proposed. Here we report a proof-of-concept experimental demonstration of a quantum fingerprinting system that is capable of transmitting less information than the best-known classical protocol. Our implementation is based on a modified version of a commercial quantum key distribution system using off-the-shelf optical components over telecom wavelengths, and is practical for messages as large as 100 Mbits, even in the presence of experimental imperfections. Our results provide a first step in the development of experimental quantum communication complexity.

  10. Experimental quantum fingerprinting with weak coherent pulses

    PubMed Central

    Xu, Feihu; Arrazola, Juan Miguel; Wei, Kejin; Wang, Wenyuan; Palacios-Avila, Pablo; Feng, Chen; Sajeed, Shihan; Lütkenhaus, Norbert; Lo, Hoi-Kwong

    2015-01-01

    Quantum communication holds the promise of creating disruptive technologies that will play an essential role in future communication networks. For example, the study of quantum communication complexity has shown that quantum communication allows exponential reductions in the information that must be transmitted to solve distributed computational tasks. Recently, protocols that realize this advantage using optical implementations have been proposed. Here we report a proof-of-concept experimental demonstration of a quantum fingerprinting system that is capable of transmitting less information than the best-known classical protocol. Our implementation is based on a modified version of a commercial quantum key distribution system using off-the-shelf optical components over telecom wavelengths, and is practical for messages as large as 100 Mbits, even in the presence of experimental imperfections. Our results provide a first step in the development of experimental quantum communication complexity. PMID:26515586

  11. Information-Technology Approach to Quantum Feedback Control

    NASA Astrophysics Data System (ADS)

    Dong, Dao-Yi; Zhang, Chen-Bin; Chen, Zong-Hai; Chen, Chun-Lin

    Quantum control theory is profitably reexamined from the perspective of quantum information, two results on the role of quantum information technology in quantum feedback control are presented and two quantum feedback control schemes, teleportation-based distant quantum feedback control and quantum feedback control with quantum cloning, are proposed. In the first feedback scheme, the output from the quantum system to be controlled is fed back into the distant actuator via teleportation to alter the dynamics of system. The result theoretically shows that it can accomplish some tasks such as distant feedback quantum control that Markovian or Bayesian quantum feedback can not complete. In the second feedback strategy, the design of quantum feedback control algorithms is separated into a state recognition step, which gives "on-off" signal to the actuator through recognizing some copies from the cloning machine, and a feedback (control) step using another copies of cloning machine. A compromise between information acquisition and measurement disturbance is established, and this strategy can perform some quantum control tasks with coherent feedback.

  12. Stepping up, stepping back, stepping forward: Student nurses' experiences as peer mentors in a pre-nursing scholarship.

    PubMed

    Smith, Annetta; Beattie, Michelle; Kyle, Richard G

    2015-11-01

    Mentorship is an essential part of the registered nurse's role, yet few opportunities exist for student nurses to mentor others during pre-registration programmes. This paper reports student nurses' experiences of mentoring school pupils during a pre-nursing scholarship. Focus groups were conducted with fifteen final year student nurses (14 female, 1 male) in two university campuses in Scotland. Discussions were audio recorded and transcribed verbatim, and data analysed thematically. Three interconnected themes emerged: 1) stepping up; 2) stepping back; 3) stepping forward. 'Stepping up' was a process through which student nurses rapidly assumed responsibility for mentoring pupils, facilitated through the attitudes and actions of students' mentors and students' control over pupils' practice experiences. 'Stepping back' encapsulated attitudes and behaviours that enabled student nurses to mentor pupils that involved considerable judgement around how unfolding events in practice could provide learning and development opportunities, and emotional acuity to support pupils through, sometimes challenging, practice situations. 'Stepping forward' described how students' mentoring experience allowed them to appraise and affirm nursing knowledge and skills, and gain greater appreciation of the reality and complexity of mentorship in clinical practice. Peer mentoring may prepare student nurses for future mentoring roles and aid their transition into clinical practice.

  13. Quantum Adiabatic Pumping by Modulating Tunnel Phase in Quantum Dots

    NASA Astrophysics Data System (ADS)

    Taguchi, Masahiko; Nakajima, Satoshi; Kubo, Toshihiro; Tokura, Yasuhiro

    2016-08-01

    In a mesoscopic system, under zero bias voltage, a finite charge is transferred by quantum adiabatic pumping by adiabatically and periodically changing two or more control parameters. We obtained expressions for the pumped charge for a ring of three quantum dots (QDs) by choosing the magnetic flux penetrating the ring as one of the control parameters. We found that the pumped charge shows a steplike behavior with respect to the variance of the flux. The value of the step heights is not universal but depends on the trajectory of the control parameters. We discuss the physical origin of this behavior on the basis of the Fano resonant condition of the ring.

  14. Simulated annealing versus quantum annealing

    NASA Astrophysics Data System (ADS)

    Troyer, Matthias

    Based on simulated classical annealing and simulated quantum annealing using quantum Monte Carlo (QMC) simulations I will explore the question where physical or simulated quantum annealers may outperform classical optimization algorithms. Although the stochastic dynamics of QMC simulations is not the same as the unitary dynamics of a quantum system, I will first show that for the problem of quantum tunneling between two local minima both QMC simulations and a physical system exhibit the same scaling of tunneling times with barrier height. The scaling in both cases is O (Δ2) , where Δ is the tunneling splitting. An important consequence is that QMC simulations can be used to predict the performance of a quantum annealer for tunneling through a barrier. Furthermore, by using open instead of periodic boundary conditions in imaginary time, equivalent to a projector QMC algorithm, one obtains a quadratic speedup for QMC, and achieve linear scaling in Δ. I will then address the apparent contradiction between experiments on a D-Wave 2 system that failed to see evidence of quantum speedup and previous QMC results that indicated an advantage of quantum annealing over classical annealing for spin glasses. We find that this contradiction is resolved by taking the continuous time limit in the QMC simulations which then agree with the experimentally observed behavior and show no speedup for 2D spin glasses. However, QMC simulations with large time steps gain further advantage: they ``cheat'' by ignoring what happens during a (large) time step, and can thus outperform both simulated quantum annealers and classical annealers. I will then address the question how to optimally run a simulated or physical quantum annealer. Investigating the behavior of the tails of the distribution of runtimes for very hard instances we find that adiabatically slow annealing is far from optimal. On the contrary, many repeated relatively fast annealing runs can be orders of magnitude faster for

  15. Quantum Baseball.

    ERIC Educational Resources Information Center

    Peterson, Ivars

    1989-01-01

    An analogy from the game of baseball can be used to examine the philosophy involved in statistics surrounding quantum mechanical events. The "Strong Baseball Principle" is proposed and discussed. (CW)

  16. Stair-stepped Mound

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-429, 22 July 2003

    This April 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a stair-stepped mound of sedimentary rock (right of center) on the floor of a large impact crater in western Arabia Terra near 11.0oN, 4.4oW. Sedimentary rock outcrops are common in the craters of this region. The repeated thickness and uniformity of the layers that make up this mound suggest that their depositional environment was one in which cyclic or episodic events occurred over some period of time. The sediments might have been deposited in a lake, or they may have settled directly out of the atmosphere. Most of the layered material was later eroded away, leaving this circular mound and the other nearby mesas and knobs. The image is illuminated by sunlight from the lower left.

  17. An Integrated Development Environment for Adiabatic Quantum Programming

    SciTech Connect

    Humble, Travis S; McCaskey, Alex; Bennink, Ryan S; Billings, Jay Jay; D'Azevedo, Eduardo; Sullivan, Blair D; Klymko, Christine F; Seddiqi, Hadayat

    2014-01-01

    Adiabatic quantum computing is a promising route to the computational power afforded by quantum information processing. The recent availability of adiabatic hardware raises the question of how well quantum programs perform. Benchmarking behavior is challenging since the multiple steps to synthesize an adiabatic quantum program are highly tunable. We present an adiabatic quantum programming environment called JADE that provides control over all the steps taken during program development. JADE captures the workflow needed to rigorously benchmark performance while also allowing a variety of problem types, programming techniques, and processor configurations. We have also integrated JADE with a quantum simulation engine that enables program profiling using numerical calculation. The computational engine supports plug-ins for simulation methodologies tailored to various metrics and computing resources. We present the design, integration, and deployment of JADE and discuss its use for benchmarking adiabatic quantum programs.

  18. Diffeomorphism invariant cosmological symmetry in full quantum gravity

    NASA Astrophysics Data System (ADS)

    Beetle, Christopher; Engle, Jonathan S.; Hogan, Matthew E.; Mendonça, Phillip

    2016-06-01

    This paper summarizes a new proposal to define rigorously a sector of loop quantum gravity at the diffeomorphism invariant level corresponding to homogeneous and isotropic cosmologies, thereby enabling a detailed comparison of results in loop quantum gravity and loop quantum cosmology. The key technical steps we have completed are (a) to formulate conditions for homogeneity and isotropy in a diffeomorphism covariant way on the classical phase-space of general relativity, and (b) to translate these conditions consistently using well-understood techniques to loop quantum gravity. Some additional steps, such as constructing a specific embedding of the Hilbert space of loop quantum cosmology into a space of (distributional) states in the full theory, remain incomplete. However, we also describe, as a proof of concept, a complete analysis of an analogous embedding of homogeneous and isotropic loop quantum cosmology into the quantum Bianchi I model of Ashtekar and Wilson-Ewing. Details will appear in a pair of forthcoming papers.

  19. Magnetoconductance of quantum wires

    NASA Astrophysics Data System (ADS)

    Ferreira, Gerson J.; Sammarco, Filipe; Egues, Carlos

    2010-03-01

    At low temperatures the conductance of a quantum wires exhibit characteristic plate-aus due to the quantization of the transverse modes [1]. In the presence of high in-plane magnetic fields these spin-split transverse modes cross. Recently, these crossings were observed experimentally [2] via measurements of the differential conductance as a function of the gate voltage and the in-plane magnetic-field. These show structures described as either anti-crossings or magnetic phase transitions. Motivated by our previous works on magnetotransport in 2DEGs via the Spin Density Functional Theory (SDFT) [3], here we propose a similar model to investigate the magnetoconductance of quantum wires. We use (i) the SDFT via the Kohn-Sham self-consistent scheme within the local spin density approximation to obtain the electronic structure and (ii) the Landauer-Buettiker formalism to calculate the conductance of a quantum wire. Our results show qualitative agreement with the data of Ref. [2]. [1] B. J. van Wees et al., Phys. Rev. Lett. 60, 848 (1988). [2] A. C. Graham et al., Phys. Rev. Lett. 100, 226804 (2008). [3] H. J. P. Freire, and J. C. Egues, Phys. Rev. Lett. 99, 026801 (2007); G. J. Ferreira, and J. Carlos Egues, J. Supercond. Nov. Mag., in press; G. J. Ferreira, H. J. P. Freire, J. Carlos Egues, submitted.

  20. Quantum Locality?

    NASA Astrophysics Data System (ADS)

    Stapp, Henry P.

    2012-05-01

    Robert Griffiths has recently addressed, within the framework of a `consistent quantum theory' that he has developed, the issue of whether, as is often claimed, quantum mechanics entails a need for faster-than-light transfers of information over long distances. He argues that the putative proofs of this property that involve hidden variables include in their premises some essentially classical-physics-type assumptions that are not entailed by the precepts of quantum mechanics. Thus whatever is proved is not a feature of quantum mechanics, but is a property of a theory that tries to combine quantum theory with quasi-classical features that go beyond what is entailed by quantum theory itself. One cannot logically prove properties of a system by establishing, instead, properties of a system modified by adding properties alien to the original system. Hence Griffiths' rejection of hidden-variable-based proofs is logically warranted. Griffiths mentions the existence of a certain alternative proof that does not involve hidden variables, and that uses only macroscopically described observable properties. He notes that he had examined in his book proofs of this general kind, and concluded that they provide no evidence for nonlocal influences. But he did not examine the particular proof that he cites. An examination of that particular proof by the method specified by his `consistent quantum theory' shows that the cited proof is valid within that restrictive version of quantum theory. An added section responds to Griffiths' reply, which cites general possibilities of ambiguities that might make what is to be proved ill-defined, and hence render the pertinent `consistent framework' ill defined. But the vagaries that he cites do not upset the proof in question, which, both by its physical formulation and by explicit identification, specify the framework to be used. Griffiths confirms the validity of the proof insofar as that pertinent framework is used. The section also shows

  1. Quantum correlations and distinguishability of quantum states

    SciTech Connect

    Spehner, Dominique

    2014-07-15

    A survey of various concepts in quantum information is given, with a main emphasis on the distinguishability of quantum states and quantum correlations. Covered topics include generalized and least square measurements, state discrimination, quantum relative entropies, the Bures distance on the set of quantum states, the quantum Fisher information, the quantum Chernoff bound, bipartite entanglement, the quantum discord, and geometrical measures of quantum correlations. The article is intended both for physicists interested not only by collections of results but also by the mathematical methods justifying them, and for mathematicians looking for an up-to-date introductory course on these subjects, which are mainly developed in the physics literature.

  2. Step bunching and ordering induced by step-edge barriers

    NASA Astrophysics Data System (ADS)

    Zhao, Yuegang; Liu, Feng; Tersoff, Jerry; Lagally, Max G.

    2000-03-01

    We derive the equation of motion of steps for step flow growth under the influence of both misfit strain and step-edge barriers. An energy barrier at a step for an atom arriving from the lower terrace causes a step bunching instability. Simulation results show that the bunching is predominantly driven by a coalescence mechanism, leading to multiple transient stages of metastable step bunch arrays, with average bunch size of 2, 4, and 8 steps. The bunch array in these transient stages exhibits a surprisingly good long-range order. Similar kinetic step-bunch ordering has been seen in a a recent experiment[1]. Reference: [1]: C. Schelling, G. Springholz, and F. Schäffler, Phys. Rev. Letts, 83(995)1999.

  3. Stochastic solution to quantum dynamics

    NASA Technical Reports Server (NTRS)

    John, Sarah; Wilson, John W.

    1994-01-01

    The quantum Liouville equation in the Wigner representation is solved numerically by using Monte Carlo methods. For incremental time steps, the propagation is implemented as a classical evolution in phase space modified by a quantum correction. The correction, which is a momentum jump function, is simulated in the quasi-classical approximation via a stochastic process. The technique, which is developed and validated in two- and three- dimensional momentum space, extends an earlier one-dimensional work. Also, by developing a new algorithm, the application to bound state motion in an anharmonic quartic potential shows better agreement with exact solutions in two-dimensional phase space.

  4. Broadband waveguide quantum memory for entangled photons.

    PubMed

    Saglamyurek, Erhan; Sinclair, Neil; Jin, Jeongwan; Slater, Joshua A; Oblak, Daniel; Bussières, Félix; George, Mathew; Ricken, Raimund; Sohler, Wolfgang; Tittel, Wolfgang

    2011-01-27

    The reversible transfer of quantum states of light into and out of matter constitutes an important building block for future applications of quantum communication: it will allow the synchronization of quantum information, and the construction of quantum repeaters and quantum networks. Much effort has been devoted to the development of such quantum memories, the key property of which is the preservation of entanglement during storage. Here we report the reversible transfer of photon-photon entanglement into entanglement between a photon and a collective atomic excitation in a solid-state device. Towards this end, we employ a thulium-doped lithium niobate waveguide in conjunction with a photon-echo quantum memory protocol, and increase the spectral acceptance from the current maximum of 100 megahertz to 5 gigahertz. We assess the entanglement-preserving nature of our storage device through Bell inequality violations and by comparing the amount of entanglement contained in the detected photon pairs before and after the reversible transfer. These measurements show, within statistical error, a perfect mapping process. Our broadband quantum memory complements the family of robust, integrated lithium niobate devices. It simplifies frequency-matching of light with matter interfaces in advanced applications of quantum communication, bringing fully quantum-enabled networks a step closer.

  5. Green Schools Energy Project: A Step-by-Step Manual.

    ERIC Educational Resources Information Center

    Quigley, Gwen

    This publication contains a step-by-step guide for implementing an energy-saving project in local school districts: the installation of newer, more energy-efficient "T-8" fluorescent tube lights in place of "T-12" lights. Eleven steps are explained in detail: (1) find out what kind of lights the school district currently uses; (2) form a group to…

  6. Carbon Fibers Conductivity Studies

    NASA Technical Reports Server (NTRS)

    Yang, C. Y.; Butkus, A. M.

    1980-01-01

    In an attempt to understand the process of electrical conduction in polyacrylonitrile (PAN)-based carbon fibers, calculations were carried out on cluster models of the fiber consisting of carbon, nitrogen, and hydrogen atoms using the modified intermediate neglect of differential overlap (MINDO) molecular orbital (MO) method. The models were developed based on the assumption that PAN carbon fibers obtained with heat treatment temperatures (HTT) below 1000 C retain nitrogen in a graphite-like lattice. For clusters modeling an edge nitrogen site, analysis of the occupied MO's indicated an electron distribution similar to that of graphite. A similar analysis for the somewhat less stable interior nitrogen site revealed a partially localized II electron distribution around the nitrogen atom. The differences in bonding trends and structural stability between edge and interior nitrogen clusters led to a two-step process proposed for nitrogen evolution with increasing HTT.

  7. Externally mode-matched cavity quantum electrodynamics with charge-tunable quantum dots.

    PubMed

    Rakher, M T; Stoltz, N G; Coldren, L A; Petroff, P M; Bouwmeester, D

    2009-03-01

    We present coherent reflection spectroscopy on a charge and dc Stark tunable quantum dot embedded in a high-quality and externally mode-matched microcavity. The addition of an exciton to a single-electron-charged quantum dot forms a trion that interacts with the microcavity just below the strong-coupling regime of cavity quantum electrodynamics. Such an integrated, monolithic system is a crucial step towards the implementation of scalable hybrid quantum-information schemes that are based on an efficient interaction between a single photon and a confined electron spin.

  8. Quantum Anomalous Hall Effect in Hg_1-yMn_yTe Quantum Wells

    SciTech Connect

    Liu, Chao-Xing; Qi, Xiao-Liang; Dai, Xi; Fang, Zhong; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-19

    The quantum Hall effect is usually observed when the two-dimensional electron gas is subjected to an external magnetic field, so that their quantum states form Landau levels. In this work we predict that a new phenomenon, the quantum anomalous Hall effect, can be realized in Hg{sub 1-y}Mn{sub y}Te quantum wells, without the external magnetic field and the associated Landau levels. This effect arises purely from the spin polarization of the Mn atoms, and the quantized Hall conductance is predicted for a range of quantum well thickness and the concentration of the Mn atoms. This effect enables dissipationless charge current in spintronics devices.

  9. Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Mandl, F.

    1992-07-01

    The Manchester Physics Series General Editors: D. J. Sandiford; F. Mandl; A. C. Phillips Department of Physics and Astronomy, University of Manchester Properties of Matter B. H. Flowers and E. Mendoza Optics Second Edition F. G. Smith and J. H. Thomson Statistical Physics Second Edition F. Mandl Electromagnetism Second Edition I. S. Grant and W. R. Phillips Statistics R. J. Barlow Solid State Physics Second Edition J. R. Hook and H. E. Hall Quantum Mechanics F. Mandl Particle Physics Second Edition B. R. Martin and G. Shaw The Physics of Stars Second Edition A. C. Phillips Computing for Scientists R. J. Barlow and A. R. Barnett Quantum Mechanics aims to teach those parts of the subject which every physicist should know. The object is to display the inherent structure of quantum mechanics, concentrating on general principles and on methods of wide applicability without taking them to their full generality. This book will equip students to follow quantum-mechanical arguments in books and scientific papers, and to cope with simple cases. To bring the subject to life, the theory is applied to the all-important field of atomic physics. No prior knowledge of quantum mechanics is assumed. However, it would help most readers to have met some elementary wave mechanics before. Primarily written for students, it should also be of interest to experimental research workers who require a good grasp of quantum mechanics without the full formalism needed by the professional theorist. Quantum Mechanics features: A flow diagram allowing topics to be studied in different orders or omitted altogether. Optional "starred" and highlighted sections containing more advanced and specialized material for the more ambitious reader. Sets of problems at the end of each chapter to help student understanding. Hints and solutions to the problems are given at the end of the book.

  10. Quantum and classical thermoelectric transport in quantum dot nanocomposites

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Yang, Ronggui

    2011-10-01

    Quantum dot nanocomposites are potentially high-efficiency thermoelectric materials, which could outperform superlattices and random nanocomposites in terms of manufacturing cost-effectiveness and material properties because of the reduction of thermal conductivity due to the phonon-interface scattering, the enhancement of Seebeck coefficient due to the formation of minibands, and the enhancement of electrical conductivity due to the phonon-bottleneck effect in electron-phonon scattering for quantum-confined electrons. In this paper, we investigate the thermoelectric transport properties of quantum dot nanocomposites through a two-channel transport model that includes the transport of quantum-confined electrons through the hopping mechanism and the semiclassical transport of bulk-like electrons. For the quantum-confined electrons whose wave functions are confined in the quantum dots with overlapping tail extending to the matrix, we develop a tight-binding model together with the Kubo formula and the Green's function method to describe the transport processes of these electrons. The formation of minibands due to the quantum confinement and the phonon-bottleneck effect on carrier-phonon scattering are considered. For transport of bulk-like electrons, a Boltzmann-transport-equation-based semiclassical model is used to describe the multiband transport processes of carriers. The intrinsic carrier scatterings as well as the carrier-interface scattering of these bulk-like electrons are considered. We then apply the two-channel transport model to predict thermoelectric transport properties of n-type PbSe/PbTe quantum dot nanocomposites with PbSe quantum dots uniformly embedded in the PbTe matrix. The dependence of thermoelectric transport coefficients on the size of quantum dots, interdot distance, doping concentration, and temperature are studied in detail. Due to the formation of minibands and the phonon-bottleneck effect on carrier-phonon scattering, we show that

  11. 1992 STEP Symposium

    NASA Astrophysics Data System (ADS)

    Lui, Tony

    The year 1992 marks the quincentenary jubilee of the famous voyage of Christopher Columbus to the New World, a trip which initiated sustained contact between Europe and the American continent. Courageous explorations often lead to advancement of mankind, be they in uncharted territory or science. As much as Columbus was unaware of what lay in store for his voyage, we were just as poorly informed about what lay beyond our home planet when we began space exploration about three decades ago. There is much similarity among the pioneering spirits characteristic of both endeavors. It is thus fitting to celebrate this quincentenary occasion by declaring 1992 International Space Year (ISY).In conjunction with the COSPAR Meeting and the International Convention of the World Space Congress to be held in Washington, D.C., from August to September 1992, a 4-day symposium on the initial results from the Solar-Terrestrial Energy Program (STEP) Facilities and Theory Campaigns will be held at Johns Hopkins University, Applied Physics Laboratory, Laurel, Md., August 24-27. 1992.

  12. Quantum transport in Sierpinski carpets

    NASA Astrophysics Data System (ADS)

    van Veen, Edo; Yuan, Shengjun; Katsnelson, Mikhail I.; Polini, Marco; Tomadin, Andrea

    2016-03-01

    Recent progress in the design and fabrication of artificial two-dimensional (2D) materials paves the way for the experimental realization of electron systems moving on complex geometries, such as plane fractals. In this work, we calculate the quantum conductance of a 2D electron gas roaming on a Sierpinski carpet (SC), i.e., a plane fractal with Hausdorff dimension intermediate between 1 and 2. We find that the fluctuations of the quantum conductance are a function of energy with a fractal graph, whose dimension can be chosen by changing the geometry of the SC. This behavior is independent of the underlying lattice geometry.

  13. Introduction to Quantum Simulation

    NASA Technical Reports Server (NTRS)

    Williams, Colin P.

    2005-01-01

    This viewgraph presentation addresses the problem of efficiently simulating the evolution of a quantum system. The contents include: 1) Quantum Simulation; 2) Extracting Answers from Quantum Simulations; 3) Quantum Fourier Transform; 4) Eigenvalue Estimation; 5) Fermionic Simulations.

  14. Quantum Physics for Beginners.

    ERIC Educational Resources Information Center

    Strand, J.

    1981-01-01

    Suggests a new approach for teaching secondary school quantum physics. Reviews traditional approaches and presents some characteristics of the three-part "Quantum Physics for Beginners" project, including: quantum physics, quantum mechanics, and a short historical survey. (SK)

  15. STEPS: JPL's Astrometric Exoplanet Survey

    NASA Technical Reports Server (NTRS)

    Shaklan, Stuart; Pravdo, Steve

    2008-01-01

    Presentation topics include: STEPS ground-based astrometry at Hale Telescope; the instrument; why astronomy and why M-dwarfs; motion of center of light about center of mass in photocentric orbit; photocentric motion vs. fractional mass; high-resolution imaging of STEPS targets; GU 802 p one possible orbit plotted with data, Keplerian frame; GJ 802 results; STEPS future; and a bibliography of STEPS papers.

  16. SPAR-H Step-by-Step Guidance

    SciTech Connect

    April M. Whaley; Dana L. Kelly; Ronald L. Boring; William J. Galyean

    2012-06-01

    Step-by-step guidance was developed recently at Idaho National Laboratory for the US Nuclear Regulatory Commission on the use of the Standardized Plant Analysis Risk-Human Reliability Analysis (SPAR-H) method for quantifying Human Failure Events (HFEs). This work was done to address SPAR-H user needs, specifically requests for additional guidance on the proper application of various aspects of the methodology. This paper overviews the steps of the SPAR-H analysis process and highlights some of the most important insights gained during the development of the step-by-step directions. This supplemental guidance for analysts is applicable when plant-specific information is available, and goes beyond the general guidance provided in existing SPAR-H documentation. The steps highlighted in this paper are: Step-1, Categorizing the HFE as Diagnosis and/or Action; Step-2, Rate the Performance Shaping Factors; Step-3, Calculate PSF-Modified HEP; Step-4, Accounting for Dependence, and; Step-5, Minimum Value Cutoff.

  17. Multiple stage miniature stepping motor

    DOEpatents

    Niven, William A.; Shikany, S. David; Shira, Michael L.

    1981-01-01

    A stepping motor comprising a plurality of stages which may be selectively activated to effect stepping movement of the motor, and which are mounted along a common rotor shaft to achieve considerable reduction in motor size and minimum diameter, whereby sequential activation of the stages results in successive rotor steps with direction being determined by the particular activating sequence followed.

  18. Powerlessness Reinterpreted: Reframing Step One.

    ERIC Educational Resources Information Center

    Young, Susan L.

    The 12 steps of the well-known mutual help group, Alcoholics Anonymous (AA), begin with Step One, admitting powerlessness. Although Step One has helped many problem drinkers and other addicts, its spiritual concepts have been criticized. The possibility of reconceptualizing powerlessness as empowering, not only within AA and its offshoot programs,…

  19. Quantum dot cascade laser

    PubMed Central

    2014-01-01

    We demonstrated an unambiguous quantum dot cascade laser based on InGaAs/GaAs/InAs/InAlAs heterostructure by making use of self-assembled quantum dots in the Stranski-Krastanow growth mode and two-step strain compensation active region design. The prototype generates stimulated emission at λ ~ 6.15 μm and a broad electroluminescence band with full width at half maximum over 3 μm. The characteristic temperature for the threshold current density within the temperature range of 82 to 162 K is up to 400 K. Moreover, our materials show the strong perpendicular mid-infrared response at about 1,900 cm-1. These results are very promising for extending the present laser concept to terahertz quantum cascade laser, which would lead to room temperature operation. PACS 42.55.Px; 78.55.Cr; 78.67.Hc PMID:24666965

  20. Feynman's simple quantum mechanics

    NASA Astrophysics Data System (ADS)

    Taylor, Edwin F.

    1997-03-01

    This sample class presents an alternative to the conventional introduction to quantum mechanics and describes its current use in a credit course. This alternative introduction rests on theory presented in professional and popular writings by Richard Feynman. Feynman showed that Nature gives a simple command to the electron: "Explore all paths." All of nonrelativistic quantum mechanics, among other fundamental results, comes from this command. With a desktop computer the student points and clicks to tell a modeled electron which paths to follow. The computer then shows the results, which embody the elemental strangeness and paradoxical behaviors of the world of the very small. Feynman's approach requires few equations and provides a largely non-mathematical introduction to the wave function of conventional quantum mechanics. Draft software and materials already used for two semesters in an e-mail computer conference credit university course show that Feynman's approach works well with a variety of students. The sample class explores computer and written material and describes the next steps in its development.

  1. Quantum Physics

    NASA Astrophysics Data System (ADS)

    Le Bellac, Michel

    2006-03-01

    Quantum physics allows us to understand the nature of the physical phenomena which govern the behavior of solids, semi-conductors, lasers, atoms, nuclei, subnuclear particles and light. In Quantum Physics, Le Bellac provides a thoroughly modern approach to this fundamental theory. Throughout the book, Le Bellac teaches the fundamentals of quantum physics using an original approach which relies primarily on an algebraic treatment and on the systematic use of symmetry principles. In addition to the standard topics such as one-dimensional potentials, angular momentum and scattering theory, the reader is introduced to more recent developments at an early stage. These include a detailed account of entangled states and their applications, the optical Bloch equations, the theory of laser cooling and of magneto-optical traps, vacuum Rabi oscillations, and an introduction to open quantum systems. This is a textbook for a modern course on quantum physics, written for advanced undergraduate and graduate students. Completely original and contemporary approach, using algebra and symmetry principles Introduces recent developments at an early stage, including many topics that cannot be found in standard textbooks. Contains 130 physically relevant exercises

  2. The case for biological quantum computer elements

    NASA Astrophysics Data System (ADS)

    Baer, Wolfgang; Pizzi, Rita

    2009-05-01

    An extension to vonNeumann's analysis of quantum theory suggests self-measurement is a fundamental process of Nature. By mapping the quantum computer to the brain architecture we will argue that the cognitive experience results from a measurement of a quantum memory maintained by biological entities. The insight provided by this mapping suggests quantum effects are not restricted to small atomic and nuclear phenomena but are an integral part of our own cognitive experience and further that the architecture of a quantum computer system parallels that of a conscious brain. We will then review the suggestions for biological quantum elements in basic neural structures and address the de-coherence objection by arguing for a self- measurement event model of Nature. We will argue that to first order approximation the universe is composed of isolated self-measurement events which guaranties coherence. Controlled de-coherence is treated as the input/output interactions between quantum elements of a quantum computer and the quantum memory maintained by biological entities cognizant of the quantum calculation results. Lastly we will present stem-cell based neuron experiments conducted by one of us with the aim of demonstrating the occurrence of quantum effects in living neural networks and discuss future research projects intended to reach this objective.

  3. Quantum walk computation

    SciTech Connect

    Kendon, Viv

    2014-12-04

    Quantum versions of random walks have diverse applications that are motivating experimental implementations as well as theoretical studies. Recent results showing quantum walks are “universal for quantum computation” relate to algorithms, to be run on quantum computers. We consider whether an experimental implementation of a quantum walk could provide useful computation before we have a universal quantum computer.

  4. Symmetry as a foundational concept in Quantum Mechanics

    NASA Astrophysics Data System (ADS)

    Ziaeepour, Houri

    2015-07-01

    Symmetries are widely used in modeling quantum systems but they do not contribute in postulates of quantum mechanics. Here we argue that logical, mathematical, and observational evidence require that symmetry should be considered as a fundamental concept in the construction of physical systems. Based on this idea, we propose a series of postulates for describing quantum systems, and establish their relation and correspondence with axioms of standard quantum mechanics. Through some examples we show that this reformulation helps better understand some of ambiguities of standard description. Nonetheless its application is not limited to explaining confusing concept and it may be a necessary step toward a consistent model of quantum cosmology and gravity.

  5. Quantum walk coherences on a dynamical percolation graph

    NASA Astrophysics Data System (ADS)

    Elster, Fabian; Barkhofen, Sonja; Nitsche, Thomas; Novotný, Jaroslav; Gábris, Aurél; Jex, Igor; Silberhorn, Christine

    2015-08-01

    Coherent evolution governs the behaviour of all quantum systems, but in nature it is often subjected to influence of a classical environment. For analysing quantum transport phenomena quantum walks emerge as suitable model systems. In particular, quantum walks on percolation structures constitute an attractive platform for studying open system dynamics of random media. Here, we present an implementation of quantum walks differing from the previous experiments by achieving dynamical control of the underlying graph structure. We demonstrate the evolution of an optical time-multiplexed quantum walk over six double steps, revealing the intricate interplay between the internal and external degrees of freedom. The observation of clear non-Markovian signatures in the coin space testifies the high coherence of the implementation and the extraordinary degree of control of all system parameters. Our work is the proof-of-principle experiment of a quantum walk on a dynamical percolation graph, paving the way towards complex simulation of quantum transport in random media.

  6. Step-step interactions on GaAs (110) nanopatterns

    SciTech Connect

    Galiana, B.; Benedicto, M.; Tejedor, P.

    2013-01-14

    The step-step interactions on vicinal GaAs (110) surface patterns have been extracted from the quantitative analysis of the terrace width distribution (TWD). We have specifically studied the interactions in near-equilibrium faceting and kinetics-driven step bunching and meandering formed by spontaneous self-organization or through the modification of GaAs growth kinetics by atomic hydrogen. We show that the experimental TWDs determined from atomic force microscopy measurements can be accurately described by a weighed sum of a generalized Wigner distribution and several Gaussians. The results of our calculations indicate that straight facets are formed during high temperature homoepitaxy due to attractive interactions between [110] steps. At low temperatures, steady state attractive interactions in [110] step bunches are preceded by a transition regime dominated by entropic and energetic repulsions between meandering [11n]-type steps (n {>=} 2), whose population density exceeds that of the [110] bunched steps. In addition, it has been found that atomic H reduces the attractive interactions between [110] bunched steps and enhances entropic and dipole-induced energetic repulsions between H-terminated [11n] steps through the inhibition of As-As bond formation at step edges. Our analysis has evidenced a correlation between the value of the adjustable parameter that accounts in our model for the specific weight of the secondary peaks in the TWD ({beta}) and the extent of transverse meandering on the vicinal surface.

  7. Hamiltonian deformations of Gabor frames: First steps

    PubMed Central

    de Gosson, Maurice A.

    2015-01-01

    Gabor frames can advantageously be redefined using the Heisenberg–Weyl operators familiar from harmonic analysis and quantum mechanics. Not only does this redefinition allow us to recover in a very simple way known results of symplectic covariance, but it immediately leads to the consideration of a general deformation scheme by Hamiltonian isotopies (i.e. arbitrary paths of non-linear symplectic mappings passing through the identity). We will study in some detail an associated weak notion of Hamiltonian deformation of Gabor frames, using ideas from semiclassical physics involving coherent states and Gaussian approximations. We will thereafter discuss possible applications and extensions of our method, which can be viewed – as the title suggests – as the very first steps towards a general deformation theory for Gabor frames. PMID:25892903

  8. Quantum Uniqueness

    NASA Astrophysics Data System (ADS)

    Sych, Denis; Leuchs, Gerd

    2015-12-01

    Classical physics allows for the existence of pairs of absolutely identical systems. Pairwise application of identical measurements to each of those systems always leads to exactly alike results irrespectively of the choice of measurements. Here we ask a question how the picture looks like in the quantum domain. Surprisingly, we get a counterintuitive outcome. Pairwise application of identical (but a priori unknown) measurements cannot always lead to exactly alike results. We interpret this as quantum uniqueness—a feature that has no classical analog.

  9. Quantum Foam

    SciTech Connect

    Lincoln, Don

    2014-10-24

    The laws of quantum mechanics and relativity are quite perplexing however it is when the two theories are merged that things get really confusing. This combined theory predicts that empty space isn’t empty at all – it’s a seething and bubbling cauldron of matter and antimatter particles springing into existence before disappearing back into nothingness. Scientists call this complicated state of affairs “quantum foam.” In this video, Fermilab’s Dr. Don Lincoln discusses this mind-bending idea and sketches some of the experiments that have convinced scientists that this crazy prediction is actually true.

  10. Flow depth and energy coefficient relatiohnships for stepped spillways

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A multi-year, large-scale physical model study of stepped chutes was conducted over a broad range of design parameters (i.e. step heights, slopes, and unit discharges). Air entrainment developed naturally as the flow descended the chute. Air entrainment began to develop downstream of the surface i...

  11. High-fidelity continuous-variable quantum teleportation toward multistep quantum operations

    SciTech Connect

    Yukawa, Mitsuyoshi; Furusawa, Akira; Benichi, Hugo

    2008-02-15

    The progress in quantum operations of continuous-variable (CV) schemes can be reduced to that in CV quantum teleportation. The fidelity of quantum teleportation of an optical setup is limited by the finite degree of quantum correlation that can be prepared with a pair of finitely squeezed states. Reports of improvement of squeezing level have appeared recently, and we adopted the improved methods in our experimental system of quantum teleportation. As a result, we teleported a coherent state with a fidelity F=0.83{+-}0.01, which is better than any other figures reported to date, to our knowledge. In this paper, we introduce a measure n{sub s}, the number of teleportations expected to be carried out sequentially. Our result corresponds to n{sub s}=5.0{+-}0.4. It suggests that our improvement would enable us to proceed toward more advanced quantum operations involving multiple steps.

  12. Nonreversal and nonrepeating quantum walks

    NASA Astrophysics Data System (ADS)

    Proctor, T. J.; Barr, K. E.; Hanson, B.; Martiel, S.; Pavlović, V.; Bullivant, A.; Kendon, V. M.

    2014-04-01

    We introduce a variation of the discrete-time quantum walk, the nonreversal quantum walk, which does not step back onto a position that it has just occupied. This allows us to simulate a dimer and we achieve it by introducing a different type of coin operator. The nonrepeating walk, which never moves in the same direction in consecutive time steps, arises by a permutation of this coin operator. We describe the basic properties of both walks and prove that the even-order joint moments of the nonrepeating walker are independent of the initial condition, being determined by five parameters derived from the coin instead. Numerical evidence suggests that the same is the case for the nonreversal walk. This contrasts strongly with previously studied coins, such as the Grover operator, where the initial condition can be used to control the standard deviation of the walker.

  13. Quantum control limited by quantum decoherence

    SciTech Connect

    Xue, Fei; Sun, C. P.; Yu, S. X.

    2006-01-15

    We describe quantum controllability under the influences of the quantum decoherence induced by the quantum control itself. It is shown that, when the controller is considered as a quantum system, it will entangle with its controlled system and then cause quantum decoherence in the controlled system. In competition with this induced decoherence, the controllability will be limited by some uncertainty relation in a well-armed quantum control process. In association with the phase uncertainty and the standard quantum limit, a general model is studied to demonstrate the possibility of realizing a decoherence-free quantum control with a finite energy within a finite time. It is also shown that if the operations of quantum control are to be determined by the initial state of the controller, then due to the decoherence which results from the quantum control itself, there exists a low bound for quantum controllability.

  14. Volume Diffusion Growth Kinetics and Step Geometry in Crystal Growth

    NASA Technical Reports Server (NTRS)

    Mazuruk, Konstantin; Ramachandran, Narayanan

    1998-01-01

    The role of step geometry in two-dimensional stationary volume diff4sion process used in crystal growth kinetics models is investigated. Three different interface shapes: a) a planar interface, b) an equidistant hemispherical bumps train tAx interface, and c) a train of right angled steps, are used in this comparative study. The ratio of the super-saturation to the diffusive flux at the step position is used as a control parameter. The value of this parameter can vary as much as 50% for different geometries. An approximate analytical formula is derived for the right angled steps geometry. In addition to the kinetic models, this formula can be utilized in macrostep growth models. Finally, numerical modeling of the diffusive and convective transport for equidistant steps is conducted. In particular, the role of fluid flow resulting from the advancement of steps and its contribution to the transport of species to the steps is investigated.

  15. One-step error correction for multipartite polarization entanglement

    SciTech Connect

    Deng Fuguo

    2011-06-15

    We present two economical one-step error-correction protocols for multipartite polarization-entangled systems in a Greenberger-Horne-Zeilinger state. One uses spatial entanglement to correct errors in the polarization entanglement of an N-photon system, resorting to linear optical elements. The other uses frequency entanglement to correct errors in the polarization entanglement of an N-photon system. The parties in quantum communication can obtain a maximally entangled state from each N-photon system transmitted with one step in these two protocols, and both of their success probabilities are 100%, in principle. That is, they both work in a deterministic way, and they do not largely consume the less-entangled photon systems, which is far different from conventional multipartite entanglement purification schemes. These features may make these two protocols more useful for practical applications in long-distance quantum communication.

  16. Simulations of two-particle interactions with 2D quantum walks in time

    SciTech Connect

    Schreiber, A.; Laiho, K.; Silberhorn, C.; Rohde, P. P.; Štefaňak, M.; Potoček, V.; Hamilton, C.; Jex, I.

    2014-12-04

    We present the experimental implementation of a quantum walk on a two-dimensional lattice and show how to employ the optical system to simulate the quantum propagation of two interacting particles. Our quantum walk in time transfers the spatial spread of a quantum walk into the time domain, which guarantees a high stability and scalability of the setup. We present with our device quantum walks over 12 steps on a 2D lattice. By changing the properties of the driving quantum coin, we investigate different kinds of two-particle interactions and reveal their impact on the occurring quantum propagation.

  17. Incoherent control of locally controllable quantum systems

    SciTech Connect

    Dong Daoyi; Zhang Chenbin; Rabitz, Herschel; Pechen, Alexander; Tarn, T.-J.

    2008-10-21

    An incoherent control scheme for state control of locally controllable quantum systems is proposed. This scheme includes three steps: (1) amplitude amplification of the initial state by a suitable unitary transformation, (2) projective measurement of the amplified state, and (3) final optimization by a unitary controlled transformation. The first step increases the amplitudes of some desired eigenstates and the corresponding probability of observing these eigenstates, the second step projects, with high probability, the amplified state into a desired eigenstate, and the last step steers this eigenstate into the target state. Within this scheme, two control algorithms are presented for two classes of quantum systems. As an example, the incoherent control scheme is applied to the control of a hydrogen atom by an external field. The results support the suggestion that projective measurements can serve as an effective control and local controllability information can be used to design control laws for quantum systems. Thus, this scheme establishes a subtle connection between control design and controllability analysis of quantum systems and provides an effective engineering approach in controlling quantum systems with partial controllability information.

  18. Reliable quantum certification of photonic state preparations

    NASA Astrophysics Data System (ADS)

    Aolita, Leandro; Gogolin, Christian; Kliesch, Martin; Eisert, Jens

    2015-11-01

    Quantum technologies promise a variety of exciting applications. Even though impressive progress has been achieved recently, a major bottleneck currently is the lack of practical certification techniques. The challenge consists of ensuring that classically intractable quantum devices perform as expected. Here we present an experimentally friendly and reliable certification tool for photonic quantum technologies: an efficient certification test for experimental preparations of multimode pure Gaussian states, pure non-Gaussian states generated by linear-optical circuits with Fock-basis states of constant boson number as inputs, and pure states generated from the latter class by post-selecting with Fock-basis measurements on ancillary modes. Only classical computing capabilities and homodyne or hetorodyne detection are required. Minimal assumptions are made on the noise or experimental capabilities of the preparation. The method constitutes a step forward in many-body quantum certification, which is ultimately about testing quantum mechanics at large scales.

  19. Experimental loss-tolerant quantum coin flipping

    PubMed Central

    Berlín, Guido; Brassard, Gilles; Bussières, Félix; Godbout, Nicolas; Slater, Joshua A.; Tittel, Wolfgang

    2011-01-01

    Coin flipping is a cryptographic primitive in which two distrustful parties wish to generate a random bit to choose between two alternatives. This task is impossible to realize when it relies solely on the asynchronous exchange of classical bits: one dishonest player has complete control over the final outcome. It is only when coin flipping is supplemented with quantum communication that this problem can be alleviated, although partial bias remains. Unfortunately, practical systems are subject to loss of quantum data, which allows a cheater to force a bias that is complete or arbitrarily close to complete in all previous protocols and implementations. Here we report on the first experimental demonstration of a quantum coin-flipping protocol for which loss cannot be exploited to cheat better. By eliminating the problem of loss, which is unavoidable in any realistic setting, quantum coin flipping takes a significant step towards real-world applications of quantum communication. PMID:22127057

  20. Materials Frontiers to Empower Quantum Computing

    SciTech Connect

    Taylor, Antoinette Jane; Sarrao, John Louis; Richardson, Christopher

    2015-06-11

    This is an exciting time at the nexus of quantum computing and materials research. The materials frontiers described in this report represent a significant advance in electronic materials and our understanding of the interactions between the local material and a manufactured quantum state. Simultaneously, directed efforts to solve materials issues related to quantum computing provide an opportunity to control and probe the fundamental arrangement of matter that will impact all electronic materials. An opportunity exists to extend our understanding of materials functionality from electronic-grade to quantum-grade by achieving a predictive understanding of noise and decoherence in qubits and their origins in materials defects and environmental coupling. Realizing this vision systematically and predictively will be transformative for quantum computing and will represent a qualitative step forward in materials prediction and control.

  1. Reliable quantum certification of photonic state preparations

    PubMed Central

    Aolita, Leandro; Gogolin, Christian; Kliesch, Martin; Eisert, Jens

    2015-01-01

    Quantum technologies promise a variety of exciting applications. Even though impressive progress has been achieved recently, a major bottleneck currently is the lack of practical certification techniques. The challenge consists of ensuring that classically intractable quantum devices perform as expected. Here we present an experimentally friendly and reliable certification tool for photonic quantum technologies: an efficient certification test for experimental preparations of multimode pure Gaussian states, pure non-Gaussian states generated by linear-optical circuits with Fock-basis states of constant boson number as inputs, and pure states generated from the latter class by post-selecting with Fock-basis measurements on ancillary modes. Only classical computing capabilities and homodyne or hetorodyne detection are required. Minimal assumptions are made on the noise or experimental capabilities of the preparation. The method constitutes a step forward in many-body quantum certification, which is ultimately about testing quantum mechanics at large scales. PMID:26577800

  2. Cat-qubits for quantum computation

    NASA Astrophysics Data System (ADS)

    Mirrahimi, Mazyar

    2016-08-01

    The development of quantum Josephson circuits has created a strong expectation for reliable processing of quantum information. While this progress has already led to various proof-of-principle experiments on small-scale quantum systems, a major scaling step is required towards many-qubit protocols. Fault-tolerant computation with protected logical qubits usually comes at the expense of a significant overhead in the hardware. Each of the involved physical qubits still needs to satisfy the best achieved properties (coherence times, coupling strengths and tunability). Here, and in the aim of addressing alternative approaches to deal with these obstacles, I overview a series of recent theoretical proposals, and the experimental developments following these proposals, to enable a hardware-efficient paradigm for quantum memory protection and universal quantum computation.

  3. Experimental loss-tolerant quantum coin flipping

    NASA Astrophysics Data System (ADS)

    Berlín, Guido; Brassard, Gilles; Bussières, Félix; Godbout, Nicolas; Slater, Joshua A.; Tittel, Wolfgang

    2011-11-01

    Coin flipping is a cryptographic primitive in which two distrustful parties wish to generate a random bit to choose between two alternatives. This task is impossible to realize when it relies solely on the asynchronous exchange of classical bits: one dishonest player has complete control over the final outcome. It is only when coin flipping is supplemented with quantum communication that this problem can be alleviated, although partial bias remains. Unfortunately, practical systems are subject to loss of quantum data, which allows a cheater to force a bias that is complete or arbitrarily close to complete in all previous protocols and implementations. Here we report on the first experimental demonstration of a quantum coin-flipping protocol for which loss cannot be exploited to cheat better. By eliminating the problem of loss, which is unavoidable in any realistic setting, quantum coin flipping takes a significant step towards real-world applications of quantum communication.

  4. Electrochemical Fabrication of Metallic Quantum Wires

    ERIC Educational Resources Information Center

    Tao, Nongjian

    2005-01-01

    The fabrication of metallic quantum wires using simple electrochemical techniques is described. The conductance of the system can be readily measured that allows one to constantly monitor the conductance during fabrication and use conductance quantization as a signature to guide the fabrication.

  5. Coulomb drag in quantum circuits.

    PubMed

    Levchenko, Alex; Kamenev, Alex

    2008-11-21

    We study the drag effect in a system of two electrically isolated quantum point contacts, coupled by Coulomb interactions. Drag current exhibits maxima as a function of quantum point contacts gate voltages when the latter are tuned to the transitions between quantized conductance plateaus. In the linear regime this behavior is due to enhanced electron-hole asymmetry near an opening of a new conductance channel. In the nonlinear regime the drag current is proportional to the shot noise of the driving circuit, suggesting that the Coulomb drag experiments may be a convenient way to measure the quantum shot noise. Remarkably, the transition to the nonlinear regime may occur at driving voltages substantially smaller than the temperature.

  6. Conducting polyaniline nanowire electrode junction

    NASA Astrophysics Data System (ADS)

    Gaikwad, Sumedh; Bodkhe, Gajanan; Deshmukh, Megha; Patil, Harshada; Rushi, Arti; Shirsat, Mahendra D.; Koinkar, Pankaj; Kim, Yun-Hae; Mulchandani, Ashok

    2015-03-01

    In this paper, a synthesis of conducting polyaniline nanowires electrode junction (CPNEJ) has been reported. Conducting polyaniline nanowires electrode junction on Si/SiO2 substrate (having 3 μm gap between two gold microelectrodes) is prepared. Polyaniline nanowires with diameter (ca. 140 nm to 160 nm) were synthesized by one step electrochemical polymerization using galvanostatic (constant current) technique to bridge this gap. The surface morphology of CPNEJ was studied by scanning electron microscope (SEM). The synthesized CPNEJ is an excellent platform for biosensor applications.

  7. Universal quantum computation with little entanglement.

    PubMed

    Van den Nest, Maarten

    2013-02-01

    We show that universal quantum computation can be achieved in the standard pure-state circuit model while the entanglement entropy of every bipartition is small in each step of the computation. The entanglement entropy required for large-scale quantum computation even tends to zero. Moreover we show that the same conclusion applies to many entanglement measures commonly used in the literature. This includes e.g., the geometric measure, localizable entanglement, multipartite concurrence, squashed entanglement, witness-based measures, and more generally any entanglement measure which is continuous in a certain natural sense. These results demonstrate that many entanglement measures are unsuitable tools to assess the power of quantum computers.

  8. Categorical aspects of reconstructing quantum theory

    NASA Astrophysics Data System (ADS)

    Lal, Raymond; Coecke, Bob

    2012-02-01

    We present steps towards a new understanding of reconstructions of quantum theory. Chiribella, D'Ariano, and Perinotti (CDP) have recently produced a fascinating reconstruction of the formalism of quantum theory, which brings to light its operational origins. We use parts of the formalism of categorical quantum mechanics to expose the underlying mathematical structures of information flow in the CDP reconstruction. Our results include an elegant relation between teleportation and local tomography, and an equivalence betweeen a purely category-theoretic description of the purification of a mixed state, and the purification axiom of CDP.

  9. Towards bulk based preconditioning for quantum dotcomputations

    SciTech Connect

    Dongarra, Jack; Langou, Julien; Tomov, Stanimire; Channing,Andrew; Marques, Osni; Vomel, Christof; Wang, Lin-Wang

    2006-05-25

    This article describes how to accelerate the convergence of Preconditioned Conjugate Gradient (PCG) type eigensolvers for the computation of several states around the band gap of colloidal quantum dots. Our new approach uses the Hamiltonian from the bulk materials constituent for the quantum dot to design an efficient preconditioner for the folded spectrum PCG method. The technique described shows promising results when applied to CdSe quantum dot model problems. We show a decrease in the number of iteration steps by at least a factor of 4 compared to the previously used diagonal preconditioner.

  10. Classical Simulated Annealing Using Quantum Analogues

    NASA Astrophysics Data System (ADS)

    La Cour, Brian R.; Troupe, James E.; Mark, Hans M.

    2016-08-01

    In this paper we consider the use of certain classical analogues to quantum tunneling behavior to improve the performance of simulated annealing on a discrete spin system of the general Ising form. Specifically, we consider the use of multiple simultaneous spin flips at each annealing step as an analogue to quantum spin coherence as well as modifications of the Boltzmann acceptance probability to mimic quantum tunneling. We find that the use of multiple spin flips can indeed be advantageous under certain annealing schedules, but only for long anneal times.

  11. An integrated programming and development environment for adiabatic quantum optimization

    NASA Astrophysics Data System (ADS)

    Humble, T. S.; McCaskey, A. J.; Bennink, R. S.; Billings, J. J.; DʼAzevedo, E. F.; Sullivan, B. D.; Klymko, C. F.; Seddiqi, H.

    2014-01-01

    Adiabatic quantum computing is a promising route to the computational power afforded by quantum information processing. The recent availability of adiabatic hardware has raised challenging questions about how to evaluate adiabatic quantum optimization (AQO) programs. Processor behavior depends on multiple steps to synthesize an adiabatic quantum program, which are each highly tunable. We present an integrated programming and development environment for AQO called Jade Adiabatic Development Environment (JADE) that provides control over all the steps taken during program synthesis. JADE captures the workflow needed to rigorously specify the AQO algorithm while allowing a variety of problem types, programming techniques, and processor configurations. We have also integrated JADE with a quantum simulation engine that enables program profiling using numerical calculation. The computational engine supports plug-ins for simulation methodologies tailored to various metrics and computing resources. We present the design, integration, and deployment of JADE and discuss its potential use for benchmarking AQO programs by the quantum computer science community.

  12. Macroscopic quantumness: Theory and applications in optical sciences

    NASA Astrophysics Data System (ADS)

    Jeong, Hyunseok; Sasaki, Masahide

    2015-02-01

    Since the early days of quantum mechanics, as illustrated by Schrödinger's Gedankenexperiment, macroscopic quantum phenomena have attracted great interest among scientists and general audience. As highlighted by the Nobel prize in Physics in 2012, the scientific community could assent that the state-of-the-art technology to measure and manipulate individual quantum systems is now available in laboratories. We believe that the next step in order is to collectively control large quantum systems even at a 'macroscopic' level. This will be an intriguing challenge, from the fundamental point of view, for testing quantum mechanics in the macroscopic limit. Furthermore, it will make another major step forward to practical implementations of quantum information technologies.

  13. Quantum dice

    SciTech Connect

    Sassoli de Bianchi, Massimiliano

    2013-09-15

    In a letter to Born, Einstein wrote [42]: “Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the ‘old one.’ I, at any rate, am convinced that He does not throw dice.” In this paper we take seriously Einstein’s famous metaphor, and show that we can gain considerable insight into quantum mechanics by doing something as simple as rolling dice. More precisely, we show how to perform measurements on a single die, to create typical quantum interference effects, and how to connect (entangle) two identical dice, to maximally violate Bell’s inequality. -- Highlights: •Rolling a die is a quantum process admitting a Hilbert space representation. •Rolling experiments with a single die can produce interference effects. •Two connected dice can violate Bell’s inequality. •Correlations need to be created by the measurement, to violate Bell’s inequality.

  14. Quantum wormholes

    SciTech Connect

    Visser, M. )

    1991-01-15

    This paper presents an application of quantum-mechanical principles to a microscopic variant of the traversable wormholes recently introduced by Morris and Thorne. The analysis, based on the surgical grafting of two Reissner-Nordstroem spacetimes, proceeds by using a minisuperspace model to approximate the geometry of these wormholes. The thin shell'' formalism is applied to this minisuperspace model to extract the effective Lagrangian appropriate to this one-degree-of-freedom system. This effective Lagrangian is then quantized and the wave function for the wormhole is explicitly exhibited. A slightly more general class of wormholes---corresponding to the addition of some dust'' to the wormhole throat---is analyzed by recourse to WKB techniques. In all cases discussed in this paper, the expectation value of the wormhole radius is calculated to be of the order of the Planck length. Accordingly, though these quantum wormholes are of considerable theoretical interest they do not appear to be useful as a means for interstellar travel. The results of this paper may also have a bearing on the question of topological fluctuations in quantum gravity. These calculations serve to suggest that topology-changing effects might in fact be {ital suppressed} by quantum-gravity effects.

  15. Quantum abacus

    NASA Astrophysics Data System (ADS)

    Cheon, Taksu; Tsutsui, Izumi; Fülöp, Tamás

    2004-09-01

    We show that the point interactions on a line can be utilized to provide U(2) family of qubit operations for quantum information processing. Qubits are realized as states localized in either side of the point interaction which represents a controllable gate. The qubit manipulation proceeds in a manner analogous to the operation of an abacus.

  16. Quantum Gravity

    NASA Astrophysics Data System (ADS)

    Goradia, Shantilal

    2009-11-01

    The continuing search for quantum gravity and never ending attempts to unify gravity with other forces of nature represent tremendous waste of public and private funds directing students' energy towards non-creative manipulative work instead of learning from the scientific creativity in Einstein's 1919 paper that unifies gravity with nuclear force. It reflects Einstein's 1919 jump beyond his own 1915 theory of gravity, including that of Newton as implicitly demanded by Newton in 1686. Einstein corrected and retracted his 1917 introduction of cosmological constant in 1919. Dislike of the fact that Einstein did not use quantum mechanics to prove his point has no real value now, because we will use key ingredients (Planck scale and probabilistic aspect) of quantum mechanics and show that they reach the same conclusion. Newton explained the solar system known after Kepler. Likewise, our quantum mechanical approach explains the strong coupling as well the solar system and shows new horizons, otherwise unexplained. Explanation of unexplained observations need no prediction per Hawking, and obviously otherwise.

  17. Quantum Interferometry

    NASA Technical Reports Server (NTRS)

    Dowling, Jonathan P.

    2000-01-01

    Recently, several researchers, including yours truly, have been able to demonstrate theoretically that quantum photon entanglement has the potential to also revolutionize the entire field of optical interferometry, by providing many orders of magnitude improvement in interferometer sensitivity. The quantum entangled photon interferometer approach is very general and applies to many types of interferometers. In particular, without nonlocal entanglement, a generic classical interferometer has a statistical-sampling shot-noise limited sensitivity that scales like 1/Sqrt[N], where N is the number of particles (photons, electrons, atoms, neutrons) passing through the interferometer per unit time. However, if carefully prepared quantum correlations are engineered between the particles, then the interferometer sensitivity improves by a factor of Sqrt[N] (square root of N) to scale like 1/N, which is the limit imposed by the Heisenberg Uncertainty Principle. For optical (laser) interferometers operating at milliwatts of optical power, this quantum sensitivity boost corresponds to an eight-order-of-magnitude improvement of signal to noise. Applications are to tests of General Relativity such as ground and orbiting optical interferometers for gravity wave detection, Laser Interferometer Gravity Observatory (LIGO) and the European Laser Interferometer Space Antenna (LISA), respectively.

  18. Quantum transformations

    SciTech Connect

    Faraggi, A.E.; Matone, M.

    1998-01-09

    We show that the quantum Hamilton-Jacobi equation can be written in the classical form with the spatial derivative {partial_derivative}{sub q} replaced by {partial_derivative}{sub q} with dq = dq/{radical}1{minus}{beta}{sup 2}(q), where {beta}{sup 2}(q) is strictly related to the quantum potential. This can be seen as the opposite of the problem of finding the wave function representation of classical mechanics as formulated by Schiller and Rosen. The structure of the above {open_quotes}quantum transformation{close_quotes}, related to the recently formulated equivalence principle, indicates that the potential deforms space geometry. In particular, a result by Flanders implies that both W(q) = V(q) {minus} E and the quantum potential Q are proportional to the curvatures {kappa}{sub W} and {kappa}{sub Q} which arise as natural invariants in an equivalence problem for curves in the projective line. In this formulation the Schroedinger equation takes the geometrical form ({partial_derivative}{sub q}{sup 2} + {kappa}{sub W}){psi} = 0.

  19. Quantum rendering

    NASA Astrophysics Data System (ADS)

    Lanzagorta, Marco O.; Gomez, Richard B.; Uhlmann, Jeffrey K.

    2003-08-01

    In recent years, computer graphics has emerged as a critical component of the scientific and engineering process, and it is recognized as an important computer science research area. Computer graphics are extensively used for a variety of aerospace and defense training systems and by Hollywood's special effects companies. All these applications require the computer graphics systems to produce high quality renderings of extremely large data sets in short periods of time. Much research has been done in "classical computing" toward the development of efficient methods and techniques to reduce the rendering time required for large datasets. Quantum Computing's unique algorithmic features offer the possibility of speeding up some of the known rendering algorithms currently used in computer graphics. In this paper we discuss possible implementations of quantum rendering algorithms. In particular, we concentrate on the implementation of Grover's quantum search algorithm for Z-buffering, ray-tracing, radiosity, and scene management techniques. We also compare the theoretical performance between the classical and quantum versions of the algorithms.

  20. Coherent superpositions of states in coupled Hilbert-space using step by step Morris-Shore transformation

    NASA Astrophysics Data System (ADS)

    Saadati-Niari, Maghsoud

    2016-09-01

    Creation of coherent superpositions in quantum systems with Na states in the lower set and Nb states in the upper set is presented. The solution is drived by using the Morris-Shore transformation, which step by step reduces the fully coupled system to a three-state Λ-like system and a set of decoupled states. It is shown that, for properly timed pulse, robust population transfer from an initial ground state (or superposition of M ground states) to an arbitrary coherent superposition of the ground states can be achieved by coincident pulses and/or STIRAP techniques.

  1. Quantum roulette: an extended quantum strategy

    NASA Astrophysics Data System (ADS)

    Wang, Xiang-Bin; Kwek, L. C.; Oh, C. H.

    2000-12-01

    In a recent paper, Meyer demonstrated that with a quantum computer, an analogous zero-sum classically strategic game played with quantum strategy essentially become a bias game under a mixture of quantum and classical strategy. To illustrate his point, Meyer used a quantum coin tossing event. In this Letter, we generalize Meyer's argument to an N-state game.

  2. Acoustoelectric Current in Suspended Quantum Point Contacts

    NASA Astrophysics Data System (ADS)

    Kreft, Dustin J.

    Here, I present a detailed analysis and discussion of acoustoelectric current and the behavior of said current under the influence of a magnetic field and its interactions with quantum point contacts (QPCs). The QPCs lie on a suspended nano-bridge, which acts as an acoustic waveguide, allowing a stronger electron-phonon coupling; and hence, a larger acoustoelectric current with amplified conductance effects at a high temperature of 4.2 K. The acoustoelectric current is first studied under the influence of a perpendicular magnetic field. Through this measurement a theoretical model was developed to accurately describe and reproduce the measurement trend; showing how the acoustoelectric current is strongly dependent on the surface acoustic wave (SAW) attenuation and the two dimensional electron gas (2DEG) conductance changes under such conditions. The next set of measurements focus on the acoustoelectric current and its interactions with the potential created by applying a negative bias to the QPCs. Here, the electronically confined region gives rise to enhanced electron-phonon interactions which manifest themselves as a change in acoustoelectric current polarity, due to phonon back scattering, and enhanced oscillations in the measured current due to subband depopulation and the change in the potential landscape. Further information is provided such as fabrication steps, theoretical background on QPCs and SAWs, additional information of SAW-QPC interactions under the influence of a magnetic field, and phase locked acoustoelectric current with QPC pinch off.

  3. Quantum state and quantum entanglement protection using quantum measurements

    NASA Astrophysics Data System (ADS)

    Wang, Shuchao; Li, Ying; Wang, Xiangbin; Kwek, Leong Chuan; Yu, Zongwen; Zou, Wenjie

    2015-03-01

    The time evolution of some quantum states can be slowed down or even stopped under frequent measurements. This is the usual quantum Zeno effect. Here we report an operator quantum Zeno effect, in which the evolution of some physical observables is slowed down through measurements even though thequantum state changes randomly with time. Based on the operator quantum Zeno effect, we show how we can protect quantum information from decoherence with two-qubit measurements, realizable with noisy two-qubit interactions. Besides, we report the quantum entanglement protection using weak measurement and measurement reversal scheme. Exposed in the nonzero temperature environment, a quantum system can both lose and gain excitations by interacting with the environment. In this work, we show how to optimally protect quantum states and quantum entanglement in such a situation based on measurement reversal from weak measurement. In particular, we present explicit formulas of protection. We find that this scheme can circumvent the entanglement sudden death in certain conditions.

  4. Elementary Excitations in Quantum Liquids.

    ERIC Educational Resources Information Center

    Pines, David

    1981-01-01

    Discusses elementary excitations and their role in condensed matter physics, focusing on quantum plasma, helium liquids, and superconductors. Considers research primarily conducted in the 1950s and concludes with a brief survey of some closely related further developments. (Author/JN)

  5. Rescuing a Quantum Phase Transition with Quantum Noise

    NASA Astrophysics Data System (ADS)

    Zhang, Gu; Novais, Eduardo; Baranger, Harold

    We show that placing a quantum system in contact with an environment can enhance non-Fermi-liquid correlations, rather than destroying quantum effects as is typical. The system consists of two quantum dots in series with two leads; the highly resistive leads couple charge flow through the dots to the electromagnetic environment (noise). The similarity to the two impurity Kondo model suggests that there will be a quantum phase transition between a Kondo phase and a local singlet phase. However, this transition is destabilized by charge tunneling between the two leads. Our main result is that sufficiently strong quantum noise suppresses this charge transfer and leads to stabilization of the quantum phase transition. We present the phase diagram, the ground state degeneracy at the four fixed points, and the leading temperature dependence of the conductance near these points. Partially supported by (1) the U.S. DOE, Division of Materials Sciences and Engineering, under Grant No. DE-SC0005237 and (2) FAPESP (BRAZIL) under Grant 2014/26356-9.

  6. Periodic Scarred States in Open Quantum Dots as Evidence of Quantum Darwinism

    NASA Astrophysics Data System (ADS)

    Burke, A. M.; Akis, R.; Day, T. E.; Speyer, Gil; Ferry, D. K.; Bennett, B. R.

    2010-04-01

    Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism.

  7. Periodic scarred States in open quantum dots as evidence of quantum Darwinism.

    PubMed

    Burke, A M; Akis, R; Day, T E; Speyer, Gil; Ferry, D K; Bennett, B R

    2010-04-30

    Scanning gate microscopy (SGM) is used to image scar structures in an open quantum dot, which is created in an InAs quantum well by electron-beam lithography and wet etching. The scanned images demonstrate periodicities in magnetic field that correlate to those found in the conductance fluctuations. Simulations have shown that these magnetic transform images bear a strong resemblance to actual scars found in the dot that replicate through the modes in direct agreement with quantum Darwinism.

  8. Open quantum dots—probing the quantum to classical transition

    NASA Astrophysics Data System (ADS)

    Ferry, D. K.; Burke, A. M.; Akis, R.; Brunner, R.; Day, T. E.; Meisels, R.; Kuchar, F.; Bird, J. P.; Bennett, B. R.

    2011-04-01

    Quantum dots provide a natural system in which to study both quantum and classical features of transport. As a closed testbed, they provide a natural system with a very rich set of eigenstates. When coupled to the environment through a pair of quantum point contacts, each of which passes several modes, the original quantum environment evolves into a set of decoherent and coherent states, which classically would compose a mixed phase space. The manner of this breakup is governed strongly by Zurek's decoherence theory, and the remaining coherent states possess all the properties of his pointer states. These states are naturally studied via traditional magnetotransport at low temperatures. More recently, we have used scanning gate (conductance) microscopy to probe the nature of the coherent states, and have shown that families of states exist through the spectrum in a manner consistent with quantum Darwinism. In this review, we discuss the nature of the various states, how they are formed, and the signatures that appear in magnetotransport and general conductance studies.

  9. Leading Change Step-by-Step: Tactics, Tools, and Tales

    ERIC Educational Resources Information Center

    Spiro, Jody

    2010-01-01

    "Leading Change Step-by-Step" offers a comprehensive and tactical guide for change leaders. Spiro's approach has been field-tested for more than a decade and proven effective in a wide variety of public sector organizations including K-12 schools, universities, international agencies and non-profits. The book is filled with proven tactics for…

  10. Step by Step to Smoke-Free Schools.

    ERIC Educational Resources Information Center

    VanSciver, James H.; Roberts, H. Earl

    1989-01-01

    This ERIC digest discusses ways of effectively banning smoking in schools so that controversies do not continue after implementation of the policy. By advocating a process approach, the document cites steps taken by the Lake Forest School Board to prohibit smoking in and around school grounds. Step one involved committee planning involving…

  11. Step-By-Step Professional Development in Technology

    ERIC Educational Resources Information Center

    Meltzer, Sarah T.

    2012-01-01

    Don't train your teachers in instructional technology without reading this resource-packed book from Sarah T. Meltzer. Meltzer presents easy-to-follow guidelines for bringing about effective professional development in technology from start to finish. She takes you step-by-step through the process of planning, implementing, and managing…

  12. Complex Rotation Quantum Dynamic Neural Networks (CRQDNN) using Complex Quantum Neuron (CQN): Applications to time series prediction.

    PubMed

    Cui, Yiqian; Shi, Junyou; Wang, Zili

    2015-11-01

    Quantum Neural Networks (QNN) models have attracted great attention since it innovates a new neural computing manner based on quantum entanglement. However, the existing QNN models are mainly based on the real quantum operations, and the potential of quantum entanglement is not fully exploited. In this paper, we proposes a novel quantum neuron model called Complex Quantum Neuron (CQN) that realizes a deep quantum entanglement. Also, a novel hybrid networks model Complex Rotation Quantum Dynamic Neural Networks (CRQDNN) is proposed based on Complex Quantum Neuron (CQN). CRQDNN is a three layer model with both CQN and classical neurons. An infinite impulse response (IIR) filter is embedded in the Networks model to enable the memory function to process time series inputs. The Levenberg-Marquardt (LM) algorithm is used for fast parameter learning. The networks model is developed to conduct time series predictions. Two application studies are done in this paper, including the chaotic time series prediction and electronic remaining useful life (RUL) prediction.

  13. Efficient quantum walk on a quantum processor.

    PubMed

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

    2016-01-01

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

  14. Efficient quantum walk on a quantum processor

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  15. Efficient quantum walk on a quantum processor.

    PubMed

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

    2016-05-05

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

  16. Efficient quantum walk on a quantum processor

    PubMed Central

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

    2016-01-01

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

  17. Quantum error correction for quantum memories

    NASA Astrophysics Data System (ADS)

    Terhal, Barbara M.

    2015-04-01

    Active quantum error correction using qubit stabilizer codes has emerged as a promising, but experimentally challenging, engineering program for building a universal quantum computer. In this review the formalism of qubit stabilizer and subsystem stabilizer codes and their possible use in protecting quantum information in a quantum memory are considered. The theory of fault tolerance and quantum error correction is reviewed, and examples of various codes and code constructions, the general quantum error-correction conditions, the noise threshold, the special role played by Clifford gates, and the route toward fault-tolerant universal quantum computation are discussed. The second part of the review is focused on providing an overview of quantum error correction using two-dimensional (topological) codes, in particular, the surface code architecture. The complexity of decoding and the notion of passive or self-correcting quantum memories are discussed. The review does not focus on a particular technology but discusses topics that will be relevant for various quantum technologies.

  18. Analysis of the efficiency of intermediate band solar cells based on quantum dot supercrystals

    SciTech Connect

    Heshmati, S; Golmohammadi, S; Abedi, K; Taleb, H

    2014-03-28

    We have studied the influence of the quantum-dot (QD) width and the quantum-dot conduction band (QD-CB) offset on the efficiency of quantum-dot intermediate band solar cells (QD-IBSCs). Simulation results demonstrate that with increasing QD-CB offset and decreasing QD width, the maximum efficiency is achieved. (laser applications and other topics in quantum electronics)

  19. On quantum effects on the surface of solid hydrogen

    SciTech Connect

    Marchenko, V. I.

    2013-10-15

    The low-frequency spectrum of hypothetical superfluidity on the free surface of a quantum crystal of hydrogen is determined. In the quantum-rough state of the surface, crystallization waves with a quadratic spectrum should propagate. In the atomically smooth state, the spectrum is linear. Crystallization waves propagating along elementary steps are also considered.

  20. Destruction of the Fractional Quantum Hall Effect by Disorder

    DOE R&D Accomplishments Database

    Laughlin, R. B.

    1985-07-01

    It is suggested that Hall steps in the fractional quantum Hall effect are physically similar to those in the ordinary quantum Hall effect. This proposition leads to a simple scaling diagram containing a new type of fixed point, which is identified with the destruction of the fractional states by disorder. 15 refs., 3 figs.