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Sample records for differential quantum tunneling

  1. Light-induced negative differential resistance in graphene/Si-quantum-dot tunneling diodes.

    PubMed

    Lee, Kyeong Won; Jang, Chan Wook; Shin, Dong Hee; Kim, Jong Min; Kang, Soo Seok; Lee, Dae Hun; Kim, Sung; Choi, Suk-Ho; Hwang, Euyheon

    2016-07-28

    One of the interesing tunneling phenomena is negative differential resistance (NDR), the basic principle of resonant-tunneling diodes. NDR has been utilized in various semiconductor devices such as frequency multipliers, oscillators, relfection amplifiers, logic switches, and memories. The NDR in graphene has been also reported theoretically as well as experimentally, but should be further studied to fully understand its mechanism, useful for practical device applications. Especially, there has been no observation about light-induced NDR (LNDR) in graphene-related structures despite very few reports on the LNDR in GaAs-based heterostructures. Here, we report first observation of LNDR in graphene/Si quantum dots-embedded SiO2 (SQDs:SiO2) multilayers (MLs) tunneling diodes. The LNDR strongly depends on temperature (T) as well as on SQD size, and the T dependence is consistent with photocurrent (PC)-decay behaviors. With increasing light power, the PC-voltage curves are more structured with peak-to-valley ratios over 2 at room temperature. The physical mechanism of the LNDR, governed by resonant tunneling of charge carriers through the minibands formed across the graphene/SQDs:SiO2 MLs and by their nonresonant phonon-assisted tunneling, is discussed based on theoretical considerations.

  2. Light-induced negative differential resistance in graphene/Si-quantum-dot tunneling diodes

    NASA Astrophysics Data System (ADS)

    Lee, Kyeong Won; Jang, Chan Wook; Shin, Dong Hee; Kim, Jong Min; Kang, Soo Seok; Lee, Dae Hun; Kim, Sung; Choi, Suk-Ho; Hwang, Euyheon

    2016-07-01

    One of the interesing tunneling phenomena is negative differential resistance (NDR), the basic principle of resonant-tunneling diodes. NDR has been utilized in various semiconductor devices such as frequency multipliers, oscillators, relfection amplifiers, logic switches, and memories. The NDR in graphene has been also reported theoretically as well as experimentally, but should be further studied to fully understand its mechanism, useful for practical device applications. Especially, there has been no observation about light-induced NDR (LNDR) in graphene-related structures despite very few reports on the LNDR in GaAs-based heterostructures. Here, we report first observation of LNDR in graphene/Si quantum dots-embedded SiO2 (SQDs:SiO2) multilayers (MLs) tunneling diodes. The LNDR strongly depends on temperature (T) as well as on SQD size, and the T dependence is consistent with photocurrent (PC)-decay behaviors. With increasing light power, the PC-voltage curves are more structured with peak-to-valley ratios over 2 at room temperature. The physical mechanism of the LNDR, governed by resonant tunneling of charge carriers through the minibands formed across the graphene/SQDs:SiO2 MLs and by their nonresonant phonon-assisted tunneling, is discussed based on theoretical considerations.

  3. Light-induced negative differential resistance in graphene/Si-quantum-dot tunneling diodes

    PubMed Central

    Lee, Kyeong Won; Jang, Chan Wook; Shin, Dong Hee; Kim, Jong Min; Kang, Soo Seok; Lee, Dae Hun; Kim, Sung; Choi, Suk-Ho; Hwang, Euyheon

    2016-01-01

    One of the interesing tunneling phenomena is negative differential resistance (NDR), the basic principle of resonant-tunneling diodes. NDR has been utilized in various semiconductor devices such as frequency multipliers, oscillators, relfection amplifiers, logic switches, and memories. The NDR in graphene has been also reported theoretically as well as experimentally, but should be further studied to fully understand its mechanism, useful for practical device applications. Especially, there has been no observation about light-induced NDR (LNDR) in graphene-related structures despite very few reports on the LNDR in GaAs-based heterostructures. Here, we report first observation of LNDR in graphene/Si quantum dots-embedded SiO2 (SQDs:SiO2) multilayers (MLs) tunneling diodes. The LNDR strongly depends on temperature (T) as well as on SQD size, and the T dependence is consistent with photocurrent (PC)-decay behaviors. With increasing light power, the PC-voltage curves are more structured with peak-to-valley ratios over 2 at room temperature. The physical mechanism of the LNDR, governed by resonant tunneling of charge carriers through the minibands formed across the graphene/SQDs:SiO2 MLs and by their nonresonant phonon-assisted tunneling, is discussed based on theoretical considerations. PMID:27465107

  4. Quantum tunneling with friction

    NASA Astrophysics Data System (ADS)

    Tokieda, M.; Hagino, K.

    2017-05-01

    Using the phenomenological quantum friction models introduced by P. Caldirola [Nuovo Cimento 18, 393 (1941), 10.1007/BF02960144] and E. Kanai [Prog. Theor. Phys. 3, 440 (1948), 10.1143/ptp/3.4.440], M. D. Kostin [J. Chem. Phys. 57, 3589 (1972), 10.1063/1.1678812], and K. Albrecht [Phys. Lett. B 56, 127 (1975), 10.1016/0370-2693(75)90283-X], we study quantum tunneling of a one-dimensional potential in the presence of energy dissipation. To this end, we calculate the tunneling probability using a time-dependent wave-packet method. The friction reduces the tunneling probability. We show that the three models provide similar penetrabilities to each other, among which the Caldirola-Kanai model requires the least numerical effort. We also discuss the effect of energy dissipation on quantum tunneling in terms of barrier distributions.

  5. Differential quantum tunneling contributions in nitroalkane oxidase catalyzed and the uncatalyzed proton transfer reaction

    PubMed Central

    Major, Dan T.; Heroux, Annie; Orville, Allen M.; Valley, Michael P.; Fitzpatrick, Paul F.; Gao, Jiali

    2009-01-01

    The proton transfer reaction between the substrate nitroethane and Asp-402 catalyzed by nitroalkane oxidase and the uncatalyzed process in water have been investigated using a path-integral free-energy perturbation method. Although the dominating effect in rate acceleration by the enzyme is the lowering of the quasiclassical free energy barrier, nuclear quantum effects also contribute to catalysis in nitroalkane oxidase. In particular, the overall nuclear quantum effects have greater contributions to lowering the classical barrier in the enzyme, and there is a larger difference in quantum effects between proton and deuteron transfer for the enzymatic reaction than that in water. Both experiment and computation show that primary KIEs are enhanced in the enzyme, and the computed Swain-Schaad exponent for the enzymatic reaction is exacerbated relative to that in the absence of the enzyme. In addition, the computed tunneling transmission coefficient is approximately three times greater for the enzyme reaction than the uncatalyzed reaction, and the origin of the difference may be attributed to a narrowing effect in the effective potentials for tunneling in the enzyme than that in aqueous solution. PMID:19926855

  6. Quantum dot resonant tunneling spectroscopy

    NASA Astrophysics Data System (ADS)

    Reed, Mark A.; Randall, John N.; Luscombe, James H.; Frensley, William R.; Aggarwal, Raj J.; Matyi, Richard J.; Moore, Tom M.; Wetsel, Anna E.

    The electronic transport through 3-dimensionally confined semiconductor quantum wells (quantum dots) is investigated and analyzed. The spectra corresponds to resonant tunneling from laterally-confined emitter contact subbands through the discrete 3-dimensionally confined quantum dot states. Momentum nonconservation is observed in these structures. Results on coupled quantum dot states (molccules) will be presented.

  7. Quantum Tunneling and Complex Trajectories

    NASA Astrophysics Data System (ADS)

    Meynig, Max; Haggard, Hal

    2017-01-01

    In general, the semiclassical approximation of quantum mechanical tunneling fails to treat tunneling through barriers if real initial conditions and trajectories are used. By analytically continuing classical dynamics to the complex plane the problems encountered in the approximation can be resolved. While, the complex methods discussed here have been previously explored, no one has exhibited an analytically solvable case. The essential features of the complex method will be discussed in the context of a novel, analytically solvable problem. These methods could be useful in quantum gravity, with applications to the tunneling of spacetime geometries.

  8. Computational multiqubit tunnelling in programmable quantum annealers

    PubMed Central

    Boixo, Sergio; Smelyanskiy, Vadim N.; Shabani, Alireza; Isakov, Sergei V.; Dykman, Mark; Denchev, Vasil S.; Amin, Mohammad H.; Smirnov, Anatoly Yu; Mohseni, Masoud; Neven, Hartmut

    2016-01-01

    Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself. Quantum tunnelling has been hypothesized as an advantageous physical resource for optimization in quantum annealing. However, computational multiqubit tunnelling has not yet been observed, and a theory of co-tunnelling under high- and low-frequency noises is lacking. Here we show that 8-qubit tunnelling plays a computational role in a currently available programmable quantum annealer. We devise a probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. In support of the design of quantum annealers we develop a nonperturbative theory of open quantum dynamics under realistic noise characteristics. This theory accurately predicts the rate of many-body dissipative quantum tunnelling subject to the polaron effect. Furthermore, we experimentally demonstrate that quantum tunnelling outperforms thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive. PMID:26739797

  9. Quantum Tunneling Time: Relativistic Extensions

    NASA Astrophysics Data System (ADS)

    Xu, Dai-Yu; Wang, Towe; Xue, Xun

    2013-11-01

    Several years ago, in quantum mechanics, Davies proposed a method to calculate particle's traveling time with the phase difference of wave function. The method is convenient for calculating the sojourn time inside a potential step and the tunneling time through a potential hill. We extend Davies' non-relativistic calculation to relativistic quantum mechanics, with and without particle-antiparticle creation, using Klein-Gordon equation and Dirac Equation, for different forms of energy-momentum relation. The extension is successful only when the particle and antiparticle creation/annihilation effect is negligible.

  10. Simulations in quantum tunneling

    NASA Astrophysics Data System (ADS)

    Smith, Kevin; Blaylock, Guy

    2017-10-01

    We study the timing effects of nonrelativistic wave packet tunneling through a barrier using a numerical simulation readily accessible to an undergraduate audience. We demonstrate that the peak of the transmitted packet can sometimes emerge from the barrier ahead of the peak of an undisturbed wave packet that does not encounter a barrier. Under the right circumstances, this effect can give the appearance that transmission through the barrier occurs at superluminal speeds. We demonstrate that this seemingly paradoxical effect is not all that puzzling. Rather, components from the front of the incoming wave packet are preferentially transmitted, forming a transmitted packet ahead of the average of the incoming wave packet but not ahead of the leading edge of that packet. Our studies also show how the timing depends on barrier height and width, consistent with expectations based on the different energy components of the wave packet.

  11. Tunneling of quantum rotobreathers

    NASA Astrophysics Data System (ADS)

    Dorignac, J.; Flach, S.

    2002-06-01

    We analyze the quantum properties of a system consisting of two nonlinearly coupled pendulums. This nonintegrable system exhibits two different symmetries: a permutational symmetry and another one related to the reversal of the total momentum of the system. Each of these symmetries is responsible for the existence of two kinds of quasidegenerate states. At sufficiently high energy, pairs of symmetry-related states glue together to form quadruplets. We show that, starting from the anticontinuous limit, particular quadruplets allow us to construct quantum states whose properties are very similar to those of classical rotobreathers. Contrary to the classical situation, the coupling between pendulums necessarily introduces a periodic exchange of energy between them at a frequency which is proportional to the energy splitting between quasidegenerate states related to the permutation symmetry. This splitting may remain very small as the coupling strength increases and is a decreasing function of the pair energy. The energy may be therefore stored in one pendulum during a time period very long as compared to the inverse of the internal rotobreather frequency.

  12. Effect of Chaos on Relativistic Quantum Tunneling

    DTIC Science & Technology

    2012-06-01

    Effect of chaos on relativistic quantum tunneling This article has been downloaded from IOPscience. Please scroll down to see the full text article...of chaos on relativistic quantum tunneling 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e...tunneling dynamics even in the relativistic quantum regime. Similar phenomena have been observed in graphene. A physical theory is developed to

  13. Direct Approach to Quantum Tunneling

    NASA Astrophysics Data System (ADS)

    Andreassen, Anders; Farhi, David; Frost, William; Schwartz, Matthew D.

    2016-12-01

    The decay rates of quasistable states in quantum field theories are usually calculated using instanton methods. Standard derivations of these methods rely in a crucial way upon deformations and analytic continuations of the physical potential and on the saddle-point approximation. While the resulting procedure can be checked against other semiclassical approaches in some one-dimensional cases, it is challenging to trace the role of the relevant physical scales, and any intuitive handle on the precision of the approximations involved is at best obscure. In this Letter, we use a physical definition of the tunneling probability to derive a formula for the decay rate in both quantum mechanics and quantum field theory directly from the Minkowski path integral, without reference to unphysical deformations of the potential. There are numerous benefits to this approach, from nonperturbative applications to precision calculations and aesthetic simplicity.

  14. Resonant tunnelling in a quantum oxide superlattice

    SciTech Connect

    Choi, Woo Seok; Lee, Sang A.; You, Jeong Ho; Lee, Suyoun; Lee, Ho Nyung

    2015-06-24

    Resonant tunneling is a quantum mechanical process that has long been attracting both scientific and technological attention owing to its intriguing underlying physics and unique applications for high-speed electronics. The materials system exhibiting resonant tunneling, however, has been largely limited to the conventional semiconductors, partially due to their excellent crystalline quality. Here we show that a deliberately designed transition metal oxide superlattice exhibits a resonant tunneling behaviour with a clear negative differential resistance. The tunneling occurred through an atomically thin, lanthanum δ- doped SrTiO3 layer, and the negative differential resistance was realized on top of the bi-polar resistance switching typically observed for perovskite oxide junctions. This combined process resulted in an extremely large resistance ratio (~105) between the high and low resistance states. Lastly, the unprecedentedly large control found in atomically thin δ-doped oxide superlattices can open a door to novel oxide-based high-frequency logic devices.

  15. Resonant tunnelling in a quantum oxide superlattice

    DOE PAGES

    Choi, Woo Seok; Lee, Sang A.; You, Jeong Ho; ...

    2015-06-24

    Resonant tunneling is a quantum mechanical process that has long been attracting both scientific and technological attention owing to its intriguing underlying physics and unique applications for high-speed electronics. The materials system exhibiting resonant tunneling, however, has been largely limited to the conventional semiconductors, partially due to their excellent crystalline quality. Here we show that a deliberately designed transition metal oxide superlattice exhibits a resonant tunneling behaviour with a clear negative differential resistance. The tunneling occurred through an atomically thin, lanthanum δ- doped SrTiO3 layer, and the negative differential resistance was realized on top of the bi-polar resistance switching typicallymore » observed for perovskite oxide junctions. This combined process resulted in an extremely large resistance ratio (~105) between the high and low resistance states. Lastly, the unprecedentedly large control found in atomically thin δ-doped oxide superlattices can open a door to novel oxide-based high-frequency logic devices.« less

  16. Quantum Tunneling Affects Engine Performance.

    PubMed

    Som, Sibendu; Liu, Wei; Zhou, Dingyu D Y; Magnotti, Gina M; Sivaramakrishnan, Raghu; Longman, Douglas E; Skodje, Rex T; Davis, Michael J

    2013-06-20

    We study the role of individual reaction rates on engine performance, with an emphasis on the contribution of quantum tunneling. It is demonstrated that the effect of quantum tunneling corrections for the reaction HO2 + HO2 = H2O2 + O2 can have a noticeable impact on the performance of a high-fidelity model of a compression-ignition (e.g., diesel) engine, and that an accurate prediction of ignition delay time for the engine model requires an accurate estimation of the tunneling correction for this reaction. The three-dimensional model includes detailed descriptions of the chemistry of a surrogate for a biodiesel fuel, as well as all the features of the engine, such as the liquid fuel spray and turbulence. This study is part of a larger investigation of how the features of the dynamics and potential energy surfaces of key reactions, as well as their reaction rate uncertainties, affect engine performance, and results in these directions are also presented here.

  17. Realism and quantum flux tunneling

    NASA Astrophysics Data System (ADS)

    Ballentine, L. E.

    1987-10-01

    The suggestion of Leggett and Garg (1985) that the phenomenon of quantum flux tunneling oscillations contradicts the predictions of quantum mechanics (QM) in the assumptions of both macroscopic realism and noninvasive measurability is reexamined. It is shown that the contradiction of QM is produced solely by the assumption of noninvasive measurability, and that no contradiction between QM and realism can be demonstrated in this case. These findings are illustrated by the calculation of the distribution function for successive flux measurements. It is noted that the previously suggested analogy between the Bell-type inequalities and the inequalities of Leggett and Garg is misleading because the physical principles of the Bell-type inequalities are not applicable to the presently considered SQUID.

  18. Virtual Processes and Quantum Tunnelling as Fictions

    ERIC Educational Resources Information Center

    Arthur, Richard T. W.

    2012-01-01

    In this paper it is argued that virtual processes are dispensable fictions. The argument proceeds by a comparison with the phenomenon of quantum tunnelling. Building on an analysis of Levy-Leblond and Balibar, it is argued that, although the phenomenon known as quantum tunnelling certainly occurs and is at the basis of many paradigmatic quantum…

  19. Virtual Processes and Quantum Tunnelling as Fictions

    ERIC Educational Resources Information Center

    Arthur, Richard T. W.

    2012-01-01

    In this paper it is argued that virtual processes are dispensable fictions. The argument proceeds by a comparison with the phenomenon of quantum tunnelling. Building on an analysis of Levy-Leblond and Balibar, it is argued that, although the phenomenon known as quantum tunnelling certainly occurs and is at the basis of many paradigmatic quantum…

  20. Quantum temporal probabilities in tunneling systems

    SciTech Connect

    Anastopoulos, Charis Savvidou, Ntina

    2013-09-15

    We study the temporal aspects of quantum tunneling as manifested in time-of-arrival experiments in which the detected particle tunnels through a potential barrier. In particular, we present a general method for constructing temporal probabilities in tunneling systems that (i) defines ‘classical’ time observables for quantum systems and (ii) applies to relativistic particles interacting through quantum fields. We show that the relevant probabilities are defined in terms of specific correlation functions of the quantum field associated with tunneling particles. We construct a probability distribution with respect to the time of particle detection that contains all information about the temporal aspects of the tunneling process. In specific cases, this probability distribution leads to the definition of a delay time that, for parity-symmetric potentials, reduces to the phase time of Bohm and Wigner. We apply our results to piecewise constant potentials, by deriving the appropriate junction conditions on the points of discontinuity. For the double square potential, in particular, we demonstrate the existence of (at least) two physically relevant time parameters, the delay time and a decay rate that describes the escape of particles trapped in the inter-barrier region. Finally, we propose a resolution to the paradox of apparent superluminal velocities for tunneling particles. We demonstrate that the idea of faster-than-light speeds in tunneling follows from an inadmissible use of classical reasoning in the description of quantum systems. -- Highlights: •Present a general methodology for deriving temporal probabilities in tunneling systems. •Treatment applies to relativistic particles interacting through quantum fields. •Derive a new expression for tunneling time. •Identify new time parameters relevant to tunneling. •Propose a resolution of the superluminality paradox in tunneling.

  1. Understanding Quantum Tunneling through Quantum Monte Carlo Simulations.

    PubMed

    Isakov, Sergei V; Mazzola, Guglielmo; Smelyanskiy, Vadim N; Jiang, Zhang; Boixo, Sergio; Neven, Hartmut; Troyer, Matthias

    2016-10-28

    The tunneling between the two ground states of an Ising ferromagnet is a typical example of many-body tunneling processes between two local minima, as they occur during quantum annealing. Performing quantum Monte Carlo (QMC) simulations we find that the QMC tunneling rate displays the same scaling with system size, as the rate of incoherent tunneling. The scaling in both cases is O(Δ^{2}), where Δ is the tunneling splitting (or equivalently the minimum spectral gap). 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, we obtain a quadratic speedup for QMC simulations, and achieve linear scaling in Δ. We provide a physical understanding of these results and their range of applicability based on an instanton picture.

  2. Dissipation and tunneling in quantum Hall bilayers.

    PubMed

    Jack, Robert L; Lee, Derek K K; Cooper, Nigel R

    2004-09-17

    We discuss the interplay between transport and intrinsic dissipation in quantum Hall bilayers, within the framework of a simple thought experiment. We compute, for the first time, quantum corrections to the semiclassical dynamics of this system. This allows us to reinterpret tunneling measurements on these systems. We find a strong peak in the zero-temperature tunneling current that arises from the decay of Josephson-like oscillations into incoherent charge fluctuations. In the presence of an in-plane field, resonances in the tunneling current develop an asymmetric line shape.

  3. Scheme for accelerating quantum tunneling dynamics

    NASA Astrophysics Data System (ADS)

    Khujakulov, Anvar; Nakamura, Katsuhiro

    2016-02-01

    We propose a scheme of the exact fast forwarding of standard quantum dynamics for a charged particle. The present idea allows the acceleration of both the amplitude and the phase of the wave function throughout the fast-forward time range and is distinct from that of Masuda and Nakamura [Proc. R. Soc. A 466, 1135 (2010), 10.1098/rspa.2009.0446], which enabled acceleration of only the amplitude of the wave function on the way. We apply the proposed method to the quantum tunneling phenomena and obtain the electromagnetic field to ensure the rapid penetration of wave functions through a tunneling barrier. Typical examples described here are (1) an exponential wave packet passing through the δ -function barrier and (2) the opened Moshinsky shutter with a δ -function barrier just behind the shutter. We elucidate the tunneling current in the vicinity of the barrier and find a remarkable enhancement of the tunneling rate (tunneling power) due to the fast forwarding. In the case of a very high barrier, in particular, we present the asymptotic analysis and exhibit a suitable driving force to recover a recognizable tunneling current. The analysis is also carried out on the exact acceleration of macroscopic quantum tunneling with use of the nonlinear Schrödinger equation, which accommodates a tunneling barrier.

  4. Quantum electron tunneling in respiratory complex I.

    PubMed

    Hayashi, Tomoyuki; Stuchebrukhov, Alexei A

    2011-05-12

    We have simulated the atomistic details of electronic wiring of all Fe/S clusters in complex I, a key enzyme in the respiratory electron transport chain. The tunneling current theory of many-electron systems is applied to the broken-symmetry (BS) states of the protein at the ZINDO level. While the one-electron tunneling approximation is found to hold in electron tunneling between the antiferromagnetic binuclear and tetranuclear Fe/S clusters without major orbital or spin rearrangement of the core electrons, induced polarization of the core electrons contributes significantly to decrease the electron transfer rates to 19-56 %. Calculated tunneling energy is about 3 eV higher than Fermi level in the band gap of the protein, which supports that the mechanism of electron transfer is quantum mechanical tunneling, as in the rest of the electron transport chain. Resulting electron tunneling pathways consist of up to three key contributing protein residues between neighboring Fe/S clusters. A signature of the wave properties of electrons is observed as distinct quantum interferences when multiple tunneling pathways exist. In N6a-N6b, electron tunnels along different pathways depending on the involved BS states, suggesting possible fluctuations of the tunneling pathways driven by the local protein environment. The calculated distance dependence of the electron transfer rates with internal water molecules included is in good agreement with a reported phenomenological relation.

  5. Quantum transport in multiple-barrier resonant-tunneling devices

    NASA Astrophysics Data System (ADS)

    Newaz, A. K. M.

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

  6. Chaos regularization of quantum tunneling rates.

    PubMed

    Pecora, Louis M; Lee, Hoshik; Wu, Dong-Ho; Antonsen, Thomas; Lee, Ming-Jer; Ott, Edward

    2011-06-01

    Quantum tunneling rates through a barrier separating two-dimensional, symmetric, double-well potentials are shown to depend on the classical dynamics of the billiard trajectories in each well and, hence, on the shape of the wells. For shapes that lead to regular (integrable) classical dynamics the tunneling rates fluctuate greatly with eigenenergies of the states sometimes by over two orders of magnitude. Contrarily, shapes that lead to completely chaotic trajectories lead to tunneling rates whose fluctuations are greatly reduced, a phenomenon we call regularization of tunneling rates. We show that a random-plane-wave theory of tunneling accounts for the mean tunneling rates and the small fluctuation variances for the chaotic systems.

  7. Decoding DNA, RNA and peptides with quantum tunnelling

    NASA Astrophysics Data System (ADS)

    di Ventra, Massimiliano; Taniguchi, Masateru

    2016-02-01

    Drugs and treatments could be precisely tailored to an individual patient by extracting their cellular- and molecular-level information. For this approach to be feasible on a global scale, however, information on complete genomes (DNA), transcriptomes (RNA) and proteomes (all proteins) needs to be obtained quickly and at low cost. Quantum mechanical phenomena could potentially be of value here, because the biological information needs to be decoded at an atomic level and quantum tunnelling has recently been shown to be able to differentiate single nucleobases and amino acids in short sequences. Here, we review the different approaches to using quantum tunnelling for sequencing, highlighting the theoretical background to the method and the experimental capabilities demonstrated to date. We also explore the potential advantages of the approach and the technical challenges that must be addressed to deliver practical quantum sequencing devices.

  8. Macroscopic Quantum Tunneling in One Dimensional Superconductor

    NASA Astrophysics Data System (ADS)

    Chang, Yongmin

    Macroscopic quantum tunneling (MQT) in a one dimensional superconductor is discussed based on the microscopic model near the critical temperature. By means of a functional integral approach, a formula for the total decay rate, which is the sum of the thermal activation and quantum mechanical tunneling rate, is derived. The Bounce solution in the imaginary time formalism gives rise to the exponent in the tunneling rate. From the study of fluctuations from the bounce path, the pre-exponential factor has been evaluated. The theory for the tunneling rate is consistent with experimental results for temperatures at which the thermal activation theory fails. As the temperature approaches to the critical temperature, thermal activation over a free energy barrier which separates metastable states is dominant and the theory shows good agreement with experiment over the whole temperature region.

  9. Revealing the quantum regime in tunnelling plasmonics.

    PubMed

    Savage, Kevin J; Hawkeye, Matthew M; Esteban, Rubén; Borisov, Andrei G; Aizpurua, Javier; Baumberg, Jeremy J

    2012-11-22

    When two metal nanostructures are placed nanometres apart, their optically driven free electrons couple electrically across the gap. The resulting plasmons have enhanced optical fields of a specific colour tightly confined inside the gap. Many emerging nanophotonic technologies depend on the careful control of this plasmonic coupling, including optical nanoantennas for high-sensitivity chemical and biological sensors, nanoscale control of active devices, and improved photovoltaic devices. But for subnanometre gaps, coherent quantum tunnelling becomes possible and the system enters a regime of extreme non-locality in which previous classical treatments fail. Electron correlations across the gap that are driven by quantum tunnelling require a new description of non-local transport, which is crucial in nanoscale optoelectronics and single-molecule electronics. Here, by simultaneously measuring both the electrical and optical properties of two gold nanostructures with controllable subnanometre separation, we reveal the quantum regime of tunnelling plasmonics in unprecedented detail. All observed phenomena are in good agreement with recent quantum-based models of plasmonic systems, which eliminate the singularities predicted by classical theories. These findings imply that tunnelling establishes a quantum limit for plasmonic field confinement of about 10(-8)λ(3) for visible light (of wavelength λ). Our work thus prompts new theoretical and experimental investigations into quantum-domain plasmonic systems, and will affect the future of nanoplasmonic device engineering and nanoscale photochemistry.

  10. Quantum Tunneling Parameter in Global Optimization

    NASA Astrophysics Data System (ADS)

    Itami, Teturo

    Quantum tunneling that helps particles escape from local minima has been applied in “quantum annealing” method to global optimization of nonlinear functions. To control size of kinetic energy of quantum particles, we form a “quantum tunneling parameter” QT≡m/HR2, where HR corresponds to a physical constant h, Planck's constant divided by 2π, that determines the lowest eigenvalue of quantum particles with mass m. Assumptions on profiles of the function V(x) around its minimum point x0, harmonic oscillator type and square well type, make us possible to write down analytical formulae of the kinetic energy K in terms of QT. The formulae tell that we can make quantum expectation value of particle coordinates x approximate to the minimum point x0 in QT→∞. For systems where we have almost degenerate eigenvalues, examination working with our QT, that x→x0 in QT→∞, is analytically shown also efficient. Similar results that x→x0 under QT→∞ are also obtained when we utilize random-walk quantum Monte Carlo method to represent tunneling phenomena according to conventional quantum annealing.

  11. The Quantum Hydrodynamic Description of Tunneling

    SciTech Connect

    Kendrick, Brian K.

    2012-06-15

    The quantum hydrodynamic approach is based on the de Broglie-Bohm formulation of quantum mechanics. The resulting fluid-like equations of motion describe the flow of probability and an accurate solution to these equations is equivalent to solving the time-dependent Schroedinger equation. Furthermore, the hydrodynamic approach provides new insight into the mechanisms as well as an alternative computational approach for treating tunneling phenomena. New concepts include well-defined 'quantum trajectories', 'quantum potential', and 'quantum force' all of which have classical analogues. The quantum potential and its associated force give rise to all quantum mechanical effects such as zero point energy, tunneling, and interference. A new numerical approach called the Iterative Finite Difference Method (IFDM) will be discussed. The IFDM is used to solve the set of non-linear coupled hydrodynamic equations. It is 2nd-order accurate in both space and time and exhibits exponential convergence with respect to the iteration count. The stability and computational efficiency of the IFDM is significantly improved by using a 'smart' Eulerian grid which has the same computational advantages as a Lagrangian or Arbitrary Lagrangian Eulerian (ALE) grid. The IFDM is also capable of treating anharmonic potentials. Example calculations using the IFDM will be presented which include: a one-dimensional Gaussian wave packet tunneling through an Eckart barrier, a one-dimensional bound-state Morse oscillator, and a two-dimensional (2D) model collinear reaction using an anharmonic potential energy surface. Approximate treatments of the quantum hydrodynamic equations will also be discussed which could allow scaling of the calculations to hundreds of degrees of freedom which is important for treating tunneling phenomena in condensed phase systems.

  12. Boundary conditions in tunneling via quantum hydrodynamics

    NASA Technical Reports Server (NTRS)

    Nassar, Antonio B.

    1993-01-01

    Via the hydrodynamical formulation of quantum mechanics, an approach to the problem of tunneling through sharp-edged potential barriers is developed. Above all, it is shown how more general boundary conditions follow from the continuity of mass, momentum, and energy.

  13. Quantum Simulation of Tunneling in Small Systems

    PubMed Central

    Sornborger, Andrew T.

    2012-01-01

    A number of quantum algorithms have been performed on small quantum computers; these include Shor's prime factorization algorithm, error correction, Grover's search algorithm and a number of analog and digital quantum simulations. Because of the number of gates and qubits necessary, however, digital quantum particle simulations remain untested. A contributing factor to the system size required is the number of ancillary qubits needed to implement matrix exponentials of the potential operator. Here, we show that a set of tunneling problems may be investigated with no ancillary qubits and a cost of one single-qubit operator per time step for the potential evolution, eliminating at least half of the quantum gates required for the algorithm and more than that in the general case. Such simulations are within reach of current quantum computer architectures. PMID:22916333

  14. Trajectories and Traversal Times in Quantum Tunneling

    NASA Astrophysics Data System (ADS)

    Huang, Zhi Hong

    The classical concepts of trajectories and traversal times applied to quantum tunneling are discussed. By using the Wentzel-Kramers-Brillouin approximation, it is found that in a forbidden region of a multidimensional space the wave function can be described by two sets of trajectories, or equivalently by two sets of wave fronts. The trajectories belonging to different sets are mutually orthogonal. An extended Huygens construction is proposed to determine these wave fronts and trajectories. In contrast to the classical results in the allowed region, these trajectories couple to each other. However, if the incident wave is normal to the turning surface, the trajectories are found to be independent and can be determined by Newton's equations of motion with inverted potential and energy. The mutlidimensional tunneling theory is then applied to the scanning tunneling microscope to calculate the current density distribution and to derive the expressions for the lateral resolution and the surface corrugation amplitude. The traversal time in quantum tunneling, i.e. tunneling time, is found to depend on model calculations and simulations. Computer simulation of a wave packet tunneling through a square barrier is performed. Several approaches, including the phase method, Larmor clock, and time-dependent barrier model, are investigated. For a square barrier, two characteristic times are found: One is equal to the barrier width divided by the magnitude of the imaginary velocity; the other is equal to the decay length divided by the incident velocity. It is believed that the tunneling time can only be defined operationally. That is, the tunneling time is a unique and meaningful concept only for definite operational procedures which are used to measure it.

  15. Quantum Beats of Resonant Tunneling between Fractional Quantum Hall Edges

    NASA Astrophysics Data System (ADS)

    Maasilta, Ilari J.; Goldman, V. J.

    1997-03-01

    We report measurements of resonant tunneling between two fractional quantum Hall edges in a quantum antidot geometry (I. J. Maasilta and V. J. Goldman, to appear in Phys. Rev. B 55),(1997).. We observe beats in the conductance oscillations, whose evolution as a function of experimental parameters is discussed. Possible explanations in terms of different models (G. Kirczenow Phys. Rev. B 53), 15767 (1996), M. Geller et. al, preprint. are presented.

  16. Tunneling current through fractional quantum Hall interferometers

    NASA Astrophysics Data System (ADS)

    Smits, O.; Slingerland, J. K.; Simon, S. H.

    2014-01-01

    We calculate the tunneling current through a Fabry-Pérot interferometer in the fractional quantum Hall regime. Within linear response theory (weak tunneling but arbitrary source-drain voltage), we find a general expression for the current due to tunneling of quasiparticles in terms of Carlson's R function. Our result is valid for fractional quantum Hall states with an edge theory consisting of a charged channel and any number of neutral channels, with possibly different edge velocities and different chiralities. We analyze the case with a single neutral channel in detail, which applies for instance to the edge of the Moore-Read state. In addition, we consider an asymmetric interferometer with different edge lengths between the point contacts on opposite edges, and we study the behavior of the current as a function of varying edge length. Recent experiments attempted to measure the Aharanov-Bohm effect by changing the area inside the interferometer using a plunger gate. Theoretical analyses of these experiments have so far not taken into account the accompanying change in the edge lengths. We show that the tunneling current exhibits multiple oscillations as a function of this edge length, with frequencies proportional to the injected edge current and inversely proportional to the edge velocities. In particular, the edge velocities can be measured by looking at the Fourier spectrum of the edge current. We provide a numerical scheme to calculate and plot the R function, and include sample plots for a variety of edge states with parameter values, which are experimentally relevant.

  17. In-in formalism on tunneling background: Multidimensional quantum mechanics

    NASA Astrophysics Data System (ADS)

    Sugimura, Kazuyuki

    2013-07-01

    We reformulate quantum tunneling in a multidimensional system where the tunneling sector is nonlinearly coupled to oscillators. The WKB wave function is explicitly constructed under the assumption that the system was in the ground state before tunneling. We find that the quantum state after tunneling can be expressed in the language of the conventional in-in formalism. Some implications of the result to cosmology are discussed.

  18. Parallel Quantum Circuit in a Tunnel Junction

    NASA Astrophysics Data System (ADS)

    Faizy Namarvar, Omid; Dridi, Ghassen; Joachim, Christian; GNS theory Group Team

    In between 2 metallic nanopads, adding identical and independent electron transfer paths in parallel increases the electronic effective coupling between the 2 nanopads through the quantum circuit defined by those paths. Measuring this increase of effective coupling using the tunnelling current intensity can lead for example for 2 paths in parallel to the now standard G =G1 +G2 + 2√{G1 .G2 } conductance superposition law (1). This is only valid for the tunnelling regime (2). For large electronic coupling to the nanopads (or at resonance), G can saturate and even decay as a function of the number of parallel paths added in the quantum circuit (3). We provide here the explanation of this phenomenon: the measurement of the effective Rabi oscillation frequency using the current intensity is constrained by the normalization principle of quantum mechanics. This limits the quantum conductance G for example to go when there is only one channel per metallic nanopads. This ef fect has important consequences for the design of Boolean logic gates at the atomic scale using atomic scale or intramolecular circuits. References: This has the financial support by European PAMS project.

  19. Macroscopic quantum tunneling in Josephson tunnel junctions and Coulomb blockade in single small tunnel junctions

    SciTech Connect

    Cleland, A.N.

    1991-04-01

    Experiments investigating the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very small capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters; the tunneling rate in the moderately damped (Q {approx} 1) junction is seen to be reduced by a factor of 300 from that predicted for an undamped junction. The phase is seen to be a good quantum-mechanical variable. The experiments on small capacitance tunnel junctions extend the measurements on the larger-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wavefunction has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias. I present the first clear observation of the Coulomb blockade in single junctions. The electrical environment of the tunnel junction, however, strongly affects the behavior of the junction: higher resistance leads are observed to greatly sharpen the Coulomb blockade over that seen with lower resistance leads. I present theoretical descriptions of how the environment influences the junctions; comparisons with the experimental results are in reasonable agreement.

  20. Quantum-Sequencing: Biophysics of quantum tunneling through nucleic acids

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    Tunneling microscopy and spectroscopy has extensively been used in physical surface sciences to study quantum tunneling to measure electronic local density of states of nanomaterials and to characterize adsorbed species. Quantum-Sequencing (Q-Seq) is a new method based on tunneling microscopy for electronic sequencing of single molecule of nucleic acids. A major goal of third-generation sequencing technologies is to develop a fast, reliable, enzyme-free single-molecule sequencing method. Here, we present the unique ``electronic fingerprints'' for all nucleotides on DNA and RNA using Q-Seq along their intrinsic biophysical parameters. We have analyzed tunneling spectra for the nucleotides at different pH conditions and analyzed the HOMO, LUMO and energy gap for all of them. In addition we show a number of biophysical parameters to further characterize all nucleobases (electron and hole transition voltage and energy barriers). These results highlight the robustness of Q-Seq as a technique for next-generation sequencing.

  1. Parallel Quantum Circuit in a Tunnel Junction

    PubMed Central

    Faizy Namarvar, Omid; Dridi, Ghassen; Joachim, Christian

    2016-01-01

    Spectral analysis of 1 and 2-states per line quantum bus are normally sufficient to determine the effective Vab(N) electronic coupling between the emitter and receiver states through the bus as a function of the number N of parallel lines. When Vab(N) is difficult to determine, an Heisenberg-Rabi time dependent quantum exchange process must be triggered through the bus to capture the secular oscillation frequency Ωab(N) between those states. Two different linear and regimes are demonstrated for Ωab(N) as a function of N. When the initial preparation is replaced by coupling of the quantum bus to semi-infinite electrodes, the resulting quantum transduction process is not faithfully following the Ωab(N) variations. Because of the electronic transparency normalisation to unity and of the low pass filter character of this transduction, large Ωab(N) cannot be captured by the tunnel junction. The broadly used concept of electrical contact between a metallic nanopad and a molecular device must be better described as a quantum transduction process. At small coupling and when N is small enough not to compensate for this small coupling, an N2 power law is preserved for Ωab(N) and for Vab(N). PMID:27453262

  2. Parallel Quantum Circuit in a Tunnel Junction

    NASA Astrophysics Data System (ADS)

    Faizy Namarvar, Omid; Dridi, Ghassen; Joachim, Christian

    2016-07-01

    Spectral analysis of 1 and 2-states per line quantum bus are normally sufficient to determine the effective Vab(N) electronic coupling between the emitter and receiver states through the bus as a function of the number N of parallel lines. When Vab(N) is difficult to determine, an Heisenberg-Rabi time dependent quantum exchange process must be triggered through the bus to capture the secular oscillation frequency Ωab(N) between those states. Two different linear and regimes are demonstrated for Ωab(N) as a function of N. When the initial preparation is replaced by coupling of the quantum bus to semi-infinite electrodes, the resulting quantum transduction process is not faithfully following the Ωab(N) variations. Because of the electronic transparency normalisation to unity and of the low pass filter character of this transduction, large Ωab(N) cannot be captured by the tunnel junction. The broadly used concept of electrical contact between a metallic nanopad and a molecular device must be better described as a quantum transduction process. At small coupling and when N is small enough not to compensate for this small coupling, an N2 power law is preserved for Ωab(N) and for Vab(N).

  3. Parallel Quantum Circuit in a Tunnel Junction.

    PubMed

    Faizy Namarvar, Omid; Dridi, Ghassen; Joachim, Christian

    2016-07-25

    Spectral analysis of 1 and 2-states per line quantum bus are normally sufficient to determine the effective Vab(N) electronic coupling between the emitter and receiver states through the bus as a function of the number N of parallel lines. When Vab(N) is difficult to determine, an Heisenberg-Rabi time dependent quantum exchange process must be triggered through the bus to capture the secular oscillation frequency Ωab(N) between those states. Two different linear and regimes are demonstrated for Ωab(N) as a function of N. When the initial preparation is replaced by coupling of the quantum bus to semi-infinite electrodes, the resulting quantum transduction process is not faithfully following the Ωab(N) variations. Because of the electronic transparency normalisation to unity and of the low pass filter character of this transduction, large Ωab(N) cannot be captured by the tunnel junction. The broadly used concept of electrical contact between a metallic nanopad and a molecular device must be better described as a quantum transduction process. At small coupling and when N is small enough not to compensate for this small coupling, an N(2) power law is preserved for Ωab(N) and for Vab(N).

  4. Hidden and unhidden information in quantum tunneling

    NASA Astrophysics Data System (ADS)

    Steinberg, A. M.; Kwiat, P. G.; Chiao, R. Y.

    1994-06-01

    We discuss the claim that when the peak of a tunneling wave packet appears on the far side of a barrier sooner than would be allowed by causal propagation of the incident peak, this must be interpreted to mean that the transmitted particles originate toward the leading edge of the incident peak. We examine the status of information about where in a wave packet a particle is, both in terms of Bohm's deterministic picture of quantum mechanics and in terms of a recently proposed Gedankenexperiment. We find that while there are very real senses in which this interpretation makes sense, attempts to explicitly bring out this extra information in the form of quantum-mechanical observables necessarily fail. It therefore remains “hidden” information, which we can deduce indirectly from multiple experiments or from the principle of causality, but which we can never observe directly in a single experiment.

  5. Dynamic quantum tunneling in mesoscopic driven Duffing oscillators.

    PubMed

    Guo, Lingzhen; Zheng, Zhigang; Li, Xin-Qi; Yan, Yijing

    2011-07-01

    We investigate the dynamic quantum tunneling between two attractors of a mesoscopic driven Duffing oscillator. We find that, in addition to inducing a remarkable quantum shift of the bifurcation point, the mesoscopic nature also results in a perfect linear scaling behavior for the tunneling rate with the driving distance to the shifted bifurcation point.

  6. Tunnelling between the edges of two lateral quantum Hall systems

    PubMed

    Kang; Stormer; Pfeiffer; Baldwin; West

    2000-01-06

    The edge of a two-dimensional electron system in a magnetic field consists of one-dimensional channels that arise from the confining electric field at the edge of the system. The crossed electric and magnetic fields cause electrons to drift parallel to the sample boundary, creating a chiral current that travels along the edge in only one direction. In an ideal two-dimensional electron system in the quantum Hall regime, all the current flows along the edge. Quantization of the Hall resistance arises from occupation of N one-dimensional edge channels, each contributing a conductance of e2/h. Here we report differential conductance measurements, in the integer quantum Hall regime, of tunnelling between the edges of a pair of two-dimensional electron systems that are separated by an atomically precise, high-quality, tunnel barrier. The resultant interaction between the edge states leads to the formation of new energy gaps and an intriguing dispersion relation for electrons travelling along the barrier: for example, we see a persistent conductance peak at zero bias voltage and an absence of tunnelling features due to electron spin. These features are unexpected and are not consistent with a model of weakly interacting edge states. Remnant disorder along the barrier and charge screening may each play a role, although detailed numerical studies will be required to elucidate these effects.

  7. Invisibility of quantum systems to tunneling of matter waves

    SciTech Connect

    Cordero, Sergio; Garcia-Calderon, Gaston

    2009-05-15

    We show that an appropriate choice of the potential parameters in one-dimensional quantum systems allows for unity transmission of the tunneling particle at all incident tunneling energies, except at controllable exceedingly small incident energies. The corresponding dwell time and the transmission amplitude are indistinguishable from those of a free particle in the unity-transmission regime. This implies the possibility of designing quantum systems that are invisible to tunneling by a passing wave packet.

  8. Josephson inplane and tunneling currents in bilayer quantum Hall system

    SciTech Connect

    Ezawa, Z. F.; Tsitsishvili, G.; Sawada, A.

    2013-12-04

    A Bose-Einstein condensation is formed by composite bosons in the quantum Hall state. A composite boson carries the fundamental charge (–e). We investigate Josephson tunneling of such charges in the bilayer quantum Hall system at the total filling ν = 1. We show the existence of the critical current for the tunneling current to be coherent and dissipationless in tunneling experiments with various geometries.

  9. Quantum terahertz electrodynamics and macroscopic quantum tunneling in layered superconductors.

    PubMed

    Savel'ev, Sergey; Rakhmanov, A L; Nori, Franco

    2007-02-16

    We derive a quantum field theory of Josephson plasma waves (JPWs) in layered superconductors, which describes two types of interacting JPW bosonic quanta (one heavy and one lighter). We propose a mechanism of enhancement of macroscopic quantum tunneling (MQT) in stacks of intrinsic Josephson junctions. Because of the long-range interaction between junctions in layered superconductors, the calculated MQT escape rate Gamma has a nonlinear dependence on the number of junctions in the stack. We show that the crossover temperature between quantum and thermal escape increases when increasing the number of junctions. This allows us to quantitatively describe striking recent experiments in Bi2Sr2CaCu2O8+delta stacks.

  10. Experimental simulation of quantum tunneling in small systems.

    PubMed

    Feng, Guan-Ru; Lu, Yao; Hao, Liang; Zhang, Fei-Hao; Long, Gui-Lu

    2013-01-01

    It is well known that quantum computers are superior to classical computers in efficiently simulating quantum systems. Here we report the first experimental simulation of quantum tunneling through potential barriers, a widespread phenomenon of a unique quantum nature, via NMR techniques. Our experiment is based on a digital particle simulation algorithm and requires very few spin-1/2 nuclei without the need of ancillary qubits. The occurrence of quantum tunneling through a barrier, together with the oscillation of the state in potential wells, are clearly observed through the experimental results. This experiment has clearly demonstrated the possibility to observe and study profound physical phenomena within even the reach of small quantum computers.

  11. Inelastic electron tunneling spectroscopy in molecular junctions showing quantum interference

    NASA Astrophysics Data System (ADS)

    Salhani, C.; Della Rocca, M. L.; Bessis, C.; Bonnet, R.; Barraud, C.; Lafarge, P.; Chevillot, A.; Martin, P.; Lacroix, J.-C.

    2017-04-01

    Destructive quantum interference effect is implemented in large area molecular junctions to improve signatures of electron-phonon interaction. Vertical molecular junctions based on a cross-conjugated anthraquinone layer were fabricated and low-noise transport measurements were performed by acquiring simultaneously the current-voltage characteristics, its second derivative, and the differential conductance. Signatures of vibrational modes excited by inelastic events are present in the whole measured voltage range and superpose to the conductance suppression induced by destructive quantum interference. As a consequence vibrational modes have improved visibility in the low energy window (<80 meV ). Inelastic electron transport spectroscopy data are compared to infrared attenuated total reflection spectroscopy on Au/anthraquinone thin films. Common vibrational modes can be clearly identified, but inelastic electron tunneling spectroscopy reveals the existence of vibrational modes in a wider energy range (0 -400 meV ) where infrared spectroscopy is lacking.

  12. Sensing the quantum limit in scanning tunnelling spectroscopy

    PubMed Central

    Ast, Christian R.; Jäck, Berthold; Senkpiel, Jacob; Eltschka, Matthias; Etzkorn, Markus; Ankerhold, Joachim; Kern, Klaus

    2016-01-01

    The tunnelling current in scanning tunnelling spectroscopy (STS) is typically and often implicitly modelled by a continuous and homogeneous charge flow. If the charging energy of a single-charge quantum sufficiently exceeds the thermal energy, however, the granularity of the current becomes non-negligible. In this quantum limit, the capacitance of the tunnel junction mediates an interaction of the tunnelling electrons with the surrounding electromagnetic environment and becomes a source of noise itself, which cannot be neglected in STS. Using a scanning tunnelling microscope operating at 15 mK, we show that we operate in this quantum limit, which determines the ultimate energy resolution in STS. The P(E)-theory describes the probability for a tunnelling electron to exchange energy with the environment and can be regarded as the energy resolution function. We experimentally demonstrate this effect with a superconducting aluminium tip and a superconducting aluminium sample, where it is most pronounced. PMID:27708282

  13. Distribution of tunnelling times for quantum electron transport

    NASA Astrophysics Data System (ADS)

    Rudge, Samuel L.; Kosov, Daniel S.

    2016-03-01

    In electron transport, the tunnelling time is the time taken for an electron to tunnel out of a system after it has tunnelled in. We define the tunnelling time distribution for quantum processes in a dissipative environment and develop a practical approach for calculating it, where the environment is described by the general Markovian master equation. We illustrate the theory by using the rate equation to compute the tunnelling time distribution for electron transport through a molecular junction. The tunnelling time distribution is exponential, which indicates that Markovian quantum tunnelling is a Poissonian statistical process. The tunnelling time distribution is used not only to study the quantum statistics of tunnelling along the average electric current but also to analyse extreme quantum events where an electron jumps against the applied voltage bias. The average tunnelling time shows distinctly different temperature dependence for p- and n-type molecular junctions and therefore provides a sensitive tool to probe the alignment of molecular orbitals relative to the electrode Fermi energy.

  14. Quantum well resonances in scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Hörmandinger, G.; Pendry, J. B.

    1993-09-01

    Thin metallic overlayers on a substrate from quantum wells perpendicular to the surface. They can give rise to resonant states, which are observable e.g. by photoemission and LEED. Recent experimental results [J.A. Kubby and W.J. Greene, Phys. Rev. Lett. 68 (1992) 329] indicate that they can also be observed in scanning tunneling microscopy, which extends the range of this extremely surface-sensitive device into the interior of the sample, and makes it possible to image features of a buried interface with the STM. We present the results of model calculations for Ni/Cu(100) and Pd/Ag(100). The variations in the tip height caused by the resonances are of order 0.1 Å, which agrees well with the observations. We find that quantum well resonances may be observable if they occur at or above the Fermi energy of the sample, in a band perpendicular to the surface. The lateral resolution of buried steps is estimated using a junction of two free-electron quantum wells. It is found to vary slowly as a function of the overlayer thickness. For a metallic layer 5 Å thick, we obtain a resolution in the order of 5 Å.

  15. Macroscopic quantum self-trapping in dynamical tunneling.

    PubMed

    Wüster, Sebastian; Dąbrowska-Wüster, Beata J; Dabrowska-Wüster, Beata J; Davis, Matthew J

    2012-08-24

    It is well known that increasing the nonlinearity due to repulsive atomic interactions in a double-well Bose-Einstein condensate suppresses quantum tunneling between the two sites. Here we find analogous behavior in the dynamical tunneling of a Bose-Einstein condensate between period-one resonances in a single driven potential well. For small nonlinearities we find unhindered tunneling between the resonances, but with an increasing period as compared to the noninteracting system. For nonlinearities above a critical value we generally observe that the tunneling shuts down. However, for certain regimes of modulation parameters we find that dynamical tunneling reemerges for large enough nonlinearities, an effect not present in spatial double-well tunneling. We develop a two-mode model in good agreement with full numerical simulations over a wide range of parameters, which allows the suppression of tunneling to be attributed to macroscopic quantum self-trapping.

  16. Non-instanton tunneling: semiclassical and quantum interpretations.

    PubMed

    Takahashi, Kin'ya; Ikeda, Kensuke S

    2011-08-01

    Tunneling essentially different from instanton-type tunneling, say noninstanton tunneling, is studied from both semiclassical and quantum viewpoints. Taking a periodically perturbed rounded-off step potential for which the instanton-type tunneling is substantially prohibited, we analyze change of the tunneling probability with change of the perturbation frequency based on the stable-unstable manifold-guided tunneling (SUMGT) theory, which we have recently introduced. In the large and small limits of the frequency, the tunneling rate rapidly decays, but it is markedly enhanced in an intermediate range. We will also make a quantum interpretation of the noninstanton tunneling by using an exactly solvable model--a periodically perturbed right-angled step potential. Analysis with this model shows that SUMGT is considered as a sort of photoassisted tunneling through a large energy gap induced with absorbing a huge number quanta, which is completely different from the instanton-type tunneling. Both approaches from the semiclassical and quantum viewpoints complement each other to cause a better understanding of noninstanton tunneling.

  17. Quantum Adiabatic Algorithms and Large Spin Tunnelling

    NASA Technical Reports Server (NTRS)

    Boulatov, A.; Smelyanskiy, V. N.

    2003-01-01

    We provide a theoretical study of the quantum adiabatic evolution algorithm with different evolution paths proposed in this paper. The algorithm is applied to a random binary optimization problem (a version of the 3-Satisfiability problem) where the n-bit cost function is symmetric with respect to the permutation of individual bits. The evolution paths are produced, using the generic control Hamiltonians H (r) that preserve the bit symmetry of the underlying optimization problem. In the case where the ground state of H(0) coincides with the totally-symmetric state of an n-qubit system the algorithm dynamics is completely described in terms of the motion of a spin-n/2. We show that different control Hamiltonians can be parameterized by a set of independent parameters that are expansion coefficients of H (r) in a certain universal set of operators. Only one of these operators can be responsible for avoiding the tunnelling in the spin-n/2 system during the quantum adiabatic algorithm. We show that it is possible to select a coefficient for this operator that guarantees a polynomial complexity of the algorithm for all problem instances. We show that a successful evolution path of the algorithm always corresponds to the trajectory of a classical spin-n/2 and provide a complete characterization of such paths.

  18. Observation of macroscopic quantum tunneling through the Coulomb energy barrier

    NASA Astrophysics Data System (ADS)

    Geerligs, L. J.; Averin, D. V.; Mooij, J. E.

    1990-12-01

    The conductance of linear arrays of two and three normal-metal small tunnel junctions is studied for bias voltages V below the Coloumb-blockade threshold. At low temperature, we find evidence for macroscopic quantum tunneling of the electric charge (q-MQT) through the Coulomb energy barrier. For double junctions the tunneling rate scales as V3, and approximately as the product of the junction conductances, as predicted by the theory of inelastic q-MQT.

  19. Quantum tunneling resonant electron transfer process in Lorentzian plasmas

    SciTech Connect

    Hong, Woo-Pyo; Jung, Young-Dae

    2014-08-15

    The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed.

  20. Interference of macroscopic states in the presence of quantum tunneling

    SciTech Connect

    Dmitrenko, I.M.; Tsoi, G.M.; Shnyrkov, V.I.

    1984-02-01

    In studying the decomposition of the metastable states of superconducting quantum interferrometers, anomalous peaks were observed in the probability density, whose appearance is associated with resonance tunneling between macroscopic states.

  1. Quantum Tunnelling to the Origin and Evolution of Life.

    PubMed

    Trixler, Frank

    2013-08-01

    Quantum tunnelling is a phenomenon which becomes relevant at the nanoscale and below. It is a paradox from the classical point of view as it enables elementary particles and atoms to permeate an energetic barrier without the need for sufficient energy to overcome it. Tunnelling might seem to be an exotic process only important for special physical effects and applications such as the Tunnel Diode, Scanning Tunnelling Microscopy (electron tunnelling) or Near-field Optical Microscopy operating in photon tunnelling mode. However, this review demonstrates that tunnelling can do far more, being of vital importance for life: physical and chemical processes which are crucial in theories about the origin and evolution of life can be traced directly back to the effects of quantum tunnelling. These processes include the chemical evolution in stellar interiors and within the cold interstellar medium, prebiotic chemistry in the atmosphere and subsurface of planetary bodies, planetary habitability via insolation and geothermal heat as well as the function of biomolecular nanomachines. This review shows that quantum tunnelling has many highly important implications to the field of molecular and biological evolution, prebiotic chemistry and astrobiology.

  2. Quantum Tunnelling to the Origin and Evolution of Life

    PubMed Central

    Trixler, Frank

    2013-01-01

    Quantum tunnelling is a phenomenon which becomes relevant at the nanoscale and below. It is a paradox from the classical point of view as it enables elementary particles and atoms to permeate an energetic barrier without the need for sufficient energy to overcome it. Tunnelling might seem to be an exotic process only important for special physical effects and applications such as the Tunnel Diode, Scanning Tunnelling Microscopy (electron tunnelling) or Near-field Optical Microscopy operating in photon tunnelling mode. However, this review demonstrates that tunnelling can do far more, being of vital importance for life: physical and chemical processes which are crucial in theories about the origin and evolution of life can be traced directly back to the effects of quantum tunnelling. These processes include the chemical evolution in stellar interiors and within the cold interstellar medium, prebiotic chemistry in the atmosphere and subsurface of planetary bodies, planetary habitability via insolation and geothermal heat as well as the function of biomolecular nanomachines. This review shows that quantum tunnelling has many highly important implications to the field of molecular and biological evolution, prebiotic chemistry and astrobiology. PMID:24039543

  3. Dynamical symmetries in Kondo tunneling through complex quantum dots.

    PubMed

    Kuzmenko, T; Kikoin, K; Avishai, Y

    2002-10-07

    Kondo tunneling reveals hidden SO(n) dynamical symmetries of evenly occupied quantum dots. As is exemplified for an experimentally realizable triple quantum dot in parallel geometry, the possible values n=3,4,5,7 can be easily tuned by gate voltages. Following construction of the corresponding o(n) algebras, scaling equations are derived and Kondo temperatures are calculated. The symmetry group for a magnetic field induced anisotropic Kondo tunneling is SU(2) or SO(4).

  4. Electron Tunneling, a Quantum Probe for the Quantum World of Nanotechnology

    ERIC Educational Resources Information Center

    Hipps, K. W.; Scudiero, L.

    2005-01-01

    A quantum-mechanical probe is essential to study the quantum world, which is provided by electron tunneling. A spectroscopic mapping to image the electron-transport pathways on a sub-molecular scale is used.

  5. Electron Tunneling, a Quantum Probe for the Quantum World of Nanotechnology

    ERIC Educational Resources Information Center

    Hipps, K. W.; Scudiero, L.

    2005-01-01

    A quantum-mechanical probe is essential to study the quantum world, which is provided by electron tunneling. A spectroscopic mapping to image the electron-transport pathways on a sub-molecular scale is used.

  6. Computational Role of Tunneling in a Programmable Quantum Annealer

    NASA Technical Reports Server (NTRS)

    Boixo, Sergio; Smelyanskiy, Vadim; Shabani, Alireza; Isakov, Sergei V.; Dykman, Mark; Amin, Mohammad; Mohseni, Masoud; Denchev, Vasil S.; Neven, Hartmut

    2016-01-01

    Quantum tunneling is a phenomenon in which a quantum state tunnels through energy barriers above the energy of the state itself. Tunneling has been hypothesized as an advantageous physical resource for optimization. Here we present the first experimental evidence of a computational role of multiqubit quantum tunneling in the evolution of a programmable quantum annealer. We developed a theoretical model based on a NIBA Quantum Master Equation to describe the multi-qubit dissipative cotunneling effects under the complex noise characteristics of such quantum devices.We start by considering a computational primitive, the simplest non-convex optimization problem consisting of just one global and one local minimum. The quantum evolutions enable tunneling to the global minimum while the corresponding classical paths are trapped in a false minimum. In our study the non-convex potentials are realized by frustrated networks of qubit clusters with strong intra-cluster coupling. We show that the collective effect of the quantum environment is suppressed in the critical phase during the evolution where quantum tunneling decides the right path to solution. In a later stage dissipation facilitates the multiqubit cotunneling leading to the solution state. The predictions of the model accurately describe the experimental data from the D-WaveII quantum annealer at NASA Ames. In our computational primitive the temperature dependence of the probability of success in the quantum model is opposite to that of the classical paths with thermal hopping. Specially, we provide an analysis of an optimization problem with sixteen qubits,demonstrating eight qubit cotunneling that increases success probabilities. Furthermore, we report results for larger problems with up to 200 qubits that contain the primitive as subproblems.

  7. Quantum tunneling recombination in a system of randomly distributed trapped electrons and positive ions.

    PubMed

    Pagonis, Vasilis; Kulp, Christopher; Chaney, Charity-Grace; Tachiya, M

    2017-09-13

    During the past 10 years, quantum tunneling has been established as one of the dominant mechanisms for recombination in random distributions of electrons and positive ions, and in many dosimetric materials. Specifically quantum tunneling has been shown to be closely associated with two important effects in luminescence materials, namely long term afterglow luminescence and anomalous fading. Two of the common assumptions of quantum tunneling models based on random distributions of electrons and positive ions are: (a) An electron tunnels from a donor to the nearest acceptor, and (b) the concentration of electrons is much lower than that of positive ions at all times during the tunneling process. This paper presents theoretical studies for arbitrary relative concentrations of electrons and positive ions in the solid. Two new differential equations are derived which describe the loss of charge in the solid by tunneling, and they are solved analytically. The analytical solution compares well with the results of Monte Carlo simulations carried out in a random distribution of electrons and positive ions. Possible experimental implications of the model are discussed for tunneling phenomena in long term afterglow signals, and also for anomalous fading studies in feldspars and apatite samples.

  8. Quantum tunneling recombination in a system of randomly distributed trapped electrons and positive ions

    NASA Astrophysics Data System (ADS)

    Pagonis, Vasilis; Kulp, Christopher; Chaney, Charity-Grace; Tachiya, M.

    2017-09-01

    During the past 10 years, quantum tunneling has been established as one of the dominant mechanisms for recombination in random distributions of electrons and positive ions, and in many dosimetric materials. Specifically quantum tunneling has been shown to be closely associated with two important effects in luminescence materials, namely long term afterglow luminescence and anomalous fading. Two of the common assumptions of quantum tunneling models based on random distributions of electrons and positive ions are: (a) An electron tunnels from a donor to the nearest acceptor, and (b) the concentration of electrons is much lower than that of positive ions at all times during the tunneling process. This paper presents theoretical studies for arbitrary relative concentrations of electrons and positive ions in the solid. Two new differential equations are derived which describe the loss of charge in the solid by tunneling, and they are solved analytically. The analytical solution compares well with the results of Monte Carlo simulations carried out in a random distribution of electrons and positive ions. Possible experimental implications of the model are discussed for tunneling phenomena in long term afterglow signals, and also for anomalous fading studies in feldspars and apatite samples.

  9. Effects of the generalised uncertainty principle on quantum tunnelling

    NASA Astrophysics Data System (ADS)

    Blado, Gardo; Prescott, Trevor; Jennings, James; Ceyanes, Joshuah; Sepulveda, Rafael

    2016-03-01

    In a previous paper (Blado et al 2014 Eur. J. Phys. 35 065011), we showed that quantum gravity effects can be discussed with only a background in non-relativistic quantum mechanics at the undergraduate level by looking at the effect of the generalised uncertainty principle (GUP) on the finite and infinite square wells. In this paper, we derive the GUP corrections to the tunnelling probability of simple quantum mechanical systems which are accessible to undergraduates (alpha decay, simple models of quantum cosmogenesis and gravitational tunnelling radiation) and which employ the WKB approximation, a topic discussed in undergraduate quantum mechanics classes. It is shown that the GUP correction increases the tunnelling probability in each of the examples discussed.

  10. Quantum simulation of collective proton tunneling in hexagonal ice crystals.

    PubMed

    Drechsel-Grau, Christof; Marx, Dominik

    2014-04-11

    The effect of proton tunneling on many-body correlated proton transfer in hexagonal ice is investigated by quantum simulation. Classical single-particle hopping along individual hydrogen bonds leads to charge defects at high temperature, whereas six protons in ringlike topologies can move concertedly as a delocalized quasiparticle via collective tunneling at low temperature, thus preventing the creation of high-energy topological defects. Our findings rationalize many-body quantum tunneling in hydrogen-bonded networks and suggest that this phenomenon might be more widespread than previously thought.

  11. Quantum Tunneling from Apparent Horizon of Rainbow-FRW Universe

    NASA Astrophysics Data System (ADS)

    Lin, Kai; Yang, Shuzheng

    2009-07-01

    The quantum tunneling from the apparent horizon of rainbow-FRW universe is studied in this paper. We apply the semi-classical approximation, which is put forward by Parikh and Wilczek et al., to research on the scalar field particles tunneling from the apparent horizon of the rainbow-FRW universe, and then use the spin 1/2 Fermions tunneling theory, which brought forward by Kerner and Mann firstly, to research on the Fermions Hawking radiation via semi-classical approximation. Finally, we discuss the meanings of the quantum effect via Finsler geometry.

  12. Single to quadruple quantum dots with tunable tunnel couplings

    SciTech Connect

    Takakura, T.; Noiri, A.; Obata, T.; Yoneda, J.; Yoshida, K.; Otsuka, T.; Tarucha, S.

    2014-03-17

    We prepare a gate-defined quadruple quantum dot to study the gate-tunability of single to quadruple quantum dots with finite inter-dot tunnel couplings. The measured charging energies of various double dots suggest that the dot size is governed by the gate geometry. For the triple and quadruple dots, we study the gate-tunable inter-dot tunnel couplings. For the triple dot, we find that the effective tunnel coupling between side dots significantly depends on the alignment of the center dot potential. These results imply that the present quadruple dot has a gate performance relevant for implementing spin-based four-qubits with controllable exchange couplings.

  13. Experimental Evidence for Quantum Tunneling Time

    NASA Astrophysics Data System (ADS)

    Camus, Nicolas; Yakaboylu, Enderalp; Fechner, Lutz; Klaiber, Michael; Laux, Martin; Mi, Yonghao; Hatsagortsyan, Karen Z.; Pfeifer, Thomas; Keitel, Christoph H.; Moshammer, Robert

    2017-07-01

    The first hundred attoseconds of the electron dynamics during strong field tunneling ionization are investigated. We quantify theoretically how the electron's classical trajectories in the continuum emerge from the tunneling process and test the results with those achieved in parallel from attoclock measurements. An especially high sensitivity on the tunneling barrier is accomplished here by comparing the momentum distributions of two atomic species of slightly deviating atomic potentials (argon and krypton) being ionized under absolutely identical conditions with near-infrared laser pulses (1300 nm). The agreement between experiment and theory provides clear evidence for a nonzero tunneling time delay and a nonvanishing longitudinal momentum of the electron at the "tunnel exit."

  14. Quantum Electron Tunneling in Respiratory Complex I1

    PubMed Central

    Hayashi, Tomoyuki; Stuchebrukhov, Alexei A.

    2014-01-01

    We have simulated the atomistic details of electronic wiring of all Fe/S clusters in complex I, a key enzyme in the respiratory electron transport chain. The tunneling current theory of many-electron systems is applied to the broken-symmetry (BS) states of the protein at the ZINDO level. One-electron tunneling approximation is found to hold in electron tunneling between the anti-ferromagnetic binuclear and tetranuclear Fe/S clusters with moderate induced polarization of the core electrons. Calculated tunneling energy is about 3 eV higher than Fermi level in the band gap of the protein, which supports that the mechanism of electron transfer is quantum mechanical tunneling, as in the rest of electron transport chain. Resulting electron tunneling pathways consist of up to three key contributing protein residues between neighboring Fe/S clusters. A distinct signature of the wave properties of electrons is observed as quantum interferences when multiple tunneling pathways exist. In N6a-N6b, electron tunnels along different pathways depending on the involved BS states, suggesting possible fluctuations of the tunneling pathways driven by the local protein environment. The calculated distance dependence of the electron transfer rates with internal water molecules included are in good agreement with a reported phenomenological relation. PMID:21495666

  15. Macroscopic quantum tunnelling in a current biased Josephson junction

    SciTech Connect

    Martinis, J.M.; Devoret, M.H.; Clarke, J.; Urbina, C.

    1984-11-01

    We discuss in this work an attempt to answer experimentally the question: do macroscopic variables obey quantum mechanics. More precisely, this experiment deals with the question of quantum-mechanical tunnelling of a macroscopic variable, a subject related to the famous Schrodinger's cat problem in the theory of measurement.

  16. Correlated dynamics of a Rabi oscillation and a quantum tunneling in coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Xie, Weidong; Chu, Bingxin; Duan, Suqing; Xie, Yan; Chu, Weidong; Yang, Ning; Zhao, Xian-Geng

    2015-08-01

    We couple the Rabi oscillation in a double quantum dot (DQD) with the quantum tunneling in another DQD by Coulomb interaction between the neighboring dots. Such a coupling leads to correlation of the Rabi oscillating electron and the quantum tunneling one, and gives a tendency of synchronizing them under appropriate Rabi frequency ΩR and tunneling rate Tc. The correlated oscillation is shown clearly in the tunneling current. As ΩR =Tc, the Rabi oscillation and the quantum tunneling reach their strongest correlation and the two electrons finish their complete transitions simultaneously. And then, a single optical signal accomplishes a gang control of two electrons. This result encourages superior design of two-qubit quantum gates based on correlated DQDs.

  17. Instantons in Quantum Annealing: Thermally Assisted Tunneling Vs Quantum Monte Carlo Simulations

    NASA Technical Reports Server (NTRS)

    Jiang, Zhang; Smelyanskiy, Vadim N.; Boixo, Sergio; Isakov, Sergei V.; Neven, Hartmut; Mazzola, Guglielmo; Troyer, Matthias

    2015-01-01

    Recent numerical result (arXiv:1512.02206) from Google suggested that the D-Wave quantum annealer may have an asymptotic speed-up than simulated annealing, however, the asymptotic advantage disappears when it is compared to quantum Monte Carlo (a classical algorithm despite its name). We show analytically that the asymptotic scaling of quantum tunneling is exactly the same as the escape rate in quantum Monte Carlo for a class of problems. Thus, the Google result might be explained in our framework. We also found that the transition state in quantum Monte Carlo corresponds to the instanton solution in quantum tunneling problems, which is observed in numerical simulations.

  18. Experimental simulation of quantum tunneling in small systems

    PubMed Central

    Feng, Guan-Ru; Lu, Yao; Hao, Liang; Zhang, Fei-Hao; Long, Gui-Lu

    2013-01-01

    It is well known that quantum computers are superior to classical computers in efficiently simulating quantum systems. Here we report the first experimental simulation of quantum tunneling through potential barriers, a widespread phenomenon of a unique quantum nature, via NMR techniques. Our experiment is based on a digital particle simulation algorithm and requires very few spin-1/2 nuclei without the need of ancillary qubits. The occurrence of quantum tunneling through a barrier, together with the oscillation of the state in potential wells, are clearly observed through the experimental results. This experiment has clearly demonstrated the possibility to observe and study profound physical phenomena within even the reach of small quantum computers. PMID:23958996

  19. Tunneling into microstate geometries: quantum effects stop gravitational collapse

    NASA Astrophysics Data System (ADS)

    Bena, Iosif; Mayerson, Daniel R.; Puhm, Andrea; Vercnocke, Bert

    2016-07-01

    Collapsing shells form horizons, and when the curvature is small classical general relativity is believed to describe this process arbitrarily well. On the other hand, quantum information theory based (fuzzball/firewall) arguments suggest the existence of some structure at the black hole horizon. This structure can only form if classical general relativity stops being the correct description of the collapsing shell before it reaches the horizon size. We present strong evidence that classical general relativity can indeed break down prematurely, by explicitly computing the quantum tunneling amplitude of a collapsing shell of branes into smooth horizonless microstate geometries. We show that the amplitude for tunneling into microstate geometries with a large number of topologically non-trivial cycles is parametrically larger than e - S BH , which indicates that the shell can tunnel into a horizonless configuration long before the horizon has any chance to form. We also use this technology to investigate the tunneling of M2 branes into LLM bubbling geometries.

  20. Experimental Evidence for Quantum Tunneling Time.

    PubMed

    Camus, Nicolas; Yakaboylu, Enderalp; Fechner, Lutz; Klaiber, Michael; Laux, Martin; Mi, Yonghao; Hatsagortsyan, Karen Z; Pfeifer, Thomas; Keitel, Christoph H; Moshammer, Robert

    2017-07-14

    The first hundred attoseconds of the electron dynamics during strong field tunneling ionization are investigated. We quantify theoretically how the electron's classical trajectories in the continuum emerge from the tunneling process and test the results with those achieved in parallel from attoclock measurements. An especially high sensitivity on the tunneling barrier is accomplished here by comparing the momentum distributions of two atomic species of slightly deviating atomic potentials (argon and krypton) being ionized under absolutely identical conditions with near-infrared laser pulses (1300 nm). The agreement between experiment and theory provides clear evidence for a nonzero tunneling time delay and a nonvanishing longitudinal momentum of the electron at the "tunnel exit."

  1. Dissipative macroscopic quantum tunneling in type-I superconductors

    NASA Astrophysics Data System (ADS)

    Zarzuela, R.; Chudnovsky, E. M.; Tejada, J.

    2011-11-01

    We study macroscopic quantum tunneling of interfaces separating normal and superconducting regions in type-I superconductors. A mathematical model is developed that describes dissipative quantum escape of a two-dimensional manifold from a planar potential well. It corresponds to, e.g., a current-driven quantum depinning of the interface from a grain boundary or from an artificially manufactured pinning layer. Effective action is derived and instantons of the equations of motion are investigated. The crossover between thermal activation and quantum tunneling is studied and the crossover temperature is computed. Our results, together with recent observation of nonthermal low-temperature magnetic relaxation in lead, suggest the possibility of a controlled measurement of quantum depinning of the interface in a type-I superconductor.

  2. Dissipative macroscopic quantum tunneling in type-I superconductors

    SciTech Connect

    Zarzuela, R.; Tejada, J.; Chudnovsky, E. M.

    2011-11-01

    We study macroscopic quantum tunneling of interfaces separating normal and superconducting regions in type-I superconductors. A mathematical model is developed that describes dissipative quantum escape of a two-dimensional manifold from a planar potential well. It corresponds to, e.g., a current-driven quantum depinning of the interface from a grain boundary or from an artificially manufactured pinning layer. Effective action is derived and instantons of the equations of motion are investigated. The crossover between thermal activation and quantum tunneling is studied and the crossover temperature is computed. Our results, together with recent observation of nonthermal low-temperature magnetic relaxation in lead, suggest the possibility of a controlled measurement of quantum depinning of the interface in a type-I superconductor.

  3. Quantum tunneling of hydrogen atom in dissociation of photoexcited methylamine.

    PubMed

    Marom, Ran; Levi, Chen; Weiss, Tal; Rosenwaks, Salman; Zeiri, Yehuda; Kosloff, Ronnie; Bar, Ilana

    2010-09-16

    The probability of hydrogen atom release, following photoexcitation of methylamine, CH(3)NH(2), is found to increase extensively as higher vibrational states on the first excited electronic state are accessed. This behavior is consistent with theoretical calculations, based on the probability of H atom tunneling through an energy barrier on the excited potential energy surface, implying that N-H bond breaking is dominated by quantum tunneling.

  4. Enhancement of macroscopic quantum tunneling by Landau-Zener transitions.

    PubMed

    Ankerhold, Joachim; Grabert, Hermann

    2003-07-04

    Motivated by recent realizations of qubits with a readout by macroscopic quantum tunneling in a Josephson junction, we study the problem of barrier penetration in the presence of coupling to a spin-1 / 2 system. It is shown that, when the diabatic potentials for fixed spin intersect in the barrier region, Landau-Zener transitions lead to an enhancement of the tunneling rate. The effect of these spin flips in imaginary time is in qualitative agreement with experimental observations.

  5. Quantum tunneling of the non-stationary BTZ black hole

    NASA Astrophysics Data System (ADS)

    Yang, Juan; Yang, Shu Zheng

    2009-07-01

    The semi-classical tunneling method is extended to study the Hawking tunneling radiation from the non-stationary BTZ black hole via general tortoise coordination transformation and WKB approximation. In this paper, we simplify the spin-0 scalar field equation and the spin-1/2 Dirac equation at the event horizon of this black hole, and then the quantum tunneling probability and Hawking temperature are obtained. Finally, the correctional tunneling rate is researched, and the results show that after considering the changed background space-time of the non-stationary BTZ black hole, the tunneling rate depends not only on the entropy change but also on the integral about {\\dot r}_H .

  6. Computational modeling of electrophotonics nanomaterials: Tunneling in double quantum dots

    SciTech Connect

    Vlahovic, Branislav Filikhin, Igor

    2014-10-06

    Single electron localization and tunneling in double quantum dots (DQD) and rings (DQR) and in particular the localized-delocalized states and their spectral distributions are considered in dependence on the geometry of the DQDs (DQRs). The effect of violation of symmetry of DQDs geometry on the tunneling is studied in details. The cases of regular and chaotic geometries are considered. It will be shown that a small violation of symmetry drastically affects localization of electron and that anti-crossing of the levels is the mechanism of tunneling between the localized and delocalized states in DQRs.

  7. Ferroelectric tunnel junctions with multi-quantum well structures

    SciTech Connect

    Ma, Zhijun; Zhang, Tianjin; Liang, Kun; Qi, Yajun; Wang, Duofa; Wang, Jinzhao; Jiang, Juan

    2014-06-02

    Ferroelectric tunnel junctions (FTJs) with multi-quantum well structures are proposed and the tunneling electroresistance (TER) effect is investigated theoretically. Compared with conventional FTJs with monolayer ferroelectric barriers, FTJs with single-well structures provide TER ratio improvements of one order of magnitude, while FTJs with optimized multi-well structures can enhance this improvement by another order of magnitude. It is believed that the increased resonant tunneling strength combined with appropriate asymmetry in these FTJs contributes to the improvement. These studies may help to fabricate FTJs with large TER ratio experimentally and put them into practice.

  8. Photon-assisted tunneling through a quantum dot

    SciTech Connect

    Kouwenhoven, L.P.; Jauhar, S.; McCormick, K.; Dixon, D.; McEuen, P.L. Materials Science Division, Lawrence Berkeley Laboratories, Mail Stop 2-200, Berkeley, California 94720 ); Nazarov, Y.V.; van der Vaart, N.C. ); Foxon, C.T. )

    1994-07-15

    We study single-electron tunneling in a two-junction device in the presence of microwave radiation. We introduce a model for numerical simulations that extends the Tien-Gordon theory for photon-assisted tunneling to encompass correlated single-electron tunneling. We predict sharp current jumps which reflect the discrete photon energy [ital hf], and a zero-bias current whose sign changes when an electron is added to the central island of the device. Measurements on split-gate quantum dots show microwave-induced features that are in good agreement with the model.

  9. Quantum tunneling between Chern states in a Topological Insulator

    NASA Astrophysics Data System (ADS)

    Liu, Minhao; Wang, Wudi; Richardella, Anthony R.; Kandala, Abhinav; Li, Jian; Yazdani, Ali; Samarth, Nitin; Ong, N. P.

    The tunneling of a macroscopic object through a barrier is a quintessentially quantum phenomenon important in field theory, low-temperature physics and quantum computing. Progress has been achieved in experiments on Josephson junctions, molecular magnets, and domain wall dynamics. However, a key feature - rapid expansion of the true vacuum triggered by a tunneling event is virtually unexplored. Here we report the detection of large jumps in the Hall resistance Ryx in a magnetized topological insulator which result from tunneling out of a metastable topological state. In the TI, the conducting electrons are confined to surface Dirac states. When magnetized, the TI enters the quantum anomalous Hall insulator state in which Ryx is strictly quantized. If the magnetic field is reversed, the sample is trapped in a metastable state. We find that, below 145 mK, Ryx exhibits abrupt jumps as large as one quantum unit on time-scales under 1 ms. If the temperature is raised, the escape rate is suppressed consistent with tunneling in the presence of dissipation. The jumps involve expansion of the thermodynamically stable state bubble over macroscopic lengths, but dissipation limits the final size. The results uncover novel effects of dissipation on macroscopic tunneling. We acknowledge support from DARPA SPAWAR (N66001-11-1-4110) and the Gordon and Betty Moore Foundations (GBMF4539).

  10. A new teaching approach to quantum mechanical tunneling

    NASA Astrophysics Data System (ADS)

    Gilfoyle, G. P.

    1999-09-01

    The transfer matrix method has been used to investigate quantum mechanical tunneling in introductory quantum mechanics. The method is applied first to calculate the transmission coefficient for tunneling through a rectangular barrier and is then extended to the problem of potential barriers of arbitrary shape, in particular, to radioactive decay. This approach uses matrix methods that are accessible to a broader range of undergraduates than other numerical techniques, the connection between the rectangular barrier problem and potential barriers of arbitrary shape is transparent, and it can be readily executed by undergraduates. The classroom experience with this approach is discussed.

  11. Tunneling phenomena in the open elliptic quantum billiard

    NASA Astrophysics Data System (ADS)

    Garcia-Gracia, Hipolito; Gutiérrez-Vega, Julio C.

    2012-07-01

    The study of open quantum billiards has gained popularity in the last decades, including different common and uncommon geometries such as the circular and stadium billiards. We present an extensive analysis of the elliptic quantum billiard with hyperbolic channels. We concentrate on the tunneling through an elliptic resonator-like structure. We analyze three different variations of the system: the first configuration has horizontal channels, then we study the system with vertical leads, and finally we displace both channels by the same angle to gain a more general perspective. We observed a very unusual phase distribution in the resonator cavity when there is no tunneling through the system.

  12. Aharonov-Bohm effect in the tunnelling of a quantum rotor in a linear Paul trap.

    PubMed

    Noguchi, Atsushi; Shikano, Yutaka; Toyoda, Kenji; Urabe, Shinji

    2014-05-13

    Quantum tunnelling is a common fundamental quantum mechanical phenomenon that originates from the wave-like characteristics of quantum particles. Although the quantum tunnelling effect was first observed 85 years ago, some questions regarding the dynamics of quantum tunnelling remain unresolved. Here we realize a quantum tunnelling system using two-dimensional ionic structures in a linear Paul trap. We demonstrate that the charged particles in this quantum tunnelling system are coupled to the vector potential of a magnetic field throughout the entire process, even during quantum tunnelling, as indicated by the manifestation of the Aharonov-Bohm effect in this system. The tunnelling rate of the structures periodically depends on the strength of the magnetic field, whose period is the same as the magnetic flux quantum φ0 through the rotor [(0.99 ± 0.07) × φ0].

  13. Quantum tunneling observed without its characteristic large kinetic isotope effects.

    PubMed

    Hama, Tetsuya; Ueta, Hirokazu; Kouchi, Akira; Watanabe, Naoki

    2015-06-16

    Classical transition-state theory is fundamental to describing chemical kinetics; however, quantum tunneling is also important in explaining the unexpectedly large reaction efficiencies observed in many chemical systems. Tunneling is often indicated by anomalously large kinetic isotope effects (KIEs), because a particle's ability to tunnel decreases significantly with its increasing mass. Here we experimentally demonstrate that cold hydrogen (H) and deuterium (D) atoms can add to solid benzene by tunneling; however, the observed H/D KIE was very small (1-1.5) despite the large intrinsic H/D KIE of tunneling (≳ 100). This strong reduction is due to the chemical kinetics being controlled not by tunneling but by the surface diffusion of the H/D atoms, a process not greatly affected by the isotope type. Because tunneling need not be accompanied by a large KIE in surface and interfacial chemical systems, it might be overlooked in other systems such as aerosols or enzymes. Our results suggest that surface tunneling reactions on interstellar dust may contribute to the deuteration of interstellar aromatic and aliphatic hydrocarbons, which could represent a major source of the deuterium enrichment observed in carbonaceous meteorites and interplanetary dust particles. These findings could improve our understanding of interstellar physicochemical processes, including those during the formation of the solar system.

  14. Quantum tunneling observed without its characteristic large kinetic isotope effects

    PubMed Central

    Hama, Tetsuya; Ueta, Hirokazu; Kouchi, Akira; Watanabe, Naoki

    2015-01-01

    Classical transition-state theory is fundamental to describing chemical kinetics; however, quantum tunneling is also important in explaining the unexpectedly large reaction efficiencies observed in many chemical systems. Tunneling is often indicated by anomalously large kinetic isotope effects (KIEs), because a particle’s ability to tunnel decreases significantly with its increasing mass. Here we experimentally demonstrate that cold hydrogen (H) and deuterium (D) atoms can add to solid benzene by tunneling; however, the observed H/D KIE was very small (1–1.5) despite the large intrinsic H/D KIE of tunneling (≳100). This strong reduction is due to the chemical kinetics being controlled not by tunneling but by the surface diffusion of the H/D atoms, a process not greatly affected by the isotope type. Because tunneling need not be accompanied by a large KIE in surface and interfacial chemical systems, it might be overlooked in other systems such as aerosols or enzymes. Our results suggest that surface tunneling reactions on interstellar dust may contribute to the deuteration of interstellar aromatic and aliphatic hydrocarbons, which could represent a major source of the deuterium enrichment observed in carbonaceous meteorites and interplanetary dust particles. These findings could improve our understanding of interstellar physicochemical processes, including those during the formation of the solar system. PMID:26034285

  15. Frustrated Total Internal Reflection applied to Quantum Tunneling

    NASA Astrophysics Data System (ADS)

    Hull, Nathaniel; Yan, Jia-An

    The objective of this project is to demonstrate an optical phenomenon, frustrated total internal reflection (FTIR), by numerically solving the time-dependent Schrodinger equation (TDSE) in quantum mechanics, and to illustrate the correlations between FTIR and the quantum tunneling in one-dimensional quantum structures. We will use a MATLAB program to numerically propagate a Gaussian wave packet to penetrate finite square barriers. The transmission coefficient is then calculated as a function of the distance between two rectangular barriers/wells. The results will be useful to elucidate the correlations between optical FTIR and quantum tunneling. This work was supported by the FCSM Undergraduate Research Committee, the FCSM Fisher General Endowment and the FDRC Grant (OSPR No. 140269) at Towson University.

  16. 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.

  17. Giant fifth-order nonlinearity via tunneling induced quantum interference in triple quantum dots

    SciTech Connect

    Tian, Si-Cong Tong, Cun-Zhu Ning, Yong-Qiang; Wan, Ren-Gang

    2015-02-15

    Schemes for giant fifth-order nonlinearity via tunneling in both linear and triangular triple quantum dots are proposed. In both configurations, the real part of the fifth-order nonlinearity can be greatly enhanced, and simultaneously the absorption is suppressed. The analytical expression and the dressed states of the system show that the two tunnelings between the neighboring quantum dots can induce quantum interference, resulting in the giant higher-order nonlinearity. The scheme proposed here may have important applications in quantum information processing at low light level.

  18. Room-temperature resonant quantum tunneling transport of macroscopic systems.

    PubMed

    Xiong, Zhengwei; Wang, Xuemin; Yan, Dawei; Wu, Weidong; Peng, Liping; Li, Weihua; Zhao, Yan; Wang, Xinmin; An, Xinyou; Xiao, Tingting; Zhan, Zhiqiang; Wang, Zhuo; Chen, Xiangrong

    2014-11-21

    A self-assembled quantum dots array (QDA) is a low dimensional electron system applied to various quantum devices. This QDA, if embedded in a single crystal matrix, could be advantageous for quantum information science and technology. However, the quantum tunneling effect has been difficult to observe around room temperature thus far, because it occurs in a microcosmic and low temperature condition. Herein, we show a designed a quasi-periodic Ni QDA embedded in a single crystal BaTiO3 matrix and demonstrate novel quantum resonant tunneling transport properties around room-temperature according to theoretical calculation and experiments. The quantum tunneling process could be effectively modulated by changing the Ni QDA concentration. The major reason was that an applied weak electric field (∼10(2) V cm(-1)) could be enhanced by three orders of magnitude (∼10(5) V cm(-1)) between the Ni QDA because of the higher permittivity of BaTiO3 and the 'hot spots' of the Ni QDA. Compared with the pure BaTiO3 films, the samples with embedded Ni QDA displayed a stepped conductivity and temperature (σ-T curves) construction.

  19. A triangular triple quantum dot with tunable tunnel couplings

    NASA Astrophysics Data System (ADS)

    Noiri, A.; Kawasaki, K.; Otsuka, T.; Nakajima, T.; Yoneda, J.; Amaha, S.; Delbecq, M. R.; Takeda, K.; Allison, G.; Ludwig, A.; Wieck, A. D.; Tarucha, S.

    2017-08-01

    A two-dimensional arrangement of quantum dots (QDs) with finite inter-dot tunnel coupling provides a promising platform for studying complicated spin correlations as well as for constructing large-scale quantum computers. Here, we fabricate a tunnel-coupled triangular triple QD with a novel gate geometry in which three dots are defined by positively biasing the surface gates. At the same time, the small area in the center of the triangle is depleted by negatively biasing the top gate placed above the surface gates. The size of the small center depleted area is estimated from the Aharonov-Bohm oscillation measured for the triangular channel but incorporating no gate-defined dots, with a value consistent with the design. With this approach, we can bring the neighboring gate-defined dots close enough to one another to maintain a finite inter-dot tunnel coupling. We finally confirm the presence of the inter-dot tunnel couplings in the triple QD from the measurement of tunneling current through the dots in the stability diagram. We also show that the charge occupancy of each dot and that the inter-dot tunnel couplings are tunable with gate voltages.

  20. Coupling quantum tunneling with cavity photons.

    PubMed

    Cristofolini, Peter; Christmann, Gabriel; Tsintzos, Simeon I; Deligeorgis, George; Konstantinidis, George; Hatzopoulos, Zacharias; Savvidis, Pavlos G; Baumberg, Jeremy J

    2012-05-11

    Tunneling of electrons through a potential barrier is fundamental to chemical reactions, electronic transport in semiconductors and superconductors, magnetism, and devices such as terahertz oscillators. Whereas tunneling is typically controlled by electric fields, a completely different approach is to bind electrons into bosonic quasiparticles with a photonic component. Quasiparticles made of such light-matter microcavity polaritons have recently been demonstrated to Bose-condense into superfluids, whereas spatially separated Coulomb-bound electrons and holes possess strong dipole interactions. We use tunneling polaritons to connect these two realms, producing bosonic quasiparticles with static dipole moments. Our resulting three-state system yields dark polaritons analogous to those in atomic systems or optical waveguides, thereby offering new possibilities for electromagnetically induced transparency, room-temperature condensation, and adiabatic photon-to-electron transfer.

  1. Quantum Tunneling Enabled Self-Assembly of Hydrogen Atoms on Cu(111)

    SciTech Connect

    Jewell, April D.; Peng, Guowen; Mattera, Michael F.; Lewis, Emily A.; Murphy, Colin J.; Kyriakou, Georgios; Mavrikakis, Manos; Sykes, E. Charles H.

    2012-11-27

    Atomic and molecular self-assembly are key phenomena that underpin many important technologies. Typically, thermally enabled diffusion allows a system to sample many areas of configurational space, and ordered assemblies evolve that optimize interactions between species. Herein we describe a system in which the diffusion is quantum tunneling in nature and report the self-assembly of H atoms on a Cu(111) surface into complex arrays based on local clustering followed by larger scale islanding of these clusters. By scanning tunneling microscope tip-induced scrambling of H atom assemblies, we are able to watch the atomic scale details of H atom self-assembly in real time. The ordered arrangements we observe are complex and very different from those formed by H on other metals that occur in much simpler geometries. We contrast the diffusion and assembly of H with D, which has a much slower tunneling rate and is not able to form the large islands observed with H over equivalent time scales. Using density functional theory, we examine the interaction of H atoms on Cu(111) by calculating the differential binding energy as a function of H coverage. At the temperature of the experiments (5 K), H(D) diffusion by quantum tunneling dominates. The quantum-tunneling-enabled H and D diffusion is studied using a semiclassically corrected transition state theory coupled with density functional theory. This system constitutes the first example of quantum-tunneling-enabled self-assembly, while simultaneously demonstrating the complex ordering of H on Cu(111), a catalytically relevant surface.

  2. Quantum Annealing and Tunable Magnetic Domain Wall Tunneling

    NASA Astrophysics Data System (ADS)

    Rosenbaum, Thomas F.

    2001-03-01

    Traditional simulated annealing utilizes thermal fluctuations for convergence in optimization problems. Quantum tunneling provides a different mechanism for moving between states, with the potential for reduced time scales. We compare thermal and quantum annealing in a model Ising ferromagnet composed of holmium dipoles in a lithium tetrafluoride matrix. The effects of quantum mechanics can be tuned in the laboratory by varying a magnetic field applied transverse to the Ising axis. This new knob permits us to: (1) tune the crossover between a classical Arrhenius response at high temperatures and an athermal response below 100 mK; (2) quantify the tunneling of magnetic domain walls through potential energy barriers in terms of an effective mass [1]; and (3) hasten convergence to the optimal state [2]. [1] "Tunable Quantum Tunneling of Magnetic Domain Walls," J. Brooke, T.F. Rosenbaum and G. Aeppli, preprint (2000). [2] "Quantum Annealing of a Disordered Magnet," J. Brooke, D. Bitko, T.F. Rosenbaum and G. Aeppli, Science 284, 779 (1999).

  3. Quantum and tunneling capacitance in charge and spin qubits

    NASA Astrophysics Data System (ADS)

    Mizuta, R.; Otxoa, R. M.; Betz, A. C.; Gonzalez-Zalba, M. F.

    2017-01-01

    We present a theoretical analysis of the capacitance of a double quantum dot in the charge and spin qubit configurations probed at high frequencies. We find that, in general, the total capacitance of the system consists of two state-dependent terms: the quantum capacitance arising from adiabatic charge motion and the tunneling capacitance that appears when repopulation occurs at a rate comparable or faster than the probing frequency. The analysis of the capacitance lineshape as a function of externally controllable variables offers a way to characterize the qubits' charge and spin state as well as relevant system parameters such as charge and spin relaxation rates, tunnel coupling, electron temperature, and electron g factor. Overall, our analysis provides a formalism to understand dispersive qubit-resonator interactions which can be applied to high-sensitivity and noninvasive quantum-state readout.

  4. Effect of quantum tunneling on spin Hall magnetoresistance

    NASA Astrophysics Data System (ADS)

    Ok, Seulgi; Chen, Wei; Sigrist, Manfred; Manske, Dirk

    2017-02-01

    We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on the spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/Y3Fe5O12) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is detrimental to the interface spin current which also affects the spin accumulation. The influence of generic material properties such as spin diffusion length, layer thickness, interface coupling, and insulating gap can be quantified in a unified manner, and experiments that reveal the quantum feature of the magnetoresistance are suggested.

  5. Kondo resonance in tunneling phenomena through a single quantum level

    SciTech Connect

    Oguri, A.; Ishii, H. ); Saso, T. )

    1995-02-15

    Effects of Coulomb repulsion on the process of resonant tunneling through a single quantum level are studied by applying the quantum Monte Carlo method and the maximum-entropy method to the Wolf model on a one-dimensional chain. In the calculated spectral function there is a sharp Kondo peak near the chemical potential [mu], which contributes to the resonance tunneling. Correspondingly, the conductance calculated by using the Friedel sum rule shows the expected transparency, i.e., the transmission probability is almost unity when [mu] is in the range [epsilon][sub 0][lt][mu][lt][epsilon][sub 0]+[ital U], where [epsilon][sub 0] is the on-site energy of the single quantum level and [ital U] is the Coulomb repulsion.

  6. Effect of quantum tunneling on spin Hall magnetoresistance.

    PubMed

    Ok, Seulgi; Chen, Wei; Sigrist, Manfred; Manske, Dirk

    2017-02-22

    We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on the spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/Y3Fe5O12) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is detrimental to the interface spin current which also affects the spin accumulation. The influence of generic material properties such as spin diffusion length, layer thickness, interface coupling, and insulating gap can be quantified in a unified manner, and experiments that reveal the quantum feature of the magnetoresistance are suggested.

  7. Evolution of Plasmonic Metamolecule Modes in the Quantum Tunneling Regime.

    PubMed

    Scholl, Jonathan A; Garcia-Etxarri, Aitzol; Aguirregabiria, Garikoitz; Esteban, Ruben; Narayan, Tarun C; Koh, Ai Leen; Aizpurua, Javier; Dionne, Jennifer A

    2016-01-26

    Plasmonic multinanoparticle systems exhibit collective electric and magnetic resonances that are fundamental for the development of state-of-the-art optical nanoantennas, metamaterials, and surface-enhanced spectroscopy substrates. While electric dipolar modes have been investigated in both the classical and quantum realm, little attention has been given to magnetic and other "dark" modes at the smallest dimensions. Here, we study the collective electric, magnetic, and dark modes of colloidally synthesized silver nanosphere trimers with varying interparticle separation using scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). This technique enables direct visualization and spatially selective excitation of individual trimers, as well as manipulation of the interparticle distance into the subnanometer regime with the electron beam. Our experiments reveal that bonding electric and magnetic modes are significantly impacted by quantum effects, exhibiting a relative blueshift and reduced EELS amplitude compared to classical predictions. In contrast, the trimer's electric dark mode is not affected by quantum tunneling for even Ångström-scale interparticle separations. We employ a quantum-corrected model to simulate the effect of electron tunneling in the trimer which shows excellent agreement with experimental results. This understanding of classical and quantum-influenced hybridized modes may impact the development of future quantum plasmonic materials and devices, including Fano-like molecular sensors and quantum metamaterials.

  8. Quantum and semiclassical Cooper-pair tunneling in finite systems

    NASA Astrophysics Data System (ADS)

    Kleber, M.

    2016-12-01

    We derive analytic solutions for the tunneling dynamics of two weakly coupled finite BCS-condensates. Pairing interaction between the finite-size condensates is taken into account. Using particle-number dependent chemical potentials the time-dependent transfer of Cooper pairs is obtained from a phenomenological calculation. The results of this theory are compared to a microscopic calculation within the quasispin formulation in its semiclassical limit. In both cases the tunneling current can be mapped onto the motion of a simple pendulum: The results are analogous to the Josephson current between two superconductors and can be used as a starting point to include quantum fluctuations and Josephson radiation.

  9. Quantum Tunneling, Field Induced Injecting Contact, and Excitons

    NASA Astrophysics Data System (ADS)

    Liu, Yixin

    1995-01-01

    This thesis consists of three parts: Quantum tunneling simulation, Schottky barrier induced injecting contact on wide band gap II-VI materials, and excitons in semiconductor heterostructures. Part I presents a new method for quantum transport calculations in semiconductor tunnel structures using multiband {bf k}cdot{bf p} theory. This method circumvents the numerical instability problems that arise in the standard transfer -matrix method. In addition to being numerically stable, efficient, and easy to implement, this method can also be easily generalized to include the magnetic field and strain effects, and extended to the calculations of electronic band structures in quantum confinement and superlattice structures. We have applied this technique to the study of magnetotunneling in InAs/GaSb/AlSb based interband tunnel structures. Part II describes a novel approach to achieve ohmic injecting contact on wide bandgap II-VI semiconductors. The method consists of forming the device structure in an electric field at elevated temperatures in the Schottky barrier region to spatially separate the ionized dopants from the compensating centers. Large net concentration of dopants in a thin surface layer can thus be obtained, resulting in a depletion layer that is sufficiently thin to allow tunneling injection. Calculations of band profiles, distributions of dopant concentrations, and current-voltage characteristics were performed on Al doped ZnTe. Results show for Schottky barrier heights above 1 eV, doping concentrations as high as 10^{20} cm ^{-3} are needed to achieve the injecting current density required for LED and laser diode operations. In part III, calculations of exciton binding energies and oscillator strengths are performed for both Type-I strained CdTe/ZnTe and Type-II strained ZnTe/ZnSe superlattices using variational approach. We have also studied exciton coherent transfer between quantum wells, quantum wires and quantum dots, respectively. The results show

  10. CoFe alloy as middle layer for strong spin dependent quantum well resonant tunneling in double barrier magnetic tunnel junctions

    SciTech Connect

    Liu, R. S.; Yang, See-Hun; Jiang, Xin; Zhang, Xiaoguang; Rice, Philip M.; Canali, Carlo M.; Parkin, S. S. P.

    2013-01-01

    We report the spin-dependent quantum well resonant tunneling effect in CoFe/MgO/CoFe/MgO/CoFeB (CoFe) double barrier magnetic tunnel junctions. The dI/dV spectra reveal clear resonant peaks for the parallel magnetization configurations, which can be matched to quantum well resonances obtained from calculation. The differential TMR exhibits an oscillatory behavior with a sign change due to the formation of the spin-dependent QW states in the middle CoFe layer. Also, we observe pronounced TMR enhancement at resonant voltages at room temperature, suggesting that it is very promising to achieve high TMR using the spin-dependent QW resonant tunneling effect.

  11. Impurity-limited quantum transport variability in magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Zhuang, Jianing; Wang, Yin; Zhou, Yan; Wang, Jian; Guo, Hong

    2017-08-01

    We report an extensive first-principles investigation of impurity-induced device-to-device variability of spin-polarized quantum tunneling through Fe/MgO/Fe magnetic tunnel junctions (MTJ). In particular, we calculated the tunnel magnetoresistance ratio (TMR) and the average values and variances of the currents and spin transfer torque (STT) of an interfacially doped Fe/MgO/Fe MTJ. Further, we predicted that N-doped MgO can improve the performance of a doped Fe/MgO/Fe MTJ. Our firstprinciples calculations of the fluctuations of the on/off currents and STT provide vital information for future predictions of the long-term reliability of spintronic devices, which is imperative for high-volume production.

  12. Tunneling between the Edges of Laterally Separated Quantum Hall Systems

    NASA Astrophysics Data System (ADS)

    Kang, Woowon

    2001-03-01

    In the quantum Hall effect (QHE) effect regime of a two-dimensional electron system (2DES), quantization of the Hall resistance, σ_xy= Ne^2/h, arises from occupation of N one-dimensional edge channels. As a prototypical one-dimensional electronic system, the physics of edge states in the QHE regime is of considerable theoretical and experimental interest. In this talk, we present our study of tunneling between two counter-flowing edge states separated by a barrier with high integrity. By embedding a thin, precise barrier in the plane of 2DES via cleaved edge overgrowth, we have successfully fabricated an in-plane tunneling device in which two 2DES's are separated by an atomically precise barrier on the order of magnetic length[1]. The tunneling in the quantum Hall regime is characterized by a rich spectrum of tunnel gaps and conductance peaks. While the relevant energy scale in the tunneling is largely determined by the bulk 2DES, evolution of the tunneling spectra with magnetic field reveals the electronic structure arising from superposition of two edge states near the barrier. However, the observed features are not consistent with a model of weakly interacting edge states and indicates importance of electron-electron interaction. In particular, absence of features due to the electron spin and the persistence of conductance peaks at zero bias point to existence of novel electronic correlation between the two edge states[2]. [1] W. Kang, H.L. Stormer, K.B. Baldwin, L.N. Pfeiffer, and K.W. West, Nature 403, 59 (2000) [2] A. Mitra and S. Girvin, preprint.

  13. Macroscopic quantum tunnelling of protons in the KHCO 3 crystal

    NASA Astrophysics Data System (ADS)

    Fillaux, François; Cousson, Alain; Gutmann, Matthias J.

    2006-06-01

    Macroscopic quantum entanglement reveals an unforeseen mechanism for proton transfer across hydrogen bonds in the solid state. We utilize neutron scattering techniques to study proton dynamics in the crystal of potassiumhydrogencarbonate (KHCO 3) composed of small planar centrosymmetric dimer entities ( linked by moderately strong hydrogen bonds. All protons are indistinguishable, they behave as fermions, and they are degenerate. The sublattice of protons is a superposition of macroscopic single-particle states. At elevated temperature, protons are progressively transferred to secondary sites at ≈0.6 Å from the main position, via tunnelling along hydrogen bonds. The macroscopic quantum entanglement, still observed at 300 K, reveals that proton transfer is a coherent process throughout the crystal arising from a superposition of macroscopic tunnelling states.

  14. Macroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions

    PubMed Central

    Massarotti, D.; Pal, A.; Rotoli, G.; Longobardi, L.; Blamire, M. G.; Tafuri, F.

    2015-01-01

    The interfacial coupling of two materials with different ordered phases, such as a superconductor (S) and a ferromagnet (F), is driving new fundamental physics and innovative applications. For example, the creation of spin-filter Josephson junctions and the demonstration of triplet supercurrents have suggested the potential of a dissipationless version of spintronics based on unconventional superconductivity. Here we demonstrate evidence for active quantum applications of S-F-S junctions, through the observation of macroscopic quantum tunnelling in Josephson junctions with GdN ferromagnetic insulator barriers. We show a clear transition from thermal to quantum regime at a crossover temperature of about 100 mK at zero magnetic field in junctions, which present clear signatures of unconventional superconductivity. Following previous demonstration of passive S-F-S phase shifters in a phase qubit, our result paves the way to the active use of spin filter Josephson systems in quantum hybrid circuits. PMID:26054495

  15. Macroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions.

    PubMed

    Massarotti, D; Pal, A; Rotoli, G; Longobardi, L; Blamire, M G; Tafuri, F

    2015-06-09

    The interfacial coupling of two materials with different ordered phases, such as a superconductor (S) and a ferromagnet (F), is driving new fundamental physics and innovative applications. For example, the creation of spin-filter Josephson junctions and the demonstration of triplet supercurrents have suggested the potential of a dissipationless version of spintronics based on unconventional superconductivity. Here we demonstrate evidence for active quantum applications of S-F-S junctions, through the observation of macroscopic quantum tunnelling in Josephson junctions with GdN ferromagnetic insulator barriers. We show a clear transition from thermal to quantum regime at a crossover temperature of about 100 mK at zero magnetic field in junctions, which present clear signatures of unconventional superconductivity. Following previous demonstration of passive S-F-S phase shifters in a phase qubit, our result paves the way to the active use of spin filter Josephson systems in quantum hybrid circuits.

  16. Nuclear quantum tunnelling in enzymatic reactions--an enzymologist's perspective.

    PubMed

    Johannissen, Linus O; Hay, Sam; Scrutton, Nigel S

    2015-12-14

    Enzyme-catalysed H-transfer reactions are ubiquitous, yet fundamental details of these reactions remain unresolved. In this perspective, we discuss the roles of nuclear quantum tunnelling and (compressive) dynamics during these reactions. Evidence for the coupling of specific substrate and/or protein vibrations to the chemical coordinate is considered and a case is made for the combination of multiple experimental and computational/theoretical approaches when studying these reactions.

  17. Quantum tunneling between bent semiconductor nanowires

    SciTech Connect

    Sousa, A. A.; Chaves, Andrey Farias, G. A.; Pereira, T. A. S.; Peeters, F. M.

    2015-11-07

    We theoretically investigate the electronic transport properties of two closely spaced L-shaped semiconductor quantum wires, for different configurations of the output channel widths as well as the distance between the wires. Within the effective-mass approximation, we solve the time-dependent Schrödinger equation using the split-operator technique that allows us to calculate the transmission probability, the total probability current, the conductance, and the wave function scattering between the energy subbands. We determine the maximum distance between the quantum wires below which a relevant non-zero transmission is still found. The transmission probability and the conductance show a strong dependence on the width of the output channel for small distances between the wires.

  18. Instanton and noninstanton tunneling in periodically perturbed barriers: semiclassical and quantum interpretations.

    PubMed

    Takahashi, Kin'ya; Ikeda, Kensuke S

    2012-11-01

    In multidimensional barrier tunneling, there exist two different types of tunneling mechanisms, instanton-type tunneling and noninstanton tunneling. In this paper we investigate transitions between the two tunneling mechanisms from the semiclassical and quantum viewpoints taking two simple models: a periodically perturbed Eckart barrier for the semiclassical analysis and a periodically perturbed rectangular barrier for the quantum analysis. As a result, similar transitions are observed with change of the perturbation frequency ω for both systems, and we obtain a comprehensive scenario from both semiclassical and quantum viewpoints for them. In the middle range of ω, in which the plateau spectrum is observed, noninstanton tunneling dominates the tunneling process, and the tunneling amplitude takes the maximum value. Noninstanton tunneling explained by stable-unstable manifold guided tunneling (SUMGT) from the semiclassical viewpoint is interpreted as multiphoton-assisted tunneling from the quantum viewpoint. However, in the limit ω→0, instanton-type tunneling takes the place of noninstanton tunneling, and the tunneling amplitude converges on a constant value depending on the perturbation strength. The spectrum localized around the input energy is observed, and there is a scaling law with respect to the width of the spectrum envelope, i.e., the width ∝ℏω. In the limit ω→∞, the tunneling amplitude converges on that of the unperturbed system, i.e., the instanton of the unperturbed system.

  19. Coulomb drag and tunneling studies in quantum Hall bilayers

    NASA Astrophysics Data System (ADS)

    Nandi, Debaleena

    The bilayer quantum Hall state at total filling factor νT=1, where the total electron density matches the degeneracy of the lowest Landau level, is a prominent example of Bose-Einstein condensation of excitons. A macroscopically ordered state is realized where an electron in one layer is tightly bound to a "hole" in the other layer. If exciton transport were the only bulk transportmechanism, a current driven in one layer would spontaneously generate a current of equal magnitude and opposite sign in the other layer. The Corbino Coulomb drag measurements presented in this thesis demonstrate precisely this phenomenon. Excitonic superfluidity has been long sought in the νT=1 state. The tunneling between the two electron gas layers exihibit a dc Josephson-like effect. A simple model of an over-damped voltage biased Josephson junction is in reasonable agreement with the observed tunneling I -- V. At small tunneling biases, it exhibits a tunneling "supercurrent". The dissipation is carefully studied in this tunneling "supercurrent" and found to remain small but finite.

  20. Comment on 'Realism and quantum flux tunneling'

    NASA Technical Reports Server (NTRS)

    Leggett, A. J.; Garg, Anupam

    1987-01-01

    A reply is presented to Ballentine's (1987) critique of the Legett and Garg (1985) experiment to discriminate between the experimental predictions of quantum mechanics (QM) and those of a class of macrorealistic theories. Legett and Garg uphold their earlier conclusions on the basis of the fact that the present critique refers to an experiment which was not in fact proposed. It is stressed that the original work involved an analysis according to macrorealism, while the calculations of Ballentine only demonstrate the internal consistency of the formalism of QM when applied to three consecutive actually performed experiments.

  1. Quantum scattering engineering of quantum well infrared photodetectors in the tunneling regime

    NASA Astrophysics Data System (ADS)

    Lhuillier, Emmanuel; Rosencher, Emmanuel; Ribet-Mohamed, Isabelle; Nedelcu, Alexandru; Doyennette, Laetitia; Berger, Vincent

    2010-12-01

    Dark current is shown to be significantly reduced in quantum well infrared photodetectors in the tunneling regime, i.e., at very low temperature, by shifting the dopant impurity layers away from the central part of the wells. This result confirms that the interwell tunneling current is dominated by charged impurity scattering in usual structures. The experimental results are in good quantitative agreement with the proposed theory. This dark current reduction is pushing further the ultimate performances of quantum well infrared photodetectors for the detection of low infrared photon fluxes. Routes to further improvements are briefly sketched.

  2. de Sitter Tunneling, Emission Spectrum and Entropy/Area Quantum

    NASA Astrophysics Data System (ADS)

    Jiang, Qing-Quan

    2012-08-01

    The Banerjee—Majhi's recent work shows that the Hawking radiation and entropy/area quantum of the black hole horizon (EH) can be well described in the tunneling picture. In this paper, we develop this idea to the case of a de Sitter tunneling from the cosmological horizon (CH), and obtain the Hawking emission spectrum and entropy/area spectroscopy from the CH of the purely de Sitter black hole as well as the Schwarzschild-de Sitter black hole. It is interestingly found that the area of the CH is quantized by ΔA = 4l2pl, as was given by Hod for the area quantum of -the EH by considering the Heisenberg uncertainty principle and Schwinger-type emission process. Also, we conclude from our derivation that the entropy/area quantum of the CH is universal in the sense that it is independent of the black hole parameters. This realization implies that, (at least) at a semiclassical level, the de Sitter gravity shares the similar quantum behavior as the usual gravity without presence of a cosmological constant.

  3. Electron tunneling characteristics of a cubic quantum dot, (PbS){sub 32}

    SciTech Connect

    Gupta, Sanjeev K. E-mail: haiying.he@valpo.edu; Banyai, Douglas; Pandey, Ravindra; He, Haiying E-mail: haiying.he@valpo.edu; Kandalam, Anil K.

    2013-12-28

    The electron transport properties of the cubic quantum dot, (PbS){sub 32}, are investigated. The stability of the quantum dot has been established by recent scanning tunneling microscope experiments [B. Kiran, A. K. Kandalam, R. Rallabandi, P. Koirala, X. Li, X. Tang, Y. Wang, H. Fairbrother, G. Gantefoer, and K. Bowen, J. Chem. Phys. 136(2), 024317 (2012)]. In spite of the noticeable energy band gap (∼2 eV), a relatively high tunneling current for (PbS){sub 32} is predicted affirming the observed bright images for (PbS){sub 32}. The calculated I-V characteristics of (PbS){sub 32} are predicted to be substrate-dependent; (PbS){sub 32} on the Au (001) exhibits the molecular diode-like behavior and the unusual negative differential resistance effect, though this is not the case with (PbS){sub 32} on the Au (110). Appearance of the conduction channels associated with the hybridized states of quantum dot and substrate together with their asymmetric distribution at the Fermi level seem to determine the tunneling characteristics of the system.

  4. Electron tunneling characteristics of a cubic quantum dot, (PbS)32

    NASA Astrophysics Data System (ADS)

    Gupta, Sanjeev K.; He, Haiying; Banyai, Douglas; Kandalam, Anil K.; Pandey, Ravindra

    2013-12-01

    The electron transport properties of the cubic quantum dot, (PbS)32, are investigated. The stability of the quantum dot has been established by recent scanning tunneling microscope experiments [B. Kiran, A. K. Kandalam, R. Rallabandi, P. Koirala, X. Li, X. Tang, Y. Wang, H. Fairbrother, G. Gantefoer, and K. Bowen, J. Chem. Phys. 136(2), 024317 (2012)]. In spite of the noticeable energy band gap (˜2 eV), a relatively high tunneling current for (PbS)32 is predicted affirming the observed bright images for (PbS)32. The calculated I-V characteristics of (PbS)32 are predicted to be substrate-dependent; (PbS)32 on the Au (001) exhibits the molecular diode-like behavior and the unusual negative differential resistance effect, though this is not the case with (PbS)32 on the Au (110). Appearance of the conduction channels associated with the hybridized states of quantum dot and substrate together with their asymmetric distribution at the Fermi level seem to determine the tunneling characteristics of the system.

  5. Vertical resonant tunneling transistors with molecular quantum dots for large-scale integration.

    PubMed

    Hayakawa, Ryoma; Chikyow, Toyohiro; Wakayama, Yutaka

    2017-08-10

    Quantum molecular devices have a potential for the construction of new data processing architectures that cannot be achieved using current complementary metal-oxide-semiconductor (CMOS) technology. The relevant basic quantum transport properties have been examined by specific methods such as scanning probe and break-junction techniques. However, these methodologies are not compatible with current CMOS applications, and the development of practical molecular devices remains a persistent challenge. Here, we demonstrate a new vertical resonant tunneling transistor for large-scale integration. The transistor channel is comprised of a MOS structure with C60 molecules as quantum dots, and the structure behaves like a double tunnel junction. Notably, the transistors enabled the observation of stepwise drain currents, which originated from resonant tunneling via the discrete molecular orbitals. Applying side-gate voltages produced depletion layers in Si substrates, to achieve effective modulation of the drain currents and obvious peak shifts in the differential conductance curves. Our device configuration thus provides a promising means of integrating molecular functions into future CMOS applications.

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

    PubMed

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

    2017-03-01

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

  7. Theory of chaos regularization of tunneling in chaotic quantum dots.

    PubMed

    Lee, Ming-Jer; Antonsen, Thomas M; Ott, Edward; Pecora, Louis M

    2012-11-01

    Recent numerical experiments of Pecora et al. [Phys. Rev. E 83, 065201 (2011)] have investigated tunneling between two-dimensional symmetric double wells separated by a tunneling barrier. The wells were bounded by hard walls and by the potential barrier which was created by a step increase from the zero potential within a well to a uniform barrier potential within the barrier region, which is a situation potentially realizable in the context of quantum dots. Numerical results for the splitting of energy levels between symmetric and antisymmetric eigenstates were calculated. It was found that the splittings vary erratically from state to state, and the statistics of these variations were studied for different well shapes with the fluctuation levels being much less in chaotic wells than in comparable nonchaotic wells. Here we develop a quantitative theory for the statistics of the energy level splittings for chaotic wells. Our theory is based on the random plane wave hypothesis of Berry. While the fluctuation statistics are very different for chaotic and nonchaotic well dynamics, we show that the mean splittings of differently shaped wells, including integrable and chaotic wells, are the same if their well areas and barrier parameters are the same. We also consider the case of tunneling from a single well into a region with outgoing quantum waves.

  8. Tunneling modulation of a quantum-well transistor laser

    NASA Astrophysics Data System (ADS)

    Feng, M.; Qiu, J.; Wang, C. Y.; Holonyak, N.

    2016-11-01

    Different than the Bardeen and Brattain transistor (1947) with the current gain depending on the ratio of the base carrier spontaneous recombination lifetime to the emitter-collector transit time, the Feng and Holonyak transistor laser current gain depends upon the base electron-hole (e-h) stimulated recombination, the base dielectric relaxation transport, and the collector stimulated tunneling. For the n-p-n transistor laser tunneling operation, the electron-hole pairs are generated at the collector junction under the influence of intra-cavity photon-assisted tunneling, with electrons drifting to the collector and holes drifting to the base. The excess charge in the base lowers the emitter junction energy barrier, allowing emitter electron injection into the base and satisfying charge neutrality via base dielectric relaxation transport (˜femtoseconds). The excess electrons near the collector junction undergo stimulated recombination at the base quantum-well or transport to the collector, thus supporting tunneling current amplification and optical modulation of the transistor laser.

  9. Observation of negative differential transconductance in tunneling emitter bipolar transistors

    NASA Astrophysics Data System (ADS)

    van Veenhuizen, Marc J.; Locatelli, Nicolas; Moodera, Jagadeesh; Chang, Joonyeon

    2009-08-01

    We report on measurement of negative differential transconductance (NDTC) of iron (Fe)/magnesium-oxide (MgO)/silicon tunneling emitter NPN bipolar transistors. Device simulations reveal that the NDTC is a consequence of an inversion layer at the tunneling-oxide/P-silicon interface for low base voltages. Electrons travel laterally through the inversion layer into the base and give rise to an increase in collector current. The NDTC results from the recombination of those electrons at the interface between emitter and base contact which is dependent on the base voltage. For larger base voltages, the inversion layer disappears marking the onset of normal bipolar transistor behavior.

  10. Quantum Tunneling Sb-Heterostructures for Millimeter Wave Radiometry

    NASA Astrophysics Data System (ADS)

    Schulman, Joel N.

    2003-03-01

    Imaging in the millimeter wavelength range has been making rapid progress as high speed electronics increase in frequency. Applications include viewing through adverse visibility conditions (fog, smoke, dust, precipitation) and also the relative transparency of clothing (concealed-weapons-detection) and some building materials (through-the-wall-detection). Atmospheric radiometry (climate assessment and weather prediction) already depend heavily on this wavelength range. Astronomical applications include incorporation in instruments for cosmic microwave background detection. An important ingredient is a diode that "rectifies" in a special way. It must convert input power, i.e., voltage squared, into a DC voltage output -- a "square-law" detector. We have recently found that quantum tunneling through an InAs/AlSb/GaAlSb heterostructure system provides the ideal physical mechanism for this purpose.1,2 We will present our results to date, demonstrating how a close coupling of semiconductor quantum tunneling theory with electrical engineering know-how have brought an "exotic" quantum phenomon to practical and economic application. 1. "Sb-heterostructure interband backward diodes" J.N. Schulman and D.H. Chow. IEEE Electron Device Letters 21, 353-355 (2000). 2. "High-Performance Antimonide-Based Heterostructure Backward Diodes for Millimeter-wave Detection" P. Fay, J. N. Schulman, S. Thomas III, D. H. Chow, Y. K. Boegeman, and K. S. Holabird, IEEE Electron Device Letters 23, 585-587 (2002).

  11. Observation of quantum tunneling between two plasmonic nanoparticles.

    PubMed

    Scholl, Jonathan A; García-Etxarri, Aitzol; Koh, Ai Leen; Dionne, Jennifer A

    2013-02-13

    The plasmon resonances of two closely spaced metallic particles have enabled applications including single-molecule sensing and spectroscopy, novel nanoantennas, molecular rulers, and nonlinear optical devices. In a classical electrodynamic context, the strength of such dimer plasmon resonances increases monotonically as the particle gap size decreases. In contrast, a quantum mechanical framework predicts that electron tunneling will strongly diminish the dimer plasmon strength for subnanometer-scale separations. Here, we directly observe the plasmon resonances of coupled metallic nanoparticles as their gap size is reduced to atomic dimensions. Using the electron beam of a scanning transmission electron microscope (STEM), we manipulate pairs of ~10-nm-diameter spherical silver nanoparticles on a substrate, controlling their convergence and eventual coalescence into a single nanosphere. We simultaneously employ electron energy-loss spectroscopy (EELS) to observe the dynamic plasmonic properties of these dimers before and after particle contact. As separations are reduced from 7 nm, the dominant dipolar peak exhibits a redshift consistent with classical calculations. However, gaps smaller than ~0.5 nm cause this mode to exhibit a reduced intensity consistent with quantum theories that incorporate electron tunneling. As the particles overlap, the bonding dipolar mode disappears and is replaced by a dipolar charge transfer mode. Our dynamic imaging, manipulation, and spectroscopy of nanostructures enables the first full spectral mapping of dimer plasmon evolution and may provide new avenues for in situ nanoassembly and analysis in the quantum regime.

  12. Intermediate-band photosensitive device with quantum dots having tunneling barrier embedded in organic matrix

    DOEpatents

    Forrest, Stephen R.

    2008-08-19

    A plurality of quantum dots each have a shell. The quantum dots are embedded in an organic matrix. At least the quantum dots and the organic matrix are photoconductive semiconductors. The shell of each quantum dot is arranged as a tunneling barrier to require a charge carrier (an electron or a hole) at a base of the tunneling barrier in the organic matrix to perform quantum mechanical tunneling to reach the respective quantum dot. A first quantum state in each quantum dot is between a lowest unoccupied molecular orbital (LUMO) and a highest occupied molecular orbital (HOMO) of the organic matrix. Wave functions of the first quantum state of the plurality of quantum dots may overlap to form an intermediate band.

  13. First-principles theory of quantum well resonance in double barrier magnetic tunnel junctions.

    PubMed

    Wang, Yan; Lu, Zhong-Yi; Zhang, X-G; Han, X F

    2006-08-25

    Quantum well (QW) resonances in Fe(001)/MgO/Fe/MgO/Fe double barrier magnetic tunnel junctions are calculated from first principles. By including the Coulomb blockade energy due to the finite size islands of the middle Fe film, we confirm that the oscillatory differential resistance observed in a recent experiment [T. Nozaki, Phys. Rev. Lett. 96, 027208 (2006)10.1103/PhysRevLett.96.027208] originates from the QW resonances from the Delta1 band of the Fe majority-spin channel. The primary source of smearing at low temperatures is shown to be the variation of the Coulomb blockade energy.

  14. Quantum control of molecular tunneling ionization in the spatiotemporal domain

    SciTech Connect

    Ohmura, Hideki; Saito, Naoaki; Morishita, Toru

    2011-06-15

    We report on a method that can control molecular photoionization in both space and time domains. The directionally asymmetric molecular tunneling ionization induced by intense (5.0 x 10{sup 13} W/cm{sup 2}) phase-controlled two-color laser pulses consisting of fundamental and second-harmonic light achieves the selective ionization of asymmetric molecules in the space domain, and manipulates the birth time and direction of photoelectron emission on an attosecond time scale. This method provides a powerful tool for tracking the quantum dynamics of photoelectrons by using phase-dependent oriented molecules as a phase reference in simultaneous ion-electron detection.

  15. Quantum-size resonance tunneling in the field emission phenomenon

    NASA Astrophysics Data System (ADS)

    Litovchenko, V.; Evtukh, A.; Kryuchenko, Yu.; Goncharuk, N.; Yilmazoglu, O.; Mutamba, K.; Hartnagel, H. L.; Pavlidis, D.

    2004-07-01

    Theoretical analyses have been performed of the quantum-size (QS) resonance tunneling in the field-emission (FE) phenomenon for different models of the emitting structures. Such experimentally observed peculiarities have been considered as the enhancement of the FE current, the deviation from the Fowler-Nordheim law, the appearance of sharp current peaks, and a negative resistance. Different types of FE cathodes with QS structures (quantized layers, wires, or dots) have been studied experimentally. Resonance current peaks have been observed, from which the values of the energy-level splitting can be estimated.

  16. Intersubband Population Inversion Under Resonance Tunneling in Wide Quantum Well Structures

    DTIC Science & Technology

    2000-06-23

    inversion under resonance tunneling in wide quantum well structures Yu. A. Mityagin, V. N. Murzin, 1. P. Kazakov, V. A. Chuenkov, A. L. Karuzskii, A. V...UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP013011 TITLE: Intersubband Population Inversion Under Resonance ... Tunneling in Wide Quantum Well Structures DISTRIBUTION: Approved for public release, distribution unlimited Availability: Hard copy only. This paper is part

  17. Quantum tunneling from the charged non-rotating BTZ black hole with GUP

    NASA Astrophysics Data System (ADS)

    Sadeghi, Jafar; Reza Shajiee, Vahid

    2017-03-01

    In the present paper, the quantum corrections to the temperature, entropy and specific heat capacity of the charged non-rotating BTZ black hole are studied by the generalized uncertainty principle in the tunneling formalism. It is shown that quantum corrected entropy would be of the form of predicted entropy in quantum gravity theories like string theory and loop quantum gravity.

  18. Quantum tunneling of vortices in two-dimensional condensates

    SciTech Connect

    Auerbach, Assa; Arovas, Daniel P.; Ghosh, Sankalpa

    2006-08-01

    The tunneling rate t{sub v}/({Dirac_h}/2{pi}) of a vortex between two pinning sites (of strength V separated by d) is computed using the Bogoliubov expansion of vortex wave-functions overlap. For BCS vortices, tunneling is suppressed beyond a few Fermi wavelengths. For Bose condensates, t{sub v}=V exp(-{pi}n{sub s}d{sup 2}/2), where n{sub s} is the boson density. The analogy between vortex hopping in a superconducting film and two-dimensional electrons in a perpendicular magnetic field is exploited. We derive the variable range hopping temperature, below which vortex tunneling contributes to magnetoresistance. Using the 'quantum Hall insulator' analogy we argue that the Hall conductivity (rather than the inverse Hall resistivity) measures the effective carrier density in domains of mobile vortices. Details of vortex wave functions and overlap calculations, and a general derivation of the Magnus coefficient for any wave function on the sphere, are provided in appendixes.

  19. Lineshape of Resonant Tunneling Peaks in Fractional Quantum Hall Regime.

    NASA Astrophysics Data System (ADS)

    Maasilta, Ilari J.; Goldman, V. J.

    1996-03-01

    Recently an experiment that measures the tunneling conductance between two fractional quantum Hall edges in a quantum antidot geometry was performed(V.J. Goldman and B. Su, Science 267), 1010 (1995).. We present measurements of the lineshape of these resonant tunneling peaks at ν=1/3 at several temperatures for 13 mK <= T < 100 mK. This subject was considered within the theories of one dimensional Luttinger liquids(X.G. Wen, Int. J. Mod. Phys. B6), 1711 (1992).(C.L. Kane and M.P.A. Fisher, Phys. Rev. Lett. 68), 1220 (1992).. Our analysis shows that, in an experiment at a given T, it is extremely difficult to distinguish between the recently calculated(K. Moon et al.), Phys. Rev. Lett. 71, 4381 (1993); P. Fendley, A.W.W. Ludwig and H. Saleur, Phys. Rev. Lett. 74, 3005 (1995). universal Luttinger liquid resonance lineshape and a regular thermally broadened Fermi liquid peak. Instead, the temperature dependence of the widths of the resonances can be analyzed, since the widths are predicted to scale as T^2/3 for ν=1/3 in the Luttinger case as opposed to T in the Fermi liquid.

  20. Quantum tunneling and vibrational dynamics of ultra-confined water

    NASA Astrophysics Data System (ADS)

    Kolesnikov, Alexander I.; Anovitz, Lawrence M.; Ehlers, Georg; Mamontov, Eugene; Podlesnyak, Andrey; Prisk, Timothy R.; Seel, Andrew; Reiter, George F.

    2015-03-01

    Vibrational dynamics of ultra-confined water in single crystals beryl, the structure of which contains ~ 5 Å diameter channels along the c-axis was studied with inelastic (INS), quasi-elastic (QENS) and deep inelastic (DINS) neutron scattering. The results reveal significantly anisotropic dynamical behavior of confined water, and show that effective potential experienced by water perpendicular to the channels is significantly softer than along them. The observed 7 peaks in the INS spectra (at energies 0.25 to 15 meV), based on their temperature and momentum transfer dependences, are explained by transitions between the split ground states of water in beryl due to water quantum tunneling between the 6-fold equivalent positions across the channels. DINS study of beryl at T=4.3 K shows narrow, anisotropic water proton momentum distribution with corresponding kinetic energy, EK=95 meV, which is much less than was previously observed in bulk water (~150 meV). We believe that the exceptionally small EK in beryl is a result of water quantum tunneling ∖ delocalization in the nanometer size confinement and weak water-cage interaction. The neutron experiment at ORNL was sponsored by the Sci. User Facilities Div., BES, U.S. DOE. This research was sponsored by the Div. Chemical Sci, Geosciences, and Biosciences, BES, U.S. DOE. The STFC RAL is thanked for access to ISIS neutron facilities.

  1. Quantum gases. Observation of many-body dynamics in long-range tunneling after a quantum quench.

    PubMed

    Meinert, Florian; Mark, Manfred J; Kirilov, Emil; Lauber, Katharina; Weinmann, Philipp; Gröbner, Michael; Daley, Andrew J; Nägerl, Hanns-Christoph

    2014-06-13

    Quantum tunneling is at the heart of many low-temperature phenomena. In strongly correlated lattice systems, tunneling is responsible for inducing effective interactions, and long-range tunneling substantially alters many-body properties in and out of equilibrium. We observe resonantly enhanced long-range quantum tunneling in one-dimensional Mott-insulating Hubbard chains that are suddenly quenched into a tilted configuration. Higher-order tunneling processes over up to five lattice sites are observed as resonances in the number of doubly occupied sites when the tilt per site is tuned to integer fractions of the Mott gap. This forms a basis for a controlled study of many-body dynamics driven by higher-order tunneling and demonstrates that when some degrees of freedom are frozen out, phenomena that are driven by small-amplitude tunneling terms can still be observed. Copyright © 2014, American Association for the Advancement of Science.

  2. Quantum-Coherence-Assisted Tunable On- and Off-Resonance Tunneling through a Quantum-Dot-Molecule Dielectric Film

    NASA Astrophysics Data System (ADS)

    Shen, Jian Qi; Zeng, Rui Xi

    2017-02-01

    Quantum-dot-molecular phase coherence (and the relevant quantum-interference-switchable optical response) can be utilized to control electromagnetic wave propagation via a gate voltage, since quantum-dot molecules can exhibit an effect of quantum coherence (phase coherence) when quantum-dot-molecular discrete multilevel transitions are driven by an electromagnetic wave. Interdot tunneling of carriers (electrons and holes) controlled by the gate voltage can lead to destructive quantum interference in a quantum-dot molecule that is coupled to an incident electromagnetic wave, and gives rise to a quantum coherence effect (e.g., electromagnetically induced transparency, EIT) in a quantum-dot-molecule dielectric film. The tunable on- and off-resonance tunneling effect of an incident electromagnetic wave (probe field) through such a quantum-coherent quantum-dot-molecule dielectric film is investigated. It is found that a high gate voltage can lead to the EIT phenomenon of the quantum-dot-molecular systems. Under the condition of on-resonance light tunneling through the present quantum-dot-molecule dielectric film, the probe field should propagate without loss if the probe frequency detuning is zero. Such an effect caused by both EIT and resonant tunneling, which is sensitive to the gate voltage, can be utilized for designing devices such as photonic switching, transistors, and logic gates.

  3. Transmission and tunneling probability in two-band metals: Influence of magnetic breakdown on the Onsager phase of quantum oscillations

    NASA Astrophysics Data System (ADS)

    Fortin, Jean-Yves; Audouard, Alain

    2017-02-01

    Tunneling amplitude through magnetic breakdown (MB) gap is considered for two-bands Fermi surfaces illustrated in many organic metals. In particular, the S-matrix associated to the wave function transmission through the MB gap for the relevant class of differential equations is the main object allowing the determination of tunneling probabilities and phases. The calculated transmission coefficients include a field-dependent Onsager phase. As a result, quantum oscillations are not periodic in 1 / B for finite magnetic breakdown gap. Exact and approximate methods are proposed for computing ratio amplitudes of the wave function in interacting two-band models.

  4. Simulation of chaos-assisted tunneling in a semiclassical regime on existing quantum computers

    SciTech Connect

    Chepelianskii, A.D.; Shepelyansky, D.L.

    2002-11-01

    We present a quantum algorithm that allows one to simulate chaos-assisted tunneling in deep semiclassical regime on existing quantum computers. This opens additional possibilities for investigation of macroscopic quantum tunneling and realization of semiclassical Schroedinger cat oscillations [E. Schroedinger, Naturwissenschaften 32, 807 (1935)]. Our numerical studies determine the decoherence rate induced by noisy gates for these oscillations and propose a suitable parameter regime for their experimental implementation.

  5. One-Dimensional Nature of InAs/InP Quantum Dashes Revealed by Scanning Tunneling Spectroscopy.

    PubMed

    Papatryfonos, Konstantinos; Rodary, Guillemin; David, Christophe; Lelarge, François; Ramdane, Abderrahim; Girard, Jean-Christophe

    2015-07-08

    We report on low-temperature cross-sectional scanning tunneling microscopy and spectroscopy on InAs(P)/InGaAsP/InP(001) quantum dashes, embedded in a diode-laser structure. The laser active region consists of nine InAs(P) quantum dash layers separated by the InGaAsP quaternary alloy barriers. The effect of the p-i-n junction built-in potential on the band structure has been evidenced and quantified on large-scale tunneling spectroscopic measurements across the whole active region. By comparing the tunneling current onset channels, a consistent energy shift has been measured in successive quantum dash or barrier layers, either for the ground state energy of similar-sized quantum dashes or for the conduction band edge of the barriers, corresponding to the band-bending slope. The extracted values are in good quantitative agreement with the theoretical band structure calculations, demonstrating the high sensitivity of this spectroscopic measurement to probe the electronic structure of individual nanostructures, relative to local potential variations. Furthermore, by taking advantage of the potential gradient, we compared the local density of states over successive quantum dash layers. We observed that it does not vanish while increasing energy, for any of the investigated quantum dashes, in contrast to what would be expected for discrete level zero-dimensional (0D) structures. In order to acquire further proof and fully address the open question concerning the quantum dash dimensionality nature, we focused on individual quantum dashes obtaining high-energy-resolution measurements. The study of the local density of states clearly indicates a 1D quantum-wirelike nature for these nanostructures whose electronic squared wave functions were subsequently imaged by differential conductivity mapping.

  6. Quantum tunneling and scattering of a composite object

    NASA Astrophysics Data System (ADS)

    Ahsan, Naureen

    Reaction physics involving composite objects with internal degrees of freedom is an important subject since it is encountered in the context of nuclear processes like fusion, fission, particle decay, as well as many other branches of science. Quantum tunneling and scattering of a composite object are explored in this work. A few model Hamiltonians are chosen as examples where a two-particle system interacts, in one dimension, with a target that poses a delta-potential or an infinite wall potential. It is assumed that only one of the two components interacts with the target. The study includes the harmonic oscillator and the infinite square well as examples of intrinsic Hamiltonians that do not allow the projectile to break up, and a finite square well and a delta-well as examples of Hamiltonians that do. The Projection Method and the Variable Phase Method are applied with the aim of an exact solution to the relevant scattering problems. These methods are discussed in the context of the pertinent convergence issues related thereto, and of their applicability. Virtual excitations of the projectile into the classically forbidden energy-domain are found to play a dominant and non-perturbative role in shaping reaction observables, giving rise to enhanced or reduced tunneling in various situations. Cusps and discontinuities are found to appear in observables as manifestations of unitarity and redistribution of flux at the thresholds. The intrinsic structure gives rise to resonancelike behavior in tunneling probabilities. It is also shown that there is charge asymmetry in the scattering of a composite object, unlike in the case of a structureless particle.

  7. S-matrix and quantum tunneling in gravitational collapse

    NASA Astrophysics Data System (ADS)

    Ciafaloni, M.; Colferai, D.

    2008-11-01

    Using the recently introduced ACV reduced-action approach to transplanckian scattering of light particles, we show that the S-matrix in the region of classical gravitational collapse is related to a tunneling amplitude in an effective field space. We understand in this way the role of both real and complex field solutions, the choice of the physical ones, the absorption of the elastic channel associated to inelastic multigraviton production and the occurrence of extra absorption below the critical impact parameter. We are also able to compute a class of quantum corrections to the original semiclassical S-matrix that we argue to be qualitatively sensible and which, generally speaking, tend to smooth out the semiclassical results.

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

    SciTech Connect

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

    2014-08-21

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

  9. Monolithic integration of electroabsorption modulators and tunnel injection distributed feedback lasers using quantum well intermixing

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Pan, Jiao-Qing; Zhao, Ling-Juan; Zhu, Hong-Liang; Wang, Wei

    2010-12-01

    Electroabsorption modulators combining Franz-Keldysh effect and quantum confined Stark effect have been monolithically integrated with tunnel-injection quantum-well distributed feedback lasers using a quantum well intermixing method. Superior characteristics such as extinction ratio and temperature insensitivity have been demonstrated at wide temperature ranges.

  10. Differential calculus on quantum spaces and quantum groups

    SciTech Connect

    Zumino, B

    1992-12-10

    A review of recent developments in the quantum differential calculus. The quantum group GLq(n) is treated by considering it as a particular quantum space. Functions on SLq(n) are defined as a subclass of functions on GLq(n). The case of SOq(n) is also briefly considered. These notes cover part of a lecture given at the XIX International Conference on Group Theoretic Methods in Physics, Salamanca, Spain 1992.

  11. Tunnel magnetoresistance in quantum dots in the presence of singlet and triplet states.

    PubMed

    Michałek, G; Bułka, B R

    2011-05-04

    We study transport through a two-level quantum dot (QD) weakly coupled to ferromagnetic electrodes, the mutual magnetization orientation of which can be changed from a parallel to an antiparallel configuration. Calculations are performed in a sequential tunnelling regime taking into account an inter-level Coulomb and an exchange interaction on the QD with many-body electronic states. Our interests are mainly focused on the role of singlet and triplet states on the tunnel magnetoresistance (TMR). We have found that TMR characteristics strongly depend on different local spin configurations in the QD, which originate from an anti- or ferromagnetic exchange coupling J as well as its strength. A strong inter-channel Coulomb blockade (which influences the TMR) appears when the ground state is singly occupied. Activation of the singlet or the triplet states and competition between various tunnelling rates are responsible for the spin accumulation even in the parallel configuration. We have also found negative TMR and negative differential resistance (NDR) effects in the system with strong coupling asymmetry.

  12. Quantum mechanical methods for calculating proton tunneling splittings and proton-coupled electron transfer vibronic couplings

    NASA Astrophysics Data System (ADS)

    Skone, Jonathan H.

    Development of quantum mechanical methods for the calculation of proton tunneling splittings and proton-coupled electron transfer vibronic couplings is presented in this thesis. The fundamental physical principles underlying proton transfer in the electronically adiabatic and nonadiabatic limits are illustrated by applying the quantum mechanical methods we developed to chemical systems exemplary of the electronically adiabatic and nonadiabatic proton-tunneling regimes. Overall, this thesis emphasizes the need for quantum chemical methods that avoid the adiabatic separation of the quantum proton and electron, are computationally tractable, and treat all quantum particles three-dimensionally. The nuclear-electronic orbital nonorthogonal configuration interaction (NEO-NOCI) approach is presented for calculating proton tunneling splittings and vibronic couplings. The NEO approach is a molecular orbital based method that avoids the Born-Oppenheimer separation of the select protons and electrons, thereby making methods developed within this scheme, such as NEO-NOCI, applicable to electronically nonadiabatic proton transfer. In the two-state NEO-NOCI approach, the ground and excited state delocalized nuclear-electronic wavefunctions are expressed as linear combinations of two nonorthogonal localized nuclear-electronic wavefunctions obtained at the NEO-Hartree-Fock level. The advantages of the NEO-NOCI approach are the removal of the adiabatic separation between the electrons and the quantum nuclei, the computational efficiency, the potential for systematic improvement by enhancing the basis sets and number of configurations, and the applicability to a broad range of chemical systems. The tunneling splitting is determined by the energy difference between these two delocalized vibronic states. The proton tunneling splittings calculated with the NEO-NOCI approach for the [He-H-He]+ model system with a range of fixed He-He distances are shown to be in excellent agreement with

  13. Magnetic quantum tunneling: insights from simple molecule-based magnets.

    PubMed

    Hill, Stephen; Datta, Saiti; Liu, Junjie; Inglis, Ross; Milios, Constantinos J; Feng, Patrick L; Henderson, John J; del Barco, Enrique; Brechin, Euan K; Hendrickson, David N

    2010-05-28

    This perspectives article takes a broad view of the current understanding of magnetic bistability and magnetic quantum tunneling in single-molecule magnets (SMMs), focusing on three families of relatively simple, low-nuclearity transition metal clusters: spin S = 4 Ni(II)(4), Mn(III)(3) (S = 2 and 6) and Mn(III)(6) (S = 4 and 12). The Mn(III) complexes are related by the fact that they contain triangular Mn(III)(3) units in which the exchange may be switched from antiferromagnetic to ferromagnetic without significantly altering the coordination around the Mn(III) centers, thereby leaving the single-ion physics more-or-less unaltered. This allows for a detailed and systematic study of the way in which the individual-ion anisotropies project onto the molecular spin ground state in otherwise identical low- and high-spin molecules, thus providing unique insights into the key factors that control the quantum dynamics of SMMs, namely: (i) the height of the kinetic barrier to magnetization relaxation; and (ii) the transverse interactions that cause tunneling through this barrier. Numerical calculations are supported by an unprecedented experimental data set (17 different compounds), including very detailed spectroscopic information obtained from high-frequency electron paramagnetic resonance and low-temperature hysteresis measurements. Comparisons are made between the giant spin and multi-spin phenomenologies. The giant spin approach assumes the ground state spin, S, to be exact, enabling implementation of simple anisotropy projection techniques. This methodology provides a basic understanding of the concept of anisotropy dilution whereby the cluster anisotropy decreases as the total spin increases, resulting in a barrier that depends weakly on S. This partly explains why the record barrier for a SMM (86 K for Mn(6)) has barely increased in the 15 years since the first studies of Mn(12)-acetate, and why the tiny Mn(3) molecule can have a barrier approaching 60% of this

  14. Quantum electromechanics: Quantum tunneling near resonance and qubits from buckling nanoscale bars

    NASA Astrophysics Data System (ADS)

    Savel'Ev, Sergey; Rakhmanov, A. L.; Hu, Xuedong; Kasumov, A.; Nori, Franco

    2007-04-01

    Analyzing recent experimental results [Reulet , Phys. Rev. Lett. 85, 2829 (2000); Izmalkov , Europhys. Lett. 65, 844 (2004)], we find strikingly similar behaviors between two very different systems: three-junction superconducting qubits and suspended carbon nanotubes. When these different systems are ac-driven near their resonances, the resonance single-peak, observed at weak driving amplitudes, splits into two subpeaks for strong driving amplitudes. We describe this unusual behavior by considering quantum tunneling in a double well potential. Inspired by these experiments, we propose a mechanical qubit based on buckling nanoscale bars (nanobars)—a nanoelectromechanical system so small as to be quantum coherent. We consider how this nanomechanical qubit can be manipulated. A comparison between nanobars and superconducting qubits suggests several future experiments on quantum electromechanics.

  15. Tunneling-assisted coherent population transfer and creation of coherent superposition states in triple quantum dots

    NASA Astrophysics Data System (ADS)

    Tian, Si-Cong; Wan, Ren-Gang; Wang, Li-Jie; Shu, Shi-Li; Tong, Cun-Zhu; Wang, Li-Jun

    2016-12-01

    A scheme is proposed for coherent population transfer and creation of coherent superposition states assisted by one time-dependent tunneling pulse and one time-independent tunneling pulse in triple quantum dots. Time-dependent tunneling, which is similar to the Stokes laser pulse used in traditional stimulated Raman adiabatic passage, can lead to complete population transfer from the ground state to the indirect exciton states. Time-independent tunneling can also create double dark states, resulting in the distribution of the population and arbitrary coherent superposition states. Such a scheme can also be extended to multiple quantum dots assisted by one time-dependent tunneling pulse and more time-independent tunneling pulses.

  16. A Planar Quantum Transistor Based on 2D-2D Tunneling in Double Quantum Well Heterostructures

    SciTech Connect

    Baca, W.E.; Blount, M.A.; Hafich, M.J.; Lyo, S.K.; Moon, J.S.; Reno, J.L.; Simmons, J.A.; Wendt, J.R.

    1998-12-14

    We report on our work on the double electron layer tunneling transistor (DELTT), based on the gate-control of two-dimensional -- two-dimensional (2D-2D) tunneling in a double quantum well heterostructure. While previous quantum transistors have typically required tiny laterally-defined features, by contrast the DELTT is entirely planar and can be reliably fabricated in large numbers. We use a novel epoxy-bond-and-stop-etch (EBASE) flip-chip process, whereby submicron gating on opposite sides of semiconductor epitaxial layers as thin as 0.24 microns can be achieved. Because both electron layers in the DELTT are 2D, the resonant tunneling features are unusually sharp, and can be easily modulated with one or more surface gates. We demonstrate DELTTs with peak-to-valley ratios in the source-drain I-V curve of order 20:1 below 1 K. Both the height and position of the resonant current peak can be controlled by gate voltage over a wide range. DELTTs with larger subband energy offsets ({approximately} 21 meV) exhibit characteristics that are nearly as good at 77 K, in good agreement with our theoretical calculations. Using these devices, we also demonstrate bistable memories operating at 77 K. Finally, we briefly discuss the prospects for room temperature operation, increases in gain, and high-speed.

  17. Discussion on event horizon and quantum ergosphere of evaporating black holes in a tunnelling framework

    SciTech Connect

    Zhang Jingyi; Zhao Zheng

    2011-03-15

    In this paper, with the Parikh-Wilczek tunnelling framework the positions of the event horizon of the Vaidya black hole and the Vaidya-Bonner black hole are calculated, respectively. We find that the event horizon and the apparent horizon of these two black holes correspond, respectively, to the two turning points of the Hawking radiation tunnelling barrier. That is, the quantum ergosphere coincides with the tunnelling barrier. Our calculation also implies that the Hawking radiation comes from the apparent horizon.

  18. Theory of quantum-circuit refrigeration by photon-assisted electron tunneling

    NASA Astrophysics Data System (ADS)

    Silveri, Matti; Grabert, Hermann; Masuda, Shumpei; Tan, Kuan Yen; Möttönen, Mikko

    2017-09-01

    We focus on a recently experimentally realized scenario of normal-metal-insulator-superconductor tunnel junctions coupled to a superconducting resonator. We develop a first-principles theory to describe the effect of photon-assisted electron tunneling on the quantum state of the resonator. Our results are in very good quantitative agreement with the previous experiments on refrigeration and heating of the resonator using the photon-assisted tunneling, thus providing a stringent verification of the developed theory. Importantly, our results provide simple analytical estimates of the voltage-tunable coupling strength and temperature of the thermal reservoir formed by the photon-assisted tunneling. Consequently, they are used to introduce optimization principles for initialization of quantum devices using such a quantum-circuit refrigerator. Thanks to the first-principles nature of our approach, extension of the theory to the full spectrum of quantum electric devices seems plausible.

  19. Quantum Tunneling of Magnetization in Ultrasmall Half-Metallic V3O4 Quantum Dots: Displaying Quantum Superparamagnetic State

    NASA Astrophysics Data System (ADS)

    Xiao, Chong; Zhang, Jiajia; Xu, Jie; Tong, Wei; Cao, Boxiao; Li, Kun; Pan, Bicai; Su, Haibin; Xie, Yi

    2012-10-01

    Quantum tunneling of magnetization (QTMs), stemming from their importance for understanding materials with unconventional properties, has continued to attract widespread theoretical and experimental attention. However, the observation of QTMs in the most promising candidates of molecular magnets and few iron-based compounds is limited to very low temperature. Herein, we first highlight a simple system, ultrasmall half-metallic V3O4 quantum dots, as a promising candidate for the investigation of QTMs at high temperature. The quantum superparamagnetic state (QSP) as a high temperature signature of QTMs is observed at 16 K, which is beyond absolute zero temperature and much higher than that of conventional iron-based compounds due to the stronger spin-orbital coupling of V3+ ions bringing high anisotropy energy. It is undoubtedly that this ultrasmall quantum dots, V3O4, offers not only a promising candidate for theoretical understanding of QTMs but also a very exciting possibility for computers using mesoscopic magnets.

  20. Full counting statistics of phonon-assisted Andreev tunneling through a quantum dot coupled to normal and superconducting leads

    NASA Astrophysics Data System (ADS)

    Dong, Bing; Ding, G. H.; Lei, X. L.

    2017-01-01

    We present a theoretical investigation for the full counting statistics of the Andreev tunneling through a quantum dot (QD) embedded between superconducting (SC) and normal leads in the presence of a strong on-site electron-phonon interaction using nonequilibrium Green function method. For this purpose, we generalize the dressed tunneling approximation (DTA) recently developed in dealing with inelastic tunneling in a normal QD system to the Andreev transport issue. This method takes account of vibrational effect in evaluation of electronic tunneling self energy in comparison with other simple approaches and meanwhile allows us to derive an explicit analytical formula for the cumulant generating function at the subgap region. We then analyze the interplay of polaronic and SC proximity effects on the Andreev reflection spectrum, current-voltage characteristics, and current fluctuations of the hybrid system. Our main findings include: (1) no phonon side peaks in the linear Andreev conductance; (2) a negative differential conductance stemming from the suppressed Andreev reflection spectrum; (3) a novel inelastic resonant peak in the differential conductance due to phonon assisted Andreev reflection; (4) enhancement or suppression of shot noise for the symmetric or asymmetric tunnel-coupling system, respectively.

  1. Room-temperature tunneling behavior of boron nitride nanotubes functionalized with gold quantum dots.

    PubMed

    Lee, Chee Huei; Qin, Shengyong; Savaikar, Madhusudan A; Wang, Jiesheng; Hao, Boyi; Zhang, Dongyan; Banyai, Douglas; Jaszczak, John A; Clark, Kendal W; Idrobo, Juan-Carlos; Li, An-Ping; Yap, Yoke Khin

    2013-09-06

    One-dimensional arrays of gold quantum dots (QDs) on insulating boron nitride nanotubes (BNNTs) can form conduction channels of tunneling field-effect transistors. We demonstrate that tunneling currents can be modulated at room temperature by tuning the lengths of QD-BNNTs and the gate potentials. Our discovery will inspire the creative use of nanostructured metals and insulators for future electronic devices.

  2. Cascade of quantum phase transitions in tunnel-coupled edge states.

    PubMed

    Yang, I; Kang, W; Baldwin, K W; Pfeiffer, L N; West, K W

    2004-02-06

    We report on the cascade of quantum phase transitions exhibited by tunnel-coupled edge states across a quantum Hall line junction. We identify a series of quantum critical points between successive strong and weak tunneling regimes in the zero-bias conductance. Scaling analysis shows that the conductance near the critical magnetic fields B(c) is a function of a single scaling argument /B-B(c)/T(-kappa), where the exponent kappa=0.42. This puzzling resemblance to a quantum Hall-insulator transition points to the importance of interedge correlation between the coupled edge states.

  3. Control of transient gain absorption via tunneling and incoherent pumping in triple quantum dots

    NASA Astrophysics Data System (ADS)

    Tian, Si-Cong; Zhang, Xiao-Jun; Wan, Ren-Gang; Wang, Li-Jie; Shu, Shi-Li; Wang, Tao; Lu, Ze-Feng; Sun, Fang-Yuan; Tong, Cun-Zhu

    2017-01-01

    The transient gain-absorption properties of the probe field in vertical triple quantum dots assisted by double tunneling and incoherent pumping are investigated. With a proper intensity value and detuning of the second tunneling, the transient gain in triple quantum dots with incoherent pumping can be completely eliminated. In addition, the incoherent pumping affects both the amplitude of the transient absorption and the steady-state value. The dependence of transient behaviors on other parameters, such as the radiative decay rate and the pure dephasing decay rate of the quantum dots, is also discussed. The scheme may have important applications in quantum information networks and communication.

  4. Tunneling spectroscopy of 5/2 fractional quantum Hall excitations in etch defined quantum point contacts

    NASA Astrophysics Data System (ADS)

    Thalakulam, Madhu; Pan, Wei; Baldwin, K. W.; West, K. W.; Pfeiffer, L.

    2012-02-01

    Ever since its discovery the fractional quantum Hall (FQH) state at the even denominator filling fraction v=5/2 has generated immense interests among researchers. 5/2 FQH excitations are believed to obey non-Abelian statistics and posses topological properties making them an ideal candidate for the proposed fault tolerant topological quantum computation. Theoretical proposals to characterize the topological properties of the5/2 state are usually based on confined geometries. In this work we report the characterization of the 5/2 state using quasiparticle tunneling experiments in quantum point contacts (QPC). We have successfully fabricated QPCs on high mobility GaAs/AlGaAs heterostructures using conventional photolithography followed by etching and evaporation of Cr/Au depletion gates. Our samples show very stable FQH plateaus at v = 7/3, 5/2 and 8/3 filling fractions. Tunneling experiments are performed in the QPCs at various temperatures and also at various pinch-off voltages to characterize the effective charge and Coulomb interaction parameters of the quasiparticles. (Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000).

  5. Suppressed Fano resonance in hybrid asymmetric parallel double quantum dot - Superconductor tunnel junction

    NASA Astrophysics Data System (ADS)

    Brogi, Bharat Bhushan; Chand, Shyam; Ahluwalia, P. K.

    2017-05-01

    Transport properties of asymmetric parallel quantum dot system coupled to superconducting leads due to Andreev reflections have been studied in Coulomb blockade regime by using Non-Equilibrium Green Function technique. Andreev Transmission Probability and Josephson supercurrent (I-V characteristics) by virtue of resonant Cooper pair tunneling, a manifestation of Josephson effect, have been calculated. Superconducting order parameter, a key parameter in hybrid superconductor - quantum dot devices, regulates the Josephson Cooper pair tunneling and Fano resonance by virtue of quantum interference phenomena in asymmetric parallel quantum dot system. It has been found that superconducting order parameter first enhances and then suppresses the Cooper pair tunneling while Fano resonance gets completely suppressed. Complete disappearance of Fano effect signifies the dominance of superconducting order parameter over Fano effect in asymmetric parallel quantum dot system coupled to conventional superconducting leads.

  6. Elastic tunneling charge transport mechanisms in silicon quantum dots / Si O 2 thin films and superlattices

    NASA Astrophysics Data System (ADS)

    Illera, S.; Prades, J. D.; Cirera, A.

    2015-05-01

    The role of different charge transport mechanisms in Si / Si O 2 structures has been studied. A theoretical model based on the Transfer Hamiltonian Formalism has been developed to explain experimental current trends in terms of three different elastic tunneling processes: (1) trap assisted tunneling; (2) transport through an intermediate quantum dot; and (3) direct tunneling between leads. In general, at low fields carrier transport is dominated by the quantum dots whereas, for moderate and high fields, transport through deep traps inherent to the SiO2 is the most relevant process. Besides, current trends in Si / Si O 2 superlattice structure have been properly reproduced.

  7. Charge stability of a triple quantum dot with a finite tunnel coupling

    NASA Astrophysics Data System (ADS)

    Lee, Soo-Young; Chung, Yunchul

    2013-01-01

    We study charge stability of a symmetric triple quantum dot by using the Hund-Milliken method. As the interdot tunnel coupling increases from zero, the stability deviates continuously from that of the capacitance model. We demonstrate how the stability diagram is modified by the tunneling coupling, especially, around the sextuple point. It is shown that the characteristic feature of the sextuple point, omnidirectional charge transport, is maintained even though the sixfold degeneracy is lifted by the tunnel coupling. This is possible because the ground state near the broken sextuple point shows election or hole delocalization over the three quantum dots.

  8. Tunneling relaxation of holes in double quantum wells with nonideal heteroboundaries

    SciTech Connect

    Vas`ko, F.T.; Raichev, O.E.

    1995-09-01

    This paper presents a calculation of the tunneling relaxation rate of holes in double quantum wells when the holes are scattered at heteroboundary roughnesses. Because of mixing of the light- and heavy-hole states (which are described analytically in the approximation of strongly differing effective masses), the interwell tunneling mechanism changes at the splitting energy of the tunnel-coupled levels increases. The dependence of the tunneling relaxation rate on the splitting energy is compared with the experimental results. 7 refs., 2 figs.

  9. Many-body Tunneling and Nonequilibrium Dynamics of Doublons in Strongly Correlated Quantum Dots.

    PubMed

    Hou, WenJie; Wang, YuanDong; Wei, JianHua; Zhu, ZhenGang; Yan, YiJing

    2017-05-30

    Quantum tunneling dominates coherent transport at low temperatures in many systems of great interest. In this work we report a many-body tunneling (MBT), by nonperturbatively solving the Anderson multi-impurity model, and identify it a fundamental tunneling process on top of the well-acknowledged sequential tunneling and cotunneling. We show that the MBT involves the dynamics of doublons in strongly correlated systems. Proportional to the numbers of dynamical doublons, the MBT can dominate the off-resonant transport in the strongly correlated regime. A T (3/2)-dependence of the MBT current on temperature is uncovered and can be identified as a fingerprint of the MBT in experiments. We also prove that the MBT can support the coherent long-range tunneling of doublons, which is well consistent with recent experiments on ultracold atoms. As a fundamental physical process, the MBT is expected to play important roles in general quantum systems.

  10. Wide bandgap, strain-balanced quantum well tunnel junctions on InP substrates

    SciTech Connect

    Lumb, M. P.; Yakes, M. K.; Schmieder, K. J.; Affouda, C. A.; Walters, R. J.; González, M.; Bennett, M. F.; Herrera, M.; Delgado, F. J.; Molina, S. I.

    2016-05-21

    In this work, the electrical performance of strain-balanced quantum well tunnel junctions with varying designs is presented. Strain-balanced quantum well tunnel junctions comprising compressively strained InAlAs wells and tensile-strained InAlAs barriers were grown on InP substrates using solid-source molecular beam epitaxy. The use of InAlAs enables InP-based tunnel junction devices to be produced using wide bandgap layers, enabling high electrical performance with low absorption. The impact of well and barrier thickness on the electrical performance was investigated, in addition to the impact of Si and Be doping concentration. Finally, the impact of an InGaAs quantum well at the junction interface is presented, enabling a peak tunnel current density of 47.6 A/cm{sup 2} to be realized.

  11. Negative tunneling magneto-resistance in quantum wires with strong spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Han, Seungju; Serra, Llorenç; Choi, Mahn-Soo

    2015-06-01

    We consider a two-dimensional magnetic tunnel junction of the FM/I/QW(FM+SO)/I/N structure, where FM, I and QW(FM+SO) stand for a ferromagnet, an insulator and a quantum wire with both magnetic ordering and Rashba spin-orbit (SOC), respectively. The tunneling magneto-resistance (TMR) exhibits strong anisotropy and switches sign as the polarization direction varies relative to the quantum-wire axis, due to interplay among the one-dimensionality, the magnetic ordering, and the strong SOC of the quantum wire.

  12. Differential-phase-shift quantum secret sharing.

    PubMed

    Inoue, K; Ohashi, T; Kukita, T; Watanebe, K; Hayashi, S; Honjo, T; Takesue, H

    2008-09-29

    A quantum secret sharing (QSS) protocol based on a differential-phase-shift scheme is proposed, which quantum mechanically provides a full secret key to one party and partial keys to two other parties. A weak coherent pulse train is utilized instead of individual photons as in conventional schemes. Compared with previous QSS protocols, the present one features a simple setup, is suitable for fiber transmission, and offers the possibility for a high key creation rate. An experiment is also carried out to demonstrate the operation.

  13. Instanton paths and coherent quantum tunneling in antiferromagnetic spin clusters subject to a strong magnetic field

    SciTech Connect

    Ivanov, B. A. Kireev, V. E.

    2008-09-15

    The coherent quantum tunneling effects in antiferromagnets in the presence of a strong external magnetic field parallel to the easy axis have been investigated using the instanton formalism. In a wide field range including the region of the phase spin-flop transition, the tunneling is described by 180{sup o} instantons for which the Euclidean action is real and destructive interference is absent. At the transition point, 90{sup o} instantons describing the tunneling between the collinear and spin-flop states appear. The Euclidean action decreases, whereas the tunneling probability and tunneling level splitting in both phases increase significantly in the immediate vicinity of the spin-flop transition point. The possibility of observing the coherent tunneling effects for artificial small particles (magnetic dots) made of antiferromagnets is discussed.

  14. Magnetic Relaxation of Superconducting Quantum Dot and Tunneling of Electron in a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Gulevich, D. R.; Kusmartsev, F. V.

    Quantum tunneling of vortices had been found to be an important novel phenomena for description of low temperature creep in high temperature superconductors (HTSCs). We speculate that quantum tunneling may be also exhibited in mesoscopic superconductors due to vortices trapped by the Bean-Livingston barrier. The London approximation and method of images is used to estimate the shape of the potential well in superconducting HTSC quantum dot. To calculate the escape rate we use the instanton technique. We model the vortex by a quantum particle tunneling from a two-dimensional ground state under magnetic field applied in the transverse direction. The resulting decay rates obtained by the instanton approach and conventional WKB are compared revealing complete coincidence with each other.

  15. Magnetic Relaxation of Superconducting Quantum Dot and Tunneling of Electron in a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Gulevich, D. R.; Kusmartsev, F. V.

    2010-12-01

    Quantum tunneling of vortices had been found to be an important novel phenomena for description of low temperature creep in high temperature superconductors (HTSCs). We speculate that quantum tunneling may be also exhibited in mesoscopic superconductors due to vortices trapped by the Bean-Livingston barrier. The London approximation and method of images is used to estimate the shape of the potential well in superconducting HTSC quantum dot. To calculate the escape rate we use the instanton technique. We model the vortex by a quantum particle tunneling from a two-dimensional ground state under magnetic field applied in the transverse direction. The resulting decay rates obtained by the instanton approach and conventional WKB are compared revealing complete coincidence with each other.

  16. Backreaction due to quantum tunneling and modification to the black hole evaporation process

    NASA Astrophysics Data System (ADS)

    Modak, Sujoy K.

    2014-08-01

    We study the effect of backreaction on the evaporation of quantum black holes. The method used is based on quantum tunneling formalism as proposed by Banerjee and Majhi [Phys. Lett. B 675, 243 (2009)]. We give a more realistic picture by considering the fact that a black hole looses its energy while modes are tunneled outside the event horizon. It is shown how the tunneling quantum field modes affect the geometry and how this change in geometry is arrested in the quantum field. Exploiting this, we calculate the modified (nonthermal) radiation spectrum and associating energy fluxes and discuss various issues related with these. The results obtained here are often expected on physical grounds, but, importantly, we find them in a quantitative manner.

  17. The role of quantum effects in proton transfer reactions in enzymes: quantum tunneling in a noisy environment?

    NASA Astrophysics Data System (ADS)

    Bothma, Jacques P.; Gilmore, Joel B.; McKenzie, Ross H.

    2010-05-01

    We consider the role of quantum effects in the transfer of hydrogen-like species in enzyme-catalyzed reactions. This review is stimulated by claims that the observed magnitude and temperature dependence of kinetic isotope effects (KIEs) implies that quantum tunneling below the energy barrier associated with the transition state significantly enhances the reaction rate in many enzymes. We review the path integral approach and the Caldeira-Leggett model, which provides a general framework to describe and understand tunneling in a quantum system that interacts with a noisy environment at nonzero temperature. Here the quantum system is the active site of the enzyme, and the environment is the surrounding protein and water. Tunneling well below the barrier only occurs for temperatures less than a temperature T0, which is determined by the curvature of the potential energy surface near the top of the barrier. We argue that for most enzymes this temperature is less than room temperature. We review typical values for the parameters in the Caldeira-Leggett Hamiltonian, including the frequency-dependent friction and noise due to the environment. For physically reasonable parameters, we show that quantum transition state theory gives a quantitative description of the temperature dependence and magnitude of KIEs for two classes of enzymes that have been claimed to exhibit signatures of quantum tunneling. The only quantum effects are those associated with the transition state, both reflection at the barrier top and tunneling just below the barrier. We establish that the friction and noise due to the environment are weak and only slightly modify the reaction rate. Furthermore, at room temperature and for typical energy barriers environmental fluctuations with frequencies much less than 1000 cm-1 do not have a significant effect on quantum corrections to the reaction rate. This is essentially because the time scales associated with the dynamics of proton transfer are faster than

  18. Tunnel spectroscopy of Majorana bound states in topological superconductor/quantum dot Josephson junctions

    NASA Astrophysics Data System (ADS)

    Huang, Guang-Yao; Leijnse, Martin; Flensberg, Karsten; Xu, H. Q.

    2014-12-01

    We theoretically investigate electronic transport through a junction where a quantum dot (QD) is tunnel coupled on both sides to semiconductor nanowires with strong spin-orbit interaction and proximity-induced superconductivity. The results are presented as stability diagrams, i.e., the differential conductance as a function of the bias voltage applied across the junction and the gate voltage used to control the electrostatic potential on the QD. A small applied magnetic field splits and modifies the resonances due to the Zeeman splitting of the QD level. Above a critical field strength, Majorana bound states (MBS) appear at the interfaces between the two superconducting nanowires and the QD, resulting in a qualitative change of the entire stability diagram, suggesting this setup as a promising platform to identify MBS. Our calculations are based on a nonequilibrium Green's function description and is exact when Coulomb interactions on the QD can be neglected. In addition, we develop a simple pictorial view of the involved transport processes, which is equivalent to a description in terms of multiple Andreev reflections, but provides an alternative way to understand the role of the QD level in enhancing transport for certain gate and bias voltages. We believe that this description will be useful in future studies of interacting QDs coupled to superconducting leads (with or without MBS), where it can be used to develop a perturbation expansion in the tunnel coupling.

  19. Density-Gradient Theory: A Macroscopic Approach to Quantum Confinement and Tunneling in Semiconductor Devices

    DTIC Science & Technology

    2011-01-01

    flow of electrons and holes in Germanium and other semiconductors. Bell Syst. Tech. J. 29, 560 (1950) 4. Maxwell, J.C.: On stresses in rarefied gases...especially by the phenomena of quantum confinement and quantum tunneling. The various mathematical descriptions of electron flow in biased semiconductors...patently inappropriate. 1.2 Quantum transport The three main “quantum” behaviors of an electron gas in a semiconductor—all of course well known—that

  20. Size dependence in tunneling spectra of PbSe quantum-dot arrays.

    PubMed

    Ou, Y C; Cheng, S F; Jian, W B

    2009-07-15

    Interdot Coulomb interactions and collective Coulomb blockade were theoretically argued to be a newly important topic, and experimentally identified in semiconductor quantum dots, formed in the gate confined two-dimensional electron gas system. Developments of cluster science and colloidal synthesis accelerated the studies of electron transport in colloidal nanocrystal or quantum-dot solids. To study the interdot coupling, various sizes of two-dimensional arrays of colloidal PbSe quantum dots are self-assembled on flat gold surfaces for scanning tunneling microscopy and scanning tunneling spectroscopy measurements at both room and liquid-nitrogen temperatures. The tip-to-array, array-to-substrate, and interdot capacitances are evaluated and the tunneling spectra of quantum-dot arrays are analyzed by the theory of collective Coulomb blockade. The current-voltage of PbSe quantum-dot arrays conforms properly to a scaling power law function. In this study, the dependence of tunneling spectra on the sizes (numbers of quantum dots) of arrays is reported and the capacitive coupling between quantum dots in the arrays is explored.

  1. Quantum tunneling splittings from path-integral molecular dynamics

    NASA Astrophysics Data System (ADS)

    Mátyus, Edit; Wales, David J.; Althorpe, Stuart C.

    2016-03-01

    We illustrate how path-integral molecular dynamics can be used to calculate ground-state tunnelling splittings in molecules or clusters. The method obtains the splittings from ratios of density matrix elements between the degenerate wells connected by the tunnelling. We propose a simple thermodynamic integration scheme for evaluating these elements. Numerical tests on fully dimensional malonaldehyde yield tunnelling splittings in good overall agreement with the results of diffusion Monte Carlo calculations.

  2. Tunneling into quantum wires: Regularization of the tunneling Hamiltonian and consistency between free and bosonized fermions

    NASA Astrophysics Data System (ADS)

    Filippone, Michele; Brouwer, Piet W.

    2016-12-01

    Tunneling between a point contact and a one-dimensional wire is usually described with the help of a tunneling Hamiltonian that contains a δ function in position space. Whereas the leading-order contribution to the tunneling current is independent of the way this δ function is regularized, higher-order corrections with respect to the tunneling amplitude are known to depend on the regularization. Instead of regularizing the δ function in the tunneling Hamiltonian, one may also obtain a finite tunneling current by invoking the ultraviolet cutoffs in a field-theoretic description of the electrons in the one-dimensional conductor, a procedure that is often used in the literature. For the latter case, we show that standard ultraviolet cutoffs lead to different results for the tunneling current in fermionic and bosonized formulations of the theory, when going beyond leading order in the tunneling amplitude. We show how to recover the standard fermionic result using the formalism of functional bosonization and revisit the tunneling current to leading order in the interacting case.

  3. Control of optical bistability and third-order nonlinearity via tunneling induced quantum interference in triangular quantum dot molecules

    SciTech Connect

    Tian, Si-Cong Tong, Cun-Zhu Zhang, Jin-Long; Shan, Xiao-Nan; Fu, Xi-Hong; Zeng, Yu-Gang; Qin, Li; Ning, Yong-Qiang; Wan, Ren-Gang

    2015-06-15

    The optical bistability of a triangular quantum dot molecules embedded inside a unidirectional ring cavity is studied. The type, the threshold and the hysteresis loop of the optical bistability curves can be modified by the tunneling parameters, as well as the probe laser field. The linear and nonlinear susceptibilities of the medium are also studied to interpret the corresponding results. The physical interpretation is that the tunneling can induce the quantum interference, which modifies the linear and the nonlinear response of the medium. As a consequence, the characteristics of the optical bistability are changed. The scheme proposed here can be utilized for optimizing and controlling the optical switching process.

  4. Quantum Calculations of Electron Tunneling in Respiratory Complex III.

    PubMed

    Hagras, Muhammad A; Hayashi, Tomoyuki; Stuchebrukhov, Alexei A

    2015-11-19

    The most detailed and comprehensive to date study of electron transfer reactions in the respiratory complex III of aerobic cells, also known as bc1 complex, is reported. In the framework of the tunneling current theory, electron tunneling rates and atomistic tunneling pathways between different redox centers were investigated for all electron transfer reactions comprising different stages of the proton-motive Q-cycle. The calculations reveal that complex III is a smart nanomachine, which under certain conditions undergoes conformational changes gating electron transfer, or channeling electrons to specific pathways. One-electron tunneling approximation was adopted in the tunneling calculations, which were performed using hybrid Broken-Symmetry (BS) unrestricted DFT/ZINDO levels of theory. The tunneling orbitals were determined using an exact biorthogonalization scheme that uniquely separates pairs of tunneling orbitals with small overlaps out of the remaining Franck-Condon orbitals with significant overlap. Electron transfer rates in different redox pairs show exponential distance dependence, in agreement with the reported experimental data; some reactions involve coupled proton transfer. Proper treatment of a concerted two-electron bifurcated tunneling reaction at the Q(o) site is given.

  5. Coherent control of quantum tunneling in different driving-frequency regions

    SciTech Connect

    Lu, Gengbiao; Hai, Wenhua; Zhong, Honghua; Xie, Qiongtao

    2010-06-15

    We investigate the coherent control of quantum tunneling for a single particle held in a driven double-well potential. For a moderate-frequency region, we demonstrate that the irregular quantum tunneling is associated with classically chaotic dynamics. A set of lower resonance-like frequencies is found, for which the coherent destruction of tunneling in the sense of the time average is illustrated numerically. For a high-frequency region, it is shown that the particle is located at the bottom of each well alternately for a long time and the time located in one well can be modulated by adjusting the driving field. The results could be useful for the experiments of controlling single-particle tunneling [see, e.g., E. Kierig, U. Schnorrberger, A. Schietinger, J. Tomkovic, and M. K. Oberthaler, Phys. Rev. Lett. 100, 190405 (2008).].

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

    PubMed

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

    2015-03-23

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

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

    PubMed Central

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

    2015-01-01

    Low-noise single-photon detectors that can resolve photon numbers are used to monitor the operation of quantum gates in linear-optical quantum computation. Exactly 0, 1 or 2 photons registered in a detector should be distinguished especially in long-distance quantum communication and quantum computation. Here we demonstrate a photon-number-resolving detector based on quantum dot coupled resonant tunneling diodes (QD-cRTD). Individual quantum-dots (QDs) coupled closely with adjacent quantum well (QW) of resonant tunneling diode operate as photon-gated switches- which turn on (off) the RTD tunneling current when they trap photon-generated holes (recombine with injected electrons). Proposed electron-injecting operation fills electrons into coupled QDs which turn “photon-switches” to “OFF” state and make the detector ready for multiple-photons detection. With proper decision regions defined, 1-photon and 2-photon states are resolved in 4.2 K with excellent propabilities of accuracy of 90% and 98% respectively. Further, by identifying step-like photon responses, the photon-number-resolving capability is sustained to 77 K, making the detector a promising candidate for advanced quantum information applications where photon-number-states should be accurately distinguished. PMID:25797442

  8. Band gap widening and quantum tunnelling effects of Ag/MgO/p-Si MOS structure

    NASA Astrophysics Data System (ADS)

    Kamarulzaman, Norlida; Badar, Nurhanna; Fadilah Chayed, Nor; Firdaus Kasim, Muhd

    2016-10-01

    MgO films of various thicknesses were fabricated via the pulsed laser deposition method. The MgO thin films obtained have the advantage of high quality mirror finish, good densification and of uniform thickness. The MgO thin films have thicknesses of between 43 to 103 nm. They are polycrystalline in nature with oriented growth mainly in the direction of the [200] and [220] crystal planes. It is observed that the band gap of the thin films increases as the thickness decreases due to quantum effects, however, turn-on voltage has the opposite effect. The decrease of the turn-on as well as the tunnelling voltage of the thinner films, despite their larger band gap, is a direct experimental evidence of quantum tunnelling effects in the thin films. This proves that quantum tunnelling is more prominent in low dimensional structures.

  9. Spin-lattice relaxation via quantum tunneling in an Er3+ -polyoxometalate molecular magnet

    NASA Astrophysics Data System (ADS)

    Luis, F.; Martínez-Pérez, M. J.; Montero, O.; Coronado, E.; Cardona-Serra, S.; Martí-Gastaldo, C.; Clemente-Juan, J. M.; Sesé, J.; Drung, D.; Schurig, T.

    2010-08-01

    We investigate the mechanism of spin-lattice relaxation of Er ions encapsulated in polyoxometalate clusters, which below 4 K can only reverse its spin via quantum tunneling processes. The temperature-independent rate τ-1 is, at zero field, ten orders of magnitude larger than the rates predicted for direct phonon-induced processes. In addition, we observe that τ-1 is suppressed by external magnetic bias and hyperfine interactions but enhanced by increasing the concentration of Er ions. The observed relaxation agrees with predictions for pure quantum tunneling, showing that this phenomenon drives the thermalization of electronic spins. A possible link between these two phenomena is discussed, involving the collective emission of phonons from particular spin configurations attained via quantum tunneling.

  10. Evidence for quantum tunneling of vortices in superconductors. [Temperature dependence in low magnetic fields

    SciTech Connect

    Liu, Y.; Haviland, D.B.; Glazman, L.I.; Goldman, A.M. )

    1992-10-01

    Flux creep in disordered superconductors may be governed by quantum tunneling of Abrikosov vortices rather than by thermal activation processes. The expectation is that in the quantum tunneling regime the creep rate would be temperature independent. This assumes that the parameters describing the pinning potential and other aspects of the superconducting films are temperature independent. In the case of extremely thin superconducting films the coherence length retains its temperature dependence well into the quantum tunneling regime, leading to an unusual temperature dependence of the electrical resistance in this regime. This was observed in ultrathin superconducting films of Pb, Al, and Bi. In low magnetic fields, at low temperatures, sheet resistances vary with temperature as R [approx] R[sub 0] exp(T/T[sub 0]), where T[sub 0] and R[sub 0] are constants.

  11. Differentiability of correlations in realistic quantum mechanics

    SciTech Connect

    Cabrera, Alejandro; Faria, Edson de; Pujals, Enrique; Tresser, Charles

    2015-09-15

    We prove a version of Bell’s theorem in which the locality assumption is weakened. We start by assuming theoretical quantum mechanics and weak forms of relativistic causality and of realism (essentially the fact that observable values are well defined independently of whether or not they are measured). Under these hypotheses, we show that only one of the correlation functions that can be formulated in the framework of the usual Bell theorem is unknown. We prove that this unknown function must be differentiable at certain angular configuration points that include the origin. We also prove that, if this correlation is assumed to be twice differentiable at the origin, then we arrive at a version of Bell’s theorem. On the one hand, we are showing that any realistic theory of quantum mechanics which incorporates the kinematic aspects of relativity must lead to this type of rough correlation function that is once but not twice differentiable. On the other hand, this study brings us a single degree of differentiability away from a relativistic von Neumann no hidden variables theorem.

  12. Black hole remnant and quantum tunnelling in three-dimensional Gödel spacetime

    NASA Astrophysics Data System (ADS)

    Li, Hui-Ling; Zu, Xiao-Tao

    2015-05-01

    Using the modified Dirac equation in a three-dimensional gravity background, we investigate the quantum correction to tunnelling radiation from a Gödel black hole, and discuss the black hole remnant employing fermion's tunnelling. The corrected tunnelling probability is derived, and the modified Hawking temperature is found as well. It is worth emphasizing that, only when the condition j> αω(3 r -- r +) is satisfied, emitting both a mass particle and a massless particle, the remnant of the Gödel black hole may arise.

  13. Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum Dots

    NASA Astrophysics Data System (ADS)

    Grove-Rasmussen, K.; Grap, S.; Paaske, J.; Flensberg, K.; Andergassen, S.; Meden, V.; Jørgensen, H. I.; Muraki, K.; Fujisawa, T.

    2012-04-01

    By means of sequential and cotunneling spectroscopy, we study the tunnel couplings between metallic leads and individual levels in a carbon nanotube quantum dot. The levels are ordered in shells consisting of two doublets with strong- and weak-tunnel couplings, leading to gate-dependent level renormalization. By comparison to a one- and two-shell model, this is shown to be a consequence of disorder-induced valley mixing in the nanotube. Moreover, a parallel magnetic field is shown to reduce this mixing and thus suppress the effects of tunnel renormalization.

  14. Time-Resolved Tunneling in Gallium-Arsenide Quantum Well Structures

    NASA Astrophysics Data System (ADS)

    Norris, Theodore Blake

    Tunneling in quantum well structures has been a subject of considerable interest in semiconductor physics in recent years. Few time-domain experiments, however, have been brought to bear on the questions of the mechanisms or time-dependence of tunneling. We have developed techniques for a measurement of picosecond and femtosecond optical spectra, and applied them for the first time to the study of tunneling in quantum well structures. We have developed a novel dye oscillator and amplifier to generate optical pulses of 100-fs duration at the 15 -muJ level with a repetition rate of 1 kHz. These pulses were used to generate a white-light continuum, which enabled us to perform optical absorption spectroscopy over the visible and near-infrared regions of the spectrum with a time resolution of about 100 fs. We have also developed an experimental setup for time-resolved photoluminescence appropriate for GaAs quantum well studies, utilizing a picosecond near-infrared dye laser in conjunction with a synchroscan streak camera. Using time resolved photoluminescence, we have studied the tunneling escape rate of electrons from a quantum well through a thin barrier into a continuum, and its dependence on barrier height and width, and on an applied electric field. The observed rates are well-described by a straightforward semiclassical theory. We have investigated the problem of tunneling between coupled quantum wells using both time-resolved luminescence and absorption spectroscopy. We have directly observed in luminescence the buildup of a "charge-transfer" state via electron and hole tunneling in opposite directions, and the dependence of this charge transfer on an electric field. At moderate fields (2.5 times 10^4 V/cm), the charge transfer occurs faster than 20 ps, indicating an unexpectedly fast hole tunneling rate. The time-resolved absorption experiments measure the time electrons initially excited into one quantum well require to tunnel into a second well. The

  15. Macroscopic quantum tunneling of a Bose-Einstein condensate through double Gaussian barriers

    NASA Astrophysics Data System (ADS)

    Maeda, Kenji; Urban, Gregor; Weidemüller, Matthias; Carr, Lincoln D.

    2015-05-01

    Macroscopic quantum tunneling is one of the great manifestations of quantum physics, not only showing passage through a potential barrier but also emerging in a many-body wave function. We study a quasi-1D Bose-Einstein condensate of Lithium, confined by two Gaussian barriers, and show that in an experimentally realistic potential tens of thousands of atoms tunnel on time scales of 10 to 100 ms. Using a combination of variational and WKB approximations based on the Gross-Pitaevskii or nonlinear Schrödinger equation, we show that many unusual tunneling features appear due to the nonlinearity, including the number of trapped atoms exhibiting non-exponential decay, severe distortion of the barriers by the mean field, and even formation of a triple barrier in certain regimes. In the first 10ms, nonlinear many-body effects make the tunneling rates significantly larger than background loss rates, from 10 to 70 Hz. Thus we conclude that macroscopic quantum tunneling can be observed on experimental time scales. Funded by NSF, AFOSR, the Alexander von Humboldt foundation, and the Heidelberg Center for Quantum Dynamics.

  16. Quantum Tunneling of Water in Beryl. A New State of the Water Molecule

    SciTech Connect

    Kolesnikov, Alexander I.; Reiter, George F.; Choudhury, Narayani; Prisk, Timothy R.; Mamontov, Eugene; Podlesnyak, Andrey; Ehlers, George; Seel, Andrew G.; Wesolowski, David J.; Anovitz, Lawrence M.

    2016-04-22

    When using neutron scattering and ab initio simulations, we document the discovery of a new “quantum tunneling state” of the water molecule confined in 5 Å channels in the mineral beryl, characterized by extended proton and electron delocalization. We observed a number of peaks in the inelastic neutron scattering spectra that were uniquely assigned to water quantum tunneling. Additionally, the water proton momentum distribution was measured with deep inelastic neutron scattering, which directly revealed coherent delocalization of the protons in the ground state.

  17. Quantum Tunneling of Water in Beryl. A New State of the Water Molecule

    SciTech Connect

    Kolesnikov, Alexander I.; Reiter, George F.; Choudhury, Narayani; Prisk, Timothy R.; Mamontov, Eugene; Podlesnyak, Andrey; Ehlers, George; Seel, Andrew G.; Wesolowski, David J.; Anovitz, Lawrence M.

    2016-04-22

    When using neutron scattering and ab initio simulations, we document the discovery of a new “quantum tunneling state” of the water molecule confined in 5 Å channels in the mineral beryl, characterized by extended proton and electron delocalization. We observed a number of peaks in the inelastic neutron scattering spectra that were uniquely assigned to water quantum tunneling. Additionally, the water proton momentum distribution was measured with deep inelastic neutron scattering, which directly revealed coherent delocalization of the protons in the ground state.

  18. Imaging correlated wave functions of few-electron quantum dots: Theory and scanning tunneling spectroscopy experimentsa)

    NASA Astrophysics Data System (ADS)

    Rontani, Massimo; Molinari, Elisa; Maruccio, Giuseppe; Janson, Martin; Schramm, Andreas; Meyer, Christian; Matsui, Tomohiro; Heyn, Christian; Hansen, Wolfgang; Wiesendanger, Roland

    2007-04-01

    We show both theoretically and experimentally that scanning tunneling spectroscopy (STS) images of semiconductor quantum dots may display clear signatures of electron-electron correlation. We apply many-body tunneling theory to a realistic model, which fully takes into account correlation effects and dot anisotropy. Comparing measured STS images of freestanding InAs quantum dots with those calculated by the full configuration interaction method, we explain the wave-function sequence in terms of images of one- and two-electron states. The STS map corresponding to double charging is significantly distorted by electron correlation with respect to the noninteracting case.

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

    NASA Astrophysics Data System (ADS)

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

    2000-07-01

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

  20. Quantum Tunneling of Water in Beryl: A New State of the Water Molecule.

    PubMed

    Kolesnikov, Alexander I; Reiter, George F; Choudhury, Narayani; Prisk, Timothy R; Mamontov, Eugene; Podlesnyak, Andrey; Ehlers, George; Seel, Andrew G; Wesolowski, David J; Anovitz, Lawrence M

    2016-04-22

    Using neutron scattering and ab initio simulations, we document the discovery of a new "quantum tunneling state" of the water molecule confined in 5 Å channels in the mineral beryl, characterized by extended proton and electron delocalization. We observed a number of peaks in the inelastic neutron scattering spectra that were uniquely assigned to water quantum tunneling. In addition, the water proton momentum distribution was measured with deep inelastic neutron scattering, which directly revealed coherent delocalization of the protons in the ground state.

  1. Entangled trajectory molecular dynamics in multidimensional systems: two-dimensional quantum tunneling through the Eckart barrier.

    PubMed

    Wang, Lifei; Martens, Craig C; Zheng, Yujun

    2012-07-21

    In this paper, we extend the entangled trajectory molecular dynamics (ETMD) method to multidimensional systems. The integrodifferential form of the evolution equation for the Wigner function is employed, allowing general potentials not represented as a polynomial to be treated. As the example, the method is applied to a two-dimensional model of scattering from an Eckart barrier. The results of ETMD are in good agreement with quantum hydrodynamics and exact quantum simulations. By comparing the quantum and classical trajectory in phase space, the quantum tunneling phenomenon is interpreted vividly.

  2. Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes

    SciTech Connect

    Verma, Jai; Kandaswamy, Prem Kumar; Protasenko, Vladimir; Verma, Amit; Grace Xing, Huili; Jena, Debdeep

    2013-01-28

    We demonstrate a GaN quantum dot ultraviolet light-emitting diode that uses tunnel injection of carriers through AlN barriers into the active region. The quantum dot heterostructure is grown by molecular beam epitaxy on AlN templates. The large lattice mismatch between GaN and AlN favors the formation of GaN quantum dots in the Stranski-Krastanov growth mode. Carrier injection by tunneling can mitigate losses incurred in hot-carrier injection in light emitting heterostructures. To achieve tunnel injection, relatively low composition AlGaN is used for n- and p-type layers to simultaneously take advantage of effective band alignment and efficient doping. The small height of the quantum dots results in short-wavelength emission and are simultaneously an effective tool to fight the reduction of oscillator strength from quantum-confined Stark effect due to polarization fields. The strong quantum confinement results in room-temperature electroluminescence peaks at 261 and 340 nm, well above the 365 nm bandgap of bulk GaN. The demonstration opens the doorway to exploit many varied features of quantum dot physics to realize high-efficiency short-wavelength light sources.

  3. Tunneling in perfect-fluid (minisuperspace) quantum cosmology

    SciTech Connect

    Brown, J.D. )

    1990-02-15

    A minisuperspace model of general relativity with a positive cosmological constant coupled to a perfect isentropic fluid is presented. The classical equations of motion are solved for a tunneling solution that consists of a Euclidean instanton of the wormhole type, connected to Lorentzian Robertson-Walker universes. The path integral is then defined as a sum over Lorentzian geometries and it is shown that the tunneling solution dominates the semiclassical evaluation of the path integral.

  4. Investigating how students think about and learn quantum physics: An example from tunneling

    NASA Astrophysics Data System (ADS)

    Morgan, Jeffrey T.

    Much of physics education research (PER) has focused on introductory courses and topics, with less research done into how students learn physics in advanced courses. Members of The University of Maine Physics Education Research Laboratory (PERL) have begun studying how students in advanced physics courses reason about classical mechanics, thermal physics, and quantum physics. Here, we describe an investigation into how students reason about quantum mechanical tunneling, and detail how those findings informed a portion of a curriculum development project. Quantum mechanical tunneling is a standard topic discussed in most modern physics and quantum physics courses. Understanding tunneling is crucial to making sense of several topics in physics, including scanning tunneling microscopy and nuclear decay. To make sense of the standard presentation of tunneling, students must track total, potential, and kinetic energies. Additionally, they must distinguish between the ideas of energy, probability density, and the wave function. They need to understand the complex nature of the wave function, as well as understand what can and cannot be inferred from a solution to the time-independent Schrodinger equation. Our investigations into student understanding of these ideas consisted of a series of interviews, as well as a survey. Both centered around asking students to reason about energy, probability, and the wave function solutions for the standard square potential energy barrier scenario presented in most textbooks. We describe ideas that students seem to successfully learn following standard instruction, as well as common difficulties that remain. Additionally, we present multiple data points from a small population of physics majors over three years and describe how some of their reasoning about tunneling changed, while other portions seemed to remain unaffected by instruction. We used the results of these investigations to write tutorials on tunneling and applications of

  5. Probing the quantum tunneling limit of plasmonic enhancement by third harmonic generation.

    PubMed

    Hajisalem, Ghazal; Nezami, Mohammedreza S; Gordon, Reuven

    2014-11-12

    Metal nanostructures provide extreme focusing of optical energy that is limited fundamentally by quantum tunneling. We directly probe the onset of the quantum tunneling regime observed by a sharp reduction in the local field intensity in subnanometer self-assembled monolayer gaps using third harmonic generation. Unlike past works that have inferred local limits from far-field spectra, this nonlinear measurement is sensitive to the near-field intensity as the third power. We calculate the local field intensity using a quantum corrected model and find good quantitative agreement with the measured third harmonic. The onset of the quantum regime occurs for double the gap size of past studies because of the reduced barrier height of the self-assembled monolayer, which will be critical for many applications of plasmonics, including nonlinear optics and surface enhanced Raman spectroscopy.

  6. In-plane chiral tunneling and out-of-plane valley-polarized quantum tunneling in twisted graphene trilayer

    NASA Astrophysics Data System (ADS)

    Qiao, Jia-Bin; He, Lin

    2014-08-01

    Here we show that a twisted graphene trilayer made by misoriented stacking of a graphene monolayer on top of a Bernal graphene bilayer can exhibit rich and tailored electronic properties. For the case that the graphene monolayer and bilayer are strongly coupled, both the massless Dirac fermions and massive chiral fermions coexist in the twisted trilayer, leading to unique in-plane chiral tunneling. For a weak coupling between the two graphene systems, the distinct chiralities and pseudospin textures of quasiparticles in monolayer and bilayer enable vertical valley-polarized quantum tunneling between them. Intriguingly, the polarity of the valley polarization can be inverted simply by either controlling the rotational angles between the two systems or tuning the Fermi levels of the two systems. Our result implies that layered van der Waals structures assembled from individual atomic planes can create materials that harbor unusual properties and alternative functionalities depending on the stacking configuration of the crystalline layers.

  7. Tunneling dynamics with a mixed quantum-classical method: Quantum corrected propagator combined with frozen Gaussian wave packets

    NASA Astrophysics Data System (ADS)

    Gelman, David; Schwartz, Steven D.

    2008-07-01

    The recently developed mixed quantum-classical propagation method is extended to treat tunneling effects in multidimensional systems. Formulated for systems consisting of a quantum primary part and a classical bath of heavier particles, the method employs a frozen Gaussian description for the bath degrees of freedom, while the dynamics of the quantum subsystem is governed by a corrected propagator. The corrections are defined in terms of matrix elements of zeroth-order propagators. The method is applied to a model system of a double-well potential bilinearly coupled to a harmonic oscillator. The extension of the method, which includes nondiagonal elements of the correction propagator, enables an accurate treatment of tunneling in an antisymmetric double-well potential.

  8. Photon-assisted tunneling in an asymmetrically coupled triple quantum dot

    SciTech Connect

    Wang, Bao-Chuan; Cao, Gang Chen, Bao-Bao; Yu, Guo-Dong; Li, Hai-Ou; Xiao, Ming; Guo, Guo-Ping

    2016-08-14

    The gate-defined quantum dot is regarded as one of the basic structures required for scalable semiconductor quantum processors. Here, we demonstrate a structure that contains three quantum dots scaled in series. The electron number of each dot and the tunnel coupling between them can be tuned conveniently using splitting gates. We tune the quantum dot array asymmetrically such that the tunnel coupling between the right dot and the central dot is much larger than that between the left dot and the central dot. When driven by microwaves, the sidebands of the photon-assisted tunneling process appear not only in the left-to-central dot transition region but also in the left-to-right dot transition region. These sidebands are both attributed to the left-to-central transition for asymmetric coupling. Our result shows that there is a region of a triple quantum dot structure that remains indistinct when studied with a normal two-dimensional charge stability diagram; this will be helpful in future studies of the scalability of quantum dot systems.

  9. Tunneling and speedup in quantum optimization for permutation-symmetric problems

    DOE PAGES

    Muthukrishnan, Siddharth; Albash, Tameem; Lidar, Daniel A.

    2016-07-21

    Tunneling is often claimed to be the key mechanism underlying possible speedups in quantum optimization via quantum annealing (QA), especially for problems featuring a cost function with tall and thin barriers. We present and analyze several counterexamples from the class of perturbed Hamming weight optimization problems with qubit permutation symmetry. We first show that, for these problems, the adiabatic dynamics that make tunneling possible should be understood not in terms of the cost function but rather the semiclassical potential arising from the spin-coherent path-integral formalism. We then provide an example where the shape of the barrier in the final costmore » function is short and wide, which might suggest no quantum advantage for QA, yet where tunneling renders QA superior to simulated annealing in the adiabatic regime. However, the adiabatic dynamics turn out not be optimal. Instead, an evolution involving a sequence of diabatic transitions through many avoided-level crossings, involving no tunneling, is optimal and outperforms adiabatic QA. We show that this phenomenon of speedup by diabatic transitions is not unique to this example, and we provide an example where it provides an exponential speedup over adiabatic QA. In yet another twist, we show that a classical algorithm, spin-vector dynamics, is at least as efficient as diabatic QA. Lastly, in a different example with a convex cost function, the diabatic transitions result in a speedup relative to both adiabatic QA with tunneling and classical spin-vector dynamics.« less

  10. Scaling analysis and instantons for thermally assisted tunneling and quantum Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Jiang, Zhang; Smelyanskiy, Vadim N.; Isakov, Sergei V.; Boixo, Sergio; Mazzola, Guglielmo; Troyer, Matthias; Neven, Hartmut

    2017-01-01

    We develop an instantonic calculus to derive an analytical expression for the thermally assisted tunneling decay rate of a metastable state in a fully connected quantum spin model. The tunneling decay problem can be mapped onto the Kramers escape problem of a classical random dynamical field. This dynamical field is simulated efficiently by path-integral quantum Monte Carlo (QMC). We show analytically that the exponential scaling with the number of spins of the thermally assisted quantum tunneling rate and the escape rate of the QMC process are identical. We relate this effect to the existence of a dominant instantonic tunneling path. The instanton trajectory is described by nonlinear dynamical mean-field theory equations for a single-site magnetization vector, which we solve exactly. Finally, we derive scaling relations for the "spiky" barrier shape when the spin tunneling and QMC rates scale polynomially with the number of spins N while a purely classical over-the-barrier activation rate scales exponentially with N .

  11. Tunneling and Speedup in Quantum Optimization for Permutation-Symmetric Problems

    NASA Astrophysics Data System (ADS)

    Muthukrishnan, Siddharth; Albash, Tameem; Lidar, Daniel A.

    2016-07-01

    Tunneling is often claimed to be the key mechanism underlying possible speedups in quantum optimization via quantum annealing (QA), especially for problems featuring a cost function with tall and thin barriers. We present and analyze several counterexamples from the class of perturbed Hamming weight optimization problems with qubit permutation symmetry. We first show that, for these problems, the adiabatic dynamics that make tunneling possible should be understood not in terms of the cost function but rather the semiclassical potential arising from the spin-coherent path-integral formalism. We then provide an example where the shape of the barrier in the final cost function is short and wide, which might suggest no quantum advantage for QA, yet where tunneling renders QA superior to simulated annealing in the adiabatic regime. However, the adiabatic dynamics turn out not be optimal. Instead, an evolution involving a sequence of diabatic transitions through many avoided-level crossings, involving no tunneling, is optimal and outperforms adiabatic QA. We show that this phenomenon of speedup by diabatic transitions is not unique to this example, and we provide an example where it provides an exponential speedup over adiabatic QA. In yet another twist, we show that a classical algorithm, spin-vector dynamics, is at least as efficient as diabatic QA. Finally, in a different example with a convex cost function, the diabatic transitions result in a speedup relative to both adiabatic QA with tunneling and classical spin-vector dynamics.

  12. Scaling for quantum tunneling current in nano- and subnano-scale plasmonic junctions

    NASA Astrophysics Data System (ADS)

    Zhang, Peng

    2015-05-01

    When two conductors are separated by a sufficiently thin insulator, electrical current can flow between them by quantum tunneling. This paper presents a self-consistent model of tunneling current in a nano- and subnano-meter metal-insulator-metal plasmonic junction, by including the effects of space charge and exchange correlation potential. It is found that the J-V curve of the junction may be divided into three regimes: direct tunneling, field emission, and space-charge-limited regime. In general, the space charge inside the insulator reduces current transfer across the junction, whereas the exchange-correlation potential promotes current transfer. It is shown that these effects may modify the current density by orders of magnitude from the widely used Simmons’ formula, which is only accurate for a limited parameter space (insulator thickness > 1 nm and barrier height > 3 eV) in the direct tunneling regime. The proposed self-consistent model may provide a more accurate evaluation of the tunneling current in the other regimes. The effects of anode emission and material properties (i.e. work function of the electrodes, electron affinity and permittivity of the insulator) are examined in detail in various regimes. Our simple model and the general scaling for tunneling current may provide insights to new regimes of quantum plasmonics.

  13. Scaling for quantum tunneling current in nano- and subnano-scale plasmonic junctions

    PubMed Central

    Zhang, Peng

    2015-01-01

    When two conductors are separated by a sufficiently thin insulator, electrical current can flow between them by quantum tunneling. This paper presents a self-consistent model of tunneling current in a nano- and subnano-meter metal-insulator-metal plasmonic junction, by including the effects of space charge and exchange correlation potential. It is found that the J-V curve of the junction may be divided into three regimes: direct tunneling, field emission, and space-charge-limited regime. In general, the space charge inside the insulator reduces current transfer across the junction, whereas the exchange-correlation potential promotes current transfer. It is shown that these effects may modify the current density by orders of magnitude from the widely used Simmons’ formula, which is only accurate for a limited parameter space (insulator thickness > 1 nm and barrier height > 3 eV) in the direct tunneling regime. The proposed self-consistent model may provide a more accurate evaluation of the tunneling current in the other regimes. The effects of anode emission and material properties (i.e. work function of the electrodes, electron affinity and permittivity of the insulator) are examined in detail in various regimes. Our simple model and the general scaling for tunneling current may provide insights to new regimes of quantum plasmonics. PMID:25988951

  14. Scaling for quantum tunneling current in nano- and subnano-scale plasmonic junctions.

    PubMed

    Zhang, Peng

    2015-05-19

    When two conductors are separated by a sufficiently thin insulator, electrical current can flow between them by quantum tunneling. This paper presents a self-consistent model of tunneling current in a nano- and subnano-meter metal-insulator-metal plasmonic junction, by including the effects of space charge and exchange correlation potential. It is found that the J-V curve of the junction may be divided into three regimes: direct tunneling, field emission, and space-charge-limited regime. In general, the space charge inside the insulator reduces current transfer across the junction, whereas the exchange-correlation potential promotes current transfer. It is shown that these effects may modify the current density by orders of magnitude from the widely used Simmons' formula, which is only accurate for a limited parameter space (insulator thickness > 1 nm and barrier height > 3 eV) in the direct tunneling regime. The proposed self-consistent model may provide a more accurate evaluation of the tunneling current in the other regimes. The effects of anode emission and material properties (i.e. work function of the electrodes, electron affinity and permittivity of the insulator) are examined in detail in various regimes. Our simple model and the general scaling for tunneling current may provide insights to new regimes of quantum plasmonics.

  15. Effect of pumping delay on the modulation bandwidth in double tunneling-injection quantum dot lasers.

    PubMed

    Asryan, Levon V

    2017-01-01

    The modulation bandwidth of double tunneling-injection (DTI) quantum dot (QD) lasers is studied, taking into account noninstantaneous pumping of QDs. In this advanced type of semiconductor lasers, carriers are first captured from the bulk waveguide region into two-dimensional regions (quantum wells [QWs]); then they tunnel from the QWs into zero-dimensional regions (QDs). The two processes are noninstantaneous and, thus, could delay the delivery of the carriers to the QDs. Here, the modulation bandwidth of DTI QD lasers is calculated as a function of two characteristic times (the capture time from the waveguide region into the QW and the tunneling time from the QW into the QD ensemble) and is shown to increase as either of these times is reduced. The capture and tunneling times of 1 and 0.1 ps, respectively, are shown to characterize fast capture and tunneling processes; as the capture and tunneling times are brought below 1 and 0.1 ps, the bandwidth remains almost unchanged and close to its upper limit.

  16. Quantum-limited detection of millimeter waves using superconducting tunnel junctions

    SciTech Connect

    Mears, C.A.

    1991-09-01

    The quasiparticle tunneling current in a superconductor-insulator- superconductor (SIS) tunnel junction is highly nonlinear. Such a nonlinearity can be used to mix two millimeter wave signals to produce a signal at a much lower intermediate frequency. We have constructed several millimeter and sub-millimeter wave SIS mixers in order to study high frequency response of the quasiparticle tunneling current and the physics of high frequency mixing. We have made the first measurement of the out-of-phase tunneling currents in an SIS tunnel junction. We have developed a method that allows us to determine the parameters of the high frequency embedding circuit by studying the details of the pumped I-V curve. We have constructed a 80--110 GHz waveguide-based mixer test apparatus that allows us to accurately measure the gain and added noise of the SIS mixer under test. Using extremely high quality tunnel junctions, we have measured an added mixer noise of 0.61 {plus minus} 0.36 quanta, which is within 25 percent of the quantum limit imposed by the Heisenberg uncertainty principle. This measured performance is in excellent agreement with that predicted by Tucker's theory of quantum mixing. We have also studied quasioptically coupled millimeter- and submillimeter-wave mixers using several types of integrated tuning elements. 83 refs.

  17. Quantum-limited detection of millimeter waves using superconducting tunnel junctions

    SciTech Connect

    Mears, C.A.

    1991-09-01

    The quasiparticle tunneling current in a superconductor-insulator- superconductor (SIS) tunnel junction is highly nonlinear. Such a nonlinearity can be used to mix two millimeter wave signals to produce a signal at a much lower intermediate frequency. We have constructed several millimeter and sub-millimeter wave SIS mixers in order to study high frequency response of the quasiparticle tunneling current and the physics of high frequency mixing. We have made the first measurement of the out-of-phase tunneling currents in an SIS tunnel junction. We have developed a method that allows us to determine the parameters of the high frequency embedding circuit by studying the details of the pumped I-V curve. We have constructed a 80--110 GHz waveguide-based mixer test apparatus that allows us to accurately measure the gain and added noise of the SIS mixer under test. Using extremely high quality tunnel junctions, we have measured an added mixer noise of 0.61 {plus_minus} 0.36 quanta, which is within 25 percent of the quantum limit imposed by the Heisenberg uncertainty principle. This measured performance is in excellent agreement with that predicted by Tucker`s theory of quantum mixing. We have also studied quasioptically coupled millimeter- and submillimeter-wave mixers using several types of integrated tuning elements. 83 refs.

  18. Tunneling spectroscopy of hole plasmons in a valence-band quantum well

    SciTech Connect

    Neves, B.R.; Foster, T.J.; Eaves, L.; Main, P.C.; Henini, M.; Fisher, D.J.; Lerch, M.L.; Martin, A.D.; Zhang, C.

    1996-10-01

    We investigate the current-voltage characteristics of a {ital p}-doped resonant tunneling diode. In the voltage range slightly above the bias corresponding to resonant tunneling of holes into the first light-hole subband of the quantum well, we observe two satellite peaks which we attribute to plasmon-assisted tunneling transitions. A theoretical model is presented to account for these peaks. The model is based on the excitation of intrasubband and intersubband heavy-hole plasmons in the quantum well by hot holes injected close to the energy of the first light-hole subband. We also study the behavior of the satellites when a magnetic field is applied either parallel to or perpendicular to the current. {copyright} {ital 1996 The American Physical Society.}

  19. Controllable double tunneling induced transparency and solitons formation in a quantum dot molecule.

    PubMed

    She, Yanchao; Zheng, Xuejun; Wang, Denglong; Zhang, Weixi

    2013-07-15

    We consider the coupling effect between interdot tunneling coupling and external optical control field to study the linear optical property and the formation of temporal optical solitons in a quantum dot molecules system, analytically. The results show that the double tunneling induced transparency (TIT) windows are appeared in the absorption curve of probe field because of the formation of dynamic Stark splitting and quantum destructive interference effect from the two upper levels. Interestingly, the width of the TIT window becomes wider with the increasing intensity of the optical control field. We also find that the Kerr nonlinear effect of the probe field can be modulated effectively through coherent control both the control field and the interdot tunneling coupling in this system. Meanwhile, we demonstrate that the formation of dark or bright solitons can be practical regulated by varying the intensity of the optical control field.

  20. Quantum Tunneling Contribution for the Activation Energy in Microwave-Induced Reactions.

    PubMed

    Kuhnen, Carlos A; Dall'Oglio, Evandro L; de Sousa, Paulo T

    2017-08-03

    In this study, a quantum approach is presented to explain microwave-enhanced reaction rates by considering the tunneling effects in chemical reactions. In the Arrhenius equation, the part of the Hamiltonian relative to the interaction energy during tunneling, between the particle that tunnels and the electrical field defined in the medium, whose spatial component is specified by its rms value, is taken into account. An approximate evaluation of the interaction energy leads to a linear dependence of the effective activation energy on the applied field. The evaluation of the rms value of the field for pure liquids and reaction mixtures, through their known dielectric properties, leads to an appreciable reduction in the activation energies for the proton transfer process in these liquids. The results indicate the need to move toward the use of more refined methods of modern quantum chemistry to calculate more accurately field-induced reaction rates and effective activation energies.

  1. Charge transport model in nanodielectric composites based on quantum tunneling mechanism and dual-level traps

    SciTech Connect

    Li, Guochang; Chen, George E-mail: sli@mail.xjtu.edu.cn; Li, Shengtao E-mail: sli@mail.xjtu.edu.cn

    2016-08-08

    Charge transport properties in nanodielectrics present different tendencies for different loading concentrations. The exact mechanisms that are responsible for charge transport in nanodielectrics are not detailed, especially for high loading concentration. A charge transport model in nanodielectrics has been proposed based on quantum tunneling mechanism and dual-level traps. In the model, the thermally assisted hopping (TAH) process for the shallow traps and the tunnelling process for the deep traps are considered. For different loading concentrations, the dominant charge transport mechanisms are different. The quantum tunneling mechanism plays a major role in determining the charge conduction in nanodielectrics with high loading concentrations. While for low loading concentrations, the thermal hopping mechanism will dominate the charge conduction process. The model can explain the observed conductivity property in nanodielectrics with different loading concentrations.

  2. Deeper Look at Student Learning of Quantum Mechanics: The Case of Tunneling

    ERIC Educational Resources Information Center

    McKagan, S. B.; Perkins, K. K.; Wieman, C. E.

    2008-01-01

    We report on a large-scale study of student learning of quantum tunneling in four traditional and four transformed modern physics courses. In the transformed courses, which were designed to address student difficulties found in previous research, students still struggle with many of the same issues found in other courses. However, the reasons for…

  3. Deeper Look at Student Learning of Quantum Mechanics: The Case of Tunneling

    ERIC Educational Resources Information Center

    McKagan, S. B.; Perkins, K. K.; Wieman, C. E.

    2008-01-01

    We report on a large-scale study of student learning of quantum tunneling in four traditional and four transformed modern physics courses. In the transformed courses, which were designed to address student difficulties found in previous research, students still struggle with many of the same issues found in other courses. However, the reasons for…

  4. Re-Examining Gravitational Tunneling Radiation when taking into account Quantum Gravity Effects

    NASA Astrophysics Data System (ADS)

    Valentine, John; Prescott, Trevor; Blado, Gardo

    2015-03-01

    Although shown to theoretically exist, Hawking Radiation has yet to be detected. The paper entitled ``Gravitational Tunneling Radiation'' by Mario Rabinowitz proposed a possible explanation by considering the gravitational tunneling effects in the presence of other bodies in the vicinity of the black hole. Rabinowitz showed that the power radiated (through gravitational radiation) by a black hole,PR, is related to the power generated by Hawking Radiation, PSH by PR/T ~PSH where T is the gravitational tunneling probability. The presence of other bodies lowers the gravitational barrier which in turn increases the gravitational tunneling probability thereby decreasing the Hawking radiation, PSH. In this paper, we examine the modification of T in the presence of quantum gravity effects by incorporating the Generalized Uncertainty Principle.

  5. Optical Blocking of Electron Tunneling into a Single Self-Assembled Quantum Dot.

    PubMed

    Kurzmann, A; Merkel, B; Labud, P A; Ludwig, A; Wieck, A D; Lorke, A; Geller, M

    2016-07-01

    Time-resolved resonance fluorescence (RF) is used to analyze electron tunneling between a single self-assembled quantum dot (QD) and an electron reservoir. In equilibrium, the RF intensity reflects the average electron occupation of the QD and exhibits a gate voltage dependence that is given by the Fermi distribution in the reservoir. In the time-resolved signal, however, we find that the relaxation rate for electron tunneling is, surprisingly, independent of the occupation in the charge reservoir-in contrast to results from all-electrical transport measurements. Using a master equation approach, which includes both the electron tunneling and the optical excitation or recombination, we are able to explain the experimental data by optical blocking, which also reduces the electron tunneling rate when the QD is occupied by an exciton.

  6. Quantum tunneling of two coupled single-molecular magnets

    NASA Astrophysics Data System (ADS)

    Hu, Jianming; Chen, Zhide; Shen, Shunqing

    2003-03-01

    Jian-Ming Hu, Zhi-De Chen and Shun-Qing Shen Department of Physics, The University of Hong Kong Pokfulam Road, Hong Kong December 02, 2002 Very recently a supramolecular dimer of two single-molecule magnets (SMM) was reported to be synthesized successfully. Two single-molecule magnets are coupled antiferromagnetically to form a supramolecule dimer. We study the coupling effect and tunneling process by the numerical exact diagonalization method. The sweeping rate effect in the derivatives of hysteresis loops has been quantitatively investigated using the modified Landau-Zener model. In addiction we find that exchange coupling between the two SMMs provides a biased field to expel the tunneling between SMMs to two new resonant points via an intermediate state, and direct tunneling is prohibited. The model parameters are calculated for the dimer based on the tunneling process. The outcome indicates that the coupling effect will not change the parameters of each SMM too much at all. This work is supported by a CRCG grant of The University of Hong Kong.

  7. Time delay of wave packets during their tunnelling through a quantum diode

    SciTech Connect

    Ivanov, N A; Skalozub, V V

    2014-04-28

    A modified saddle-point method is used to investigate the process of propagation of a wave packet through a quantum diode. A scattering matrix is constructed for the structure in question. The case of tunnelling of a packet with a Gaussian envelope through the diode is considered in detail. The time delay and the shape of the wave packet transmitted are calculated. The dependence of the delay time on the characteristics of the input packet and the internal characteristics of the quantum diode is studied. Possible applications of the results obtained are discussed. (laser applications and other topics in quantum electronics)

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  9. Thermionic tunneling through Coulomb barriers in charged self-assembled quantum dots

    NASA Astrophysics Data System (ADS)

    Schramm, A.; Schulz, S.; Zander, T.; Heyn, Ch.; Hansen, W.

    2009-10-01

    The temperature and electric-field dependence of the electron emission from charged semiconductor quantum dots is studied with transient capacitance spectroscopy. The self-assembled InAs quantum dots are embedded within Schottky diodes grown with molecular-beam epitaxy on GaAs(001). In accordance with the different activation energies the emission from the s and the p shell of the quantum dots takes place with strongly different rates. In addition, the emission rates depend on the charge state of the shells. The behavior can quantitatively be understood with a thermionic-tunneling model in which the tunnel barrier is assumed to consist of a Coulomb barrier arising from the charge within the dot and a triangular contribution from remote charges.

  10. Multi-color tunneling quantum dot infrared photodetectors operating at room temperature

    NASA Astrophysics Data System (ADS)

    Ariyawansa, G.; Perera, A. G. U.; Su, X. H.; Chakrabarti, S.; Bhattacharya, P.

    2007-04-01

    Quantum dot structures designed for multi-color infrared detection and high temperature (or room temperature) operation are demonstrated. A novel approach, tunneling quantum dot (T-QD), was successfully demonstrated with a detector that can be operated at room temperature due to the reduction of the dark current by blocking barriers incorporated into the structure. Photoexcited carriers are selectively collected from InGaAs quantum dots by resonant tunneling, while the dark current is blocked by AlGaAs/InGaAs tunneling barriers placed in the structure. A two-color tunneling-quantum dot infrared photodetector (T-QDIP) with photoresponse peaks at 6 μm and 17 μm operating at room temperature will be discussed. Furthermore, the idea can be used to develop terahertz T-QD detectors operating at high temperatures. Successful results obtained for a T-QDIP designed for THz operations are presented. Another approach, bi-layer quantum dot, uses two layers of InAs quantum dots (QDs) with different sizes separated by a thin GaAs layer. The detector response was observed at three distinct wavelengths in short-, mid-, and far-infrared regions (5.6, 8.0, and 23.0 μm). Based on theoretical calculations, photoluminescence and infrared spectral measurements, the 5.6 and 23.0 μm peaks are connected to the states in smaller QDs in the structure. The narrow peaks emphasize the uniform size distribution of QDs grown by molecular beam epitaxy. These detectors can be employed in numerous applications such as environmental monitoring, spectroscopy, medical diagnosis, battlefield-imaging, space astronomy applications, mine detection, and remote-sensing.

  11. Time-dependent quantum transport through an interacting quantum dot beyond sequential tunneling: second-order quantum rate equations.

    PubMed

    Dong, B; Ding, G H; Lei, X L

    2015-05-27

    A general theoretical formulation for the effect of a strong on-site Coulomb interaction on the time-dependent electron transport through a quantum dot under the influence of arbitrary time-varying bias voltages and/or external fields is presented, based on slave bosons and the Keldysh nonequilibrium Green's function (GF) techniques. To avoid the difficulties of computing double-time GFs, we generalize the propagation scheme recently developed by Croy and Saalmann to combine the auxiliary-mode expansion with the celebrated Lacroix's decoupling approximation in dealing with the second-order correlated GFs and then establish a closed set of coupled equations of motion, called second-order quantum rate equations (SOQREs), for an exact description of transient dynamics of electron correlated tunneling. We verify that the stationary solution of our SOQREs is able to correctly describe the Kondo effect on a qualitative level. Moreover, a comparison with other methods, such as the second-order von Neumann approach and Hubbard-I approximation, is performed. As illustrations, we investigate the transient current behaviors in response to a step voltage pulse and a harmonic driving voltage, and linear admittance as well, in the cotunneling regime.

  12. Extracting inter-dot tunnel couplings between few donor quantum dots in silicon

    NASA Astrophysics Data System (ADS)

    Gorman, S. K.; Broome, M. A.; Keizer, J. G.; Watson, T. F.; Hile, S. J.; Baker, W. J.; Simmons, M. Y.

    2016-05-01

    The long term scaling prospects for solid-state quantum computing architectures relies heavily on the ability to simply and reliably measure and control the coherent electron interaction strength, known as the tunnel coupling, t c. Here, we describe a method to extract the t c between two quantum dots (QDs) utilising their different tunnel rates to a reservoir. We demonstrate the technique on a few donor triple QD tunnel coupled to a nearby single-electron transistor (SET) in silicon. The device was patterned using scanning tunneling microscopy-hydrogen lithography allowing for a direct measurement of the tunnel coupling for a given inter-dot distance. We extract {t}{{c}}=5.5+/- 1.8 {{GHz}} and {t}{{c}}=2.2+/- 1.3 {{GHz}} between each of the nearest-neighbour QDs which are separated by 14.5 nm and 14.0 nm, respectively. The technique allows for an accurate measurement of t c for nanoscale devices even when it is smaller than the electron temperature and is an ideal characterisation tool for multi-dot systems with a charge sensor.

  13. Subgap tunneling via a quantum interference effect: Insulators and charge density waves

    NASA Astrophysics Data System (ADS)

    Duhot, S.; Mélin, R.

    2007-11-01

    A quantum interference effect is discussed for subgap tunneling over a distance comparable to the coherence length, which is a consequence of “advanced-advanced” and “retarded-retarded” transmission modes [Altland and Zirnbauer, Phys. Rev. B 55, 1142 (1997)]. Effects typical of disorder are obtained from the interplay between multichannel averaging and higher order processes in the tunnel amplitudes. Quantum interference effects similar to those occurring in normal tunnel junctions explain magnetoresistance oscillations of a CDW pierced by nanoholes [Latyshev , Phys. Rev. Lett. 78, 919 (1997)], having periodicity h/2e as a function of the flux enclosed in the nanohole. Subgap tunneling is coupled to the sliding motion by charge accumulation in the interrupted chains. The effect is within the same trend as random matrix theory for normal metal-CDW hybrids [Visscher , Phys. Rev. B 62, 6873 (2000)]. We suggest that the experiment by Latyshev probes weak localizationlike properties of evanescent quasiparticles, not an interference effect related to the quantum-mechanical ground state.

  14. Size-dependent energy levels of InSb quantum dots measured by scanning tunneling spectroscopy.

    PubMed

    Wang, Tuo; Vaxenburg, Roman; Liu, Wenyong; Rupich, Sara M; Lifshitz, Efrat; Efros, Alexander L; Talapin, Dmitri V; Sibener, S J

    2015-01-27

    The electronic structure of single InSb quantum dots (QDs) with diameters between 3 and 7 nm was investigated using atomic force microscopy (AFM) and scanning tunneling spectroscopy (STS). In this size regime, InSb QDs show strong quantum confinement effects which lead to discrete energy levels on both valence and conduction band states. Decrease of the QD size increases the measured band gap and the spacing between energy levels. Multiplets of equally spaced resonance peaks are observed in the tunneling spectra. There, multiplets originate from degeneracy lifting induced by QD charging. The tunneling spectra of InSb QDs are qualitatively different from those observed in the STS of other III-V materials, for example, InAs QDs, with similar band gap energy. Theoretical calculations suggest the electron tunneling occurs through the states connected with L-valley of InSb QDs rather than through states of the Γ-valley. This observation calls for better understanding of the role of indirect valleys in strongly quantum-confined III-V nanomaterials.

  15. Resonant tunneling spectroscopy of valley eigenstates on a donor-quantum dot coupled system

    SciTech Connect

    Kobayashi, T. Heijden, J. van der; House, M. G.; Hile, S. J.; Asshoff, P.; Simmons, M. Y.; Rogge, S.; Gonzalez-Zalba, M. F.; Vinet, M.

    2016-04-11

    We report on electronic transport measurements through a silicon double quantum dot consisting of a donor and a quantum dot. Transport spectra show resonant tunneling peaks involving different valley states, which illustrate the valley splitting in a quantum dot on a Si/SiO{sub 2} interface. The detailed gate bias dependence of double dot transport allows a first direct observation of the valley splitting in the quantum dot, which is controllable between 160 and 240 μeV with an electric field dependence 1.2 ± 0.2 meV/(MV/m). A large valley splitting is an essential requirement for implementing a physical electron spin qubit in a silicon quantum dot.

  16. Transport through an impurity tunnel coupled to a Si/SiGe quantum dot

    SciTech Connect

    Foote, Ryan H. Ward, Daniel R.; Thorgrimsson, Brandur; Savage, D. E.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.; Prance, J. R.; Gamble, John King; Nielsen, Erik; Saraiva, A. L.

    2015-09-07

    Achieving controllable coupling of dopants in silicon is crucial for operating donor-based qubit devices, but it is difficult because of the small size of donor-bound electron wavefunctions. Here, we report the characterization of a quantum dot coupled to a localized electronic state and present evidence of controllable coupling between the quantum dot and the localized state. A set of measurements of transport through the device enable the determination that the most likely location of the localized state is consistent with a location in the quantum well near the edge of the quantum dot. Our results are consistent with a gate-voltage controllable tunnel coupling, which is an important building block for hybrid donor and gate-defined quantum dot devices.

  17. Which Is Better at Predicting Quantum-Tunneling Rates: Quantum Transition-State Theory or Free-Energy Instanton Theory?

    PubMed

    Zhang, Yanchuan; Stecher, Thomas; Cvitaš, Marko T; Althorpe, Stuart C

    2014-11-20

    Quantum transition-state theory (QTST) and free-energy instanton theory (FEIT) are two closely related methods for estimating the quantum rate coefficient from the free-energy at the reaction barrier. In calculations on one-dimensional models, FEIT typically gives closer agreement than QTST with the exact quantum results at all temperatures below the crossover to deep tunneling, suggesting that FEIT is a better approximation than QTST in this regime. Here we show that this simple trend does not hold for systems of greater dimensionality. We report tests on several collinear and three-dimensional reactions, in which QTST outperforms FEIT over a range of temperatures below crossover, which can extend down to half the crossover temperature (below which FEIT outperforms QTST). This suggests that QTST-based methods such as ring-polymer molecular dynamics (RPMD) may often give closer agreement with the exact quantum results than FEIT.

  18. The effects of two-dimensional bifurcations and quantum beats in a system of combined atomic force and scanning tunneling microscopes with quantum dots

    NASA Astrophysics Data System (ADS)

    Zhukovsky, V. Ch.; Krevchik, V. D.; Semenov, M. B.; Krevchik, P. V.; Zaytsev, R. V.; Egorov, I. A.

    2016-11-01

    The field and temperature dependence of the probability of two-dimensional dissipative tunneling is studied in the framework of one-instanton approximation for a model double-well oscillator potential in an external electric field at finite temperature with account for the influence of two local phonon modes for quantum dots in a system of a combined atomic force and a scanning tunneling microscope. It is demonstrated that in the mode of synchronous parallel transfer of tunneling particles from the cantilever tip to the quantum dot the two local phonon modes result in the occurrence of two stable peaks in the curve of the 2D dissipative tunneling probability as a function of the field. Qualitative comparison of the theoretical curve in the limit of weak dissociation and the experimental current-voltage characteristic for quantum dots that grow from colloidal gold under a cantilever tip at the initial stage of quantum-dot formation when the quantum dot size does not exceed 10 nm is performed. It is established that one of the two stable peaks that correspond to interaction of tunneling particles with two local phonon modes in the temperature dependence of the 2D dissipative tunneling probability can be split in two, which corresponds to the tunneling channel interference mechanism. It is found that the theoretically predicted and experimentally observed mode of quantum beats occurs near the bifurcation point.

  19. Ultrafast spin tunneling and injection in coupled nanostructures of InGaAs quantum dots and quantum well

    SciTech Connect

    Yang, Xiao-Jie Kiba, Takayuki; Yamamura, Takafumi; Takayama, Junichi; Subagyo, Agus; Sueoka, Kazuhisa; Murayama, Akihiro

    2014-01-06

    We investigate the electron-spin injection dynamics via tunneling from an In{sub 0.1}Ga{sub 0.9}As quantum well (QW) to In{sub 0.5}Ga{sub 0.5}As quantum dots (QDs) in coupled QW-QDs nanostructures. These coupled nanostructures demonstrate ultrafast (5 to 20 ps) spin injection into the QDs. The degree of spin polarization up to 45% is obtained in the QDs after the injection, essentially depending on the injection time. The spin injection and conservation are enhanced with thinner barriers due to the stronger electronic coupling between the QW and QDs.

  20. Quantum Coherent Atomic Tunneling between Two Trapped Bose-Einstein Condensates

    SciTech Connect

    Smerzi, A.; Fantoni, S.; Giovanazzi, S.

    1997-12-01

    We study the coherent atomic tunneling between two zero-temperature Bose-Einstein condensates (BEC) confined in a double-well magnetic trap. Two Gross-Pitaevskii equations for the self-interacting BEC amplitudes, coupled by a transfer matrix element, describe the dynamics in terms of the interwell phase difference and population imbalance. In addition to the anharmonic generalization of the familiar ac Josephson effect and plasma oscillations occurring in superconductor junctions, the nonlinear BEC tunneling dynamics sustains a self-maintained population imbalance: a novel {open_quotes}macroscopic quantum self-trapping{close_quotes} effect. {copyright} {ital 1997} {ital The American Physical Society}

  1. Limitation of tunneling between edge states by a mesoscopic island in narrow quantum Hall conductors

    NASA Astrophysics Data System (ADS)

    Liu, Z. H.; Nachtwei, G.; Groß, J.; Gerhardts, R. R.; Weis, J.; von Klitzing, K.; Eberl, K.

    1998-12-01

    We observed current plateaus in the I- V characteristics of Corbino or quasi-Corbino devices with a narrow constriction, containing a mesoscopic island, in the quantum Hall regime. We investigated the features of the current plateaus for different filling factors, island sizes and orientations. A qualitative physical picture including the quasi-elastic inter-Landau-level tunneling and the limitation of tunneling current due to charging of the nonequilibrium electron states around the island is proposed to explain the current plateau phenomenon.

  2. Electronic states of InAs/GaAs quantum dots by scanning tunneling spectroscopy

    SciTech Connect

    Gaan, S.; He, Guowei; Feenstra, R. M.; Walker, J.; Towe, E.

    2010-09-20

    InAs/GaAs quantum-dot (QD) heterostructures grown by molecular-beam epitaxy are studied using cross-sectional scanning tunneling microscopy and spectroscopy. Individual InAs QDs are resolved in the images. Tunneling spectra acquired 3-4 nm from the QDs show a peak located in the upper part of the GaAs band gap originating from the lowest electron confined state, together with a tail extending out from the valence band from hole confined states. A line-shape analysis is used to deduce the binding energies of the electron and hole QD states.

  3. Piezoelectric polarization and quantum size effects on the vertical transport in AlGaN/GaN resonant tunneling diodes

    NASA Astrophysics Data System (ADS)

    H, Dakhlaoui; S, Almansour

    2016-06-01

    In this work, the electronic properties of resonant tunneling diodes (RTDs) based on GaN-Al x Ga(1-x)N double barriers are investigated by using the non-equilibrium Green functions formalism (NEG). These materials each present a wide conduction band discontinuity and a strong internal piezoelectric field, which greatly affect the electronic transport properties. The electronic density, the transmission coefficient, and the current-voltage characteristics are computed with considering the spontaneous and piezoelectric polarizations. The influence of the quantum size on the transmission coefficient is analyzed by varying GaN quantum well thickness, Al x Ga(1-x)N width, and the aluminum concentration x Al. The results show that the transmission coefficient more strongly depends on the thickness of the quantum well than the barrier; it exhibits a series of resonant peaks and valleys as the quantum well width increases. In addition, it is found that the negative differential resistance (NDR) in the current-voltage (I-V) characteristic strongly depends on aluminum concentration x Al. It is shown that the peak-to-valley ratio (PVR) increases with x Al value decreasing. These findings open the door for developing vertical transport nitrides-based ISB devices such as THz lasers and detectors. Project supported by the Deanship of Scientific Research of University of Dammam (Grant No. 2014137).

  4. Luminescence of Quantum Dots by Coupling with Nonradiative Surface Plasmon Modes in a Scanning Tunneling Microscope

    SciTech Connect

    Romero, M. J.; van de Lagemaat, J.

    2009-01-01

    The electronic coupling between quantum dots (QDs) and surface plasmons (SPs) is investigated by a luminescence spectroscopy based on scanning tunneling microscopy (STM). We show that tunneling luminescence from the dot is excited by coupling with the nonradiative plasmon mode oscillating at the metallic tunneling gap formed during the STM operation. This approach to the SP excitation reveals aspects of the SP-QD coupling not accessible to the more conventional optical excitation of SPs. In the STM, luminescence from the dot is observed when and only when the SP is in resonance with the fundamental transition of the dot. The tunneling luminescence spectrum also suggests that excited SP-QD hybrid states can participate in the excitation of QD luminescence. Not only the SP excitation regulates the QD luminescence but the presence of the dot at the tunneling gap imposes restrictions to the SP that can be excited in the STM, in which the SP cannot exceed the energy of the fundamental transition of the dot. The superior SP-QD coupling observed in the STM is due to the tunneling gap acting as a tunable plasmonic resonator in which the dot is fully immersed.

  5. The impact of disorder on charge transport in three dimensional quantum dot resonant tunneling structures

    SciTech Connect

    Puthen-Veettil, B. Patterson, R.; König, D.; Conibeer, G.; Green, M. A.

    2014-10-28

    Efficient iso-entropic energy filtering of electronic waves can be realized through nanostructures with three dimensional confinement, such as quantum dot resonant tunneling structures. Large-area deployment of such structures is useful for energy selective contacts but such configuration is susceptible to structural disorders. In this work, the transport properties of quantum-dot-based wide-area resonant tunneling structures, subject to realistic disorder mechanisms, are studied. Positional variations of the quantum dots are shown to reduce the resonant transmission peaks while size variations in the device are shown to reduce as well as broaden the peaks. Increased quantum dot size distribution also results in a peak shift to lower energy which is attributed to large dots dominating transmission. A decrease in barrier thickness reduces the relative peak height while the overall transmission increases dramatically due to lower “series resistance.” While any shift away from ideality can be intuitively expected to reduce the resonance peak, quantification allows better understanding of the tolerances required for fabricating structures based on resonant tunneling phenomena/.

  6. S-Matrix and Quantum Tunneling in Gravitational Collapse

    NASA Astrophysics Data System (ADS)

    Ciafaloni, Marcello; Colferai, Dimitri

    Using the recently introduced ACV reduced-action approach to transplanckian scattering of light particles, we show that the S-matrix in the region of classical gravitational collapse is related to a tunneling amplitude in an effective field space. The resulting model exhibits some non-unitary S-matrix eigenvalues for parameters b < bc, a critical value of the order of the gravitational radius R = 2G√ s, thus showing that some (inelastic)unitarity defect is generally present, and can be studied quantitatively.

  7. Nonlinear tunneling of Bose-Einstein condensates in an optical lattice: Signatures of quantum collapse and revival

    SciTech Connect

    Shchesnovich, V. S.; Konotop, V. V.

    2007-06-15

    Quantum theory of the intraband resonant tunneling of a Bose-Einstein condensate loaded in a two-dimensional optical lattice is considered. It is shown that the phenomena of quantum collapse and revival can be observed in the fully quantum problem. The mean-field limit of the theory is analyzed using the WKB approximation for discrete equations, establishing in this way a direct connection between the two approaches conventionally used in very different physical contexts. More specifically we show that there exist two different regimes of tunneling and study dependence of quantum collapse and revival on the number of condensed atoms.

  8. Optical precursors with tunneling-induced transparency in asymmetric quantum wells

    NASA Astrophysics Data System (ADS)

    Peng, Yandong; Niu, Yueping; Qi, Yihong; Yao, Haifeng; Gong, Shangqing

    2011-01-01

    A scheme for separating optical precursors from a square-modulated laser pulse through an asymmetric double AlxGa1-xAs/GaAs quantum-well structure via resonant tunneling is proposed. Destructive interference inhibits linear absorption, and a tunneling-induced transparency (TIT) window appears with normal dispersion, which delays the main pulse; then optical precursors are obtained. Due to resonant tunneling, constructive interference for nonlinear susceptibility is created. The enhanced dispersion in a narrow TIT window is about one order of magnitude larger than that of the linear case. In this case, the main pulse is much delayed and the precursor signals are easier to obtain. Moreover, the main pulse builds up due to the gain introduced by the enhanced cross-nonlinearity.

  9. Zero-bias anomalies in narrow tunnel junctions in the quantum Hall regime.

    PubMed

    Jiang, P; Chien, C-C; Yang, I; Kang, W; Baldwin, K W; Pfeiffer, L N; West, K W

    2010-12-10

    We report on the study of cleaved-edge-overgrown line junctions with a serendipitously created narrow opening in an otherwise thin, precise line barrier. Two sets of zero-bias anomalies are observed with an enhanced conductance for filling factors ν>1 and a strongly suppressed conductance for ν<1. A transition between the two behaviors is found near ν≈1. The zero-bias anomaly (ZBA) line shapes find explanation in Luttinger liquid models of tunneling between quantum Hall edge states. The ZBA for ν<1 occurs from strong backscattering induced by suppression of quasiparticle tunneling between the edge channels for the n=0 Landau levels. The ZBA for ν>1 arises from weak tunneling of quasiparticles between the n=1 edge channels.

  10. Quantum Tunneling Rates of Gas-Phase Reactions from On-the-Fly Instanton Calculations.

    PubMed

    Beyer, Adrian N; Richardson, Jeremy O; Knowles, Peter J; Rommel, Judith; Althorpe, Stuart C

    2016-11-03

    The instanton method obtains approximate tunneling rates from the minimum-action path (known as the instanton) linking reactants to the products at a given temperature. An efficient way to find the instanton is to search for saddle-points on the ring-polymer potential surface, which is obtained by expressing the quantum Boltzmann operator as a discrete path-integral. Here we report a practical implementation of this ring-polymer form of instanton theory into the Molpro electronic-structure package, which allows the rates to be computed on-the-fly, without the need for a fitted analytic potential-energy surface. As a test case, we compute tunneling rates for the benchmark H + CH4 reaction, showing how the efficiency of the instanton method allows the user systematically to converge the tunneling rate with respect to the level of electronic-structure theory.

  11. Quasiparticle Tunneling in the Fractional Quantum Hall effect at filling fraction ν=5/2

    NASA Astrophysics Data System (ADS)

    Radu, Iuliana P.

    2009-03-01

    In a two-dimensional electron gas (2DEG), in the fractional quantum Hall regime, the quasiparticles are predicted to have fractional charge and statistics, as well as modified Coulomb interactions. The state at filling fraction ν=5/2 is predicted by some theories to have non-abelian statistics, a property that might be exploited for topological quantum computing. However, alternative models with abelian properties have been proposed as well. Weak quasiparticle tunneling between counter-propagating edges is one of the methods that can be used to learn about the properties of the state and potentially distinguish between models describing it. We employ an electrostatically defined quantum point contact (QPC) fabricated on a high mobility GaAs/AlGaAs 2DEG to create a constriction where quasiparticles can tunnel between counter-propagating edges. We study the temperature and dc bias dependence of the tunneling conductance, while preserving the same filling fraction in the constriction and the bulk of the sample. The data show scaling of the bias-dependent tunneling over a range of temperatures, in agreement with the theory of weak quasiparticle tunneling, and we extract values for the effective charge and interaction parameter of the quasiparticles. The ranges of values obtained are consistent with those predicted by certain models describing the 5/2 state, indicating as more probable a non-abelian state. This work was done in collaboration with J. B. Miller, C. M. Marcus, M. A. Kastner, L. N. Pfeiffer and K. W. West. This work was supported in part by the Army Research Office (W911NF-05-1-0062), the Nanoscale Science and Engineering Center program of NSF (PHY-0117795), NSF (DMR-0701386), the Center for Materials Science and Engineering program of NSF (DMR-0213282) at MIT, the Microsoft Corporation Project Q, and the Center for Nanoscale Systems at Harvard University.

  12. Spin dynamics and magneto-optical response in charge-neutral tunnel-coupled quantum dots

    NASA Astrophysics Data System (ADS)

    Gawełczyk, Michał; Machnikowski, Paweł

    2017-04-01

    We model the electron and hole spin dynamics in an undoped double quantum dot structure, considering the carrier tunneling between quantum dots. Taking the presence of an additional in-plane or tilted magnetic field into account, we enable the simulation of magneto-optical experiments, like the time-resolved Kerr rotation measurement, which are currently performed on such structures to probe the temporal spin dynamics. With our model, we reproduce the experimentally observed effect of the extension of the spin polarization lifetime caused by spatial charge separation, which may occur in structures of this type. Moreover, we provide a number of qualitative predictions concerning the necessary conditions for observation of this effect as well as about possible channels of its suppression, including the spin-orbit coupling, which leads to tunneling of carriers accompanied by a spin flip. We also consider the impact of the magnetic field tilting, which results in an interesting spin polarization dynamics.

  13. Klein tunnelling and electron trapping in nanometre-scale graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Gutiérrez, Christopher; Brown, Lola; Kim, Cheol-Joo; Park, Jiwoong; Pasupathy, Abhay N.

    2016-11-01

    Relativistic fermions that are incident on a high potential barrier can pass through unimpeded, a striking phenomenon termed the `Klein paradox’ in quantum electrodynamics. Electrostatic potential barriers in graphene provide a solid-state analogue to realize this phenomenon. Here, we use scanning tunnelling microscopy to directly probe the transmission of electrons through sharp circular potential wells in graphene created by substrate engineering. We find that electrons in this geometry display quasi-bound states where the electron is trapped for a finite time before escaping via Klein tunnelling. We show that the continuum Dirac equation can be successfully used to model the energies and wavefunctions of these quasi-bound states down to atomic dimensions. We demonstrate that by tuning the geometry of the barrier it is possible to trap particular energies and angular momentum states with increased efficiency, showing that atomic-scale electrostatic potentials can be used to engineer quantum transport through graphene.

  14. Manipulation of tunneling induced transparency windows and optical switching features in fivefold quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Hamedi, H. R.; Reza Mehmannavaz, Mohammad

    2015-09-01

    Transient and steady-state behavior of the probe absorption in a multiple quantum dot (QD) molecule composed of five quantum dots molecules (with a center dot and four satellite dots) is explored with application in all-optical switching. We find that the absorption spectra of the light pulse can be efficiently modified via the effect of inter-dot tunnel couplings of QDs and incoherent pumping field. Results show that depending on the values of system parameters, at least one and at most four tunneling induced transparency (TIT) windows can be established in the multiple QD medium. We then investigate the dynamical behavior of the probe absorption-amplification as well as the optical switching in pulsed regime. By adjusting the incoherent pumping rate, the required switching time for changing the gain to the absorption or vice versa is then estimated approximately to be 20.7 nanosecond (ns), that is an appropriate time for such a QDM-based switch.

  15. Infra-red tunneling absorption in semiconductor double quantum wells in tilted magnetic fields

    SciTech Connect

    Lyo, S.K.

    1996-12-31

    Using a linear response theory, interwell-tunneling absorption is calculated in a double-quantum-well structure with a wide center barrier in tilted magnetic fields. Tunneling absorption of infra-red photons occurs between the ground sublevels of the two quantum wells, with an energy difference that is tunable. In zero magnetic field, the absorption intensity decreases significantly as the linewidth increases with temperature. The absorption also depends strongly on the carrier densities of the wells. In magnetic fields, both the in-plane and perpendicular components of the field sensitively control and tune the absorption lineshape in very different ways, affecting the absorption threshold, the resonance energy of absorption, and the linewidth.

  16. Reversal of the circulation of a vortex by quantum tunneling in trapped Bose systems

    SciTech Connect

    Watanabe, Gentaro; Pethick, C. J.

    2007-08-15

    We study the quantum dynamics of a model for a vortex in a Bose gas with repulsive interactions in an anisotropic, harmonic trap. By solving the Schroedinger equation numerically, we show that the circulation of the vortex can undergo periodic reversals by quantum-mechanical tunneling. With increasing interaction strength or particle number, vortices become increasingly stable, and the period for reversals increases. Tunneling between vortex and antivortex states is shown to be described to a good approximation by a superposition of vortex and antivortex states (Schroedinger cat state), rather than the mean-field state, and we derive an analytical expression for the oscillation period. The problem is shown to be equivalent to that of the two-site Bose-Hubbard model with attractive interactions.

  17. Tunneling-induced giant Goos-Hänchen shift in quantum wells.

    PubMed

    Yang, Wen-Xing; Liu, Shaopeng; Zhu, Zhonghu; Ziauddin; Lee, Ray-Kuang

    2015-07-01

    Tunneling-induced quantum interference experienced by an incident probe in the asymmetric double AlGaAs/GaAs quantum well (QW) structure can be modulated by means of an external control light beam and the tunable coupling strengths of resonant tunneling. These phenomena can be exploited to devise a novel intracavity medium to control Goos-Hänchen (GH) shifts of a mid-infrared probe beam incident on a cavity. For a suitably designed QW structure, our results show that maximum negative shift of 2.62 mm and positive shift of 0.56 mm are achievable for GH shifts in the reflected and transmitted light.

  18. I-V and Differential Conduction Characteristics of an AlGaAs/GaAs Lateral Quantum Dot Infrared Photodetector

    NASA Astrophysics Data System (ADS)

    Guidry, D. H.; Morath, C. P.; Cowan, V. M.; Cardimona, D. A.

    2012-10-01

    A new infrared detector design, henceforth referred to as a lateral quantum dot infrared photodetector (LQDIP), with the potential for a tunable internal spectral response was investigated. In this design, InAs quantum dots are buried in a GaAs quantum well, which is in turn tunnel-coupled to a second GaAs quantum well. Photoexcited electrons from the quantum dots are expected to tunnel over to the second well, where they are then swept out via a lateral (perpendicular to the growth direction) bias voltage. The lateral photocurrent is in part directed to tunnel into the second quantum well by the depletion field of a narrow pinch-off gate, applied vertically (parallel to the growth direction). Under a proper biasing arrangement, this detector architecture is expected to exhibit the ability to tune to select infrared frequencies as well as operate with reduced dark currents and unity gain in the second well. The LQDIP detector architecture, operating principles and conditions, and preliminary results of I- V, photocurrent, and differential conductance measurements are all discussed.

  19. Conversion efficiency of an energy harvester based on resonant tunneling through quantum dots with heat leakage

    NASA Astrophysics Data System (ADS)

    Kano, Shinya; Fujii, Minoru

    2017-03-01

    We study the conversion efficiency of an energy harvester based on resonant tunneling through quantum dots with heat leakage. Heat leakage current from a hot electrode to a cold electrode is taken into account in the analysis of the harvester operation. Modeling of electrical output indicates that a maximum heat leakage current is not negligible because it is larger than that of the heat current harvested into electrical power. A reduction of heat leakage is required in this energy harvester in order to obtain efficient heat-to-electrical conversion. Multiple energy levels of a quantum dot can increase the output power of the harvester. Heavily doped colloidal semiconductor quantum dots are a possible candidate for a quantum-dot monolayer in the energy harvester to reduce heat leakage, scaling down device size, and increasing electrical output via multiple discrete energy levels.

  20. Conversion efficiency of an energy harvester based on resonant tunneling through quantum dots with heat leakage.

    PubMed

    Kano, Shinya; Fujii, Minoru

    2017-03-03

    We study the conversion efficiency of an energy harvester based on resonant tunneling through quantum dots with heat leakage. Heat leakage current from a hot electrode to a cold electrode is taken into account in the analysis of the harvester operation. Modeling of electrical output indicates that a maximum heat leakage current is not negligible because it is larger than that of the heat current harvested into electrical power. A reduction of heat leakage is required in this energy harvester in order to obtain efficient heat-to-electrical conversion. Multiple energy levels of a quantum dot can increase the output power of the harvester. Heavily doped colloidal semiconductor quantum dots are a possible candidate for a quantum-dot monolayer in the energy harvester to reduce heat leakage, scaling down device size, and increasing electrical output via multiple discrete energy levels.

  1. Scanning tunneling spectroscopy of lead sulfide quantum wells fabricated by atomic layer deposition

    SciTech Connect

    Lee, W. J.; Dasgupta, N. P.; Jung, H. J.; Lee, J. R.; Sinclair, R.; Prinz, F. B.

    2010-11-10

    We report the use of scanning tunneling spectroscopy (STS) to investigate one-dimensional quantum confinement effects in lead sulfide (PbS) thin films. Specifically, quantum confinement effects on the band gap of PbS quantum wells were explored by controlling the PbS film thickness and potential barrier height. PbS quantum well structures with a thickness range of 1–20 nm were fabricated by atomic layer deposition (ALD). Two barrier materials were selected based on barrier height: aluminum oxide as a high barrier material and zinc oxide as a low barrier material. Band gap measurements were carried out by STS, and an effective mass theory was developed to compare the experimental results. Our results show that the band gap of PbS thin films increased as the film thickness decreased, and the barrier height increased from 0.45 to 2.19 eV.

  2. Interaction of Single Electron Tunneling and Collective Modes in Quantum Dot Matter

    NASA Astrophysics Data System (ADS)

    Stopa, Michael

    1996-03-01

    We consider arrays of N^d quantum dots in d dimensions coupled by tunnel junctions and we define the limit of N arrow ∞ as ``quantum dot matter'' (QDM). For d=1 QDM we determine the dispersion relation for collective oscillations of the junction charges by ascribing a capacitance to ground and two small internal inductances to each dot. We consider the influence of this electromagnetic environment on single electron tunneling (SET). This differs from the standard treatment (G. -L. Ingold and Yu. V. Nazarov in Single Charge Tunneling), edited by H. Grabert and M. H. Devoret, NATO ASI, Ser. B (Plenum Press, New York, 1992), Chap. 2 where electrons in an array are assumed to be isolated from the environment by the presence of other junctions and tunneling is assumed to be between equilibrium charge states. We compute the junction charge fluctuation <δ Q_k^2> and show that, as in the single junction case, charging effects are suppressed by the environment. Finally, we consider modifications to the ``global rule'' from the finite speed of electromagnetic waves in QDM.

  3. Nuclear magnetic resonance studies of tunneling in quantum solids at very low temperatures.

    PubMed

    Sullivan, N S

    2015-11-01

    A review is given of recent NMR experiments at ultra-low temperatures that explore properties of quantum fluids and solids in regimes where unusual dynamics characterizes the low temperature behavior. It is shown how careful analysis of the NMR spin-spin and spin-lattice relaxation rates and spectral properties can determine fundamental thermodynamic features that are otherwise difficult to observe using standard thermodynamic methods. The review focuses on the observation of the diffusion of vacancies and isotopic impurities in solid hydrogen and solid helium by quantum tunneling at low temperatures. Copyright © 2015 Elsevier B.V. All rights reserved.

  4. Improved WKB approximation for quantum tunneling: Application to heavy-ion fusion

    NASA Astrophysics Data System (ADS)

    Toubiana, A. J.; Canto, L. F.; Hussein, M. S.

    2017-02-01

    In this paper we revisit the one-dimensional tunnelling problem. We consider Kemble's approximation for the transmission coefficient. We show how this approximation can be extended to above-barrier energies by performing the analytical continuation of the radial coordinate to the complex plane. We investigate the validity of this approximation by comparing their predictions for the cross section and for the barrier distribution with the corresponding quantum-mechanical results. We find that the extended Kemble's approximation reproduces the results of quantum mechanics with great accuracy.

  5. Multi-Dimensional Quantum Tunneling and Transport Using the Density-Gradient Model

    NASA Technical Reports Server (NTRS)

    Biegel, Bryan A.; Yu, Zhi-Ping; Ancona, Mario; Rafferty, Conor; Saini, Subhash (Technical Monitor)

    1999-01-01

    We show that quantum effects are likely to significantly degrade the performance of MOSFETs (metal oxide semiconductor field effect transistor) as these devices are scaled below 100 nm channel length and 2 nm oxide thickness over the next decade. A general and computationally efficient electronic device model including quantum effects would allow us to monitor and mitigate these effects. Full quantum models are too expensive in multi-dimensions. Using a general but efficient PDE solver called PROPHET, we implemented the density-gradient (DG) quantum correction to the industry-dominant classical drift-diffusion (DD) model. The DG model efficiently includes quantum carrier profile smoothing and tunneling in multi-dimensions and for any electronic device structure. We show that the DG model reduces DD model error from as much as 50% down to a few percent in comparison to thin oxide MOS capacitance measurements. We also show the first DG simulations of gate oxide tunneling and transverse current flow in ultra-scaled MOSFETs. The advantages of rapid model implementation using the PDE solver approach will be demonstrated, as well as the applicability of the DG model to any electronic device structure.

  6. Fabrication and characterization of low loss and high inductance Josephson tunnel junction chains for quantum circuits

    NASA Astrophysics Data System (ADS)

    Grabon, Nicholas; Solovyeva, Natalya; Nguyen, Long; Lin, Yen-Hsiang; Manucharyan, Vladimir

    Linear chains of tightly packed Josephson junctions can realize a very high kinetic inductance circuit element, superinductance, with minimal losses. Superinductance is used in a conventional fluxonium qubit, but it has also been put forward as a key element of a fault-tolerant quantum circuits toolbox. We report fabrication and microwave characterization of linear Al/AlOx/Al Josephson tunnel junction chains and discuss their advantages and limitations as superinductors

  7. Negative differential resistance in GaN tunneling hot electron transistors

    SciTech Connect

    Yang, Zhichao; Nath, Digbijoy; Rajan, Siddharth

    2014-11-17

    Room temperature negative differential resistance is demonstrated in a unipolar GaN-based tunneling hot electron transistor. Such a device employs tunnel-injected electrons to vary the electron energy and change the fraction of reflected electrons, and shows repeatable negative differential resistance with a peak to valley current ratio of 7.2. The device was stable when biased in the negative resistance regime and tunable by changing collector bias. Good repeatability and double-sweep characteristics at room temperature show the potential of such device for high frequency oscillators based on quasi-ballistic transport.

  8. Quantum tunnelling and charge accumulation in organic ferroelectric memory diodes

    NASA Astrophysics Data System (ADS)

    Ghittorelli, Matteo; Lenz, Thomas; Sharifi Dehsari, Hamed; Zhao, Dong; Asadi, Kamal; Blom, Paul W. M.; Kovács-Vajna, Zsolt M.; de Leeuw, Dago M.; Torricelli, Fabrizio

    2017-06-01

    Non-volatile memories--providing the information storage functionality--are crucial circuit components. Solution-processed organic ferroelectric memory diodes are the non-volatile memory candidate for flexible electronics, as witnessed by the industrial demonstration of a 1 kbit reconfigurable memory fabricated on a plastic foil. Further progress, however, is limited owing to the lack of understanding of the device physics, which is required for the technological implementation of high-density arrays. Here we show that ferroelectric diodes operate as vertical field-effect transistors at the pinch-off. The tunnelling injection and charge accumulation are the fundamental mechanisms governing the device operation. Surprisingly, thermionic emission can be disregarded and the on-state current is not space charge limited. The proposed model explains and unifies a wide range of experiments, provides important design rules for the implementation of organic ferroelectric memory diodes and predicts an ultimate theoretical array density of up to 1012 bit cm-2.

  9. Quantum tunneling at zero temperature in the strong friction regime.

    PubMed

    Bolivar, A O

    2005-01-21

    In the large damping limit we derive a Fokker-Planck equation in configuration space (the so-called Smoluchowski equation) describing a Brownian particle immersed into a thermal environment and subjected to a nonlinear external force. We quantize this stochastic system and survey the problem of escape over a double-well potential barrier. Our finding is that the quantum Kramers rate does not depend on the friction coefficient at low temperatures; i.e., we predict a superfluidity phenomenon in overdamped open systems. Moreover, at zero temperature we show that the quantum escape rate does not vanish in the strong friction regime. This result, therefore, is in contrast with the work by Ankerhold et al. [Phys. Rev. Lett. 87, 086802 (2001)

  10. Differential evolution for many-particle adaptive quantum metrology.

    PubMed

    Lovett, Neil B; Crosnier, Cécile; Perarnau-Llobet, Martí; Sanders, Barry C

    2013-05-31

    We devise powerful algorithms based on differential evolution for adaptive many-particle quantum metrology. Our new approach delivers adaptive quantum metrology policies for feedback control that are orders-of-magnitude more efficient and surpass the few-dozen-particle limitation arising in methods based on particle-swarm optimization. We apply our method to the binary-decision-tree model for quantum-enhanced phase estimation as well as to a new problem: a decision tree for adaptive estimation of the unknown bias of a quantum coin in a quantum walk and show how this latter case can be realized experimentally.

  11. Quantum force of tunneling macrospins with a mechanical resonator

    NASA Astrophysics Data System (ADS)

    Kim, Gwang-Hee

    2017-09-01

    We study force dynamics of macropsin of molecular magnets coupled to a torsional resonator. In the presence of an ac field and a static field with a gradient, the force is shown to display various types of quantum oscillations which depend upon the coupling strength and the frequency of torsional oscillations. Optimal conditions for observing them will be discussed within the framework of experimentally controllable parameters.

  12. Quantum dynamics of tunneling dominated reactions at low temperatures

    NASA Astrophysics Data System (ADS)

    Hazra, Jisha; Balakrishnan, N.

    2015-05-01

    We report a quantum dynamics study of the Li + HF → LiF + H reaction at low temperatures of interest to cooling and trapping experiments. Contributions from non-zero partial waves are analyzed and results show narrow resonances in the energy dependence of the cross section that survive partial wave summation. The computations are performed using the ABC code and a simple modification of the ABC code that enables separate energy cutoffs for the reactant and product rovibrational energy levels is found to dramatically reduce the basis set size and computational expense. Results obtained using two ab initio electronic potential energy surfaces for the LiHF system show strong sensitivity to the choice of the potential. In particular, small differences in the barrier heights of the two potential surfaces are found to dramatically influence the reaction cross sections at low energies. Comparison with recent measurements of the reaction cross section (Bobbenkamp et al 2011 J. Chem. Phys. 135 204306) shows similar energy dependence in the threshold regime and an overall good agreement with experimental data compared to previous theoretical results. Also, usefulness of a recently introduced method for ultracold reactions that employ the quantum close-coupling method at short-range and the multichannel quantum defect theory at long-range, is demonstrated in accurately evaluating product state-resolved cross sections for D + H2 and H + D2 reactions.

  13. Student Understanding of Tunneling in Quantum Mechanics: Examining Interview and Survey Results for Clues to Student Reasoning

    NASA Astrophysics Data System (ADS)

    Morgan, Jeffrey T.; Wittmann, Michael C.; Thompson, John R.

    2004-09-01

    Members of the University of Maine Physics Education Research Laboratory are studying student understanding of the phenomenon of quantum tunneling through a potential barrier, a standard topic in most introductory quantum physics courses. When a series of interviews revealed that many students believe energy is lost in the tunneling process, a survey was designed to investigate the prevalence of the energy-loss idea. This survey was administered to populations of physics majors at the sophomore and senior levels. Data indicate that interview results are shared by a somewhat larger population of students and give insight into additional models of reasoning (e.g. analogies to macroscopic tunnels) not found in the interviews.

  14. Elastic tunneling charge transport mechanisms in silicon quantum dots /SiO{sub 2} thin films and superlattices

    SciTech Connect

    Illera, S. Prades, J. D.; Cirera, A.

    2015-05-07

    The role of different charge transport mechanisms in Si/SiO{sub 2} structures has been studied. A theoretical model based on the Transfer Hamiltonian Formalism has been developed to explain experimental current trends in terms of three different elastic tunneling processes: (1) trap assisted tunneling; (2) transport through an intermediate quantum dot; and (3) direct tunneling between leads. In general, at low fields carrier transport is dominated by the quantum dots whereas, for moderate and high fields, transport through deep traps inherent to the SiO{sub 2} is the most relevant process. Besides, current trends in Si/SiO{sub 2} superlattice structure have been properly reproduced.

  15. Quantum-Like Tunnelling and Levels of Arbitrage

    NASA Astrophysics Data System (ADS)

    Haven, Emmanuel; Khrennikov, Andrei

    2013-11-01

    We apply methods of wave mechanics to financial modelling. We proceed by assigning a financial interpretation to wave numbers. This paper makes a plea for the use of the concept of ‘tunnelling’ (in the mathematical formalism of quantum mechanics) in the modelling of financial arbitrage. Financial arbitrage is a delicate concept to model in social science (i.e. in this case economics and finance) as its presence affects the precision of benchmark financial asset prices. In this paper, we attempt to show how ‘tunnelling’ can be used to positive effect in the modelling of arbitrage in a financial asset pricing context.

  16. Advanced-Retarded Differential Equations in Quantum Photonic Systems

    NASA Astrophysics Data System (ADS)

    Alvarez-Rodriguez, Unai; Perez-Leija, Armando; Egusquiza, Iñigo L.; Gräfe, Markus; Sanz, Mikel; Lamata, Lucas; Szameit, Alexander; Solano, Enrique

    2017-02-01

    We propose the realization of photonic circuits whose dynamics is governed by advanced-retarded differential equations. Beyond their mathematical interest, these photonic configurations enable the implementation of quantum feedback and feedforward without requiring any intermediate measurement. We show how this protocol can be applied to implement interesting delay effects in the quantum regime, as well as in the classical limit. Our results elucidate the potential of the protocol as a promising route towards integrated quantum control systems on a chip.

  17. Advanced-Retarded Differential Equations in Quantum Photonic Systems

    PubMed Central

    Alvarez-Rodriguez, Unai; Perez-Leija, Armando; Egusquiza, Iñigo L.; Gräfe, Markus; Sanz, Mikel; Lamata, Lucas; Szameit, Alexander; Solano, Enrique

    2017-01-01

    We propose the realization of photonic circuits whose dynamics is governed by advanced-retarded differential equations. Beyond their mathematical interest, these photonic configurations enable the implementation of quantum feedback and feedforward without requiring any intermediate measurement. We show how this protocol can be applied to implement interesting delay effects in the quantum regime, as well as in the classical limit. Our results elucidate the potential of the protocol as a promising route towards integrated quantum control systems on a chip. PMID:28230090

  18. Quantum tunnelling and charge accumulation in organic ferroelectric memory diodes

    PubMed Central

    Ghittorelli, Matteo; Lenz, Thomas; Sharifi Dehsari, Hamed; Zhao, Dong; Asadi, Kamal; Blom, Paul W. M.; Kovács-Vajna, Zsolt M.; de Leeuw, Dago M.; Torricelli, Fabrizio

    2017-01-01

    Non-volatile memories—providing the information storage functionality—are crucial circuit components. Solution-processed organic ferroelectric memory diodes are the non-volatile memory candidate for flexible electronics, as witnessed by the industrial demonstration of a 1 kbit reconfigurable memory fabricated on a plastic foil. Further progress, however, is limited owing to the lack of understanding of the device physics, which is required for the technological implementation of high-density arrays. Here we show that ferroelectric diodes operate as vertical field-effect transistors at the pinch-off. The tunnelling injection and charge accumulation are the fundamental mechanisms governing the device operation. Surprisingly, thermionic emission can be disregarded and the on-state current is not space charge limited. The proposed model explains and unifies a wide range of experiments, provides important design rules for the implementation of organic ferroelectric memory diodes and predicts an ultimate theoretical array density of up to 1012 bit cm−2. PMID:28604664

  19. Quantum Tunneling of Charge-Density Waves in Quasi One-Dimensional Conductors

    NASA Astrophysics Data System (ADS)

    Miller, John Harris, Jr.

    The charge-density wave (CDW) dynamics of the linear chain compound orthorhombic TaS(,3) is characterized by extensive measurements of dc conductivity, ac admittance, direct mixing, harmonic mixing, second harmonic generation, and third harmonic generation as functions of dc bias voltage, applied frequencies, and, in some cases, the amplitude of an additional ac signal. Measurements of the direct and harmonic mixing responses of NbSe(,3) are also reported. The results are analyzed in terms of an extension of the tunneling theory of CDW depinning, proposed by John Bardeen, coupled to the theory of photon-assisted tunneling (PAT). Where possible, the results are also compared with predictions of the classical overdamped oscillator model of CDW transport. The tunneling model is shown to provide a complete and semiquantitative interpretation of the entire small -signal ac dynamics at megahertz frequencies, using only the measured dc I-V curve and an experimentally inferred frequency-voltage scaling parameter, and also accounts for much of the large-signal behavior studied thus far. The observation of both an induced ac harmonic mixing current and a third harmonic generation current whose amplitudes peak at output frequencies far below the measured "cross -over frequency" for ac conductivity agrees with the phenomenological tunneling model, but is in serious disagreement with the classical overdamped oscillator model of CDW motion. Furthermore, the absence of any observed quadrature component in the harmonic mixing response, even though the measured linear response at the applied frequencies has substantial frequency -dependent in-phase and quadrature components, is probably impossible to reconcile with any classical theory. The results reported here thus provide compelling evidence in favor of collective, coherent quantum tunneling as the mechanism of charge-density wave depinning, and indicate that macroscopic quantum effects are observed in the megahertz frequency

  20. Real-time detection of electron tunnelling in a quantum dot.

    PubMed

    Lu, Wei; Ji, Zhongqing; Pfeiffer, Loren; West, K W; Rimberg, A J

    2003-05-22

    Nanostructures in which strong (Coulomb) interactions exist between electrons are predicted to exhibit temporal electronic correlations. Although there is ample experimental evidence that such correlations exist, electron dynamics in engineered nanostructures have been observed directly only on long timescales. The faster dynamics associated with electrical currents or charge fluctuations are usually inferred from direct (or quasi-direct) current measurements. Recently, interest in electron dynamics has risen, in part owing to the realization that additional information about electronic interactions can be found in the shot noise or higher statistical moments of a direct current. Furthermore, interest in quantum computation has stimulated investigation of quantum bit (qubit) readout techniques, which for many condensed-matter systems ultimately reduces to single-shot measurements of individual electronic charges. Here we report real-time observation of individual electron tunnelling events in a quantum dot using an integrated radio-frequency single-electron transistor. We use electron counting to measure directly the quantum dot's tunnelling rate and the occupational probabilities of its charge state. Our results provide evidence in favour of long (10 micros or more) inelastic scattering times in nearly isolated dots.

  1. Real-time Feynman path integral with Picard–Lefschetz theory and its applications to quantum tunneling

    SciTech Connect

    Tanizaki, Yuya; Koike, Takayuki

    2014-12-15

    Picard–Lefschetz theory is applied to path integrals of quantum mechanics, in order to compute real-time dynamics directly. After discussing basic properties of real-time path integrals on Lefschetz thimbles, we demonstrate its computational method in a concrete way by solving three simple examples of quantum mechanics. It is applied to quantum mechanics of a double-well potential, and quantum tunneling is discussed. We identify all of the complex saddle points of the classical action, and their properties are discussed in detail. However a big theoretical difficulty turns out to appear in rewriting the original path integral into a sum of path integrals on Lefschetz thimbles. We discuss generality of that problem and mention its importance. Real-time tunneling processes are shown to be described by those complex saddle points, and thus semi-classical description of real-time quantum tunneling becomes possible on solid ground if we could solve that problem. - Highlights: • Real-time path integral is studied based on Picard–Lefschetz theory. • Lucid demonstration is given through simple examples of quantum mechanics. • This technique is applied to quantum mechanics of the double-well potential. • Difficulty for practical applications is revealed, and we discuss its generality. • Quantum tunneling is shown to be closely related to complex classical solutions.

  2. An entropic quantum drift-diffusion model for electron transport in resonant tunneling diodes

    SciTech Connect

    Degond, Pierre; Gallego, Samy . E-mail: gallego@mip.ups-tlse.fr; Mehats, Florian

    2007-01-20

    We present an entropic quantum drift-diffusion model (eQDD) and show how it can be derived on a bounded domain as the diffusive approximation of the Quantum Liouville equation with a quantum BGK operator. Some links between this model and other existing models are exhibited, especially with the density gradient (DG) model and the Schroedinger-Poisson drift-diffusion model (SPDD). Then a finite difference scheme is proposed to discretize the eQDD model coupled to the Poisson equation and we show how this scheme can be slightly modified to discretize the other models. Numerical results show that the properties listed for the eQDD model are checked, as well as the model captures important features concerning the modeling of a resonant tunneling diode. To finish, some comparisons between the models stated above are realized.

  3. Coherent tunneling through a double quantum dot coupled to Majorana bound states

    NASA Astrophysics Data System (ADS)

    Ivanov, T. I.

    2017-07-01

    We consider a double quantum dot coupled to a one-dimensional superconducting quantum wire with Majorana bound states at the ends of the wire. We compute the conductance of the double dot in the coherent tunneling regime. When only one of the dots is coupled to one Majorana bound state the conductance is enhanced/diminished in the vicinity of zero voltage if it has minimum/maximum at this voltage with no Majorana bound state and has two local maximums/minimums at voltage equal plus or minus the Majorana bound states overlapping energy. When each dot is coupled to one Majorana bound state with zero overlapping energy it is possible by tuning the magnetic flux through the system to change the zero-voltage conductance from minimum to local maximum. We show that when both electron levels in the double quantum dot are below the right chemical potential the Fano resonance occurs only for the lower energy level.

  4. Magnetoresistance of One-Dimensional Subbands in Tunnel-Coupled Double Quantum Wires

    SciTech Connect

    Moon, J.S.; Blount, M.A.; Simmons, J.A.; Wendt, J.R.; Lyo, S.K.; Reno, J.L.

    1999-08-04

    The authors study the low-temperature in-plane magnetoresistance of tunnel-coupled quasi-one-dimensional quantum wires. The wires are defined by two pairs of mutually aligned split gates on opposite sides of a {le} 1 micron thick AlGaAs/GaAs double quantum well heterostructure, allowing independent control of the width of each quantum well. In the ballistic regime, when both wires are defined and the field is perpendicular to the current, a large resistance peak at {approximately}6 Tesla is observed with a strong gate voltage dependence. The data is consistent with a counting model whereby the number of subbands crossing the Fermi level changes with field due to the formation of an anticrossing in each pair of 1D subbands.

  5. Spin Dynamics and Quantum Tunneling in Fe8 Nanomagnet and in AFM Rings by NMR

    SciTech Connect

    Ho-Baek, Seung

    2004-01-01

    In this thesis, our main interest has been to investigate the spin dynamics and quantum tunneling in single molecule magnets (SMMs), For this we have selected two different classes of SMMs: a ferrimagnetic total high spin S = 10 cluster Fe8 and antiferromagnetic (AFM) ring-type clusters. For Fe8, our efforts have been devoted to the investigation of the quantum tunneling of magnetization in the very low temperature region. The most remarkable experimental finding in Fe8 is that the nuclear spin-lattice relaxation rate (1/T{sub l}) at low temperatures takes place via strong collision mechanism, and thus it allows to measure directly the tunneling rate vs T and H for the first time. For AFM rings, we have shown that 1/T{sub l} probes the thermal fluctuations of the magnetization in the intermediate temperature range. We find that the fluctuations are dominated by a single characteristic frequency which has a power law T-dependence indicative of fluctuations due to electron-acoustic phonon interactions.

  6. Spectral-gap analysis for efficient tunneling in quantum adiabatic optimization

    NASA Astrophysics Data System (ADS)

    Brady, Lucas T.; van Dam, Wim

    2016-09-01

    We investigate the efficiency of quantum adiabatic optimization when overcoming potential barriers to get from a local to a global minimum. Specifically we look at n qubit systems with symmetric cost functions f :{0,1 } n→R , where the ground state must tunnel through a potential barrier of width nα and height nβ. By the quantum adiabatic theorem the time delay sufficient to ensure tunneling grows quadratically with the inverse spectral gap during this tunneling process. We analyze barrier sizes with 1 /2 ≤α +β and α <1 /2 and show that the minimum gap scales polynomially as n1 /2 -α -β when 2 α +β ≤1 and exponentially as n-β /2exp(-C n(2 α +β -1 )/2) when 1 <2 α +β . Our proof uses elementary techniques and confirms and extends an unpublished folklore result by Goldstone from 2002, which used large spin and instanton methods. Parts of our result also refine recent results by Kong and Crosson [arXiv:1511.06991] and Jiang et al. [arXiv:1603.01293] about the exponential gap scaling.

  7. Conditional probabilities in quantum theory and the tunneling-time controversy

    NASA Astrophysics Data System (ADS)

    Steinberg, Aephraim M.

    1995-07-01

    It is argued that there is a sensible way to define conditional probabilities in quantum mechanics, assuming only Bayes's theorem and standard quantum theory. These probabilities are equivalent to the ``weak measurement'' predictions due to Aharonov, Albert, and Vaidman [Phys. Rev. Lett. 60, 1351 (1988)] and hence describe the outcomes of real measurements made on subensembles. In particular, this approach is used to address the question of the history of a particle that has tunneled across a barrier. A gedanken experiment is presented to demonstrate the physically testable implications of the results of these calculations, along with graphs of the time evolution of the conditional probability distribution for a tunneling particle and for one undergoing allowed transmission. Numerical results are also presented for the effects of loss in a band-gap medium on transmission and on reflection, as a function of the position of the lossy region; such loss should provide a feasible, though indirect, test of the present conclusions. It is argued that the effects of loss on the pulse delay time are related to the imaginary value of the momentum of a tunneling particle and it is suggested that this might help explain a small discrepancy in an earlier experiment.

  8. Inter-dot tunneling control of optical bistability in triple quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Reza Hamedi, Hamid

    2014-09-01

    The behavior of optical bistability (OB) and optical multistability (OM) in a triple coupled quantum dot (QD) system is theoretically explored. It is found that the tunneling coupling between electronic levels has major effect on controlling the threshold and the hysteresis cycle shape of the optical bistability. The impact of incoherent pump field on the OB and OM behavior of such medium is then discussed. We realize that the threshold intensity reduces remarkably through increasing the rate of incoherent pumping. It is also demonstrated that the switch between OB and OM can be obtained just through proper adjusting the frequency detuning of probe field. It should be pointed that in this QD system we used tunneling instead of coupling lasers. These presented results may be applicable in real experiments for realizing an all-optical bistate switching or coding element in a solid-state platform.

  9. Can a man-made universe be achieved by quantum tunneling without an initial singularity?

    NASA Astrophysics Data System (ADS)

    Guth, Alan H.; Haller, K.; Caldi, D. B.; Islam, M. M.; Mallett, R. L.; Mannheim, P. D.; Swanson, M. S.

    Essentially all modern particle theories suggest the possible existence of a false vacuum state; a metastable state with an energy density that cannot be lowered except by means of a very slow phase transition. Inflationary cosmology makes use of such a state to drive the expansion of the big bang, allowing the entire observed universe to evolve from a very small initial mass. A sphere of false vacuum in the present universe, if larger than a certain critical mass, could inflate to form a new universe which would rapidly detach from its parent. A false vacuum bubble of this size, however, cannot be produced classically unless an initial singularity is present from the outset. The possibility is explored that a bubble of subcritical size, which classically would evolve to a maximum size and collapse, might instead tunnel through a barrier to produce a new universe. The tunneling rate using semiclassical quantum gravity is estimated, and some interesting ambiguities in the formulas are discovered.

  10. Can a man-made universe be created by quantum tunneling without an initial singularity?

    NASA Astrophysics Data System (ADS)

    Guth, Alan H.

    Essentially all modern particle theories suggest the possible existence of a false vacuum state - a metastable state with an energy density that cannot be lowered except by means of a very slow phase transition. Inflationary cosmology makes use of such a state to drive the expansion of the big bang, allowing the entire observed universe to evolve from a very small initial mass. A sphere of false vacuum in the present universe, if larger than a certain critical mass, could inflate to form a new universe which would rapidly detach from its parent. A false vacuum bubble of this size, however, cannot be produced classically unless an initial singularity is present from the outset. The possibility that a bubble of subcritical size, which classically would evolve to a maximum size and collapse, might instead tunnel through a barrier to produce a new universe is explored. The tunneling rate using semiclassical quantum gravity is estimated, and some interesting ambiguities in the formalism are discovered.

  11. Shot noise in magnetic tunneling structures with two-level quantum dots

    NASA Astrophysics Data System (ADS)

    Szczepański, T.; Dugaev, V. K.; Barnaś, J.; Martinez, I.; Cascales, J. P.; Hong, J.-Y.; Lin, M.-T.; Aliev, F. G.

    2016-12-01

    We analyze shot noise in a magnetic tunnel junction with a two-level quantum dot attached to the magnetic electrodes. The considerations are limited to the case when some transport channels are suppressed at low temperatures. Coupling of the two dot's levels to the electrodes are assumed to be generally different and also spin dependent. To calculate the shot noise we apply the approach based on the full counting statistics. The approach is used to account for experimental data obtained in magnetic tunnel junctions with organic barriers. The experimentally observed Fano factors correspond to the super-Poissonian statistics, and also depend on relative orientation of the electrodes' magnetic moments. We have also calculated the corresponding spin shot noise, which is associated with fluctuations of spin current.

  12. Improved dynamics of a tunnelling-injection quantum-dot laser under optical feedback

    NASA Astrophysics Data System (ADS)

    Asadi, Faezeh; Zarifkar, Abbas

    2016-10-01

    We report an investigation of the optical feedback effect on the dynamics of a tunnelling-injection quantum dot (TI QD) semiconductor laser. Assuming the external cavity to be short and using a small signal analysis, the modulation response of a TI QD laser is calculated under optical feedback conditions. The impact of the tunnelling probability, bias-current density, feedback ratio, external cavity length and linewidth enhancement factor on the modulation response of a TI laser is studied. With the optical feedback taken into account, the modulation responses of conventional and TI QD lasers are compared. The obtained results demonstrate that at an appropriate feedback ratio and external cavity length, the laser bandwidth and its relaxation frequency can be improved.

  13. Can a man-made universe be achieved by quantum tunneling without an initial singularity?

    NASA Technical Reports Server (NTRS)

    Guth, Alan H.; Haller, K. (Editor); Caldi, D. B. (Editor); Islam, M. M. (Editor); Mallett, R. L. (Editor); Mannheim, P. D. (Editor); Swanson, M. S. (Editor)

    1991-01-01

    Essentially all modern particle theories suggest the possible existence of a false vacuum state; a metastable state with an energy density that cannot be lowered except by means of a very slow phase transition. Inflationary cosmology makes use of such a state to drive the expansion of the big bang, allowing the entire observed universe to evolve from a very small initial mass. A sphere of false vacuum in the present universe, if larger than a certain critical mass, could inflate to form a new universe which would rapidly detach from its parent. A false vacuum bubble of this size, however, cannot be produced classically unless an initial singularity is present from the outset. The possibility is explored that a bubble of subcritical size, which classically would evolve to a maximum size and collapse, might instead tunnel through a barrier to produce a new universe. The tunneling rate using semiclassical quantum gravity is estimated, and some interesting ambiguities in the formulas are discovered.

  14. 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.

  15. Fractional quantum Hall bilayers at half filling: Tunneling-driven non-Abelian phase

    NASA Astrophysics Data System (ADS)

    Zhu, W.; Liu, Zhao; Haldane, F. D. M.; Sheng, D. N.

    2016-12-01

    Multicomponent quantum Hall systems with internal degrees of freedom provide a fertile ground for the emergence of exotic quantum liquids. Here, we investigate the possibility of non-Abelian topological order in the half-filled fractional quantum Hall (FQH) bilayer system driven by the tunneling effect between two layers. By means of the state-of-the-art density-matrix renormalization group, we unveil "fingerprint" evidence of the non-Abelian Moore-Read Pfaffian state emerging in the intermediate-tunneling regime, including the ground-state degeneracy on the torus geometry and the topological entanglement spectroscopy (entanglement spectrum and topological entanglement entropy) on the spherical geometry, respectively. Remarkably, the phase transition from the previously identified Abelian (331) Halperin state to the non-Abelian Moore-Read Pfaffian state is determined to be continuous, which is signaled by the continuous evolution of the universal part of the entanglement spectrum, and discontinuities in the excitation gap and the derivative of the ground-state energy. Our results not only provide a "proof-of-principle" demonstration of realizing a non-Abelian state through coupling different degrees of freedom, but also open up a possibility in FQH bilayer systems for detecting different chiral p -wave pairing states.

  16. Differential geometry on Hopf algebras and quantum groups

    SciTech Connect

    Watts, Paul

    1994-12-15

    The differential geometry on a Hopf algebra is constructed, by using the basic axioms of Hopf algebras and noncommutative differential geometry. The space of generalized derivations on a Hopf algebra of functions is presented via the smash product, and used to define and discuss quantum Lie algebras and their properties. The Cartan calculus of the exterior derivative, Lie derivative, and inner derivation is found for both the universal and general differential calculi of an arbitrary Hopf algebra, and, by restricting to the quasitriangular case and using the numerical R-matrix formalism, the aforementioned structures for quantum groups are determined.

  17. Long-Range Phase Coherence in Double-Barrier Magnetic Tunnel Junctions with a Large Thick Metallic Quantum Well.

    PubMed

    Tao, B S; Yang, H X; Zuo, Y L; Devaux, X; Lengaigne, G; Hehn, M; Lacour, D; Andrieu, S; Chshiev, M; Hauet, T; Montaigne, F; Mangin, S; Han, X F; Lu, Y

    2015-10-09

    Double-barrier heterostructures are model systems for the study of electron tunneling and discrete energy levels in a quantum well (QW). Until now resonant tunneling phenomena in metallic QWs have been observed for limited thicknesses (1-2 nm) under which electron phase coherence is conserved. In the present study we show evidence of QW resonance states in Fe QWs up to 12 nm thick and at room temperature in fully epitaxial double MgAlO_{x} barrier magnetic tunnel junctions. The electron phase coherence displayed in this QW is of unprecedented quality because of a homogenous interface phase shift due to the small lattice mismatch at the Fe-MgAlO_{x} interface. The physical understanding of the critical role of interface strain on QW phase coherence will greatly promote the development of spin-dependent quantum resonant tunneling applications.

  18. Assessment of field-induced quantum confinement in heterogate germanium electron–hole bilayer tunnel field-effect transistor

    SciTech Connect

    Padilla, J. L. Alper, C.; Ionescu, A. M.; Gámiz, F.

    2014-08-25

    The analysis of quantum mechanical confinement in recent germanium electron–hole bilayer tunnel field-effect transistors has been shown to substantially affect the band-to-band tunneling (BTBT) mechanism between electron and hole inversion layers that constitutes the operating principle of these devices. The vertical electric field that appears across the intrinsic semiconductor to give rise to the bilayer configuration makes the formerly continuous conduction and valence bands become a discrete set of energy subbands, therefore increasing the effective bandgap close to the gates and reducing the BTBT probabilities. In this letter, we present a simulation approach that shows how the inclusion of quantum confinement and the subsequent modification of the band profile results in the appearance of lateral tunneling to the underlap regions that greatly degrades the subthreshold swing of these devices. To overcome this drawback imposed by confinement, we propose an heterogate configuration that proves to suppress this parasitic tunneling and enhances the device performance.

  19. Gate tunneling current and quantum capacitance in metal-oxide-semiconductor devices with graphene gate electrodes

    NASA Astrophysics Data System (ADS)

    An, Yanbin; Shekhawat, Aniruddh; Behnam, Ashkan; Pop, Eric; Ural, Ant

    2016-11-01

    Metal-oxide-semiconductor (MOS) devices with graphene as the metal gate electrode, silicon dioxide with thicknesses ranging from 5 to 20 nm as the dielectric, and p-type silicon as the semiconductor are fabricated and characterized. It is found that Fowler-Nordheim (F-N) tunneling dominates the gate tunneling current in these devices for oxide thicknesses of 10 nm and larger, whereas for devices with 5 nm oxide, direct tunneling starts to play a role in determining the total gate current. Furthermore, the temperature dependences of the F-N tunneling current for the 10 nm devices are characterized in the temperature range 77-300 K. The F-N coefficients and the effective tunneling barrier height are extracted as a function of temperature. It is found that the effective barrier height decreases with increasing temperature, which is in agreement with the results previously reported for conventional MOS devices with polysilicon or metal gate electrodes. In addition, high frequency capacitance-voltage measurements of these MOS devices are performed, which depict a local capacitance minimum under accumulation for thin oxides. By analyzing the data using numerical calculations based on the modified density of states of graphene in the presence of charged impurities, it is shown that this local minimum is due to the contribution of the quantum capacitance of graphene. Finally, the workfunction of the graphene gate electrode is extracted by determining the flat-band voltage as a function of oxide thickness. These results show that graphene is a promising candidate as the gate electrode in metal-oxide-semiconductor devices.

  20. Spin bottleneck in resonant tunneling through double quantum dots with different Zeeman splittings.

    PubMed

    Huang, S M; Tokura, Y; Akimoto, H; Kono, K; Lin, J J; Tarucha, S; Ono, K

    2010-04-02

    We investigated the electron transport property of the InGaAs/GaAs double quantum dots, the electron g factors of which are different from each other. We found that in a magnetic field, the resonant tunneling is suppressed even if one of the Zeeman sublevels is aligned. This is because the other misaligned Zeeman sublevels limit the total current. A finite broadening of the misaligned sublevel partially relieves this bottleneck effect, and the maximum current is reached when interdot detuning is half the Zeeman energy difference.

  1. Adsorbate-induced quantum Hall system probed by scanning tunneling spectroscopy combined with transport measurements

    SciTech Connect

    Masutomi, Ryuichi Okamoto, Tohru

    2015-06-22

    An adsorbate-induced quantum Hall system at the cleaved InSb surfaces is investigated in magnetic fields up to 14 T using low-temperature scanning tunneling microscopy and spectroscopy combined with transport measurements. We show that an enhanced Zeeman splitting in the Shubnikov-de Haas oscillations is explained by an exchange enhancement of spin splitting and potential disorder, both of which are obtained from the spatially averaged density of states (DOS). Moreover, the Altshuler–Aronov correlation gap is observed in the spatially averaged DOS at 0 T.

  2. Electronic-state-controlled reset operation in quantum dot resonant-tunneling single-photon detectors

    SciTech Connect

    Weng, Q. C.; Zhu, Z. Q.; An, Z. H.; Song, J. D.; Choi, W. J.

    2014-02-03

    The authors present a systematic study of an introduced reset operation on quantum dot (QD) single photon detectors operating at 77 K. The detectors are based on an AlAs/GaAs/AlAs double-barrier resonant tunneling diode with an adjacent layer of self-assembled InAs QDs. Sensitive single-photon detection in high (dI)/(dV) region with suppressed current fluctuations is achieved. The dynamic detection range is extended up to at least 10{sup 4} photons/s for sensitive imaging applications by keeping the device far from saturation by employing an appropriate reset frequency.

  3. Hybrid driven three-terminal thermoelectric refrigerators based on resonant tunneling quantum dots

    NASA Astrophysics Data System (ADS)

    Shi, Zhicheng; Qin, Weifeng; He, Jizhou

    2016-11-01

    In this paper, we propose a pair of symmetric three-terminal refrigerator models with a hot cavity connected to two colder reservoirs via ideal tunneling quantum dots. The cooling of the refrigerators is achieved by investing thermal power from a hot reservoir and electric power from an applied voltage. Based on the model proposed, we numerically analyze the performance of the refrigerators with different half width of energy levels, and particularly discuss the coefficient of performance for zero applied voltage in the limit of a small half level width. Finally, we optimize with half width of energy levels and get the optimal region of the refrigerators.

  4. Metastable states and macroscopic quantum tunneling in a cold atom josephson ring

    SciTech Connect

    Solenov, Dmitry; Mozyrsky, Dmitry

    2009-01-01

    We study macroscopic properties of a system of weakly interacting neutral bosons confined in a ring-shaped potential with a Josephson junction. We derive an effective low energy action for this system and evaluate its properties. In particular we find that the system possesses a set of metastable current-carrying states and evaluate the rates of transitions between these states due to macroscopic quantum tunneling. Finally we discuss signatures of different metastable states in the time-of-flight images and argue that the effect is observable within currently available experimental technique.

  5. Correlation Effects in Scanning Tunneling Microscopy Images of Molecules Revealed by Quantum Monte Carlo.

    PubMed

    Barborini, Matteo; Sorella, Sandro; Rontani, Massimo; Corni, Stefano

    2016-11-08

    Scanning tunneling microscopy (STM) and spectroscopy probe the local density of states of single molecules electrically insulated from the substrate. The experimental images, although usually interpreted in terms of single-particle molecular orbitals, are associated with quasiparticle wave functions dressed by the whole electron-electron interaction. Here we propose an ab initio approach based on quantum Monte Carlo to calculate the quasiparticle wave functions of molecules. Through the comparison between Monte Carlo wave functions and their uncorrelated Hartree-Fock counterparts we visualize the electronic correlation embedded in the simulated STM images, highlighting the many-body features that might be observed.

  6. Quantum groups, non-commutative differential geometry and applications

    SciTech Connect

    Schupp, Peter

    1993-12-09

    The topic of this thesis is the development of a versatile and geometrically motivated differential calculus on non-commutative or quantum spaces, providing powerful but easy-to-use mathematical tools for applications in physics and related sciences. A generalization of unitary time evolution is proposed and studied for a simple 2-level system, leading to non-conservation of microscopic entropy, a phenomenon new to quantum mechanics. A Cartan calculus that combines functions, forms, Lie derivatives and inner derivations along general vector fields into one big algebra is constructed for quantum groups and then extended to quantum planes. The construction of a tangent bundle on a quantum group manifold and an BRST type approach to quantum group gauge theory are given as further examples of applications. The material is organized in two parts: Part I studies vector fields on quantum groups, emphasizing Hopf algebraic structures, but also introducing a ``quantum geometric`` construction. Using a generalized semi-direct product construction we combine the dual Hopf algebras A of functions and U of left-invariant vector fields into one fully bicovariant algebra of differential operators. The pure braid group is introduced as the commutant of {Delta}(U). It provides invariant maps A {yields} U and thereby bicovariant vector fields, casimirs and metrics. This construction allows the translation of undeformed matrix expressions into their less obvious quantum algebraic counter parts. We study this in detail for quasitriangular Hopf algebras, giving the determinant and orthogonality relation for the ``reflection`` matrix. Part II considers the additional structures of differential forms and finitely generated quantum Lie algebras -- it is devoted to the construction of the Cartan calculus, based on an undeformed Cartan identity.

  7. Trap-assisted tunneling in InGaN/GaN single-quantum-well light-emitting diodes

    SciTech Connect

    Auf der Maur, M. Di Carlo, A.; Galler, B.; Pietzonka, I.; Strassburg, M.; Lugauer, H.

    2014-09-29

    Based on numerical simulation and comparison with measured current characteristics, we show that the current in InGaN/GaN single-quantum-well light-emitting diodes at low forward bias can be accurately described by a standard trap-assisted tunneling model. The qualitative and quantitative differences in the current characteristics of devices with different emission wavelengths are demonstrated to be correlated in a physically consistent way with the tunneling model parameters.

  8. Dissipative Quantum Tunneling of a Single Defect in a Submicron Bismuth Wire Below 1 K

    NASA Astrophysics Data System (ADS)

    Chun, Kookjin

    The quantum mechanical problem of a particle tunneling in a double-well potential is of great theoretical and experimental interest. Interaction of the tunneling system with a dissipative environment can have a striking effect on the tunneling dynamics. A very interesting case is that of ohmic dissipation, which occurs when an atom tunnels in a metal in the presence of conduction electrons. We have studied the electrical resistance of submicron Bi wires at low temperature. Due to quantum interference of the conduction electrons, the resistance is highly sensitive to the motion of even a single scattering center. We observe discrete switching of the resistance due to the motion of bistable defects in the sample. We have measured the tunneling rates of a particular defect over the temperature range 0.1-2 K and magnetic field range 0-7 T. The energy asymmetry, varepsilon, of this defect varied over the range 40-420 mK depending on the value of the magnetic field. The temperature dependence of the tunneling rates is qualitatively different for the cases k_{B}T << varepsilon and k_{B}T gg varepsilon . We observe that for k_{B }T << varepsilon, the fast rate (transition rate from upper state to lower state) is roughly temperature independent and the slow rate (transition from lower state to upper state) decreases exponentially, as expected from a simple picture of spontaneous emission and stimulated absorption. When k_{B }T gg varepsilon, however, both rates increase as the temperature is lowered, as predicted by dissipative quantum tunneling theory. We fit our data to the theory and discuss the defect-electron bath coupling parameter alpha, and the renormalized tunneling matrix element Delta_{ rm r}. We have also studied the effect of Joule heating on the dynamics of the defect in the same sample. The ratio of the fast and slow transition rates of a defect depends on temperature through the detailed balance relation, gamma_{f}/ gamma_{s} e^ {varepsilon / k_{B}T}. We

  9. Harmonic oscillator wave functions of a self-assembled InAs quantum dot measured by scanning tunneling microscopy.

    PubMed

    Teichmann, Karen; Wenderoth, Martin; Prüser, Henning; Pierz, Klaus; Schumacher, Hans W; Ulbrich, Rainer G

    2013-08-14

    InAs quantum dots embedded in an AlAs matrix inside a double barrier resonant tunneling diode are investigated by cross-sectional scanning tunneling spectroscopy. The wave functions of the bound quantum dot states are spatially and energetically resolved. These bound states are known to be responsible for resonant tunneling phenomena in such quantum dot diodes. The wave functions reveal a textbook-like one-dimensional harmonic oscillator behavior showing up to five equidistant energy levels of 80 meV spacing. The derived effective oscillator mass of m* = 0.24m0 is 1 order of magnitude higher than the effective electron mass of bulk InAs that we attribute to the influence of the surrounding AlAs matrix. This underlines the importance of the matrix material for tailored QD devices with well-defined properties.

  10. Photon-Assisted Resonant Tunneling and 2-D Plasmon Modes in Double Quantum Wells in Intense Terahertz Electric Fields

    NASA Astrophysics Data System (ADS)

    Peralta, X. G.; Allen, S. J.; Lin, S. Y.; Simmons, J. A.; Blount, M. A.; Baca, W. E.

    1998-03-01

    We explore photon-assisted resonant tunneling in double quantum well systems in intense terahertz electric fields that have separately- contacted wells. We have two goals in mind: 1) increase the basic understanding of photon assisted tunneling in semiconductors and 2) assess the potential of this structure as a detector. We can control the tunneling current by varying the electron density of each 2D electron gas or by changing the relative separation of the Fermi levels. This allows us to prepare the system in such a way that photons of the appropriate energy may induce resonant tunneling, which is monitored by a change in conductance. We also examine the possible enhancement of the resonant tunneling by resonant excitations of acoustic plasmon modes. This work is supported by ONR, the U. S. Dept. of Energy under Contract DE-AC04-94AL85000 and Consejo Nacional de Ciencia y Tecnología, México.

  11. Slow terahertz light via resonant tunneling induced transparency in quantum well heterostructures

    NASA Astrophysics Data System (ADS)

    Tzenov, Petar; Jirauschek, Christian

    2016-01-01

    We present a theoretical and computational investigation of the possibility of achieving slow terahertz light by exploiting the tunneling induced transparency (TIT) effect in suitably engineered quantum well heterostructure devices. We design such a meta-material and show how TIT could lead to large values of the group refractive index, unfortunately at the cost of strong field attenuation due to decoherence. As a suitable alternative, we propose a grating, consisting of a buffer and a quantum cascade amplifier regions, arranged in such a way as to achieve slow light and simultaneously compensate for the large signal losses. Our calculations show that a binary message could be reliably transmitted through this system, with non-critical reduction of the signal to noise ratio, as we achieve a slow-down factor of more than 70.

  12. Thermally activated tunneling in porous silicon nanowires with embedded Si quantum dots

    NASA Astrophysics Data System (ADS)

    Rezvani, S. J.; Pinto, N.; Enrico, E.; D'Ortenzi, L.; Chiodoni, A.; Boarino, L.

    2016-03-01

    Electronic transport properties of porous Si nanowires either with embedded Si quantum dots or with a percolative crystalline path are studied as a function of the temperature for the first time. We show that unlike bulk porous Si, the predesigned structure of the wires results in a single distinct conduction mechanism such as tunneling in the former case and variable range hopping in the latter case. We demonstrate that the geometry of the systems with a large internal surface area and high density of the Si quantum dots have a significant conduction enhancement compared to bulk porous silicon. These results can also improve the understanding of the basis of the different electronic transport mechanisms reported in bulk porous silicon.

  13. Magnetoresistance of One-Dimensional Subbands in Tunnel-Coupled Double Quantum Wires

    SciTech Connect

    Blount, M.A.; Lyo, S.K.; Moon, J.S.; Reno, J.L.; Simmons, J.A.; Wendt, J.R.

    1999-04-27

    We study the low-temperature in-plane magnetoresistance of tunnel-coupled quasi-one-dimensional quantum wires. The wires are defined by two pairs of mutually aligned split gates on opposite sides of a < 1 micron thick AlGaAs/GaAs double quantum well heterostructure, allowing independent control of their widths. In the ballistic regime, when both wires are defined and the field is perpendicular to the current, a large resistance peak at ~6 Tesla is observed with a strong gate voltage dependence. The data is consistent with a counting model whereby the number of subbands crossing the Fermi level changes with field due to the formation of an anticrossing in each pair of 1D subbands.

  14. Spin-valley resolved photon-assisted tunneling in carbon nanotube double quantum dots

    NASA Astrophysics Data System (ADS)

    Osika, E. N.; Szafran, B.

    2017-05-01

    We consider photon-assisted tunneling (PAT) and the Landau-Zener-Stueckelberg (LZS) interference for double quantum dots induced electrostatically along a semiconducting carbon nanotube. An atomistic tight-binding approach and the time-dependent configuration-interaction method are employed to describe systems of a few confined electrons and holes. We reproduce the patterns of the LZS interference recently observed for quantum double dots describing transport across hole-localized states. Moreover, we indicate that for charge configurations for which the ground state is Pauli-blocked, PAT can be used for resolution of the transitions that involve spin-flip or intervalley transitions without the spin-valley conserving background signal.

  15. Is it possible to create a universe in the laboratory by quantum tunneling?

    NASA Technical Reports Server (NTRS)

    Farhi, Edward; Guth, Alan H.; Guven, Jemal

    1990-01-01

    We explore the possibility that a new universe can be created by producing a small bubble of false vacuum. The initial bubble is small enough to be produced without an initial singularity, but classically it could not become a universe - instead it would reach a maximum radius and then collapse. We investigate the possibility that quantum effects allow the bubble to tunnel into a larger bubble, of the same mass, which would then classically evolve to become a new universe. The calculation of the tunneling amplitude is attempted, in lowest order semiclassical approximation (in the thin-wall limit), using both a canonical and a functional integral approach. The canonical approach is found to have flaws, attributable to our method of space-time slicing. The functional integral approach leads to a Euclidean interpolating solution that is not a manifold. To describe it, we define an object which we call a 'pseudomanifold', and give a prescription to define its action. We conjecture that the tunneling probability to produce a new universe can be approximated using this action, and we show that this leads to a plausible result.

  16. Terahertz time domain interferometry of a SIS tunnel junction and a quantum point contact

    SciTech Connect

    Karadi, Chandu

    1995-09-01

    The author has applied the Terahertz Time Domain Interferometric (THz-TDI) technique to probe the ultrafast dynamic response of a Superconducting-Insulating-Superconducting (SIS) tunnel junction and a Quantum Point Contact (QPC). The THz-TDI technique involves monitoring changes in the dc current induced by interfering two picosecond electrical pulses on the junction as a function of time delay between them. Measurements of the response of the Nb/AlOxNb SIS tunnel junction from 75--200 GHz are in full agreement with the linear theory for photon-assisted tunneling. Likewise, measurements of the induced current in a QPC as a function of source-drain voltage, gate voltage, frequency, and magnetic field also show strong evidence for photon-assisted transport. These experiments together demonstrate the general applicability of the THz-TDI technique to the characterization of the dynamic response of any micron or nanometer scale device that exhibits a non-linear I-V characteristic.

  17. Scanning tunneling microscopy studies of charge transport in cadmium selenide/zinc sulfide quantum dots

    NASA Astrophysics Data System (ADS)

    Hummon, Marissa Rachel

    2009-12-01

    This thesis examines charge transport in individual colloidal nanocrystals (quantum dots) using a scanning tunneling microscope. We observe coulomb blockade (CB) at room temperature and extract the charging energy of the quantum dot (QD). We analyze time-dependent CB measurements to determine the lifetime and energy of the trapped charge on the QD. A model of the lifetime is presented, furthering our analysis of the charge detrapping mechanism. We observe a hysteresis in the current-voltage (IV) tunneling spectra as the substrate bias is swept from empty to filled states and then back to empty states. This hysteresis is consistent with trapped charge(s) presenting an additional potential barrier to tunneling, a measure of CB. Traditional CB experiments measure a coulomb repulsion due to charge build-up on the island between two electrodes. We observe CB, hysteresis in successive IV sweeps, due to charge trapping/detrapping in a state other than the transport level. This trap state may be related to the dark state in blinking experiments. Optical and electrical measurements of QD trap states are often related to a puzzling physical phenomena observed universally in QDs: blinking. Blinking is the stochastic photoluminescence behavior of quantum dots, where, under constant excitation by a laser, a QD does not emit a continuous stream of photons. In fact, the QD will blink "on" and "off" for completely unpredictable durations that are thought to be related to the QD being in either a neutral or charged state. We measure a lifetime for the charged state of 15 +/- 7 s when Vsub ≤ 1.5 V and 170 +/- 140 ms when Vsub ≥ 1.6 V. The abrupt transition in lifetime between 1.5 and 1.6 V implies that this is the voltage necessary to lower the Au Fermi level equal to the trap state energy, thus allowing the trapped charge to tunnel out of the trap state. The voltage drop between the QD and substrate, determined from a self-consistent calculation of the relative capacitance

  18. Modeling direct band-to-band tunneling: From bulk to quantum-confined semiconductor devices

    SciTech Connect

    Carrillo-Nuñez, H.; Ziegler, A.; Luisier, M.; Schenk, A.

    2015-06-21

    A rigorous framework to study direct band-to-band tunneling (BTBT) in homo- and hetero-junction semiconductor nanodevices is introduced. An interaction Hamiltonian coupling conduction and valence bands (CVBs) is derived using a multiband envelope method. A general form of the BTBT probability is then obtained from the linear response to the “CVBs interaction” that drives the system out of equilibrium. Simple expressions in terms of the one-electron spectral function are developed to compute the BTBT current in two- and three-dimensional semiconductor structures. Additionally, a two-band envelope equation based on the Flietner model of imaginary dispersion is proposed for the same purpose. In order to characterize their accuracy and differences, both approaches are compared with full-band, atomistic quantum transport simulations of Ge, InAs, and InAs-Si Esaki diodes. As another numerical application, the BTBT current in InAs-Si nanowire tunnel field-effect transistors is computed. It is found that both approaches agree with high accuracy. The first one is considerably easier to conceive and could be implemented straightforwardly in existing quantum transport tools based on the effective mass approximation to account for BTBT in nanodevices.

  19. The dependence of the characteristics of THz current oscillations on the quantum-well width in resonant tunneling diode

    NASA Astrophysics Data System (ADS)

    Montecillo, R.; Otadoy, R. E. S.; Lee, M. L. A. D.; Buot, F. A.; Nacar, M. D.

    2017-08-01

    The dependence on the quantum-well width of the characteristics of ultrafast (THz) current oscillations in resonant tunneling diode nanostructures is investigated through large-scale numerical simulations using non-equilibrium quantum transport equations. It is shown that decreasing the quantum-well width results to higher applied voltage biases in which intrinsic current oscillations occur. This can be attributed to higher resonant-energy level for narrower quantum-well widths requiring a large amount of applied voltage bias for the creation of emitter quantum-well whose coupling with the main quantum well allows the current oscillations to occur. In addition, there is no apparent trend in the relation between the amplitudes as well as the frequencies of oscillations and the quantum-well width.

  20. Methyl quantum tunneling and nitrogen-14 NQR NMR studies using a SQUID magnetic resonance spectrometer

    SciTech Connect

    Black, Bruce Elmer

    1993-07-01

    Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) techniques have been very successful in obtaining molecular conformation and dynamics information. Unfortunately, standard NMR and NQR spectrometers are unable to adequately detect resonances below a few megahertz due to the frequency dependent sensitivity of their Faraday coil detectors. For this reason a new spectrometer with a dc SQUID (Superconducting Quantum Interference Device) detector, which has no such frequency dependence, has been developed. Previously, this spectrometer was used to observe 11B and 27Al NQR resonances. The scope of this study was increased to include 23Na, 51V, and 55Mn NQR transitions. Also, a technique was presented to observe 14N NQR resonances through cross relaxation of the nitrogen polarization to adjacent proton spins. When the proton Zeeman splitting matches one nitrogen quadrupoler transition the remaining two 14N transitions can be detected by sweeping a saturating rf field through resonance. Additionally, simultaneous excitation of two nitrogen resonances provides signal enhancement which helps to connect transitions from the same site. In this way, nitrogen-14 resonances were observed in several amino acids and polypeptides. This spectrometer has also been useful in the direct detection of methyl quantum tunneling splittings at 4.2 K. Tunneling, frequencies of a homologous series of carboxylic acids were measured and for solids with equivalent crystal structures, an exponential correlation between the tunneling frequency and the enthalpy of fusion is observed. This correlation provides information about the contribution of intermolecular interactions to the energy barrier for methyl rotation.

  1. Theoretical simulation of negative differential transconductance in lateral quantum well nMOS devices

    NASA Astrophysics Data System (ADS)

    Vyas, P. B.; Naquin, C.; Edwards, H.; Lee, M.; Vandenberghe, W. G.; Fischetti, M. V.

    2017-01-01

    We present a theoretical study of the negative differential transconductance (NDT) recently observed in the lateral-quantum-well Si n-channel field-effect transistors [J. Appl. Phys. 118, 124505 (2015)]. In these devices, p+ doping extensions are introduced at the source-channel and drain-channel junctions, thus creating two potential barriers that define the quantum well across whose quasi-bound states resonant/sequential tunneling may occur. Our study, based on the quantum transmitting boundary method, predicts the presence of a sharp NDT in devices with a nominal gate length of 10-to-20 nm at low temperatures ( ˜10 K). At higher temperatures, the NDT weakens and disappears altogether as a result of increasing thermionic emission over the p+ potential barriers. In larger devices (with a gate length of 30 nm or longer), the NDT cannot be observed because of the low transmission probability and small energetic spacing (smaller than kBT ) of the quasi-bound states in the quantum well. We speculate that the inability of the model to predict the NDT observed in 40 nm gate-length devices may be due to an insufficiently accurate knowledge of the actual doping profiles. On the other hand, our study shows that NDT suitable for novel logic applications may be obtained at room temperature in devices of the current or near-future generation (sub-10 nm node), provided an optimal design can be found that minimizes the thermionic emission (requiring high p+ potential-barriers) and punch-through (that meets the opposite requirement of potential-barriers low enough to favor the tunneling current).

  2. Tunneling through stacked InAs/InGaAs/InP self-assembled quantum dots in a magnetic field

    NASA Astrophysics Data System (ADS)

    Silva, A. G.; Lopez, F. E.; Guimarães, P. S. S.; Pires, M. P.; Souza, P. L.; Landi, S. M.; Villas-Bôas, J. M.; Vieira, G. S.; Vinck-Posada, H.; Rodriguez, B. A.

    2011-10-01

    We report results of an investigation of vertical transport in stacked InAs/InGaAs/InP self-assembled quantum dot multi-layers and show evidence of tunneling between quantum dot states in adjacent layers. In the presence of magnetic fields up to 12 T applied parallel to the current, tunneling through Zeeman-split quasi-zero dimensional states is observed. The difference in the g factor of two quantum dots in adjacent layers, which is due to the difference in confinement, is estimated from the data. The experimental value obtained for the difference in g factor is in good agreement with that obtained from a calculation of the quantum dots' energy levels in the presence of the magnetic field.

  3. Tunable negative differential resistance in planar graphene superlattice resonant tunneling diode

    NASA Astrophysics Data System (ADS)

    Sattari-Esfahlan, S. M.; Fouladi-Oskuei, J.; Shojaei, S.

    2017-04-01

    Here, we study the negative differential resistance (NDR) of Dirac electrons in biased planar graphene superlattice (PGSL) and investigate the transport characteristics by adopted transfer matrix method within Landauer-Buttiker formalism. Our model device is based on one-dimensional Kronig-Penney type electrostatic potential in monolayer graphene deposited on a substrate, where the bias voltage is applied by two electrodes in the left and right. At Low bias voltages, we found that NDR appears due to breaking of minibands to Wannier-Stark ladders (WSLs). At the critical bias voltage, delocalization appeared by WS states leads to tunneling peak current in current-voltage (I-V) characteristics. With increasing bias voltage, crossing of rungs from various WSL results in multi-peak NDR. The results demonstrate that the structure parameters like barrier/well thickness and barrier height have remarkable effect on I-V characteristics of PGSL. In addition, Dirac gap enhances peak to valley (PVR) value due to suppressing Klein tunneling. Our results show that the tunable PVR in PGSL resonant tunneling diode can be achievable by structure parameters engineering. NDR at ultra-low bias voltages, such as 100 mV, with giant PVR of 20 is obtained. In our device, the multiple same NDR peaks with ultra-low bias voltage provide promising prospect for multi-valued memories and the low power nanoelectronic tunneling devices.

  4. Quantum tunneling of spin-1 particles from a 5D Einstein-Yang-Mills-Gauss-Bonnet black hole beyond semiclassical approximation

    NASA Astrophysics Data System (ADS)

    Jusufi, K.

    2016-12-01

    In the present paper we study the Hawking radiation as a quantum tunneling effect of spin-1 particles from a five-dimensional, spherically symmetric, Einstein-Yang-Mills-Gauss-Bonnet (5D EYMGB) black hole. We solve the Proca equation (PE) by applying the WKB approximation and separation of variables via Hamilton-Jacobi (HJ) equation which results in a set of five differential equations, and reproduces, in this way, the Hawking temperature. In the second part of this paper, we extend our results beyond the semiclassical approximation. In particular, we derive the logarithmic correction to the entropy of the EYMGB black hole and show that the quantum corrected specific heat indicates the possible existence of a remnant.

  5. Asymmetric quantum-well structures for AlGaN/GaN/AlGaN resonant tunneling diodes

    NASA Astrophysics Data System (ADS)

    Yang, Lin'an; Li, Yue; Wang, Ying; Xu, Shengrui; Hao, Yue

    2016-04-01

    Asymmetric quantum-well (QW) structures including the asymmetric potential-barrier and the asymmetric potential-well are proposed for AlGaN/GaN/AlGaN resonant tunneling diodes (RTDs). Theoretical investigation gives that an appropriate decrease in Al composition and thickness for emitter barrier as well as an appropriate increase of both for collector barrier can evidently improve the negative-differential-resistance characteristic of RTD. Numerical simulation shows that RTD with a 1.5-nm-thick GaN well sandwiched by a 1.3-nm-thick Al0.15Ga0.85N emitter barrier and a 1.7-nm-thick Al0.25Ga0.75N collector barrier can yield the I-V characteristic having the peak current (Ip) and the peak-to-valley current ratio (PVCR) of 0.39 A and 3.6, respectively, about double that of RTD with a 1.5-nm-thick Al0.2Ga0.8N for both barriers. It is also found that an introduction of InGaN sub-QW into the diode can change the tunneling mode and achieve higher transmission coefficient of electron. The simulation demonstrates that RTD with a 2.8-nm-thick In0.03Ga0.97N sub-well in front of a 2.0-nm-thick GaN main-well can exhibit the I-V characteristic having Ip and PVCR of 0.07 A and 11.6, about 7 times and double the value of RTD without sub-QW, respectively. The purpose of improving the structure of GaN-based QW is to solve apparent contradiction between the device structure and the device manufacturability of new generation RTDs for sub-millimeter and terahertz applications.

  6. Nonlinear current-voltage characteristics due to quantum tunneling of phase slips in superconducting Nb nanowire networks

    SciTech Connect

    Trezza, M.; Cirillo, C.; Sabatino, P.; Carapella, G.; Attanasio, C.; Prischepa, S. L.

    2013-12-16

    We report on the transport properties of an array of N∼30 interconnected Nb nanowires, grown by sputtering on robust porous Si substrates. The analyzed system exhibits a broad resistive transition in zero magnetic field, H, and highly nonlinear V(I) characteristics as a function of H, which can be both consistently described by quantum tunneling of phase slips.

  7. Nonlinear current-voltage characteristics due to quantum tunneling of phase slips in superconducting Nb nanowire networks

    NASA Astrophysics Data System (ADS)

    Trezza, M.; Cirillo, C.; Sabatino, P.; Carapella, G.; Prischepa, S. L.; Attanasio, C.

    2013-12-01

    We report on the transport properties of an array of N ˜30 interconnected Nb nanowires, grown by sputtering on robust porous Si substrates. The analyzed system exhibits a broad resistive transition in zero magnetic field, H, and highly nonlinear V(I) characteristics as a function of H, which can be both consistently described by quantum tunneling of phase slips.

  8. Turbulence measurements in high-speed wind tunnels using focusing laser differential interferometry

    NASA Astrophysics Data System (ADS)

    Fulghum, Matthew R.

    Characterization of freestream disturbances and their effect on laminar boundary layer transition is of great importance in high-speed wind tunnel testing, where significant differences between the behavior of scale-model and free-flight transition have long been noted. However, the methods traditionally used to perform this characterization in low-speed flows present significant difficulties when applied to supersonic and especially hypersonic wind tunnels. The design and theory of a focusing laser differential interferometer (FLDI) instrument, originally invented by Smeets at the Institut Saint-Louis in the 1970s and used recently by Parziale in the CalTech T5 shock tunnel, is presented. It is a relatively-simple, non-imaging common-path interferometer for measuring refractive signals from transition and turbulence, and it has a unique ability to look through facility windows, ignore sidewall boundary-layers and vibration, and concentrate only on the refractive signal near a pair of sharp beam foci in the core flow. The instrument's low cost and ease of implementation make it a promising alternative to traditional hot-wire anemometry and particle-based methods for turbulence characterization. Benchtop experiments using a turbulent supersonic air jet demonstrate its focusing ability, frequency response, unwanted signal rejection, and ease of use. The instrument is used to optically interrogate the flow in the Penn State University Supersonic Wind Tunnel and USAF AEDC Hypervelocity Tunnel 9 for measurement of the overall intensity and spectra of freestream disturbances. Precise characterization of the strength and spectral content of the disturbances provides insight into their nature and potential effect upon boundary layer transition. A special feature of the FLDI instrument used here is the replacement of traditional fixed Wollaston prisms with variable Sanderson prisms for laser-beam separation and recombination.

  9. Quantum tunneling injection of hot electrons in Au/TiO2 plasmonic photocatalysts.

    PubMed

    Shiraishi, Yasuhiro; Yasumoto, Naoki; Imai, Jun; Sakamoto, Hirokatsu; Tanaka, Shunsuke; Ichikawa, Satoshi; Ohtani, Bunsho; Hirai, Takayuki

    2017-06-22

    Visible light absorption of plasmonic Au nanoparticles supported on semiconductor TiO2 leads to injection of their photoactivated "hot electrons (ehot(-))" into the TiO2 conduction band. This charge separation facilitates several oxidation and reduction reactions. These plasmonic systems, however, suffer from low quantum yields because the Schottky barrier created at the Au-TiO2 interface suppresses ehot(-) injection. Here we report that Au nanoparticles supported on the anatase particles isolated from Degussa (Evonik) P25 TiO2 promote ehot(-) injection with much higher efficiency than those supported on other commercially-available TiO2 and catalyze aerobic oxidation with very high quantum yield (7.7% at 550 nm). Photoelectrochemical and spectroscopic analysis revealed that the number of Ti(4+) atoms located at the Au-TiO2 interface is the crucial factor. These Ti(4+) atoms neutralize the negative charge of the Au particles and create a Schottky barrier with narrower depletion layer. This facilitates efficient ehot(-) injection by "quantum tunneling" through the Schottky barrier without overbarrier energy. The ehot(-) injection depends on several factors, and loading of 2 wt% Au particles with 3.5-4 nm diameters at around room temperature exhibits the highest activity of plasmonic photocatalysis.

  10. Transport through an impurity tunnel coupled to a Si/SiGe quantum dot

    NASA Astrophysics Data System (ADS)

    Foote, Ryan H.; Ward, Daniel R.; Prance, J. R.; Gamble, John King; Nielsen, Erik; Thorgrimsson, Brandur; Savage, D. E.; Saraiva, A. L.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.

    Here we present measurements of transport through a gate-defined quantum dot formed in a Si/SiGe heterostructure, demonstrating controllable tunnel coupling between the quantum dot and a localized electronic state.1 Combining experimental stability diagram measurements with 3D capacitive modeling based on the expected electron density profiles, we determine the most likely location of the localized state in the quantum well. This work is supported in part by NSF (DMR-1206915, IIA-1132804), ARO (W911NF-12-1-0607) and the William F. Vilas Estate Trust. Development and maintenance of the growth facilities used for fabricating samples supported by DOE (DE-FG02-03ER46028). This research utilized facilities supported by the NSF (DMR-0832760, DMR-1121288). The work of J.K.G. and E.N. was supported in part by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. 1Ryan H. Foote et al., Appl. Phys. Lett. 107, 103112 (2015)

  11. Spectral function and responsivity of resonant tunneling and superlattice quantum dot infrared photodetectors using Green's function

    NASA Astrophysics Data System (ADS)

    Naser, M. A.; Deen, M. J.; Thompson, D. A.

    2007-10-01

    Theoretical modeling of resonant tunneling (RT) and superlattice (SL) quantum dot infrared photodetectors (QDIPs) using Green's function is reported. The RT QDIP gives very low dark current which improves the detectivity of the device and allows for high temperature operation. The SL QDIP gives high responsivity and is suitable for low-level signal detection. The theoretical model is based on Green's function method which is used to calculate the spectral function and the density of states of the two detectors. The kinetic equation that governs Green's functions is solved numerically using the method of finite differences. From the information obtained from the density of states, the possible energy transitions are obtained. The bound states are calculated by solving the eigenvalue problem using the method of finite differences, while the continuum states localized in the quantum dot region are calculated using Green's functions. Using the first order dipole approximation and Fermi golden rule, the eigenstates are used to calculate the responsivity of the detectors which is compared with available experimental results. The theoretical model is then used for studying the effect of changing the quantum dot height-to-diameter ratio on the normal incidence responsivity of the SL structure.

  12. Photon assisted tunneling through three quantum dots with spin-orbit-coupling

    SciTech Connect

    Tang, Han-Zhao; An, Xing-Tao; Wang, Ai-Kun; Liu, Jian-Jun

    2014-08-14

    The effect of an ac electric field on quantum transport properties in a system of three quantum dots, two of which are connected in parallel, while the third is coupled to one of the other two, is investigated theoretically. Based on the Keldysh nonequilibrium Green's function method, the spin-dependent current, occupation number, and spin accumulation can be obtained in our model. An external magnetic flux, Rashba spin-orbit-coupling (SOC), and intradot Coulomb interactions are considered. The magnitude of the spin-dependent average current and the positions of the photon assisted tunneling (PAT) peaks can be accurately controlled and manipulated by simply varying the strength of the coupling and the frequency of the ac field. A particularly interesting result is the observation of a new kind of PAT peak and a multiple-PAT effect that can be generated and controlled by the coupling between the quantum dots. In addition, the spin occupation number and spin accumulation can be well controlled by the Rashba SOC and the magnetic flux.

  13. Quantum mechanical solver for confined heterostructure tunnel field-effect transistors

    SciTech Connect

    Verreck, Devin Groeseneken, Guido; Van de Put, Maarten; Sorée, Bart; Magnus, Wim; Verhulst, Anne S.; Collaert, Nadine; Thean, Aaron; Vandenberghe, William G.

    2014-02-07

    Heterostructure tunnel field-effect transistors (HTFET) are promising candidates for low-power applications in future technology nodes, as they are predicted to offer high on-currents, combined with a sub-60 mV/dec subthreshold swing. However, the effects of important quantum mechanical phenomena like size confinement at the heterojunction are not well understood, due to the theoretical and computational difficulties in modeling realistic heterostructures. We therefore present a ballistic quantum transport formalism, combining a novel envelope function approach for semiconductor heterostructures with the multiband quantum transmitting boundary method, which we extend to 2D potentials. We demonstrate an implementation of a 2-band version of the formalism and apply it to study confinement in realistic heterostructure diodes and p-n-i-n HTFETs. For the diodes, both transmission probabilities and current densities are found to decrease with stronger confinement. For the p-n-i-n HTFETs, the improved gate control is found to counteract the deterioration due to confinement.

  14. Interaction-Assisted Quantum Tunneling of a Bose-Einstein Condensate Out of a Single Trapping Well.

    PubMed

    Potnis, Shreyas; Ramos, Ramon; Maeda, Kenji; Carr, Lincoln D; Steinberg, Aephraim M

    2017-02-10

    We experimentally study tunneling of Bose-condensed ^{87}Rb atoms prepared in a quasibound state and observe a nonexponential decay caused by interatomic interactions. A combination of a magnetic quadrupole trap and a thin 1.3  μm barrier created using a blue-detuned sheet of light is used to tailor traps with controllable depth and tunneling rate. The escape dynamics strongly depend on the mean-field energy, which gives rise to three distinct regimes-classical spilling over the barrier, quantum tunneling, and decay dominated by background losses. We show that the tunneling rate depends exponentially on the chemical potential. Our results show good agreement with numerical solutions of the 3D Gross-Pitaevskii equation.

  15. Interaction-Assisted Quantum Tunneling of a Bose-Einstein Condensate Out of a Single Trapping Well

    NASA Astrophysics Data System (ADS)

    Potnis, Shreyas; Ramos, Ramon; Maeda, Kenji; Carr, Lincoln D.; Steinberg, Aephraim M.

    2017-02-01

    We experimentally study tunneling of Bose-condensed Rb 87 atoms prepared in a quasibound state and observe a nonexponential decay caused by interatomic interactions. A combination of a magnetic quadrupole trap and a thin 1.3 μ m barrier created using a blue-detuned sheet of light is used to tailor traps with controllable depth and tunneling rate. The escape dynamics strongly depend on the mean-field energy, which gives rise to three distinct regimes—classical spilling over the barrier, quantum tunneling, and decay dominated by background losses. We show that the tunneling rate depends exponentially on the chemical potential. Our results show good agreement with numerical solutions of the 3D Gross-Pitaevskii equation.

  16. Direct Observation of Double Hydrogen Transfer via Quantum Tunneling in a Single Porphycene Molecule on a Ag(110) Surface.

    PubMed

    Koch, Matthias; Pagan, Mark; Persson, Mats; Gawinkowski, Sylwester; Waluk, Jacek; Kumagai, Takashi

    2017-09-13

    Quantum tunneling of hydrogen atoms (or protons) plays a crucial role in many chemical and biological reactions. Although tunneling of a single particle has been examined extensively in various one-dimensional potentials, many-particle tunneling in high-dimensional potential energy surfaces remains poorly understood. Here we present a direct observation of a double hydrogen atom transfer (tautomerization) within a single porphycene molecule on a Ag(110) surface using a cryogenic scanning tunneling microscope (STM). The tautomerization rates are temperature independent below ∼10 K, and a large kinetic isotope effect (KIE) is observed upon substituting the transferred hydrogen atoms by deuterium, indicating that the process is governed by tunneling. The observed KIE for three isotopologues and density functional theory calculations reveal that a stepwise transfer mechanism is dominant in the tautomerization. It is also found that the tautomerization rate is increased by vibrational excitation via an inelastic electron tunneling process. Moreover, the STM tip can be used to manipulate the tunneling dynamics through modification of the potential landscape.

  17. Quantum light emission of two lateral tunnel-coupled (In,Ga)As/GaAs quantum dots controlled by a tunable static electric field.

    PubMed

    Beirne, G J; Hermannstädter, C; Wang, L; Rastelli, A; Schmidt, O G; Michler, P

    2006-04-07

    Lateral quantum coupling between two self-assembled (In,Ga)As quantum dots has been observed. Photon statistics measurements between the various excitonic and biexcitonic transitions of these lateral quantum dot molecules display strong antibunching confirming the presence of coupling. Furthermore, we observe an anomalous exciton Stark shift with respect to static electric field. A simple model indicates that the lateral coupling is due to electron tunneling between the dots when the ground states are in resonance. The electron probability can then be shifted to either dot and the system can be used to create a wavelength-tunable single-photon emitter by simply applying a voltage.

  18. Tunnelling of the 3rd kind: A test of the effective non-locality of quantum field theory

    NASA Astrophysics Data System (ADS)

    Gardiner, Simon A.; Gies, Holger; Jaeckel, Joerg; Wallace, Chris J.

    2013-03-01

    Integrating out virtual quantum fluctuations in an originally local quantum field theory results in an effective theory which is non-local. In this letter we argue that tunnelling of the 3rd kind —where particles traverse a barrier by splitting into a pair of virtual particles which recombine only after a finite distance— provides a direct test of this non-locality. We sketch a quantum-optical setup to test this effect, and investigate observable effects in a simple toy model.

  19. Simulation of Quantum Dynamics Based on the Quantum Stochastic Differential Equation

    PubMed Central

    2013-01-01

    The quantum stochastic differential equation derived from the Lindblad form quantum master equation is investigated. The general formulation in terms of environment operators representing the quantum state diffusion is given. The numerical simulation algorithm of stochastic process of direct photodetection of a driven two-level system for the predictions of the dynamical behavior is proposed. The effectiveness and superiority of the algorithm are verified by the performance analysis of the accuracy and the computational cost in comparison with the classical Runge-Kutta algorithm. PMID:23781156

  20. Simulation of quantum dynamics based on the quantum stochastic differential equation.

    PubMed

    Li, Ming

    2013-01-01

    The quantum stochastic differential equation derived from the Lindblad form quantum master equation is investigated. The general formulation in terms of environment operators representing the quantum state diffusion is given. The numerical simulation algorithm of stochastic process of direct photodetection of a driven two-level system for the predictions of the dynamical behavior is proposed. The effectiveness and superiority of the algorithm are verified by the performance analysis of the accuracy and the computational cost in comparison with the classical Runge-Kutta algorithm.

  1. Quantum simulators by design: Many-body physics in reconfigurable arrays of tunnel-coupled traps

    NASA Astrophysics Data System (ADS)

    Sturm, M. R.; Schlosser, M.; Walser, R.; Birkl, G.

    2017-06-01

    We present a platform for the bottom-up construction of itinerant many-body systems: ultracold atoms transferred from a Bose-Einstein condensate into freely configurable arrays of microlens generated focused-beam dipole traps. This complements traditional optical lattices and provides a different access to the field of two-dimensional quantum simulators. The ultimate control of topology, well depth, atom number, and interaction strength is matched by sufficient tunneling. We characterize the required light fields, derive the Bose-Hubbard parameters for several alkali-metal species, and investigate the loading procedures and heating mechanisms. To demonstrate the potential of this approach, we analyze coupled annular Josephson contacts exhibiting many-body resonances.

  2. Concerted hydrogen-bond breaking by quantum tunneling in the water hexamer prism.

    PubMed

    Richardson, Jeremy O; Pérez, Cristóbal; Lobsiger, Simon; Reid, Adam A; Temelso, Berhane; Shields, George C; Kisiel, Zbigniew; Wales, David J; Pate, Brooks H; Althorpe, Stuart C

    2016-03-18

    The nature of the intermolecular forces between water molecules is the same in small hydrogen-bonded clusters as in the bulk. The rotational spectra of the clusters therefore give insight into the intermolecular forces present in liquid water and ice. The water hexamer is the smallest water cluster to support low-energy structures with branched three-dimensional hydrogen-bond networks, rather than cyclic two-dimensional topologies. Here we report measurements of splitting patterns in rotational transitions of the water hexamer prism, and we used quantum simulations to show that they result from geared and antigeared rotations of a pair of water molecules. Unlike previously reported tunneling motions in water clusters, the geared motion involves the concerted breaking of two hydrogen bonds. Similar types of motion may be feasible in interfacial and confined water.

  3. Nonresonant tunneling phonon depopulated GaN based terahertz quantum cascade structures

    NASA Astrophysics Data System (ADS)

    Freeman, Will; Karunasiri, Gamani

    2013-04-01

    GaN based terahertz quantum cascade structures are theoretically studied. Since the Fröhlich interaction is ˜15 times higher in GaN than in GaAs, level broadening makes obtaining appreciable optical gain difficult even with a large population inversion. A density matrix Monte Carlo method is used to calculate the broadening of the optical gain spectra as a function of lattice temperature. We find by using a proposed method of nonresonant tunneling and electron-longitudinal-optical phonon scattering for depopulation of the lower lasing state, that it is possible to sufficiently isolate the upper lasing state and control the lower lasing state lifetime to obtain high optical gain in GaN. The results predict lasing out to 300 K which is significantly higher than for GaAs based structures.

  4. Universality of the edge-tunneling exponent of fractional quantum Hall liquids.

    PubMed

    Wan, Xin; Evers, F; Rezayi, E H

    2005-04-29

    In a microscopic model of fractional quantum Hall liquids with electron-electron interactions and confinement, we calculate the edge Green's function via exact diagonalization. Our results for nu=1/3 and 2/3 suggest that, in the presence of Coulomb interaction, "external" parameters such as the sharpness of the edge and the strength of the edge confining potential, which can lead to edge reconstruction, may cause deviations from universality in the edge-tunneling I-V exponent. In particular, we do not find any direct dependence of this exponent on the range of the interaction potential as suggested by recent calculations in contradiction to the topological nature of the edge.

  5. Atomic-Scale Visualization of Quantum Interference on a Weyl Semimetal Surface by Scanning Tunneling Microscopy.

    PubMed

    Zheng, Hao; Xu, Su-Yang; Bian, Guang; Guo, Cheng; Chang, Guoqing; Sanchez, Daniel S; Belopolski, Ilya; Lee, Chi-Cheng; Huang, Shin-Ming; Zhang, Xiao; Sankar, Raman; Alidoust, Nasser; Chang, Tay-Rong; Wu, Fan; Neupert, Titus; Chou, Fangcheng; Jeng, Horng-Tay; Yao, Nan; Bansil, Arun; Jia, Shuang; Lin, Hsin; Hasan, M Zahid

    2016-01-26

    Weyl semimetals may open a new era in condensed matter physics, materials science, and nanotechnology after graphene and topological insulators. We report the first atomic scale view of the surface states of a Weyl semimetal (NbP) using scanning tunneling microscopy/spectroscopy. We observe coherent quantum interference patterns that arise from the scattering of quasiparticles near point defects on the surface. The measurements reveal the surface electronic structure both below and above the chemical potential in both real and reciprocal spaces. Moreover, the interference maps uncover the scattering processes of NbP's exotic surface states. Through comparison between experimental data and theoretical calculations, we further discover that the orbital and/or spin texture of the surface bands may suppress certain scattering channels on NbP. These results provide a comprehensive understanding of electronic properties on Weyl semimetal surfaces.

  6. Ligand-protein docking using a quantum stochastic tunneling optimization method.

    PubMed

    Mancera, Ricardo L; Källblad, Per; Todorov, Nikolay P

    2004-04-30

    A novel hybrid optimization method called quantum stochastic tunneling has been recently introduced. Here, we report its implementation within a new docking program called EasyDock and a validation with the CCDC/Astex data set of ligand-protein complexes using the PLP score to represent the ligand-protein potential energy surface and ScreenScore to score the ligand-protein binding energies. When taking the top energy-ranked ligand binding mode pose, we were able to predict the correct crystallographic ligand binding mode in up to 75% of the cases. By using this novel optimization method run times for typical docking simulations are significantly shortened. Copyright 2004 Wiley Periodicals, Inc. J Comput Chem 25: 858-864, 2004

  7. Spin Texture of Bi2Se3 Thin Films in the Quantum Tunneling Limit

    NASA Astrophysics Data System (ADS)

    Landolt, Gabriel; Schreyeck, Steffen; Eremeev, Sergey V.; Slomski, Bartosz; Muff, Stefan; Osterwalder, Jürg; Chulkov, Evgueni V.; Gould, Charles; Karczewski, Grzegorz; Brunner, Karl; Buhmann, Hartmut; Molenkamp, Laurens W.; Dil, J. Hugo

    2014-02-01

    By means of spin- and angle-resolved photoelectron spectroscopy we studied the spin structure of thin films of the topological insulator Bi2Se3 grown on InP(111). For thicknesses below six quintuple layers the spin-polarized metallic topological surface states interact with each other via quantum tunneling and a gap opens. Our measurements show that the resulting surface states can be described by massive Dirac cones which are split in a Rashba-like manner due to the substrate induced inversion asymmetry. The inner and the outer Rashba branches have distinct localization in the top and the bottom part of the film, whereas the band apices are delocalized throughout the entire film. Supported by ab initio calculations, our observations help in the understanding of the evolution of the surface states at the topological phase transition and provide the groundwork for the realization of two-dimensional spintronic devices based on topological semiconductors.

  8. InGaAs tunnel diodes for the calibration of semi-classical and quantum mechanical band-to-band tunneling models

    SciTech Connect

    Smets, Quentin; Verreck, Devin; Vandervorst, Wilfried; Groeseneken, Guido; Heyns, Marc M.; Verhulst, Anne S.; Rooyackers, Rita; Merckling, Clément; Simoen, Eddy; Collaert, Nadine; Thean, Voon Y.; Van De Put, Maarten; Sorée, Bart

    2014-05-14

    Promising predictions are made for III-V tunnel-field-effect transistor (FET), but there is still uncertainty on the parameters used in the band-to-band tunneling models. Therefore, two simulators are calibrated in this paper; the first one uses a semi-classical tunneling model based on Kane's formalism, and the second one is a quantum mechanical simulator implemented with an envelope function formalism. The calibration is done for In{sub 0.53}Ga{sub 0.47}As using several p+/intrinsic/n+ diodes with different intrinsic region thicknesses. The dopant profile is determined by SIMS and capacitance-voltage measurements. Error bars are used based on statistical and systematic uncertainties in the measurement techniques. The obtained parameters are in close agreement with theoretically predicted values and validate the semi-classical and quantum mechanical models. Finally, the models are applied to predict the input characteristics of In{sub 0.53}Ga{sub 0.47}As n- and p-lineTFET, with the n-lineTFET showing competitive performance compared to MOSFET.

  9. Experimental determination of quantum-well lifetime effect on large-signal resonant tunneling diode switching time

    NASA Astrophysics Data System (ADS)

    Growden, Tyler A.; Brown, E. R.; Zhang, Weidong; Droopad, Ravi; Berger, Paul R.

    2015-10-01

    An experimental determination is presented of the effect the quantum-well lifetime has on a large-signal resonant tunneling diode (RTD) switching time. Traditional vertical In0.53Ga0.47As/AlAs RTDs were grown, fabricated, and characterized. The switching time was measured with a high-speed oscilloscope and found to be close to the sum of the calculated RC-limited 10%-90% switching time and the quantum-well quasibound-state lifetime. This method displays experimental evidence that the two intrinsic resonant-tunneling characteristic times act independently, and that the quasibound-state lifetime then serves as a quantum-limit on the large-signal speed of RTDs.

  10. Experimental determination of quantum-well lifetime effect on large-signal resonant tunneling diode switching time

    SciTech Connect

    Growden, Tyler A.; Berger, Paul R.; Brown, E. R.; Zhang, Weidong; Droopad, Ravi

    2015-10-12

    An experimental determination is presented of the effect the quantum-well lifetime has on a large-signal resonant tunneling diode (RTD) switching time. Traditional vertical In{sub 0.53}Ga{sub 0.47}As/AlAs RTDs were grown, fabricated, and characterized. The switching time was measured with a high-speed oscilloscope and found to be close to the sum of the calculated RC-limited 10%–90% switching time and the quantum-well quasibound-state lifetime. This method displays experimental evidence that the two intrinsic resonant-tunneling characteristic times act independently, and that the quasibound-state lifetime then serves as a quantum-limit on the large-signal speed of RTDs.

  11. Field electron emission based on resonant tunneling in diamond/CoSi2/Si quantum well nanostructures

    PubMed Central

    Gu, Changzhi; Jiang, Xin; Lu, Wengang; Li, Junjie; Mantl, Siegfried

    2012-01-01

    Excellent field electron emission properties of a diamond/CoSi2/Si quantum well nanostructure are observed. The novel quantum well structure consists of high quality diamond emitters grown on bulk Si substrate with a nanosized epitaxial CoSi2 conducting interlayer. The results show that the main emission properties were modified by varying the CoSi2 thickness and that stable, low-field, high emission current and controlled electron emission can be obtained by using a high quality diamond film and a thicker CoSi2 interlayer. An electron resonant tunneling mechanism in this quantum well structure is suggested, and the tunneling is due to the long electron mean free path in the nanosized CoSi2 layer. This structure meets most of the requirements for development of vacuum micro/nanoelectronic devices and large-area cold cathodes for flat-panel displays. PMID:23082241

  12. Molecular structure and ring tunneling of phenyl formate as observed by microwave spectroscopy and quantum chemistry

    NASA Astrophysics Data System (ADS)

    Ferres, Lynn; Mouhib, Halima; Stahl, Wolfgang; Schwell, Martin; Nguyen, Ha Vinh Lam

    2017-07-01

    Phenyl formate has been investigated by molecular jet Fourier-transform microwave spectroscopy in the frequency range from 2 to 26.5 GHz. Quantum chemical calculations at the MP2/6-311++G(d,p) level of theory indicate that this molecule does not have a plane of symmetry at equilibrium, and that the phenyl ring performs a large amplitude tunneling motion from one side of the Cs configuration to the other. The tilt angle of the ring out of the Hsbnd (Cdbnd O)O plane is ±70° and the calculated tunneling barrier is only 28 cm-1. The two lowest torsional states vt = 0 and 1 are assigned in the experimental spectrum and fitted using the program SPFIT/SPCAT. The Coriolis splitting ΔE between these states is 46.2231(25) GHz, very close to the value of 48.24 GHz calculated using a simple two-top torsional Hamiltonian of the formate group and the phenyl ring.

  13. Detection of single photons by a resonant tunneling heterostructure with a quantum dot layer

    SciTech Connect

    Khanin, Yu. N. Vdovin, E. E.

    2010-08-15

    Light absorption by GaAs/AlAs heterostructures with a layer of self-assembled InAs quantum dots (QDs) at resonant tunneling through an energy-selected QD has been investigated. A high sensitivity of the current through this selected tunneling channel to the absorption of single photons with a wavelength {lambda} {<=} 860 nm up to a temperature of 50 K is demonstrated; this sensitivity is caused by the Coulomb effect of the photoexcited holes captured by surrounding QDs on the resonance conditions. It is shown that single-photon absorption can discretely change the current through the system under study by a factor of more than 50. The captured-hole lifetimes have been measured, and a model has been developed to qualitatively describe the experimental data. It is also demonstrated that the InAs monolayer can effectively absorb photons. The properties of the heterostructure studied can be used not only to detect photons but also to design logical valves and optical memory devices.

  14. Investigation of quantum confinement within the tunneling-percolation transition for ultrathin bismuth films

    NASA Astrophysics Data System (ADS)

    Oller, Declan; Fernandes, Gustavo E.; Kim, Jin Ho; Xu, Jimmy

    2015-10-01

    We investigate conduction phenomena in ultrathin bismuth (Bi) films that are thermally evaporated onto flat quartz. Critical points in the conductance as a function of deposition time are identified and used to scale the data from time dependence to coverage dependence. The resulting nonlinear coverage scaling equation is verified independently via analysis done on transmission electron microscope images of the evaporated films. The scaled data yields critical exponents in very good agreement with classical percolation theory, and clearly shows the transition from the tunneling regime into percolation. Surprisingly, no noticeable signatures of size-quantization effects in the nucleation sites as a function of deposition time is observed in either regime. We discuss our findings in light of Boltzmann transport modeling of 1D conduction as an approximation to the narrow percolative paths that form at the onset of percolation. Our results suggest that lack of a preferred crystallite orientation in the nucleation process may indeed cause quantum-confinement to be too smeared out to be observable in the tunneling to percolation transition.

  15. Single-electron tunneling and Coulomb blockade in carbon-based quantum dots

    NASA Astrophysics Data System (ADS)

    Fan, Wei; Zhang, Rui-Qin

    2009-09-01

    Single-electron tunneling (SET) and Coulomb blockade (CB) phenomena have been widely observed in nanoscaled electronics and have received intense attention around the world. In the past few years, we have studied SET in carbon nanotube fragments and fullerenes by applying the so-called “Orthodox” theory [28]. As outlined in this review article, we investigated the single-electron charging and discharging process via current-voltage characteristics, gate effect, and electronic structure-related factors. Because the investigated geometric structures are three-dimensionally confined, resulting in a discrete spectrum of energy levels resembling the property of quantum dots, we evidenced the CB and Coulomb staircases in these structures. These nanostructures are sufficiently small that introducing even a single electron is sufficient to dramatically change the transport properties as a result of the charging energy associated with this extra electron. We found that the Coulomb staircases occur in the I-V characteristics only when the width of the left barrier junction is smaller than that of the right barrier junction. In this case, the transmission coefficient of the emitter junction is larger than that of the collector junction; also, occupied levels enter the bias window, thereby enhancing the tunneling extensively.

  16. A Simple Quantum Integro-Differential Solver (SQuIDS)

    NASA Astrophysics Data System (ADS)

    Argüelles Delgado, Carlos A.; Salvado, Jordi; Weaver, Christopher N.

    2015-11-01

    Simple Quantum Integro-Differential Solver (SQuIDS) is a C++ code designed to solve semi-analytically the evolution of a set of density matrices and scalar functions. This is done efficiently by expressing all operators in an SU(N) basis. SQuIDS provides a base class from which users can derive new classes to include new non-trivial terms from the right hand sides of density matrix equations. The code was designed in the context of solving neutrino oscillation problems, but can be applied to any problem that involves solving the quantum evolution of a collection of particles with Hilbert space of dimension up to six.

  17. Coherent Interlayer Tunneling and Negative Differential Resistance with High Current Density in Double Bilayer Graphene-WSe2 Heterostructures.

    PubMed

    Burg, G William; Prasad, Nitin; Fallahazad, Babak; Valsaraj, Amithraj; Kim, Kyounghwan; Taniguchi, Takashi; Watanabe, Kenji; Wang, Qingxiao; Kim, Moon J; Register, Leonard F; Tutuc, Emanuel

    2017-06-14

    We demonstrate gate-tunable resonant tunneling and negative differential resistance between two rotationally aligned bilayer graphene sheets separated by bilayer WSe2. We observe large interlayer current densities of 2 and 2.5 μA/μm(2) and peak-to-valley ratios approaching 4 and 6 at room temperature and 1.5 K, respectively, values that are comparable to epitaxially grown resonant tunneling heterostructures. An excellent agreement between theoretical calculations using a Lorentzian spectral function for the two-dimensional (2D) quasiparticle states, and the experimental data indicates that the interlayer current stems primarily from energy and in-plane momentum conserving 2D-2D tunneling, with minimal contributions from inelastic or non-momentum-conserving tunneling. We demonstrate narrow tunneling resonances with intrinsic half-widths of 4 and 6 meV at 1.5 and 300 K, respectively.

  18. Wind tunnel unsteady pressure measurements using a differential optical fiber Fabry-Perot pressure sensor

    NASA Astrophysics Data System (ADS)

    Correia, Ricardo; Staines, Stephen E.; James, Stephen W.; Lawson, Nicholas; Garry, Kevin; Tatam, Ralph P.

    2014-05-01

    A differential extrinsic optical fiber Fabry-Perot based pressure sensor has been developed and benchmarked against a conventional piezoresistive Kulite pressure sensor. The sensors were placed on the fuselage of a 1:10/3 sub-scale model of a Scottish aviation Bulldog, which was placed in a wind-tunnel. Pressure tappings that surrounded the sensors aided the mapping of pressure distribution around this section of the fuselage. The results obtained from the fibre optic pressure sensor are in good agreement with those obtained from the Kulite and from the pressure tappings.

  19. Carrier-tunneling-induced photovoltaic effect of InAs/GaAs quantum-dot solar cells

    NASA Astrophysics Data System (ADS)

    Lee, Seung Hyun; Kim, Jong Su; Lee, Sang Jun

    2016-08-01

    This study reports the observation of the carrier-tunneling-induced photovoltaic (PV) effect in an InAs/GaAs quantum-dot solar cell (QDSC). The illuminated current-voltage (J-V) characteristics and the applied-bias-dependent electroreflectance (ER) were measured at 12 K by using an excitation laser with a wavelength of 975 nm (1.27 eV), which excites only the quantum-dot (QD) states below the GaAs band gap. The J-V results showed a peculiar current curve in the reverse bias region caused by carrier tunneling. The ER results showed that the junction electric field ( F) decreased with increasing intensity of the excitation laser ( I ex ) at different applied-bias-voltages ( V a ) due to the tunneling-induced PV effect. The PV effect was enhanced by improved tunneling with increasing reverse bias voltage. We also evaluated the tunneling carrier density ( σ pv ) as a function of V a in the QDSC.

  20. Large-amplitude dynamics in vinyl radical: the role of quantum tunneling as an isomerization mechanism.

    PubMed

    Sharma, Amit R; Bowman, Joel M; Nesbitt, David J

    2012-01-21

    We report tunneling splittings associated with the large amplitude 1,2 H-atom migration to the global minima in the vinyl radical. These are obtained using a recent full-dimensional ab initio potential energy surface (PES) [A. R. Sharma, B. J. Braams, S. Carter, B. C. Shepler, and J. M. Bowman, J. Chem. Phys. 130(17), 174301 (2009)] and independently, directly calculated "reaction paths." The PES is a multidimensional fit to coupled cluster single and double and perturbative treatment of triple excitations coupled-cluster single double triple (CCSD(T)) with the augmented correlation consistent triple zeta basis set (aug-cc-pVTZ). The reaction path potentials are obtained from a series of CCSD(T)/aug-cc-pVnTZ calculations extrapolated to the complete basis set limit. Approximate 1D calculations of the tunneling splitting for these 1,2-H atom migrations are obtained using each of these potentials as well as quite different 1D Hamiltonians. The splittings are calculated over a large energy ranges, with results from the two sets of calculations in excellent agreement. Though negligibly slow (>1 s) for the vibrational ground state, this work predicts tunneling-promoted 1,2 hydride shift dynamics in vinyl to exhibit exponential growth with internal vibrational excitation, specifically achieving rates on the sub-μs time scale at energies above E ≈ 7500 cm(-1). Most importantly, these results begin to elucidate the possible role of quantum isomerization through barriers without dissociation, in competition with the more conventional picture of classical roaming permitted over a much narrower window of energies immediately below the bond dissociation limit. Furthermore, when integrated over a Boltzmann distribution of thermal energies, these microcanonical tunneling rates are consistent with sub-μs time scales for 1,2 hydride shift dynamics at T > 1400 K. These results have potential relevance for combustion modeling of low-pressure flames, as well as recent

  1. Fast detection of single-charge tunneling to a graphene quantum dot in a multi-level regime

    NASA Astrophysics Data System (ADS)

    Müller, T.; Güttinger, J.; Bischoff, D.; Hellmüller, S.; Ensslin, K.; Ihn, T.

    2012-07-01

    In situ-tunable radio-frequency reflectometry is used for fast charge-detection measurements on a graphene single quantum dot. The variable capacitance of our special matching network both grants tunability and compensates for the large stray capacitance between the charge sensor's contacts and the doped silicon oxide backgate. To demonstrate the high detection bandwidth thus achieved, the rates for tunneling into and out of the dot through the same barrier are determined. Finally, an analytical model for calculating these rates in the multi-level tunneling regime is presented and found to correspond very well to our experimental observations.

  2. Interplay between Switching Driven by the Tunneling Current and Atomic Force of a Bistable Four-Atom Si Quantum Dot.

    PubMed

    Yamazaki, Shiro; Maeda, Keisuke; Sugimoto, Yoshiaki; Abe, Masayuki; Zobač, Vladimír; Pou, Pablo; Rodrigo, Lucia; Mutombo, Pingo; Pérez, Ruben; Jelínek, Pavel; Morita, Seizo

    2015-07-08

    We assemble bistable silicon quantum dots consisting of four buckled atoms (Si4-QD) using atom manipulation. We demonstrate two competing atom switching mechanisms, downward switching induced by tunneling current of scanning tunneling microscopy (STM) and opposite upward switching induced by atomic force of atomic force microscopy (AFM). Simultaneous application of competing current and force allows us to tune switching direction continuously. Assembly of the few-atom Si-QDs and controlling their states using versatile combined AFM/STM will contribute to further miniaturization of nanodevices.

  3. Lossless Kerr-phase gate in a quantum-well system via tunneling interference effect for weak fields

    NASA Astrophysics Data System (ADS)

    Shi, Y. L.; Huang, Y. C.; Wu, J. X.; Zhu, C. J.; Xu, J. P.; Yang, Y. P.

    2015-06-01

    We examine a lossless Kerr-phase gate in a semiconductor quantum-well system via the tunneling interference effect for weak fields. We show that there exists a magic detuning for the signal field, at which the absorption or amplification for the probe field can be eliminated by increasing the tunneling interference effect. Simultaneously, the probe field will acquire a -π phase shift at the exit of the medium. We demonstrate with numerical simulations that a lossless Kerr-phase gate is achieved, which may result in many applications in information science and telecommunication.

  4. Inter-layer edge tunneling and transport properties in separately contacted double-layer quantum-Hall systems

    NASA Astrophysics Data System (ADS)

    Yoshioka, Daijiro

    1998-01-01

    A theory of transport in the quantum-Hall regime is developed for separately contacted double-layer electron systems. Inter-layer tunneling provides a channel for equilibration of the distribution functions in the two layers at the edge states. Resistances and transresistances for various configurations of the electrodes are calculated as functions of the inter-layer tunneling amplitude. Induced current in one of the layer by a current in the other is also calculated. It is shown that reflection at the leads causes change in the results for some electrode configurations. The results obtained in this work is consistent with recent experiments.

  5. Separation of noncommutative differential calculus on quantum Minkowski space

    SciTech Connect

    Bachmaier, Fabian; Blohmann, Christian

    2006-02-15

    Noncommutative differential calculus on quantum Minkowski space is not separated with respect to the standard generators, in the sense that partial derivatives of functions of a single generator can depend on all other generators. It is shown that this problem can be overcome by a separation of variables. We study the action of the universal L-matrix, appearing in the coproduct of partial derivatives, on generators. Powers of the resulting quantum Minkowski algebra valued matrices are calculated. This leads to a nonlinear coordinate transformation which essentially separates the calculus. A compact formula for general derivatives is obtained in form of a chain rule with partial Jackson derivatives. It is applied to the massive quantum Klein-Gordon equation by reducing it to an ordinary q-difference equation. The rest state solution can be expressed in terms of a product of q-exponential functions in the separated variables.

  6. Theoretical analysis of AlGaN/GaN resonant tunnelling diodes with step heterojunctions spacer and sub-quantum well

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Gao, B.; Gong, M.

    2017-06-01

    In this paper, we proposed to use step heterojunctions emitter spacer (SHES) and InGaN sub-quantum well in AlGaN/GaN/AlGaN double barrier resonant tunnelling diodes (RTDs). Theoretical analysis of RTD with SHES and InGaN sub-quantum well was presented, which indicated that the negative differential resistance (NDR) characteristic was improved. And the simulation results, peak current density JP=82.67 mA/μm2, the peak-to-valley current ratio PVCR=3.38, and intrinsic negative differential resistance RN=-0.147Ω at room temperature, verified the improvement of NDR characteristic brought about by SHES and InGaN sub-quantum well. Both the theoretical analysis and simulation results showed that the device performance, especially the average oscillator output power presented great improvement and reached 2.77mW/μm2 magnitude. And the resistive cut-off frequency would benefit a lot from the relatively small RN as well. Our works provide an important alternative to the current approaches in designing new structure GaN based RTD for practical high frequency and high power applications.

  7. Playing with quantum Hall effects and single-electron-tunneling effects

    NASA Astrophysics Data System (ADS)

    Komiyama, S.

    2003-05-01

    The usefulness of quantum Hall effect (QHE) conductors and quantum dot (QD) devices is revealed by reviewing five remarkable effects. The first is the sensitive detection of terahertz (THz) radiation by QHE conductors. The second is the imaging of THz emission from non-equilibrium carriers in QHE conductors, by using scanning THz microscopes. The third is the single-photon detection of THz radiation in strong magnetic fields, which is carried out by incorporating a QHE electron system into a QD. Individual events of single-THz-photon absorption within the QD via cyclotron resonance cause the QD to electrically polarize, which, in turn, is detected as switches of the tunnel conductance through the QD. The fourth is the single-photon detection of THz radiation by using double QDs in the absence of a magnetic field. Both of the photon detectors are implemented in gate-voltage-induced lateral GaAs/AlGaAs QDs, and exploiting the extraordinary sensitivity of single-electron transistors to the charge. The fifth is the coherent control of nuclear spins in QHE conductors. Nuclear spins are (i) electrically polarized by unequally populating spin-split QHE edge channels via the hyperfine interaction, (ii) coherently controlled via pulsed nuclear magnetic resonance induced by local RF magnetic fields, and (iii) finally detected by the edge channels through resistance change of the Hall device. The controlled nuclear spins are limited to those along the edge channels, on the order of 10 9.

  8. Electrochemical quantum tunneling for electronic detection and characterization of biological toxins

    NASA Astrophysics Data System (ADS)

    Gupta, Chaitanya; Walker, Ross M.; Gharpuray, Rishi; Shulaker, Max M.; Zhang, Zhiyong; Javanmard, Mehdi; Davis, Ronald W.; Murmann, Boris; Howe, Roger T.

    2012-06-01

    This paper introduces a label-free, electronic biomolecular sensing platform for the detection and characterization of trace amounts of biological toxins within a complex background matrix. The mechanism for signal transduction is the electrostatic coupling of molecule bond vibrations to charge transport across an insulated electrode-electrolyte interface. The current resulting from the interface charge flow has long been regarded as an experimental artifact of little interest in the development of traditional charge based biosensors like the ISFET, and has been referred to in the literature as a "leakage current". However, we demonstrate by experimental measurements and theoretical modeling that this current has a component that arises from the rate-limiting transition of a quantum mechanical electronic relaxation event, wherein the electronic tunneling process between a hydrated proton in the electrolyte and the metallic electrode is closely coupled to the bond vibrations of molecular species in the electrolyte. Different strategies to minimize the effect of quantum decoherence in the quantized exchange of energy between the molecular vibrations and electron energy will be discussed, as well as the experimental implications of such strategies. Since the mechanism for the transduction of chemical information is purely electronic and does not require labels or tags or optical transduction, the proposed platform is scalable. Furthermore, it can achieve the chemical specificity typically associated with traditional micro-array or mass spectrometry-based platforms that are used currently to analyze complex biological fluids for trace levels of toxins or pathogen markers.

  9. Edge magnetoplasmons in double quantum wells: Influence of Coulomb coupling and tunneling

    NASA Astrophysics Data System (ADS)

    Vasilopoulos, P.; Balev, O. G.

    1998-12-01

    A random-phase approximation (RPA) treatment of fundamental edge magnetoplasmons (EMPs) in a double quantum well (DQW) is presented for strong magnetic fields, low temperatures, and total filling factor ν=2. It is valid for lateral confining potentials that allow Landau-level flattening to be neglected. The cyclotron and Zeeman energies are larger than the DQW energy splitting ( Δ2+4 T2) 1/2, where Δ is the splitting of the isolated wells and T the tunneling strength. For negligible T the inter-well Coulomb coupling drastically renormalizes the fundamental EMP of the corresponding single quantum well ( ν=1) and gives rise to two DQW fundamental EMPs. These modes can be affected further by varying the inter-well distance, along the z axis, and/or the separation of the wells' edges along the y axis. The charge profile of the fast and slow mode varies, respectively, in an acoustic and optical manner along the y axis. For strong T these modes can be modified essentially when Δ is changed by applying a transverse electric field to the DQW.

  10. Arrhenius-kinetics evidence for quantum tunneling in microbial “social” decision rates

    PubMed Central

    2010-01-01

    . Nonlinear Arrhenius kinetics in ciliate decision making suggest transitions from one signaling strategy to another result from a computational analogue of quantum tunneling in social information processing. PMID:21331234

  11. Arrhenius-kinetics evidence for quantum tunneling in microbial "social" decision rates.

    PubMed

    Clark, Kevin B

    2010-11-01

    . Nonlinear Arrhenius kinetics in ciliate decision making suggest transitions from one signaling strategy to another result from a computational analogue of quantum tunneling in social information processing.

  12. Differentiating amino acid residues and side chain orientations in peptides using scanning tunneling microscopy.

    PubMed

    Claridge, Shelley A; Thomas, John C; Silverman, Miles A; Schwartz, Jeffrey J; Yang, Yanlian; Wang, Chen; Weiss, Paul S

    2013-12-11

    Single-molecule measurements of complex biological structures such as proteins are an attractive route for determining structures of the large number of important biomolecules that have proved refractory to analysis through standard techniques such as X-ray crystallography and nuclear magnetic resonance. We use a custom-built low-current scanning tunneling microscope to image peptide structures at the single-molecule scale in a model peptide that forms β sheets, a structural motif common in protein misfolding diseases. We successfully differentiate between histidine and alanine amino acid residues, and further differentiate side chain orientations in individual histidine residues, by correlating features in scanning tunneling microscope images with those in energy-optimized models. Beta sheets containing histidine residues are used as a model system due to the role histidine plays in transition metal binding associated with amyloid oligomerization in Alzheimer's and other diseases. Such measurements are a first step toward analyzing peptide and protein structures at the single-molecule level.

  13. Bilayer Graphene-Hexagonal Boron Nitride Heterostructure Negative Differential Resistance Interlayer Tunnel FETs

    NASA Astrophysics Data System (ADS)

    Kang, Sangwoo; Fallahazad, Babak; Lee, Kayoung; Movva, Hema; Kim, Kyounghwan; Corbet, Chris; Taniguchi, Takashi; Watanabe, Kenji; Colombo, Luigi; Register, Leonard; Tutuc, Emanuel; Banerjee, Sanjay

    2015-03-01

    We present the operation of a vertical tunneling field effect transistor using a stacked double bilayer graphene (BLG) and hexagonal boron nitride (hBN) heterostructure. The device is fabricated with the so-called Van der Waals transfer method with the edges of the top and bottom BLG flakes being rotationally aligned to roughly 60°. The device shows multiple negative differential resistance (NDR) peaks which can be adjusted through the gate bias. Temperature dependent measurements show that the peak width of the differential conductance broadens and the height lowered when the temperature is increased, which is indicative of resonant tunneling. Through electrostatic calculations, it is shown that the multiple peaks occur when the two conduction bands at the K-point of the top and bottom bilayer graphene become aligned at certain bias conditions. It is also shown that by adjusting the rotational alignment of the bands of the top and bottom BLG through an in-plane magnetic field, the conductance peaks can be broadened. In addition, utilizing the NDR characteristic of the device, one-transistor latch or SRAM operation is demonstrated.

  14. Quantum Tunneling of the Non-stationary Kerr-Newman Black Hole via a New Type of General Tortoise Coordinate Transformation

    NASA Astrophysics Data System (ADS)

    Feng, Zhong-Wen; Deng, Juan; Li, Guo-Ping; Yang, Shu-Zheng

    2012-10-01

    In this paper, the quantum tunneling of the non-stationary Kerr-Newman black hole is investigated via Hamilton-Jacobi equation and two types of general tortoise coordinate transformations. The tunneling rates, the Hawking temperatures and radiation spectrums are derived respectively. Our result shows that the new type of general tortoise coordinate transformation is more reasonable.

  15. Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots

    NASA Astrophysics Data System (ADS)

    Wang, H.; Lhuillier, E.; Yu, Q.; Mottaghizadeh, A.; Ulysse, C.; Zimmers, A.; Descamps-Mandine, A.; Dubertret, B.; Aubin, H.

    2015-07-01

    We present a tunnel spectroscopy study of single PbS quantum dots (QDs) as a function of temperature and gate voltage. Three distinct signatures of strong electron-phonon coupling are observed in the electron tunneling spectrum (ETS) of these QDs. In the shell-filling regime, the 8 × degeneracy of the electronic levels is lifted by the Coulomb interactions and allows the observation of phonon subbands that result from the emission of optical phonons. At low bias, a gap is observed in the ETS that cannot be closed with the gate voltage, which is a distinguishing feature of the Franck-Condon blockade. From the data, a Huang-Rhys factor in the range S ˜1.7 -2.5 is obtained. Finally, in the shell-tunneling regime, the optical phonons appear in the inelastic ETS d2I /d V2 .

  16. Resonant tunneling diodes based on ZnO for quantum cascade structures (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Hinkov, Borislav; Schwarz, Benedikt; Harrer, Andreas; Ristanic, Daniela; Schrenk, Werner; Hugues, Maxime; Chauveau, Jean-Michel; Strasser, Gottfried

    2017-02-01

    The terahertz (THz) spectral range (lambda 30µm - 300µm) is also known as the "THz-gap" because of the lack of compact semiconductor devices. Various real-world applications would strongly benefit from such sources like trace-gas spectroscopy or security-screening. A crucial step is the operation of THz-emitting lasers at room temperature. But this seems out of reach with current devices, of which GaAs-based quantum cascade lasers (QCLs) seem to be the most promising ones. They are limited by the parasitic, non-optical LO-phonon transitions (36meV in GaAs), being on the same order as the thermal energy at room temperature (kT = 26meV). This can be solved by using larger LO-phonon materials like ZnO (E_LO = 72meV). But to master the fabrication of ZnO-based QC structures, a high quality epitaxial growth is crucial followed by a well-controlled fabrication process including ZnO/ZnMgO etching. We use devices grown on m-plane ZnO-substrate by molecular beam epitaxy. They are patterned by reactive ion etching in a CH4-based chemistry (CH4:H2:Ar/30:3:3 sccm) into 50μm to 150μm square mesas. Resonant tunneling diode structures are investigated in this geometry and are presented including different barrier- and well-configurations. We extract contact resistances of 8e-5 Omega cm^2 for un-annealed Ti/Au contacts and an electron mobility of above 130cm^2/Vs, both in good agreement with literature. Proving that resonant electron tunneling can be achieved in ZnO is one of the crucial building blocks of a QCL. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 665107.

  17. 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.

  18. Quantum tunneling of vortices in single crystal Tl2CaBa2Cu2O8 superconductors

    NASA Astrophysics Data System (ADS)

    Zuo, F.; Shi, A. C.; Berlinsky, A. J.; Duan, H. M.; Hermann, A. M.

    1994-12-01

    Data are presented on the temperature-dependent time-logarithmic magnetic relaxation rate S(T) = ¦dM/din t¦ of the high-Tc superconductor Tl2CaBa2 Cu2O8. It is found that at low temperatures the relaxation rate has the form S(T) = A(H) exp[(T/T*)2], which does not extrapolate to zero at T = 0, thus excluding conventional thermally activated flux creep and providing evidence of quantum vortex tunneling. From a quantum flux tunneling theory, it is shown that S(T) ∝ I/ηer{p/2}. The measurements of the relaxation rate thus provide information about the effective viscosity ηe of fluxons.

  19. Tuning inter-dot tunnel coupling of an etched graphene double quantum dot by adjacent metal gates

    PubMed Central

    Wei, Da; Li, Hai-Ou; Cao, Gang; Luo, Gang; Zheng, Zhi-Xiong; Tu, Tao; Xiao, Ming; Guo, Guang-Can; Jiang, Hong-Wen; Guo, Guo-Ping

    2013-01-01

    Graphene double quantum dots (DQDs) open to use charge or spin degrees of freedom for storing and manipulating quantum information in this new electronic material. However, impurities and edge disorders in etched graphene nano-structures hinder the ability to control the inter-dot tunnel coupling, tC, the most important property of the artificial molecule. Here we report measurements of tC in an all-metal-side-gated graphene DQD. We find that tC can be controlled continuously about a factor of four by employing a single gate. Furthermore, tC, can be changed monotonically about another factor of four as electrons are gate-pumped into the dot one by one. The results suggest that the strength of tunnel coupling in etched graphene DQDs can be varied in a rather broad range and in a controllable manner, which improves the outlook to use graphene as a base material for qubit applications. PMID:24213723

  20. Electron-tunneling modulation in percolating network of graphene quantum dots: fabrication, phenomenological understanding, and humidity/pressure sensing applications.

    PubMed

    Sreeprasad, T S; Rodriguez, Alfredo Alexander; Colston, Jonathan; Graham, Augustus; Shishkin, Evgeniy; Pallem, Vasanta; Berry, Vikas

    2013-04-10

    The two-dimensional (2D) electron cloud, flexible carbon-carbon bonds, chemical modifiability, and size-dependent quantum-confinement and capacitance makes graphene nanostructures (GN) a widely tunable material for electronics. Here we report the oxidation-led edge-roughening and cleavage of long graphene nanoribbons (GNRs) (150 nm wide) synthesized via nanotomy (nanoscale cutting) of graphite (with 2 nm edged diamond knife) to produce graphene quantum dots (GQD). These GQDs (~100-200 nm) selectively interfaced with polyelectrolyte microfiber (diameter = 2-20 μm) form an electrically percolating-network exhibiting a characteristic Coulomb blockade signature with a dry tunneling distance of 0.58 nm and conduction activation energy of 3 meV. We implement this construct to demonstrate the functioning of humidity and pressure sensors and outline their governing model. Here, a 0.36 nm decrease in the average tunneling-barrier-width between GQDs (tunneling barrier = 5.11 eV) increases the conductivity of the device by 43-fold. These devices leverage the modulation in electron tunneling distances caused by pressure and humidity induced water transport across the hygroscopic polymer microfiber (Henry's constant = 0.215 Torr(-1)). This is the foremost example of GQD-based electronic sensors. We envision that this polymer-interfaced GQD percolating network will evolve a new class of sensors leveraging the low mass, low capacitance, high conductivity, and high sensitivity of GQD and the interfacial or dielectric properties of the polymer fiber.

  1. Theory of two-dimensional macroscopic quantum tunneling in a Josephson junction coupled with an LC circuit

    NASA Astrophysics Data System (ADS)

    Kawabata, Shiro; Kato, Takeo; Bauch, Thilo

    2009-03-01

    We investigate classical thermal activation (TA) and macroscopic quantum tunneling (MQT) for a Josephson junction coupled with an LC circuit theoretically. The TA and MQT escape rate are calculated analytically by taking into account the two-dimensional nature of the classical and quantum phase dynamics. We find that the MQT escape rate is largely suppressed by the coupling to the LC circuit. On the other hand, this coupling gives rise to slight reduction of the TA escape rate. These results are relevant for the interpretation of a recent experiment on the MQT and TA phenomena in grain boundary YBCO Josephson junctions.

  2. Localized phase structures growing out of quantum fluctuations in a quench of tunnel-coupled atomic condensates.

    PubMed

    Neuenhahn, Clemens; Polkovnikov, Anatoli; Marquardt, Florian

    2012-08-24

    We investigate the relative phase between two weakly interacting 1D condensates of bosonic atoms after suddenly switching on the tunnel coupling. The following phase dynamics is governed by the quantum sine-Gordon equation. In the semiclassical limit of weak interactions, we observe the parametric amplification of quantum fluctuations leading to the formation of breathers with a finite lifetime. The typical lifetime and density of these "quasibreathers" are derived employing exact solutions of the classical sine-Gordon equation. Both depend on the initial relative phase between the condensates, which is considered as a tunable parameter.

  3. The ground state tunneling splitting and the zero point energy of malonaldehyde: a quantum Monte Carlo determination.

    PubMed

    Viel, Alexandra; Coutinho-Neto, Maurício D; Manthe, Uwe

    2007-01-14

    Quantum dynamics calculations of the ground state tunneling splitting and of the zero point energy of malonaldehyde on the full dimensional potential energy surface proposed by Yagi et al. [J. Chem. Phys. 1154, 10647 (2001)] are reported. The exact diffusion Monte Carlo and the projection operator imaginary time spectral evolution methods are used to compute accurate benchmark results for this 21-dimensional ab initio potential energy surface. A tunneling splitting of 25.7+/-0.3 cm-1 is obtained, and the vibrational ground state energy is found to be 15 122+/-4 cm-1. Isotopic substitution of the tunneling hydrogen modifies the tunneling splitting down to 3.21+/-0.09 cm-1 and the vibrational ground state energy to 14 385+/-2 cm-1. The computed tunneling splittings are slightly higher than the experimental values as expected from the potential energy surface which slightly underestimates the barrier height, and they are slightly lower than the results from the instanton theory obtained using the same potential energy surface.

  4. Band structure effects on resonant tunneling in III-V quantum wells versus two-dimensional vertical heterostructures

    NASA Astrophysics Data System (ADS)

    Campbell, Philip M.; Tarasov, Alexey; Joiner, Corey A.; Ready, W. Jud; Vogel, Eric M.

    2016-01-01

    Since the invention of the Esaki diode, resonant tunneling devices have been of interest for applications including multi-valued logic and communication systems. These devices are characterized by the presence of negative differential resistance in the current-voltage characteristic, resulting from lateral momentum conservation during the tunneling process. While a large amount of research has focused on III-V material systems, such as the GaAs/AlGaAs system, for resonant tunneling devices, poor device performance and device-to-device variability have limited widespread adoption. Recently, the symmetric field-effect transistor (symFET) was proposed as a resonant tunneling device incorporating symmetric 2-D materials, such as transition metal dichalcogenides (TMDs), separated by an interlayer barrier, such as hexagonal boron-nitride. The achievable peak-to-valley ratio for TMD symFETs has been predicted to be higher than has been observed for III-V resonant tunneling devices. This work examines the effect that band structure differences between III-V devices and TMDs has on device performance. It is shown that tunneling between the quantized subbands in III-V devices increases the valley current and decreases device performance, while the interlayer barrier height has a negligible impact on performance for barrier heights greater than approximately 0.5 eV.

  5. Band structure effects on resonant tunneling in III-V quantum wells versus two-dimensional vertical heterostructures

    SciTech Connect

    Campbell, Philip M.; Tarasov, Alexey; Joiner, Corey A.; Vogel, Eric M.; Ready, W. Jud

    2016-01-14

    Since the invention of the Esaki diode, resonant tunneling devices have been of interest for applications including multi-valued logic and communication systems. These devices are characterized by the presence of negative differential resistance in the current-voltage characteristic, resulting from lateral momentum conservation during the tunneling process. While a large amount of research has focused on III-V material systems, such as the GaAs/AlGaAs system, for resonant tunneling devices, poor device performance and device-to-device variability have limited widespread adoption. Recently, the symmetric field-effect transistor (symFET) was proposed as a resonant tunneling device incorporating symmetric 2-D materials, such as transition metal dichalcogenides (TMDs), separated by an interlayer barrier, such as hexagonal boron-nitride. The achievable peak-to-valley ratio for TMD symFETs has been predicted to be higher than has been observed for III-V resonant tunneling devices. This work examines the effect that band structure differences between III-V devices and TMDs has on device performance. It is shown that tunneling between the quantized subbands in III-V devices increases the valley current and decreases device performance, while the interlayer barrier height has a negligible impact on performance for barrier heights greater than approximately 0.5 eV.

  6. Asymmetric quantum-well structures for AlGaN/GaN/AlGaN resonant tunneling diodes

    SciTech Connect

    Yang, Lin'an Li, Yue; Wang, Ying; Xu, Shengrui; Hao, Yue

    2016-04-28

    Asymmetric quantum-well (QW) structures including the asymmetric potential-barrier and the asymmetric potential-well are proposed for AlGaN/GaN/AlGaN resonant tunneling diodes (RTDs). Theoretical investigation gives that an appropriate decrease in Al composition and thickness for emitter barrier as well as an appropriate increase of both for collector barrier can evidently improve the negative-differential-resistance characteristic of RTD. Numerical simulation shows that RTD with a 1.5-nm-thick GaN well sandwiched by a 1.3-nm-thick Al{sub 0.15}Ga{sub 0.85}N emitter barrier and a 1.7-nm-thick Al{sub 0.25}Ga{sub 0.75}N collector barrier can yield the I-V characteristic having the peak current (Ip) and the peak-to-valley current ratio (PVCR) of 0.39 A and 3.6, respectively, about double that of RTD with a 1.5-nm-thick Al{sub 0.2}Ga{sub 0.8}N for both barriers. It is also found that an introduction of InGaN sub-QW into the diode can change the tunneling mode and achieve higher transmission coefficient of electron. The simulation demonstrates that RTD with a 2.8-nm-thick In{sub 0.03}Ga{sub 0.97}N sub-well in front of a 2.0-nm-thick GaN main-well can exhibit the I-V characteristic having Ip and PVCR of 0.07 A and 11.6, about 7 times and double the value of RTD without sub-QW, respectively. The purpose of improving the structure of GaN-based QW is to solve apparent contradiction between the device structure and the device manufacturability of new generation RTDs for sub-millimeter and terahertz applications.

  7. Gap state charge induced spin-dependent negative differential resistance in tunnel junctions

    NASA Astrophysics Data System (ADS)

    Jiang, Jun; Zhang, X.-G.; Han, X. F.

    2016-04-01

    We propose and demonstrate through first-principles calculation a new spin-dependent negative differential resistance (NDR) mechanism in magnetic tunnel junctions (MTJ) with cubic cation disordered crystals (CCDC) AlO x or Mg1-x Al x O as barrier materials. The CCDC is a class of insulators whose band gap can be changed by cation doping. The gap becomes arched in an ultrathin layer due to the space charge formed from metal-induced gap states. With an appropriate combination of an arched gap and a bias voltage, NDR can be produced in either spin channel. This mechanism is applicable to 2D and 3D ultrathin junctions with a sufficiently small band gap that forms a large space charge. It provides a new way of controlling the spin-dependent transport in spintronic devices by an electric field. A generalized Simmons formula for tunneling current through junction with an arched gap is derived to show the general conditions under which ultrathin junctions may exhibit NDR.

  8. Tunnel transport and interlayer excitons in bilayer fractional quantum Hall systems

    NASA Astrophysics Data System (ADS)

    Zhang, Yuhe; Jain, J. K.; Eisenstein, J. P.

    2017-05-01

    In a bilayer system consisting of a composite-fermion (CF) Fermi sea in each layer, the tunnel current is exponentially suppressed at zero bias, followed by a strong peak at a finite-bias voltage Vmax. This behavior, which is qualitatively different from that observed for the electron Fermi sea, provides fundamental insight into the strongly correlated non-Fermi-liquid nature of the CF Fermi sea and, in particular, offers a window into the short-distance high-energy physics of this highly nontrivial state. We identify the exciton responsible for the peak current and provide a quantitative account of the value of Vmax. The excitonic attraction is shown to be quantitatively significant, and its variation accounts for the increase of Vmax with the application of an in-plane magnetic field. We also estimate the critical Zeeman energy where transition occurs from a fully spin-polarized composite-fermion Fermi sea to a partially spin-polarized one, carefully incorporating corrections due to finite width and Landau level mixing, and find it to be in satisfactory agreement with the Zeeman energy where a qualitative change has been observed for the onset bias voltage [J. P. Eisenstein et al., Phys. Rev. B 94, 125409 (2016), 10.1103/PhysRevB.94.125409]. For fractional quantum Hall states, we predict a substantial discontinuous jump in Vmax when the system undergoes a transition from a fully spin-polarized state to a spin singlet or a partially spin-polarized state.

  9. A complete description of tunnelling using direct quantum dynamics simulation: Salicylaldimine proton transfer.

    PubMed

    Polyak, Iakov; Allan, Charlotte S M; Worth, Graham A

    2015-08-28

    We demonstrate here conclusively that the variational multiconfiguration Gaussian (vMCG) method converges to the grid based full quantum dynamics multiconfiguration time-dependent Hartree result for a tunnelling problem in many dimensions, using the intramolecular proton transfer in salicylaldimine as a model system. The 13-dimensional model potential energy surface was obtained from Hartree Fock energies with the 6-31G* basis set and the expectation value of the flux operator along the transition mode was used as a benchmark characteristic. As well as showing excellent convergence of the vMCG method on the model surface using a local harmonic approximation and a moderate number of basis functions, we show that the direct dynamics version of the vMCG also performs very well, usually needs the same number of Gaussians to converge, and converges to exact results if those are obtained on an accurately fitted surface. Finally, we make an important observation that the width of the Gaussian basis functions must be chosen very carefully to obtain accurate results with the use of the frozen-width approximation.

  10. Suppression of the Berezinskii-Kosterlitz-Thouless transition in 2D superconductors by macroscopic quantum tunneling.

    PubMed

    Lin, Yen-Hsiang; Nelson, J; Goldman, A M

    2012-07-06

    The evolution with thickness of the properties of quench-deposited homogeneous amorphous bismuth (a-Bi) thin films with a 14.67 Å amorphous antimony (a-Sb) underlayer has been studied. In contrast with the results of previous investigations on similar systems the transition between the insulating and superconducting regimes is not direct, but involves an intervening metallic regime over a range of thicknesses. For these metallic films the temperature dependencies of the resistances at temperatures above the metallic regime can be described by the Halperin-Nelson form suggesting the occurrence of a Berezinskii-Kosterlitz-Thouless (BKT) transition at lower temperatures. However, this transition never occurs as curves of R(T) flatten out as temperature is reduced. We suggest that this phenomenon is evidence of a crossover between a classical regime of thermal vortex unbinding at high temperatures and a regime of macroscopic quantum tunneling at low temperatures. The latter prevents the BKT transition from occurring.

  11. Photoconduction in tunnel-coupled Ge/Si quantum dot arrays

    SciTech Connect

    Stepina, N. P. Yakimov, A. I.; Nenashev, A. V.; Dvurechenskii, A. V.; Sobolev, N. A.; Leitao, J. P.; Kirienko, V. V.; Nikiforov, A. I.; Koptev, E. S.; Pereira, L.; Carmo, M. C.

    2006-08-15

    The photoconduction in a tunnel-coupled Ge/Si quantum dot (QD) array has been studied. The photoconductance (PC) sign can be either positive or negative, depending on the initial filling of QDs with holes. The PC kinetics has a long-term character (10{sup 2}-10{sup 4} s at T = 4.2 K) and is accompanied by persistent photoconduction (PPC), whereby the PC value is not restored on the initial level even after relaxation for several hours. These phenomena are observed upon illumination by light with photon energies both greater and smaller than the silicon bandgap. A threshold light wavelength corresponding to a long-term PC kinetics depends on the QD filling with holes. A model describing the observed PC kinetics is proposed, according to which the main contribution to the PC is related to the degree of QD filling with holes. By applying the proposed model to the analysis of PC kinetics at various excitation levels, it is possible to determine the dependence of the hopping conductance on the number of holes per QD. The rate of the charge carrier density relaxation exponentially depends on the carrier density.

  12. A complete description of tunnelling using direct quantum dynamics simulation: Salicylaldimine proton transfer

    SciTech Connect

    Polyak, Iakov; Allan, Charlotte S. M.; Worth, Graham A.

    2015-08-28

    We demonstrate here conclusively that the variational multiconfiguration Gaussian (vMCG) method converges to the grid based full quantum dynamics multiconfiguration time-dependent Hartree result for a tunnelling problem in many dimensions, using the intramolecular proton transfer in salicylaldimine as a model system. The 13-dimensional model potential energy surface was obtained from Hartree Fock energies with the 6-31G* basis set and the expectation value of the flux operator along the transition mode was used as a benchmark characteristic. As well as showing excellent convergence of the vMCG method on the model surface using a local harmonic approximation and a moderate number of basis functions, we show that the direct dynamics version of the vMCG also performs very well, usually needs the same number of Gaussians to converge, and converges to exact results if those are obtained on an accurately fitted surface. Finally, we make an important observation that the width of the Gaussian basis functions must be chosen very carefully to obtain accurate results with the use of the frozen-width approximation.

  13. Method and apparatus for differential spectroscopic atomic-imaging using scanning tunneling microscopy

    DOEpatents

    Kazmerski, Lawrence L.

    1990-01-01

    A Method and apparatus for differential spectroscopic atomic-imaging is disclosed for spatial resolution and imaging for display not only individual atoms on a sample surface, but also bonding and the specific atomic species in such bond. The apparatus includes a scanning tunneling microscope (STM) that is modified to include photon biasing, preferably a tuneable laser, modulating electronic surface biasing for the sample, and temperature biasing, preferably a vibration-free refrigerated sample mounting stage. Computer control and data processing and visual display components are also included. The method includes modulating the electronic bias voltage with and without selected photon wavelengths and frequency biasing under a stabilizing (usually cold) bias temperature to detect bonding and specific atomic species in the bonds as the STM rasters the sample. This data is processed along with atomic spatial topography data obtained from the STM raster scan to create a real-time visual image of the atoms on the sample surface.

  14. Phase transitions in two tunnel-coupled HgTe quantum wells: Bilayer graphene analogy and beyond

    NASA Astrophysics Data System (ADS)

    Krishtopenko, S. S.; Knap, W.; Teppe, F.

    2016-08-01

    HgTe quantum wells possess remarkable physical properties as for instance the quantum spin Hall state and the “single-valley” analog of graphene, depending on their layer thicknesses and barrier composition. However, double HgTe quantum wells yet contain more fascinating and still unrevealed features. Here we report on the study of the quantum phase transitions in tunnel-coupled HgTe layers separated by CdTe barrier. We demonstrate that this system has a 3/2 pseudo spin degree of freedom, which features a number of particular properties associated with the spin-dependent coupling between HgTe layers. We discover a specific metal phase arising in a wide range of HgTe and CdTe layer thicknesses, in which a gapless bulk and a pair of helical edge states coexist. This phase holds some properties of bilayer graphene such as an unconventional quantum Hall effect and an electrically-tunable band gap. In this “bilayer graphene” phase, electric field opens the band gap and drives the system into the quantum spin Hall state. Furthermore, we discover a new type of quantum phase transition arising from a mutual inversion between second electron- and hole-like subbands. This work paves the way towards novel materials based on multi-layered topological insulators.

  15. Phase transitions in two tunnel-coupled HgTe quantum wells: Bilayer graphene analogy and beyond

    PubMed Central

    Krishtopenko, S. S.; Knap, W.; Teppe, F.

    2016-01-01

    HgTe quantum wells possess remarkable physical properties as for instance the quantum spin Hall state and the “single-valley” analog of graphene, depending on their layer thicknesses and barrier composition. However, double HgTe quantum wells yet contain more fascinating and still unrevealed features. Here we report on the study of the quantum phase transitions in tunnel-coupled HgTe layers separated by CdTe barrier. We demonstrate that this system has a 3/2 pseudo spin degree of freedom, which features a number of particular properties associated with the spin-dependent coupling between HgTe layers. We discover a specific metal phase arising in a wide range of HgTe and CdTe layer thicknesses, in which a gapless bulk and a pair of helical edge states coexist. This phase holds some properties of bilayer graphene such as an unconventional quantum Hall effect and an electrically-tunable band gap. In this “bilayer graphene” phase, electric field opens the band gap and drives the system into the quantum spin Hall state. Furthermore, we discover a new type of quantum phase transition arising from a mutual inversion between second electron- and hole-like subbands. This work paves the way towards novel materials based on multi-layered topological insulators. PMID:27476745

  16. Differential cohomology and locally covariant quantum field theory

    NASA Astrophysics Data System (ADS)

    Becker, Christian; Schenkel, Alexander; Szabo, Richard J.

    We study differential cohomology on categories of globally hyperbolic Lorentzian manifolds. The Lorentzian metric allows us to define a natural transformation whose kernel generalizes Maxwell's equations and fits into a restriction of the fundamental exact sequences of differential cohomology. We consider smooth Pontryagin duals of differential cohomology groups, which are subgroups of the character groups. We prove that these groups fit into smooth duals of the fundamental exact sequences of differential cohomology and equip them with a natural presymplectic structure derived from a generalized Maxwell Lagrangian. The resulting presymplectic Abelian groups are quantized using the CCR-functor, which yields a covariant functor from our categories of globally hyperbolic Lorentzian manifolds to the category of C∗-algebras. We prove that this functor satisfies the causality and time-slice axioms of locally covariant quantum field theory, but that it violates the locality axiom. We show that this violation is precisely due to the fact that our functor has topological subfunctors describing the Pontryagin duals of certain singular cohomology groups. As a byproduct, we develop a Fréchet-Lie group structure on differential cohomology groups.

  17. Radio frequency measurements of tunnel couplings and singlet–triplet spin states in Si:P quantum dots

    PubMed Central

    House, M. G.; Kobayashi, T.; Weber, B.; Hile, S. J.; Watson, T. F.; van der Heijden, J.; Rogge, S.; Simmons, M. Y.

    2015-01-01

    Spin states of the electrons and nuclei of phosphorus donors in silicon are strong candidates for quantum information processing applications given their excellent coherence times. Designing a scalable donor-based quantum computer will require both knowledge of the relationship between device geometry and electron tunnel couplings, and a spin readout strategy that uses minimal physical space in the device. Here we use radio frequency reflectometry to measure singlet–triplet states of a few-donor Si:P double quantum dot and demonstrate that the exchange energy can be tuned by at least two orders of magnitude, from 20 μeV to 8 meV. We measure dot–lead tunnel rates by analysis of the reflected signal and show that they change from 100 MHz to 22 GHz as the number of electrons on a quantum dot is increased from 1 to 4. These techniques present an approach for characterizing, operating and engineering scalable qubit devices based on donors in silicon. PMID:26548556

  18. Negative Differential Resistance of CaF 2/CdF 2 Triple-Barrier Resonant-Tunneling Diode on Si(111) Grown by Partially Ionized Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Watanabe, Masahiro; Aoki, Yuichi; Saito, Wataru; Tsuganezawa, Mika

    1999-02-01

    Room-temperature negative differential resistance (NDR) of triple-barrier cadmium di-fluoride (CdF2)/calcium di-fluoride (CaF2) heterostructure resonant-tunneling diode (RTD) on a Si(111) substrate has been demonstrated. CdF2/CaF2 multilayered heterostructures were grown on a Si(111) substrate using partially ionized beam epitaxy to obtain atomically flat interfaces. The RTD structures, which consist of triple CaF2 energy barriers and double CdF2 quantum wells, were fabricated by electron beam (EB) lithography and dry etching to avoid thermal and chemical damage to the CdF2 layers. In the current-voltage characteristics of the RTD, NDR was clearly observed even at room temperature and the maximum peak-to-valley (P/V) ratio was about 6.

  19. A classical treatment of optical tunneling in plasmonic gaps: extending the quantum corrected model to practical situations.

    PubMed

    Esteban, Rubén; Zugarramurdi, Asier; Zhang, Pu; Nordlander, Peter; García-Vidal, Francisco J; Borisov, Andrei G; Aizpurua, Javier

    2015-01-01

    The optical response of plasmonic nanogaps is challenging to address when the separation between the two nanoparticles forming the gap is reduced to a few nanometers or even subnanometer distances. We have compared results of the plasmon response within different levels of approximation, and identified a classical local regime, a nonlocal regime and a quantum regime of interaction. For separations of a few Ångstroms, in the quantum regime, optical tunneling can occur, strongly modifying the optics of the nanogap. We have considered a classical effective model, so called Quantum Corrected Model (QCM), that has been introduced to correctly describe the main features of optical transport in plasmonic nanogaps. The basics of this model are explained in detail, and its implementation is extended to include nonlocal effects and address practical situations involving different materials and temperatures of operation.

  20. Simulation of quantum dot floating gate MOSFET memory performance using various high-k material as tunnel oxide

    NASA Astrophysics Data System (ADS)

    Aji, Adha Sukma; Darma, Yudi

    2012-06-01

    In this paper, performance of quantum dot floating gate MOSFET memory is simulated by replacing the SiO2 tunnel oxide with high-Κ material. There are three high-k material simulated in this paper, HfO2, ZrO2, and Y2O3. As we know that high-Κ material is used nowadays to reduce leakage current, so this paper demonstrates the application of high-Κ material to reduce leakage current in non-volatile memory quantum dot based floating gate MOSFET. Simulation results of this paper show the leakage current can be suppressed by using high-Κ material as tunnel oxide up to 10 times. Furthermore, this paper also shows that the memory performance can be properly sustained. The writing and erasing time are depend on tunneling current probability which calculated using transfer matrix method. The writing time and erasing time for HfO2 and ZrO2 are 150 nanosecond and 15 nanosecond.

  1. Instantons and scaling of the transitions rates in Quantum Monte Carlo simulations of thermally-assisted quantum tunneling in spin systems

    NASA Astrophysics Data System (ADS)

    Smelyanskiy, Vadim; Jiang, Zhang; Boixo, Sergio; Issakov, Sergei; Mazzola, Guglielmo; Troyer, Matthias; Neven, Hartmut

    We study analytically and numerically the dynamics of the quantum Monte Carlo (QMC) algorithm to simulate thermally-assisted tunneling in mean-field spin models without conservation of total spin. We use Kramers escape rate theory to calculate the scaling of the QMC time with the problem size to simulate the tunneling transitions. We develop path-integral instanton approach in coherent state and Suzuki-Trotter representations to calculate the escape rate and most probable escape path in QMC dynamics. Analtytical results are in a good agreement with numerical studies. We identify the class of models where the exponent in the scaling of the QMC time is the same as that in physical tunneling but the pre-factor depends very significantly on the QMC path representation. We propose the classes of problems where QMC can fail to simulate tunneling efficiently. The work of GM and MT has been supported by the Swiss National Science Foundation through the National Competence Center in Research QSIT and by ODNI, IARPA via MIT Lincoln Laboratory Air Force Contract No. FA8721-05-C-0002.

  2. Simulation of Leakage Current in Si/Ge/Si Quantum Dot Floating Gate MOSFET Using High-K Material as Tunnel Oxide

    NASA Astrophysics Data System (ADS)

    Aji, Adha Sukma; Nugraha, Mohamad Insan; Yudhistira; Rahayu, Fitria; Darma, Yudi

    2011-12-01

    Leakage current in nano-scale MOSFET has been calculated using variety of tunnel oxides. Firstly, this paper evaluates the leakage current in MOSFET devices when using SiO2 as tunnel oxide. When the thickness of tunnel oxide decreases into 1,4 nm, the leakage current will raise and cause power dissipation about 40 percent. Leakage current can be reduced by using high-K materials as tunnel oxides. Thicker high-K materials as tunnel oxides are easier to fabricate than SiO2 tunnel oxides with the thickness down to 1,4 nm. In term of Equivalent Oxide Thickness (EOT), using high-K materials for tunnel oxides could give the better performance as 1,4nm SiO2 which is also more simple in the fabrication. Here, we also evaluates the leakage current as the function of temperature, channel length, and oxide thickness. Computational result shows that using HfO2 to replace SiO2 as tunnel oxides can make leakage current decrease up to seven times. For practically use, HfO2 were suiTable as tunnel oxide in memory devices, particularly in quantum dot (QD) floating gate memory. In this case we use heterostructure QD consisting Si/Ge/Si as electronic storage node. The results demonstrated that the memory operation using HfO2 as tunnel oxide has a better performance rather than SiO2.

  3. Magnetotunneling spectroscopy of polarons in a quantum well of a resonant-tunneling diode

    SciTech Connect

    Popov, V. G. Krishtop, V. G.; Makarovskii, O. N.; Henini, M.

    2010-08-15

    Resonant tunneling of electrons is thoroughly studied in in-plane magnetic fields. Anticrossing is revealed in a spectrum of two-dimensional electrons at energies of optical phonons. The magnetic field changes the momentum of tunneling electrons and causes a voltage shift of a resonance in the tunnel spectra in accordance with the electron dispersion curve. Anticrossing is clearly observed in second derivative current-voltage characteristics of a resonant tunneling diode made of a double-barrier Al{sub 0.4}Ga{sub 0.6}As/GaAs heterostructure.

  4. Spin polarization of carriers in resonant tunneling devices containing InAs self-assembled quantum dots

    NASA Astrophysics Data System (ADS)

    Nobrega, J. Araújo e.; Gordo, V. Orsi; Galeti, H. V. A.; Gobato, Y. Galvão; Brasil, M. J. S. P.; Taylor, D.; Orlita, M.; Henini, M.

    2015-12-01

    In this work, we have investigated transport and optical properties of n-i-n resonant tunneling diodes (RTDs) containing a layer of InAs self-assembled quantum dots (QDs) grown on a (311)B oriented GaAs substrate. Polarization-resolved photoluminescence (PL) and magneto-transport measurements were performed under applied voltage and magnetic fields up to 15 T at 2 K under linearly polarized laser excitation. It was observed that the QD circular polarization degree depends strongly on the applied voltage. Its voltage dependence is explained by the formation of excitonic complexes such as positively (X+) and negatively (X-) charged excitons in the QDs. Our results demonstrate an effective electrical control of an ensemble of InAs QD properties by tuning the applied voltage across a RTD device into the resonant tunneling condition.

  5. The fractional acoustoelectric current plateau induced by the energy-dependent tunnelling from dynamic quantum dots into an impurity dot

    NASA Astrophysics Data System (ADS)

    Chen, S. W.; Song, L.

    2016-08-01

    The fractional acoustoelectric (AE) current plateau in surface-acoustic-waves (SAW) single-electron transport devices is studied by measuring the current plateau as a function of the SAW power and gate bias as well as a function of perpendicular magnetic filed. Our investigation indicates that the fractional plateau is induced by the tunnelling effect from the dynamic quantum dots (QDs) into a static impurity dot. Rate equations are used to extract the tunnelling rates, which change a lot with the number of electrons in the dynamic QDs, the SAW power and gate bias. In addition, the current plateau evolves into a fractional structure, when a strong perpendicular magnetic field is applied to the system.

  6. Electron-Electron and Electron-Phonon interactions effects on the tunnel electronic spectrum of PbS quantum dots

    NASA Astrophysics Data System (ADS)

    Wang, Hongyue; Lhuillier, Emmanuel; Yu, Qian; Mottaghizadeh, Alireza; Ulysse, Christian; Zimmers, Alexandre; Dubertret, Benoit; Aubin, Herve

    2015-03-01

    We present a tunnel spectroscopy study of the electronic spectrum of single PbS Quantum Dots (QDs) trapped between nanometer-spaced electrodes, measured at low temperature T=5 K. The carrier filling of the QD can be controlled either by the drain voltage in the shell filling regime or by a gate voltage. In the empty QD, the tunnel spectrum presents the expected signature of the 8x degenerated excited levels. In the drain controlled shell filling regime, the levels degeneracies are lifted by the global electrostatic Coulomb energy of the QD; in the gate controlled shell filling regime, the levels degeneracies are lifted by the intra-Coulomb interactions. In the charged quantum dot, electron-phonons interactions lead to the apparition of Franck-Condon side bands on the single excited levels and possibly Franck Condon blockade at low energy. The sharpening of excited levels at higher gate voltage suggests that the magnitude of electron-phonon interactions is decreased upon increasing the electron filling in the quantum dot. This work was supported by the French ANR Grants 10-BLAN-0409-01, 09-BLAN-0388-01, by the Region Ile-de-France in the framework of DIM Nano-K and by China Scholarship Council.

  7. Quantum confinement modulation on the performance of nanometer thin body GaSb/InAs tunnel field-effect transistors

    NASA Astrophysics Data System (ADS)

    Wang, Zhi; Wang, Liwei; En, Yunfei; Jiang, Xiang-Wei

    2017-06-01

    In this paper, we have presented an atomistic quantum simulation study to investigate the device performances of GaSb/InAs heterojunction tunnel field-effect transistors (TFETs) with nanometer body thicknesses. It is revealed that the thin junction induced quantum confinement effect results in a heterojunction type transition from type-III to type-II as the junction thickness reduces, which can be used as an effective modulation of the TFET device performance. It is found that as the channel thickness decreases, both the ON current and OFF current of the device decrease significantly due to the quantum confinement induced effective band gap enlargement. In addition, the OFF current of the heterojunction GaSb/InAs TFET is always larger than that of the homojunction InAs TFET, which is possibly caused by the GaSb/InAs interfacial state assisted tunneling. It is also revealed that the subthreshold swing of the heterojunction TFET does not change much as the channel thickness is reduced.

  8. Multiple Andreev reflections in s -wave superconductor-quantum dot-topological superconductor tunnel junctions and Majorana bound states

    NASA Astrophysics Data System (ADS)

    Golub, Anatoly

    2015-05-01

    We calculate the current as a function of applied voltage in a nontopological s -wave superconductor-quantum dot-topological superconductor (TS) tunnel junction. We consider the type of TS which hosts two Majorana bound states (MBSs) at the ends of a semiconductor quantum wire or of a chain of magnetic atoms in the proximity with an s -wave superconductor. We find that the I -V characteristic of such a system in the regime of big voltages has a typical two-dot shape and is ornamented by peaks of multiple Andreev reflections. We also consider the other options when the zero-energy states are created by disorder (hereby Shiba states) or by Andreev zero-energy bound states at the surface of a quantum dot and a superconductor. The later are obtained by tuning the magnetic field to a specific value. Unlike the last two cases the MBS I -V curves are robust to change the magnetic field. Therefore, the magnetic-field dependence of the tunneling current can serve as a unique signature for the presence of a MBS.

  9. Impact of field-induced quantum confinement on the onset of tunneling field-effect transistors: Experimental verification

    SciTech Connect

    Smets, Quentin Verreck, Devin; Heyns, Marc M.; Verhulst, Anne S.; Martens, Koen; Lin, Han Chung; Kazzi, Salim El; Simoen, Eddy; Collaert, Nadine; Thean, Aaron; Raskin, Jean-Pierre

    2014-11-17

    The Tunneling Field-Effect Transistor (TFET) is a promising device for future low-power logic. Its performance is often predicted using semiclassical simulations, but there is usually a large discrepancy with experimental results. An important reason is that Field-Induced Quantum Confinement (FIQC) is neglected. Quantum mechanical simulations show FIQC delays the onset of Band-To-Band Tunneling (BTBT) with hundreds of millivolts in the promising line-TFET configuration. In this letter, we provide experimental verification of this delayed onset. We accomplish this by developing a method where line-TFET are modeled using highly doped MOS capacitors (MOS-CAP). Using capacitance-voltage measurements, we demonstrate AC inversion by BTBT, which was so far unobserved in MOS-CAP. Good agreement is shown between the experimentally obtained BTBT onset and quantum mechanical predictions, proving the need to include FIQC in all TFET simulations. Finally, we show that highly doped MOS-CAP is promising for characterization of traps deep into the conduction band.

  10. Photons and evolution: quantum mechanical processes modulate sexual differentiation.

    PubMed

    Davis, George E; Lowell, Walter E

    2009-09-01

    This paper will show that the fractional difference in the human gender ratio (GR) between the GR(at death) for those born in solar cycle peak years (maxima) and the GR(at death) in those born in solar cycle non-peak years (minima), e.g., 0.023, divided by Pi, yields a reasonable approximation of the quantum mechanical constant, alpha, or the fine structure constant (FSC) approximately 0.007297... or approximately 1/137. This finding is based on a sample of approximately 50 million cases using common, readily available demographic data, e.g., state of birth, birth date, death date, and gender. Physicists Nair, Geim et al. had found precisely the same fractional difference, 0.023, in the absorption of white light (sunlight) by a single-atom thick layer of graphene, a carbon skeleton resembling chicken wire fencing. This absorption fraction, when divided by Pi, yielded the FSC and was the first time this constant could "so directly be assessed practically by the naked eye". As the GR is a reflection of sexual differentiation, this paper reveals that a quantum mechanical process, as manifested by the FSC, is playing a role in the primordial process of replication, a necessary requirement of life. Successful replication is the primary engine driving evolution, which at a biochemical level, is a quantum mechanical process dependent upon photonic energy from the Sun. We propose that a quantum-mechanical, photon-driven chemical evolution preceded natural selection in biology and the mechanisms of mitosis and meiosis are manifestations of this chemical evolution in ancient seas over 3 billion years ago. Evolutionary processes became extant first in self-replicating molecules forced to adapt to high energy photons, mostly likely in the ultraviolet spectrum. These events led to evolution by natural selection as complex mixing of genetic material within species creating the variety needed to match changing environments reflecting the same process initiated at the dawn of life

  11. Differential geometry based solvation model. III. Quantum formulation.

    PubMed

    Chen, Zhan; Wei, Guo-Wei

    2011-11-21

    Solvation is of fundamental importance to biomolecular systems. Implicit solvent models, particularly those based on the Poisson-Boltzmann equation for electrostatic analysis, are established approaches for solvation analysis. However, ad hoc solvent-solute interfaces are commonly used in the implicit solvent theory. Recently, we have introduced differential geometry based solvation models which allow the solvent-solute interface to be determined by the variation of a total free energy functional. Atomic fixed partial charges (point charges) are used in our earlier models, which depends on existing molecular mechanical force field software packages for partial charge assignments. As most force field models are parameterized for a certain class of molecules or materials, the use of partial charges limits the accuracy and applicability of our earlier models. Moreover, fixed partial charges do not account for the charge rearrangement during the solvation process. The present work proposes a differential geometry based multiscale solvation model which makes use of the electron density computed directly from the quantum mechanical principle. To this end, we construct a new multiscale total energy functional which consists of not only polar and nonpolar solvation contributions, but also the electronic kinetic and potential energies. By using the Euler-Lagrange variation, we derive a system of three coupled governing equations, i.e., the generalized Poisson-Boltzmann equation for the electrostatic potential, the generalized Laplace-Beltrami equation for the solvent-solute boundary, and the Kohn-Sham equations for the electronic structure. We develop an iterative procedure to solve three coupled equations and to minimize the solvation free energy. The present multiscale model is numerically validated for its stability, consistency and accuracy, and is applied to a few sets of molecules, including a case which is difficult for existing solvation models. Comparison is made

  12. Structural changes in R-phycoerythrin upon CdS quantum dot synthesis in tunnel cavities of protein molecules.

    PubMed

    Bekasova, O D; Shubin, V V; Safenkova, I V; Kovalyov, L I; Kurganov, B I

    2013-11-01

    Structural changes in R-phycoerythrin used as a matrix for the synthesis of CdS quantum dots have been analyzed by circular dichroism spectrometry. In deionized water, quantum dot synthesis in the tunnel cavity of the R-phycoerythrin molecule proved to be accompanied by uncoiling of α-helices and changes in the conformation of its chromophore groups, with consequent decay of protein fluorescence. Since R-phycoerythrin fluorescence is important for practical applications, conditions for quantum dot synthesis have been optimized by replacing deionized water with 0.01 M MES buffer, pH 5.7. Under such conditions, the size of the CdS quantum dots (determined from atomic force microscopy images) remains the same as in deionized water, but quantum dots cause only minor structural changes in protein molecules, as follows from circular dichroism and absorption spectra. The thermostability of R-phycoerythrin is enhanced, as indicated by an increase in the experimental activation energy for denaturation (from 140.8 to 149.9 kJ/mol) and the intensity of R-phycoerythrin fluorescence is also enhanced approximately twofold. Copyright © 2013 Elsevier B.V. All rights reserved.

  13. Perturbative calculations of quantum spin tunneling in effective spin systems with a transversal magnetic field and transversal anisotropy

    NASA Astrophysics Data System (ADS)

    Krizanac, M.; Vedmedenko, E. Y.; Wiesendanger, R.

    2017-01-01

    We present a perturbative approach for the resonant tunnel splittings of an arbitrary effective single spin system. The Hamiltonian of such a system contains a uniaxial anisotropy, a transversal magnetic field and a second-order transversal anisotropy. Further, we investigate the influence of the transversal magnetic field on the energy splittings for higher integer quantum spins and we introduce an exact formula, which defines values of the transversal magnetic field, the transversal anisotropy and the uniaxial anisotropy where the contribution of the transversal magnetic field to the energy splitting is at least equal to the contribution of the transversal anisotropy.

  14. Waiting time distributions for the transport through a quantum-dot tunnel coupled to one normal and one superconducting lead.

    PubMed

    Rajabi, Leila; Pöltl, Christina; Governale, Michele

    2013-08-09

    We have studied the waiting time distributions (WTDs) for subgap transport through a single-level quantum-dot tunnel coupled to one normal and one superconducting lead. The WTDs reveal the internal dynamics of the system, in particular, the coherent transfer of Cooper pairs between the dot and the superconductor. The WTDs exhibit oscillations that can be directly associated to the coherent oscillation between the empty and doubly occupied dot. The oscillation frequency is equal to the energy splitting between the Andreev bound states. These effects are more pronounced when the empty state and double-occupied state are in resonance.

  15. Differential geometric treewidth estimation in adiabatic quantum computation

    NASA Astrophysics Data System (ADS)

    Wang, Chi; Jonckheere, Edmond; Brun, Todd

    2016-10-01

    The D-Wave adiabatic quantum computing platform is designed to solve a particular class of problems—the Quadratic Unconstrained Binary Optimization (QUBO) problems. Due to the particular "Chimera" physical architecture of the D-Wave chip, the logical problem graph at hand needs an extra process called minor embedding in order to be solvable on the D-Wave architecture. The latter problem is itself NP-hard. In this paper, we propose a novel polynomial-time approximation to the closely related treewidth based on the differential geometric concept of Ollivier-Ricci curvature. The latter runs in polynomial time and thus could significantly reduce the overall complexity of determining whether a QUBO problem is minor embeddable, and thus solvable on the D-Wave architecture.

  16. Unipolar Complementary Circuits Using Double Electron Layer Tunneling Tansistors

    SciTech Connect

    Blount, M.A.; Hafich, M.J.; Moon, J.S.; Reno, J.L.; Simmons, J.A.

    1998-10-19

    We demonstrate unipolar complementary circuits consisting of a pair of resonant tunneling transistors based on the gate control of 2D-2D interlayer tunneling, where a single transistor - in addition to exhibiting a welldefined negative-differential-resistance can be operated with either positive or negative transconductance. Details of the device operation are analyzed in terms of the quantum capacitance effect and band-bending in a double quantum well structure, and show good agreement with experiment. Application of resonant tunneling complementary logic is discussed by demonstrating complementary static random access memory using two devices connected in series.

  17. Power-dependent spin amplification in (In, Ga)As/GaAs quantum well via Pauli blocking by tunnel-coupled quantum dot ensembles

    SciTech Connect

    Chen, S. L. Takayama, J.; Murayama, A.; Kiba, T.; Yang, X. J.

    2016-04-11

    Power-dependent time-resolved optical spin orientation measurements were performed on In{sub 0.1}Ga{sub 0.9}As quantum well (QW) and In{sub 0.5}Ga{sub 0.5}As quantum dot (QD) tunnel-coupled structures with an 8-nm-thick GaAs barrier. A fast transient increase of electron spin polarization was observed at the QW ground state after circular-polarized pulse excitation. The temporal maximum of polarization increased with increasing pumping fluence owing to enhanced spin blocking in the QDs, yielding a highest amplification of 174% with respect to the initial spin polarization. Further elevation of the laser power gradually quenched the polarization dynamics, which was induced by saturated spin filling of both the QDs and the QW phase spaces.

  18. Complementary Barrier Infrared Detector (CBIRD) with Double Tunnel Junction Contact and Quantum Dot Barrier Infrared Detector (QD-BIRD)

    NASA Technical Reports Server (NTRS)

    Ting, David Z.-Y; Soibel, Alexander; Khoshakhlagh, Arezou; Keo, Sam A.; Nguyen, Jean; Hoglund, Linda; Mumolo, Jason M.; Liu, John K.; Rafol, Sir B.; Hill, Cory J.; hide

    2012-01-01

    The InAs/GaSb type-II superlattice based complementary barrier infrared detector (CBIRD) has already demonstrated very good performance in long-wavelength infrared (LWIR) detection. In this work, we describe results on a modified CBIRD device that incorporates a double tunnel junction contact designed for robust device and focal plane array processing. The new device also exhibited reduced turn-on voltage. We also report results on the quantum dot barrier infrared detector (QD-BIRD). By incorporating self-assembled InSb quantum dots into the InAsSb absorber of the standard nBn detector structure, the QD-BIRD extend the detector cutoff wavelength from approximately 4.2 micrometers to 6 micrometers, allowing the coverage of the mid-wavelength infrared (MWIR) transmission window. The device has been observed to show infrared response at 225 K.

  19. Atom Tunneling in the Hydroxylation Process of Taurine/α-Ketoglutarate Dioxygenase Identified by Quantum Mechanics/Molecular Mechanics Simulations.

    PubMed

    Álvarez-Barcia, Sonia; Kästner, Johannes

    2017-06-01

    Taurine/α-ketoglutarate dioxygenase is one of the most studied α-ketoglutarate-dependent dioxygenases (αKGDs), involved in several biotechnological applications. We investigated the key step in the catalytic cycle of the αKGDs, the hydrogen transfer process, by a quantum mechanics/molecular mechanics approach (B3LYP/CHARMM22). Analysis of the charge and spin densities during the reaction demonstrates that a concerted mechanism takes place, where the H atom transfer happens simultaneously with the electron transfer from taurine to the Fe═O cofactor. We found the quantum tunneling of the hydrogen atom to increase the rate constant by a factor of 40 at 5 °C. As a consequence, a quite high kinetic isotope effect close to 60 is obtained, which is consistent with the experimental value.

  20. Nonequilibrium noise in transport across a tunneling contact between ν =2/3 fractional quantum Hall edges

    NASA Astrophysics Data System (ADS)

    Shtanko, O.; Snizhko, K.; Cheianov, V.

    2014-03-01

    In a recent experimental paper [Bid et al., Nature 466, 585 (2010), 10.1038/nature09277] a qualitative confirmation of the existence of upstream neutral modes at the ν =2/3 quantum Hall edge was reported. Using the chiral Luttinger liquid theory of the quantum Hall edge we develop a quantitative model of the experiment of Bid et al. A good quantitative agreement of our theory with the experimental data reinforces the conclusion of the existence of the upstream neutral mode. Our model also enables us to extract important quantitative information about nonequilibrium processes in Ohmic and tunneling contacts from the experimental data. In particular, for ν =2/3, we find a power-law dependence of the neutral mode temperature on the charge current injected from the Ohmic contact.

  1. Complementary Barrier Infrared Detector (CBIRD) with Double Tunnel Junction Contact and Quantum Dot Barrier Infrared Detector (QD-BIRD)

    NASA Technical Reports Server (NTRS)

    Ting, David Z.-Y; Soibel, Alexander; Khoshakhlagh, Arezou; Keo, Sam A.; Nguyen, Jean; Hoglund, Linda; Mumolo, Jason M.; Liu, John K.; Rafol, Sir B.; Hill, Cory J.; Gunapala, Sarath D.

    2012-01-01

    The InAs/GaSb type-II superlattice based complementary barrier infrared detector (CBIRD) has already demonstrated very good performance in long-wavelength infrared (LWIR) detection. In this work, we describe results on a modified CBIRD device that incorporates a double tunnel junction contact designed for robust device and focal plane array processing. The new device also exhibited reduced turn-on voltage. We also report results on the quantum dot barrier infrared detector (QD-BIRD). By incorporating self-assembled InSb quantum dots into the InAsSb absorber of the standard nBn detector structure, the QD-BIRD extend the detector cutoff wavelength from approximately 4.2 micrometers to 6 micrometers, allowing the coverage of the mid-wavelength infrared (MWIR) transmission window. The device has been observed to show infrared response at 225 K.

  2. Enhancing efficiency and power of quantum-dots resonant tunneling thermoelectrics in three-terminal geometry by cooperative effects

    SciTech Connect

    Jiang, Jian-Hua

    2014-11-21

    We propose a scheme of multilayer thermoelectric engine where one electric current is coupled to two temperature gradients in three-terminal geometry. This is realized by resonant tunneling through quantum dots embedded in two thermal and electrical resisting polymer matrix layers between highly conducting semiconductor layers. There are two thermoelectric effects, one of which is pertaining to inelastic transport processes (if energies of quantum dots in the two layers are different), while the other exists also for elastic transport processes. These two correspond to the transverse and longitudinal thermoelectric effects, respectively, and are associated with different temperature gradients. We show that cooperation between the two thermoelectric effects leads to markedly improved figure of merit and power factor, which is confirmed by numerical calculation using material parameters. Such enhancement is robust against phonon heat conduction and energy level broadening. Therefore, we demonstrated cooperative effect as an additional way to effectively improve performance of thermoelectrics in three-terminal geometry.

  3. Signatures of Quantum-Tunneling Diffusion of Hydrogen Atoms on Water Ice at 10 K.

    PubMed

    Kuwahata, K; Hama, T; Kouchi, A; Watanabe, N

    2015-09-25

    Reported here is the first observation of the tunneling surface diffusion of a hydrogen (H) atom on water ice. Photostimulated desorption and resonance-enhanced multiphoton ionization methods were used to determine the diffusion rates at 10 K on amorphous solid water and polycrystalline ice. H-atom diffusion on polycrystalline ice was 2 orders of magnitude faster than that of deuterium atoms, indicating the occurrence of tunneling diffusion. Whether diffusion is by tunneling or thermal hopping also depends on the diffusion length of the atoms and the morphology of the surface. Our findings contribute to a better understanding of elementary physicochemical processes of hydrogen on cosmic ice dust.

  4. Investigations of quantum effect semiconductor devices: The tunnel switch diode and the velocity modulation transistor

    NASA Astrophysics Data System (ADS)

    Daniel, Erik Stephen

    In this thesis we present the results of experimental and theoretical studies of two quantum effect devices--the Tunnel Switch Diode (TSD) and the Velocity Modulation Transistor (VMT). We show that TSD devices can be fabricated such that they behave (semi-quantitatively) as predicted by simple analytical models and more advanced drift-diffusion simulations. These devices possess characteristics, such as on-state currents which range over nearly five orders of magnitude, and on/off current ratios which are even larger, which may allow for a practical implementation of a very dense transistorless SRAM architecture and possibly other novel circuit designs. We demonstrate that many TSD properties can be explained by analogy to a thyristor. In particular, we show that the thin oxide layer in the TSD plays a critical role, and that this can be understood in terms of current injection through the oxide, analogous to transport through the "current limiting" layer in a thyristor. As this oxide layer can be subjected to extreme stress during device operation, we have studied the effect of this stress on device behavior. We demonstrate many significant stress-dependent effects, and identify structures and operation modes which minimize these effects. We propose an InAs/GaSb/AlSb VMT which may allow for larger conductance modulation and higher temperature operation than has been demonstrated in similar GaAs/AlAs structures. Fundamental differences in device operation in the two materials systems and unusual transport mechanisms in the InAs/GaSb/AlSb system are identified as a result of the band lineups in the two systems. Boltzmann transport simulations are developed and presented, allowing a qualitative description of the transport in the InAs/GaSb/AlSb structure. Band structure calculations are carried out, allowing for device design. While no working VMT devices were produced, this is believed to be due to processing and crystal growth problems. We present methods used to

  5. Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots

    NASA Astrophysics Data System (ADS)

    Zimmers, A.; Wang, H.; Lhuillier, E.; Yu, Q.; Mottaghizadeh, A.; Ulysse, C.; Descamps-Mandine, A.; Dubertret, B.; Aubin, H.

    We present a tunnel spectroscopy study of single PbS and HgSe quantum dots (QDs) as a function of temperature and gate voltage. The samples are fabricated through high-vacuum projection of the QDs on the chip circuit. For PbS, three distinct signatures of strong electron-phonon coupling are observed in the electron tunneling spectrum (ETS) of these QDs. In the shell-filling regime, the 8x degeneracy of the electronic levels is lifted by the Coulomb interactions and allows the observation of phonon subbands that result from the emission of optical phonons. At low bias, a gap is observed in the ETS that cannot be closed with the gate voltage, which is a distinguishing feature of the Franck-Condon blockade. From the data, a Huang-Rhys factor in the range S similar to 1.7-2.5 is obtained. Finally, in the shell-tunneling regime, the optical phonons appear in the inelastic ETS d(2)I/dV(2). For HgSe, the data show that the inter-band and intra-band gap can be clearly identified in the ETS.

  6. Revealing energy level structure of individual quantum dots by tunneling rate measured by single-electron sensitive electrostatic force spectroscopy.

    PubMed

    Roy-Gobeil, Antoine; Miyahara, Yoichi; Grutter, Peter

    2015-04-08

    We present theoretical and experimental studies of the effect of the density of states of a quantum dot (QD) on the rate of single-electron tunneling that can be directly measured by electrostatic force microscopy (e-EFM) experiments. In e-EFM, the motion of a biased atomic force microscope cantilever tip modulates the charge state of a QD in the Coulomb blockade regime. The charge dynamics of the dot, which is detected through its back-action on the capacitavely coupled cantilever, depends on the tunneling rate of the QD to a back-electrode. The density of states of the QD can therefore be measured through its effect on the energy dependence of tunneling rate. We present experimental data on individual 5 nm colloidal gold nanoparticles that exhibit a near continuous density of state at 77 K. In contrast, our analysis of already published data on self-assembled InAs QDs at 4 K clearly reveals discrete degenerate energy levels.

  7. Observation of quantum-tunnelling-modulated spin texture in ultrathin topological insulator Bi2Se3 films.

    PubMed

    Neupane, Madhab; Richardella, Anthony; Sánchez-Barriga, Jaime; Xu, SuYang; Alidoust, Nasser; Belopolski, Ilya; Liu, Chang; Bian, Guang; Zhang, Duming; Marchenko, Dmitry; Varykhalov, Andrei; Rader, Oliver; Leandersson, Mats; Balasubramanian, Thiagarajan; Chang, Tay-Rong; Jeng, Horng-Tay; Basak, Susmita; Lin, Hsin; Bansil, Arun; Samarth, Nitin; Hasan, M Zahid

    2014-05-12

    Understanding the spin-texture behaviour of boundary modes in ultrathin topological insulator films is critically essential for the design and fabrication of functional nanodevices. Here, by using spin-resolved photoemission spectroscopy with p-polarized light in topological insulator Bi2Se3 thin films, we report tunnelling-dependent evolution of spin configuration in topological insulator thin films across the metal-to-insulator transition. We report a systematic binding energy- and wavevector-dependent spin polarization for the topological surface electrons in the ultrathin gapped-Dirac-cone limit. The polarization decreases significantly with enhanced tunnelling realized systematically in thin insulating films, whereas magnitude of the polarization saturates to the bulk limit faster at larger wavevectors in thicker metallic films. We present a theoretical model that captures this delicate relationship between quantum tunnelling and Fermi surface spin polarization. Our high-resolution spin-based spectroscopic results suggest that the polarization current can be tuned to zero in thin insulating films forming the basis for a future spin-switch nanodevice.

  8. Asymmetric tunneling rates for electrons and holes at CdSe quantum dot/carbon nanotube interfaces

    NASA Astrophysics Data System (ADS)

    Ismail-Beigi, Sohrab; Jiang, Jie

    2014-03-01

    Decorating carbon nanotubes with CdSe quantum dots (QDs) is one potential approach for creating high efficiency photovoltaics. Our collaborators at Yale recently produced a ligand-free covalent attachment of CdSe QDs to carbon nanotubes through an organic ligand exchange mechanism. Our prior first principles work described the energetics of the various binding processes and rationalized the experimental growth methodology. After a brief review of the system, we will describe our intriguing finding that excited electrons and holes tunnel with different rates out of the QD and into the carbon nanotubes. The asymmetric tunneling rate itself can, in principle, boost the separation of photo-excited charge at the interface even if there are insufficient band energy differences across the interface. We describe our results for the tunneling rates computed using (i) a brute force approach with increasing simulation cell size to remove periodic effects, and (ii) a Green's function method that directly connects the QD to a thermodynamically large electron reservoir (e.g., a very long pristine nanotube). Supported by NSF SOLAR DMR 0934520.

  9. Resonant tunneling device with two-dimensional quantum well emitter and base layers

    DOEpatents

    Simmons, J.A.; Sherwin, M.E.; Drummond, T.J.; Weckwerth, M.V.

    1998-10-20

    A double electron layer tunneling device is presented. Electrons tunnel from a two dimensional emitter layer to a two dimensional tunneling layer and continue traveling to a collector at a lower voltage. The emitter layer is interrupted by an isolation etch, a depletion gate, or an ion implant to prevent electrons from traveling from the source along the emitter to the drain. The collector is similarly interrupted by a backgate, an isolation etch, or an ion implant. When the device is used as a transistor, a control gate is added to control the allowed energy states of the emitter layer. The tunnel gate may be recessed to change the operating range of the device and allow for integrated complementary devices. Methods of forming the device are also set forth, utilizing epoxy-bond and stop etch (EBASE), pre-growth implantation of the backgate or post-growth implantation. 43 figs.

  10. Resonant tunneling device with two-dimensional quantum well emitter and base layers

    DOEpatents

    Simmons, Jerry A.; Sherwin, Marc E.; Drummond, Timothy J.; Weckwerth, Mark V.

    1998-01-01

    A double electron layer tunneling device is presented. Electrons tunnel from a two dimensional emitter layer to a two dimensional tunneling layer and continue traveling to a collector at a lower voltage. The emitter layer is interrupted by an isolation etch, a depletion gate, or an ion implant to prevent electrons from traveling from the source along the emitter to the drain. The collector is similarly interrupted by a backgate, an isolation etch, or an ion implant. When the device is used as a transistor, a control gate is added to control the allowed energy states of the emitter layer. The tunnel gate may be recessed to change the operating range of the device and allow for integrated complementary devices. Methods of forming the device are also set forth, utilizing epoxy-bond and stop etch (EBASE), pre-growth implantation of the backgate or post-growth implantation.

  11. Tunnel determinants from spectral zeta functions. Instanton effects in quantum mechanics

    SciTech Connect

    Izquierdo, A. Alonso; Guilarte, J. Mateos

    2014-07-23

    In this paper we develop an spectral zeta function regularization procedure on the determinants of instanton fluctuation operators that describe the semi-classical order of tunnel effects between degenerate vacua.

  12. Quantum dynamics of H2 in a carbon nanotube: Separation of time scales and resonance enhanced tunneling

    NASA Astrophysics Data System (ADS)

    Mondelo-Martell, Manel; Huarte-Larrañaga, Fermín; Manthe, Uwe

    2017-08-01

    Quantum confinement effects are known to affect the behavior of molecules adsorbed in nanostructured materials. In order to study these effects on the transport of a single molecule through a nanotube, we present a quantum dynamics study on the diffusion of H2 in a narrow (8,0) carbon nanotube in the low pressure limit. Transmission coefficients for the elementary step of the transport process are calculated using the flux correlation function approach and diffusion rates are obtained using the single hopping model. The different time scales associated with the motion in the confined coordinates and the motion along the nanotube's axis are utilized to develop an efficient and numerically exact approach, in which a diabatic basis describing the fast motion in the confined coordinate is employed. Furthermore, an adiabatic approximation separating the dynamics of confined and unbound coordinates is studied. The results obtained within the adiabatic approximation agree almost perfectly with the numerically exact ones. The approaches allow us to accurately study the system's dynamics on the picosecond time scale and resolve resonance structures present in the transmission coefficients. Resonance enhanced tunneling is found to be the dominant transport mechanism at low energies. Comparison with results obtained using transition state theory shows that tunneling significantly increases the diffusion rate at T < 120 K.

  13. Non-equilibrium quantum transport of spin-polarized electrons and back action on molecular magnet tunnel-junction

    NASA Astrophysics Data System (ADS)

    Zhang, Chao; Yao, Hui; Nie, Yi-Hang; Liang, J.-Q.

    2016-11-01

    We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.

  14. Quantum dynamics of H2 in a carbon nanotube: Separation of time scales and resonance enhanced tunneling.

    PubMed

    Mondelo-Martell, Manel; Huarte-Larrañaga, Fermín; Manthe, Uwe

    2017-08-28

    Quantum confinement effects are known to affect the behavior of molecules adsorbed in nanostructured materials. In order to study these effects on the transport of a single molecule through a nanotube, we present a quantum dynamics study on the diffusion of H2 in a narrow (8,0) carbon nanotube in the low pressure limit. Transmission coefficients for the elementary step of the transport process are calculated using the flux correlation function approach and diffusion rates are obtained using the single hopping model. The different time scales associated with the motion in the confined coordinates and the motion along the nanotube's axis are utilized to develop an efficient and numerically exact approach, in which a diabatic basis describing the fast motion in the confined coordinate is employed. Furthermore, an adiabatic approximation separating the dynamics of confined and unbound coordinates is studied. The results obtained within the adiabatic approximation agree almost perfectly with the numerically exact ones. The approaches allow us to accurately study the system's dynamics on the picosecond time scale and resolve resonance structures present in the transmission coefficients. Resonance enhanced tunneling is found to be the dominant transport mechanism at low energies. Comparison with results obtained using transition state theory shows that tunneling significantly increases the diffusion rate at T < 120 K.

  15. The diffusion of hydrogen monomers on hole-doped graphitic lattices: over-barrier transition and quantum tunneling.

    PubMed

    Huang, Liang Feng; Ni, Mei Yan; Zeng, Zhi

    2011-11-02

    The diffusion of hydrogen and deuterium monomers on hole-doped graphene (a planar graphitic lattice), the outside wall and the inside wall of hole-doped (6, 0) single-walled carbon nanotubes (a curved graphitic lattice) was investigated using density functional theory and density functional perturbation theory. The jump frequencies for the over-barrier transition and phonon-assisted quantum tunneling were calculated by transition state theory and small-polaron theory, respectively. The effects of the local curvature of the surface and the hole doping on the thermodynamic and kinetic properties of a hydrogen monomer on these graphitic lattices are discussed. Our results demonstrate that it is sufficient to judge the diffusional mobility of a hydrogen monomer on graphitic lattices from just the over-barrier transition, no matter how much it is curved and hole doped, while the quantum tunneling can be safely neglected because it is significantly suppressed by the covalent bonding of hydrogen with the graphitic lattice.

  16. Graphene-SnO2 nanocomposites decorated with quantum tunneling junctions: preparation strategies, microstructures and formation mechanism.

    PubMed

    Wang, Qingxiu; Wu, Xianzheng; Wang, Lijun; Chen, Zhiwen; Wang, Shilong

    2014-09-28

    Tin dioxide (SnO2) and graphene are versatile materials that are vitally important for creating new functional and smart materials. A facile, simple and efficient ultrasonic-assisted hydrothermal synthesis approach has been developed to prepare graphene-SnO2 nanocomposites (GSNCs), including three samples with graphene/Sn weight ratios = 1 : 2 (GSNC-2), 1 : 1 (GSNC-1), and graphene oxide/Sn weight ratio = 1 : 1 (GOSNC-1). Low-magnification electron microscopy analysis indicated that graphene was exfoliated and adorned with SnO2 nanoparticles, which were dispersed uniformly on both the sides of the graphene nanosheets. High-magnification electron microscopy analysis confirmed that the graphene-SnO2 nanocomposites presented network tunneling frameworks, which were decorated with the SnO2 quantum tunneling junctions. The size distribution of SnO2 nanoparticles was estimated to range from 3 to 5.5 nm. Comparing GSNC-2, GSNC-1, and GOSNC-1, GOSNC-1 was found to exhibit a significantly better the homogeneous distribution and a considerably smaller size distribution of SnO2 nanoparticles, which indicated that it was better to use graphene oxide as a supporting material and SnCl4·5H2O as a precursor to synthesize hybrid graphene-SnO2 nanocomposites. Experimental results suggest that the graphene-SnO2 nanocomposites with interesting SnO2 quantum tunneling junctions may be a promising material to facilitate the improvement of the future design of micro/nanodevices.

  17. Solving the quantum brachistochrone equation through differential geometry

    NASA Astrophysics Data System (ADS)

    You, Chenglong; Wilde, Mark; Dowling, Jonathan; Wang, Xiaoting

    2016-05-01

    The ability of generating a particular quantum state, or model a physical quantum device by exploring quantum state transfer, is important in many applications such as quantum chemistry, quantum information processing, quantum metrology and cooling. Due to the environmental noise, a quantum device suffers from decoherence causing information loss. Hence, completing the state-generation task in a time-optimal way can be considered as a straightforward method to reduce decoherence. For a quantum system whose Hamiltonian has a fixed type and a finite energy bandwidth, it has been found that the time-optimal quantum evolution can be characterized by the quantum brachistochrone equation. In addition, the brachistochrone curve is found to have a geometric interpretation: it is the limit of a one-parameter family of geodesics on a sub-Riemannian model. Such geodesic-brachistochrone connection provides an efficient numerical method to solve the quantum brachistochrone equation. In this work, we will demonstrate this numerical method by studying the time-optimal state-generating problem on a given quantum spin system. We also find that the Pareto weighted-sum optimization turns out to be a simple but efficient method in solving the quantum time-optimal problems. We would like to acknowledge support from NSF under Award No. CCF-1350397.

  18. Mixed quantum classical calculation of proton transfer reaction rates: From deep tunneling to over the barrier regimes

    SciTech Connect

    Xie, Weiwei; Xu, Yang; Zhu, Lili; Shi, Qiang

    2014-05-07

    We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula.

  19. Mixed quantum classical calculation of proton transfer reaction rates: from deep tunneling to over the barrier regimes.

    PubMed

    Xie, Weiwei; Xu, Yang; Zhu, Lili; Shi, Qiang

    2014-05-07

    We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula.

  20. Quantum decrease of capacitance in a nanometer-sized tunnel junction

    NASA Astrophysics Data System (ADS)

    Untiedt, C.; Saenz, G.; Olivera, B.; Corso, M.; Sabater, C.; Pascual, J. I.

    2013-03-01

    We have studied the capacitance of the tunnel junction defined by the tip and sample of a Scanning Tunnelling Microscope through the measurement of the electrostatic forces and impedance of the junction. A decrease of the capacitance when a tunnel current is present has shown to be a more general phenomenon as previously reported in other systems. On another hand, an unexpected reduction of the capacitance is also observed when increasing the applied voltage above the work function energy of the electrodes to the Field Emission (FE) regime, and the decrease of capacitance due to a single FE-Resonance has been characterized. All these effects should be considered when doing measurements of the electronic characteristics of nanometer-sized electronic devices and have been neglected up to date. Spanish government (FIS2010-21883-C02-01, CONSOLIDER CSD2007-0010), Comunidad Valenciana (ACOMP/2012/127 and PROMETEO/2012/011)

  1. Ab initio large-amplitude quantum-tunneling dynamics in vinyl radical: a vibrationally adiabatic approach.

    PubMed

    Nesbitt, David J; Dong, Feng

    2008-04-21

    Large-amplitude tunneling in vinyl radical over a C2v planar transition state involves CCH bending excitation coupled to all other internal coordinates, resulting in a significant dependence of barrier height and shape on vibrational degrees of freedom at the zero-point level. An ab initio potential surface for vinyl radical has been calculated at the CCSD(T) level (AVnZ; n=2, 3, 4, 5) for vibrationally adiabatic 1D motion along the planar CCH bending tunneling coordinate, extrapolated to the complete basis set (CBS) limit and corrected for anharmonic zero-point effects. The polyatomic reduced moment of inertia is calculated explicitly as a function of tunneling coordinate, with eigenvalues and tunneling splittings obtained from numerical solution of the resulting 1D Schrödinger equation. Linear scaling of the CBS potential to match predicted and observed tunneling splittings empirically yields an adiabatic barrier height of DeltaEadiab=1696(20) cm(-1) which, when corrected for zero-point energy contributions, translates into an effective barrier of DeltaEeff=1602(20) cm(-1) consistent with estimates (DeltaE=1580(100) cm(-1)) by Tanaka and coworkers [J. Chem. Phys., 2004, 120, 3604-3618]. These zero-point-corrected potential surfaces are used to predict tunneling dynamics in vibrationally excited states of vinyl radical, providing strong support for previous jet-cooled high-resolution infrared studies [Dong et al., J. Phys. Chem. A, 2006, 110, 3059-3070] in the symmetric CH2 stretch mode.

  2. Investigating Quantum Mechanical Tunneling at the Nanoscale via Analogy: Development and Assessment of a Teaching Tool for Upper-Division Chemistry

    ERIC Educational Resources Information Center

    Muniz, Marc N.; Oliver-Hoyo, Maria T.

    2014-01-01

    We report a novel educational activity designed to teach quantum mechanical tunneling to upper-division undergraduate students in the context of nanochemistry. The activity is based on a theoretical framework for analogy and is split into three parts that are linked pedagogically through the framework: classical ball-and-ramp system, tunneling…

  3. Investigating Quantum Mechanical Tunneling at the Nanoscale via Analogy: Development and Assessment of a Teaching Tool for Upper-Division Chemistry

    ERIC Educational Resources Information Center

    Muniz, Marc N.; Oliver-Hoyo, Maria T.

    2014-01-01

    We report a novel educational activity designed to teach quantum mechanical tunneling to upper-division undergraduate students in the context of nanochemistry. The activity is based on a theoretical framework for analogy and is split into three parts that are linked pedagogically through the framework: classical ball-and-ramp system, tunneling…

  4. Quantum Tunneling in Testosterone 6β-Hydroxylation by Cytochrome P450: Reaction Dynamics Calculations Employing Multiconfiguration Molecular-Mechanical Potential Energy Surfaces

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Lin, Hai

    2009-05-01

    Testosterone hydroxylation is a prototypical reaction of human cytochrome P450 3A4, which metabolizes about 50% of oral drugs on the market. Reaction dynamics calculations were carried out for the testosterone 6β-hydrogen abstraction and the 6β-d1-testosterone 6β-duterium abstraction employing a model that consists of the substrate and the active oxidant compound I. The calculations were performed at the level of canonical variational transition state theory with multidimensional tunneling and were based on a semiglobal full-dimensional potential energy surface generated by the multiconfiguration molecular mechanics technique. The tunneling coefficients were found to be around 3, indicating substantial contributions by quantum tunneling. However, the tunneling made only modest contributions to the kinetic isotope effects. The kinetic isotope effects were computed to be about 2 in the doublet spin state and about 5 in the quartet spin state.

  5. On a differential geometric viewpoint of Jaynes' MaxEnt method and its quantum extension

    NASA Astrophysics Data System (ADS)

    Ali, S. A.; Cafaro, C.; Giffin, A.; Lupo, C.; Mancini, S.

    2012-05-01

    We present a differential geometric viewpoint of the quantum MaxEnt estimate of a density operator when only incomplete knowledge encoded in the expectation values of a set of quantum observables is available. Finally, the additional possibility of considering some prior bias towards a certain density operator (the prior) is taken into account and the unsolved issues with its quantum relative entropic inference criterion are pointed out.

  6. Covariant differential calculi on quantum symplectic superspace S Pq 1 | 2

    NASA Astrophysics Data System (ADS)

    Celik, Salih

    2017-02-01

    A unitary orthosymplectic quantum supergroup is introduced. Two covariant differential calculi on the quantum superspace S Pq 1 | 2 are presented. The h-deformed symplectic superspaces via a contraction of the q-deformed symplectic superspaces are obtained. A new h-deformation of the Heisenberg superalgebra is given.

  7. Existence of mild solution of impulsive quantum stochastic differential equation with nonlocal conditions

    NASA Astrophysics Data System (ADS)

    Bishop, S. A.; Ayoola, E. O.; Oghonyon, G. J.

    2016-08-01

    New results on existence and uniqueness of solution of impulsive quantum stochastic differential equation with nonlocal conditions are established. The nonlocal conditions are completely continuous. The methods applied here are simple extension of the methods applied in the classical case to this noncummutative quantum setting.

  8. Negative differential resistance of metal (CoSi2)/insulator (CaF2) triple-barrier resonant tunneling diode

    NASA Astrophysics Data System (ADS)

    Watanabe, Masahiro; Suemasu, Takashi; Muratake, Shigeki; Asada, Masahiro

    1993-01-01

    The electron transport and negative differential resistance in metal-insulator nanometer-thick heterostructures are reported for the first time. The structure of the samples is a resonant tunneling diode with three-barriers of 0.9-nm-thick CaF2 layers and two wells of 1.9- and 2.8-nm-thick CoSi2 layers. These layers were grown by means of partially ionized beam epitaxy for CaF2 and a two step growth technique for CoSi2. In the current-voltage characteristics at 77 K, negative differential resistance was observed in the significant number of samples and the typical peak-to-valley ratio was as high as 2. The negative differential resistance observed here can be attributed to the electron transport through the resonant levels in metal/insulator multilayered heterostructures.

  9. Using tunnel junctions to grow monolithically integrated optically pumped semipolar III-nitride yellow quantum wells on top of electrically injected blue quantum wells.

    PubMed

    Kowsz, Stacy J; Young, Erin C; Yonkee, Benjamin P; Pynn, Christopher D; Farrell, Robert M; Speck, James S; DenBaars, Steven P; Nakamura, Shuji

    2017-02-20

    We report a device that monolithically integrates optically pumped (20-21) III-nitride quantum wells (QWs) with 560 nm emission on top of electrically injected QWs with 450 nm emission. The higher temperature growth of the blue light-emitting diode (LED) was performed first, which prevented thermal damage to the higher indium content InGaN of the optically pumped QWs. A tunnel junction (TJ) was incorporated between the optically pumped and electrically injected QWs; this TJ enabled current spreading in the buried LED. Metalorganic chemical vapor deposition enabled the growth of InGaN QWs with high radiative efficiency, while molecular beam epitaxy was leveraged to achieve activated buried p-type GaN and the TJ. This initial device exhibited dichromatic optically polarized emission with a polarization ratio of 0.28. Future improvements in spectral distribution should enable phosphor-free polarized white light emission.

  10. Quantum-tunneling dynamics of a spin-polarized Fermi gas in a double-well potential

    SciTech Connect

    Salasnich, L.; Mazzarella, G.; Toigo, F.; Salerno, M.

    2010-02-15

    We study the exact dynamics of a one-dimensional spin-polarized gas of fermions in a double-well potential at zero and finite temperature. Despite the system being made of noninteracting fermions, its dynamics can be quite complex, showing strongly aperiodic spatio-temporal patterns during the tunneling. The extension of these results to the case of mixtures of spin-polarized fermions interacting with self-trapped Bose-Einstein condensates (BECs) at zero temperature is considered as well. In this case we show that the fermionic dynamics remains qualitatively similar to that observed in the absence of BEC but with the Rabi frequencies of fermionic excited states explicitly depending on the number of bosons and on the boson-fermion interaction strength. From this, the possibility of controlling quantum fermionic dynamics by means of Feshbach resonances is suggested.

  11. Optical properties and effect of carrier tunnelling in CdSe colloidal quantum dots: A comparative study with different ligands

    NASA Astrophysics Data System (ADS)

    Goswami, Syamanta Kumar; Kim, Tae Soo; Oh, Eunsoon; Challa, Kiran Kumar; Kim, Eui-Tae

    2012-09-01

    We studied both cw and time-resolved photoluminescence of colloidal CdSe/ZnS core-shell quantum dots capped with chemical ligands. For the trioctylphosphine oxide capped CdSe/ZnS QDs, both the luminescence intensity and lifetime were found to be increased with increasing temperatures, which can be explained by the thermal activation of the carriers trapped at shallow trapping centers. After the ligand exchange into 3-mercaptopropionic acid, the non-radiative recombination rate was increased and the luminescence efficiency was decreased at room temperature. When the QDs were employed in photovoltaic devices, photocurrent was found to be increased after the ligand exchange. The improved photocurrents observed in photovoltaic devices can be explained by the improved tunnelling probability between the neighbouring QDs.

  12. GaSb/GaAs quantum dot formation and demolition studied with cross-sectional scanning tunneling microscopy

    SciTech Connect

    Smakman, E. P.; Garleff, J. K.; Rambabu, P.; Koenraad, P. M.; Young, R. J.; Hayne, M.

    2012-04-02

    We present a cross-sectional scanning tunneling microscopy study of GaSb/GaAs quantum dots grown by molecular beam epitaxy. Various nanostructures are observed as a function of the growth parameters. During growth, relaxation of the high local strain fields of the nanostructures plays an important role in their formation. Pyramidal dots with a high Sb content are often accompanied by threading dislocations above them. GaSb ring formation is favored by the use of a thin GaAs first cap layer and a high growth temperature of the second cap layer. At these capping conditions, strain-driven Sb diffusion combined with As/Sb exchange and Sb segregation remove the center of a nanostructure, creating a ring. Clusters of GaSb without a well defined morphology also appear regularly, often with a highly inhomogeneous structure which is sometimes divided up in fragments.

  13. Hyperfine-Interaction-Driven Suppression of Quantum Tunneling at Zero Field in a Holmium(III) Single-Ion Magnet.

    PubMed

    Chen, Yan-Cong; Liu, Jun-Liang; Wernsdorfer, Wolfgang; Liu, Dan; Chibotaru, Liviu F; Chen, Xiao-Ming; Tong, Ming-Liang

    2017-03-15

    An extremely rare non-Kramers holmium(III) single-ion magnet (SIM) is reported to be stabilized in the pentagonal-bipyramidal geometry by a phosphine oxide with a high energy barrier of 237(4) cm(-1) . The suppression of the quantum tunneling of magnetization (QTM) at zero field and the hyperfine structures originating from field-induced QTMs can be observed even from the field-dependent alternating-current magnetic susceptibility in addition to single-crystal hysteresis loops. These dramatic dynamics were attributed to the combination of the favorable crystal-field environment and the hyperfine interactions arising from (165) Ho (I=7/2) with a natural abundance of 100 %.

  14. Quantum Interference between Energy Absorption Processes of Molecular Exciton and Interface Plasmons on Luminescence Induced by Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Miwa, Kuniyuki; Imasa, Hiroshi; Sakaue, Mamoru; Kasai, Hideaki; Kim, Yousoo

    2015-03-01

    Luminescence induced by the tunneling current of a scanning tunneling microscope (STM) from molecule-covered metal surfaces is attributed to radiative decays of molecules and interface plasmons localized near the tip-substrate gap region. Since the dynamics of molecule and interface plasmons strongly influence each other, the interplay between these dynamics gives rise to peculiar phenomena originating from quantum many-body effects. In this study, we develop the effective model of the system and investigate the luminescence properties using the nonequilibrium Green's function method. The results show that, in addition to the dynamics of molecule, energy reabsorption by interface plasmons have a critical role in determining the luminescence spectral profile of interface plasmons. The additional peak structure arises owing to the interference between these energy absorption processes. Origin of prominent peak and dip structures observed in recent experiments are identified by the developed theory. The details of the interference effects on the luminescence properties will be discussed. This work was supported by JSPS KAKENHI Grant Number 26886013.

  15. Fabrication and characterization of high-quality all-NbN Josephson tunnel junctions for superconductive quantum interference devices

    NASA Astrophysics Data System (ADS)

    Liu, Quansheng; Wang, Huiwu; Zhang, Qiyu; Peng, Wei; Wang, Zhen

    2017-06-01

    We have developed high-quality NbN/AlN/NbN Josephson tunnel junctions for direct current-superconducting quantum interference devices (DC-SQUIDs). The junctions were fabricated with epitaxial NbN/AlN/NbN trilayers on single crystal MgO (100) substrates and showed excellent tunneling properties with a quality factor Rsg/Rn above 20, a large gap voltage about 5.7 mV, and a large IcRn product above 3.8 mV. The critical current density Jc of the NbN/AlN/NbN junctions is controlled by the AlN barrier thickness dAlN in the junctions. The performance of DC-SQUIDs comprising NbN junctions was measured at 4.2 K, and the white noise in a flux-locked-loop mode was 5 μΦ0/Hz1/2, thus demonstrating the feasibility of all-NbN junctions for SQUID development.

  16. Differentiate low impedance media in closed steel tank using ultrasonic wave tunneling.

    PubMed

    Wang, Chunying; Chen, Zhaojiang; Cao, Wenwu

    2017-08-02

    Ultrasonic wave tunneling through seriously mismatched media, such as steel and water, is possible only when the frequency matches the resonance of the steel plate. But it is nearly impossible to realize continuous wave tunneling if the low acoustic impedance media is air because the transducer frequency cannot be made so accurate. The issue might be resolved using tone-burst signals. Using finite element simulations, we found that for air media when the cycle number is 20, the -6dB bandwidth of energy transmission increased from 0.001% to 5.9% compared with that of continuous waves. We show that the tunneling waves can give us enough information to distinguish low acoustic impedance media inside a steel tank. Copyright © 2017. Published by Elsevier B.V.

  17. Two-particle quantum interference in tunnel-coupled optical tweezers.

    PubMed

    Kaufman, A M; Lester, B J; Reynolds, C M; Wall, M L; Foss-Feig, M; Hazzard, K R A; Rey, A M; Regal, C A

    2014-07-18

    The quantum statistics of atoms is typically observed in the behavior of an ensemble via macroscopic observables. However, quantum statistics modifies the behavior of even two particles. Here, we demonstrate near-complete control over all the internal and external degrees of freedom of two laser-cooled (87)Rb atoms trapped in two optical tweezers. This controllability allows us to observe signatures of indistinguishability via two-particle interference. Our work establishes laser-cooled atoms in optical tweezers as a promising route to bottom-up engineering of scalable, low-entropy quantum systems.

  18. Melorheostosis of the humerus: a rare differential diagnosis of carpal tunnel syndrome.

    PubMed

    De Vos, J; Mulliez, A; De Loore, G

    2010-04-01

    Melorheostosis is an uncommon and rare linear hyperostosis, which can be complicated by soft tissue changes. We present a case of this disorder in the humerus, clinically referred because of carpal tunnel syndrome. Although treatment is usually conservative, in this case, a neurolysis and resection of the sclerotic bone were done with good clinical result. Copyright 2010 Elsevier Masson SAS. All rights reserved.

  19. Stress Test for Quantum Dynamics Approximations: Deep Tunneling in the Muonium Exchange Reaction D + HMu → DMu + H.

    PubMed

    Pérez de Tudela, Ricardo; Suleimanov, Yury V; Richardson, Jeremy O; Sáez Rábanos, Vicente; Green, William H; Aoiz, F J

    2014-12-04

    Quantum effects play a crucial role in chemical reactions involving light atoms at low temperatures, especially when a light particle is exchanged between two heavier partners. Different theoretical methodologies have been developed in the last decades attempting to describe zero-point energy and tunneling effects without abandoning a classical or semiclassical framework. In this work, we have chosen the D + HMu → DMu + H reaction as a stress test system for three well-established methods: two representative versions of transition state theory (TST), canonical variational theory and semiclassical instanton, and ring polymer molecular dynamics (RPMD). These calculations will be compared with accurate quantum mechanical results. Despite its apparent simplicity, the exchange of the extremely light muonium atom (0.114 u) becomes a most challenging reaction for conventional methods. The main result of this work is that RPMD provides an overall better performance than TST-based methods for such a demanding reaction. RPMD might well turn out to be a useful tool beyond TST applicability.

  20. Differential and integral cross sections of the N(2D)+H2-->NH+H reaction from exact quantum and quasi-classical trajectory calculations.

    PubMed

    Lin, Shi Ying; Bañares, Luis; Guo, Hua

    2007-03-29

    Exact quantum mechanical state-to-state differential and integral cross sections and their energy dependence have been calculated on an accurate NH2 potential energy surface (PES), using a newly proposed Chebyshev wave packet method. The NH product is found to have a monotonically decaying vibrational distribution and an inverted rotational distribution. The product angular distributions peak in both forward and backward directions, but with a backward bias. This backward bias is more pronounced than that observed previously on a less accurate PES. Both the differential and integral cross sections oscillate mildly with collision energy, indicating the dominance of short-lived resonances. The quantum mechanical results are compared with those obtained from quasi-classical trajectories. The agreement is generally reasonable and the discrepancies can be attributed to the neglect of quantum effects such as tunneling. Detailed analysis of the trajectories revealed that the backward bias in the differential cross section stems overwhelmingly from the fast insertion component of the reaction, augmented with some flux from the abstraction channel, particularly at high collision energies.

  1. Chiral glycine formation on cold interstellar grains by quantum tunneling hydrogen-deuterium substitution reactions

    NASA Astrophysics Data System (ADS)

    Oba, Yasuhiro; Watanabe, Naoki; Osamura, Yoshihiro; Kouchi, Akira

    2015-08-01

    We report experimental evidence that chiral glycine (NH2CHDCOOH) is formed by the surface reaction of normal glycine (NH2CH2COOH) solid with deuterium (D) atom at 12 K under the simulative conditions of interstellar molecular clouds. Chiral glycine formation is most likely initiated by the tunneling abstraction reaction of H atom by D atom followed by the addition of D atom to the glycine radical (NH2CHCOOH). Given that chiral glycine can form in such a primordial low-temperature environment, it might source molecular chirality as molecular clouds evolve into planetary systems.

  2. Matter waves and quantum tunneling engineered by time-dependent interactions

    SciTech Connect

    Bludov, Yu. V.; Konotop, V. V.; Salerno, M.

    2010-05-15

    We report the possibility of steering gap solitons in Bose-Einstein condensates loaded in optical lattices by means of time-dependent nonlinearities, which allow one to control in a nondestructive manner both Bloch oscillations and Landau-Zener tunneling (i.e., Rabi oscillations) across band gaps. As an example we show how to move a matter-wave soliton in real and in reciprocal space from a lower to higher bands, avoiding dynamical instabilities. This opens the possibility of experimental access to gap solitons of higher bands and forcing of soliton motion through a lattice via the Feshbach resonance technique.

  3. Performance Evaluation and Design Considerations of Electrically Activated Drain Extension Tunneling GNRFET: A Quantum Simulation Study

    NASA Astrophysics Data System (ADS)

    Ghoreishi, Seyed Saleh; Yousefi, Reza; Taghavi, Neda

    2017-07-01

    In this paper, a tunneling graphene nanoribbon field effect transistor with electrically activated drain extension, namely, EA-T-GNRFET, is proposed. The proposed structure includes a side gate at the drain side with a constant voltage and length of 0.4 V and 15 nm, respectively. Simulations are performed based on the non-equilibrium Green's function method coupled with the Poisson equation in the mode space representation. This side gate creates an additional step in potential profile at the drain side, which increases and decreases the width of tunneling barrier and leakage current, respectively. Furthermore, the proposed structure has lower drain induced barrier thinning, lower sub-threshold swing (SS) and higher I ON/I OFF ratio than the conventional structure. Also, other characteristics of the device such as switching delay ( τ ), power delay product (PDP) and unity-gain frequency (f t) are improved in the proposed device. These advantages make EA-T-GNRFET more suitable for digital and analog applications.

  4. The Particle inside a Ring: A Two-Dimensional Quantum Problem Visualized by Scanning Tunneling Microscopy

    ERIC Educational Resources Information Center

    Ellison, Mark D.

    2008-01-01

    The one-dimensional particle-in-a-box model used to introduce quantum mechanics to students suffers from a tenuous connection to a real physical system. This article presents a two-dimensional model, the particle confined within a ring, that directly corresponds to observations of surface electrons in a metal trapped inside a circular barrier.…

  5. Model of tunnelling through periodic array of quantum dots in a magnetic field

    NASA Astrophysics Data System (ADS)

    Yu. Popov, I.; A. Osipov, S.

    2012-11-01

    A two-dimensional periodic array of quantum dots with two laterally coupled leads in a magnetic field is considered. The model of electron transport through the system based on the theory of self-adjoint extensions of symmetric operators is suggested. We obtain the formula for the transmission coefficient and investigate its dependence on the magnetic field.

  6. The Particle inside a Ring: A Two-Dimensional Quantum Problem Visualized by Scanning Tunneling Microscopy

    ERIC Educational Resources Information Center

    Ellison, Mark D.

    2008-01-01

    The one-dimensional particle-in-a-box model used to introduce quantum mechanics to students suffers from a tenuous connection to a real physical system. This article presents a two-dimensional model, the particle confined within a ring, that directly corresponds to observations of surface electrons in a metal trapped inside a circular barrier.…

  7. Peltier Coefficient and Photon-Assisted Tunnelling in Quantum Point Contact

    NASA Astrophysics Data System (ADS)

    H. Aly, Arafa

    2008-12-01

    We present the Peltier coefficient and thermal transport in quantum point contact (QPC), under the influence of external fields and different temperatures. Also we obtain the oscillations of the Peltier coefficient in external fields. Numerical calculations of the Peltier coefficient are performed at different applied voltages, amplitudes and temperatures. The obtained results are consistent with the experimental data in the literature.

  8. Four-electron model for singlet and triplet excitation energy transfers with inclusion of coherence memory, inelastic tunneling and nuclear quantum effects

    NASA Astrophysics Data System (ADS)

    Suzuki, Yosuke; Ebina, Kuniyoshi; Tanaka, Shigenori

    2016-08-01

    A computational scheme to describe the coherent dynamics of excitation energy transfer (EET) in molecular systems is proposed on the basis of generalized master equations with memory kernels. This formalism takes into account those physical effects in electron-bath coupling system such as the spin symmetry of excitons, the inelastic electron tunneling and the quantum features of nuclear motions, thus providing a theoretical framework to perform an ab initio description of EET through molecular simulations for evaluating the spectral density and the temporal correlation function of electronic coupling. Some test calculations have then been carried out to investigate the dependence of exciton population dynamics on coherence memory, inelastic tunneling correlation time, magnitude of electronic coupling, quantum correction to temporal correlation function, reorganization energy and energy gap.

  9. Workshop on quantum stochastic differential equations for the quantum simulation of physical systems

    DTIC Science & Technology

    2016-09-22

    of Post Doctorates Names of Faculty Supported Names of Under Graduate students supported Received Book Chapter TOTAL: PERCENT_SUPPORTEDNAME FTE...forming a Banach space under the operator norm topology. Thus, probability theory and statistics, along with standard tools of functional analysis...quantum systems under noise is a challenging frontier in quantum science and technology. In developing reliable controls for open quantum systems, one

  10. Effect of transverse electric field and temperature on light absorption in GaAs/AlGaAs tunnel-coupled quantum wells

    SciTech Connect

    Firsov, D. A.; Vorobjev, L. E.; Vinnichenko, M. Ya. Balagula, R. M.; Kulagina, M. M.; Vasil’iev, A. P.

    2015-11-15

    The photoluminescence and intersubband absorption spectra are studied in GaAs/AlGaAs tunnel- coupled quantum well structures. The peak positions in the photoluminescence and absorption spectra are consistent with the theoretically calculated energies of optical carrier transitions. The effect of a transverse electric field and temperature on intersubband light absorption is studied. It is caused by electron redistribution between the size-quantization levels and a variation in the energy spectrum of quantum wells. The variation in the refractive index in the energy region of observed intersubband transitions is estimated using Kramers–Kronig relations.

  11. Spin Polarization of Carriers in InGaAs Self-Assembled Quantum Rings Inserted in GaAs-AlGaAs Resonant Tunneling Devices

    NASA Astrophysics Data System (ADS)

    Orsi Gordo, V.; Gobato, Y. Galvão; Galeti, H. V. A.; Brasil, M. J. S. P.; Taylor, D.; Henini, M.

    2017-07-01

    In this work, we have investigated transport and polarization resolved photoluminescence (PL) of n-type GaAs-AlGaAs resonant tunneling diodes (RTDs) containing a layer of InGaAs self-assembled quantum rings (QRs) in the quantum well (QW). All measurements were performed under applied voltage, magnetic fields up to 15 T and using linearly polarized laser excitation. It was observed that the QRs' PL intensity and the circular polarization degree (CPD) oscillate periodically with applied voltage under high magnetic fields at 2 K. Our results demonstrate an effective voltage control of the optical and spin properties of InGaAs QRs inserted into RTDs.

  12. Spin Polarization of Carriers in InGaAs Self-Assembled Quantum Rings Inserted in GaAs-AlGaAs Resonant Tunneling Devices

    NASA Astrophysics Data System (ADS)

    Orsi Gordo, V.; Gobato, Y. Galvão; Galeti, H. V. A.; Brasil, M. J. S. P.; Taylor, D.; Henini, M.

    2017-03-01

    In this work, we have investigated transport and polarization resolved photoluminescence (PL) of n-type GaAs-AlGaAs resonant tunneling diodes (RTDs) containing a layer of InGaAs self-assembled quantum rings (QRs) in the quantum well (QW). All measurements were performed under applied voltage, magnetic fields up to 15 T and using linearly polarized laser excitation. It was observed that the QRs' PL intensity and the circular polarization degree (CPD) oscillate periodically with applied voltage under high magnetic fields at 2 K. Our results demonstrate an effective voltage control of the optical and spin properties of InGaAs QRs inserted into RTDs.

  13. Bosonization theory for tunneling spectra in smooth edges of quantum Hall systems

    NASA Astrophysics Data System (ADS)

    Conti, Sergio; Vignale, Giovanni

    1998-01-01

    We calculate the spectral function of a smooth edge of a quantum Hall system in the lowest Landau level by means of a bosonization technique. We obtain a general relationship between the one electron spectral function and the dynamical structure factor. The resulting I-V characteristics exhibit, at low voltage and temperature, power law scaling, generally different from the one predicted by the chiral Luttinger liquid theory, and in good agreement with recent experimental results.

  14. Practical Quantum Private Database Queries Based on Passive Round-Robin Differential Phase-shift Quantum Key Distribution

    NASA Astrophysics Data System (ADS)

    Li, Jian; Yang, Yu-Guang; Chen, Xiu-Bo; Zhou, Yi-Hua; Shi, Wei-Min

    2016-08-01

    A novel quantum private database query protocol is proposed, based on passive round-robin differential phase-shift quantum key distribution. Compared with previous quantum private database query protocols, the present protocol has the following unique merits: (i) the user Alice can obtain one and only one key bit so that both the efficiency and security of the present protocol can be ensured, and (ii) it does not require to change the length difference of the two arms in a Mach-Zehnder interferometer and just chooses two pulses passively to interfere with so that it is much simpler and more practical. The present protocol is also proved to be secure in terms of the user security and database security.

  15. Practical Quantum Private Database Queries Based on Passive Round-Robin Differential Phase-shift Quantum Key Distribution

    PubMed Central

    Li, Jian; Yang, Yu-Guang; Chen, Xiu-Bo; Zhou, Yi-Hua; Shi, Wei-Min

    2016-01-01

    A novel quantum private database query protocol is proposed, based on passive round-robin differential phase-shift quantum key distribution. Compared with previous quantum private database query protocols, the present protocol has the following unique merits: (i) the user Alice can obtain one and only one key bit so that both the efficiency and security of the present protocol can be ensured, and (ii) it does not require to change the length difference of the two arms in a Mach-Zehnder interferometer and just chooses two pulses passively to interfere with so that it is much simpler and more practical. The present protocol is also proved to be secure in terms of the user security and database security. PMID:27539654

  16. Practical Quantum Private Database Queries Based on Passive Round-Robin Differential Phase-shift Quantum Key Distribution.

    PubMed

    Li, Jian; Yang, Yu-Guang; Chen, Xiu-Bo; Zhou, Yi-Hua; Shi, Wei-Min

    2016-08-19

    A novel quantum private database query protocol is proposed, based on passive round-robin differential phase-shift quantum key distribution. Compared with previous quantum private database query protocols, the present protocol has the following unique merits: (i) the user Alice can obtain one and only one key bit so that both the efficiency and security of the present protocol can be ensured, and (ii) it does not require to change the length difference of the two arms in a Mach-Zehnder interferometer and just chooses two pulses passively to interfere with so that it is much simpler and more practical. The present protocol is also proved to be secure in terms of the user security and database security.

  17. Significant negative differential resistance predicted in scanning tunneling spectroscopy for a C60 monolayer on a metal surface

    NASA Astrophysics Data System (ADS)

    Shi, X. Q.; Pai, Woei Wu; Xiao, X. D.; Cerdá, J. I.; Zhang, R. Q.; Minot, C.; van Hove, M. A.

    2009-08-01

    We theoretically predict the occurrence of negative differential resistance (NDR) in scanning tunneling spectroscopy for a pure C60 monolayer deposited on a metal surface using metal tips, namely, on a Cu(111) surface and using various W tips. It is proposed that the likely reason why NDR has not been observed under such conditions is that NDR can be reduced if an oxidized or Cu-terminated tip is used. A detailed decomposition of the total tunneling current into its contributions from individual molecular orbitals reveals that only some of the orbitals on the tip and on the C60 can be “matched up” to give a contribution to the current and that the NDR is a consequence of the mismatch between these specific orbitals within particular ranges of bias voltage. Moreover, the NDR characteristics, including the peak positions and the peak-to-valley ratios, are found to depend on the tip material, tip geometry, and tip-to-molecule position.

  18. Two-color In0.4Ga0.6As/Al0.1Ga0.9As quantum dot infrared photodetector with double tunneling barriers

    NASA Astrophysics Data System (ADS)

    Huang, Jianliang; Ma, Wenquan; Wei, Yang; Zhang, Yanhua; Huo, Yongheng; Cui, Kai; Chen, Lianghui

    2011-03-01

    We report a two-color quantum dot infrared photodetector (QDIP) using double tunneling barriers (DTBs) on one side of the InGaAs/AlGaAs dots. The two-color detection is achieved by changing the polarity of the applied bias voltages. In contrast, the same QDIP structure without the DTBs does not exhibit this detection wavelength tunability by switching the bias polarity. The two-color detection is ascribed to a different escape mechanism of electrons between positive and negative biases. The electrons escape out of the quantum well through resonant tunneling for a positive bias voltage while tunnel through a triangular barrier for a negative bias voltage.

  19. Negative differential gain in quantum dot systems: Interplay of structural properties and many-body effects

    SciTech Connect

    Goldmann, E. Jahnke, F.; Lorke, M.; Frauenheim, T.

    2014-06-16

    The saturation behaviour of optical gain with increasing excitation density is an important factor for laser device performance. For active materials based on self-organized InGaAs/GaAs quantum dots, we study the interplay between structural properties of the quantum dots and many-body effects of excited carriers in the optical properties via a combination of tight-binding and quantum-kinetic calculations. We identify regimes where either phase-space filling or excitation-induced dephasing dominates the saturation behavior of the optical gain. The latter can lead to the emergence of a negative differential material gain.

  20. Algorithmic differentiation and the calculation of forces by quantum Monte Carlo.

    PubMed

    Sorella, Sandro; Capriotti, Luca

    2010-12-21

    We describe an efficient algorithm to compute forces in quantum Monte Carlo using adjoint algorithmic differentiation. This allows us to apply the space warp coordinate transformation in differential form, and compute all the 3M force components of a system with M atoms with a computational effort comparable with the one to obtain the total energy. Few examples illustrating the method for an electronic system containing several water molecules are presented. With the present technique, the calculation of finite-temperature thermodynamic properties of materials with quantum Monte Carlo will be feasible in the near future.

  1. The Photovoltaic Effect of CdS Quantum Dots Synthesized in Inverse Micelles and R-Phycoerythrin Tunnel Cavities.

    PubMed

    Bekasova, Olga D; Revina, Alexandra A; Kornienko, Ekaterina S; Kurganov, Boris I

    2015-06-01

    CdS quantum dots (CdS QDs) 4.3 nm in diameter synthesized in an AOT/isooctane/water microemulsion and in R-phycoerythrin tunnel cavities (3.5 × 6.0 nm) were analyzed for photoelectrochemical properties. The CdS QDs preparations were applied onto a platinum electrode to obtain solid films. Experiments were performed in a two-section vessel, with one section filled with ethanol and the other, with 3 M KCl. The sections were connected through an agar stopper. It was found that illumination of the films resulted in a change of the electrode potential. The magnitude of this change and the kinetics of the appearance and disappearance of the photopotential, i.e., the difference between the electrode potential on the light and in dark, depended on the nature of the QD shell. The photovoltaic effect of CdS QDs in R-phycoerythrin, compared to that of CdS QDs in AOT/isooctane micelles, is three to four times greater due to the photosensitizing action of R-phycoerythrin. The photosensitized effect was markedly higher than the photoelectric sensitivity of R-phycoerythrin and had the opposite polarity. Changes in the potential upon turning the light on and off could be observed repeatedly.

  2. Deciphering the origin of giant magnetic anisotropy and fast quantum tunnelling in Rhenium(IV) single-molecule magnets

    PubMed Central

    Singh, Saurabh Kumar; Rajaraman, Gopalan

    2016-01-01

    Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices. Among others, 4d/5d elements such as Re(IV) ion are found to exhibit very large magnetic anisotropy, and inclusion of this ion-aggregated clusters yields several attractive molecular magnets. Here, using ab intio calculations, we unravel the source of giant magnetic anisotropy associated with the Re(IV) ions by studying a series of mononuclear Re(IV) six coordinate complexes. The low-lying doublet states are found to be responsible for large magnetic anisotropy and the sign of the axial zero-field splitting parameter (D) can be categorically predicted based on the position of the ligand coordination. Large transverse anisotropy along with large hyperfine interactions opens up multiple relaxation channels leading to a fast quantum tunnelling of the magnetization (QTM) process. Enhancing the Re-ligand covalency is found to significantly quench the QTM process. PMID:26883278

  3. Deciphering the origin of giant magnetic anisotropy and fast quantum tunnelling in Rhenium(IV) single-molecule magnets

    NASA Astrophysics Data System (ADS)

    Singh, Saurabh Kumar; Rajaraman, Gopalan

    2016-02-01

    Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices. Among others, 4d/5d elements such as Re(IV) ion are found to exhibit very large magnetic anisotropy, and inclusion of this ion-aggregated clusters yields several attractive molecular magnets. Here, using ab intio calculations, we unravel the source of giant magnetic anisotropy associated with the Re(IV) ions by studying a series of mononuclear Re(IV) six coordinate complexes. The low-lying doublet states are found to be responsible for large magnetic anisotropy and the sign of the axial zero-field splitting parameter (D) can be categorically predicted based on the position of the ligand coordination. Large transverse anisotropy along with large hyperfine interactions opens up multiple relaxation channels leading to a fast quantum tunnelling of the magnetization (QTM) process. Enhancing the Re-ligand covalency is found to significantly quench the QTM process.

  4. Quantum-state transfer via resonant tunneling through local-field-induced barriers

    NASA Astrophysics Data System (ADS)

    Lorenzo, S.; Apollaro, T. J. G.; Sindona, A.; Plastina, F.

    2013-04-01

    Efficient quantum-state transfer is achieved in a uniformly coupled spin-1/2 chain, with open boundaries, by application of local magnetic fields on the second and last-but-one spins, respectively. These effective barriers induce the appearance of two eigenstates, bilocalized at the edges of the chain, which allow a high-quality transfer also at relatively long distances. The same mechanism may be used to send an entire e-bit (e.g., an entangled qubit pair) from one to the other end of the chain.

  5. Photon-assisted resonant tunneling through variably spaced superlattice energy filters

    NASA Technical Reports Server (NTRS)

    Larsson, A.; Borenstain, S. I.; Jonsson, B.; Andersson, I.; Westin, J.

    1991-01-01

    The observation of photon-assisted resonant tunneling in a multiple quantum well structure composed of doped quantum wells separated by variably space superlattice energy filters is reported. Electrons confined in the quantum wells are excited to the second quantized state by intersubband absorption of incident infrared radiation and are subsequently emitted through the filters under appropriate bias conditions. This is manifested by a distinct peak, with an associated negative differential photoconductance, in the photocurrent versus bias voltage characteristic at low temperatures.

  6. Quantum decay of the supercurrent and intrinsic capacitance of Josephson junctions beyond the tunnel limit

    NASA Astrophysics Data System (ADS)

    Antonenko, Daniil S.; Skvortsov, Mikhail A.

    2015-12-01

    A nondissipative supercurrent state of a Josephson junction is metastable with respect to the formation of a finite-resistance state. This transition is driven by fluctuations, thermal at high temperatures and quantum at low temperatures. We evaluate the lifetime of such a state due to quantum fluctuations in the limit when the supercurrent is approaching the critical current. The decay probability is determined by the instanton action for the superconducting phase difference across the junction. At low temperatures, the dynamics of the phase is massive and is determined by the effective capacitance, which is a sum of the geometric and intrinsic capacitance of the junction. We model the central part of the Josephson junction either by an arbitrary short mesoscopic conductor described by the set of its transmission coefficients, or by a diffusive wire of an arbitrary length. The intrinsic capacitance can generally be estimated as C*˜G /Eg , where G is the normal-state conductance of the junction and Eg is the proximity minigap in its normal part. The obtained capacitance is sufficiently large to qualitatively explain the hysteretic behavior of the current-voltage characteristic even in the absence of overheating.

  7. Canonical differential calculus on quantum general linear groups and supergroups

    NASA Astrophysics Data System (ADS)

    Sudbery, A.

    1992-06-01

    We specify a set of relations between non-commuting matrix elements and their differentials, defined in terms of an R-matrix satisfying the braid relation, which are uniquely determined by the requirements of consistency with the relations between non-commuting coordinates and their differentials. We also give a necessary condition for the existence of a matrix inverse (antipode) in the form of an additional equation to be satisfied by the R-matrix.

  8. Normal metal tunnel junction-based superconducting quantum interference proximity transistor

    SciTech Connect

    D'Ambrosio, Sophie Meissner, Martin; Blanc, Christophe; Ronzani, Alberto; Giazotto, Francesco

    2015-09-14

    We report the fabrication and characterization of an alternative design for a superconducting quantum interference proximity transistor (SQUIPT) based on a normal metal (N) probe. The absence of direct Josephson coupling between the proximized metal nanowire and the N probe allows us to observe the full modulation of the wire density of states around zero voltage and current via the application of an external magnetic field. This results into a drastic suppression of power dissipation which can be as low as a few ∼10{sup −17} W. In this context, the interferometer allows an improvement of up to four orders of magnitude with respect to earlier SQUIPT designs and makes it ideal for extra-low power cryogenic applications. In addition, the N-SQUIPT has been recently predicted to be the enabling candidate for the implementation of coherent caloritronic devices based on proximity effect.

  9. Resonant Tunnelling in Semiconductor Heterostructures

    NASA Astrophysics Data System (ADS)

    Leadbeater, Mark Levence

    1990-01-01

    Available from UMI in association with The British Library. A number of physical processes are investigated in this thesis, with particular regard to the effect of high magnetic fields on the tunnelling process. A brief outline is as follows: In the remainder of this chapter, the fundamental properties of GaAs and (AlGa)As relevant to this thesis are presented followed by a brief outline of some of the basic concepts in the theory of resonant tunnelling. In Chapter 2 the experimental techniques used to obtain the results are described and details of the samples are given. Chapter 3 describes several aspects of both resonant and non-resonant tunnelling in double barrier structures. Section 3.3 uses magnetoquantum oscillations in the tunnel current and differential capacitance to characterise the 2DEG in the emitter accumulation layer, Section 3.4 presents an investigation of the contributions of elastic scattering and scLO phonon scattering to the valley current using high magnetic fields, the temperature dependence of the I(V) characteristics is analysed in Section 3.5 and Section 3.6 discusses ballistic transport and quantum interference effects in wide quantum wells. Chapter 4 presents a detailed study of bistability in double barrier devices, showing first how charge buildup in the quantum well or high-frequency oscillations in the measuring circuit can lead to hysteresis in the current-voltage characteristics and then using an asymmetric structure to enhance charge buildup and observe a genuinely intrinsic bistability. Fourier analysis of magnetoquantum oscillations in a magnetic field applied parallel to the current demonstrates that carriers undergo energy relaxation in the well and therefore the tunnelling process is sequential. Two new effects are noted, the enhancement of charge buildup in high magnetic fields and the observation of a region of inverted bistability in a very asymmetric structure where the off-resonant current actually exceeds the resonant

  10. Functional differentiability in time-dependent quantum mechanics

    NASA Astrophysics Data System (ADS)

    Penz, Markus; Ruggenthaler, Michael

    2015-03-01

    In this work, we investigate the functional differentiability of the time-dependent many-body wave function and of derived quantities with respect to time-dependent potentials. For properly chosen Banach spaces of potentials and wave functions, Fréchet differentiability is proven. From this follows an estimate for the difference of two solutions to the time-dependent Schrödinger equation that evolve under the influence of different potentials. Such results can be applied directly to the one-particle density and to bounded operators, and present a rigorous formulation of non-equilibrium linear-response theory where the usual Lehmann representation of the linear-response kernel is not valid. Further, the Fréchet differentiability of the wave function provides a new route towards proving basic properties of time-dependent density-functional theory.

  11. Differential-phase-shift quantum key distribution with segmented pulse trains

    SciTech Connect

    Kawahara, Hiroki; Inoue, Kyo

    2011-06-15

    We present a modified scheme of differential-phase-shift (DPS) quantum key distribution (QKD) for improving its performance. A transmitter sends a weak coherent pulse train segmented with vacant pulses. Then, a receiver can find eavesdropping by monitoring the photon detection rate at particular time slots. Simulations show that the proposed scheme is robust against a sequential attack and a general individual attack.

  12. Probing DNA in nanopores via tunneling: from sequencing to ``quantum'' analogies

    NASA Astrophysics Data System (ADS)

    di Ventra, Massimiliano

    2012-02-01

    Fast and low-cost DNA sequencing methods would revolutionize medicine: a person could have his/her full genome sequenced so that drugs could be tailored to his/her specific illnesses; doctors could know in advance patients' likelihood to develop a given ailment; cures to major diseases could be found faster [1]. However, this goal of ``personalized medicine'' is hampered today by the high cost and slow speed of DNA sequencing methods. In this talk, I will discuss the sequencing protocol we suggest which requires the measurement of the distributions of transverse currents during the translocation of single-stranded DNA into nanopores [2-5]. I will support our conclusions with a combination of molecular dynamics simulations coupled to quantum mechanical calculations of electrical current in experimentally realizable systems [2-5]. I will also discuss recent experiments that support these theoretical predictions. In addition, I will show how this relatively unexplored area of research at the interface between solids, liquids, and biomolecules at the nanometer length scale is a fertile ground to study quantum phenomena that have a classical counterpart, such as ionic quasi-particles, ionic ``quantized'' conductance [6,7] and Coulomb blockade [8]. Work supported in part by NIH. [4pt] [1] M. Zwolak, M. Di Ventra, Physical Approaches to DNA Sequencing and Detection, Rev. Mod. Phys. 80, 141 (2008).[0pt] [2] M. Zwolak and M. Di Ventra, Electronic signature of DNA nucleotides via transverse transport, Nano Lett. 5, 421 (2005).[0pt] [3] J. Lagerqvist, M. Zwolak, and M. Di Ventra, Fast DNA sequencing via transverse electronic transport, Nano Lett. 6, 779 (2006).[0pt] [4] J. Lagerqvist, M. Zwolak, and M. Di Ventra, Influence of the environment and probes on rapid DNA sequencing via transverse electronic transport, Biophys. J. 93, 2384 (2007).[0pt] [5] M. Krems, M. Zwolak, Y.V. Pershin, and M. Di Ventra, Effect of noise on DNA sequencing via transverse electronic transport

  13. Systematic modulation of quantum (electron) tunneling behavior by atomic layer deposition on nanoparticulate SnO2 and TiO2 photoanodes.

    PubMed

    Prasittichai, Chaiya; Avila, Jason R; Farha, Omar K; Hupp, Joseph T

    2013-11-06

    Ultrathin films of TiO2, ZrO2, and Al2O3 were conformally created on SnO2 and TiO2 photoelectrodes via atomic layer deposition (ALD) to examine their influence upon electron transfer (ET) from the electrodes to a representative molecular receptor, I3(-). Films thicker than 2 Å engender an exponential decrease in ET time with increasing film thickness, consistent with tunneling theory. Increasing the height of the barrier, as measured by the energy difference between the transferring electron and the bottom of the conduction band of the barrier material, results in steeper exponential drops in tunneling rate or probability. The variations are quantitatively consistent with a simple model of quantum tunneling of electrons through square barriers (i.e., barriers of individually uniform energy height) that are characterized by individually uniform physical thickness. The findings demonstrate that ALD is a remarkably uniform and precise method for modifying electrode surfaces and imply that standard tunneling theory can be used as a quantitative guide to intentionally and predictively modulating rates of ET between molecules and electrodes.

  14. Tunneling above the crossover temperature.

    PubMed

    Alvarez-Barcia, Sonia; Flores, Jesús R; Kästner, Johannes

    2014-01-09

    Quantum mechanical tunneling of atoms plays a significant role in many chemical reactions. The crossover temperature between classical and quantum movement is a convenient preliminary indication of the importance of tunneling for a particular reaction. Here we show, using instanton theory, that quantum tunneling is possible significantly above this crossover temperature for specific forms of the potential energy surface. We demonstrate the effect on an analytic potential as well as a chemical system. While protons move asynchronously along a Grotthuss chain in the classical high-temperature range, the onset of tunneling results in a synchronization of their movement.

  15. Quantum interference in coherent tunneling through branched molecular junctions containing ferrocene centers

    NASA Astrophysics Data System (ADS)

    Zhao, Xin; Kastlunger, Georg; Stadler, Robert

    2017-08-01

    In our theoretical study where we combine a nonequilibrium Green's function approach with density functional theory we investigate branched compounds containing ferrocene moieties in both branches which, due to their metal centers, are designed to allow for asymmetry induced by local charging. In these compounds the ferrocene moieties are connected to pyridyl anchor groups either directly or via acetylenic spacers in a metaconnection, where we also compare our results with those obtained for the respective single-branched molecules with both meta- and paraconnections between the metal center and the anchors. We find a destructive quantum interference (DQI) feature in the transmission function slightly below the lowest unoccupied molecular orbital, which dominates the conductance even for the uncharged branched compound with spacer groups inserted. In an analysis based on mapping the structural characteristics of the range of molecules in our article onto tight-binding models, we identify the structural source of the DQI minimum as the through-space coupling between the pyridyl anchor groups. We also find that local charging in one of the branches changes the conductance only by about one order of magnitude, which we explain in terms of the spatial distributions of the relevant molecular orbitals for the branched compounds.

  16. Phonon assisted resonant tunneling and its phonons control

    NASA Astrophysics Data System (ADS)

    Kusmartsev, F. V.; Krevchik, V. D.; Semenov, M. B.; Filatov, D. O.; Shorokhov, A. V.; Bukharaev, A. A.; Dakhnovsky, Y.; Nikolaev, A. V.; Pyataev, N. A.; Zaytsev, R. V.; Krevchik, P. V.; Egorov, I. A.; Yamamoto, K.; Aringazin, A. K.

    2016-09-01

    We observe a series of sharp resonant features in the tunneling differential conductance of InAs quantum dots. We found that dissipative quantum tunneling has a strong influence on the operation of nanodevices. Because of such tunneling the current-voltage characteristics of tunnel contact created between atomic force microscope tip and a surface of InAs/GaAs quantum dots display many interesting peaks. We found that the number, position, and heights of these peaks are associated with the phonon modes involved. To describe the found effect we use a quasi-classical approximation. There the tunneling current is related to a creation of a dilute instanton-anti-instanton gas. Our experimental data are well described with exactly solvable model where one charged particle is weakly interacting with two promoting phonon modes associated with external medium. We conclude that the characteristics of the tunnel nanoelectronic devices can thus be controlled by a proper choice of phonons existing in materials, which are involved.

  17. The Role of Wrist Magnetic Resonance Imaging in the Differential Diagnosis of the Carpal Tunnel Syndrome.

    PubMed

    Onen, Mehmet Resid; Kayalar, Ali Erhan; Ilbas, Elif Nurbegum; Gokcan, Recai; Gulec, Ilker; Naderi, Sait

    2015-01-01

    The carpal tunnel syndrome (CTS) is the commonest compressive neuropathy. Electromyography (EMG) is accepted as gold standard in diagnosis of CTS. However, pathologies and variations that are associated with a various findings may lead to failure. Magnetic resonance Imaging (MRI) was applied to 69 wrists of 55 patients, who received a diagnosis of CTS by means of clinical and electrodiagnostic testing (EDT) during the years 2011 and 2013. We detected a total of 71 additional pathologies in MRI analyses: 29 degenerative bone cysts, 28 ganglion cysts, 8 tenosynovitis, and 6 avascular necroses. While the MRI detected 44 (59.5%) additional radiological pathologies in 39 wrists diagnosed with mid-level CTS by means of EMG, the number of detected additional pathologies was 27 (36.5%) in 30 wrists diagnosed with advanced-level CTS. Wrist MRI is an effective means to reveal associated pathologies in patients diagnosed with CTS by means of clinical testing and EDT. Additional pathologies may not only change the applicable type of surgery, but also decrease the number of postoperative failures. Wrist MRI is recommended, especially for young cases with unilateral CTS history accompanied by dubious clinical symptoms and lacking any pronounced predisposing factors.

  18. Differential identity of Filopodia and Tunneling Nanotubes revealed by the opposite functions of actin regulatory complexes

    PubMed Central

    Delage, Elise; Cervantes, Diégo Cordero; Pénard, Esthel; Schmitt, Christine; Syan, Sylvie; Disanza, Andrea; Scita, Giorgio; Zurzolo, Chiara

    2016-01-01

    Tunneling Nanotubes (TNTs) are actin enriched filopodia-like protrusions that play a pivotal role in long-range intercellular communication. Different pathogens use TNT-like structures as “freeways” to propagate across cells. TNTs are also implicated in cancer and neurodegenerative diseases, making them promising therapeutic targets. Understanding the mechanism of their formation, and their relation with filopodia is of fundamental importance to uncover their physiological function, particularly since filopodia, differently from TNTs, are not able to mediate transfer of cargo between distant cells. Here we studied different regulatory complexes of actin, which play a role in the formation of both these structures. We demonstrate that the filopodia-promoting CDC42/IRSp53/VASP network negatively regulates TNT formation and impairs TNT-mediated intercellular vesicle transfer. Conversely, elevation of Eps8, an actin regulatory protein that inhibits the extension of filopodia in neurons, increases TNT formation. Notably, Eps8-mediated TNT induction requires Eps8 bundling but not its capping activity. Thus, despite their structural similarities, filopodia and TNTs form through distinct molecular mechanisms. Our results further suggest that a switch in the molecular composition in common actin regulatory complexes is critical in driving the formation of either type of membrane protrusion. PMID:28008977

  19. Quantum tunneling time of a Bose-Einstein condensate traversing through a laser-induced potential barrier

    SciTech Connect

    Duan Zhenglu; Fan Bixuan; Yuan Chunhua; Zhang Weiping; Cheng Jing; Zhu Shiyao

    2010-05-15

    We theoretically study the effect of atomic nonlinearity on the tunneling time in the case of an atomic Bose-Einstein condensate (BEC) traversing the laser-induced potential barrier. The atomic nonlinearity is controlled to appear only in the region of the barrier by employing the Feshbach resonance technique to tune interatomic interaction in the tunneling process. Numerical simulation shows that the atomic nonlinear effect dramatically changes the tunneling behavior of the BEC matter wave packet and results in the violation of the Hartman effect and the occurrence of negative tunneling time.

  20. Optimization of the configuration of a symmetric three-barrier resonant-tunneling structure as an active element of a quantum cascade detector

    SciTech Connect

    Tkach, N. V. Seti, Ju. A.

    2011-03-15

    On the basis of a model of rectangular potentials and different electron effective masses in wells and barriers of an open resonant-tunneling structure with identical outer barriers, a theory has been developed and the dynamic conductance caused by the interaction of the electromagnetic field with electrons passing through the structure has been calculated. Using the example of the three-barrier resonant-tunneling structure with In{sub 0.53}Ga{sub 0.47}As wells and In{sub 0.52}Al{sub 0.48}As barriers, it is shown that, independently of the geometrical sizes of potential wells and barriers, there exist three geometrical configurations (positions of the inner barrier with respect to outer ones) at which the nanosystem, as an active element, provides optimum operating conditions of the quantum cascade detector.