NASA Astrophysics Data System (ADS)
Ramos, Roberto; Carabello, Steve; Lambert, Joseph; Mlack, Jerome; Dai, Wenqing; Shen, Yi.; Li, Qi; Cunnane, Daniel; Zhuang, C. G.; Chen, Ke; Xi, X. X.
2012-02-01
The Josephson junction is an experimental testbed widely used to study resonant activation and macroscopic quantum tunneling. These phenomena have been observed in junctions based on conventional low-temperature superconductors such as Nb and Al, and even in high-Tc, intrinsic superconductors. We report results of superconducting-to normal state switching experiments below 1 K using MgB2-based Josephson heterojunctions with Pb and Nb counter-electrodes. Measurements were made with and without RF excitation. With microwaves, we see evidence of a resonant peak, in addition to the primary escape (from ground state) peak -- consistent with resonant activation. We also observe features suggestive of macroscopic quantum tunneling including peaks in the escape rate enhancements and an ``elbow'' in the graph of calculated escape temperatures Tesc versus sample temperature.
Computational multiqubit tunnelling in programmable quantum annealers.
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
Computational multiqubit tunnelling in programmable quantum annealers
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
Quantum tunneling through graphene nanorings
NASA Astrophysics Data System (ADS)
Wu, Zhenhua; Zhang, Z. Z.; Chang, Kai; Peeters, F. M.
2010-05-01
We investigate theoretically quantum transport through graphene nanorings in the presence of a perpendicular magnetic field. Our theoretical results demonstrate that the graphene nanorings behave like a resonant tunneling device, contrary to the Aharonov-Bohm oscillations found in conventional semiconductor rings. The resonant tunneling can be tuned by the Fermi energy, the size of the central part of the graphene nanorings and the external magnetic field.
Quantum tunneling through graphene nanorings.
Wu, Zhenhua; Zhang, Z Z; Chang, Kai; Peeters, F M
2010-05-01
We investigate theoretically quantum transport through graphene nanorings in the presence of a perpendicular magnetic field. Our theoretical results demonstrate that the graphene nanorings behave like a resonant tunneling device, contrary to the Aharonov-Bohm oscillations found in conventional semiconductor rings. The resonant tunneling can be tuned by the Fermi energy, the size of the central part of the graphene nanorings and the external magnetic field. PMID:20388970
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.
Quantum Tunneling Affects Engine Performance.
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. PMID:26283246
Quantum tunneling beyond semiclassical approximation
NASA Astrophysics Data System (ADS)
Banerjee, Rabin; Ranjan Majhi, Bibhas
2008-06-01
Hawking radiation as tunneling by Hamilton-Jacobi method beyond semiclassical approximation is analysed. We compute all quantum corrections in the single particle action revealing that these are proportional to the usual semiclassical contribution. We show that a simple choice of the proportionality constants reproduces the one loop back reaction effect in the spacetime, found by conformal field theory methods, which modifies the Hawking temperature of the black hole. Using the law of black hole mechanics we give the corrections to the Bekenstein-Hawking area law following from the modified Hawking temperature. Some examples are explicitly worked out.
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…
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.
Quantum tunneling with global charge
Lee, K. )
1994-10-15
We investigate quantum tunneling in the theory of a complex scalar field with a global U(1) symmetry when the charge density of the initial configuration does not vanish. We discuss the possible final configurations and set up the Euclidean path integral formalism to find the bubble nucleation and to study the bubble evolution. For the stationary path, or the bounce solution, in the Euclidean time, the phase variable becomes pure imaginary so that the charge density remains real. We apply this formalism to examples when the initial charge density is small. While the phase transition considered here occurs in zero temperature, the bubble dynamics is richly complicated, involving conserved charge, the sound wave, and the supersonic bubble wall.
Quantum temporal probabilities in tunneling systems
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.
Tunneling through a quantum dot in a quantum waveguide
NASA Astrophysics Data System (ADS)
Arsen'ev, A. A.
2010-07-01
The problem is considered of scattering in a system consisting of a quantum waveguide and a quantum dot weakly coupled to the waveguide. It is assumed that the quantum waveguide is described by the Pauli equations, and the Rashba spin-orbit interaction is taken into account. The possibility of tunneling through the quantum dot is proved.
Quantum Monte Carlo simulations of tunneling in quantum adiabatic optimization
NASA Astrophysics Data System (ADS)
Brady, Lucas T.; van Dam, Wim
2016-03-01
We explore to what extent path-integral quantum Monte Carlo methods can efficiently simulate quantum adiabatic optimization algorithms during a quantum tunneling process. Specifically we look at symmetric cost functions defined over n bits with a single potential barrier that a successful quantum adiabatic optimization algorithm will have to tunnel through. The height and width of this barrier depend on n , and by tuning these dependencies, we can make the optimization algorithm succeed or fail in polynomial time. In this article we compare the strength of quantum adiabatic tunneling with that of path-integral quantum Monte Carlo methods. We find numerical evidence that quantum Monte Carlo algorithms will succeed in the same regimes where quantum adiabatic optimization succeeds.
Quantum temporal probabilities in tunneling systems
NASA Astrophysics Data System (ADS)
Anastopoulos, Charis; Savvidou, Ntina
2013-09-01
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.
Understanding Quantum Tunneling through Quantum Monte Carlo Simulations
NASA Astrophysics Data System (ADS)
Boixo, Sergio; Isakov, Sergei; Mazzola, Guglielmo; Smelyanskiy, Vadim; Jiang, Zhang; Neven, Hartmut; Troyer, Matthias
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 (in the exponent) with system size, as the rate of incoherent tunneling. The scaling in both cases is O (Δ2) , where Δ is the tunneling splitting. An important consequence is that QMC simulations can be used to predict the performance of a quantum annealer for tunneling through a barrier. Furthermore, by using open instead of periodic boundary conditions in imaginary time, equivalent to a projector QMC algorithm, we obtain a quadratic speedup for QMC, and achieve linear scaling in Δ. We provide a physical understanding of these results and their range of applicability based on an instanton picture.
Tunneling rate in double quantum dots
NASA Astrophysics Data System (ADS)
Filikhin, Igor; Matinyan, Sergei; Vlahovic, Branislav
2014-03-01
We study spectral properties of electron tunneling in double quantum dots (DQDs) (and double quantum wells (DQWs)) and their relation to the geometry. In particular we compare the tunneling in DQW with chaotic and regular geometry, taking into account recent evidence about regularization of the tunneling rate when the QW geometry is chaotic. Our calculations do not support this assumption. We confirm high influence of the QW geometry boundaries on the rate fluctuation along the spectrum. The factors of the effective mass anisotropy and violation of the symmetry of DQD and DQW are also considered. Generally, we found that the small violation of the symmetry drastically affects tunneling. This work is supported by the NSF (HRD-0833184) and NASA (NNX09AV07A).
Dissipative macroscopic quantum tunneling in type-I superconductors
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.
The Quantum Hydrodynamic Description of Tunneling
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.
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.
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.
Comment on ``Quantum tunneling time''
NASA Astrophysics Data System (ADS)
Hahne, G. E.
2005-02-01
In this Comment on the paper by Wanget al., Phys. Rev. A692004052108], it is pointed out that (i) a group-theoretical argument advanced in the first part of their derivation is both flawed and not needed in what follows, (ii) they then assert a formula that leads to a physically incorrect phase (as distinguished from group) delay time in the motion of a free particle, and (iii) their subsequent derivation contains a mathematical error, such that the outcome is a new formula for the tunneling time that avoids the second problem, but such that the result is unfounded and is therefore of unknown physical content.
Quantum tunneling dynamics using hydrodynamic trajectories
NASA Astrophysics Data System (ADS)
Bittner, Eric R.
2000-06-01
In this paper we compute quantum trajectories arising from Bohm's causal description of quantum mechanics. Our computational methodology is based upon a finite-element moving least-squares method (MWLS) presented recently by Wyatt and co-workers [Lopreore and Wyatt, Phys. Rev. Lett. 82, 5190 (1999)]. This method treats the "particles" in the quantum Hamilton-Jacobi equation as Lagrangian fluid elements that carry the phase, S, and density, ρ, required to reconstruct the quantum wave function. Here, we compare results obtained via the MWLS procedure to exact results obtained either analytically or by numerical solution of the time-dependent Schrödinger equation. Two systems are considered: first, dynamics in a harmonic well and second, tunneling dynamics in a double well potential. In the case of tunneling in the double well potential, the quantum potential acts to lower the barrier, separating the right- and left-hand sides of the well, permitting trajectories to pass from one side to another. However, as probability density passes from one side to the other, the effective barrier begins to rise and eventually will segregate trajectories in one side from the other. We note that the MWLS trajectories exhibited long time stability in the purely harmonic cases. However, this stability was not evident in the barrier crossing dynamics. Comparisons to exact trajectories obtained via wave packet calculations indicate that the MWLS trajectories tend to underestimate the effects of constructive and destructive interference effects.
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.
Macroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions.
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
Macroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions
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
Resonant tunnelling in a quantum oxide superlattice
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 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
Resonant tunnelling in a quantum oxide superlattice
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 SrTiO_{3} 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 (~10^{5}) 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.
Quantum Tunneling Current in Nanoscale Plasmonic Junctions
NASA Astrophysics Data System (ADS)
Zhang, Peng; Lau, Y. Y.; Gilgenbach, R. M.
2014-10-01
Recently, electron tunneling between plasmonic resonators is found to support quantum plasmon resonances, which may introduce new regimes in nano-optoelectronics and nonlinear optics. This revelation is of substantial interest to the fundamental problem of electron transport in nano-scale, for example, in a metal-insulator-metal junction (MIM), which has been continuously studied for decades. Here, we present a self-consistent model of electron transport in a nano-scale MIM, by solving the coupled Schrödinger and Poisson equations. The effects of space charge, exchange-correlation, anode emission, and material properties of the electrodes and insulator are examined in detail. The self-consistent calculations are compared with the widely used Simmons formula. Transition from the direct tunneling regime to the space-charge-limited regime is demonstrated. This work was supported by AFOSR.
NASA Astrophysics Data System (ADS)
Kitano, H.; Ota, K.; Hamada, K.; Takemura, R.; Ohmaki, M.; Maeda, A.; Suzuki, M.
2009-03-01
A nanometer-thick small mesa consiting of only two or three Bi2Sr2CaCu2Oy intrinsic Josephson junctions (IJJs) is studied through the switching current distribution measurements down to 0.4 K. Experimental results clearly show that the first switching events from the zero-voltage state for 1 K < T < 4 K are successfully described by a conventional thermal activation (TA) theory for a single Josephson junction, and that they become independent of temperature below T* ~ 0.7 K. We observe the microwave-induced peak in the switching distribution at 0.4 K, which is induced by the microwave irradiation at 55 GHz. These results strongly suggest that the system crossovers to macroscopic quantum tunneling (MQT) regime below T*, which is as high as the previously reported value for a stacked IJJs with several tens of junctions, in contrast to the recent result on a similar mesa-structured surface IJJ.
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.
Parallel Quantum Circuit in a Tunnel Junction.
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 N(2) power law is preserved for Ωab(N) and for Vab(N). PMID:27453262
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).
Parallel Quantum Circuit in a Tunnel Junction
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
Mesoscopic quantum tunneling of the magnetization
NASA Astrophysics Data System (ADS)
Barbara, B.; Wernsdorfer, W.; Sampaio, L. C.; Park, J. G.; Paulsen, C.; Novak, M. A.; Ferré, R.; Mailly, D.; Sessoli, R.; Caneschi, A.; Hasselbach, K.; Benoit, A.; Thomas, L.
1995-02-01
Magnetic relaxation plateaux observed at low temperature in complex systems, are generally attributed to Quantum Tunneling of the Magnetization (QTM). If the experiments are not performed down to low enough temperatures, alternative interpretations can be given in terms of powerlaw distributions resulting from either switching field distributions or/and coupling between switching blocks leading to self-organized criticality. Besides, the first low-temperature/time-dependent magnetization experiments, performed on single sub-micronic particles and on arrays nanoparticles in molecular crystals, are described.
Virtual Processes and Quantum Tunnelling as Fictions
NASA Astrophysics Data System (ADS)
Arthur, Richard T. W.
2012-10-01
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 Lévy-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 effects, the implied conceptualization of it as a free particle burrowing through a potential barrier is flawed. An alpha particle, for example, does not exist as a free particle inside a uranium nucleus and then "burrow through" the massive potential barrier of the repulsive Coulomb potential: rather, it can be interpreted as existing in a bound state which gives it a corresponding (absolutely tiny, but) finite probability of appearing on the other side of the barrier. If the part of the state function representing the transmission through the barrier is conceived as representing a particle trajectory, the particle will have imaginary momentum and negative kinetic energy. A similar analysis then applies to virtual processes. For example, if (as in Hawking's conception of black hole radiation) one imagines a pair of particles created at the Schwarzschild radius, one of which drops into the black hole, at its creation that particle will have imaginary momentum and negative kinetic energy; so will the pion that is imagined as mediating the nuclear exchange force on the standard model. In each case, it is argued, the phenomenon can be understood in terms of a finite probability of transmission predicted by quantum theory, without appealing to particle trajectories. The idea that a particle "penetrates" a barrier that it does not have the energy to surmount, or that a pair of particles is "virtually" produced one on either side of the Schwarzschild radius, in defiance of energy conservation, should be discarded as unphysical.
Quasilinearization method applied to multidimensional quantum tunneling
NASA Astrophysics Data System (ADS)
Razavy, M.; Cote, Vincent J.
1994-04-01
We apply the quasilinearization method of Bellman and Kalaba [Quasilinearization and Nonlinear Boundary-Value Problems (Elsevier, New York, 1965)] to find approximate solutions for the multidimensional quantum tunneling for separable as well as nonseparable wave equations. By introducing the idea of the complex ``semiclassical trajectory'' which is valid for the motion over and under the barrier, and which, in the proper limit, reduces to the real classical trajectory in the allowed region, we obtain an eigenvalue equation for the characteristic wave numbers. This eigenvalue equation is similar to the corresponding equation obtained from the WKB approximation and yields complex eigenvalues with negative imaginary parts. When the barrier changes very rapidly as a function of the radial distance, we can replace the concept of the semiclassical trajectory, which may not be applicable in this case, by the concept of a complex ``quantum trajectory.'' The trajectory defined either way depends on a constant of integration, and by minimizing the action with respect to this constant we can obtain the minimum escape path. The case of two-dimensional tunneling is discussed as an example of this method.
Invisibility of quantum systems to tunneling of matter waves
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.
Concrete quantum tunneling spectrum of Schwarzschild black holes
NASA Astrophysics Data System (ADS)
Chen, Si-Na; Zhang, Jing-Yi
2015-02-01
In this paper, a canonical ensemble model for black hole quantum tunneling radiation is introduced. We find that the probability distribution function is the same as the emission rate of a spherical shell in the Parikh-Wilczek tunneling framework. With this model, the probability distribution function corresponding to the emission shell system is calculated. Therefore, the concrete quantum tunneling spectrum of the Schwarzschild black hole is obtained. Project supported by the National Natural Science Foundation of China (Grant Nos. 11273009 and 11303006).
Josephson inplane and tunneling currents in bilayer quantum Hall system
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.
Distribution of tunnelling times for quantum electron transport.
Rudge, Samuel L; Kosov, Daniel S
2016-03-28
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. PMID:27036425
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.
Optically Modulated Bistability in Quantum Dot Resonant Tunneling Diodes
NASA Astrophysics Data System (ADS)
Weng, Qian-Chun; An, Zheng-Hua; Hou, Ying; Zhu, Zi-Qiang
2013-04-01
InAs quantum dots are introduced into resonant tunneling diodes to study the electronic transport behavior, and a wide bistability (ΔV ~ 0.8 V) is observed in the negative differential resistance region. Based on an analytic model, we attribute the observed distinct bistability of a resonant tunneling diodes with quantum dots to the feedback dependence of energy of the electron-storing quantum dots on the tunneling current density. Meanwhile, we find that this wide bistable region can be modulated sensitively by light illumination and becomes narrower with increasing light intensity. Our results suggest that the present devices can be potentially used as sensitive photodetectors in optoelectronic fields.
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.
Quantum tunneling from scalar fields in rotating black strings
NASA Astrophysics Data System (ADS)
Gohar, H.; Saifullah, K.
2013-08-01
Using the Hamilton-Jacobi method of quantum tunneling and complex path integration, we study Hawking radiation of scalar particles from rotating black strings. We discuss tunneling of both charged and uncharged scalar particles from the event horizons. For this purpose, we use the Klein-Gordon equation and find the tunneling probability of outgoing scalar particles. The procedure gives Hawking temperature for rotating charged black strings as well.
Quantum tunneling resonant electron transfer process in Lorentzian plasmas
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.
Single electron tunneling in double and triple quantum wells
NASA Astrophysics Data System (ADS)
Filikhin, I.; Karoui, A.; Vlahovic, B.
2016-03-01
Electron localization and tunneling in laterally distributed double quantum well (DQW) and triple quantum well (TQW) are studied. Triangular configuration for the TQWs as well as various quantum well (QW) shapes and asymmetry are considered. The effect of adding a third well to a DQW is investigated as a weakly coupled system. InAs/GaAs DQWs and TQWs were modeled using single subband effective mass approach with effective potential simulating the strain effect. Electron localization dynamics in DQW and TQW over the whole spectrum is studied by varying the inter-dot distances. The electron tunneling appeared highly sensitive to small violations of the DQW mirror symmetry. We show that the presence of a third dot increases the tunneling in the DQW. The dependence of the tunneling in quantum dot (QD) arrays on inter-dot distances is also discussed.
Macroscopic quantum tunneling of polarization in the hydrogenbonded chain
NASA Astrophysics Data System (ADS)
Tomchuk, P. M.; Krasnoholovets, V. V.
1997-10-01
The probability of macroscopic quantum tunneling of polarization in a finite H-bonded chain is treated theoretically with regard to the influence of chain anisotropy. It is shown that the anisotropy stipulated by different microscopical effects plays a major role in the tunneling rate of polarization.
Quantum Tunnelling to the Origin and Evolution of Life.
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. PMID:24039543
Quantum Tunnelling to the Origin and Evolution of Life
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
Multielectron dynamics in the tunneling ionization of correlated quantum systems
NASA Astrophysics Data System (ADS)
Hollstein, Maximilian; Pfannkuche, Daniela
2015-11-01
The importance of multielectron dynamics during the tunneling ionization of a correlated quantum system is investigated. By comparison of the solution of the time-dependent Schrödinger equation with the time-dependent configuration-interaction singles approach, we demonstrate the importance of a multielectron description of the tunneling ionization process especially for weakly confined quantum systems. Within this context, we observe that adiabatic driving by an intense light field can even enhance the correlations between still trapped electrons.
Dynamical symmetries in Kondo tunneling through complex quantum dots.
Kuzmenko, T; Kikoin, K; Avishai, Y
2002-10-01
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). PMID:12366008
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.
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.
Quantum tunneling switch in a planar four-well system
NASA Astrophysics Data System (ADS)
Lu, Gengbiao; Hai, Wenhua
2011-05-01
We investigate the tunneling dynamics of a single atom in a planar four-well potential driven by a high-frequency ac field. The quasienergy spectrum exhibits anticrossing and crossing, which are related to selective coherent destruction of tunneling (CDT) with several selectable directions. By using the CDTs of different directions, the switchlike effect is shown for the six tunneling pathways among the four wells. Applying the present results, we suggest a scheme for designing a single-atom quantum motor with the driving field as a quantum starter.
Quantum tunneling switch in a planar four-well system
Lu Gengbiao; Hai Wenhua
2011-05-15
We investigate the tunneling dynamics of a single atom in a planar four-well potential driven by a high-frequency ac field. The quasienergy spectrum exhibits anticrossing and crossing, which are related to selective coherent destruction of tunneling (CDT) with several selectable directions. By using the CDTs of different directions, the switchlike effect is shown for the six tunneling pathways among the four wells. Applying the present results, we suggest a scheme for designing a single-atom quantum motor with the driving field as a quantum starter.
Single to quadruple quantum dots with tunable tunnel couplings
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.
Quantum dot resonant tunneling FET on graphene
NASA Astrophysics Data System (ADS)
Mohammadpour, Hakimeh
2016-07-01
At this paper a field effect transistor based on graphene nanoribbon (GNR) is modeled. Like in most GNR-FETs the GNR is chosen to be semiconductor with a gap, through which the current passes at on state of the device. The regions at the two ends of GNR are highly n-type doped and play the role of metallic reservoirs so called source and drain contacts. Two dielectric layers are placed on top and bottom of the GNR and a metallic gate is located on its top above the channel region. At this paper it is assumed that the gate length is less than the channel length so that the two ends of the channel region are un-gated. As a result of this geometry, the two un-gated regions of channel act as quantum barriers between channel and the contacts. By applying gate voltage, discrete energy levels are generated in channel and resonant tunneling transport occurs via these levels. By solving the NEGF and 3D Poisson equations self consistently, we have obtained electron density, potential profile and current. The current variations with the gate voltage give rise to negative transconductance.
Ultrafast hole tunneling in asymmetric double quantum wells
NASA Astrophysics Data System (ADS)
Krol, Mark F.; Ten, Sergey Y.; McGinnis, Brian P.; Hayduk, Michael J.; Khitrova, Galina; Peyghambarian, Nasser
1995-04-01
We present the results of an experimental study of tunneling in Asymmetric Double Quantum Well (ADQW) structures for which holes were found to tunnel from the narrow well to the wide well on sub-picosecond time-scales. These times are as fast, or faster than electron tunneling times despite the absence of resonances between hole states. Valence band structure calculations for our ADQW structures indicate that ultrafast hole tunneling can be attributed spin-dependent delocalization of the hole wavefunctions with a concomitant singularity (in principle) in the density of final wide well states.
Tunneling and Speedup in Permutation-Invariant Quantum Optimization Problem
NASA Astrophysics Data System (ADS)
Albash, Tameem
Tunneling is often claimed to be the key mechanism underlying possible speedups in quantum optimization via the quantum adiabatic algorithm. Restricting ourselves to qubit-permutation invariant problems, we show that tunneling in these problems can be understood using the semi-classical potential derived from the spin-coherent path integral formalism. Using this, we show that the class of problems that fall under Reichardt's bound (1), i.e., have a constant gap and hence can be efficiently solved using the quantum adiabatic algorithm, do not exhibit tunneling in the large system-size limit. We proceed to construct problems that do not fall under Reichardt's bound but numerically have a constant gap and do exhibit tunneling. However, perhaps counter-intuitively, tunneling does not provide the most efficient mechanism for finding the solution to these problems. Instead, an evolution involving a sequence of diabatic transitions through many avoided level-crossings, involving no tunneling, is optimal and outperforms tunneling in the adiabatic regime. In yet another twist, we show that in this case, classical spin-vector dynamics is as efficient as the diabatic quantum evolution (2).
Classical oscillators in the control of quantum tunneling: Numerical experiments
NASA Astrophysics Data System (ADS)
Kar, Susmita; Bhattacharyya, S. P.
2016-06-01
The dynamics of a classical anharmonic oscillator is exploited to control the tunneling dynamics of a quantum particle to which the classical oscillator is coupled. The mixed quantum classical problem is investigated at a mean-field like level. The anharmonic strength (λ) , particle mass (Mc) and harmonic stiffness (ωc) of the classical controller are explored as possible control parameters for the tunneling dynamics. The strength, the type of coupling between the quantum system and classical controller and the effective frequency of the controller emerge as crucial factors in shaping the nature and extent of the control. A whole spectrum of possibilities starting from enhancement, suppression to complete destruction of tunneling emerge depending on values assigned to the control parameters, the type of coupling and the control configuration used. When classical controller is replaced by a quantum controller, the control landscape becomes much simpler.
Quantum Monte Carlo Simulation of Tunneling Devices Using Bohm Trajectories
NASA Astrophysics Data System (ADS)
Oriols, X.; García-García, J. J.; Martín, F.; Suñé, J.; González, T.; Mateos, J.; Pardo, D.
1997-11-01
A generalization of the classical Monte Carlo (MC) device simulation technique is proposed to simultaneously deal with quantum-mechanical phase-coherence effects and scattering interactions in tunneling devices. The proposed method restricts the quantum treatment of transport to the regions of the device where the potential profile significantly changes in distances of the order of the de Broglie wavelength of the carriers (the quantum window). Bohm trajectories associated to time-dependent Gaussian wavepackets are used to simulate the electron transport in the quantum window. Outside this window, the classical ensemble simulation technique is used. Classical and quantum trajectories are smoothly matched at the boundaries of the quantum window according to a criterium of total energy conservation. A simple one-dimensional simulator for resonant tunneling diodes is presented to demonstrate the feasibility of our proposal.
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.
Marinica, Dana Codruta; Zapata, Mario; Nordlander, Peter; Kazansky, Andrey K.; M. Echenique, Pedro; Aizpurua, Javier; Borisov, Andrei G.
2015-01-01
The ability of localized surface plasmons to squeeze light and engineer nanoscale electromagnetic fields through electron-photon coupling at dimensions below the wavelength has turned plasmonics into a driving tool in a variety of technological applications, targeting novel and more efficient optoelectronic processes. In this context, the development of active control of plasmon excitations is a major fundamental and practical challenge. We propose a mechanism for fast and active control of the optical response of metallic nanostructures based on exploiting quantum effects in subnanometric plasmonic gaps. By applying an external dc bias across a narrow gap, a substantial change in the tunneling conductance across the junction can be induced at optical frequencies, which modifies the plasmonic resonances of the system in a reversible manner. We demonstrate the feasibility of the concept using time-dependent density functional theory calculations. Thus, along with two-dimensional structures, metal nanoparticle plasmonics can benefit from the reversibility, fast response time, and versatility of an active control strategy based on applied bias. The proposed electrical manipulation of light using quantum plasmonics establishes a new platform for many practical applications in optoelectronics. PMID:26824066
Marinica, Dana Codruta; Zapata, Mario; Nordlander, Peter; Kazansky, Andrey K; M Echenique, Pedro; Aizpurua, Javier; Borisov, Andrei G
2015-12-01
The ability of localized surface plasmons to squeeze light and engineer nanoscale electromagnetic fields through electron-photon coupling at dimensions below the wavelength has turned plasmonics into a driving tool in a variety of technological applications, targeting novel and more efficient optoelectronic processes. In this context, the development of active control of plasmon excitations is a major fundamental and practical challenge. We propose a mechanism for fast and active control of the optical response of metallic nanostructures based on exploiting quantum effects in subnanometric plasmonic gaps. By applying an external dc bias across a narrow gap, a substantial change in the tunneling conductance across the junction can be induced at optical frequencies, which modifies the plasmonic resonances of the system in a reversible manner. We demonstrate the feasibility of the concept using time-dependent density functional theory calculations. Thus, along with two-dimensional structures, metal nanoparticle plasmonics can benefit from the reversibility, fast response time, and versatility of an active control strategy based on applied bias. The proposed electrical manipulation of light using quantum plasmonics establishes a new platform for many practical applications in optoelectronics. PMID:26824066
Quantum revivals and magnetization tunneling in effective spin systems
NASA Astrophysics Data System (ADS)
Krizanac, M.; Altwein, D.; Vedmedenko, E. Y.; Wiesendanger, R.
2016-03-01
Quantum mechanical objects or nano-objects have been proposed as bits for information storage. While time-averaged properties of magnetic, quantum-mechanical particles have been extensively studied experimentally and theoretically, experimental investigations of the real time evolution of magnetization in the quantum regime were not possible until recent developments in pump-probe techniques. Here we investigate the quantum dynamics of effective spin systems by means of analytical and numerical treatments. Particular attention is paid to the quantum revival time and its relation to the magnetization tunneling. The quantum revival time has been initially defined as the recurrence time of a total wave-function. Here we show that the quantum revivals of wave-functions and expectation values in spin systems may be quite different which gives rise to a more sophisticated definition of the quantum revival within the realm of experimental research. Particularly, the revival times for integer spins coincide which is not the case for half-integer spins. Furthermore, the quantum revival is found to be shortest for integer ratios between the on-site anisotropy and an external magnetic field paving the way to novel methods of anisotropy measurements. We show that the quantum tunneling of magnetization at avoided level crossing is coherent to the quantum revival time of expectation values, leading to a connection between these two fundamental properties of quantum mechanical spins.
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.
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 .
Computational modeling of electrophotonics nanomaterials: Tunneling in double quantum dots
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.
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).
Quantum Gravity Corrections to the Tunneling Radiation of Scalar Particles
NASA Astrophysics Data System (ADS)
Wang, Peng; Yang, Haitang; Ying, Shuxuan
2016-05-01
The original derivation of Hawking radiation shows the complete evaporation of black holes. However, theories of quantum gravity predict the existence of the minimal observable length. In this paper, we investigate the tunneling radiation of the scalar particles by introducing the quantum gravity effects influenced by the generalized uncertainty principle. The Hawking temperatures are not only determined by the properties of the black holes, but also affected by the quantum numbers of the emitted particles. The quantum gravity corrections slow down the increase of the temperatures. The remnants are found during the evaporation.
Aharonov-Bohm effect in the tunnelling of a quantum rotor in a linear Paul trap.
Noguchi, Atsushi; Shikano, Yutaka; Toyoda, Kenji; Urabe, Shinji
2014-01-01
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]. PMID:24820051
NASA Astrophysics Data System (ADS)
Hasaneen, El-Sayed; Heller, Evan; Bansal, Rajeev; Jain, Faquir
2003-10-01
In this paper, we compute the tunneling of electrons in a nonvolatile quantum dot memory (NVQDM) cell during the WRITE operation. The transition rate of electrons from a quantum well channel to the quantum dots forming the floating gate is calculated using a recently reported method by Chuang et al.[1]. Tunneling current is computed based on transport of electrons from the channel to the floating quantum dots. The maximum number of electrons on a dot is calculated using surface electric field and break down voltage of the tunneling dielectric material. Comparison of tunneling for silicon oxide and high-k dielectric gate insulators is also described. Capacitance-Voltage characteristics of a NVQDM device are calculated by solving the Schrodinger and Poisson equations self-consistently. In addition, the READ operation of the memory has been investigated analytically. Results for 70 nm channel length Si NVQDMs are presented. Threshold voltage is calculated including the effect of the charge on nanocrystal quantum dots. Current-voltage characteristics are obtained using BSIM3v3 model [2-3]. This work is supported by Office of Navel Research (N00014210883, Dr. D. Purdy, Program Monitor), Connecticut Innovations Inc./TranSwitch (CII # 00Y17), and National Science Foundation (CCR-0210428) grants. [1] S. L. Chuang and N. Holonyak, Appl. Phys. Lett., 80, pp. 1270, 2002. [2] Y. Chen et. al., BSIM3v3 Manual, Elect. Eng. and Comp. Dept., U. California, Berkeley, CA, 1996. [3] W. Liu, MOSFET Models for SPICE Simulation, John Wiley & Sons, Inc., 2001.
Quantum tunneling observed without its characteristic large kinetic isotope effects
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
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.
Decoding DNA, RNA and peptides with quantum tunnelling.
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. PMID:26839257
Room-temperature resonant quantum tunneling transport of macroscopic systems.
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. PMID:25307500
Coupling quantum tunneling with cavity photons.
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. PMID:22491095
Giant fifth-order nonlinearity via tunneling induced quantum interference in triple quantum dots
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.
Giant fifth-order nonlinearity via tunneling induced quantum interference in triple quantum dots
NASA Astrophysics Data System (ADS)
Tian, Si-Cong; Wan, Ren-Gang; Tong, Cun-Zhu; Ning, Yong-Qiang
2015-02-01
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.
Asymptotic Formula for Quantum Harmonic Oscillator Tunneling Probabilities
NASA Astrophysics Data System (ADS)
Jadczyk, Arkadiusz
2015-10-01
Using simple methods of asymptotic analysis it is shown that for a quantum harmonic oscillator in n-th energy eigenstate the probability of tunneling into the classically forbidden region obeys an unexpected but simple asymptotic formula: the leading term is inversely proportional to the cube root of n.
Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes
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.
Neuroreceptor Activation by Vibration-Assisted Tunneling
Hoehn, Ross D.; Nichols, David; Neven, Hartmut; Kais, Sabre
2015-01-01
G protein-coupled receptors (GPCRs) constitute a large family of receptor proteins that sense molecular signals on the exterior of a cell and activate signal transduction pathways within the cell. Modeling how an agonist activates such a receptor is fundamental for an understanding of a wide variety of physiological processes and it is of tremendous value for pharmacology and drug design. Inelastic electron tunneling spectroscopy (IETS) has been proposed as a model for the mechanism by which olfactory GPCRs are activated by a bound agonist. We apply this hyothesis to GPCRs within the mammalian nervous system using quantum chemical modeling. We found that non-endogenous agonists of the serotonin receptor share a particular IET spectral aspect both amongst each other and with the serotonin molecule: a peak whose intensity scales with the known agonist potencies. We propose an experiential validation of this model by utilizing lysergic acid dimethylamide (DAM-57), an ergot derivative, and its deuterated isotopologues; we also provide theoretical predictions for comparison to experiment. If validated our theory may provide new avenues for guided drug design and elevate methods of in silico potency/activity prediction. PMID:25909758
Neuroreceptor activation by vibration-assisted tunneling.
Hoehn, Ross D; Nichols, David; Neven, Hartmut; Kais, Sabre
2015-01-01
G protein-coupled receptors (GPCRs) constitute a large family of receptor proteins that sense molecular signals on the exterior of a cell and activate signal transduction pathways within the cell. Modeling how an agonist activates such a receptor is fundamental for an understanding of a wide variety of physiological processes and it is of tremendous value for pharmacology and drug design. Inelastic electron tunneling spectroscopy (IETS) has been proposed as a model for the mechanism by which olfactory GPCRs are activated by a bound agonist. We apply this hyothesis to GPCRs within the mammalian nervous system using quantum chemical modeling. We found that non-endogenous agonists of the serotonin receptor share a particular IET spectral aspect both amongst each other and with the serotonin molecule: a peak whose intensity scales with the known agonist potencies. We propose an experiential validation of this model by utilizing lysergic acid dimethylamide (DAM-57), an ergot derivative, and its deuterated isotopologues; we also provide theoretical predictions for comparison to experiment. If validated our theory may provide new avenues for guided drug design and elevate methods of in silico potency/activity prediction. PMID:25909758
Quantum tunneling radiation from self-dual black holes
NASA Astrophysics Data System (ADS)
Silva, C. A. S.; Brito, F. A.
2013-10-01
Black holes are considered as objects that can reveal quantum aspects of spacetime. Loop Quantum Gravity (LQG) is a theory that propose a way to model the quantum spacetime behavior revealed by a black hole. One recent prediction of this theory is the existence of sub-Planckian black holes, which have the interesting property of self-duality. This property removes the black hole singularity and replaces it with another asymptotically flat region. In this work, we obtain the thermodynamical properties of this kind of black holes, called self-dual black holes, using the Hamilton-Jacobi version of the tunneling formalism. Moreover, using the tools of the tunneling approach, we investigate the emission spectrum of self-dual black holes, and investigate if some information about the black hole initial state can be recovered during the evaporation process. Back-reaction effects are included.
Evolution of Plasmonic Metamolecule Modes in the Quantum Tunneling Regime.
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. PMID:26639023
Macroscopic quantum tunneling in small Josephson junctions in a magnetic field.
Ovchinnikov, Yu. N.; Barone, A.; Varlamov, A. A.; Materials Science Division; Max-Planck Inst. for Physics of Complex Systems; Landau Inst. Theoretical Physics; Univ. di Napoli Federico II; Coherentia-INFM, CNR
2007-01-01
We study the phenomenon of macroscopic quantum tunneling (MQT) in small Josephson junctions (JJ) with an externally applied magnetic field. The latter results in the appearance of the Fraunhofer type modulation of the current density along the barrier. The problem of MQT for a pointlike JJ is reduced to the motion of the quantum particle in the washboard potential. In the case of a finite size JJ under consideration, this problem corresponds to a MQT in a potential which itself, besides the phase, depends on space variables. The general expression for the crossover temperature To between thermally activated and macroscopic quantum tunneling regimes and the escaping time {tau}{sub esc} have been calculated.
Quantum tunneling between bent semiconductor nanowires
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.
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.
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. PMID:23214856
Coherent tunnelling across a quantum point contact in the quantum Hall regime.
Martins, F; Faniel, S; Rosenow, B; Sellier, H; Huant, S; Pala, M G; Desplanque, L; Wallart, X; Bayot, V; Hackens, B
2013-01-01
The unique properties of quantum hall devices arise from the ideal one-dimensional edge states that form in a two-dimensional electron system at high magnetic field. Tunnelling between edge states across a quantum point contact (QPC) has already revealed rich physics, like fractionally charged excitations, or chiral Luttinger liquid. Thanks to scanning gate microscopy, we show that a single QPC can turn into an interferometer for specific potential landscapes. Spectroscopy, magnetic field and temperature dependences of electron transport reveal a quantitatively consistent interferometric behavior of the studied QPC. To explain this unexpected behavior, we put forward a new model which relies on the presence of a quantum Hall island at the centre of the constriction as well as on different tunnelling paths surrounding the island, thereby creating a new type of interferometer. This work sets the ground for new device concepts based on coherent tunnelling. PMID:23475303
Coherent tunnelling across a quantum point contact in the quantum Hall regime
Martins, F.; Faniel, S.; Rosenow, B.; Sellier, H.; Huant, S.; Pala, M. G.; Desplanque, L.; Wallart, X.; Bayot, V.; Hackens, B.
2013-01-01
The unique properties of quantum hall devices arise from the ideal one-dimensional edge states that form in a two-dimensional electron system at high magnetic field. Tunnelling between edge states across a quantum point contact (QPC) has already revealed rich physics, like fractionally charged excitations, or chiral Luttinger liquid. Thanks to scanning gate microscopy, we show that a single QPC can turn into an interferometer for specific potential landscapes. Spectroscopy, magnetic field and temperature dependences of electron transport reveal a quantitatively consistent interferometric behavior of the studied QPC. To explain this unexpected behavior, we put forward a new model which relies on the presence of a quantum Hall island at the centre of the constriction as well as on different tunnelling paths surrounding the island, thereby creating a new type of interferometer. This work sets the ground for new device concepts based on coherent tunnelling. PMID:23475303
NASA Astrophysics Data System (ADS)
Tian, Si-Cong; Wan, Ren-Gang; Xing, En-Bo; Tong, Cun-Zhu; Ning, Yong-Qiang
2014-10-01
A scheme for tunneling control of cavity linewidth narrowing by quantum interference in triangular-type triple quantum dots (TQDs) is proposed. In such system, quantum interference induced by tunneling between the TQDs can result in the appearance of two transparency windows and a steep dispersion. Furthermore, when the sample is embedded in a ring cavity, an ultranarrow transmission peak is obtained within the narrowed transparency windows. And by varying the tunneling, the linewidth and the position of the ultranarrow transmission peak can be engineered. Because no coupling laser is required, the scheme proposed here is more convenient for future experiments and applications in optics, and may be useful in designing novel optoelectronic devices.
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.
NASA Astrophysics Data System (ADS)
Tian, Si-Cong; Wan, Ren-Gang; Tong, Cun-Zhu; Ning, Yong-Qiang; Qin, Li; Liu, Yun
2014-08-01
Optical spectroscopy, a powerful tool for probing and manipulating quantum dots (QDs), has been used to investigate the resonance fluorescence spectrum from linear triple quantum dot molecules controlled by tunneling, using atomic physics methods. Interesting features such as quenching and narrowing of the fluorescence are observed. In such molecules the tunneling between the quantum dots can also induce a dark state. The results are explained by the transition properties of the dressed states generated by the coupling of the laser and the tunneling. Unlike the atomic system, in such quantum dot molecules quantum coherence can be induced using tunneling, requiring no coupling lasers, which will allow tunneling controllable quantum dot molecules to be applied to quantum optics and photonics.
Study and manipulation of electron tunneling through quantum dots
NASA Astrophysics Data System (ADS)
Bhadrachalam, Pradeep Krishna
Fermi-Dirac distribution is the fundamental property which governs the electron energy distribution in solids. At finite temperatures, Fermi-Dirac thermal smearing of electron energies limits the operation of many electronic, opto-electronic and spintronic devices. Examples include single electron transistors, quantum dot resonant tunnel diodes for single photon detection, and single electron turnstile devices. To overcome this intrinsic limitation of Fermi-Dirac thermal smearing, these devices have typically been operated at cryogenic temperatures. Room temperature operation of these devices could be realized, however, if the thermal smearing of electron energies could be suppressed. Until now, studies in the fields of electron-tunneling refrigerators and double quantum dot devices have demonstrated limited manipulation/suppression of electron energy distribution, but those have been carried out at cryogenic temperatures. Using a double barrier tunneling junction structure as a model system this research has accomplished the following: * Demonstrated suppression of thermal smearing of electrons at room temperature, without any physical cooling of the system * Demonstrated that cold electrons whose effective temperature as low as ˜45 K can be created at room temperature without any physical cooling * Systematically investigated the phenomenon responsible for suppression in thermal smearing of electron energies * Systematically investigated the cold electron transport in the double barrier tunnel junction structure One of the key achievements of this research was demonstration of effective electron temperature of ˜45K at room temperature without any physical cooling of the system. This was realized by filtering out the thermally excited electrons in a double barrier tunneling junction structure. A discrete energy state of a quantum well, created by band bending of Cr2O3 conduction band, acted as an electron energy filter, effectively suppressing energy
Using Mathematics to Inform Conceptual Reasoning about Quantum Tunneling
NASA Astrophysics Data System (ADS)
Morgan, Jeffrey T.; Wittmann, M. C.
2006-12-01
Previously, we have reported on work at the University of Maine investigating how undergraduate physics students reason about the phenomenon of quantum mechanical tunneling.(1) The majority of our interview sessions involved a series of qualitative questions regarding a square-barrier tunneling scenario. For a select group of students, we began second interview sessions by asking them to solve the time-independent Schrodinger equation prior to answering a series of conceptual questions. All were able to produce reasonably correct solutions, which could be used throughout the interview to reason about the answers to many of our questions. However, in several instances students either failed to refer to the mathematics when responding, or seemed to struggle with understanding their equations and how the mathematics informed the correct responses, suggesting a discontinuity between their mathematical reasoning and their physical reasoning. 1. M. C. Wittman, J. T. Morgan, and L. Bao. Addressing student models of energy loss in quantum tunneling. Eur. J. Phys. 26, 939-950 (2005).
Quantum Adiabatic Pumping by Modulating Tunnel Phase in Quantum Dots
NASA Astrophysics Data System (ADS)
Taguchi, Masahiko; Nakajima, Satoshi; Kubo, Toshihiro; Tokura, Yasuhiro
2016-08-01
In a mesoscopic system, under zero bias voltage, a finite charge is transferred by quantum adiabatic pumping by adiabatically and periodically changing two or more control parameters. We obtained expressions for the pumped charge for a ring of three quantum dots (QDs) by choosing the magnetic flux penetrating the ring as one of the control parameters. We found that the pumped charge shows a steplike behavior with respect to the variance of the flux. The value of the step heights is not universal but depends on the trajectory of the control parameters. We discuss the physical origin of this behavior on the basis of the Fano resonant condition of the ring.
NASA Astrophysics Data System (ADS)
García-García, J.; Martín, F.; Oriols, X.; Suñé, J.
1998-12-01
A tool for the simulation of resonant tunneling diodes (RTDs) has been developed. This is based on the solution of the quantum Liouville equation in the active region of the device and the Boltzman transport equation in the regions adjacent to the contacts by means of a Monte Carlo algorithm. By accurately coupling both approaches to current transport, we have developed a quantum simulation tool that allows the use of simulation domains much larger and realistic than those previously considered, without a significant increase in computational burden. The main characteristics expected for the considered devices are clearly obtained, thus supporting the validity of our tool for the simulation of RTDs.
Interlayer tunneling in double-layer quantum hall pseudoferromagnets.
Balents, L; Radzihovsky, L
2001-02-26
We show that the interlayer tunneling I-V in double-layer quantum Hall states displays a rich behavior which depends on the relative magnitude of sample size, voltage length scale, current screening, disorder, and thermal lengths. For weak tunneling, we predict a negative differential conductance of a power-law shape crossing over to a sharp zero-bias peak. An in-plane magnetic field splits this zero-bias peak, leading instead to a "derivative" feature at V(B)(B(parallel)) = 2 pi Planck's over 2 pi upsilon B(parallel)d/e phi(0), which gives a direct measurement of the dispersion of the Goldstone mode corresponding to the spontaneous symmetry breaking of the double-layer Hall state. PMID:11290258
Quantum Tunneling and Spectroscopy of Noncommutative Inspired Kerr Black Hole
NASA Astrophysics Data System (ADS)
Miao, Yan-Gang; Xue, Zhao; Zhang, Shao-Jun
We discuss the thermodynamics of the noncommutative inspired Kerr black hole by means of a reformulated Hamilton-Jacobi method and a dimensional reduction technique. In order to investigate the effect of the angular momentum of the tunneling particle, we calculate the wave function to the first order of the WKB ansatz. Then, using a density matrix technique we derive the radiation spectrum from which the radiation temperature can be read out. Our results show that the radiation of this noncommutative inspired black hole corresponds to a modified temperature which involves the effect of noncommutativity. However, the angular momentum of the tunneling particle has no influence on the radiation temperature. Moreover, we analyze the entropy spectrum and verify that its quantization is modified neither by the noncommutativity of spacetime nor by the quantum correction of wave functions.
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).
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.
The pilot-wave perspective on quantum scattering and tunneling
NASA Astrophysics Data System (ADS)
Norsen, Travis
2013-04-01
The de Broglie-Bohm "pilot-wave" theory replaces the paradoxical wave-particle duality of ordinary quantum theory with a more mundane and literal kind of duality: each individual photon or electron comprises a quantum wave (evolving in accordance with the usual quantum mechanical wave equation) and a particle that, under the influence of the wave, traces out a definite trajectory. The definite particle trajectory allows the theory to account for the results of experiments without the usual recourse to additional dynamical axioms about measurements. Instead, one need simply assume that particle detectors click when particles arrive at them. This alternative understanding of quantum phenomena is illustrated here for two elementary textbook examples of one-dimensional scattering and tunneling. We introduce a novel approach to reconcile standard textbook calculations (made using unphysical plane-wave states) with the need to treat such phenomena in terms of normalizable wave packets. This approach allows for a simple but illuminating analysis of the pilot-wave theory's particle trajectories and an explicit demonstration of the equivalence of the pilot-wave theory predictions with those of ordinary quantum theory.
Quantum tunneling photoacoustic spectroscopy for the characterization of thin films
NASA Astrophysics Data System (ADS)
Goldschmidt, Benjamin S.; Rudy, Anna M.; Mandal, Swarnasri; Nowak, Charissa A.; Viator, John A.; Hunt, Heather K.
2015-03-01
Thin films continue to show great promise for improving a wide variety of devices in applications such as medical instrumentation, material processing, and astronomical instrumentation. While ellipsometry and reflectometry are standard characterization techniques for determining thickness and refractive index, these techniques tend to require highly reflective or polished films and rely on empirical equations. We have created Quantum Tunneling Photoacoustic Spectroscopy (QTPAS) that uses light induced ultrasound to obtain thickness and refractive index estimates of transparent films. We present QTPAS to be used for the estimation of properties of single layer films as an alternative to ellipsometry and give qualitative sample measurements of the technique's estimated parameters.
Creation of wormholes by quantum tunnelling in modified gravity theories
NASA Astrophysics Data System (ADS)
Battarra, Lorenzo; Lavrelashvili, George; Lehners, Jean-Luc
2014-12-01
We study the process of quantum tunnelling in scalar-tensor theories in which the scalar field is nonminimally coupled to gravity. In these theories gravitational instantons can deviate substantially from sphericity and can in fact develop a neck—a feature prohibited in theories with minimal coupling. Such instantons with necks lead to the materialization of bubble geometries containing a wormhole region. We clarify the relationship of neck geometries to violations of the null energy condition, and also derive a bound on the size of the neck relative to that of the instanton.
Quantum control of molecular tunneling ionization in the spatiotemporal domain
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.
Quantum tunneling of massive spin-1 particles from non-stationary metrics
NASA Astrophysics Data System (ADS)
Sakalli, I.; Övgün, A.
2016-01-01
We focus on the HR of massive vector (spin-1) particles tunneling from Schwarzschild BH expressed in the Kruskal-Szekeres and dynamic Lemaitre coordinates. Using the Proca equation together with the Hamilton-Jacobi and the WKB methods, we show that the tunneling rate, and its consequence Hawking temperature are well recovered by the quantum tunneling of the massive vector particles.
Quantum tunneling of the magnetic moment in the S/F/S Josephson φ0 junction
NASA Astrophysics Data System (ADS)
Chudnovsky, Eugene M.
2016-04-01
We show that the S/F/S Josephson φ0 junction permits detection of macroscopic quantum tunneling and quantum oscillation of the magnetic moment by measuring the ac voltage across the junction. Exact expression for the tunnel splitting renormalized by the interaction with the superconducting order parameter is obtained. It is demonstrated that magnetic tunneling may become frozen at a sufficiently large φ0. The quality factor of quantum oscillations of the magnetic moment due to finite ohmic resistance of the junction is computed. It is shown that magnetic tunneling rate in the φ0 junction can be controlled by the bias current, with no need for the magnetic field.
Quantum tunneling of vortices in two-dimensional condensates
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.
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.
The Concrete Quantum Tunneling Spectrum of Reissner-Nordstrom Black Holes
NASA Astrophysics Data System (ADS)
Chen, Sina; Zhang, Jingyi
2016-03-01
A canonical ensemble model for a R-N black hole quantum tunneling radiation is introduced in this paper. We discover that the probability distribution function is equal to the emission rate of a spherical shell in the Parikh-Wilczek tunneling framework. Taking the generalized uncertainty principle into account, the probability distribution function corresponding to the emission shell system can be calculated with this model. As a result the concrete quantum tunneling spectrum for a R-N black hole is obtained.
NASA Astrophysics Data System (ADS)
Tian, Si-Cong; Wan, Ren-Gang; Tong, Cun-Zhu; Fu, Xi-Hong; Cao, Jun-Sheng; Ning, Yong-Qiang
2015-12-01
A scheme for giant Kerr nonlinearity via tunneling in triangular triple quantum dot molecules is proposed. In such a system, the linear absorption and the Kerr nonlinearity depend critically on the energy splitting of the excited states and the tunneling intensity. With proper parameters, giant Kerr nonlinearity accompanied by vanishing absorption can be realized. The enhancement of Kerr nonlinearity is attributed to the interacting double dark resonances induced by the tunneling between the quantum dots, requiring no extra coupling laser fields.
Controllable optical bistability in triple quantum dot nanostructure via double tunnel coupling
NASA Astrophysics Data System (ADS)
Jafarzadeh, Hossein
2014-08-01
The behavior of optical bistability in triple quantum dot nanostructure using double tunnel coupling inside a unidirectional ring cavity is investigated. Also, the linear and nonlinear absorption of the system are investigated. The double tunneling between the quantum dots can change the absorption of the system. The threshold of OB can be controlled by the intensity of the double tunneling and the detuning of probe field. This may be employed for the development of new types of nanoelectronic devices for realizing switching process.
NASA Astrophysics Data System (ADS)
Owerre, S. A.; Paranjape, M. B.
2015-01-01
This article presents a review on the theoretical and the experimental developments on macroscopic quantum tunneling and quantum-classical phase transitions of the escape rate in large spin systems. A substantial amount of research work has been done in this area of research over the years, so this article does not cover all the research areas that have been studied, for instance the effect of dissipation is not discussed and can be found in other review articles. We present the basic ideas with simplified calculations so that it is readable to both specialists and nonspecialists in this area of research. A brief derivation of the path integral formulation of quantum mechanics in its original form using the orthonormal position and momentum basis is reviewed. For tunneling of a particle into the classically forbidden region, the imaginary time (Euclidean) formulation of path integral is useful, we review this formulation and apply it to the problem of tunneling in a double well potential. For spin systems such as single molecule magnets, the formulation of path integral requires the use of non-orthonormal spin coherent states in (2 s + 1) dimensional Hilbert space, the coordinate independent and the coordinate dependent form of the spin coherent state path integral are derived. These two (equivalent) forms of spin coherent state path integral are applied to the tunneling of single molecule magnets through a magnetic anisotropy barrier. Most experimental and numerical results are presented. The suppression of tunneling for half-odd integer spin (spin-parity effect) at zero magnetic field is derived using both forms of spin coherent state path integral, which shows that this result (spin-parity effect) is independent of the choice of coordinate. At nonzero magnetic field we present both the experimental and the theoretical results of the oscillation of tunneling splitting as a function of the applied magnetic field applied along the spin hard anisotropy axis
Quantum mechanical tunneling of composite particle systems: Linkage to sub-barrier nuclear reactions
Shotter, A. C.; Shotter, M. D.
2011-05-15
A variety of physical phenomena have at their foundation the quantum tunneling of particles through potential barriers. Many of these phenomena can be associated with the tunneling of single inert particles. The tunneling of composite systems is more complex than for single particles due to the coupling of the tunneling coordinate with the internal degrees of freedom of the tunneling system. Reported here are the results of a study for the tunneling of a two-component projectile incident on a potential energy system which differs for the two components. A specific linkage is made to sub-Coulomb nuclear reactions.
Subpicosecond hole tunneling by nonresonant delocalization in asymmetric double quantum wells
NASA Astrophysics Data System (ADS)
Krol, M. F.; Ten, S.; McGinnis, B. P.; Hayduk, M. J.; Khitrova, G.; Peyghambarian, N.
1995-11-01
We present experimental evidence for subpicosecond hole tunneling in asymmetric double-quantum-well structures. A single tunneling time is observed at low carrier densities indicating that hole tunneling times are at least as fast as electron tunneling times despite the absence of resonances between hole states. We have conducted band-structure and tunneling-time calculations suggesting that nonresonant delocalization of hole wave functions combined with alloy scattering provides an efficient mechanism for fast hole transfer from the narrow well (NW) to the wide well (WW) at finite in-plane momenta. We suggest that holes tunnel to the WW before reaching the bottom of the lowest subband in the NW.
Quantum interference effect in electron tunneling through a quantum-dot-ring spin valve
NASA Astrophysics Data System (ADS)
Ma, Jing-Min; Zhao, Jia; Zhang, Kai-Cheng; Peng, Ya-Jing; Chi, Feng
2011-12-01
Spin-dependent transport through a quantum-dot (QD) ring coupled to ferromagnetic leads with noncollinear magnetizations is studied theoretically. Tunneling current, current spin polarization and tunnel magnetoresistance (TMR) as functions of the bias voltage and the direct coupling strength between the two leads are analyzed by the nonequilibrium Green's function technique. It is shown that the magnitudes of these quantities are sensitive to the relative angle between the leads' magnetic moments and the quantum interference effect originated from the inter-lead coupling. We pay particular attention on the Coulomb blockade regime and find the relative current magnitudes of different magnetization angles can be reversed by tuning the inter-lead coupling strength, resulting in sign change of the TMR. For large enough inter-lead coupling strength, the current spin polarizations for parallel and antiparallel magnetic configurations will approach to unit and zero, respectively. PACS numbers:
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.
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.
Transient gain-absorption of the probe field in triple quantum dots coupled by double tunneling
NASA Astrophysics Data System (ADS)
Tian, Si-Cong; Zhang, Xiao-Jun; Wan, Ren-Gang; Zhao, Shuai; Wu, Hao; Shu, Shi-Li; Wang, Li-Jie; Tong, Cun-Zhu
2016-06-01
The transient gain-absorption property of the probe field in a linear triple quantum dots coupled by double tunneling is investigated. It is found that the additional tunneling can dramatically affect the transient behaviors under the transparency condition. The dependence of transient behaviors on other parameters, such as probe detuning, the pure dephasing decay rate of the quantum dots and the initial conditions of the population, are also discussed. The results can be explained by the properties of the dressed states generated by the additional tunneling. The scheme may have important application in quantum information network and communication.
A Planar Quantum Transistor Based on 2D-2D Tunneling in Double Quantum Well Heterostructures
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.
Kiyama, H. Fujita, T.; Teraoka, S.; Oiwa, A.; Tarucha, S.
2014-06-30
Spin filtering with electrically tunable efficiency is achieved for electron tunneling between a quantum dot and spin-resolved quantum Hall edge states by locally gating the two-dimensional electron gas (2DEG) leads near the tunnel junction to the dot. The local gating can change the potential gradient in the 2DEG and consequently the edge state separation. We use this technique to electrically control the ratio of the dot–edge state tunnel coupling between opposite spins and finally increase spin filtering efficiency up to 91%, the highest ever reported, by optimizing the local gating.
Resonant tunneling and quantum fluctuation in a driven triple-well system
NASA Astrophysics Data System (ADS)
Lu, Wei-Tao; Wang, Shun-Jin; Zhang, Hua
2010-02-01
The influence of parameters such as the strength and frequency of a periodic driving force on the tunneling dynamics is investigated in a symmetric triple-well potential. It is shown that for some special values of the parameters, tunneling could be enhanced considerably or suppressed completely. Quantum fluctuation during the tunneling is discussed as well and the numerical results are presented and analysed by virtue of Floquet formalism.
Quantum Tunneling of Water in Beryl: A New State of the Water Molecule
NASA Astrophysics Data System (ADS)
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.
2016-04-01
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.
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.
Driven quantum tunneling and pair creation with graphene Landau levels
NASA Astrophysics Data System (ADS)
Gagnon, Denis; Fillion-Gourdeau, François; Dumont, Joey; Lefebvre, Catherine; MacLean, Steve
2016-05-01
Driven tunneling between graphene Landau levels is theoretically linked to the process of pair creation from vacuum, a prediction of quantum electrodynamics (QED). Landau levels are created by the presence of a strong, constant, quantizing magnetic field perpendicular to a graphene monolayer. Following the formal analogy between QED and the description of low-energy excitations in graphene, solutions of the fully interacting Dirac equation are used to compute electron-hole pair creation driven by a circularly or linearly polarized field. This is achieved via the coupled channel method, a numerical scheme for the solution of the time-dependent Dirac equation in the presence of bound states. The case of a monochromatic driving field is first considered, followed by the more realistic case of a pulsed excitation. We show that the pulse duration yields an experimental control parameter over the maximal pair yield. Orders of magnitude of the pair yield are given for experimentally achievable magnetic fields and laser intensities weak enough to preserve the Landau level structure.
NASA Astrophysics Data System (ADS)
Rajput, Gagan; Kumar, Rajendra; Ajay
2014-09-01
Using non-equilibrium Green's function approach, we study electronic transport through a parallel double quantum dot (DQD) system symmetrically coupled to conventional superconducting leads. Andreev bound states (ABS) and corresponding resonant Cooper pair electron transmission through such a DQD-superconductor tunnel junction around the Fermi energy, a manifestation of Josephson effect, occur due to proximity effect as a result of superconducting order parameter. Interdot tunnel coupling in parallel coupled DQD system and Coulomb interactions regulate the Josephson effect in a very significant manner. Further, it is also found that interdot tunnel coupling has reverse effect on ABS and Cooper pair tunneling in the presence and absence of Coulomb interactions.
Wide bandgap, strain-balanced quantum well tunnel junctions on InP substrates
NASA Astrophysics Data System (ADS)
Lumb, M. P.; Yakes, M. K.; González, M.; Bennett, M. F.; Schmieder, K. J.; Affouda, C. A.; Herrera, M.; Delgado, F. J.; Molina, S. I.; Walters, R. J.
2016-05-01
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/cm2 to be realized.
Quantum Gravity Effects on the Tunneling Radiation of the Einstein-Maxwell-Dilaton-Axion Black Hole
NASA Astrophysics Data System (ADS)
Cheng, Tianhu; Ren, Ruyi; Chen, Deyou; Liu, Zixiang; Li, Guopin
2016-07-01
Taking into account effects of quantum gravity, we investigate the evaporation of an Einstein-Maxwell-Dilaton-Axion black hole. The corrected Hawking temperature is gotten respectively by the scalar particle's and the fermion's tunneling across the horizon. This temperature is lower than the original one derived by Hawking, which means quantum gravity effects slow down the rise of the temperature.
Danshita, Ippei; Polkovnikov, Anatoli
2010-09-01
We study the quantum dynamics of supercurrents of one-dimensional Bose gases in a ring optical lattice to verify instanton methods applied to coherent macroscopic quantum tunneling (MQT). We directly simulate the real-time quantum dynamics of supercurrents, where a coherent oscillation between two macroscopically distinct current states occurs due to MQT. The tunneling rate extracted from the coherent oscillation is compared with that given by the instanton method. We find that the instanton method is quantitatively accurate when the effective Planck's constant is sufficiently small. We also find phase slips associated with the oscillations.
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.
Quantitative description of Josephson-like tunneling in {nu}{sub T}=1 quantum Hall bilayers
Hyart, Timo; Rosenow, Bernd
2011-04-15
At total filling factor {nu}{sub T}=1, interlayer phase coherence in quantum Hall bilayers can result in a tunneling anomaly resembling the Josephson effect in the presence of strong fluctuations. The most robust experimental signature of this effect is a strong enhancement of the tunneling conductance at small voltages. The height and width of the conductance peak depend strongly on the area and tunneling amplitude of the samples, applied parallel magnetic field, and temperature. We find that the tunneling experiments are in quantitative agreement with a theory that treats fluctuations due to meron excitations phenomenologically and takes tunneling into account perturbatively. We also discuss the qualitative changes caused by larger tunneling amplitudes, and provide a possible explanation for recently observed critical currents in counterflow geometry.
Quantum tunneling splittings from path-integral molecular dynamics.
Mátyus, Edit; Wales, David J; Althorpe, Stuart C
2016-03-21
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. PMID:27004863
Size dependence in tunneling spectra of PbSe quantum-dot arrays.
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. PMID:19546498
Exchange interaction and the tunneling induced transparency in coupled quantum dots
NASA Astrophysics Data System (ADS)
Borges, Halyne; Alcalde, Augusto; Ulloa, Sergio
2014-03-01
Stacked semiconductor quantum dots coupled by tunneling are unique ``quantum molecule'' where it is possible to create a multilevel structure of excitonic states. This structure allows the investigation of quantum interference processes and their control via electric external fields. In this work, we investigate the optical response of a quantum molecule coherently driven by a polarized laser, considering the splitting in excitonic levels caused by isotropic and anisotropic exchange interactions. In our model we consider interdot transitions mediated by the the hole tunneling between states with the same total spin and, between bright and dark exciton states. Using realistic experimental parameters, we demonstrate that the excitonic states coupled by tunneling exhibit an enriched and controllable optical response. Our results show that through the appropriate control of the external electric field and light polarization, the tunneling coupling establishes an efficient destructive quantum interference path that creates a transparency window in the absorption spectra, whenever states of appropriate symmetry are mixed by the hole tunneling. We explore the relevant parameters space that would allows with the experiments. CAPES, INCT-IQ and MWN/CIAM-NSF.
Hu, Q.; Mears, C.A.; Richards, P.L. Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA ); Lloyd, F.L. )
1990-12-01
We have made the first direct measurement of the quantum susceptance that arises from the nondissipative part of quasiparticle tunneling in a superconductor-insulator-superconductor tunnel junction. The junction is coupled to an antenna and a superconducting microstrip stub to form a resonator; the resonant frequency is determined from the response of the junction to broadband radiation from a Fourier-transform spectrometer. A 19% shift of the resonant frequency, from 73 to 87 GHz, is observed, which arises from the change of the quantum susceptance of the junction with dc bias voltage. This shift is in excellent agreement with calculations based on the Werthamer-Tucker theory, which includes the quantum susceptance. We also demonstrate that it is essential to include the quantum susceptance in our theoretical computation to explain the photon-assisted-tunneling steps, which have negative dynamic conductance. Such steps are observed when the junction is pumped at slightly below the resonant frequency of the capacitor and the stub. The quantum susceptance should exist in all tunnel devices whose nonlinear {ital I}-{ital V} characteristics are due to elastic tunneling.
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.
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…
NASA Astrophysics Data System (ADS)
Weng, Qianchun; An, Zhenghua; Zhang, Bo; Chen, Pingping; Chen, Xiaoshuang; Zhu, Ziqiang; Lu, Wei
2015-03-01
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.
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
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
Quantum spin models with long-range interactions and tunnelings: a quantum Monte Carlo study
NASA Astrophysics Data System (ADS)
Maik, Michał; Hauke, Philipp; Dutta, Omjyoti; Zakrzewski, Jakub; Lewenstein, Maciej
2012-11-01
We use a quantum Monte Carlo method to investigate various classes of two-dimensional spin models with long-range interactions at low temperatures. In particular, we study a dipolar XXZ model with U(1) symmetry that appears as a hard-core boson limit of an extended Hubbard model describing polarized dipolar atoms or molecules in an optical lattice. Tunneling, in such a model, is short-range, whereas density-density couplings decay with distance following a cubic power law. We also investigate an XXZ model with long-range couplings of all three spin components—such a model describes a system of ultracold ions in a lattice of microtraps. We describe an approximate phase diagram for such systems at zero and at finite temperature, and compare their properties. In particular, we compare the extent of crystalline, superfluid and supersolid phases. Our predictions apply directly to current experiments with mesoscopic numbers of polar molecules and trapped ions.
Tunneling in quantum field theory and semiclassical gravity
NASA Astrophysics Data System (ADS)
Wohns, Dan Funch
In this dissertation we discuss aspects of the transitions between metastable vacua in scalar field theories. These transitions are caused by nucleation of bubbles of one vacuum in a background of another vacuum, and may have relevance in cosmology. Such processes are typically exponentially suppressed in the height and width of the barriers between the vacua. We demonstrate several scenarios where this intuition fails. We use a functional Schrodinger approach to show that tunneling of a scalar field through two barriers can be exponentially faster than tunneling through a single barrier. We determine the conditions that the effective potential must satisfy for a large enhancement in the tunneling rate to be possible. Both the tunneling rate to nearby vacua and to distant vacua in field space can be enhanced by this process. It may be possible to test this phenomenon using superfluid Helium-3. Nucleation of the B phase in samples of the supercooled A phase of superfluid Helium-3 is observed in seconds or minutes, while the characteristic decay time is calculated to be longer than the age of the universe. We propose a resolution to this discrepancy using resonant tunneling. This explanation makes the distinctive prediction that there exist multiple peaks in the nucleation probability as a function of temperature, pressure, and magnetic field. Next we investigate in detail Coleman-de Luccia tunneling. We show that there are four types of tunneling, depending on the importance of thermal and horizon effects. We estimate corrections to the Hawking-Moss tunneling rate, which can be large. Finally, the tunneling rate for a scalar field described by the Dirac-Born-Infeld action is calculated in the Hawking-Moss limit using a stochastic approach.
Quantum tunneling from rotating black holes with scalar hair in three dimensions
NASA Astrophysics Data System (ADS)
Sakalli, I.; Gursel, H.
2016-06-01
We study the Hawking radiation of scalar and Dirac particles (fermions) emitted from a rotating scalar hair black hole (RSHBH) within the context of three dimensional (3 D) Einstein gravity using non-minimally coupled scalar field theory. Amalgamating the quantum tunneling approach with the Wentzel-Kramers-Brillouin approximation, we obtain the tunneling rates of the outgoing particles across the event horizon. Inserting the resultant tunneling rates into the Boltzmann formula, we then obtain the Hawking temperature (T_H) of the 3 D RSHBH.
Theory of High-Energy Features in the Tunneling Spectra of Quantum-Hall Systems
NASA Astrophysics Data System (ADS)
MacDonald, A. H.
2010-11-01
We show that the low-temperature sash features in lowest Landau-level (LLL) tunneling spectra recently discovered by Dial and Ashoori are intimately related to the discrete Haldane-pseudopotential interaction energy scales that govern fractional quantum-Hall physics. Our analysis is based on expressions for the tunneling density of states which become exact at filling factors close to ν=0 and ν=1, where the sash structure is most prominent. We comment on other aspects of LLL correlation physics that can be revealed by accurate temperature-dependent tunneling data.
Theory of high-energy features in the tunneling spectra of quantum-Hall systems.
MacDonald, A H
2010-11-12
We show that the low-temperature sash features in lowest Landau-level (LLL) tunneling spectra recently discovered by Dial and Ashoori are intimately related to the discrete Haldane-pseudopotential interaction energy scales that govern fractional quantum-Hall physics. Our analysis is based on expressions for the tunneling density of states which become exact at filling factors close to ν=0 and ν=1, where the sash structure is most prominent. We comment on other aspects of LLL correlation physics that can be revealed by accurate temperature-dependent tunneling data. PMID:21231254
Xiao, Chong; Zhang, Jiajia; Xu, Jie; Tong, Wei; Cao, Boxiao; Li, Kun; Pan, Bicai; Su, Haibin; Xie, Yi
2012-01-01
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. PMID:23091695
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.
Quantum Tunneling of Water in Beryl. A New State of the Water Molecule
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.
Quantum Tunneling of Water in Beryl: A New State of the Water Molecule.
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. PMID:27152824
Wu, Feng
2016-06-01
We present a quantum mechanical study of mode-specific tunneling upon fundamental excitation in malonaldehyde with a multidimensional theory that utilizes the saddle-point normal coordinates. We find that a ring-deformation normal mode is as essential as the well-known imaginary-frequency normal mode in the multidimensional investigation. The changes in tunneling splittings upon fundamental excitation are calculated. The results are competitive with those from a recently developed mixed classical-quantum method. Moreover, the results are qualitatively consistent with experiment for about half of all the modes. PMID:27192182
NASA Astrophysics Data System (ADS)
Tian, Si-Cong; Wan, Ren-Gang; Li, Lian-He; Tong, Cun-Zhu; Ning, Yong-Qiang
2015-01-01
A scheme for obtaining a tunable ultranarrow cavity transmission controlled by two tunneling in triple quantum dots system is proposed. In such system, the tunneling can induce double dark resonances, resulting in the appearance of two transparency windows. With the steep dispersion within the narrowed transparency windows, an ultranarrow transmission peak can be obtained, compared with that of double quantum dots system. Furthermore, by varying the energy splitting, the linewidth and the position of the ultranarrow transmission peak can be engineered. Because no coupling laser is required, the scheme proposed here is more convenient for future experiments and applications in optics, and may be useful in designing novel optoelectronic devices.
The Stokes phenomenon and quantum tunneling for de Sitter radiation in nonstationary coordinates
NASA Astrophysics Data System (ADS)
Kim, Sang Pyo
2010-09-01
We study quantum tunneling for the de Sitter radiation in the planar coordinates and global coordinates, which are nonstationary coordinates and describe the expanding geometry. Using the phase-integral approximation for the Hamilton-Jacobi action in the complex plane of time, we obtain the particle-production rate in both coordinates and derive the additional sinusoidal factor depending on the dimensionality of spacetime and the quantum number for spherical harmonics in the global coordinates. This approach resolves the factor of two problem in the tunneling method.
Significant Quantum Effects in Hydrogen Activation
Kyriakou, Georgios; Davidson, Erlend R.; Peng, Guowen; Roling, Luke T.; Singh, Suyash; Boucher, Matthew B.; Marcinkowski, Matthew D.; Mavrikakis, Manos; Michaelides, Angelos; Sykes, E. Charles H.
2014-03-31
Dissociation of molecular hydrogen is an important step in a wide variety of chemical, biological, and physical processes. Due to the light mass of hydrogen, it is recognized that quantum effects are often important to its reactivity. However, understanding how quantum effects impact the reactivity of hydrogen is still in its infancy. Here, we examine this issue using a well-defined Pd/Cu(111) alloy that allows the activation of hydrogen and deuterium molecules to be examined at individual Pd atom surface sites over a wide range of temperatures. Experiments comparing the uptake of hydrogen and deuterium as a function of temperature reveal completely different behavior of the two species. The rate of hydrogen activation increases at lower sample temperature, whereas deuterium activation slows as the temperature is lowered. Density functional theory simulations in which quantum nuclear effects are accounted for reveal that tunneling through the dissociation barrier is prevalent for H_{2} up to 190 K and for D_{2} up to 140 K. Kinetic Monte Carlo simulations indicate that the effective barrier to H_{2} dissociation is so low that hydrogen uptake on the surface is limited merely by thermodynamics, whereas the D_{2} dissociation process is controlled by kinetics. These data illustrate the complexity and inherent quantum nature of this ubiquitous and seemingly simple chemical process. Examining these effects in other systems with a similar range of approaches may uncover temperature regimes where quantum effects can be harnessed, yielding greater control of bond-breaking processes at surfaces and uncovering useful chemistries such as selective bond activation or isotope separation.
Significant Quantum Effects in Hydrogen Activation
2014-01-01
Dissociation of molecular hydrogen is an important step in a wide variety of chemical, biological, and physical processes. Due to the light mass of hydrogen, it is recognized that quantum effects are often important to its reactivity. However, understanding how quantum effects impact the reactivity of hydrogen is still in its infancy. Here, we examine this issue using a well-defined Pd/Cu(111) alloy that allows the activation of hydrogen and deuterium molecules to be examined at individual Pd atom surface sites over a wide range of temperatures. Experiments comparing the uptake of hydrogen and deuterium as a function of temperature reveal completely different behavior of the two species. The rate of hydrogen activation increases at lower sample temperature, whereas deuterium activation slows as the temperature is lowered. Density functional theory simulations in which quantum nuclear effects are accounted for reveal that tunneling through the dissociation barrier is prevalent for H2 up to ∼190 K and for D2 up to ∼140 K. Kinetic Monte Carlo simulations indicate that the effective barrier to H2 dissociation is so low that hydrogen uptake on the surface is limited merely by thermodynamics, whereas the D2 dissociation process is controlled by kinetics. These data illustrate the complexity and inherent quantum nature of this ubiquitous and seemingly simple chemical process. Examining these effects in other systems with a similar range of approaches may uncover temperature regimes where quantum effects can be harnessed, yielding greater control of bond-breaking processes at surfaces and uncovering useful chemistries such as selective bond activation or isotope separation. PMID:24684530
Active Control of Wind Tunnel Noise
NASA Technical Reports Server (NTRS)
Hollis, Patrick (Principal Investigator)
1991-01-01
The need for an adaptive active control system was realized, since a wind tunnel is subjected to variations in air velocity, temperature, air turbulence, and some other factors such as nonlinearity. Among many adaptive algorithms, the Least Mean Squares (LMS) algorithm, which is the simplest one, has been used in an Active Noise Control (ANC) system by some researchers. However, Eriksson's results, Eriksson (1985), showed instability in the ANC system with an ER filter for random noise input. The Restricted Least Squares (RLS) algorithm, although computationally more complex than the LMS algorithm, has better convergence and stability properties. The ANC system in the present work was simulated by using an FIR filter with an RLS algorithm for different inputs and for a number of plant models. Simulation results for the ANC system with acoustic feedback showed better robustness when used with the RLS algorithm than with the LMS algorithm for all types of inputs. Overall attenuation in the frequency domain was better in the case of the RLS adaptive algorithm. Simulation results with a more realistic plant model and an RLS adaptive algorithm showed a slower convergence rate than the case with an acoustic plant as a delay plant. However, the attenuation properties were satisfactory for the simulated system with the modified plant. The effect of filter length on the rate of convergence and attenuation was studied. It was found that the rate of convergence decreases with increase in filter length, whereas the attenuation increases with increase in filter length. The final design of the ANC system was simulated and found to have a reasonable convergence rate and good attenuation properties for an input containing discrete frequencies and random noise.
NASA Astrophysics Data System (ADS)
Gerard, Valerie; Govan, Joseph; Loudon, Alexander; Baranov, Alexander V.; Fedorov, Anatoly V.; Gun'ko, Yurii K.
2015-10-01
The main goal of our research is to develop new types of technologically important optically active quantum dot (QD) based materials, study their properties and explore their biological applications. For the first time chiral II-VI QDs have been prepared by us using microwave induced heating with the racemic (Rac), D- and L-enantiomeric forms of penicillamine as stabilisers. Circular dichroism (CD) studies of these QDs have shown that D- and L-penicillamine stabilised particles produced mirror image CD spectra, while the particles prepared with a Rac mixture showed only a weak signal. It was also demonstrated that these QDs show very broad emission bands between 400 and 700 nm due to defects or trap states on the surfaces of the nanocrystals. These QDs have demonstrated highly specific chiral recognition of various biological species including aminoacids. The utilisation of chiral stabilisers also allowed the preparation of new water soluble white emitting CdS nano-tetrapods, which demonstrated circular dichroism in the band-edge region of the spectrum. Biological testing of chiral CdS nanotetrapods displayed a chiral bias for an uptake of the D- penicillamine stabilised nano-tetrapods by cancer cells. It is expected that this research will open new horizons in the chemistry of chiral nanomaterials and their application in nanobiotechnology, medicine and optical chemo- and bio-sensing.
Construction monitoring activities in the ESF starter tunnel
Pott, J.; Carlisle, S.
1994-05-01
In situ design verification activities am being conducted in the North Ramp Starter Tunnel of the Yucca Mountain Project Exploratory Studies Facility. These activities include: monitoring the peak particle velocities and evaluating the damage to the rock mass associated with construction blasting, assessing the rock mass quality surrounding the tunnel, monitoring the performance of the installed ground support, and monitoring the stability of the tunnel. In this paper, examples of the data that have been collected and preliminary conclusions from the data are presented.
Charged Fermions Tunnel from the Kerr-Newman Black Hole Influenced by Quantum Gravity Effects
NASA Astrophysics Data System (ADS)
Ren, Ruyi; Chen, Deyou; Pu, Jin
2016-03-01
Taking into account quantum gravity effects, we investigate the tunnelling radiation of charged fermions in the Kerr-Newman black hole. The result shows that the corrected Hawking temperature is determined not only by the parameters of the black hole, but also by the energy, angular momentum and mass of the emitted fermion. Meanwhile, an interesting found is that the temperature is affected by the angle 𝜃. The quantum gravity correction slows down the evaporation.
NASA Astrophysics Data System (ADS)
Buchholz, S. S.; Fischer, S. F.; Kunze, U.; Schuh, D.; Abstreiter, G.
2008-03-01
Vertically stacked quantum point contacts (QPCs) are prepared by atomic force microscope (AFM) lithography from an asymmetric GaAs/AlGaAs double quantum well (DQW) heterostructure. Top- and back-gate voltages are used to tune the tunnel-coupled QPCs, and back-gate bias cooling is employed to investigate coupled and decoupled one-dimensional (1D) modes. Parity dependent mode coupling is invoked by the particular asymmetry in the vertical DQW confinement.
Gelman, David; Schwartz, Steven D.
2008-07-14
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.
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.
Quantum chaotic tunneling in graphene systems with electron-electron interactions
NASA Astrophysics Data System (ADS)
Ying, Lei; Wang, Guanglei; Huang, Liang; Lai, Ying-Cheng
2014-12-01
An outstanding and fundamental problem in contemporary physics is to include and probe the many-body effect in the study of relativistic quantum manifestations of classical chaos. We address this problem using graphene systems described by the Hubbard Hamiltonian in the setting of resonant tunneling. Such a system consists of two symmetric potential wells separated by a potential barrier, and the geometric shape of the whole domain can be chosen to generate integrable or chaotic dynamics in the classical limit. Employing a standard mean-field approach to calculating a large number of eigenenergies and eigenstates, we uncover a class of localized states with near-zero tunneling in the integrable systems. These states are not the edge states typically seen in graphene systems, and as such they are the consequence of many-body interactions. The physical origin of the non-edge-state type of localized states can be understood by the one-dimensional relativistic quantum tunneling dynamics through the solutions of the Dirac equation with appropriate boundary conditions. We demonstrate that, when the geometry of the system is modified to one with chaos, the localized states are effectively removed, implying that in realistic situations where many-body interactions are present, classical chaos is capable of facilitating greatly quantum tunneling. This result, besides its fundamental importance, can be useful for the development of nanoscale devices such as graphene-based resonant-tunneling diodes.
Effects of the interfacial polarization on tunneling in surface coupled quantum dots
NASA Astrophysics Data System (ADS)
Virk, Kuljit S.; Reichman, David R.; Hybertsen, Mark S.
2012-10-01
Polarization effects are included exactly in a model for a quantum dot in close proximity to a planar interface. Efficient incorporation of this potential into the Schrödinger equation is utilized to map out the influence of the image potential effects on carrier tunneling in such heterostructures. In particular, the interplay between carrier mass and the dielectric constants of a quantum dot, its surrounding matrix, and the electrode is studied. We find that the polarizability of the planar electrode structure can significantly increase the tunneling rates for heavier carriers, potentially resulting in a qualitative change in the dependence of tunneling rate on mass. Our method for treating polarization can be generalized to the screening of two-particle interactions and can thus be applied to calculations such as exciton dissociation and the Coulomb blockade. In contrast to tunneling via intermediate surface localized states of the quantum dot, our work identifies the parameter space over which volume states undergo significant modification in their tunneling characteristics.
Photon-assisted tunneling in an asymmetrically coupled triple quantum dot
NASA Astrophysics Data System (ADS)
Wang, Bao-Chuan; Cao, Gang; Chen, Bao-Bao; Yu, Guo-Dong; Li, Hai-Ou; Xiao, Ming; Guo, Guo-Ping
2016-08-01
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.
Scaling for quantum tunneling current in nano- and subnano-scale plasmonic junctions
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
Quantum-limited detection of millimeter waves using superconducting tunnel junctions
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.
Quantum-limited detection of millimeter waves using superconducting tunnel junctions
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.
Quantum dots as active material for quantum cascade lasers: comparison to quantum wells
NASA Astrophysics Data System (ADS)
Michael, Stephan; Chow, Weng W.; Schneider, Hans Christian
2016-03-01
We review a microscopic laser theory for quantum dots as active material for quantum cascade lasers, in which carrier collisions are treated at the level of quantum kinetic equations. The computed characteristics of such a quantum-dot active material are compared to a state-of-the-art quantum-well quantum cascade laser. We find that the current requirement to achieve a comparable gain-length product is reduced compared to that of the quantum-well quantum cascade laser.
Piprek, Joachim
2014-07-07
This Letter investigates the output power enhancement achieved by tunnel junction insertion into the InGaN multi-quantum well (MQW) active region of a 410 nm vertical-cavity surface-emitting laser which enables the repeated use of carriers for light generation (carrier recycling). While the number of quantum wells remains unchanged, the tunnel junction eliminates absorption caused by the non-uniform MQW carrier distribution. The thermal resistance drops and the excess bias lead to a surprisingly small rise in self-heating.
Overspinning a nearly extreme charged black hole via a quantum tunneling process.
Matsas, George E A; da Silva, André R R
2007-11-01
We examine a nearly extreme macroscopic Reissner-Nördstrom black hole in the context of semiclassical gravity. The absorption rate associated with the quantum tunneling process of scalar particles whereby this black hole can acquire enough angular momentum to violate the weak cosmic-censorship conjecture is shown to be nonzero. PMID:17995395
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…
Optical Blocking of Electron Tunneling into a Single Self-Assembled Quantum Dot
NASA Astrophysics Data System (ADS)
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.
Quantum Tunneling Enabled Self-Assembly of Hydrogen Atoms on Cu(111)
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.
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.
Time delay of wave packets during their tunnelling through a quantum diode
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)
Phonon-Assisted Resonant Tunnelling through a Triple-Quantum-Dot: a Phonon-Signal Detector
NASA Astrophysics Data System (ADS)
Shen, Xiao-Yun; Dong, Bing; Lei, Xiao-lin
2008-02-01
We study the effect of electron-phonon interaction on current and zero-frequency shot noise in resonant tunnelling through a series triple-quantum-dot coupling to a local phonon mode by means of a nonperturbative mapping technique along with the Green function formulation. By fixing the energy difference between the first two quantum dots to be equal to phonon frequency and sweeping the level of the third quantum dot, we find a largely enhanced current spectrum due to phonon effect, and in particular we predict current peaks corresponding to phonon-absorption and phonon-emission assisted resonant tunnelling processes, which show that this system can be acted as a sensitive phonon-signal detector or as a cascade phonon generator.
Nuclear quantum effects of hydrogen bonds probed by tip-enhanced inelastic electron tunneling.
Guo, Jing; Lü, Jing-Tao; Feng, Yexin; Chen, Ji; Peng, Jinbo; Lin, Zeren; Meng, Xiangzhi; Wang, Zhichang; Li, Xin-Zheng; Wang, En-Ge; Jiang, Ying
2016-04-15
We report the quantitative assessment of nuclear quantum effects on the strength of a single hydrogen bond formed at a water-salt interface, using tip-enhanced inelastic electron tunneling spectroscopy based on a scanning tunneling microscope. The inelastic scattering cross section was resonantly enhanced by "gating" the frontier orbitals of water via a chlorine-terminated tip, so the hydrogen-bonding strength can be determined with high accuracy from the red shift in the oxygen-hydrogen stretching frequency of water. Isotopic substitution experiments combined with quantum simulations reveal that the anharmonic quantum fluctuations of hydrogen nuclei weaken the weak hydrogen bonds and strengthen the relatively strong ones. However, this trend can be completely reversed when a hydrogen bond is strongly coupled to the polar atomic sites of the surface. PMID:27081066
NASA Astrophysics Data System (ADS)
Dong, B.; Ding, G. H.; Lei, X. L.
2015-05-01
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.
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.
Transport through an impurity tunnel coupled to a Si/SiGe quantum dot
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.
Resonant tunneling spectroscopy of valley eigenstates on a donor-quantum dot coupled system
NASA Astrophysics Data System (ADS)
Kobayashi, T.; van der Heijden, J.; House, M. G.; Hile, S. J.; Asshoff, P.; Gonzalez-Zalba, M. F.; Vinet, M.; Simmons, M. Y.; Rogge, S.
2016-04-01
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/SiO2 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.
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.
2015-09-01
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.
NASA Astrophysics Data System (ADS)
Kubo, Yuimaru; Sboychakov, A. O.; Nori, Franco; Takahide, Y.; Ueda, S.; Tanaka, I.; Islam, A. T. M. N.; Takano, Y.
2012-10-01
We performed measurements of switching current distribution in a submicrometer La2-xSrxCuO4 (LSCO) intrinsic Josephson junction (IJJ) stack in a wide temperature range. The escape rate saturates below approximately 2 K, indicating that the escape event is dominated by a macroscopic quantum tunneling (MQT) process with a crossover temperature T*≈2K. We applied the theory of MQT for IJJ stacks, taking into account dissipation and the phase retrapping effect in the LSCO IJJ stack. The theory is in good agreement with the experiment both in the MQT and in the thermal activation regimes.
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.
Quantum heat engine based on photon-assisted Cooper pair tunneling
NASA Astrophysics Data System (ADS)
Hofer, Patrick P.; Souquet, J.-R.; Clerk, A. Â. A.
2016-01-01
We propose and analyze a simple mesoscopic quantum heat engine that exhibits both high power and high efficiency. The system consists of a biased Josephson junction coupled to two microwave cavities, with each cavity coupled to a thermal bath. Resonant Cooper pair tunneling occurs with the exchange of photons between cavities, and a temperature difference between the baths can naturally lead to a current against the voltage, and hence work. As a consequence of the unique properties of Cooper-pair tunneling, the heat current is completely separated from the charge current. This combined with the strong energy selectivity of the process leads to an extremely high efficiency.
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.
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.
Zhang, Yan; Lin, Hai
2009-10-29
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 6beta-hydrogen abstraction and the 6beta-d(1)-testosterone 6beta-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. PMID:19480428
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/.
Bounces and the calculation of quantum tunneling effects
NASA Astrophysics Data System (ADS)
Liang, Jiu-Qing; Müller-Kirsten, H. J. W.
1992-04-01
The imaginary part of the energy of the metastable ground state for the inverted double-well potential is calculated by using the path-integral method. The tunneling process is dominated by bounces. It is shown that the evaluation of the determinant of the second variation of the action at the bounce can be avoided, and that the imaginary part of the energy results directly from characteristic properties of the bounce itself, namely, the antisymmetry of its first time derivative under time reversal. The imaginary part of the result is in exact agreement with that of the well-known WKB calculation of Bender and Wu.
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.
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.
Confined acoustic and optical plasmons in double-layered quantum-wire arrays with strong tunneling
NASA Astrophysics Data System (ADS)
Dethlefsen, A. F.; Heyn, Ch.; Heitmann, D.; Schüller, C.
2006-05-01
We investigate electronic excitations in GaAs-AlxGa1-xAs double-layered quantum wire arrays with strong tunneling coupling by resonant inelastic light scattering. By applying an external electric field, we can change the one-dimensional (1D) electron density and the symmetry of the double quantum-well (DQW) structure at the same time. We identify confined optical 1D intersubband plasmons (COP) and confined acoustic 1D intersubband plasmons (CAP). Due to the tunneling coupling, the energies of the CAP exhibit a minimum for a symmetric DQW potential, whereas the energies of the COP are dominated by the total carrier density, and are nearly insensitive to the symmetry of the potential.
Quantum-gravity effects outside the horizon spark black to white hole tunneling
NASA Astrophysics Data System (ADS)
Haggard, Hal M.; Rovelli, Carlo
2015-11-01
We show that there is a classical metric satisfying the Einstein equations outside a finite spacetime region where matter collapses into a black hole and then emerges from a white hole. We compute this metric explicitly. We show how quantum theory determines the (long) time for the process to happen. A black hole can thus quantum tunnel into a white hole. For this to happen, quantum gravity should affect the metric also in a small region outside the horizon; we show that, contrary to what is commonly assumed, this is not forbidden by causality or by the semiclassical approximation, because quantum effects can pile up over a long time. This scenario alters radically the discussion on the black hole information puzzle.
Scanning tunneling spectroscopy of lead sulfide quantum wells fabricated by atomic layer deposition
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.
Macroscopic Quantum Tunneling in a Bi2Sr2CaCu2O8+δ Single Crystalline Whisker
NASA Astrophysics Data System (ADS)
Kubo, Yuimaru; Takahide, Yamaguchi; Ueda, Shinya; Takano, Yoshihiko; Ootuka, Youiti
2010-06-01
Macroscopic quantum tunneling (MQT) has been observed in an intrinsic Josephson junction (IJJ) stack of a Bi2Sr2CaCu2O8+δ (BSCCO) single crystalline whisker with high precision using a home made setup. The cross-over temperature between thermal activation and MQT was about 260 mK, and the Josephson plasma frequency was estimated to be 86 GHz. Both the thermal escape theory and the MQT theory are consistent with the experiments. These facts strongly suggest that single crystalline BSCCO whiskers are high enough quality to be used as intrinsic Josephson quantum devices such as intrinsic Josephson phase qubits. This is the first demonstration of MQT in BSCCO single crystalline whiskers.
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.
NASA Astrophysics Data System (ADS)
Herz, Markus; Bouvron, Samuel; Ćavar, Elizabeta; Fonin, Mikhail; Belzig, Wolfgang; Scheer, Elke
2013-09-01
We present a measurement scheme that enables quantitative detection of the shot noise in a scanning tunnelling microscope while scanning the sample. As test objects we study defect structures produced on an iridium single crystal at low temperatures. The defect structures appear in the constant current images as protrusions with curvature radii well below the atomic diameter. The measured power spectral density of the noise is very near to the quantum limit with Fano factor F = 1. While the constant current images show detailed structures expected for tunnelling involving d-atomic orbitals of Ir, we find the current noise to be without pronounced spatial variation as expected for shot noise arising from statistically independent events.We present a measurement scheme that enables quantitative detection of the shot noise in a scanning tunnelling microscope while scanning the sample. As test objects we study defect structures produced on an iridium single crystal at low temperatures. The defect structures appear in the constant current images as protrusions with curvature radii well below the atomic diameter. The measured power spectral density of the noise is very near to the quantum limit with Fano factor F = 1. While the constant current images show detailed structures expected for tunnelling involving d-atomic orbitals of Ir, we find the current noise to be without pronounced spatial variation as expected for shot noise arising from statistically independent events. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02216a
Macroscopic quantum tunneling in a stack of capacitively-coupled intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Koyama, Tomio; Machida, Masahiko
2008-04-01
A macroscopic quantum theory for the phase dynamics in capacitively-coupled intrinsic Josephson junctions (IJJ's) is constructed. We quantize the capacitively-coupled IJJ model in terms of the canonical quantization method. The multi-junction effect for the macroscopic quantum tunneling (MQT) to the first resistive branch is clarified. It is shown that the escape rate is greatly enhanced by the capacitive coupling between junctions. We also discuss the origin of the N2 -enhancement in the escape rate observed in the uniformly switching in Bi-2212 IJJ's.
Optical bistability in triple quantum dot molecules in weak tunneling regime
NASA Astrophysics Data System (ADS)
Wang, Zhiping; Yu, Benli
2015-08-01
We investigated the optical bistability of a triple quantum dot molecule under coherent excitation and considering the spontaneous exciton decay and pure dephasing as two decoherence channels. By manipulating the laser detuning, electric field, and tunneling coupling, the threshold value and the hysteresis cycle width of OB can easily be controlled. Our scheme opens the possibility to control OB with electric gates, which are very useful in building all-optical switches and logic-gate devices for optical computing and quantum information processing.
Quantum tunnelling of the magnetization in a monolayer of oriented single-molecule magnets.
Mannini, M; Pineider, F; Danieli, C; Totti, F; Sorace, L; Sainctavit, Ph; Arrio, M-A; Otero, E; Joly, L; Cezar, J C; Cornia, A; Sessoli, R
2010-11-18
A fundamental step towards atomic- or molecular-scale spintronic devices has recently been made by demonstrating that the spin of an individual atom deposited on a surface, or of a small paramagnetic molecule embedded in a nanojunction, can be externally controlled. An appealing next step is the extension of such a capability to the field of information storage, by taking advantage of the magnetic bistability and rich quantum behaviour of single-molecule magnets (SMMs). Recently, a proof of concept that the magnetic memory effect is retained when SMMs are chemically anchored to a metallic surface was provided. However, control of the nanoscale organization of these complex systems is required for SMMs to be integrated into molecular spintronic devices. Here we show that a preferential orientation of Fe(4) complexes on a gold surface can be achieved by chemical tailoring. As a result, the most striking quantum feature of SMMs-their stepped hysteresis loop, which results from resonant quantum tunnelling of the magnetization-can be clearly detected using synchrotron-based spectroscopic techniques. With the aid of multiple theoretical approaches, we relate the angular dependence of the quantum tunnelling resonances to the adsorption geometry, and demonstrate that molecules predominantly lie with their easy axes close to the surface normal. Our findings prove that the quantum spin dynamics can be observed in SMMs chemically grafted to surfaces, and offer a tool to reveal the organization of matter at the nanoscale. PMID:20981008
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.
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
NASA Astrophysics Data System (ADS)
Bauke, Heiko; Klaiber, Michael; Yakaboylu, Enderalp; Hatsagortsyan, Karen Z.; Ahrens, Sven; Müller, Carsten; Keitel, Christoph H.
2013-05-01
Computational methods are indispensable to study the quantum dynamics of relativistic light-matter interactions in parameter regimes where analytical methods become inapplicable. We present numerical methods for solving the time-dependent Dirac equation and the time-dependent Klein-Gordon equation and their implementation on high performance graphics cards. These methods allow us to study tunneling from hydrogen-like highly charged ions in strong laser fields and Kapitza-Dirac scattering in the relativistic regime.
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.
Electron tunneling characteristics of a cubic quantum dot, (PbS){sub 32}
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.
Electron tunneling characteristics of a cubic quantum dot, (PbS)32.
Gupta, Sanjeev K; He, Haiying; Banyai, Douglas; Kandalam, Anil K; Pandey, Ravindra
2013-12-28
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. PMID:24387370
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.
NASA Astrophysics Data System (ADS)
Schnedler, M.; Dunin-Borkowski, R. E.; Ebert, Ph.
2016-05-01
Photoexcited scanning tunneling spectroscopy is a promising technique for the determination of carrier concentrations, surface photovoltages, and potentials of semiconductors with atomic spatial resolution. However, extraction of the desired quantities requires computation of the electrostatic potential induced by the proximity of the tip and the tunnel current. This calculation is based on an accurate solution of the Poisson as well as the continuity equations for the tip-vacuum-semiconductor system. For this purpose, the carrier current densities are modeled by classical drift and diffusion equations. However, for small tip radii and highly doped materials, the drift and diffusion transport model significantly overestimates a semiconductor's carrier concentration near the surface, making the quantification of physical properties impossible. In this paper, we apply quantum correction to the drift and diffusion model, in order to account for the so-called quantum compressibility, i.e., reduced compressibility of the carrier gas due to the Pauli principle, in the region of the tip-induced band bending. We compare carrier concentrations, potentials, and tunnel currents derived with and without quantum correction for GaN (10 1 ¯0 ) and GaAs(110) surfaces to demonstrate its necessity.
Light-induced negative differential resistance in graphene/Si-quantum-dot tunneling diodes
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
Light-induced negative differential resistance in graphene/Si-quantum-dot tunneling diodes.
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
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.
Characterization of Deep Tunneling Activity through Remote-Sensing Techniques
R. G. Best, P. J. Etzler, and J. D. Bloom
1997-10-01
This work is a case study demonstrating the uses of multispectral and multi-temporal imagery to characterize deep tunneling activity. A drainage tunnel excavation in Quincy, MA is the case locality. Data used are aerial photographs (digitized) and Daedalus 3600 MSS image data that were collected in July and October of 1994. Analysis of the data includes thermal characterization, spectral characterization, multi-temporal analysis, and volume estimation using digital DEM generation. The results demonstrate the type of information that could be generated by multispectral, multi-temporal data if the study locality were a clandestine excavation site with restricted surface access.
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.
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.
NASA Astrophysics Data System (ADS)
Emamipour, Hamidreza; Mehrabzad, Narges
2016-07-01
We study tunneling conductance in a quantum wire-insulator-ferromagnetic d-wave superconductor junction. The results show that exchange field of superconductor has a strong impact on tunneling spectra depending on the junction parameters. We have found a gap like structure in the tunneling limit when we have an interface normal to the (100) axis of superconductor. In the case of (110) axis of superconductor, there is not any zero- bias conductance peaks in tunneling spectra. For a metallic junction the dips disappear.
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
Influence of device geometry on tunneling in the ν=(5)/(2) quantum Hall liquid
NASA Astrophysics Data System (ADS)
Yang, Guang; Feldman, D. E.
2013-08-01
Two recent experiments [Radu , ScienceSCIEAS0036-807510.1126/science.1157560 320, 899 (2008); Lin , Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.85.165321 85, 165321 (2012)] measured the temperature and voltage dependence of the quasiparticle tunneling through a quantum point contact in the ν=5/2 quantum Hall liquid. The results led to conflicting conclusions about the nature of the quantum Hall state. In this paper, we show that the conflict can be resolved by recognizing different geometries of the devices in the experiments. We argue that in some of those geometries there is significant unscreened electrostatic interaction between the segments of the quantum Hall edge on the opposite sides of the point contact. Coulomb interaction affects the tunneling current. We compare experimental results with theoretical predictions for the Pfaffian, SU(2)2, 331, and K=8 states and their particle-hole conjugates. After Coulomb corrections are taken into account, measurements in all geometries agree with the spin-polarized and spin-unpolarized Halperin 331 states.
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.
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.
High performance tunnel injection quantum dot comb laser
Lee, C.-S.; Guo Wei; Basu, Debashish; Bhattacharya, Pallab
2010-03-08
A high-speed multiwavelength quantum dot comb laser, grown by molecular beam epitaxy, is demonstrated. The device is characterized with a 75.9 nm (full width at half maximum) and a 91.4 nm (DELTA{sub -15dB}) wide lasing spectrum. There are 105 and 185 simultaneously emitted longitudinal modes with a maximum channel intensity nonuniformity of less than 3 dB in the spectral range of 1231-1252 nm and 1274-1311 nm, respectively, for a laser with 1040 mum cavity length. The channel spacing can be tuned with cavity length and remains invariant in the temperature range of 300-323 K. The small signal modulation bandwidth is 7.5 GHz.
Magnetoresistance of One-Dimensional Subbands in Tunnel-Coupled Double Quantum Wires
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.
Spin Dynamics and Quantum Tunneling in Fe8 Nanomagnet and in AFM Rings by NMR
Seung-Ho-Baek
2004-12-19
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.
Suppression of quantum tunneling for all spins for easy-axis systems
NASA Astrophysics Data System (ADS)
Khare, Avinash; Paranjape, M. B.
2011-05-01
The semiclassical limit of quantum spin systems corresponds to a dynamical Lagrangian which contains the usual kinetic energy, the couplings and interactions of the spins, and an additional, first-order kinematical term which corresponds to the Wess-Zumino-Novikov-Witten (WZNW) term for the spin degree of freedom. It was shown that in the case of the kinetic dynamics determined only by the WZNW term, half-odd integer spin systems show a lack of tunneling phenomena, whereas integer spin systems are subject to it in the case of potentials with easy-plane easy-axis symmetry. Here we prove for the theory with a normal quadratic kinetic term of arbitrary strength or the first-order theory with azimuthal symmetry (which is equivalently the so-called easy-axis situation), that the tunneling is in fact suppressed for all nonzero values of spin. This model exemplifies the concept that in the presence of complex Euclidean action, it is necessary to use the ensuing complex critical points in order to define the quantum (perturbation) theory. In the present example, if we do not do so, exactly the opposite, erroneous conclusion that the tunneling is unsuppressed for all spins, is reached.
Visualizing hybridized quantum plasmons in coupled nanowires: From classical to tunneling regime
NASA Astrophysics Data System (ADS)
Andersen, Kirsten; Jensen, Kristian L.; Mortensen, N. Asger; Thygesen, Kristian S.
2013-06-01
We present full quantum-mechanical calculations of the hybridized plasmon modes of two nanowires at small separation, providing real-space visualization of the modes in the transition from the classical to the quantum tunneling regime. The plasmon modes are obtained as certain eigenfunctions of the dynamical dielectric function, which is computed using time-dependent density functional theory (TDDFT). For freestanding wires, the energy of both surface and bulk plasmon modes deviate from the classical result for low wire radii and high momentum transfer due to effects of electron spill-out, nonlocal response, and coupling to single-particle transitions. For the wire dimer, the shape of the hybridized plasmon modes are continuously altered with decreasing separation, and below 6 Å, the energy dispersion of the modes deviate from classical results due to the onset of weak tunneling. Below 2-3 Å separation, this mode is replaced by a charge-transfer plasmon, which blue shifts with decreasing separation in agreement with experiment and marks the onset of the strong tunneling regime.
Observation of spin-dependent quantum well resonant tunneling in textured CoFeB layers
Teixeira, J. M. Costa, J. D.; Ventura, J.; Sousa, J. B.; Wisniowski, P.; Freitas, P. P.
2014-03-17
We report the observation of spin-dependent quantum well (QW) resonant tunneling in textured CoFeB free layers of single MgO magnetic tunnel junctions (MTJs). The inelastic electron tunneling spectroscopy spectra clearly show the presence of resonant oscillations in the parallel configuration, which are related with the appearance of majority-spin Δ{sub 1} QW states in the CoFeB free layer. To gain a quantitative understanding, we calculated QW state positions in the voltage-thickness plane using the so-called phase accumulation model (PAM) and compared the PAM solutions with the experimental resonant voltages observed for a set of MTJs with different CoFeB free layer thicknesses (t{sub fl} = 1.55, 1.65, 1.95, and 3.0 nm). An overall good agreement between experiment and theory was obtained. An enhancement of the tunnel magnetoresistance with bias is observed in a bias voltage region corresponding to the resonant oscillations.
Analysis of Hydrogen Tunneling in an Enzyme Active Site using von Neumann Measurements
Sumner, Isaiah; Iyengar, Srinivasan S.
2010-01-01
We build on our earlier quantum wavepacket study of hydrogen transfer in the biological enzyme, soybean lipoxygenase-1, by using von Neumann quantum measurement theory to gain qualitative insights into the transfer event. We treat the enzyme active site as a measurement device which acts on the tunneling hydrogen nucleus via the potential it exerts at each configuration. A series of changing active site geometries during the tunneling process effects a sequential projection of the initial, reactant state onto the final, product state. We study this process using several different kinds of von Neumann measurements and show how a discrete sequence of such measurements not only progressively increases the projection of the hydrogen nuclear wavepacket onto the product side but also favors proton over deuteron transfer. Several qualitative features of the hydrogen tunneling problem found in wavepacket dynamics studies are also recovered here. These include the shift in the “transition state” towards the reactant as a result of nuclear quantization, greater participation of excited states in the case of deuterium, and presence of critical points along the reaction coordinate that facilitate hydrogen and deuterium transfer and coincide with surface crossings. To further “tailor” the dynamics, we construct a perturbation to the sequence of measurements, that is a perturbation to the dynamical sequence of active site geometry evolution, which leads us to insight on the existence of sensitive regions of the reaction profile where subtle changes to the dynamics of the active site can have an effect on the hydrogen and deuterium transfer process. PMID:22933858
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.
Resonant and Inelastic Andreev Tunneling Observed on a Carbon Nanotube Quantum Dot.
Gramich, J; Baumgartner, A; Schönenberger, C
2015-11-20
We report the observation of two fundamental subgap transport processes through a quantum dot (QD) with a superconducting contact. The device consists of a carbon nanotube contacted by a Nb superconducting and a normal metal contact. First, we find a single resonance with position, shape, and amplitude consistent with the theoretically predicted resonant Andreev tunneling (AT) through a single QD level. Second, we observe a series of discrete replicas of resonant AT at a separation of ~145 μeV, with a gate, bias, and temperature dependence characteristic for boson-assisted, inelastic AT, in which energy is exchanged between a bosonic bath and the electrons. The magnetic field dependence of the replica's amplitudes and energies suggest that two different bosons couple to the tunnel process. PMID:26636862
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.
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.
Herz, Markus; Bouvron, Samuel; Ćavar, Elizabeta; Fonin, Mikhail; Belzig, Wolfgang; Scheer, Elke
2013-10-21
We present a measurement scheme that enables quantitative detection of the shot noise in a scanning tunnelling microscope while scanning the sample. As test objects we study defect structures produced on an iridium single crystal at low temperatures. The defect structures appear in the constant current images as protrusions with curvature radii well below the atomic diameter. The measured power spectral density of the noise is very near to the quantum limit with Fano factor F = 1. While the constant current images show detailed structures expected for tunnelling involving d-atomic orbitals of Ir, we find the current noise to be without pronounced spatial variation as expected for shot noise arising from statistically independent events. PMID:23989889
Major, Dan T; Heroux, Annie; Orville, Allen M; Valley, Michael P; Fitzpatrick, Paul F; Gao, Jiali
2009-12-01
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
Major , D.; Heroux , A; Orville , A; Valley , M; Fitzpatrick , P; Gao , J
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.
Wind Tunnel Test of the SMART Active Flap Rotor
NASA Technical Reports Server (NTRS)
Straub, Friedrich K.; Anand, Vaidyanthan R.; Birchette, Terrence S.; Lau, Benton H.
2009-01-01
Boeing and a team from Air Force, NASA, Army, DARPA, MIT, UCLA, and U. of Maryland have successfully completed a wind-tunnel test of the smart material actuated rotor technology (SMART) rotor in the 40- by 80-foot wind-tunnel of the National Full-Scale Aerodynamic Complex at NASA Ames Research Center. The Boeing SMART rotor is a full-scale, five-bladed bearingless MD 900 helicopter rotor modified with a piezoelectric-actuated trailing edge flap on each blade. The eleven-week test program evaluated the forward flight characteristics of the active-flap rotor at speeds up to 155 knots, gathered data to validate state-of-the-art codes for rotor aero-acoustic analysis, and quantified the effects of open and closed loop active flap control on rotor loads, noise, and performance. The test demonstrated on-blade smart material control of flaps on a full-scale rotor for the first time in a wind tunnel. The effectiveness of the active flap control on noise and vibration was conclusively demonstrated. Results showed significant reductions up to 6dB in blade-vortex-interaction and in-plane noise, as well as reductions in vibratory hub loads up to 80%. Trailing-edge flap deflections were controlled within 0.1 degrees of the commanded value. The impact of the active flap on control power, rotor smoothing, and performance was also demonstrated. Finally, the reliability of the flap actuation system was successfully proven in more than 60 hours of wind-tunnel testing.
Quantum Mechanical Change Control and Time-Dependent Tunneling Phenomena in Heterostructures.
NASA Astrophysics Data System (ADS)
Saadat, Irfan Abdulqayyum
1990-01-01
Charge transfer and tunneling of electrons through heterostructures has been investigated using a self-consistent solution of Schrodinger and Poisson equations. The generalized solver developed can determine the charge distribution and the energy band edge for any number-of-heterojunctions and material compositions. The solver takes into consideration the position dependent effective mass and dielectric constant. The limitations and computational aspects of the solver are discussed. The solver is used to examine charge control in multi-channel modulation doped field effect transistors (MODFET's). Characteristics of fabricated multi-channel MODFET's have been analyzed. The deviation of the total sheet charge density in multi-channel MODFET's from the single-channel superposition value is explained. The influence of the gate potential to modulate the channel charge is examined. The role of the channel potential in creating parallel conduction is explored via a pseudo two-dimensional approach. Present methods for time dependent tunneling analysis are critically examined. A time dependent approach to solve the time-dependent Schrodinger equation is presented. It also examines the tunneling transient response. The formation of the initial wavefunction (superposition state) and the sensitivity of the time dependent solution to initial conditions has been explored. Two structures are proposed and analyzed based on the understanding acquired. The first one is a double quantum well tunneling resonator. The oscillation modes, tuning the frequency of oscillations, and potential applications have been analyzed in details. The conversion of this oscillator into a three terminal device and the effect of the third terminal are also examined using the time-dependent solver. The second device structure is a memory cell, where the charge is stored behind a tunnel barrier in the storage well. The device consists of two quantum wells separated by thin potential barrier. The upper well
The active flexible wing aeroservoelastic wind-tunnel test program
NASA Technical Reports Server (NTRS)
Noll, Thomas; Perry, Boyd
1989-01-01
For a specific application of aeroservoelastic technology, Rockwell International Corporation developed a concept known as the Active Flexible Wing (AFW). The concept incorporates multiple active leading-and trailing-edge control surfaces with a very flexible wing such that wing shape is varied in an optimum manner resulting in improved performance and reduced weight. As a result of a cooperative program between the AFWAL's Flight Dynamics Laboratory, Rockwell, and NASA LaRC, a scaled aeroelastic wind-tunnel model of an advanced fighter was designed, fabricated, and tested in the NASA LaRC Transonic Dynamics Tunnel (TDT) to validate the AFW concept. Besides conducting the wind-tunnel tests NASA provided a design of an Active Roll Control (ARC) System that was implemented and evaluated during the tests. The ARC system used a concept referred to as Control Law Parameterization which involves maintaining constant performance, robustness, and stability while using different combinations of multiple control surface displacements. Since the ARC system used measured control surface stability derivatives during the design, the predicted performance and stability results correlated very well with test measurements.
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.
Long wavelength quantum-dot lasers selectively populated using tunnel injection
NASA Astrophysics Data System (ADS)
George, A. A.; Smowton, P. M.; Mi, Z.; Bhattacharya, P.
2007-05-01
Using measured amplified spontaneous emission data, we have derived and analysed the carrier distribution of a five-layer tunnelling injection quantum-dot structure at temperatures of 300 K and 350 K. The results are consistent with the direct injection of electrons from the injector well into a subset of lower energy dot states. The carrier distribution spectra contain features which suggest that dots of a particular size within the ensemble are preferentially populated leading to a reduced spectral broadening of the emission.
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.
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.
Trap-assisted tunneling in InGaN/GaN single-quantum-well light-emitting diodes
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.
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. PMID:23777509
NASA Astrophysics Data System (ADS)
Thrapsaniotis, E. G.
2001-07-01
The present paper deals with the motion of a Brownian particle on two identical but shifted potential surfaces, coupled via a tunneling matrix element in an external electric field. Dissipation is induced by a heat bath represented by an infinite set of harmonic oscillators with a continuum range of frequencies. We derive a perturbative solution for the quantum coherence term of the particle system after performing a small-polaron-like transformation. This is subsequently necessary for the extraction of an equation that describes the reduced dynamics and the minimal action path of the Brownian particle. Finally we extract expressions for the population relaxation rate and the pure quantum-dephasing rate of the two-level system.
Room-temperature resonant tunneling of electrons in carbon nanotube junction quantum wells
NASA Astrophysics Data System (ADS)
Biswas, Sujit K.; Schowalter, Leo J.; Jung, Yung Joon; Vijayaraghavan, Aravind; Ajayan, Pulickel M.; Vajtai, Robert
2005-05-01
Resonant tunneling structures [M. Bockrath, W. Liang, D. Bozovic, J. H. Hafner, C. B. Lieber, M. Tinkham, and H. Park, Science 291, 283 (2001)], formed between the junction of two single walled nanotubes and the conductive atomic force microscopy tip contact were investigated using current sensing atomic force microscopy. Oscillations in the current voltage characteristics were measured at several positions of the investigated nanotube. The oscillatory behavior is shown to follow a simple quantum mechanical model, dependent on the energy separation in the quantum well formed within the two junctions. Our model shows that these observations seen over several hundreds of nanometers, are possible only if the scattering cross section at defects is small resulting in long phase coherence length, and if the effective mass of the carrier electrons is small. We have calculated the approximate mass of the conduction electrons to be 0.003me.
Magnetoresistance of One-Dimensional Subbands in Tunnel-Coupled Double Quantum Wires
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.
Multistate transitions and quantum oscillations of optical activity
NASA Astrophysics Data System (ADS)
Blanco, Celia; Hochberg, David
2012-02-01
We consider the effects of multistate transitions on the tunneling racemization of chiral molecules. This requires going beyond simple two-state models of enantiomers and to include transitions within a multiple-level quantum-mechanical system. We derive an effective two-level description which accounts for transitions from the enantiomers to an arbitrary number of excited states as an application of the Weisskopf-Wigner approximation scheme. Modifications to the optical activity from these additional states are considered in general terms under the assumption of CPT invariance and then under T invariance. Some formal dynamical analogies between enantiomers and the neutral K-meson system are discussed.
NASA Astrophysics Data System (ADS)
Nomura, Yoshiki; Mizuno, Takaaki; Kambara, Hitoshi; Nakagawa, Yuya; Kakeya, Itsuhiro
2015-01-01
Macroscopic quantum tunneling (MQT) in an intrinsic Josephson junction (IJJ) stack of Bi1.9Pb0.1Sr1.39La0.63CuO6+δ (BiPb2201) has been investigated. For the first switch, from superconducting to the first resistive branch in current-voltage characteristics, the crossover between MQT and thermal activation (TA) takes place at 0.6 K. On the other hand, for the second switch, the MQT-TA crossover temperature is increased to 2.0 K. This result is interpreted as follows: the MQT rate of the second switch is enhanced by the charge coupling between adjacent IJJs as well as in Bi2Sr2CaCu2O8+δ. We consider that the enhancement of the MQT rate is a common feature among bismuth-cuprates with single and double CuO2 layers in their crystal structures.