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
2016-01-07
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.
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
NASA Astrophysics Data System (ADS)
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.
Revealing the quantum regime in tunnelling plasmonics.
Savage, Kevin J; Hawkeye, Matthew M; Esteban, Rubén; Borisov, Andrei G; Aizpurua, Javier; Baumberg, Jeremy J
2012-11-22
When two metal nanostructures are placed nanometres apart, their optically driven free electrons couple electrically across the gap. The resulting plasmons have enhanced optical fields of a specific colour tightly confined inside the gap. Many emerging nanophotonic technologies depend on the careful control of this plasmonic coupling, including optical nanoantennas for high-sensitivity chemical and biological sensors, nanoscale control of active devices, and improved photovoltaic devices. But for subnanometre gaps, coherent quantum tunnelling becomes possible and the system enters a regime of extreme non-locality in which previous classical treatments fail. Electron correlations across the gap that are driven by quantum tunnelling require a new description of non-local transport, which is crucial in nanoscale optoelectronics and single-molecule electronics. Here, by simultaneously measuring both the electrical and optical properties of two gold nanostructures with controllable subnanometre separation, we reveal the quantum regime of tunnelling plasmonics in unprecedented detail. All observed phenomena are in good agreement with recent quantum-based models of plasmonic systems, which eliminate the singularities predicted by classical theories. These findings imply that tunnelling establishes a quantum limit for plasmonic field confinement of about 10(-8)λ(3) for visible light (of wavelength λ). Our work thus prompts new theoretical and experimental investigations into quantum-domain plasmonic systems, and will affect the future of nanoplasmonic device engineering and nanoscale photochemistry.
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.
New treatment of quantum tunneling
NASA Astrophysics Data System (ADS)
Defendi, Antonio; Roncadelli, Marco
1994-04-01
We explore the implications of the recently proposed Langevin quantization for quantum tunneling, working within the semiclassical approximation. As far as we can see, the present treatment is simpler and more straightforward than the path integral approach. In fact, no extra trick is needed and the correct result follows at once - as a consequence of general principles - from the representation of the propagator supplied by the Langevin quantization. Further applications of the strategy discussed in this Letter are pointed out.
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.
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.
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.
Scheme for accelerating quantum tunneling dynamics
NASA Astrophysics Data System (ADS)
Khujakulov, Anvar; Nakamura, Katsuhiro
2016-02-01
We propose a scheme of the exact fast forwarding of standard quantum dynamics for a charged particle. The present idea allows the acceleration of both the amplitude and the phase of the wave function throughout the fast-forward time range and is distinct from that of Masuda and Nakamura [Proc. R. Soc. A 466, 1135 (2010), 10.1098/rspa.2009.0446], which enabled acceleration of only the amplitude of the wave function on the way. We apply the proposed method to the quantum tunneling phenomena and obtain the electromagnetic field to ensure the rapid penetration of wave functions through a tunneling barrier. Typical examples described here are (1) an exponential wave packet passing through the δ -function barrier and (2) the opened Moshinsky shutter with a δ -function barrier just behind the shutter. We elucidate the tunneling current in the vicinity of the barrier and find a remarkable enhancement of the tunneling rate (tunneling power) due to the fast forwarding. In the case of a very high barrier, in particular, we present the asymptotic analysis and exhibit a suitable driving force to recover a recognizable tunneling current. The analysis is also carried out on the exact acceleration of macroscopic quantum tunneling with use of the nonlinear Schrödinger equation, which accommodates a tunneling barrier.
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).
Resonant tunneling in graphene pseudomagnetic quantum dots.
Qi, Zenan; Bahamon, D A; Pereira, Vitor M; Park, Harold S; Campbell, D K; Neto, A H Castro
2013-06-12
Realistic relaxed configurations of triaxially strained graphene quantum dots are obtained from unbiased atomistic mechanical simulations. The local electronic structure and quantum transport characteristics of y-junctions based on such dots are studied, revealing that the quasi-uniform pseudomagnetic field induced by strain restricts transport to Landau level- and edge state-assisted resonant tunneling. Valley degeneracy is broken in the presence of an external field, allowing the selective filtering of the valley and chirality of the states assisting in the resonant tunneling. Asymmetric strain conditions can be explored to select the exit channel of the y-junction.
Quantum tunneling in flux compactifications
NASA Astrophysics Data System (ADS)
Blanco-Pillado, Jose J.; Schwartz-Perlov, Delia; Vilenkin, Alexander
2009-12-01
We identify instantons representing vacuum decay in a 6-dimensional toy model for string theory flux compactifications, with the two extra dimensions compactified on a sphere. We evaluate the instanton action for tunneling between different flux vacua, as well as for the decompactification decay channel. The bubbles resulting from flux tunneling have an unusual structure. They are bounded by two-dimensional branes, which are localized in the extra dimensions. This has important implications for bubble collisions.
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.
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 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.
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
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.
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
2016-07-25
Spectral analysis of 1 and 2-states per line quantum bus are normally sufficient to determine the effective Vab(N) electronic coupling between the emitter and receiver states through the bus as a function of the number N of parallel lines. When Vab(N) is difficult to determine, an Heisenberg-Rabi time dependent quantum exchange process must be triggered through the bus to capture the secular oscillation frequency Ωab(N) between those states. Two different linear and regimes are demonstrated for Ωab(N) as a function of N. When the initial preparation is replaced by coupling of the quantum bus to semi-infinite electrodes, the resulting quantum transduction process is not faithfully following the Ωab(N) variations. Because of the electronic transparency normalisation to unity and of the low pass filter character of this transduction, large Ωab(N) cannot be captured by the tunnel junction. The broadly used concept of electrical contact between a metallic nanopad and a molecular device must be better described as a quantum transduction process. At small coupling and when N is small enough not to compensate for this small coupling, an N(2) power law is preserved for Ωab(N) and for Vab(N).
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
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.
Dynamic quantum tunneling in mesoscopic driven Duffing oscillators.
Guo, Lingzhen; Zheng, Zhigang; Li, Xin-Qi; Yan, Yijing
2011-07-01
We investigate the dynamic quantum tunneling between two attractors of a mesoscopic driven Duffing oscillator. We find that, in addition to inducing a remarkable quantum shift of the bifurcation point, the mesoscopic nature also results in a perfect linear scaling behavior for the tunneling rate with the driving distance to the shifted bifurcation point. PMID:21867149
Multidimensional quantum tunneling in the Schwinger effect
NASA Astrophysics Data System (ADS)
Dumlu, Cesim K.
2016-03-01
We study the Schwinger effect, in which the external field having a spatiotemporal profile creates electron-positron pairs via multidimensional quantum tunneling. Our treatment is based on the trace formula for the QED effective action, whose imaginary part is represented by a sum over complex worldline solutions. The worldlines are multiperiodic, and the periods of motion collectively depend on the strength of spatial and temporal inhomogeneity. We argue that the classical action that leads to the correct tunneling amplitude must take into account both the full period, T ˜ and the first fundamental period, T1. In view of this argument we investigate pair production in an exponentially damped sinusoidal field and find that the initial momenta for multiperiodic trajectories lie on parabolic curves, such that on each curve the ratio T ˜/T1 stays uniform. Evaluation of the tunneling amplitude using these trajectories shows that vacuum decay rate is reduced by an order of magnitude, with respect to the purely time-dependent case, due to the presence of magnetic field.
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.
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.
Sensing the quantum limit in scanning tunnelling spectroscopy
Ast, Christian R.; Jäck, Berthold; Senkpiel, Jacob; Eltschka, Matthias; Etzkorn, Markus; Ankerhold, Joachim; Kern, Klaus
2016-01-01
The tunnelling current in scanning tunnelling spectroscopy (STS) is typically and often implicitly modelled by a continuous and homogeneous charge flow. If the charging energy of a single-charge quantum sufficiently exceeds the thermal energy, however, the granularity of the current becomes non-negligible. In this quantum limit, the capacitance of the tunnel junction mediates an interaction of the tunnelling electrons with the surrounding electromagnetic environment and becomes a source of noise itself, which cannot be neglected in STS. Using a scanning tunnelling microscope operating at 15 mK, we show that we operate in this quantum limit, which determines the ultimate energy resolution in STS. The P(E)-theory describes the probability for a tunnelling electron to exchange energy with the environment and can be regarded as the energy resolution function. We experimentally demonstrate this effect with a superconducting aluminium tip and a superconducting aluminium sample, where it is most pronounced. PMID:27708282
Sensing the quantum limit in scanning tunnelling spectroscopy
NASA Astrophysics Data System (ADS)
Ast, Christian R.; Jäck, Berthold; Senkpiel, Jacob; Eltschka, Matthias; Etzkorn, Markus; Ankerhold, Joachim; Kern, Klaus
2016-10-01
The tunnelling current in scanning tunnelling spectroscopy (STS) is typically and often implicitly modelled by a continuous and homogeneous charge flow. If the charging energy of a single-charge quantum sufficiently exceeds the thermal energy, however, the granularity of the current becomes non-negligible. In this quantum limit, the capacitance of the tunnel junction mediates an interaction of the tunnelling electrons with the surrounding electromagnetic environment and becomes a source of noise itself, which cannot be neglected in STS. Using a scanning tunnelling microscope operating at 15 mK, we show that we operate in this quantum limit, which determines the ultimate energy resolution in STS. The P(E)-theory describes the probability for a tunnelling electron to exchange energy with the environment and can be regarded as the energy resolution function. We experimentally demonstrate this effect with a superconducting aluminium tip and a superconducting aluminium sample, where it is most pronounced.
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.
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.
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
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.
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
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).
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.
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.
Unusual Tunneling Characteristics of Double-quantum-well Heterostructures
NASA Astrophysics Data System (ADS)
Lin, Y.; Nitta, J.; Newaz, A. K. M.; Song, W.; Mendez, E. E.
2005-06-01
We report tunneling phenomena in double In0.53Ga0.47As quantum-well structures that are at odds with the conventional parallel-momentum-conserving picture of tunneling between two-dimensional systems. We found that the tunneling current was mostly determined by the correlation between the emitter and the state in one well, and not by that between those in both wells. Clear magnetic-field-dependent features were first observed before the main resonance, corresponding to tunneling channels into the Landau levels of the well near the emitter. These facts provide evidence of the violation of in-plane momentum conservation in two-dimensional systems.
Macroscopic quantum tunnelling in a current biased Josephson junction
Martinis, J.M.; Devoret, M.H.; Clarke, J.; Urbina, C.
1984-11-01
We discuss in this work an attempt to answer experimentally the question: do macroscopic variables obey quantum mechanics. More precisely, this experiment deals with the question of quantum-mechanical tunnelling of a macroscopic variable, a subject related to the famous Schrodinger's cat problem in the theory of measurement.
Correlated dynamics of a Rabi oscillation and a quantum tunneling in coupled quantum dots
NASA Astrophysics Data System (ADS)
Xie, Weidong; Chu, Bingxin; Duan, Suqing; Xie, Yan; Chu, Weidong; Yang, Ning; Zhao, Xian-Geng
2015-08-01
We couple the Rabi oscillation in a double quantum dot (DQD) with the quantum tunneling in another DQD by Coulomb interaction between the neighboring dots. Such a coupling leads to correlation of the Rabi oscillating electron and the quantum tunneling one, and gives a tendency of synchronizing them under appropriate Rabi frequency ΩR and tunneling rate Tc. The correlated oscillation is shown clearly in the tunneling current. As ΩR =Tc, the Rabi oscillation and the quantum tunneling reach their strongest correlation and the two electrons finish their complete transitions simultaneously. And then, a single optical signal accomplishes a gang control of two electrons. This result encourages superior design of two-qubit quantum gates based on correlated DQDs.
No resonant tunneling in standard scalar quantum field theory
NASA Astrophysics Data System (ADS)
Copeland, Edmund J.; Padilla, Antonio; Saffin, Paul M.
2008-01-01
We investigate the nature of resonant tunneling in standard scalar Quantum Field Theory. Following the pioneering work of Banks, Bender and Wu we describe the quantum field theory in terms of infinite dimensional quantum mechanics and utilize the ``Most probable escape path'' (MPEP) as the class of paths which dominate the path integral in the classically forbidden region. Considering a 1+1 dimensional field theory example we show that there are five conditions that any associated bound state in the classically allowed region must satisfy if resonant tunnelling is to occur, and we then proceed to show that it is impossible to satisfy all five conditions simultaneously.
Tunneling at νT=1 in quantum Hall bilayers
NASA Astrophysics Data System (ADS)
Nandi, D.; Khaire, T.; Finck, A. D. K.; Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.
2013-10-01
Interlayer tunneling measurements in the strongly correlated bilayer quantized Hall phase at νT=1 are reported. The maximum, or critical, current for tunneling at νT=1 is shown to be a well-defined global property of the coherent phase, insensitive to extrinsic circuit effects and the precise configuration used to measure it, but also exhibiting a surprising scaling behavior with temperature. Comparisons between the experimentally observed tunneling characteristics and a recent theory are favorable at high temperatures, but not at low temperatures where the tunneling closely resembles the dc Josephson effect. The zero-bias tunneling resistance becomes extremely small at low temperatures, vastly less than that observed at zero magnetic field, but nonetheless remains finite. The temperature dependence of this tunneling resistance is similar to that of the ordinary in-plane resistivity of the quantum Hall phase.
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.
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.
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.
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
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.
NASA Astrophysics Data System (ADS)
Bothma, Jacques P.; Gilmore, Joel B.; McKenzie, Ross H.
2010-05-01
We consider the role of quantum effects in the transfer of hydrogen-like species in enzyme-catalyzed reactions. This review is stimulated by claims that the observed magnitude and temperature dependence of kinetic isotope effects (KIEs) implies that quantum tunneling below the energy barrier associated with the transition state significantly enhances the reaction rate in many enzymes. We review the path integral approach and the Caldeira-Leggett model, which provides a general framework to describe and understand tunneling in a quantum system that interacts with a noisy environment at nonzero temperature. Here the quantum system is the active site of the enzyme, and the environment is the surrounding protein and water. Tunneling well below the barrier only occurs for temperatures less than a temperature T0, which is determined by the curvature of the potential energy surface near the top of the barrier. We argue that for most enzymes this temperature is less than room temperature. We review typical values for the parameters in the Caldeira-Leggett Hamiltonian, including the frequency-dependent friction and noise due to the environment. For physically reasonable parameters, we show that quantum transition state theory gives a quantitative description of the temperature dependence and magnitude of KIEs for two classes of enzymes that have been claimed to exhibit signatures of quantum tunneling. The only quantum effects are those associated with the transition state, both reflection at the barrier top and tunneling just below the barrier. We establish that the friction and noise due to the environment are weak and only slightly modify the reaction rate. Furthermore, at room temperature and for typical energy barriers environmental fluctuations with frequencies much less than 1000 cm-1 do not have a significant effect on quantum corrections to the reaction rate. This is essentially because the time scales associated with the dynamics of proton transfer are faster than
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 .
Ferroelectric tunnel junctions with multi-quantum well structures
Ma, Zhijun; Zhang, Tianjin; Liang, Kun; Qi, Yajun; Wang, Duofa; Wang, Jinzhao; Jiang, Juan
2014-06-02
Ferroelectric tunnel junctions (FTJs) with multi-quantum well structures are proposed and the tunneling electroresistance (TER) effect is investigated theoretically. Compared with conventional FTJs with monolayer ferroelectric barriers, FTJs with single-well structures provide TER ratio improvements of one order of magnitude, while FTJs with optimized multi-well structures can enhance this improvement by another order of magnitude. It is believed that the increased resonant tunneling strength combined with appropriate asymmetry in these FTJs contributes to the improvement. These studies may help to fabricate FTJs with large TER ratio experimentally and put them into practice.
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.
Photon-assisted tunneling through a quantum dot
Kouwenhoven, L.P.; Jauhar, S.; McCormick, K.; Dixon, D.; McEuen, P.L. Materials Science Division, Lawrence Berkeley Laboratories, Mail Stop 2-200, Berkeley, California 94720 ); Nazarov, Y.V.; van der Vaart, N.C. ); Foxon, C.T. )
1994-07-15
We study single-electron tunneling in a two-junction device in the presence of microwave radiation. We introduce a model for numerical simulations that extends the Tien-Gordon theory for photon-assisted tunneling to encompass correlated single-electron tunneling. We predict sharp current jumps which reflect the discrete photon energy [ital hf], and a zero-bias current whose sign changes when an electron is added to the central island of the device. Measurements on split-gate quantum dots show microwave-induced features that are in good agreement with the model.
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 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.
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.
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.
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
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.
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
Dynamic characteristics of double tunneling-injection quantum dot lasers
NASA Astrophysics Data System (ADS)
Asryan, Levon V.
2015-03-01
Dynamic characteristics of double tunneling-injection (DTI) quantum dot (QD) lasers are studied. To reveal the potential of such lasers for high-speed direct modulation of their optical output by pump current, fast carrier injection into QDs and no carrier leakage from QDs are assumed. The small-signal analysis of rate equations is applied. The modulation bandwidth is calculated as a function of the dc component of the injection current density and parameters of the laser structure.
Quantum tunneling between bent semiconductor nanowires
NASA Astrophysics Data System (ADS)
Sousa, A. A.; Chaves, Andrey; Pereira, T. A. S.; Farias, G. A.; Peeters, F. M.
2015-11-01
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.
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.
Subbarrier Fusion Reactions and Many-Particle Quantum Tunneling
NASA Astrophysics Data System (ADS)
Hagino, K.; Takigawa, N.
2012-12-01
Low-energy heavy-ion fusion reactions are governed by quantum tunneling through the Coulomb barrier formed by the strong cancellation of the repulsive Coulomb force with the attractive nuclear interaction between the colliding nuclei. Extensive experimental as well as theoretical studies have revealed that fusion reactions are strongly influenced by couplings of the relative motion of the colliding nuclei to several nuclear intrinsic motions. Heavy-ion subbarrier fusion reactions thus provide a good opportunity to address the general problem of quantum tunneling in the presence of couplings, which has been a popular subject in recent decades in many branches of physics and chemistry. Here, we review theoretical aspects of heavy-ion subbarrier fusion reactions from the viewpoint of quantum tunneling in systems with many degrees of freedom. Particular emphases are put on the coupled-channels approach to fusion reactions and the barrier distribution representation for multichannel penetrability. We also discuss an application of the barrier distribution method to elucidate the mechanism of the dissociative adsorption of H_2 molecules in surface science.
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.
NASA Astrophysics Data System (ADS)
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.
Tunneling decay rate in quantum cosmology
NASA Astrophysics Data System (ADS)
Mithani, Audrey T.; Vilenkin, Alexander
2015-06-01
In canonical quantum cosmology, the wave function of the Universe lacks explicit time dependence. However, time evolution may be present implicitly through the semiclassical superspace variables, which themselves depend on time in classical dynamics. In this paper, we apply this approach to an oscillating universe model recently introduced by Graham et al. [A simple harmonic universe, J. High Energy Phys. 02 (2014) 029.] By extending the model to include a massless, minimally coupled scalar field ϕ which has little effect on the dynamics but can play the role of a "clock," we determine the decay rate of the oscillating universe.
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.
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
Tunnelling between the edges of two lateral quantum Hall systems
Kang; Stormer; Pfeiffer; Baldwin; West
2000-01-01
The edge of a two-dimensional electron system in a magnetic field consists of one-dimensional channels that arise from the confining electric field at the edge of the system. The crossed electric and magnetic fields cause electrons to drift parallel to the sample boundary, creating a chiral current that travels along the edge in only one direction. In an ideal two-dimensional electron system in the quantum Hall regime, all the current flows along the edge. Quantization of the Hall resistance arises from occupation of N one-dimensional edge channels, each contributing a conductance of e2/h. Here we report differential conductance measurements, in the integer quantum Hall regime, of tunnelling between the edges of a pair of two-dimensional electron systems that are separated by an atomically precise, high-quality, tunnel barrier. The resultant interaction between the edge states leads to the formation of new energy gaps and an intriguing dispersion relation for electrons travelling along the barrier: for example, we see a persistent conductance peak at zero bias voltage and an absence of tunnelling features due to electron spin. These features are unexpected and are not consistent with a model of weakly interacting edge states. Remnant disorder along the barrier and charge screening may each play a role, although detailed numerical studies will be required to elucidate these effects.
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.
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.
Macroscopic Quantum Tunneling of Solitons in Bose-Einstein Condensates
NASA Astrophysics Data System (ADS)
Glick, Joseph A.; Carr, Lincoln D.
2011-05-01
We study the macroscopic quantum tunneling of ultracold bosons in one-dimensional optical lattices. A bright matter-wave soliton behind a potential barrier is allowed to tunnel out of confinement by tuning the barrier width and the attractive particle-particle interactions. We predict the escape time for the soliton, that is, when the norm remaining behind the barrier drops to 1/e, modeling how the interaction strength, the system size, and the barrier dimensions affect the escape time. We preform quasi-exact simulations of the quantum many-body entangled dynamics with Time-Evolving Block Decimation (TEBD), a matrix product state numerical method. Independently, we check our results near the weakly interacting limit with mean-field theory. Our findings show the regimes in which mean-field theory is widely inadequate, and the appreciable differences between a mean-field and a full quantum many-body approach. We then use TEBD to model the dynamics far beyond the mean-field limit. We calculate the entropy of entanglement between the soliton body behind the barrier and the escaped soliton tail past the barrier over time. We use density-density correlation functions to examine how particles in different regions of the system (behind, under, or past the barrier) are entangled to one another. Funded by NSF
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.
Theory of interlayer tunneling in bilayer quantum Hall ferromagnets.
Stern, A; Girvin, S M; MacDonald, A H; Ma, N
2001-02-26
Spielman et al. [Phys. Rev. Lett. 84, 5808 (2000] recently observed a large and sharp Josephson-like zero-bias peak in the tunnel conductance of a bilayer system in a quantum Hall ferromagnet state. We argue that disorder-induced topological defects in the pseudospin order parameter limit the peak size and destroy the predicted Josephson effect. We predict that the peak would be split and shifted by an in-plane magnetic field in a way that maps the dispersion relation of the ferromagnet's Goldstone mode. We also predict resonant structures in the dc I-V characteristic under bias by an ac electric field.
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.
NASA Astrophysics Data System (ADS)
Alcala, Diego; Glick, Joseph; Carr, Lincoln D.
2015-05-01
The quantum escape problem is famous in the context of quasi-bound states and chemical and nuclear reactions. We address three outstanding questions in this form of quantum tunneling. (1) How are tunneling rates modified by many-body effects, in particular beyond the mean field? (2) What is the role of higher order quantum effects like entanglement and correlations? (3) What is the dynamics of the escape process? To this end we study both repulsive and attractive Bose-Einstein condensates via matrix-product state methods for entangled dynamics. We find that entanglement is maximized when about half the particles have escaped. We find preliminary evidence that the time derivative of number fluctuations serves as an entanglement witness. Funded by NSF.
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.
Quantum gases. Observation of many-body dynamics in long-range tunneling after a quantum quench.
Meinert, Florian; Mark, Manfred J; Kirilov, Emil; Lauber, Katharina; Weinmann, Philipp; Gröbner, Michael; Daley, Andrew J; Nägerl, Hanns-Christoph
2014-06-13
Quantum tunneling is at the heart of many low-temperature phenomena. In strongly correlated lattice systems, tunneling is responsible for inducing effective interactions, and long-range tunneling substantially alters many-body properties in and out of equilibrium. We observe resonantly enhanced long-range quantum tunneling in one-dimensional Mott-insulating Hubbard chains that are suddenly quenched into a tilted configuration. Higher-order tunneling processes over up to five lattice sites are observed as resonances in the number of doubly occupied sites when the tilt per site is tuned to integer fractions of the Mott gap. This forms a basis for a controlled study of many-body dynamics driven by higher-order tunneling and demonstrates that when some degrees of freedom are frozen out, phenomena that are driven by small-amplitude tunneling terms can still be observed. PMID:24926015
Quantum interference effect in electron tunneling through a quantum-dot-ring spin valve.
Ma, Jing-Min; Zhao, Jia; Zhang, Kai-Cheng; Peng, Ya-Jing; Chi, Feng
2011-01-01
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: PMID:21711779
Quantum 1/f Noise in Resonant Tunneling Diodes
NASA Astrophysics Data System (ADS)
Handel, Peter H.
2001-03-01
Resonant tunneling diodes consist of two potential barriers enclosing a quantum well. If the electron energy is close to the energy level in the well, resonance occurs and a peak IP of the current occurs, for the voltage VP. If the voltage increases further, only a negligibly small non-resonant current trickle remains at the voltage V=VV. Scattering processes that reduce the energy of the carriers to a value close to eVP will always be present, generating a finite current minimum IV at VV. Between VP and VV there is a negative differential conductance G=-(IP-IV)/(VV-VP) on the I/V curve, that is used to generate oscillations. The 1/f noise in IV is given by the conventional quantum 1/f effect with (Dv/c)2=2eVV/m. This yields IV-2SIv(f) =2aA/f N. Here N is given by N =tIV/e, where t is the life time of the carriers. The quantum 1/f frequency fluctuations can be obtained from the formula Sdw/w =(1/4Q4)SdG/G ,which was derived in 1978. This yields Sdw/w =(1/4Q4)(4a/3p)(2eVV/mc2) for the fractional frequency fluctuation spectrum exhibited by the RTD if included in an RF circuit of quality factor Q.
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.
One-Dimensional Nature of InAs/InP Quantum Dashes Revealed by Scanning Tunneling Spectroscopy.
Papatryfonos, Konstantinos; Rodary, Guillemin; David, Christophe; Lelarge, François; Ramdane, Abderrahim; Girard, Jean-Christophe
2015-07-01
We report on low-temperature cross-sectional scanning tunneling microscopy and spectroscopy on InAs(P)/InGaAsP/InP(001) quantum dashes, embedded in a diode-laser structure. The laser active region consists of nine InAs(P) quantum dash layers separated by the InGaAsP quaternary alloy barriers. The effect of the p-i-n junction built-in potential on the band structure has been evidenced and quantified on large-scale tunneling spectroscopic measurements across the whole active region. By comparing the tunneling current onset channels, a consistent energy shift has been measured in successive quantum dash or barrier layers, either for the ground state energy of similar-sized quantum dashes or for the conduction band edge of the barriers, corresponding to the band-bending slope. The extracted values are in good quantitative agreement with the theoretical band structure calculations, demonstrating the high sensitivity of this spectroscopic measurement to probe the electronic structure of individual nanostructures, relative to local potential variations. Furthermore, by taking advantage of the potential gradient, we compared the local density of states over successive quantum dash layers. We observed that it does not vanish while increasing energy, for any of the investigated quantum dashes, in contrast to what would be expected for discrete level zero-dimensional (0D) structures. In order to acquire further proof and fully address the open question concerning the quantum dash dimensionality nature, we focused on individual quantum dashes obtaining high-energy-resolution measurements. The study of the local density of states clearly indicates a 1D quantum-wirelike nature for these nanostructures whose electronic squared wave functions were subsequently imaged by differential conductivity mapping.
Cascade of quantum phase transitions in tunnel-coupled edge states.
Yang, I; Kang, W; Baldwin, K W; Pfeiffer, L N; West, K W
2004-02-01
We report on the cascade of quantum phase transitions exhibited by tunnel-coupled edge states across a quantum Hall line junction. We identify a series of quantum critical points between successive strong and weak tunneling regimes in the zero-bias conductance. Scaling analysis shows that the conductance near the critical magnetic fields B(c) is a function of a single scaling argument /B-B(c)/T(-kappa), where the exponent kappa=0.42. This puzzling resemblance to a quantum Hall-insulator transition points to the importance of interedge correlation between the coupled edge states.
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.
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.
Tunnel magnetoresistance in quantum dots in the presence of singlet and triplet states.
Michałek, G; Bułka, B R
2011-05-01
We study transport through a two-level quantum dot (QD) weakly coupled to ferromagnetic electrodes, the mutual magnetization orientation of which can be changed from a parallel to an antiparallel configuration. Calculations are performed in a sequential tunnelling regime taking into account an inter-level Coulomb and an exchange interaction on the QD with many-body electronic states. Our interests are mainly focused on the role of singlet and triplet states on the tunnel magnetoresistance (TMR). We have found that TMR characteristics strongly depend on different local spin configurations in the QD, which originate from an anti- or ferromagnetic exchange coupling J as well as its strength. A strong inter-channel Coulomb blockade (which influences the TMR) appears when the ground state is singly occupied. Activation of the singlet or the triplet states and competition between various tunnelling rates are responsible for the spin accumulation even in the parallel configuration. We have also found negative TMR and negative differential resistance (NDR) effects in the system with strong coupling asymmetry.
Scaling and non-Abelian signature in fractional quantum Hall quasiparticle tunneling amplitude
NASA Astrophysics Data System (ADS)
Hu, Zi-Xiang; Lee, Ki H.; Rezayi, Edward H.; Wan, Xin; Yang, Kun
2011-03-01
We study the scaling behavior in the tunneling amplitude when quasiparticles tunnel along a straight path between the two edges of a fractional quantum Hall annulus. Such scaling behavior originates from the propagation and tunneling of charged quasielectrons and quasiholes in an effective field analysis. In the limit when the annulus deforms continuously into a quasi-one-dimensional (1D) ring, we conjecture the exact functional form of the tunneling amplitude for several cases, which reproduces the numerical results in finite systems exactly. The results for Abelian quasiparticle tunneling is consistent with the scaling analysis; this allows for the extraction of the conformal dimensions of the quasiparticles. We analyze the scaling behavior of both Abelian and non-Abelian quasiparticles in the Read-Rezayi { Z}_k -parafermion states. Interestingly, the non-Abelian quasiparticle tunneling amplitudes exhibit non-trivial k-dependent corrections to the scaling exponent.
Quantum tunneling splittings from path-integral molecular dynamics
NASA Astrophysics Data System (ADS)
Mátyus, Edit; Wales, David J.; Althorpe, Stuart C.
2016-03-01
We illustrate how path-integral molecular dynamics can be used to calculate ground-state tunnelling splittings in molecules or clusters. The method obtains the splittings from ratios of density matrix elements between the degenerate wells connected by the tunnelling. We propose a simple thermodynamic integration scheme for evaluating these elements. Numerical tests on fully dimensional malonaldehyde yield tunnelling splittings in good overall agreement with the results of diffusion Monte Carlo calculations.
Quantum Tunneling Enhancement of the C + H2O and C + D2O Reactions at Low Temperature.
Hickson, Kevin M; Loison, Jean-Christophe; Nuñez-Reyes, Dianailys; Méreau, Raphaël
2016-09-15
Recent studies of neutral gas-phase reactions characterized by barriers show that certain complex forming processes involving light atoms are enhanced by quantum mechanical tunneling at low temperature. Here, we performed kinetic experiments on the activated C((3)P) + H2O reaction, observing a surprising reactivity increase below 100 K, an effect that is only partially reproduced when water is replaced by its deuterated analogue. Product measurements of H- and D-atom formation allowed us to quantify the contribution of complex stabilization to the total rate while confirming the lower tunneling efficiency of deuterium. This result, which is validated through statistical calculations of the intermediate complexes and transition states has important consequences for simulated interstellar water abundances and suggests that tunneling mechanisms could be ubiquitous in cold dense clouds.
Quantum Tunneling Enhancement of the C + H2O and C + D2O Reactions at Low Temperature.
Hickson, Kevin M; Loison, Jean-Christophe; Nuñez-Reyes, Dianailys; Méreau, Raphaël
2016-09-15
Recent studies of neutral gas-phase reactions characterized by barriers show that certain complex forming processes involving light atoms are enhanced by quantum mechanical tunneling at low temperature. Here, we performed kinetic experiments on the activated C((3)P) + H2O reaction, observing a surprising reactivity increase below 100 K, an effect that is only partially reproduced when water is replaced by its deuterated analogue. Product measurements of H- and D-atom formation allowed us to quantify the contribution of complex stabilization to the total rate while confirming the lower tunneling efficiency of deuterium. This result, which is validated through statistical calculations of the intermediate complexes and transition states has important consequences for simulated interstellar water abundances and suggests that tunneling mechanisms could be ubiquitous in cold dense clouds. PMID:27574866
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.
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.
Light-current curve of a tunneling-injection quantum dot laser
NASA Astrophysics Data System (ADS)
Han, Dae-Seob; Asryan, Levon V.
2008-02-01
The potential for high-power operation of a laser exploiting tunneling-injection of electrons and holes into quantum dots (QDs) from two separate quantum wells (QWs) is studied. An extended theoretical model is developed to account for out-tunneling leakage of carriers from QDs. Even in the presence of out-tunneling from QDs, the parasitic recombination flux outside QDs is shown to remain restricted with increasing injection current; correspondingly, the LCC becomes more and more linear and the slope efficiency closer to unity at high injection currents. The linearity is due to the fact that the current paths connecting the opposite sides of the structure lie entirely within QDs - in view of the threedimensional confinement in QDs, the out-tunneling fluxes of carriers from dots are limited.
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.
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
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.
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…
Tsiper, E V
2006-08-18
The concept of fractional charge is central to the theory of the fractional quantum Hall effect. Here I use exact diagonalization as well as configuration space renormalization to study finite clusters which are large enough to contain two independent edges. I analyze the conditions of resonant tunneling between the two edges. The "computer experiment" reveals a periodic sequence of resonant tunneling events consistent with the experimentally observed fractional quantization of electric charge in units of e/3 and e/5.
NASA Astrophysics Data System (ADS)
Asai, Hidehiro; Ota, Yukihiro; Kawabata, Shiro; Machida, Masahiko; Nori, Franco
2014-06-01
Collective excitations reveal fundamental properties and potential applications of superconducting states. We theoretically study macroscopic quantum tunneling (MQT) in a Josephson junction composed of multiband superconductors, focusing on a phase mode induced by interband fluctuations: the Josephson-Leggett (JL) collective excitation mode. Using the imaginary-time path-integral method, we derive a formula for the MQT escape rate for low-temperature switching events. We clarify that the JL mode has two major effects on the MQT: (i) the zero-point fluctuations enhance the escape rate, and (ii) the quantum dissipation induced by the couplings to the gauge-invariant phase difference suppresses the quantum tunneling. We show that the enhancement exceeds the suppression for a wide range of junction parameters. This enhancement originates from the single-mode interaction between the tunneling variable and the interband fluctuations.
Band gap widening and quantum tunnelling effects of Ag/MgO/p-Si MOS structure
NASA Astrophysics Data System (ADS)
Kamarulzaman, Norlida; Badar, Nurhanna; Fadilah Chayed, Nor; Firdaus Kasim, Muhd
2016-10-01
MgO films of various thicknesses were fabricated via the pulsed laser deposition method. The MgO thin films obtained have the advantage of high quality mirror finish, good densification and of uniform thickness. The MgO thin films have thicknesses of between 43 to 103 nm. They are polycrystalline in nature with oriented growth mainly in the direction of the [200] and [220] crystal planes. It is observed that the band gap of the thin films increases as the thickness decreases due to quantum effects, however, turn-on voltage has the opposite effect. The decrease of the turn-on as well as the tunnelling voltage of the thinner films, despite their larger band gap, is a direct experimental evidence of quantum tunnelling effects in the thin films. This proves that quantum tunnelling is more prominent in low dimensional structures.
Tunneling Spectroscopy of the Edge in Quantum Hall Systems in Cleaved-Edge Overgrowth Devices
NASA Astrophysics Data System (ADS)
Oh, J. H.; Hilke, M.; Tsui, D. C.; Pfeiffer, L. N.; West, K. W.
2004-03-01
We present experimental results on the tunneling into the edge of a two dimensional electron gas (2DEG) obtained with a GaAs/AlGaAs cleaved edge overgrown structure in a strong perpendicular magnetic field. While the 2DEG shows typical fractional quantum Hall features of a very high mobility system, the tunneling into the edge exhibits a cross-over from a many-particle behavior (Luttinger liquid) at low tunneling voltages to a single particle characteristic at high voltages, which reflects absence of a many-body state away from the Fermi level. At high enough voltages, the single particle characteristic induces an asymmetry when tunneling into the 2DEG compared to tunneling out of it, which can be understood in the context of the single particle Landau level spectral distribution at the edge.
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
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.
Black hole remnant and quantum tunnelling in three-dimensional Gödel spacetime
NASA Astrophysics Data System (ADS)
Li, Hui-Ling; Zu, Xiao-Tao
2015-05-01
Using the modified Dirac equation in a three-dimensional gravity background, we investigate the quantum correction to tunnelling radiation from a Gödel black hole, and discuss the black hole remnant employing fermion's tunnelling. The corrected tunnelling probability is derived, and the modified Hawking temperature is found as well. It is worth emphasizing that, only when the condition j> αω(3 r -- r +) is satisfied, emitting both a mass particle and a massless particle, the remnant of the Gödel black hole may arise.
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.
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.
Quasiparticle tunneling amplitute in fractional quantum Hall states
NASA Astrophysics Data System (ADS)
Hu, Zixiang; Lee, Kihoon; Rezayi, Edward H.; Wan, Xin; Yang, Kun
2011-03-01
We study qp tunneling in the MR state, in which qp of charge e/4 and e/2 may co-exist and both contribute to edge transport. The tunneling amplitude for charge e/2 qp is exponentially smaller than that for e/4 qh, and the ratio between them can be (partially) attributed to their charge difference. The tunneling amplitude shows some scaling behavior which originates from the propagation and tunneling of charged qhs in an effective field analysis. In the ring limit, we conjecture the exact functional form for several cases. The results for Abelian qp tunneling is consistent with the scaling anaysis; this allows for the extraction of conformal dimensions of the qps. We analyze the scaling behavior of both Abelian and non-Abelian qps in the Zk parafermion states. Interestingly, the non-Abelian qp tunneling amplitudes exhibit nontrivial k -dependent corrections to the scaling exponent. This work was supported by DOE grant DE-SC0002140 and APCTP.
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
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.
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.
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.
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.
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)
Li, Guochang; Chen, George; Li, Shengtao
2016-08-01
Charge transport properties in nanodielectrics present different tendencies for different loading concentrations. The exact mechanisms that are responsible for charge transport in nanodielectrics are not detailed, especially for high loading concentration. A charge transport model in nanodielectrics has been proposed based on quantum tunneling mechanism and dual-level traps. In the model, the thermally assisted hopping (TAH) process for the shallow traps and the tunnelling process for the deep traps are considered. For different loading concentrations, the dominant charge transport mechanisms are different. The quantum tunneling mechanism plays a major role in determining the charge conduction in nanodielectrics with high loading concentrations. While for low loading concentrations, the thermal hopping mechanism will dominate the charge conduction process. The model can explain the observed conductivity property in nanodielectrics with different loading concentrations.
Tunneling spectroscopy of hole plasmons in a valence-band quantum well
Neves, B.R.; Foster, T.J.; Eaves, L.; Main, P.C.; Henini, M.; Fisher, D.J.; Lerch, M.L.; Martin, A.D.; Zhang, C.
1996-10-01
We investigate the current-voltage characteristics of a {ital p}-doped resonant tunneling diode. In the voltage range slightly above the bias corresponding to resonant tunneling of holes into the first light-hole subband of the quantum well, we observe two satellite peaks which we attribute to plasmon-assisted tunneling transitions. A theoretical model is presented to account for these peaks. The model is based on the excitation of intrasubband and intersubband heavy-hole plasmons in the quantum well by hot holes injected close to the energy of the first light-hole subband. We also study the behavior of the satellites when a magnetic field is applied either parallel to or perpendicular to the current. {copyright} {ital 1996 The American Physical Society.}
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…
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
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.
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.
Nonresonant tunneling in single asymmetric pairs of vertically stacked InP quantum dots
NASA Astrophysics Data System (ADS)
Reischle, M.; Beirne, G. J.; Roßbach, R.; Jetter, M.; Schweizer, H.; Michler, P.
2007-08-01
Single pairs of vertically stacked asymmetric pairs of InP quantum dots embedded in GaInP barriers have been investigated as a function of interdot spacer thickness. Time integrated and time-resolved photoluminescence measurements have been performed, with the former showing a change in the intensity ratio between the two dots and the latter an increasing difference in the photoluminescence decay time of the two dots when reducing the spacer thickness. Hence, we suggest transitions from vanishing tunnel coupling to electron tunneling and, finally, to electron and hole tunneling for decreasing barrier widths. The different times are estimated from the measurement data, and the changes are described by a rate equation model. The results clearly show the nonresonant character of the tunneling process as a result of the different ground state energies (approximately 40meV ) of the unequally sized dots.
Re-Examining Gravitational Tunneling Radiation when taking into account Quantum Gravity Effects
NASA Astrophysics Data System (ADS)
Valentine, John; Prescott, Trevor; Blado, Gardo
2015-03-01
Although shown to theoretically exist, Hawking Radiation has yet to be detected. The paper entitled ``Gravitational Tunneling Radiation'' by Mario Rabinowitz proposed a possible explanation by considering the gravitational tunneling effects in the presence of other bodies in the vicinity of the black hole. Rabinowitz showed that the power radiated (through gravitational radiation) by a black hole,PR, is related to the power generated by Hawking Radiation, PSH by PR/T ~PSH where T is the gravitational tunneling probability. The presence of other bodies lowers the gravitational barrier which in turn increases the gravitational tunneling probability thereby decreasing the Hawking radiation, PSH. In this paper, we examine the modification of T in the presence of quantum gravity effects by incorporating the Generalized Uncertainty Principle.
Optical Blocking of Electron Tunneling into a Single Self-Assembled Quantum Dot.
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. PMID:27419589
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.
Tunneling at νT = 1 in a bilayer quantum Hall exciton condensate
NASA Astrophysics Data System (ADS)
Nandi, D.; Khaire, T.; Finck, A. D. K.; Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.
2014-03-01
Closely-spaced bilayer quantum Hall systems at total filling factor νT = 1 exhibit spontaneous interlayer phase coherence. This phase coherence, which is tantamount to excitonic Bose condensation, is most dramatically revealed via interlayer tunneling measurements.In the condensed phase the tunneling current-voltage (IV) characteristic of this semiconductor system strongly resembles the dc Josephson effect observed in superconducting tunnel junctions. Here we report on a detailed study of this phenomenon. We find the maximum, or critical tunneling current Ic to be a well-defined global property of the macroscopic tunnel junction, insensitive to external circuit elements and the precise contact configuration used to observe it. Interestingly, the temperature dependence of Ic displays an unexpected scaling behavior. At the lowest temperatures the slope of the ``supercurrent'' branch of the tunneling IV curve, while extremely large, remains finite. Careful measurements in this regime suggest that dissipative processes arising from in-plane exciton transport limit the maximum tunneling conductance. Finally, comparisons of the experimentally observed IV with recent theoretical predictions will be discussed.
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.
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)
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.
Subgap tunneling via a quantum interference effect: Insulators and charge density waves
NASA Astrophysics Data System (ADS)
Duhot, S.; Mélin, R.
2007-11-01
A quantum interference effect is discussed for subgap tunneling over a distance comparable to the coherence length, which is a consequence of “advanced-advanced” and “retarded-retarded” transmission modes [Altland and Zirnbauer, Phys. Rev. B 55, 1142 (1997)]. Effects typical of disorder are obtained from the interplay between multichannel averaging and higher order processes in the tunnel amplitudes. Quantum interference effects similar to those occurring in normal tunnel junctions explain magnetoresistance oscillations of a CDW pierced by nanoholes [Latyshev , Phys. Rev. Lett. 78, 919 (1997)], having periodicity h/2e as a function of the flux enclosed in the nanohole. Subgap tunneling is coupled to the sliding motion by charge accumulation in the interrupted chains. The effect is within the same trend as random matrix theory for normal metal-CDW hybrids [Visscher , Phys. Rev. B 62, 6873 (2000)]. We suggest that the experiment by Latyshev probes weak localizationlike properties of evanescent quasiparticles, not an interference effect related to the quantum-mechanical ground state.
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.
Zhang, Yanchuan; Stecher, Thomas; Cvitaš, Marko T; Althorpe, Stuart C
2014-11-20
Quantum transition-state theory (QTST) and free-energy instanton theory (FEIT) are two closely related methods for estimating the quantum rate coefficient from the free-energy at the reaction barrier. In calculations on one-dimensional models, FEIT typically gives closer agreement than QTST with the exact quantum results at all temperatures below the crossover to deep tunneling, suggesting that FEIT is a better approximation than QTST in this regime. Here we show that this simple trend does not hold for systems of greater dimensionality. We report tests on several collinear and three-dimensional reactions, in which QTST outperforms FEIT over a range of temperatures below crossover, which can extend down to half the crossover temperature (below which FEIT outperforms QTST). This suggests that QTST-based methods such as ring-polymer molecular dynamics (RPMD) may often give closer agreement with the exact quantum results than FEIT.
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.
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.
NASA Astrophysics Data System (ADS)
Büsser, C. A.; de Vega, I.; Heidrich-Meisner, F.
2014-11-01
We consider two quantum dots described by the Anderson-impurity model with one electron per dot. The goal of our work is to study the decay of a maximally entangled state between the two electrons localized in the dots. We prepare the system in a perfect singlet and then tunnel couple one of the dots to leads, which induces nonequilibrium dynamics. We identify two cases: If the leads are subject to a sufficiently large voltage and thus a finite current, then direct-tunneling processes cause decoherence and the entanglement as well as spin correlations decay exponentially fast. At zero voltage or small voltages and beyond the mixed-valence regime, virtual-tunneling processes dominate and lead to a slower loss of coherence. We analyze this problem by studying the real-time dynamics of the spin correlations and the concurrence using two techniques, namely, the time-dependent density matrix renormalization group method and a master-equation method. The results from these two approaches are in excellent agreement in the direct-tunneling regime for the case in which the dot is weakly tunnel coupled to the leads. We present a quantitative analysis of the decay rates of the spin correlations and the concurrence as a function of tunneling rate, interaction strength, and voltage.
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.
Zero-bias anomalies in narrow tunnel junctions in the quantum Hall regime.
Jiang, P; Chien, C-C; Yang, I; Kang, W; Baldwin, K W; Pfeiffer, L N; West, K W
2010-12-10
We report on the study of cleaved-edge-overgrown line junctions with a serendipitously created narrow opening in an otherwise thin, precise line barrier. Two sets of zero-bias anomalies are observed with an enhanced conductance for filling factors ν>1 and a strongly suppressed conductance for ν<1. A transition between the two behaviors is found near ν≈1. The zero-bias anomaly (ZBA) line shapes find explanation in Luttinger liquid models of tunneling between quantum Hall edge states. The ZBA for ν<1 occurs from strong backscattering induced by suppression of quasiparticle tunneling between the edge channels for the n=0 Landau levels. The ZBA for ν>1 arises from weak tunneling of quasiparticles between the n=1 edge channels.
Bekasova, O D; Shubin, V V; Safenkova, I V; Kovalyov, L I; Kurganov, B I
2013-11-01
Structural changes in R-phycoerythrin used as a matrix for the synthesis of CdS quantum dots have been analyzed by circular dichroism spectrometry. In deionized water, quantum dot synthesis in the tunnel cavity of the R-phycoerythrin molecule proved to be accompanied by uncoiling of α-helices and changes in the conformation of its chromophore groups, with consequent decay of protein fluorescence. Since R-phycoerythrin fluorescence is important for practical applications, conditions for quantum dot synthesis have been optimized by replacing deionized water with 0.01 M MES buffer, pH 5.7. Under such conditions, the size of the CdS quantum dots (determined from atomic force microscopy images) remains the same as in deionized water, but quantum dots cause only minor structural changes in protein molecules, as follows from circular dichroism and absorption spectra. The thermostability of R-phycoerythrin is enhanced, as indicated by an increase in the experimental activation energy for denaturation (from 140.8 to 149.9 kJ/mol) and the intensity of R-phycoerythrin fluorescence is also enhanced approximately twofold.
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.
Nonvolatile Memories Using Quantum Dot (QD) Floating Gates Assembled on II-VI Tunnel Insulators
NASA Astrophysics Data System (ADS)
Suarez, E.; Gogna, M.; Al-Amoody, F.; Karmakar, S.; Ayers, J.; Heller, E.; Jain, F.
2010-07-01
This paper presents preliminary data on quantum dot gate nonvolatile memories using nearly lattice-matched ZnS/Zn0.95Mg0.05S/ZnS tunnel insulators. The GeO x -cladded Ge and SiO x -cladded Si quantum dots (QDs) are self-assembled site-specifically on the II-VI insulator grown epitaxially over the Si channel (formed between the source and drain region). The pseudomorphic II-VI stack serves both as a tunnel insulator and a high- κ dielectric. The effect of Mg incorporation in ZnMgS is also investigated. For the control gate insulator, we have used Si3N4 and SiO2 layers grown by plasma- enhanced chemical vapor deposition.
Reversal of the circulation of a vortex by quantum tunneling in trapped Bose systems
Watanabe, Gentaro; Pethick, C. J.
2007-08-15
We study the quantum dynamics of a model for a vortex in a Bose gas with repulsive interactions in an anisotropic, harmonic trap. By solving the Schroedinger equation numerically, we show that the circulation of the vortex can undergo periodic reversals by quantum-mechanical tunneling. With increasing interaction strength or particle number, vortices become increasingly stable, and the period for reversals increases. Tunneling between vortex and antivortex states is shown to be described to a good approximation by a superposition of vortex and antivortex states (Schroedinger cat state), rather than the mean-field state, and we derive an analytical expression for the oscillation period. The problem is shown to be equivalent to that of the two-site Bose-Hubbard model with attractive interactions.
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.
Scanning tunneling spectroscopy of lead sulfide quantum wells fabricated by atomic layer deposition.
Lee, Wonyoung; Dasgupta, Neil P; Jung, Hee Joon; Lee, Jung-Rok; Sinclair, Robert; Prinz, Fritz B
2010-12-01
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.
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.
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.
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.
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)
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.
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.
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.
Active quantum walks: a framework for quantum walks with adiabatic quantum evolution
NASA Astrophysics Data System (ADS)
Wu, Nan; Song, Fangmin; Li, Xiangdong
2016-05-01
We study a new methodology for quantum walk based algorithms. Different from the passive quantum walk, in which a walker is guided by a quantum walk procedure, the new framework that we developed allows the walker to move by an adiabatic procedure of quantum evolution, as an active way. The use of this active quantum walk is helpful to develop new quantum walk based searching and optimization algorithms.
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.
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
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.
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.
An entropic quantum drift-diffusion model for electron transport in resonant tunneling diodes
Degond, Pierre; Gallego, Samy . E-mail: gallego@mip.ups-tlse.fr; Mehats, Florian
2007-01-20
We present an entropic quantum drift-diffusion model (eQDD) and show how it can be derived on a bounded domain as the diffusive approximation of the Quantum Liouville equation with a quantum BGK operator. Some links between this model and other existing models are exhibited, especially with the density gradient (DG) model and the Schroedinger-Poisson drift-diffusion model (SPDD). Then a finite difference scheme is proposed to discretize the eQDD model coupled to the Poisson equation and we show how this scheme can be slightly modified to discretize the other models. Numerical results show that the properties listed for the eQDD model are checked, as well as the model captures important features concerning the modeling of a resonant tunneling diode. To finish, some comparisons between the models stated above are realized.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Xue, N. T.; Xie, H. Q.; Xue, H. B.; Liang, J.-Q.
2014-05-01
By means of the Rate equation approach in sequential tunneling regime, we study spin-polarized transport through series double quantum dots (DQD) weakly coupled to collinear ferromagnetic leads with particular attention on the effect of interdot spin exchange interaction (SEI). For the asymmetric DQD giant negative differential conductance is realized, which depends on the energy-level spacing between two dots. It is demonstrated that the voltage dependencies of the tunnel magnetoresistance (TMR) and the shot noise are sensitive to the SEI, which leads to the additional imbalance between spin-polarized currents. The super-Poissonian statistics is enhanced in the parallel leads’ configuration by the ferromagnetic SEI, which favorites the spin bunching, while it is suppressed by stronger antiferromagnetic SEI in antiparallel configuration for a symmetric DQD. The voltage dependencies of the TMR and shot noise may be used to probe the SEI.
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.
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.
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.
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.
Quantum mechanical solver for confined heterostructure tunnel field-effect transistors
NASA Astrophysics Data System (ADS)
Verreck, Devin; van de Put, Maarten; Soree, Bart; Verhulst, Anne; Magnus, Wim; Vandenberghe, William; Groeseneken, Guido
2014-03-01
Although the tunnel field-effect transistor (TFET) is a promising candidate to replace the MOSFET in low-power applications because of its sub-60mV/dec subthreshold swing (SS), on-currents are typically too low. Introducing a heterostructure of III-V materials at the tunnel junction enables higher on-currents, but the influence of quantum effects like size confinement is poorly understood. We therefore present a ballistic quantum transport formalism, combining for the first time a novel heterostructure envelope function formalism with the multiband quantum transmitting boundary method, extended to 2D potentials. First, the subband modes are obtained in the contacts, where the potential is assumed constant in the transport direction. Next, the modes are injected one by one into the device. Finally, the resulting transmission probabilities are integrated, weighted with a Fermi-Dirac distribution, to obtain the current. This multiband formalism has been implemented for the 2-band case. First, heterostructure diodes were simulated, showing a decrease in transmission probabilities for thin devices. Next, p-n-i-n heterostructure TFETs were studied. It was found that the improved gate control in thin devices counteracts the size confinement.
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.
First-principles theory of quantum well resonance in double barrier magnetic tunnel junctions.
Wang, Yan; Lu, Zhong-Yi; Zhang, X-G; Han, X F
2006-08-25
Quantum well (QW) resonances in Fe(001)/MgO/Fe/MgO/Fe double barrier magnetic tunnel junctions are calculated from first principles. By including the Coulomb blockade energy due to the finite size islands of the middle Fe film, we confirm that the oscillatory differential resistance observed in a recent experiment [T. Nozaki, Phys. Rev. Lett. 96, 027208 (2006)10.1103/PhysRevLett.96.027208] originates from the QW resonances from the Delta1 band of the Fe majority-spin channel. The primary source of smearing at low temperatures is shown to be the variation of the Coulomb blockade energy.
Ligand-protein docking using a quantum stochastic tunneling optimization method.
Mancera, Ricardo L; Källblad, Per; Todorov, Nikolay P
2004-04-30
A novel hybrid optimization method called quantum stochastic tunneling has been recently introduced. Here, we report its implementation within a new docking program called EasyDock and a validation with the CCDC/Astex data set of ligand-protein complexes using the PLP score to represent the ligand-protein potential energy surface and ScreenScore to score the ligand-protein binding energies. When taking the top energy-ranked ligand binding mode pose, we were able to predict the correct crystallographic ligand binding mode in up to 75% of the cases. By using this novel optimization method run times for typical docking simulations are significantly shortened.
WATER FORMATION THROUGH A QUANTUM TUNNELING SURFACE REACTION, OH + H{sub 2}, AT 10 K
Oba, Y.; Watanabe, N.; Hama, T.; Kuwahata, K.; Hidaka, H.; Kouchi, A.
2012-04-10
The present study experimentally demonstrated that solid H{sub 2}O is formed through the surface reaction OH + H{sub 2} at 10 K. This is the first experimental evidence of solid H{sub 2}O formation using hydrogen in its molecular form at temperatures as low as 10 K. We further found that H{sub 2}O formation through the reaction OH + H{sub 2} is about one order of magnitude more effective than HDO formation through the reaction OH + D{sub 2}. This significant isotope effect results from differences in the effective mass of each reaction, indicating that the reactions proceed through quantum tunneling.
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.
Metastable states and macroscopic quantum tunneling in a cold atom josephson ring
Solenov, Dmitry; Mozyrsky, Dmitry
2009-01-01
We study macroscopic properties of a system of weakly interacting neutral bosons confined in a ring-shaped potential with a Josephson junction. We derive an effective low energy action for this system and evaluate its properties. In particular we find that the system possesses a set of metastable current-carrying states and evaluate the rates of transitions between these states due to macroscopic quantum tunneling. Finally we discuss signatures of different metastable states in the time-of-flight images and argue that the effect is observable within currently available experimental technique.
Spin bottleneck in resonant tunneling through double quantum dots with different Zeeman splittings.
Huang, S M; Tokura, Y; Akimoto, H; Kono, K; Lin, J J; Tarucha, S; Ono, K
2010-04-01
We investigated the electron transport property of the InGaAs/GaAs double quantum dots, the electron g factors of which are different from each other. We found that in a magnetic field, the resonant tunneling is suppressed even if one of the Zeeman sublevels is aligned. This is because the other misaligned Zeeman sublevels limit the total current. A finite broadening of the misaligned sublevel partially relieves this bottleneck effect, and the maximum current is reached when interdot detuning is half the Zeeman energy difference.
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.
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
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
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.
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.
Non-resonant tunneling in single pairs of vertically stacked asymmetric InP/GaInP quantum dots
NASA Astrophysics Data System (ADS)
Reischle, M.; Beirne, G. J.; Roßbach, R.; Jetter, M.; Schweizer, H.; Michler, P.
2008-04-01
In this work, single vertically stacked asymmetric InP/GaInP quantum dot (QD) pairs that are separated by different barrier widths have been investigated. We have found that for large (20 nm) inter-dot distances no tunneling is possible, that for medium spacer widths (10 nm) electrons can tunnel from the large dot to the small dot, and that finally, for very small (5 nm) barriers both electrons and holes can tunnel. We have simulated our results using a rate-equation model and have found a good agreement between simulation and experiment.
NMR Studies of Quantum Tunneling in Monolayers of Helium Three
NASA Astrophysics Data System (ADS)
Parks, Charles; Stachowiak, Piotr; Sullivan, Neil
2002-03-01
The results of NMR studies of the nuclear spin-spin relaxation are reported for commensurate monolayers of helium three adsorbed on hexagonal boron nitride. The measurements were made using pulsed NMR techniques for low temperatures, 0.01 < T < 5.0 K, and for moderately high magnetic fields (up to 6 T). The relaxation rate is independent of temperature at low temperatures, 0.12 < T < 0.85 K, and this behavior is interpreted in terms of particle-particle exchange motions of the adsorbed helium atoms. The effective exchange rates were observed to change significantly on replacing a fraction of the helium atoms with relatively immobile neon atoms. This is understood if there is a significant 3-particle exchange in addition to 2-particle exchange. The analyses of the experimental results indicate that the 3-spin exchange term in the exchange Hamiltonian is of opposite sign to that of the 2-spin exchange and also has a larger amplitude. At high temperatures, 0.8 < T < 5.0 K, an exponential temperature dependence of the rate is observed that is attributed to the thermal activation of vacancies.
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.
Terahertz time domain interferometry of a SIS tunnel junction and a quantum point contact
Karadi, C
1995-09-01
The author has applied the Terahertz Time Domain Interferometric (THz-TDI) technique to probe the ultrafast dynamic response of a Superconducting-Insulating-Superconducting (SIS) tunnel junction and a Quantum Point Contact (QPC). The THz-TDI technique involves monitoring changes in the dc current induced by interfering two picosecond electrical pulses on the junction as a function of time delay between them. Measurements of the response of the Nb/AlO{sub x}/Nb SIS tunnel junction from 75--200 GHz are in full agreement with the linear theory for photon-assisted tunneling. Likewise, measurements of the induced current in a QPC as a function of source-drain voltage, gate voltage, frequency, and magnetic field also show strong evidence for photon-assisted transport. These experiments together demonstrate the general applicability of the THz-TDI technique to the characterization of the dynamic response of any micron or nanometer scale device that exhibits a non-linear I-V characteristic. 133 refs., 49 figs.
Is it possible to create a universe in the laboratory by quantum tunneling?
NASA Technical Reports Server (NTRS)
Farhi, Edward; Guth, Alan H.; Guven, Jemal
1990-01-01
We explore the possibility that a new universe can be created by producing a small bubble of false vacuum. The initial bubble is small enough to be produced without an initial singularity, but classically it could not become a universe - instead it would reach a maximum radius and then collapse. We investigate the possibility that quantum effects allow the bubble to tunnel into a larger bubble, of the same mass, which would then classically evolve to become a new universe. The calculation of the tunneling amplitude is attempted, in lowest order semiclassical approximation (in the thin-wall limit), using both a canonical and a functional integral approach. The canonical approach is found to have flaws, attributable to our method of space-time slicing. The functional integral approach leads to a Euclidean interpolating solution that is not a manifold. To describe it, we define an object which we call a 'pseudomanifold', and give a prescription to define its action. We conjecture that the tunneling probability to produce a new universe can be approximated using this action, and we show that this leads to a plausible result.
Indeterminate form 0/0 and tunneling in double quantum wells
NASA Astrophysics Data System (ADS)
Filikhin, Igor; Vlahovic, Branislav
2015-03-01
We study single electron tunneling between localized and delocalized states in double InAs/GaAs quantum wells (DQWs). Spectral distribution of localized (or delocalized) states demonstrates high sensitivity on inter-dot distance. The tunneling goes consecutively from the higher energy levels to the ground state when the inter-dot distance decreases. The spectrum is presented by set of quasi-doublets and may be described by three parts: localized states, delocalized states, and states with different probability for localization in each QW of DQW. For the last states, the ratio W/ ΔE of the wave functions overlapping integral W and the electron energy difference ΔE of isolated left and right QWs is a weight coefficient in the expansion of wave function on the basis of the wave functions of isolated QWs. In case of weakly coupled QWs in DQW the indeterminate form 0/0 takes a place for the electron wave function. It is found that a small violation of the DQW shape symmetry drastically affects tunneling. This effect also appears as a numerical instability calculations for small variations of input parameters of numerical procedure. This work is supported by the NSF (HRD-1345219) and NASA (NNX09AV07A).
Modeling direct band-to-band tunneling: From bulk to quantum-confined semiconductor devices
Carrillo-Nuñez, H.; Ziegler, A.; Luisier, M.; Schenk, A.
2015-06-21
A rigorous framework to study direct band-to-band tunneling (BTBT) in homo- and hetero-junction semiconductor nanodevices is introduced. An interaction Hamiltonian coupling conduction and valence bands (CVBs) is derived using a multiband envelope method. A general form of the BTBT probability is then obtained from the linear response to the “CVBs interaction” that drives the system out of equilibrium. Simple expressions in terms of the one-electron spectral function are developed to compute the BTBT current in two- and three-dimensional semiconductor structures. Additionally, a two-band envelope equation based on the Flietner model of imaginary dispersion is proposed for the same purpose. In order to characterize their accuracy and differences, both approaches are compared with full-band, atomistic quantum transport simulations of Ge, InAs, and InAs-Si Esaki diodes. As another numerical application, the BTBT current in InAs-Si nanowire tunnel field-effect transistors is computed. It is found that both approaches agree with high accuracy. The first one is considerably easier to conceive and could be implemented straightforwardly in existing quantum transport tools based on the effective mass approximation to account for BTBT in nanodevices.
Rabi oscillations at different tunnel couplings for an ac-gated quantum dot qubit
NASA Astrophysics Data System (ADS)
Thorgrimsson, Brandur; Kim, Dohun; Simmons, C. B.; Ward, Daniel R.; Foote, Ryan H.; Savage, D. E.; Lagally, M. G.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.
2015-03-01
One way to create a qubit is to use two distinct positions of a single electron as qubit states. Such a system can be achieved by using the left and right positions in a gated double quantum dot. In this system the qubit is strongly coupled to electric fields and has potential for high-speed operations. By tuning specific gate voltages, the tunnel coupling between the left and right quantum dots can be changed. Here, by using resonant ac microwave driving and gate tuning, we explore variations of T2* and the Rabi frequency on the tunnel coupling and microwave drive power, and we study strong driving effects such as generation of second harmonics. This work was supported in part by ARO (W911NF-12-0607) and NSF (DMR-1206915 and PHY-1104660). Development and maintenance of the growth facilities used for fabricating samples is sup- ported by DOE (DE-FG02-03ER46028). This research utilized NSF-supported shared facilities at the University of Wisconsin-Madison.
Black, B.E. |
1993-07-01
Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) techniques have been very successful in obtaining molecular conformation and dynamics information. Unfortunately, standard NMR and NQR spectrometers are unable to adequately detect resonances below a few megahertz due to the frequency dependent sensitivity of their Faraday coil detectors. For this reason a new spectrometer with a dc SQUID (Superconducting Quantum Interference Device) detector, which has no such frequency dependence, has been developed. Previously, this spectrometer was used to observe {sup 11}B and {sup 27}Al NQR resonances. The scope of this study was increased to include {sup 23}Na, {sup 51}V, and {sup 55}Mn NQR transitions. Also, a technique was presented to observe {sup 14}N NQR resonances through cross relaxation of the nitrogen polarization to adjacent proton spins. When the proton Zeeman splitting matches one nitrogen quadrupoler transition the remaining two {sup 14}N transitions can be detected by sweeping a saturating rf field through resonance. Additionally, simultaneous excitation of two nitrogen resonances provides signal enhancement which helps to connect transitions from the same site. In this way, nitrogen-14 resonances were observed in several amino acids and polypeptides. This spectrometer has also been useful in the direct detection of methyl quantum tunneling splittings at 4.2 K. Tunneling, frequencies of a homologous series of carboxylic acids were measured and for solids with equivalent crystal structures, an exponential correlation between the tunneling frequency and the enthalpy of fusion is observed. This correlation provides information about the contribution of intermolecular interactions to the energy barrier for methyl rotation.
Tunable lateral tunnel coupling between two self-assembled InGaAs quantum dots
NASA Astrophysics Data System (ADS)
Beirne, Gareth J.; Hermannstädter, Claus; Wang, Lijuan; Rastelli, Armando; Müller, Elisabeth; Schmidt, Oliver G.; Michler, Peter
2007-02-01
We demonstrate direct control over the level of lateral quantum coupling between two self-assembled InGaAs/GaAs quantum dots. This coupled system, which we also refer to as a lateral quantum dot molecule, was produced using a unique technique which combines molecular beam epitaxy and in-situ atomic layer etching. Atomic force microscopy measurements show that each molecule consists of two structurally distinct dots, which are aligned along the [1-10] direction. Each molecule exhibits a characteristic photoluminescence spectrum primarily consisting of two neutral excitonic and two biexcitonic transitions. The various transitions have been investigated using micro-photoluminescence measurements as a function of excitation power density, time, and applied electric field. Photon statistics experiments between the excitonic emission lines display strong antibunching in the second-order cross-correlation function which confirms that the two dots are quantum coupled. Cascaded emission between corresponding biexcitonic and excitonic emission has also been observed. Using a parallel electric field we can control the quantum coupling between the dots. This control manifests itself as an ability to reversibly switch the relative intensities of the two neutral excitonic transitions. Furthermore, detailed studies of the emission energies of the two neutral excitonic transitions as a function of parallel lateral electric field show a clear anomalous Stark shift which further demonstrates the presence of quantum coupling between the dots. In addition, this shift allows for a reasonable estimate of the coupling energy. Finally, a simple one-dimensional model, which assumes that the coupling is due to electron tunneling, is used to qualitatively describe the observed effects.
Trezza, M.; Cirillo, C.; Sabatino, P.; Carapella, G.; Attanasio, C.; Prischepa, S. L.
2013-12-16
We report on the transport properties of an array of N∼30 interconnected Nb nanowires, grown by sputtering on robust porous Si substrates. The analyzed system exhibits a broad resistive transition in zero magnetic field, H, and highly nonlinear V(I) characteristics as a function of H, which can be both consistently described by quantum tunneling of phase slips.
Quantum mechanical solver for confined heterostructure tunnel field-effect transistors
Verreck, Devin Groeseneken, Guido; Van de Put, Maarten; Sorée, Bart; Magnus, Wim; Verhulst, Anne S.; Collaert, Nadine; Thean, Aaron; Vandenberghe, William G.
2014-02-07
Heterostructure tunnel field-effect transistors (HTFET) are promising candidates for low-power applications in future technology nodes, as they are predicted to offer high on-currents, combined with a sub-60 mV/dec subthreshold swing. However, the effects of important quantum mechanical phenomena like size confinement at the heterojunction are not well understood, due to the theoretical and computational difficulties in modeling realistic heterostructures. We therefore present a ballistic quantum transport formalism, combining a novel envelope function approach for semiconductor heterostructures with the multiband quantum transmitting boundary method, which we extend to 2D potentials. We demonstrate an implementation of a 2-band version of the formalism and apply it to study confinement in realistic heterostructure diodes and p-n-i-n HTFETs. For the diodes, both transmission probabilities and current densities are found to decrease with stronger confinement. For the p-n-i-n HTFETs, the improved gate control is found to counteract the deterioration due to confinement.
Photon assisted tunneling through three quantum dots with spin-orbit-coupling
Tang, Han-Zhao; An, Xing-Tao; Wang, Ai-Kun; Liu, Jian-Jun
2014-08-14
The effect of an ac electric field on quantum transport properties in a system of three quantum dots, two of which are connected in parallel, while the third is coupled to one of the other two, is investigated theoretically. Based on the Keldysh nonequilibrium Green's function method, the spin-dependent current, occupation number, and spin accumulation can be obtained in our model. An external magnetic flux, Rashba spin-orbit-coupling (SOC), and intradot Coulomb interactions are considered. The magnitude of the spin-dependent average current and the positions of the photon assisted tunneling (PAT) peaks can be accurately controlled and manipulated by simply varying the strength of the coupling and the frequency of the ac field. A particularly interesting result is the observation of a new kind of PAT peak and a multiple-PAT effect that can be generated and controlled by the coupling between the quantum dots. In addition, the spin occupation number and spin accumulation can be well controlled by the Rashba SOC and the magnetic flux.
Transport through an impurity tunnel coupled to a Si/SiGe quantum dot
NASA Astrophysics Data System (ADS)
Foote, Ryan H.; Ward, Daniel R.; Prance, J. R.; Gamble, John King; Nielsen, Erik; Thorgrimsson, Brandur; Savage, D. E.; Saraiva, A. L.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.
Here we present measurements of transport through a gate-defined quantum dot formed in a Si/SiGe heterostructure, demonstrating controllable tunnel coupling between the quantum dot and a localized electronic state.1 Combining experimental stability diagram measurements with 3D capacitive modeling based on the expected electron density profiles, we determine the most likely location of the localized state in the quantum well. This work is supported in part by NSF (DMR-1206915, IIA-1132804), ARO (W911NF-12-1-0607) and the William F. Vilas Estate Trust. Development and maintenance of the growth facilities used for fabricating samples supported by DOE (DE-FG02-03ER46028). This research utilized facilities supported by the NSF (DMR-0832760, DMR-1121288). The work of J.K.G. and E.N. was supported in part by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. 1Ryan H. Foote et al., Appl. Phys. Lett. 107, 103112 (2015)
NASA Astrophysics Data System (ADS)
Medvedev, Igor G.
2009-07-01
Pronounced effects of the interdot Coulomb repulsion on the tunnel current/gate voltage dependence at the ambient conditions are predicted for the double quantum dot system in the serial configuration immersed in the electrolyte solution in the case of the weak tunneling of electrons both between the dots and between the dots and leads. Electrons at the dots are coupled strongly to the classical phonon modes and Debye screening of the electric field is taken into account. The infinite intradot Coulomb repulsion limit is used. The effects consist of (i) a very large width of the maximum of the tunnel current/gate voltage dependence [of the order of -kBTln(k0/k) , where k0 and k are the characteristic rates of the electron tunneling between the dots and between the dots and leads, respectively] in the limit k0/k→0 , (ii) the dependence of the positions of the maxima of the current/gate voltage curve and their widths on the sign of the difference of the electron energy levels δ of the quantum dots and the energy of the polaron shift, and (iii) narrow-width Coulomb blockade peaks in the tunnel current/gate voltage curve for k0≥k . The dependence of the differential conductance on the gate voltage, the energy of the interdot Coulomb repulsion, the Debye screening length, and values of k0/k and δ are studied. It is shown that the curves of the differential conductance/bias voltage dependence can be very different for different values of these parameters. These parameters also determine the position of the regions of the negative differential conductance which exist in the general case.
Beirne, G J; Hermannstädter, C; Wang, L; Rastelli, A; Schmidt, O G; Michler, P
2006-04-01
Lateral quantum coupling between two self-assembled (In,Ga)As quantum dots has been observed. Photon statistics measurements between the various excitonic and biexcitonic transitions of these lateral quantum dot molecules display strong antibunching confirming the presence of coupling. Furthermore, we observe an anomalous exciton Stark shift with respect to static electric field. A simple model indicates that the lateral coupling is due to electron tunneling between the dots when the ground states are in resonance. The electron probability can then be shifted to either dot and the system can be used to create a wavelength-tunable single-photon emitter by simply applying a voltage. PMID:16712031
NASA Astrophysics Data System (ADS)
Beirne, G. J.; Hermannstädter, C.; Wang, L.; Rastelli, A.; Schmidt, O. G.; Michler, P.
2006-04-01
Lateral quantum coupling between two self-assembled (In,Ga)As quantum dots has been observed. Photon statistics measurements between the various excitonic and biexcitonic transitions of these lateral quantum dot molecules display strong antibunching confirming the presence of coupling. Furthermore, we observe an anomalous exciton Stark shift with respect to static electric field. A simple model indicates that the lateral coupling is due to electron tunneling between the dots when the ground states are in resonance. The electron probability can then be shifted to either dot and the system can be used to create a wavelength-tunable single-photon emitter by simply applying a voltage.
Tunnelling of the 3rd kind: A test of the effective non-locality of quantum field theory
NASA Astrophysics Data System (ADS)
Gardiner, Simon A.; Gies, Holger; Jaeckel, Joerg; Wallace, Chris J.
2013-03-01
Integrating out virtual quantum fluctuations in an originally local quantum field theory results in an effective theory which is non-local. In this letter we argue that tunnelling of the 3rd kind —where particles traverse a barrier by splitting into a pair of virtual particles which recombine only after a finite distance— provides a direct test of this non-locality. We sketch a quantum-optical setup to test this effect, and investigate observable effects in a simple toy model.
Lyo, S.K.; Harff, N.E.; Simmons, J.A.
1998-07-01
We present a linear-response theory of magneto-quantum-resistance oscillations of the in-plane resistances R{sub xx} and R{sub yy} in two coupled quasi-two-dimensional electron layers in tilted magnetic fields {bold B}=(B{sub {parallel}},B{sub {perpendicular}}), and explain recent data from GaAs/Al{sub x}Ga{sub 1{minus}x}As double quantum wells. In this system, the electrons are in the two tunnel-split ground sublevels. The cyclotron masses of the two orbits on the Fermi surface have opposite dependences on the in-plane field B{sub {parallel}}: one increases monotonically, while the other decreases as a function of B{sub {parallel}} in the regime of interest. As a result, the rungs of one Landau ladder sweep up through the Fermi level, while those of the other Landau ladder sweep down when B{sub {parallel}} is increased at a fixed perpendicular field B{sub {perpendicular}}. Ridges are obtained in the three-dimensional plots of both R{sub xx} and R{sub yy} and the density of states versus (B{sub {parallel}},B{sub {perpendicular}}) due to Fermi-level crossing by the rungs of the Landau ladders. Giant peaks are obtained when two ridges intersect each other. The (B{sub {parallel}},B{sub {perpendicular}}) dependence of R{sub xx} as well as theoretical evidence of magnetic breakdown yields good agreement with recent data from GaAs/Al{sub x}Ga{sub 1{minus}x}As double quantum wells. {copyright} {ital 1998} {ital The American Physical Society}
Photon-assisted tunneling and charge dephasing in a carbon nanotube double quantum dot
NASA Astrophysics Data System (ADS)
Mavalankar, A.; Pei, T.; Gauger, E. M.; Warner, J. H.; Briggs, G. A. D.; Laird, E. A.
2016-06-01
We report microwave-driven photon-assisted tunneling in a suspended carbon nanotube double quantum dot. From the resonant linewidth at a temperature of 13 mK, the charge-dephasing time is determined to be 280 ±30 ps. The linewidth is independent of driving frequency, but increases with increasing temperature. The moderate temperature dependence is inconsistent with expectations from electron-phonon coupling alone, but consistent with charge noise arising in the device. The extracted level of charge noise is comparable with that expected from previous measurements of a valley-spin qubit, where it was hypothesized to be the main cause of qubit decoherence. Our results suggest a possible route towards improved valley-spin qubits.
Modulation bandwidth of a double tunnelling-injection quantum dot laser
NASA Astrophysics Data System (ADS)
Asryan, Levon V.
2015-03-01
The modulation response of a double tunnelling-injection (DTI) quantum dot (QD) laser is studied. Closed-form expressions are obtained for the dynamic characteristics of the laser and the upper limit for the modulation bandwidth is estimated. The optimum cavity length, surface density of QDs, and dc injection current density, maximizing the modulation bandwidth, are shown to exist. The higher the dc injection current density, the smaller should be the optimum values of the cavity length and the surface density of QDs. While the maximum bandwidth is shown to be the same in DTI and conventional QD lasers and unaffected by the differential gain, the optimum dc current density, being inversely proportional to the differential gain, is lower in a DTI laser.
NASA Astrophysics Data System (ADS)
Granata, Carmine; Vettoliere, Antonio; Fretto, Matteo; Leo, Natascia De; Vincenzo, Lacquaniti
2015-06-01
The ultra high sensitivity exhibited by Superconducting Quantum Interference Device (SQUIDs) could be the key to explore new field of nanoscience such as the investigation of small cluster of elementary magnetic moments. In this paper, an ultra high sensitive niobium nanoSQUID based on submicron Josephson tunnel junction is presented. It has been fabricated in a vertical configuration by using a three-dimensional focused ion beam sculpting technique. In such a configuration, the nanosensor loop (area of 0.25 μm2) is perpendicular to the substrate plane allowing to drastically reduce the spurious effects of the external magnetic field employed to excite the nano-objects under investigation. Main device characteristics have been measured at T=4.2 K by using a low noise readout electronics. Due to high voltage responsivity, the nanosensor has exhibited a spectral density of the magnetic flux noise as low as 1.6 μΦ0/Hz1/2.
Zheng, Hao; Xu, Su-Yang; Bian, Guang; Guo, Cheng; Chang, Guoqing; Sanchez, Daniel S; Belopolski, Ilya; Lee, Chi-Cheng; Huang, Shin-Ming; Zhang, Xiao; Sankar, Raman; Alidoust, Nasser; Chang, Tay-Rong; Wu, Fan; Neupert, Titus; Chou, Fangcheng; Jeng, Horng-Tay; Yao, Nan; Bansil, Arun; Jia, Shuang; Lin, Hsin; Hasan, M Zahid
2016-01-26
Weyl semimetals may open a new era in condensed matter physics, materials science, and nanotechnology after graphene and topological insulators. We report the first atomic scale view of the surface states of a Weyl semimetal (NbP) using scanning tunneling microscopy/spectroscopy. We observe coherent quantum interference patterns that arise from the scattering of quasiparticles near point defects on the surface. The measurements reveal the surface electronic structure both below and above the chemical potential in both real and reciprocal spaces. Moreover, the interference maps uncover the scattering processes of NbP's exotic surface states. Through comparison between experimental data and theoretical calculations, we further discover that the orbital and/or spin texture of the surface bands may suppress certain scattering channels on NbP. These results provide a comprehensive understanding of electronic properties on Weyl semimetal surfaces. PMID:26743693
Quantum analysis of shot noise suppression in a series of tunnel barriers
NASA Astrophysics Data System (ADS)
Marconcini, P.; Macucci, M.; Iannaccone, G.; Pellegrini, B.
2009-06-01
We report the results of an analysis, based on a straightforward quantum-mechanical model, of shot noise suppression in a structure containing cascaded tunneling barriers. Our results exhibit a behavior that is in sharp contrast with existing semiclassical models for this particular type of structure, which predict a limit of 1/3 for the Fano factor as the number of barriers is increased. The origin of this discrepancy is investigated and attributed to the presence of localization on the length scale of the mean free path, as a consequence of the strictly one-dimensional (1D) nature of disorder, which does not create mode mixing, while no localization appears in common semiclassical models. We expect localization to be indeed present in practical situations with prevalent 1D disorder, and the existing experimental evidence appears to be consistent with such a prediction.
Quantum tunneling of the excited rotational bands in the superdeformed nucleus 143Eu
NASA Astrophysics Data System (ADS)
Leoni, S.; Bracco, A.; Camera, F.; Million, B.; Algora, A.; Axelsson, A.; Benzoni, G.; Bergström, M.; Blasi, N.; Castoldi, M.; Frattini, S.; Gadea, A.; Herskind, B.; Kmiecik, M.; Lo Bianco, G.; Maj, A.; Nyberg, J.; Pignanelli, M.; Styczen, J.; Vigezzi, E.; Zieblinski, M.; Zucchiatti, A.
2001-01-01
The properties of the thermally excited rotational motion up to the region of rotational damping are studied experimentally in the superdeformed nucleus 143Eu. The effective lifetime of the excited discrete rotational bands forming ridge structures in /γ-/γ matrices is measured at the EUROBALL array using the DSAM technique, giving a quadrupole moment Qt~10 /eb, consistent with the deformation of the superdeformed yrast band. In addition, the effective number of excited superdeformed bands is extracted by a statistical analysis of the ridge structure, for transition energies down to the region where the effect of the decay-out into the normal deformed well shows up. The experimental data are compared with microscopic cranked shell model calculations including a residual interaction of surface delta type. Satisfactory agreement between data and theory is obtained when the quantum tunneling of the excited superdeformed states is included in the model.
Wu, Feng; Ren, Yinghui; Bian, Wensheng
2016-08-21
The accurate time-independent quantum dynamics calculations on the ground-state tunneling splitting of malonaldehyde in full dimensionality are reported for the first time. This is achieved with an efficient method developed by us. In our method, the basis functions are customized for the hydrogen transfer process which has the effect of greatly reducing the size of the final Hamiltonian matrix, and the Lanczos method and parallel strategy are used to further overcome the memory and central processing unit time bottlenecks. The obtained ground-state tunneling splitting of 24.5 cm(-1) is in excellent agreement with the benchmark value of 23.8 cm(-1) computed with the full-dimensional, multi-configurational time-dependent Hartree approach on the same potential energy surface, and we estimate that our reported value has an uncertainty of less than 0.5 cm(-1). Moreover, the role of various vibrational modes strongly coupled to the hydrogen transfer process is revealed. PMID:27544107
NASA Astrophysics Data System (ADS)
Wu, Feng; Ren, Yinghui; Bian, Wensheng
2016-08-01
The accurate time-independent quantum dynamics calculations on the ground-state tunneling splitting of malonaldehyde in full dimensionality are reported for the first time. This is achieved with an efficient method developed by us. In our method, the basis functions are customized for the hydrogen transfer process which has the effect of greatly reducing the size of the final Hamiltonian matrix, and the Lanczos method and parallel strategy are used to further overcome the memory and central processing unit time bottlenecks. The obtained ground-state tunneling splitting of 24.5 cm-1 is in excellent agreement with the benchmark value of 23.8 cm-1 computed with the full-dimensional, multi-configurational time-dependent Hartree approach on the same potential energy surface, and we estimate that our reported value has an uncertainty of less than 0.5 cm-1. Moreover, the role of various vibrational modes strongly coupled to the hydrogen transfer process is revealed.
Smets, Quentin; Verreck, Devin; Vandervorst, Wilfried; Groeseneken, Guido; Heyns, Marc M.; Verhulst, Anne S.; Rooyackers, Rita; Merckling, Clément; Simoen, Eddy; Collaert, Nadine; Thean, Voon Y.; Van De Put, Maarten; Sorée, Bart
2014-05-14
Promising predictions are made for III-V tunnel-field-effect transistor (FET), but there is still uncertainty on the parameters used in the band-to-band tunneling models. Therefore, two simulators are calibrated in this paper; the first one uses a semi-classical tunneling model based on Kane's formalism, and the second one is a quantum mechanical simulator implemented with an envelope function formalism. The calibration is done for In{sub 0.53}Ga{sub 0.47}As using several p+/intrinsic/n+ diodes with different intrinsic region thicknesses. The dopant profile is determined by SIMS and capacitance-voltage measurements. Error bars are used based on statistical and systematic uncertainties in the measurement techniques. The obtained parameters are in close agreement with theoretically predicted values and validate the semi-classical and quantum mechanical models. Finally, the models are applied to predict the input characteristics of In{sub 0.53}Ga{sub 0.47}As n- and p-lineTFET, with the n-lineTFET showing competitive performance compared to MOSFET.
Field electron emission based on resonant tunneling in diamond/CoSi2/Si quantum well nanostructures
Gu, Changzhi; Jiang, Xin; Lu, Wengang; Li, Junjie; Mantl, Siegfried
2012-01-01
Excellent field electron emission properties of a diamond/CoSi2/Si quantum well nanostructure are observed. The novel quantum well structure consists of high quality diamond emitters grown on bulk Si substrate with a nanosized epitaxial CoSi2 conducting interlayer. The results show that the main emission properties were modified by varying the CoSi2 thickness and that stable, low-field, high emission current and controlled electron emission can be obtained by using a high quality diamond film and a thicker CoSi2 interlayer. An electron resonant tunneling mechanism in this quantum well structure is suggested, and the tunneling is due to the long electron mean free path in the nanosized CoSi2 layer. This structure meets most of the requirements for development of vacuum micro/nanoelectronic devices and large-area cold cathodes for flat-panel displays. PMID:23082241
Growden, Tyler A.; Berger, Paul R.; Brown, E. R.; Zhang, Weidong; Droopad, Ravi
2015-10-12
An experimental determination is presented of the effect the quantum-well lifetime has on a large-signal resonant tunneling diode (RTD) switching time. Traditional vertical In{sub 0.53}Ga{sub 0.47}As/AlAs RTDs were grown, fabricated, and characterized. The switching time was measured with a high-speed oscilloscope and found to be close to the sum of the calculated RC-limited 10%–90% switching time and the quantum-well quasibound-state lifetime. This method displays experimental evidence that the two intrinsic resonant-tunneling characteristic times act independently, and that the quasibound-state lifetime then serves as a quantum-limit on the large-signal speed of RTDs.
NASA Astrophysics Data System (ADS)
Growden, Tyler A.; Brown, E. R.; Zhang, Weidong; Droopad, Ravi; Berger, Paul R.
2015-10-01
An experimental determination is presented of the effect the quantum-well lifetime has on a large-signal resonant tunneling diode (RTD) switching time. Traditional vertical In0.53Ga0.47As/AlAs RTDs were grown, fabricated, and characterized. The switching time was measured with a high-speed oscilloscope and found to be close to the sum of the calculated RC-limited 10%-90% switching time and the quantum-well quasibound-state lifetime. This method displays experimental evidence that the two intrinsic resonant-tunneling characteristic times act independently, and that the quasibound-state lifetime then serves as a quantum-limit on the large-signal speed of RTDs.
Magnetic Quantum Tunneling in Single Molecule Magnets: Mn-12 and Others
NASA Astrophysics Data System (ADS)
del Barco, Enrique
2004-03-01
Magnetic quantum tunneling (MQT) has been studied in single molecule magnets (SMMs) using a micro-Hall effect magnetometer in a superconducting high field vector magnet system that incorporates the possibility of applying pulsed microwave fields. Mn_12-acetate has been studied extensively over the years. However, only recently the symmetry of MQT and the nature of the transverse interactions important to MQT have been determined [1,2]. Magnetic measurements in the pure quantum tunneling regime (0.6 K) illustrate that an average crystal fourfold MQT symmetry is due to local molecular environments of twofold symmetry that are rotated by 90 degrees with respect to one another, confirming that disorder which lowers the molecule symmetry is important to MQT. We have studied a subset of these lower site symmetry molecules and present evidence for a Berry phase that results from a combination of second and forth order contributions to the transverse magnetic anisotropy. These observations are consistent with high frequency EPR studies of the transverse interactions in Mn_12-acetate [3]. Finally, we discuss recent experiments in which microwave radiation is applied to modulate MQT and characterize the lifetimes and coherence times of states that are superpositions of "up" and "down" high spin-projections. [1] E. del Barco, et al., Phys. Rev. Lett. 91, 047203 (2003) [2] S. Hill, et al., Phys. Rev. Lett. 90, 217204 (2003). [3] E. del Barco, A, D. Kent, R. S. Edwards, S. I. Jones, S. Hill, J. M. North, N. S. Dalal, E. M. Rumnberger, D. N. Hendrickson and G. Christou, to be published.
Magnetic quantum tunneling: key insights from multi-dimensional high-field EPR.
Lawrence, J; Yang, E-C; Hendrickson, D N; Hill, S
2009-08-21
Multi-dimensional high-field/frequency electron paramagnetic resonance (HFEPR) spectroscopy is performed on single-crystals of the high-symmetry spin S = 4 tetranuclear single-molecule magnet (SMM) [Ni(hmp)(dmb)Cl](4), where hmp(-) is the anion of 2-hydroxymethylpyridine and dmb is 3,3-dimethyl-1-butanol. Measurements performed as a function of the applied magnetic field strength and its orientation within the hard-plane reveal the four-fold behavior associated with the fourth order transverse zero-field splitting (ZFS) interaction, (1/2)B(S + S), within the framework of a rigid spin approximation (with S = 4). This ZFS interaction mixes the m(s) = +/-4 ground states in second order of perturbation, generating a sizeable (12 MHz) tunnel splitting, which explains the fast magnetic quantum tunneling in this SMM. Meanwhile, multi-frequency measurements performed with the field parallel to the easy-axis reveal HFEPR transitions associated with excited spin multiplets (S < 4). Analysis of the temperature dependence of the intensities of these transitions enables determination of the isotropic Heisenberg exchange constant, J = -6.0 cm(-1), which couples the four spin s = 1 Ni(II) ions within the cluster, as well as a characterization of the ZFS within excited states. The combined experimental studies support recent work indicating that the fourth order anisotropy associated with the S = 4 state originates from second order ZFS interactions associated with the individual Ni(II) centers, but only as a result of higher-order processes that occur via S-mixing between the ground state and higher-lying (S < 4) spin multiplets. We argue that this S-mixing plays an important role in the low-temperature quantum dynamics associated with many other well known SMMs.
Carrier-tunneling-induced photovoltaic effect of InAs/GaAs quantum-dot solar cells
NASA Astrophysics Data System (ADS)
Lee, Seung Hyun; Kim, Jong Su; Lee, Sang Jun
2016-08-01
This study reports the observation of the carrier-tunneling-induced photovoltaic (PV) effect in an InAs/GaAs quantum-dot solar cell (QDSC). The illuminated current-voltage (J-V) characteristics and the applied-bias-dependent electroreflectance (ER) were measured at 12 K by using an excitation laser with a wavelength of 975 nm (1.27 eV), which excites only the quantum-dot (QD) states below the GaAs band gap. The J-V results showed a peculiar current curve in the reverse bias region caused by carrier tunneling. The ER results showed that the junction electric field ( F) decreased with increasing intensity of the excitation laser ( I ex ) at different applied-bias-voltages ( V a ) due to the tunneling-induced PV effect. The PV effect was enhanced by improved tunneling with increasing reverse bias voltage. We also evaluated the tunneling carrier density ( σ pv ) as a function of V a in the QDSC.
Yamazaki, Shiro; Maeda, Keisuke; Sugimoto, Yoshiaki; Abe, Masayuki; Zobač, Vladimír; Pou, Pablo; Rodrigo, Lucia; Mutombo, Pingo; Pérez, Ruben; Jelínek, Pavel; Morita, Seizo
2015-07-01
We assemble bistable silicon quantum dots consisting of four buckled atoms (Si4-QD) using atom manipulation. We demonstrate two competing atom switching mechanisms, downward switching induced by tunneling current of scanning tunneling microscopy (STM) and opposite upward switching induced by atomic force of atomic force microscopy (AFM). Simultaneous application of competing current and force allows us to tune switching direction continuously. Assembly of the few-atom Si-QDs and controlling their states using versatile combined AFM/STM will contribute to further miniaturization of nanodevices.
Improved performance of GaAs tunnel diode by embedding InAs quantum dot layer for tandem solar cells
NASA Astrophysics Data System (ADS)
Park, Kwang Wook; Kang, Seok Jin; Ravindran, Sooraj; Min, Jung Wook; Lee, Soo Kyung; Park, Min Su; Tak Lee, Yong
2015-06-01
GaAs tunnel diodes (TDs) embedded with an InAs quantum dot (QD) layer were grown and their performance was compared with that of TDs without a QD layer. The TDs embedded with a QD layer showed enhanced peak tunnel current density and lower differential resistivity at zero bias compared with the TDs without a QD layer. The samples were then annealed to mimic the overlayer growth process. It was found that the performance degradation after annealing was smaller for the QD-layer-embedded TDs. The improved characteristics of the QD-layer-embedded GaAs TDs make them advantageous for interconnecting unit cells in tandem solar cells.
Arrhenius-kinetics evidence for quantum tunneling in microbial “social” decision rates
2010-01-01
. Nonlinear Arrhenius kinetics in ciliate decision making suggest transitions from one signaling strategy to another result from a computational analogue of quantum tunneling in social information processing. PMID:21331234
Arrhenius-kinetics evidence for quantum tunneling in microbial "social" decision rates.
Clark, Kevin B
2010-11-01
. Nonlinear Arrhenius kinetics in ciliate decision making suggest transitions from one signaling strategy to another result from a computational analogue of quantum tunneling in social information processing.
NASA Astrophysics Data System (ADS)
Osborne, M. A.; Fisher, A. A. E.
2016-07-01
Correction for `Charge-tunnelling and self-trapping: common origins for blinking, grey-state emission and photoluminescence enhancement in semiconductor quantum dots' by M. A. Osborne, et al., Nanoscale, 2016, 8, 9272-9283.
NASA Astrophysics Data System (ADS)
Feng, Zhong-Wen; Deng, Juan; Li, Guo-Ping; Yang, Shu-Zheng
2012-10-01
In this paper, the quantum tunneling of the non-stationary Kerr-Newman black hole is investigated via Hamilton-Jacobi equation and two types of general tortoise coordinate transformations. The tunneling rates, the Hawking temperatures and radiation spectrums are derived respectively. Our result shows that the new type of general tortoise coordinate transformation is more reasonable.
NASA Astrophysics Data System (ADS)
Hermannstädter, C.; Beirne, G. J.; Witzany, M.; Heldmaier, M.; Peng, J.; Bester, G.; Wang, L.; Rastelli, A.; Schmidt, O. G.; Michler, P.
2010-08-01
We report on the charge carrier dynamics in single lateral quantum dot molecules and the effect of an applied electric field on the molecular states. Controllable electron tunneling manifests itself in a deviation from the typical excitonic decay behavior in dot molecules. It results in a faster population decay and can be strongly influenced by the tuning electric field and intermolecular Coulomb energies. A rate equation model is developed and compared to the experimental data to gain more insight into the charge transfer and tunneling mechanisms. Nonresonant (phonon-mediated) electron tunneling which changes the molecular exciton character from direct to indirect, and vice versa, is found to be the dominant tunable decay mechanism of excitons besides radiative recombination.
Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots
NASA Astrophysics Data System (ADS)
Wang, H.; Lhuillier, E.; Yu, Q.; Mottaghizadeh, A.; Ulysse, C.; Zimmers, A.; Descamps-Mandine, A.; Dubertret, B.; Aubin, H.
2015-07-01
We present a tunnel spectroscopy study of single PbS quantum dots (QDs) as a function of temperature and gate voltage. Three distinct signatures of strong electron-phonon coupling are observed in the electron tunneling spectrum (ETS) of these QDs. In the shell-filling regime, the 8 × degeneracy of the electronic levels is lifted by the Coulomb interactions and allows the observation of phonon subbands that result from the emission of optical phonons. At low bias, a gap is observed in the ETS that cannot be closed with the gate voltage, which is a distinguishing feature of the Franck-Condon blockade. From the data, a Huang-Rhys factor in the range S ˜1.7 -2.5 is obtained. Finally, in the shell-tunneling regime, the optical phonons appear in the inelastic ETS d2I /d V2 .
A comparison of the photocatalytic activity of six tunneled titanates
Sanford, Stephen; Misture, Scott T.; Edwards, Doreen D.
2013-04-15
The photocatalytic behavior of six tunneled titanates—Na{sub 0.7}Ga{sub 4.7}Ti{sub 0.3}O{sub 8}, Na{sub 0.8}Ga{sub 4.8}Ti{sub 1.2}O{sub 10}, Na{sub 0.8}Ga{sub 4.8}Ti{sub 2.2}O{sub 12}, K{sub 1}Ga{sub 17}Ti{sub 15}O{sub 56}, K{sub 1.5}Ga{sub 1.5}Ti{sub 6.5}O{sub 16}, and BaTi{sub 4}O{sub 9}—was investigated using methylene blue as an indicator and a xenon arc lamp as the radiation source. Powders prepared by solid state reaction had surface areas ranging from 0.40 to 1.58 m{sup 2}/g and particle sizes ranging from 1 to 25 μm. Bandgaps, as measured from diffuse reflectance data, ranged from 2.84 to 4.15 eV. Two of the tunneled titanates—Na{sub 0.8}Ga{sub 4.8}Ti{sub 1.2}O{sub 10} and Na{sub 0.7}Ga{sub 4.7}Ti{sub 0.3}O{sub 8}—exhibited negligible photocatalytic activity. The activities of Na{sub 0.8}Ga{sub 4.8}Ti{sub 2.2}O{sub 12}, KGa{sub 17}Ti{sub 15}O{sub 56}, and K{sub 1.5}Ga{sub 1.5}Ti{sub 6.5}O{sub 16} were similar to each other, exhibiting apparent first-order reaction rates of 0.275 to 0.31 h{sup −1} using 100 mg of powder in 125 ml of 20 μM methylene blue at room temperature. The BaTi{sub 4}O{sub 9} sample exhibited the highest photocatalytic activity with an apparent first-order reaction rate of 0.53 h{sup −1} under the same conditions. The addition of a RuO{sub 2} co-catalyst improved the photocatalytic activity of Na{sub 0.7}Ga{sub 4.7}Ti{sub 0.3}O{sub 8}, decreased the activity of BaTi{sub 4}O{sub 9}, and had little effect on the activity of the other powders. A comparison of the structural features in the six materials shows that photocatalytic activity is strongly related to the density of TiO{sub 6} octahedra in the different crystal structures. Among the gallium-containing tunneled titanates, photocatalytic activity increased with decreasing band gap. - Graphical abstract: Na{sub 0.7}Ga{sub 4.7}Ti{sub 0.3}O{sub 8}—One of the tunneled titanates investigated. Highlights: ► The photocatalytic activity of six tunneled titanates was
Tuning inter-dot tunnel coupling of an etched graphene double quantum dot by adjacent metal gates
Wei, Da; Li, Hai-Ou; Cao, Gang; Luo, Gang; Zheng, Zhi-Xiong; Tu, Tao; Xiao, Ming; Guo, Guang-Can; Jiang, Hong-Wen; Guo, Guo-Ping
2013-01-01
Graphene double quantum dots (DQDs) open to use charge or spin degrees of freedom for storing and manipulating quantum information in this new electronic material. However, impurities and edge disorders in etched graphene nano-structures hinder the ability to control the inter-dot tunnel coupling, tC, the most important property of the artificial molecule. Here we report measurements of tC in an all-metal-side-gated graphene DQD. We find that tC can be controlled continuously about a factor of four by employing a single gate. Furthermore, tC, can be changed monotonically about another factor of four as electrons are gate-pumped into the dot one by one. The results suggest that the strength of tunnel coupling in etched graphene DQDs can be varied in a rather broad range and in a controllable manner, which improves the outlook to use graphene as a base material for qubit applications. PMID:24213723
Conte, Riccardo; Aspuru-Guzik, Alán; Ceotto, Michele
2013-10-17
A time-dependent semiclassical approach for vibrational spectra calculations is shown to describe deep tunneling splittings, resonances, and quantum frequencies in multidimensional multiwell systems, by propagating a very limited number of classical trajectories. The approach is tested on ammonia by evolving eight trajectories on a full-dimensional PES. Quantum effects are reproduced, and results are in good agreement with time-independent quantum calculations. All the features are maintained when ab initio "on-the-fly" dynamics is adopted, thus demonstrating that precomputation of the PES can be avoided. The approach overcomes the typical scaling issues of quantum mechanical techniques without introducing any simplifications nor reductions of dimensionality of the problem. The proposed methodology is promising for further applications to systems of major complexity. PMID:26705583
Fermions Tunnelling from Black String and Kerr AdS Black Hole with Consideration of Quantum Gravity
NASA Astrophysics Data System (ADS)
Li, Zhong-hua; Zhang, Li-mei
2016-01-01
In this paper, using the Hamilton-Jacobi Ansatz, we discuss the tunnelling of fermions when effects of quantum gravity are taken into account. We investigate two cases, black string and Kerr AdS black hole. For black string, the uncharged and un-rotating case, we find that the correction of Hawking temperature is only affected by the mass of emitted fermions and the quantum gravitational corrections slow down the increases of the temperature, which naturally leads to remnants left in the evaporation. For another case, the Kerr AdS black hole, we find that the quantum gravitational corrections are not only determined by the mass of the emitted fermions but also affected by the rotating properties of the AdS black hole. So with consideration of the quantum gravity corrections, an offset around the standard temperature always exists.
NASA Astrophysics Data System (ADS)
Seabaugh, A. C.; Kao, Y.-C.; Frensley, W. R.; Randall, J. N.; Reed, M. A.
1991-12-01
A new transistor effect is demonstrated in a 120-nm base, bipolar quantum-well, resonant-tunneling transistor (BiQuaRTT). In this BiQuaRTT, a strong, multiple negative differential resistance (NDR) characteristic is obtained at room temperature with high-current gain. The effect is shown to be the consequence of an asymmetric, quantum-well-base heterostructure whose shape is controlled by the base/collector bias. Changes in the quantum-well shape lead to large modulations of the transmission coefficient for quasi-thermalized minority electrons crossing the quantum-well base. In this letter, the transport characteristics of these transistors are described, including also temperature and magnetic field dependence.
NASA Astrophysics Data System (ADS)
Jiang, Xiang-Wei; Li, Shu-Shen
2012-02-01
By using the linear combination of bulk band (LCBB) method incorporated with the top of the barrier splitting (TBS) model, we present a comprehensive study on the quantum confinement effects and the source-to-drain tunneling in the ultra-scaled double-gate (DG) metal—oxide—semiconductor field-effect transistors (MOSFETs). A critical body thickness value of 5 nm is found, below which severe valley splittings among different X valleys for the occupied charge density and the current contributions occur in ultra-thin silicon body structures. It is also found that the tunneling current could be nearly 100% with an ultra-scaled channel length. Different from the previous simulation results, it is found that the source-to-drain tunneling could be effectively suppressed in the ultra-thin body thickness (2.0 nm and below) by the quantum confinement and the tunneling could be suppressed down to below 5% when the channel length approaches 16 nm regardless of the body thickness.
NASA Astrophysics Data System (ADS)
Pillet, J.-D.; Joyez, P.; Žitko, Rok; Goffman, M. F.
2013-07-01
We performed tunneling spectroscopy of a carbon nanotube quantum dot (QD) coupled to a metallic reservoir either in the normal or in the superconducting state. We explore how the Kondo resonance, observed when the QD's occupancy is odd and the reservoir is normal, evolves towards Andreev bound states (ABS) in the superconducting state. Within this regime, the ABS spectrum observed is consistent with a quantum phase transition from a singlet to a degenerate magnetic doublet ground state, in quantitative agreement with a single-level Anderson model with superconducting leads.
NASA Astrophysics Data System (ADS)
Fain, B.; Robert-Philip, I.; Beveratos, A.; David, C.; Wang, Z. Z.; Sagnes, I.; Girard, J. C.
2012-03-01
The topography and the electronic structure of InAsP/InP quantum dots are probed by cross-sectional scanning tunneling microscopy and spectroscopy. The study of the local density of states in such large quantum dots confirms the discrete nature of the electronic levels whose wave functions are measured by differential conductivity mapping. Because of their large dimensions, the energy separation between the discrete electronic levels is low, allowing for quantization in both the lateral and growth directions as well as the observation of the harmonicity of the dot lateral potential.
Fain, B; Robert-Philip, I; Beveratos, A; David, C; Wang, Z Z; Sagnes, I; Girard, J C
2012-03-23
The topography and the electronic structure of InAsP/InP quantum dots are probed by cross-sectional scanning tunneling microscopy and spectroscopy. The study of the local density of states in such large quantum dots confirms the discrete nature of the electronic levels whose wave functions are measured by differential conductivity mapping. Because of their large dimensions, the energy separation between the discrete electronic levels is low, allowing for quantization in both the lateral and growth directions as well as the observation of the harmonicity of the dot lateral potential.
Electron tunnelling through azurin is mediated by the active site Cu ion
NASA Astrophysics Data System (ADS)
Alessandrini, Andrea; Gerunda, Mimmo; Canters, G. W.; Verbeet, M. Ph.; Facci, Paolo
2003-07-01
Cu- and Zn-azurin chemisorbed on Au(1 1 1) have been comparatively investigated by electrochemical scanning tunnelling microscopy in buffer solution. Cu-azurin shows a marked tunnelling current resonance upon substrate potential at -0.21 V (vs SCE), whereas Zn counterparts do not. These data, discussed in terms of current theories on electron tunnelling through redox adsorbates, demonstrate the role of the electroactive metal ion present in the active site in assisting electron transfer via this metalloprotein.
Jiang, Yan; Zhang, Xing; Ge, Qian-Qing; Yu, Bin-Bin; Zou, Yu-Gang; Jiang, Wen-Jie; Song, Wei-Guo; Wan, Li-Jun; Hu, Jin-Song
2014-01-01
Quantum-dot-sensitized solar cell (QDSSC) has been considered as an alternative to new generation photovoltaics, but it still presents very low power conversion efficiency. Besides the continuous effort on improving photoanodes and electrolytes, the focused investigation on charge transfer at interfaces and the rational design for counter electrodes (CEs) are recently receiving much attention. Herein, core-shell nanowire arrays with tin-doped indium oxide (ITO) nanowire core and Cu2S nanocrystal shell (ITO@Cu2S) were dedicatedly designed and fabricated as new efficient CEs for QDSSCs in order to improve charge collection and transport and to avoid the intrinsic issue of copper dissolution in popular and most efficient Cu/Cu2S CEs. The high-quality tunnel junctions formed between n-type ITO nanowires and p-type Cu2S nanocrystals led to the considerable decrease in sheet resistance and charge transfer resistance and thus facilitated the electron transport during the operation of QDSSCs. The three-dimensional structure of nanowire arrays provided high surface area for more active catalytic sites and easy accessibility for an electrolyte. As a result, the power conversion efficiency of QDSSCs with the designed ITO@Cu2S CEs increased by 84.5 and 33.5% compared to that with planar Au and Cu2S CEs, respectively.
NASA Astrophysics Data System (ADS)
Kakeya, I.; Hamada, K.; Tachiki, T.; Watanabe, T.; Suzuki, M.
2009-11-01
The current-voltage characteristics and switching dynamics are studied in over-doped (Pb,Bi)2Sr2CaCu2O8+δ (PbBi2212) and Bi2Sr2Ca2Cu3O10+δ (Bi2223) mesa structures containing a few atomic-scale intrinsic Josephson junctions (IJJ) along the c axis. The cleave-in-vacuum method enables us to avoid the contact problems that are always accompanied by mesa structures. The highest critical current density of the zero-voltage state as Jc1 = 3.2 kA cm-2 among our micron-scale mesa structures of BSCCO cuprates are achieved. Narrowing of the switching probability distribution (SPD) due to suppression of the thermal fluctuation tends to saturate at 5 K, which is regarded as a symptom of macroscopic quantum tunneling (MQT). The crossover temperature between the MQT and the thermal escape regions is estimated as 2.2 K for the sample with the highest Jc1. In the high temperature region, another narrowing in SPD is observed that was attributed to the phase retrapping.
Polyak, Iakov; Allan, Charlotte S. M.; Worth, Graham A.
2015-08-28
We demonstrate here conclusively that the variational multiconfiguration Gaussian (vMCG) method converges to the grid based full quantum dynamics multiconfiguration time-dependent Hartree result for a tunnelling problem in many dimensions, using the intramolecular proton transfer in salicylaldimine as a model system. The 13-dimensional model potential energy surface was obtained from Hartree Fock energies with the 6-31G* basis set and the expectation value of the flux operator along the transition mode was used as a benchmark characteristic. As well as showing excellent convergence of the vMCG method on the model surface using a local harmonic approximation and a moderate number of basis functions, we show that the direct dynamics version of the vMCG also performs very well, usually needs the same number of Gaussians to converge, and converges to exact results if those are obtained on an accurately fitted surface. Finally, we make an important observation that the width of the Gaussian basis functions must be chosen very carefully to obtain accurate results with the use of the frozen-width approximation.
Tunneling behavior of ultracold atoms in optical traps
NASA Astrophysics Data System (ADS)
Wang, Binglu; Ma, Yanhua; Shen, Man; Li, Hong
2016-07-01
We investigate the tunneling of ultracold atoms in optical traps by using the path-integral method. We obtain the decay rate for tunneling out of a single-well and discuss how the rate is affected by the level splitting caused by the presence of a second adjacent well. Our calculations show that the transition through the potential barrier can be divided into three regions: the quantum tunneling region, the thermally assisted region and the thermal activation region. The tunneling process is found to be a second-order transition. We also show that level splitting due to tunneling can increase the tunneling rate.
Phase transitions in two tunnel-coupled HgTe quantum wells: Bilayer graphene analogy and beyond
Krishtopenko, S. S.; Knap, W.; Teppe, F.
2016-01-01
HgTe quantum wells possess remarkable physical properties as for instance the quantum spin Hall state and the “single-valley” analog of graphene, depending on their layer thicknesses and barrier composition. However, double HgTe quantum wells yet contain more fascinating and still unrevealed features. Here we report on the study of the quantum phase transitions in tunnel-coupled HgTe layers separated by CdTe barrier. We demonstrate that this system has a 3/2 pseudo spin degree of freedom, which features a number of particular properties associated with the spin-dependent coupling between HgTe layers. We discover a specific metal phase arising in a wide range of HgTe and CdTe layer thicknesses, in which a gapless bulk and a pair of helical edge states coexist. This phase holds some properties of bilayer graphene such as an unconventional quantum Hall effect and an electrically-tunable band gap. In this “bilayer graphene” phase, electric field opens the band gap and drives the system into the quantum spin Hall state. Furthermore, we discover a new type of quantum phase transition arising from a mutual inversion between second electron- and hole-like subbands. This work paves the way towards novel materials based on multi-layered topological insulators. PMID:27476745
Phase transitions in two tunnel-coupled HgTe quantum wells: Bilayer graphene analogy and beyond
NASA Astrophysics Data System (ADS)
Krishtopenko, S. S.; Knap, W.; Teppe, F.
2016-08-01
HgTe quantum wells possess remarkable physical properties as for instance the quantum spin Hall state and the “single-valley” analog of graphene, depending on their layer thicknesses and barrier composition. However, double HgTe quantum wells yet contain more fascinating and still unrevealed features. Here we report on the study of the quantum phase transitions in tunnel-coupled HgTe layers separated by CdTe barrier. We demonstrate that this system has a 3/2 pseudo spin degree of freedom, which features a number of particular properties associated with the spin-dependent coupling between HgTe layers. We discover a specific metal phase arising in a wide range of HgTe and CdTe layer thicknesses, in which a gapless bulk and a pair of helical edge states coexist. This phase holds some properties of bilayer graphene such as an unconventional quantum Hall effect and an electrically-tunable band gap. In this “bilayer graphene” phase, electric field opens the band gap and drives the system into the quantum spin Hall state. Furthermore, we discover a new type of quantum phase transition arising from a mutual inversion between second electron- and hole-like subbands. This work paves the way towards novel materials based on multi-layered topological insulators.
NASA Astrophysics Data System (ADS)
House, M. G.; Kobayashi, T.; Weber, B.; Hile, S. J.; Watson, T. F.; van der Heijden, J.; Rogge, S.; Simmons, M. Y.
2015-11-01
Spin states of the electrons and nuclei of phosphorus donors in silicon are strong candidates for quantum information processing applications given their excellent coherence times. Designing a scalable donor-based quantum computer will require both knowledge of the relationship between device geometry and electron tunnel couplings, and a spin readout strategy that uses minimal physical space in the device. Here we use radio frequency reflectometry to measure singlet-triplet states of a few-donor Si:P double quantum dot and demonstrate that the exchange energy can be tuned by at least two orders of magnitude, from 20 μeV to 8 meV. We measure dot-lead tunnel rates by analysis of the reflected signal and show that they change from 100 MHz to 22 GHz as the number of electrons on a quantum dot is increased from 1 to 4. These techniques present an approach for characterizing, operating and engineering scalable qubit devices based on donors in silicon.
NASA Astrophysics Data System (ADS)
Suzuki, K.; Kanisawa, K.; Perraud, S.; Ueki, M.; Takashina, K.; Hirayama, Y.
2007-04-01
The spatial distribution of the electron local density of states (LDOS) in InAs/GaSb double quantum wells (DQWs) was investigated by low-temperature scanning tunneling spectroscopy on cleaved surfaces. For DQW with a thick central barrier, clear standing wave patterns corresponding to subbands confined to each InAs single quantum well appeared in the spatial variation of LDOS spectra. In contrast, for the DQW with a thin central barrier, the standing wave patterns extended over both quantum wells. The deviation of the pattern arising from the asymmetry due to a slight difference of the well thickness appeared clearly. The observed spectra are well explained by the calculated LDOS taken to be the sum of LDOS contributed from all energetically accessible subbands.
NASA Technical Reports Server (NTRS)
Waszak, Martin R.
1998-01-01
This report describes the formulation of a model of the dynamic behavior of the Benchmark Active Controls Technology (BACT) wind tunnel model for active control design and analysis applications. The model is formed by combining the equations of motion for the BACT wind tunnel model with actuator models and a model of wind tunnel turbulence. The primary focus of this report is the development of the equations of motion from first principles by using Lagrange's equations and the principle of virtual work. A numerical form of the model is generated by making use of parameters obtained from both experiment and analysis. Comparisons between experimental and analytical data obtained from the numerical model show excellent agreement and suggest that simple coefficient-based aerodynamics are sufficient to accurately characterize the aeroelastic response of the BACT wind tunnel model. The equations of motion developed herein have been used to aid in the design and analysis of a number of flutter suppression controllers that have been successfully implemented.
Rempel, D; Manojlovic, R; Levinsohn, D G; Bloom, T; Gordon, L
1994-01-01
We investigated how repetitive hand activity normally affects carpal tunnel pressure and whether a flexible wrist splint can influence this effect. Nineteen healthy subjects were evaluated under four test conditions: at rest with and without a wrist splint (baseline) and while performing a repetitive task with and without a wrist splint. The task involved loading and unloading 1 lb. cans from a box at a rate of 20 cans per minute for period of 5 minutes. Carpal tunnel pressure and wrist angles were continuously monitored by means of a fluid-filled catheter inserted into the carpal canal and a two-channel electrogoniometer mounted on the dorsum of the hand and forearm. Without the splint, carpal tunnel pressure rose from a median baseline level of 8 +/- 6 mmHg to 18 +/- 13 mmHg during activity. With the splint, carpal tunnel pressure rose from a baseline of 13 +/- 5 mmHg to 21 +/- 12 mmHg during activity. Median carpal tunnel pressure during activity with the splint was no different from that without the splint. Our data indicate that the median nerve is subjected to increased pressure within the carpal tunnel during repetitive hand activity. Wearing a flexible wrist splint during activity limits the range of wrist motion but has no significant effect on carpal tunnel pressure.
Influence of InGaN sub-quantum-well on performance of InAlN/GaN/InAlN resonant tunneling diodes
NASA Astrophysics Data System (ADS)
Chen, Haoran; Yang, Lin'an; Hao, Yue
2014-08-01
The resonant tunneling mechanism of the GaN based resonant tunneling diode (RTD) with an InGaN sub-quantum-well has been investigated by means of numerical simulation. At resonant-state, Electrons in the InGaN/InAlN/GaN/InAlN RTD tunnel from the emitter region through the aligned discrete energy levels in the InGaN sub-quantum-well and GaN main-quantum-well into the collector region. The implantation of the InGaN sub-quantum-well alters the dominant transport mechanism, increase the transmission coefficient and give rise to the peak current and peak-to-valley current ratio. We also demonstrate that the most pronounced negative-differential-resistance characteristic can be achieved by choosing appropriately the In composition of InxGa1-xN at around x = 0.06.
Influence of InGaN sub-quantum-well on performance of InAlN/GaN/InAlN resonant tunneling diodes
Chen, Haoran; Yang, Lin'an Hao, Yue
2014-08-21
The resonant tunneling mechanism of the GaN based resonant tunneling diode (RTD) with an InGaN sub-quantum-well has been investigated by means of numerical simulation. At resonant-state, Electrons in the InGaN/InAlN/GaN/InAlN RTD tunnel from the emitter region through the aligned discrete energy levels in the InGaN sub-quantum-well and GaN main-quantum-well into the collector region. The implantation of the InGaN sub-quantum-well alters the dominant transport mechanism, increase the transmission coefficient and give rise to the peak current and peak-to-valley current ratio. We also demonstrate that the most pronounced negative-differential-resistance characteristic can be achieved by choosing appropriately the In composition of In{sub x}Ga{sub 1−x}N at around x = 0.06.
NASA Astrophysics Data System (ADS)
Smelyanskiy, Vadim; Jiang, Zhang; Boixo, Sergio; Issakov, Sergei; Mazzola, Guglielmo; Troyer, Matthias; Neven, Hartmut
We study analytically and numerically the dynamics of the quantum Monte Carlo (QMC) algorithm to simulate thermally-assisted tunneling in mean-field spin models without conservation of total spin. We use Kramers escape rate theory to calculate the scaling of the QMC time with the problem size to simulate the tunneling transitions. We develop path-integral instanton approach in coherent state and Suzuki-Trotter representations to calculate the escape rate and most probable escape path in QMC dynamics. Analtytical results are in a good agreement with numerical studies. We identify the class of models where the exponent in the scaling of the QMC time is the same as that in physical tunneling but the pre-factor depends very significantly on the QMC path representation. We propose the classes of problems where QMC can fail to simulate tunneling efficiently. The work of GM and MT has been supported by the Swiss National Science Foundation through the National Competence Center in Research QSIT and by ODNI, IARPA via MIT Lincoln Laboratory Air Force Contract No. FA8721-05-C-0002.
NASA Astrophysics Data System (ADS)
Sarkar, Deblina; Gossner, Harald; Hansch, Walter; Banerjee, Kaustav
2013-01-01
A gas-sensor based on tunnel-field-effect-transistor (TFET) is proposed that leverages the unique current injection mechanism in the form of quantum-mechanical band-to-band tunneling to achieve substantially improved performance compared to conventional metal-oxide-semiconductor field-effect-transistors (MOSFETs) for detection of gas species under ambient conditions. While nonlocal phonon-assisted tunneling model is used for detailed device simulations, in order to provide better physical insights, analytical formula for sensitivity is derived for both metal as well as organic conducting polymer based sensing elements. Analytical derivations are also presented for capturing the effects of temperature on sensor performance. Combining the developed analytical and numerical models, intricate properties of the sensor such as gate bias dependence of sensitivity, relationship between the required work-function modulation and subthreshold swing, counter-intuitive increase in threshold voltage for MOSFETs and reduction in tunneling probability for TFETs with temperature are explained. It is shown that TFET gas-sensors can not only lead to more than 10 000× increase in sensitivity but also provide design flexibility and immunity against screening of work-function modulation through non-specific gases as well as ensure stable operation under temperature variations.
Plasmons in tunnel-coupled graphene layers: Backward waves with quantum cascade gain
NASA Astrophysics Data System (ADS)
Svintsov, D.; Devizorova, Zh.; Otsuji, T.; Ryzhii, V.
2016-09-01
We theoretically demonstrate that graphene-insulator-graphene tunnel structures can serve as plasmonic gain media due to the possibility of stimulated electron tunneling accompanied by emission of plasmons under application of interlayer voltage. The probability of plasmon-assisted tunneling is resonantly large at certain values of frequency and interlayer voltage corresponding to the transitions between chiral electron states with collinear momenta, which is a feature unique to the linear bands of graphene. The plasmon dispersion develops an anticrossing with the resonances in tunnel conductivity and demonstrates negative group velocity in several frequency ranges.
Magnetotunneling spectroscopy of polarons in a quantum well of a resonant-tunneling diode
Popov, V. G. Krishtop, V. G.; Makarovskii, O. N.; Henini, M.
2010-08-15
Resonant tunneling of electrons is thoroughly studied in in-plane magnetic fields. Anticrossing is revealed in a spectrum of two-dimensional electrons at energies of optical phonons. The magnetic field changes the momentum of tunneling electrons and causes a voltage shift of a resonance in the tunnel spectra in accordance with the electron dispersion curve. Anticrossing is clearly observed in second derivative current-voltage characteristics of a resonant tunneling diode made of a double-barrier Al{sub 0.4}Ga{sub 0.6}As/GaAs heterostructure.
NASA Astrophysics Data System (ADS)
Chen, S. W.; Song, L.
2016-08-01
The fractional acoustoelectric (AE) current plateau in surface-acoustic-waves (SAW) single-electron transport devices is studied by measuring the current plateau as a function of the SAW power and gate bias as well as a function of perpendicular magnetic filed. Our investigation indicates that the fractional plateau is induced by the tunnelling effect from the dynamic quantum dots (QDs) into a static impurity dot. Rate equations are used to extract the tunnelling rates, which change a lot with the number of electrons in the dynamic QDs, the SAW power and gate bias. In addition, the current plateau evolves into a fractional structure, when a strong perpendicular magnetic field is applied to the system.
NASA Astrophysics Data System (ADS)
Nobrega, J. Araújo e.; Gordo, V. Orsi; Galeti, H. V. A.; Gobato, Y. Galvão; Brasil, M. J. S. P.; Taylor, D.; Orlita, M.; Henini, M.
2015-12-01
In this work, we have investigated transport and optical properties of n-i-n resonant tunneling diodes (RTDs) containing a layer of InAs self-assembled quantum dots (QDs) grown on a (311)B oriented GaAs substrate. Polarization-resolved photoluminescence (PL) and magneto-transport measurements were performed under applied voltage and magnetic fields up to 15 T at 2 K under linearly polarized laser excitation. It was observed that the QD circular polarization degree depends strongly on the applied voltage. Its voltage dependence is explained by the formation of excitonic complexes such as positively (X+) and negatively (X-) charged excitons in the QDs. Our results demonstrate an effective electrical control of an ensemble of InAs QD properties by tuning the applied voltage across a RTD device into the resonant tunneling condition.
Smets, Quentin Verreck, Devin; Heyns, Marc M.; Verhulst, Anne S.; Martens, Koen; Lin, Han Chung; Kazzi, Salim El; Simoen, Eddy; Collaert, Nadine; Thean, Aaron; Raskin, Jean-Pierre
2014-11-17
The Tunneling Field-Effect Transistor (TFET) is a promising device for future low-power logic. Its performance is often predicted using semiclassical simulations, but there is usually a large discrepancy with experimental results. An important reason is that Field-Induced Quantum Confinement (FIQC) is neglected. Quantum mechanical simulations show FIQC delays the onset of Band-To-Band Tunneling (BTBT) with hundreds of millivolts in the promising line-TFET configuration. In this letter, we provide experimental verification of this delayed onset. We accomplish this by developing a method where line-TFET are modeled using highly doped MOS capacitors (MOS-CAP). Using capacitance-voltage measurements, we demonstrate AC inversion by BTBT, which was so far unobserved in MOS-CAP. Good agreement is shown between the experimentally obtained BTBT onset and quantum mechanical predictions, proving the need to include FIQC in all TFET simulations. Finally, we show that highly doped MOS-CAP is promising for characterization of traps deep into the conduction band.
Piprek, Joachim
2014-02-03
This Letter investigates the efficiency enhancement achieved by tunnel junction insertion into the InGaN/GaN multi-quantum well (MQW) active region of blue light emitting diodes (LEDs). The peak quantum efficiency of such LED exceeds 100%, but the maximum wall-plug efficiency (WPE) hardly changes. However, due to the increased bias, the WPE peaks at much higher input power, i.e., the WPE droop is significantly delayed, and the output power is strongly enhanced. The main physical reason for this improvement lies in the non-uniform vertical carrier distribution typically observed within InGaN MQWs.
Tunneling Ionization Time Resolved by Backpropagation.
Ni, Hongcheng; Saalmann, Ulf; Rost, Jan-Michael
2016-07-01
We determine the ionization time in tunneling ionization by an elliptically polarized light pulse relative to its maximum. This is achieved by a full quantum propagation of the electron wave function forward in time, followed by a classical backpropagation to identify tunneling parameters, in particular, the fraction of electrons that has tunneled out. We find that the ionization time is close to zero for single active electrons in helium and in hydrogen if the fraction of tunneled electrons is large. We expect our analysis to be essential to quantify ionization times for correlated electron motion. PMID:27447504
NASA Astrophysics Data System (ADS)
Muraguchi, Masakazu; Shiraishi, Kenji; Okunishi, Takuma; Takeda, Kyozaburo
2009-02-01
We have studied numerically the time-dependent photon-assisted tunneling (TD-PAT) process for electrons confined in quantum dots (QDs) by employing the finite difference method under the scheme of the TD-density functional theory (DFT). We have found the quasi-dark state (quasi-DS), where the injected electron remains in the QD. By varying the barrier thickness, we have calculated the TD profile of the electron density in a QD, and found the optimal geometry of the lozenge QD. We have also discussed how the charged QD modulates the PAT process.
Chaldyshev, V. V. Shkol'nik, A. S.; Evtikhiev, V. P.; Holden, T.
2007-12-15
Contactless optical electroreflectance measurements at different temperatures are used to study exciton states in a structure involving a periodic system of 36 GaAs quantum wells separated by tunneling-nontransparent AlGaAs barriers with thickness 104 nm. In the structure, the width of 32 of the quantum wells is 15 nm, while the width of the remaining four quantum wells, numbered 5, 14, 23, and 32, is 20 nm. The periodicity of the structure corresponds to the Bragg interference condition at the excitonic frequency in quantum wells at the angle of incidence of light {approx}43 deg. From the quantitative analysis of the shape of the contactless electroreflectance line, the parameters of the exciton ground states and excited states are determined for both types of quantum wells. It is established that, for the system of four 20-nm-wide quantum wells separated by a distance of 830 nm, the size-quantization energy in the ground state is 8.4 {+-} 0.1 meV, and the parameter of broadening of the excitonic peak is 1.8 {+-} 0.1 meV at 17 K and increases with temperature up to 2.0 {+-} 0.1 meV at 80 K. For the system of 32 wells with the width 15 nm, the quantum confinement energy in the ground state is 14.9 {+-} 0.1 meV, and the parameter of broadening of the excitonic peak is 2.2 {+-} 0.1 and 2.6 {+-} 0.1 meV at 17 and 80 K, respectively. The possible causes of radiative and nonradiative broadening of exciton states in the systems are discussed.
Verma, Jai Islam, S. M.; Protasenko, Vladimir; Kumar Kandaswamy, Prem; Xing, Huili; Jena, Debdeep
2014-01-13
Efficient semiconductor optical emitters in the deep-ultraviolet spectral window are encountering some of the most deep rooted problems of semiconductor physics. In III-Nitride heterostructures, obtaining short-wavelength photon emission requires the use of wide bandgap high Al composition AlGaN active regions. High conductivity electron (n-) and hole (p-) injection layers of even higher bandgaps are necessary for electrical carrier injection. This approach requires the activation of very deep dopants in very wide bandgap semiconductors, which is a difficult task. In this work, an approach is proposed and experimentally demonstrated to counter the challenges. The active region of the heterostructure light emitting diode uses ultrasmall epitaxially grown GaN quantum dots. Remarkably, the optical emission energy from GaN is pushed from 365 nm (3.4 eV, the bulk bandgap) to below 240 nm (>5.2 eV) because of extreme quantum confinement in the dots. This is possible because of the peculiar bandstructure and band alignments in the GaN/AlN system. This active region design crucially enables two further innovations for efficient carrier injection: Tunnel injection of carriers and polarization-induced p-type doping. The combination of these three advances results in major boosts in electroluminescence in deep-ultraviolet light emitting diodes and lays the groundwork for electrically pumped short-wavelength lasers.
MgB{sub 2} tunnel junctions and 19 K low-noise dc superconducting quantum interference devices.
Zhang, Y.; Kinion, D.; Chen, J.; Clarke, J.; Hinks, D. G.; Crabtree, G. W.; Materials Science Division; Univ. of California at Berkeley
2001-01-01
Point contact junctions made from two pieces of MgB{sub 2} can be adjusted to exhibit either superconductor-insulator-superconductor (SIS) or superconductor-normal metal-superconductor (SNS) current-voltage characteristics. The SIS characteristics are in good agreement with the standard tunneling model for s-wave superconductors, and yield an energy gap of (2.02{+-}0.08) meV. The SNS characteristics are in good agreement with the predictions of the resistively-shunted junction model. DC superconducting quantum interference devices made from two SNS junctions yield magnetic flux and field noise as low as 4 {mu}{Phi}{sub 0} Hz{sup -1/2} and 35 fT Hz{sup -1/2} at 19 K; {Phi}{sub 0} is the flux quantum.
Jiang, Jian-Hua
2014-11-21
We propose a scheme of multilayer thermoelectric engine where one electric current is coupled to two temperature gradients in three-terminal geometry. This is realized by resonant tunneling through quantum dots embedded in two thermal and electrical resisting polymer matrix layers between highly conducting semiconductor layers. There are two thermoelectric effects, one of which is pertaining to inelastic transport processes (if energies of quantum dots in the two layers are different), while the other exists also for elastic transport processes. These two correspond to the transverse and longitudinal thermoelectric effects, respectively, and are associated with different temperature gradients. We show that cooperation between the two thermoelectric effects leads to markedly improved figure of merit and power factor, which is confirmed by numerical calculation using material parameters. Such enhancement is robust against phonon heat conduction and energy level broadening. Therefore, we demonstrated cooperative effect as an additional way to effectively improve performance of thermoelectrics in three-terminal geometry.
NASA Astrophysics Data System (ADS)
Ting, David Z.-Y.; Soibel, Alexander; Khoshakhlagh, Arezou; Keo, Sam A.; Nguyen, Jean; Höglund, Linda; Mumolo, Jason M.; Liu, John K.; Rafol, B., , Sir; Hill, Cory J.; Gunapala, Sarath D.
2013-07-01
The InAs/GaSb type-II superlattice based complementary barrier infrared detector (CBIRD) has already demonstrated very good performance in long-wavelength infrared (LWIR) detection. In this work, we describe results on a modified CBIRD device that incorporates a double tunnel junction contact designed for robust device and focal plane array processing. The new device also exhibited reduced turn-on voltage. We also report results on the quantum dot barrier infrared detector (QD-BIRD). By incorporating self-assembled InSb quantum dots into the InAsSb absorber of the standard nBn detector structure, the QD-BIRD extend the detector cutoff wavelength from ˜4.2 μm to 6 μm, allowing the coverage of the mid-wavelength infrared (MWIR) transmission window. The device has been observed to show infrared response at 225 K.
NASA Technical Reports Server (NTRS)
Ting, David Z.-Y; Soibel, Alexander; Khoshakhlagh, Arezou; Keo, Sam A.; Nguyen, Jean; Hoglund, Linda; Mumolo, Jason M.; Liu, John K.; Rafol, Sir B.; Hill, Cory J.; Gunapala, Sarath D.
2012-01-01
The InAs/GaSb type-II superlattice based complementary barrier infrared detector (CBIRD) has already demonstrated very good performance in long-wavelength infrared (LWIR) detection. In this work, we describe results on a modified CBIRD device that incorporates a double tunnel junction contact designed for robust device and focal plane array processing. The new device also exhibited reduced turn-on voltage. We also report results on the quantum dot barrier infrared detector (QD-BIRD). By incorporating self-assembled InSb quantum dots into the InAsSb absorber of the standard nBn detector structure, the QD-BIRD extend the detector cutoff wavelength from approximately 4.2 micrometers to 6 micrometers, allowing the coverage of the mid-wavelength infrared (MWIR) transmission window. The device has been observed to show infrared response at 225 K.
Wind tunnel productivity status and improvement activities at NASA Langley Research Center
NASA Technical Reports Server (NTRS)
Putnam, Lawrence E.
1996-01-01
Over the last three years, a major effort has been underway to re-engineering the way wind tunnel testing is accomplished at the NASA Langley Research Center. This effort began with the reorganization of the LaRC and the consolidation of the management of the wind tunnels in the Aerodynamics Division under one operations branch. This paper provides an overview of the re-engineering activities and gives the status of the improvements in the wind tunnel productivity and customer satisfaction that have resulted from the new ways of working.
LCS/CINDER`90 accelerator tunnel activation calculations for the APT 1700-MeV accelerator tunnel
Court, J.D.; Snow, E.C.; Wilson, W.B.; Pitcher, E.R.
1998-09-01
Calculations have been done to determine the amount of activation in the linac components and tunnel air for the Accelerator Production of Tritium 1700-MeV superconducting linac. Proton transport is accomplished through the use of the LAHET Code System. Particle production and depletion from proton and high-energy neutron reactions, calculated in LAHET, as well as low-energy neutron fluxes calculated by MCNP, are passed to the radionuclide production code CINDER`90 to determine the source terms at various times after irradiation. The upper limit on total air activation based on conservative assumptions, for the entire tunnel air volume, was found to be 4.77 Ci after a nine-month irradiation. This is reduced to 0.09 Ci after a 10-hour cooling off period. The total activation for the full 1-km of beamline components was found to be less than 4 kCi, with the half-lives of the highest contributors ranging from 12 years to 2 minutes. This beamline component activation calculation was done for an irradiation time of 40 years, which is the anticipated lifetime of the superconducting linac.
Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots
NASA Astrophysics Data System (ADS)
Zimmers, A.; Wang, H.; Lhuillier, E.; Yu, Q.; Mottaghizadeh, A.; Ulysse, C.; Descamps-Mandine, A.; Dubertret, B.; Aubin, H.
We present a tunnel spectroscopy study of single PbS and HgSe quantum dots (QDs) as a function of temperature and gate voltage. The samples are fabricated through high-vacuum projection of the QDs on the chip circuit. For PbS, three distinct signatures of strong electron-phonon coupling are observed in the electron tunneling spectrum (ETS) of these QDs. In the shell-filling regime, the 8x degeneracy of the electronic levels is lifted by the Coulomb interactions and allows the observation of phonon subbands that result from the emission of optical phonons. At low bias, a gap is observed in the ETS that cannot be closed with the gate voltage, which is a distinguishing feature of the Franck-Condon blockade. From the data, a Huang-Rhys factor in the range S similar to 1.7-2.5 is obtained. Finally, in the shell-tunneling regime, the optical phonons appear in the inelastic ETS d(2)I/dV(2). For HgSe, the data show that the inter-band and intra-band gap can be clearly identified in the ETS.
Tunnel determinants from spectral zeta functions. Instanton effects in quantum mechanics
Izquierdo, A. Alonso; Guilarte, J. Mateos
2014-07-23
In this paper we develop an spectral zeta function regularization procedure on the determinants of instanton fluctuation operators that describe the semi-classical order of tunnel effects between degenerate vacua.
Resonant tunneling device with two-dimensional quantum well emitter and base layers
Simmons, Jerry A.; Sherwin, Marc E.; Drummond, Timothy J.; Weckwerth, Mark V.
1998-01-01
A double electron layer tunneling device is presented. Electrons tunnel from a two dimensional emitter layer to a two dimensional tunneling layer and continue traveling to a collector at a lower voltage. The emitter layer is interrupted by an isolation etch, a depletion gate, or an ion implant to prevent electrons from traveling from the source along the emitter to the drain. The collector is similarly interrupted by a backgate, an isolation etch, or an ion implant. When the device is used as a transistor, a control gate is added to control the allowed energy states of the emitter layer. The tunnel gate may be recessed to change the operating range of the device and allow for integrated complementary devices. Methods of forming the device are also set forth, utilizing epoxy-bond and stop etch (EBASE), pre-growth implantation of the backgate or post-growth implantation.
Resonant tunneling device with two-dimensional quantum well emitter and base layers
Simmons, J.A.; Sherwin, M.E.; Drummond, T.J.; Weckwerth, M.V.
1998-10-20
A double electron layer tunneling device is presented. Electrons tunnel from a two dimensional emitter layer to a two dimensional tunneling layer and continue traveling to a collector at a lower voltage. The emitter layer is interrupted by an isolation etch, a depletion gate, or an ion implant to prevent electrons from traveling from the source along the emitter to the drain. The collector is similarly interrupted by a backgate, an isolation etch, or an ion implant. When the device is used as a transistor, a control gate is added to control the allowed energy states of the emitter layer. The tunnel gate may be recessed to change the operating range of the device and allow for integrated complementary devices. Methods of forming the device are also set forth, utilizing epoxy-bond and stop etch (EBASE), pre-growth implantation of the backgate or post-growth implantation. 43 figs.
Huang, Liang Feng; Ni, Mei Yan; Zeng, Zhi
2011-11-01
The diffusion of hydrogen and deuterium monomers on hole-doped graphene (a planar graphitic lattice), the outside wall and the inside wall of hole-doped (6, 0) single-walled carbon nanotubes (a curved graphitic lattice) was investigated using density functional theory and density functional perturbation theory. The jump frequencies for the over-barrier transition and phonon-assisted quantum tunneling were calculated by transition state theory and small-polaron theory, respectively. The effects of the local curvature of the surface and the hole doping on the thermodynamic and kinetic properties of a hydrogen monomer on these graphitic lattices are discussed. Our results demonstrate that it is sufficient to judge the diffusional mobility of a hydrogen monomer on graphitic lattices from just the over-barrier transition, no matter how much it is curved and hole doped, while the quantum tunneling can be safely neglected because it is significantly suppressed by the covalent bonding of hydrogen with the graphitic lattice. PMID:21971019
NASA Astrophysics Data System (ADS)
H, Dakhlaoui; S, Almansour
2016-06-01
In this work, the electronic properties of resonant tunneling diodes (RTDs) based on GaN-Al x Ga(1-x)N double barriers are investigated by using the non-equilibrium Green functions formalism (NEG). These materials each present a wide conduction band discontinuity and a strong internal piezoelectric field, which greatly affect the electronic transport properties. The electronic density, the transmission coefficient, and the current-voltage characteristics are computed with considering the spontaneous and piezoelectric polarizations. The influence of the quantum size on the transmission coefficient is analyzed by varying GaN quantum well thickness, Al x Ga(1-x)N width, and the aluminum concentration x Al. The results show that the transmission coefficient more strongly depends on the thickness of the quantum well than the barrier; it exhibits a series of resonant peaks and valleys as the quantum well width increases. In addition, it is found that the negative differential resistance (NDR) in the current-voltage (I-V) characteristic strongly depends on aluminum concentration x Al. It is shown that the peak-to-valley ratio (PVR) increases with x Al value decreasing. These findings open the door for developing vertical transport nitrides-based ISB devices such as THz lasers and detectors. Project supported by the Deanship of Scientific Research of University of Dammam (Grant No. 2014137).
Wang, Qingxiu; Wu, Xianzheng; Wang, Lijun; Chen, Zhiwen; Wang, Shilong
2014-09-28
Tin dioxide (SnO2) and graphene are versatile materials that are vitally important for creating new functional and smart materials. A facile, simple and efficient ultrasonic-assisted hydrothermal synthesis approach has been developed to prepare graphene-SnO2 nanocomposites (GSNCs), including three samples with graphene/Sn weight ratios = 1 : 2 (GSNC-2), 1 : 1 (GSNC-1), and graphene oxide/Sn weight ratio = 1 : 1 (GOSNC-1). Low-magnification electron microscopy analysis indicated that graphene was exfoliated and adorned with SnO2 nanoparticles, which were dispersed uniformly on both the sides of the graphene nanosheets. High-magnification electron microscopy analysis confirmed that the graphene-SnO2 nanocomposites presented network tunneling frameworks, which were decorated with the SnO2 quantum tunneling junctions. The size distribution of SnO2 nanoparticles was estimated to range from 3 to 5.5 nm. Comparing GSNC-2, GSNC-1, and GOSNC-1, GOSNC-1 was found to exhibit a significantly better the homogeneous distribution and a considerably smaller size distribution of SnO2 nanoparticles, which indicated that it was better to use graphene oxide as a supporting material and SnCl4·5H2O as a precursor to synthesize hybrid graphene-SnO2 nanocomposites. Experimental results suggest that the graphene-SnO2 nanocomposites with interesting SnO2 quantum tunneling junctions may be a promising material to facilitate the improvement of the future design of micro/nanodevices.
Quantum entanglement and informational activities of biomolecules
NASA Astrophysics Data System (ADS)
Al-Shargi, Hanan; Berkovich, Simon
2009-03-01
Our model of holographic Universe [1] explains the surprising property of quantum entanglement and reveals its biological implications. The suggested holographic mechanism handles 2D slices of the physical world as a whole. Fitting this simple holistic process in the Procrustean bed of individual particles interactions leads to intricacies of quantum theory with an unintelligible protrusion of distant correlations. Holographic medium imposes dependence of quantum effects on absolute positioning. Testing this prediction for a non-exponential radioactive decay could resolutely point to outside ``memory.'' The essence of Life is in the sophistication of macromolecules. Distinctions in biological information processing of nucleotides in DNA and amino acids in proteins are related to entropies of their structures. Randomness of genetic configurations as exposed by their maximal entropy is characteristic of passive identification rather than active storage functionality. Structural redundancy of proteins shows their operability, of which different foldings of prions is most indicative. Folding of one prion can reshape another prion without a direct contact appearing like ``quantum entanglement,'' or ``teleportation.'' Testing the surmised influence of absolute orientation on the prion reshaping can uncover the latency effects in the ``mad cow'' disease. 1. Simon Berkovich, TR-GWU-CS-07-006, http://www.cs.gwu.edu/research/reports.php
Hot-bench simulation of the active flexible wing wind-tunnel model
NASA Technical Reports Server (NTRS)
Buttrill, Carey S.; Houck, Jacob A.
1990-01-01
Two simulations, one batch and one real-time, of an aeroelastically-scaled wind-tunnel model were developed. The wind-tunnel model was a full-span, free-to-roll model of an advanced fighter concept. The batch simulation was used to generate and verify the real-time simulation and to test candidate control laws prior to implementation. The real-time simulation supported hot-bench testing of a digital controller, which was developed to actively control the elastic deformation of the wind-tunnel model. Time scaling was required for hot-bench testing. The wind-tunnel model, the mathematical models for the simulations, the techniques employed to reduce the hot-bench time-scale factors, and the verification procedures are described.
NASA Astrophysics Data System (ADS)
Fratini, F.; Safari, L.
2014-08-01
We discuss the form of the wave-function of a state subjected to a scalar linear potential, focusing on quantum tunneling. We analyze the phases acquired by the evolved state and show that some are of a pure quantum mechanical origin. We propose a simple experimental scenario to measure one of these phases. We apply the evolution equations to re-analyze the Stern and Gerlach experiment and to demonstrate how to manipulate spin by employing constant electric fields.
Xie, Weiwei; Xu, Yang; Zhu, Lili; Shi, Qiang
2014-05-07
We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula.
Quantum decrease of capacitance in a nanometer-sized tunnel junction
NASA Astrophysics Data System (ADS)
Untiedt, C.; Saenz, G.; Olivera, B.; Corso, M.; Sabater, C.; Pascual, J. I.
2013-03-01
We have studied the capacitance of the tunnel junction defined by the tip and sample of a Scanning Tunnelling Microscope through the measurement of the electrostatic forces and impedance of the junction. A decrease of the capacitance when a tunnel current is present has shown to be a more general phenomenon as previously reported in other systems. On another hand, an unexpected reduction of the capacitance is also observed when increasing the applied voltage above the work function energy of the electrodes to the Field Emission (FE) regime, and the decrease of capacitance due to a single FE-Resonance has been characterized. All these effects should be considered when doing measurements of the electronic characteristics of nanometer-sized electronic devices and have been neglected up to date. Spanish government (FIS2010-21883-C02-01, CONSOLIDER CSD2007-0010), Comunidad Valenciana (ACOMP/2012/127 and PROMETEO/2012/011)
Quantum Speedup for Active Learning Agents
NASA Astrophysics Data System (ADS)
Paparo, Giuseppe Davide; Dunjko, Vedran; Makmal, Adi; Martin-Delgado, Miguel Angel; Briegel, Hans J.
2014-07-01
Can quantum mechanics help us build intelligent learning agents? A defining signature of intelligent behavior is the capacity to learn from experience. However, a major bottleneck for agents to learn in real-life situations is the size and complexity of the corresponding task environment. Even in a moderately realistic environment, it may simply take too long to rationally respond to a given situation. If the environment is impatient, allowing only a certain time for a response, an agent may then be unable to cope with the situation and to learn at all. Here, we show that quantum physics can help and provide a quadratic speedup for active learning as a genuine problem of artificial intelligence. This result will be particularly relevant for applications involving complex task environments.
Liu, Y.; Xiao, X.R.; Zeng, Y.P.; Pan, D.
1999-11-25
The photovoltaic spectral features and the behaviors of photocurrent versus the electrode potential for near surface In{sub 0.15}Ga{sub 0.85}As/GaAs quantum well electrodes have been investigated in nonaqueous solutions of ferrocene and acetylferrocene. The photovoltaic spectrum shows a sharp structure that reflects confined state-to-state exciton transition in the quantum well. Deep dips are observed in the photocurrent versus the electrode potential curves in both electrolytes at the different electrode potentials under the illumination of exciton resonance wavelength. These dips are qualitatively explained by considering the interfacial tunneling transfer of photogenerated electron within the quantum well.
Quantum-tunneling dynamics of a spin-polarized Fermi gas in a double-well potential
Salasnich, L.; Mazzarella, G.; Toigo, F.; Salerno, M.
2010-02-15
We study the exact dynamics of a one-dimensional spin-polarized gas of fermions in a double-well potential at zero and finite temperature. Despite the system being made of noninteracting fermions, its dynamics can be quite complex, showing strongly aperiodic spatio-temporal patterns during the tunneling. The extension of these results to the case of mixtures of spin-polarized fermions interacting with self-trapped Bose-Einstein condensates (BECs) at zero temperature is considered as well. In this case we show that the fermionic dynamics remains qualitatively similar to that observed in the absence of BEC but with the Rabi frequencies of fermionic excited states explicitly depending on the number of bosons and on the boson-fermion interaction strength. From this, the possibility of controlling quantum fermionic dynamics by means of Feshbach resonances is suggested.
Capacitance estimation for InAs Tunnel FETs by means of full-quantum k · p simulation
NASA Astrophysics Data System (ADS)
Gnani, E.; Baravelli, E.; Gnudi, A.; Reggiani, S.; Baccarani, G.
2015-06-01
We report for the first time a quantum mechanical simulation study of gate capacitance components in aggressively scaled InAs Nanowire Tunnel Field-Effect Transistors. It will be shown that the gate-drain capacitance exhibits the same functional dependence over the whole Vgs range as the total gate capacitance, albeit with smaller values. However, as opposed to the previous capacitance estimations provided by semiclassical TCAD tools, we find that the gate capacitance exhibits a non-monotonic behavior vs. gate voltage, with plateaus and bumps related with energy quantization and subband formation determined by the device cross-sectional size, as well as with the position of channel-conduction subbands relative to the Fermi level in the drain contact. From this point of view, semiclassical TCAD tools seem to be inaccurate for capacitance estimation in aggressively-scaled TFET devices.
Spin-lattice relaxation via quantum tunneling in diluted crystals of Fe4 single-molecule magnets
NASA Astrophysics Data System (ADS)
Repollés, A.; Cornia, A.; Luis, F.
2014-02-01
We investigate the dynamic susceptibility of Fe4 single-molecule magnets with integer spin (S =5) in the form of pure crystals as well as diluted in crystals of isostructural, but nonmagnetic, Ga4 clusters. Below approximately 1 K, the spin-lattice relaxation becomes dominated by a temperature-independent process. The spin-lattice relaxation time τ measured in this "quantum regime" is 12 orders of magnitude shorter than the characteristic time scale of direct phonon-induced processes but agrees with the relaxation times of pure (i.e., not assisted by phonons) spin tunneling events. The present results show that the latter phenomenon, despite conserving the energy of the ensemble of electronic and nuclear spins, drives the thermalization of electronic spins at very low temperatures. The spin-lattice relaxation time scales with the concentration of Fe4, thus suggesting that the main effect of dipolar interactions is to block tunneling. The data show therefore no evidence for the contribution of collective phonon emission processes, such as phonon superradiance, to the spin-lattice relaxation.
NASA Astrophysics Data System (ADS)
Lim, Seong Joon; Prezhdo, Oleg V.; Lee, Minjun; Kwon, Jeonghoon; Cho, Kyung-Sang; Choi, Byoung Lyong; Kuk, Young
2014-03-01
Recent studies on fluorescence intermittency, or called blinking, in quantum dots (QDs) show that complete control of this phenomenon is near at hand. Although a number of models deal with the transitions between on/off states in the intermittency, they do not consider the spatial and energy distribution of traps in a single QD. In this study, we measured the spatial and energy distribution of traps using scanning tunneling microscopy and spectroscopy. The trap states of CdSe/ZnS QD exhibit two distinct energy states and intensities in the tunneling spectra according to their residing positions (inside or surface of QD). We were able to simulate trapping dynamics of the fluorescence intermittency from the measured energy and spatial distribution. We used Monte Carlo method to render transitions between the trap states in this model. We can successfully explain the power-law distribution of on/off time, which is a characteristic feature of the blinking. The dependence is a consequence of a two-step trapping process through inner and surface traps. The simulation also predicts the suppression of the long tail in the power-law distribution by reducing the surface traps. This result is in good agreement with a recent fluorescence lifetime-intensity distribution measurement.
NASA Technical Reports Server (NTRS)
Waszak, Martin R.
1996-01-01
This paper describes the formulation of a model of the dynamic behavior of the Benchmark Active Controls Technology (BACT) wind-tunnel model for application to design and analysis of flutter suppression controllers. The model is formed by combining the equations of motion for the BACT wind-tunnel model with actuator models and a model of wind-tunnel turbulence. The primary focus of this paper is the development of the equations of motion from first principles using Lagrange's equations and the principle of virtual work. A numerical form of the model is generated using values for parameters obtained from both experiment and analysis. A unique aspect of the BACT wind-tunnel model is that it has upper- and lower-surface spoilers for active control. Comparisons with experimental frequency responses and other data show excellent agreement and suggest that simple coefficient-based aerodynamics are sufficient to accurately characterize the aeroelastic response of the BACT wind-tunnel model. The equations of motion developed herein have been used to assist the design and analysis of a number of flutter suppression controllers that have been successfully implemented.
Two-particle quantum interference in tunnel-coupled optical tweezers.
Kaufman, A M; Lester, B J; Reynolds, C M; Wall, M L; Foss-Feig, M; Hazzard, K R A; Rey, A M; Regal, C A
2014-07-18
The quantum statistics of atoms is typically observed in the behavior of an ensemble via macroscopic observables. However, quantum statistics modifies the behavior of even two particles. Here, we demonstrate near-complete control over all the internal and external degrees of freedom of two laser-cooled (87)Rb atoms trapped in two optical tweezers. This controllability allows us to observe signatures of indistinguishability via two-particle interference. Our work establishes laser-cooled atoms in optical tweezers as a promising route to bottom-up engineering of scalable, low-entropy quantum systems.
Resonant tunneling through discrete quantum states in stacked atomic-layered MoS2.
Nguyen, Linh-Nam; Lan, Yann-Wen; Chen, Jyun-Hong; Chang, Tay-Rong; Zhong, Yuan-Liang; Jeng, Horng-Tay; Li, Lain-Jong; Chen, Chii-Dong
2014-05-14
Two-dimensional crystals can be assembled into three-dimensional stacks with atomic layer precision, which have already shown plenty of fascinating physical phenomena and been used for prototype vertical-field-effect-transistors.1,2 In this work, interlayer electron tunneling in stacked high-quality crystalline MoS2 films were investigated. A trilayered MoS2 film was sandwiched between top and bottom electrodes with an adjacent bottom gate, and the discrete energy levels in each layer could be tuned by bias and gate voltages. When the discrete energy levels aligned, a resonant tunneling peak appeared in the current-voltage characteristics. The peak position shifts linearly with perpendicular magnetic field, indicating formation of Landau levels. From this linear dependence, the effective mass and Fermi velocity are determined and are confirmed by electronic structure calculations. These fundamental parameters are useful for exploitation of its unique properties.
Time-Resolved Optical Spectroscopy of Tunnel Coupled Lateral Quantum Dot Molecules
NASA Astrophysics Data System (ADS)
Hermannstädter, C.; Beirne, G. J.; Wang, L.; Rastelli, A.; Schmidt, O. G.; Michler, P.
2007-04-01
The two laterally coupled quantum dots, also referred to as lateral quantum dot molecules, exhibit a characteristic photoluminescence spectrum consisting of six dominant emission lines that are due to neutral and charged excitonic as well as biexcitonic recombination. All of these lines are found to originate from the same single quantum emitter following photon statistics measurements. Using a parallel electric field we are able to control the quantum coupling between the dots. This control manifests itself as an ability to reversibly switch the relative intensities of the two neutral excitonic transitions, which results in a possible application of the molecules as tunable single-photon emitters. To further investigate the exact origin of the photoluminescence lines we have also investigated the decay times of the molecule emission.
Tunneling of a heavily damped macroscopic variable
Schwartz, D.B.
1987-01-01
The author studied the effect of damping upon fluxoid transitions in simple microfabricated circuits consisting of an inductor and small-area Josephson tunnel junctions. In order to provide an easily characterized source of damping, the tunnel junctions were fabricated with low-inductance resistive shunts across them. To keep tunneling from being suppressed to unreachably low temperatures, the samples were designed to exhibit tunneling at high temperatures in the absence of damping. This was achieved by having junction areas of approximately 0.1 ..mu../sup 2/, which pushes the characteristic time scales to over 10/sup 12/ s/sup -1/. Tunneling was unambiguously observed at 2K in the unshunted samples. The temperature where thermal activation won over tunneling in determining the escape rate was suppressed by an order of magnitude in the shunted samples, in good agreement with theoretical predictions. The predicted T/sup 2/ dependence of the exponent of the tunneling rate upon temperature was also clearly observed in the data. At temperatures where thermal activation dominates the escape-rate quantum corrections to the escape rate are predicted. Analysis of these effects upon the data is complicated by the high frequencies involved. Although the data does not constitute a clear test of these corrections, it seems clear that simple thermal activation without quantum corrections does not suffice to explain it.
Experimental Results from the Active Aeroelastic Wing Wind Tunnel Test Program
NASA Technical Reports Server (NTRS)
Heeg, Jennifer; Spain, Charles V.; Florance, James R.; Wieseman, Carol D.; Ivanco, Thomas G.; DeMoss, Joshua; Silva, Walter A.; Panetta, Andrew; Lively, Peter; Tumwa, Vic
2005-01-01
The Active Aeroelastic Wing (AAW) program is a cooperative effort among NASA, the Air Force Research Laboratory and the Boeing Company, encompassing flight testing, wind tunnel testing and analyses. The objective of the AAW program is to investigate the improvements that can be realized by exploiting aeroelastic characteristics, rather than viewing them as a detriment to vehicle performance and stability. To meet this objective, a wind tunnel model was crafted to duplicate the static aeroelastic behavior of the AAW flight vehicle. The model was tested in the NASA Langley Transonic Dynamics Tunnel in July and August 2004. The wind tunnel investigation served the program goal in three ways. First, the wind tunnel provided a benchmark for comparison with the flight vehicle and various levels of theoretical analyses. Second, it provided detailed insight highlighting the effects of individual parameters upon the aeroelastic response of the AAW vehicle. This parameter identification can then be used for future aeroelastic vehicle design guidance. Third, it provided data to validate scaling laws and their applicability with respect to statically scaled aeroelastic models.
Quantum Tunneling of ^3He in Solid ^4He: A New Analysis
NASA Astrophysics Data System (ADS)
Huan, C.; Kim, S. S.; Candela, D.; Sullivan, N. S.
2016-11-01
We discuss the analysis of the experimental values of the nuclear spin-lattice and spin-spin relaxation times for the tunneling of ^3He as isotopic impurities in solid ^4He. These two relaxation times cannot be described quantitatively using a unique correlation time although it is often presented as such in the literature. In this paper, we discuss how to distinguish the high-frequency portion of the spectral densities that determine the spin-lattice relaxation rates from the low-frequency components which determine the spin-spin relaxation rates.
On a Quantum Model of Brain Activities
NASA Astrophysics Data System (ADS)
Fichtner, K.-H.; Fichtner, L.; Freudenberg, W.; Ohya, M.
2010-01-01
One of the main activities of the brain is the recognition of signals. A first attempt to explain the process of recognition in terms of quantum statistics was given in [6]. Subsequently, details of the mathematical model were presented in a (still incomplete) series of papers (cf. [7, 2, 5, 10]). In the present note we want to give a general view of the principal ideas of this approach. We will introduce the basic spaces and justify the choice of spaces and operations. Further, we bring the model face to face with basic postulates any statistical model of the recognition process should fulfill. These postulates are in accordance with the opinion widely accepted in psychology and neurology.
Quantum-corrected self-dual black hole entropy in tunneling formalism with GUP
NASA Astrophysics Data System (ADS)
Anacleto, M. A.; Brito, F. A.; Passos, E.
2015-10-01
In this paper we focus on the Hamilton-Jacobi method to determine the entropy of a self-dual black hole by using linear and quadratic GUPs (generalized uncertainty principles). We have obtained the Bekenstein-Hawking entropy of self-dual black holes and its quantum corrections that are logarithm and also of several other types.
ERIC Educational Resources Information Center
Ellison, Mark D.
2008-01-01
The one-dimensional particle-in-a-box model used to introduce quantum mechanics to students suffers from a tenuous connection to a real physical system. This article presents a two-dimensional model, the particle confined within a ring, that directly corresponds to observations of surface electrons in a metal trapped inside a circular barrier.…
Asymmetric quantum-well structures for AlGaN/GaN/AlGaN resonant tunneling diodes
NASA Astrophysics Data System (ADS)
Yang, Lin'an; Li, Yue; Wang, Ying; Xu, Shengrui; Hao, Yue
2016-04-01
Asymmetric quantum-well (QW) structures including the asymmetric potential-barrier and the asymmetric potential-well are proposed for AlGaN/GaN/AlGaN resonant tunneling diodes (RTDs). Theoretical investigation gives that an appropriate decrease in Al composition and thickness for emitter barrier as well as an appropriate increase of both for collector barrier can evidently improve the negative-differential-resistance characteristic of RTD. Numerical simulation shows that RTD with a 1.5-nm-thick GaN well sandwiched by a 1.3-nm-thick Al0.15Ga0.85N emitter barrier and a 1.7-nm-thick Al0.25Ga0.75N collector barrier can yield the I-V characteristic having the peak current (Ip) and the peak-to-valley current ratio (PVCR) of 0.39 A and 3.6, respectively, about double that of RTD with a 1.5-nm-thick Al0.2Ga0.8N for both barriers. It is also found that an introduction of InGaN sub-QW into the diode can change the tunneling mode and achieve higher transmission coefficient of electron. The simulation demonstrates that RTD with a 2.8-nm-thick In0.03Ga0.97N sub-well in front of a 2.0-nm-thick GaN main-well can exhibit the I-V characteristic having Ip and PVCR of 0.07 A and 11.6, about 7 times and double the value of RTD without sub-QW, respectively. The purpose of improving the structure of GaN-based QW is to solve apparent contradiction between the device structure and the device manufacturability of new generation RTDs for sub-millimeter and terahertz applications.
NASA Astrophysics Data System (ADS)
Suzuki, Yosuke; Ebina, Kuniyoshi; Tanaka, Shigenori
2016-08-01
A computational scheme to describe the coherent dynamics of excitation energy transfer (EET) in molecular systems is proposed on the basis of generalized master equations with memory kernels. This formalism takes into account those physical effects in electron-bath coupling system such as the spin symmetry of excitons, the inelastic electron tunneling and the quantum features of nuclear motions, thus providing a theoretical framework to perform an ab initio description of EET through molecular simulations for evaluating the spectral density and the temporal correlation function of electronic coupling. Some test calculations have then been carried out to investigate the dependence of exciton population dynamics on coherence memory, inelastic tunneling correlation time, magnitude of electronic coupling, quantum correction to temporal correlation function, reorganization energy and energy gap.
Techniques For Mass Production Of Tunneling Electrodes
NASA Technical Reports Server (NTRS)
Kenny, Thomas W.; Podosek, Judith A.; Reynolds, Joseph K.; Rockstad, Howard K.; Vote, Erika C.; Kaiser, William J.
1993-01-01
Techniques for mass production of tunneling electrodes developed from silicon-micromachining, lithographic patterning, and related microfabrication processes. Tunneling electrodes named because electrons travel between them by quantum-mechanical tunneling; tunneling electrodes integral parts of tunneling transducer/sensors, which act in conjunction with feedback circuitry to stabilize tunneling currents by maintaining electrode separations of order of 10 Angstrom. Essential parts of scanning tunneling microscopes and related instruments, and used as force and position transducers in novel microscopic accelerometers and infrared detectors.
Li, Shao-Xiong; Qiu, Wei; Han, Siyuan; Wei, Y F; Zhu, X B; Gu, C Z; Zhao, S P; Wang, H B
2007-07-20
We report on the first unambiguous observation of macroscopic quantum tunneling (MQT) in a single submicron Bi(2)Sr(2)CaCu(2)O(8+delta) surface intrinsic Josephson junction (IJJ) by measuring its temperature-dependent switching current distribution. All relevant junction parameters were determined in situ in the classical regime and were used to predict the behavior of the IJJ in the quantum regime via MQT theory. Experimental results agree quantitatively with the theoretical predictions, thus confirming the MQT picture. Furthermore, the data also indicate that the surface IJJ, where the current flows along the c axis of the crystal, has the conventional sinphi current-phase relationship. PMID:17678315
NASA Astrophysics Data System (ADS)
Li, Shao-Xiong; Qiu, Wei; Han, Siyuan; Wei, Y. F.; Zhu, X. B.; Gu, C. Z.; Zhao, S. P.; Wang, H. B.
2007-07-01
We report on the first unambiguous observation of macroscopic quantum tunneling (MQT) in a single submicron Bi2Sr2CaCu2O8+δ surface intrinsic Josephson junction (IJJ) by measuring its temperature-dependent switching current distribution. All relevant junction parameters were determined in situ in the classical regime and were used to predict the behavior of the IJJ in the quantum regime via MQT theory. Experimental results agree quantitatively with the theoretical predictions, thus confirming the MQT picture. Furthermore, the data also indicate that the surface IJJ, where the current flows along the c axis of the crystal, has the conventional sinφ current-phase relationship.
Mi, Z.; Bhattacharya, P.; Yang, J.
2006-10-09
The molecular beam epitaxial growth and characteristics of 1.45 {mu}m metamorphic InAs quantum dot tunnel injection lasers on GaAs have been studied. Under optimized growth conditions, the quantum dots exhibit photoluminescence linewidths {approx}30 meV and high intensity at room temperature. The lasers are characterized by ultralow threshold current (63 A/cm{sup 2}), large frequency response (f{sub -3dB}=8 GHz), and near-zero {alpha} parameter and chirp.
Firsov, D. A.; Vorobjev, L. E.; Vinnichenko, M. Ya. Balagula, R. M.; Kulagina, M. M.; Vasil’iev, A. P.
2015-11-15
The photoluminescence and intersubband absorption spectra are studied in GaAs/AlGaAs tunnel- coupled quantum well structures. The peak positions in the photoluminescence and absorption spectra are consistent with the theoretically calculated energies of optical carrier transitions. The effect of a transverse electric field and temperature on intersubband light absorption is studied. It is caused by electron redistribution between the size-quantization levels and a variation in the energy spectrum of quantum wells. The variation in the refractive index in the energy region of observed intersubband transitions is estimated using Kramers–Kronig relations.
NASA Astrophysics Data System (ADS)
Shumilov, A. A.; Vinnichenko, M. Ya; Balagula, R. M.; Vorobjev, L. E.; Firsov, D. A.; Kulagina, M. M.; Vasil'iev, A. P.; Duque, C. A.; Tiutiunnyk, A.; Akimov, V.; Restrepo, R. L.; Tulupenko, V. N.; Ter-Martirosyan, A. L.
2015-11-01
Modulation of refraction index under transverse electric field was studied in structures with multiple tunnel-coupled GaAs/AlGaAs quantum wells in the spectral range corresponding to intersubband light absorption. The change of refraction index in electric field was calculated using Kramers-Kronig relation and experimentally determined spectra of intersubband light absorption in equilibrium conditions and under transverse electric field.
NASA Astrophysics Data System (ADS)
Zuo, Zheng-Wei; Kang, Da-wei; Wang, Zhao-Wu; Li, Liben
2016-08-01
The tunneling junction between one-dimensional topological superconductor and integer (fractional) topological insulator (TI), realized via point contact, is investigated theoretically with bosonization technology and renormalization group methods. For the integer TI case, in a finite range of edge interaction parameter, there is a non-trivial stable fixed point which corresponds to the physical picture that the edge of TI breaks up into two sections at the junction, with one side coupling strongly to the Majorana fermion and exhibiting perfect Andreev reflection, while the other side decouples, exhibiting perfect normal reflection at low energies. This fixed point can be used as a signature of the Majorana fermion and tested by nowadays experiment techniques. For the fractional TI case, the universal low-energy transport properties are described by perfect normal reflection, perfect Andreev reflection, or perfect insulating fixed points dependent on the filling fraction and edge interaction parameter of fractional TI.
NASA Astrophysics Data System (ADS)
Maniv, E.; Ron, A.; Goldstein, M.; Palevski, A.; Dagan, Y.
2016-07-01
A unique nanolithography technique compatible with conducting oxide interfaces, which requires a single lithographic step with no additional amorphous deposition or etching, is presented. It is demonstrated on a SrTiO3/LaAlO3 interface where a constriction is patterned in the electron liquid. We find that an additional backgating can further confine the electron liquid into an isolated island. Conductance and differential conductance measurements show resonant tunneling through the island. The data at various temperatures and magnetic fields are analyzed and the effective island size is found to be of the order of 10 nm. The magnetic field dependence suggests the absence of spin degeneracy in the island. Our method is suitable for creating superconducting and oxide-interface-based electronic devices.
Description of sub-barrier heavy ion fusion in a semiclassical quantum tunneling model
Yahlali, N.; Diaz, J.; Sami, T.
1996-04-01
In this paper we apply the semiclassical method based on the Feynman path integral formalism to sub-barrier fusion of heavy nuclei. Cross sections are calculated and compared to experimental data and to coupled-channel calculations for different mass systems: {sup 32}S+{sup 24}Mg, {sup 58}Ni+{sup 64}Ni, and {sup 16}O+{sup 208}Pb. The semiclassical method and coupled-channel calculations give comparable results. It is found that the coupling produces a renormalization of the barrier that is responsible for the enhancement of sub-barrier fusion cross sections and a dissipative force along the classical tunneling path. {copyright} {ital 1996 The American Physical Society.}
Interaction effects on the tunneling of electron-hole pairs in coupled quantum dots
NASA Astrophysics Data System (ADS)
Guerrero, Hector M.; Cocoletzi, Gregorio H.; Ulloa, Sergio E.
2001-03-01
The transit time of carriers is beginning to be an important parameter in the physical operation of semiconductor quantum dot `devices'. In the present work, we study the coherent propagation of electron-hole pairs in coupled self-assembled quantum dots in close proximity. These systems, achieved experimentally in a number of different geometries, have been recently implemented as a novel storage of optical information that may give rise to smart pixel technology in the near future [1]. Here, we apply an effective mass hamiltonian approach and solve numerically the time dependent Schroedinger equation of a system of photo-created electron-hole pairs in the dots. Our approach takes into account both Coulomb interactions and confinement effects. The time evolution is investigated in terms of the structural parameters for typical InAs-GaAs dots. Different initial conditions are considered, reflecting the basic processes that would take place in these experiments. We study the probabilities of finding the electron and hole in either the same or adjacent quantum dot, and study carefully the role of interactions in this behavior. [1] T. Lundstrom, W. Schoenfeld, H. Lee, and P. M. Petroff, Science 286, 2312 (1999).
Colussi, Francieli; Sørensen, Trine H.; Alasepp, Kadri; Kari, Jeppe; Cruys-Bagger, Nicolaj; Windahl, Michael S.; Olsen, Johan P.; Borch, Kim; Westh, Peter
2015-01-01
Cellobiohydrolases break down cellulose sequentially by sliding along the crystal surface with a single cellulose strand threaded through the catalytic tunnel of the enzyme. This so-called processive mechanism relies on a complex pattern of enzyme-substrate interactions, which need to be addressed in molecular descriptions of processivity and its driving forces. Here, we have used titration calorimetry to study interactions of cellooligosaccharides (COS) and a catalytically deficient variant (E212Q) of the enzyme Cel7A from Trichoderma reesei. This enzyme has ∼10 glucopyranose subsites in the catalytic tunnel, and using COS ligands with a degree of polymerization (DP) from 2 to 8, different regions of the tunnel could be probed. For COS ligands with a DP of 2–3 the binding constants were around 105 m−1, and for longer ligands (DP 5–8) this value was ∼107 m−1. Within each of these groups we did not find increased affinity as the ligands got longer and potentially filled more subsites. On the contrary, we found a small but consistent affinity loss as DP rose from 6 to 8, particularly at the higher investigated temperatures. Other thermodynamic functions (ΔH, ΔS, and ΔCp) decreased monotonously with both temperature and DP. Combined interpretation of these thermodynamic results and previously published structural data allowed assessment of an affinity profile along the length axis of the active tunnel. PMID:25477511
Colussi, Francieli; Sørensen, Trine H; Alasepp, Kadri; Kari, Jeppe; Cruys-Bagger, Nicolaj; Windahl, Michael S; Olsen, Johan P; Borch, Kim; Westh, Peter
2015-01-23
Cellobiohydrolases break down cellulose sequentially by sliding along the crystal surface with a single cellulose strand threaded through the catalytic tunnel of the enzyme. This so-called processive mechanism relies on a complex pattern of enzyme-substrate interactions, which need to be addressed in molecular descriptions of processivity and its driving forces. Here, we have used titration calorimetry to study interactions of cellooligosaccharides (COS) and a catalytically deficient variant (E212Q) of the enzyme Cel7A from Trichoderma reesei. This enzyme has ∼10 glucopyranose subsites in the catalytic tunnel, and using COS ligands with a degree of polymerization (DP) from 2 to 8, different regions of the tunnel could be probed. For COS ligands with a DP of 2-3 the binding constants were around 10(5) m(-1), and for longer ligands (DP 5-8) this value was ∼10(7) m(-1). Within each of these groups we did not find increased affinity as the ligands got longer and potentially filled more subsites. On the contrary, we found a small but consistent affinity loss as DP rose from 6 to 8, particularly at the higher investigated temperatures. Other thermodynamic functions (ΔH, ΔS, and ΔCp) decreased monotonously with both temperature and DP. Combined interpretation of these thermodynamic results and previously published structural data allowed assessment of an affinity profile along the length axis of the active tunnel. PMID:25477511
NASA Technical Reports Server (NTRS)
Noll, Thomas E.; Perry, Boyd, III; Tiffany, Sherwood H.; Cole, Stanley R.; Buttrill, Carey S.; Adams, William M., Jr.; Houck, Jacob A.; Srinathkumar, S.; Mukhopadhyay, Vivek; Pototzky, Anthony S.
1989-01-01
The status of the joint NASA/Rockwell Active Flexible Wing Wind-Tunnel Test Program is described. The objectives are to develop and validate the analysis, design, and test methodologies required to apply multifunction active control technology for improving aircraft performance and stability. Major tasks include designing digital multi-input/multi-output flutter-suppression and rolling-maneuver-load alleviation concepts for a flexible full-span wind-tunnel model, obtaining an experimental data base for the basic model and each control concept and providing comparisons between experimental and analytical results to validate the methodologies. The opportunity is provided to improve real-time simulation techniques and to gain practical experience with digital control law implementation procedures.
Understanding Data Analysis from Multiple Viewpoints: An Example from Quantum Tunneling
NASA Astrophysics Data System (ADS)
Wittmann, Michael C.; Morgan, Jeffrey T.
2004-09-01
During individual clinical interviews, the interaction between researcher and interviewee leads to a specific set of data that can later be interpreted from several viewpoints. In this paper, we describe three analyses of a student's reasoning. First, we describe her "physics reasoning" in terms of the physical situation she describes and the "difficulties" she has in reasoning about the interview question. Second, we describe some "reasoning resources" that she uses. Finally, we describe "epistemological resources" that may influence her reasoning about quantum physics. We conclude with a discussion of implications about the practice of interviews and their analysis.
Bekasova, Olga D; Revina, Alexandra A; Kornienko, Ekaterina S; Kurganov, Boris I
2015-06-01
CdS quantum dots (CdS QDs) 4.3 nm in diameter synthesized in an AOT/isooctane/water microemulsion and in R-phycoerythrin tunnel cavities (3.5 × 6.0 nm) were analyzed for photoelectrochemical properties. The CdS QDs preparations were applied onto a platinum electrode to obtain solid films. Experiments were performed in a two-section vessel, with one section filled with ethanol and the other, with 3 M KCl. The sections were connected through an agar stopper. It was found that illumination of the films resulted in a change of the electrode potential. The magnitude of this change and the kinetics of the appearance and disappearance of the photopotential, i.e., the difference between the electrode potential on the light and in dark, depended on the nature of the QD shell. The photovoltaic effect of CdS QDs in R-phycoerythrin, compared to that of CdS QDs in AOT/isooctane micelles, is three to four times greater due to the photosensitizing action of R-phycoerythrin. The photosensitized effect was markedly higher than the photoelectric sensitivity of R-phycoerythrin and had the opposite polarity. Changes in the potential upon turning the light on and off could be observed repeatedly.
Singh, Saurabh Kumar; Rajaraman, Gopalan
2016-01-01
Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices. Among others, 4d/5d elements such as Re(IV) ion are found to exhibit very large magnetic anisotropy, and inclusion of this ion-aggregated clusters yields several attractive molecular magnets. Here, using ab intio calculations, we unravel the source of giant magnetic anisotropy associated with the Re(IV) ions by studying a series of mononuclear Re(IV) six coordinate complexes. The low-lying doublet states are found to be responsible for large magnetic anisotropy and the sign of the axial zero-field splitting parameter (D) can be categorically predicted based on the position of the ligand coordination. Large transverse anisotropy along with large hyperfine interactions opens up multiple relaxation channels leading to a fast quantum tunnelling of the magnetization (QTM) process. Enhancing the Re-ligand covalency is found to significantly quench the QTM process. PMID:26883278
Bekasova, Olga D; Revina, Alexandra A; Kornienko, Ekaterina S; Kurganov, Boris I
2015-06-01
CdS quantum dots (CdS QDs) 4.3 nm in diameter synthesized in an AOT/isooctane/water microemulsion and in R-phycoerythrin tunnel cavities (3.5 × 6.0 nm) were analyzed for photoelectrochemical properties. The CdS QDs preparations were applied onto a platinum electrode to obtain solid films. Experiments were performed in a two-section vessel, with one section filled with ethanol and the other, with 3 M KCl. The sections were connected through an agar stopper. It was found that illumination of the films resulted in a change of the electrode potential. The magnitude of this change and the kinetics of the appearance and disappearance of the photopotential, i.e., the difference between the electrode potential on the light and in dark, depended on the nature of the QD shell. The photovoltaic effect of CdS QDs in R-phycoerythrin, compared to that of CdS QDs in AOT/isooctane micelles, is three to four times greater due to the photosensitizing action of R-phycoerythrin. The photosensitized effect was markedly higher than the photoelectric sensitivity of R-phycoerythrin and had the opposite polarity. Changes in the potential upon turning the light on and off could be observed repeatedly. PMID:25935221
Singh, Saurabh Kumar; Rajaraman, Gopalan
2016-02-17
Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices. Among others, 4d/5d elements such as Re(IV) ion are found to exhibit very large magnetic anisotropy, and inclusion of this ion-aggregated clusters yields several attractive molecular magnets. Here, using ab intio calculations, we unravel the source of giant magnetic anisotropy associated with the Re(IV) ions by studying a series of mononuclear Re(IV) six coordinate complexes. The low-lying doublet states are found to be responsible for large magnetic anisotropy and the sign of the axial zero-field splitting parameter (D) can be categorically predicted based on the position of the ligand coordination. Large transverse anisotropy along with large hyperfine interactions opens up multiple relaxation channels leading to a fast quantum tunnelling of the magnetization (QTM) process. Enhancing the Re-ligand covalency is found to significantly quench the QTM process.
Singh, Saurabh Kumar; Rajaraman, Gopalan
2016-01-01
Single-molecule magnets represent a promising route to achieve potential applications such as high-density information storage and spintronics devices. Among others, 4d/5d elements such as Re(IV) ion are found to exhibit very large magnetic anisotropy, and inclusion of this ion-aggregated clusters yields several attractive molecular magnets. Here, using ab intio calculations, we unravel the source of giant magnetic anisotropy associated with the Re(IV) ions by studying a series of mononuclear Re(IV) six coordinate complexes. The low-lying doublet states are found to be responsible for large magnetic anisotropy and the sign of the axial zero-field splitting parameter (D) can be categorically predicted based on the position of the ligand coordination. Large transverse anisotropy along with large hyperfine interactions opens up multiple relaxation channels leading to a fast quantum tunnelling of the magnetization (QTM) process. Enhancing the Re-ligand covalency is found to significantly quench the QTM process. PMID:26883278
NASA Technical Reports Server (NTRS)
Waszak, Martin R.
1997-01-01
The Benchmark Active Controls Technology (BACT) project is part of NASA Langley Research Center s Benchmark Models Program for studying transonic aeroelastic phenomena. In January of 1996 the BACT wind-tunnel model was used to successfully demonstrate the application of robust multivariable control design methods (H and -synthesis) to flutter suppression. This paper addresses the design and experimental evaluation of robust multivariable flutter suppression control laws with particular attention paid to the degree to which stability and performance robustness was achieved.
NASA Astrophysics Data System (ADS)
Cao, Jiang; Cresti, Alessandro; Esseni, David; Pala, Marco
2016-02-01
We simulate a band-to-band tunneling field-effect transistor based on a vertical heterojunction of single-layer MoS2 and WTe2, by exploiting the non-equilibrium Green's function method and including electron-phonon scattering. For both in-plane and out-of-plane transport, we attempt to calibrate out models to the few available experimental results. We focus on the role of chemical doping and back-gate biasing, and investigate the off-state physics of this device by analyzing the influence of the top-gate geometrical alignment on the device performance. The device scalability as a function of gate length is also studied. Finally, we present two metrics for the switching delay and energy of the device. Our simulations indicate that vertical field-effect transistors based on transition metal dichalcogenides can provide very small values of sub-threshold swing when properly designed in terms of doping concentration and top-gate extension length.
Active Vertical Tail Buffeting Alleviation on a Twin-Tail Fighter Configuration in a Wind Tunnel
NASA Technical Reports Server (NTRS)
Moses, Robert W.
1997-01-01
A 1/6-scale F-18 wind-tunnel model was tested in the Transonic Dynamics Tunnel at the NASA Langley Research Center as part of the Actively Controlled Response Of Buffet-Affected Tails (ACROBAT) program to assess the use of active controls in reducing vertical tail buffeting. The starboard vertical tail was equipped with an active rudder and other aerodynamic devices, and the port vertical tail was equipped with piezoelectric actuators. The tunnel conditions were atmospheric air at a dynamic pressure of 14 psf. By using single-input-single-output control laws at gains well below the physical limits of the control effectors, the power spectral density of the root strains at the frequency of the first bending mode of the vertical tail was reduced by as much as 60 percent up to angles of attack of 37 degrees. Root mean square (RMS) values of root strain were reduced by as much as 19 percent. Stability margins indicate that a constant gain setting in the control law may be used throughout the range of angle of attack tested.
Active Vertical Tail Buffeting Alleviation on an F/A-18 Model in a Wind Tunnel
NASA Technical Reports Server (NTRS)
Moses, Robert W.
1999-01-01
A 1/6-scale F-18 wind-tunnel model was tested in the Transonic Dynamics Tunnel at the NASA Langley Research Center as part of the Actively Controlled Response Of Buffet-Affected Tails (ACROBAT) program to assess the use of active controls in reducing vertical tail buffeting. The starboard vertical tail was equipped with an active rudder and other aerodynamic devices, and the port vertical tail was equipped with piezoelectric actuators. The tunnel conditions were atmospheric air at a dynamic pressure of 14 psf. By using single-input-single-output control laws at gains well below the physical limits of the control effectors, the power spectral density of the root strains at the frequency of the first bending mode of the vertical tail was reduced by as much as 60 percent up to angles of attack of 37 degrees. Root mean square (RMS) values of root strain were reduced by as much as 19 percent. Stability margins indicate that a constant gain setting in the control law may be used throughout the range of angle of attack tested.
Active mode-locking of mid-infrared quantum cascade lasers with short gain recovery time.
Wang, Yongrui; Belyanin, Alexey
2015-02-23
We investigate the dynamics of actively modulated mid-infrared quantum cascade lasers (QCLs) using space- and time-domain simulations of coupled density matrix and Maxwell equations with resonant tunneling current taken into account. We show that it is possible to achieve active mode locking and stable generation of picosecond pulses in high performance QCLs with a vertical laser transition and a short gain recovery time by bias modulation of a short section of a monolithic Fabry-Perot cavity. In fact, active mode locking in QCLs with a short gain recovery time turns out to be more robust to the variation of parameters as compared to previously studied lasers with a long gain recovery time. We investigate the effects of spatial hole burning and phase locking on the laser output.
Quantum teleportation over 143 kilometres using active feed-forward.
Ma, Xiao-Song; Herbst, Thomas; Scheidl, Thomas; Wang, Daqing; Kropatschek, Sebastian; Naylor, William; Wittmann, Bernhard; Mech, Alexandra; Kofler, Johannes; Anisimova, Elena; Makarov, Vadim; Jennewein, Thomas; Ursin, Rupert; Zeilinger, Anton
2012-09-13
The quantum internet is predicted to be the next-generation information processing platform, promising secure communication and an exponential speed-up in distributed computation. The distribution of single qubits over large distances via quantum teleportation is a key ingredient for realizing such a global platform. By using quantum teleportation, unknown quantum states can be transferred over arbitrary distances to a party whose location is unknown. Since the first experimental demonstrations of quantum teleportation of independent external qubits, an internal qubit and squeezed states, researchers have progressively extended the communication distance. Usually this occurs without active feed-forward of the classical Bell-state measurement result, which is an essential ingredient in future applications such as communication between quantum computers. The benchmark for a global quantum internet is quantum teleportation of independent qubits over a free-space link whose attenuation corresponds to the path between a satellite and a ground station. Here we report such an experiment, using active feed-forward in real time. The experiment uses two free-space optical links, quantum and classical, over 143 kilometres between the two Canary Islands of La Palma and Tenerife. To achieve this, we combine advanced techniques involving a frequency-uncorrelated polarization-entangled photon pair source, ultra-low-noise single-photon detectors and entanglement-assisted clock synchronization. The average teleported state fidelity is well beyond the classical limit of two-thirds. Furthermore, we confirm the quality of the quantum teleportation procedure without feed-forward by complete quantum process tomography. Our experiment verifies the maturity and applicability of such technologies in real-world scenarios, in particular for future satellite-based quantum teleportation. PMID:22951967
Quantum teleportation over 143 kilometres using active feed-forward.
Ma, Xiao-Song; Herbst, Thomas; Scheidl, Thomas; Wang, Daqing; Kropatschek, Sebastian; Naylor, William; Wittmann, Bernhard; Mech, Alexandra; Kofler, Johannes; Anisimova, Elena; Makarov, Vadim; Jennewein, Thomas; Ursin, Rupert; Zeilinger, Anton
2012-09-13
The quantum internet is predicted to be the next-generation information processing platform, promising secure communication and an exponential speed-up in distributed computation. The distribution of single qubits over large distances via quantum teleportation is a key ingredient for realizing such a global platform. By using quantum teleportation, unknown quantum states can be transferred over arbitrary distances to a party whose location is unknown. Since the first experimental demonstrations of quantum teleportation of independent external qubits, an internal qubit and squeezed states, researchers have progressively extended the communication distance. Usually this occurs without active feed-forward of the classical Bell-state measurement result, which is an essential ingredient in future applications such as communication between quantum computers. The benchmark for a global quantum internet is quantum teleportation of independent qubits over a free-space link whose attenuation corresponds to the path between a satellite and a ground station. Here we report such an experiment, using active feed-forward in real time. The experiment uses two free-space optical links, quantum and classical, over 143 kilometres between the two Canary Islands of La Palma and Tenerife. To achieve this, we combine advanced techniques involving a frequency-uncorrelated polarization-entangled photon pair source, ultra-low-noise single-photon detectors and entanglement-assisted clock synchronization. The average teleported state fidelity is well beyond the classical limit of two-thirds. Furthermore, we confirm the quality of the quantum teleportation procedure without feed-forward by complete quantum process tomography. Our experiment verifies the maturity and applicability of such technologies in real-world scenarios, in particular for future satellite-based quantum teleportation.
Normal metal tunnel junction-based superconducting quantum interference proximity transistor
D'Ambrosio, Sophie Meissner, Martin; Blanc, Christophe; Ronzani, Alberto; Giazotto, Francesco
2015-09-14
We report the fabrication and characterization of an alternative design for a superconducting quantum interference proximity transistor (SQUIPT) based on a normal metal (N) probe. The absence of direct Josephson coupling between the proximized metal nanowire and the N probe allows us to observe the full modulation of the wire density of states around zero voltage and current via the application of an external magnetic field. This results into a drastic suppression of power dissipation which can be as low as a few ∼10{sup −17} W. In this context, the interferometer allows an improvement of up to four orders of magnitude with respect to earlier SQUIPT designs and makes it ideal for extra-low power cryogenic applications. In addition, the N-SQUIPT has been recently predicted to be the enabling candidate for the implementation of coherent caloritronic devices based on proximity effect.
Long-lived binary tunneling spectrum in the quantum Hall Tomonaga-Luttinger liquid
NASA Astrophysics Data System (ADS)
Washio, K.; Nakazawa, R.; Hashisaka, M.; Muraki, K.; Tokura, Y.; Fujisawa, T.
2016-02-01
The existence of long-lived nonequilibrium states without showing thermalization, which has previously been demonstrated in time evolution of ultracold atoms, suggests the possibility of their spatial analog in transport behavior of interacting electrons in solid-state systems. Here we report long-lived nonequilibrium states in one-dimensional edge channels in the integer quantum Hall regime. An indirect heating scheme in a counterpropagating configuration is employed to generate a nontrivial binary spectrum consisting of high- and low-temperature components. This unusual spectrum is sustained even after traveling 5-10 μ m , much longer than the length for electronic relaxation (about 0.1 μ m ), without showing significant thermalization. This observation is consistent with the integrable model of Tomonaga-Luttinger liquid. The long-lived spectrum implies that the system is well described by noninteracting plasmons, which are attractive for carrying information for a long distance.
NASA Technical Reports Server (NTRS)
Cole, Stanley R.; Johnson, R. Keith; Piatak, David J.; Florance, Jennifer P.; Rivera, Jose A., Jr.
2003-01-01
The Langley Transonic Dynamics Tunnel (TDT) has provided a unique capability for aeroelastic testing for over forty years. The facility has a rich history of significant contributions to the design of many United States commercial transports, military aircraft, launch vehicles, and spacecraft. The facility has many features that contribute to its uniqueness for aeroelasticity testing, perhaps the most important feature being the use of a heavy gas test medium to achieve higher test densities compared to testing in air. Higher test medium densities substantially improve model-building requirements and therefore simplify the fabrication process for building aeroelastically scaled wind tunnel models. This paper describes TDT capabilities that make it particularly suited for aeroelasticity testing. The paper also discusses the nature of recent test activities in the TDT, including summaries of several specific tests. Finally, the paper documents recent facility improvement projects and the continuous statistical quality assessment effort for the TDT.
Probing DNA in nanopores via tunneling: from sequencing to ``quantum'' analogies
NASA Astrophysics Data System (ADS)
di Ventra, Massimiliano
2012-02-01
Fast and low-cost DNA sequencing methods would revolutionize medicine: a person could have his/her full genome sequenced so that drugs could be tailored to his/her specific illnesses; doctors could know in advance patients' likelihood to develop a given ailment; cures to major diseases could be found faster [1]. However, this goal of ``personalized medicine'' is hampered today by the high cost and slow speed of DNA sequencing methods. In this talk, I will discuss the sequencing protocol we suggest which requires the measurement of the distributions of transverse currents during the translocation of single-stranded DNA into nanopores [2-5]. I will support our conclusions with a combination of molecular dynamics simulations coupled to quantum mechanical calculations of electrical current in experimentally realizable systems [2-5]. I will also discuss recent experiments that support these theoretical predictions. In addition, I will show how this relatively unexplored area of research at the interface between solids, liquids, and biomolecules at the nanometer length scale is a fertile ground to study quantum phenomena that have a classical counterpart, such as ionic quasi-particles, ionic ``quantized'' conductance [6,7] and Coulomb blockade [8]. Work supported in part by NIH. [4pt] [1] M. Zwolak, M. Di Ventra, Physical Approaches to DNA Sequencing and Detection, Rev. Mod. Phys. 80, 141 (2008).[0pt] [2] M. Zwolak and M. Di Ventra, Electronic signature of DNA nucleotides via transverse transport, Nano Lett. 5, 421 (2005).[0pt] [3] J. Lagerqvist, M. Zwolak, and M. Di Ventra, Fast DNA sequencing via transverse electronic transport, Nano Lett. 6, 779 (2006).[0pt] [4] J. Lagerqvist, M. Zwolak, and M. Di Ventra, Influence of the environment and probes on rapid DNA sequencing via transverse electronic transport, Biophys. J. 93, 2384 (2007).[0pt] [5] M. Krems, M. Zwolak, Y.V. Pershin, and M. Di Ventra, Effect of noise on DNA sequencing via transverse electronic transport
Cryogenic wind-tunnel model technology development activities at the NASA Langley Research Center
NASA Technical Reports Server (NTRS)
Young, C. P., Jr.; Bradshaw, J. F.; Rush, H. F., Jr.; Wallace, J. W.; Watkins, V. E., Jr.
1984-01-01
This paper summarizes the current cryogenic wind-tunnel model technology development activities at the NASA Langley Research Center. These research and development activities are being conducted in support of the design and fabrication of models for the new National Transonic Facility (NTF). The scope and current status of major research and development work is described and where available, data are presented from various investigations conducted to date. In addition, design and fabrication experience for existing developmental models to be tested in the NTF is discussed.
NASA Technical Reports Server (NTRS)
Doggett, R. V., Jr.; Abel, I.; Ruhlin, C. L.
1976-01-01
A status report and review of wind tunnel model experimental techniques that have been developed to study and validate the use of active control technology for the minimization of aeroelastic response are presented. Modeling techniques, test procedures, and data analysis methods used in three model studies are described. The studies include flutter mode suppression on a delta-wing model, flutter mode suppression and ride quality control on a 1/30-size model of the B-52 CCV airplane, and an active lift distribution control system on a 1/22 size C-5A model.
NASA Astrophysics Data System (ADS)
Nguyen, Khoi; Lilly, Michael; Bishop, Nathaniel; Nielsen, Erik; Rahman, Rajib; Wendt, Joel; Dominguez, Jason; Pluym, Tammy; Stevens, Jeff; Ten Eyck, Greg; Carroll, Malcolm
2013-03-01
The combination of asymmetric tunnel rates and finite temperature can shift the average charge occupation within a double quantum dot (DQD) stability diagram. DQD charge sensing shows the transitions in electron occupation dependence on gate bias. Applied source-drain bias further introduces shifts in the charge transition lines including the formation of bias triangles. In some material systems, tunnel barrier uniformity can be difficult to achieve. Asymmetry in tunnel barriers can lead to vanishingly small transitions in regions. Finite temperature effects with asymmetric barriers further leads to kinks in the stability diagram. In this talk we present measurements of DQDs with asymmetric barriers and compare them to simulation of stability diagrams using a capacitance network including the rate equation and temperature dependent tunneling. The model provides quantitative insight about finite temperature effects as well as the vanishing charge transition lines that is not readily available in the literature. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's NNSA under contract DE-AC04-94AL85000.
Control Surface Interaction Effects of the Active Aeroelastic Wing Wind Tunnel Model
NASA Technical Reports Server (NTRS)
Heeg, Jennifer
2006-01-01
This paper presents results from testing the Active Aeroelastic Wing wind tunnel model in NASA Langley s Transonic Dynamics Tunnel. The wind tunnel test provided an opportunity to study aeroelastic system behavior under combined control surface deflections, testing for control surface interaction effects. Control surface interactions were observed in both static control surface actuation testing and dynamic control surface oscillation testing. The primary method of evaluating interactions was examination of the goodness of the linear superposition assumptions. Responses produced by independently actuating single control surfaces were combined and compared with those produced by simultaneously actuating and oscillating multiple control surfaces. Adjustments to the data were required to isolate the control surface influences. Using dynamic data, the task increases, as both the amplitude and phase have to be considered in the data corrections. The goodness of static linear superposition was examined and analysis of variance was used to evaluate significant factors influencing that goodness. The dynamic data showed interaction effects in both the aerodynamic measurements and the structural measurements.
Tunnelling from black holes and tunnelling into white holes
NASA Astrophysics Data System (ADS)
Chatterjee, Bhramar; Ghosh, A.; Mitra, P.
2008-03-01
Hawking radiation is nowadays being understood as tunnelling through black hole horizons. Here, the extension of the Hamilton-Jacobi approach to tunnelling for non-rotating and rotating black holes in different non-singular coordinate systems not only confirms this quantum emission from black holes but also reveals the new phenomenon of absorption into white holes by quantum mechanical tunnelling. The rôle of a boundary condition of total absorption or emission is also clarified.
Experimental entanglement activation from discord in a programmable quantum measurement.
Adesso, Gerardo; D'Ambrosio, Vincenzo; Nagali, Eleonora; Piani, Marco; Sciarrino, Fabio
2014-04-11
In quantum mechanics, observing is not a passive act. Consider a system of two quantum particles A and B: if a measurement apparatus M is used to make an observation on B, the overall state of the system AB will typically be altered. When this happens, no matter which local measurement is performed, the two objects A and B are revealed to possess peculiar correlations known as quantum discord. Here, we demonstrate experimentally that the very act of local observation gives rise to an activation protocol which converts discord into distillable entanglement, a stronger and more useful form of quantum correlations, between the apparatus M and the composite system AB. We adopt a flexible two-photon setup to realize a three-qubit system (A, B, M) with programmable degrees of initial correlations, measurement interaction, and characterization processes. Our experiment demonstrates the fundamental mechanism underpinning the ubiquitous act of observing the quantum world and establishes the potential of discord in entanglement generation.
NASA Astrophysics Data System (ADS)
Daqiq, Reza; Ghobadi, Nader
2016-07-01
We study the quantum size effects of an MgO-based double barrier magnetic tunnel junction with a nonmagnetic-metal (DBMTJ-NM) (semiconductor (DBMTJ-SC)) spacer on the charge current and the spin-transfer torque (STT) components using non-equilibrium Green's function (NEGF) formalism. The results show oscillatory behavior due to the resonant tunneling effect depending on the structure parameters. We find that the charge current and the STT components in the DBMTJ-SC demonstrate the magnitude enhancement in comparison with the DBMTJ-NM. The bias dependence of the STT components in a DBMTJ-NM shows different behavior in comparison with spin valves and conventional MTJs. Therefore, by choosing a specific SC spacer with suitable thickness in a DBMTJ the charge current and the STT components significantly increase so that one can design a device with high STT and faster magnetization switching.
Varade, Vaibhav Jagtap, Amardeep M.; Koteswara Rao, K. S. R.; Ramesh, K. P.; Menon, R.; Anjaneyulu, P.
2015-06-07
Temperature and photo-dependent current–voltage characteristics are investigated in thin film devices of a hybrid-composite comprising of organic semiconductor poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and cadmium telluride quantum dots (CdTe QDs). A detailed study of the charge injection mechanism in ITO/PEDOT:PSS-CdTe QDs/Al device exhibits a transition from direct tunneling to Fowler–Nordheim tunneling with increasing electric field due to formation of high barrier at the QD interface. In addition, the hybrid-composite exhibits a huge photoluminescence quenching compared to aboriginal CdTe QDs and high increment in photoconductivity (∼ 400%), which is attributed to the charge transfer phenomena. The effective barrier height (Φ{sub B} ≈ 0.68 eV) is estimated from the transition voltage and the possible origin of its variation with temperature and photo-illumination is discussed.
Meisner, Jan; Kästner, Johannes
2016-04-25
Quantum mechanical tunneling of atoms is increasingly found to play an important role in many chemical transformations. Experimentally, atom tunneling can be indirectly detected by temperature-independent rate constants at low temperature or by enhanced kinetic isotope effects. In contrast, the influence of tunneling on the reaction rates can be monitored directly through computational investigations. The tunnel effect, for example, changes reaction paths and branching ratios, enables chemical reactions in an astrochemical environment that would be impossible by thermal transition, and influences biochemical processes. PMID:26990917
Wang, Yimin; Braams, Bastiaan J; Bowman, Joel M; Carter, Stuart; Tew, David P
2008-06-14
Quantum calculations of the ground vibrational state tunneling splitting of H-atom and D-atom transfer in malonaldehyde are performed on a full-dimensional ab initio potential energy surface (PES). The PES is a fit to 11 147 near basis-set-limit frozen-core CCSD(T) electronic energies. This surface properly describes the invariance of the potential with respect to all permutations of identical atoms. The saddle-point barrier for the H-atom transfer on the PES is 4.1 kcalmol, in excellent agreement with the reported ab initio value. Model one-dimensional and "exact" full-dimensional calculations of the splitting for H- and D-atom transfer are done using this PES. The tunneling splittings in full dimensionality are calculated using the unbiased "fixed-node" diffusion Monte Carlo (DMC) method in Cartesian and saddle-point normal coordinates. The ground-state tunneling splitting is found to be 21.6 cm(-1) in Cartesian coordinates and 22.6 cm(-1) in normal coordinates, with an uncertainty of 2-3 cm(-1). This splitting is also calculated based on a model which makes use of the exact single-well zero-point energy (ZPE) obtained with the MULTIMODE code and DMC ZPE and this calculation gives a tunneling splitting of 21-22 cm(-1). The corresponding computed splittings for the D-atom transfer are 3.0, 3.1, and 2-3 cm(-1). These calculated tunneling splittings agree with each other to within less than the standard uncertainties obtained with the DMC method used, which are between 2 and 3 cm(-1), and agree well with the experimental values of 21.6 and 2.9 cm(-1) for the H and D transfer, respectively.
NASA Astrophysics Data System (ADS)
Feng, Zhong-wen; Li, Guo-ping; Zhang, Yan; Zu, Xiao-tao
2015-02-01
In this paper, we combine the Hamilton-Jacobi equation with a new general tortoise coordinate transformation to study quantum tunneling of scalar particles and fermions from the non-stationary higher dimensional Vaidya-de Sitter black hole. The results show that Hamilton-Jacobi equation is a semi-classical foundation equation which can easily derived from the particles' dynamic equations, it can helps us understand the origin of Hawking radiation. Besides, based on the dimensional analysis, we believed that the new general tortoise coordinate transformation is more reasonable than old ones.
Harack, B.; Leary, A.; Coish, W. A.; Hilke, M.; Yu, G.; Gupta, J. A.; Payette, C.; Austing, D. G.
2013-12-04
We outline power spectra and auto correlation analysis performed on temporal oscillations in the tunneling current of coupled vertical quantum dots. The current is monitored for ∼2325 s blocks as the magnetic field is stepped through a high bias feature displaying hysteresis and switching: hallmarks of the hyperfine interaction. Quasi-periodic oscillations of ∼2 pA amplitude and of ∼100 s period are observed in the current inside the hysteretic feature. Compared to the baseline current outside the hysteretic feature the power spectral density is enhanced by up to three orders of magnitude and the auto correlation displays clear long lived oscillations about zero.
Active load control during rolling maneuvers. [performed in the Langley Transonic Dynamics Tunnel
NASA Technical Reports Server (NTRS)
Woods-Vedeler, Jessica A.; Pototzky, Anthony S.; Hoadley, Sherwood T.
1994-01-01
A rolling maneuver load alleviation (RMLA) system has been demonstrated on the active flexible wing (AFW) wind tunnel model in the Langley Transonic Dynamics Tunnel (TDT). The objective was to develop a systematic approach for designing active control laws to alleviate wing loads during rolling maneuvers. Two RMLA control laws were developed that utilized outboard control-surface pairs (leading and trailing edge) to counteract the loads and that used inboard trailing-edge control-surface pairs to maintain roll performance. Rolling maneuver load tests were performed in the TDT at several dynamic pressures that included two below and one 11 percent above open-loop flutter dynamic pressure. The RMLA system was operated simultaneously with an active flutter suppression system above open-loop flutter dynamic pressure. At all dynamic pressures for which baseline results were obtained, torsion-moment loads were reduced for both RMLA control laws. Results for bending-moment load reductions were mixed; however, design equations developed in this study provided conservative estimates of load reduction in all cases.
NASA Astrophysics Data System (ADS)
Ota, K.; Hamada, K.; Takemura, R.; Ohmaki, M.; Machi, T.; Tanabe, K.; Suzuki, M.; Maeda, A.; Kitano, H.
2009-04-01
We investigated macroscopic quantum tunneling (MQT) of Bi2Sr2CaCu2Oy intrinsic Josephson junctions (IJJs) for two device structures. One is a small mesa, which is a few nanometers thick with only two or three IJJs, and the other is a stack of a few hundred IJJs in a narrow bridge structure. The experimental results regarding the switching-current distribution for the first switch from the zero-voltage state were in good agreement with the conventional theory for a single Josephson junction, indicating that the crossover temperature from thermal activation to the MQT regime for the former device structure was similar to that for the latter device structure. Together with the observation of multiphoton transitions between quantized energy levels in the MQT regime, these results strongly suggest that the observed MQT behavior is intrinsic to a single IJJ in high- Tc cuprates and is independent of the device structure. The switching-current distribution for the second switch from the first resistive state, which was carefully distinguished from the first switch, was also compared with respect to the two device structures. In spite of the differences between the heat transfer environments, the second switch exhibited a similar temperature-independent behavior for both devices up to a much higher temperature than the crossover temperature for the first switch. We argue that this cannot be explained in terms of self-heating caused by dissipative currents after the first switch. As possible candidates for this phenomenon, the MQT process for the second switch and the effective increase in the electronic temperature due to the quasiparticle injection are discussed.
NASA Astrophysics Data System (ADS)
Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying
2015-03-01
Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.
Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying
2015-01-01
Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated. PMID:25749635
Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying
2015-01-01
Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO₂), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi₂O₃)₀.₀₇(CoO)₀.₀₃(ZnO)₀.₉ semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.
Active-region designs in quantum cascade lasers
Zasavitskii, I I
2012-10-31
This paper analyses the development of active-region designs in quantum cascade lasers. Active-region designs have been demonstrated to date that employ various radiative transitions (vertical, diagonal, interminiband and interband). The lower laser level is depopulated through nonradiative transitions, such as one- or two-phonon (and even three-phonon) relaxation or bound state {yields} continuum transitions. Advances in active-region designs and energy diagram optimisation in the past few years have led to significant improvements in important characteristics of quantum cascade lasers, such as their output power, emission bandwidth, characteristic temperature and efficiency. (invited paper)
Xie, Xufen; Yan, Jiawei; Liang, Jinghong; Li, Jijun; Zhang, Meng; Mao, Bingwei
2013-10-01
We present quantum conductance measurements of germanium by means of an electrochemical scanning tunneling microscope (STM) break junction based on a jump-to-contact mechanism. Germanium nanowires between a platinum/iridium tip and different substrates were constructed to measure the quantum conductance. By applying appropriate potentials to the substrate and the tip, the process of heterogeneous contact and homogeneous breakage was realized. Typical conductance traces exhibit steps at 0.025 and 0.05 G0. The conductance histogram indicates that the conductance of germanium nanowires is located between 0.02 and 0.15 G0 in the low-conductance region and is free from the influence of substrate materials. However, the distribution of conductance plateaus is too discrete to display distinct peaks in the conductance histogram of the high-conductance region. PMID:23704043
Development of an Active Twist Rotor for Wind: Tunnel Testing (NLPN97-310
NASA Technical Reports Server (NTRS)
Cesnik, Carlos E. S.; Shin, SangJoon; Hagood, Nesbitt W., IV
1998-01-01
The development of the Active Twist Rotor prototype blade for hub vibration and noise reduction studies is presented in this report. Details of the modeling, design, and manufacturing are explored. The rotor blade is integrally twisted by direct strain actuation. This is accomplished by distributing embedded piezoelectric fiber composites along the span of the blade. The development of the analysis framework for this type of active blade is presented. The requirements for the prototype blade, along with the final design results are also presented. A detail discussion on the manufacturing aspects of the prototype blade is described. Experimental structural characteristics of the prototype blade compare well with design goals, and preliminary bench actuation tests show lower performance than originally predicted. Electrical difficulties with the actuators are also discussed. The presented prototype blade is leading to a complete fully articulated four-blade active twist rotor system for future wind tunnel tests.
Analysis of a modified recessed active tunneling field-effect transistor
NASA Astrophysics Data System (ADS)
Kim, HuiJung; Choi, Seongwook; Yoo, NakWon; Rhee, SeungMan; Lee, Myoung Jin; Park, Young June
2016-07-01
To enhance the on-current (I ON) of a tunneling field-effect transistor (TFET), we investigated the structures of a TFET with a recessed active (RA) region, known as the “RA-TFET”, using three-dimensional (3D) simulation. The analyzed structure is different from the recessed dynamic random-access memory (DRAM) channel in terms of the positions of the source and drain. The benefit of this structure is that the tunneling length remains unchanged as the depth increases so that the current can be easily scaled up, thereby maintaining the subthreshold slope (SS) and active area. Using an RA-TFET with a 100 nm Si depth, a 9.45 × 10-7 A I ON is achieved with a minimum SS of 35 mV/dec; in addition, we propose RA-TFET modifications to mitigate the ambipolar characteristics and reduce the capacitance between the gate and the drain (C GD) by up to 40%.
Analysis of a modified recessed active tunneling field-effect transistor
NASA Astrophysics Data System (ADS)
Kim, HuiJung; Choi, Seongwook; Yoo, NakWon; Rhee, SeungMan; Lee, Myoung Jin; Park, Young June
2016-07-01
To enhance the on-current (I ON) of a tunneling field-effect transistor (TFET), we investigated the structures of a TFET with a recessed active (RA) region, known as the “RA-TFET”, using three-dimensional (3D) simulation. The analyzed structure is different from the recessed dynamic random-access memory (DRAM) channel in terms of the positions of the source and drain. The benefit of this structure is that the tunneling length remains unchanged as the depth increases so that the current can be easily scaled up, thereby maintaining the subthreshold slope (SS) and active area. Using an RA-TFET with a 100 nm Si depth, a 9.45 × 10‑7 A I ON is achieved with a minimum SS of 35 mV/dec; in addition, we propose RA-TFET modifications to mitigate the ambipolar characteristics and reduce the capacitance between the gate and the drain (C GD) by up to 40%.
Tkach, N. V. Seti, Ju. A.; Grynyshyn, Yu. B.
2015-04-15
The theory of electron tunneling through an open nanostructure as an active element of a quantum cascade detector is developed, which takes into account the interaction of electrons with confined and interface phonons. Using the method of finite-temperature Green’s functions and the electron-phonon Hamiltonian in the representation of second quantization over all system variables, the temperature shifts and electron-level widths are calculated and the contributions of different electron-phonon-interaction mechanisms to renormalization of the spectral parameters are analyzed depending on the geometrical configuration of the nanosystem. Due to weak electron-phonon coupling in a GaAs/Al{sub 0.34}Ga{sub 0.66}As-based resonant tunneling nanostructure, the temperature shift and rf field absorption peak width are not very sensitive to the electron-phonon interaction and result from a decrease in potential barrier heights caused by a difference in the temperature dependences of the well and barrier band gaps.
Coupled CFD/CSD Analysis of an Active-Twist Rotor in a Wind Tunnel with Experimental Validation
NASA Technical Reports Server (NTRS)
Massey, Steven J.; Kreshock, Andrew R.; Sekula, Martin K.
2015-01-01
An unsteady Reynolds averaged Navier-Stokes analysis loosely coupled with a comprehensive rotorcraft code is presented for a second-generation active-twist rotor. High fidelity Navier-Stokes results for three configurations: an isolated rotor, a rotor with fuselage, and a rotor with fuselage mounted in a wind tunnel, are compared to lifting-line theory based comprehensive rotorcraft code calculations and wind tunnel data. Results indicate that CFD/CSD predictions of flapwise bending moments are in good agreement with wind tunnel measurements for configurations with a fuselage, and that modeling the wind tunnel environment does not significantly enhance computed results. Actuated rotor results for the rotor with fuselage configuration are also validated for predictions of vibratory blade loads and fixed-system vibratory loads. Varying levels of agreement with wind tunnel measurements are observed for blade vibratory loads, depending on the load component (flap, lag, or torsion) and the harmonic being examined. Predicted trends in fixed-system vibratory loads are in good agreement with wind tunnel measurements.
Wind Tunnel Testing of Microtabs and Microjets for Active Load Control of Wind Turbine Blades
NASA Astrophysics Data System (ADS)
Cooperman, Aubryn Murray
Increases in wind turbine size have made controlling loads on the blades an important consideration for future turbine designs. One approach that could reduce extreme loads and minimize load variation is to incorporate active control devices into the blades that are able to change the aerodynamic forces acting on the turbine. A wind tunnel model has been constructed to allow testing of different active aerodynamic load control devices. Two such devices have been tested in the UC Davis Aeronautical Wind Tunnel: microtabs and microjets. Microtabs are small surfaces oriented perpendicular to an airfoil surface that can be deployed and retracted to alter the lift coefficient of the airfoil. Microjets produce similar effects using air blown perpendicular to the airfoil surface. Results are presented here for both static and dynamic performance of the two devices. Microtabs, located at 95% chord on the lower surface and 90% chord on the upper surface, with a height of 1% chord, produce a change in the lift coefficient of 0.18, increasing lift when deployed on the lower surface and decreasing lift when deployed on the upper surface. Microjets with a momentum coefficient of 0.006 at the same locations produce a change in the lift coefficient of 0.19. The activation time for both devices is less than 0.3 s, which is rapid compared to typical gust rise times. The potential of active device to mitigate changes in loads was tested using simulated gusts. The gusts were produced in the wind tunnel by accelerating the test section air speed at rates of up to 7 ft/s 2. Open-loop control of microtabs was tested in two modes: simultaneous and sequential tab deployment. Activating all tabs along the model span simultaneously was found to produce a change in the loads that occurred more rapidly than a gust. Sequential tab deployment more closely matched the rates of change due to gusts and tab deployment. A closed-loop control system was developed for the microtabs using a simple
NASA Astrophysics Data System (ADS)
Campbell, Philip M.; Tarasov, Alexey; Joiner, Corey A.; Ready, W. Jud; Vogel, Eric M.
2016-01-01
Since the invention of the Esaki diode, resonant tunneling devices have been of interest for applications including multi-valued logic and communication systems. These devices are characterized by the presence of negative differential resistance in the current-voltage characteristic, resulting from lateral momentum conservation during the tunneling process. While a large amount of research has focused on III-V material systems, such as the GaAs/AlGaAs system, for resonant tunneling devices, poor device performance and device-to-device variability have limited widespread adoption. Recently, the symmetric field-effect transistor (symFET) was proposed as a resonant tunneling device incorporating symmetric 2-D materials, such as transition metal dichalcogenides (TMDs), separated by an interlayer barrier, such as hexagonal boron-nitride. The achievable peak-to-valley ratio for TMD symFETs has been predicted to be higher than has been observed for III-V resonant tunneling devices. This work examines the effect that band structure differences between III-V devices and TMDs has on device performance. It is shown that tunneling between the quantized subbands in III-V devices increases the valley current and decreases device performance, while the interlayer barrier height has a negligible impact on performance for barrier heights greater than approximately 0.5 eV.
NASA Astrophysics Data System (ADS)
Balageas, D.; Boscher, D.; Deom, A.; Gardette, G.
Over the past few years, a major intellectual and technical investment has been made at ONERA to use data acquisition systems and data reduction procedures using an infrared camera as a detector under routine wind tunnel conditions. This allows a really quantitative mapping of heat transfer rate distributions on models in supersonic and hypersonic flows. Sufficient experience has now been acquired to allow us to give an overview of: (1) the systems and data reduction procedures developed for both passive and active methods; (2) typical results obtained on various configurations such as supersonic axisymmetrical flow around an ogival body (passive and active thermography), heat flux modulation in the reattachment zone of a flap in hypersonic regime, transitional heating on very slightly blunted spheroconical bodies in hypersonic flows, and materials testing in high-enthalpy hypersonic flow (passive thermography).
NASA Technical Reports Server (NTRS)
Perry, Boyd, III; Noll, Thomas E.; Scott, Robert C.
2000-01-01
By the 1960s, researchers began to investigate the feasibility of using active controls technology (ACT) for increasing the capabilities of military and commercial aircraft. Since then many researchers, too numerous to mention, have investigated and demonstrated the usefulness of ACT for favorably modifying the aeroelastic response characteristics of flight vehicles. As a result, ACT entered the limelight as a viable tool for answering some very difficult design questions and had the potential for obtaining structural weight reductions optimizing maneuvering performance, and satisfying the multimission requirements being imposed on future military and commercial aircraft designs. Over the past 40 years, the NASA Langley Research Center (LaRC) has played a major role in developing ACT in part by its participation in many wind-tunnel programs conducted in the Transonic Dynamics Tunnel (TDT). These programs were conducted for the purposes of: (1) establishing concept feasibility; (2) demonstrating proof of concept; and (3) providing data for validating new modeling, analysis, and design methods. This paper provides an overview of the ACT investigations conducted in the TDT. For each program discussed herein, the objectives of the effort, the testing techniques, the test results, any, signIficant findings, and the lessons learned with respect to ACT testing are presented.
Huang, Lulu; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Chen, Disong; Zhang, Juan; Zhong, Hongying
2016-01-01
A new mass spectrometric imaging approach based on laser activated electron tunneling (LAET) was described and applied to analysis of endogenous metabolites of plant leaves. LAET is an electron-directed soft ionization technique. Compressed thin films of semiconductor nanoparticles of bismuth cobalt zinc oxide were placed on the sample plate for proof-of-principle demonstration because they can not only absorb ultraviolet laser but also have high electron mobility. Upon laser irradiation, electrons are excited from valence bands to conduction bands. With appropriate kinetic energies, photoexcited electrons can tunnel away from the barrier and eventually be captured by charge deficient atoms present in neutral molecules. Resultant unpaired electron subsequently initiates specific chemical bond cleavage and generates ions that can be detected in negative ion mode of the mass spectrometer. LAET avoids the co-crystallization process of routinely used organic matrix materials with analyzes in MALDI (matrix assisted-laser desorption ionization) analysis. Thus uneven distribution of crystals with different sizes and shapes as well as background peaks in the low mass range resulting from matrix molecules is eliminated. Advantages of LAET imaging technique include not only improved spatial resolution but also photoelectron capture dissociation which produces predictable fragment ions. PMID:27053227
NASA Astrophysics Data System (ADS)
Huang, Lulu; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Chen, Disong; Zhang, Juan; Zhong, Hongying
2016-04-01
A new mass spectrometric imaging approach based on laser activated electron tunneling (LAET) was described and applied to analysis of endogenous metabolites of plant leaves. LAET is an electron-directed soft ionization technique. Compressed thin films of semiconductor nanoparticles of bismuth cobalt zinc oxide were placed on the sample plate for proof-of-principle demonstration because they can not only absorb ultraviolet laser but also have high electron mobility. Upon laser irradiation, electrons are excited from valence bands to conduction bands. With appropriate kinetic energies, photoexcited electrons can tunnel away from the barrier and eventually be captured by charge deficient atoms present in neutral molecules. Resultant unpaired electron subsequently initiates specific chemical bond cleavage and generates ions that can be detected in negative ion mode of the mass spectrometer. LAET avoids the co-crystallization process of routinely used organic matrix materials with analyzes in MALDI (matrix assisted-laser desorption ionization) analysis. Thus uneven distribution of crystals with different sizes and shapes as well as background peaks in the low mass range resulting from matrix molecules is eliminated. Advantages of LAET imaging technique include not only improved spatial resolution but also photoelectron capture dissociation which produces predictable fragment ions.
Benabbas, Abdelkrim; Salna, Bridget; Sage, J Timothy; Champion, Paul M
2015-03-21
Analytical models describing the temperature dependence of the deep tunneling rate, useful for proton, hydrogen, or hydride transfer in proteins, are developed and compared. Electronically adiabatic and non-adiabatic expressions are presented where the donor-acceptor (D-A) motion is treated either as a quantized vibration or as a classical "gating" distribution. We stress the importance of fitting experimental data on an absolute scale in the electronically adiabatic limit, which normally applies to these reactions, and find that vibrationally enhanced deep tunneling takes place on sub-ns timescales at room temperature for typical H-bonding distances. As noted previously, a small room temperature kinetic isotope effect (KIE) does not eliminate deep tunneling as a major transport channel. The quantum approach focuses on the vibrational sub-space composed of the D-A and hydrogen atom motions, where hydrogen bonding and protein restoring forces quantize the D-A vibration. A Duschinsky rotation is mandated between the normal modes of the reactant and product states and the rotation angle depends on the tunneling particle mass. This tunnel-mass dependent rotation contributes substantially to the KIE and its temperature dependence. The effect of the Duschinsky rotation is solved exactly to find the rate in the electronically non-adiabatic limit and compared to the Born-Oppenheimer (B-O) approximation approach. The B-O approximation is employed to find the rate in the electronically adiabatic limit, where we explore both harmonic and quartic double-well potentials for the hydrogen atom bound states. Both the electronically adiabatic and non-adiabatic rates are found to diverge at high temperature unless the proton coupling includes the often neglected quadratic term in the D-A displacement from equilibrium. A new expression is presented for the electronically adiabatic tunnel rate in the classical limit for D-A motion that should be useful to experimentalists working near
Benabbas, Abdelkrim; Salna, Bridget; Sage, J. Timothy; Champion, Paul M.
2015-03-21
Analytical models describing the temperature dependence of the deep tunneling rate, useful for proton, hydrogen, or hydride transfer in proteins, are developed and compared. Electronically adiabatic and non-adiabatic expressions are presented where the donor-acceptor (D-A) motion is treated either as a quantized vibration or as a classical “gating” distribution. We stress the importance of fitting experimental data on an absolute scale in the electronically adiabatic limit, which normally applies to these reactions, and find that vibrationally enhanced deep tunneling takes place on sub-ns timescales at room temperature for typical H-bonding distances. As noted previously, a small room temperature kinetic isotope effect (KIE) does not eliminate deep tunneling as a major transport channel. The quantum approach focuses on the vibrational sub-space composed of the D-A and hydrogen atom motions, where hydrogen bonding and protein restoring forces quantize the D-A vibration. A Duschinsky rotation is mandated between the normal modes of the reactant and product states and the rotation angle depends on the tunneling particle mass. This tunnel-mass dependent rotation contributes substantially to the KIE and its temperature dependence. The effect of the Duschinsky rotation is solved exactly to find the rate in the electronically non-adiabatic limit and compared to the Born-Oppenheimer (B-O) approximation approach. The B-O approximation is employed to find the rate in the electronically adiabatic limit, where we explore both harmonic and quartic double-well potentials for the hydrogen atom bound states. Both the electronically adiabatic and non-adiabatic rates are found to diverge at high temperature unless the proton coupling includes the often neglected quadratic term in the D-A displacement from equilibrium. A new expression is presented for the electronically adiabatic tunnel rate in the classical limit for D-A motion that should be useful to experimentalists working
Benabbas, Abdelkrim; Salna, Bridget; Sage, J Timothy; Champion, Paul M
2015-03-21
Analytical models describing the temperature dependence of the deep tunneling rate, useful for proton, hydrogen, or hydride transfer in proteins, are developed and compared. Electronically adiabatic and non-adiabatic expressions are presented where the donor-acceptor (D-A) motion is treated either as a quantized vibration or as a classical "gating" distribution. We stress the importance of fitting experimental data on an absolute scale in the electronically adiabatic limit, which normally applies to these reactions, and find that vibrationally enhanced deep tunneling takes place on sub-ns timescales at room temperature for typical H-bonding distances. As noted previously, a small room temperature kinetic isotope effect (KIE) does not eliminate deep tunneling as a major transport channel. The quantum approach focuses on the vibrational sub-space composed of the D-A and hydrogen atom motions, where hydrogen bonding and protein restoring forces quantize the D-A vibration. A Duschinsky rotation is mandated between the normal modes of the reactant and product states and the rotation angle depends on the tunneling particle mass. This tunnel-mass dependent rotation contributes substantially to the KIE and its temperature dependence. The effect of the Duschinsky rotation is solved exactly to find the rate in the electronically non-adiabatic limit and compared to the Born-Oppenheimer (B-O) approximation approach. The B-O approximation is employed to find the rate in the electronically adiabatic limit, where we explore both harmonic and quartic double-well potentials for the hydrogen atom bound states. Both the electronically adiabatic and non-adiabatic rates are found to diverge at high temperature unless the proton coupling includes the often neglected quadratic term in the D-A displacement from equilibrium. A new expression is presented for the electronically adiabatic tunnel rate in the classical limit for D-A motion that should be useful to experimentalists working near
Arapov, Yu. G.; Gudina, S. V. Klepikova, A. S.; Neverov, V. N.; Podgornykh, S. M.; Yakunin, M. V.; Zvonkov, B. N.
2013-11-15
The effects of tunneling between two parallel two-dimensional electron gases in n-InGaAs/GaAs nanostructures with strongly coupled double quantum wells with a change in the in-plane component of a tilted magnetic field (up to B{sub Double-Vertical-Line} = 9.0 T) in the temperature range T = 1.8-70.0 K are investigated. A nonmonotonic temperature dependence of the inverse quantum lifetime {tau}{sub q}{sup -}(T) is obtained from analysis of the dependence of the longitudinal resistance on the parallel component of the tilted magnetic field at fixed temperatures, {rho}{sub xx}(B{sub Double-Vertical-Line }, T). The quadratic portion of this dependence is found to be due to the contribution of inelastic electron-electron scattering. The decrease in the inverse quantum lifetime {tau}{sub q}{sup -}(T) at T > 0.1T{sub F} cannot be described within known theories; it seems, it is not related to the processes of electron momentum relaxation.
NASA Technical Reports Server (NTRS)
Rais-Rohani, Masoud
1991-01-01
In this paper an effort is made to improve the analytical open-loop flutter predictions for the Active Flexible Wing wind-tunnel model using a sensitivity based optimization approach. The sensitivity derivatives of the flutter frequency and dynamic pressure of the model with respect to the lag terms appearing in the Roger's unsteady aerodynamics approximations are evaluated both analytical and by finite differences. Then, the Levenberg-Marquardt method is used to find the optimum values for these lag-terms. The results obtained here agree much better with the experimental (wind tunnel) results than those found in the previous studies.
Davidge, Kelly S; Singh, Sandip; Bowman, Lesley AH; Tinajero-Trejo, Mariana; Carballal, Sebastián; Radi, Rafael; Poole, Robert K; Dikshit, Kanak; Estrin, Dario A; Marti, Marcelo A; Boechi, Leonardo
2015-01-01
Mycobacterium tuberculosis, the causative agent of human tuberculosis, has two proteins belonging to the truncated hemoglobin (trHb) family. Mt-trHbN presents well-defined internal hydrophobic tunnels that allow O 2 and •NO to migrate easily from the solvent to the active site, whereas Mt-trHbO possesses tunnels that are partially blocked by a few bulky residues, particularly a tryptophan at position G8. Differential ligand migration rates allow Mt-trHbN to detoxify •NO, a crucial step for pathogen survival once under attack by the immune system, much more efficiently than Mt-trHbO. In order to investigate the differences between these proteins, we performed experimental kinetic measurements, •NO decomposition, as well as molecular dynamics simulations of the wild type Mt-trHbN and two mutants, VG8F and VG8W. These mutations introduce modifications in both tunnel topologies and affect the incoming ligand capacity to displace retained water molecules at the active site. We found that a single mutation allows Mt-trHbN to acquire ligand migration rates comparable to those observed for Mt-trHbO, confirming that ligand migration is regulated by the internal tunnel architecture as well as by water molecules stabilized in the active site. PMID:26478812
Boron, Ignacio; Bustamante, Juan Pablo; Davidge, Kelly S; Singh, Sandip; Bowman, Lesley Ah; Tinajero-Trejo, Mariana; Carballal, Sebastián; Radi, Rafael; Poole, Robert K; Dikshit, Kanak; Estrin, Dario A; Marti, Marcelo A; Boechi, Leonardo
2015-01-01
Mycobacterium tuberculosis, the causative agent of human tuberculosis, has two proteins belonging to the truncated hemoglobin (trHb) family. Mt-trHbN presents well-defined internal hydrophobic tunnels that allow O 2 and (•)NO to migrate easily from the solvent to the active site, whereas Mt-trHbO possesses tunnels that are partially blocked by a few bulky residues, particularly a tryptophan at position G8. Differential ligand migration rates allow Mt-trHbN to detoxify (•)NO, a crucial step for pathogen survival once under attack by the immune system, much more efficiently than Mt-trHbO. In order to investigate the differences between these proteins, we performed experimental kinetic measurements, (•)NO decomposition, as well as molecular dynamics simulations of the wild type Mt-trHbN and two mutants, VG8F and VG8W. These mutations introduce modifications in both tunnel topologies and affect the incoming ligand capacity to displace retained water molecules at the active site. We found that a single mutation allows Mt-trHbN to acquire ligand migration rates comparable to those observed for Mt-trHbO, confirming that ligand migration is regulated by the internal tunnel architecture as well as by water molecules stabilized in the active site.
Habdank-Wojewódzki, Tadeusz; Habdank, Josef; Cwik, Przemyslaw; Zimowski, Slawomir
2016-01-01
CuO and V₂O₅ graphene quantum tunneling composites (GQTC) presented in this article were produced and their sensory properties were analyzed. The composites were synthesised using two stage high-power milling process, which resulted in materials that have good temeprature and pressure sensory properties. Described production process defines internal structure of materials such that when used as sensor in the desired range, it exhibits a strong percolation effect. The experiment, with controlled changing physical conditions during electrotribological measurement, enabled analyzing of the composites' conductivity as a function of the sensory properties: applied temperature, pressure, tangential force and wear. The sensory characteristic was successfully modelled by invertible generalized equations, and used to create sensor capable of estimating temperature or pressure in the real time. The developed materials have the potential to be applied in the areas where miniaturization is essential, due to the materials exhibiting good sensory properties in mini and micro scale. PMID:26742044
NASA Astrophysics Data System (ADS)
Kuwata, Yuya; Suda, Keita; Watanabe, Masahiro
2016-07-01
A novel resistance switching memory using CaF2/Si/CaF2 resonant-tunneling quantum well heterostructures sandwiched by nanocrystalline Si (nc-Si) as secondary barrier layers has been proposed and the room temperature current–voltage characteristics of the basic resistance switching memory operation have been demonstrated. A resistance switching voltage of 1.0 V, a peak current density of approximately 42 kA/cm2, and an ON/OFF ratio of 2.8 were observed. In particular, more than 28000 write-read-erase cyclic memory operations have been demonstrated by applying pulsed input voltage sequences, which suggests better endurance than the device using a CaF2/CdF2/CaF2 heterostructure.
Habdank-Wojewódzki, Tadeusz; Habdank, Josef; Cwik, Przemyslaw; Zimowski, Slawomir
2016-01-05
CuO and V₂O₅ graphene quantum tunneling composites (GQTC) presented in this article were produced and their sensory properties were analyzed. The composites were synthesised using two stage high-power milling process, which resulted in materials that have good temeprature and pressure sensory properties. Described production process defines internal structure of materials such that when used as sensor in the desired range, it exhibits a strong percolation effect. The experiment, with controlled changing physical conditions during electrotribological measurement, enabled analyzing of the composites' conductivity as a function of the sensory properties: applied temperature, pressure, tangential force and wear. The sensory characteristic was successfully modelled by invertible generalized equations, and used to create sensor capable of estimating temperature or pressure in the real time. The developed materials have the potential to be applied in the areas where miniaturization is essential, due to the materials exhibiting good sensory properties in mini and micro scale.
Habdank-Wojewódzki, Tadeusz; Habdank, Josef; Cwik, Przemyslaw; Zimowski, Slawomir
2016-01-01
CuO and V2O5 graphene quantum tunneling composites (GQTC) presented in this article were produced and their sensory properties were analyzed. The composites were synthesised using two stage high-power milling process, which resulted in materials that have good temeprature and pressure sensory properties. Described production process defines internal structure of materials such that when used as sensor in the desired range, it exhibits a strong percolation effect. The experiment, with controlled changing physical conditions during electrotribological measurement, enabled analyzing of the composites’ conductivity as a function of the sensory properties: applied temperature, pressure, tangential force and wear. The sensory characteristic was successfully modelled by invertible generalized equations, and used to create sensor capable of estimating temperature or pressure in the real time. The developed materials have the potential to be applied in the areas where miniaturization is essential, due to the materials exhibiting good sensory properties in mini and micro scale. PMID:26742044
NASA Astrophysics Data System (ADS)
Kuwata, Yuya; Suda, Keita; Watanabe, Masahiro
2016-07-01
A novel resistance switching memory using CaF2/Si/CaF2 resonant-tunneling quantum well heterostructures sandwiched by nanocrystalline Si (nc-Si) as secondary barrier layers has been proposed and the room temperature current-voltage characteristics of the basic resistance switching memory operation have been demonstrated. A resistance switching voltage of 1.0 V, a peak current density of approximately 42 kA/cm2, and an ON/OFF ratio of 2.8 were observed. In particular, more than 28000 write-read-erase cyclic memory operations have been demonstrated by applying pulsed input voltage sequences, which suggests better endurance than the device using a CaF2/CdF2/CaF2 heterostructure.
NASA Astrophysics Data System (ADS)
Muraguchi, Masakazu; Takeda, Kyozaburo
2007-03-01
We theoretically study the dynamical properties of an electron confined in a two-dimensional (2D) quantum dot (QD) under photon illumination, by solving the time-dependent (TD) Schrödinger equation numerically by the finite difference method in both real space and actual time. To deepen our understanding of the TD features of photon-assisted tunneling (PAT), we employ projection analysis, in which the TD wave function at a QD is decomposed into (static) resonant states by calculating the inner products among them. This analysis further enables the deduction of effective lifetime, by which one can infer the actual period of the electron confined in the QD. The wave number distribution for the transmitted electron is also discussed to examine the propagation of the electron through the system.
NASA Astrophysics Data System (ADS)
Han, B. G.; Han, B. Z.; Yu, X.
2009-06-01
The voltage-current characteristics of a nickel powder (NP)-filled cement-based composite (NPCC) and the variation of electrical resistivity of NPCC under compression are studied by using a four-pole method based on embedded loop electrodes. The generation of conductivity and piezoresistivity in NPCC is investigated by examining the morphology of NPCC by SEM and studying the variation of distance between NP particles under compression. Experimental results indicate that the electrical conductivity of NPCC is ohmic when the voltage is below 3.5 V. Although NP particles are dispersed in the cement matrix and they do not form a connected conductive network, NPCC has a low electrical resistivity of 2.29 × 103Ω cm without loading. A decrease of 0.042% in the fractional change in volume of NPCC under compression causes the tunneling distance to decrease 0.60-1.42 nm and the fractional change in electrical resistivity to reach 62.61%. It is therefore concluded that the improvement of conductivity and piezoresistivity of NPCC is due to the quantum tunneling effect.
Wong, Kin-Yiu; Gao, Jiali
2008-09-01
In this paper, we describe an automated integration-free path-integral (AIF-PI) method, based on Kleinert's variational perturbation (KP) theory, to treat internuclear quantum-statistical effects in molecular systems. We have developed an analytical method to obtain the centroid potential as a function of the variational parameter in the KP theory, which avoids numerical difficulties in path-integral Monte Carlo or molecular dynamics simulations, especially at the limit of zero-temperature. Consequently, the variational calculations using the KP theory can be efficiently carried out beyond the first order, i.e., the Giachetti-Tognetti-Feynman-Kleinert variational approach, for realistic chemical applications. By making use of the approximation of independent instantaneous normal modes (INM), the AIF-PI method can readily be applied to many-body systems. Previously, we have shown that in the INM approximation, the AIF-PI method is accurate for computing the quantum partition function of a water molecule (3 degrees of freedom) and the quantum correction factor for the collinear H(3) reaction rate (2 degrees of freedom). In this work, the accuracy and properties of the KP theory are further investigated by using the first three order perturbations on an asymmetric double-well potential, the bond vibrations of H(2), HF, and HCl represented by the Morse potential, and a proton-transfer barrier modeled by the Eckart potential. The zero-point energy, quantum partition function, and tunneling factor for these systems have been determined and are found to be in excellent agreement with the exact quantum results. Using our new analytical results at the zero-temperature limit, we show that the minimum value of the computed centroid potential in the KP theory is in excellent agreement with the ground state energy (zero-point energy) and the position of the centroid potential minimum is the expectation value of particle position in wave mechanics. The fast convergent property
Wong, Kin-Yiu; Gao, Jiali
2009-01-01
In this paper, we describe an automated integration-free path-integral (AIF-PI) method, based on Kleinert’s variational perturbation (KP) theory, to treat internuclear quantum-statistical effects in molecular systems. We have developed an analytical method to obtain the centroid potential as a function of the variational parameter in the KP theory, which avoids numerical difficulties in path-integral Monte Carlo or molecular dynamics simulations, especially at the limit of zero-temperature. Consequently, the variational calculations using the KP theory can be efficiently carried out beyond the first order, i.e., the Giachetti-Tognetti-Feynman-Kleinert variational approach, for realistic chemical applications. By making use of the approximation of independent instantaneous normal modes (INM), the AIF-PI method can readily be applied to many-body systems. Previously, we have shown that in the INM approximation, the AIF-PI method is accurate for computing the quantum partition function of a water molecule (3 degrees of freedom) and the quantum correction factor for the collinear H3 reaction rate (2 degrees of freedom). In this work, the accuracy and properties of the KP theory are further investigated by using the first three order perturbations on an asymmetric double-well potential, the bond vibrations of H2, HF, and HCl represented by the Morse potential, and a proton-transfer barrier modeled by the Eckart potential. The zero-point energy, quantum partition function, and tunneling factor for these systems have been determined and are found to be in excellent agreement with the exact quantum results. Using our new analytical results at the zero-temperature limit, we show that the minimum value of the computed centroid potential in the KP theory is in excellent agreement with the ground state energy (zero-point energy) and the position of the centroid potential minimum is the expectation value of particle position in wave mechanics. The fast convergent property of
Microwave resonant activation in hybrid single-gap/two-gap Josephson tunnel junctions
NASA Astrophysics Data System (ADS)
Carabello, Steven; Lambert, Joseph G.; Mlack, Jerome; Dai, Wenqing; Li, Qi; Chen, Ke; Cunnane, Daniel; Xi, X. X.; Ramos, Roberto C.
2016-09-01
Microwave resonant activation is a powerful, straightforward technique to study classical and quantum systems, experimentally realized in Josephson junction devices cooled to very low temperatures. These devices typically consist of two single-gap superconductors separated by a weak link. We report the results of the first resonant activation experiments on hybrid thin film Josephson junctions consisting of a multi-gap superconductor (MgB2) and a single-gap superconductor (Pb or Sn). We can interpret the plasma frequency in terms of theories both for conventional and hybrid junctions. Using these models, we determine the junction parameters including critical current, resistance, and capacitance and find moderately high quality factors of Q0˜ 100 for these junctions.
Tunnelling with wormhole creation
Ansoldi, S.; Tanaka, T.
2015-03-15
The description of quantum tunnelling in the presence of gravity shows subtleties in some cases. We discuss wormhole production in the context of the spherically symmetric thin-shell approximation. By presenting a fully consistent treatment based on canonical quantization, we solve a controversy present in the literature.
Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Zhong, Hongying
2015-03-01
Identification of endogenous and exogenous chemicals contained in latent fingerprints is important for forensic science in order to acquire evidence of criminal identities and contacts with specific chemicals. Mass spectrometry has emerged as a powerful technique for such applications without any derivatization or fluorescent tags. Among these techniques, MALDI (Matrix Assisted Laser Desorption Ionization) provides small beam size but has interferences with MALDI matrix materials, which cause ion suppressions as well as limited spatial resolution resulting from uneven distribution of MALDI matrix crystals with different sizes. LAET (Laser Activated Electron Tunneling) described in this work offers capabilities for chemical imaging through electron-directed soft ionization. A special film of semiconductors has been designed for collection of fingerprints. Nanoparticles of bismuth cobalt zinc oxide were compressed on a conductive metal substrate (Al or Cu sticky tape) under 10 MPa pressure. Resultant uniform thin films provide tight and shining surfaces on which fingers are impressed. Irradiation of ultraviolet laser pulses (355 nm) on the thin film instantly generates photoelectrons that can be captured by adsorbed organic molecules and subsequently cause electron-directed ionization and fragmentation. Imaging of latent fingerprints is achieved by visualization of the spatial distribution of these molecular ions and structural information-rich fragment ions. Atomic electron emission together with finely tuned laser beam size improve spatial resolution. With the LAET technique, imaging analysis not only can identify physical shapes but also reveal endogenous metabolites present in females and males, detect contacts with prohibited substances, and resolve overlapped latent fingerprints. PMID:25647159
Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Zhong, Hongying
2015-03-01
Identification of endogenous and exogenous chemicals contained in latent fingerprints is important for forensic science in order to acquire evidence of criminal identities and contacts with specific chemicals. Mass spectrometry has emerged as a powerful technique for such applications without any derivatization or fluorescent tags. Among these techniques, MALDI (Matrix Assisted Laser Desorption Ionization) provides small beam size but has interferences with MALDI matrix materials, which cause ion suppressions as well as limited spatial resolution resulting from uneven distribution of MALDI matrix crystals with different sizes. LAET (Laser Activated Electron Tunneling) described in this work offers capabilities for chemical imaging through electron-directed soft ionization. A special film of semiconductors has been designed for collection of fingerprints. Nanoparticles of bismuth cobalt zinc oxide were compressed on a conductive metal substrate (Al or Cu sticky tape) under 10 MPa pressure. Resultant uniform thin films provide tight and shining surfaces on which fingers are impressed. Irradiation of ultraviolet laser pulses (355 nm) on the thin film instantly generates photoelectrons that can be captured by adsorbed organic molecules and subsequently cause electron-directed ionization and fragmentation. Imaging of latent fingerprints is achieved by visualization of the spatial distribution of these molecular ions and structural information-rich fragment ions. Atomic electron emission together with finely tuned laser beam size improve spatial resolution. With the LAET technique, imaging analysis not only can identify physical shapes but also reveal endogenous metabolites present in females and males, detect contacts with prohibited substances, and resolve overlapped latent fingerprints.
NASA Astrophysics Data System (ADS)
Xu, N. W.; Li, T. B.; Dai, F.; Zhang, R.; Tang, C. A.; Tang, L. X.
2016-03-01
Rockbursts were frequently encountered during the construction of deep tunnels at the Jinping II hydropower station, Southwest China. Investigations of the possibility of rockbursts during tunnel boring machine (TBM) and drilling and blasting (D&B) advancement are necessary to guide the construction of tunnels and to protect personnel and TBM equipment from strainburst-related accidents. A real-time, movable microseismic monitoring system was installed to forecast strainburst locations ahead of the tunnel faces. The spatiotemporal distribution evolution of microseismic events prior to and during strainbursts was recorded and analysed. The concentration of microseismic events prior to the occurrence of strainbursts was found to be a significant precursor to strainbursts in deep rock tunnelling. During a 2-year microseismic investigation of strainbursts in the deep tunnels at the Jinping II hydropower station, a total of 2240 strainburst location forecasts were issued, with 63 % correctly forecasting the locations of strainbursts. The successful forecasting of strainburst locations proved that microseismic monitoring is essential for the assessment and mitigation of strainburst hazards, and can be used to minimise damage to equipment and personnel. The results of the current study may be valuable for the construction management and safety assessment of similar underground rock structures under high in situ stress.
Modernization and Activation of the NASA Ames 11- by 11-Foot Transonic Wind Tunnel
NASA Technical Reports Server (NTRS)
Kmak, Frank J.
2000-01-01
The Unitary Plan Wind Tunnel (UPWT) was modernized to improve performance, capability, productivity, and reliability. Automation systems were installed in all three UPWT tunnel legs and the Auxiliaries facility. Major improvements were made to the four control rooms, model support systems, main drive motors, and main drive speed control. Pressure vessel repairs and refurbishment to the electrical distribution system were also completed. Significant changes were made to improve test section flow quality in the 11-by 11-Foot Transonic leg. After the completion of the construction phase of the project, acceptance and checkout testing was performed to demonstrate the capabilities of the modernized facility. A pneumatic test of the tunnel circuit was performed to verify the structural integrity of the pressure vessel before wind-on operations. Test section turbulence, flow angularity, and acoustic parameters were measured throughout the tunnel envelope to determine the effects of the tunnel flow quality improvements. The new control system processes were thoroughly checked during wind-off and wind-on operations. Manual subsystem modes and automated supervisory modes of tunnel operation were validated. The aerodynamic and structural performance of both the new composite compressor rotor blades and the old aluminum rotor blades was measured. The entire subsonic and supersonic envelope of the 11-by 11-Foot Transonic leg was defined up to the maximum total pressure.
Chaloupková, Radka; Sýkorová, Jana; Prokop, Zbynek; Jesenská, Andrea; Monincová, Marta; Pavlová, Martina; Tsuda, Masataka; Nagata, Yuji; Damborský, Jirí
2003-12-26
Structural comparison of three different haloalkane dehalogenases suggested that substrate specificity of these bacterial enzymes could be significantly influenced by the size and shape of their entrance tunnels. The surface residue leucine 177 positioned at the tunnel opening of the haloalkane dehalogenase from Sphingomonas paucimobilis UT26 was selected for modification based on structural and phylogenetic analysis; the residue partially blocks the entrance tunnel, and it is the most variable pocket residue in haloalkane dehalogenase-like proteins with nine substitutions in 14 proteins. Mutant genes coding for proteins carrying all possible substitutions in position 177 were constructed by site-directed mutagenesis and heterologously expressed in Escherichia coli. In total, 15 active protein variants were obtained, suggesting a relatively high tolerance of the site for the introduction of mutations. Purified protein variants were kinetically characterized by determination of specific activities with 12 halogenated substrates and steady-state kinetic parameters with two substrates. The effect of mutation on the enzyme activities varied dramatically with the structure of the substrates, suggesting that extrapolation of one substrate to another may be misleading and that a systematic characterization of the protein variants with a number of substrates is essential. Multivariate analysis of activity data revealed that catalytic activity of mutant enzymes generally increased with the introduction of small and nonpolar amino acid in position 177. This result is consistent with the phylogenetic analysis showing that glycine and alanine are the most commonly occurring amino acids in this position among haloalkane dehalogenases. The study demonstrates the advantages of using rational engineering to develop enzymes with modified catalytic properties and substrate specificities. The strategy of using site-directed mutagenesis to modify a specific entrance tunnel residue
THz quantum cascade lasers with wafer bonded active regions.
Brandstetter, M; Deutsch, C; Benz, A; Cole, G D; Detz, H; Andrews, A M; Schrenk, W; Strasser, G; Unterrainer, K
2012-10-01
We demonstrate terahertz quantum-cascade lasers with a 30 μm thick double-metal waveguide, which are fabricated by stacking two 15 μm thick active regions using a wafer bonding process. By increasing the active region thickness more optical power is generated inside the cavity, the waveguide losses are decreased and the far-field is improved due to a larger facet aperture. In this way the output power is increased by significantly more than a factor of 2 without reducing the maximum operating temperature and without increasing the threshold current.
Activation of molecular catalysts using semiconductor quantum dots
Meyer, Thomas J.; Sykora, Milan; Klimov, Victor I.
2011-10-04
Photocatalytic materials based on coupling of semiconductor nanocrystalline quantum dots (NQD) and molecular catalysts. These materials have capability to drive or catalyze non-spontaneous chemical reactions in the presence of visible radiation, ultraviolet radiation, or both. The NQD functions in these materials as a light absorber and charge generator. Following light absorption, the NQD activates a molecular catalyst adsorbed on the surface of the NQD via transfer of one or more charges (either electrons or electron-holes) from the NQD to the molecular catalyst. The activated molecular catalyst can then drive a chemical reaction. A photoelectrolytic device that includes such photocatalytic materials is also described.
Tunnelling in van der Waals heterostructures
NASA Astrophysics Data System (ADS)
Mishchenko, Artem; Novoselov, Kostya; Geim, Andre; Eaves, Laurence; Falko, Vladimir
When graphene and other conductive two-dimensional (2D) materials are separated by an atomically thin insulating 2D crystal, quantum mechanical tunnelling leads to appreciable current between two 2D conductors due to the overlap of their wavefunctions. These tunnel devices demonstrate interesting physics and potential for applications: such effects as resonant tunnelling, negative differential conductance, light emission and detection have already been demonstrated. In this presentation we will outline the current status and perspectives of tunnelling transistors based on 2D materials assembled into van der Waals heterostructures. Particularly, we will present results on mono- and bilayer graphene tunnelling, tunnelling in 2D crystal-based quantum wells, and tunnelling in superconducting 2D materials. Such effects as momentum and chirality conservation, phonon- and impurity-assisted tunnelling will also be discussed. Finally, we will ponder the implications of discovered effects for practical applications.
Karadag, Omer; Kalyoncu, Umut; Akdogan, Ali; Karadag, Yesim Sucullu; Bilgen, Sule Apras; Ozbakır, Senay; Filippucci, Emilio; Kiraz, Sedat; Ertenli, Ihsan; Grassi, Walter; Calgüneri, Meral
2012-08-01
Carpal tunnel syndrome (CTS) is one of the most frequent extra-articular manifestations of rheumatoid arthritis (RA). High frequency ultrasonography (US) is a sensitive and specific method in diagnosis of CTS. This study is aimed to: firstly assess diameter frequency of CTS in RA with US and compare with a control group; secondly, investigate relationship of CTS with disease activity. One hundred consecutive RA patients (women/men: 78/22) fulfilling ACR 1987 RA criteria and 45 healthy controls (women/control: 34/11) were enrolled into study. Disease activity parameters, RA and CTS patient global assessment and health assessment questionnaire (HAQ-DI) were recorded. Both patient and control group were questioned about secondary causes of CTS, and Katz hand diagram, Boston CTS questionnaire and Phalen ve Tinel tests were applied once for each hand. Wrist joint and carpal tunnel were assessed with US grey scale and power Doppler US, then cross-sectional area of median nerve (CSA) was calculated. Patients with median nerve CSA between 10.0 and 13.0 mm(2) were evaluated with electromyography (EMG). CTS was diagnosed if CSA of median nerve >13.0 mm(2) or CTS was shown with NCS. Although there was no difference between RA patients and controls in age, sex, history of DM (+) and goitre, CTS was more frequent in RA group (respectively, 17.0% vs. 4.4%, P = 0.038). In RA group with CTS, age, history of DM, disease duration, HAQ-DI score, CTS patient global score, Boston symptom severity and functional status scores were elevated compared to without CTS [respectively, 57 (36-73) vs. 50 (24-76), P = 0.041; 35.3% vs. 6.0%, P < 0.001; 108 (12-396) months vs. 72 (6-360) months, P = 0.036; 1.93 (0.75-2.87) vs. 1.125 (0-2.75), P = 0.013; 52 (1-97) vs. 25 (0-91), P = 0.001; 2.81 (1.18-4.17) vs. 2.0 (1.0-4.01), P = 0.01; 3.37 (1.37-5.0) vs. 2.25 (1.0-5.0), P = 0.008]. No difference was found between CTS (+) and (-) RA patients in acute phase reactants, disease activity and US findings
Constantino, Jason; Long, Yun; Ashihara, Takashi; Trayanova, Natalia A.
2010-01-01
Background Following near-defibrillation threshold (DFT) shocks from an ICD, the first postshock activation that leads to defibrillation failure arises focally after an isolelectric window (IW). The mechanisms underlying the IW remain incompletely understood. Objective The goal of this study was to provide mechanistic insight into the origins of postshock activations and IW following ICD shocks, and to link shock outcome to the preshock state of the ventricles. We hypothesized that the non-uniform ICD field results in the formation of an intramural excitable area (tunnel) only in the LV free wall, through which both pre-existing and new shock-induced wavefronts propagate during the IW. Methods Simulations were conducted using a realistic 3-D model of defibrillation in the rabbit ventricles. Biphasic ICD shocks of varying strengths were delivered to 27 different fibrillatory states. Results Following near-DFT shocks, regardless of preshock state, the main postshock excitable area was always located within LV free wall, creating an intramural tunnel. Either preexisting fibrillatory or shock-induced wavefronts propagated during the IW (duration of up to 74ms) in this tunnel and emerged as breakthroughs on LV epicardium. Preshock activity within the LV played a significant role in shock outcome: large number of preshock filaments resulted in an IW associated with tunnel propagation of preexisting rather than shock-induced wavefronts. Furthermore, shocks were more likely to succeed if LV excitable area was smaller. Conclusions The LV intramural excitable area is the primary reason for near-DFT failure. Any intervention that decreases the extent of this area will improve the likelihood of defibrillation success. PMID:20348028
ERIC Educational Resources Information Center
Lawrence, I.
1996-01-01
Discusses a teaching strategy for introducing quantum ideas into the school classroom using modern devices. Develops the concepts of quantization, wave-particle duality, nonlocality, and tunneling. (JRH)
Cavalli, S; Aquilanti, V; Mundim, K C; De Fazio, D
2014-08-21
For the reaction between F and HD, giving HF + D and DF + H, the rate constants, obtained from rigorous quantum scattering calculations at temperatures ranging from 350 K down to 100 K, show deviations from the Arrhenius behavior that have been interpreted in terms of tunneling of either H or D atoms through a potential energy barrier. The interval of temperature investigated extends from above to below a crossover value Tc, a transition temperature separating the moderate and deep quantum tunneling regimes. Below Tc, the rate of the H or D exchange reaction is controlled by the prevalence of tunneling over the thermal activation mechanism. In this temperature range, Bell's early treatment of quantum tunneling, based on a semiclassical approximation for the barrier permeability, provides a reliable tool to quantitatively account for the contribution of the tunneling effect. This treatment is here applied for extracting from rate constants properties of the effective tunneling path, such as the activation barrier height and width. We show that this is a way of parametrizing the dependence of the apparent activation energy on temperature useful for both calculated and experimental rate constants in an ample interval of temperature, from above to below Tc, relevant for modelization of astrophysical and in general very low-temperature environments.
Sun, Zhiyuan; Hazut, Ori; Huang, Bo-Chao; Chiu, Ya-Ping; Chang, Chia-Seng; Yerushalmi, Roie; Lauhon, Lincoln J; Seidman, David N
2016-07-13
Dopants play a critical role in modulating the electric properties of semiconducting materials, ranging from bulk to nanoscale semiconductors, nanowires, and quantum dots. The application of traditional doping methods developed for bulk materials involves additional considerations for nanoscale semiconductors because of the influence of surfaces and stochastic fluctuations, which may become significant at the nanometer-scale level. Monolayer doping is an ex situ doping method that permits the post growth doping of nanowires. Herein, using atom-probe tomography (APT) with subnanometer spatial resolution and atomic-ppm detection limit, we study the distributions of boron and phosphorus in ex situ doped silicon nanowires with accurate control. A highly phosphorus doped outer region and a uniformly boron doped interior are observed, which are not predicted by criteria based on bulk silicon. These phenomena are explained by fast interfacial diffusion of phosphorus and enhanced bulk diffusion of boron, respectively. The APT results are compared with scanning tunneling spectroscopy data, which yields information concerning the electrically active dopants. Overall, comparing the information obtained by the two methods permits us to evaluate the diffusivities of each different dopant type at the nanowire oxide, interface, and core regions. The combined data sets permit us to evaluate the electrical activation and compensation of the dopants in different regions of the nanowires and understand the details that lead to the sharp p-i-n junctions formed across the nanowire for the ex situ doping process.
NASA Astrophysics Data System (ADS)
Qu, Ailan; Xie, Haolong; Xu, Xinmei; Zhang, Yangyu; Wen, Shengwu; Cui, Yifan
2016-07-01
Graphene quantum dots (GQDs) with high quantum yield (about 23.6% at an excitation wavelength of 320 nm) and GQDs/TiO2 nanotubes (GQDs/TiO2 NTs) composites were achieved by a simple hydrothermal method at low temperature. Photoluminescence characterization showed that the GQDs exhibited the down-conversion PL features at excitation from 300 to 420 nm and up-conversion photoluminescence in the range of 600-800 nm. The photocatalytic activity of prepared GQDs/TiO2 NTs composites on the degradation of methyl orange (MO) was significantly enhanced compared with that of pure TiO2 nanotubes (TiO2 NTs). For the composites coupling with 1.5%, 2.5% and 3.5% GQDs, the degradation of MO after 20 min irradiation under UV-vis light irradiation (λ = 380-780 nm) were 80.52%, 94.64% and 51.91%, respectively, which are much higher than that of pure TiO2 NTs (35.41%). It was inferred from the results of characterization that the improved photocatalytic activity of the GQDs/TiO2 NTs composites was attributed to the synergetic effect of up-conversion properties of the GQDs, enhanced visible light absorption and efficient separation of photogenerated electron-holes of the GQDs/TiO2 composite.
NASA Astrophysics Data System (ADS)
Osborne, M. A.; Fisher, A. A. E.
2016-04-01
Understanding instabilities in the photoluminescence (PL) from light emitting materials is crucial to optimizing their performance for different applications. Semiconductor quantum dots (QDs) offer bright, size tunable emission, properties that are now being exploited in a broad range of developing technologies from displays and solar cells to biomaging and optical storage. However, instabilities such as photoluminescence intermittency, enhancement and bleaching of emission in these materials can be detrimental to their utility. Here, we report dielectric dependent blinking, intensity-``spikes'' and low-level, ``grey''-state emission, as well as PL enhancement in ZnS capped CdSe QDs; observations that we found consistent with a charge-tunnelling and self-trapping (CTST) description of exciton-dynamics on the QD-host system. In particular, modulation of PL in grey-states and PL enhancement are found to have a common origin in the equilibrium between exciton charge carrier core and surface-states within the CTST framework. Parameterized in terms of size and electrostatic properties of the QD and its nanoenvironment, the CTST offers predictive insight into exciton-dynamics in these nanomaterials.Understanding instabilities in the photoluminescence (PL) from light emitting materials is crucial to optimizing their performance for different applications. Semiconductor quantum dots (QDs) offer bright, size tunable emission, properties that are now being exploited in a broad range of developing technologies from displays and solar cells to biomaging and optical storage. However, instabilities such as photoluminescence intermittency, enhancement and bleaching of emission in these materials can be detrimental to their utility. Here, we report dielectric dependent blinking, intensity-``spikes'' and low-level, ``grey''-state emission, as well as PL enhancement in ZnS capped CdSe QDs; observations that we found consistent with a charge-tunnelling and self-trapping (CTST
Observing remnants by fermions' tunneling
Chen, D.Y.; Wu, H.W.; Yang, H. E-mail: iverwu@uestc.edu.cn
2014-03-01
The standard Hawking formula predicts the complete evaporation of black holes. In this paper, we introduce effects of quantum gravity into fermions' tunneling from Reissner-Nordstrom and Kerr black holes. The quantum gravity effects slow down the increase of Hawking temperatures. This property naturally leads to a residue mass in black hole evaporation. The corrected temperatures are affected by the quantum numbers of emitted fermions. Meanwhile, the temperature of the Kerr black hole is a function of θ due to the rotation.
Leary, A.; Wicha, A.; Harack, B.; Coish, W. A.; Hilke, M.; Yu, G.; Gupta, J. A.; Payette, C.; Austing, D. G.
2013-12-04
We outline the properties of the hyperfine-induced funnel structure observed in the two-electron spin blockade region of a weakly coupled vertical double quantum dot device. Hysteretic steps in the leakage current occur due to dynamic nuclear polarization when either the bias voltage or the magnetic field is swept up and down. When the bias voltage is swept, an intriguing ∼3 mT wide cusp near 0 T appears in the down-sweep position, and when the magnetic field is swept, the current at 0 T can be switched from 'low' to 'high' as the bias is increased.
NASA Astrophysics Data System (ADS)
Yost, Andrew J.; Rimal, Gaurab; Tang, Jinke; Chien, Teyu
A thorough understanding of the phenomena associated with doping of transition metals in semiconductors is important for the development of semiconducting electronic technologies such as semiconducting quantum dot sensitized solar cells (QDSSC). Manganese doping is of particular interest in a PbS QD as it is potentially capable of increasing overall QDSSC performance. Here we present scanning tunneling microscopy and spectroscopy studies about the effects of Manganese doping on the energy band structures of PbS semiconducting QD thin films, grown using pulsed laser deposition. As a result of Manganese doping in the PbS QD thin films, a widening of the electronic band gap was observed, which is responsible for the observed increase in resistivity. Furthermore, a loss of long range periodicity observed by XRD, upon incorporation of Manganese, indicates that the Manganese dopants also induce a large amount of grain boundaries. This work was supported by the following: U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering, DEFG02-10ER46728 and the National Science Foundation Grant #0948027.
Osborne, M A; Fisher, A A E
2016-04-28
Understanding instabilities in the photoluminescence (PL) from light emitting materials is crucial to optimizing their performance for different applications. Semiconductor quantum dots (QDs) offer bright, size tunable emission, properties that are now being exploited in a broad range of developing technologies from displays and solar cells to biomaging and optical storage. However, instabilities such as photoluminescence intermittency, enhancement and bleaching of emission in these materials can be detrimental to their utility. Here, we report dielectric dependent blinking, intensity-"spikes" and low-level, "grey"-state emission, as well as PL enhancement in ZnS capped CdSe QDs; observations that we found consistent with a charge-tunnelling and self-trapping (CTST) description of exciton-dynamics on the QD-host system. In particular, modulation of PL in grey-states and PL enhancement are found to have a common origin in the equilibrium between exciton charge carrier core and surface-states within the CTST framework. Parameterized in terms of size and electrostatic properties of the QD and its nanoenvironment, the CTST offers predictive insight into exciton-dynamics in these nanomaterials. PMID:27088542
Tunneling of squeezed states with an eye to evaporating black holes
NASA Astrophysics Data System (ADS)
Kontou, Eleni-Alexandra; Haggard, Hal
2016-03-01
In this work we study how tunneling time depends on the squeezing parameter of quantum states. Squeezed quantum states are investigated for optical communications and appear in the emission from black holes. A surprising property of these states is reduced tunneling time. Treating Hawking radiation as a quantum tunneling process, we study the interplay of squeezing with the radiation process.
NASA Technical Reports Server (NTRS)
Hanson, P. W.
1984-01-01
Active controls technology is assessed based on a review of most of the wind-tunnel and flight tests and actual applications of active control concepts since the late sixties. The distinction is made between so-called ""rigid-body'' active control functions and those that involve significant modification of structural elastic response or stability. Both areas are reviewed although the focus is on the latter area. The basic goals and major results of the various studies or applications are summarized, and the anticipated use of active controls on current and near-future research and demonstration aircraft is discussed. Some of the ""holes'' remaining in the feasbility/benefits demonstration of active controls technology are examined.
Active Control of Wind-Tunnel Model Aeroelastic Response Using Neural Networks
NASA Technical Reports Server (NTRS)
Scott, Robert C.
2000-01-01
NASA Langley Research Center, Hampton, VA 23681 Under a joint research and development effort conducted by the National Aeronautics and Space Administration and The Boeing Company (formerly McDonnell Douglas) three neural-network based control systems were developed and tested. The control systems were experimentally evaluated using a transonic wind-tunnel model in the Langley Transonic Dynamics Tunnel. One system used a neural network to schedule flutter suppression control laws, another employed a neural network in a predictive control scheme, and the third employed a neural network in an inverse model control scheme. All three of these control schemes successfully suppressed flutter to or near the limits of the testing apparatus, and represent the first experimental applications of neural networks to flutter suppression. This paper will summarize the findings of this project.
Fermi resonance in dynamical tunneling in a chaotic billiard
NASA Astrophysics Data System (ADS)
Yi, Chang-Hwan; Kim, Ji-Hwan; Yu, Hyeon-Hye; Lee, Ji-Won; Kim, Chil-Min
2015-08-01
We elucidate that Fermi resonance ever plays a decisive role in dynamical tunneling in a chaotic billiard. Interacting with each other through an avoided crossing, a pair of eigenfunctions are coupled through tunneling channels for dynamical tunneling. In this case, the tunneling channels are an islands chain and its pair unstable periodic orbit, which equals the quantum number difference of the eigenfunctions. This phenomenon of dynamical tunneling is confirmed in a quadrupole billiard in relation with Fermi resonance.
NASA Technical Reports Server (NTRS)
Perry, B., III
1981-01-01
Comparisons are presented analytically predicted and experimental turbulence responses of a wind tunnel model of a DC-10 derivative wing equipped with an active control system. The active control system was designed for the purpose of flutter suppression, but it had additional benefit of alleviating gust loads (wing bending moment) by about 25%. Comparisions of various wing responses are presented for variations in active control system parameters and tunnel speed. The analytical turbulence responses were obtained using DYLOFLEX, a computer program for dynamic loads analyses of flexible airplanes with active controls. In general, the analytical predictions agreed reasonably well with the experimental data.
A New Quantum Sensor for Measuring Photosynthetically Active Radiation
NASA Astrophysics Data System (ADS)
Johnson, D.; Thomas, T.; Heinicke, D.; Peterson, R.; Morgan, P.; McDermitt, D. K.; Burba, G. G.
2015-12-01
A quantum sensor measures photosynthetically active radiation (PAR, in μmol of photons m-2 s-1) in the 400 nm to 700 nm waveband. Plants utilize this radiation to drive photosynthesis, though individual plant responses to incident radiation may vary within this range. The new quantum sensor (model LI-190R, LI-COR Biosciences, Lincoln, NE), with an optical filter and silicon photodiode detector housed in a cosine-corrected head, is designed to provide a better response to incident radiation across the 400-700 nm range. The new design is expected to significantly improve spectral response due to uniformity across the PAR waveband, but particularly in the wavebands from 520 nm to 600 nm and 665 nm to 680 nm, and sharp cutoffs in the regions below and above the PAR waveband. Special care was taken to make sure that PAR sensor would not substantially respond to incident radiation above the 700 nm threshold because this can lead to errors when performing measurements in environments with a large proportion of near-infrared radiation, such as canopy understory. The physical housing of the sensor is designed to be weather-resistant, to effectively shed precipitation, provide protection at high temperature and high humidity conditions, and has a cosine-corrected response to 82° zenith angle. The latter is particularly important when measuring incident radiation at low elevation angles, diffuse light, or low light conditions. This presentation describes the principles of the new design, and shows the performance results from field experiments and laboratory tests.
NASA Technical Reports Server (NTRS)
Micol, John R.
2001-01-01
Description, capabilities, initiatives, and utilization of the NASA Langley Research Center's Unitary Plan Wind Tunnel are presented. A brief overview of the facility's operational capabilities and testing techniques is provided. A recent Construction of Facilities (CoF) project to improve facility productivity and efficiency through facility automation has been completed and is discussed. Several new and maturing thrusts are underway that include systematic efforts to provide credible assessment for data quality, modifications to the new automation control system for increased compatibility with the Modern Design Of Experiments (MDOE) testing methodology, and process improvements for better test coordination, planning, and execution.
NASA Technical Reports Server (NTRS)
Micol, John R.
2001-01-01
Description, capabilities, initiatives, and utilization of the NASA Langley Research Center's Unitary Plan Wind Tunnel are presented. A brief overview of the facility's operational capabilities and testing techniques is provided. A recent Construction of Facilities (Car) project to improve facility productivity and efficiency through facility automation has been completed and is discussed. Several new and maturing thrusts are underway that include systematic efforts to provide credible assessment for data quality, modifications to the new automation control system for increased compatibility with the Modern Design of Experiments (MDOE) testing methodology, and process improvements for better test coordination, planning, and execution.
A self-assembled quantum dot probe for detecting {beta}-lactamase activity
Xu Chenjie; Xing Bengang; Rao Jianghong . E-mail: jrao@stanford.edu
2006-06-09
This communication describes a quantum dot probe that can be activated by a reporter enzyme, {beta}-lactamase. Our design is based on the principle of fluorescence resonance energy transfer (FRET). A biotinylated {beta}-lactamase substrate was labeled with a carbocyanine dye, Cy5, and immobilized on the surface of quantum dots through the binding of biotin to streptavidin pre-coated on the quantum dots. In assembling this nanoprobe, we have found that both the distance between substrates and the quantum dot surface, and the density of substrates are important for its function. The fluorescence emission from quantum dots can be efficiently quenched (up to 95%) by Cy5 due to FRET. Our final quantum dot probe, assembled with QD605 and 1:1 mixture of biotin and a Cy5-labeled lactam, can be activated by 32 {mu}g/mL of {beta}-lactamase with 4-fold increase in the fluorescence emission.
NASA Astrophysics Data System (ADS)
Carabello, Steve; Lambert, Joseph; Dai, Wenqing; Li, Qi; Chen, Ke; Cunnane, Daniel; Xi, X. X.; Ramos, Roberto
We report results of superconducting-to-normal switching experiments on MgB2/I/Pb and MgB2/I/Sn junctions, with and without microwaves. These results suggest that the switching behavior is dominated by quantum tunneling through the washboard potential barrier, rather than thermal excitations or electronic noise. Evidence includes a leveling in the standard deviation of the switching current distribution below a crossover temperature, a Lorentzian shape of the escape rate enhancement peak upon excitation by microwaves, and a narrowing in the histogram of escape counts in the presence of resonant microwave excitation relative to that in the absence of microwaves. These are the first such results reported in ``hybrid'' Josephson tunnel junctions, consisting of multi-gap and single-gap superconducting electrodes.
Optically active quantum dots in monolayer WSe2.
Srivastava, Ajit; Sidler, Meinrad; Allain, Adrien V; Lembke, Dominik S; Kis, Andras; Imamoğlu, A
2015-06-01
Semiconductor quantum dots have emerged as promising candidates for the implementation of quantum information processing, because they allow for a quantum interface between stationary spin qubits and propagating single photons. In the meantime, transition-metal dichalcogenide monolayers have moved to the forefront of solid-state research due to their unique band structure featuring a large bandgap with degenerate valleys and non-zero Berry curvature. Here, we report the observation of zero-dimensional anharmonic quantum emitters, which we refer to as quantum dots, in monolayer tungsten diselenide, with an energy that is 20-100 meV lower than that of two-dimensional excitons. Photon antibunching in second-order photon correlations unequivocally demonstrates the zero-dimensional anharmonic nature of these quantum emitters. The strong anisotropic magnetic response of the spatially localized emission peaks strongly indicates that radiative recombination stems from localized excitons that inherit their electronic properties from the host transition-metal dichalcogenide. The large ∼1 meV zero-field splitting shows that the quantum dots have singlet ground states and an anisotropic confinement that is most probably induced by impurities or defects. The possibility of achieving electrical control in van der Waals heterostructures and to exploit the spin-valley degree of freedom renders transition-metal-dichalcogenide quantum dots interesting for quantum information processing.
NASA Astrophysics Data System (ADS)
Useinov, Arthur; Lai, Chih-Huang
2016-02-01
Temperature dependence of the tunnel magnetoresistance (TMR) was calculated in range of the quantum-ballistic model in the magnetic tunnel junction (MTJ) with embedded nanoparticles (NPs). The electron tunnel transport through NP was simulated in range of double barrier approach, which was integrated into the model of the magnetic point-like contact. The resonant TMR conditions and temperature impact were explored in detail. Moreover, the possible reasons of the temperature induced resonant conditions were discussed in the range of the lead-tunneling cell (TC)-lead model near Kondo temperature. We also found that redistribution of the voltage drop becomes crucial in this model. Furthermore, the direct tunneling plays the dominant role and cannot be omitted in the quantum systems with the total tunneling thickness up to 5-6nm. Hence, Coulomb blockade model cannot explain Kondo-induced TMR anomalies in nanometer-sized tunnel junctions.
[Effects of quantum nonlocality in the water activation process].
Zatsepina, O V; Stekhin, A A; Yakovleva, G V
2014-01-01
The dynamic alterations of the magnetic flux density of the water volume, activated with structurally stressed calcium carbonate in micellar form have been investigated. The phase of the associated water was established to exhibit electrical and magnetic properties, recorded by in B&E meter in the frequency range of 5Hz - 2kHz. Alterations in water Eh (redox) potential and the magnetic flux density B testify to synchronous auto-oscillatory changes. This gives evidence of non-linearity of the relationship between auto-oscillatory processes excited in the water; and reflects the nonlocal in time the relationship between the states of water, manifesting in a change of water activity on the 1st and 2nd day in negative time. The mechanism of action of associated water phase is shown to be described by de Broglie concept of matter waves with taking into account delocalized in time states of phase of electron wave packet in accordance with the transactional interpretation of quantum physics. PMID:24749297
[Effects of quantum nonlocality in the water activation process].
Zatsepina, O V; Stekhin, A A; Yakovleva, G V
2014-01-01
The dynamic alterations of the magnetic flux density of the water volume, activated with structurally stressed calcium carbonate in micellar form have been investigated. The phase of the associated water was established to exhibit electrical and magnetic properties, recorded by in B&E meter in the frequency range of 5Hz - 2kHz. Alterations in water Eh (redox) potential and the magnetic flux density B testify to synchronous auto-oscillatory changes. This gives evidence of non-linearity of the relationship between auto-oscillatory processes excited in the water; and reflects the nonlocal in time the relationship between the states of water, manifesting in a change of water activity on the 1st and 2nd day in negative time. The mechanism of action of associated water phase is shown to be described by de Broglie concept of matter waves with taking into account delocalized in time states of phase of electron wave packet in accordance with the transactional interpretation of quantum physics.
Ultrafast scanning tunneling microscopy
Botkin, D.A. |
1995-09-01
I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.
Farrugia, Mark A; Wang, Beibei; Feig, Michael; Hausinger, Robert P
2015-10-20
Nickel-containing urease from Klebsiella aerogenes requires four accessory proteins for proper active site metalation. The metallochaperone UreE delivers nickel to UreG, a GTPase that forms a UreD/UreF/UreG complex, which binds to urease apoprotein via UreD. Prior in silico analysis of the homologous, structurally characterized UreH/UreF/UreG complex from Helicobacter pylori identified a water tunnel originating at a likely nickel-binding motif in UreG, passing through UreF, and exiting UreH, suggestive of a role for the channel in providing the metal to urease apoprotein for its activation; however, no experimental support was reported for the significance of this tunnel. Here, specific variants were designed to disrupt a comparable 34.6 Å predicted internal tunnel, alternative channels, and surface sites for UreD. Cells producing a set of tunnel-disrupting variants of UreD exhibited greatly reduced urease specific activities, whereas other mutants had no appreciable effect on activity. Affinity pull-down studies of cell-free extracts from tunnel-disrupting mutant cultures showed no loss of UreD interactions with urease or UreF/UreG. The nickel contents of urease samples enriched from activity-deficient cultures were decreased, while zinc and iron incorporation increased. Molecular dynamics simulations revealed size restrictions in the internal channels of the UreD variants. These findings support the role of a molecular tunnel in UreD as a direct facilitator of nickel transfer into urease, illustrating a new paradigm in active site metallocenter assembly.
Farrugia, Mark A; Wang, Beibei; Feig, Michael; Hausinger, Robert P
2015-10-20
Nickel-containing urease from Klebsiella aerogenes requires four accessory proteins for proper active site metalation. The metallochaperone UreE delivers nickel to UreG, a GTPase that forms a UreD/UreF/UreG complex, which binds to urease apoprotein via UreD. Prior in silico analysis of the homologous, structurally characterized UreH/UreF/UreG complex from Helicobacter pylori identified a water tunnel originating at a likely nickel-binding motif in UreG, passing through UreF, and exiting UreH, suggestive of a role for the channel in providing the metal to urease apoprotein for its activation; however, no experimental support was reported for the significance of this tunnel. Here, specific variants were designed to disrupt a comparable 34.6 Å predicted internal tunnel, alternative channels, and surface sites for UreD. Cells producing a set of tunnel-disrupting variants of UreD exhibited greatly reduced urease specific activities, whereas other mutants had no appreciable effect on activity. Affinity pull-down studies of cell-free extracts from tunnel-disrupting mutant cultures showed no loss of UreD interactions with urease or UreF/UreG. The nickel contents of urease samples enriched from activity-deficient cultures were decreased, while zinc and iron incorporation increased. Molecular dynamics simulations revealed size restrictions in the internal channels of the UreD variants. These findings support the role of a molecular tunnel in UreD as a direct facilitator of nickel transfer into urease, illustrating a new paradigm in active site metallocenter assembly. PMID:26401965
Decoherence and tunneling of an interacting gas
NASA Astrophysics Data System (ADS)
Anglin, James; Rico-Perez, Luis; Wohlfarth, Daniel
2015-05-01
In quasi-steady escape of a confined interacting gas by quantum tunneling, collisional decoherence can reduce the escape rate through a many-body version of the Caldeira-Leggett effect. This explains why classical fluids fail to tunnel, even though they are composed of particles small enough to be quantum mechanical. We compute this effect in the Maxwell-Boltzmann regime by deriving a quantum generalization of the Boltzmann equation. We show that decoherence effectively makes tunneling of an interacting gas into an irreversible process: a uniquely quantum mechanical form of throttling. The rate of entropy production in tunneling is related in the semi-classical limit to the imaginary part of the single-particle action.
Help Students Tunnel Their Way to Math and Writing Skills.
ERIC Educational Resources Information Center
MacMath, Russ
1987-01-01
A teacher describes how a cardboard box tunnel was used to capitalize on children's fascination with boxes. The finished tunnel offers opportunities for honing math and writing skills. Layouts for tunnels and related activities are suggested. (MT)
Optical Properties of Active Regions in Terahertz Quantum Cascade Lasers
NASA Astrophysics Data System (ADS)
Dyksik, M.; Motyka, M.; Rudno-Rudziński, W.; Sęk, G.; Misiewicz, J.; Pucicki, D.; Kosiel, K.; Sankowska, I.; Kubacka-Traczyk, J.; Bugajski, M.
2016-07-01
In this work, AlGaAs/GaAs superlattice, with layers' sequence and compositions imitating the active and injector regions of a quantum cascade laser designed for emission in the terahertz spectral range, was investigated. Three independent absorption-like optical spectroscopy techniques were employed in order to study the band structure of the minibands formed within the conduction band. Photoreflectance measurements provided information about interband transitions in the investigated system. Common transmission spectra revealed, in the target range of intraband transitions, mainly a number of lines associated with the phonon-related processes, including two-phonon absorption. In contrast, differential transmittance realized by means of Fourier-transform spectroscopy was utilized to probe the confined states of the conduction band. The obtained energy separation between the second and third confined electron levels, expected to be predominantly contributing to the lasing, was found to be ~9 meV. The optical spectroscopy measurements were supported by numerical calculations performed in the effective mass approximation and XRD measurements for layers' width verification. The calculated energy spacings are in a good agreement with the experimental values.
NASA Astrophysics Data System (ADS)
Suarez, Ernesto; Chan, Pik-Yiu; Lingalugari, Murali; Ayers, John E.; Heller, Evan; Jain, Faquir
2013-11-01
This paper describes the use of II-VI lattice-matched gate insulators in quantum dot gate three-state and flash nonvolatile memory structures. Using silicon-on-insulator wafers we have fabricated GeO x -cladded Ge quantum dot (QD) floating gate nonvolatile memory field-effect transistor devices using ZnS-Zn0.95Mg0.05S-ZnS tunneling layers. The II-VI heteroepitaxial stack is nearly lattice-matched and is grown using metalorganic chemical vapor deposition on a silicon channel. This stack reduces the interface state density, improving threshold voltage variation, particularly in sub-22-nm devices. Simulations using self-consistent solutions of the Poisson and Schrödinger equations show the transfer of charge to the QD layers in three-state as well as nonvolatile memory cells.
Promoting and inhibiting tunneling via nuclear motions.
Császár, Attila G; Furtenbacher, Tibor
2016-01-14
Accurate, experimental rotational-vibrational energy levels determined via the MARVEL (Measured Active Rotational-Vibrational Energy Levels) algorithm and published recently for the symmetric-top (14)NH3 molecule in J. Quant. Spectrosc. Radiat. Transfer, 2015, 116, 117-130 are analyzed to unravel the promoting and inhibiting effects of vibrations and rotations on the tunneling splittings of the corresponding symmetric (s) and antisymmetric (a) rovibrational energy level pairs. The experimental transition data useful from the point of view of the present analysis cover the range 0.7-7000 cm(-1), sufficiently detailed rovibrational energy sets worth analyzing are available for 20 vibrational bands. The highest J value, where J stands for the rotational quantum number, within the experimental dataset employed is 30. Coupling of the "umbrella" motion of (14)NH3 with other vibrational degrees of freedom has only a minor effect on the a-s tunneling splitting characterizing the ground vibrational state, 0.79436(70) cm(-1). In the majority of the cases rotation around the C3 axis increases, while rotation around the two perpendicular axes decreases the tunneling splittings. For example, for the pair of vibrational ground states, 0(+) and 0(-), the tunneling splitting basically disappears at around J = 25 for the (J,K) = (J,1) states, where K = |k| is the usual quantum number characterizing the projection of the rotational angular momentum on the principal axis. The tunneling splittings, defined as energy differences E(a) - E(s) of corresponding energy level pairs, as a function of J and K show a very regular behavior for the ground state (GS) and the nν2 bands. For the other bands investigated exceptions from a regular behavior do occur, especially for bands characterized by degenerate vibrations, and occasionally the data available are not sufficient to arrive at definitive conclusions. The most irregular behavior is observed for rotational states characterized by the k
NASA Technical Reports Server (NTRS)
Ting, David Z.
2007-01-01
The resonant tunneling spin pump is a proposed semiconductor device that would generate spin-polarized electron currents. The resonant tunneling spin pump would be a purely electrical device in the sense that it would not contain any magnetic material and would not rely on an applied magnetic field. Also, unlike prior sources of spin-polarized electron currents, the proposed device would not depend on a source of circularly polarized light. The proposed semiconductor electron-spin filters would exploit the Rashba effect, which can induce energy splitting in what would otherwise be degenerate quantum states, caused by a spin-orbit interaction in conjunction with a structural-inversion asymmetry in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. Theoretical studies have suggested the possibility of devices in which electron energy states would be split by the Rashba effect and spin-polarized currents would be extracted by resonant quantum-mechanical tunneling.
Bao, Junwei Lucas; Zhang, Xin; Truhlar, Donald G
2016-06-22
Understanding the falloff in rate constants of gas-phase unimolecular reaction rate constants as the pressure is lowered is a fundamental problem in chemical kinetics, with practical importance for combustion, atmospheric chemistry, and essentially all gas-phase reaction mechanisms. In the present work, we use our recently developed system-specific quantum RRK theory, calibrated by canonical variational transition state theory with small-curvature tunneling, combined with the Lindemann-Hinshelwood mechanism, to model the dissociation reaction of fluoroform (CHF3), which provides a definitive test for falloff modeling. Our predicted pressure-dependent thermal rate constants are in excellent agreement with experimental values over a wide range of pressures and temperatures. The present validation of our methodology, which is able to include variational transition state effects, multidimensional tunneling based on the directly calculated potential energy surface along the tunneling path, and torsional and other vibrational anharmonicity, together with state-of-the-art reaction-path-based direct dynamics calculations, is important because the method is less empirical than models routinely used for generating full mechanisms, while also being simpler in key respects than full master equation treatments and the full reduced falloff curve and modified strong collision methods of Troe. PMID:27273734
Bao, Junwei Lucas; Zhang, Xin; Truhlar, Donald G
2016-06-22
Understanding the falloff in rate constants of gas-phase unimolecular reaction rate constants as the pressure is lowered is a fundamental problem in chemical kinetics, with practical importance for combustion, atmospheric chemistry, and essentially all gas-phase reaction mechanisms. In the present work, we use our recently developed system-specific quantum RRK theory, calibrated by canonical variational transition state theory with small-curvature tunneling, combined with the Lindemann-Hinshelwood mechanism, to model the dissociation reaction of fluoroform (CHF3), which provides a definitive test for falloff modeling. Our predicted pressure-dependent thermal rate constants are in excellent agreement with experimental values over a wide range of pressures and temperatures. The present validation of our methodology, which is able to include variational transition state effects, multidimensional tunneling based on the directly calculated potential energy surface along the tunneling path, and torsional and other vibrational anharmonicity, together with state-of-the-art reaction-path-based direct dynamics calculations, is important because the method is less empirical than models routinely used for generating full mechanisms, while also being simpler in key respects than full master equation treatments and the full reduced falloff curve and modified strong collision methods of Troe.
Mandal, Debasish; Shaik, Sason
2016-02-24
The study of C-H bond activation reactions by nonheme Fe(IV)O species with nine hydrocarbons shows that the kinetic isotope effect (KIE) involves strong tunneling and is a signature of the reactive spin states. Theory reproduces the observed spike-like appearance of plots of KIE(exp) against the C-H bond dissociation energy, and its origins are discussed. The experimentally observed Bell-Evans-Polanyi correlations, in the presence of strong tunneling, are reproduced, and the pattern is rationalized. PMID:26824716
Mandal, Debasish; Shaik, Sason
2016-02-24
The study of C-H bond activation reactions by nonheme Fe(IV)O species with nine hydrocarbons shows that the kinetic isotope effect (KIE) involves strong tunneling and is a signature of the reactive spin states. Theory reproduces the observed spike-like appearance of plots of KIE(exp) against the C-H bond dissociation energy, and its origins are discussed. The experimentally observed Bell-Evans-Polanyi correlations, in the presence of strong tunneling, are reproduced, and the pattern is rationalized.
NASA Astrophysics Data System (ADS)
Campagnolo, Filippo; Bottasso, Carlo L.; Bettini, Paolo
2014-06-01
In the research described in this paper, a scaled wind turbine model featuring individual pitch control (IPC) capabilities, and equipped with aero-elastically scaled blades featuring passive load reduction capabilities (bend-twist coupling, BTC), was constructed to investigate, by means of wind tunnel testing, the load alleviation potential of BTC and its synergy with active load reduction techniques. The paper mainly focus on the design of the aero-elastic blades and their dynamic and static structural characterization. The experimental results highlight that manufactured blades show desired bend-twist coupling behavior and are a first milestone toward their testing in the wind tunnel.
NASA Technical Reports Server (NTRS)
Chin, J.; Barbero, P.
1975-01-01
The revision of an existing digital program to analyze the stability of models mounted on a two-cable mount system used in a transonic dynamics wind tunnel is presented. The program revisions and analysis of an active feedback control system to be used for controlling the free-flying models are treated.
Prospects For Quantum Integrated Circuits
NASA Astrophysics Data System (ADS)
Bate, R. T.; Frazier, G. A.; Frensley, W. R.; Lee, J. W.; Reed, M. A.
1987-08-01
Recent progress in research on resonant tunneling diodes, and on lateral quantization effects in quantum wells renews hope for the development of active unipolar heterojunction devices which incorporate no depletion layers, and hence can be extremely compact in both vertical and lateral dimensions. If such devices meeting the fundamental requirements for ultrahigh density integrated circuits can be developed, and if revolutionary chip architectures which overcome current interconnection limitations can be devised, then a new generation of integrated circuits approaching the ultimate limits of functional density and functional throughput may eventually ensue. Although many of the most challenging problems in this scenario have not yet been addressed, progress is being made in the areas of fabrication and characterization of resonant tunneling devices, simulation of such devices using quantum transport theory, and simulation of nearest-neighbor connected (two-dimensional cellular automaton) architectures. This paper reviews the progress in these areas at Texas Instruments, and discusses the prospects for the future.
Lindsay, Stuart; He, Jin; Sankey, Otto; Hapala, Prokop; Jelinek, Pavel; Zhang, Peiming; Chang, Shuai; Huang, Shuo
2010-01-01
Single molecules in a tunnel junction can now be interrogated reliably using chemically-functionalized electrodes. Monitoring stochastic bonding fluctuations between a ligand bound to one electrode and its target bound to a second electrode (“tethered molecule-pair” configuration) gives insight into the nature of the intermolecular bonding at a single molecule-pair level, and defines the requirements for reproducible tunneling data. Simulations show that there is an instability in the tunnel gap at large currents, and this results in a multiplicity of contacts with a corresponding spread in the measured currents. At small currents (i.e. large gaps) the gap is stable, and functionalizing a pair of electrodes with recognition reagents (the “free analyte” configuration) can generate a distinct tunneling signal when an analyte molecule is trapped in the gap. This opens up a new interface between chemistry and electronics with immediate implications for rapid sequencing of single DNA molecules. PMID:20522930
Sutcliffe, Michael J; Scrutton, Nigel S
2002-07-01
Recent years have witnessed high levels of activity in identifying enzyme systems that catalyse H-transfer by quantum tunneling. Rather than being restricted to a small number of specific enzymes as perceived initially, it has now become an accepted mechanism for H-transfer in a growing number of enzymes. Furthermore, H-tunneling is driven by the thermally induced dynamics of the enzyme. In some of those enzymes that break stable C-H bonds the reaction proceeds purely by quantum tunneling, without the need to partially ascend the barrier. Enzymes studied that fall into this category include the flavoprotein and quinoprotein amine dehydrogenases, which have proved to be excellent model systems. These enzymes have enabled us to study the relationship between barrier shape and reaction kinetics. This has involved studies with "slow" and "fast" substrates and enzymes impaired by mutagenesis. A number of key questions now remain, including the nature of the coupling between protein dynamics and quantum tunneling. The wide-ranging implications of quantum tunneling introduce a paradigm shift in the conceptual framework for enzyme catalysis, inhibition and design.
Deterministic generation of remote entanglement with active quantum feedback
Martin, Leigh; Motzoi, Felix; Li, Hanhan; Sarovar, Mohan; Whaley, K. Birgitta
2015-12-10
We develop and study protocols for deterministic remote entanglement generation using quantum feedback, without relying on an entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average-sense locally optimal feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols that can deterministically create maximal entanglement: a semiclassical feedback protocol for low-efficiency measurements and a quantum feedback protocol for high-efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can bemore » modeled by a Wiseman-Milburn feedback master equation, which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics and we exploit this feature to derive a superior hybrid protocol for arbitrary nonunit measurement efficiency that switches between quantum and semiclassical protocols. Lastly, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.« less
Deterministic generation of remote entanglement with active quantum feedback
Martin, Leigh; Motzoi, Felix; Li, Hanhan; Sarovar, Mohan; Whaley, K. Birgitta
2015-12-10
We develop and study protocols for deterministic remote entanglement generation using quantum feedback, without relying on an entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average-sense locally optimal feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols that can deterministically create maximal entanglement: a semiclassical feedback protocol for low-efficiency measurements and a quantum feedback protocol for high-efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can be modeled by a Wiseman-Milburn feedback master equation, which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics and we exploit this feature to derive a superior hybrid protocol for arbitrary nonunit measurement efficiency that switches between quantum and semiclassical protocols. Lastly, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.
Horiguchi, Gen; Aoki, Takafumi; Ito, Hiromoto
2011-01-01
The main cause of carpal tunnel syndrome (CTS) remains unknown. Stiffness of the subcutaneous area of the volar aspect of the carpal tunnel is present in many patients and suggests that the stiffness of muscles attached to the transverse carpal ligament is increased. We performed an electrophysiological study to investigate muscle activities and to clarify whether the stiffness of muscles attached to the transverse carpal ligament is involved in the pathogenesis of CTS. The subjects of this study included 16 patients with early CTS showing no motor dysfunction. Both thenar muscles (opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis) and hypothenar muscles (opponens digiti minimi, abductor digiti minimi, flexor digiti minimi brevis) were investigated. Surface electrodes were placed on each muscle, and maximum voluntary contractions with the thumb and little finger in opposition were maintained for 3 seconds in all patients and in 7 control subjects. Electromyographs were subjected to fast Fourier transform analysis, and the root mean square (RMS) and the mean power frequency (MPF) were determined for each muscle. The RMS of the opponens pollicis was significantly less in hands affected by CTS (292.8 µV) than in healthy hands (405.9 µV). The RMS did not differ between affected hands and healthy hands for the other 2 thenar muscles but did differ significantly for the hypothenar muscles. The MPF did not differ between affected hands and healthy hands for any muscle. The results show that electrophysiological differences are present among muscles innervated by the median nerve and that hypothenar muscles originally unrelated to median nerve dysfunction are also affected in early CTS. These results suggest that modulation of muscles attached to the transverse carpal ligament is involved in the pathogenesis of CTS.
Quantum phenomena in superconductors
Clarke, J.
1987-08-01
This paper contains remarks by the author on aspects of macroscopic quantum phenomena in superconductors. Some topics discussed are: Superconducting low-inductance undulatory galvanometer (SLUGS), charge imbalance, cylindrical dc superconducting quantum interference device (SQUIDS), Geophysics, noise theory, magnetic resonance with SQUIDS, and macroscopic quantum tunneling. 23 refs., 4 figs. (LSP)
High-speed linear optics quantum computing using active feed-forward.
Prevedel, Robert; Walther, Philip; Tiefenbacher, Felix; Böhi, Pascal; Kaltenbaek, Rainer; Jennewein, Thomas; Zeilinger, Anton
2007-01-01
As information carriers in quantum computing, photonic qubits have the advantage of undergoing negligible decoherence. However, the absence of any significant photon-photon interaction is problematic for the realization of non-trivial two-qubit gates. One solution is to introduce an effective nonlinearity by measurements resulting in probabilistic gate operations. In one-way quantum computation, the random quantum measurement error can be overcome by applying a feed-forward technique, such that the future measurement basis depends on earlier measurement results. This technique is crucial for achieving deterministic quantum computation once a cluster state (the highly entangled multiparticle state on which one-way quantum computation is based) is prepared. Here we realize a concatenated scheme of measurement and active feed-forward in a one-way quantum computing experiment. We demonstrate that, for a perfect cluster state and no photon loss, our quantum computation scheme would operate with good fidelity and that our feed-forward components function with very high speed and low error for detected photons. With present technology, the individual computational step (in our case the individual feed-forward cycle) can be operated in less than 150 ns using electro-optical modulators. This is an important result for the future development of one-way quantum computers, whose large-scale implementation will depend on advances in the production and detection of the required highly entangled cluster states.
Deterministic generation of remote entanglement with active quantum feedback
NASA Astrophysics Data System (ADS)
Martin, Leigh; Motzoi, Felix; Li, Hanhan; Sarovar, Mohan; Whaley, K. Birgitta
2015-12-01
We consider the task of deterministically entangling two remote qubits using joint measurement and feedback, but no directly entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average-sense locally optimal feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols that can deterministically create maximal entanglement: a semiclassical feedback protocol for low-efficiency measurements and a quantum feedback protocol for high-efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can be modeled by a Wiseman-Milburn feedback master equation, which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics and we exploit this feature to derive a superior hybrid protocol for arbitrary nonunit measurement efficiency that switches between quantum and semiclassical protocols. Finally, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.
He, Yuezhen; Sun, Jian; Feng, Dexiang; Chen, Hongqi; Gao, Feng; Wang, Lun
2015-12-15
In this paper, a simple and sensitive photoluminescence method is developed for the hydroquinone quantitation by using graphene quantum dots which simultaneously serve as a peroxidase-mimicking catalyst and a photoluminescence indicator. In the presence of dissolved oxygen, graphene quantum dots with intrinsic peroxidase-mimicking catalytic activity can catalyze the oxidation of hydroquinone to produce p-benzoquinone, an intermediate, which can efficiently quench graphene quantum dots' photoluminescence. Based on this effect, a novel fluorescent platform is proposed for the sensing of hydroquinone, and the detection limit of 5 nM is found. PMID:26164014
Improved multidimensional semiclassical tunneling theory.
Wagner, Albert F
2013-12-12
We show that the analytic multidimensional semiclassical tunneling formula of Miller et al. [Miller, W. H.; Hernandez, R.; Handy, N. C.; Jayatilaka, D.; Willets, A. Chem. Phys. Lett. 1990, 172, 62] is qualitatively incorrect for deep tunneling at energies well below the top of the barrier. The origin of this deficiency is that the formula uses an effective barrier weakly related to the true energetics but correctly adjusted to reproduce the harmonic description and anharmonic corrections of the reaction path at the saddle point as determined by second order vibrational perturbation theory. We present an analytic improved semiclassical formula that correctly includes energetic information and allows a qualitatively correct representation of deep tunneling. This is done by constructing a three segment composite Eckart potential that is continuous everywhere in both value and derivative. This composite potential has an analytic barrier penetration integral from which the semiclassical action can be derived and then used to define the semiclassical tunneling probability. The middle segment of the composite potential by itself is superior to the original formula of Miller et al. because it incorporates the asymmetry of the reaction barrier produced by the known reaction exoergicity. Comparison of the semiclassical and exact quantum tunneling probability for the pure Eckart potential suggests a simple threshold multiplicative factor to the improved formula to account for quantum effects very near threshold not represented by semiclassical theory. The deep tunneling limitations of the original formula are echoed in semiclassical high-energy descriptions of bound vibrational states perpendicular to the reaction path at the saddle point. However, typically ab initio energetic information is not available to correct it. The Supporting Information contains a Fortran code, test input, and test output that implements the improved semiclassical tunneling formula. PMID:24224758
NASA Astrophysics Data System (ADS)
Ren, Fei; Wang, Feng-Jiao; Liu, Shu-Man; Ning, Zhen-Dong; Zhuo, Ning; Ye, Xiao-Ling; Liu, Jun-Qi; Wang, Li-Jun; Liu, Feng-Qi; Wang, Zhan-Guo
2016-05-01
Double-wavelength intersubband electroluminescence at ∼7 and ∼10 µm was obtained using a simple five-well quantum cascade structure. Electron injection from a common injector level to two neighboring emitting wells was realized by resonant tunneling or phonon-assisted tunneling, determined by the energy separation between the injector level E 0 and the upper-emitting levels under various bias electric fields. Such simple quantum cascade structures might lead to a new solution for dual-color mid-infrared lasers.
Hydrogen Tunneling Links Protein Dynamics to Enzyme Catalysis
Klinman, Judith P.; Kohen, Amnon
2014-01-01
The relationship between protein dynamics and function is a subject of considerable contemporary interest. Although protein motions are frequently observed during ligand binding and release steps, the contribution of protein motions to the catalysis of bond making/breaking processes is more difficult to probe and verify. Here, we show how the quantum mechanical hydrogen tunneling associated with enzymatic C–H bond cleavage provides a unique window into the necessity of protein dynamics for achieving optimal catalysis. Experimental findings support a hierarchy of thermodynamically equilibrated motions that control the H-donor and -acceptor distance and active-site electrostatics, creating an ensemble of conformations suitable for H-tunneling. A possible extension of this view to methyl transfer and other catalyzed reactions is also presented. The impact of understanding these dynamics on the conceptual framework for enzyme activity, inhibitor/drug design, and biomimetic catalyst design is likely to be substantial. PMID:23746260
Li, Changqing; Junaid, Muhammad; Almuqri, Eman Abdullah; Hao, Shiguang; Zhang, Houjin
2016-05-01
FrbJ is a member of the Fe(2+)/α-ketoglutarate-dependent dioxygenase family which hydroxylates the natural product FR-900098 of Streptomyces rubellomurinus, yielding the phosphonate antibiotic FR-33289. Here, the crystal structure of FrbJ, which shows structural homology to taurine dioxygenase (TauD), a key member of the same family, is reported. Unlike other members of the family, FrbJ has an unusual lid structure which consists of two β-strands with a long loop between them. To investigate the role of this lid motif, a molecular-dynamics simulation was performed with the FrbJ structure. The molecular-dynamics simulation analysis implies that the lid-loop region is highly flexible, which is consistent with the fact that FrbJ has a relatively broad spectrum of substrates with different lengths. Interestingly, an access tunnel is found at the back of the active site which connects the putative binding site of α-ketoglutarate to the solvent outside. PMID:27139827
Mezey, Paul G
2014-09-16
Conspectus Just as complete molecules have no boundaries and have "fuzzy" electron density clouds approaching zero density exponentially at large distances from the nearest nucleus, a physically justified choice for electron density fragments exhibits similar behavior. Whereas fuzzy electron densities, just as any fuzzy object, such as a thicker cloud on a foggy day, do not lend themselves to easy visualization, one may partially overcome this by using isocontours. Whereas a faithful representation of the complete fuzzy density would need infinitely many such isocontours, nevertheless, by choosing a selected few, one can still obtain a limited pictorial representation. Clearly, such images are of limited value, and one better relies on more complete mathematical representations, using, for example, density matrices of fuzzy fragment densities. A fuzzy density fragmentation can be obtained in an exactly additive way, using the output from any of the common quantum chemical computational techniques, such as Hartree-Fock, MP2, and various density functional approaches. Such "fuzzy" electron density fragments properly represented have proven to be useful in a rather wide range of applications, for example, (a) using them as additive building blocks leading to efficient linear scaling macromolecular quantum chemistry computational techniques, (b) the study of quantum chemical functional groups, (c) using approximate fuzzy fragment information as allowed by the holographic electron density theorem, (d) the study of correlations between local shape and activity, including through-bond and through-space components of interactions between parts of molecules and relations between local molecular shape and substituent effects, (e) using them as tools of density matrix extrapolation in conformational changes, (f) physically valid averaging and statistical distribution of several local electron densities of common stoichiometry, useful in electron density databank mining, for
Integrating an electrically active colloidal quantum dot photodiode with a graphene phototransistor
Nikitskiy, Ivan; Goossens, Stijn; Kufer, Dominik; Lasanta, Tania; Navickaite, Gabriele; Koppens, Frank H. L.; Konstantatos, Gerasimos
2016-01-01
The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics. Two classes of photodetectors that have been developed are photodiodes and phototransistors, each of them with specific drawbacks. Here we merge both types into a hybrid photodetector device by integrating a colloidal quantum dot photodiode atop a graphene phototransistor. Our hybrid detector overcomes the limitations of a phototransistor in terms of speed, quantum efficiency and linear dynamic range. We report quantum efficiencies in excess of 70%, gain of 105 and linear dynamic range of 110 dB and 3 dB bandwidth of 1.5 kHz. This constitutes a demonstration of an optoelectronically active device integrated directly atop graphene and paves the way towards a generation of flexible highly performing hybrid two-dimensional (2D)/0D optoelectronics. PMID:27311710
Activated scaling in disorder-rounded first-order quantum phase transitions
NASA Astrophysics Data System (ADS)
Bellafard, Arash; Chakravarty, Sudip
2016-09-01
First-order phase transitions, classical or quantum, subject to randomness coupled to energylike variables (bond randomness) can be rounded, resulting in continuous transitions (emergent criticality). We study perhaps the simplest such model, the quantum three-color Ashkin-Teller model, and show that the quantum critical point in (1 +1 ) dimension is an unusual one, with activated scaling at the critical point and Griffiths-McCoy phase away from it. The behavior is similar to the transverse random field Ising model, even though the pure system has a first-order transition in this case. We believe that this fact must be attended to when discussing quantum critical points in numerous physical systems.
Integrating an electrically active colloidal quantum dot photodiode with a graphene phototransistor
NASA Astrophysics Data System (ADS)
Nikitskiy, Ivan; Goossens, Stijn; Kufer, Dominik; Lasanta, Tania; Navickaite, Gabriele; Koppens, Frank H. L.; Konstantatos, Gerasimos
2016-06-01
The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics. Two classes of photodetectors that have been developed are photodiodes and phototransistors, each of them with specific drawbacks. Here we merge both types into a hybrid photodetector device by integrating a colloidal quantum dot photodiode atop a graphene phototransistor. Our hybrid detector overcomes the limitations of a phototransistor in terms of speed, quantum efficiency and linear dynamic range. We report quantum efficiencies in excess of 70%, gain of 105 and linear dynamic range of 110 dB and 3 dB bandwidth of 1.5 kHz. This constitutes a demonstration of an optoelectronically active device integrated directly atop graphene and paves the way towards a generation of flexible highly performing hybrid two-dimensional (2D)/0D optoelectronics.
Testing Quantum Mechanics on New Ground
NASA Astrophysics Data System (ADS)
Ghose, Partha
2006-11-01
Preface; Acknowledgements; 1. Wave-particle duality; 2. Cavity quantum electrodynamics; 3. Quantum nondemolition measurements; 4. Topological phases; 5. Macroscopic quantum coherence; 6. The quantum Zeno paradox; 7. Testing collapse; 8. Macroscopic quantum jumps; 9. Nonlocality; 10. Tunneling times; References; Indexes.
Bao, Junwei Lucas; Zheng, Jingjing; Truhlar, Donald G
2016-03-01
Pressure-dependent reactions are ubiquitous in combustion and atmospheric chemistry. We employ a new calibration procedure for quantum Rice-Ramsperger-Kassel (QRRK) unimolecular rate theory within a chemical activation mechanism to calculate the pressure-falloff effect of a radical association with an aromatic ring. The new theoretical framework is applied to the reaction of H with toluene, which is a prototypical reaction in the combustion chemistry of aromatic hydrocarbons present in most fuels. Both the hydrogen abstraction reactions and the hydrogen addition reactions are calculated. Our system-specific (SS) QRRK approach is adjusted with SS parameters to agree with multistructural canonical variational transition state theory with multidimensional tunneling (MS-CVT/SCT) at the high-pressure limit. The new method avoids the need for the usual empirical estimations of the QRRK parameters, and it eliminates the need for variational transition state theory calculations as a function of energy, although in this first application we do validate the falloff curves by comparing SS-QRRK results without tunneling to multistructural microcanonical variational transition state theory (MS-μVT) rate constants without tunneling. At low temperatures, the two approaches agree well with each other, but at high temperatures, SS-QRRK tends to overestimate falloff slightly. We also show that the variational effect is important in computing the energy-resolved rate constants. Multiple-structure anharmonicity, torsional-potential anharmonicity, and high-frequency-mode vibrational anharmonicity are all included in the rate computations, and torsional anharmonicity effects on the density of states are investigated. Branching fractions, which are both temperature- and pressure-dependent (and for which only limited data is available from experiment), are predicted as a function of pressure. PMID:26841076
Bao, Junwei Lucas; Zheng, Jingjing; Truhlar, Donald G
2016-03-01
Pressure-dependent reactions are ubiquitous in combustion and atmospheric chemistry. We employ a new calibration procedure for quantum Rice-Ramsperger-Kassel (QRRK) unimolecular rate theory within a chemical activation mechanism to calculate the pressure-falloff effect of a radical association with an aromatic ring. The new theoretical framework is applied to the reaction of H with toluene, which is a prototypical reaction in the combustion chemistry of aromatic hydrocarbons present in most fuels. Both the hydrogen abstraction reactions and the hydrogen addition reactions are calculated. Our system-specific (SS) QRRK approach is adjusted with SS parameters to agree with multistructural canonical variational transition state theory with multidimensional tunneling (MS-CVT/SCT) at the high-pressure limit. The new method avoids the need for the usual empirical estimations of the QRRK parameters, and it eliminates the need for variational transition state theory calculations as a function of energy, although in this first application we do validate the falloff curves by comparing SS-QRRK results without tunneling to multistructural microcanonical variational transition state theory (MS-μVT) rate constants without tunneling. At low temperatures, the two approaches agree well with each other, but at high temperatures, SS-QRRK tends to overestimate falloff slightly. We also show that the variational effect is important in computing the energy-resolved rate constants. Multiple-structure anharmonicity, torsional-potential anharmonicity, and high-frequency-mode vibrational anharmonicity are all included in the rate computations, and torsional anharmonicity effects on the density of states are investigated. Branching fractions, which are both temperature- and pressure-dependent (and for which only limited data is available from experiment), are predicted as a function of pressure.
Heavy-atom tunneling in the ring opening of a strained cyclopropene at very low temperatures.
Ertelt, Melanie; Hrovat, David A; Borden, Weston Thatcher; Sander, Wolfram
2014-04-14
The highly strained 1H-bicyclo[3.1.0]-hexa-3,5-dien-2-one 1 is metastable, and rearranges to 4-oxacyclohexa-2,5-dienylidene 2 in inert gas matrices (neon, argon, krypton, xenon, and nitrogen) at temperatures as low as 3 K. The kinetics for this rearrangement show pronounced matrix effects, but in a given matrix, the reaction rate is independent of temperature between 3 and 20 K. This temperature independence means that the activation energy is zero in this temperature range, indicating that the reaction proceeds through quantum mechanical tunneling from the lowest vibrational level of the reactant. At temperatures above 20 K, the rate increases, resulting in curved Arrhenius plots that are also indicative of thermally activated tunneling. These experimental findings are supported by calculations performed at the CASSCF and CASPT2 levels by using the small-curvature tunneling (SCT) approximation. PMID:24616081
Influence of classical resonances on chaotic tunneling
Mouchet, Amaury; Eltschka, Christopher; Schlagheck, Peter
2006-08-15
Dynamical tunneling between symmetry-related stable modes is studied in the periodically driven pendulum. We present strong evidence that the tunneling process is governed by nonlinear resonances that manifest within the regular phase-space islands on which the stable modes are localized. By means of a quantitative numerical study of the corresponding Floquet problem, we identify the trace of such resonances not only in the level splittings between near-degenerate quantum states, where they lead to prominent plateau structures, but also in overlap matrix elements of the Floquet eigenstates, which reveal characteristic sequences of avoided crossings in the Floquet spectrum. The semiclassical theory of resonance-assisted tunneling yields good overall agreement with the quantum-tunneling rates, and indicates that partial barriers within the chaos might play a prominent role.
Fractional Quantum Hall States in a Ge Quantum Well
NASA Astrophysics Data System (ADS)
Mironov, O. A.; d'Ambrumenil, N.; Dobbie, A.; Leadley, D. R.; Suslov, A. V.; Green, E.
2016-04-01
Measurements of the Hall and dissipative conductivity of a strained Ge quantum well on a SiGe /(001 )Si substrate in the quantum Hall regime are reported. We analyze the results in terms of thermally activated quantum tunneling of carriers from one internal edge state to another across saddle points in the long-range impurity potential. This shows that the gaps for different filling fractions closely follow the dependence predicted by theory. We also find that the estimates of the separation of the edge states at the saddle are in line with the expectations of an electrostatic model in the lowest spin-polarized Landau level (LL), but not in the spin-reversed LL where the density of quasiparticle states is not high enough to accommodate the carriers required.
Single-photon tunneling via localized surface plasmons.
Smolyaninov, I I; Zayats, A V; Gungor, A; Davis, C C
2002-05-01
Strong evidence of a single-photon tunneling effect, a direct analog of single-electron tunneling, has been obtained in the measurements of light tunneling through individual subwavelength pinholes in a gold film covered with a layer of polydiacetylene. The transmission of some pinholes reached saturation because of the optical nonlinearity of polydiacetylene at a very low light intensity of a few thousand photons per second. This result is explained theoretically in terms of a "photon blockade," similar to the Coulomb blockade phenomenon observed in single-electron tunneling experiments. Single-photon tunneling may find applications in the fields of quantum communication and information processing.
Pflügl, Christian; Diehl, Laurent; Lyakh, Arkadiy; Wang, Qi Jie; Maulini, Richard; Tsekoun, Alexei; Patel, C Kumar N; Wang, Xiaojun; Capasso, Federico
2010-01-18
We present a method to study current paths through quantum cascade lasers (QCLs). The temperature dependence of the current is measured at a fixed voltage. At low temperatures we find activation energies that correspond to the energy difference between the injector ground state and the upper laser level. At higher temperatures additional paths with larger activation energies are found. Application of this method to high performance QCLs based on strained InGaAs/InAlAs quantum wells and barriers with different band-offsets allows us to identify individual parasitic current paths through the devices. The results give insight into the transport properties of quantum cascade lasers thus providing a useful tool for device optimization.
NASA Technical Reports Server (NTRS)
Waszak, Martin R.; Fung, Jimmy
1998-01-01
This report describes the development of transfer function models for the trailing-edge and upper and lower spoiler actuators of the Benchmark Active Control Technology (BACT) wind tunnel model for application to control system analysis and design. A simple nonlinear least-squares parameter estimation approach is applied to determine transfer function parameters from frequency response data. Unconstrained quasi-Newton minimization of weighted frequency response error was employed to estimate the transfer function parameters. An analysis of the behavior of the actuators over time to assess the effects of wear and aerodynamic load by using the transfer function models is also presented. The frequency responses indicate consistent actuator behavior throughout the wind tunnel test and only slight degradation in effectiveness due to aerodynamic hinge loading. The resulting actuator models have been used in design, analysis, and simulation of controllers for the BACT to successfully suppress flutter over a wide range of conditions.
The path decomposition expansion and multidimensional tunneling
NASA Astrophysics Data System (ADS)
Auerbach, Assa; Kivelson, S.
This paper consists of two main topics. (i) The path decomposition expansion: a new path integral technique which allows us to break configuration space into disjoint regions and express the dynamics of the full system in terms of its parts. (ii) The application of the PDX and semiclassical methods for solving quantum-mechanical tunneling problems in multidimensions. The result is a conceptually simple, computationally straightforward method for calculating tunneling effects in complicated multidimensional potentials, even in cases where the nature of the states in the classically allowed regions is nontrivial. Algorithms for computing tunneling effects in general classes of problems are obtained.In addition, we present the detailed solutions to three model problems of a tunneling coordinate coupled to a phonon. This enables us to define various well-controlled approximation schemes, which help to reduce the dimensions of complicated tunneling calculations in real physical systems.
Dynamical quenching of tunneling in molecular magnets
NASA Astrophysics Data System (ADS)
José Santander, María; Nunez, Alvaro S.; Roldán-Molina, A.; Troncoso, Roberto E.
2015-12-01
It is shown that a single molecular magnet placed in a rapidly oscillating magnetic field displays the phenomenon of quenching of tunneling processes. The results open a way to manipulate the quantum states of molecular magnets by means of radiation in the terahertz range. Our analysis separates the time evolution into slow and fast components thereby obtaining an effective theory for the slow dynamics. This effective theory presents quenching of the tunnel effect, in particular, stands out its difference with the so-called coherent destruction of tunneling. We support our prediction with numerical evidence based on an exact solution of Schrödinger's equation.
Simulation of wave packet tunneling of interacting identical particles
NASA Astrophysics Data System (ADS)
Lozovik, Yu. E.; Filinov, A. V.; Arkhipov, A. S.
2003-02-01
We demonstrate a different method of simulation of nonstationary quantum processes, considering the tunneling of two interacting identical particles, represented by wave packets. The used method of quantum molecular dynamics (WMD) is based on the Wigner representation of quantum mechanics. In the context of this method ensembles of classical trajectories are used to solve quantum Wigner-Liouville equation. These classical trajectories obey Hamiltonian-like equations, where the effective potential consists of the usual classical term and the quantum term, which depends on the Wigner function and its derivatives. The quantum term is calculated using local distribution of trajectories in phase space, therefore, classical trajectories are not independent, contrary to classical molecular dynamics. The developed WMD method takes into account the influence of exchange and interaction between particles. The role of direct and exchange interactions in tunneling is analyzed. The tunneling times for interacting particles are calculated.
Galdiero, Emilia; Siciliano, Antonietta; Maselli, Valeria; Gesuele, Renato; Guida, Marco; Fulgione, Domenico; Galdiero, Stefania; Lombardi, Lucia; Falanga, Annarita
2016-01-01
This study attempts to evaluate the antimicrobial activity and the ecotoxicity of quantum dots (QDs) alone and coated with indolicidin. To meet this objective, we tested the level of antimicrobial activity on Gram-positive and Gram-negative bacteria, and we designed an ecotoxicological battery of test systems and indicators able to detect different effects using a variety of end points. The antibacterial activity was analyzed against Staphylococcus aureus (ATCC 6538), Pseudomonas aeruginosa (ATCC 1025), Escherichia coli (ATCC 11229), and Klebsiella pneumoniae (ATCC 10031), and the results showed an improved germicidal action of QDs-Ind. Toxicity studies on Daphnia magna indicated a decrease in toxicity for QDs-Ind compared to QDs alone, lack of bioluminescence inhibition on Vibrio fisheri, and no mutations in Salmonella typhimurium TA 100. The comet assay and oxidative stress experiments performed on D. magna showed a genotoxic and an oxidative damage with a dose–response trend. Indolicidin retained its activity when bound to QDs. We observed an enhanced activity for QDs-Ind. The presence of indolicidin on the surface of QDs was able to decrease its QDs toxicity. PMID:27616887
Galdiero, Emilia; Siciliano, Antonietta; Maselli, Valeria; Gesuele, Renato; Guida, Marco; Fulgione, Domenico; Galdiero, Stefania; Lombardi, Lucia; Falanga, Annarita
2016-01-01
This study attempts to evaluate the antimicrobial activity and the ecotoxicity of quantum dots (QDs) alone and coated with indolicidin. To meet this objective, we tested the level of antimicrobial activity on Gram-positive and Gram-negative bacteria, and we designed an ecotoxicological battery of test systems and indicators able to detect different effects using a variety of end points. The antibacterial activity was analyzed against Staphylococcus aureus (ATCC 6538), Pseudomonas aeruginosa (ATCC 1025), Escherichia coli (ATCC 11229), and Klebsiella pneumoniae (ATCC 10031), and the results showed an improved germicidal action of QDs-Ind. Toxicity studies on Daphnia magna indicated a decrease in toxicity for QDs-Ind compared to QDs alone, lack of bioluminescence inhibition on Vibrio fisheri, and no mutations in Salmonella typhimurium TA 100. The comet assay and oxidative stress experiments performed on D. magna showed a genotoxic and an oxidative damage with a dose–response trend. Indolicidin retained its activity when bound to QDs. We observed an enhanced activity for QDs-Ind. The presence of indolicidin on the surface of QDs was able to decrease its QDs toxicity.
Galdiero, Emilia; Siciliano, Antonietta; Maselli, Valeria; Gesuele, Renato; Guida, Marco; Fulgione, Domenico; Galdiero, Stefania; Lombardi, Lucia; Falanga, Annarita
2016-01-01
This study attempts to evaluate the antimicrobial activity and the ecotoxicity of quantum dots (QDs) alone and coated with indolicidin. To meet this objective, we tested the level of antimicrobial activity on Gram-positive and Gram-negative bacteria, and we designed an ecotoxicological battery of test systems and indicators able to detect different effects using a variety of end points. The antibacterial activity was analyzed against Staphylococcus aureus (ATCC 6538), Pseudomonas aeruginosa (ATCC 1025), Escherichia coli (ATCC 11229), and Klebsiella pneumoniae (ATCC 10031), and the results showed an improved germicidal action of QDs-Ind. Toxicity studies on Daphnia magna indicated a decrease in toxicity for QDs-Ind compared to QDs alone, lack of bioluminescence inhibition on Vibrio fisheri, and no mutations in Salmonella typhimurium TA 100. The comet assay and oxidative stress experiments performed on D. magna showed a genotoxic and an oxidative damage with a dose-response trend. Indolicidin retained its activity when bound to QDs. We observed an enhanced activity for QDs-Ind. The presence of indolicidin on the surface of QDs was able to decrease its QDs toxicity. PMID:27616887
NASA Astrophysics Data System (ADS)
Boche, Holger; Cai, Minglai; Deppe, Christian; Nötzel, Janis
2016-08-01
We establish the Ahlswede dichotomy for arbitrarily varying classical-quantum wiretap channels, i.e., either the deterministic secrecy capacity of the channel is zero, or it equals its randomness-assisted secrecy capacity. We analyze the secrecy capacity of these channels when the sender and the receiver use various resources. It turns out that randomness, common randomness, and correlation as resources are very helpful for achieving a positive secrecy capacity. We prove the phenomenon "super-activation" for arbitrarily varying classical-quantum wiretap channels, i.e., two channels, both with zero deterministic secrecy capacity, if used together allow perfect secure transmission.
Mars Surface Tunnel Element Concept
NASA Technical Reports Server (NTRS)
Rucker, Michelle A.; Jefferies, Sharon; Howe, A. Scott; Howard, Robert; Mary, Natalie; Watson, Judith; Lewis, Ruthan
2016-01-01
When the first human visitors on Mars prepare to return to Earth, they will have to comply with stringent planetary protection requirements. Apollo Program experience warns that opening an EVA hatch directly to the surface will bring dust into the ascent vehicle. To prevent inadvertent return of potential Martian contaminants to Earth, careful consideration must be given to the way in which crew ingress their Mars Ascent Vehicle (MAV). For architectures involving more than one surface element-such as an ascent vehicle and a pressurized rover or surface habitat-a retractable tunnel that eliminates extravehicular activity (EVA) ingress is an attractive solution. Beyond addressing the immediate MAV access issue, a reusable tunnel may be useful for other surface applications, such as rover to habitat transfer, once its primary mission is complete. A National Aeronautics and Space Administration (NASA) team is studying the optimal balance between surface tunnel functionality, mass, and stowed volume as part of the Evolvable Mars Campaign (EMC). The study team began by identifying the minimum set of functional requirements needed for the tunnel to perform its primary mission, as this would presumably be the simplest design, with the lowest mass and volume. This Minimum Functional Tunnel then becomes a baseline against which various tunnel design concepts and potential alternatives can be traded, and aids in assessing the mass penalty of increased functionality. Preliminary analysis indicates that the mass of a single-mission tunnel is about 237 kg, not including mass growth allowance.
NASA Astrophysics Data System (ADS)
Nugroho, Christopher; Orlyanchik, Vladimir; van Harlingen, Dale
2014-03-01
Two level system (TLS) defects in AlOx tunnel barriers can lead to low-frequency 1 / f critical current noise and losses in coherent superconducting circuits. Understanding the nature of these defects and how to eliminate them are critical in order to achieve ultra-long coherence times. We present measurements of the tunneling conductance of ultrasmall, A <(100nm) 2 , Al/AlOx/Al shadow evaporated junctions. The tunneling conductance of these junctions exhibits several isolated TLSs, which permitted the detailed analysis of the individual switching rates and behavior of the TLSs. We have studied the thermal activation behavior of these TLSs, and in some cases observe a crossover into quantum-limited tunneling at lower temperatures. Tracking the TLS switching rates as a function of the applied voltage bias provides an estimate of the TLS charge dipole moment. In some quantum tunneling limited TLSs we have observed a non-equilibrium enhancement of the switching rates that cannot be explained by simple dissipative heating of the TLSs. Further investigations into these TLS defects may lead to the identification of their physical origins and strategies to eliminate them. Research funded by the Intelligence Advanced Research Projects Activity (IARPA).
Azamacrocycle activated quantum dot for zinc ion detection.
Ruedas-Rama, Maria Jose; Hall, Elizabeth A H
2008-11-01
A new fluorescent nanosensor family for Zn (2+) determination is reported based on azamacrocycle derivatization of CdSe/ZnS core/shell quantum dot nanoparticles. They are the first zinc ion sensors using QD nanoparticles in a host-guest and receptor-fluorophore system. Three azamacrocycles are demonstrated as receptors: TACN (1,4,7-triazacyclononane), cyclen (1,4,7,10-tetraazacyclododecane), and cyclam (1,4,8,11-tetraazacyclotetradecane). Azamacrocycles conjugated to QDs via an amide link interact directly with one of the photoinduced QD charge carriers, probably transferring the hole in the QD to the azamacrocycle, thereby disrupting the radiative recombination process. When zinc ion enters the aza-crown, the lone pair electrons of the nitrogen atom become involved in the coordination and the energy level is no longer available for the hole-transfer mechanism, switching on the QD emission and a dramatic increase of the fluorescence intensity results, allowing the detection of low concentrations of zinc ions. Using this operating principle, three zinc ion sensors based on CdSe-ZnS core-shell QD nanoparticles showed a very good linearity in the range 5-500 microM, with detection limits lower than 2.4 microM and RSDs approximately 3% ( n = 10). In addition, the versatility of the sensors was demonstrated, since different sizes (and colors) of QDs can be employed and will respond to zinc in a similar way. In a study of interferences, the zinc-sensitive QDs showed good selectivity in comparison with other physiologically important cations and other transition metals tested. The results from fetal calf serum and samples mimicking physiological conditions suggested very good applicability in the determination of zinc ion in physiological samples.
ERIC Educational Resources Information Center
Hinshaw, Craig
1999-01-01
Describes how to make tunnel books, which are viewed by looking into a "tunnel" created by accordion-folded expanding sides. Suggests possible themes. Describes how to create a walk-through tunnel book for first grade students. (CMK)
... arm. Just a passing cramp? It could be carpal tunnel syndrome. The carpal tunnel is a narrow passageway of ligament and ... difficult. Often, the cause is having a smaller carpal tunnel than other people do. Other causes include ...
Simulations of Resonant Intraband and Interband Tunneling Spin Filters
NASA Technical Reports Server (NTRS)
Ting, David; Cartoixa-Soler, Xavier; McGill, T. C.; Smith, Darryl L.; Schulman, Joel N.
2001-01-01
This viewgraph presentation reviews resonant intraband and interband tunneling spin filters It explores the possibility of building a zero-magnetic-field spin polarizer using nonmagnetic III-V semiconductor heterostructures. It reviews the extensive simulations of quantum transport in asymmetric InAs/GaSb/AlSb resonant tunneling structures with Rashba spin splitting and proposes a. new device concept: side-gated asymmetric Resonant Interband Tunneling Diode (a-RITD).
NASA Technical Reports Server (NTRS)
2006-01-01
The Channel Tunnel is a 50.5 km-long rail tunnel beneath the English Channel at the Straits of Dover. It connects Dover, Kent in England with Calais, northern France. The undersea section of the tunnel is unsurpassed in length in the world. A proposal for a Channel tunnel was first put forward by a French engineer in 1802. In 1881, a first attempt was made at boring a tunnel from the English side; the work was halted after 800 m. Again in 1922, English workers started boring a tunnel, and advanced 120 m before it too was halted for political reasons. The most recent attempt was begun in 1987, and the tunnel was officially opened in 1994. At completion it was estimated that the project cost around $18 billion. It has been operating at a significant loss since its opening, despite trips by over 7 million passengers per year on the Eurostar train, and over 3 million vehicles per year.
With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), ASTER images Earth to map and monitor the changing surface of our planet.
ASTER is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products.
The broad spectral coverage and high spectral resolution of ASTER provides scientists in numerous disciplines with critical information for surface mapping, and monitoring of dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; wetlands evaluation; thermal pollution monitoring; coral reef degradation; surface temperature mapping of soils and geology; and measuring
Trevors, J T; Masson, L
2011-01-01
During his famous 1943 lecture series at Trinity College Dublin, the reknown physicist Erwin Schrodinger discussed the failure and challenges of interpreting life by classical physics alone and that a new approach, rooted in Quantum principles, must be involved. Quantum events are simply a level of organization below the molecular level. This includes the atomic and subatomic makeup of matter in microbial metabolism and structures, as well as the organic, genetic information code of DNA and RNA. Quantum events at this time do not elucidate, for example, how specific genetic instructions were first encoded in an organic genetic code in microbial cells capable of growth and division, and its subsequent evolution over 3.6 to 4 billion years. However, due to recent technological advances, biologists and physicists are starting to demonstrate linkages between various quantum principles like quantum tunneling, entanglement and coherence in biological processes illustrating that nature has exerted some level quantum control to optimize various processes in living organisms. In this article we explore the role of quantum events in microbial processes and endeavor to show that after nearly 67 years, Schrödinger was prophetic and visionary in his view of quantum theory and its connection with some of the fundamental mechanisms of life. PMID:21368338
Cold prebiotic evolution, tunneling, chirality and exobiology
NASA Astrophysics Data System (ADS)
Goldanskii, Vitalii I.
1996-07-01
The extra-terrestrial scenario of the origin of life suggested by Svante Arrhenius (1) as the `panspermia' hypothesis was revived by the discovery of a low-temperature quantum limit of a chemical reaction rate caused by the molecular tunneling (2). Entropy factors play no role near absolute zero, and slow molecular tunneling can lead to the exothermic formation of quite complex molecules. Interstellar grains or particles of cometary tails could serve as possible cold seeds of life, with acetic acid, urea and products of their polycondensation as quasi-equilibrium intermediates. Very cold solid environment hinders racemization and stabilizes optical activity under conditions typical for outer space. Neither `advantage' factors can secure the evolutionary formation of chiral purity of initial prebiotic monomeric medium-even being temporary achieved it cannot be maintained at subsequent stages of prebiotic evolution because of counteraction of `enantioselective pressure'. Only bifurcational mechanism of the formation of prebiotic homochiral-monomeric and afterwards polymeric-medium and its subsequent transformation in `homochiral chemical automata' (`biological big bang'-passage from `stochastic' to `algorithmic' chemistry) is possible and can be realized. Extra-terrestrial (cold, solid phase) scenarios of the origin of life seem to be more promising from that point of view than terrestrial (warm) scenarios. Within a scheme of five main stages of prebiological evolution some problems important for further investigation are briefly discussed.
Entanglement activation and the robustness of quantum correlations
Brandao, Fernando G. S. L.
2007-09-15
We show that the usefulness of a state as an activator in teleportation protocols is equivalent to the robustness of its entanglement to noise. The robustness of entanglement of a bipartite state {sigma} is linked to the maximum increase in the fidelity of teleportation of any other state when {sigma} is used as an extra resource. On the one hand, this connection gives an operational meaning to the robustness of entanglement. On the other hand, it shows that the activation capability--which has a central role as an operational way of quantifying bound entangled states -- can be estimated experimentally by measuring entanglement witnesses.