arXiv subjects

Shmuel Gurvitz

Publications and source records attributed to Shmuel Gurvitz.

18 recordsLinked to original sources

arXiv2025

Tunneling Dynamics and Time Delay in Electron Transport through Time-Dependent Barriers with Finite-Bandwidth Reservoirs

We study a model system consisting of a tunneling barrier driven by an external harmonic field and coupled to two leads with finite bandwidth. Avoiding Floquet expansions, we derive simple expressions for the time-dependent tunneling current in the adiabatic regime. Our approach relates the barrier modulation to a measurable time delay in the steady-state periodic current. It provides a physically consistent definition of the tunneling time inside the barrier by subtracting the time delay associated with the leads from the total time delay. We find that the tunneling time always vanishes for wide/high barriers. Remarkably, the time delay persists even when the barrier becomes static, i.e., in the limit where the modulation frequency vanishes. This indicates that the time delay obtained through the introduction of an external periodic perturbation actually reflects an intrinsic property of the tunneling dynamics, rather than an effect of the external drive or of a particular system. We apply our results to the analysis of tunneling times in optical experiments and find good agreement with the experimental data.

cond-mat.mes-hall↗

arXiv2025

Many-body tunneling in a double-well potential

We present an approach for evaluating Wannier functions, offering an alternative perspective on their role in many-body systems. Unlike traditional methods, such as the maximally localized Wannier functions approach, which focuses on minimizing the function tails, our approach emphasizes these tails. Using perturbative analytical approximations and extensive numerical simulations on an exactly solvable model, we address nonstandard Hubbard terms and demonstrate their critical influence on many-body dynamics. Specifically, we study tunneling dynamics in arbitrary double-well potentials, moving beyond the standard Hubbard model to include nonstandard terms such as density-induced tunneling and pair tunneling. Our results reveal that these terms significantly modify the dynamics predicted by the standard Hubbard model: density-induced tunneling modifies the single-particle tunneling parameter $Ω_0$, while pair tunneling enables coherent propagation not captured by the standard model. We show that the discrepancies between the standard and nonstandard Hubbard models grow with increasing interaction strength, potentially leading to novel transport behaviors. However, at lower interaction strengths, both models converge, as nonstandard terms become negligible. These findings have important implications for phenomena such as superconductivity in twisted bilayer graphene and metal-insulator transitions. Our model aligns well with numerical simulations of lowest-band parameters and is strongly supported by experimental observations of second-order atom tunneling in optical double-well potentials. This strong agreement with experimental data highlights the accuracy and potential of our approach in providing a more comprehensive framework for describing complex many-body systems than the standard Hubbard model.

cond-mat.str-el↗

arXiv2021

Zero-bias current induced by periodic drive of any shape

We investigate time-dependent electron current through a quantum dot under external drive (pulses), coupled to leads at zero bias. Simple analytic expressions for current, generated by periodic pulses of any shape, are obtained without any use of the Floquet expansion. We demonstrate that the current, follows a local quench, displays the transient and steady-state behavior, which are described by the same universal function of an external drive. The results are applied for an analysis of the current generated by rectangular and linear form pulses, in comparison with ultra-fast pulses of very high amplitude. Our results are also applicable for study of On-Demand Single-Electron sources and laser driven junctions.

cond-mat.mes-hall↗

arXiv2020

Multiscale cyclic dynamics in light harvesting complex in presence of vibrations and noise

Starting from the many-body Schrödinger equation, we derive a new type of Lindblad Master equations describing a cyclic exciton/electron dynamics in the light harvesting complex and the reaction center. These equations resemble the Master equations for the electric current in mesoscopic systems, and they go beyond the single-exciton description by accounting for the multi-exciton states accumulated in the antenna, as well as the charge-separation, fluorescence and photo-absorption. Although these effects take place on very different timescales, their inclusion is necessary for a consistent description of the exciton dynamics. Our approach reproduces both coherent and incoherent dynamics of exciton motion along the antenna in the presence of vibrational modes and noise. We applied our results to evaluate energy (exciton) and fluorescent currents as a function of sunlight intensity.

physics.chem-ph↗

arXiv2019

Generalized Landauer formula for time-dependent potentials and noise-induced zero-bias dc current

Using a new developed Single-Electron approach, we derive the Landauer-type formula for electron transport in arbitrary time-dependent potentials. This formula is applied for randomly fluctuating potentials represented by a dichotomic noise. We found that the noise can produce dc-current in quantum system under zero-bias voltage by breaking the time-reversal symmetry of the transmission coefficient. We show that this effect is due to decoherence, produced by the noise, which can take place in many different systems.

cond-mat.mes-hall↗

arXiv2018

Time-dependent treatment of tunneling and Time's Arrow problem

New time-dependent treatment of tunneling from localized state to continuum is proposed. It does not use the Laplace transform (Green's function's method) and can be applied for time-dependent potentials, as well. This approach results in simple expressions describing dynamics of tunneling to Markovian and non-Markovian reservoirs in the time-interval $-\infty<t<\infty$. It can provide a new outlook for tunneling in the negative time region, illuminating the origin of the time's arrow problem in quantum mechanics. We also concentrate on singularity at $t=0$, which affects the perturbative expansion of the evolution operator. In addition, the decay to continuum in periodically modulated tunneling Hamiltonian is investigated. Using our results, we extend the Tien-Gordon approach for periodically driven transport, to oscillating tunneling barriers.

quant-ph↗

arXiv2017

Multi-Scale Exciton and Electron Transfer in Multi-Level Donor-Acceptor System

We study theoretically the noise-assisted quantum exciton (electron) transfer (ET) in bio-complexes consisting of a single-level electron donor and an acceptor which has a complicated internal structure, and is modeled by many electron energy levels. Interactions are included between the donor and the acceptor energy levels and with the protein-solvent noisy environment. Different regions of parameters are considered, which characterize (i) the number of the acceptor levels, (ii) the acceptor \band-width", and (iii) the amplitude of noise and its correlation time. Under some conditions, we derive analytical expressions for the ET rate and efficiency. We obtain equal occupation of all levels at large times, independently of the structure of the acceptor band and the noise parameters, but under the condition of non-degeneracy of the acceptor energy levels. We discuss the multi-scale dynamics of the acceptor population, and the accompanying effect of quantum coherent oscillations. We also demonstrate that for large number of levels in the acceptor band, the efficiency of ET can be close to 100%, for both downhill and uphill transitions and for sharp and at redox potentials.

physics.bio-ph↗

arXiv2017

Multiscale Multiexciton Cyclic Dynamics in Light Harvesting Complex

Usually the study of energy-transfer in the light harvesting complex is limited by a single-exciton motion along the antenna. Starting from the many-body Schrödinger equation, we derived Lindblad-type Master equations describing the cyclic exciton-electron dynamics of the light harvesting complex, originated from charge reduction of a donor. These equations, resembling the Master equations for the electric current in mesoscopic systems, go beyond the single-exciton description by accounting for the multi-exciton states accumulated in the antenna, as well as the charge-separation, fluorescence and initial photo-absorption. Although these effects take place on very different time-scales, we demonstrate that their inclusion is necessary for a consistent description of the exciton dynamics. We applied our results to evaluate the energy (exciton) current and for the fluorescent current depending on the light-intensity.

physics.chem-ph↗

arXiv2016

Wave-function approach to Master equations for quantum transport and measurement

This paper presents a comprehensive review of the wave-function approach for derivation of the number-resolved Master equations, used for description of transport and measurement in mesoscopic systems. The review contains important amendments, clarifying subtle points in derivation of the Master equations and their validity. This completes the earlier works on the subject. It is demonstrated that the derivation does not assume weak coupling with the environment and reservoirs, but needs only high bias condition. This condition is very essential for validity of the Markovian Master equations, widely used for a phenomenological description of different physical processes.

cond-mat.mes-hall↗

arXiv2016

Temporal evolution of resonant transmission under telegraph noise

The environment of a quantum dot, which is connected to two leads, is modeled by telegraph noise, i.e. random Markovian jumps of the (spinless) electron energy on the dot between two levels. The temporal evolutions of the charge on the dot and of the currents in the leads are studied using a recently developed single-particle basis approach, which is particularly convenient for the averaging over the histories of the noise. In the steady state limit we recover the Landauer formula. At a very fast jump rate between the two levels, the noise does not affect the transport. As the jump rate decreases, the effective average transmission crosses over from the transmission through a single (average) level to an incoherent sum of the transmissions through the two levels. 13 pages, 6 figuresThe transient temporal evolution towards the steady state is dominated by the displacement current at short times, and by the Landauer current at long times. It contains oscillating terms, which decay to zero faster than for the case without noise. When the average chemical potential on the leads equals the dot's "original" energy, without the noise, the oscillations disappear completely and the transient evolution becomes independent of the noise.

cond-mat.mes-hall↗

arXiv2016

Does the measurement take place when nobody observes it?

We consider {\em non-selective} continuous measurements of a particle tunneling to a reservoir of finite band-width ($Λ$). The particle is continuously monitored by frequent projective measurements ("quantum trajectory"), separated by a time-interval $τ$. A simple analytical expression for the decay rate has been obtained. For Markovian reservoirs ($Λ\to\infty$), no effect of the measurements is found. Otherwise for a finite $Λ$, the decay rate always depends on the measurement time $τ$. This result is compared with alternative calculations, with no intermediate measurements, but when the measurement device is included in the Schrödinger evolution. We found that the detector affects the system by the decoherence rate ($Γ_d$), related to the detector's signal. Although both treatments are different, the final results become very close for $τ=2/Γ_d$. This $τ$ corresponds to the minimal time for which the detector's signal can be distinguished by an "observer". This indicates a fundamental role of information in quantum motion and can be used for the extension of the quantum trajectory method for non-Markovian environments.

quant-ph↗

arXiv2015

Single-electron approach for time-dependent electron transport

We develop a new approach to electron transport in mesoscopic systems by using a particular single-particle basis. Although this basis generates redundant many-particle amplitudes, it greatly simplifies the treatment. By using our method for transport of non-interacting electrons, we generalize the Landauer formula for transient currents and for time-dependent potentials. The result has a very simple form and clear physical interpretation. As an example, we apply it to resonant tunneling through a quantum dot where the tunneling barriers are oscillating in time. We obtain analytical expression for the time-dependent (ac) resonant current. However, in the adiabatic limit this expression displays the dc current for zero bias (electron pumping).

cond-mat.mes-hall↗

arXiv2014

Possible Role of Interference and Sink Effects in Nonphotochemical Quenching in Photosynthetic Complexes

We describe a simple and consistent quantum mathematical model that simulates the possible role of quantum interference and sink effects in the nonphotochemical quenching (NPQ) in light-harvesting complexes (LHCs). Our model consists of a network of five interconnected sites (excitonic states) responsible for the NPQ mechanism: (i) Two excited states of chlorophyll molecules, $ChlA^*$ and $ChlB^*$, forming an LHC dimer, which is initially populated; (ii) A "damaging" site which is responsible for production of singlet oxygen and other destructive outcomes; (iii) The $(ChlA-Zea)^*$ heterodimer excited state (Zea indicates zeaxanthin); and (iv) The charge transfer state of this heterodimer, $(ChlA^{-}-Zea^{+})^*$. In our model, both damaging and charge transfer states are described by discrete electron energy levels attached to their sinks, that mimic the continuum part of electron energy spectrum, as at these sites the electron participates in quasi-irreversible chemical reactions. All five excitonic sites interact with the protein environment that is modeled using a stochastic approach. As an example, we apply our model to demonstrate possible contributions of quantum interference and sink effects in the NPQ mechanism in the CP29 minor LHC. Our numerical results on the quantum dynamics of the reduced density matrix, demonstrate a possible way to significantly suppress, under some conditions, the damaging channel using quantum interference effects and sinks. The results demonstrate the possible role of interference and sink effects for modeling, engineering, and optimizing the performance of the NPQ processes in both natural and artificial light-harvesting complexes.

physics.bio-ph↗

arXiv2014

Quantum transfer through a non-Markovian environment under frequent measurements and Zeno effect

We study transitions of a particle between two wells, separated by a reservoir, under the condition that the particle is not detected in the reservoir. Conventional quantum trajectory theory predicts that such no-result continuous measurement would not affect these transitions. We demonstrate that it holds only for Markovian reservoirs (infinite bandwidth $Λ$). In the case of finite $Λ$, the probability of the particle's interwell transition is a function of the ratio $Λ/ν$, where $ν$ is the frequency of measurements. This scaling tells us that in the limit $ν\to\infty$, the measurement freezes the initial state (the quantum Zeno effect), whereas for $Λ\to\infty$ it does not affect the particle's transition across the reservoir. The scaling is proved analytically by deriving a simple formula, which displays two regimes, with the Zeno effect and without the Zeno effect. It also supports a simple explanation of the Zeno effect entirely in terms of the energy-time uncertainty relation, with no explicit use of the projection postulate. Experimental tests of our predictions are discussed.

quant-ph↗

arXiv2013

Undetectable quantum transfer through a continuum

We demonstrate that a quantum particle, initially prepared in a quantum well, can propagate through a reservoir with a continuous spectrum and reappear in a distant well without being registered in the reservoir. It is shown that such a passage through the reservoir takes place even if the latter is {\em continuously} monitored. We discuss a possible experimental realization of such a teleportation phenomenon in mesoscopic systems.

quant-ph↗

arXiv2012

Partial decoherence in mesoscopic systems

The coupling of a mesoscopic system with its environment usually causes total decoherence: at long times the reduced density matrix of the system evolves in time to a limit which is independent of its initial value, losing all the quantum information stored in its initial state. Under special circumstances, a subspace of the system's Hilbert space remains coherent, or "decoherence free", and the reduced density matrix approaches a non-trivial limit which contains information on its initial quantum state, despite the coupling to the environment. This situation is called "partial decoherence". Here we find the conditions for partial decoherence for a mesoscopic system (with $N$ quantum states) which is coupled to an environment. When the Hamiltonian of the system commutes with the total Hamiltonian, one has "adiabatic decoherence", which yields N-1 time-independent combinations of the reduced density matrix elements. In the presence of a magnetic flux, one can measure circulating currents around loops in the system even at long times, and use them to retrieve information on the initial state. For N=2, we demonstrate that partial decoherence can happen only under adiabatic decoherence conditions. However, for $N>2$ we find partial decoherence even when the Hamiltonian of the system does not commute with the total Hamiltonian, and we obtain the general conditions for such non-adiabatic partial decoherence. For an electron moving on a ring, with $N>2$ single-level quantum dots, non-adiabatic partial decoherence can arise only when the total flux through the ring vanishes (or equals an integer number of flux quanta), and therefore there is no asymptotic circulating current.

cond-mat.mes-hall↗

arXiv2011

Decoherence and the retrieval of lost information

We found that in contrast with the common premise, a measurement on the environment of an open quantum system can {\em reduce} its decoherence rate. We demonstrate it by studying an example of indirect qubit's measurement, where the information on its state is hidden in the environment. This information is extracted by a distant device, coupled with the environment. We also show that the reduction of decoherence generated by this device, is accompanied with diminution of the environmental noise in a vicinity of the qubit. An interpretation of these results in terms of quantum interference on large scales is presented.

cond-mat.mes-hall↗

arXiv2011

Quantum coherence and entanglement induced by the continuum between distant localized states

It is demonstrated that two distant quantum wells separated by a reservoir with a continuous spectrum can possess bound eigenstates embedded in the continuum. These represent a linear superposition of quantum states localized in the wells. We show that such a state can be isolated in the course of free evolution from any initial state by a null-result measurement in the reservoir. The latter might not be necessary in the many-body case. The resulting superposition is regulated by ratio of couplings between the wells and the reservoir. In particular, one can lock the system in one of the wells by enhancing this ratio. By tuning parameters of the quantum wells, many-body entangled states in distant wells can be produced through interactions and statistics.

quant-ph↗