arXiv subjects

Valentin V. Sokolov

Publications and source records attributed to Valentin V. Sokolov.

15 recordsLinked to original sources

arXiv2015

Elastic Enhancement Factor: from Mesoscopic Systems to Macroscopic Analogous Devices

Excess of probabilities of elastic processes over inelastic ones is a characteristic feature of the chaotic resonance scattering predicted by the random matrix theory (RMT). Quantitatively, this phenomenon is characterized by the elastic enhancement factor $F^{(β)}$ that is, essentially, a typical ratio of elastic and inelastic cross sections. Being measured experimentally, this quantity can provide important information on the character of dynamics of the complicated intermediate open system formed on the intermediate stage of various resonance scattering processes. We discuss properties of the enhancement factor in a wide scope from mesoscopoic systems as, for example, heavy nuclei to macroscopic electromagnetic analogous devices imitating two-dimensional quantum billiards. We demonstrate a substantial qualitative distinction between the elastic enhancement factor's peculiarities in these two cases. A complete analytical solution is found for the case of systems without time-reversal symmetry and only a few equivalent open scattering channels.

nucl-th↗

arXiv2013

Chaotic Interference and Quantum-Classical Correspondence: Mechanisms of Decoherence and State Mixing

The famous Nils Bohr's quantum-classical correspondence principle states that the classical mechanics is a limiting case of the more general quantum mechanics. This implies that ``under certain conditions" quantum laws of motion become equivalent to classical laws. One of the conditions is fairly obvious: the corresponding classical action should be very large as compared with the Planck's constant. But this condition is not sufficient. Suppression of effects of quantum interference ("decoherence") is the phenomenon of primary importance for understanding of the Bohr's principle. Being, in essence, of quite general nature, this problem takes on special significance in the case of non-linear classically chaotic quantum systems. Whereas the rapid decay of phase correlations is an underlying feature of the classical dynamical chaos, the "quantum chaos" by itself is not capable of destroying the quantum phase coherence. Strictly speaking, any initially pure quantum state remains pure during an arbitrary long unitary evolution. Basically, formation of incoherent mixed states (decoherence) results only from the process of preparation of a mixed initial state or interaction with a noisy environment. Just the decoherence brigdes the quantum and classical worlds. Peculiarities of the time behavior of Peres fidelity, state purity, Shanon and von Neumann entropies are analyzed in detail. We demonstrate the ways the decoherence shows up in periodically driven systems that can be associated with Ramsey-type interferomentry experiments with ion traps. Finally, decoherence in ballistic electron quantum transport caused by interaction with a disordered environment is considered.

quant-ph↗

arXiv2012

Elastic enhancement factor as a quantum chaos probe

Recent development of the resonance scattering theory with a transient from the regular to chaotic internal dynamics inspires renewed interest to the problem of the elastic enhancement phenomenon. We reexamine the question what the experimentally observed value of the elastic enhancement factor can tell us about the character of dynamics of the intermediate system. Noting first a remarkable connection of this factor with the time delays variance in the case of the standard Gaussian ensembles we then prove the universal nature of such a relation. This reduces our problem to that of calculation of the Dyson's binary form factor in the whole transition region. By the example of systems with no time-reversal symmetry we then demonstrate that the enhancement can serve as a measure of the degree of internal chaos.

quant-ph↗

arXiv2010

Ballistic Electron Quantum Transport in Presence of a Disordered Background

Effect of a complicated many-body environment is analyzed on the electron random scattering by a 2D mesoscopic open ballistic structure. A new mechanism of decoherence is proposed. The temperature of the environment is supposed to be zero whereas the energy of the incoming particle $E_{in}$ can be close to or somewhat above the Fermi surface in the environment. The single-particle doorway resonance states excited in the structure via external channels are damped not only because of escape through such channels but also due to the ulterior population of the long-lived environmental states. Transmission of an electron with a given incoming $E_{in}$ through the structure turns out to be an incoherent sum of the flow formed by the interfering damped doorway resonances and the retarded flow of the particles re-emitted into the structure by the environment. Though the number of the particles is conserved in each individual event of transmission, there exists a probability that some part of the electron's energy can be absorbed due to environmental many-body effects. In such a case the electron can disappear from the resonance energy interval and elude observation at the fixed transmission energy $E_{in}$ thus resulting in seeming loss of particles, violation of the time reversal symmetry and, as a consequence, suppression of the weak localization. The both decoherence and absorption phenomena are treated within the framework of a unit microscopic model based on the general theory of the resonance scattering. All the effects discussed are controlled by the only parameter: the spreading width of the doorway resonances, that uniquely determines the decoherence rate

cond-mat.mes-hall↗

arXiv2009

Quantum Dynamics Against a Noisy Background

By the example of a kicked quartic oscillator we investigate the dynamics of classically chaotic quantum systems with few degrees of freedom affected by persistent external noise. Stability and reversibility of the motion are analyzed in detail in dependence on the noise level $σ$. The critical level $σ_c(t)$, below which the response of the system to the noise remains weak, is studied versus the evolution time. In the regime with the Ehrenfest time interval $t_E$ so short that the classical Lyapunov exponential decay of the Peres fidelity does not show up the time dependence of this critical value is proved to be power-like. We estimate also the decoherence time after which the motion turns into a Markovian process.

quant-ph↗

arXiv2008

Complexity of Quantum States and Reversibility of Quantum Motion

We present a quantitative analysis of the reversibility properties of classically chaotic quantum motion. We analyze the connection between reversibility and the rate at which a quantum state acquires a more and more complicated structure in its time evolution. This complexity is characterized by the number ${\cal M}(t)$ of harmonics of the (initially isotropic, i.e. ${\cal M}(0)=0$) Wigner function, which are generated during quantum evolution for the time $t$. We show that, in contrast to the classical exponential increase, this number can grow not faster than linearly and then relate this fact with the degree of reversibility of the quantum motion. To explore the reversibility we reverse the quantum evolution at some moment $T$ immediately after applying at this moment an instant perturbation governed by a strength parameter $ξ$. It follows that there exists a critical perturbation strength, $ξ_c\approx \sqrt{2}/{\cal M}(T)$, below which the initial state is well recovered, whereas reversibility disappears when $ξ\gtrsim ξ_c(T)$. In the classical limit the number of harmonics proliferates exponentially with time and the motion becomes practically irreversible. The above results are illustrated in the example of the kicked quartic oscillator model.

nlin.CD↗

arXiv2008

How Well a Chaotic Quantum System Can Retain Memory of Its Initial State?

In classical mechanics the local exponential instability effaces the memory of initial conditions and leads to practical irreversibility. In striking contrast, quantum mechanics appears to exhibit strong memory of the initial state. We relate the latter fact to the low (at most linear) rate with which the system's Wigner function gets during evolution more and more complicated structure and establish existence of a critical strength of external influence below which such a memory still survives.

nlin.CD↗

arXiv2007

Decay Rate Statistics of Unstable Classically Chaotic Systems

Decay law of a complicated unstable state formed in a high energy collision is described by the Fourier transform of the two-point correlation function of the scattering matrix. Although each constituent resonance state decays exponentially the decay of a state composed of a large number of such interfering resonances is not, generally, exponential. We introduce the decay rates distribution function by representing the decay law in the form of the mean-weighted decay exponent. In the framework of the random matrix approach we investigate the properties of the new distribution function and its relation to the more conventional statistics of the decay widths. The latter is not in fact conclusive as concerns the evolution during the time shorter than the characteristic Heisenberg time. Exact analytical consideration is presented for the case of systems without time reversal symmetry.

cond-mat.mes-hall↗

arXiv2006

Dynamical chaos versus quantum interference

We discuss the dephasing induced by the internal classical chaotic motion in the absence of any external environment. To this end a new extension of fidelity for mixed states is introduced, which we name {\it allegiance}. Such quantity directly accounts for quantum interference and is measurable in a Ramsey interferometry experiment. We show that in the semiclassical limit the decay of the allegiance is exactly expressed, due to the dephasing, in terms of an appropriate classical correlation function. Our results are derived analytically for the case of a nonlinear driven oscillator and then numerically confirmed for the kicked rotor model.

quant-ph↗

arXiv2006

Quantum dephasing and decay of classical correlation functions in chaotic systems

We discuss the dephasing induced by the internal classical chaotic motion in the absence of any external environment. To this end we consider a suitable extension of fidelity for mixed states which is measurable in a Ramsey interferometry experiment. We then relate the dephasing to the decay of this quantity which, in the semiclassical limit, is expressed in terms of an appropriate classical correlation function. Our results are derived analytically for the example of a nonlinear driven oscillator and then numerically confirmed for the kicked rotor model.

quant-ph↗

arXiv2004

Dephasing and delay time fluctuations in the chaotic scattering of a quantum particle weakly coupled to a complicated background

Effect of a complicated many-body environment is analyzed on the chaotic motion of a quantum particle in a mesoscopic ballistic structure. The dephasing and absorption phenomena are treated on the same footing in the framework of a schematic microscopic model. The single-particle doorway resonance states excited in the structure via an external channel are damped not only because of the escape onto such channels but also due to ulterior population of the long-lived background states. The transmission through the structure is presented as an incoherent sum of the flow formed by the interfering damped doorway resonances and the retarded flow of the particles reemitted by the environment. The resulting internal damping as well as the dephasing rate are uniquely expressed in terms of the spreading width which controls the coupling to the background. The formation of the long-lived fine-structure resonances strongly enhances delay time fluctuations thus broadening the delay time distribution.

cond-mat.mes-hall↗

arXiv2003

Chaotic scattering of a quantum particle weakly coupled to a very complicated background

Effect of a complicated many-body environment is analyzed on the chaotic motion of a quantum particle in a mesoscopic ballistic structure. The dephasing and absorption phenomena are treated on the same footing in the framework of a model which is free of the ambiguities inherent to earlier models. The single-particle doorway resonance states excited via an external channel are damped not only because of the escape onto such channels but also due to ulterior population of long-lived background states, the resulting internal damping being uniquely characterized by the spreading width. On the other hand, the formation of the fine-structure resonances strongly enhances the delay time fluctuations thus broadening the delay time distribution.

cond-mat.mes-hall↗

arXiv2001

Distribution of proper delay times in quantum chaotic scattering: A crossover from ideal to weak coupling

The probability distribution of the proper delay times during scattering on a chaotic system is derived in the framework of the random matrix approach and the supersymmetry method. The result obtained is valid for an arbitrary number of scattering channels as well as arbitrary coupling to the energy continuum. The case of statistically equivalent channels is studied in detail. In particular, the semiclassical limit of infinite number of weak channels is paid appreciable attention.

cond-mat.dis-nn↗

arXiv1997

Quantum Versus Classical Decay Laws in Open Chaotic Systems

We study analytically the time evolution in decaying chaotic systems and discuss in detail the hierarchy of characteristic time scales that appeared in the quasiclassical region. There exist two quantum time scales: the Heisenberg time t_H and the time t_q=t_H/\sqrt{κT} (with κ>> 1 and T being the degree of resonance overlapping and the transmission coefficient respectively) associated with the decay. If t_q < t_H the quantum deviation from the classical decay law starts at the time t_q and are due to the openness of the system. Under the opposite condition quantum effects in intrinsic evolution begin to influence the decay at the time t_H. In this case we establish the connection between quantities which describe the time evolution in an open system and their closed counterparts.

cond-mat.mes-hall↗

arXiv1997

Invariant Correlation Entropy and Complexity of Quantum States

We define correlational (von Neumann) entropy for an individual quantum state of a system whose time-independent hamiltonian contains random parameters and is treated as a member of a statistical ensemble. This entropy is representation independent and can be calculated as a trace functional of the density matrix which describes the system in its interaction with the noise source. We analyze perturbation theory in order to show the evolution from the pure state to the mixed one. Exactly solvable examples illustrate the use of correlational entropy as a measure of the degree of complexity in comparison with other available suggestions such as basis-dependent information entropy. It is shown in particular that a harmonic oscillator in a uniform field of random strength comes to a quasithermal equilibrium; we discuss the relation between effective temperature and canonical equilibrium temperature. The notion of correlational entropy is applied to a realistic numerical caculation in the framework of the nuclear shell model. In this system, which reveals generic signatures of quantum chaos, correlational entropy and information entropy calculated in the mean field basis display similar qualitative behavior.

chao-dyn↗