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At least 595 records · Page 33Linked to original sources

arXiv1999

Quantum baker map on the sphere

We define a class of dynamical systems on the sphere analogous to the baker map on the torus. The classical maps are characterized by dynamical entropy equal to ln 2. We construct and investigate a family of the corresponding quantum maps. In the simplest case of the model the system does not possess a time reversal symmetry and the quantum map is represented by real, orthogonal matrices of even dimension. The semiclassical ensemble of quantum maps, obtained by averaging over a range of matrix sizes, displays statistical properties characteristic of circular unitary ensemble. Time evolution of such systems may be studied with the help of the SU(2) coherent states and the generalized Husimi distribution.

chao-dyn↗

arXiv1998

Entropy production, dynamical localization and criteria for quantum chaos in the open quantum kicked rotor

The von Neumann entropy production for a quantum mechanical kicked rotor coupled to a thermal environment is calculated. This rate of entropy increase is shown to be a good criterion to distinguish between quantum mechanical counterparts of chaotic and regular classical motion. We show that for high temperatures the entropy production rate increases linearly with the Kolmogorov-Sinai entropy of the classical system. However, for lower temperatures we also show that there are fluctuations in this linear behaviour due to dynamical localization.

chao-dyn↗

arXiv1999

Porosities and dimensions of measures

We introduce a concept of porosity for measures and study relations between dimensions and porosities for two classes of measures: measures on $R^n$ which satisfy the doubling condition and strongly porous measures on $R$.

chao-dyn↗

arXiv1999

Quantization of multidimensional cat maps

In this work we study cat maps with many degrees of freedom. Classical cat maps are classified using the Cayley parametrization of symplectic matrices and the closely associated center and chord generating functions. Particular attention is dedicated to loxodromic behavior, which is a new feature of two-dimensional maps. The maps are then quantized using a recently developed Weyl representation on the torus and the general condition on the Floquet angles is derived for a particular map to be quantizable. The semiclassical approximation is exact, regardless of the dimensionality or of the nature of the fixed points.

chao-dyn↗

arXiv1999

Action Correlations in Integrable Systems

In many problems of quantum chaos the calculation of sums of products of periodic orbit contributions is required. A general method of computation of these sums is proposed for generic integrable models where the summation over periodic orbits is reduced to the summation over integer vectors uniquely associated with periodic orbits. It is demonstrated that in multiple sums over such integer vectors there exist hidden saddle points which permit explicit evaluation of these sums. Saddle point manifolds consist of periodic orbits vectors which are almost mutually parallel. Different problems has been treated by this saddle point method, e.g. Berry's bootstrap relations, mean values of Green function products etc. In particular, it is obtained that suitably defined 2-point correlation form-factor for periodic orbit actions in generic integrable models is proportional to quantum density of states and has peaks at quantum eigenenergies.

chao-dyn↗

arXiv1994

Statistical Properties of the Zeros of Zeta Functions - Beyond the Riemann Case

We investigate the statistical distribution of the zeros of Dirichlet $L$--functions both analytically and numerically. Using the Hardy--Littlewood conjecture about the distribution of prime numbers we show that the two--point correlation function of these zeros coincides with that for eigenvalues of the Gaussian unitary ensemble of random matrices, and that the distributions of zeros of different $L$--functions are statistically independent. Applications of these results to Epstein's zeta functions are shortly discussed.

chao-dyn↗

arXiv1995

Enhancement of localization length for two interacting kicked rotators

We study the effect of coherent propagation of two interacting particles in a disordered potential. The dependence of the enhancement factor for coherent localization length due to interaction is investigated numerically in the model of quantum chaos. The effect of interaction for two particles in many dimensions is also discussed.

cond-mat↗

arXiv1996

The semiclassical resonance spectrum of Hydrogen in a constant magnetic field

We present the first purely semiclassical calculation of the resonance spectrum in the Diamagnetic Kepler problem (DKP), a hydrogen atom in a constant magnetic field with $L_z =0$. The classical system is unbound and completely chaotic for a scaled energy $ε\sim E B^{-2/3}$ larger than a critical value $ε_c >0$. The quantum mechanical resonances can in semiclassical approximation be expressed as the zeros of the semiclassical zeta function, a product over all the periodic orbits of the underlying classical dynamics. Intermittency originating from the asymptotically separable limit of the potential at large electron--nucleus distance causes divergences in the periodic orbit formula. Using a regularisation technique introduced in [G.\ Tanner and D.\ Wintgen, Phys.~Rev.~Lett.~{\bf 75}, 2928 (1995)] together with a modified cycle expansion, we calculate semiclassical resonances, both position and width, which are in good agreement with quantum mechanical results obtained by the method of complex rotation. The method also provides good estimates for the bound state spectrum obtained here from the classical dynamics of a scattering system. A quasi Einstein--Brillouin--Keller (QEBK) quantisation is derived that allows for a description of the spectrum in terms of approximate quantum numbers and yields the correct asymptotic behaviour of the Rydberg--like series converging towards the different Landau thresholds.

chao-dyn↗

arXiv1996

Chaotic features in classical scattering processes between ions and atoms

A numerical study has been done of collisions between protons and hydrogen atoms, treated as classical particles, at low impact velocities. The presence of chaos has been looked for by investigating the processes with standard techniques of the chaotic--scattering theory. The evidence of a sharp transition from nearly regular scattering to fully developed chaos has been found at the lower velocities.

chao-dyn↗

arXiv1999

Emergence of macroscopic temperatures in systems that are not thermodynamical microscopically: towards a thermodynamical description of slow granular rheology

A scenario for systems with slow dynamics is characterised by stating that there are several temperatures coexisting in the sample, with a single temperature shared by all observables at each (widely separate) time-scale. In preparation for the study of granular rheology, we show within this framework that glassy systems with driving and friction that are generic and do not correspond to a thermal bath --- and whose microscopic `fast' motion is hence not thermal --- have a well-defined macroscopic temperature associated to the slow degrees of freedom. This temperature is what a thermometer coupled to the system will measure if tuned to respond to low frequencies, and since it can be related to the number of stationary configurations, it is the formalisation of Edwards' `compactivity' ideas.

cond-mat.stat-mech↗

arXiv1999

Can the trace formula describe weak localisation?

We attempt to systematically derive perturbative quantum corrections to the Berry diagonal approximation of the two-level correlation function (TLCF) for chaotic systems. To this end, we develop a ``weak diagonal approximation'' based on a recent description of the first weak localisation correction to conductance in terms of the Gutzwiller trace formula. This semiclassical method is tested by using it to derive the weak localisation corrections to the TLCF for a semiclassically disordered system. Unfortunately the method is unable to correctly reproduce the ``Hikami boxes'' (the relatively small regions where classical paths are glued together by quantum processes). This results in the method failing to reproduce the well known weak localisation expansion. It so happens that for the first order correction it merely produces the wrong prefactor. However for the second order correction, it is unable to reproduce certain contributions, and leads to a result which is of a different form to the standard one.

cond-mat.mes-hall↗

arXiv1999

Quantization Ambiguity, Ergodicity, and Semiclassics

A simple argument shows that eigenstates of a classically ergodic system are individually ergodic on coarse-grained scales. This has implications for the quantization ambiguity in ergodic systems: the difference between alternative quantizations is suppressed compared with the $O(\hbar^2)$ ambiguity in the integrable case. For two-dimensional ergodic systems in the high-energy regime, individual eigenstates are independent of the choice of quantization procedure, in contrast with the regular case, where even the ordering of eigenlevels is ambiguous. Surprisingly, semiclassical methods are shown to be much more precise for chaotic than for integrable systems.

quant-ph↗

arXiv1998

Duality in Perturbation Theory and the Quantum Adiabatic Approximation

Duality is considered for the perturbation theory by deriving, given a series solution in a small parameter, its dual series with the development parameter being the inverse of the other. A dual symmetry in perturbation theory is identified. It is then shown that the dual to the Dyson series in quantum mechanics is given by a recent devised series having the adiabatic approximation as leading order. A simple application of this result is given by rederiving a theorem for strongly perturbed quantum systems.

hep-th↗

arXiv1995

Spectral Statistics in the Lowest Landau Band

We study the spectral statistics in the center of the lowest Landau band of a 2D disordered system with smooth potential and strong transverse magnetic field. Due to the finite size of the system, the energy range in which there are extended states is finite as well. The behavior in this range can be viewed as the analogue of the Anderson metal-insulator transition for the case of the Hall system. Accordingly, we verify recent predictions regarding the exponent of the asymptotic power law of $Σ^2 (\bar N)$, $γ$, and that of the stretched exponential dominating the large $s$ behavior of the spacings distribution, $α$. Both the relations, $α= 1- γ$, and $γ= 1 - {1\over{νd}}$ where $ν$ is the critical exponent of the localization length and $d$ is the dimension, are found to hold within the accuracy of our computations. However, we find that none of several possible models of the entire spacings distribution correctly describes our situation. Finally, for very large $\bar N$, $\bar N > 60$, we find a new regime in which $Σ^2 (\bar N)$ behaves as a power law with an unexpectedly large power, $γ_1 = 1.38 \pm 0.02$.

cond-mat↗

arXiv1996

Reflection Symmetric Ballistic Microstructures: Quantum Transport Properties

We show that reflection symmetry has a strong influence on quantum transport properties. Using a random S-matrix theory approach, we derive the weak-localization correction, the magnitude of the conductance fluctuations, and the distribution of the conductance for three classes of reflection symmetry relevant for experimental ballistic microstructures. The S-matrix ensembles used fall within the general classification scheme introduced by Dyson, but because the conductance couples blocks of the S-matrix of different parity, the resulting conductance properties are highly non-trivial.

cond-mat↗

arXiv1995

Nuclear Mass Dependence of Chaotic Dynamics in Ginocchio Model

The chaotic dynamics in nuclear collective motion is studied in the framework of a schematic shell model which has only monopole and quadrupole degrees of freedom. The model is shown to reproduce the experimentally observed global trend toward less chaotic motion in heavier nuclei. The relation between current approach and the earlier studies with bosonic models is discussed.

nucl-th↗

arXiv1995

Transition to nonchaotic behavior in a Brownian-type motion

A theoretical and numerical analysis of the transition from chaotic to nonchaotic behavior in an ensemble of particles with different initial conditions which move according to Newton's equations in a bounding potential and are driven by an identical sequence of random forces (see S. Fahy and D. R. Hamann, Phys. Rev. Lett. {\bf 69}, 761 (1992)) is presented. The threshold values of the parameters for transition from chaotic to nonchaotic behavior are defined on the basis of the map for distances between the particles and differences of velocity. Numerical analysis is fulfilled for one-dimensional Duffing $V(x)=x^4-x^2$ and $V(x)=x^4$ potentials.

chao-dyn↗

arXiv1995

Dynamical Simulation of Fluidized Beds --- Hydrodynamically Interacting Granular Particles

A numerical simulation of a gas-fluidized bed is performed without introduction of any empirical parameters. Realistic bubbles and slugs are observed in our simulation. It is found that the convective motion of particles is important for the bubbling phase and there is no convection in the slugging phase. From the simulation results, non-Gaussian distributions are found in the particle velocities and the relation between the deviation from Gaussian and the local density of particles is suggested. It is also shown that the power spectra of particle velocities obey power laws. A brief explanation on the relationship between the simulation results and the Kolmogorov scaling argument is discussed.

chao-dyn↗