3,443 research outputs found
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.Comment: 17 pages in revtex, 9 figures (postscript obtained upon request via
e-mail at [email protected]) submitted to Nonlinearit
Shielding and localization in presence of long range hopping
We investigate a paradigmatic model for quantum transport with both
nearest-neighbor and infinite range hopping coupling (independent of the
position). Due to long range homogeneous hopping, a gap between the ground
state and the excited states can be induced, which is mathematically equivalent
to the superconducting gap. In the gapped regime, the dynamics within the
excited states subspace is shielded from long range hopping, namely it occurs
as if long range hopping would be absent. This is a cooperative phenomenon
since shielding is effective over a time scale which diverges with the system
size. We named this effect {\it Cooperative Shielding}. We also discuss the
consequences of our findings on Anderson localization. Long range hopping is
usually thought to destroy localization due to the fact that it induces an
infinite number of resonances. Contrary to this common lore we show that the
excited states display strong localized features when shielding is effective
even in the regime of strong long range coupling. A brief discussion on the
extension of our results to generic power-law decaying long range hopping is
also given. Our preliminary results confirms that the effects found for the
infinite range case are generic.Comment: 7 pages, 9 figur
Effect of noise for two interacting particles in a random potential
We investigated the effect of noise on propagation of two interacting
particles pairs in a quasi one--dimensional random potential. It is shown that
pair diffusion is strongly enhanced by short range interaction comparing with
the non--interacting case.Comment: 8 Latex pages + 3 postscript figures uu- compressed submitted to
Europhysics Letter
Cooperative Robustness to Static Disorder: Superradiance and localization in a nanoscale ring to model natural light-harvesting systems
We analyze a 1-d ring structure composed of many two-level systems, in the
limit where only one excitation is present. The two-level systems are coupled
to a common environment, where the excitation can be lost, which induces super
and subradiant behavior, an example of cooperative quantum coherent effect. We
consider time-independent random fluctuations of the excitation energies. This
static disorder, also called inhomogeneous broadening in literature, induces
Anderson localization and is able to quench Superradiance. We identify two
different regimes: weak opening, in which Superradiance is quenched at the
same critical disorder at which the states of the closed system localize;
strong opening, with a critical disorder strength proportional to both the
system size and the degree of opening, displaying robustness of cooperativity
to disorder. Relevance to photosynthetic complexes is discussed.Comment: 12 pages, 7 figs., Superradiance, Anderson Localization, Cooperative
effects. Accepted for publication in Phys. Rev.
The Topological Non-connectivity Threshold in quantum long-range interacting spin systems
Quantum characteristics of the Topological Non-connectivity Threshold (TNT),
introduced in F.Borgonovi, G.L.Celardo, M.Maianti, E.Pedersoli, J. Stat. Phys.,
116, 516 (2004), have been analyzed in the hard quantum regime. New interesting
perspectives in term of the possibility to study the intriguing
quantum-classical transition through Macroscopic Quantum Tunneling have been
addressed.Comment: contribution to NEXTSIGMAPHI 3r
Broken Ergodicity in classically chaotic spin systems
A one dimensional classically chaotic spin chain with asymmetric coupling and
two different inter-spin interactions, nearest neighbors and all-to-all, has
been considered. Depending on the interaction range, dynamical properties, as
ergodicity and chaoticity are strongly different. Indeed, even in presence of
chaoticity, the model displays a lack of ergodicity only in presence of all to
all interaction and below an energy threshold, that persists in the
thermodynamical limit. Energy threshold can be found analytically and results
can be generalized for a generic XY model with asymmetric coupling.Comment: 6 pages, 3 figure
Enhancement of magnetic anisotropy barrier in long range interacting spin systems
Magnetic materials are usually characterized by anisotropy energy barriers
which dictate the time scale of the magnetization decay and consequently the
magnetic stability of the sample. Here we present a unified description, which
includes coherent rotation and nucleation, for the magnetization decay in
generic anisotropic spin systems. In particular, we show that, in presence of
long range exchange interaction, the anisotropy energy barrier grows as the
volume of the particle for on site anisotropy, while it grows even faster than
the volume for exchange anisotropy, with an anisotropy energy barrier
proportional to , where is the particle volume, is the range of interaction and is the embedding dimension. These
results shows a relevant enhancement of the anisotropy energy barrier w.r.t.
the short range case, where the anisotropy energy barrier grows as the particle
cross sectional area for large particle size or large particle aspect ratio.Comment: 7 pages, 6 figures. Theory of Magnetic decay in nanosystem. Non
equilibrium statistical mechanics of many body system
A semiquantal approach to finite systems of interacting particles
A novel approach is suggested for the statistical description of quantum
systems of interacting particles. The key point of this approach is that a
typical eigenstate in the energy representation (shape of eigenstates, SE) has
a well defined classical analog which can be easily obtained from the classical
equations of motion. Therefore, the occupation numbers for single-particle
states can be represented as a convolution of the classical SE with the quantum
occupation number operator for non-interacting particles. The latter takes into
account the wavefunctions symmetry and depends on the unperturbed energy
spectrum only. As a result, the distribution of occupation numbers can be
numerically found for a very large number of interacting particles. Using the
model of interacting spins we demonstrate that this approach gives a correct
description of even in a deep quantum region with few single-particle
orbitals.Comment: 4 pages, 2 figure
Quantum Chaos and Thermalization in Isolated Systems of Interacting Particles
This review is devoted to the problem of thermalization in a small isolated
conglomerate of interacting constituents. A variety of physically important
systems of intensive current interest belong to this category: complex atoms,
molecules (including biological molecules), nuclei, small devices of condensed
matter and quantum optics on nano- and micro-scale, cold atoms in optical
lattices, ion traps. Physical implementations of quantum computers, where there
are many interacting qubits, also fall into this group. Statistical
regularities come into play through inter-particle interactions, which have two
fundamental components: mean field, that along with external conditions, forms
the regular component of the dynamics, and residual interactions responsible
for the complex structure of the actual stationary states. At sufficiently high
level density, the stationary states become exceedingly complicated
superpositions of simple quasiparticle excitations. At this stage, regularities
typical of quantum chaos emerge and bring in signatures of thermalization. We
describe all the stages and the results of the processes leading to
thermalization, using analytical and massive numerical examples for realistic
atomic, nuclear, and spin systems, as well as for models with random
parameters. The structure of stationary states, strength functions of simple
configurations, and concepts of entropy and temperature in application to
isolated mesoscopic systems are discussed in detail. We conclude with a
schematic discussion of the time evolution of such systems to equilibrium.Comment: 69 pages, 31 figure
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