182 research outputs found
Statistical properties of energy levels of chaotic systems: Wigner or non-Wigner
For systems whose classical dynamics is chaotic, it is generally believed
that the local statistical properties of the quantum energy levels are well
described by Random Matrix Theory. We present here two counterexamples - the
hydrogen atom in a magnetic field and the quartic oscillator - which display
nearest neighbor statistics strongly different from the usual Wigner
distribution. We interpret the results with a simple model using a set of
regular states coupled to a set of chaotic states modeled by a random matrix.Comment: 10 pages, Revtex 3.0 + 4 .ps figures tar-compressed using uufiles
package, use csh to unpack (on Unix machine), to be published in Phys. Rev.
Let
Postquench prethermalization in a disordered quantum fluid of light
We study the coherence of a disordered and interacting quantum light field
after propagation along a nonlinear optical fiber. Disorder is generated by a
cross-phase modulation with a randomized auxiliary classical light field, while
interactions are induced by self-phase modulation. When penetrating the fiber
from free space, the incoming quantum light undergoes a disorder and
interaction quench. By calculating the coherence function of the transmitted
quantum light, we show that the decoherence induced by the quench spreads in a
light-cone fashion in the nonequilibrium many-body quantum system, leaving the
latter prethermalize with peculiar features originating from disorder.Comment: 18 pages, 5 figure
Coherent Backscattering with Nonlinear Atomic Scatterers
We study coherent backscattering of a quasi-monochromatic laser by a dilute
gas of cold two-level atoms. We consider the perturbative regime of weak
intensities, where nonlinear effects arise from {\em inelastic} two-photon
scattering processes. Here, coherent backscattering can be formed by
interference between {\em three} different scattering amplitudes. Consequently,
if elastically scattered photons are filtered out from the photodetection
signal by means of suitable frequency-selective detection, we find the
nonlinear backscattering enhancement factor to exceed the linear barrier two.Comment: 4 pages, 3 figure
Cooperative emission of a pulse train in an optically thick scattering medium
An optically thick cold atomic cloud emits a coherent flash of light in the
forward direction when the phase of an incident probe field is abruptly
changed. Because of cooperativity, the duration of this phenomena can be much
shorter than the excited lifetime of a single atom. Repeating periodically the
abrupt phase jump, we generate a train of pulses with short repetition time,
high intensity contrast and high efficiency. In this regime, the emission is
fully governed by cooperativity even if the cloud is dilute.Comment: 5 pages, 3 figure
Comment on ``Intensity correlations and mesoscopic fluctuations of diffusing photons in cold atoms''
In a recent Letter (Phys. Rev. Lett. \textbf{98}, 083601 (2007),
arXiv:cond-mat/0610804), O. Assaf and E. Akkermans claim that the angular
correlations of the light intensity scattered by a cloud of cold atoms with
internal degeneracy (Zeeman sublevels) of the ground state overcome the usual
Rayleigh law. More precisely, they found that they become exponentially large
with the size of the sample. In what follows, we will explain why their results
are wrong and, in contrary, why the internal degeneracy leads to lower
intensity correlations.Comment: 1 page. Comment submitted to PR
A second-order PHD filter with mean and variance in target number
The Probability Hypothesis Density (PHD) and Cardinalized PHD (CPHD) filters
are popular solutions to the multi-target tracking problem due to their low
complexity and ability to estimate the number and states of targets in
cluttered environments. The PHD filter propagates the first-order moment (i.e.
mean) of the number of targets while the CPHD propagates the cardinality
distribution in the number of targets, albeit for a greater computational cost.
Introducing the Panjer point process, this paper proposes a second-order PHD
filter, propagating the second-order moment (i.e. variance) of the number of
targets alongside its mean. The resulting algorithm is more versatile in the
modelling choices than the PHD filter, and its computational cost is
significantly lower compared to the CPHD filter. The paper compares the three
filters in statistical simulations which demonstrate that the proposed filter
reacts more quickly to changes in the number of targets, i.e., target births
and target deaths, than the CPHD filter. In addition, a new statistic for
multi-object filters is introduced in order to study the correlation between
the estimated number of targets in different regions of the state space, and
propose a quantitative analysis of the spooky effect for the three filters
Residual Symmetries in the Spectrum of Periodically Driven Alkali Rydberg States
We identify a fundamental structure in the spectrum of microwave driven
alkali Rydberg states, which highlights the remnants of the Coulomb symmetry in
the presence of a non-hydrogenic core. Core-induced corrections with respect to
the hydrogen spectrum can be accounted for by a perturbative approach.Comment: 7 pages, 2 figures, to be published in Europhysics Letter
Extracting information from non adiabatic dynamics: excited symmetric states of the Bose-Hubbard model
Using Fourier transform on a time series generated by unitary evolution, we
extract many-body eigenstates of the Bose-Hubbard model corresponding to low
energy excitations, which are generated when the insulator-superfluid phase
transition is realized in a typical experiment. The analysis is conducted in a
symmetric external potential both without and with and disorder. A simple
classification of excitations in the absence disorder is provided. The
evolution is performed assuming the presence of the parity symmetry in the
system rendering many-body quantum states either symmetric or antisymmetric.
Using symmetry-breaking technique, those states are decomposed into elementary
one-particle processes.Comment: inv. talk at 5th Workshop on Quantum Chaos and Localization
Phenomena, Warsaw 201
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