13,052 research outputs found
Correlations and fluctuations of a confined electron gas
The grand potential and the response of a phase-coherent confined noninteracting electron gas depend
sensitively on chemical potential or external parameter . We compute
their autocorrelation as a function of , and temperature. The result
is related to the short-time dynamics of the corresponding classical system,
implying in general the absence of a universal regime. Chaotic, diffusive and
integrable motions are investigated, and illustrated numerically. The
autocorrelation of the persistent current of a disordered mesoscopic ring is
also computed.Comment: 12 pages, 1 figure, to appear in Phys. Rev.
Coherent Backscattering of Light with Nonlinear Atomic Scatterers
We study coherent backscattering of a monochromatic laser by a dilute gas of
cold two-level atoms in the weakly nonlinear regime. The nonlinear response of
the atoms results in a modification of both the average field propagation
(nonlinear refractive index) and the scattering events. Using a perturbative
approach, the nonlinear effects arise from inelastic two-photon scattering
processes. We present a detailed diagrammatic derivation of the elastic and
inelastic components of the backscattering signal both for scalar and vectorial
photons. Especially, we show that the coherent backscattering phenomenon
originates in some cases from the interference between three different
scattering amplitudes. This is in marked contrast with the linear regime where
it is due to the interference between two different scattering amplitudes. In
particular we show that, if elastically scattered photons are filtered out from
the photo-detection signal, the nonlinear backscattering enhancement factor
exceeds the linear barrier two, consistently with a three-amplitude
interference effect.Comment: 18 pages, 13 figures, submitted to Phys. Rev.
Localization of correlated fermions in optical lattices with speckle disorder
Strongly correlated fermions in three- and two-dimensional optical lattices
with experimentally realistic speckle disorder are investigated. We extend and
apply the statistical dynamical mean-field theory, which treats local
correlations non-perturbatively, to incorporate on-site and hopping-type
randomness on equal footing. Localization due to disorder is detected via the
probability distribution function of the local density of states. We obtain a
complete paramagnetic ground state phase diagram for experimentally realistic
parameters and find a strong suppression of the correlation-induced metal
insulator transition due to disorder. Our results indicate that the
Anderson-Mott and the Mott insulator are not continuously connected due to the
specific character of speckle disorder. Furthermore, we discuss the effect of
finite temperature on the single-particle spectral function.Comment: 12 pages, 16 figures, published versio
Dynamic Correlation in Wave Propagation in Random Media
We report time-resolved measurements of the statistics of pulsed transmission
through quasi-one-dimensional dielectric media with static disorder. The
normalized intensity correlation function with displacement and polarization
rotation for an incident pulse of linewidth at delay time t is a
function only of the field correlation function, which is identical to that
found for steady-state excitation, and of , the residual
degree of intensity correlation at points at which the field correlation
function vanishes. The dynamic probability distribution of normalized intensity
depends only upon . Steady-state statistics are recovered
in the limit ->0, in which is the steady-state
degree of correlation.Comment: 4 RevTex pages, 4 figure
Multiangle static and dynamic light scattering in the intermediate scattering angle range
We describe a light scattering apparatus based on a novel optical scheme
covering the scattering angle range 0.5\dg \le \theta \le 25\dg, an
intermediate regime at the frontier between wide angle and small angle setups
that is difficult to access by existing instruments. Our apparatus uses
standard, readily available optomechanical components. Thanks to the use of a
charge-coupled device detector, both static and dynamic light scattering can be
performed simultaneously at several scattering angles. We demonstrate the
capabilities of our apparatus by measuring the scattering profile of a variety
of samples and the Brownian dynamics of a dilute colloidal suspension
Statistics of fluctuations for two types of crossover: from ballistic to diffusive regime and from orthogonal to unitary ensemble
In our previous publication [Kogan et al, Phys. Rev. {\bf 48}, 9404 (1993)]
we considered the issue of statistics of radiation diffusively propagating in a
disordered medium. The consideration was in the framework of diagrammatic
techniques and a new representation for the intensity distribution function in
terms of connected diagrams only was proposed. Here we use similar approach to
treat the issue of statistics in the regime of the crossover between ballistic
and diffusive transport. We find that even small contribution from coherent
component decreases by one half the intensity distribution function for small
values of intensity and also produces oscillations of the distribution
function. We also apply this method to study statistics of fluctuations of wave
functions of chaotic electrons in a quantum dot in an arbitrary magnetic field,
by calculating the single state local density in the regime of the crossover
between the orthogonal and unitary ensemble.Comment: Revtex, 3 pages + 2 ps.figures in uuencoded file, a version which
clarifies and unites the results of two previous submission
Mesoscopic phase statistics of diffuse ultrasound in dynamic matter
Temporal fluctuations in the phase of waves transmitted through a dynamic,
strongly scattering, mesoscopic sample are investigated using ultrasonic waves,
and compared with theoretical predictions based on circular Gaussian
statistics. The fundamental role of phase in Diffusing Acoustic Wave
Spectroscopy is revealed, and phase statistics are also shown to provide a
sensitive and accurate way to probe scatterer motions at both short and long
time scales.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
Phase statistics of seismic coda waves
We report the analysis of the statistics of the phase fluctuations in the
coda of earthquakes recorded during a temporary experiment deployed at Pinyon
Flats Observatory, California. The practical measurement of the phase is
discussed and the main pitfalls are underlined. For large values, the
experimental distributions of the phase first, second and third derivatives
obey universal power-law decays whose exponents are remarkably well predicted
by circular Gaussian statistics. For small values, these distributions are
flat. The details of the transition between the plateau and the power-law
behavior are governed by the wavelength. The correlation function of the first
phase derivative along the array shows a simple algebro-exponential decay with
the mean free path as the only length scale. Although only loose bounds are
provided in this study, our work suggests a new method to estimate the degree
of heterogeneity of the crComment: 4 figures, submitted to Physical Review Letter
Study of muons near shower cores at sea level using the E594 neutrino detector
The E594 neutrino detector has been used to study the lateral distribution of muons of energy 3 GeV near shower cores. The detector consists of a 340 ton fine grain calorimeter with 400,000 cells of flash chamber and dimensions of 3.7 m x 20 m x 3.7 m (height). The average density in the calorimeter is 1.4 gm/sq cm, and the average Z is 21. The detector was triggered by four 0.6 sq m scintillators placed immediately on the top of the calorimeter. The trigger required at least two of these four counters. The accompanying extensive air showers (EAS) was sampled by 14 scintillation counters located up to 15 m from the calorimeter. Several off line cuts have been applied to the data. Demanding five particles in at least two of the trigger detectors, a total of 20 particles in all of them together, and an arrival angle for the shower 450 deg reduced the data sample to 11053 events. Of these in 4869 cases, a computer algorithm found at least three muons in the calorimeter
Transform-limited X-ray pulse generation from a high-brightness self-amplified spontaneous-emission free-electron laser
A method to achieve high-brightness self-amplified spontaneous emission (HB-SASE) in the free-electron laser (FEL) is described. The method uses repeated nonequal electron beam delays to delocalize the collective FEL interaction and break the radiation coherence length dependence on the FEL cooperation length. The method requires no external seeding or photon optics and so is applicable at any wavelength or repetition rate. It is demonstrated, using linear theory and numerical simulations, that the radiation coherence length can be increased by approximately 2 orders of magnitude over SASE with a corresponding increase in spectral brightness. Examples are shown of HB-SASE generating transform-limited FEL pulses in the soft x-ray and near transform-limited pulses in the hard x-ray. Such pulses may greatly benefit existing applications and may also open up new areas of scientific research
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