4,369 research outputs found
Satellite material contaminant optical properties
The Air Force Wright Research and Development Center and the Arnold Engineering Development Center are continuing a program for measuring optical effects of satellite material outgassing products on cryo-optic surfaces. Presented here are infrared (4000 to 700 cm(-1)) transmittance data for contaminant films condensed on a 77 K geranium window. From the transmittance data, the contaminant film refractive and absorptive indices (n, k) were derived using an analytical thin-film interference model with a nonlinear least-squares algorithm. To date 19 materials have been studied with the optical contents determined for 13 of those. The materials include adhesives, paints, composites, films, and lubricants. This program is continuing and properties for other materials will be available in the future
Localized states and interaction induced delocalization in Bose gases with quenched disorder
Very diluted Bose gas placed into a disordered environment falls into a
fragmented localized state. At some critical density the repulsion between
particles overcomes the disorder. The gas transits into a coherent superfluid
state. In this article the geometrical and energetic characteristics of the
localized state at zero temperature and the critical density at which the
quantum phase transition from the localized to the superfluid state proceeds
are found.Comment: 17 pages, 5 figur
Controlling ultracold atoms in multi-band optical lattices for simulation of Kondo physics
We show that ultracold atoms can be controlled in multi-band optical lattices
through spatially periodic Raman pulses for investigation of a class of
strongly correlated physics related to the Kondo problem. The underlying
dynamics of this system is described by a spin-dependent fermionic or bosonic
Kondo-Hubbard lattice model even if we have only spin-independent atomic
collision interaction. We solve the bosonic Kondo-Hubbard lattice model through
a mean-field approximation, and the result shows a clear phase transition from
the ferromagnetic superfluid to the Kondo-signet insulator at the integer
filling.Comment: 4 pages, 2 figure
Finding Gravitational Lenses With X-rays
There are , 0.1 and 0.01 gravitationally lensed X-ray sources per
square degree with soft X-ray fluxes exceeding and
respectively. These sources will be detected
serendipitously with the Chandra X-ray Observatory at a rate of 1--3 lenses per
year of high resolution imaging. The low detection rate is due to the small
area over which the HRC and ACIS cameras have the <1\farcs5 FWHM resolution
necessary to find gravitational lenses produced by galaxies. Deep images of
rich clusters at intermediate redshifts should yield one wide separation
(\Delta\theta \gtorder 5\farcs0) multiply-imaged background X-ray source for
every , 30 and 300 clusters imaged to the same flux limits.Comment: 13 pages, including 5 figures, submitted to ApJ Letter
Speed and entropy of an interacting continuous time quantum walk
We present some dynamic and entropic considerations about the evolution of a
continuous time quantum walk implementing the clock of an autonomous machine.
On a simple model, we study in quite explicit terms the Lindblad evolution of
the clocked subsystem, relating the evolution of its entropy to the spreading
of the wave packet of the clock. We explore possible ways of reducing the
generation of entropy in the clocked subsystem, as it amounts to a deficit in
the probability of finding the target state of the computation. We are thus
lead to examine the benefits of abandoning some classical prejudice about how a
clocking mechanism should operate.Comment: 25 pages, 14 figure
Correlation function of weakly interacting bosons in a disordered lattice
One of the most important issues in disordered systems is the interplay of
the disorder and repulsive interactions. Several recent experimental advances
on this topic have been made with ultracold atoms, in particular the
observation of Anderson localization, and the realization of the disordered
Bose-Hubbard model. There are however still questions as to how to
differentiate the complex insulating phases resulting from this interplay, and
how to measure the size of the superfluid fragments that these phases entail.
It has been suggested that the correlation function of such a system can give
new insights, but so far little experimental investigation has been performed.
Here, we show the first experimental analysis of the correlation function for a
weakly interacting, bosonic system in a quasiperiodic lattice. We observe an
increase in the correlation length as well as a change in shape of the
correlation function in the delocalization crossover from Anderson glass to
coherent, extended state. In between, the experiment indicates the formation of
progressively larger coherent fragments, consistent with a fragmented BEC, or
Bose glass.Comment: 16 pages, 8 figure
Anderson localization in Bose-Einstein condensates
The understanding of disordered quantum systems is still far from being
complete, despite many decades of research on a variety of physical systems. In
this review we discuss how Bose-Einstein condensates of ultracold atoms in
disordered potentials have opened a new window for studying fundamental
phenomena related to disorder. In particular, we point our attention to recent
experimental studies on Anderson localization and on the interplay of disorder
and weak interactions. These realize a very promising starting point for a
deeper understanding of the complex behaviour of interacting, disordered
systems.Comment: 15 pages review, to appear in Reports on Progress in Physic
Analyticity of the SRB measure of a lattice of coupled Anosov diffeomorphisms of the torus
We consider the "thermodynamic limit"of a d-dimensional lattice of hyperbolic
dynamical systems on the 2-torus, interacting via weak and nearest neighbor
coupling. We prove that the SRB measure is analytic in the strength of the
coupling. The proof is based on symbolic dynamics techniques that allow us to
map the SRB measure into a Gibbs measure for a spin system on a
(d+1)-dimensional lattice. This Gibbs measure can be studied by an extension
(decimation) of the usual "cluster expansion" techniques.Comment: 28 pages, 2 figure
Transport regimes of cold gases in a two-dimensional anisotropic disorder
We numerically study the dynamics of cold atoms in a two-dimensional
disordered potential. We consider an anisotropic speckle potential and focus on
the classical regime, which is relevant to some recent experiments. First, we
study the behavior of particles with a fixed energy and identify different
transport regimes. For low energy, the particles are classically localized due
to the absence of a percolating cluster. For high energy, the particles undergo
normal diffusion and we show that the diffusion constants scale algebraically
with the particle energy, with an anisotropy factor which significantly differs
from that of the disordered potential. For intermediate energy, we find a
transient sub-diffusive regime, which is relevant to the time scale of typical
experiments. Second, we study the behavior of a cold-atomic gas with an
arbitrary energy distribution, using the above results as a groundwork. We show
that the density profile of the atomic cloud in the diffusion regime is
strongly peaked and, in particular, that it is not Gaussian. Its behavior at
large distances allows us to extract the energy-dependent diffusion constants
from experimental density distributions. For a thermal cloud released into the
disordered potential, we show that our numerical predictions are in agreement
with experimental findings. Not only does this work give insights to recent
experimental results, but it may also serve interpretation of future
experiments searching for deviation from classical diffusion and traces of
Anderson localization.Comment: 19 pages, 16 figure
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