552 research outputs found

### Feshbach resonances in a quasi-2D atomic gas

Strongly confining an ultracold atomic gas in one direction to create a
quasi-2D system alters the scattering properties of this gas. We investigate
the effects of confinement on Feshbach scattering resonances and show that
strong confinement results in a shift in the position of the Feshbach resonance
as a function of the magnetic field. This shift, as well as the change of the
width of the resonance, are computed. We find that the resonance is strongly
damped in the thermal gas, but in the condensate the resonance remains sharp
due to many-body effects. We introduce a 2D model system, suited for the study
of resonant superfluidity, and having the same scattering properties as the
tightly confined real system near a Feshbach resonance. Exact relations are
derived between measurable quantities and the model parameters.Comment: 8 pages, 2 figure

### A general T-matrix approach applied to two-body and three-body problems in cold atomic gases

We propose a systematic T-matrix approach to solve few-body problems with
s-wave contact interactions in ultracold atomic gases. The problem is generally
reduced to a matrix equation expanded by a set of orthogonal molecular states,
describing external center-of-mass motions of pairs of interacting particles;
while each matrix element is guaranteed to be finite by a proper
renormalization for internal relative motions. This approach is able to
incorporate various scattering problems and the calculations of related
physical quantities in a single framework, and also provides a physically
transparent way to understand the mechanism of resonance scattering. For
applications, we study two-body effective scattering in 2D-3D mixed dimensions,
where the resonance position and width are determined with high precision from
only a few number of matrix elements. We also study three fermions in a
(rotating) harmonic trap, where exotic scattering properties in terms of mass
ratios and angular momenta are uniquely identified in the framework of
T-matrix.Comment: 14 pages, 4 figure

### Expansion of a Bose-Einstein Condensate in an atomic waveguide

The expansion of a Bose-Einstein condensate in an atomic waveguide is
analyzed. We study different regimes of expansion, and identify a transient
regime between one-dimensional and three-dimensional dynamics, in which the
properties of the condensate and its further expansion can be well explained by
reducing the transversal dynamics to a two-level system. The relevance of this
regime in current experiments is discussed.Comment: 4 pages, 3 figs, Accepted for publication in Phys. Rev.

### Production of a Fermi gas of atoms in an optical lattice

We prepare a degenerate Fermi gas of potassium atoms by sympathetic cooling
with rubidium atoms in a one-dimensional optical lattice. In a tight lattice we
observe a change of the density of states of the system, which is a signature
of quasi two dimensional confinement. We also find that the dipolar
oscillations of the Fermi gas along the tight lattice are almost completely
suppressed.Comment: 4 pages, 4 figures, revised versio

### Dimensional and Temperature Crossover in Trapped Bose Gases

We investigate the long-range phase coherence of homogeneous and trapped Bose
gases as a function of the geometry of the trap, the temperature, and the
mean-field interactions in the weakly interacting limit. We explicitly take
into account the (quasi)condensate depletion due to quantum and thermal
fluctuations, i.e., we include the effects of both phase and density
fluctuations. In particular, we determine the phase diagram of the gas by
calculating the off-diagonal one-particle density matrix and discuss the
various crossovers that occur in this phase diagram and the feasibility of
their experimental observation in trapped Bose gases.Comment: One figure added, typos corrected, refernces adde

### Using parallel computing in modeling and optimization of mineral reserves extraction systems

Annotation This article describes algorithm for solving ultimate pit limit problem (UPIT), or a maximum weight closure problem. There are several method for solving this problem. We provide new approach, for solving ultimate pit limit problem using precedence model. Block model of open pit can be easily represented as an oriented graph. Then to solve ultimate pit limit problem it is required to find such a sub graph in a graph whose sum of weights will be maximal. One of the possible solutions of this problem is using genetic algorithms. We use a parallel genetic algorithm for accelerating of computational process. In this version of algorithm fitness function of each individual calculating in different thread. It allows reducing running time of algorithm. Details of implementation parallel genetic algorithm for searching open pit limits are provided. Comparison with other methods and results of computational experiments provided.Keywords: open pit limits, genetics algorithms, high-performance computin

### Mean field effects in a trapped classical gas

In this article, we investigate mean field effects for a bosonic gas
harmonically trapped above the transition temperature in the collisionless
regime. We point out that those effects can play also a role in low dimensional
system. Our treatment relies on the Boltzmann equation with the inclusion of
the mean field term.
The equilibrium state is first discussed. The dispersion relation for
collective oscillations (monopole, quadrupole, dipole modes) is then derived.
In particular, our treatment gives the frequency of the monopole mode in an
isotropic and harmonic trap in the presence of mean field in all dimensions.Comment: 4 pages, no figure submitted to Phys. Rev.

### Universal physics of 2+1 particles with non-zero angular momentum

The zero-energy universal properties of scattering between a particle and a
dimer that involves an identical particle are investigated for arbitrary
scattering angular momenta. For this purpose, we derive an integral equation
that generalises the Skorniakov - Ter-Martirosian equation to the case of
non-zero angular momentum. As the mass ratio between the particles is varied,
we find various scattering resonances that can be attributed to the appearance
of universal trimers and Efimov trimers at the collisional threshold.Comment: 6 figure

### The Lieb-Liniger Model as a Limit of Dilute Bosons in Three Dimensions

We show that the Lieb-Liniger model for one-dimensional bosons with repulsive
$\delta$-function interaction can be rigorously derived via a scaling limit
from a dilute three-dimensional Bose gas with arbitrary repulsive interaction
potential of finite scattering length. For this purpose, we prove bounds on
both the eigenvalues and corresponding eigenfunctions of three-dimensional
bosons in strongly elongated traps and relate them to the corresponding
quantities in the Lieb-Liniger model. In particular, if both the scattering
length $a$ and the radius $r$ of the cylindrical trap go to zero, the
Lieb-Liniger model with coupling constant $g \sim a/r^2$ is derived. Our bounds
are uniform in $g$ in the whole parameter range $0\leq g\leq \infty$, and apply
to the Hamiltonian for three-dimensional bosons in a spectral window of size
$\sim r^{-2}$ above the ground state energy.Comment: LaTeX2e, 19 page

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