115 research outputs found
A cesium gas strongly confined in one dimension : sideband cooling and collisional properties
We study one-dimensional sideband cooling of Cesium atoms strongly confined
in a far-detuned optical lattice. The Lamb-Dicke regime is achieved in the
lattice direction whereas the transverse confinement is much weaker. The
employed sideband cooling method, first studied by Vuletic et al.\cite{Vule98},
uses Raman transitions between Zeeman levels and produces a spin-polarized
sample. We present a detailed study of this cooling method and investigate the
role of elastic collisions in the system. We accumulate of the atoms
in the vibrational ground state of the strongly confined motion, and elastic
collisions cool the transverse motion to a temperature of K=, where is the oscillation
frequency in the strongly confined direction. The sample then approaches the
regime of a quasi-2D cold gas. We analyze the limits of this cooling method and
propose a dynamical change of the trapping potential as a mean of cooling the
atomic sample to still lower temperatures. Measurements of the rate of
thermalization between the weakly and strongly confined degrees of freedom are
compatible with the zero energy scattering resonance observed previously in
weak 3D traps. For the explored temperature range the measurements agree with
recent calculations of quasi-2D collisions\cite{Petr01}. Transparent analytical
models reproduce the expected behavior for and also for where the 2D
features are prominent.Comment: 18 pages, 12 figure
Exact nonequilibrium dynamics of finite-temperature Tonks-Girardeau gases
Describing finite-temperature nonequilibrium dynamics of interacting
many-particle systems is a notoriously challenging problem in quantum many-body
physics. Here we provide an exact solution to this problem for a system of
strongly interacting bosons in one dimension in the Tonks-Girardeau regime of
infinitely strong repulsive interactions. Using the Fredholm determinant
approach and the Bose-Fermi mapping we show how the problem can be reduced to a
single-particle basis, wherein the finite-temperature effects enter the
solution via an effective "dressing" of the single-particle wavefunctions by
the Fermi-Dirac occupation factors. We demonstrate the utility of our approach
and its computational efficiency in two nontrivial out-of-equilibrium
scenarios: collective breathing mode oscillations in a harmonic trap and
collisional dynamics in the Newton's cradle setting involving real-time
evolution in a periodic Bragg potential.Comment: Final published version in PRA style; moved Supplemental Material
into main text; 6 pages, 3 figure
Experimental evidence for the breakdown of a Hartree-Fock approach in a weakly interacting Bose gas
We study the formation of a quasi-condensate in a nearly one dimensional,
weakly interacting trapped atomic Bose gas. We show that a Hartree Fock
(mean-field) approach fails to explain the presence of the quasi-condensate in
the center of the cloud: the quasi-condensate appears through an
interaction-driven cross-over and not a saturation of the excited states.
Numerical calculations based on Bogoliubov theory give an estimate of the
cross-over density in agreement with experimental results.Comment: submitted to Phys. Rev. Letter
Preparation of spin squeezed atomic states by optical phase shift measurement
In this paper we present a state vector analysis of the generation of atomic
spin squeezing by measurement of an optical phase shift. The frequency
resolution is improved when a spin squeezed sample is used for spectroscopy in
place of an uncorrelated sample. When light is transmitted through an atomic
sample some photons will be scattered out of the incident beam, and this has a
destructive effect on the squeezing. We present quantitative studies for three
limiting cases: the case of a sample of atoms of size smaller than the optical
wavelength, the case of a large dilute sample and the case of a large dense
sample.Comment: 18 page
Limitation of the modulation method to smooth wire guide roughness
It was recently demonstrated that wire guide roughness can be suppressed by
modulating the wire currents so that the atoms experience a time-averaged
potential without roughness. We theoretically study the limitations of this
technique. At low modulation frequency, we show that the longitudinal potential
modulation produces a heating of the cloud and we compute the heating rate. We
also give a quantum derivation of the rough conservative potential associated
with the micro-motion of the atoms. At large modulation frequency, we compute
the loss rate due to non adiabatic spin flip and show it presents resonnances
at multiple modulation frequencies. These studies show that the modulation
technique works for a wide range of experimental parameters. We also give
conditions to realise radio-frequency evaporative cooling in such a modulated
trap.Comment: 11 page
Quasi 2D Bose-Einstein condensation in an optical lattice
We study the phase transition of a gas of Rb atoms to quantum degeneracy in
the combined potential of a harmonically confining magnetic trap and the
periodic potential of an optical lattice. For high optical lattice potentials
we observe a significant change in the temperature dependency of the population
of the ground state of the system. The experimental results are explained by
the subsequent formation of quasi 2D condensates in the single lattice sites.Comment: 7 pages (including 3 figures
Realizing a stable magnetic double-well potential on an atom chip
We discuss design considerations and the realization of a magnetic
double-well potential on an atom chip using current-carrying wires. Stability
requirements for the trapping potential lead to a typical size of order microns
for such a device. We also present experiments using the device to manipulate
cold, trapped atoms
Two-body momentum correlations in a weakly interacting one-dimensional Bose gas
We analyze the two-body momentum correlation function for a uniform weakly
interacting one-dimensional Bose gas. We show that the strong positive
correlation between opposite momenta, expected in a Bose-Einstein condensate
with a true long-range order, almost vanishes in a phase-fluctuating
quasicondensate where the long-range order is destroyed. Using the Luttinger
liquid approach, we derive an analytic expression for the momentum correlation
function in the quasicondensate regime, showing (i) the reduction and
broadening of the opposite-momentum correlations (compared to the singular
behavior in a true condensate) and (ii) an emergence of anticorrelations at
small momenta. We also numerically investigate the momentum correlations in the
crossover between the quasicondensate and the ideal Bose-gas regimes using a
classical field approach and show how the anticorrelations gradually disappear
in the ideal-gas limit.Comment: Final published versio
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