426 research outputs found
Spontaneous excitation of an accelerated hydrogen atom coupled with electromagnetic vacuum fluctuations
We consider a multilevel hydrogen atom in interaction with the quantum
electromagnetic field and separately calculate the contributions of the vacuum
fluctuation and radiation reaction to the rate of change of the mean atomic
energy of the atom for uniform acceleration. It is found that the acceleration
disturbs the vacuum fluctuations in such a way that the delicate balance
between the contributions of vacuum fluctuation and radiation reaction that
exists for inertial atoms is broken, so that the transitions to higher-lying
states from ground state are possible even in vacuum. In contrast to the case
of an atom interacting with a scalar field, the contributions of both
electromagnetic vacuum fluctuations and radiation reaction to the spontaneous
emission rate are affected by the acceleration, and furthermore the
contribution of the vacuum fluctuations contains a non-thermal
acceleration-dependent correction, which is possibly observable.Comment: 8 pages, Revtex4, accepted for publication in PR
Spontaneous absorption of an accelerated hydrogen atom near a conducting plane in vacuum
We study, in the multipolar coupling scheme, a uniformly accelerated
multilevel hydrogen atom in interaction with the quantum electromagnetic field
near a conducting boundary and separately calculate the contributions of the
vacuum fluctuation and radiation reaction to the rate of change of the mean
atomic energy. It is found that the perfect balance between the contributions
of vacuum fluctuations and radiation reaction that ensures the stability of
ground-state atoms is disturbed, making spontaneous transition of ground-state
atoms to excited states possible in vacuum with a conducting boundary. The
boundary-induced contribution is effectively a nonthermal correction, which
enhances or weakens the nonthermal effect already present in the unbounded
case, thus possibly making the effect easier to observe. An interesting feature
worth being noted is that the nonthermal corrections may vanish for atoms on
some particular trajectories.Comment: 19 pages, no figures, Revtex
Loading of a cold atomic beam into a magnetic guide
We demonstrate experimentally the continuous and pulsed loading of a slow and
cold atomic beam into a magnetic guide. The slow beam is produced using a vapor
loaded laser trap, which ensures two-dimensional magneto-optical trapping, as
well as cooling by a moving molasses along the third direction. It provides a
continuous flux larger than atoms/s with an adjustable mean velocity
ranging from 0.3 to 3 m/s, and with longitudinal and transverse temperatures
smaller than K. Up to atoms/s are injected into the magnetic
guide and subsequently guided over a distance of 40 cm.Comment: 10 pages, 10 figures, accepted for publication to EPJ
Three-body decay of a rubidium Bose-Einstein condensate
We have measured the three-body decay of a Bose-Einstein condensate of
rubidium (Rb) atoms prepared in the doubly polarized ground state
. Our data are taken for a peak atomic density in the condensate
varying between cm at initial time and cm, 16 seconds later. Taking into account the influence of the
uncondensed atoms onto the decay of the condensate, we deduce a rate constant
for condensed atoms cms. For
these densities we did not find a significant contribution of two-body
processes such as spin dipole relaxation.Comment: 14 pages, 4 figure
Practical scheme for a light-induced gauge field in an atomic Bose gas
We propose a scheme to generate an Abelian gauge field in an atomic gas using
two crossed laser beams. If the internal atomic state follows adiabatically the
eigenstates of the atom-laser interaction, Berry's phase gives rise to a vector
potential that can nucleate vortices in a Bose gas. The present scheme operates
even for a large detuning with respect to the atomic resonance, making it
applicable to alkali-metal atoms without significant heating due to spontaneous
emission. We test the validity of the adiabatic approximation by integrating
the set of coupled Gross-Pitaevskii equations associated with the various
internal atomic states, and we show that the steady state of the interacting
gas indeed exhibits a vortex lattice, as expected from the adiabatic gauge
field.Comment: 4 pages, 3 figure
Evaporative Cooling of a Guided Rubidium Atomic Beam
We report on our recent progress in the manipulation and cooling of a
magnetically guided, high flux beam of atoms. Typically
atoms per second propagate in a magnetic guide providing a
transverse gradient of 800 G/cm, with a temperature K, at an
initial velocity of 90 cm/s. The atoms are subsequently slowed down to cm/s using an upward slope. The relatively high collision rate (5 s)
allows us to start forced evaporative cooling of the beam, leading to a
reduction of the beam temperature by a factor of ~4, and a ten-fold increase of
the on-axis phase-space density.Comment: 10 pages, 8 figure
Homogenization of linear transport equations in a stationary ergodic setting
We study the homogenization of a linear kinetic equation which models the
evolution of the density of charged particles submitted to a highly oscillating
electric field. The electric field and the initial density are assumed to be
random and stationary. We identify the asymptotic microscopic and macroscopic
profiles of the density, and we derive formulas for these profiles when the
space dimension is equal to one.Comment: 24 page
Dynamics of a single vortex line in a Bose-Einstein condensate
We study experimentally the line of a single quantized vortex in a rotating
prolate Bose-Einstein condensate confined by a harmonic potential. In agreement
with predictions, we find that the vortex line is in most cases curved at the
ends. We monitor the vortex line leaving the condensate. Its length is measured
as a function of time and temperature. For a low temperature, the survival time
can be as large as 10 seconds. The length of the line and its deviation from
the center of the trap are related to the angular momentum per particle along
the condensate axis.Comment: 4 pages, 4 figures, submitted to PR
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