334 research outputs found
Asymptotic behaviour of a rapidly rotating fluid with random stationary surface stress
The goal of this paper is to describe in mathematical terms the effect on the
ocean circulation of a random stationary wind stress at the surface of the
ocean. In order to avoid singular behaviour, non-resonance hypotheses are
introduced, which ensure that the time frequencies of the wind-stress are
different from that of the Earth rotation. We prove a convergence result for a
three-dimensional Navier-Stokes-Coriolis system in a bounded domain, in the
asymptotic of fast rotation and vanishing vertical viscosity, and we exhibit
some random and stationary boundary layer profiles. At last, an average
equation is derived for the limit system in the case of the non-resonant torus.Comment: 45 page
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
Experimental tests of Bell's inequalities: A first-hand account by Alain Aspect
On 04 October 2022, the Royal Swedish Academy of Sciences announced that the
Nobel Prize for Physics of 2022 was awarded jointly to Alain Aspect, John
Clauser, and Anton Zeilinger "for experiments with entangled photons,
establishing the violation of Bell inequalities and pioneering quantum
information science". What follows is an interview of Alain Aspect, conducted
by Bill Phillips and Jean Dalibard, during the summer of 2022, and completed
not long before the announcement of the Nobel Prize. The subject matter is
essentially that for which the Nobel Prize was awarded.Comment: Accepted for publication in the topical issue "Quantum Optics of
Light and Matter" of EPJD, Edts. D. Cl\'ement, P. Grangier and J. Thywisse
Reconstruction of Rb-Rb inter-atomic potential from ultracold Bose-gas collision
Scattering phase shifts obtained from 87Rb Bose-gas collision experiments are
used to reconstruct effective potentials resulting, self-consistently, in the
same scattering events observed in the experiments at a particular energy. We
have found that the interaction strength close to the origin suddenly changes
from repulsion to attraction when the collision energy crosses, from below, the
l=2 shape resonance position at E = 275 mikroK. This observation may be
utilized in outlining future Bose-gas collision experiments.Comment: 4 pages, 4 figure
High-Resolution Magnetometry with a Spinor Bose-Einstein Condensate
We demonstrate a precision magnetic microscope based on direct imaging of the
Larmor precession of a Rb spinor Bose-Einstein condensate. This
magnetometer attains a field sensitivity of 8.3 pT/Hz over a
measurement area of 120 m, an improvement over the low-frequency field
sensitivity of modern SQUID magnetometers. The corresponding atom shot-noise
limited sensitivity is estimated to be 0.15 pT/Hz for unity duty cycle
measurement. The achieved phase sensitivity is close to the atom shot-noise
limit suggesting possibilities of spatially resolved spin-squeezed
magnetometry. This magnetometer marks a significant application of degenerate
atomic gases to metrology
Self-trapping of impurities in Bose-Einstein condensates: Strong attractive and repulsive coupling
We study the interaction-induced localization -- the so-called self-trapping
-- of a neutral impurity atom immersed in a homogeneous Bose-Einstein
condensate (BEC). Based on a Hartree description of the BEC we show that --
unlike repulsive impurities -- attractive impurities have a singular ground
state in 3d and shrink to a point-like state in 2d as the coupling approaches a
critical value. Moreover, we find that the density of the BEC increases
markedly in the vicinity of attractive impurities in 1d and 2d, which strongly
enhances inelastic collisions between atoms in the BEC. These collisions result
in a loss of BEC atoms and possibly of the localized impurity itself.Comment: 7 pages, 5 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
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