973 research outputs found
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
Bose-Einstein condensation of metastable helium: some experimental aspects
We describe our recent realization of BEC using metastable helium. All
detection is done with a micruchannel plate which detects the metastables or
ions coming from the trapped atom cloud. This discussion emphasizes some of the
diagnostic experiments which were necessary to quantitatively analyse our
results.Comment: 5 pages, 3 figure
Hanbury Brown and Twiss correlations in atoms scattered from colliding condensates
Low energy elastic scattering between clouds of Bose condensed atoms leads to
the well known s-wave halo with atoms emerging in all directions from the
collision zone. In this paper we discuss the emergence of Hanbury Brown and
Twiss coincidences between atoms scattered in nearly parallel directions. We
develop a simple model that explains the observations in terms of an
interference involving two pairs of atoms each associated with the elementary s
wave scattering process.Comment: Minor corrections. reference update
Effect of trap symmetry and atom-atom interactions on a trapped atom interferometer with internal state labelling
In this paper, we study the dynamics of a trapped atom interferometer with
internal state labelling in the presence of interactions. We consider two
situations: an atomic clock in which the internal states remain superposed, and
an inertial sensor configuration in which they are separated. From the average
spin evolution, we deduce the fringe contrast and the phase-shift. In the clock
configuration, we recover the well-known identical spin rotation effect (ISRE)
which can significantly increase the spin coherence time. We also find that the
magnitude of the effect depends on the trap geometry in a way that is
consistent with our recent experimental results in a clock configuration [M.
Dupont-Nivet, and al., New J. Phys., 20, 043051 (2018)], where ISRE was not
observed. In the case of an inertial sensor, we show that despite the spatial
separation it is still possible to increase the coherence time by using mean
field interactions to counteract asymmetries of the trapping potential.Comment: 18 pages, 5 figure
Hanbury Brown Twiss effect for ultracold quantum gases
We have studied 2-body correlations of atoms in an expanding cloud above and
below the Bose-Einstein condensation threshold. The observed correlation
function for a thermal cloud shows a bunching behavior, while the correlation
is flat for a coherent sample. These quantum correlations are the atomic
analogue of the Hanbury Brown Twiss effect. We observe the effect in three
dimensions and study its dependence on cloud size.Comment: Figure 1 availabl
Fast production of Bose-Einstein condensates of metastable Helium
We report on the Bose-Einstein condensation of metastable Helium-4 atoms
using a hybrid approach, consisting of a magnetic quadrupole and a crossed
optical dipole trap. In our setup we cross the phase transition with 2x10^6
atoms, and we obtain pure condensates of 5x10^5 atoms in the optical trap. This
novel approach to cooling Helium-4 provides enhanced cycle stability, large
optical access to the atoms and results in production of a condensate every 6
seconds - a factor 3 faster than the state-of-the-art. This speed-up will
dramatically reduce the data acquisition time needed for the measurement of
many particle correlations, made possible by the ability of metastable Helium
to be detected individually
Thermal counting statistics in an atomic two-mode squeezed vacuum state
We measure the population distribution in one of the atomic twin beams
generated by four-wave mixing in an optical lattice.
Although the produced two-mode squeezed vacuum state is pure, each individual
mode is described as a statistical mixture.
We confirm the prediction that the particle number follows an exponential
distribution when only one spatio-temporal mode is selected.
We also show that this distribution accounts well for the contrast of an
atomic Hong--Ou--Mandel experiment.
These experiments constitute an important validation of our twin beam source
in view of a future test of a Bell inequalities.Comment: SciPost submissio
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