926 research outputs found
One-dimensional description of a Bose-Einstein condensate in a rotating closed-loop waveguide
We propose a general procedure for reducing the three-dimensional Schrodinger
equation for atoms moving along a strongly confining atomic waveguide to an
effective one-dimensional equation. This procedure is applied to the case of a
rotating closed-loop waveguide. The possibility of including mean-field atomic
interactions is presented. Application of the general theory to characterize a
new concept of atomic waveguide based on optical tweezers is finally discussed
Momentum spectroscopy of 1D phase fluctuations in Bose-Einstein condensates
We measure the axial momentum distribution of Bose-Einstein condensates with
an aspect ratio of 152 using Bragg spectroscopy. We observe the Lorentzian
momentum distribution characteristic of one-dimensional phase fluctuations. The
temperature dependence of the width of this distribution provides a
quantitative test of quasi-condensate theory. In addition, we observe a
condensate length consistent with the absence of density fluctuations, even
when phase fluctuations are large.Comment: 4 pages, 3 figures; submitted to Phys. Rev. Let
Feedback control of trapped coherent atomic ensembles
We demonstrate how to use feedback to control the internal states of trapped
coherent ensembles of two-level atoms, and to protect a superposition state
against the decoherence induced by a collective noise. Our feedback scheme is
based on weak optical measurements with negligible back-action and coherent
microwave manipulations. The efficiency of the feedback system is studied for a
simple binary noise model and characterized in terms of the trade-off between
information retrieval and destructivity from the optical probe. We also
demonstrate the correction of more general types of collective noise. This
technique can be used for the operation of atomic interferometers beyond the
standard Ramsey scheme, opening the way towards improved atomic sensors.Comment: 9 pages, 6 figure
Understanding the production of dual BEC with sympathetic cooling
We show, both experimentally and theoretically, that sympathetic cooling of
Rb atoms in the state by evaporatively cooled atoms in the
state can be precisely controlled to produce dual or single
condensate in either state. We also study the thermalization rate between two
species. Our model renders a quantitative account of the observed role of the
overlap between the two clouds and points out that sympathetic cooling becomes
inefficient when the masses are very different. Our calculation also yields an
analytical expression of the thermalization rate for a single species.Comment: 3 figure
Momentum Spectroscopy of Phase Fluctuations of an Elongated Bose-Einstein Condensate
We have measured the momentum distribution of an elongated BEC (aspect ratio
of 152), for temperatures below the critical temperature. The corresponding
coherence length is significantly smaller than the condensate length in a wide
range of temperature, in quantitative agreement with theoretical predictions.
The Lorentzian shape of the momentum spectrum supports the image of a phase
fluctuating quasicondensate.Comment: Proceedings of the International Conference on Laser Spectroscopy
(ICOLS 03), Cairns, Australia, july 200
The critical temperature of a trapped, weakly interacting Bose gas
We report on measurements of the critical temperature of a harmonically
trapped, weakly interacting Bose gas as a function of atom number. Our results
exclude ideal-gas behavior by more than two standard deviations, and agree
quantitatively with mean-field theory. At our level of sensitivity, we find no
additional shift due to critical fluctuations. In the course of this
measurement, the onset of hydrodynamic expansion in the thermal component has
been observed. Our thermometry method takes this feature into account.Comment: version 2, 20 octobre 200
One-dimensional behavior of elongated Bose-Einstein condensates
We study the properties of elongated Bose-Einstein condensates. First, we
show that the dimensions of the condensate after expansion differs from the 3D
Thomas-Fermi regime. We also study the coherence length of such elongated
condensates.Comment: proceeding of Quantum Gases in Low Dimension, Les Houches 2003, 8
pages, 5 figure
Spin-squeezing and Dicke state preparation by heterodyne measurement
We investigate the quantum non-demolition (QND) measurement of an atomic
population based on a heterodyne detection and show that the induced
back-action allows to prepare both spin-squeezed and Dicke states. We use a
wavevector formalism to describe the stochastic process of the measurement and
the associated atomic evolution. Analytical formulas of the atomic distribution
momenta are derived in the weak coupling regime both for short and long time
behavior, and they are in good agreement with those obtained by a Monte-Carlo
simulation. The experimental implementation of the proposed heterodyne
detection scheme is discussed. The role played in the squeezing process by the
spontaneous emission is considered
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