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Dynamique collisionnelle des gaz d'alcalins lourds : du refroidissement évaporatif à la condensation de Bose-Einstein

Abstract : One can reach the quantum degeneracy regime for a dilute alkali
gas using evaporative cooling in a magnetic trap. This technique
relies on elastic collisions between cold atoms. In order to
employ this method with cesium atoms, we have studied the elastic
cross section. We report a strong temperature dependance of the
s-wave cross section. This behavior is explained by a zero energy
resonance. In addition, we observe strong limitations on the gain
in phase-space density due to inelastic collisions. The increase
of spatial density as a result of evaporative cooling enhances the
probability of inelastic collisions. The inelastic rate for the
stretched state and the lower hyperfine level of cesium was found
to be huge in comparison with other alkalis. In both cases, the
temperature dependance of these inelastic rates was investigated.
For the lowest hyperfine level, a run-away evaporation has been
observed, and a gain of more than five orders of magnitude in
phase space density is reported. Nevertheless, the degeneracy
regime was not reached because of depolarizing collisions. For the
lowest hyperfine level, a strong dependance on the magnetic field
was observed. The experiment was adapted for rubidium 87, and
Bose-Einstein condensation was achieved. The characterization of
the condensate and the measurement of its lifetime are reported at
the end of the thesis.
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https://tel.archives-ouvertes.fr/tel-00001134
Contributor : David Guery-Odelin <>
Submitted on : Friday, February 22, 2002 - 5:54:07 PM
Last modification on : Thursday, December 10, 2020 - 12:37:10 PM
Long-term archiving on: : Friday, April 2, 2010 - 7:52:01 PM

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  • HAL Id : tel-00001134, version 1

Citation

David Guéry-Odelin. Dynamique collisionnelle des gaz d'alcalins lourds : du refroidissement évaporatif à la condensation de Bose-Einstein. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 1998. Français. ⟨tel-00001134⟩

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