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Condensation de Bose-Einstein de l'hélium métastable

Abstract : We present in this thesis the experimental
achievement of Bose-Einstein condensation of polarized metastable
$2^3S_1$ helium atoms. First, we summarize the theoretical
predictions on elastic and inelastic collision rates between
polarized metastable helium atoms. Our hope of reaching
Bose-Einstein condensation of metastable helium relied on those
promising predictions. We then decribe the experimental set-up we
have built. The technique we use consists in pre-cooling a sample
of gar in a magneto-optical trap which is loaded from an intense
and Zeeman slowed atomic beam. The density in the magneto-optical
trap is limited by very high inelastic collision rates, which we
studied for a wide range of trapping parameters. The cold gas is
then transferred in a magnetostatic trap, where it is further
cooled by evaporative cooling, down to the threshold of quantum
degeneracy. We measured lifetimes of the atoms in the
magnetostatic trap of the order of one minute, which shows that
inelastic collisions are suppressed by two orders of magnitude
when the atoms are polarized. Using a purely optical detection
scheme, based on the absorption of a resonant laser beam which
travels through the cloud, we have been able to demonstrate
Bose-Einstein condensation. Finally, from the measurements of the
number of atoms and the size of the condensate, we have deduced an
estimate for the scattering length, $a=(16\pm8)$ nm.
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Contributor : Franck Pereira dos Santos <>
Submitted on : Tuesday, January 14, 2003 - 1:51:28 PM
Last modification on : Tuesday, December 8, 2020 - 3:37:49 AM
Long-term archiving on: : Friday, April 2, 2010 - 6:44:28 PM


  • HAL Id : tel-00002267, version 1


Franck Pereira dos Santos. Condensation de Bose-Einstein de l'hélium métastable. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 2002. Français. ⟨tel-00002267⟩



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