Réalisation d'un condensat de Bose-Einstein d'atomes d'hélium métastable

Alice Robert 1
1 laboratoire Charles Fabry de l'Institut d'Optique / Optique atomique
LCFIO - Laboratoire Charles Fabry de l'Institut d'Optique
Abstract : This thesis presents the first experimental realization of a Bose-Einstein condensate of metastable helium. The 20 eV internaI energy of metastable helium atoms enables the use of an electronic detection system of atoms, very fast and efficient. This thesis describes the followed experimental way to achieve condensation, starting from the loading of the pre-cooled atomic cloud in the magnetic trap. Studies of the trapping magnetic field, especially of the field decay after switching off the trap, are realized in situ by directly probing the atoms. Sorne spectroscopy measurements of the magnetic trap are also performed to test equilibrium of atoms in the trap. To next start an efficient evaporative cooling, the elastic collision rate between trapped atoms must be large enough. Since we had no sufficient experimental data to know the value of this collision rate, we have performed sorne thermalization measurements on the atomic sample. It consists in placing the trapped cloud out of equilibrium, and then in monitoring relaxation dynamics towards a new equilibrium, reached thanks to collisions between trapped atoms. Modelization of these experiments enables us to infer the elastic collision rate from experimental results. The deduced value encouraged us to carry on with evaporative cooling of the atomic cloud, leading eventually to the formation of a Bose-Einstein condensate. The shape of the observed experimental signaIs, influenced by the cutoff of the magnetic fields, is explained. Exploitation of these signaIs allows to deduce a value for the scattering length. The observation of the ion signal produced by the condensate represents a non-destructive method of monitoring the condensate, from which its formation kinetics can be deduced.
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Submitted on : Wednesday, March 25, 2009 - 1:59:29 PM
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  • HAL Id : tel-00370797, version 1

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Alice Robert. Réalisation d'un condensat de Bose-Einstein d'atomes d'hélium métastable. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 2001. Français. ⟨tel-00370797⟩

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