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Développement d'un piège atomique lumineux et magnétique : Etude du régime de collisions ; Perspectives pour la condensation de Bose-Einstein du césium

Abstract : This thesis work is part of a research effort made since 1996 in the field of the Bose-Einstein condensation (BEC) of cesium atoms. The first attempts carried out in 1996 using magnetic trapping and rf evaporative cooling failed because of the unusually high inelastic collision rates encountered by this atom. The solution consists in trapping the atoms in the lowest energy state. This can be performed in an optical trap or in a hybrid trap, both magnetic and optical. In October 2002, R. Grimm's group demonstrated cesium BEC with an optical trap. The solution discussed in this work combines a vertical magnetic trap and a transversal optical trap created by a laser beam Nd:YAG. The experimental apparatus has been completed, and the hybrid trap has been partly characterized. The 4 s lifetime is the current limitation of the trap and is discussed on the basis of some assumptions. The collisionnal dynamics are analysed from the atomic cloud oscillations while varying the magnetic field. Actually, the elastic collision rate of the atoms inside the trap is low, because of a low density. In the same time, numerical calculations have been performed. This theoretical work has two parts. The first one consists in a Monte-Carlo simulation of one dimension evaporative cooling in our set-up.These results figure out the direction we should follow towards BEC. The second part relies on the application of an asymptotic method for studying collisions in a magnetic field between two atoms in their ground state f=3, mf=3. This study motivated by the existence of a Feshbach resonance for this state allows the interpretation of a photoassociation experiment. In this experiment, the tunability of the scattering length with respect of the magnetic field has been observed.
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Submitted on : Wednesday, April 28, 2004 - 7:56:10 PM
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Nathalie Hoang. Développement d'un piège atomique lumineux et magnétique : Etude du régime de collisions ; Perspectives pour la condensation de Bose-Einstein du césium. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 2003. Français. ⟨tel-00005990⟩

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