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CONDENSATION DE BOSE-EINSTEIN AVEC UN ÉLECTROAIMANT À NOYAU FERROMAGNÉTIQUE : STRATÉGIES DE REFROIDISSEMENT DANS DES CHAMPS MAGNÉTIQUES INTENSES

Vincent Boyer 1
1 laboratoire Charles Fabry de l'Institut d'Optique / Optique atomique
LCFIO - Laboratoire Charles Fabry de l'Institut d'Optique
Abstract : Radio-frequency evaporation of atoms in a magnetic trap is the only way to obtain Bose-Einstein Condensation that has been demonstrated for a dilute atomic gas. In order to magnetically trap, and cool a gas of rubidium 87 atoms, we designed an electromagnet which uses ferromagnetic materials and is capable of generating strong magnetic gradients with a low power consumption. Our first electromagnet had a strong magnetic field, of the order of 100 Gauss, at the centre of the trap, for which the non-linear Zeeman effect lifted the degeneracy of the radio-frequency transitions between the magnetic sublevels. We studied evaporation using a single radio-frequency in this regime and found that the non-linear Zeeman effect did not hinder the evaporation of atoms in the F = 1 hyperfine level, where we were able to observe Bose-Einstein condensation. However, in the F = 2 hyperfine level, it was impossible to condense the gas because the process of evaporation is inhibited by the lack of degeneracy for a magnetic field greater than 15 Gauss. To overcome this difficulty, we performed the cooling either by simultaneously using three different radio-frequencies to evaporate, or by sympathetic cooling of the atoms in F = 2 through thermal contact with atoms in F = 1. Both these techniques allowed condensation to be obtained for atoms in F = 2 in a relatively strong magnetic field. We have since designed and built a second electromagnet which can still generate strong gradients, but has a small magnetic field at the centre of the trap. This new generation will ease the evaporation of atoms in F = 2 and allow experiments which require a strong confinement or an anisotropic trapping potential.
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https://pastel.archives-ouvertes.fr/tel-00003491
Contributor : Philippe Bouyer <>
Submitted on : Monday, October 6, 2003 - 12:29:31 PM
Last modification on : Wednesday, October 14, 2020 - 3:41:27 AM
Long-term archiving on: : Wednesday, September 12, 2012 - 10:40:17 AM

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  • HAL Id : tel-00003491, version 1

Citation

Vincent Boyer. CONDENSATION DE BOSE-EINSTEIN AVEC UN ÉLECTROAIMANT À NOYAU FERROMAGNÉTIQUE : STRATÉGIES DE REFROIDISSEMENT DANS DES CHAMPS MAGNÉTIQUES INTENSES. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 2000. Français. ⟨tel-00003491⟩

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