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Accumulation and thermalization of cold atoms in a finite-depth magnetic trap

R. Chicireanu, Q. Beaufils, A. Pouderous, B. Laburthe-Tolra, E. Marechal, J. V. Porto, L. Vernac, J. C. Keller, O. Gorceix

physics.atom-pharXiv:physics/0612133

Abstract

We experimentally and theoretically study the continuous accumulation of cold atoms from a magneto-optical trap (MOT) into a finite depth trap, consisting in a magnetic quadrupole trap dressed by a radiofrequency (RF) field. Chromium atoms (52 isotope) in a MOT are continuously optically pumped by the MOT lasers to metastable dark states. In presence of a RF field, the temperature of the metastable atoms that remain magnetically trapped can be as low as 25 microK, with a density of 1017 atoms.m-3, resulting in an increase of the phase-space density, still limited to 7.10-6 by inelastic collisions. To investigate the thermalization issues in the truncated trap, we measure the free evaporation rate in the RF-truncated magnetic trap, and deduce the average elastic cross section for atoms in the 5D4 metastable states, equal to 7.0 10-16m2.

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