Experimental study of the thermodynamics of an interacting, trapped Bose-Einstein condensed gas
Résumé
We have investigated experimentally the finite-temperatureproperties of a Bose-Einstein condensed cloud of $^{87}$Rb atomsin a harmonic trap. Focusing primarily on condensed fraction andexpansion energy, we measure unambiguous deviations from ideal-gasthermodynamics, and obtain good agreement with a Hartree-Fockdescription of the mixed cloud. Our results offer for the firsttime clear evidence of the mutual interaction between thecondensed and thermal components. To probe the low-temperatureregion unaccessible to the usual time-of-flight technique, we usecoherent Bragg scattering as a filtering technique for thecondensate. This allows us to separate spatially the condensedand normal components in time of flight, and to measure reliablytemperatures as low as $0.2~T_{\\rm c}^0$ and thermal fractions aslow as 10\\%.Finally, we observe evidence for thelimitations of the usual image analysis procedure, pointing out tothe need for a more elaborate model of the expansion of the mixedcloud.
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