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We have investigated experimentally the finite-temperature properties of a Bose-Einstein condensed
cloud of 87Rb atoms in a harmonic trap. Focusing primarily on condensed
We have investigated experimentally the finite-temperature properties of a Bose-Einstein condensed
cloud of 87Rb atoms in a harmonic trap. Focusing primarily on condensed
fraction and expansion
energy, we measure unambiguous deviations from ideal-gas thermodynamics. Our results offer for the
first time clear evidence of the mutual interaction between the condensed and thermal components.
To probe the low-temperature region inaccessible to the usual time-of-flight technique, we use
coherent Bragg scattering as a filtering technique for the condensate. This allows us to separate
spatially the condensed and normal components in time of flight, and to measure reliably
temperatures as low as 0.2 T_c and thermal fractions as low as 10%.
Comparisons with predictions of a Hartree-Fock description of the mixed cloud provide evidence for
the limitations of the usual assumptions about mixed clouds after a time of flight expansion,
pointing out to the need for a further theoretical work. |