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arXiv:0811.1672 · Journal of Physics B Atomic Molecular and Optical Physics

Free-fall expansion of finite-temperature Bose–Einstein condensed gas in the non-Thomas–Fermi regime

M. Zawada, R Abdoul, Jan Chwedeńczuk, R. Gartman, J. Szczepkowski, Łukasz Tracewski, Marcin Witkowski, Wojciech Gawlik

Published Dec 1, 2008• 14 citations
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Abstract

We report on our study of the free-fall expansion of a finite-temperature Bose-Einstein condensed cloud of 87Rb. The experiments are performed with a variable total number of atoms while keeping constant the number of atoms in the condensate. The results provide evidence that the BEC dynamics depends on the interaction with thermal fraction. In particular, they provide experimental evidence that thermal cloud compresses the condensate.

DOI
10.1088/0953-4075/41/24/241001

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We have investigated experimentally the finite-temperature properties of a Bose-Einstein condensed cloud of 87Rb{}^{87}\mathrm{Rb}87Rb atoms in a harmonic trap. Focusing primarily on condensed fraction and expansion energy, we measure unambiguous deviations from ideal-gas thermodynamics and obtain good agreement with a Hartree-Fock description of the mixed cloud. Our results offer clear evidence of the mutual interaction between the condensed and thermal components. To probe the low-temperature region unaccessible 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 0.2Tc00.2{T}_{c}^{0}0.2Tc0​ and thermal fractions as low as 10%. Finally, we observe evidence for the limitations of the usual image analysis procedure, pointing out to the need for a more elaborate model of the expansion of the mixed cloud.