arXiv:0912.3629 · Journal of Physics B Atomic Molecular and Optical Physics

Free expansion of a Bose–Einstein condensate in the presence of a thermal cloud

Krzysztof Gawryluk, Mirosław Brewczyk, Mariusz Gajda, Kazimierz Rza̧żewski

Published May 5, 2010• 5 citations

Abstract

We investigate numerically the free-fall expansion of a 87 Rb atom condensate at nonzero temperatures. The classical field approximation is used to separate the condensate and the thermal cloud during the expansion. We calculate the radial and axial widths of the expanding condensate and find clear evidence that the thermal component changes the dynamics of the condensate. Our results are contrasted with the experimental data.

DOI: 10.1088/0953-4075/43/10/105303

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arXiv:0912.3629 · Journal of Physics B Atomic Molecular and Optical Physics

Free expansion of a Bose–Einstein condensate in the presence of a thermal cloud

Krzysztof Gawryluk, Mirosław Brewczyk, Mariusz Gajda, Kazimierz Rza̧żewski

Published May 5, 2010• 5 citations

arXiv HTML PDF

Abstract

DOI: 10.1088/0953-4075/43/10/105303

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We have investigated experimentally the finite-temperature properties of a Bose-Einstein condensed cloud of

{}^{87}\mathrm{Rb}

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

0.2{T}_{c}^{0}

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.