Fluctuational susceptibility of ultracold bosons in the vicinity of condensation

Abstract

We study the behaviour of ultracold bosonic gas in the critical region above the Bose-Einstein condensation in the presence of an artificial magnetic field, $B_{\mathrm{art}}$. We show that the condensate fluctuations above the critical temperature $T_c$ cause the fluctuational susceptibility, ${\chi }_{\mathrm{fl}}$, of a uniform gas to have a stronger power-law divergence than in an analogous superconducting system. Measuring such a divergence opens new ways of exploring critical properties of the ultracold gas and an opportunity of an accurate determination of $T_c$. We describe a method of measuring ${\chi }_{\mathrm{fl}}$ which requires a constant gradient in $B_{\mathrm{art}}$ and suggest a way of creating such a field in experiment.

5 pages, 3 figures, 5 pages of Supplement; the text is rewritten and rearranged, and the figures are modified

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