Microcanonical and Canonical Fluctuations in Bose-Einstein Condensates -- Fock state sampling approach

• URL: http://arxiv.org/abs/2207.04536v1
• Date: Sun, 10 Jul 2022 20:54:30 GMT
• Title: Microcanonical and Canonical Fluctuations in Bose-Einstein Condensates -- Fock state sampling approach
• Authors: Maciej Bart{\l}omiej Kruk, Dawid Hryniuk, Mick Kristensen, Toke Vibel, Krzysztof Paw{\l}owski, Jan Arlt, Kazimierz Rz\k{a}\.zewski
• Abstract summary: The fluctuations of the atom number between a Bose-Einstein condensate and the surrounding thermal gas have been the subject of a long standing theoretical debate. Here we introduce the so-called Fock state sampling method to solve this classic problem of current experimental interest for weakly interacting gases. A suppression of the predicted peak fluctuations is observed when using a microcanonical with respect to a canonical ensemble. Moreover, interactions lead to a shift of the temperature of peak fluctuations for harmonically trapped gases.
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• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: The fluctuations of the atom number between a Bose-Einstein condensate and the surrounding thermal gas have been the subject of a long standing theoretical debate. This discussion is centered around the appropriate thermodynamic ensemble to be used for theoretical predictions and the effect of interactions on the observed fluctuations. Here we introduce the so-called Fock state sampling method to solve this classic problem of current experimental interest for weakly interacting gases. A suppression of the predicted peak fluctuations is observed when using a microcanonical with respect to a canonical ensemble. Moreover, interactions lead to a shift of the temperature of peak fluctuations for harmonically trapped gases. The absolute size of the fluctuations furthermore depends on the total number of atoms and the aspect ratio of the trapping potential. Due to the interplay of these effect, there is no universal suppression or enhancement of fluctuations.

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