Second sound in the crossover from the Bose-Einstein condensate to the Bardeen-Cooper-Schrieffer superfluid

Daniel K. Hoffmann, Vijay Pal Singh, Thomas Paintner, Manuel Jäger, Wolfgang Limmer, Ludwig Mathey and Johannes Hecker Denschlag ()
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Daniel K. Hoffmann: Universität Ulm
Vijay Pal Singh: Leibniz Universität Hannover
Thomas Paintner: Universität Ulm
Manuel Jäger: Universität Ulm
Wolfgang Limmer: Universität Ulm
Ludwig Mathey: Universität Hamburg
Johannes Hecker Denschlag: Universität Ulm

Nature Communications, 2021, vol. 12, issue 1, 1-6

Abstract: Abstract Second sound is an entropy wave which propagates in the superfluid component of a quantum liquid. Because it is an entropy wave, it probes the thermodynamic properties of the quantum liquid. Here, we study second sound propagation for a large range of interaction strengths within the crossover between a Bose-Einstein condensate (BEC) and the Bardeen-Cooper-Schrieffer (BCS) superfluid, extending previous work at unitarity. In particular, we investigate the strongly-interacting regime where currently theoretical predictions only exist in terms of an interpolation in the crossover. Working with a quantum gas of ultracold fermionic 6Li atoms with tunable interactions, we show that the second sound speed varies only slightly in the crossover regime. By varying the excitation procedure, we gain deeper insight on sound propagation. We compare our measurement results with classical-field simulations, which help with the interpretation of our experiments.

Date: 2021
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DOI: 10.1038/s41467-021-27149-z

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