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

authored by

Daniel K. Hoffmann, Vijay Pal Singh, Thomas Paintner, Manuel Jäger, Wolfgang Limmer, Ludwig Mathey, Johannes Hecker Denschlag

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.

Organisation(s)

Institute of Theoretical Physics
QuantumFrontiers

External Organisation(s)

Ulm University
Universität Hamburg

Type

Article

Journal

Nature Communications

Volume

12

ISSN

2041-1723

Publication date

06.12.2021

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Chemistry(all), Biochemistry, Genetics and Molecular Biology(all), Physics and Astronomy(all)

Electronic version(s)

https://doi.org/10.1038/s41467-021-27149-z (Access: Open)