TY - JOUR

T1 - Second sound in the crossover from the Bose-Einstein condensate to the Bardeen-Cooper-Schrieffer superfluid

AU - Hoffmann, Daniel K.

AU - Singh, Vijay Pal

AU - Paintner, Thomas

AU - Jäger, Manuel

AU - Limmer, Wolfgang

AU - Mathey, Ludwig

AU - Hecker Denschlag, Johannes

N1 - Funding Information: The authors thank Benjamin Deissler and Wladimir Schoch for the support in the stages of the experiment. In addition, the authors thank Sandro Stringari, Hui Hu, Xia-Ji Liu, and Jia Wang for encouraging and illuminating discussions. V.P.S. and L.M. acknowledge the support from the DFG in the framework of SFB 925 and the excellence clusters ‘The Hamburg Centre for Ultrafast Imaging’-EXC 1074 - project ID 194651731, ‘Advanced Imaging of Matter’ - EXC 2056 - project ID 390715994 and Germany’s Excellence Strategy, EXC-2123 QuantumFrontiers, Project No. 390837967. D.K.H., T.P., M.J., W.L., and J.H.D. acknowledge support from the Deutsche Forschungsgemeinschaft within SFB/TRR 21 (project part B4) and project LI988/6-1, the Baden-Württemberg Foundation, and the Center for Integrated Quantum Science and Technology (IQST).

PY - 2021/12/6

Y1 - 2021/12/6

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85120880711&partnerID=8YFLogxK

U2 - 10.1038/s41467-021-27149-z

DO - 10.1038/s41467-021-27149-z

M3 - Article

AN - SCOPUS:85120880711

VL - 12

JO - Nature Communications

JF - Nature Communications

SN - 2041-1723

IS - 1

M1 - 7074

ER -