Hoffmann Daniel K, Singh Vijay Pal, Paintner Thomas, Jäger Manuel, Limmer Wolfgang, Mathey Ludwig, Hecker Denschlag Johannes
Institut für Quantenmaterie and Center for Integrated Quantum Science and Technology (IQST), Universität Ulm, D-89069, Ulm, Germany.
Institut für Theoretische Physik, Leibniz Universität Hannover, Appelstraße 2, 30167, Hannover, Germany.
Nat Commun. 2021 Dec 6;12(1):7074. doi: 10.1038/s41467-021-27149-z.
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 Li 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.
第二声是一种在量子液体的超流组分中传播的熵波。由于它是一种熵波，所以它能探测量子液体的热力学性质。在此，我们研究了玻色 - 爱因斯坦凝聚（BEC）与巴丁 - 库珀 - 施里弗（BCS）超流体之间交叉区域内大范围相互作用强度下的第二声传播，扩展了之前关于幺正性的工作。特别地，我们研究了强相互作用 regime，目前理论预测仅以交叉区域内的插值形式存在。我们使用具有可调相互作用的超冷费米锂原子量子气体进行研究，结果表明第二声速在交叉区域内变化很小。通过改变激发过程，我们对声传播有了更深入的了解。我们将测量结果与经典场模拟进行比较，这有助于对我们的实验进行解释。
