Hannover 2020 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 18: Ultracold atoms, ions, and BEC III (joint session A/Q)
Q 18.6: Talk
Tuesday, March 10, 2020, 15:30–15:45, f303
Observation of First and Second Sound in a Homogeneous Bose Gas — •Timon Hilker1, Lena Dogra1, Jake Glidden1, Christoph Eigen1, Robert Smith1,2 und Zoran Hadzibabic1 — 1Cavendish Laboratory, University of Cambridge, UK — 2Clarendon Laboratory, University of Oxford, UK
The existence of two distinct sound velocities is one of the hallmarks of superfluids. In a compressible quantum gas both modes couple to density, which allows us to observe, for the first time, both sound velocities in a moderately interacting ultracold Bose gas. Using a magnetic field gradient, we excite centre-of-mass oscillations of a homogeneous K-39 Bose gas in a three-dimensional box trap, revealing two distinct resonant oscillations. In a microscopic analysis of the mode structure, we find quantitative agreement for the first (and second) sound with the hydrodynamic description of Landau’s two-fluid model in terms of in-phase (out-of-phase) oscillations dominated by the thermal (BEC) atoms. We study the speed and the damping of both modes for various interaction strengths and temperatures and investigate in particular the crossover from collisionless to hydrodynamic behaviour above TC.