Year: 2022
Type: article
Abstract: The two-fluid model is fundamental for the description of superfluidity. In the nearly incompressible liquid regime, it successfully describes first and second sound, corresponding, respectively, to density and entropy waves, in both liquid helium and unitary Fermi gases. Here, we study the two sounds in the opposite regime of a highly compressible fluid, using an ultracold ^{39}K Bose gas in a three-dimensional box trap. We excite the longest-wavelength mode of our homogeneous gas, and observe two distinct resonant oscillations below the critical temperature, of which only one persists above it. In a microscopic mode-structure analysis, we find agreement with the hydrodynamic theory, where first and second sound involve density oscillations dominated by, respectively, thermal and condensed atoms. Varying the interaction strength, we explore the crossover from hydrodynamic to collisionless behavior in a normal gas.
Source: Physical Review Letters
Institutions: University of Cambridge, University of Oxford
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Awards: Phase Transitions and Non-equilibrium Dynamics in Homogeneous Quantum Gases, NAQUAS: Non-equilibrium dynamics in Atomic systems for QUAntum Simulation., G2887104535, Designing Out-of-Equilibrium Many-Body Quantum Systems, Non-equilibrium dynamics in Atomic systems fo QUantum Simulation, G8753739443
OpenAlex ID: W4225757813