Isotopes of helium

Quantum mechanics

Superfluidity

Bose–Einstein condensate

Phase (matter)

Matter wave

Superfluid film

Superfluid helium-4

Scattering

Speed of sound

Bose gas

Atomic physics

Helium

Sound (geography)

Acoustics

Roton

Acoustic wave

Quantum vortex

Physics

Second sound

Liquid helium

Condensed matter physics

Quantum

Excited state

Physical Review Letters

In superfluid systems several sound modes can be excited, such as, for example, first and second sound in liquid helium. Here, we excite running and standing waves in a uniform two-dimensional Bose gas and we characterize the propagation of sound in both the superfluid and normal regimes. In the superfluid phase, the measured speed of sound is in good agreement with the prediction of a two-fluid hydrodynamic model, and the weak damping is well explained by the scattering with thermal excitations. In the normal phase we observe a stronger damping, which we attribute to a departure from hydrodynamic behavior.Received 5 April 2018DOI:https://doi.org/10.1103/PhysRevLett.121.145301© 2018 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBose-Einstein condensatesCold atoms & matter wavesPhase transitionsSuperfluid densitySuperfluidityCondensed Matter, Materials & Applied PhysicsAtomic, Molecular & Optical

Sound Propagation in a Uniform Superfluid Two-Dimensional Bose Gas