PerspectiveQuantum Gases

Quantum-limited sound attenuation

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Science  04 Dec 2020:
Vol. 370, Issue 6521, pp. 1162-1163
DOI: 10.1126/science.abb6155

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Summary

Ordinary sound is a harmonic oscillation in the density, temperature, and velocity of air. Sound intensity decreases because of the spreading of the sound wave, but ultimately, sound attenuation is due to the diffusion of momentum and energy from the crest to the trough of the wave. This effect can be characterized in terms of the diffusivity D of sound. In air, there is a very large separation of scales between the shortest scale, the distance between molecules; an intermediate scale, the mean free path of air molecules, which controls the diffusivity; and the longest scale, the wavelength of the sound mode. On page 1222 of this issue, Patel et al. (1) study a very different and deeply quantum version of sound attenuation. The authors' result illuminates the transport properties of strongly correlated quantum fluids (2), with direct implications for the stability of spinning neutron stars (3).

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