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Universal Quantum Viscosity in a Unitary Fermi Gas

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Science  07 Jan 2011:
Vol. 331, Issue 6013, pp. 58-61
DOI: 10.1126/science.1195219

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Abstract

A Fermi gas of atoms with resonant interactions is predicted to obey universal hydrodynamics, in which the shear viscosity and other transport coefficients are universal functions of the density and temperature. At low temperatures, the viscosity has a universal quantum scale ħ n, where n is the density and ħ is Planck’s constant h divided by 2π, whereas at high temperatures the natural scale is pT3/ħ2, where pT is the thermal momentum. We used breathing mode damping to measure the shear viscosity at low temperature. At high temperature T, we used anisotropic expansion of the cloud to find the viscosity, which exhibits precise T3/2 scaling. In both experiments, universal hydrodynamic equations including friction and heating were used to extract the viscosity. We estimate the ratio of the shear viscosity to the entropy density and compare it with that of a perfect fluid.

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