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Universal Quantum Viscosity in a Unitary Fermi Gas

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Science  09 Dec 2010:
1195219
DOI: 10.1126/science.1195219

Abstract

A Fermi gas of atoms with resonant interactions is predicted to obey universal hydrodynamics, where 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, while at high temperatures the natural scale is pT32 where pT  is the thermal momentum. We employ breathing mode damping to measure the shear viscosity at low temperature. At high temperature T, we employ 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 are used to extract the viscosity. We estimate the ratio of the shear viscosity to the entropy density and compare to that of a perfect fluid.