Cao, C; Elliott, E; Joseph, J; Wu, H; Petricka, J; Schäfer, T; Thomas, JE, *Universal quantum viscosity in a unitary Fermi gas.*,
Science, vol. 331 no. 6013
(January, 2011),
pp. 58-61(This is the first measurement of a transport property in a universal Fermi gas, the quantum viscosity, currently of great interest in the search for "perfect fluids," which relates the highest temperature matter in the universe, a quark-gluon plasma at 2 trillion degrees, to the coldest matter, a strongly interacting Fermi gas at 0.1 microdegree.)
[21148347], [doi] .
**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 p(T)(3)/ħ(2), where p(T) 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 T(3/2) 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.*