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Abstract: We use all-optical methods to produce a highly-degenerate Fermi gas ofspin-1-2 $^6$Li atoms. A magnetic field tunes the gas near a collisionalFeshbach resonance, producing strong interactions between spin-up andspin-down atoms. This atomic gas is a paradigm for strong interactions innature, and provides tests of current quantum many-body calculational methodsfor diverse systems, including very high temperature superconductors, nuclearmatter in neutron stars, and the quark-gluon plasma of the Big Bang. We havemeasured properties of a breathing mode over a wide range of temperatures. Attemperatures both below and well above the superfluid transition, the frequencyof the mode is nearly constant and very close to the hydrodynamic value.However, explaining both the frequency and the damping rate in the normalcollisional regime has not been achieved. Our measurements of the damping rateas a function of the energy of the gas are used to estimate an upper bound onthe viscosity. Using our new measurements of the entropy of the gas, weestimate the ratio of the shear viscosity to the entropy density, and comparethe result with the lower bound for quantum viscosity recently predicted usingstring theory methods.



Author: A. Turlapov, J. Kinast, B. Clancy, Le Luo, J. Joseph, J. E. Thomas

Source: https://arxiv.org/







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