On the Ratio of the Viscosity to Entropy Density for Quantum Gases in the Unitary Limit

          @misc{ scivideos_PIRSA:11080024,
            doi = {10.48660/11080024},
            url = {https://pirsa.org/11080024},
            author = {LeClair, Andre},
            keywords = {},
            language = {en},
            title = {On the Ratio of the Viscosity to Entropy Density for Quantum Gases in the Unitary Limit},
            publisher = {Perimeter Institute for Theoretical Physics},
            year = {2011},
            month = {aug},
            note = {PIRSA:11080024 see, \url{https://scivideos.org/index.php/pirsa/11080024}}
          }
          

Abstract

In the so-called unitary limit of quantum gases, the scattering length diverges and the theory becomes scale invariant with dynamical exponent z=2. This point occurs precisely at the crossover between strongly coupled BEC and BCS. These systems are currently under intense experimental study using cold atoms and Feshbach resonances to tune the scattering length. We developed a new approach to the statistical mechanics of gases in higher dimensions modeled after the thermodynamic Bethe ansatz, i.e. based on the exact 2-body S-matrix. Calculations of the critical temperature Tc/T_F = 0.1 are in good agreement with experiments and Monte-Carlo studies. We also calculated the ratio of viscosity to entropy density and obtained 4.7 times the conjectured lower bound of 1/4 pi, in good agreement with very recent experiments. We also present evidence for a strongly interacting version of BEC.