A Tale of Quantum Viscosity in Universal Fermi Gases John E. Thomas, Fritz London Professor, Duke University

An optically-trapped mixture of spin ½-up and spin ½-down 6Li atoms provides a unique paradigm for exploring strongly interacting Fermi systems in nature. This ultracold atomic gas offers unprecedented opportunities to test theoretical techniques that cross interdisciplinary boundaries. A bias magnetic field is used to tune the gas to a Feshbach resonance, where the s-wave scattering length diverges, so that the interparticle spacing and thermal de Broglie wavelength set the only length scales. In this regime, the thermodynamic and hydrodynamic properties of gas are universal. Even though it is dilute, an atomic Fermi gas near a Feshbach resonance is the most strongly interacting nonrelativistic system known, enabling tests of recent theories in disciplines from high temperature superconductors to nuclear matter. I will describe our recent measurements of universal viscosity and entropy in a resonantly interacting Fermi gas and compare the ratio to that of a recent string theory conjecture defining a perfect normal fluid.