Duke Physics Colloquium: Testing String Theory? Scale Invariance in Expanding Strongly Interacting Fermi Gases
"Testing String Theory? Scale Invariance in Expanding Strongly Interacting Fermi Gases" Optically-trapped, ultra-cold gases of spin ½-up and spin ½-down 6Li atoms model high temperature superconductors, neutron matter, and even the quark-gluon plasma that existed microseconds after the Big Bang. A bias magnetic field tunes the gas to a collisional (Feshbach) resonance, where the dilute atomic cloud becomes the most strongly interacting, non-relativistic fluid known: Shock waves are produced when two clouds collide. I will describe our recent observations of scale-invariant expansion and new measurements of quantum viscosity η and entropy s in such clouds. The η/s ratio obtained in the experiments is comparable to that of a quark-gluon plasma, close to the minimum conjectured for a "perfect fluid" using scale-invariant string theory methods. Coffee and cookies will be served before the event in room 128.
