Quantum Hydrodynamics in Interacting Fermi Gases

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This project explores the nearly perfect fluid-flow properties of a special class of ultra-cold atoms, Fermi gases, which are tightly confined in a bowl made of laser light and cooled to temperatures just billionths of a degree above absolute zero. The bowl is turned off to release the ultra-cold atoms into a high vacuum and they are imaged during expansion by laser flash-photography. By just turning a knob in these tabletop experiments, an expanding atom cloud can be made to simulate the behavior of electrons in superconductors, neutrons in neutron stars, or even an exotic state of matter that existed just microseconds after the Big Bang. The study of these nearly perfect fluids has practical significance in testing theories of high temperature superconductors, which will one day enable energy-saving power transmission, and fundamental significance in testing theories of perfect fluid flow that may have occurred just after the Big Bang. The goal of this project is to measure precisely the nearly perfect hydrodynamic transport properties of an ultra-cold atomic Fermi gas. Spin-up and spin-down atoms are made to strongly interact by means of a bias magnetic field, tuned near a collisional (Feshbach) resonance. A collision between two such clouds produces shock waves as the strongly-interacting clouds bounce off each other. Measurements of the shear viscosity above, at, and below resonance will enable new tests of the lower bound predicted for a perfect fluid using string theory methods. Studies of scale-invariant flow at resonance will determine the bulk viscosity and test general predictions for scale invariant systems. The experiments cross interdisciplinary boundaries by testing state-of-the-art theory for the transport properties of strongly-correlated matter, which can be simulated in these cold atom experiments, such as high-temperature superconductors, nuclear matter, and quark-gluon plasmas that are created in heavy ion collisions.