Universal quantum viscosity in a unitary Fermi gas.

A Fermi gas of atoms with resonant interactions is predicted to obey universal hydrodynamics, in which the shear viscosity and other transport coefficients are universal functions of the density and temperature. At low temperatures, the viscosity has a universal quantum scale h n, where n is the density and h is Planck's constant h divided by 2π, whereas at high temperatures the natural scale is p(T)(3)/h(2), where p(T) is the thermal momentum. We used breathing mode damping to measure the shear viscosity at low temperature. At high temperature T, we used anisotropic expansion of the cloud to find the viscosity, which exhibits precise T(3/2) scaling. In both experiments, universal hydrodynamic equations including friction and heating were used to extract the viscosity. We estimate the ratio of the shear viscosity to the entropy density and compare it with that of a perfect fluid.

Controlling spin current in a trapped Fermi gas.

We study fundamental features of spin current in a very weakly interacting Fermi gas of 6Li. By creating a spin current and then reversing its flow, we demonstrate control of the spin current. This reversal is predicted by a spin vector evolution equation in energy representation, which shows how the spin and energy of individual atoms become correlated in the nearly undamped regime of the experiments. The theory provides a simple physical description of the spin current and explains both the large amplitude and the slow temporal evolution of the data. Our results have applications in studying and controlling fundamental spin interactions and spin currents in ultracold gases.

High-flux beam source for cold, slow atoms or molecules.

We demonstrate and characterize a high-flux beam source for cold, slow atoms or molecules. The desired species is vaporized using laser ablation, then cooled by thermalization in a cryogenic cell of buffer gas. The beam is formed by particles exiting a hole in the buffer gas cell. We characterize the properties of the beam (flux, forward velocity, temperature) for both an atom (Na) and a molecule (PbO) under varying buffer gas density, and discuss conditions for optimizing these beam parameters. Our source compares favorably to existing techniques of beam formation, for a variety of applications.