Searching for Perfect Fluids: Quantum Viscosity in a Universal Fermi Gas

Understand

We measure the shear viscosity in a two-component Fermi gas of atoms, tuned to a broad s-wave collisional (Feshbach) resonance.

• At resonance, the atoms strongly interact and exhibit universal behavior, where the equilibrium thermodynamic properties and the transport coefficients are universal functions of the density $n$ and temperature $T$.
• We present a new calibration of the temperature as a function of global energy, which is directly measured from the cloud profiles.
• Using the calibration, the trap-averaged shear viscosity in units of $\hbar\,n$ is determined as a function of the reduced temperature at the trap center, from nearly the ground state to the unitary two-body regime.