Quantum Transport and Scale Invariance in Expanding Fermi Gases

Loading...
Thumbnail Image

Date

2014

Authors

Elliott, Ethan

Journal Title

Journal ISSN

Volume Title

Repository Usage Stats

524
views
385
downloads

Abstract

This dissertation describes the first experimental measurement of the energy and interaction dependent shear viscosity $\eta$ and bulk viscosity $\zeta$ in the hydrodynamic expansion of a two-component Fermi gas near a broad collisional (Feshbach) resonance. This expansion also provides a precise test of scale invariance and an examination of local thermal equilibrium as a function of interaction strength. After release from an anisotropic optical trap, we observe that a resonantly interacting gas obeys scale-invariant hydrodynamics, where the mean square cloud size $\langle{\mathbf{r}}^2\rangle=\langle x^2+y^2+z^2\rangle$ expands ballistically (like a noninteracting gas) and the energy-averaged bulk viscosity is consistent with zero, $0.00(0.04)\,\hbar\,n$, with $n$ the density. In contrast, the aspect ratios of the cloud exhibit anisotropic ``elliptic" flow with an energy-dependent shear viscosity. Tuning away from resonance, we observe conformal symmetry breaking, where $\langle{\mathbf{r}}^2\rangle$ deviates from ballistic flow. We find that $\eta$ has both a quadratic and a linear dependence on the interaction strength $1/({k_{FI}a})$, where $a$ is the s-wave scattering length and $k_{FI}$ is the Fermi wave vector for an ideal gas at the trap center. At low energy, the minimum is less than the resonant value and is significantly shifted toward the BEC side of resonance, to $1/(k_{FI}a) = 0.2$.

Department

Description

Provenance

Subjects

Citation

Citation

Elliott, Ethan (2014). Quantum Transport and Scale Invariance in Expanding Fermi Gases. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/8787.

Collections


Dukes student scholarship is made available to the public using a Creative Commons Attribution / Non-commercial / No derivative (CC-BY-NC-ND) license.