Author ORCID Identifier

https://orcid.org/0000-0002-7212-9028

Date of Award

Fall 11-1-2023

Document Type

Thesis (Ph.D.)

Department or Program

Physics and Astronomy

First Advisor

Kevin Wright

Abstract

The unique capability to precisely tune the few and many-body configurations of
ultracold Fermi gases provides a multi-dimensional platform for studying novel, ex-
otic aspects of quantum systems. These aspects include superfluid/superconducting
phenomena supported by potentially exotic pairing mechanisms, non-equilibrium and
critical dynamics, and proposed quantum sensing or computing applications based on
atomtronics.
Ring geometries provide natural arenas for probing transport properties of super-
fluids. Metastable states of quantized superfluid flow —persistent currents— exhibit
remarkable properties, and the manner in which they form is an incredibly rich sub-
ject. Studies of quenched superfluids demonstrate that persistent currents can form
from fragments of spontaneous symmetry breaking as second-order phase transitions
are crossed at finite rates. The extent of these fragments of the higher-symmetry
phase can in some limits be predicted by the Kibble-Zurek mechanism (KZM), which
is fundamentally tied to the universal properties characterizing the transition. Thus,
studies of spontaneous currents in superfluid rings can shed light on universality
classes that microscopically distinct systems fall into.
This thesis describes the experimental results of two separate yet complimen-
tary investigations of the physics of ultracold 6Li atoms confined to ring geometries.
The subject of the first investigation is the heating of degenerate fermionic rings
subject to collisions with background molecules. The most important result of this study was that the heating due to these ever-present collisions can be substantially reduced by maintaining a reservoir of non-degenerate fermions in contact with the
deeply-degenerate atoms in the ring. These findings permit the possibility to perform
seconds-long experiments that require maintaining low temperatures. The second
part of the thesis describes the first experimental studies of the KZM ever conducted
with ultracold fermions in ring-shaped traps. By exploiting long lifetimes offered
by the trapping potential utilized in the aforementioned heating studies, we reveal
two distinct regimes of quench dynamics. The fast-quench regime agrees with KZM
predictions, while the slow-quench regime governed by finite-size effects follows a dif-
ferent trend. Our KZM studies should be readily extendable to scenarios that include
current biases, inhomogeneities and disorder, where these controls can be employed
to obtain additional information about the phase transition.

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