Experimental realization of BCS-BEC crossover physics with a Fermi gas of atoms

TL;DR

This thesis demonstrates experimental control over ultracold fermionic gases to explore the BCS-BEC crossover, observing phase transitions and pairing phenomena that bridge molecular Bose-Einstein condensation and BCS superfluidity.

Contribution

It pioneers the use of fermionic Feshbach resonances for tunable studies of the BCS-BEC crossover in ultracold gases, including observing phase transitions and pairing behavior.

Findings

Observation of a phase transition at the BCS-BEC crossover

Condensation of fermionic atom pairs confirmed crossover nature

Controlled tuning of fermion interactions using Feshbach resonances

Abstract

This thesis presents experiments probing physics in the crossover between Bose-Einstein condensation (BEC) and BCS superconductivity using an ultracold gas of atomic fermions. Scattering resonances in these ultracold gases (known as Feshbach resonances) provide the unique ability to tune the fermion-fermion interactions. The work presented here pioneered the use of fermionic Feshbach resonances as a highly controllable and tunable system ideal for studying the cusp of the BCS-BEC crossover problem. Here pairs of fermionic atoms have some properties of diatomic molecules and some properties of Cooper pairs. I present studies of a normal Fermi gas at a Feshbach resonance and the work required to cool the gas to temperatures where superfluidity in the crossover is predicted. These studies culminated in our observation of a phase transition at the cusp of the BCS-BEC crossover through condensation of fermionic atom pairs. I also discuss subsequent work that confirmed the crossover nature of the pairs in these condensates.