Experimental Realization of the BCS-BEC Crossover with a Fermi Gas of Atoms

Abstract

Abstract Ultracold atomic gases have proven to be remarkable model systems for exploring quantum mechanical phenomena. Experimental work on gases of fermionic atoms in particular has seen astounding recent progress. In the short span of time between 2001 and 2004 accessible Fermi gas systems evolved from normal Fermi liquids at moderate temperatures to superfluids in the BCS-BEC crossover. This was made possible by unique control over interparticle interactions using Feshbach resonances in 6 Li and 40 K gases. In this chapter we present the story of the experimental realization of BCS-BEC crossover physics from the point of view of studies using 40 K at JILA. We start with some historical context and an introduction to the theory of the BCS-BEC crossover and Feshbach resonances. We then present studies of a normal 40 K 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 the first observation of a phase transition in the BCS-BEC crossover regime, a task accomplished through detection of condensation of fermionic atom pairs. We also discuss subsequent work that confirmed the crossover nature of the pairs in these condensates.