Probing the BCS-BEC crossover with persistent currents

TL;DR

This paper investigates how persistent currents in an attractive Fermi gas confined in a ring evolve across the BCS-BEC crossover, revealing signatures of pair formation and changes in current periodicity.

Contribution

It provides a theoretical analysis of persistent currents across the BCS-BEC crossover, highlighting how current behavior signals pairing and bound state formation.

Findings

Parity effect in persistent currents on the BCS side

Doubling of energy periodicity on the BEC side

Disappearance of parity effect indicating pair formation

Abstract

We study the persistent currents of an attractive Fermi gas confined in a tightly-confining ring trap and subjected to an artificial gauge field all through the BCS-BEC crossover. At weak attractions, on the BCS side, fermions display a parity effect in the persistent currents, ie their response to the gauge field is paramagnetic or diamagnetic depending on the number of pairs on the ring. At resonance and on the BEC side of the crossover we find a doubling of the periodicity of the ground-state energy as a function of the artificial gauge field and disappearance of the parity effect, indicating that persistent currents can be used to infer the formation of tightly-bound bosonic pairs. Our predictions can be accessed in ultracold atoms experiments through noise interferograms.