Josephson effect in fermionic superfluids across the BEC-BCS crossover

TL;DR

This paper demonstrates the Josephson effect in strongly interacting fermionic superfluids across the BEC-BCS crossover, revealing coherent oscillations, non-monotonic coupling behavior, and vortex-induced dissipation, advancing understanding of superfluid dynamics.

Contribution

It provides the first observation of the Josephson effect across the BEC-BCS crossover and characterizes the dynamical variables and dissipation mechanisms involved.

Findings

Observation of Josephson oscillations in fermionic superfluids

Non-monotonic behavior of plasma frequency and coupling energy

Transition from coherent to dissipative dynamics due to vortices

Abstract

We report on the observation of the Josephson effect between two strongly interacting fermionic superfluids coupled through a thin tunneling barrier. We prove that the relative population and phase are canonically conjugate dynamical variables, coherently oscillating throughout the entire crossover from molecular Bose-Einstein condensates (BEC) to Bardeen-Cooper-Schrieffer (BCS) superfluids. We measure the plasma frequency and we extract the Josephson coupling energy, both exhibiting a non-monotonic behavior with a maximum near the crossover regime. We also observe the transition from coherent to dissipative dynamics, which we directly ascribe to the propagation of vortices through the superfluid bulk. Our results highlight the robust nature of resonant superfluids, opening the door to the study of the dynamics of superfluid Fermi systems in the presence of strong correlations and fluctuations.