Time-resolved observation of competing attractive and repulsive short-range correlations in strongly interacting Fermi gases

TL;DR

This study uses time-resolved spectroscopy to observe the out-of-equilibrium dynamics of a strongly interacting ultracold Fermi gas, revealing the competition between anti-correlations and pairing processes.

Contribution

It provides the first direct observation of the coexistence of attractive and repulsive short-range correlations in a quenched Fermi gas.

Findings

Rapid growth of anti-correlations at critical interactions

Coexistence of correlations and pairing at longer times

Insights into the dynamics of repulsive Fermi gases

Abstract

We exploit a time-resolved pump-probe spectroscopic technique to study the out-of-equilibrium dynamics of an ultracold two-component Fermi gas, selectively quenched to strong repulsion along the upper branch of a broad Feshbach resonance. For critical interactions, we find the rapid growth of short-range anti-correlations between repulsive fermions to initially overcome concurrent pairing processes. At longer evolution times, these two competing mechanisms appear to macroscopically coexist in a short-range correlated state of fermions and pairs, unforeseen thus far. Our work provides fundamental insights into the fate of a repulsive Fermi gas, and offers new perspectives towards the exploration of complex dynamical regimes of fermionic matter.