Density and spin response of a strongly-interacting Fermi gas in the attractive and quasi-repulsive regime

TL;DR

This paper calculates the density and spin response functions of a strongly-interacting Fermi gas across attractive and quasi-repulsive regimes, comparing theoretical results with experimental data to understand non-adiabatic evolution.

Contribution

It provides a theoretical analysis of response functions in the quasi-repulsive regime, addressing the challenge of avoiding two-body bound states in strongly-interacting Fermi gases.

Findings

Response functions match experimental data across regimes

Non-adiabatic evolution impacts response behavior

Quasi-repulsive regime characterized without bound state formation

Abstract

Recent experimental advances in ultra-cold Fermi gases allow for exploring response functions under different dynamical conditions. In particular, the issue of obtaining a "quasi-repulsive" regime starting from a Fermi gas with an attractive inter-particle interaction while avoiding the formation of the two-body bound state is currently debated. Here, we provide a calculation of the density and spin response for a wide range of temperature and coupling both in the attractive and quasi-repulsive regime, whereby the system is assumed to evolve non-adiabatically toward the "upper branch" of the Fermi gas. A comparison is made with the available experimental data for these two quantities.