Beyond linear response spectroscopy of ultracold Fermi gases

TL;DR

This paper develops a higher order theoretical framework for RF-spectroscopy of ultracold Fermi gases, capturing virtual processes and energy conservation effects beyond linear response, aligning well with experimental results.

Contribution

It introduces an effective higher order theory that accurately describes pairing gaps and explains experimental observations without mean-field shifts.

Findings

Quantitative agreement with experimental pairing gap measurements

Consistent explanation for the absence of mean-field shifts in spin-flip experiments

Demonstrates the importance of higher order processes in ultracold Fermi gas spectroscopy

Abstract

We study RF-spectroscopy of ultracold Fermi gas by going beyond the linear response in the field-matter interaction. Higher order perturbation theory allows virtual processes and energy conservation beyond the single particle level. We formulate an effective higher order theory which agrees quantitatively with experiments on the pairing gap, and is consistent with the absence of the mean-field shift in the spin-flip experiment.