Spectroscopic signatures of nonequilibrium pairing in atomic Fermi gases

TL;DR

This paper investigates the RF spectra of non-stationary fermionic condensates, revealing unique spectral features due to excited pairs and oscillating order parameters, advancing understanding of nonequilibrium pairing.

Contribution

It provides the first detailed analysis of RF spectra in non-stationary fermionic condensates, highlighting features caused by excited pairs and oscillating order parameters.

Findings

Non-stationary states show two spectral peaks unlike equilibrium.

Oscillating order parameters produce two sequences of RF peaks.

Satellite peaks arise from photon interactions with oscillation quanta.

Abstract

We determine the radio-frequency (RF) spectra for non-stationary states of a fermionic condensate produced by a rapid switch of the scattering length. The RF spectrum of the nonequilibrium state with constant BCS order parameter has two features in contrast to equilibrium where there is a single peak. The additional feature reflects the presence of excited pairs in the steady state. In the state characterized by periodically oscillating order parameter RF-absorption spectrum contains two sequences of peaks spaced by the frequency of oscillations. Satellite peaks appear due to a process where an RF photon in addition to breaking a pair emits/absorbs oscillation quanta.