Rapid ramps across the BEC-BCS crossover: a novel route to measuring the superfluid gap

TL;DR

This paper explores how rapid changes in interaction strength in superfluid Fermi gases induce oscillations in the order parameter, proposing experimental methods to measure the superfluid gap via these oscillations.

Contribution

It introduces two experimental protocols to measure the superfluid gap by analyzing oscillations caused by rapid interaction ramps and sinusoidal modulations.

Findings

Oscillations in the order parameter || perform damped oscillations with frequency related to the superfluid gap.

Continued driving causes revivals in the oscillations, revealing dynamic responses.

Proposed protocols enable experimental measurement of the superfluid gap _{gap}.

Abstract

We investigate the response of superfluid Fermi gases to rapid changes of the three-dimensional s-wave scattering length a by solving the time-dependent Bogoliubov-de Gennes equations. In general the magnitude of the order parameter |\Delta| performs oscillations, which are sometimes called the "Higgs" mode, with the angular frequency 2 \Delta_{gap}/ \hbar, where \Delta_{gap} is the gap in the spectrum of fermionic excitations. Firstly, we excite the oscillations with a linear ramp of 1/a and study the evolution of |\Delta|. Secondly, we continously drive the system with a sinusoidal modulation of 1/a. In the first case, the oscillations in |\Delta| damp according to a power law. In the second case, the continued driving causes revivals in the oscillations. In both cases, the excitation of the oscillations causes a reduction in the time-averaged value of |\Delta|. We propose two experimental protocols, based around the two approaches, to measure the frequency and damping of the oscillations, and hence \Delta_{gap}.