Few-body precursor of the Higgs mode in a superfluid Fermi gas

TL;DR

This paper identifies a few-body precursor to the Higgs mode in a trapped Fermi gas, showing its non-monotonic frequency dependence on interaction strength and its relation to the many-body Higgs mode.

Contribution

It demonstrates the existence of a few-body Higgs mode analogue in a trapped Fermi gas using exact diagonalisation, highlighting its properties and excitation methods.

Findings

Lowest monopole mode frequency depends non-monotonically on interaction strength.

The mode's minimum deepens with increasing particle number.

The mode mainly involves coherent excitations of time-reversed pairs.

Abstract

We demonstrate that an undamped few-body precursor of the Higgs mode can be investigated in a harmonically trapped Fermi gas. Using exact diagonalisation, the lowest monopole mode frequency is shown to depend non-monotonically on the interaction strength, having a minimum in a crossover region. The minimum deepens with increasing particle number, reflecting that the mode is the few-body analogue of a many-body Higgs mode in the superfluid phase, which has a vanishing frequency at the quantum phase transition point to the normal phase. We show that this mode mainly consists of coherent excitations of time-reversed pairs, and that it can be selectively excited by modulating the interaction strength, using for instance a Feshbach resonance in cold atomic gases.