Unconventional pairing in few-fermion systems tuned by external confinement

TL;DR

This paper demonstrates how external confinement can induce exotic superfluid phases with finite momentum pairing in few-fermion systems, providing a controllable way to explore FFLO-like states in cold atom experiments.

Contribution

It introduces a method to induce and identify FFLO-like phases in few-fermion systems through external potential tuning without altering spin populations.

Findings

External potential barriers can create finite momentum pairing.

Exotic superfluid phases are detectable via noise correlation functions.

Results are applicable to current cold atom experimental setups.

Abstract

We study the ground-state properties of a two-component one-dimensional system of a few ultra-cold fermions with attractive interactions. We show that, by ramping up an external potential barrier felt by one of the components, it is possible to induce regions of exotic superfluid phases, characterized by a tunable finite net momentum of the Cooper pair, without changing the overall spin populations. We show that these phases, which are the few-body analogs of the celebrated Fulde-Ferrell-Larkin-Ovchinnikov state, can be distinguished by analyzing a specific two-particle correlation encoded in the noise correlation function. Our theoretical results can be addressed in current experiments with cold atoms confined in spin-selective optical traps.