Proposal for interferometric detection of topological defects in modulated superfluids

TL;DR

This paper proposes an interferometric experiment to detect topological defects in modulated superfluids, specifically the LO phase, by observing interference patterns in expanding fermion clouds with population imbalance.

Contribution

It introduces a novel interferometric method to directly observe the elusive LO phase and its topological defects in imbalanced superfluids.

Findings

Zipper pattern in interference fringes indicates LO phase presence

Method remains effective at finite temperatures despite thermal fluctuations

Provides a clear experimental signature for topological defects in superfluids

Abstract

Attractive interactions between fermions can produce a superfluid ground state, in which pairs of up and down spins swirl together in a coordinated, coherent dance. How is this dance affected by an imbalance in the population of up and down fermions? Do the extra fermions stand on the sides, or do they disrupt the dance? The most intriguing possibility is the formation of a modulated superfluid state, known as an LO phase, in which the excess fermions self-organize into domain walls where the pairing amplitude changes sign. Despite fifty years of theoretical and experimental work, there has so far been no direct observation of an LO phase. Here we propose an experiment in which two fermion clouds, prepared with unequal population imbalances, are allowed to expand and interfere. A zipper pattern in the interference fringes is unequivocal evidence of LO physics. Furthermore, because the experiment is resolved in time and in two spatial directions, we expect an observable signature even at finite temperatures (when thermal fluctuations destroy long-range LO order averaged over time).