Nonlocal order parameter of pair superfluids

TL;DR

This paper introduces a nonlocal order parameter called odd parity to characterize pair superfluids, demonstrating its experimental accessibility and applicability across different models and dimensions, thus advancing understanding of exotic quantum phases.

Contribution

The paper defines a nonlocal order parameter for pair superfluids, showing its effectiveness in various models and dimensions, and proposes its experimental detection in ultracold atomic systems.

Findings

Pair superfluidity identified at strong attractive interactions.

Odd parity operator serves as a universal order parameter.

Method applicable to different Bose-Hubbard models and dimensions.

Abstract

Order parameters represent a fundamental resource to characterize quantum matter. We show that pair superfluids can be rigorously defined in terms of a nonlocal order parameter, named odd parity, which derivation is experimentally accessible by local density measurements. As a case of study, we first investigate a constrained Bose-Hubbard model at different densities, both in one and two spatial dimensions. Here, our analysis finds pair superfluidity for relatively strong attractive interactions. The odd parity operator acts as the unique order parameter for such phase irrespectively to the density of the system and its dimensionality in regimes of total particle number conservation. In order to enforce our finding, we confirm the generality of our approach also on a two-component Bose-Hubbard Hamiltonian, which experimental realization represents a timely topic in ultracold atomic systems. Our results shed new light on the role of correlated density fluctuations in pair superfluids. In addition, they provide a powerful tool for the experimental detection of such exotic phases and the characterization of their transition to the atomic superfluid phase.