Proposed Fermi-surface reservoir-engineering and application to realizing unconventional Fermi superfluids

TL;DR

This paper introduces a reservoir engineering approach to modify Fermi surfaces in non-equilibrium systems, enabling the realization of unconventional Fermi superfluids without spin imbalance, expanding possibilities for quantum many-body states.

Contribution

It proposes a novel reservoir engineering method to create multiple Fermi edges, facilitating the realization of exotic non-equilibrium Fermi superfluids in driven-dissipative systems.

Findings

Demonstrates non-equilibrium Fermi superfluid with Fulde-Ferrell-like order parameter

Shows the system achieves a two-edge momentum distribution in steady state

Provides a framework for exploring quantum phenomena beyond thermal equilibrium

Abstract

We theoretically propose an idea based on reservoir engineering to process the structure of a Fermi edge to split into multiple Fermi edges, so as to be suitable for the state which we want to realize. When one appropriately tunes the chemical-potential difference between two reservoirs being coupled with the system, the system is shown to be in the non-equilibrium steady state with the momentum distribution having a two-edge structure. We argue that these edges play similar roles to two Fermi surfaces, which can be designed to realize exotic quantum many-body states. To demonstrate this, we consider a model driven-dissipative two-component Fermi gas with an attractive interaction as a paradigmatic example and show that it exhibits an unconventional Fermi superfluid. While the superfluid order parameter of this state has the same form as that in the Fulde-Ferrell state discussed in metallic superconductivity under an external magnetic field, the former non-equilibrium pairing state is not accompanied by any spin imbalance. Our proposed reservoir engineering to process the Fermi momentum distribution would provide further possibilities of many-body quantum phenomena beyond the thermal equilibrium case.