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

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.

Fermi-surface-engineered unconventional superfluid states in a driven-dissipative non-equilibrium Fermi gas

“…Although we expect our scheme to work for generic Fermi systems, as a paradigmatic example, we consider here an attractively interacting Fermi gas as our main system. In the accompanying paper [33], we predicted that an unconventional Fermi condensate may be realized in this non-equilibrium system, when T env = 0 [34]. In this paper, in addition to providing the full description of our analysis, we extend Ref.…”

“…As pointed out in Ref. [33], the answer to this question is considered to depend on how to tune the environment parameters. We also note that Refs.…”

“…In this paper, in addition to providing the full description of our analysis, we extend Ref. [33] to the case with T env > 0, to explore possible non-equilibrium superfluid states within the mean-field level. We also present detailed stability analyses of these mean-field superfluid solutions.…”