Collective Excitations and Nonequilibrium Phase Transition in Dissipative Fermionic Superfluids.

Kazuki Yamamoto,Naoto Tsuji,Norio Kawakami,Masahito Ueda,Masaya Nakagawa

doi:10.1103/physrevlett.127.055301

Abstract

We predict a new mechanism to induce collective excitations and a nonequilibrium phase transition of fermionic superfluids via a sudden switch on of two-body loss, for which we extend the BCS theory to fully incorporate a change in particle number. We find that a sudden switch on of dissipation induces an amplitude oscillation of the superfluid order parameter accompanied by a chirped phase rotation as a consequence of particle loss. We demonstrate that when dissipation is introduced to one of the two superfluids coupled via a Josephson junction, it gives rise to a nonequilibrium dynamical phase transition characterized by the vanishing dc Josephson current. The dissipation-induced collective modes and nonequilibrium phase transition can be realized with ultracold fermionic atoms subject to inelastic collisions.

Highlights

We predict a new mechanism to induce collective excitations and a nonequilibrium phase transition of fermionic superfluids via a sudden switch on of two-body loss, for which we extend the BCS theory to fully incorporate a change in particle number
We find that a sudden switch on of dissipation induces an amplitude oscillation of the superfluid order parameter accompanied by a chirped phase rotation as a consequence of particle loss
We demonstrate that when dissipation is introduced to one of the two superfluids coupled via a Josephson junction, it gives rise to a nonequilibrium dynamical phase transition characterized by the vanishing dc Josephson current

Summary

Published by the American Physical Society

Josephson current around a nonvanishing dc component. When dissipation becomes strong, the coupled system undergoes a nonequilibrium phase transition characterized by the vanishing dc Josephson current, which can be regarded as a generalization of a dynamical phase transition [11,12,72,73] to dissipative quantum systems. Our findings can experimentally be tested with ultracold atoms through introduction of dissipation via a photoassociation process [50,59]. Dissipative BCS theory.—We consider ultracold fermionic atoms described by the three-dimensional attractive

Hubbard model

We also find amplitude oscillations in jΔj as shown in