Many-body localization in waveguide QED

TL;DR

This paper demonstrates that a waveguide QED system with disordered atoms can exhibit many-body localization, even though it is an open quantum system, due to suppressed energy transport and dissipation effects.

Contribution

It provides the first evidence that MBL can occur in open, dissipative waveguide QED systems, bridging the gap between theory and experimental realizability.

Findings

MBL phase occurs when atoms are less than half excited.

Dissipation can induce a transition from delocalized to MBL phase.

MBL phenomena are observable in current experimental setups.

Abstract

At the quantum many-body level, atom-light interfaces generally remain challenging to solve for or understand in a non-perturbative fashion. Here, we consider a waveguide quantum electrodynamics model, where two-level atoms interact with and via propagating photons in a one-dimensional waveguide, and specifically investigate the interplay of atomic position disorder, multiple scattering of light, quantum nonlinear interactions and dissipation. We develop qualitative arguments and present numerical evidence that such a system exhibits a many-body localized~(MBL) phase, provided that atoms are less than half excited. Interestingly, while MBL is usually formulated with respect to closed systems, this system is intrinsically open. However, as dissipation originates from transport of energy to the system boundaries and the subsequent radiative loss, the lack of transport in the MBL phase makes the waveguide QED system look essentially closed and makes applicable the notions of MBL. Conversely, we show that if the system is initially in a delocalized phase due to a large excitation density, rapid initial dissipation can leave the system unable to efficiently transport energy at later times, resulting in a dynamical transition to an MBL phase. These phenomena can be feasibly realized in state-of-the-art experimental setups.