Non-Hermitian Quantum Many-Body Scar Phase

TL;DR

This paper introduces a new non-Hermitian quantum phase where many-body scar states are stabilized through non-Hermitian dynamics, leading to non-equilibrium steady states distinct from thermalization.

Contribution

It establishes the existence of a non-Hermitian quantum many-body scar phase and characterizes its phase transition from an ergodic phase using analytical and numerical methods.

Findings

Identification of a non-Hermitian QMBS phase with stabilized scarred states.

Observation of a first-order phase transition from ergodic to scarred phase.

Validation across multiple models including quantum circuits and spin systems.

Abstract

We introduce a novel non-equilibrium phase -- the quantum many-body scar (QMBS) phase -- that emerges in non-Hermitian many-body dynamics when scarred wavefunctions are selectively stabilized via non-Hermitian driving. Projective measurements, or non-Hermitian counterparts, preferentially reinforce QMBS, counteracting the entropy growth that drives thermalization. As a result, atypical, high-energy scarred wavefunctions that are negligible in the long-time dynamics of closed systems become non-equilibrium steady states. We establish the existence of the QMBS phase and its sharp, first-order phase transition from an ergodic thermal phase, through both analytical arguments and numerical simulations of three representative models: a random quantum circuit model, the $SU(q)$ spin model, and the paradigmatic spin-1 XY model.