Quantum many-body scars in random unitary circuits

TL;DR

This paper constructs an analytically solvable quantum circuit that hosts a rare non-thermal state called a scar, revealing how it influences entanglement dynamics and thermalization.

Contribution

It introduces a new random unitary circuit model with a quantum many-body scar and explains its thermalization mechanism from first principles.

Findings

The constructed circuit hosts a single quantum many-body scar.

The scar affects entanglement dynamics without altering local observables.

A transition in entanglement behavior occurs as perturbation strength varies.

Abstract

Quantum many-body scars are rare exceptions to thermalization: they sustain non-thermal stationary states without the protection of any local conservation law, and are generally expected to be fragile. Here we construct an analytically tractable random unitary circuit hosting a single scar, and derive from first principles the thermalization mechanism governing perturbations thereof - described by a picture of fluctuating interfaces. Surprisingly, despite being thermodynamically irrelevant for local observables, the scar leaves a sharp fingerprint in the entanglement dynamics, driving a transition as a function of perturbation strength that is not probed by any local measurement.