Quantum Noise as a Symmetry-Breaking Field

TL;DR

This paper explores how quantum noise influences measurement-induced phase transitions in monitored quantum circuits, revealing a crossover behavior and symmetry-breaking effects that impact entanglement dynamics.

Contribution

It demonstrates that quantum noise broadens the phase transition into a crossover and maps the problem to a classical statistical mechanics model, highlighting symmetry-breaking effects.

Findings

Quantum noise turns the sharp transition into a crossover.

The phase diagram exhibits multiple regimes influenced by noise.

Symmetry breaking in the classical model explains the effects of noise.

Abstract

We investigate the effect of quantum noise on the measurement-induced quantum phase transition in monitored random quantum circuits. Using the efficient simulability of random Clifford circuits, we find that the transition is broadened into a crossover and that the phase diagram as a function of projective measurements and noise exhibits several distinct regimes. We show that a mapping to a classical statistical mechanics problem accounts for the main features of the random circuit phase diagram. The bulk noise maps to an explicit permutation symmetry breaking coupling; this symmetry is spontaneously broken when the noise is switched off. These results have implications for the realization of entanglement transitions in noisy quantum circuits.