Decoherent histories with(out) objectivity in a (broken) apparatus

TL;DR

This paper investigates monitored quantum dynamics in a solvable model, revealing how decoherent histories and classicality emerge differently in phases associated with measurement apparatus and scrambling, highlighting distinctions between decoherent histories and environment-induced decoherence.

Contribution

It introduces a solvable model showing phase transition between measurement and scrambling, analyzing how decoherent histories and classicality emerge in each phase.

Findings

Decoherent histories appear in both phases with respect to a coarse-grained observable.

The apparatus phase exhibits non-ergodic histories correlated with the measured qubit.

A distinction between decoherent histories and environment-induced decoherence is demonstrated.

Abstract

We characterize monitored quantum dynamics in a solvable model exhibiting a phase transition between a measurement apparatus and a scrambler. We show that approximate decoherent histories emerge in both phases with respect to a coarse-grained extensive observable. However, the apparatus phase, where quantum Darwinism emerges, is distinguished by the non-ergodicity of the histories and their correlation with the measured qubit, which selects an ensemble of preferred pointer states. Our results demonstrate a clear distinction between two notions of classicality, decoherent histories and environment-induced decoherence.