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arXiv:2306.12166

Elusive phase transition in the replica limit of monitored systems

Guido Giachetti, Andrea De Luca

Published Jun 21, 2023• 0 citations
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Abstract

We study an exactly solvable model of monitored dynamics in a system of $N$ spin-$1/2$ particles with pairwise all-to-all noisy interactions, where each spin is continuously weakly measured along a random direction. Using the replica trick to incorporate the Born-rule weighting of measurement outcomes, we obtain an exact large-$N$ description of purification and of the statistics of local observables. We find that the nature of the phase transition strongly depends on the number $n$ of replicas: non-perturbative logarithmic corrections appear in the physically relevant $n\to1$ limit and destroy the purifying phase present at finite integer $n$. As a consequence, the purification time of an initially mixed state is always exponentially long in the system size, even at arbitrarily large measurement rate.

DOI
10.48550/arxiv.2306.12166

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