Geometric phases along quantum trajectories

TL;DR

This paper investigates the distribution and properties of geometric phases in monitored quantum systems, revealing stochastic behavior, topological transitions, and experimental implications for open quantum systems.

Contribution

It introduces a comprehensive analysis of geometric phase distributions in monitored quantum trajectories, including topological transitions and experimental protocols.

Findings

Distribution of geometric phases is stochastic and depends on quantum jumps.

Identifies a topological transition in phase for trajectories with no jumps.

Proposes an echo protocol linking interference patterns to geometric phases.

Abstract

A monitored quantum system undergoing a cyclic evolution of the parameters governing its Hamiltonian accumulates a geometric phase that depends on the quantum trajectory followed by the system on its evolution. The phase value will be determined both by the unitary dynamics and by the interaction of the system with the environment. Consequently, the geometric phase will acquire a stochastic character due to the occurrence of random quantum jumps. Here we study the distribution function of geometric phases in monitored quantum systems and discuss when/if different quantities, proposed to measure geometric phases in open quantum systems, are representative of the distribution. We also consider a monitored echo protocol and discuss in which cases the distribution of the interference pattern extracted in the experiment is linked to the geometric phase. Furthermore, we unveil, for the single trajectory exhibiting no quantum jumps, a topological transition in the phase acquired after a cycle and show how this critical behavior can be observed in an echo protocol. For the same parameters, the density matrix does not show any singularity. We illustrate all our main results by considering a paradigmatic case, a spin-1/2 immersed in time-varying a magnetic field in presence of an external environment. The major outcomes of our analysis are however quite general and do not depend, in their qualitative features, on the choice of the model studied.