Current fluctuations in boundary-driven quantum spin chains

TL;DR

This paper demonstrates that large fluctuation analysis in boundary-driven quantum spin chains can distinguish quantum from classical transport, revealing quantum-specific suppression of current due to the Zeno effect and correlations like hyperuniformity.

Contribution

It introduces a method to differentiate quantum and classical transport by analyzing large fluctuations and their relation to boundary activity and correlations.

Findings

Quantum and classical transport differ in fluctuation regimes.

Quantum Zeno effect suppresses large-current trajectories.

Large currents are linked to hyperuniform correlations.

Abstract

Boundary-driven spin chains are paradigmatic non-equilibrium systems in both classical and quantum settings. In general it may not be possible to distinguish classical from quantum transport through monitoring the mean current, as both ballistic as well as diffusive regimes occur in either setting. Here we show that genuine quantum features become manifest in large fluctuations which allow a discrimination between classical and quantum transport: in the classical case, realizations that are characterized by atypically large boundary activity are associated with larger than typical currents, i.e. an enhanced number of events at the boundaries goes together with a large current. Conversely, in the quantum case the Zeno effect leads to the suppression of current in trajectories with large activity at the boundary. We analyze how these different dynamical regimes are reflected in the structure of rare fluctuations. We show furthermore that realizations supporting a large current are generated via weak long-range correlations within the spin chain, typically associated with hyperuniformity.