Information Transport in Classical-Quantum Hybrid System

TL;DR

This paper develops a new formalism to track entropy and other non-linear quantum information quantities in strongly coupled quantum-classical systems, overcoming previous limitations to weak coupling regimes.

Contribution

It extends the multi-replica approach to strong coupling, enabling direct evaluation of entropy flow in hybrid quantum-classical systems.

Findings

Quantum coherence suppresses entropy transfer.

Hybridization creates a thermodynamic bottleneck.

Framework aids in designing robust quantum hardware.

Abstract

Many important quantities in quantum information science, such as entropy and entanglement, are non-linear functions of the density matrix and cannot be expressed as operator observables. Standard open-system approaches evolve only a single copy of the density matrix, making it impossible to track the dynamics of such quantities. A formalism proposed by some of the present authors addressed this challenge by evolving multiple virtual replicas, but was limited to the weak-coupling regime. Here, we extend this approach to strong coupling between a quantum system and classical environments. The resulting multi-replica master equation enables direct evaluation of entropy flow and related metrics in strongly hybridized quantum-classical systems. Our results show that quantum coherence and hybridization jointly suppress net entropy transfer, creating a thermodynamic bottleneck. This framework provides a general tool for studying entropy dynamics and guiding the design of more robust, resource-efficient quantum hardware.