Structured quantum collision models: generating coherence with thermal resources

TL;DR

This paper extends quantum collision models by using structured ancillary systems to generate steady-state coherence in open quantum systems, providing insights into the thermodynamic costs involved.

Contribution

It introduces structured ancilla systems into collision models, enabling the study of coherence generation and thermodynamic costs in open quantum systems.

Findings

Structured ancillas modify the master equation for system evolution.

Coherence can be generated in the steady state with thermal ancillas.

Generating coherence requires work, respecting thermodynamic laws.

Abstract

Quantum collision models normally consist of a system interacting with a set of ancillary units representing the environment. While these ancillary systems are usually assumed to be either two level systems (TLS) or harmonic oscillators, in this work we move further and represent each ancillary system as a structured system, i.e., a system made out of two or more subsystems. We show how this scenario modifies the kind of master equation that one can obtain for the evolution of the open systems. Moreover, we are able to consider a situation where the ancilla state is thermal yet has some coherence. This allows the generation of coherence in the steady state of the open system and, thanks to the simplicity of the collision model, this allows us to better understand the thermodynamic cost of creating coherence in a system. Specifically, we show that letting the system interact with the coherent degrees of freedom requires a work cost, leading to the natural fulfillment of the first and second law of thermodynamics without the necessity of {\it ad hoc} formulations.