# Strong coupling corrections in quantum thermodynamics

## TL;DR

This paper investigates how strong coupling between quantum systems and thermal baths affects thermodynamic laws, providing corrections to the second law, bounds on heat engine power, and illustrating these effects with quantum Brownian motion.

## Contribution

It introduces strong-coupling corrections to the second law of thermodynamics and bounds on heat engine power, extending thermodynamics to the strong coupling regime.

## Key findings

- Strong-coupling corrections to the second law are derived.
- Bounds on power enhancement due to strong coupling are established.
- Results are exemplified using non-Markovian quantum Brownian motion.

## Abstract

Quantum systems strongly coupled to many-body systems equilibrate to the reduced state of a global thermal state, deviating from the local thermal state of the system as it occurs in the weak-coupling limit. Taking this insight as a starting point, we study the thermodynamics of systems strongly coupled to thermal baths. First, we provide strong-coupling corrections to the second law applicable to general systems in three of its different readings: As a statement of maximal extractable work, on heat dissipation, and bound to the Carnot efficiency. These corrections become relevant for small quantum systems and always vanish in first order in the interaction strength. We then move to the question of power of heat engines, obtaining a bound on the power enhancement due to strong coupling. Our results are exemplified on the paradigmatic situation of non-Markovian quantum Brownian motion.