Work, Heat and Internal Energy in Open Quantum Systems: A Comparison of Four Approaches from the Autonomous System Framework

TL;DR

This paper compares four approaches to defining and splitting internal energy into work and heat in open quantum systems, emphasizing their differences, ambiguities, and suitability for various environments and couplings.

Contribution

It provides a comprehensive comparison of four autonomous system frameworks for energy definitions in open quantum systems, including analysis of ambiguities and practical implications.

Findings

Different approaches yield varying definitions of work and heat.

Ambiguities arise in energy partitioning, especially with non-thermal environments.

The minimal dissipation approach is argued to be most consistent.

Abstract

We compare definitions of the internal energy of an open quantum system and strategies to split the internal energy into work and heat contributions as given by four different approaches from autonomous system framework. Our discussion focuses on methods that allow for arbitrary environments (not just heat baths) and driving by a quantum mechanical system. As a simple application we consider an atom as the system of interest and an oscillator field mode as the environment. Three different types of coupling are analyzed. We discuss ambiguities in the definitions and highlight differences that appear if one aims at constructing environments that act as pure heat or work reservoirs. Further, we identify different sources of work (e.g. coherence, correlations, or frequency offset), depending on the underlying framework. Finally, we give arguments to favour the approach based on minimal dissipation.