Non-conjugate quantum subsystems

Adam Stokes

Published 2021-06-21Version 1

We introduce the notion of non-conjugate quantum subsystems as an alternative way to understand the decomposition of a quantum system into interacting parts. The definition is shown to be natural in situations where a conventional decomposition is incompatible with fundamental and operationally motivated identifications of physical subsystem observables, such as in non-relativistic quantum electrodynamics. We apply the concept to quantum thermodynamics, obtaining a reduced state of the working system that unlike the usual reduced state is compatible with the definition of the working system's energy often used within the literature. This yields non-trivial and purely quantum corrections to previous results.