Curator's Take
This article tackles a fundamental challenge in quantum thermodynamics: how to accurately measure thermodynamic quantities like work and heat in realistic quantum systems that interact with their environment. The researchers have developed a clever measurement protocol that requires access only to the quantum system itself, not the surrounding environment, making it practically feasible for experimental implementation in quantum devices. Most intriguingly, they discovered that systems undergoing pure decoherence (where quantum coherences decay without energy exchange) naturally satisfy Jarzynski's equality exactly, providing a special class of quantum dynamics where fundamental thermodynamic relations hold perfectly regardless of how strongly the system couples to its environment. This work bridges theoretical quantum thermodynamics with experimental quantum sensing, potentially enabling more precise characterization of energy flows in quantum computers and other quantum technologies.
— Mark Eatherly
Summary
We propose a method to evaluate general thermodynamic fluctuations in open quantum systems, based on performing a two-point measurement scheme on the system using dynamics-dependent thermodynamic observables. Our approach allows one to obtain exact equalities for fluctuations of path-dependent thermodynamic quantities such as work and heat, and to isolate correction factors to Jarzynski's equality, requiring only access to the system degrees of freedom. This framework is flexible and can be applied to the limiting case of closed systems, recovering previous, yet seemingly contradictory, results from the literature. Moreover, the formalism admits a straightforward extension to strongly coupled open quantum systems. We investigate the effect of specific dynamical classes on the fluctuation relations, and show that the pure decoherence case is particularly special, as it deterministically does not contain any heat contribution and thus constitutes a class of open system dynamics for which the Jarzynski equality for work fluctuations is identically true at any coupling strength. Finally, we look explicitly at the shape and size of the correction factors to Jarzynski's equality for a qubit undergoing phase covariant dynamics, both in the weakly-coupled regime and in the deep non-Markovian regime.