Open system trajectories specify fluctuating work but not heat

TL;DR

This paper explores the thermodynamics of open systems with strong coupling, showing that while the Hamiltonian of mean force determines equilibrium states, it does not uniquely define the underlying stochastic thermodynamics, highlighting fundamental ambiguities.

Contribution

It demonstrates the limitations of defining stochastic thermodynamics for open systems based solely on the Hamiltonian of mean force, emphasizing the lack of a guiding physical principle.

Findings

Equilibrium phase space density is determined by the Hamiltonian of mean force.

Knowledge of the Hamiltonian alone is insufficient for defining stochastic thermodynamics.

Ambiguity arises in extending thermodynamic structures to fluctuating quantities.

Abstract

Based on the explicit knowledge of a Hamiltonian of mean force, the classical statistical mechanics and equilibrium thermodynamics of open systems in contact with a thermal environment at arbitrary interaction strength can be formulated. Even though the Hamiltonian of mean force uniquely determines the equilibrium phase space probability density of a strongly coupled open system the knowledge of this probability density alone is insufficient to determine the Hamiltonian of mean force, needed in constructing the underlying statistical mechanics and thermodynamics. We demonstrate that under the assumption that the Hamiltonian of mean force is known, an extension of thermodynamic structures from the level of averaged quantities to fluctuating objects (i.e. a stochastic thermodynamics) is possible. However, such a construction undesirably involves also a vast ambiguity. This situation is rooted in the eminent lack of a physical guiding principle allowing to distinguish a physically meaningful theory out of a multitude of other equally conceivable ones.