On the measurability of nonequilibrium thermodynamics in terms of the Hamiltonian of mean force

Philipp Strasberg, Massimiliano Esposito

Published 2020-01-24Version 1

The nonequilibrium thermodynamics of an open (classical or quantum) system in strong contact with a single heat bath can be conveniently described in terms of the Hamiltonian of mean force. However, the conventional formulation is limited by the necessity to measure differences in equilibrium properties of the system-bath composite. We make use of the freedom involved in defining thermodynamic state functions, which leaves the thermodynamics unchanged, to show that the Hamiltonian of mean force can be inferred from measurements on the system alone, up to that irrelevant freedom. In doing so, we refute a key criticism expressed in Phys. Rev. E 94, 022143 and arXiv:1911.11660. We also discuss the remaining part of the criticism.