Heat operator approach to quantum stochastic thermodynamics in the strong-coupling regime

Abstract: Open quantum systems exchange heat with their environments and the fluctuations of this heat carry crucial signatures of the underlying dynamical processes. Within the well-established two-point measurement scheme and employing thermofield dynamics, we identify a 'heat operator,' whose moments with respect to the vacuum state correspond to the stochastic moments of the heat exchanged with a thermal bath. This recasts the computation of heat statistics as a standard unitary time-evolution problem, allowing us to leverage powerful tensor-network techniques for simulating quantum dynamics. In particular, we exploit the chain mapping of thermodynamic reservoirs to compute heat fluctuations in the Ohmic spin-boson model. The method, however, is general and applies to arbitrary open quantum systems coupled to non-interacting (bosonic or fermionic) thermal environments, offering a powerful, non-perturbative framework for understanding heat transfer in open quantum systems.