Intrinsic Hamiltonian of Mean Force and Strong-Coupling Quantum Thermodynamics

We present a universal thermodynamic framework for quantum systems that may be strongly coupled to thermal environments. Unlike previous approaches, our method enables a clear definition of thermostatic properties while preserving the same gauge freedoms as in the standard weak-coupling regime and retaining the von Neumann expression for thermodynamic entropy. Furthermore, it provides a formulation of general first and second laws using only variables accessible through microscopic control of the system, thereby enhancing experimental feasibility. We validate the framework by applying it to a paradigmatic model of strong coupling with a structured bosonic reservoir.