Quantum stochastic thermodynamics of macroscopic systems: an algebraic approach
Thermodynamics describes macroscopic systems using only a limited number of observables, yet quantum formulations often rely on knowledge of the full density matrix. In this talk, I will present a framework for quantum thermodynamics based on the information accessible through coarse-grained measurements. Starting from observational entropy, we introduce a generalized entropy associated with an algebra of observables, allowing us to account for genuinely quantum features such as non-commutativity. Within this framework, we derive a second law that captures irreversibility arising not only from interactions with the environment but also from internal equilibration under unitary dynamics. We also establish fluctuation theorems and introduce quantum macroscopic notions of work and heat, including an additional work contribution associated with changes in the accessible algebra, induced by external constraints or measurement backaction. This approach provides a unified description of macroscopic and stochastic thermodynamics in quantum systems, while requiring access to only a restricted set of observables.