Classical and quantum thermodynamics in a non-equilibrium regime: Application to Stirling engine

TL;DR

This paper develops a non-equilibrium thermodynamic theory applicable to quantum systems, validated through simulations of a Stirling engine, enabling analysis of thermodynamic processes across different interaction regimes.

Contribution

It introduces a novel non-equilibrium thermodynamic framework that does not require initial factorization and applies to quantum entangled systems, validated with numerical simulations.

Findings

Validated the theory with quantum and classical Stirling engine simulations.

Demonstrated analysis of thermodynamic processes from weak to strong system-bath interactions.

Provided a non-equilibrium work diagram analogous to equilibrium thermodynamics.

Abstract

We have developed a thermodynamic theory in the non-equilibrium regime, which we describe as a thermodynamic system-bath model [S. Koyanagi and Y. Tanimura, J. Chem. Phys. \textbf{160}, 234112 (2024)]. Based on the dimensionless (DL) minimum work principle, non-equilibrium thermodynamic potentials are expressed in terms of non-equilibrium extensive and intensive variables in time derivative form. This is made possible by incorporating the entropy production rate into the definitions of non-equilibrium thermodynamic potentials. These potentials can be evaluated from the DL non-equilibrium-to-equilibrium minimum work principle, which is derived from the principle of DL minimum work and is equivalent to the second law of thermodynamics. We thus obtain the non-equilibrium Massieu-Planck potentials as entropic potentials and the non-equilibrium Helmholtz-Gibbs potentials as free energies. Unlike fluctuation theorem and stochastic thermodynamics theory, this theory does not require the assumption of a factorized initial condition and is valid in the full quantum regime where the system and bath are quantum mechanically entangled. Our results are numerically verified by simulating a thermostatic Stirling engine consisting of two isothermal processes and two thermostatic processes using the quantum hierarchical Fokker--Planck equations and the classical Kramers equation derived from the thermodynamic system-bath model. We then show that, from weak to strong system-bath interactions, the thermodynamic process can be analyzed using a non-equilibrium work diagram analogous to the equilibrium one for given time-dependent intensive variables. The results can be used to develop efficient heat machines in non-equilibrium regimes.