Nonperturbative renormalization of quantum thermodynamics from weak to strong couplings

TL;DR

This paper develops a nonperturbative framework for quantum thermodynamics in open systems, revealing how to accurately renormalize thermodynamic quantities across weak to strong couplings and recover standard statistical mechanics.

Contribution

It introduces an exact, nonperturbative method to renormalize thermodynamic quantities in open quantum systems, bridging weak and strong coupling regimes.

Findings

Steady states approach Gibbs-type distributions.

Thermodynamic quantities require nonperturbative renormalization.

Exact solutions recover standard statistical mechanics.

Abstract

By solving the exact master equation of open quantum systems, we formulate the quantum thermodynamics from weak to strong couplings. The open quantum systems exchange matters, energies and information with their reservoirs through quantum particles tunnelings that are described by the generalized Fano-Anderson Hamiltonians. We find that the exact solution of the reduced density matrix of these systems approaches a Gibbs-type state in the steady-state limit for both the weak and strong system-reservoir coupling strengths. When the couplings become strong, thermodynamic quantities of the system must be renormalized. The renormalization effects are obtained nonperturbatively after exactly traced over all reservoir states through the coherent state path integrals. The renormalized system Hamiltonian is characterized by the renormalized system energy levels and interactions, corresponding to the quantum work done by the system. The renormalized temperature is introduced to characterize the entropy production counting the heat transfer between the system and the reservoir. We further find that only with the renormalized system Hamiltonian and other renormalized thermodynamic quantities, can the exact steady state of the system be expressed as the standard Gibbs state. Consequently, the corresponding exact steady-state particle occupations in the renormalized system energy levels obey the Bose-Einstein and the Fermi-Dirac distributions for bosonic and fermionic systems, respectively. Thus, the conventional statistical mechanics and thermodynamics are thereby rigorously deduced from quantum dynamical evolution.