Thermodynanics from Quantum Mechanics

Origin of the Canonical Ensemble: Thermalization with Decoherence

It is shown that a system embedded in a closed quantum mechanical system relaxes to its canonical ensemble equilibrium state if the environment drives this system to a fully decoherent state and the excess energy can release from the system to the environment or backward. Our findings show that the canonical ensemble is a special state that may result from pure quantum dynamics, suggesting that quantum mechanics may be regarded as the foundation of quantum statistical mechanics

Statistical mechanics is one of cornerstones of modern physics but its foundations and basic postulates are still under debate [1, 2, 3, 4]. There is a common believe that a generic “system” that interacts with a generic environment evolves into a state described by the canonical ensemble. Experience shows that this is true but a detailed understanding of this process, which is crucial for a rigorous justification of statistical physics and thermodynamics, is still lacking.