Laws of thermodynamics and their application to quantum physics

[Priscilaifrj]

TL;DR

The Second Law of Thermodynamics states that the total entropy of an isolated system never decreases. But in a time-reversal experiment in quantum systems, would it be possible to observe an effective decrease in entropy? How does this reconcile with the classical view of irreversibility?

A Segunda Lei da Termodinâmica afirma que a entropia total de um sistema isolado nunca diminui. Mas em um experimento de reversão de tempo em sistemas quânticos, seria possível observar uma diminuição efetiva na entropia? Como isso se reconcilia com a visão clássica da irreversibilidade?

 

[PeterDonis]

a time-reversal experiment

How would you run such an experiment?

 

[Demystifier]

And how exactly do you define quantum entropy of a closed system? (There are several inequivalent definitions, see e.g. Sec. 5.3 of my https://arxiv.org/abs/2308.10500)