# Information-theoretical bound of the irreversibility in thermal relaxation processes

## TL;DR

This paper derives an information-theoretical bound on entropy production during thermal relaxation, revealing a universal law that constrains irreversibility beyond the traditional second law of thermodynamics.

## Contribution

It introduces a variational principle involving Kullback-Leibler divergence to establish a stronger bound on entropy production in thermal processes.

## Key findings

- The bound surpasses the conventional second law in strength.
- It provides an information-geometric interpretation of thermal relaxation.
- A universal law governing irreversibility in thermal processes is revealed.

## Abstract

We establish that entropy production, which is crucial to the characterization of thermodynamic irreversibility, is obtained through a variational principle involving the Kulback-Leibler divergence. A simple application of this representation leads to an information-theoretical bound on entropy production in thermal relaxation processes; this is a stronger inequality than the conventional second law of thermodynamics. This bound is also interpreted as a constraint on the possible path of a thermal relaxation process in terms of information geometry. Our results reveal a hidden universal law inherent to general thermal relaxation processes.