A brief introduction to observational entropy

TL;DR

This paper provides a comprehensive, accessible overview of observational entropy, a unifying framework for classical and quantum entropy concepts, including its construction, properties, and applications.

Contribution

It offers a self-contained, pedagogical review of observational entropy, highlighting its development, interpretation, and relevance to both classical and quantum thermodynamics.

Findings

Clarifies the construction and interpretation of observational entropy

Summarizes key properties and theoretical foundations

Discusses applications in classical and quantum thermodynamics

Abstract

In the past several years, observational entropy has been developed as both a (time-dependent) quantum generalization of Boltzmann entropy, and as a rather general framework to encompass classical and quantum equilibrium and non-equilibrium coarse-grained entropy. In this paper we review the construction, interpretation, most important properties, and some applications of this framework. The treatment is self-contained and relatively pedagogical, aimed at a broad class of researchers.