Relative Entropy and Catalytic Relative Majorization

TL;DR

This paper establishes that for commuting quantum states, catalytic transformations are possible if and only if the relative entropy decreases, providing a new operational interpretation of relative entropy in quantum resource theory.

Contribution

It demonstrates that catalytic transformations between quasi-classical states are characterized by the monotonicity of relative entropy, revealing a fundamental operational meaning.

Findings

Catalytic transformations are possible if and only if relative entropy decreases.

The result applies specifically to commuting (quasi-classical) quantum states.

Provides a new operational interpretation of relative entropy in resource theory.

Abstract

Given two pairs of quantum states, a fundamental question in the resource theory of asymmetric distinguishability is to determine whether there exists a quantum channel converting one pair to the other. In this work, we reframe this question in such a way that a catalyst can be used to help perform the transformation, with the only constraint on the catalyst being that its reduced state is returned unchanged, so that it can be used again to assist a future transformation. What we find here, for the special case in which the states in a given pair are commuting, and thus quasi-classical, is that this catalytic transformation can be performed if and only if the relative entropy of one pair of states is larger than that of the other pair. This result endows the relative entropy with a fundamental operational meaning that goes beyond its traditional interpretation in the setting of independent and identical resources. Our finding thus has an immediate application and interpretation in the resource theory of asymmetric distinguishability, and we expect it to find application in other domains.