Catalysis always degrades external quantum correlations

TL;DR

This paper demonstrates that quantum correlations in catalysts always degrade during quantum processes, and only classical correlations can effectively facilitate catalysis, highlighting a fundamental limitation of quantum resources.

Contribution

The authors fully characterize totally quantum systems and prove they cannot serve as catalysts, establishing that only classical correlations enable catalysis in quantum resource theories.

Findings

Totally quantum systems cannot catalyze quantum processes.

Quantum correlations in catalysts always degrade upon use.

Classical correlations are necessary for effective catalysis.

Abstract

Catalysts used in quantum resource theories need not be in isolation and therefore are possibly correlated with external systems, which the agent does not have access to. Do such correlations help or hinder catalysis, and does the classicality or quantumness of such correlations matter? To answer this question, we first focus on the existence of a non-invasively measurable observable that yields the same outcomes for repeated measurements, since this signifies macro-realism, a key property distinguishing classical systems from quantum systems. We show that a system quantumly correlated with an external system so that the joint state is necessarily perturbed by any repeatable quantum measurement, also has the same property against general quantum channels. Our full characterization of such systems called totally quantum systems, solves the open problem of characterizing tomographically sensitive systems raised in [Lie and Jeong, Phys. Rev. Lett. 130, 020802 (2023)]. An immediate consequence is that a totally quantum system cannot catalyze any quantum process, even when a measure of correlation with its environment is arbitrarily low. It generalizes to a stronger result, that the mutual information of totally quantum systems cannot be used as a catalyst either. These results culminate in the conclusion that, out of the correlations that a generic quantum catalyst has with its environment, only classical correlations allow for catalysis, and therefore using a correlated catalyst is equivalent to using an ensemble of uncorrelated catalysts.