Contextuality of all optimal quantum cloning

TL;DR

This paper introduces a new method to analyze quantum contextuality using observed statistics, proving its necessity in optimal quantum cloning and providing a streamlined proof for quantum state discrimination.

Contribution

It establishes contextuality as a fundamental resource in all optimal quantum cloning scenarios and offers a novel, efficient approach to studying contextuality in quantum information tasks.

Findings

Contextuality is necessary for optimal quantum cloning.

The new method simplifies proofs of contextuality in quantum protocols.

Established the fundamental role of contextuality in quantum cloning.

Abstract

Quantum contextuality is a key nonclassical feature underlying advantages in quantum computation and communication. We introduce a new method to study contextuality in quantum information-processing tasks and protocols, relying solely on observed information-processing statistics. Building on the framework of Shahandeh, Yianni and Doosti in arXiv:2512.10000 and employing rank separation techniques, we prove that contextuality is the necessary resource in both phase-covariant and universal optimal quantum cloning, thereby establishing its role as a fundamental source of nonclassicality in all known optimal cloning scenarios and resolving an open problem on the connection between cloning and contextuality. As a second application, we demonstrate the power of our method by providing a new, streamlined proof of contextuality in minimum-error quantum state discrimination.