The Asymmetric Quantum Cloning Region

TL;DR

This paper characterizes the set of all possible qualities for asymmetric quantum cloning, introducing a new norm and providing explicit formulas for optimal cloners, advancing understanding of quantum information limits.

Contribution

It introduces the $ ext{Q}$-norm to characterize clone qualities and derives explicit formulas for optimal asymmetric quantum cloners across all dimensions.

Findings

Characterization of all possible clone qualities using the $ ext{Q}$-norm.

Explicit formulas for optimal asymmetric quantum cloners.

Analysis based on Schur-Weyl duality and spectral properties.

Abstract

Quantum cloning is a fundamental protocol of quantum information theory. Perfect universal quantum cloning is prohibited by the laws of quantum mechanics, only imperfect copies being reachable. Symmetric quantum cloning is concerned with case when the quality of the clones is identical. In this work, we study the general case of $1 \to N$ asymmetric cloning, where one asks for arbitrary qualities of the clones. We characterize, for all Hilbert space dimensions and number of clones, the set of all possible clone qualities. This set is realized as the nonnegative part of the unit ball of a newly introduced norm, which we call the $\mathcal{Q}$-norm. We also provide a closed form expression for the quantum cloner achieving a given clone quality vector. Our analysis relies on the Schur-Weyl duality and on the study of the spectral properties of partially transposed permutation operators.