Enhancing phase-covariant channel performance with non-unitality

TL;DR

This paper investigates how non-unitality affects the performance of phase-covariant quantum channels, deriving formulas and demonstrating that increased non-unitality can enhance fidelity, purity, and entanglement properties.

Contribution

It introduces a measure of non-unitality, provides analytical formulas for channel fidelity and purity, and shows how non-unitality can improve quantum communication metrics.

Findings

Maximal fidelity increases with non-unitality

Maximal output purity is enhanced by non-unitality

Non-unitality can prolong and revive quantum entanglement

Abstract

We analyze quantum communication properties of phase-covariant channels depending on their degree of non-unitality. In particular, we derive analytical formulas for minimal and maximal channel fidelity on pure states and maximal output purity. Next, we introduce a measure of non-unitality and show how to manipulate between unital and maximally non-unital maps by considering classical mixtures of quantum channels. Finally, we prove that maximal fidelity and maximal output purity increase with non-unitality and present several examples. Interestingly, non-unitality can also prolong quantum entanglement and lead to its rebirth.