Improving classical capacity of qubit dynamical maps through stationary state manipulation

TL;DR

This paper demonstrates that manipulating the stationary state of phase-covariant qubit channels, especially increasing non-unitality, can enhance their classical capacities beyond traditional limits, revealing non-unitality as a valuable quantum resource.

Contribution

It introduces methods to engineer channel parameters to improve classical capacities by exploiting non-unitality, a novel approach in quantum channel capacity optimization.

Findings

Capacity can be increased by adjusting the stationary state.

Highly non-unital channels temporarily surpass unital channel capacities.

Non-unitality can serve as a quantum resource for information transfer.

Abstract

We analyze the evolution of Holevo and entanglement-assisted classical capacities for a special class of phase-covariant channels. In particular, we show that these capacities can be improved by changing the stationary state of the channel, which is closely related to its non-unitality degree. The more non-unital the channel, the greater its capacity. The channel parameters are engineered through mixtures on the level of dynamical maps, time-local generators, and memory kernels, for which we propose construction methods. For highly non-unital maps, we achieve a temporary increase in the classical capacity that exceeds the entanglement-assisted classical capacity of the unital map. This shows that non-unitality can become a better quantum resource for information transition purposes than quantum entanglement.