Super-additivity of quantum-correlating power

TL;DR

This paper proves that the quantum-correlating power of combined channels is at least the sum of individual powers, revealing super-activation effects and conditions for additivity in quantum channels.

Contribution

It establishes the super-additivity of quantum-correlating power for parallel channels and identifies conditions under which additivity occurs.

Findings

Super-additivity of QCP for parallel channels.

Super-activation of QCP in certain local channels.

Additivity of QCP for measuring-and-preparing and decohering channels.

Abstract

We prove that, when two local quantum channels are used paralleled, the quantum-correlating power (QCP) of the composed channel is no less than the sum of QCP of the two channels. For local channels with zero QCP, the super-activation of QCP is a fairly common effect, and proved to exist except for the trivial case where both of the channels are completely decohering channels or unitary operators. For general quantum channels, we show that the (not-so-common) additivity of QCP can be observed for the situation where a measuring-and-preparing channel is used together with a completely decohering channel.