Hybrid Zero-capacity Channels

TL;DR

This paper introduces hybrid zero-capacity quantum channels that create bound entangled states which are highly cloneable, challenging existing superactivation protocols and expanding understanding of quantum channel capacities.

Contribution

It presents the first explicit examples of hybrid channels that generate cloneable bound entangled states, and provides methods to construct such channels from binding entanglement channels.

Findings

Hybrid channels produce cloneable bound entangled states.

Superactivation protocols fail for these highly cloneable channels.

Constructive methods to generate hybrid channels from binding entanglement channels.

Abstract

There are only two known kinds of zero-capacity channels. The first kind produces entangled states that have positive partial transpose, and the second one - states that are cloneable. We consider the family of 'hybrid' quantum channels, which lies in the intersection of the above classes of channels and investigate its properties. It gives rise to the first explicit examples of the channels, which create bound entangled states that have the property of being cloneable to the arbitrary finite number of parties. Hybrid channels provide the first example of highly cloneable binding entanglement channels, for which known superactivation protocols must fail - superactivation is the effect where two channels each with zero quantum capacity having positive capacity when used together. We give two methods to construct a hybrid channel from any binding entanglement channel. We also find the low-dimensional counterparts of hybrid states - bipartite qubit states which are extendible and possess two-way key.