Subadditivity of the minimum output entropy and superactivation of the classical capacity of quantum multiple access channels

TL;DR

This paper demonstrates that the minimum output entropy of quantum multiple access channels can violate classical additivity, leading to superactivation of their classical capacity, revealing new quantum information phenomena.

Contribution

It provides explicit examples showing subadditivity of minimum output entropy and superactivation of classical capacity in quantum MACs, challenging classical assumptions.

Findings

Violation of additivity of $H_{min}$ in quantum MACs

Explicit construction of channels exhibiting superactivation

Demonstration of superadditivity of classical capacity region

Abstract

We study subadditivity of the minimum output entropy ($H_{min}$) of quantum multiple access channels (MACs). We provide an example of violation of the additivity theorem for $H_{min}$ known in classical information theory. Our result is based on a fundamental property of $MACs$ i.e. independence of each sender. The channels used in the example can be constructed explicitly. On the basis of subadditivity of $H_{min}$ we also provide an example of extremal superadditivity (super activation) of the classical capacity region of MACs.