Nonadditivity effects in classical capacities of quantum multiple-access channels

TL;DR

This paper investigates the nonadditivity of classical capacities in quantum multi-access channels, revealing a purely quantum effect where capacity regions are not additive, unlike classical channels, with implications for quantum information theory.

Contribution

It demonstrates the first known instance of nonadditivity in quantum multi-access channel capacities without extra resources, highlighting a fundamental quantum phenomenon.

Findings

Nonadditivity of quantum channel capacities shown

Purely quantum effect without classical resources

Resembles butterfly effect in classical channels

Abstract

We study classical capacities of quantum multi-access channels in geometric terms revealing breaking of additivity of Holevo-like capacity. This effect is purely quantum since, as one points out, any classical multi-access channels have their regions additive. The observed non-additivity in quantum version presented here seems to be the first effect of this type with no additional resources like side classical or quantum information (or entanglement) involved. The simplicity of quantum channels involved resembles butterfly effect in case of classical channel with two senders and two receivers.