Entanglement between Two Uses of a Noisy Multipartite Quantum Channel Enables Perfect Transmission of Classical Information

TL;DR

This paper demonstrates that quantum entanglement can enable perfect classical information transmission over noisy multipartite channels with just two uses, even when a single use is insufficient, unlike classical channels.

Contribution

It introduces a quantum channel exhibiting superadditivity of classical capacity, enabled by entanglement, which is a novel phenomenon not present in classical channels.

Findings

Single use cannot transmit information.

Two uses enable perfect transmission due to entanglement.

Quantum channels can outperform classical ones in capacity.

Abstract

Suppose that $m$ senders want to transmit classical information to $n$ receivers with zero probability of error using a noisy multipartite communication channel. The senders are allowed to exchange classical, but not quantum, messages among themselves, and the same holds for the receivers. If the channel is classical, a single use can transmit information if and only if multiple uses can. In sharp contrast, we exhibit, for each $m$ and $n$ with $m\ge 2$ or $n\ge 2$, a quantum channel of which a single use is not able to transmit information yet two uses can. This latter property requires and is enabled by quantum entanglement.