Computable limits of optical multiple-access communications

TL;DR

This paper establishes computable limits for optical multiple-access quantum channels, demonstrating how entanglement enhances communication rates and providing bounds and conjectures for capacity regions.

Contribution

It generalizes the additivity of entanglement-assisted capacity to multiple-access channels and proves Gaussian states optimize total rate in optical models.

Findings

Optimal total rate achieved by Gaussian entanglement.

Provided computable outer bounds for capacity regions.

Formulated an entanglement-assisted minimum entropy conjecture.

Abstract

Communication rates over quantum channels can be boosted by entanglement, via superadditivity phenomena or entanglement assistance. Superadditivity refers to the capacity improvement from entangling inputs across multiple channel uses. Nevertheless, when unlimited entanglement assistance is available, the entanglement between channel uses becomes unnecessary -- the entanglement-assisted (EA) capacity of a single-sender and single-receiver channel is additive. We generalize the additivity of EA capacity to general multiple-access channels (MACs) for the total communication rate. Furthermore, for optical communication modelled as phase-insensitive bosonic Gaussian MACs, we prove that the optimal total rate is achieved by Gaussian entanglement and therefore can be efficiently evaluated. To benchmark entanglement's advantage, we propose computable outer bounds for the capacity region without entanglement assistance. Finally, we formulate an EA version of minimum entropy conjecture, which leads to the additivity of the capacity region of phase-insensitive bosonic Gaussian MACs if it is true. The computable limits confirm entanglement's boosts in optical multiple-access communications.