Entanglement-assisted capacity regions and protocol designs for quantum multiple-access channels

We solve the entanglement-assisted (EA) classical capacity region of quantum multiple-access channels with an arbitrary number of senders, which was conjectured by Hsieh, Devetak and Winter. As an example, we consider the bosonic Gaussian multiple-access channel, which is prevalent in optical communications. For the total communication rate, we find that the EA capacity is additive and achieved by an entanglement source composed of sender-receiver pairwise two-mode squeezed vacuum (TMSV) states; for the individual rates, we derive a computationally friendly outer bound for the EA capacity region. As an example, we evaluate the one-shot capacity region enabled by the pairwise TMSV states. The EA capacity region is strictly larger than the capacity region without entanglement-assistance. Practical protocols based on pairwise TMSV states generated by spontaneous parametric down-conversion, phase modulation and optical parametric amplifiers are presented to benefit from entanglement. In the parameter region of a large noise background, the receivers can enable a simultaneous rate advantage of 82.0% for each sender. Due to teleportation and superdense coding, our results for EA classical communication can be directly extended to EA quantum communication at half of the rates.