We consider quantum channels with two senders and one receiver. For an arbitrary such channel, we give multi-letter characterizations of two different two-dimensional capacity regions. The first region characterizes the rates at which it is possible for one sender to send classical information, while the other sends quantum information. The second region gives the rates at which each sender can send quantum information. We give examples of channels for which both regions have single-letter characterizations. We conclude with connections to other work and a conjecture on a generalization where each user simultaneously sends classical and quantum information.
This represents joint work with Igor Devetak and Patrick Hayden.