Universal random codes: Capacity regions of the compound quantum multiple-access channel with one classical and one quantum sender. (arXiv:1801.03692v1 [quant-ph])
We consider the compound memoryless quantum multiple-access channel (QMAC)
with two sending terminals. In this model, the transmission is governed by the
memoryless extensions of a completely positive and trace preserving map which
can be any element of a prescribed set of possible maps. We study a
communication scenario, where one of the senders shares classical message
transmission goals with the receiver while the other sends quantum information.
Combining powerful universal random coding results for classical and quantum
information transmission over point-to-point channels, we establish universal
codes for the mentioned two-sender task. Conversely, we prove that the
two-dimensional rate region achievable with these codes is optimal. In
consequence, we obtain a multi-letter characterization of the capacity region
of each compound QMAC for the present transmission task.