Quantum trade-off coding for bosonic communication
Mark M. Wilde, Patrick J. Hayden, Saikat Guha · Physical Review A · 2012
The trade-off capacity region of a quantum channel characterizes the optimal net rates at which a sender can communicate classical, quantum, and entangled bits to a receiver by exploiting many independent uses of the channel, along with the help of the same resources. Similarly, one can consider a trade-off capacity region when the noiseless resources are public, private, and secret-key bits. We identified [see Wilde, Hayden, and Guha, Phys. Rev. Lett. 108, 140501 (2012)] these trade-off rate regions for the pure-loss bosonic channel and proved that they are optimal provided that a long-standing minimum-output entropy conjecture is true. Additionally, we showed that the performance gains of a trade-off coding strategy when compared to a time-sharing strategy can be quite significant. In this paper, we provide detailed derivations of the results announced there, and we extend the application of these ideas to thermal-noise and amplifying bosonic channels. We also derive a ``rule of thumb'' for trade-off coding, which determines how to allocate photons in a coding strategy if a large mean photon number is available at the channel input. Our results on the amplifying bosonic channel also apply to the ``Unruh channel'' considered in the context of relativistic quantum information theory.