Coherent communication with continuous quantum variables

The coherent bit (cobit) channel is a resource intermediate between classical and quantum communication. It produces coherent versions of teleportation and superdense coding. We extend the cobit channel to continuous variables by providing a definition of the coherent nat (conat) channel. We construct several coherent protocols that use both a position-quadrature and a momentum-quadrature conat channel with finite squeezing. Finally, we show that the quality of squeezing diminishes through successive compositions of coherent teleportation and superdense coding.

Figure 1

Coherent teleportation. $\pi$ is a reflection operation. C-X and C-P are a controlled-position displacement and a controlled-momentum displacement respectively.

Figure 2

Alternate coherent teleportation protocol.

Figure 3

Coherent superdense coding implements two conat channels.