** Quantum communication protocol beyond standard quantum limit** - Min Namkung

In optical communication, a sender encodes a message in an optical signal and sends it to a receiver who detects the signal to decode the message. However, the success probability or the mutual information of the conventional communication protocol cannot surpass the standard quantum limit due to the statistical and physical properties of the signal and the measurement device.
For this reason, an unconventional quantum communication protocol surpassing the standard quantum limit needs to be designed. In this talk, we provide a quantum communication protocol with an indirect measurement based on the Jaynes-Cummings model. We show that our scheme can nearly perform an optimal quantum communication enhanced by the generalization of coherent signals. Moreover, our indirect measurement can outperform the other feedback-excluded measurements in the existence of the phase-diffusion noise.
Also, enhancing the optimal success probability of N-ary unconventional quantum communication with the generalization of the coherent signal is necessary, since N-ary signal has been widely used for sending log_2N bits in one signal pulse. We show that the optimal success probability of the N-ary phase-shift-keying quantum communication can be improved by some non-sub-Poissonian, non-standard coherent state.

Reference:

[1] M. Namkung and J. S. Kim, "Enhanced Optimal Quantum Communication by Generalized Phase Shift Keying Coherent Signal", Phys. Rev. A 105, 042428 (2022).

[2] M. Namkung and J. S. Kim, "Indirect Measurement for Optimal Quantum Communication Enhanced by Binary Non-standard Coherent States", J. Opt. Soc. Am. B 39, 1247 (2022).