Coherent State Based Quantum Optical Communication with Mature Classical Infrastructure

Coherent state based quantum optical communication is able to offer high speed secret key rate with relatively easy operation by the use of mature classical optical communication infrastructure. While it involves the discrete modulation format, the phase noises due to the operation of those classical coherent optical communication devices may impact the security. We analyzed the security with respect to coherent state based quantum cryptography by taking a concrete 4 state modulation into account in this paper. Our numerical simulation results revealed that the phase noise resulting from the discrete modulation degrades the secret key rate remarkably.