Capacity of Lossy Photon Channels with Input Constraints
Fumio Kanaya · Institutional Repositories DataBase (IRDB) · 1996
Recently, considerable interest has emerged in quantum states of light fields other than a classical coherent state. One example of such nonclassical quantum states is the number state which features zero uncertainty for the photon number. Because of this unique property, the number states are promising as information bearing lights in direct-detection optical communications. However, if a channel is lossy, the benefit of using the number state is lessened because random photon deletions due to dissipative effect of the channel introduce inherent uncertainty to the photon number measurement at a receiver. Therefore, even in noiseless optical channels, the lossy effect must be taken into account as an important degradation factor which limits the channel performance. In this paper we compute the capacity of lossy photon channels which utilize the number state light under a certain input constraint. For binary and ternary PAM schemes, we obtain the capacity C (Γ) which is subject to the input constraint that the average number of photons per transmitted symbol can not exceed the fixed number Γ.