Long-distance continuous-variable quantum key distribution using non-Gaussian state-discrimination detection

Abstract

We propose a long-distance continuous-variable quantum key distribution\n(CVQKD) with four-state protocol using non-Gaussian state-discrimination\ndetection. A photon subtraction operation, which is deployed at the\ntransmitter, is used for splitting the signal required for generating the\nnon-Gaussian operation to lengthen the maximum transmission distance of CVQKD.\nWhereby an improved state-discrimination detector, which can be deemed as an\noptimized quantum measurement that allows the discrimination of nonorthogonal\ncoherent states beating the standard quantum limit, is applied at the receiver\nto codetermine the measurement result with conventional coherent detector. By\ntactfully exploiting multiplexing technique, the resulting signals can be\nsimultaneously transmitted through an untrusted quantum channel, and\nsubsequently sent to the state-discrimination detector and coherent detector\nrespectively. Security analysis shows that the proposed scheme can lengthen the\nmaximum transmission distance up to hundreds of kilometers. Furthermore, by\ntaking finite-size effect and composable security into account we obtain the\ntightest bound of the secure distance, which is more practical than that\nobtained in the asymptotic limit.\n