Low-complexity conjugate homodyne detection scheme for SPAD-free DV-QKD

Abstract We demonstrate a polarization diversity conjugate homodyne detection scheme for DV-QKD, that does not require complex high computational demanding post-processing or single-photon detection. Unlike CV-QKD based on coherent detection, this work presents the advantage for saving computational resources highly-demanded by sophisticated carrier phase and frequency recovery schemes. A complete physical model of the DV-QKD system is assessed under a finite-key size analysis of the BB84 with 1 decoy state protocol and phase randomization between consecutive pulses. We show that, for practical post-processing block sizes of 108 bits, the system is able for key generation up to a secrete key fraction of 4% obtained after a post-selection stage to obtain discrete outcomes. Also, we demonstrate experimentally the decoding of quantum polarization states can be achieved with a inherent QBER lower than 1%.