Scalable Implementation of Temporal and Phase Encoding QKD with Phase‐Randomized States

Abstract

AbstractQuantum key distribution (QKD), that is, exchanging cryptographic keys encoded in quantum particles exploiting the laws of quantum physics, is already a reality in our society. Current implementations are based on attenuated laser technique, a practical replacement of single photons which requires a random phase for each quantum state in order to achieve the highest level of security. In particular, the time‐bin and phase encoding techniques are mainly exploiting laser in gain‐switching modes combined with asymmetric interferometers or multiple laser sources in a master–slave configuration, which present limitations in terms of stability and scalability. In this work, a novel scheme for implementing a reconfigurable and scalable QKD transmitter based on the time‐bin encoding protocol with a decoy‐state method employing phase‐randomized weak coherent states is proposed and demonstrated. The scheme is tested and validated up to 26 dB‐attenuation channel using standard single‐photon detectors working in the telecom wavelength range.