Efficient quantum key distribution based on hybrid degrees of freedom.

Round-robin differential-phase-shift (RRDPS) quantum key distribution (QKD) protocol is a practical QKD protocol without monitoring the signal disturbance. However, how to further increase the secure key rate is still a challenge in practice. In the paper, we propose a high efficient QKD protocol based on RRDPS-QKD, where the photon-states are encoded in two degrees of freedom (DOFs), phase and polarization. The key generation rate and the security of the proposal protocol are analyzed. The simulation results show that the secure key rate is greatly improved in comparison with the original RRDPS-QKD protocol by breaking the limitation of quantum state in a single DOF. Moreover, our protocol can still maintain the high error tolerance of RRDPS-QKD protocol. [ABSTRACT FROM AUTHOR]