High dimensional quantum key distribution with temporal and polarization hybrid encoding

High dimensional quantum key distribution is regarded as one of the most promising ways to boost the performance of quantum communication. In this paper, we propose a new scheme of high dimensional quantum key distribution in advantage of improving the efficiency by hybridly encoding the temporal and polarization degrees of freedom. The experimental setup consisting of merely off-the-shelf components is also discussed. Only two time slots are used to achieve 4-dimensional encoding, which can enhance the system frequency or reduce the requirement for the time resolution of the detector. The interference efficiency is increased to 100% during the phase basis decoding, which improves the secure key rate and the working distance. The performance of the proposed scheme is analyzed with finite-size effect. Numerical results show that the secure key rate is much higher than the previous protocol or the 2-dimensional version.