Hybrid Entangled States with Multi-Degree of Freedom and High Purity for Internet of Vehicles

The development of intelligent Internet of vehicles (IoV) is based on communication technology, especially the quantum communication of hybrid entangled states based on orbital angular momentum (OAM). The quantum key distribution (QKD) method is demonstrated using hybrid entangled states with multi-degree of freedom and high purity based on OAM. First, the polarization entangled photon pairs are produced by two type I BBO crystals by means of spontaneous parametric down-conversion (SPDC). The polarization-OAM hybrid entangled states are created by q-plate (QP) to realize QKD. It is found that the polarization entangled photon pairs have the characteristics of OAM. A single mode fiber (SMF) is proposed to filter the topological charge non-zero photons and purify the polarization entangled photon pairs. Then the purification setup with M-Z interferometer and beam rotator (BR) is presented which can purify the polarization-OAM hybrid entangled states. The high purity polarization-OAM hybrid entangled states are implemented, and the QP conversion rate of 3 secondary feedbacks is 99.84% theoretically. Analysis indicates that precise purity polarization-OAM hybrid entangled state can increase the fidelity of information and improve the anti-interference ability in this program without mutually unbiased bases (MUBs). The photon utilization rate, energy-efficient and low-latency communication can be greatly improved by using the OAM carrying information.