Study of multiple degrees of freedom entanglement in optical fiber

The orbital angular momentum (OAM) has attracted widespread attention due to its ability to carry information in multiple dimensions. However, a high-dimensional entanglement carrying OAM can be affected by environment and undergoes decoherence. How to control the entangled states and ensure the stability and high fidelity of entangled states is a crucial part of quantum communication. In this paper, we produce the polarization entangled photon pairs by spontaneous parametric down-conversion, we achieve the polarization-OAM hybrid entangled states by manipulating the multi-degrees of freedom of the quantum state. The polarization entangled photon pairs have the characteristics of OAM. We use polarization degree of freedom to modulate OAM degree of freedom, our polarization-OAM hybrid entangled states can slow down the reduction of the fidelity in the transmission process. This method can provide a theoretical guidance for improving the transmission fidelity of OAM states in fiber.