Quantum Storage of High-D OAM Entanglement in an Atomic Ensemble

Abstract

In this Chapter, I focus on the key goal as described in the beginning, that is the realization of high-dimensional entanglement storage and establishment high-dimensional entanglement between two atomic states. Quantum states entangled in high-dimensional OAM space show more advantages that entangled in two-dimensional space, like photonic polarization DOF. They enable quantum communication with enhanced channel capacity, quantum-information processing in more efficient way, and be more feasible to close the detection loophole in the fundamental quantum physics of Bell test experiments, etc. Preparing high-dimensional OAM entangled state and establishing distant memories in high-dimensional OAM entanglement are significant for long-distance communication in high-space, but its experimental demonstration was lacking before this work has been implemented. Herein, we have experimentally established high-dimensional entanglement in OAM space between two atomic ensembles separated 1 m apart through the technique of Raman storing photonic OAM high-dimensional entangled state. We reconstructed the density matrix for a three-dimensional entanglement, and obtained an entanglement fidelity of $83.9\pm 2.9$%. More importantly, we confirmed the successful preparation of a state entangled in more than three-dimensional space (up to seven-dimensional) using general and conditional entanglement witnesses. Achieving high-dimensional entanglement may represent a significant step towards a high-capacity quantum information processing, quantum communications in high-dimension.