Quantum Storage of Orbital Angular Momentum Entanglement in an Atomic   Ensemble
  Constructing a quantum memory for a photonic entanglement is vital for realizing quantum communication and network. Besides enabling the realization of high channel capacity communication, entangled photons of high-dimensional space are of great interest because of many extended applications in quantum information and fundamental physics fields. Photons entangled in a two-dimensional space had been stored in different system, but there have been no any report on the storage of a photon pair entangled in a high-dimensional space. Here, we report the first experimental realization of storing an entangled orbital angular momentum (OAM) state through a far off-resonant two-photon transition (FORTPT) in a cold atomic ensemble. We reconstruct the matrix density of an OAM entangled state postselected in a two-dimensional subspace with a fidelity of 90.3%+/-0.8% and obtain the Clauser, Horne and Shimony and Holt inequality parameter S of 2.41+/-0.06 after a programmed storage time. All results clearly show the preservation of entanglement during the storage. Besides, we also realize the storage of a true-single-photon via FORTPT for the first time. 
Dong-Sheng Ding, Wei Zhang, Zhi-Yuan Zhou, Shuai Shi, Guo-Yong Xiang,   Xi-Shi Wang, Yun-Kun Jiang, Bao-Sen Shi and Guang-Ca...
quant-ph