D. S. Ding, W. Zhang, Z. Y. Zhou, S. Shi, G. Y. Xiang, X. S. Wang, Y. K. Jiang, B. S. Shi and G. C. Guo (2015) Quantum Storage of Orbital Angular Momentum Entanglement in an Atomic Ensemble. Journal/Physical Review Letters 114 5. [In English]
Web link: http://dx.doi.org/10.1103/PhysRevLett.114.050502
Keywords: HIDDEN-VARIABLE THEORIES, BELL INEQUALITY, MEMORY, PHOTONS, LIGHT, COMMUNICATION, VIOLATION, DISTANCE
Abstract: Constructing a quantum memory for a photonic entanglement is vital for realizing quantum communication and network. Because of the inherent infinite dimension of orbital angular momentum (OAM), the photon's OAM has the potential for encoding a photon in a high-dimensional space, enabling the realization of high channel capacity communication. Photons entangled in orthogonal polarizations or optical paths had been stored in a different system, but there have been no reports on the storage of a photon pair entangled in OAM space. Here, we report the first experimental realization of storing an entangled OAM state through the Raman protocol in a cold atomic ensemble. We reconstruct the density matrix of an OAM entangled state with a fidelity of 90.3% +/- 0.8% and obtain the Clauser-Horne-Shimony-Holt inequality parameter S of 2.41 +/- 0.06 after a programed storage time. All results clearly show the preservation of entanglement during the storage.

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