Storing a single photon as a spin wave entangled with a flying photon in the telecommunication bandwidth

Quantum memory is an essential building block for quantum communication and scalable linear quantum computation. Storing two color entangled photons, with one photon being at telecom-wavelength while the other photon being compatible of quantum memory, has great advantages toward the realization of the fiber based long-distance quantum communication with the aid of quantum repeaters. Here, we report an experimental realization of storing a photon entangled with a telecom photon in polarization as an atomic spin wave in a cold atomic ensemble, thus establishing the entanglement between the telecom-band photon and the atomic ensemble memory in polarization degree of freedom. The reconstructed density matrix and the violation of Clauser Horne Shimony Holt inequality clearly show the preservation of quantum entanglement during storage. Our result is very promising for establishing a long-distance quantum network based on cold atomic ensembles.

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