Phys.org February 13, 2020
Researchers in China have demonstrated entanglement of two atomic ensembles in one laboratory via photon transmission through city-scale optical fibres. The atomic ensembles function as quantum memories that store quantum states. They used cavity enhancement to efficiently create atom–photon entanglement and quantum frequency conversion to shift the atomic wavelength to telecommunications wavelengths. They realized entanglement over 22 kilometres of field-deployed fibres via two-photon interference and entanglement over 50 kilometres of coiled fibres via single-photon interference. The experiment could be extended to nodes physically separated by similar distances, which would thus form a functional segment of the atomic quantum network, paving the way towards establishing atomic entanglement over many nodes and over much longer distances…read more. TECHNICAL ARTICLE
Schematic of the remote entanglement generation between atomic ensembles. Credit: Nature  volume 578, pages240–245(2020)