(SpectrumIEEE) Julien Laurat, a professor and leader of the quantum networks team at the Kastler Brossel Laboratory at Sorbonne University in France has achieved a pivotal step on the road to eventually building large-scale quantum communication networks spanning entire continents. Laurat said, “We learned how to achieve a 85-90 percent [efficiency] benchmark–This is the best in any physical platform.”
Boosting storage-and-retrieval efficiency from 25 percent to 90 percent makes a big difference in the speed and size of the quantum network such memory devices could support. For instance, Laurat and colleagues note, increasing efficiency from 60 percent to 90 percent would accelerate quantum memory speeds by two orders of magnitude over a distance of 600 km.
The experiment involved two quantum memory devices based on ensembles of laser-cooled cesium atoms. Researchers demonstrated how cesium atoms can store and retrieve single-photon entanglement from entangled light beams. Entangled photons could connect the various quantum nodes in a future quantum internet
Laurat and his team already have their sights set on tackling some of those next milestones. If all goes well, they envision a pan-European quantum network becoming possible within the next five to 10 years. “The next few years should see demonstrations over a few tens of kilometers,” Laurat says.

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