Entanglement sent over 50 km of optical fiber

Researchers from the University of Innsbruck and at the Institute of Quantum Optics and Quantum Information of the Austrian Academy of Sciences have achieved a record for the transfer of quantum entanglement over a distance of 50 kilometers using fiber optic cables.

The photon emitted by a calcium ion has a wavelength of 854 nm and would be quickly absorbed by the optical fiber. So the idea was to send the photon through a nonlinear crystal illuminated by a strong laser. Thereby the photon wavelength is converted to the current telecommunications standard wavelength of 1550 nm. (Phys.org)

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