NIST Sends Entangled Photons 62 km Over Existing Fiber, Keeping 92.8% Uptime

2 articles · Updated · ScienceAlert · Aug 18

62 kilometers of mostly above-ground fiber between NIST and the University of Maryland carried entangled photons without breaking their quantum link, showing the technique can work outside controlled lab conditions.
A laser reference signal let researchers measure twisting in the noisy cable and correct the photons’ polarization, with stabilization overhead taking 7.2% of operating time and leaving 92.8% for quantum transmission.
The test used aerial cables exposed to wind, temperature swings, traffic vibrations and even birds—conditions the team called close to the worst case for polarization-based quantum networking.
Transmission rates of 200 to 1,500 entangled photons per second still need improvement, but the result points toward practical quantum networks for ultra-secure communications, linked quantum computers and distributed instruments.