In our letter published in Nature Photonics we have demonstrated quantum key distribution (QKD) over 307 km. The research has also been highlighted by several local newspapers, including Tribune de Genève.

This is the first time that such a distance has been achieved, whilst maintaining a quantifiable security measure of the whole protocol. That is to say, we can quantify the probability of an unwanted person learning part of the secret key. In our case, the probability of this happening was very low (about 10-9), even though the maximum operating distance of the system sets a new record.

In addition, our demonstration makes use of practical single photon detectors, which can be very compact due to their higher operating temperature. Previous long distance QKD demonstrations always used cryogenic detectors, which would need to be cooled to around 3 K or less, whilst our detectors operate at much higher temperatures of about 150 K.

This demonstration was helped through a collaboration with Corning Incorporated, who are able to manufacture an optical fiber with ultra-low loss, which is important to achieving long distance QKD transmission.

Further Reading

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If you wish to use the image from this article, it can be downloaded below. Image credit: Boris Korzh.

QKD, University of Geneva, Quantum Technologies, Boris Korzh, Hugo Zbinden