Twin-Field Quantum Key Distribution (QKD)
Until recently, the typical range of QKD had been limited to a few hundred kilometers of fibre-optic cable. Toshiba has discovered a way to enhance the key rate and transmission distance of QKD, potentially allowing fibre links beyond 500km via a Twin-Field QKD protocol. This enables the protection of sensitive data transmitted in optical networks between cities, allowing for the creation of a secure link between cities like London, Paris, Brussels, Amsterdam and Dublin.
In Twin-Field QKD, light pulses are sent from both ends of the fibre to a central location, where a photon is detected. Provided it is impossible to tell which end of the fibre the photon came from, this technique effectively doubles the transmission distance at a given rate. Although conventional systems may be daisy-chained together to increase the total transmission distance, this requires that the intermediate stations are in a secure location. In contrast, no physical protection in the central location is necessary for the security of Twin-Field QKD. This would enable a bank in London, for instance, to move highly sensitive customer data to a data centre in Leeds within the current conventional fibre-optic network without the fear of the data being compromised.
Very recently Toshiba has made the first experimental demonstration of Twin-Field QKD, reporting the first demonstration of QKD with a channel loss exceeding 80dB, corresponding to over 500km of ultra-low loss optical fibre.