Toshiba Cambridge Research Laboratory
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Network Field Trials

For general operation it is important that QKD can operate in ordinary communication networks. Toshiba have been involved in several international demonstrations of QKD networks. They include the SECOQC network in Vienna, Austria in 2008 and more recent trials the Tokyo QKD network in Japan collaboration with the National Institute for Information and Communication Technologies (NICT).

The Tokyo QKD network field trials showcased a QKD system with bit rates in excess of 1 Mbit/s. This allows high bandwidth applications such as high speed video encryption to be secure by quantum methods. Both secure video encryption and a foiled eavesdropping attack were demonstrated.

Long term field trials have also been performed. The transmitter was installed in a server room of a high rise building in the Otemachi area of central Tokyo. The receiver was located at NICT’s Koganei premises in Greater Tokyo. The two ends were linked by a 45 km metropolitan optical fibre. Although around 50% of this fibre was routed over-ground on utility poles, and therefore subject to weather and traffic disturbances, the resulting QKD secure bit rate was found to be very stable.

Graph showing the Secure Bit Rate as a function of time over a range of 34 days.

The high bit rate prototype QKD system distributed a total of 878 Gbit of secure key data over a 34 day period corresponding to a sustained key rate of around 300 kbit/s. The system was deployed over a standard 45 km link of an installed metropolitan telecommunication fibre network in central Tokyo. The prototype QKD system is compact, robust and automatically stabilised, enabling key distribution during diverse weather conditions. It operates at GHz clock rates and all necessary optics and high speed electronics are enclosed inside compact 19" rack units.

Satellite image showing 45km link from Alice in Otemachi to Bob in Koganei outside Tokyo.
Image courtesy of the U.S. Geological Survey

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