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Toshiba Research Europe Ltd., Cambridge Research Laboratory

Quantum Information Group, World Record QKD Bit Rates

Toshiba have succeeded in achieving continuous operation of QKD with a secure bit rate exceeding 1 Megabit/sec over a fibre spool with a length of 50 km. Averaged over a 36-hour period, the bit rate is 100–1000 times higher than anything reported previously for a 50-km link.

Toshiba's high bit rate QKD system has been implemented in the Tokyo QKD network launched in October 2010. Operating over a 45-km link (with 14.5 dB of optical loss) the system demonstrated stable operation with an average secure bit rate of 304 kb/s. This is the world-best key rate for installed fibre.

The advance derives from two innovations: a novel light detector and a feedback system. Using a ‘self-differencing’ circuit for single photon detection, Toshiba have increased the operating frequency of InGaAs avalanche photodiodes by a factor of 100, to beyond 2 GHz, with a maximum count rate of 500 MHz. Active feedback maintains a high bit rate at all times and requires no manual set-up or adjustment.

This dramatic enhancement of the bit rate is significant for two reasons. It will allow QKD to be implemented on networks that connect many users. While the previous bit rate has been sufficient for simple point-to-point links, it was not enough to allow frequent key refresh on multi-user networks, in which the bit rate must be shared.

These higher bit rates will allow one-time-pad encryption to be used for video conferencing and other high bandwidth applications. The one-time-pad is the only encryption algorithm that allows unconditionally secure communication and is often regarded as the Holy Grail of information security. However, its implementation has been hampered in the past by the requirement for a secret key of the same length as the data. Toshiba's advance with the QKD bit rate allows the one-time pad to be implemented for data streams of up to 1 Mb/s over 50 km fibre.

Image: Bit rate over time showing 1 Mbit/s average.

Further Reading

  Type Title and author(s) Source
1 Technical Continuous operation of high bit rate quantum key distribution
by A R Dixon et al.
Applied Physics Letters 96, 161102 (2010)
Download preprint
[preprint is open access]
2 Press release World record quantum cryptography bit rate enables ultra-secure networks Toshiba Research Europe Ltd., 19 April 2010
[open access]
3 Technical Multi-gigahertz operation of photon counting InGaAs avalanche photodiodes
by Z L Yuan et al.
Applied Physics Letters 96, 071101 (2010)
Link to Quantum Information Group - Quantum Cryptography Solutions for Network Security
Link to Speech Technology Group
Link to Toshiba Fellowship Programme - Join Toshiba's R&D team in Japan for up to two years
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