Quantum cryptography: Japanese researchers achieve record 50 km secure transmission with single-photon emitter

Tokyo and Kawasaki, Japan--After just achieving the world's first quantum-dot-laser-based 25 Gbps high-speed data transmission in May 2010 by many of the same researchers, the Institute for Nano Quantum Information Electronics at The University of Tokyo (director Yasuhiko Arakawa), Fujitsu Laboratories Limited, and NEC Corporation have now achieved quantum cryptographic key distribution at a world-record distance of 50 km using transmission from a single-photon emitter.

This result was the product of the three-way collaboration between the University of Tokyo, Fujitsu, and NEC, and represents a milestone in quantum key distribution because it combines a single-photon emitter, which is ideal for optical transmission bands, with a prototype of a practical quantum cryptography system. Experimental success at a practical level with a single-photon emitter brings one step closer the practical use of quantum cryptography in the 1.5 µm band, which is most desirable for long-distance data transmissions.

With quantum cryptography, a quantum cryptographic key is transmitted one photon at a time, the smallest increment possible. If an eavesdropper is listening in on the transmission line, the basic principles of quantum theory mean that the act of eavesdropping will change the signal in a way that the intended recipient can immediately detect. The ability to detect eavesdropping as a basic consequence of physical laws is quantum cryptography's greatest advantage over previous cryptographic methods and is the focus of intensive R&D efforts around the world.

The Japanese researchers worked together to develop a new system that brought together a 1.5 µm single-photon emitter and a practical quantum cryptography system, and jointly conducted tests of quantum cryptographic key distribution. Using analyses based on security theory, the researchers demonstrated secure transmissions at distances of 50 km using 1.5 µm single-photon transmissions and showed that a quantum-dot single-photon emitter used as the quantum cryptographic system's light source could be used on a practical level.

This research can be considered the first in the world to bring together work in quantum-dot optical devices with quantum information technology. Future work will focus on making systems using single-photon emitters more efficient, with the goal of practical implementations in five to ten years. Also being developed is a current-injected 1.5 µm single-photon emitter, which promises simpler and more compact quantum cryptographic communications systems in the future.

SOURCE: Fujitsu; www.fujitsu.com/global/news/pr/archives/month/2010/20100910-02.html

Posted by:Gail Overton

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