Researchers in Japan have achieved quantum cryptographic key distribution at a world-record distance of 50 km using transmission from a single-photon emitter. The University of Tokyo, Fujitsu Laboratories, and NEC collaborated to developed a 1.5 µm single-photon emitter suitable for long distance data transmission. This overcomes two obstacles in quantum cryptography — previously, a single pulse from a light source would often emit two or more photons, which meant that eavesdropping might go undetected, and secondly, the distance required for any practical system.
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.
Fujitsu said 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 5–10 years.
http://www.fujitsu.com/global/news/pr/archives/month/2010/20100910-02.html
