Research Update: Optical switch routes single photons of quantum cryptography

Researchers at NTT (Nippon Telegraph and Telephone), Japan, demonstrated switching of single photons for use in ultrasecure quantum cryptography, which may supersede public-key systems for even more secure links. (Any attempt to measure or eavesdrop on the photon changes its quantum state.) NTT developed the technique in collaboration with Stanford University.

The 8×8 optical matrix uses an interferometer to steer the photons, along with much more intense optical signals using the same pathways. By changing the temperature of one of the two arms of the interferometer, its refractive index and, thus, optical-path length changes. The fragile single photon changes paths, as well, in accordance with principles of the dual-particle/wave nature of light and quantum theory. You can find details at www.ntt.co.jp/news/news05e/0506/050614.html.

Nippon Telegraph and Telephone, www.ntt.co.jp.