A high-speed quantum cryptography system that allows “Alice” and “Bob” to discuss things in absolute secrecy earned a 2007 R&D 100 Award for a team of researchers at the National Institute of Standards and Technology (NIST).
The R&D 100 Awards are made annually by the editors of R&D Magazine to recognize “the 100 most technologically significant products” introduced in the past year.
The award-winning “High-Speed Fiber Quantum Key Distribution System” uses lasers to generate individual photons that are transmitted down a fiber-optic communications line. The sender, notionally “Alice,” can send an unbreakable message encryption key to the receiver, “Bob,” encoded in the polarization directions of individual photons. The rules of quantum mechanics say that the polarization of any individual photon cannot be measured or “read” without destroying the photon, so no potential eavesdropper can intercept the transmission from Alice to Bob without being detected.
Of course, it’s harder than that.
Practical high-speed quantum key distribution (QKD) systems have to contend with physical realities. Photons get lost, absorbed or reflected by the transmission system, so a working system has to be able to account for the lost ones and keep Alice and Bob in sync. The installed base of fiber-optic communications equipment does not work at the best frequencies for sensitive photon detectors, but it is the installed base, so a practical system has to work with that as well. And the system should be fast enough to handle modern communications requirements, such as streaming video or lots of high-speed messages.
The NIST system relies on high-efficiency, low noise detectors that use a clever frequency conversion device to get optimum performance from both the photon detectors and the optical fiber in between. The research team has demonstrated their ability to generate and transmit secure keys at a rate of over half a million bits per second over 10 km of optical fiber - fast enough to encrypt streaming digital video using a theoretically unbreakable one-time-pad encryption in real time. The group also has transmitted secure keys at rates near 10 kilobits per second at five times that distance.