A team of researchers at the National Institute of Standards and Technology in Gaithersburg, Md., has developed a quantum key distribution system that generates code keys over a 1-km length of SMF-28 optical fiber from Corning Inc. in New York at 4.14 Mb/s and over a 4-km span of the fiber at nearly 1 Mb/s. The group presented a report on its work at the SPIE Defense & Security Symposium in Orlando, Fla., on April 18.

The cryptography system relies on the no-cloning theorem in quantum mechanics to guarantee that a code key for subsequent encryption can be produced without the threat of its interception by an eavesdropper. It employs the polarization states of individual 850-nm photons from attenuated vertical-cavity surface-emitting lasers, following an approach proposed by Charles H. Bennett and Giles Brassard in 1984, and incorporates automated polarization-compensation and timing-alignment functions.

With further refinements, the system should be practical for integration into existing local area networks, the researchers suggest. Potential applications include the encryption of sensitive data, such as in finance, defense and health care.