Abstract

Cryptography–the ancient art of secret messages–has broadened its scope to cover all situations in which it is desired to control the flow of information among two or more parties, not all of whom trust one another. Non-orthogonal quantum states of the optical radiation field, by virtue of the inherent limitations on measuring them imposed by the uncertainty principle, have recently emerged as a valuable adjunct to the traditional mathematical tools of cryptography. In particular, quantum optical communications systems can achieve a goal unattainable by classical mathematical means alone: to enable two parties, who share no secret Information initially, to exchange secret information even though all their transmissions are subject to monitoring by an eavesdropper.

© 1993 Optical Society of America