Experimental quantum cryptography

We describe results from an apparatus and protocol designed to implement quantum key distribution, by which two users, who share no secret information initially: (1) exchange a random quantum transmission, consisting of very faint flashes of polarized light; (2) by subsequent public discussion of the sent and received versions of this transmission estimate the extent of eavesdropping that might have taken place on it, and finally (3) if this estimate is small enough, distill from the sent and received versions a smaller body of shared random information, which is certifiably secret in the sense that any third party's expected information on it is an exponentially small fraction of one bit. Because the system depends on the uncertainty principle of quantum physics, instead of the usual mathematical assumptions such as the difficulty of factoring, it remains secure against an adversary with unlimited computing power.This paper was accepted prior to the present Editor-in-Chief taking responsibility. A preliminary version of this paper was presented at Eurocrypt '90, May 21–24, Århus, Denmark, and has appeared in the proceedings, pp. 253–265. François Bessette was supported in part by an NSERC Postgraduate Scholarship. Gilles Brassard was supported in part by Canada's NSERC. This work was performed while John Smolin was visiting IBM Research.