 He illustrated his idea with a design of unforgeable bank notes.A decade later, building upon this work, Charles H. Bennett, of the IBM Thomas J. Watson Research Center, and Gilles Brassard, of the University of Montreal, proposed a method for secure communication based on Wiesner’s "conjugate observables".In 1990, Artur Ekert, then a Ph.D. student at Wolfson College, University of Oxford, developed a different approach to quantum key distribution based on quantum entanglement.