OPTIMAL EAVESDROPPING IN QUANTUM CRYPTOGRAPHY WITH 6 STATES

A generalization of the quantum cryptographic protocol by Bennett and Brassard is discussed, using three conjugrate bases, i.e., six states. By calculating the optimal mutual information between sender and eave sdropper it is shown that this scheme is safer against eavesdropping o n single qubits than the one based on two conjugate bases. We also add ress the question for a connection between the maximal classical corre lation in a generalized Bell inequality and the intersection of mutual informations between sender/receiver and sender/eavesdropper.