Inconclusive rate in quantum key distribution

Summary form only given. The inconclusive rate can be a useful disturbance measure in quantum cryptography. Bennett´s two-state protocol is considered for the case in which a positive operator-valued measure is optically implemented by the legitimate receiver in the presence of an individual attack by a general unitary disturbing eavesdropping probe. The maximum Renyi information gain by the disturbing probe is calculated for given receiver error and inconclusive rates. It is shown explicitly that less information is available to an eavesdropper at fixed inconclusive rate and error rate than is available at fixed error rate only.