The quantum cryptography and the unambiguous measurement of quantum nonorthogonal states

摘要

We discuss the unambiguous measurement of quantum nonorthogonal states inconnection with the quantum cryptography. We show that checking a ratio of nullone to signal is essential in detecting a certain kind of eavesdropping in thecase of two nonorthogonal states quantum cryptography. We prove that it is notneeded in the case of the four states quantum cryptography.