2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/150916We discuss the unambiguous measurement of quantum nonorthogonal states in connection with the quantum cryptography. We show that checking a ratio of null one to signal is essential in detecting a certain kind of eavesdropping in the case of two nonorthogonal states quantum cryptography. We prove that it is not needed in the case of the four states quantum cryptography.withdrawalQuantum Physicstext