A noisy states in semi quantum key distribution

This work presents a security analysis of the semi-quantum key distribution protocol when the transmitted states are modeled as a depolarizing channel i.e. a mixture of the ideal state and the maximally mixed state. This scenario can occur either by the deliberate addition of noise by Alice to the states before their transmission, or in a practical situation where Eve cannot substitute the noisy quantum channel with an ideal one. We derive the maximum amount of information that Eve can obtain from Alice in the case of individual attacks, for protocols employing two and three mutually unbiased bases. The findings show that depolarization decreases Eve’s information gain compared to that of Bob.