Positive-operator and projection valued measurements in quantum key distribution

摘要

Following a brief review of positive-operator and projection valued measures in quantum mechanics, some applications to quantum key distribution are described. The positive operator valued measure (POVM) can be usefully implemented in a quantum key receiver used in the B92 two-state protocol of quantum key distribution. In this case the measurement is conclusive, at least some of the time. The projection valued (PV) measure is useful in the measurement of a quantum cryptographic entangling probe for tapping quantum key in the BB84 four-state protocol. In the case addressed here, the measurement determines correlations with the measurements made by the legitimate receiver and therewith the maximum information gain by the probe.