Decoy state protocols for quantum cryptography with parametric down conversion sources

In this paper, we show that decoy states are very simple to implement for quantum key distribution (QKD) with parametric down conversion (PDC) sources. Indeed, with no modification in the hardware at all, by using the AYKI scheme, one can achieve a key generation rate that is close to the theoretical limit of infinite decoy states. Therefore, we expect decoy state QKD to become a standard technique not only in the coherent state QKD, but also in QKD with PDC sources.