SARG04 decoy-state quantum key distribution based on an unstable source

A three-state protocol for the SARG04 decoy-state quantum key distribution (QKD) based on an unstable source is presented. The lower bound to the secure key generation rate is derived without using the basic hypothesis of the original decoy-state idea. The three-state SARG04 decoy-state protocol with an unstable parametric down-conversion source is considered in the simulation. The simulation results show that the protocol in this paper with an unstable source gives a key generation rate that is close to that with a stable source, and only slight advantage appears by using a stable source when the transmission distance is long. So the SARG04 decoy-state protocol with an unstable source still can obtain the unconditional security with a slightly shortened final key.