Quantum Key Distribution with Vacua or Dim Pulses as Decoy States
  Recently, Hwang has proposed a decoy state method in quantum key distribution (QKD). In Hwang's proposal, the average photon number of the decoy state is about two. Here, we propose a new decoy state scheme using vacua or very weak coherent states as decoy states and discuss its advantages. 
Hoi-Kwong Lo (Center for Quantum Information and Quantum Control,   Department of ECE & Dept. of Physics, University of Toronto)