Weak+Vacuum and One Decoy State with Two Way Quantum Key Distribution   Protocol
  We present relevant bounds for the case of weak+vacuum decoy state and one decoy state for a two way four states Quantum Key Distribution (QKD) protocol. The numerical simulation result was significant given that an improvement in maximum secure distance of nearly double is achieved. 
M. F. Abdul Khir, Iskandar Bahari, S. Ali, S. Shaari
quant-ph