Efficient W state entanglement concentration using quantum-dot and   optical microcavities
  We present an entanglement concentration protocols (ECPs) for less-entangled W state with quantum-dot and microcavity coupled system. The present protocol uses the quantum nondemolition measurement on the spin parity to construct the parity check gate. Different from other ECPs, this less-entangled W state with quantum-dot and microcavity coupled system can be concentrated with the help of some single photons. The whole protocol can be repeated to get a higher success probability. It may be useful in current quantum information processing. 
Yu-Bo Sheng, Lan Zhou, Chuan Wang, and Sheng-Mei Zhao
quant-ph