Entanglement concentration for concatenated Greenberger-Horne-Zeiglinger   state with feasible linear optics
  The concatenated Greenberger-Horne-Zeiglinger (C-GHZ) state which is a new type of logic-qubit entanglement has attracted a lot of attentions recently. We present a feasible entanglement concentration protocol (ECP) for logic-qubit entanglement. This ECP is based on the linear optics, and it does not know the initial coefficients of the less-entangled C-GHZ state. This protocol can be extended to arbitrary C-GHZ state. This protocol may be useful in future quantum information processing tasks. 
Yu-Bo Sheng, Chang-Cheng Qu, and Lan Zhou
quant-ph