Concentration for unknown atomic entangled states via cavity decay
  We present a physical scheme for entanglement concentration of unknown atomic entangled states via cavity decay. In the scheme, the atomic state is used as stationary qubit and photonic state as flying qubit, and a close maximally entangled state can be obtained from pairs of partially entangled states probabilistically. 
Zhuo-Liang Cao, Li-Hua Zhang, and Ming Yang