Scheme for entanglement concentration of unknown partially entangled three-atom W states in cavity QED

We propose a practical scheme to concentrate entanglement in a pair of unknown partially entangled three-atom W states in cavity quantum electrodynamics (QED). In the scheme, Alice, Bob, and Charlie at three distant parties can obtain one maximally entangled three-atom W state with the certain success probability from two identical partially entangled three-atom W states by local operations and classical communication. We propose the detailed process of entanglement concentration and analyze the experimental feasibility of the scheme.