Entanglement concentration for unknown W class states

In this paper, we propose a theoretical entanglement concentration protocol for unknown triparticle W class states, and then the physical implementation of this proposal has also been presented in cavity QED. The general protocol is mainly based on the appropriate Bell state measurements. In the feasible physical scheme, the interaction between two driven atoms and a cavity mode is a large-detuned one, so the scheme is insensitive to both the cavity decay and the thermal field.