Dense coding with multi-atom entanglement channel in cavity QED

Dense coding of multi-atom entangled states in cavity QED is studied. If the quantum channel is generalized GHZ states, dense coding can be directly realized in a simple way. As fro the partially entangled pure states, we propose a feasible protocol for entanglement concentration, and the efficiency of information transmitted is calculated. The schemes are insensitive to the cavity decay and the field state, due to the fact that the interaction here is large-detuned one between atoms and the cavity.