Optimal entanglement concentration via photonic Faraday rotation in cavity QED

We propose optimal entanglement concentration protocols (ECPs) for photonic or atomic entanglement via photonic Faraday rotation in cavity QED system. It is shown that with the assistance of atomic or photonic qubits, photonic or atomic entanglement can be concentrated with optimal successful probability by iterating the concentration procedure. It is indicated that these ECPs are feasible with current technology in cavity QED since they work in the bad cavity regime and only involve virtual excitations of atoms, so they are insensitive to both cavity decay and atomic spontaneous emission.