  We propose two alternative entanglement concentration protocols (ECPs) using
the Faraday rotation of photonic polarization. Through the single-photon
input-output process in cavity QED, it is shown that the maximally entangled
atomic (photonic) state can be extracted from two partially entangled states.
The distinct feature of our protocols is that we can concentrate both atomic
and photonic entangled states via photonic Faraday rotation, and thus they may
be universal and useful for entanglement concentration in the experiment.
Furthermore, as photonic Faraday rotation works in low-$Q$ cavities and only
involves virtual excitation of atoms, our ECPs are insensitive to both cavity
decay and atomic spontaneous emission.
