Entanglement Purification Through Cavity Input-Output Process

We propose a scheme to purify entanglement of two atoms from not-too-impure entangled states by checking the parity of the two atoms through the cavity input-output process. As the parity check is made by measurement on single-photon polarization, which would not affect the entanglement of the two atoms, our scheme has the successful probability double of that in a previous well-known scheme with linear optical elements [Nature (London) 410 (2001) 1067], and is insensitive to the photon loss and the detection inefficiency. Experimental feasibility of our scheme with current technology is discussed