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.