Practical scheme for entanglement concentration - art. no. 014301

We present a realistic purification scheme for pure nonmaximally entangled states. In the scheme, two distant parties Alice and Bob first start with t wo shared but less entangled photon pairs to produce a conditional four-pho ton Greenberger-Horne-Zeilinger state, and then perform a 45 degrees polari zation measurement onto one of the two photons at each location such that t he remaining two photons are projected onto a maximally entangled state.