Polarization-Entanglement Purification for Ideal Sources Using Weak Cross-Kerr Nonlinearity

We propose an entanglement purification protocol (EPP) for ideal entangled photon sources resorting to weak cross-Kerr nonlinearities. The key element of this EPP is the quantum nondemolition detector (QND) which uses weak cross-Kerr nonlinearity effect to generate phase shifts on the coherent states conditionally. By exploiting the double cross-phase modulation (XPM) method in QND, we present an efficient EPP protocol, which reduces the requirement for coupling strength of the cross-Kerr nonlinearity medium. The proposed protocol may open up promising possibilities for the practicability of quantum information processing using weak cross-Kerr nonlinearities.