Feasible Entanglement Purification for Quantum Communication

Abstract

The distribution of entangled states between distant locations will be\nessential for the future large scale realization of quantum communication\nschemes such as quantum cryptography and quantum teleportation. Because of the\nunavoidable noise in the quantum communication channel, the entanglement\nbetween two particles is more and more degraded the further they propagate.\nEntanglement purification is thus essential to distill highly entangled states\nfrom less entangled ones. Existing general purification protocols are based on\nthe quantum controlled-NOT (CNOT) or similar quantum logic operations, which\nare very difficult to implement experimentally. Present realizations of CNOT\ngates are much too imperfect to be useful for long-distance quantum\ncommunication. Here we present a feasible scheme for the entanglement\npurification of general mixed entangled states, which does not require any CNOT\noperations, but only simple linear optical elements. Since the perfection of\nsuch elements is very high, the local operations necessary for purification can\nbe performed with the required precision. Our procedure is within the reach of\ncurrent technology and should significantly simplify the implementation of\nlong-distance quantum communication.\n