Efficient entanglement concentration for partially entangled cluster states with weak cross-Kerr nonlinearity

In this paper, we propose an optimal entanglement concentration protocol (ECP) for partially entangled cluster states with the help of the weak cross-Kerr nonlinearity. We can obtain the maximally entangled cluster states assisted with the projection measurements on the additional photons. The protocol is based on optical elements, single polarization photons, cross-Kerr nonlinearity, and the conventional photon detectors, which are feasible with existing experimental technology. Numerical simulation demonstrates that by iterating the entanglement concentration process n=m=6\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$n=m=6$$\end{document} times, the ECP has the approximate maximal success probability 100 %. Moreover, the present protocol is also suitable for partially entangled 4N\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$4N$$\end{document}-photon cluster states concentration. All these advantages make this protocol more efficient and more convenient than others in the applications in quantum communication.