Quantum repeater Single-photon quantum repeater L.M. Duan et al., Nature 414, 413 (2001) tWo-photon quantum repeater B. Zhao et al., Phys. Rev. Lett. 98, 240502(2007) Z B Chen et al., Phys. Rev. A 76, 022329 (2007)Quantum repeater Single-photon quantum repeater two-photon quantum repeater L.M. Duan et al., Nature 414, 413 (2001) B. Zhao et al., Phys. Rev. Lett. 98, 240502 (2007) Z. B. Chen et al., Phys. Rev. A 76, 022329 (2007)