Zhang Chao, Huang Yun-Feng, Zhang Cheng-Jie, Wang Jian, Liu Bi-Heng, Li Chuan-Feng, Guo Guang-Can
Opt Express. 2016 Nov 28;24(24):27059-27069. doi: 10.1364/OE.24.027059.
High-quality entangled photon pairs generated via spontaneous parametric down-conversion have made great contributions to the modern quantum information science and the fundamental tests of quantum mechanics. However, the quality of the entangled states decreases sharply when moving from biphoton to multiphoton experiments, mainly due to the lack of interactions between photons. Here, for the first time, we generate a four-photon Greenberger-Horne-Zeilinger state with a fidelity of 98%, which is even comparable to the best fidelity of biphoton entangled states. Thus, it enables us to demonstrate an ultrahigh-fidelity entanglement swapping-the key ingredient in various quantum information tasks. Our results push the fidelity of multiphoton entanglement generation to a new level and would be useful in some demanding tasks, e.g., we successfully demonstrate the genuine multipartite nonlocality of the observed state in the nonsignaling scenario by violating a novel Hardy-like inequality, which requires very high state-fidelity.
通过自发参量下转换产生的高质量纠缠光子对，对现代量子信息科学和量子力学的基础测试做出了巨大贡献。然而，从双光子实验过渡到多光子实验时，纠缠态的质量会急剧下降，主要原因是光子之间缺乏相互作用。在此，我们首次生成了保真度为98%的四光子格林伯格-霍恩-蔡林格态，这一保真度甚至可与最佳的双光子纠缠态相媲美。因此，这使我们能够演示超保真度的纠缠交换——这是各种量子信息任务中的关键要素。我们的结果将多光子纠缠生成的保真度提升到了一个新水平，并且在一些苛刻的任务中将会很有用，例如，我们通过违反一个新颖的类似哈迪不等式，成功地在无信号场景中证明了所观测状态的真正多方非局域性，这需要非常高的态保真度。
