Liu Jun, Nape Isaac, Wang Qainke, Vallés Adam, Wang Jian, Forbes Andrew
Wuhan National Laboratory for Optoelectronics and School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China.
School of Physics, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa.
Sci Adv. 2020 Jan 24;6(4):eaay0837. doi: 10.1126/sciadv.aay0837. eCollection 2020 Jan.
The global quantum network requires the distribution of entangled states over long distances, with substantial advances already demonstrated using polarization. While Hilbert spaces with higher dimensionality, e.g., spatial modes of light, allow higher information capacity per photon, such spatial mode entanglement transport requires custom multimode fiber and is limited by decoherence-induced mode coupling. Here, we circumvent this by transporting multidimensional entangled states down conventional single-mode fiber (SMF). By entangling the spin-orbit degrees of freedom of a biphoton pair, passing the polarization (spin) photon down the SMF while accessing multiple orbital angular momentum (orbital) subspaces with the other, we realize multidimensional entanglement transport. We show high-fidelity hybrid entanglement preservation down 250 m SMF across multiple 2 × 2 dimensions, confirmed by quantum state tomography, Bell violation measures, and a quantum eraser scheme. This work offers an alternative approach to spatial mode entanglement transport that facilitates deployment in legacy networks across conventional fiber.
全球量子网络需要长距离分发纠缠态，利用偏振已经取得了重大进展。虽然具有更高维度的希尔伯特空间，例如光的空间模式，允许每个光子具有更高的信息容量，但这种空间模式纠缠传输需要定制的多模光纤，并且受到退相干诱导的模式耦合的限制。在这里，我们通过在传统单模光纤（SMF）中传输多维纠缠态来规避这一问题。通过纠缠双光子对的自旋 - 轨道自由度，让偏振（自旋）光子沿SMF传输，同时让另一个光子访问多个轨道角动量（轨道）子空间，我们实现了多维纠缠传输。我们通过量子态断层扫描、贝尔不等式违背测量和量子橡皮擦方案证实，在250米长的SMF中跨多个2×2维度实现了高保真混合纠缠保持。这项工作为空间模式纠缠传输提供了一种替代方法，便于在传统光纤的现有网络中进行部署。
