标题： 互补传播自发参量下转换源在绝缘体上铌酸锂 显示英文标题

标题： Counter-propagating spontaneous parametric down-conversion source in lithium niobate on insulator

摘要： 量子光子技术依赖于在可扩展平台上生成、操控和干涉不可区分的单光子的能力。 在各种方法中，自发参量下转换（SPDC）仍然是生成纠缠或纯光子对最常用的方法之一。 然而，大多数依赖共传播几何结构的集成SPDC光源的后选择光子纯度有限，或者需要损耗性过滤。 类型-2 SPDC过程可以产生纯的可分离光子，但通常由于偏振管理而效率较低且复杂度增加。 在这里，我们展示了基于绝缘体上铌酸锂的首个集成反向传播光子对源，其中信号光子和闲置光子在相反方向上生成。 反向传播几何结构使得光子对在没有光谱过滤的情况下光谱不相关。 联合光谱强度测量和无后选择的$g^{(2)}$相关性，得到了纯度为 (92$\pm$3)%。 两个独立光源之间的干涉实现了 (71$\pm$3)% 的后选择可见度，证实了该平台的可扩展性。 这些结果建立了一条通向集成、高纯度和可调光子源的新途径。 所展示的反向传播几何结构为量子光子网络提供了一个可扩展的解决方案。 显示英文摘要

摘要： Quantum photonic technologies rely on the ability to generate, manipulate, and interfere indistinguishable single photons on a scalable platform. Among the various approaches, spontaneous parametric down-conversion (SPDC) remains one of the most widely used methods for generating entangled or pure photon pairs. However most integrated SPDC sources relying on co-propagating geometries have a limited purity of heralded photons, or require lossy filtering. Type-2 SPDC processes can produce pure separable photons but typically suffer from lower efficiency and added complexity due to polarisation management. Here we show the first integrated counter-propagating photon-pair source on lithium niobate on insulator, where signal and idler photons are generated in opposite directions. The counter-propagating geometry leads to spectrally uncorrelated photon pairs without spectral filtering. The joint spectral intensity measurements and unheralded $g^{(2)}$ correlations, yield purities of (92$\pm$3)%. Interference between two independent sources achieves heralded visibilities of (71$\pm$3)%, confirming the scalability of the platform. These results establish a new route toward integrated, high-purity, and tunable photon sources. The demonstrated counter-propagating geometry offers a scalable solution for quantum photonic networks.