AI 中文总结
本研究通过分析II型SPDC双光子波函数的实空间偏振态分布，设计关联对齐孔径，提升了纠缠纯度与光子收集效率，为高亮度高纯度SPDC纠缠源提供了新设计原则。
AI 中文摘要
自发参量下转换（SPDC）是偏振纠缠光子对最广泛使用的光源之一，理解产生的双光子态对实现高亮度、高纯度的纠缠光子源至关重要。特别是，II型SPDC因双折射产生了空间与偏振自由度间存在复杂耦合的双光子波函数。本研究计算了在β-偏硼酸钡（BBO）晶体中产生的II型SPDC双光子波函数的双光子偏振态实空间分布；通过确定偏振与实空间坐标间的空间关联方向，设计了沿该关联方向限制收集的孔径形状。通过数值模拟和实验，证明此类与关联对齐的孔径可同时实现更高的纠缠纯度和改进的光子收集效率。这些结果确立了基于实空间双光子波函数优化孔径几何的实用设计原则，为实现高纯度、高亮度的SPDC纠缠光子源提供了新方法。
英文摘要
Spontaneous parametric down-conversion (SPDC) is one of the most widely used sources of polarization-entangled photon pairs, and understanding the generated biphoton state is essential for realizing high-brightness and high-purity entangled-photon sources. In particular, Type-II SPDC produces a biphoton wavefunction with a complex coupling between the spatial and polarization degrees of freedom owing to birefringence. In this study, we calculate the real-space distribution of the two-photon polarization state from the biphoton wavefunction of Type-II SPDC generated in a \b{eta}-barium borate (BBO) crystal. By identifying the spatial correlation direction between polarization and real-space coordinates, we designed aperture shapes that restrict the collection along this correlation direction. Through both numerical simulations and experiments, we demonstrate that such correlation-aligned apertures simultaneously achieve higher entanglement purity and improved photon collection efficiency. These results establish a practical design principle for optimizing aperture geometries based on the real-space biphoton wavefunction, providing a new approach to realizing high-purity and high-brightness SPDC entangled-photon sources.
Comments12 pages, 5 figures
