AI 中文总结
该研究实验发现OAM施密特谱随非线性晶体厚度的非单调变化，揭示了空间走离效应的作用，为高维纠缠态产生提供了重要启示。
AI 中文摘要
光子的轨道角动量（OAM）为量子信息协议提供了高维资源。通过自发参量下转换（SPDC）产生的OAM纠缠态的维度由角施密特谱量化。本文实验研究了角施密特谱与非线性晶体厚度的依赖关系。与此前报道的施密特数随晶体厚度增加单调下降的研究相反，我们首次实验观测到非单调行为：当晶体厚度超过某一阈值后，施密特数会上升。我们将此归因于各向异性非线性晶体中的空间走离效应，并采用不含标准相位匹配近似的理论模型对其进行解释。这些发现对高维纠缠态的产生具有重要意义。
英文摘要
The orbital angular momentum (OAM) of photons provides a high-dimensional resource for quantum information protocols. The dimensionality of OAM-entangled states generated via spontaneous parametric down-conversion (SPDC) is quantified by the angular Schmidt spectrum. Here, we experimentally investigate the dependence of the angular Schmidt spectrum on the thickness of the nonlinear crystal. Contrary to previous studies reporting a monotonic decrease in the Schmidt number with increasing crystal thickness, we report the first experimental observation of a nonmonotonic behavior, as we demonstrate an increase in the Schmidt number beyond a certain crystal thickness. We attribute this to the spatial walk-off effect in the anisotropic nonlinear crystal and explain it using a theoretical model that is devoid of standard phase-matching approximations. These findings can have important implications for high-dimensional entangled state generation.
Comments19 pages, 6 figures
