AI 中文总结
本研究提出基于符合计数的光谱工程，通过调整泵浦光子光谱实现级联下转换的光谱匹配，经实验验证可提升转换概率，为优化级联下转换提供实用工具。
AI 中文摘要
通过级联自发参量下转换产生的三光子态为多体纠缠提供了直接途径。然而，当前的实现需要在连续的非线性级之间进行精细的光谱匹配，这限制了下转换源的选择。在本研究中，我们证明基于符合计数的光谱滤波可通过有针对性地调整进入第二级的泵浦光子光谱来放宽这一要求。通过对预示光子进行滤波，我们有条件地调整其伙伴光子的光谱，使其与次级非线性过程的接收带宽相匹配，从而在不改变源本身的情况下实现宽带级与窄带级之间的高效耦合。我们采用电光门控光谱仪直接测量支配级联过程的条件光谱，这使我们能够定量预测每个检测到的预示光子对应的第二级转换概率的提升。随后，我们通过光子三联体测量验证了这一预测，证明在固定预示率下性能得到提升。我们的结果确立了基于符合计数的光谱工程作为优化级联下转换的实用工具，尤其适用于受探测器饱和或光谱不兼容限制的场景。
英文摘要
Three-photon states generated via cascaded spontaneous parametric downconversion provide a direct route to multipartite entanglement. However, current implementations require careful spectral matching between successive nonlinear stages, which constrains the choice of downconversion sources. In this work, we show that coincidence-based spectral filtering relaxes this requirement by conditionally tailoring the spectrum of the pump photon entering the second stage. By filtering the herald photon, we conditionally tailor the spectrum of its partner to match the acceptance bandwidth of the secondary nonlinear process, enabling efficient coupling between broadband and narrowband stages without altering the sources themselves. Using an electro-optically gated spectrometer, we directly measure the conditional spectra that govern the cascaded process, allowing us to quantitatively predict the enhancement in second-stage conversion probability per detected herald. We then verify this prediction through photon-triplet measurements, demonstrating improved performance at fixed heralding rates. Our results establish coincidence-based spectral engineering as a practical tool for optimizing cascaded downconversion, particularly in regimes limited by detector saturation or spectral incompatibility.
Comments11 pages, 4 figures
