AI 中文总结
本研究利用量子脉冲门（QPG）对多模参量下转换（PDC）源进行相干时域滤波，其产生的预示光子纯度高于0.90，优于传统强度滤波，可用于量子网络应用。
AI 中文摘要
光谱纯净且不可区分的单光子是量子网络平台的核心要素，高可见度干涉支撑着诸多量子信息协议。然而，多数实用单光子源发射的是光谱多模态，纯度有所降低。传统光谱强度滤波可部分提升纯度，但无法选出定义明确的时域模式（TM）。在此，我们展示利用量子脉冲门（QPG）对多模参量下转换（PDC）源进行相干时域滤波，并将其性能与传统强度滤波对比。产生的PDC光子呈现强光谱关联，这使得从光子对中提取纯净的预示光子颇具挑战。我们证明，无论滤波形状如何，QPG滤波都能持续产生纯度高于0.90的预示光子；相反，使用光谱强度滤波会产生混合光子。光子纯度通过时间域Q函数层析成像探测。此外，我们通过提取结构化时域模式（包括皮秒时间 bin 的叠加态）展示了QPG滤波的通用性。这些结果确立了QPG作为量子网络应用实用相干滤波工具的地位。
英文摘要
Spectrally pure and indistinguishable single photons are essential for quantum network platforms, where high-visibility interference underpins many quantum information protocols. However, most practical single-photon sources emit spectrally multimode states with reduced purity. Conventional spectral intensity filtering can partially improve purity but cannot select a well-defined temporal mode (TM). Here, we demonstrate coherent temporal filtering of a multimode parametric down-conversion (PDC) source using a quantum pulse gate (QPG) and benchmark its performance against conventional intensity filtering. The generated PDC photons exhibit strong spectral correlations, rendering extraction of pure heralded photons from the pair a challenge. We demonstrate that QPG filtering consistently generates heralded photons with purities above 0.90 regardless of the filter shape. Contrariwise, using spectral intensity filters yields mixed photons. Photon purities are probed with chronocyclic Q-function tomography. Furthermore, we demonstrate the versatility of QPG filtering by extracting structured TMs, including superposition of picosecond time bins. These results establish the QPG as a practical coherent filtering tool for quantum network applications.
