发表机构
Paderborn University（帕德博恩大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
针对PDC源因器件缺陷导致的非纯态问题，提出一种设备无关的表征框架，通过黑箱假设和模式分辨测量确定纯度下界，实现全面质量评估，无需详细模型。
AI 中文摘要
可靠验证压缩光源对于光子量子技术至关重要。高维量子光学网络需要单模、纯压缩态，原则上可通过精心设计基于参量下转换（PDC）的源来产生。然而，由于光学元件的不完善，产生的态从不纯净，通常包含内部模式结构。现有的表征技术，无论是基于联合光谱强度还是归一化二阶相关函数，都在假设被探测态为纯态的条件下工作，因此可能导致对源质量的不完整或误导性评估。在此，我们开发了一种与设备无关的表征框架，适用于具有可区分信号场和闲频场的PDC源。将源视为产生混合多模高斯态的黑箱，我们找到了态纯度的下界，该下界可通过模式分辨测量实验确定。我们的方法能够全面评估实际压缩光源的质量，无需非线性器件及其周围光学网络的详细模型，为优化面向最先进量子应用的源提供了实用基准。
英文摘要
Reliable verification of squeezed-light sources is essential for photonic quantum technologies. High-dimensional quantum optical networks demand single-mode, pure squeezed states which, in principle, can be generated through careful engineering of parametric down-conversion-based (PDC) sources. However, due to the imperfections of optical components, the generated state is never pure and commonly contains internal mode structure. Existing characterisation techniques, based on either joint spectral intensity or normalized second-order correlation functions, work under the assumption that the probed state is pure, and therefore can result in incomplete or misleading assessment of the source quality. Here, we develop a device-agnostic characterisation framework for PDC-based sources with distinguishable signal and idler fields. Treating the source as a black box producing a mixed multimode Gaussian state, we find a lower bound for the state purity, which can be experimentally determined via mode-unresolved measurements. Our approach enables a holistic assessment of realistic squeezed-light source quality without requiring a detailed model of the nonlinear device and its surrounding optical network, providing practical benchmarks for optimizing sources for state-of-the-art quantum applications.
