Photon indistinguishability plays a fundamental role in information processing, with applications such as linear-optical quantum computation and metrology. It is then necessary to develop appropriate tools to quantify the amount of this resource in a multiparticle scenario. Here we report a four-photon experiment in a linear-optical interferometer designed to simultaneously estimate the degree of indistinguishability between three pairs of photons. The interferometer design dispenses with the need of heralding for parametric down-conversion sources, resulting in an efficient and reliable optical scheme. We then use a recently proposed theoretical framework to quantify genuine four-photon indistinguishability, as well as to obtain bounds on three unmeasured two-photon overlaps. Our findings are in high agreement with the theory, and represent a new resource-effective technique for the characterization of multiphoton interference.

中文翻译：

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四光子不可区分性的实验量化

光子不可区分性在信息处理中起着重要作用，其应用包括线性光量子计算和计量学。然后有必要开发适当的工具来量化多粒子场景中这种资源的数量。在这里，我们报告了线性光学干涉仪中的四光子实验，旨在同时估计三对光子之间的不可区分程度。干涉仪设计无需预告参数下变频源，从而实现高效可靠的光学方案。然后，我们使用最近提出的理论框架来量化真正的四光子不可区分性，并获得三个未测量的双光子重叠的界限。我们的发现与理论高度一致，