We report on a universal method to measure the genuine indistinguishability of $n$ photons—a crucial parameter that determines the accuracy of optical quantum computing. Our approach relies on a low-depth cyclic multiport interferometer with $N=2n$ modes, leading to a quantum interference fringe whose visibility is a direct measurement of the genuine $n$-photon indistinguishability. We experimentally demonstrate this technique for an eight-mode integrated interferometer fabricated using femtosecond laser micromachining and four photons from a quantum dot single-photon source. We measure a four-photon indistinguishability up to $0.81\pm 0.03$. This value decreases as we intentionally alter the photon pairwise indistinguishability. The low-depth and low-loss multiport interferometer design provides an original path to evaluate the genuine indistinguishability of resource states of increasing photon number.

中文翻译：

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使用循环集成干涉仪量化光子不可区分性

我们报告了一种通用方法来衡量真正的不可区分性$n$光子——决定光量子计算精度的关键参数。我们的方法依赖于一个低深度循环多端口干涉仪$ñ=2n$模式，导致量子干涉条纹，其可见性是真实的直接测量$n$-光子不可区分性。我们通过实验证明了这种技术用于使用飞秒激光微加工和来自量子点单光子源的四个光子制造的八模式集成干涉仪。我们测量四光子不可区分性高达$0.81\pm 0.03$. 当我们有意改变光子成对不可区分性时，该值会减小。低深度和低损耗的多端口干涉仪设计提供了一种原始途径来评估增加光子数的资源状态的真正不可区分性。