A higher-order parametric down-conversion (PDC) photon state is amazingly different from the states involving independent photon pairs. We focus on the third-order PDC photons. Firstly, we present a symmetry detector which is capable of analyzing twin-beam six-photon symmetric states in the regime of weak nonlinearities. By cascading symmetry detectors, then, it is shown that one can generate third-order PDC photons from a class of twin-beam six-photon symmetric states. Finally, as an example, we describe an application of third-order PDC photons for exploring six-mode-photon entangled states with linear optics.

中文翻译：

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通过弱非线性产生三阶参数下变频光子

高阶参数下转换 (PDC) 光子状态与涉及独立光子对的状态惊人地不同。我们专注于三阶 PDC 光子。首先，我们提出了一种对称检测器，它能够在弱非线性范围内分析双光束六光子对称状态。然后，通过级联对称探测器，表明可以从一类双光束六光子对称状态生成三阶 PDC 光子。最后，作为一个例子，我们描述了三阶 PDC 光子的应用，用于探索线性光学的六模光子纠缠态。