We show that the standard method of introducing the quantum description of the electromagnetic field – by canonical field quantization – is not the only one. We have chosen here the relativistic quantum mechanics of the photon as the starting point. The treatment of photons as elementary particles merges smoothly with the description in terms of the quantized electromagnetic field but it also reveals some essential differences. The most striking result is the appearance of various measures of fidelity for quantum states of photons. These measures are used to characterize the localization of photons.

中文翻译：

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光子态保真度的三种测量

我们表明，引入标准场量化的电磁场量子描述的标准方法并不是唯一的方法。我们在这里选择了光子的相对论量子力学作为起点。将光子作为基本粒子的处理与量化电磁场方面的描述顺利融合，但也揭示了一些本质差异。最惊人的结果是出现了光子量子态保真度的各种度量。这些措施用于表征光子的定位。