The curve of the spatial distribution of the photon velocity is obtained with numerical method.
用数值方法得到了光子速度的空间分布曲线。
The scientists found that the precursor wave front of a single photon always travels at c, like the signal velocity of large groups of photons.
科学家发现，单个光子的前驱波头一般以光速c传播，就像由大量光子携带的信号的传播速度一样。
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