Measuring small separations between two optical sources, either in space or in time, constitutes an important metrological challenge as standard intensity-only measurements fail for vanishing separations. Contrarily, it has been established that appropriate coherent mode projections can appraise arbitrarily small separations with quantum-limited precision. However, the question of whether the optical coherence brings any metrological advantage to mode projections is still a point of debate. Here, we elucidate this problem by experimentally investigating the effect of varying coherence on estimating the temporal separation between two single-photon pulses. We show that, for an accurate interpretation, special attention must be paid to properly normalize the quantum Fisher information to account for the strength of the signal.

中文翻译：

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相干性对时间分辨率的影响

在空间或时间上测量两个光源之间的小间距构成了一项重要的计量挑战，因为标准的仅强度测量无法实现消失的间距。相反，已经确定适当的相干模式投影可以评估具有量子限制精度的任意小间距。然而，光学相干性是否为模式投影带来任何计量优势的问题仍然存在争议。在这里，我们通过实验研究不同相干性对估计两个单光子脉冲之间的时间间隔的影响来阐明这个问题。我们表明，为了准确解释，必须特别注意正确归一化量子 Fisher 信息以解释信号强度。