发表机构
School of Electronics, Peking University; State Key Laboratory of Precision Spectroscopy, East China Normal University; International Center for Quantum Materials, School of Physics, Peking University; National Key Laboratory of Advanced Micro and Nano Manufacture Technology; Hefei National Laboratory（北京大学电子学院; 华东师范大学精密光谱科学国家重点实验室; 北京大学物理学院量子材料国际中心; 先进微纳制造技术全国重点实验室; 合肥国家实验室）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究提出一种无需第三台激光器即可从拍频统计中精确恢复两条隐藏线宽的方法，并验证了其在超稳激光器数据上的有效性，有望推动光学钟和精密计量学的发展。
AI 中文摘要
来自超稳激光器的光子可以在接近地球-太阳距离的尺度上保持相干性，这使得预计在宇宙年龄内误差小于一秒的光学钟成为可能。然而，表征这些光子存在一个可识别性问题：双激光外差测量产生单一的拍频线宽，该线宽混淆了两台激光器的贡献。半个多世纪以来，标准解决方案是三角帽（TCH）方法，它需要三台独立的超稳激光器。在此，我们推导了由有限光子波列引起的非对称拍频线宽分布的数学形式，并阐明其物理起源，这是一个长期观察到但未被典型高斯或洛伦兹统计捕获的特征。这一发现无需第三台激光器即可精确恢复隐藏在激光拍频统计中的两条线宽。该框架一致地捕获了光子的观测相干长度和相干时间统计，而与TCH测量的比较证实了在跨越近两个数量级的五个独立超稳激光器数据集中提取的个体线宽的定量有效性。最值得注意的是，该方法解决了低温硅腔激光器与更宽激光器拍频时7.8-mHz线宽的测量问题。拍频线宽分布的这一变革性功能，连同由此产生的方法，可能从根本上推进光学钟和精密计量学的发展。
英文摘要
Photons from ultrastable lasers can remain coherent over distances approaching the Earth-Sun separation, enabling optical clocks projected to lose less than one second over the age of the Universe. Yet characterizing these photons poses an identifiability problem: a two-laser heterodyne measurement produces a single beatnote linewidth that conflates contributions from both lasers. For more than half a century, the standard solution has been the three-cornered-hat (TCH) method, which requires three independent ultrastable lasers. Here we derive the mathematical form and elucidate the physical origin of asymmetric beatnote-linewidth distributions arising from finite photon wave trains, a long-observed feature not captured by canonical Gaussian or Lorentzian statistics. This finding accurately recovers two linewidths hidden in laser beatnote statistics without a third laser. The framework consistently captures the observed coherence-length and coherence-time statistics of photons, while comparison with TCH measurements confirms the quantitative validity of the extracted individual linewidths across five independent ultrastable-laser datasets spanning nearly two orders of magnitude. Most notably, the method resolves the 7.8-mHz linewidth of a cryogenic silicon-cavity laser beating with a broader laser. This transformative function of beatnote-linewidth distributions, together with the resulting method, could fundamentally advance optical clocks and precision metrology.
