一小时内具有$6\times 10^{-19}$精度的光钟比对
Optical clock intercomparison with $6\times 10^{-19}$ precision in one hour
摘要：
原子光相干性的改善是量子信息科学、量子光学和精密计量学进步的基础。光学原子钟要求本机振荡器具有特殊的光学相干性，这是由于在其超窄线宽时钟跃迁上执行光谱学的挑战。因此，激光稳定性的进步使时钟精度迅速提高。基于低温硅参考腔的一类新的超稳定激光器最近被证明是迄今为止最长的光学相干时间。在这项工作中，我们利用这样的本地振荡器，以及一个国家的最先进的频率梳相干转移，两个Sr光晶格时钟，以实现前所未有的时钟稳定性水平。通过反同步比较，对于以秒为单位的平均时间$τ$，两个时钟的分数不稳定性被评估为$4.8\times 10^{-17}/\sqrtτ$。同步询问揭示了$3.5(2)\times10^{-17}/\sqrtτ$的量子投影噪声主导的不稳定性，导致在单个小时的平均之后的$5.8(3)\times 10^{-19}$的精度。在如此短的时间尺度内测量亚$10^{-18}$水平频率偏移的能力将影响量子传感和基础物理中的时钟的广泛应用。例如，这种精度允许人们在20分钟内解决1厘米高度变化的引力红移。
英文摘要：
Improvements in atom-light coherence are foundational to progress in quantum information science, quantum optics, and precision metrology. Optical atomic clocks require local oscillators with exceptional optical coherence due to the challenge of performing spectroscopy on their ultra-narrow linewidth clock transitions. Advances in laser stabilization have thus enabled rapid progress in clock precision. A new class of ultrastable lasers based on cryogenic silicon reference cavities has recently demonstrated the longest optical coherence times to date. In this work we utilize such a local oscillator, along with a state-of-the-art frequency comb for coherence transfer, with two Sr optical lattice clocks to achieve an unprecedented level of clock stability. Through an anti-synchronous comparison, the fractional instability of both clocks is assessed to be $4.8\times 10^{-17}/\sqrtτ$ for an averaging time $τ$ in seconds. Synchronous interrogation reveals a quantum projection noise dominated instability of $3.5(2)\times10^{-17}/\sqrtτ$, resulting in a precision of $5.8(3)\times 10^{-19}$ after a single hour of averaging. The ability to measure sub-$10^{-18}$ level frequency shifts in such short timescales will impact a wide range of applications for clocks in quantum sensing and fundamental physics. For example, this precision allows one to resolve the gravitational red shift from a 1 cm elevation change in only 20 minutes.
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