We report the realization of the closed-loop operation of an optical lattice clock based on ⁸⁷Sr atoms. A cavity-stabilized 698 nm laser is used to probe the 1S0→3P0 clock transition of strontium atoms trapped in optical lattices. Therein, we obtain a Fourier-limited Rabi spectrum with 0.6 Hz linewidth. The two transitions from mF=±9/2 ground states are alternatively interrogated to realize the closed-loop operation of the clock, and the clock laser light is frequency-stabilized to the center of the two transitions. Based on the interleaved measurement, the frequency instability of a single optical clock is optimized for the Dick effect, which is demonstrated to be 4.5×10−16/τ , with τ being the averaging time for measurement. Further, we build another similar setup of the strontium lattice clock, which is used for the asynchronous comparison between the two clocks, where the stability is measured as 2.1×10−18 at 47 000 s. Moreover, we carefully calibrate the systematic effects of the Sr1 optical clock, and the total uncertainty is evaluated as 4.4×10−18 .

中文翻译：

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稳定性和不确定性均低于 5×10−18 的锶晶格钟

^{我们报道了基于87 个}Sr 原子的光学晶格时钟的闭环操作的实现。使用腔稳定 698 nm 激光器来探测 1S0→3磷0 捕获在光学晶格中的锶原子的时钟跃迁。其中，我们获得了线宽为 0.6 Hz 的傅里叶极限拉比谱。两个转变从 米F=±9/2 交替地询问基态以实现时钟的闭环操作，并且时钟激光被频率稳定到两个跃迁的中心。基于交错测量，针对迪克效应优化了单个光时钟的频率不稳定性，结果证明： 4.5×10-16/τ ， 和τ是测量的平均时间。此外，我们构建了另一个类似的锶晶格时钟设置，用于两个时钟之间的异步比较，其中稳定性测量为 2.1×10-18 47 000 秒。此外，我们仔细校准了Sr1光钟的系统效应，总不确定度评估为 4.4×10-18 。