State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China.
Key Laboratory of Atomic Frequency Standards, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China.
Phys Rev Lett. 2016 Jan 8;116(1):013001. doi: 10.1103/PhysRevLett.116.013001. Epub 2016 Jan 6.
Based upon an over-one-month frequency comparison of two (40)Ca(+) optical clocks, the frequency difference between the two clocks is measured to be 3.2×10(-17) with a measurement uncertainty of 5.5×10(-17), considering both the statistic (1.9×10(-17)) and the systematic (5.1×10(-17)) uncertainties. This is the first performance of a (40)Ca(+) clock better than that of Cs fountains. A fractional stability of 7×10(-17) in 20,000 s of averaging time is achieved. The evaluation of the two clocks shows that the shift caused by the micromotion in one of the two clocks limits the uncertainty of the comparison. By carefully compensating the micromotion, the absolute frequency of the clock transition is measured to be 411 042 129 776 401.7(1.1) Hz.
基于对两个 (40)Ca(+) 光学钟进行的一个多月的频率比对，考虑到统计（1.9×10(-17)) 和系统（5.1×10(-17)) 不确定度，这两个钟的频率差值测量值为 3.2×10(-17)，测量不确定度为 5.5×10(-17)。这是首次实现优于铯喷泉钟的 (40)Ca(+) 钟性能。在 20000 秒的平均时间内，实现了 7×10(-17) 的分数稳定度。对两个钟的评估表明，其中一个钟的微运动引起的频移限制了比较的不确定度。通过仔细补偿微运动，测量到钟跃迁的绝对频率为 411 042 129 776 401.7(1.1) Hz。
