A liquid nitrogen-cooled Ca+ optical clock with systematic uncertainty of 3×10-18
A liquid nitrogen-cooled Ca+ optical clock with systematic uncertainty of 3×10-18
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DOI：
10.21203/rs.3.rs-333884/v1
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发表时间：
2021-03
期刊：
影响因子：
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通讯作者：
Yao Huang;Baolin Zhang;Mengyan Zeng;Yanmei Hao;Huaqing Zhang;H. Guan;Zheng Chen;Miao Wang;K. Gao
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文献类型：
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作者：
Yao Huang;Baolin Zhang;Mengyan Zeng;Yanmei Hao;Huaqing Zhang;H. Guan;Zheng Chen;Miao Wang;K. Gao
本文介绍了一个液氮冷却的Ca ~+光学钟，其系统总不确定度为3×10 ~（-18）。与我们以前报道的室温Ca ~+光钟相比，真空中的黑体辐射（BBR）屏蔽层的温度已经用液氮降低到82（5）K。还介绍了一种具有较低加热速率的离子阱和改进的冷却激光器。这允许在时钟操作期间将离子温度冷却到多普勒冷却极限，并且由于离子的长期（热）运动引起的系统不确定性降低到< 1×10-18。采用超Ramsey方法和高阶伺服算法，探测光漂移和伺服误差的不确定度分别降低到1×10-19和4×10-19以下。通过比较低温时钟和室温时钟的输出频率，测量了两者之间的差分BBR漂移，分数统计不确定度为7×10-18。用微分BBR位移计算了静态微分极化率，发现与我们以前用不同方法测量的结果非常吻合。这项工作表明，光学时钟的BBR漂移可以很好地抑制在液氮环境中。这是有利的，因为用于光学时钟的常规液氦低温系统更昂贵且更复杂。此外，该系统可用于抑制其他类型的光钟，如Yb+，Sr+，Yb，Sr等的BBR移位显着。
Here we present a liquid nitrogen-cooled Ca+ optical clock with an overall systematic uncertainty of 3×10-18. In contrast with the room-temperature Ca+ optical clock that we have reported previously, the temperature of the blackbody radiation (BBR) shield in vacuum has been reduced to 82(5) K using liquid nitrogen. An ion trap with a lower heating rate and improved cooling lasers were also introduced. This allows cooling the ion temperature to the Doppler cooling limit during the clock operation, and the systematic uncertainty due to the ion’s secular (thermal) motion is reduced to < 1×10-18. The uncertainty due to the probe laser light shift and the servo error are also reduced to < 1×10-19 and 4×10-19 with the hyper-Ramsey method and the higher-order servo algorithm, respectively. By comparing the output frequency of the cryogenic clock to that of a room-temperature clock, the differential BBR shift between the two was measured with a fractional statistical uncertainty of 7×10-18. The differential BBR shift was used to calculate the static differential polarizability, and it was found in excellent agreement with our previous measurement with a different method. This work suggests that the BBR shift of optical clocks can be well suppressed in a liquid nitrogen environment. This is advantageous because conventional liquid-helium cryogenic systems for optical clocks are more expensive and complicated. Moreover, the proposed system can be used to suppress the BBR shift significantly in other types of optical clocks such as Yb+, Sr+, Yb, Sr, etc.