铯原子喷泉钟腔相位分布频移的抑制及评估研究

The cesium atomic fountain clock is the primary frequency standard that realizes the definition of the SI second. It is very significant for the security of a country to develop high performance cesium atomic fountain clock. At the moment, the best type-B frequency uncertainty of cesium atomic fountain clocks has reached a level of 1.1×10^(-16). Many systematic errors caused by different physical effects limit the further improvement of the frequency uncertainty of the atomic fountain clock. Among them the distributed cavity phase frequency shifts (DCP) caused by microwave spatial phase variations in the microwave cavity is one of the most important effects. To further improve the performance of atomic fountain clocks, it is important to accurately reduce and evaluate the DCP. In this proposal, on the basis of our previous work, we plan to calculate the microwave spatial phase variations with different parameters and structure of the microwave cavity via the COMSOL software. And we will further theoretically calculate the distributed cavity phase shifts induced by the phase variations. At the same, we will design two microwave cavities with different structure parameters according to the theoretical simulation. The distributed cavity phase shifts will be measured by differential measurement method, which will decouple the distributed cavity phase shifts with the frequency shifts induced by microwave power and microwave leakage. Therefore, the distributed cavity phase shifts would be precisely evaluated. Our goal is to design a cavity with the spatial phase variations of less than ±1 μrad by optimizing the cavity structural parameters, which will produce the DCP fractional frequency uncertainty of no more than 5×10^(-17). This proposal will lay a solid foundation for further improvement and evaluation of the frequency uncertainty of atomic fountain clocks.

铯原子喷泉钟是直接复现国际单位“秒”的时间频率基准，对国家安全有着重要战略意义。目前国际上性能最好的铯原子喷泉钟的B类不确定度已达到1.1×10^(-16)。不同物理效应引起的系统误差限制了铯原子喷泉钟频率不确定度的进一步提高，其中微波腔内微波场空间相位变化引起的腔相位分布频移是一项重要限制因素，因此，从根本上减小并准确评估腔相位分布频移是进一步提高铯原子喷泉钟性能的关键。本项目将在前期工作基础上，理论上通过COMSOL软件详细仿真微波腔结构参数对微波场空间相位变化的影响，通过原子敏感度函数计算其腔相位分布频移；依据理论，实验上设计两个不同结构的微波腔，通过差分测量方法减小微波功率及微波泄露频移与腔相位分布频移的耦合效应，实现对腔相位分布频移的准确评估。目标是将腔相位分布频移引起的不确定度降低至优于5×10^(-17)。本项目研究将为进一步提高并准确评估铯原子喷泉钟频率不确定度奠定基础。

铯原子喷泉钟是目前实现国际秒定义精度最高的基准时钟，是国家守时授时体系建设的重要装置，对国家安全有重要战略意义。由微波相位变化引起的腔相位分布频移是限制铯原子喷泉钟系统误差的主要限制因素之一。本项目开展了铯原子喷泉钟腔相位分布频移的抑制及评估研究：通过理论仿真并实验上实现了一种用于冷原子喷泉钟的微波腔，理论上分析可实现腔相位分布频移引起的不确定度优于5E-17；将所研制的微波腔应用于铯原子喷泉钟研制中，实现了高质量的Ramsey干涉条纹，条纹对比度达到90.8%，条纹中心线线宽0.911(2)Hz，铯原子喷泉钟整机频率稳定度达到3.2E-13/1s，与国际同类指标相当；初步评估腔相位分布频移不确定度为3.6E-15。基于本项目研究，发表SCI论文1篇，EI论文1篇，协助培养研究生4名，已毕业2名。