铯原子喷泉钟二阶塞曼频移的测量方法及实验

The evaluation methods and experiment of second-order Zeeman frequency shift for Cs fountain clock

二阶塞曼频移是影响铯原子喷泉钟频率不确定度的主要因素之一,传统的评定方法是通过测量铯原子磁敏跃迁的Ramsey中心条纹获得原子运行路径上的磁场分布,再应用BreitRabi公式计算二阶塞曼频移。喷泉钟闭环运行初期,由于诸多磁场的加入,实验上往往观测不到磁敏跃迁的Ramsey条纹。首先应用低频跃迁的方法测出了谐振腔上方45cm范围内的磁场分布,通过调节C场线圈电流及补偿线圈电流使磁场起伏最小,从而获得Ramsey条纹,再应用传统方法评定二阶塞曼频移。实验表明应用低频跃迁与Ramsey跃迁获得的磁场分布基本一致。C场的二阶塞曼频移为56.57×10^(-15),由C场的空间不均匀引起的不确定度为1.55×10^(-18),C场随时间变化引起的不确定度为2.93×10^(-16)。

The second-order Zeeman shift is one of the main factors of uncertainty of the cesium fountain clock.The traditional evaluation method is to measure the magnetic field distribution by tracking the center fringe in the path of the atomic operation,and then the second-order Zeeman shift could be calculated by the Breit-Rabi formula.However,in the initial stage of the fountain clock's operation,the magnetic sensitive Ramsey fringes can't be observed because of the mixture of many other magnetic fields.In this paper,we firstly measured the magnetic field distribution above the resonant cavity in the rang,of45cm by applying the low-frequency transition method,and got the best magnetic field distribution by adjusting the current of the C field coil and compensation coils.Then we got the Ramsey fringe,and evaluated the second-order Zeeman frequency shift using the traditional method.The experimental results show that the magnetic field distributions obtained by the low frequency transition and Ramsey transition are basically the same.The second-order Zeeman shift of the C field is56.57×10^-15,the uncertainty caused by the ununiformed C field in space is1.55×10^-18,and the uncertainty induced by the time-varying C field is2.93×10^-16.