锶原子光钟驾驭氢钟的模拟分析

Simulation Analysis of the Steering Hydrogen Maser by Strontium Optical Lattice Clock

基于光频跃迁的光晶格原子钟展示了优异的频率稳定度和不确定度,是重定义时间单位“秒”的有力候选者之一。然而,目前的局限性是光学时钟仍处于实验室阶段,不能长时间自主运行,这使得基于光钟的连续时间尺度输出变得困难。在本文中,我们模拟了间歇性运行的锶原子光钟驾驭作为飞轮的氢钟来实现连续时间尺度输出,详细讨论了卡尔曼滤波驾驭算法中关键参数的计算与选取,研究了锶原子光钟不同驾驭策略下对光学时间尺度性能的影响。结果表明锶原子光钟8.3%运行率下,30 d的累积时间误差可保持在0.8 ns以内,频率稳定度达4×10^(-17)@30 d。

Objective Optical lattice clocks based on optical frequency transitions of neutral atoms have demonstrated excellent stability and uncertainty, which are one of the most promising candidates for the next generation of second replications. However,the current limitation is that optical lattice clocks are still in the laboratory prototype stage and cannot operate autonomously for extended periods, making a continuous realization of a timescale impractical. Therefore, it is crucial to assess the impact of this limited availability on the generated time scale.Method This paper studies how to build a time scale with an intermittently operating optical lattice clock, based on simulations. A simulation approach is employed to construct a time scale composed of a continuously operating active hydrogen maser and an intermittent 87Sr optical lattice clock, utilizing Kalman filter algorithm for steering. The hydrogen maser serves as a flywheel clock to ensure the continuity of the time scale, while the 87Sr optical lattice clock acts as the frequency reference. The Kalman filter algorithm, widely employed for estimating the frequency and frequency drift of the free-running time scale in relation to the optical clock, is a prominent method used for steering the frequency and frequency drift of the time scale based on such estimates. The selection of key parameters in the Kalman filter algorithm is discussed in detail. Additionally, the study investigates the influence of various operational strategies for optical lattice clocks. This is done by considering several different scenarios for the availability of the optical lattice clock, such as the different uptime ratios(the optical lattice clock operating for 0.4 hours, 2 hours and 12 hours per day) and different operating interval with the same uptime ratio(the optical lattice clock operating for 2 hours per day, 4 hours per 2 days and 4 hours per 8 days).Results and Discussions Our findings reveal that the longer the optical lattice clocks operate, the better the frequency stability of time scales is. Moreover, the performance of the timescale can be improved by dividing the total uptime of the optical lattice clock into multiple sub-periods, while keeping the overall uptime the same. More frequent measurements and steering effectively reduce the Dick effect in the steering process. The simulation result shows that 8.3% uptime ratio of the OLC, the root-meansquare(RMS) of the time errors is less than 0.8 ns after 30 days, while the frequency stability of the time scale reaches 4×10^(-17) at 30 days.Conclusion This paper presents a novel approach for building a time scale with an intermittently operating optical lattice clock. We establish a frequency difference model to prove the feasibility of frequency steering in theory, calculate the key parameters in the Kalman filter algorithm and find out the rules to be followed in choosing the steering strength and steering frequency. This research should be useful for applying the proposed scheme to other combinations of optical frequency standards and flywheels, and promote the development of optical clock technologies.