The Influence Of Magnetic Field On The Stability Of ¹⁷¹Yb Optical Lattice Clocks

Up to now,the performance of optical atomic clocks has surpassed the present state-of-art microwave atomic clocks.Optical atomic clocks are diversified into ion optical clocks and neutral-atomic optical clocks.In the future,the optical atomic clocks are expected to refresh the definition of"second",one of the fundamental physical quantities of SI.Additionally,the research of optical atomic clocks can be widely exploited to geodesy,satellite navigation and positioning and other field of updated subjects.The State Key Laboratory of Precision Spectroscopy Science and Technology,East China Normal University has successfully developed two sets of cold ytterbium optical lattice clocks.The neutral-atomic optical clock has the advantages by optical lattice technique to greatly diminish the influence of fundamental noise and effectively improve Signal to Noise Ratio?SNR?.The Zeeman shift induced by the magnetic field will affect the neutral-atomic optical clock performance.Meanwhile,the stability of the neutral-atomic optical clock will be degraded by the magnetic field shift,and thus may directly lead to servo unlocks,which is unbeneficial to long-term clock operation.Additionally,the comprehensive setup of the neutral-atomic optical clocks are normally more complex than the ion optical clocks.Thus,the active compensation approaches are currently more feasible than the passive shielding approach,to weaken the impact of the stray magnetic field.Here a real-time detection and feedback compensation method is utilized in our scheme.The fluctuation of the stray magnetic field near the experimental vacuum cavity is detected and recorded through highly resolution digital magnetometers.A set of 3-dimensional compensation coils is controlled to adjust the feedback current,in the purpose to achieve real-time compensation of the stray magnetic field and avoid inducing the additional time delay.The dependence of the magnetic field in the center of chamber as well as at the position of the detector on the currents is numerically calculated and used in the feedback control of magnetic field.The compensating process is monitored and the fluctuation of magnetic field as well as the effect on the performance of optical clock is analyzed before and after the stabilization.A binomial probability distribution model is employed to simulate the change of Allan deviation and is further test by experiments.By the experiments,the necessity of magnetic field compensation is shown through improving the short-term stability of the ¹⁷¹Yb optical lattice clocks by almost one order of magnitude.In addition,through the experimental data,the residual first order Zeeman shift and the second order Zeeman shift of our optical lattice clocks are evaluated respectively.The evaluation method and evaluation results of corresponding uncertainty component are obtained,among which the relative uncertainty of the second order Zeeman shift reaches 10^-17level.