The Development And Performance Evaluation Of A Liquid Nitrogen-Cooled ⁴⁰Ca⁺ Optical Clock

Optical clocks are currently the most accurate frequency standards,and their extremely high accuracy and stability are helpful for the development of science and technology.For example,optical clocks are commonly used in navigation and geodesy,as well as in fundamental physics experiments.Benefitting from a five-orders-ofmagnitude larger transition frequency than that of cesium fountain clocks and the development of techniques,most of optical clocks have surpassed the primary Cs standard that provide the present definition of the ’second’,in terms of both uncertainty and stability.One of the outstanding advantages of the 40Ca+ optical clock is that only five lasers are required to operate a clock,and all of them can be directly generated by diode lasers.Another is its negative differential static scalar polarizability of the clock transition,corresponding to a magic drive frequency in which the clock transition frequency is extremely insensitive to micromotion.The work during my Ph.D.period is mainly based on 40Ca+ optical clocks,which can be summarized as follows:1.A liquid nitrogen 40Ca+ optical clock system has been built,including ion trap,liquid nitrogen vacuum chamber,laser system and magnetic field control system,etc.2.The uncertainty of the liquid-nitrogen ion 40Ca+optical clock has been reduced to 3.0×10-18.3.The frequency difference between the room temperature clock and the liquidnitrogen temperature clock has been measured to-336(9)mHz,which is in good agreement with the theoretical value-335(8)mHz,showing the reliability of the systematic uncertainties of the two clocks.4.The relationship between the frequency stability of optical clocks caused by quantum projection noise and probe time has been deeply studied by the Monte Carlo method.5.The frequency stability of the 40Ca+ optical clock has been improved to 2.5×10-15/(?)with a continuous operation rate of 93%by introducing the Ramsey locking method,the Ramsey locking fringe monitoring algorithm and the peak-finding algorithm based on the Rabi locking method.