Cadmium Ion Microwave Atomic Clock

Microwave clocks have been widely applied in precision measurement of time and frequency,time-keeping and navigation for their high stability and reliability.By confining ions within Lamb-Dicke regime,the first-order Doppler shift can be eliminated,and it is beneficial for the miniaturization of the atomic clock.Thus,microwave clock based on ion trap attracts a lot attention.Because the hyperfine splitting of¹¹³Cd⁺ 2P3/2state is 800 MHz,only one laser is needed for laser cooling,optical pumping,and detection.Thus¹¹³Cd⁺ion clock has the unique potential in miniaturization compared to the clocks based on neutral atoms.Since 2010,a project to build a microwave clock based on¹¹³Cd⁺ions has been carried out in the Joint Institute of Measurement?JMI?,Tsinghua University.In the past several years,we have built the experimental setup,obtained the Rabi and Ramsey fringes of the clock transition and realized the preliminary closed-loop locked clock.Based on previous work,this dissertation reports the improvement of the short-term frequency instability of¹¹³Cd⁺microwave clock by optimizing the magnetic field shield,optics controlling and closed-loop locking parameters.The short-term frequency instability is improved from 1.0 1.7 × 10-12/??? to 6.1 × 10-13/??? which is better than the commercial cesium beam clock and rubidium clock.Taking advantage of closed-loop locking of the¹¹³Cd⁺clock,the output signal of the clock is measured continuously for a long period of time,and the frequency of the ground-state hyperfine splitting of¹¹³Cd⁺ions at zero magnetic field is obtained precisely.After estimating all the systematic shifts and uncertainties,the final frequency is 15199862855.0192?10?Hz and the fractional uncertainty of the measurement is 6.6 × 10^-14.This result is consistent with previous results,and the measurement precision is improved by nearly one order than the result of our previous measurement in 2013,and it is nearly 200 times better than the result of JPL in 2006.This dissertation carried out theoretical and experimental research on the fluorescence decay during detection and the Dick effect of the¹¹³Cd⁺clock.With the rate equation method,we built a model of the detection process,and the calculated results agree with the experimental results well.This research reveals that the fluorescence decay comes from Doppler effect of ions and the nonuniformity of the magnetic field.We also estimated the influence of the Dick effect in the¹¹³Cd⁺clock by measuring the phase noise of the local oscillator,and proposed some methods to reduce the Dick effect.Based on the analysis,new design of¹¹³Cd⁺clock with sympathetic cooing and double traps is proposed,and a short introduction of the current progresses on it is reported.