Research Progress on Mercury Ion Microwave Clock for Time Keeping

Mercury ion microwave clock has great prospect in timekeeping and space applications for its excellent frequency stability and very low drift rate. In recent years, we have been studying the method to maintain the sealed vacuum system with getters for mercury ion microwave clock. This technology, which can reduce the size, weight and power consumption (SWaP) and greatly improve the reliability of the vacuum system, plays the key role in developing the mercury ion microwave clock from laboratory to practical application. In this letter, we present a multipole trap mercury ion clock developed for ground timekeeping applications using sealed vacuum system. Based on the ion shuttling between the quadrupole and 12-pole trap, the sensitivity of ion number dependence effect and external magnetic field could be effectively suppressed, which promising a better long-term stability than conventional single quadrupole trap system. The optical system is also optimized to enhance the signal to noise ratio (SNR) of the clock spectral line. To date, the ion clock physical package has been built. The clock transition spectral is measured in quadrupole trap region firstly. That shows a stability limit of 7.29  × 10^–14 at 1s according to the shot noise. The signal of ions shuttling between the two traps is also observed. The near 100% shuttling efficiency has been demonstrated even after 50 times ion shuttling.