A cryogenic radio-frequency ion trap for a 40Ca^(+) optical clock

A liquid-nitrogen cryogenic40Ca^(+)optical clock is presented that is designed to greatly reduce the blackbody radiation(BBR) shift. The ion trap, the electrodes and the in-vacuum BBR shield are installed under the liquid-nitrogen container,keeping the ions in a cryogenic environment at liquid-nitrogen temperature. Compared with the first design in our previous work, many improvements have been made to increase the performance. The liquid-nitrogen maintenance time has been increased by about three times by increasing the volume of the liquid-nitrogen container;the trap position recovery time after refilling the liquid-nitrogen container has been decreased more than three times by using a better fixation scheme in the liquid-nitrogen container;and the magnetic field noise felt by the ions has been decreased more than three times by a better design of the magnetic shielding system. These optimizations make the scheme for reducing the BBR shift uncertainty of liquid-nitrogen-cooled optical clocks more mature and stable, and develop a stable lock with a narrower linewidth spectrum,which would be very beneficial for further reducing the overall systematic uncertainty of optical clocks.

A combined magnetic field stabilization system for improving the stability of 40Ca^(+) optical clock

Future applications of portable40Ca^(+)optical clocks require reliable magnetic field stabilization to improve frequency stability, which can be achieved by implementing an active and passive magnetic field noise suppression system. On the one hand, we have optimized the magnetic shielding performance of the portable optical clock by reducing its apertures and optimizing its geometry;on the other hand, we have introduced an active magnetic field noise suppression system to further suppress the magnetic field noise experienced by the ions. These efforts reduced the ambient magnetic field noise by about 10000 times, significantly reduced the linewidth of the clock transition spectrum, improved the stability of the portable40Ca+optical clock, and created the conditions for using portable optical clocks in non-laboratory magnetic field environments. This active magnetic field suppression scheme has the advantages of simple installation and wide applicability.

Progress on the^40Ca^+ion optical clock

Progress of the ^40Ca^+ion optical clock based on the 4^2S1/2-3d ^2D5/2 electric quadrupole transition is reported.By setting the drive frequency to the“magic”frequencyΩ0,the frequency uncertainty caused by the scalar Stark shift and second-order Doppler shift induced by micromotion is reduced to the 10^-19 level.By precisely measuring the differential static scalar polarizability∆α0,the uncertainty due to the blackbody radiation(BBR)shift(coefficient)is reduced to the 10^-19 level.With the help of a second-order integrating servo algorithm,the uncertainty due to the servo error is reduced to the 10^-18 level.The total fractional uncertainty of the ^40Ca^+ion optical clock is then improved to 2.2×10^-17,whereas this value is mainly restricted by the uncertainty of the BBR shift due to temperature fluctuations.The state preparation is introduced together with improvements in the pulse sequence,and furthermore,a better signal to noise ratio(SNR)and less dead time are achieved.The clock stability of a single clock is improved to 4.8×10^-15√τ(in seconds).

可搬运钙离子光钟的集成化激光冷却系统

时间单位“秒”是人类计量最为精准的国际单位,目前国际单位制(SI)“秒”的定义是基于微波跃迁的铯原子(^(133)Cs)喷泉钟。光钟的参考跃迁频率为光学频率,理论上精度会比微波钟高4个数量级,因此可能成为未来的国际“秒”定义。可搬运光钟的研制使光钟迈进实际应用,除了在时间基准以及卫星导航方面的应用,也在验证洛伦兹不变性、基本物理常数是否随时间变化、引力波和暗物质探测等方面具有广泛的应用。针对可搬运钙离子光钟,设计了一套集成化激光冷却系统,利用Pound-Drever-Hall方法将钙离子光钟397nm和866nm冷却激光的频率锁定在一个超低热膨胀系数的Fabry-Perot振腔上,以获得窄线宽和低频率漂移的稳频激光。同时,实验中采用了基于FPGA的高分辨率时序控制系统,并采用“预冷和冷却”两步Doppler冷却方式更好地冷却离子。通过以上方法,将可搬运钙离子光钟的宏运动引起的二阶Doppler频移的不确定度抑制到小系数10^(-18)水平。