国家授时中心锶原子光钟的实验研制进展

Experiment Study on Optical Lattice Clock of Strontium at NTSC

目前光钟的稳定度和不确定度均已进入10^-18量级。介绍了中国科学院国家授时中心的锶原子光晶格钟的研究情况。以锶原子四种同位素中自然丰度最大的^88Sr为研究对象，依次实现了^88Sr的一级冷却和二级冷却。为消除一阶多普勒频移和反冲频移对冷原子运动的影响，充分发挥原子极窄钟跃迁谱线线宽的优点，冷原子被囚禁于光晶格中。而由光晶格导致的原子能级频移的问题可被“魔术”波长解决，对锶原子光钟，光晶格波长为813．4nm。实验中采用功率放大的半导体激光器输出“魔术”波长激光，通过一维驻波光场搭建将^88Sr装载进一维光品格中。测量得到囚禁于光晶格中的冷原子寿命为270ms，温度为3．5μK，数目为1．2×10^5。光晶格囚禁为下一步的钟跃迁信号提供了较长的探测时间并且有利于获得极窄线宽的钟跃迁谱线，因此是光钟研制中很重要的一步。

The accuracy and stability of optical clocks has achieved 10^-18 level currently. The progress on the optical lattice clocks of Strontium （Sr） atoms at National Time Service Center is presented. ^88Sr, which has the highest natural abundance in four isotopes of Sr, is cooled on the basis of transitions （5s5s） ^1S0-（5s5p）^1P1 and （5s5s）^1 S0- （5s5p）^3P1. In order to cancel the effect of Doppler shift and recoil shift these cold atoms are trapped in the optical lattice. However, the optical lattice where atoms are trapped can make the energy level shift, called A. C. Stark shift. The ＂magic＂ wavelength for clock transition （5s5s）^1S0-（5s5p）3P0 can make the same Stark light-shift for both of them, being value 813.4 nm. Then those cold ^88 Sr atoms are confined in a 1-D optical lattice constituted by the laser outputting from an amplified diode laser, operating on the ＂magic＂ wavelength 813nm. Consequently, the lifetime of atoms in 1-D optical lattice is measured and the value is 270 ms. The temperature and the number are about 3.5 μK and 1.2 ×10^5 respectively. Atoms confined in the optical lattice can provide a long interrogation time for probing the clock transition, furthermore make the foundation for developing the optical lattice clock of Sr atoms.