史庭云++高克林++严宗朝++钟振祥++张佩佩
摘 要：精细结构常数是无量纲的基本物理常数，它表征电磁相互作用强度，其高精度确定对基本物理理论的验证及新物理预言至关重要。氦原子及类氦离子是最简单的多电子体系，其（1s2p）P三重态精细结构劈裂强烈依赖于精细结构常数。开展对氦原子及类氦离子2S～2P态精密光谱测量可以检验现有的两电子量子电动力学（QED）理论计算，同时也提供了高精度确定精细结构常数的独立方法。目前，氦原子的2P三重态精细结构光谱测量实验达到ppb精度，已触及到高阶QED效应，而与之有相似能谱结构的Li+离子测量精度要低2～3个量级。由于QED高阶效应对电荷数Z极其敏感，提高Li+的光谱测量精度，可对QED理论计算进行更为严格的检验。该研究拟采用激光冷却的Ca+对由Li+亚稳态进行协同冷却，实现对Li+内外自由度的精确控制，获得几十mK量级处于亚稳态的Li+离子晶体，进而对2S～2P三重态548.5 nm跃迁进行光谱测量，预期相对精度达到10～8，较目前Li+同类实验精度提高两个量级；同时，开展对现有QED理论进行独立检验，提高理论预言的可靠性；通过实验光谱与理论预言的对比在10～8相对精度上独立确定精细结构常数。
关键词：Li+离子 精密光谱 量子电动力学 精细结构常数 离子阱 协同冷却
Li+ Ion Precision Spectroscopy and Determination of Fine Structure Constant
Shi Tingyun Gao Kelin Yan Zongchao Zhong Zhenxiang Zhang Peipei
（Wuhan institute of Physice and Mathenatics，Chinese Academy of Sciences）
Abstract：The fine structure constant is a dimensionless fundamental physical constant， charactering the strength of electromagnetic interaction. To determine this constant with high precision is of great importance both for the verifications of the basic physical theories and predictions of new physics go beyond particle-physics Standard Model. Helium and helium-like ions is the simplest many-electron systems， whose fine structure of triplet （1s2p）P state strongly depend on the fine structure constant. Precision spectroscopy measurement of Helium and helium-like ions provide stringent test of existent two-electron bound state QED theory and calculation， and an independent method for determination of fine structure constant. Up to now， high accuracy of the fine structure intervals have been achieved to a degree of ppb， which means high-order QED effects can be touched. Li+ ion has a similar energy structure to helium. However， experimental measurement for Li+ ion fine structure intervals with lower accuracy， 2～3 order of magnitude then helium. Since the high-order QED effects are extremely sensitive on charge number Z， the improvement of measurement accuracy for Li+ spectroscopy would provide more stringent test of bound state QED. In this project， metastable 1s2sS triplet state of Li+ ions will be sympathetically cooled by the laser-cooled Ca+ ions， to realize the accurate controlling of the internal and external degree of freedom. Then， metastable Li+ ions， with the transitional kinetic energy around several-tens mK can be obtained. The 548.5 nm transition frequency from triplet 2S state to the triplet 2P states will be measured by the precision spectroscopy method with the relative accuracy about 10～10， more accuracy with two order of magnitude higher than the results up to date. Meanwhile， an independent check for two-electron QED theory and calculation will be carried out to guarantee the correctness of QED theoretic prediction. Comparing the results from our experimental spectroscopy and theoretical prediction， the fine structure constant is expected to be determined with the relative accuracy about 10～8.
Key Words：Li+ ion；Precision spectroscopy；Quantum dynamic mechamics；Fine structure constant；Ion trap；Sympathetic cooling
閱读全文链接（需实名注册）：http：//www.nstrs.cn/xiangxiBG.aspx？id=49428&flag=1
