氦原子2S-2P精密谱实验研究

Helium is the simplest multielectron atom and typically play the role for studying the quantum electrodynamic theory (QED) of bound-three-body system. Although its quantum description has no exact solutions even in the nonrelativistic limit, the approximation calculation method can achieve great precision by using only quantum theory and fundamental physical constant. Precise measurements in helium thus often served as a testing ground for quantum electrodynamic theory in atomic physics..This project will take advantage of the helium precision spectroscopy systems, which already has been built in our laboratory, to produce a high brightness and single quantum state of helium beams. The measurement of the absolute frequency of 23^S_1 to 23^P_J energy level of He-4/He-3 atoms will be made by our frequency comb systems, and will achieve a better accuracy of around 1kHz. This will lead a finer test of various discrepancy between theory and experiment, and can be used to test the QED theory.

氦原子是最简单的多电子原子，是束缚态的三体量子电动力学理论的经典研究对象，也是少数几个基于量子力学和基本物理常数、而不需要任何可调参数就可以计算达到极高精度的量子体系之一。因此，氦原子精密谱一直是一个十分理想的在原子分子体系中检验量子电动力学理论的平台。本项目计划利用现有的氦原子精密光谱系统，制备高强度、单一量子态的氦原子束流，利用光频梳测频的方法，完成He-4/He-3原子23^S_1-23^P_J能级跃迁的绝对频率测量，预期精度达到1kHz，得到He-4/He-3同位素位移的结果，在更高的精度上明确理论计算和实验测量上可能存在的偏差，检验量子电动力学理论。

项目“氦原子2S-2P精密谱实验研究”，计划通过高强度氦原子束流技术，利用精密激光光谱测量获得氦原子2S-2P能级结构，并结合理论获得氦原子核的特性，检验量子电动力学。项目已成功搭建了氦原子束流减速装置，可实现亚稳态氦原子束流从60m/s到400m/s的纵向速度调控。通过理论结合实验的方法明确了测量中探测激光功率带来的误差。项目测量获得了氦-4原子2S-2P能级跃迁频率，其测量精度为1.6kHz，理论学家认为该测量结果可以满足测量氦-4原子核电荷半径到千分之一的精度。未来有望可以通过比对μ-He离子的测量结果，获得标准模型的检验。另一方面，该结果的获得，表明为解决之前国际上He-3/He-4核电荷半径测量偏差问题，需要更多的关注在实验测量上，该结果目前已经发表在PRL上。