利用钙离子魔幻波长高精度测量4S-4P跃迁振子强度

High precision measurements of oscillator strengths are important in many current areas of research, including the development of optical frequency standards, studies of fundamental symmetries and degenerate quantum gases, quantum information, plasma physics, and astrophysics. Electric-dipole oscillator strengths can be achieved by theoretical calculation and experimental measurement. The measurement precision of the electric-dipole oscillator strengths is 3-4 significant digits. The method for measurement of ions' electric-dipole oscillator strengths is adopted the combination of the lifetime and branch ratio measurement. The measurement precision of 4S-4P oscillator strengths of calcium ion is only 2 significant digits, and the difference between theoretical and experimental results is about 10%. This project present a new method for measuring the 4S-4P oscillator strength of 40Ca+ ion, which is based on the calcium ion optical frequency standard, measuring the ac Stark shift of 4S1/2-3D5/2 clock transition in a 395 nm laser field (the wavelength is predicted by the theoretical method), where the magic wavelengths around the this transition can be obtained according to the ac Stark shift. Then, the oscillator strengths of the 4S-4P transition can be deduced by combination the measured magic wavelengths and theoretical calculation. The measurement precision is expected to be improved to 4 significant digits. The reduced matrix elements, oscillator strength ratio and transition line strength ratio can be deduced. This project can provide a new method for measuring the ion electric-dipole oscillator strengths, and can serve as a new benchmark test of atomic structure calculations.

振子强度的高精度测量对于光频标、基本对称性、简并量子气体、量子信息、等离子体以及天文学等方面的研究具有重要意义。偶极跃迁振子强度可以通过理论计算和实验测量得到。中性原子偶极跃迁振子强度的实验测量精度为3-4位有效数位，离子振子强度的实验测量主要是采用测量激发态寿命和分支比相结合的方式得到，对钙离子4S-4P振子强度的测量精度目前只有两位，实验测量和理论计算结果之间偏差在10%左右。本项目提出基于钙离子光频标平台，入射395nm激光（理论预测波长），测量该激光造成的钙离子4S1/2-3D5/2钟跃迁谱线的ac Stark频移，得到钙离子钟跃迁的魔幻波长，利用该魔幻波长，结合理论计算，得到钙离子4S-4P跃迁的振子强度，有望将测量精度提高到四位，同时可以得到约化矩阵元、振子强度比和跃迁线强比等数据，本项目的实施可以提供一种新的测量离子偶极跃迁振子强度的方法，同时可以对原子结构理论提供实验检验。

振子强度的高精度测量对于光频标、基本对称性、简并量子气体、量子信息、等离子体以及天文学等方面的研究具有重要意义。.本项目实现了729 nm钟跃迁激光稳频，线宽达到1 Hz，稳定度达到2E-15（1-100秒），利用该激光器扫描获得了线宽为6 Hz的钙离子钟跃迁谱线。搭建了用于测量钙离子钟跃迁魔幻波长的装置，在40Ca+离子体系中首次测量了钟跃迁魔幻波长，其中，对应于2D5/2态磁子能级|m| = 1/2的魔幻波长为λ|mj|=1/2 = 395.7992(2) nm，对应于2D5/2态磁子能级|m| = 3/2的魔幻波长为λ|mj|=3/2= 395.7990(2) nm，实验结果和之前发表的理论结果相符合。基于实验获得的魔幻波长，得到40Ca+离子4S1/2-4P1/2和4S1/2-4P3/2跃迁的振子强度比为2.027(5)，对应的线强比为2.009(5)。结合之前其他研究组获得的4S1/2-4P1/2跃迁矩阵元2.8928(43)，以及我们实验获得4S1/2-4P1/2和4S1/2-4P3/2跃迁线强比，可得4S1/2-4P3/2跃迁矩阵元为4.099(8)，该结果与之前发表的理论结果相符合。.同时，为了进行基于全光囚禁离子光频标研究，我们测量了钙离子钟跃迁红外魔幻波长，结果为：1056.37(9) nm，实验结果的精度比之前发表的理论计算结果提高了两个量级，利用实验测量的魔幻波长，获得了3D5/2-4P3/2跃迁的跃迁矩阵元为3.295(15)，结合之前实验获得的4S1/2-4P1/2和4S1/2-4P3/2跃迁矩阵元，可以获得钙离子钟跃迁上下两个态的静态极化率之差为44.32(32) a.u.，对应温度为300K时的钙离子钟跃迁频移为0.3816 Hz，不确定度为6.8E-18。.此外，基于钙离子研究平台，获得了钙离子亚稳态3D3/2和 3D5/2 态的寿命，分别为1.1649(44) s和1.195(8) s。同时，在实验上测量了3d 2D5/2-4s 2S1/2跃迁的分支比为0.998(12)，通过实验测量的3D5/2态寿命和3d 2D5/2-4s 2S1/2跃迁分支比，首次在实验上获得了钙离子3D5/2-4S1/2跃迁的四极跃迁矩阵元为9.733(52) ea0^2。