Progress on the <sup>40</sup>Ca<sup>+</sup> ion optical clock

Progress on the ⁴⁰Ca⁺ ion optical clock

Zhang Baolin^{1, 2, 3}, Huang Yao^{1, 2}, Zhang Huaqing^{1, 2, 3}, Hao Yanmei^{1, 2, 3}, Zeng Mengyan^{1, 2, 5}, Guan Hua^{1, 2, †}, Gao Kelin^{1, 2, 4, ‡}

Schematic diagram of the state preparation. Firstly the ⁴⁰Ca⁺ ion is excited to the metastable ²D_5/2(m = +1/2) state form the ²S_1/2(m = +1/2) state by the 729-nm laser, then to the ²P_3/2 state by the 854-nm laser, and spontaneously decay to the two grounds with equal probability from the ²P_3/2 state. After several times, the ⁴⁰Ca⁺ ion would be pumped to the ²S_1/2(m = –1/2) state.