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, ‡}

Zeeman-resolved spectra of the ²S_1/2 → ²D_5/2 transition of a single ⁴⁰Ca⁺ ion obtained at the same probe laser power. The ground state sublevel m_J = ± 1/2 and the upper state sublevel m_J′ (²D_5/2) are shown below and above each arrow respectively. (a) Spectrum shows 10 Zeeman components completely and is obtained without state preparation. In the (b) spectrum, the ⁴⁰Ca⁺ ion has been pumped to the ²S_1/2(m = +1/2) state; thus, only 5 Zeeman components are obtained, but with a higher transition probability.