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, ‡}

Frequency difference between the two ⁴⁰Ca⁺ ion clocks as a function of the RF drive frequency of clock 2. The red curve is a fit to the data and gives Ω₀ = 2π × 24.81(1) MHz. The shaded area illustrates the uncertainty in the theoretical result.^[15]