Efficiently loading ⁴⁰Ca⁺-²⁷Al⁺ ion crystal using sympathetic cooling and pulsed laser ablation

We demonstrate a method to efficiently load a pair of ⁴⁰Ca⁺-²⁷Al⁺ ion crystals with sympathetic cooling and pulsed laser ablation, serving as a starting step for the ²⁷Al⁺ clock. We achieved a technique to rapidly detect the loading of hot ions by monitoring the ²S_1/2 → ²D_5/2 narrow transition of ⁴⁰Ca⁺ that couples to the shared motional modes between the two ions. The sympathetic cooling time of the ⁴⁰Ca⁺-²⁷Al⁺ ion pair is measured. Two traps are employed to compare the loading time from two directions and it was found that the loading from the axial direction takes much shorter time than loading from the radial direction of the trap. With the help of adaptively controlled trap potential, our method reduced the average loading time of a ⁴⁰Ca⁺-²⁷Al⁺ pair from 26 to 1 min. This research is an important step for increasing the uptime ratio of the ²⁷Al⁺ optical clock and is useful for other mixed-species ion crystals based on sympathetic cooling.