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 2S1/2 → 2D5/2 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.

Integrated multiple wavelength stabilization on a multi-channel cavity for a transportable optical clock.

We present a simple, compact, and efficient scheme for integrated multiple wavelength stabilization and continuous operation of a transportable 40Ca+ optical clock using a multi-channel cavity. The fractional frequency instability of 729 nm clock laser is ∼ 1.5 ×10-15 at 10 s with an approximate linewidth of 1 Hz. Meanwhile, frequency fluctuations of all the other lasers are less than ± 330 kHz/day. The one-day stability of this clock is measured as ∼ 5 ×10-17 through 72 h continuous operation. This scheme is potentially useful for the realization of next-generation transportable optical clocks and other metrological systems.