Improvement of Stability of ^40Ca^+ Optical Clock with State Preparation

Stability is one of most important performances of an atomic clock. Here we describe our recent work on improving the stability of our ^40Ca^+ optical clock. State preparation is adopted to transfer the ion to the ground-state magnetic sublevel of the clock transition, after the quenching laser transfers the ion to the ground state at each cycle. Using this method, the stability for ^40Ca^+ optical clock is improved to about 6.3\times 10^-15/\sqrt\tau. Compared with 1.0\times 10^-14/\sqrt \tau in previous work, the averaging time is decreased to reach a given level of statistical uncertainty in a clock comparison.