Improving Optical Clocks

Travis Nicholson

Tatiana Nazarova, C. Degenhardt, Christian Lisdat +3 more

Mengyan Zeng, Yao Huang, H. Shao +5 more

Stability is one of most important performances of an atomic clock. Here we describe our recent work on improving the stability of our 40 Ca + 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 40 Ca + optical clock is improved to about . Compared with in previous work, the averaging time is decreased to reach a given level of statistical uncertainty in a clock comparison .

S. Bize

Ruming Hu, Zixiao Ma, Baolin Zhang +12 more

Abstract Here, we develop a compact multilayer magnetic shield for a transportable optical clock, achieving shielding factors of up to 10 5 . To improve the frequency stability of the transportable optical clock, we improved the magnetic-field environment of a transportable 40 Ca + ion optical clock (TCIOC) using the newly developed magnetic shielding system and reduced the clock-laser frequency noise by transferring the stability of an ultrastable reference laser through an optical frequency comb. These improvements enabled the coherent interrogation time to be extended from 40 ms to 320 ms . A time-interleaved self-comparison yielded a measured short-term fractional frequency instability of 1.6 × 10 − 15 / τ , close to the estimated quantum projection noise-limited instability of 1.18 × 10 − 15 / τ . Meanwhile, the uncertainty contributions associated with the DC second-order Zeeman shift and the servo error were reduced to 1.1 × 10 − 21 and 4.5 × 10 − 19 . These results provide a practical basis for further improving the performance of transportable optical clocks.