A research group led by Prof. ZHANG Shougang and Prof. YUN Enxue (Peter Yun) from the National Time Service Center (NTSC) of the Chinese academy of sciences (CAS) developed a high-performance and compact coherent population trapping (CPT) atomic clock, which solves the miniaturization problem of high-performance CPT atomic clock.

The study was published in Metrologia on July 1.

The current chip-scale atomic clocks (CSAC) based on the CPT occupy volume similar to that of a matchbox. There is still much room for its frequency stability to be improved for the applications that need higher precision time signal, such as deep space exploration, satellite navigation, fire and underground search and rescue.

NTSC researchers proposed and implemented a CPT atomic clock based on the direct modulation of a large-modulation-bandwidth and narrow-linewidth distributed Bragg reflector laser, which replaces the usually used external bulk modulator in high-performance CPT clocks.

The method retains the high performance while significantly reducing the clock size. Using this highly compact bichromatic light source and simplest CPT configuration, a CPT signal of clock transition with a narrow linewidth and high contrast is observed.

They locked the local oscillator frequency to the CPT resonance and demonstrated a short-term frequency stability of 3.6 × 10^-13 τ^-1/2 (4 s ≤ τ ≤ 200 s).

"We attribute it to the ultralow laser frequency and intensity noise as well as to the high-quality-factor CPT signal. This study can pave the way for the development of compact high-performance CPT clocks based on our scheme," said Prof. YUN.

"The work has merit of novelty to the extent that for the first time it demonstrates state-of-the-art short-term stability based on direct laser modulation, along with the potential to simplify the realization of high-performance CPT vapour-cell clocks," commented by the reviewer.

Experimental setup for high-performance miniaturized CPT atomic clock and its frequency stability measurement (Image by YUN Enxue)