Frequency Stability of Atomic Clocks Based on Coherent Population Trapping Resonance in ⁸⁵Rb

An atomic clock system based on coherent population trapping (CPT) resonance in ⁸⁵Rb is reported, while most past works about the CPT clock are in 87Rb. A new modulation method (full-hyperfine-frequency-splitting modulation) is presented to reduce the effect of light shift to improve the frequency stability of the CPT clock in ⁸⁵Rb. The experimental results show that the short-term frequency stability of the CPT clock in ⁸⁵Rb is in the order of 10^-10/s and the long-term frequency stability can achieve 1.5×10^-11/80000s, which performs as well as ⁸⁷Rb in CPT resonance. This very good frequency stability performance associated with the low-cost and low-power properties of ⁸⁵Rb indicates that an atomic clock based on CPT in ⁸⁵Rb should be a promising candidate for making the chip scale atomic clock.