Miniaturized atomic fountain clock

A miniaturized 87Rb fountain clock has been developed and tested. It preserves the possibility of launching the atoms to 30 cm above the Ramsey cavity, which is typical for high-performance fountain clocks, while the physics package size is reduced to 80 cm in height and 36 dm3 in volume, by a factor of 2.5 and 20, respectively, compared to National Physical Laboratory Cs fountain clocks. A short-term fractional instability of 4.2 × 10−13/τ/s, and averaging down below 10−15, has been shown. The long-term stability of the systematic effects most affected by the miniaturization (second-order Zeeman shift and light shift) is also discussed. The mini-fountain clock has potential application as an ultra-stable holdover clock and a secondary frequency standard realizing the SI second.