A chip-scale atomic clock based on 87Rb with improved frequency stability
Svenja A. Knappe, P Schwindt, V Shah, Leo W. Hollberg, John E. Kitching, Li-Anne Liew, John Moreland
We demonstrate a microfabricated atomic clock physics package based on coherent population trapping (CPT) of 87Rb atoms. The package occupies a volume of 12 mm3 and requires 195 mW of power to operate. Compared to a previous microfabricated clock exciting the D2 transition in Cs, this 87Rb clock shows significantly improved short- and long-term stability. The instability at short times is 4 × 10-11 / τ1/2 and the improvement over the Cs device is mainly due to an increase in resonance amplitude. At longer times (τ > 50 sec), the improvement results from the reduction of a slow drift to –5 × 10-9 / day. The drift is most likely caused by a chemical reaction of nitrogen and barium inside the cell. When probing the atoms on the D1 line, spin-exchange collisions between Rb atoms and optical pumping have increased importance.