Ultra-stable Hg/sup +/ trapped ion frequency standard

The authors report the development of a fieldable frequency standard based on /sup 199/Hg/sup +/ ions confined in a hybrid RF/DC linear ion trap. This trap permits storage of large numbers of ions with reduced susceptibility to the second-order Doppler effect caused by the RF confining fields. A 160-mHz-wide atomic resonance line for the 40.5-GHz clock transition is used to steer the output of a 5-MHz crystal oscillator to obtain a stability of 2*10/sup -15/ for 24000 second averaging times. For long averaging intervals measurements are limited by instabilities in available hydrogen maser frequency standards.<
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