Time and Frequency Standards Based on Charged Particle Trapping

Microwave or optical frequency standards based on internal resonance transitions of ions confined in electromagnetic traps have the fundamental advantages of long observation times and small perturbations. These advantages are somewhat offset by low signal to noise ratios. Work at NBS has concentrated on microwave hyperfine transitions of atomic ions stored in Penning-type ion traps. The use of narrowband, tunable light sources for state selection and detection and for reducing the average kinetic energy of the ions (laser cooling) is an important feature of this work. Results to date include the fluorescence detection and cooling to about 50 mK of a single Mg+ ion and the observation of a 0.012 Hz linewidth on a 300 MHz 25Mg+ hyperfine transition. A frequency standard based on 201Hg+ ions is under development. Related work, mostly based on RF-type ion traps, is underway at several other labs.