Ion Traps as Frequency Standards

The present status of precision spectroscopy on trapped ions is reviewed with respect to frequency standard Applications. In several opto-microwave experiments the line-Q of th ground state hyperfine transitions in alkali-like ions is 2-3 orders of nagnitude larger than in the frequency standards which are presently in use. Further progress to even higher Q-values seems possible. Measurements of the stability in the time domain between 10 and 104 s on different ions give very similar results to Cs beam standards. Estimates of the ultimate uncertainty of ion trap standards are in the 10-15 region. Two main problems remain to be solved at present; efficient ion cooling to suppress the second-order Doppler effect, so far demonstrated only on small ion clouds, and a recently observed change of the ion cloud density distribution has to be understood and eliminated.