Microwave-Optical Double Resonance on a Single Laser-Cooled 171 Yb + Ion

A single ion whose energy levels are hyperfine split, 171 Yb + , was electrodynamically trapped and laser cooled. The residual energy of both its driven motion and its secular motion was 11 μeV. Radiofrequency-optical double-resonance excitation yields spectra whose 40 Hz wide lines are determined so far by the duration of the ion's interaction with the 12.6 GHz radiation. These results prove that a microwave clock is feasible with its fractional systematic uncertainty not exceeding 10 −16 .