Precise determination of the171Yb+ ground state Hyperfine separation

We performed a microwave-optical double resonance experiment on the ground state of¹⁷¹Yb⁺ ions. About 10⁵ particles were confined in a r.f. quadrupole trap for periods of several hours in the presence of He buffer gas. Hyperfine pumping by a pulsed dye laser was followed by microwave transitions, which we observed via changes in the ionic fluorescence intensity. The ground state hyperfine splitting has been determined togD W=12642812124.2±1.4 Hz. The ultimate line width obtained in this experiment was 33 mHz, corresponding to a lineQ of 3.8·10¹¹. The final error ofgD W is mainly determined by the accuracy of the available frequency reference.