High-Resolution Magnetic Hyperfine Resonance in Harmonically Bound Ground-StateHg199Ions

The field-independent ($\Delta F=\pm 1$, $M_F^{}{}_{}{}^{\prime }=0\mathrm{}\to M_F=0\mathrm{}$) magnetic hyperfine transition has been observed in ground-state ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ ions by optical pumping with a ${}_{}{}^{202}{}_{}{}^{}\mathrm{Hg}$ lamp. The ions were confined by a quadrupole rf electric field, imparting to them a discrete motional spectrum which leads to Doppler sidebands which can readily be resolved. The central line was observed to have a fractional linewidth not exceeding 2× ${10}^{-10\mathrm{}}$, a degree of resolution surpassed only by the Mössbauer effect. A preliminary value for the center frequency is given as 40 507 348 050 ± 50 Hz.