Ultrahigh-Resolution Microwave Spectroscopy on TrappedYb+171Ions

A laser optical-pumping, double-resonance experiment was performed on electrodynamically confined ${}_{}{}^{171}{}_{}{}^{}\mathrm{Yb}_{}^{+}{}_{}{}^{}$ ions. The ground-state hyperfine splitting has been determined to be $\Delta W_{\mathrm{h}\mathrm{f}\mathrm{s}}=12\mathrm{}642812124.2\pm 1.4$ Hz. The ultimate linewidth obtained in this experiment was 60 mHz, corresponding to a line $Q$ of 0.2×${10}^{12}$. It was limited by the stability of the available frequency reference.