Observation of the nuclear magnetic octupole moment of173Yb from precise measurements of the hyperfine structure in the3P2state

Abstract

We measure hyperfine structure in the metastable ${{}^{3}P}_{2}$ state of ${}^{173}$Yb and extract the nuclear magnetic octupole moment. We populate the state using dipole-allowed transitions through the ${{}^{3}P}_{1}$ and ${{}^{3}S}_{1}$ states. We measure frequencies of hyperfine transitions of the ${{}^{3}P}_{2}\ensuremath{\rightarrow}{{}^{3}S}_{1}$ line at 770 nm using a Rb-stabilized ring cavity resonator with a precision of 200 kHz. Second-order corrections due to perturbations from the nearby ${{}^{3}P}_{1}$ and ${{}^{1}P}_{1}$ states are below 30 kHz. We obtain the hyperfine coefficients as $A=\ensuremath{-}742.11(2)$ MHz and $B=1339.2(2)$ MHz, which represent a two orders-of-magnitude improvement in precision, and $C=0.54(2)$ MHz. From atomic structure calculations, we obtain the nuclear moments quadrupole $Q=2.46(12)$ b and octupole $\ensuremath{\Omega}=\ensuremath{-}34.4(21)$ $\mathrm{b}\ifmmode\times\else\texttimes\fi{}{\ensuremath{\mu}}_{N}$.