Measurement of the forbidden ${6s}^2{}^1{S}_0\to 5d6s{}^3{D}_1$ magnetic-dipole transition amplitude in atomic ytterbium

We report on a measurement of a highly forbidden magnetic-dipole transition amplitude in ytterbium using the Stark-interference technique. This amplitude is important in interpreting a future parity nonconservation experiment that exploits the same transition. We find $|〈{5d6s}^3{D}_1|M1\mathrm{}|{6s}^{21}{S}_0〉|{=1.33\mathrm{}\left(6\right)\mathrm{}}_{\mathrm{Stat}}{\mathrm{}\left(20\right)\mathrm{}}_{\beta }\times {10}^{-4}{\mu }_0,$ where the larger uncertainty comes from the previously measured vector transition polarizability $\beta .$ The $M1\mathrm{}$ amplitude is small and should not limit the precision of the parity nonconservation experiment.