Absolute Frequency Measurements of the D Lines in 9Be+ Using a Single Trapped Ion

D. M. Fairbank, A. L. Banducci, R. W. Gunkelman, J. B. VanArsdale, M. L. Vildibill, and S. M. Brewer, Phys. Rev. Lett. 131, 093001 – Published 1 September 2023

Optical frequencies of the D line transitions in 9Be+ were measured with a relative uncertainty of Δν/ν=5×1011. The results represent the highest accuracy achieved on a broad electric dipole-allowed (E1) transition in a trapped ion experiment to date, enabled in part by detailed consideration of photon recoil and quantum interference. Measurements were made on a single laser-cooled ion stored in a radio frequency Paul trap, using a spectroscopy laser stabilized to an optical frequency comb and referenced to UTC (NIST). The uncertainties in the D1 and D2 lines have been reduced by a factor of 10 and 30, respectively, compared to previous work. We have extracted the 2P fine structure splitting, Δνfs=197064.54(7)MHz, and the 2P1/2 hyperfine constant, AP1/2=117.92(4)MHz.