Observation of a narrow inner-shell orbital transition in atomic erbium at 1299 nm

Abstract

We report on the observation and coherent excitation of atoms on the narrow inner-shell orbital transition, connecting the erbium ground state $[\mathrm{Xe}]4f^{12}{(}^3{\text{H}}_6)6s^2$ to the excited state $[\mathrm{Xe}]4f^{11}{(}^4{\text{I}}_{15/2}{)}^{0}5d{(}^5{\text{D}}_{3/2})6s^2(15/2,3/2{)}_7^0$. This transition corresponds to a wavelength of 1299 nm and is optically closed. We perform high-resolution spectroscopy to extract the $g_J$-factor of the $1299$-nm state and to determine the frequency shift for four bosonic isotopes. We further demonstrate coherent control of the atomic state and extract a lifetime of 178(19) ms which corresponds to a linewidth of 0.9(1) Hz. The experimental findings are in good agreement with our semi-empirical model. In addition, we present theoretical calculations of the atomic polarizability, revealing several different magic-wavelength conditions. Finally, we make use of the vectorial polarizability and confirm a possible magic wavelength at 532 nm.

14 pages, 6 figures