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 [Xe]4f^{12}(^{3}H_{6})6s^{2} to the excited state [Xe]4f^{11}((^{4}I_{15/2})^{0})5d(^{5}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.