Investigation of the 6s6p P03−4f</…

High-precision atomic spectroscopy provides an invaluable and sensitive tool for exploring a wide range of physical questions. Here, we investigate the forbidden optical transition of the 6s6pP30−4f135d6s2 (J=2) in Y171b atoms at the wavelength of 1695 nm, which exhibits the highest sensitivity to the variation of the fine-structure constant α compared to the current neutral optical clock. We obtain high-resolution transition spectroscopy in a one-dimensional optical lattice, and the measurement of its absolute frequency achieves kHz-level accuracy. Meanwhile, several essential atomic constants are also determined, including the electric-dipole (E1) magic wavelengths, as well as the hyperpolarizabilities and tensor polarizabilities around the E1 magic wavelengths. Additionally, we derive the hyperfine constant for the J=2 state from the measured absolute frequencies 1123 252.3±2.0 kHz, providing a sixfold enhancement in the uncertainty reduction compared to the recent result. We anticipate that this work will prompt further investigation of the additional clock transition at 1695 nm in Y171b atoms. Together with the well-established S01−P03 transition, many fundamental and new physics research, such as the time variation of α, ultralight dark-matter searches, Lorentz violation, etc., will enable new bounds and measurements with unprecedented precision. Published by the American Physical Society 2024