Towards an Optical Lattice Clock with a New Clock Transition in Ytterbium*

Optical lattice clocks play an important role in state-of-the-art atomic clocks, with multiple species achieving fractional uncertainties of 10¹⁸ or less. Such highly accurate clocks are now used as quantum sensors for fundamental physics searches. One of the transitions suitable for such quantum sensors is the 6s^{2 1}S₀-4f¹³5d6s²(J=2) transition in neutral ytterbium at 431 nm. The excited state of this transition is theoretically predicted to be highly sensitive to multiple fundamental physics searches. The transition was recently observed experimentally for the first time [1,2]. With a complete list of absolute frequencies of the transitions for all stable isotopes and an initial analysis of isotope shifts for a fifth force search [3], spectroscopy with smaller uncertainty is expected to enhance sensitivity. We are developing an optical lattice clock system based on this clock transition. In this talk, we will describe the latest developments in the system and the current status of the spectroscopy, initially targeting an uncertainty below 1 Hz. The realization of an optical lattice clock with this new clock transition in Yb is expected to enable continuous frequency comparison with conventional optical lattice clocks, providing a stringent constraint on the time variation of the fine structure constant. Also, isotope shift measurements with this high accuracy can deepen our understanding of nuclear structure and the search for fifth forces between an electron and a neutron. 

[1]AK, et al.: Phys. Rev. A 107, L060801 (2023)

[2]Ishiyama et al.: Phys. Rev. Lett. 130, 153402 (2023)

[3]AK, et al.: Phys. Rev. A 109, 062806 (2024)