Towards an Untrapped Three-Photon Optical Clock with Bosonic Ytterbium

Atomic clocks provide the most precise time and frequency standards, with applications in navigation, telecommunications, and precision tests of fundamental physics. We present the design and ongoing implementation of an optical clock architecture based on a three-photon transition in untrapped bosonic ytterbium. By interrogating ballistic ytterbium atoms using a coherent three-photon transition and arranging the three clock lasers to cancel the net Doppler shift, this approach is designed to suppress dominant systematic effects associated with optical clocks, including Zeeman and lattice light shifts. Analytical modeling and numerical simulations describe the effective two-level dynamics of the three-photon transition and we optimize Ramsey interrogation pulse sequences under realistic experimental conditions. We also sweep the laser detunings in simulations of the atomic dynamics, revealing dressed-state features associated with intermediate resonances and identifying detuning regions that maintain high-contrast population transfer. For this clock architecture, the dominant sources of systematic uncertainty are expected to include second-order Zeeman shifts, blackbody radiation, and residual light shifts from the clock lasers.