Towards an infrared frequency standard using CaF molecules in a lattice

Clock comparisons provide exceptionally precise constraints on present day variations of the fine structure constant (α) and the electron-to-proton mass ratio (m_e/m_p) [1]. These measurements constrain the parameter spaces of ultralight dark matter models and probe models of Lorentz violation, dark energy, grand unification theories and quantum gravity [2]. By comparing a molecular vibrational frequency to an optical atomic clock, it seems possible to make improved measurements of the variations of m_e/m_p. Moreover, vibrational frequency measurements can serve as frequency standards in the infrared, a region of the spectrum where current standards are poor. We propose a molecular clock based on the 17 μm fundamental vibrational transition of ultracold CaF molecules in an optical lattice. We calculate the differential ac polarizability of the vibrational states and find several convenient magic wavelengths where the clock transition is insensitive to the lattice intensity. We show that the transition has low sensitivity to electric fields, magnetic fields and blackbody radiation and project that a fractional inaccuracy below 10^-17 is feasible. We will report our progress on cooling molecules into an optical lattice, developing a 17 μm laser system to drive the vibrational transition directly, and developing a Raman laser system for the clock.

[1] R. Lange et al, Phys. Rev. Lett 126, 011102 (2021).

[2] G. Barontini et al, EPJ Quantum Technology 9, 12 (2022).