Magneto-optical trapping of SrOH molecules for ultralight dark matter searches

Ultralight bosonic particles comprise a broad and well-motivated class of dark matter candidates in the mass range of 10^-24 eV < m < 1 eV. This type of dark matter behaves as a field that coherently oscillates at the Compton frequency of the particle (for the mass range above, 100 pHz < f < 100 THz). A coupling of this oscillating field to ordinary matter particles will induce corresponding oscillations in the measured properties of those particles. To probe such an interaction, we aim to measure the possible temporal variations in the proton-to-electron mass ratio, μ = m_p/m_e, via precision spectroscopy of rovibrational energies in the polyatomic molecule SrOH. By employing about a dozen lasers to repump all significantly populated states in a nearly closed optical cycle, we have captured thousands of SrOH molecules in a magneto-optical trap and cooled them to the ultracold regime. By transferring the molecules to a conservative trap, we will measure molecular energy levels with second-scale coherence times. A fortuitous near-degeneracy between distinct vibrational states within the same electronic manifold (which cannot occur in diatomic molecules) enables microwave-frequency rovibrational transitions, which possess orders-of-magnitude improved sensitivity to μ-variation compared to typical transitions at the same frequency scale. We anticipate measurements in the near future that will probe previously unexplored dark matter parameter-space. We report ongoing and future work to further improve the magneto-optical trap and to transfer the ultracold SrOH molecules into an optical dipole trap.