Magneto-optical trapping and sub-Doppler cooling of a polyatomic molecule

We demonstrate magneto-optical trapping (MOT) of a polyatomic molecule, calcium monohydroxide (CaOH). Compared to atoms and diatomic molecules, polyatomic molecules have unique rotational and vibrational degrees of freedom that, while appealing for applications in quantum science, complicate the task of forming a photon cycling scheme sufficient to perform laser cooling. By addressing these degrees of freedom with 11 repumping lasers, we scatter >10,000 photons on average per molecule before loss to dark states occurs. This enables radiative slowing of a buffer gas-cooled beam of CaOH, followed by trapping, cooling, and compression in a radio-frequency (rf) MOT. We further cool the CaOH molecular cloud with a blue-detuned molasses to temperatures near 100 μK. These results represent a starting point for optical trapping of CaOH, e.g., in arrays of optical tweezers.