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

Laser cooling and trapping1,2, and magneto-optical trapping methods in particular2, have enabled groundbreaking advances in science, including Bose–Einstein condensation3–5, quantum computation with neutral atoms6,7 and high-precision optical clocks8. Recently, magneto-optical traps (MOTs) of diatomic molecules have been demonstrated9–12, providing access to research in quantum simulation13 and searches for physics beyond the standard model14. Compared with diatomic molecules, polyatomic molecules have distinct rotational and vibrational degrees of freedom that promise a variety of transformational possibilities. For example, ultracold polyatomic molecules would be uniquely suited to applications in quantum computation and simulation15–17, ultracold collisions18, quantum chemistry19 and beyond-the-standard-model searches20,21. However, the complexity of these molecules has so far precluded the realization of MOTs for polyatomic species. Here we demonstrate magneto-optical trapping of a polyatomic molecule, calcium monohydroxide (CaOH). After trapping, the molecules are laser cooled in a blue-detuned optical molasses to a temperature of 110 μK, which is below the Doppler cooling limit. The temperatures and densities achieved here make CaOH a viable candidate for a wide variety of quantum science applications, including quantum simulation and computation using optical tweezer arrays15,17,22,23. This work also suggests that laser cooling and magneto-optical trapping of many other polyatomic species24–27 will be both feasible and practical.