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.