Order of Magnitude Improved Optical Trapping of Molecules Through Transverse Cooling

We demonstrate a two-dimensional Sisyphus laser cooling method that increases the number of strontium monohydroxide (SrOH) molecules loaded into a magneto-optical trap by a factor of 12. Subsequent loading into an optical dipole trap (ODT) achieves $2.2 (3)\times10^4$ ultracold SrOH molecules with a peak density of $\sim2(1)\times10^{10}~\mathrm{cm^{-3}}$. The lifetime of molecules in the ODT is limited by two-body collisions characterized by a measured collision rate constant $\beta \sim 4\times10^{-10}~\mathrm{cm^3/s}$. The cooling method developed here is generally applicable to all known cases of direct molecular laser cooling, including symmetric and asymmetric top molecules. Increases in trapped molecule number will directly improve the search for ultralight dark matter, position polyatomic molecules as a platform for probing CP-violating new particles with masses $\gg$10 TeV, and facilitate a broad range of further research in quantum science.