Sisyphus Laser Cooling of a Polyatomic Molecule
  We perform magnetically-assisted Sisyphus laser cooling of the triatomic free radical strontium monohydroxide (SrOH). This is achieved with principal optical cycling in the rotationally closed $P\left(N"=1\right)$ branch of either the $\tilde{X}^{2}\Sigma^{+}\left(000\right)\leftrightarrow\tilde{A}^{2}\Pi_{1/2}\left(000\right)$ or the $\tilde{X}^{2}\Sigma^{+}\left(000\right)\leftrightarrow\tilde{B}^{2}\Sigma^{+}\left(000\right)$ vibronic transitions. Molecules lost into the excited vibrational states during the cooling process are repumped back through the $\tilde{B}\left(000\right)$ state for both the $\left(100\right)$ level of the Sr-O stretching mode and the $\left(02^{0}0\right)$ level of the bending mode. The transverse temperature of a SrOH molecular beam is reduced in one dimension by two orders of magnitude to $\sim700\ {\rm \mu K}$. This approach opens a path towards creating a variety of ultracold polyatomic molecules, including much larger ones, by means of direct laser cooling. 
Ivan Kozyryev, Louis Baum, Kyle Matsuda, Benjamin L. Augenbraun, Loic   Anderegg, Alexander P. Sedlack, John M. Doyle
physics.atom-ph