Cold collisions between trapped polyatomic molecules

Understanding the world around us requires understanding molecules and their interaction with other molecules at the most fundamental quantum level. Towards this goal, radically new cooling and trapping techniques have been developed for molecules which cannot straightforwardly be manipulated with lasers. Exploiting the presence of a permanent electric dipole moment especially of polyatomic molecules, the new techniques include electrostatic skimming, guiding and trapping, as well as centrifuge deceleration, cryogenic buffer-gas and Sisyphus cooling. With these techniques implemented in one setting for the first time, we now prepare samples of simultaneously cold, dense, and slow molecules for, e.g., high-resolution spectroscopy and controlled-collision studies. The talk presents most recent achievements obtained with the conceptually and technologically favorable class of symmetric-top molecules. Most important, with trapped CH₃F molecules in predominantly a single rotational and vibrational state, we reach the cold collision regime, understand the nature of the collision process, and control the collisions with an external field. Our achievement opens up new possibilities for a plethora of experiments in various research fields ranging from cold chemistry to quantum information.