Direct Laser Cooling of Molecules

Ultracold molecules provide strong and long-range dipolar interactions, which offer a new toolbox for quantum simulations, such as those of quantum magnetism. By achieving full control over all degrees of freedom—including rotation and vibration—ultracold molecules also open new pathways for studying quantum chemistry. Ultracold molecules also find applications in precision tests of fundamental physics, such as searches for violations of time-reversal symmetry through the measurement of the electron’s electric dipole moment, a pursuit that exceeds the energy scales probed by large-scale particle physics experiments like those at the Large Hadron Collider.

However, direct laser cooling of molecules has historically been hindered by a lack of suitable cycling transitions due to the complexity of molecular structure. Researchers have found success by focusing on special molecules with diagonal Franck-Condon factors and using angular momentum selection rules to prevent population leakage into dark vibrational and rotational states. This approach has led to significant achievements over the past decade, including the magneto-optical trapping (MOT) of molecules, sub-Doppler cooling to microkelvin temperatures, and the loading of molecules into optical dipole traps and optical tweezers, as well as studies of molecular collisions in ultracold environments.

Our group is working on laser cooling of yttrium monoxide (YO) molecules.