Direct laser cooling and trapping of diatomic molecules

It has been roughly three decades since laser cooling techniques produced ultracold atoms, leading to rapid advances in a wide array of fields. Until recently, laser cooling had not been extended to molecules because of their complex internal structure, which precludes the realization of a true optical cycling transition. However, this complexity makes molecules potentially useful for a wide range of applications. For example, heteronuclear molecules possess permanent electric dipole moments that lead to long-range, tunable, anisotropic dipole–dipole interactions. The combination of the dipole–dipole interaction and the precise control over molecular degrees of freedom possible at ultracold temperatures makes ultracold molecules attractive candidates for use in quantum simulations of condensed-matter systems and in quantum computation. In addition, ultracold molecules could provide unique opportunities for studying chemical dynamics and for tests of fundamental symmetries.

Our group has demonstrated the first laser cooling of a diatomic molecule, in addition to deflection and, most recently, slowing of a molecular beam through radiative forces. Our current work is focussed on extending this technique to allow trapping of these molecules in a magneto-optical trap (MOT) or a microwave trap. This work is enabled by a scheme to create a quasi-cycling transition in strontium monofluoride (SrF), which allows up to ~105 photon scattering events before the accessible molecular population decays by 1/e.