Laser cooling of a diatomic molecule David P. DeMille, Yale University, DMR 0653377 It has been roughly three decades since laser cooling techniques produced ultracold atoms, leading to rapid advances in many areas. Unfortunately laser cooling has not yet been extended to molecules because of their complex internal structure. However, this same complexity makes ultracold molecules potentially useful for a wide range of applications including quantum computation, quantum simulation, ultracold chemistry, and precision measurement. In the last year we have demonstrated the first laser cooling of a molecule. Examples of our results are shown below. We have observed both Doppler and Sisyphus laser cooling, and we expect to use our techniques to produce trapped, ultracold molecules within the next year. Molecular beam profile under Doppler (red) and Sisyphus (blue) laser cooling conditions, and when unperturbed (black). The transverse temperature of the beam is indicated for each case. As shown under both Doppler and Sisyphus cooling conditions, the molecular beam width is substantially reduced, indicating cooling of the molecular beam. Sisyphus cooling produces a much colder (narrower) molecular beam than Doppler cooling. -6 -4 -2 0 2 4 6 0.0 0.2 0.4 0.6 0.8 1.0 U nperturbed D oppler cooled R e la tive N um b e r o fM olecules R elative P osition (m m) -6 -4 -2 0 2 4 6 0.0 0.2 0.4 0.6 0.8 1.0 U nperturbed S isyphus cooled R e la tive N um b e r o fM olecules R elative P osition (m m) Doppler Cooled ~ 5mK Unperturbed ~ 50mK Sisyphus Cooled ~ 300 K Unperturbed ~ 50mK