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A Conveyor Belt MOT of Diatomic Molecules
Ultracold molecules provide a powerful and versatile platform for quantum computing,simulation, and metrology applications. The cornerstone technique for generating these cold, dense samples of molecular gasses is the magneto-optical trap (MOT). Conventional molecular MOTs use red-detuned light, limiting them to relatively high temperatures and low densities, leading to small spatial overlap and low loading efficiency into optical traps.
In our recent work we introduced a novel “conveyor-belt” MOT for ultracold Calcium Fluoride (CaF) molecules. This MOT employs a unique frequency scheme that introduces the conveyor-belt physical effect, producing significantly stronger trapping forces than those found in conventional MOTs. This technique allowed us to produce a highly compressed and dense cloud of CaF molecules, achieving a peak number density over 600 times higher than that of red-detuned MOTs—a record density for molecular MOTs. We then efficiently transferred the molecules into an optical dipole trap, resulting in the highest recorded number of directly laser-cooled molecules in an optical trap. Our publication includes detailed characterization of the loading dynamics into the optical trap and identifies the primary loss mechanisms.
The molecular number density we obtain in the optical trap is comparable to the high densities routinely obtained in atomic systems. This opens up new possibilities for applications of ultracold molecular gasses, including precision measurement and evaporative cooling towards quantum degeneracy. The effectiveness and simplicity of the conveyor-belt MOT make it readily adaptable to other atomic and molecular systems, promising wide utility across the laser-cooling community.
Caption: Fitted MOT width (Left axis) and peak number density (Right axis) of the conveyor-belt assisted blue MOT as a function of time (with dashed lines as a guide to the eye). Top Images show the molecular cloud taken by collecting 2ms of in-situ fluorescence following the compression time.
Reference: Yu, S.S., You, J., Bao, Y., Anderegg, L., Hallas, C., Li, G.K., Lim, D., Chae, E., Ketterle, W., Ni, K.K. and Doyle, J.M., 2024. A conveyor-belt magneto-optical trap of CaF. arXiv preprint arXiv:2409.15262. https://arxiv.org/abs/2409.15262