Molecules cooled below the Doppler limit


Magneto-optical trapping and sub-Doppler cooling have been essential to most experiments with quantum degenerate gases, optical lattices, atomic fountains and many other applications. A broad set of new applications await ultracold molecules1, and the extension of laser cooling to molecules has begun2,3,4,5,6. A magneto-optical trap (MOT) has been demonstrated for a single molecular species, SrF7,8,9, but the sub-Doppler temperatures required for many applications have not yet been reached. Here we demonstrate a MOT of a second species, CaF, and we show how to cool these molecules to 50 μK, well below the Doppler limit, using a three-dimensional optical molasses. These ultracold molecules could be loaded into optical tweezers to trap arbitrary arrays10 for quantum simulation11, launched into a molecular fountain12,13 for testing fundamental physics14,15,16,17,18, and used to study collisions and chemistry19 between atoms and molecules at ultracold temperatures.

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Figure 1: Schematic of the experiment.
Figure 2: Characterization of the MOT.
Figure 3: Cooling the MOT by ramping down the intensity.
Figure 4: Sub-Doppler cooling.


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We thank J. Devlin for his assistance and insight. We are grateful to J. Dyne, G. Marinaro and V. Gerulis for technical assistance. The research has received funding from EPSRC under grants EP/I012044, EP/M027716, and EP/P01058X/1, and from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement 320789.

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All authors contributed to all aspects of this work.

Correspondence to M. R. Tarbutt.

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Truppe, S., Williams, H., Hambach, M. et al. Molecules cooled below the Doppler limit. Nature Phys 13, 1173–1176 (2017) doi:10.1038/nphys4241

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