Azerbaijan National Academy of Sciences

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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