Ultracold molecules for measuring the electron's electric dipole moment

We demonstrate one-dimensional sub-Doppler laser cooling of a beam of YbF molecules to 100 $\mu$K. This is a key step towards a measurement of the electron’s electric dipole moment using ultracold molecules. We compare the effectiveness of magnetically-assisted and polarization-gradient sub-Doppler cooling mechanisms. We model the experiment and find good agreement with our data.