Prospects for a Narrow Line MOT in YO

In addition to being suitable for laser cooling and trapping in a magneto-optical trap (MOT) using a relatively broad ($sim$5 MHz) transition, the molecule YO possesses a narrow-line transition. This forbidden transition between the $X^{2}Sigma$ and $A^{2}Delta_{3/2}$ states has linewidth $sim$2$pitimes$160 kHz. After cooling in a MOT on the $X^{2}Sigma$ to $A^{2}Pi_{1/2}$ (orange) transition, the narrow (red) transition can be used to further cool the sample, requiring only minimal additions to the first stage system. The narrow line cooling stage will bring the temperature from $sim$1 mK to $sim$10 $mu$K, significantly advancing the frontier on direct cooling achievable for molecules.

Rotational state microwave mixing for laser cooling of complex diatomic molecules

We demonstrate the mixing of rotational states in the ground electronic state using microwave radiation to enhance optical cycling in the molecule yttrium (II) monoxide (YO). This mixing technique is used in conjunction with a frequency modulated and chirped continuous wave laser to slow longitudinally a cryogenic buffer gas beam of YO. We generate a measurable flux of YO below 10~m/s, directly loadable into a three-dimensional magneto-optical trap. This technique opens the door for laser cooling of molecules with more complex structure.