Narrowline Laser Cooling and Spectroscopy of Molecules via Stark States

Abstract

The electronic energy level structure of yttrium monoxide (YO) provides a long-lived, low-lying ${}^2\hat{I}”$ state ideal for high-precision molecular spectroscopy, narrowline laser cooling at the single photon-recoil limit, and studying dipolar physics with unprecedented interaction strength. High-resolution laser spectroscopy of ultracold laser-cooled YO molecules is used to study the Stark effect in the A${}^{\prime }{}^2\hat{I}{”}_{3/2}J=3/2$ state. An immediate onset of the linear Stark effect is observed in the presence of weak applied electric fields due to the near degenerate $\hat{I}›$-doublet and the large electric dipole moment. By applying a small electric field the Stark insensitive state is spectroscopically isolated and the absolute transition frequency to the X${}^2\hat{I}{\pounds }^{+}$ electronic ground state is determined with a fractional frequency uncertainty of 9 $\times$ 10${}^{-12}$. This electric field control is necessary to implement a quasi-closed photon cycling scheme that preserves parity. With this scheme the first narrowline laser cooling of a molecules is demonstrated, reducing the temperature of sub-Doppler cooled YO in two dimensions.