Formation of Ultracold Polar Molecules in the Rovibrational Ground State

Ultracold LiCs molecules in the absolute ground state $X{}^1\Sigma ^{+}$, $v^{\prime \prime }=0$, $J^{\prime \prime }=0$ are formed via a single photoassociation step starting from laser-cooled atoms. The selective production of $v^{\prime \prime }=0$, $J^{\prime \prime }=2$ molecules with a 50-fold higher rate is also demonstrated. The rotational and vibrational state of the ground state molecules is determined in a setup combining depletion spectroscopy with resonant-enhanced multiphoton ionization time-of-flight spectroscopy. Using the determined production rate of up to $5\times {10}^3\mathrm{\text{molecules}}/\mathrm{s}$, we describe a simple scheme which can provide large samples of externally and internally cold dipolar molecules.