Production and State-Selective Detection of Ultracold RbCs Molecules

Using resonance-enhanced two-photon ionization, we detect ultracold, metastable RbCs molecules formed in their lowest triplet state $a{}^3\Sigma ^{+}$ via photoassociation in a laser-cooled mixture of ${}^{85}\mathrm{Rb}$ and ${}^{133}\mathrm{Cs}$ atoms. We obtain extensive bound-bound excitation spectra of these molecules, which provide detailed information about their vibrational distribution, as well as spectroscopic data on several RbCs molecular states including $a{}^3\Sigma ^{+}$, $(2){}^3\Sigma ^{+}$, and $(1){}^1\Pi$. Analysis of this data allows us to predict strong transitions from observed levels to the absolute vibronic ground state of RbCs, potentially allowing the production of stable, ultracold polar molecules at rates in excess of ${10}^6{\mathrm{s}}^{-1}$.