Optical production of ultracold polar molecules

We demonstrate the production of a sample of ultracold RbCs molecules in their absolute vibrational ground state with a translational temperature of ∼100 muK and a narrow distribution of rotational states. The molecules are initially formed from laser-cooled 85Rb and 133Cs atoms via photoassociation and are produced in excited electronic vibrational levels. A fraction of these excited molecules subsequently spontaneously decay to ground electronic states, populating many excited vibrational levels. We transfer the population of one such level to the X 1Sigma+(v = 0) ground state by a stimulated emission pumping (SEP) technique. In order to efficiently produce these ground state molecules it is necessary to have detailed spectroscopic information about the levels to which we photoassociate the molecules, the levels to which they spontaneously decay, and the levels involved in the SEP transfer. To this end, we carry out and analyze photoassociation spectroscopy and resonance enhanced multi-photon ionization spectroscopy of relevant vibrational levels of excited and ground state electronic potentials.