Formation and detection of ultracold ground-state polar molecules

We report on the formation of translationally cold NaCs molecules starting from a laser-cooled atomic vapor of Na and Cs atoms. Colliding atoms are transferred into bound molecular states in a two-step photoactivated process in which the atoms are first photoassociated by trap photons into an excited state molecular complex and then allowed to decay into a bound molecular ground state. Time-of-flight measurements show a translational temperature T=260±130  μK that reflects the measured temperature of the initial atomic gas.