Ultracold Gas of Bosonic Na 23 K 39 Ground-State Molecules

We report the creation of ultracold bosonic dipolar Na23K39 molecules in their absolute rovibrational ground state. Starting from weakly bound molecules immersed in an ultracold atomic mixture, we coherently transfer the dimers to the rovibrational ground state using an adiabatic Raman passage. We analyze the two-body decay in a pure molecular sample and in molecule-atom mixtures and find an unexpectedly low two-body decay coefficient for collisions between molecules and K39 atoms in a selected hyperfine state. The preparation of bosonic Na23K39 molecules opens the way for future comparisons between fermionic and bosonic ultracold ground-state molecules of the same chemical species.