Quantum Engineering of a Low-Entropy Gas of Heteronuclear Bosonic Molecules in an Optical Lattice

We present a novel method to prepare low-entropy samples of heteronuclear molecules confined to an optical lattice as an ideal starting point for dipolar quantum gas experiments based on ultracold molecules.\footnote{arXiv:1607.06536} Starting from two spatially separated BECs we efficiently form Rb-Cs atom pairs by overlapping a Cs Mott insulator with a superfluid Rb sample in an optical lattice. For sample mixing the Rb-Cs interaction is nulled at a Feshbach resonance's zero crossing. Subsequently the Rb atoms are localized by increasing the lattice depth. The paired atoms are then associated to Feshbach molecules. With this method we obtain low-entropy molecular samples with a filling fraction exceeding 30\%. Our method can now be combined with stimulated ground-state transfer (STIRAP) to produce dense and low-entropy samples of dipolar ground-state molecules as demonstrated on our previous work.\footnote{Phys. Rev. Lett. 113, 205301 (2014)} Our preparation procedure compares favorably with recent results from the JILA group on fermionic KRb molecules.\footnote{Science 350 , 659 (2015)}