Photoassociation of ultracold long-range polyatomic molecules

We theoretically investigate optical formation of long-range tetratomic and larger polyatomic molecules in the ground electronic state from ultracold pairs of polar molecules. Depending on their relative orientation, we predict that two types of complexes could be produced: a weakly bound and very extended halo state and a pure long-range molecule composed of nearly-collinear diatomic molecules. The second category represents a novel type of bound tetratomic molecules. These complexes are predicted to be stable at cold and ultracold temperatures.

We carried out specific numerical studies for pairs of ultracold KRb and RbCs molecules, leading to the production of (KRb)₂ and (RbCs)₂ complexes. The results and conclusions were generalized to larger complexes based on universal properties of long-range interactions between polar molecules. Thus, we identified several triatomic and tetratomic linear polar molecules with favorable ratios of dipole and quadrupole electric moments for which the proposed approach could be used. Such cold or ultracold complexes should also be stable enough to allow experimental confirmation.