Universalities in ultracold reactions of alkali polar molecules

Abstract

We consider ultracold collisions of ground-state, heteronuclear alkali dimers that are susceptible to four-center chemical reactions 2 AB -> A2 + B2 even at sub-microKelvin temperature. These reactions depend strongly on species, temperature, electric field, and confinement in an optical lattice. We calculate ab initio van der Walls coefficients for these interactions, and use a quantum formalism to study the scattering properties of such molecules under an external electric field and optical lattice. We also apply a quantum threshold model to explore the dependence of reaction rates on the various parameters. We find that, among the heteronuclear alkali fermionic species, LiNa is the least reactive, whereas LiCs is the most reactive. For the bosonic species, LiK is the most reactive in zero field, but all species considered - LiNa, LiK, LiRb, LiCs, and KRb - share a universal reaction rate once a sufficiently high electric field is applied.