Universalities in ultracold reactions of alkali-metal polar molecules

Abstract

We consider ultracold collisions of ground-state heteronuclear alkali-metal dimers that are susceptible to four-center chemical reactions 2AB → A 2 + B 2 even at submicrokelvin temperatures. These reactions depend strongly on species, temperature, electric field, and confinement in an optical lattice. We calculate ab initio van der Waals 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-metal 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. For indistinguishable bosons, the inelastic/reactive rate increases as d 2 in the quantum regime, where d is the dipole moment induced by the electric field. This is a weaker power-law dependence than for indistinguishable fermions, for which the rate behaves as d 6 .

Efficient method for quantum calculations of molecule-molecule scattering properties in a magnetic field

“…However, not all regimes of molecular collisions are universal, and details of collision dynamics often depend on the intricate interplay between intermolecular and intramolecular interactions at short range. Our work complements recent theoretical efforts [58][59][60] by providing an efficient numerical technique for computing the collision properties of polar molecules for arbitrary collision energies, external field strengths, and interaction potentials. Our proposed methodology can be extended to include the effects of external electric fields, multiple potential energy surfaces and non-adiabatic couplings, and hyperfine interactions, providing a valuable numerical tool for future exploration of molecular collision dynamics in the quantum regime.…”

“…Recent theoretical work on dipolar collisions and chemical reactions of ultracold molecules [58][59][60] began to uncover the universal properties of molecule-molecule scattering in the quantum regime. However, not all regimes of molecular collisions are universal, and details of collision dynamics often depend on the intricate interplay between intermolecular and intramolecular interactions at short range.…”

Perspective: Ultracold molecules and the dawn of cold controlled chemistry

“…[74][75][76][77][78][79]81 Recent works of Julienne and coworkers 74,75,253 and Gao 76,77 have focused on the development of universal models for ultracold reactions within the MQDT framework. The universal model of Julienne et al, 74,75,253 the quantum reflection model of Kotochigova,254 and the quantum threshold (QT) models of Quém'ener et al 212,255 were successful in estimating the overall reaction rate coefficients for KRb + KRb and K + KRb reactions reported by the JILA group. The basic idea of MQDT is to solve the Schrödinger equation accurately for the long-range potential and use an approximate description at short range.…”

“…Atom-exchange reactions in collisions of heteronuclear alkali metal dimers have received much attention recently. Zuchowski and Hutson, 210 Meyer and Bohn, 211 Quéméner et al, 212 Byrd et al, 213,214 and Tomza et al 215,216 have carried out detailed electronic structure calculations of energetics and reaction paths in these systems. While atom-exchange in KRb + KRb → K 2 + Rb 2 is exoergic, it is not energetically allowed for many other heteronuclear alkali metal dimers in their ground rovibrational level.…”

Long-range interactions between polar alkali-metal diatoms in external electric fields

“…The most spectacular experimental achievements on ultracold dipolar molecular gases have been performed on KRb molecules [8,9,11,19] which motivated a wealth of theoretical investigations on this species [17,[20][21][22][23]. An * maxence.lepers@u-psud.fr accurate description of long-range interactions involving the other heteronuclear alkali diatoms is strongly needed since they draw rising attention [24][25][26][27][28][29][30][31][32]. Considering two identical polar molecules at large distances R (in atomic units 1 a.u.…”