Long-range additive and nonadditive potentials in a hybrid system: Ground state atom, excited state atom, and ion

TL;DR

This theoretical study calculates long-range additive and nonadditive potentials in a three-body hybrid atom-atom-ion system, revealing strong three-body effects and providing new coefficients for ultracold trimer formation.

Contribution

The paper introduces highly accurate calculations of long-range potentials and first-principles coefficients for a specific atom-atom-ion system, highlighting the significance of three-body nonadditive interactions.

Findings

Three-body nonadditive interactions can dominate at certain geometries.

Two-body interactions can cancel out, leaving only three-body effects.

New electrostatic, induction, and dispersion coefficients for Li$^+_2$ states.

Abstract

We report a theoretical study on the long-range additive and nonadditive potentials for a three-body hybrid atom-atom-ion system composed of one ground $S$ state Li atom, one excited $P$ state Li atom and one ground $S$ state Li$^+$ ion, Li($2\,^{2}S$)-Li($2\,^{2}P$)-Li$^+(1\,^{1}S$). The interaction coefficients are evaluated with highly accurate wave functions calculated variationally in Hylleraas coordinates. For this hybrid system the three-body nonadditive collective interactions (appearing in second-order) induced by the energy degeneracy and enhanced by the induction effect of the Li$^+$ ion through the internal electric field can be strong and even stronger than the two-body additive interactions at the same order. We find that for particular geometries the two-body additive interactions of the system sum to zero leaving only three-body nonadditive collective interactions making the present system potentially a platform to explore quantum three-body collective effects. We also extract first-principles leading coefficients of the long-range electrostatic, induction, and dispersion energies of Li$^+_2$ electronic states correlating to Li($2\,^{2}P$)-Li$^+(1\,^{1}S$), which until now were not available in the literature. The results should be especially valuable for the exploration of schemes to create trimers with ultracold atoms and ions in optical lattices.