C6 coefficients for interacting Rydberg atoms and alkali-metal dimers

Abstract

We study the van der Waals interaction between Rydberg alkali-metal atoms with fine structure (${n}^{2}{L}_{j}$; $L\ensuremath{\le}2$) and heteronuclear alkali-metal dimers in the ground rovibrational state ($X^{1}\mathrm{\ensuremath{\Sigma}}^{+}$; $v=0, J=0$). We compute the associated ${C}_{6}$ dispersion coefficients of atom-molecule pairs involving $^{133}\mathrm{Cs}$ and $^{85}\mathrm{Rb}$ atoms interacting with KRb, LiCs, LiRb, and RbCs molecules. The obtained dispersion coefficients can be accurately fitted to a state-dependent polynomial $O({n}^{7})$ over the range of principal quantum numbers $40\ensuremath{\le}n\ensuremath{\le}150$. For all atom-molecule pairs considered, Rydberg states $n^{2}S_{j}$ and $n^{2}P_{j}$ result in attractive $1/{R}^{6}$ potentials. In contrast, $n^{2}D_{j}$ states can give rise to repulsive potentials for specific atom-molecule pairs. The interaction energy at the LeRoy distance approximately scales as ${n}^{\ensuremath{-}5}$ for $n>40$. For intermediate values of $n\ensuremath{\lesssim}40$, both repulsive and attractive interaction energies of the order of 10--$1000\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$ can be achieved with specific atomic and molecular species. The accuracy of the reported ${C}_{6}$ coefficients is limited by the quality of the atomic quantum defects, with relative errors $\mathrm{\ensuremath{\Delta}}{C}_{6}/{C}_{6}$ estimated to be no greater than 1% on average.