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Physics, Atomic Physics, physics.atom-ph
Abstract:
We investigate the influence of the appearance of excitonic states on van der
Waals interactions among two Rydberg atoms. The atoms are assumed to be in
different Rydberg states, e.g., in the $|ns\rangle$ and $|np\rangle$ states.
The resonant dipole-dipole interactions yield symmetric and antisymmetric
excitons, with energy splitting that give rise to new resonances as the atoms
approach each other. Only far from these resonances the van der Waals
coefficients, $C_6^{sp}$, can be defined. We calculate the $C_6$ coefficients
for alkali atoms and present the results for lithium by applying perturbation
theory. At short interatomic distances of several $\mu m$, we show that the
widely used simple model of two-level systems for excitons in Rydberg atoms
breaks down, and the correct representation implies multi-level atoms. Even
though, at larger distances one can keep the two-level systems but in including
van der Waals interactions among the atoms.
