Casimir-Polder interaction between an atom and a Chern insulator: topological signature and long-range repulsion

We consider the Casimir-Polder interaction between a two-level atomic system and a Chern insulator for both the resonant and nonresonant channels. For a right circularly polarized excited atomic state near a Chern insulator with a negative Chern number $C$, the resonant Casimir-Polder force can be monotonically repulsive over a large range of separations. In the presence of the same Chern insulator, a right circularly polarized metastable atomic state is expected to experience a repulsive nonresonant Casimir-Polder force over a certain range of atom-surface separations in the far-field region. At still greater separations, the nonresonant Casimir-Polder force is expected to become attractive and exhibit a topological signature, being proportional to $(C\alpha)^2/(1+(C\alpha)^2)$, where $\alpha$ is the fine-structure constant.