An excited atom interacting with a Chern insulator: toward a far-field resonant Casimir–Polder repulsion

We investigate the resonant Casimir–Polder interaction of an excited atom which has a single (electric dipole) transition with a Chern insulator, using the approach of quantum linear response theory. The Chern insulator has a nonzero, time-reversal symmetry breaking Hall conductance, leading to an additional contribution to the resonant Casimir–Polder interaction which depends on the coupling between the Hall conductance and the circular polarization state of the atomic transition. We find that the resonant Casimir–Polder shift can be significantly enhanced if the atomic de-excitation frequency is near a value associated with a van Hove singularity of the Chern insulator. Furthermore, we find that the resonant Casimir–Polder force can become monotonically decaying and repulsive for a relatively large atom–surface distance. This happens if the atomic dipole transition is right (left) circularly polarized and the Chern number of the Chern insulator is −1 (+1), and the atomic de-excitation energy is comparable to the bandgap energy of the Chern insulator. This has potential implications for the design of atom–surface interaction which can be tuned repulsive over a relatively large range of separations.