Abstract
Atoms coupled to optical fields strongly confined in two spatial dimensions, as in solid-state microstructures, can experience large Lamb shifts due to a spectrally strongly asymmetric mode density. We use the generic example of a quasi–one-dimensional waveguide structure driven close to cutoff frequency of a new transverse branch of propagating modes. We analytically find strong shifts of the atomic resonance frequency due to the modified vacuum, which can be an order of magnitude larger than the atomic linewidth. At the same time one gets significantly enhanced scattering of the guided light by the atom, which could be used as a tool to investigate these effects or to build non-destructive single-atom detectors.