Strong coupling between single atoms and non-transversal photons

The interaction between single quantum emitters and non-transversally polarized photons for which the electric field vector amplitude has a significant component in the direction of propagation is investigated. Even though this situation seems to be at odds with the description of light as a transverse wave, it regularly occurs when interfacing or manipulating emitters with non-paraxial, guided, or evanescent light. Here, this phenomenon for the case of single atoms that strongly interact with whispering-gallery-mode (WGM) microresonators is quantitatively investigated. These resonators confine light by continuous total internal reflection and offer the advantage of very long photon lifetimes in conjunction with near-lossless in- and out-coupling of light via tapered fiber couplers. In the setup, a novel type of high-Q WGM microresonator - a so-called bottle microresonator, which has the additional advantage of being fully tunable and provides a mode geometry that enables near-lossless simultaneous coupling of two independent tapered fiber couplers, is employed.