Abstract

Strong coupling between a local quantum system (qubit or atom) and one-dimensional bosonic states has recently become experimentally feasible in a variety of plasmonic, photonic, circuit-QED, and cold-atom contexts. This has opened up a new field dubbed "waveguide QED". I first introduce several of the experimental systems and the basic quantum non-linear optics problems they can address. The key ingredient is inelastic scattering into the one-dimensional continuum. Using such scattering as a unifying theme, I shall then discuss theoretical results on (i) photon-photon correlations, (ii) capture and storage of a single photon in a bound state in the continuum, and (iii) photon production when the coupling is ultrastrong.