Collective atom-photon interactions in waveguide QED*

The interaction between a collection of atoms and light can be cooperatively modified via quantum correlations between the atoms. Such cooperative light-matter interaction can be understood as a constructive or destructive interference between the atomic dipoles and the emitted radiation, which manifests as an enhancement (superradiance) or suppression (subradiance) of the total spontaneous emission from the atomic ensemble. I will present an overview of collective atom-field interactions going from short interatomic separations to distances comparable to coherence length of the emitted photons, wherein the memory effects of the intermediary electromagnetic environment become pronounced. We demonstrate that such a system can exhibit surprisingly rich non-Markovian dynamics, with collective spontaneous emission rates exceeding those of Dicke superradiance (`superduperradiance'), formation of highly delocalized atom-photon bound states and spontaneous generation of emitter-emitter entanglement in the presence of delay. Our results are pertinent to analyzing retardation effects in quantum networks and distributed quantum information protocols based on long-distance emitters.