Two photons on an atomic beam-splitter: nonlinear scattering and induced   correlations
  Optical emitters strongly coupled to photons propagating in one-dimensional waveguides are a promising platform for optical quantum information processing. Here, we present a theoretical study of the scattering of two indistinguishable photons on a single two-level atom in a Hong-Ou-Mandel set-up. By computing the dynamics, we can describe the system at any time of the scattering event. This allows us to highlight the one-to-one correspondence between the saturation of the atom and the effective interaction induced between the photons. Furthermore, we discuss the integrability of the atomic beamsplitter and provide an intuitive picture for the correlations observed between the outgoing photons. 
Alexandre Roulet, Huy Nguyen Le, Valerio Scarani
quant-ph