Scattering of two photons from two distant qubits: Exact solution
  We consider the inelastic scattering of two photons from two qubits separated by an arbitrary distance $R$ and coupled to a one-dimensional transmission line. We present an exact, analytical solution to the problem, and use it to explore a particular configuration of qubits which is transparent to single-photon scattering, thus highlighting non-Markovian effects of inelastic two-photon scattering: Strong two-photon interference and momentum dependent photon (anti-)bunching. This latter effect can be seen as an inelastic generalization of the Hong--Ou--Mandel effect. 
Matti Laakso and Mikhail Pletyukhov
quant-ph cond-mat.mes-hall