Photon correlations generated by inelastic scattering in a one-dimensional waveguide coupled to three-level systems

• Study non-classical light in a waveguide coupled to three-level systems (3LS).
• Optimize parameters for strong correlations using total inelastically scattered flux.
• Show 3LS are better candidates for experimental study of photon–photon correlations.
• Show how slow light effect is expressed in correlations.
• Find two-photon wavefunction for (i) two 3LS far apart and (ii) one 3LS plus a mirror.

We study photon correlations generated by scattering from three-level systems (3LS) in one dimension. The two systems studied are a 3LS in a semi-infinite waveguide (3LS plus a mirror) and two 3LS in an infinite waveguide (double 3LS). Our two-photon scattering approach naturally connects photon correlation effects with inelastically scattered photons; it corresponds to input–output theory in the weak-probe limit. At the resonance where electromagnetically induced transparency (EIT) occurs, we find that no photons are scattered inelastically and hence there are no induced correlations. Slightly away from EIT, the total inelastically scattered flux is large, being substantially enhanced due to the additional interference paths. This enhancement carries over to the two-photon correlation function, which exhibits non-classical behavior such as strong bunching with a very long time-scale. The long time scale originates from the slow-light effect associated with EIT.