  We investigate two-color photon correlations in the light emitted by strongly
coupled two-level emitters. Spectral filtering allows us to manipulate the
collected light statistics and we show that the resonances induced by
dipole-dipole interactions give rise to specific correlations, where the
time-symmetry of the correlations is broken. Based on the collective dressed
states, our study encompasses both the case of real processes, where the
photons are associated with specific resonances and classical correlations
between each other, and virtual processes, where pairs of photons are emitted
with non-classical correlations.
