Fig. 5: Two-time, non-stationary, second-order correlation function for various excitation energies.

Experimental data (a) can be compared with quantum trajectories simulations (b) and a semi-analytic quantum regression approach based on a master equation expansion up to second order (c). In both cases, good agreement with the experiment requires a spontaneous emission background, as discussed in “Zero-time statistics” section. The dashed curves in the experimental data correspond to the diagonal and off-diagonal regions of g⁽²⁾(t₁, t₂) depicted in greater detail in Fig. 6. The cavity cutoff is set to λ₀ = 595 nm. Despite the slightly lower cutoff wavelength than used in “One-time statistics” section, the qualitative features of the average cavity output are the same as before.