Figure 2. Dual-channel cross-correlations and triple coincidence histogram.

(a–c) Normalized cross-correlations of X_R, X_LX_R and XX_LX_R versus delay time measured at the excitation intensity of 6.9 W mm⁻² showing a sequential triple cascade recombination. The antibunching dips are fitted with (τ<0), where the anticorrelation floor is limited by the background noise. (d) The triple coincidence histogram (total recording time 3 h) was measured at an intensity of 460 mW mm⁻² and is plotted versus τ₂₁ and τ₃₁, linearly interpolated with a colour-mapped surface. The threefold coincidence peak near the origin signifies the strong temporal correlations of the emitted photons. (e) Events above the two-fold cascade threshold from d without interpolation plotted in 512 ps × 512 ps wide bins. The threshold level (yellow plane) was determined as the (peak) value of averaged over t_D3 outside the triple coincidence window. For comparison the expected level of accidental triplet events is shown in blue.