rate (per second) every ten seconds over the whole measurement time of 11.5 hours. The plot shows the relative change of the count rate with respect to the averaged value. We see that the relative fluctuations are less than 2% over the full measurement duration. After 2.5 hours of elapsed time, there is practically no residual drift, and the individual data points scatter with standard deviation of less than 0.5% around zero. This result is evidence for the unprecedented long-term stability of our integrated quantum circuit.[]{data-label="stability"}](fig03.eps){width="0.75\linewidth"}

Results and discussion
======================

Our data analysis benefits from the pulsed pump, which allows us to distinguish between time-correlated photon triplets and noise-related three-fold coincidences. The latter appear due to dark counts of the detector and the blackbody radiation emitted by our heated integrated device. The effect of noise is shown in Fig. \[16-bin\] (left) for a time window of about $40\,\mathrm{ns}\times40\,\mathrm{ns}$. At relative arrival time delays between individual detection events of $\tau_3-\tau_2=\tau_1-\tau_2=\left(-0.165\pm0.001\right)\,\mathrm{ns}$, we notice time-correlations as an indicator for photon-triplet detection. However, due to the pulsed operation, this result alone does not prove the generation of genuine photon-triplet states. For the verification we have to make sure that the influence of accidental three-fold-coincidences 