a coherence time of about $\tau_{{\mathrm{coh}} } = 8.7 \, {\mathrm{ps}}$. This is more than 50 times larger than the lifetime of the uncondensed polaritons of about 160 fs, which is deduced from the spectral linewidth of the polariton emission for $P \leq P_{{\mathrm{th}}}$ and for an energy range similar to the condensate energy at $P = P_{{\mathrm{th}}}$. Consequently, the coherence of the investigated quantum system is conserved during the multiple reabsorption and reemission processes, which can thus be identified as a condensate. We note that the experimentally estimated coherence time is a lower limit for the real value. We identify two experimental artifacts that restrict the determination of the real condensate’s coherence time, namely a spectrally and path difference dependent phase shift $\phi_{12}(\lambda, \Delta s)$ (artifact A) as well as a fast decay of the condensate emission intensity due to the short excitation pulses of about 2 ps that are used for the coherence time measurement (artifact B). By analyzing the impact of these artifacts quantitatively (cf. Supplemental Material, Sec. \[sec:SM\_limits\_cohTime\]), we roughly estimated the expected real values for the coherence time of $\tau^A_{\mathrm{corr}} = 10.3$ ps and $\tau^B_{\mathrm{corr}} = 14$ ps. By applying both corrections simultaneously, a maximum 