(a) Sketch of the experimental setup. By means of a notch filter, the molecule emission collected in an epifluorescence-microscope configuration is separated in two parts containing the ZPL and the PSB. Both components can then be analyzed with a spectrometer and a free-space-coupled single photon avalanche diode (SPAD). The ZPL component can also enter the fibered circuit for probing purity and indistinguishability of the photon wave packet. (b) Excitation spectroscopy. Fluorescence intensity in the PSB as the frequency of a resonant laser is scanned across the ZPL. A Lorentzian fit to the data yields a FWHM of 55.1 ± 0.5 MHz. (c) Suppression of multi-photon emission events under CW operation. Histogram of the relative arrival time between the two SPADs in HBT configuration (no photons in the delay line arm). Solid line is a single exponential fit to the data, yielding $g(2)(0)=0.03±0.02$ and $τ1=3.5±0.2$ ns. (d) HOM results under CW operation. Histogram of the relative photon arrival times for parallel (red) and orthogonal (blue) polarizations are superimposed with shifted y-axis scale for clarity. Solid and dashed lines are fits to the data with expression (1). (c) and (d) are obtained integrating 100 kcps on each SPAD for 10 min (normalization level corresponding to around 250 coincidences; binning size 256 ps).