Not a physicist, just here to observe single photons weren't reliably emitted until the modern era. like the 1970s. The double slit experiment pre-dates this. it's from 1801. The one which confirms "self interaction" was 1974. I was in high school 1973-78 so the stuff we did, was comparatively "new" physics in that sense. Not a message I remember receiving at the time.

From the pop-sci history reading I do, "detecting" reliable generation of single photon STREAMS in the early days depended on using mechanisms which inherently would release a sequence of photons on a time base, over time, and then gating the time sufficiently accurately to have high confidence you know the time base, and can discriminate an "individual" from the herd.

I don't doubt quantum theory. I only observe it's mostly for young students (like almost all received wisdom) grounded in experiments which don't actually do what people think they do. The ones you run in the school lab are illustrative not probative.

What people do in places like the BIPM in Paris, or CERN, isn't the same as that experiment you did with a ticker-tape and a weighted trolleycar down a ramp. "it's been confirmed" is the unfortunate reality of received wisdom, and inherently depends on trust in science. I do trust science.

Now we have quantum dots, and processes which will depend on reliably emitting single photons and single electrons, the trust has moved beyond "because they did it in CERN" into "because it's implemented in the chipset attached to the system I am using" -QC will need massive amounts of reliably generated single instance signals.