They did it by splitting a beam of particles into a pair of entangled particles and then setting up a way to measure the polarity of one of them after the point in time where it even hits the final screen. If you measure the polarity then, after the other stream of particles from the beam had already had time to make the pattern, the pattern will be two clusters. If you don't, it goes back to an interference pattern.
That one really cemented the notion in my head that this is just how the Universe is and not some local weirdness with particles and measurements.
https://www.youtube.com/watch?v=RQv5CVELG3U
This is the video if you're interested. Again, I'm no physicist and don't know if explanations are legit or statistically correct. But that little || trick that all other popsci videos play on you, that's a true concern.
You can check it out here.
Summary https://www.stonybrook.edu/laser/_amarch/eraser/index.html
Paper https://www.stonybrook.edu/laser/_amarch/eraser/Walborn.pdf
My fascination with these experiments has never been due neat clusters of impacts, although popsci depictions have clearly tainted my memory.
https://iopscience.iop.org/article/10.1088/2058-7058/12/11/4
> The largest entities for which the double-slit experiment has been performed were molecules that each comprised 2000 atoms (whose total mass was 25,000 atomic mass units).[19]
The electron/proton entering a slit is affected by gravity!
Presumably a gravity based detector would have similar issues as these particles are affected by gravity (as can be seen around black holes)
"two photons come out" part makes no sense though. On a target side, there's always single hit after single photon/electron, but distribution of theses hits as if said electron got through both slits and interfered with itself
P.S. the funny thing is - this works on any small thingy, measured up to 2000 atoms-big, as if it's the property of the universe itself