alt Hacker NewsI had a conversation about this in HN some months back. It's a surprisingly modern experiment. It demanded an ability to reliably emit single photons. Young's theory may be 1800 but single photon emission is 1970-80.
(This is what I was told, exploring my belief it's always been fringes in streams of photons not emerging over repeated applications of single photons and I was wrong)
To get single photons, you just need to stack up enough stained glass infront of a light source. That's been acheivable for aeons (the photon will go through at random time though).
The difficult part is single photon _detectors_, they're the key technology to explore the single-photon version of Young's experiment (which originally showed that light has wave-like properties).