Sometimes, the slits are in the range of nanometers, but I often bump into comments saying you can try this at home with lasers and polarized glass. Recently, I even found clearly macroscopic pictures (eg. a bedromm wall) showing interferences of sunlight with itself.
So I wonder if macroscopic interferences are just analogous to the particle-level ones, or if, on the contrary, they have the very same causes and nature.
As I recently learnt (thanks to @anna v), light rays are emerging from the electromagnetic field, which itself comes from the superposition of a lot of photons' wavefunctions. Therefore, one could suppose that the answer to the question is : what you see at the macroscopic level (including sun light and lasers) comes from the electromagnetic field, not from the photon's wave function.
The problem is that you may observe a wave collapse (interferences disappearing) with the laser by neutralizing polarisation with a third polarized glass, which seems to indicate a typically quantum behaviour...??? I'm puzzled.