In the double-slit experiment, when particles such as photons are sent through two slits and allowed to pass onto a screen, an interference pattern can be observed. This pattern arises due to the wave-like nature of particles and the phenomenon of wave interference.
If you send one photon per minute through the double slits and do not detect which slit the photon goes through, you will still observe an interference pattern. The reason for this is that even with a low intensity of one photon at a time, each photon behaves like a wave and passes through both slits simultaneously, interfering with itself. Over time, as more and more photons are sent through the slits, the accumulation of their wave-like behavior leads to the formation of an interference pattern on the screen.
The key aspect is that the probability distribution for a single photon to arrive at a specific location on the screen exhibits an interference pattern. This pattern becomes more pronounced as the number of photons increases, eventually resulting in the characteristic pattern of alternating bright and dark fringes. So, even with a low photon count, the interference pattern will gradually emerge as more photons are observed over time.