# Quantum Mechanics – In a Double Slit Experiment, Does Each Photon Leave a Dot in the Bright Area?

double-slit-experimentelectromagnetismphotonsquantum mechanics

I have read this question:

Why does the photon strike at one or another place on the tape?

where PhysicsDave says:

All photons passing thru the slits leave a dot on the screen, this is true for single or multiple photon intensities. Destructive interference is a violation of conservation of energy, destructive interference is best explained by QM, there is low probability of photons arriving in the dark areas and that is why the dark areas are dark.

Now there are two opinions on this site:

1. When a single photon is shot, it passes through both slits as a wave and the partial waves of the photon interfere with each other, and create constructive (bright area) or destructive (dark area) interference.

2. Each and every single photon shot leaves a spot on the screen in the bright areas, there is a low probability for a photon to land in the dark area

These are two different meanings. One says that some photons never reach the screen, and never interact with the screen, that is why we see dark areas.

The other one says, that each and every single photon shot will leave a dot on the screen in the bright areas, and it is just that there is low probability for the photons to arrive in the dark areas, that is why we see dark areas.

Question:

Which one is right? Does every single photon shot leave a dot on the screen in the bright area?

The photon is a quantum mechanical entity.

Number 1) cannot be right, because the experiments with single photons at a time give single dots as photon footprints not bright regions .

Single-photon camera recording of photons from a double slit illuminated by very weak laser light. Left to right: single frame, superposition of 200, 1’000, and 500’000 frames.

The photons arrive one at a time at the left, the interference appearing slowly with the accumulations on the right, a probability distribution.

The boundary condition problem "photon + two slits of given width a distance apart" defines the wave function of the system,$$Ψ$$ . The $$Ψ^*Ψ$$ is the probability distribution for the accumulation of photons.

It will depend on the experiment if every photon that leaves the source and hits the double slits leaves a footprint, the efficiency of the screen. There will be experimental errors. In principle every photon that passes the double slit should end on the screen.