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This question already has an answer here:

Is there a simple generally accepted explanation for single photon interference?

Does each photon interact with or see both slits?

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marked as duplicate by G. Smith, John Rennie quantum-mechanics May 26 at 8:19

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  • $\begingroup$ What do you mean by “single photon interference”? $\endgroup$ – G. Smith May 25 at 21:19
  • $\begingroup$ Young's two-slit experiment, one photon at a time ,interference pattern detected over time. $\endgroup$ – Mart May 26 at 8:16
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    $\begingroup$ Possible duplicate of Double Slit experiment with just one photon or electron $\endgroup$ – John Rennie May 26 at 8:19
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    $\begingroup$ The "top" current theory is called quantum mechanics. You might have heard of it. $\endgroup$ – Emilio Pisanty May 26 at 14:32
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If you are talking about the double slit experiment, then it is a misconception that it is done with just a single photon. It is done with a single photon shot at the screen one at a time, repeated many times. The interference pattern is built by many photons.

Now there are two mentioning of interference on this site, usually with photons and the double slit experiment:

  1. the interference pattern itself, that is built up by many photons, shot one at a time. The reason for the pattern in this case is that the photons' are emitted by the same experimental setup laser (or other lightsource), and their wavefunctions entanglement is described mostly the same way as per QM, thus the same characteristics for the photons shot after each other will make them entangle with the slits and the whole system (photons and slits) will cause the photons' landing positions on the screen to show the same pattern, some bright areas, where the photons are landing that created constructive interference and a dark areas where you see no photons land because those created destructive interference

  2. the interference of the single photon that is shot at a time, meaning that the photon's partial waves travel through both slits and then after the slits these partial waves interfere with each other. Now this interference can be constructive, meaning a bright spot on the screen, meaning that a real photon reached the screen and interacted with the screens atoms. This interference can be desctructive too, where the partial waves of the photon interfere so that they basically annihilate the photon as a real particle itself, which would have landed on the (theoretically) dark area. But it does not land on the screen at all, and does not interact with the screen's atoms at all, because it was annihilated on the fly. Particles can be annihilated by their antiparticles, and the photon happens to be its own antiparticle.

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  • $\begingroup$ maybe you can add this link $\endgroup$ – santimirandarp May 25 at 21:41
  • $\begingroup$ didn't know about the last part of point 2. that's crazy $\endgroup$ – santimirandarp May 25 at 21:49
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    $\begingroup$ Crazy, and also not correct. There has never been an observation of two photons annihilating each other. $\endgroup$ – S. McGrew May 25 at 21:55
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    $\begingroup$ Point 2 is deeply wrong, photons are never "annihilated on the fly", and destructive interference has nothing to do with some photonic analog of particle-antiparticle annihilation. $\endgroup$ – Mitchell Porter May 25 at 21:57
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    $\begingroup$ Typically, "annihilation" refers to the conversion of, e.g., an electron and a positron into a pair of photons. Destructive interference is a completely different (classical) phenomenon. In the double-slit experiment, a single photon is representable as a spread-out wave that passes through both slits. A single photon does not produce an observable interference pattern. The interference pattern is only observed when a large number of photons are detected - whether "all at once" or one at a time. $\endgroup$ – S. McGrew May 26 at 0:57

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