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In the standard double-slit experiment, the setup is static, and the interference pattern can be predicted from considering all the potential paths a photon could have traveled. My question is: how long do these possible paths (from the source to the screen) need to exist prior to the photon traveling them? Would it be sufficient for the slits to exist only for the briefest moment the photon can pass through?

Has this type of experiment been theorized or conducted?

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    $\begingroup$ Can you give not detail on what you are asking about? A photon will be detected is what will happen. $\endgroup$
    – BioPhysicist
    Commented Oct 21 at 7:13
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    $\begingroup$ The slits being open cannot be spacelike separated from the photon hitting the screen because by definition the photon passing through the slits is null separated from that same photon reaching the screen. Can you clarify what you are trying to do? Are you trying to change the causal separation between the slits and the screen? Perhaps to isolate "which slit the photon passed through" from the "collapse of superposition at the screen"? $\endgroup$
    – John Rennie
    Commented Oct 21 at 7:38
  • $\begingroup$ The slit being open is not a single event but a series of events. Please clarify. $\endgroup$
    – Vincent Thacker
    Commented Oct 21 at 12:06

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Apart from the space separation element, which is unclear, this is the same experiment as sending in a very short pulse of light. The effect is just a broadening of the frequency spectrum of the light. The result is a superposition of diffraction patterns corresponding to the various frequencies with their intensity proportional to the spectral weight.

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  • $\begingroup$ Although you won't see an entire diffraction pattern for what the OP describes $\endgroup$
    – BioPhysicist
    Commented Oct 21 at 13:15
  • $\begingroup$ How is this the same experiment as a short pulse of light ? isn't a single photon the shortest pulse of light ? isn't the classic setup is a static setup with a single photons of light, repeated many times ? If so, I would like to point out that my question possibly describes a different experiment. $\endgroup$
    – nir
    Commented Oct 22 at 7:59
  • $\begingroup$ @nir A photon is not a pulse of light. $\endgroup$
    – my2cts
    Commented Oct 24 at 19:03
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Your question might be connected with the Wheeler Delayed choice Experiment, where the possible paths seems to change during the photon's flight. Please also check the Elitzur-Vaidman-bomb tester, where this possibilities are changed in a more dramatic way.

Both articles will guide you through thought experiments where the possible paths changes during the experiment and what is the possible interpretations about it. Basically, the intuition that photons should have well pre defined trajectories in the beginning of the experiment fails and we should always avoid counter-factual reasoning to understand these experiments.

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  • $\begingroup$ The bomb tester describes a static setup. delayed choice is more like it but still different. since second beam splitter is either placed or removed at an arbitrary time while the photon is en route, the outcome is binary, it either affected it or it didn't. the setup does undergo a change, but it is static before the change and remains static after it. I think I am asking something a little different. $\endgroup$
    – nir
    Commented Oct 22 at 8:09
  • $\begingroup$ So I think the question need more clarification. The dual slit is also static and if the slits "disappear" after photon pass it, this is the same reasoning about the delayed choice for me. The outcome is binary cause it's based on Mach-Zehnder Interferometer instead of Young Interferometer, but it doesn't matter in terms of principles. To study Interference phenomena, you can consider any Interferometer you wish. $\endgroup$
    – Ruffolo
    Commented Oct 22 at 9:28
  • $\begingroup$ I am asking in the question what would happen if the slits would open/appear just for the briefest moment enough to let a photon through. $\endgroup$
    – nir
    Commented Oct 22 at 10:28
  • $\begingroup$ for example, shine an intense beam on the plate and open the slits for such a brief time such that only one or a few photons reach the screen. $\endgroup$
    – nir
    Commented Oct 22 at 10:33
  • $\begingroup$ The problem with your description is that it rather assumes that a photon is a point-like particle with well defined position, which is not a precise notion. If you send a one-photon pulse, it will not necessarily be short: a photon with well defined frequency will be spread over whole space. A photon with a narrow position uncertainty will be a superposition of many different frequencies. $\endgroup$
    – Ruffolo
    Commented Oct 22 at 12:23

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