Could somebody explain the results of the following experiment (please no conjecture/interpretation, only observation)? In the double-slit experiment, if we shoot a single photon (not a series of photons, just a single photon), and detectors are off, will we observe an interference pattern?

  • $\begingroup$ How will you see anything if your detectors are off? The screen IS usually the detector. $\endgroup$
    – ohneVal
    Nov 5, 2021 at 13:17
  • 1
    $\begingroup$ Also, how do you get an interference pattern from a single detection?? $\endgroup$ Nov 5, 2021 at 13:20
  • $\begingroup$ You should see this experiment : youtu.be/I9Ab8BLW3kA $\endgroup$
    – paul230_x
    Nov 5, 2021 at 13:44
  • $\begingroup$ +1: I think it is important that we distinguish interpretation carefully from observation. $\endgroup$
    – Galen
    Nov 5, 2021 at 22:39

2 Answers 2


Yes. Probability for where the photon hits on the detection screen is given by the usual interference pattern. In other words, the interference pattern is not caused by photons interfering with each other.

(To actually see the interference pattern we of course need to send many photons but this can be done sending only one at a time.)

  • $\begingroup$ Thats it. A photon have an interpretation as a wave function, and this wave function interferes with itself, i.e. the photon interfere with itself, so the probability of end on some position of the detector is given by the interference pattern. $\endgroup$
    – Euler
    Nov 5, 2021 at 13:51

Suppose you send a single photon through a barrier with two slits so that it reaches a photographic plate beyond the barrier. The photon will interact with the photographic plate at a single point, causing a dot there. If you send many photons through one at a time, they will each strike the photographic plate at a point and leave a dot. The cumulative effect of the single points of contact between individual photons and the photographic plate will be a pattern of dots forming light and dark bands- the light bands will be areas where lots of individual photons have produced dots on the plate, and the darkest parts will be areas in which no photons have impinged upon the plate. The overall effect of the light and dark bands is an interference pattern, of exactly the sort you would have predicted by considering the light to be a wave, even though it was produced over time by the interactions of individual particles.


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