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Ive been thinking a lot about Young's double slit experiment lately and have even considered attempting to reproduce some variant of it. Ive seen videos on youtube and feel like i have a good grasp of the experiment and how to create an interference pattern pretty simply at home, however i was curious to know if an observed-instance of this experiment was a reproducible effect, basically, is there a means of forcing the observational state where the photons would act as particles and create 2 lines instead of acting as waves? Ive seen plenty of videos showing the interference patterns, but literally none showing the detection at its particle state. The experiment states, and was proven, that both instances are a possibility correct? what variable effects this, can it be reproduced at home? (Ive been told observation, may even count as interaction with the air, or particles in it, so would performing the experiment under vacuum produce better results?)

Im willing to spend a fair amount here on making a demonstrative model. My basic setup was a laser spaced with a 2 slit light blocking surface, spaced from a high resolution camera with the pattern directed into the lens, my hope was to sort of map the light intensity the pixels were receiving. i own cnc mills, laser cutters and 3d printers, im fairly confident in my accurate build ability here.

Thanks in advance!

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  • $\begingroup$ I'm not sure what you want. Take a look at Figure 1 in this paper. Is that the kind of thing you want to reproduce? $\endgroup$
    – garyp
    Commented Mar 25, 2018 at 22:20
  • $\begingroup$ Well, i would like to reproduce that interfercne pattern, But also the pattern when the photons act as particles and not waves. i think this photo demonstrates both states. google.com/…: $\endgroup$
    – Zack Riley
    Commented Mar 25, 2018 at 22:25
  • $\begingroup$ That's what I don't get. What do you mean by "photons acting as particles". They do just that in that paper. What is it that you would like to demonstrate? $\endgroup$
    – garyp
    Commented Mar 25, 2018 at 22:29
  • $\begingroup$ in that paper they act like waves, which is why interference patterns are shown. I want to produce them as particles too. so i can see the 2 distinct segments chosen when fired at the two slits. $\endgroup$
    – Zack Riley
    Commented Mar 25, 2018 at 22:30
  • $\begingroup$ If you're trying to do this with photons, you're out of luck. From the Wikipedia article: "Naive implementations of the textbook gedanken experiment [i.e. the particle-like pattern in the double-slit experiment] are not possible because photons cannot be detected without absorbing the photon." Usually this experiment is done with electrons, which can be observed without absorbing them. $\endgroup$
    – probably_someone
    Commented Mar 25, 2018 at 23:22

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Whether you are talking photons or subatomic particles, the knowledge I have is that you cannot observe both the particle nature and the wave nature at the same time. One of the fundamental principles of quantum mechanics is that the observer affects the event, i.e. "You get what you look for".

If you conduct the double slit experiment, you will get wave interference, meaning that you are observing the wave nature of light.

If you want to detect photons as particles, then you need to use a photon detector. Placing the photon counter behind the slits will not allow you to detect simple particle behaviour because the light behaves as a wave beyond the slits. At a particular location, you will detect 'photon events' through the photon detector, provided the detector is within the defraction projection area, but the frequency will be probabilistic, and much less frequent than having the photon detector in front of the slits. To be able to more easily understand the photon events beyond the slit, you would need to place many photon detectors spread throughout the defraction projection area, which will allow you to see how the differences in photon detection frequency by position represent a defraction pattern, which has brighter and darker areas. Still, at a particular moment, you would see a particle. The wave nature is evident from the behavior of the particle events over time.

In another futile effort, if you place the photon detector before the slits, the photon detector will detect photons but there will be no interference pattern beyond the slits. You have brought out only the particle nature of the light.

More on the dual nature of 'quantic entities' here and here. The phenomenon of the effect of an observer on an event is explained here. These phenomena are among the reasons why we need quantum mechanics.

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    $\begingroup$ Thank you for your informational response, it was along the lines of what im looking for. I want to create the different states, at different times, with the option to switch the experiment to the other state. Could you perhaps elaborate a bit on the detectors, i am confident in my ability to produce a double-slit interference pattern and setup, I need to know more about how to make the detectors, and how they can be positioned/work without interfering with the photon its observing. if i am correct i change the detectors status (oberseve or not), in order to change the state? $\endgroup$
    – Zack Riley
    Commented Mar 26, 2018 at 17:38
  • $\begingroup$ I am pretty sure this answer is incorrect. As stated in a comment, you cannot detect a photon without absorbing it. If I understand correctly you would like to show that if you "look" from which slit the photon passes, then the interference pattern disappears. While this is true in theory, it is not possible to realise with photons since to be able to "look" through which slit the photon passes, you would have to absorb it, and nothing would make it to the screen. As stated in a comment, to highlight this kind of behavior you should use electrons, for example. $\endgroup$
    – Frotaur
    Commented Mar 11, 2020 at 17:10
  • $\begingroup$ Also the claim "Placing the photon counter behind the slits will not help you because the light behaves as a wave beyond the slits. You will not detect any 'photon events' through the photon detector." is wrong, you will indeed detect photon events through the photon detector even if placed after the slits, but the distribution probability of the detection will obey the characteristic interference pattern, since the photon will have interfered with itself before being detected. $\endgroup$
    – Frotaur
    Commented Mar 11, 2020 at 17:13
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    $\begingroup$ @Frotaur I agree with your second comment. I augmented the paragraph starting "If you want to detect photons as particles,...". Thank you. $\endgroup$
    – Dlamini
    Commented Mar 13, 2020 at 11:56
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The paper referenced by @garyp shows the wave nature of light via interference; and the particle nature of light via single-photon detection using a photomultiplier as a single-photon detector, and an attenuator that reduces the number of photons per second to a countable level.

The fact that light can be observed as a series of individual detection events is an indication of the particle nature of light. So, for your experiment you just need a photomultiplier, a really good light attenuator, and a black box inside of which to put the apparatus.

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You might want to take a look at this setup.

Basically, as others have pointed out, the particle nature of light or any other "particle" can be detected by the fact that energy received at a detector is always in quanta, and not half of particle here and the other half there. The interference pattern is explained on wave-nature of particles.

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To observed the wave interference pattern, mount your laser and double slit in a darkened room so that the light passes through the slits and strikes a light colored wall about 2 meters beyound the slits. The pattern you will see on the wall is from double slit interference modulated by single slit diffraction.

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