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Double Slit, Detector, Light -- Pattern?

  1. Sep 7, 2015 #1
    I have a question about how the double-slit-with-detector experiment works out with a beam of light.

    (1) When you fire electrons through the double-slit apparatus, it creates an interference pattern on the screen. (2) When you place a detector at one of the slits, the interference pattern is ruined and you just get two corpuscular bands.

    My question is: Does the same thing happen with light? I know that light does create an interference pattern under double-slit conditions (1). But if you place the same kind of detector (2) at one of the slits when light, rather than electrons, is streaming through -- does the interference pattern get collapsed into two corpuscular bands?

    An additional question: Can somebody please point me in the direction of a peer-reviewed paper offering evidence of the phenomenon under discussion, in which the presence of a detector collapses the interference pattern of electrons? Everyone talks about it, but I want to be able to reference something substantive.

    One more question: Does the double slit experiment produce similar results with electrically neutral particles (excluding photons). Come to think of it, are there any fundamentally electrically neutral particles, that aren't composed of more primary charged particles?

    Many thanks!
     
  2. jcsd
  3. Sep 7, 2015 #2

    Drakkith

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    Unfortunately you can't use the same kind of detector to detect light as you can electrons. Whenever you detect a photon you destroy it, so you can't get a double band pattern by placing a detector at one of the slits as you can with electrons. However, there are other ways of working with photons that allow you to 'know' which path the photon took which will break the interference pattern and give you two bands. I believe these usually involve polarizers. So you don't really detect the photons, but you do know which path they must have taken to get to the final detector and you will see a double band pattern.
     
  4. Sep 7, 2015 #3

    Nugatory

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    Yes, but of course it requires a completely different sort of detector because we're dealing with different particles that interact in different ways.

    The most interesting and non-classical result in all of these experiments is the way that the interference pattern builds up when both slits are open and the particles are sent one at a time, so the experiment is most often done simply by closing one slit instead of placing a detector there. However, there are a number of peer-reviewed experiments in which both slits were kept open and clever techniques were employed to detect which slit the particle went. One of my favorites is https://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser#The_experiment_of_Kim_et_al._.282000.29

    That's two more questions :smile:, and the the photon is not the only electrically neutral fundamental particle - for example, there's the neutino. It's not practical to do a double-slit experiment with these because they're too hard to reliably detect.
     
  5. Sep 7, 2015 #4

    Drakkith

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    Would a neutrino even see any practical double slit we could build as an actual barrier?
     
  6. Sep 7, 2015 #5

    Nugatory

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    No. For that matter, it wouldn't see most of the impractical barriers we can imagine either.
     
  7. Sep 7, 2015 #6
    I guess I don't even know what kind of detectors they use to detect electrons at the slits. How is it that these detectors would destroy photons?
     
  8. Sep 7, 2015 #7

    bhobba

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    It's usually absorbed by the detector and that absorption leaves some kind of 'mark' where that happened eg if it was a photographic plate that absorption would trigger a chemical reaction that would appear when developed.

    Thanks
    Bill
     
  9. Sep 7, 2015 #8

    Drakkith

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    Like Bhobba said, the photon is absorbed by the detector. For a photographic plate or film, this causes a chemical reaction that turns the spot a different shade/color. For a digital sensor, the absorption usually excites an electron(s), which is then manipulated into an electrical signal and amplified. Either way requires that the photon be absorbed and destroyed.
     
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