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B Double slit experiment wave collapse

  1. Feb 5, 2017 #1
    I would like to ask this question.
    In the double slit experiment on wave particle duality of photon, we know that the wave function collapses and the photon behave like a particle whenever we peek.
    Has anyone ever placed a second double slit behind the detector to see whether a particle regain its wave function ? Or the particle remains a particle ?
    What i meant is this :
    Single photon ... go through double slit... peek...wave collapse... we get clump on detector ... create a hole on detector... photon go through double slit again behind the detector.. this time no peek .... on the detector, do we get interference or clump ?
  2. jcsd
  3. Feb 5, 2017 #2


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    I think you have a bit of a misunderstanding here.

    When you are able to determine which-way the quantum particle (i.e. photon, electron, neutron, buckyball, etc.) goes through, then it is the superposition of paths that has been "collapsed", or determined. Then, the pattern on your screen will be the same pattern that you get with a single-slit diffraction.

    If you add another set of double-slit AFTER that, then the original experiment remains intact, i.e. the quantum particle once again will have a superposition of paths UNTIL you make a determination which one it will go through. Then what I wrote above gets repeated.

    Notice that in the whole setup, you know nothing about the source. All you care about is that quantum particle with identical properties are hitting your setup. Yet, I could have easily generated electrons or photons that came out of some interferometer, and I've selected the ones with the right, single frequency to send to your setup. In other words, your whole setup would be using something that came out of some interference setup already. And this will not be highly unusual, because we do this at synchrotron facilities all over the world. It is how we select the single frequency of light coming from undulators/wigglers placed in the synchrotron rings.

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