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Entangled particle through double slit

  1. Apr 12, 2015 #1
    I create 1000 pairs of entangled particles and let them travel very far away.
    Then I let the 1000 right particles pass through a double slit experiment.

    At the time when the right particle has passed the slit, but not yet hit the screen, I can choose to detect the 1000 left particles. If I detect/collapse the left particles, then I know which path the right particle took? If so, then there is no interference pattern on the screen?

    Then I, located where the left particles are in space, can choose what pattern appears on the right particle screen instantaneously? ie faster-than-light.
     
  2. jcsd
  3. Apr 12, 2015 #2

    Nugatory

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    You might want to take a look at http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser#The_experiment_of_Kim_et_al._.282000.29 - but note carefully how the interference pattern is detected - there's no image formed on a screen.
     
  4. Apr 12, 2015 #3
    In the delayed choice experiment the original photon is down-converted after it has passed the silt.
    In my scenario, the original photon is down-converted way way before the right particle passes the slit. Does that make a difference?
     
  5. Apr 12, 2015 #4

    DrChinese

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    A stream of entangled particles do not produce the usual interference effects while still entangled. So do whatever you like, the pattern is the same. No interference, and no FTL signalling. See:

    http://www.hep.yorku.ca/menary/courses/phys2040/misc/foundations.pdf

    Figure 2, S290.
     
  6. Apr 13, 2015 #5
    My understanding of the linked PDF is that :

    the usual interference pattern is NOT observed for the right particles if the left stream of particles are just left alone;
    but if the left stream of particles (which-path information) are quantum erased, the the usual interference pattern can be observed for the right side particles.

    So in my original scenario:
    I, located where the left particles are in space, can choose to erase or not erase the left which-path information, thus choosing what pattern appears on the right particle screen? even if the left particle and right particle are far far apart?
     
  7. Apr 13, 2015 #6

    DrChinese

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    You are mixing scenarios and their results.

    Scenario A, where there is no quantum erasure, produces no interference (as the reference notes).

    Scenario B, where there is quantum erasure, produces no obvious interference pattern either. However, by using coincidence counting (results from both sides), an interference pattern can be seen.

    By the way, welcome to PhysicsForums!
     
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