Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Even another 2-slit experiment setup

  1. May 19, 2007 #1
    I'm interested in knowing what would happen in this setup, if anybody knows. I don't have a way to make a diagram, but the setup is pretty easy.

    Say that in a central location, call it L, you have a source of entangled photons that emit one to the left side and the other to the right side 180 degrees away. I don't know if you need beam splitters to make it work, but we can put some in anyway just in case .. so ..

    The left hand photon travels length L1 and encounters its beam splitter and the right hand photon travels length R1 and enounters its beam splitter. L1 = R1. In both segments the photons have a choice of traveling straight on, or deflecting 90 degrees (downward on your page if you are making a diagram). Consider only the photons that get deflected downward.

    On the R side at distance R2 from its beam splitter is a screen with 2 slits, and beyond that is a solid screen. On the L side at distance L2 from its beam splitter is only a solid screen. L2 = R2, but the experiment is built so that distance L2 can be varied to a distance shorter or longer than R2.

    I'm assuming the experiment can be set up so that an interference pattern will appear on the solid screen on the R side.

    My question is this: As you adjust the solid screen on the L side, distance L2, longer than R2 to shorter than R2, will that have any effect on whether an interference pattern developes on the R side?

    I would think that as long as L2 > R2 a pattern can be observed, but when L2 < R2 the interference pattern would disappear.
  2. jcsd
  3. May 20, 2007 #2
    This is essentially what was discussed in the 'EPR and FTL' thread. If is possible, even in principle, to determine which slit a photon went through, you don't get interference. To determine which slit each photon went through, you need the 'which path' information, since this is not accessible after a photon goes through a regular double slit setup, you get interference. In your setup, the which path information is carried by the left hand photons, and it is possible to extract this information without measuring the right hand one directly, so you don't get interference.

    However... I think if it is somehow impossible to tell which left hand photon corresponds to which right hand photon, it is impossible to tell which slit each right hand photon went through, so you should get interference. So basically I don't know what would happen! :( I'll leave it to someone more knowledgable to answer. But I would say read the EPR and FTL thread, it might answer some of your questions.
  4. May 21, 2007 #3
    Hmmm .. I take back what I thought it would do, as if it did you could fashion a sort of Morse Code FTL communication. I don't know what it would do.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook