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Interference between photons that never meet

  1. Apr 16, 2008 #1


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    The pantheon of impossible photon tricks grows ever larger. Today, a new addition from Andrew Shields and pals at Toshiba Research Europe in Cambridge, UK:

    “We report an experiment in which two-photon interference occurs between degenerate single photons that never meet. The two photons travel in opposite directions through our fibre-optic interferometer and interference occurs when the photons reach two different, spatially separated, 2-by-2 couplers at the same time.”


  2. jcsd
  3. Apr 18, 2008 #2
    Correct me if I'm wrong, but if photons had the ability to observe the world, since they move at the speed of light, everything would be a singularity, since 'time' to them is nonexistant? Ie space to them is nonexistant because they can 'move' instantaneously from point A to point B, according to their own observations, which obviously conflicts with ours.

    So is it so unpredictable to observe photons interfering with each other, when the only seperation is space which to them doesn't exist in the first place?

    If my rambling makes no sense whatsoever, I apologize... I'm only 16, not an expert.
  4. Apr 18, 2008 #3


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    You need to read through the Relativity forum here to see the validity of your transformation into the photon reference frame.

  5. Apr 18, 2008 #4
    Does this destroy Bohmian mechanics?
  6. Apr 18, 2008 #5
    This is somewhat similar to a suggestion I had which was to arrange a hundred double slits and send one photon through at a time and see if an interference pattern emerged when the 100 images were superimposed. Not a very practical experiment but this tests the same idea, and confirms once agan that the QM predictions are right.
  7. May 6, 2008 #6
    Hey guys, My name is Raj, I'm actually a student @ toshiba and Anthony Bennett and Andrew Shields are my supervisors. We have a couple of papers soon to be published in APL and PRL ( see http://arxiv.org/abs/0803.3700 and http://arxiv.org/abs/0804.1897)

    The experiment that anthony performed was first carried out using photons from parametric downconversion by Franson (John Hopkins). When we talk-about two-photon interference we're not talking about a "physical" interference but rather cancellation of probability amplitudes.
  8. May 6, 2008 #7


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    This certainly does not destroy Bohmian mechanics. Why do you think that the experiment reported by SF could destroy it?
  9. May 6, 2008 #8

    Hans de Vries

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    Thank you for posting the links Raj.

    I do agree. Actually, scanning through the paper, the interference is what one would expect
    from classical electromagnetics. The EM fields of both photons split in both directions and
    always interfere. The actual "clicks" (the detections) are however unitary (only one click
    per photon at one place) as predicted by quantum mechanics.

    Regards, Hans
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