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Photon-photon anihilation

  1. Jan 12, 2015 #1
    Consider this report:

    http://www.physics-astronomy.com/2015/01/quantum-teleportation-of-subatomic.html
    "Then, the researchers shot a third particle of light at the photon traveling down the cable. When the two collided, they obliterated each other. Though both photons vanished, the quantum information from the collision appeared in the crystal that held the second entangled photon."
    There have been several reports of this result, all claiming photon-photon annihilation.
    Is that possible? I am not asking if it is rare, I am asking if it is at all possible. The two photons that annihilated each other were not in this case even entangled.
    If it is possible (however rare) for a neutrino and an antineutrino to annihilate giving a photon pair, then the time reversal would be photon-photon annihilation... but I'd guess you would have to get the phase just right. In which case you would not need the MEV energy of an electron-positron pair, but only the rest-mass energy of twice the neutrino, meaning that very-long-wavelength photons would work.

    Is this result some kind of artifact of being in an optical fiber? The researchers do not seem to have any concern for conservation of energy; they do not mention what products of the annihilation there might be, the photons simply vanish, in their view.
     
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  3. Jan 12, 2015 #2

    mfb

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    Photon-photon interactions in vacuum are unlikely, but possible. There are concepts of a photon-photon collider (e.g. http://www.nature.com/nphoton/journal/v8/n6/full/nphoton.2014.95.html), but it would be expensive and the scientific use is probably not so great.
    Electron/positron pairs would be the most interesting result (starting at 1 MeV center of mass energy), the reaction to neutrinos (starting somewhere below 1 eV) would be extremely rare and impossible to observe.

    In matter, light behaves different, and two photons can go missing simply by absorption in the material, for example. This has nothing to do with the vacuum process.
     
    Last edited by a moderator: May 7, 2017
  4. Jan 12, 2015 #3
    But this report stated clearly that the disappearance was the result of annihilation; the third photon was what annihilated the other one. This was essential to the claimed teleportation. What is more, the experiment seems to have been able to do this on a regular basis, so it can't be rare at all.
     
    Last edited by a moderator: May 7, 2017
  5. Jan 12, 2015 #4

    mfb

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    No I don't think so.
    There is also two-photon microscopy where two photons get absorbed ("vanish") together.

    The entanglement of one of the photon does not change anything. Yes the third photon gets the state from a different photon - so what. Interesting for entanglement, but irrelevant for the absorption process.

    And again, this has nothing to do with photon-photon interactions in a vacuum.
     
  6. Jan 12, 2015 #5
    I am pretty sure that the report did make that claim. The photon would not have "vanished" without that third photon, otherwise why did they bother? And the word that was used was Obliterated, which I can't find a definition for.
    So what was going on there was simply some kind of double-absorption that would not occur unless they fired that third photon, is that what you are saying? And the same experiment in a vacuum could not possibly have that result.
     
  7. Jan 12, 2015 #6

    mfb

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    It would have, but then there would be nothing interesting to study.

    Yes. The material is absolutely necessary for the experiment they did.
     
  8. Jan 12, 2015 #7
    Usually one does one's best to reduce absorption in an optical fiber. Here they rely on it.
     
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