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Quantum electromagnetic interference

  1. Jan 3, 2010 #1

    I wonder if I could get help with some questions that have puzzled me related to the two split experiment and electromagnetic interference in general.

    I know that if you shine a laser beam through the two split experiment then inference patterns will appear, and that if the path of a photon travelling through the experiment is measured or known then the interference patterns break down.
    I have also read that this also works if two (identical) laser beams are combined, i.e interference occurs. If the laser beams were 180deg out of phase then the peaks and troughs would cancel out the beam.
    1. Can I assume that, if I were able to determine which laser beam an individual photon came from the interference would also break down?

    2. I was wondering whether this works exactly the same for radiowaves? If I were to position a receiving aerial between two radio transmitters, (some distance apart), that were transmitting the same frequency radio signal but 180deg out of phase the radio signal would be cancelled out and the aerial should not receive anything.

    3. If I now added two more receiving aerials, each one positioned slightly closer to one of the transmitters. By comparing the difference in signal and phase between the first aerial and the second new pair of aerials I should surely should be able to work out the path of the radiowaves. Does the interference breakdown? Do I suddenly receive a signal from all the aerials or just the second pair or maybe nothing changes?

    4. If this is true what happens if the two transmitters are now brought close together (I guess near field). Do the same effects happen?

    I may be well off track so please forgive my lack of knowledge. I may have to go and buy some radio equipment...

  2. jcsd
  3. Jan 12, 2010 #2

    I guess my question is really this, is there an equivalent experiment/or research to the double slit experiment, carried out at Radio frequencies?

    i.e that radiowaves also travel as a wave but arrive as a particle, and interference can be made to break down when the path of the radiowaves are known.

    hope someone can help?

  4. Jan 12, 2010 #3
    Photons associated with radio waves have very small energy, so they cannot induce any visible particle-type effects (photo-electric effect or blackening of photographic plates). So, it is very difficult (almost impossible) to see particle-like properties of radio waves. Nevertheless, it is reasonable to assume that all physical properties of visible light and radio waves are the same. So, there should be no fundamental differences in the double-slit experiment performed with these two kinds of radiation.

  5. Jan 12, 2010 #4
    Your first experiment with the two laser beams would be a very good one to run, as it might give insight into the nature of the double slit experiment. It sounds like a good alternative that could demonstrate the same principle. However, off the top of my head I can't quite think of a way to tell which laser beam a given photon came from if the beams are combined.

    If what you say about interfering lasers is true we should get interference even if both lasers are firing single photons, which to me is intuitively wierder than the double slit. Maybe there is a way to determine which it came from with individual photons
  6. Jan 15, 2010 #5

    Thanks for the responses. I have seen several references to the fact that two laser beams will produce interference patterns. I have been trying to find them, one is below.
    When I find another I will add it in.

    OK, I've done a bit more research and proving radiowaves act like a particles is the problem. So for interference patterns to stop single photons have to be effectly observable, is this correct? I wonder if this has ever been done, maybe by indirect means?

  7. Jan 18, 2010 #6
    Well, keep in mind that while visible light is of course composed of photons, but so are radio waves, microwaves, x-rays, etc...
    To my knowlege, all photons have wave-particle duality.
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