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Two interfering antennas with single photon radiation

  1. Apr 5, 2014 #1
    Consider this:

    Two antennas are set up in a vacuum. They both radiate electromagnetic waves of the exact same frequency, and an interference pattern can be observed on a screen placed some distance away. Now suppose the emission density was reduced (in both antennas) to one photon at a time, such that when either of the antennas is firing a photon, the other one isn't until the first photon reaches the screen. We don't know which antenna is firing the photon at any certain time.

    Assuming the coherence time of the antennas is large enough to allow 5 (or any other random number more than 1) of these alternating photon emissions.

    Will interference occur?

    can we even control the photon emission in the way I described?

    If interference occurs, will it also occur if we set the antennas to randomly shutdown, one at a time, between single photon emissions?
  2. jcsd
  3. Apr 5, 2014 #2


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    Staff: Mentor

    If you modify that statement to read "We cannot know...", I would expect that there would be interference.

    I've never heard of such a thing being done with RF sources, and I would be rather surprised because the photons involved have such low energies. However, Greenstein and Zajonc refer in their book to a similar experiment involving lasers. In that case, you get an interference pattern only if it is impossible to distinguish which laser each individual photon comes from. In effect, the two lasers must be "locked together" to behave as a single source.

    On further thought... multi-element RF antennas generally have "nulls" in various directions in their radiation pattern. I suppose you could consider this as the result of interference between the radiation emitted by the individual elements. If you drive the whole antenna from a single source, it's impossible to say which element emits which photon.
  4. Apr 5, 2014 #3
    ok but why could low energy radiation reduce interference visibility?
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