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Is there any experiment that would show that radio waves (I am talking about macroscopic wavelength, say between 0.01m - 2m) are made out of individual photons? Sort of an equivalent of the photo-electric effect? Or maybe a photon-multiplier for radio waves? Can a single photon of radio waves be picked up by 2 antennas at the same time? Or is it absolutely senseless to see radio waves as a stream of individual photons?

Eiver
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  • It is certainly true that all electrmagnetic radiation is made up out of photons. I don't know, however, what experiments have been done to demonstrate this for radio waves specifically. – Danu Oct 02 '13 at 10:35

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Yes, single photon radio waves have been constructed.

Radio communication is now possible on the most elementary level: scientists at the ETH Zurich and the Max Planck Institute for the Science of Light in Erlangen have used two molecules as antennas and transmitted signals in the form of single photons, i.e. light particles, from one to the other. Since a single photon usually has very little interaction with a molecule, the physicists had to use a few experimental tricks for the receiver molecule to register the light signal. A radio connection established via individual photons would be ideal for various applications in quantum communication – in quantum cryptography or in a quantum computer, for example.

The discussion in this question should enlighten you, and the links given there. There is a one to one correspondence between classical and quantum electrodynamics, both rely on the Maxwell equations as you will see if you read the detailed answer. In the link in my answer the way one goes mathematically from one to the other is shown. No need for extra experiments since the mathematics is rigorous.

For low energies of the electromagnetic waves it is not very smart to use all the mathematical panoply if one can do the job with the classical representation, except as in this case of single photon transmissions.

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anna v
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  • I believe the question was whether photons corresponding to radio frequencies (1 cm to 2 m ) could be detected; not whether "radio" communication could be carried out at light frequencies. I demonstrated transmission of music signals over a free space light beam (red LED) in 1966; and I certainly wasn't the first. –  Oct 03 '13 at 21:05
  • @GeorgeE.Smith You are correct about the wavelength, but this ink demonstrates individual photons used for encoding a radio signal. There is no reason to doubt that the same happens with cm wavelength photons. This link gives even applications of single photons at large wavelengths http://www.singlequantum.com/applications/ and a list of publications. – anna v Oct 04 '13 at 03:28