Photons and radio transmitters

[trevorb]

I believe all electromagnetic radiation is comprised of photons.

Is there any experimental evidence that radio transmitters emit photons rather than continuous em waves?

[ajb]

The best evidence for photons can be found in the paper below. However, it does not really answer your question.

 

Now, my understanding is that the thermal noise at radio frequencies produced by aerials swamps the photons and we cannot observe them. This is also important for radio astronomy. I'd need to look up things to give you any figures on temperatures and frequencies etc. Maybe someone else here is more familiar with aerial theory?

 

P. Grangier, G. Roger, and A. Aspect, "Experimental evidence for a photon anticorrelation effect on a beam splitter: A new light on single-photon interferences," Europhys. Lett. 1, 173-179 (1986).

[twistor59]

I believe all electromagnetic radiation is comprised of photons.

Is there any experimental evidence that radio transmitters emit photons rather than continuous em waves?

 

Interesting question. The problem is that radio frequency photons are so weak (i.e. low energy) that they don't ionise atoms, so I can't see how to construct something like a photomultiplier, which could respond to a single photon.

[swansont]

Photon antibunching is also evidence of photons.

 

Kimble, Dagenais, and Mandel. Phys. Rev. Lett. 39, 691 - 695 (1977)

 

But this is in the context of transitions in atoms rather than acceleration of electrons.

[trevorb]

Thanks for these posts which I have found inspiring. On the microwave power front I calculate that for a cavity magnetron transmitting at a wavelength of 1 x 10**-3 m to achieve a photon rate as low as 1000 photons per second a power of 2 x 10**-24 watts would be required. It would be difficult to envisage a system where this would not be swamped by noise. I chose 1000 photons per second as rate that one might expect to be detectable. This supports AJB's post.

[FooFiFum]

This is a very interesting topic!

 

Here is my understanding of the matter that I submit for correction.

 

1) The entire electromagnetic spectrum is composed of photons of vastly differing energies that correspond with wave length.

 

2) All photons travel at the same speed. That seems to rule out the possibility the photon itself has any lenth at all, no mater what the wave length, otherwise a long wave length photon would take longer to pass by us then a short one, even though the entire thing was traveling at c.

 

3) So, what we call wave length is simply the distance a photon travels over the period of one cycle. Antennas being 'tuned' to simply resonate in sympathy in both transmission and reception.

[swansont]

Interesting question. The problem is that radio frequency photons are so weak (i.e. low energy) that they don't ionise atoms, so I can't see how to construct something like a photomultiplier, which could respond to a single photon.

 

A system with a metastable state, with an available low-energy excitation to a state that quickly decayed. Amplify the emitted photon. I imagine it would be tough to find, and you'd have to do it at low-temperature so that thermal excitation didn't trigger the response.