Additional info:
Single-photon emission from single-electron transport in a SAW-driven lateral light-emitting diode

While the article claims how they got single photon emissions, the article shows how they use a radio-transmission.
The electromagnetic waves in the transmission have a saw like structure.

They tune it in a way that the receiver only receives EM-energy in cycles, and these cycles are called "photons". The cycles seem directly related to the threshold of the receiver.

The article argues that the receiver only gets photons, because the energy should not be received in cycles if it was purely electromagnetism. But they do not know about any threshold.

In my short read, it seems to me that in figure 3, the threshold fills up, and then goes back to zero in a clear cycle.

But research like this is interesting, and more specialized experiments might reveal more physics.