What is the current understanding of the photon and its interaction with matter?

[Karthiksrao]

I have been going through the paper "Evolution of the modern photon" by Kidd,Ardini and Anton. This was published in 1989.

In the paper, he describes the various 'models' of photons that have come up over time including the corpuscular model, the singularity model, wave packet model and the QED model.

He lays stress on the fact that 'at present' (in 1989) the QED model seems to fit the bill quite well, in the sense that most of the phenomena observed can be explained using this model.

I wish to know what has changed in the last 20 years. Is the QED model still holding its ground.

Also, I've understood the QED model as that which postulates that interaction of light with matter as being quantized but the field or radiation itself is un-quantized/continuous. Have I understood it correctly?

Thanks,
Karthik

 

[Parlyne]

QED is a quantum field theory. This means that all particles (photons included) are treated as excitations of a quantized field. So, no, you have not understood it correctly. In QED, the EM field is quantized and the photon is the quantum of that field. A model in which unquantized (or "classical") EM fields interact with quantum mechanical matter is usually termed a "semi-classical" model.

 

[Karthiksrao]

By 'excitation', do you mean a ripple, which propagates through space at speed of light?

 

[Parlyne]

Not a terrible analogy, provided you include the understanding that ripples of a given frequency can only have discrete quantities of energy, with the size of the discrete unit being proportional to the frequency of the ripple.