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I have read this question where anna v says:

The photon is an elementary particle in the standard model of particle physics. It does not have a wavelength.

What exactly is meant by the wavelength of a photon?

And this one where Emilio Pisanty says:

Photon frequency and wavelength are the same as the corresponding classical mode. If the state of the field is such that there is, whenever you look, only one excitation present, then we say the field is in a single-mode, single photon state. This photon then has a well-defined frequency (ν=ω/2π) and wavelength (λ=2π/k).

Frequency and wavelength of photons

And if you look on this site, you find numerous occasions where people talk about the wavelength of a single photon.

Relation between radio waves and photons generated by a classical current

How many wavelengths does a single photon span?

Naively, I would think that a photon does have energy, and frequency associated with it, and since frequency and wavelength are inversely related (in vacuum), even a single photon could have a wavelength too. But if I interpret it as a point particle defined in the standard model, then the meaning of wavelength is not so obvious.

Question:

  1. Does a single photon have a wavelength or not?
Árpád Szendrei
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1 Answers1

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This is a long comment.

In the standard model of particle physics the photon is an axiomatic point particle,has spin +/-1 only , energy=hnu , mass zero and speed the velocity of light. Wavelength is meaningless for point particles. The standard model is continuously validated as far as photon behavior goes.

After a number of discussions on similar questions I have come to the conclusion that the term "photon" as defined in particle physics, is defined differently in quantum optics, and the use of the same term to describe two different things gives rise to the confusion .

To start with, one can have many useful and mathematically consistent field theories with creation and annihilation operators operating on fields. (I first learned of field theory in a nuclear physics calculation back in 1962.)

I believe that in quantum optics, they have a field theory that describes well the classical electromagnetic wave behavior in a quantum state, as a collective photonic field on which excitations , with creation and annihilation operators, are created. Those excitations they call "photons" , creating the semantic confusion.

These "photons" are composite states of the elementary particle photons, but are fundamental in their field theory, and can have a wavelength.

In this question here and discussions, including chat, I understood the semantic difference.

In my opinion, in physics it is wrong to have the same word defining two different entities, particularly confusing elementary particle ones of the standard model with other, very useful models in physics sub-disciplines.

All physics sub-disciplenes emerge from the elementary particle standard model and, imo, terminology should be consistent and not confusing.

anna v
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