How to quantum mechanically describe the photon?

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Discussion Overview

The discussion centers on how to quantum mechanically describe the momentum eigenfunctions of photons, particularly in relation to monochromatic light and the quantization of the electromagnetic field. Participants explore various theoretical frameworks and resources related to quantum field theory and quantum optics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • Some participants express confusion about how to represent momentum eigenfunctions of photons, seeking a quantum mechanical description similar to classical representations.
  • A participant mentions that a quantum description requires quantizing the electromagnetic field, leading to operators that create and destroy photons with specific momentum and polarization.
  • There is a suggestion that acting on the vacuum state with a single-photon creation operator produces a momentum eigenfunction, while an exponential of a creation operator can create a coherent state of photons.
  • Some participants reference specific textbooks and lecture notes, such as David Tong's lecture notes and Weinberg's "The Quantum Theory of Fields," as resources for understanding momentum eigenstates.
  • Discussion includes the concept of helicity states, with mentions of both right and left helicity in relation to momentum eigenstates.
  • Several posts introduce humorous or light-hearted remarks, diverging from the technical discussion.

Areas of Agreement / Disagreement

Participants generally agree on the need for a quantum mechanical framework to describe photons, but there is no consensus on a single, straightforward equation or representation. Multiple competing views and interpretations remain regarding the specifics of the quantum description.

Contextual Notes

Participants note the complexity of the topic, with references to various theoretical approaches and the absence of a simple one-liner equation for the quantum description of photons. The discussion reflects a range of assumptions and interpretations that are not fully resolved.

Somali_Physicist
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This might sound stupid , but I am wondering how exactly could I describe the momentum eigenfunctions of photons?

EDIT:
to destroy ambiguity, I am searching for a quantum mechanic description of monochromatic light similar to how we represent it classically as:

E-> = a->cos(wt+phi)
 
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Somali_Physicist said:
This might sound stupid , but I am wondering how exactly could I describe the momentum eigenfunctions of photons?
##|p>## :biggrin:
 
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Demystifier said:
##|p>## :biggrin:
more precisely, ##|p\rangle##
 
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witty responses and as true as true can be. does it help our @Somali_Physicist ?
 
A quantum description of photons requires quantizing the electromagnetic field. This is discussed in any textbook on quantum field theory or quantum optics, and in many quantum-mechanics textbooks. This will result in operators that create and destroy photons with definite momentum and polarization. Acting on the vacuum (the state of no particles) with a single-photon creation operator produces a momentum eigenfunction. Acting with the exponential of a creation operator (with a specific coefficient) will create a "coherent state" of photons, all with the same momentum, which is as close as you can get to a classical field in the quantum theory.
 
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Avodyne said:
A quantum description of photons requires quantizing the electromagnetic field. This is discussed in any textbook on quantum field theory or quantum optics, and in many quantum-mechanics textbooks. This will result in operators that create and destroy photons with definite momentum and polarization. Acting on the vacuum (the state of no particles) with a single-photon creation operator produces a momentum eigenfunction. Acting with the exponential of a creation operator (with a specific coefficient) will create a "coherent state" of photons, all with the same momentum, which is as close as you can get to a classical field in the quantum theory.
Thank you
So there is no one liner equation ?

What is your textbook called
 
Somali_Physicist said:
This might sound stupid , but I am wondering how exactly could I describe the momentum eigenfunctions of photons?
Weinberg's "The Quantum Theory of Fields" Chapter 2 has a nice discussion of momentum eigenstates of various particle types.

Demystifier said:
##|p>## :biggrin:
A. Neumaier said:
more precisely, ##|p\rangle##
There should also be helicity right? ##|p,\sigma\rangle##
 
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DarMM said:
There should also be helicity right? ##|p,\sigma\rangle##
Or helicity left, ##|p, - \sigma\rangle ##
 
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  • #10
Somali_Physicist said:
So there is no one liner equation
The relevant equation is that for the vector potential of the e/m field in Lorentz gauge.
 
  • #11
A. Neumaier said:
Or helicity left, ##|p, - \sigma\rangle ##
What's the difference between the left and and right side of the brain? On the right side there is nothing right, while on the left side there is nothing left.
 
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  • #12
Demystifier said:
On the right side there is nothing right, while on the left side there is nothing left.

I prefer this: On the left side there is nothing right, while on the right side there is nothing left.
 
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  • #13
Pony said:
I prefer this: On the left side there is nothing right, while on the right side there is nothing left.
It's not sufficiently paradoxical. A quantum description is not good if it does not look like a paradox. :biggrin:
 
  • #14
It's not even right since on the right hand the thumb is at the left...
 

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