Classical Circular Polarization vs. Photon Spin Eigenstates

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Discussion Overview

The discussion centers on the relationship between classical circular polarization of electromagnetic waves and the quantum mechanical properties of photons, particularly regarding their spin eigenstates. It explores the implications of classical descriptions in the context of quantum mechanics.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions whether a classical electromagnetic wave that is not circularly polarized corresponds to a photon with a zero spin eigenstate.
  • Another participant asserts that photons do not possess a spin 0 eigenstate, emphasizing that they are massless spin 1 particles and cautioning against conflating classical fields with photons.
  • A different participant claims that a non-circularly polarized wave corresponds to a superposition of spin +1 and -1 states, similar to how classical waves can be expressed as a sum of circularly polarized waves.
  • There is a clarification regarding the reference to "spin +1" and "-1," with a participant inquiring if these refer to two of the three eigenvalues of the spin 1 operator for the Z direction.
  • Another participant notes that a massless spin 1 particle has only two eigenstates.
  • A later reply indicates understanding of the discussion, thanking the contributors.

Areas of Agreement / Disagreement

Participants express differing views on the nature of photon spin eigenstates and their relationship to classical polarization, indicating that multiple competing views remain without consensus.

Contextual Notes

The discussion involves assumptions about the treatment of classical fields versus quantum states, and the implications of massless spin 1 particle properties, which may not be fully resolved.

LarryS
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Hello,

Given an electromagnetic wave that is, from a classical point-of-view, not circular polarized. Does that correspond in QM to photons with the ZERO spin eigenstate?

Thanks in advance.
 
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Photons do not have a spin 0 eigenstate, since they are massless spin 1 particles. Also be very careful in trying to treat classical fields as photons. Classical fields are generally described by coherent quantum states and not states carrying a particular number of photons.
 
No, it corresponds to a superposition of states with spin +1 and -1, just like the classical wave can be written as a superposition (sum) of circularly polarized waves.
 
So, by "spin +1" and "-1", are you referring to 2 of the 3 eigenvalues of the spin 1 operator/matrix for the Z direction?
 
This is the thing, a massless spin 1 particle has only 2 eigenstates.
 
I just got it. Thank you both.
 

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