What is polarization in the language of photons and QM?

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Discussion Overview

The discussion focuses on the concept of polarization in the context of photons and quantum mechanics (QM), exploring its relationship to classical electromagnetism (EM) and the notion of spin. Participants seek to understand how these concepts interrelate and what literature might provide further insights.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants express a desire to understand polarization in terms of photons and QM, suggesting a connection to spin.
  • Photon polarization is described in terms of helicity, with helicity states of +1 and -1 corresponding to left and right circular polarization, respectively.
  • It is noted that a plane polarized photon can be represented as a linear combination of circular polarizations, similar to classical EM descriptions.
  • One participant questions the relationship between helicity and polarization, indicating a need for further reading on the subject.
  • Another participant clarifies that polarization and helicity stem from different areas of physics, with polarization being an EM concept and helicity being a QM concept related to spin.
  • Polarization is mentioned as applicable to both materials and EM waves, highlighting its broader context.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of helicity and its relation to circular polarization, but there is uncertainty regarding the direct relationship between helicity and polarization, indicating that the discussion remains unresolved.

Contextual Notes

There are limitations in the discussion regarding the definitions of polarization and helicity, as well as the lack of a direct formula connecting the two concepts. The discussion also reflects varying levels of familiarity with the subject matter among participants.

touqra
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I know what polarization is in classical EM. But what is polarization in the language of photons and QM? I am thinking that it's something to do with spin.
 
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touqra said:
I know what polarization is in classical EM. But what is polarization in the language of photons and QM? I am thinking that it's something to do with spin.

It is said that two eigenstates of spin correspond to two kinds of circularly polarized states, but I don't know the details too.

Anyone knows what subject deals with this stuff?

Thank u!
 
Photon polarization is usually described in terms of helicity, which can be
+1 or -1 for a photon. The helicity +1 state correspond to Left circular polarization and the -1 to Right circular polarization. A plane polarized photon is the same linear combination of circular polarizations as in Classical EM. The reason H=+1 corrsponds to LH circular polarization is that particle physicsts use a z=axis in the direction the photon is moving, while the classical circular polarization is how the E vector rotates as you look toward the oncoming photon.
 
Meir Achuz said:
Photon polarization is usually described in terms of helicity, which can be
+1 or -1 for a photon. The helicity +1 state correspond to Left circular polarization and the -1 to Right circular polarization. A plane polarized photon is the same linear combination of circular polarizations as in Classical EM. The reason H=+1 corrsponds to LH circular polarization is that particle physicsts use a z=axis in the direction the photon is moving, while the classical circular polarization is how the E vector rotates as you look toward the oncoming photon.

I still want to know how helicity is related to polarization.
Can you recommend some readings?

Thank you!
 
zhangpujumbo said:
I still want to know how helicity is related to polarization.
Can you recommend some readings?

Thank you!

Well, they are not directly related in terms of a formula because both concepts come from different "places" in physics. Polarization comes from EM and helicity is a QM concept since you need the concept of SPIN to define helicity. You do not need spin to define polarization.

Polarization can be defined for both materials (local fluctuations in the electronic density that lead to dipoles or quadrupoles) as well as EM waves

marlon
 

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