Coherent state between a fermion and a photon

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Discussion Overview

The discussion revolves around the possibility of a coherent state between a fermion and a photon, specifically exploring the concept of a fermionic polariton. Participants examine the interactions between fermions and photons and the implications of these interactions on the nature of quasiparticles.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions whether a coherent state can exist between a fermion and a photon, specifically inquiring about the existence of a fermionic polariton.
  • Another participant suggests clarifying the question by considering a simple atomic system where a photon interacts with an electron, flipping its spin while maintaining the electron's fermionic nature.
  • A participant references a distinction between polaritons as bosonic quasiparticles and polarons as fermionic, indicating a potential misunderstanding in the original question.
  • It is noted that a superposition of states with an even and odd number of fermions is not possible due to the univalence superselection rule, which is explained in terms of invariance under rotation.

Areas of Agreement / Disagreement

Participants express differing views on the nature of coherent states involving fermions and photons, with no consensus reached on the possibility of a fermionic polariton or the implications of the superselection rule.

Contextual Notes

The discussion includes assumptions about the nature of quasiparticles and the conditions under which fermionic and bosonic states can interact, which remain unresolved.

sugeet
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Can we have a coherent state between a fermion and a photon! I mean can there ever be a fermionic polariton?
 
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You may have to clarify your question a bit. Imagine a simple atomic system with one electron in a magnetic field. The photon can interact with the system by flipping the electrons spin from down to up, total change of spin by 1, but the electron remains a fermion. What situation were you thinking of? What part of the system should be fermionic?
 
Thank you Zarqon for replying, I did some search and got my answer.
The Wiki page says :"The polariton is a bosonic quasiparticle, and should not be confused with the polaron, a fermionic one, e.g. an electron plus attached phonon cloud. ".

Precisely something I was looking for, if you are still interested we can discuss
 
Note also that you cannot have a superposition of states with an even and odd number of fermions.
This is calles univalence superselection rule. It is easiest to see from the fact that such a superposition is not invariant (not even up to a phase) under a rotation by 2π.
 

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