Exploring the Impact of Photon Polarization on Electron State Changes

In summary: Sorry, I misinterpreted your comment. You're correct that in QM you can have polarization states that are admixtures of spin states.
  • #1
msumm21
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TL;DR Summary
How does the polarization of a photon impact the state change of an electron that absorbs it
How does the polarization of a photon impact the state change of an electron that absorbs it? Presumably the change of an electrons state (including spin) differs based on the polarization of the photon it absorbs.
 
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  • #2
Polarization is the direction of the electric field. It's the direction the electron moves if the photon isn't absorbed. Absorbtion just complicates matters.
 
  • #3
Vanadium 50 said:
Polarization is the direction of the electric field.
Not in QM. In QM polarization is the spin of the photon. Which will in turn change the spin of the electron if the electron absorbs it. (Restrictions on what spin the electron can have also restrict what photons a particular electron can absorb.)
 
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  • #4
msumm21 said:
Presumably the change of an electrons state (including spin) differs based on the polarization of the photon it absorbs.
Your presumption is correct.
 
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  • #5
Thanks. Are there some simple examples available like
1. if a photon has polarization state X it can't be absorbed by an electron with spin Y
2. if a photon with polarization X is absorbed by an electron with spin Z it will change the electron's spin to U
 
  • #6
msumm21 said:
Are there some simple examples available
For free electrons, not really, because it's not really possible (at least not with our current technology) to observe a single free electron absorbing a single photon.

For electrons in atoms, we can at least observe transitions as spectral lines (although even then we're observing transitions in many atoms in, say, a gas, not just one atom), but I don't know how much experimental work has been done on this with light that has particular polarizations.

I believe many QM textbooks discuss the basic theoretical framework involved for electrons in atoms emitting and absorbing photons and the spin selection rules involved.
 
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  • #7
A single free electron can never absorb a single photon. It's kinematically impossible, i.e., you can't fulfill energy-momentum conservation and the on-shell conditions for electron and photon. Indeed in almost all textbooks on quantum mechanics you find at least the dipole selection rules derived.
 
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  • #8
msumm21 said:
Thanks. Are there some simple examples available like
1. if a photon has polarization state X it can't be absorbed by an electron with spin Y
2. if a photon with polarization X is absorbed by an electron with spin Z it will change the electron's spin to U
Feynman's Lectures on Physics, vol. 3, ch. 18-1 on electric dipole radiation.
Or (more fleshed out): Gordon Baym, Lectures on Quantum Mechanics, pp. 281ff.
 
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  • #9
PeterDonis said:
For electrons in atoms, we can at least observe transitions as spectral lines (although even then we're observing transitions in many atoms in, say, a gas, not just one atom), but I don't know how much experimental work has been done on this with light that has particular polarizations.

I believe many QM textbooks discuss the basic theoretical framework involved for electrons in atoms emitting and absorbing photons and the spin selection rules involved.

Bransden and Joachain discuss this in quite some detail in their book on the physics of atoms and molecules.

However, I would like to point out one thing that people often are not aware of: You cannot simply flip a spin using photon absorption. In dipole approximation (and also beyond) the interaction matrix element is proportional to r and acts only on position space, not on spin space, so there is no direct interaction. The magnetic part of the light field would of course work in principle, but is far too weak in any realistic scenario.
If spins are indeed flipped by optical means, in most cases the process involves spin-orbit coupling which provides some kind of link between position space and spin space.
 
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  • #10
Cthugha said:
You cannot simply flip a spin using photon absorption.
What about NMR? Or are you reluctant to talk of photons at radio frequencies?
 
  • #11
PeterDonis said:
Not in QM. In QM polarization is the spin of the photon.
A. The correspondaance theorem says these are (statistically) the same thing.
B. In QM you can have polarization states that are admixtures of spin states,
 
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  • #12
WernerQH said:
What about NMR? Or are you reluctant to talk of photons at radio frequencies?

Sorry, for being unclear. I was interpreting the initial remark about spectral lines to imply atomic transitions that change the principal quantum number. For magnetic dipole transitions, these are forbidden in the non-relativistic case, but become weakly allowed due to relativistic effects (spin orbit coupling). Magnetic dipole transitions such as hyperfine transitions or Zeeman transitions that do not change the principal quantum number are not subject to this limitation.
 
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What is the purpose of exploring the impact of photon polarization on electron state changes?

The purpose of this research is to understand how the polarization of photons, which are particles of light, affects the state of electrons, which are fundamental particles in atoms. This can provide insights into the behavior of matter and potentially lead to new applications in fields such as quantum computing and telecommunications.

How is the polarization of photons measured?

The polarization of photons can be measured using polarizers, which are filters that only allow light waves with a specific orientation of electric field to pass through. By analyzing the intensity and orientation of the light that passes through the polarizer, the polarization of the photons can be determined.

What methods are used to study the impact of photon polarization on electron state changes?

There are various experimental techniques used to study this phenomenon, including pump-probe spectroscopy, two-photon absorption, and angle-resolved photoemission spectroscopy. These methods involve shining polarized light onto a sample and measuring the resulting changes in the electron state using specialized equipment.

What are some potential applications of this research?

Understanding how photon polarization affects electron states can have practical applications in fields such as quantum computing, where the manipulation of electron states is crucial. This research can also contribute to the development of new technologies in telecommunications, such as using polarized light for secure communication.

What are some challenges faced in studying the impact of photon polarization on electron state changes?

One of the main challenges is the complexity of the interactions between photons and electrons. These interactions involve both classical and quantum mechanics, making it a difficult phenomenon to study and understand. Additionally, the experimental techniques used to study this impact require sophisticated equipment and precise control of experimental conditions.

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