Polarization of photons quantum mechanically

In summary, polarization is the spin degree of freedom of a photon in its quantum state. It is not something that is added on or changed by acting on the photon, but rather a fundamental aspect of its nature.
  • #1
sol47739
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I have some fundamental questions about the polarization of photons from the quantum mechanical perspective.
What is it of the photon that gets polarized from a quantum mechanical perspective? In the classical perspective it is often thought that it is the oscillating electric field that gets polarized. But in the quantum case: Is it the de Broglie wave function? Or is it the spin and in case it is the spin, how is the polarizing filter able to determine which kind of spin gets through? What is the polarizing filter made of incase it determines what kind of spin of the photons get’s through?
 
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  • #2
sol47739 said:
What is it of the photon that gets polarized from a quantum mechanical perspective?
The question is unanswerable because it is based on a false assumption. A photon doesn't "get polarized" by acting on some part of it. Polarization is just the spin part of the photon's quantum state.

Thinking of what is classically called "unpolarized light" is not a good way to approach photon polarization in QED. Classical "unpolarized light", in quantum terms, is (highly heuristically) just a huge number of photons with random polarizations, so the total polarization is negligible. But there is no such thing as an "unpolarized" single photon.
 
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  • #3
PeterDonis said:
But there is no such thing as an "unpolarized" single photon.
But that is a bit too facile it seems to me. Absent some asymmetry (perhaps a filter) the description of the photon is basis dependent. In particular one can have RHCP and LHCP or X and Y .
PeterDonis said:
A photon doesn't "get polarized" by acting on some part of it.
The polarization of "the photon" will produce an answer that depends upon the question. In that sense one "acts upon it".
 
  • #4
hutchphd said:
the description of the photon is basis dependent
The photon's state is not basis dependent. Its components might be, but that is true of any quantum system.

hutchphd said:
The polarization of "the photon" will produce an answer that depends upon the question.
You can change the polarization part of a photon's state by measuring its polarization, yes. But that's true of any quantum system: a measurement, unless it already happens to be in an eigenstate of the measurement operator, will change the state.

hutchphd said:
In that sense one "acts upon it".
Perhaps, but I don't think that's what the OP meant. The OP seemed to me to be thinking of polarization as something you "do" to some part of the photon. That's not correct. Polarization is, as I said, the spin part of the photon's state. Or, if you like, it's the spin degree of freedom of the photon. It's not something you "add on" to a photon by doing something to it: that spin degree of freedom is always there.
 
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FAQ: Polarization of photons quantum mechanically

1. What is the concept of polarization of photons in quantum mechanics?

The polarization of photons refers to the direction of the electric field oscillation of a photon. In quantum mechanics, photons can exist in a superposition of different polarization states, meaning they can have multiple orientations of their electric field simultaneously.

2. How is the polarization of photons measured in quantum mechanics?

In quantum mechanics, the polarization of photons can be measured using a polarizer, which is a device that only allows photons with a specific polarization to pass through. By rotating the polarizer, the polarization of the photons can be determined based on the intensity of light that passes through.

3. Can the polarization of photons be changed in quantum mechanics?

Yes, the polarization of photons can be changed in quantum mechanics through a process called quantum entanglement. By entangling two photons, their polarizations become correlated, meaning that changing the polarization of one photon will also change the polarization of the other.

4. How does the polarization of photons affect their behavior in quantum mechanics?

The polarization of photons plays a crucial role in various quantum phenomena, such as the double-slit experiment and quantum teleportation. It also affects the interaction of photons with matter, as certain materials only interact with photons of specific polarizations.

5. Is the polarization of photons a fundamental property in quantum mechanics?

Yes, the polarization of photons is considered a fundamental property in quantum mechanics. It is one of the intrinsic quantum numbers that describes the state of a photon and is conserved in all interactions. It also plays a significant role in the quantum description of light and its interactions with matter.

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