Experimentally Verifying Photon Spin: Beyond Stern-Gerlach

In summary: I hope you can help me and explain for its. Thank you very much!why is graviton said to have spin 2.From what I know of thermal emmission, as long as a transition between two states has a net oscillating electric or magnetic moment, the transition will procede. Regardless of the net change of spin.
  • #1
jostpuur
2,116
19
I just realized I don't know a simple thing. How do you experimentally verify, that photons are spin 1 particles? At least you cannot do it with the Stern-Gerlach experiment, because photons are not charged. The polarization effect is usually somewhat identified with the spin, but is it really the same? How do you calculate the theory of polarization measurements from the quantum mechanical principles? I've seen only classical explanations.

Suppose I throw a wild idea, that the electromagnetic potential is a 2nd-rank tensor [itex]A^{\mu\nu}[/itex], and four component potential has worked as an approximation of this, because they both give the Coulomb's force similarly, and the weak magnetic effects are the same (hopefully, I'm not 100% sure). What's the experimental results that contradict this?
 
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  • #2
SG should work on photons -- it depends on the magnetic moment, not the charge. However, I don't know if the experiment can be done that way.

Does your wild idea have any predictions which are different from the usual models? If not, then occam's razor gets used on the extra components.
 
  • #3
I haven't thought about this much yet, which of course makes this a bad post. But I thought I could use some information, before trying to calculate stuff.

The 2nd-rank potential would be analogous to the gravitation, so I might guess the photon would be spin 2 then, as the gravitons are. I haven't really solved angular momentum of 2nd-rank field with Noether's theorem yet, but I've heard that the spin 2 is the result.
 
  • #4
jostpuur said:
I just realized I don't know a simple thing. How do you experimentally verify, that photons are spin 1 particles? At least you cannot do it with the Stern-Gerlach experiment, because photons are not charged. The polarization effect is usually somewhat identified with the spin, but is it really the same? How do you calculate the theory of polarization measurements from the quantum mechanical principles? I've seen only classical explanations.

Suppose I throw a wild idea, that the electromagnetic potential is a 2nd-rank tensor [itex]A^{\mu\nu}[/itex], and four component potential has worked as an approximation of this, because they both give the Coulomb's force similarly, and the weak magnetic effects are the same (hopefully, I'm not 100% sure). What's the experimental results that contradict this?

Er.. shouldn't this be verified simply via conservation laws?

For example, the dipole transition in atoms that resulted in the emission of photons requires a specific selection rule as far as the change in the angular momentum quantum number between the initial and final state. Unless one doesn't believe in that conservation law, one already has the evidence that the emitted photon must have a spin angular momentum of 1.

Zz.
 
  • #5
ZapperZ said:
Er.. shouldn't this be verified simply via conservation laws?

For example, the dipole transition in atoms that resulted in the emission of photons requires a specific selection rule as far as the change in the angular momentum quantum number between the initial and final state. Unless one doesn't believe in that conservation law, one already has the evidence that the emitted photon must have a spin angular momentum of 1.

Zz.

mhh... okey then.
 
  • #6
Hi everybody,
Can I ask about the photon spin. Photon as the theory has spin 1, in which -1 for left-circular polarization and +1 for right-circllar, but the spin 0 state data actually exists. So, the spin of photon in the ellipse polarization and linear polarization, and with natural light we can understand how? I hope you can help me and explain for its. Thank you very much!
 
  • #7
raj07 said:
why is graviton said to have spin 2.

are you not familiar with forum behaviour?

i) first try to google it

ii) ask question ONCE

iii) don't ask new, unrelated questions in already existing threads.
 
  • #8
ZapperZ said:
...shouldn't this be verified simply via conservation laws?

Zz.

Er...I don't think so. You would need to show that there is a particular transition which ought to otherwise occur, and the only reason it doesn't occur is because of spin conservation.

From what I know of thermal emmission, as long as a transition between two states has a net oscillating electric or magnetic moment, the transition will procede. Regardless of the net change of spin.
 
  • #9
conway said:
Er...I don't think so. You would need to show that there is a particular transition which ought to otherwise occur, and the only reason it doesn't occur is because of spin conservation.

Er... that's what the selection rule is!

Zz.
 
  • #10
katsiusa said:
Hi everybody,
Can I ask about the photon spin. Photon as the theory has spin 1, in which -1 for left-circular polarization and +1 for right-circllar, but the spin 0 state data actually exists. So, the spin of photon in the ellipse polarization and linear polarization, and with natural light we can understand how?

Circular polarization just specifies a particular pair of basis vectors. Photon
polarization can be expressed wrt other bases, eg linear. The circular
polarization basis is convenient because those states are eigenstates of
the angular momentum operator. A linear-polarized state can be
regarded as a superposition of those two circularly polarized eigenstates.

"Natural" light (by which I presume you mean incoherent light from the sun,
or some other hot substance) needs to be described by a mixed state.
Cf. http://en.wikipedia.org/wiki/Mixed_state

See also "Stokes parameters",
http://en.wikipedia.org/wiki/Stokes_parameters

Jackson, "Classical Electrodynamics", also explains a bit more
about the relevance of Stokes parameters in measurements
of polarization.

HTH.
 
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  • #11
ZapperZ said:
Er... that's what the selection rule is!

Zz.

I don't believe you can name a specific transition which illustrates your point.
 
  • #12
conway said:
I don't believe you can name a specific transition which illustrates your point.

I already had! Read the post that I made earlier!

ZapperZ said:
For example, the dipole transition in atoms that resulted in the emission of photons requires a specific selection rule as far as the change in the angular momentum quantum number between the initial and final state. Unless one doesn't believe in that conservation law, one already has the evidence that the emitted photon must have a spin angular momentum of 1.

Do you dispute this?

Zz.
 
  • #13
Yes, I dispute the "evidence" part. I don't believe the transitions, say, of the Hydrogen atom prove anything about the spin of the photon. Is that what you're claiming?
 
  • #14
conway said:
Yes, I dispute the "evidence" part. I don't believe the transitions, say, of the Hydrogen atom prove anything about the spin of the photon. Is that what you're claiming?

Yes.

So you're claiming that the atomic spectrum, as described in standard QM, is wrong?

Zz.
 
  • #15
If the standard QM is correct, the spin 1 of the photon is correct.
If we deny the spin 1 of the photon, we must insist other theories.

For example, in Sommerfeld's theory, the spectrum of the hydrogen (fine structure) is explained by the relativistic mass change (s and p orbital).

Later, in QM, using the selection rule (2S -- x -- 1S, 2P --O - 1S), the fine structure was explained by the spin-orbital interaction.

The energy difference between 2P1/2 and 2P3/2 state was accidentally consistent with the the energy difference by the relativistic mass diffference between S and P orbitals.
 
  • #16
We are not arguing whether quantum mechanics is correct or not. The claim was made that you can find experimental evidence for the spin of photons in the thermal spectrum of hydrogen gas. I believe this is incorrect.
 
  • #17
conway said:
We are not arguing whether quantum mechanics is correct or not. The claim was made that you can find experimental evidence for the spin of photons in the thermal spectrum of hydrogen gas. I believe this is incorrect.

Zz gave a standard correct texbook argument, cf the wiki article on http://en.wikipedia.org/wiki/Selection_rule" [Broken], and this argument can also be found as an example in books like Sakurai's, near the discussion of Wigner-Eckart.
 
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  • #18
conway said:
We are not arguing whether quantum mechanics is correct or not. The claim was made that you can find experimental evidence for the spin of photons in the thermal spectrum of hydrogen gas. I believe this is incorrect.

I know that you are incorrect. Open any QM text. You disputed what I said, which is right out of standard QM for a standard selection rule.

Based on the responses given by several others, and now based on the nature of YOUR responses, I believe this thread is now done.
 

1. What is photon spin and why is it important to verify experimentally?

Photon spin refers to the intrinsic angular momentum of a photon, a fundamental particle of light. It is important to verify experimentally because it is a fundamental property of photons and understanding it can help us better understand the nature of light and its interactions with matter.

2. How is the Stern-Gerlach experiment used to verify photon spin?

The Stern-Gerlach experiment involves passing a beam of particles through a magnetic field, which causes the particles to split into two beams based on their spin orientation. By performing this experiment on photons, we can observe the two resulting beams and determine the spin orientation of the photons.

3. What are some other experimental methods used to verify photon spin?

In addition to the Stern-Gerlach experiment, other methods such as Compton scattering, polarization measurements, and interference experiments can also be used to verify photon spin. These methods involve analyzing the behavior of photons when interacting with matter or other photons.

4. What challenges are faced when experimentally verifying photon spin?

One of the main challenges is that photons are massless particles, making it difficult to manipulate their spin orientation. Additionally, the act of measuring photon spin can also affect its state, making it challenging to obtain accurate results.

5. How does verifying photon spin contribute to our understanding of quantum mechanics?

Verifying photon spin helps us better understand the principles of quantum mechanics, which govern the behavior of particles at the subatomic level. It also allows us to test and refine our current theories and models of particle behavior, leading to a deeper understanding of the fundamental nature of our universe.

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