Stern–Gerlach experiment with photons?

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SUMMARY

The discussion centers on the application of the Stern-Gerlach experiment to photons, highlighting that photons, which always possess a spin of 1, cannot be subjected to this experiment due to their lack of a magnetic dipole moment. Instead, the conversation suggests using calcite crystals to measure polarization, drawing parallels between the measurement of spin in particles like neutrons and polarization in photons. Participants clarify the distinctions between spin, magnetic dipole moments, and the behavior of different particles, including neutrons and neutrinos, in magnetic fields.

PREREQUISITES
  • Understanding of quantum mechanics concepts, specifically spin and polarization.
  • Familiarity with the Stern-Gerlach experiment and its implications.
  • Knowledge of particle physics, particularly regarding photons, neutrons, and neutrinos.
  • Basic understanding of magnetic dipole moments and their significance in particle behavior.
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  • Research the properties of photons, focusing on spin and polarization techniques.
  • Study the Stern-Gerlach experiment in detail, including its historical context and applications.
  • Explore the use of calcite crystals in measuring polarization and their experimental setups.
  • Investigate the role of magnetic dipole moments in particle physics, particularly for neutrons and neutrinos.
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Physicists, students of quantum mechanics, and anyone interested in the experimental measurement of particle properties, particularly in the context of spin and polarization.

cragar
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If we did this experiment with photons , the photon can have a spin of 1, 0 , -1 ,
right , so then we would expect to see 3 paths correct .
 
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cragar said:
If we did this experiment with photons , the photon can have a spin of 1, 0 , -1 ,
right , so then we would expect to see 3 paths correct .

No, because photons are unaffected by gradient of magnetic field. I believe we discussed this three weeks ago. See:

https://www.physicsforums.com/showthread.php?t=385607

There is a difference between spin and magnetic dipole moment.
 
ok i see , thanks for the answer. Then why are neutrons affected by the magnetic field
 
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cragar said:
ok i see , thanks for the answer. Then why are neutrons affected by the magnetic field

They have magnetic dipole moment. Reason this is so is neutron is composite particle made of three charged quarks.
 
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cragar said:
... the photon can have a spin of 1, 0 , -1 , right , so then we would expect to see 3 paths correct .

And, just to be clear - photons always have spin 1. They can have different projections of spin 1 and -1. If it was ordinary particle, it would also have 0 projection, but it doesn't. Long story short: lack of rest mass removes that state. If photons had 0 projection state, that would be seen as longitudinal polarized light.
 
cragar said:
If we did this experiment with photons , the photon can have a spin of 1, 0 , -1 ,
right , so then we would expect to see 3 paths correct .

If you replace the Stern-Gerlach apparatus with a calcite crystal then you can do the analogous experiment with photons.
 
eaglelake said:
If you replace the Stern-Gerlach apparatus with a calcite crystal then you can do the analogous experiment with photons.

Fair enough, but what would be the point? With AgBr (or some other silver) -> Silver Halide you're exploring the photographic process. With photons you'd be doing some kind of bastardized version of better experimental apparatus'.
 
Frame Dragger said:
Fair enough, but what would be the point? With AgBr (or some other silver) -> Silver Halide you're exploring the photographic process. With photons you'd be doing some kind of bastardized version of better experimental apparatus'.

I thought that the original post had to do with doing the
Stern-Gerlach experiment with photons. As pointed out, we cannot do the Stern-Gerlach experiment with photons. I am only pointing out that, just as Stern-Gerlach magnets are used to measure spin, Calcite crystals can be used to measure polarization. As you know, spin 1/2 particles have two eigenvalues, as does polarization. The Stern-Gerlach (Calcite crystal) experiment has two output channels, one for each possible value the spin (polarization). The physics of the two experiments is almost identical. If you understand one, then you understand the other. That's all I was trying to say!
Best wishes
 
eaglelake said:
I thought that the original post had to do with doing the
Stern-Gerlach experiment with photons. As pointed out, we cannot do the Stern-Gerlach experiment with photons. I am only pointing out that, just as Stern-Gerlach magnets are used to measure spin, Calcite crystals can be used to measure polarization. As you know, spin 1/2 particles have two eigenvalues, as does polarization. The Stern-Gerlach (Calcite crystal) experiment has two output channels, one for each possible value the spin (polarization). The physics of the two experiments is almost identical. If you understand one, then you understand the other. That's all I was trying to say!
Best wishes

Hence the "fair enough" that preceeded everything I said. I take your point.
 
  • #10
xlines said:
They have magnetic dipole moment. Reason this is so is neutron is composite particle made of three charged quarks.

ok so if we did this experiment with neutrons , then would we see two different paths for the neutrons , and would the neutrons deflect because of their spin or because of their magnetic moment .
And if we did this experiment with neutrinos what would we excpect to see , Neutrino's are neutral in charge but have a spin of 1/2
 
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  • #11
cragar said:
ok so if we did this experiment with neutrons , then would we see two different paths for the neutrons , and would the neutrons deflect because of their spin or because of their magnetic moment .
And if we did this experiment with neutrinos what would we excpect to see , Neutrino's are neutral in charge but have a spin of 1/2

WRONG>They would behave as a silver atom would, determined by their dipole moment, not their spin.<WRONG

EDIT: Ok... that's true for neutrons, which is what I read in the first sentence, then apparently ran with it an ignored that you were talking about neutrinos. The spin really should have given it away... sorry!
 
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  • #12
so a neutrino with no charge has a dipole moment , what gives it a dipole moment
 
  • #13
cragar said:
so a neutrino with no charge has a dipole moment , what gives it a dipole moment

EDIT: Sorry, tired... I forget we're talking about a neutrino, not a neutron; In my post #11 I was thinking "neutron".

Here is the answer to your question about neutrinos: http://www.fnal.gov/pub/inquiring/questions/neutrinospin.html

So, yes, their spin can be determined, but they have no magnetic dipole moment, but maybe a gravitoelectric one. and would fly past the apparatus as they would pass through the Earth.

Truly sorry, I shouldn't comment when tired... I tend to miss things like "-ino" at the end of "neutron" and I probably could have spared you confusion.
 
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  • #14
Frame Dragger said:
See post #4. If you want to do a bit of research you could take a crack at QCD, a fasciniting subject, but maybe basic E&M first.

But the neutrino has no subparticles
 
  • #15
cragar said:
But the neutrino has no subparticles

Yeah, I'm in EST (Eastern Standard time aka GMT -5:00) so... yeah, I was just being stupid and sleepy. Sorry crager.
 
  • #16
i see , thanks for your answers .
 
  • #17
cragar said:
i see , thanks for your answers .

Yeah, pity I couldn't have just made it an "answer" (singular) and not contradictory ones relating to completely different particles!

Thanks for letting me off easy. :wink:
 

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