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Old Sep 5th 2015, 12:27 PM   #1
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Eigen Vector for Photon

I know that the spin matrix for the photon represents the photon's intrinsic angular momentum. Does the eigenvector for the photon's spin matrix represent something as well? It seems to me that it would be natural to think of it as giving the intrinsic angular velocity of the photon. But I don't know enough physics to know whether that makes any sense.
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Old Sep 5th 2015, 02:45 PM   #2
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I would have thought that it would be the eigenvalue that gives the angular momentum. I'm not a QM expert but thats how the energy operator works so I imagine its similar for angular momentum. That seems to be what the time independent Scrodinger equation seems to imply.

The eigenvector represents the quantum state.

Last edited by kiwiheretic; Sep 5th 2015 at 02:47 PM.
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Old Sep 7th 2015, 01:33 PM   #3
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kiwiheretic is correct, but I wish to make a comment.

Massless particles do not have (spin) angular momentum. For massless particles we talk about "helicity." I'm not going to post a link for this as you can pretty much describe helicity in terms of angular momentum, which negates what I just said. But strictly speaking the Mathematics involved with helicity are different from that of angular momentum.

For example, a massive particle with (spin) angular momentum of 1 is in one of three possible states: spin 1, spin 0, and spin -1. A massless particle with helicity 1 is in one of two possible states: helicity 1 and helicity -1. There is no such thing as a 0 helicity state. The photon is a helicity 1 particle.

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Old Sep 27th 2016, 05:06 AM   #4
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Eigen Vector for Photon

An eigenvector of a linear transformation is a vector that keeps pointing in the same direction if you apply the transformation to it.
Spin is intrinsic angular momentum and is quantized (as is all angular momentum) in half-integer units of h bar. Photons are spin-1 particles in contrast to electrons being spin 1/2.
Photons are quanta of the electromagnetic field and are traveling waves that have a time varying electric and magnetic field. The electric and magnetic fields are transverse to the direction of travel: that is if it is traveling in the z-direction the electric field can be in the x-direction and the magnetic field in the y-direction.
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