# Heisenburg and polarization

Hello, I am doing a small presentation on Quantum Cryptology this next week, and need a little help relating HUP and polarization of photons.

I understand that when you polarize a photon on a basis of say 45* the photon simultaneously exist in both the horizontal and vertical polarizations at the same time. With that said, I really need someone to break down HUP with polarization...

What I don't get: When you vertically polarize a photon (light) how you can set a second filter to polarize it at 45* but not 0* (horizontally, where it will be fully absorbed).

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What I don't get: When you vertically polarize a photon (light) how you can set a second filter to polarize it at 45* but not 0* (horizontally, where it will be fully absorbed).
That's already true in classical EM.

DrChinese
Gold Member
Hello, I am doing a small presentation on Quantum Cryptology this next week, and need a little help relating HUP and polarization of photons.

I understand that when you polarize a photon on a basis of say 45* the photon simultaneously exist in both the horizontal and vertical polarizations at the same time. With that said, I really need someone to break down HUP with polarization...

What I don't get: When you vertically polarize a photon (light) how you can set a second filter to polarize it at 45* but not 0* (horizontally, where it will be fully absorbed).
Assuming I understand the question: This is done with something that alters the phase of the wave, usually a wave plate. A half-wave plate will do the trick, and can be used to shift the polarization to any specific angle. A filter will do it too, but half of the light is not transmitted.

To relate to the HUP: If you know the polarization is vertical, then you end up with complete uncertainty of the polarization at 45 degrees - and vice versa. Any angle in-between corresponds to know some about one and some about the other.