# Entangled spin correlation

Given two entangled particles, and the spin of both is measured along two separate axes making an angle of "a", what is the correlation between the two? So how much of the particles will give the same "answer" to the spin measurement?

I've tried googling, but the answers I did find were mathematically too complex for me, though from what I have read it seems it shouldn't be much more than "cos a" or "cos^2 a" for an angle of a < 45 degrees.

gespex

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DrChinese
Gold Member
Given two entangled particles, and the spin of both is measured along two separate axes making an angle of "a", what is the correlation between the two? So how much of the particles will give the same "answer" to the spin measurement?

I've tried googling, but the answers I did find were mathematically too complex for me, though from what I have read it seems it shouldn't be much more than "cos a" or "cos^2 a" for an angle of a < 45 degrees.

gespex
For spin 1/2 particles, such as electrons: cos a
For spin 1 particles, such as photons: cos^2 a

Thank you, once again! ;-)

I have another question about this after all. Imagine two stern-gerlach devices in a row, where the particles with up-spin go through the second with an angle a relative to the first. What is the chance the particle has an up-spin at the second stern-gerlach device as well?

I expected it to be the same (cos a), but I tested it in an applet and it seems to be different after all...

Edit: Never mind, I found the answer. cos^2(a/2).