How Does the Angle Between Axes Affect Spin Correlation in Entangled Particles?

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Discussion Overview

The discussion centers on the correlation of spin measurements between two entangled particles when measured along axes that form a specific angle "a". Participants explore the mathematical relationships governing this correlation, particularly for spin 1/2 particles and spin 1 particles, and consider implications in experimental setups like Stern-Gerlach devices.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant, gespex, inquires about the correlation between spin measurements of entangled particles at an angle "a", suggesting that it might be expressed as "cos a" or "cos^2 a" for angles less than 45 degrees.
  • Another participant clarifies that for spin 1/2 particles, the correlation is "cos a", while for spin 1 particles, it is "cos^2 a".
  • A later post introduces a scenario involving two Stern-Gerlach devices, questioning the probability of measuring up-spin at the second device, initially expecting it to be "cos a", but later finding it to be "cos^2(a/2)".

Areas of Agreement / Disagreement

Participants express differing views on the correlation formulas for various types of particles and the implications of measurement setups, indicating that multiple competing views remain without a consensus on the exact relationships.

Contextual Notes

Some assumptions about the nature of entangled particles and the specific conditions of measurement setups are not fully detailed, leading to potential ambiguities in the discussion.

gespex
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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.

Thanks in advance,
gespex
 
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gespex said:
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.

Thanks in advance,
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).

Thanks in advance
 
Last edited:

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