Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Spin 1/2 correlation

  1. Mar 12, 2012 #1
    Hello all,

    Imagine two spin 1/2 particles that are entangled, going towards two stern-gerlach apparatuses, with some relative angle. Now imagine one stern-gerlach device measures the spin of one of the particles as up. What is the chance that the other stern-gerlach device measures the spin to be down?

    For 90 degrees it would be 50/50, right? So my guess is [itex]cos^2 ({1 \over 2} \alpha)[/itex]. Is that correct?

    Thanks in advance
  2. jcsd
  3. Mar 13, 2012 #2
    You can look here , it is the same quastion.
  4. Mar 13, 2012 #3


    User Avatar
    Science Advisor
    Gold Member

    Yes, that's correct. I may have steered you wrong at an earlier time.
  5. Mar 13, 2012 #4
    Thanks for your answer. It doesn't seem to be the same question though - the question of that guy is a lot more advanced than mine. He is asking a question about the implication of the correlations, while I am simply looking for the actual formula for the correlation.

    From what I understand from that source, he takes into account two possibilities for the case [itex]\alpha = 90°[/itex]: a 50% correlation and a 100% correlation. I thought it was 50%, which would I believe indicate that I was right thinking the correlation is [itex]cos^2({1 \over 2} \alpha[/itex]. However, I'm not sure what he meant with the 100% correlation.

  6. Mar 13, 2012 #5
    I did ask the question earlier, and you were the one to answer it. But reading up later I assumed you were talking about the correlation as (a - b)/(a + b)? So I did wonder if it was simply a miscommunication, hence me asking the question again.

    But thank you again, for your answer now and for your answer last time.
  7. Mar 13, 2012 #6
    I am thet guy. :smile:
    As I understood of the answers to my question, the correct answer to your quastion it is
  8. Mar 13, 2012 #7
    Thus, yes, it is correct.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook