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Quick question on Quantum Entanglement

  1. Jun 1, 2010 #1
    I'm sorry for the trouble, but I was hoping you guys could help me understand something about Quantum Entanglement.

    So if I measure the x-axis spin of an electron and get +1, then that implies the the other particle must have spin -1, correct? Also, what if I measure the spin of the particle, 6 times in a row? Will I continue to get the same spin of the particle or will the spin still be random? I'm guess that as soon as I measure the spin the first time, the wave function collapses and I am left with a definite spin.
  2. jcsd
  3. Jun 1, 2010 #2


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    Yup, that's it. You ask the same question, you get the same answer. (OK, maybe I oversimplified that one.)
  4. Jun 2, 2010 #3
    You are right in the first, but in measuring once you break the entangled state, and need a new set of test particles. Now you are stuck with the probabilistic nature of QM as you measure unique pair, after unique pair.
  5. Jun 2, 2010 #4
    Ah, so I guess that's why you can't send information instantaneously using Quantum Entanglement. Thanks for the help btw. I'm going to be visiting this forum more in hopes to better understanding Physics/Quantum Physics.
  6. Jun 2, 2010 #5
    From what I've read, Dr. Chinese is the well deserved guru of entanglement, and welcome to PF!
  7. Jun 3, 2010 #6
    Thank you, Geigerclick. I am actually going for my Ph.D in Mathematics (Almost finished with undergrad now). Mathematics is easily the most appealing of the Sciences to me; of course, Quantum Mechanics and Astrophysics are next. I really want to be a Theoretical Physicist one day, and I think there is no better way to start on that journey than here.
  8. Jun 3, 2010 #7
    If you subsequently measure the spin along the same axis it will be the same each time. You only return to probabilistic results if you try to measure spin along a different orthogonal axis (spin in x,y,z directions cannot be simultaneously fixed)

    You can demonstrate this by passing electrons through multiple filters arranged at different orientations in a Stern-Gerlach experiment. (Eg 50% will pass through the first "spin up" filter, but subsequently 100% of those will pass through another "spin up" filter)

    eg http://www.upscale.utoronto.ca/PVB/Harrison/SternGerlach/SternGerlach.html

    (The x-spin entanglement will be broken on the first measurement, it may be possible to measure in such a way that spin entanglement along the other orthogonal axes remains intact, DrC may have a reference)
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