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Homework Help: Quantum commutators

  1. Nov 21, 2006 #1


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    I have a question where I need to calculate commutators, but I just need to check one detail of this.

    I need to work out [x,xp]

    What I need to check is the following:

    [x,xp] = xxp - xpx

    but does this then mean that I get (x^2 p - X^2 p)
    or (X^2 p - something else)??

    Sorry about the lack of formatting, but hopefully you'll get what I mean.

  2. jcsd
  3. Nov 21, 2006 #2
    Assuming that you're talking one-dimension, is [x,p] = 0?
  4. Nov 21, 2006 #3

    Doc Al

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    Staff: Mentor

    No. Since x & p do not commute, you cannot swap their order.
  5. Nov 21, 2006 #4


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    So, I'll need to work that part out literally in order ie xpx ?

    Thanks, I'll give it a go
  6. Nov 22, 2006 #5


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    Science Advisor
    Homework Helper




    P.S. Certain care with the ops x & p_x is needed.
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