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Homework Help: 1d potential and switching between operators

  1. Nov 8, 2008 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    As a group we're stuck on this as a result of the lecturer saying that he wouldn't help us because we should work as a group and find other ways other than asking him about it. Which is fair enough - but none of us understand whats going on!

    So far I have tried substituting in for p in the middle of the bracket with -ihd/dx and then used the commutation relationship to try substituting ih for xp - px, but this seems to leave me being nowhere.

    I also tried starting with the bracket having H in the middle and substituting for that - this kind of left me with a bracket with p in the middle and one with x in the middle, but whilst this kind of left things in a format that almost looked correct the two brackets were not equal to one another, only additive.

    Could anyone suggest a starting point to look at or just any other helpful information that I may have missed when rereading my notes.
  2. jcsd
  3. Nov 8, 2008 #2
    Well, have you calculated [x,H]?

    Then you can calculate <n|[x,H]|n'> in two different ways: equating the two answers gives you the desired result.
  4. Nov 9, 2008 #3
    No I hadn't - I thought that was to do with the second part of the question.

    I shall give that a go now!
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