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Homework Help: Quantum expectation values

  1. Sep 28, 2010 #1
    I'm not sure why PhysicsForums.com isn't displaying my latex properly so I have attached a PDF of the question.

    1. The problem statement, all variables and given/known data
    Show that, for a 3D wavepacket,

    [itex] \frac{d\langle x^2 \rangle}{dt} $=$ \frac{1}{m}(\langle xp_{x} \rangle+\langle p_{x}x \rangle) [/itex]

    3. The attempt at a solution
    Through several pages of algebra and taking divergences I have come to the following.

    [itex] \frac{d\langle x^2\rangle}{dt} $=$ \frac{ih}{2m}\int\int\int{x^{2}(\psi\frac{\partial^{2}{\psi^{*}}}{\partial{x^{2}}}-\psi^{*}\frac{\partial^{2}{\psi}}{\partial{x^{2}}})+4x(\psi\frac{\partial{\psi^{*}}}{\partial{x}}}-\psi^{*}\frac{\partial{\psi}}{\partial{x}})\,dx\,dy\,dz [/itex]

    I know the values of <x> and <p> and that my equation must, somehow (if correct), equate to the problem statement. I'm not quite sure if I just don't know how to finish this problem or if my solution thus far is incorrect.
     

    Attached Files:

  2. jcsd
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