# expectation vaules of commutator and anti commutator (momentum and position)

what is expectation vaules of commutator and anti commutator when the case is momentum and position. when the case is commutator: $$\langle i\hbar\rangle=?$$ when the case is anti commutator: $$\langle - i\hbar \rangle=?$$

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$i\hbar$ is simply a number, or if you must regard it as an operator, a multiple of the identity. So $\langle i\hbar \rangle=i\hbar$, and so is $\langle -i\hbar \rangle$.
By the way, anticommutator of $\hat{x}$ and $\hat{p}$ is not $[\hat{p},\hat{x}]$, but $\{\hat{x},\hat{p}\}=\hat{x}\hat{p}+\hat{p}\hat{x}$.
you means that $\langle -i\hbar\rangle=i\hbar$!? –  user8784 Jun 16 '12 at 11:32
$\langle -i\hbar\rangle= -i\hbar$. The expectation of any constant is just that constant. –  Siyuan Ren Jun 16 '12 at 13:00