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So we have an observable K = [tex] \begin{bmatrix} 0 & -i \\ -i & 0 \end{bmatrix}[/tex]

and its eigenvectors are v1 = (-i, 1)^{T}and v2 = (i, 1)^{T}corresponding to eigenvalues 1 and -1, respectively.

Now if we take the outer products, we get these...

|1><1| = (-i, 1)^{T}*(i, 1) = [tex] \begin{bmatrix} 1 & -i \\ i & 1 \end{bmatrix}[/tex]

|-1><-1| = (i, 1)^{T}*(-i, 1) = [tex] \begin{bmatrix} 1 & i \\ -i & 1 \end{bmatrix}[/tex]

Then we add them and they sum up to form 2*(identity operator).

But isn't it supposed to sum up to the identity operator? What's wrong, or what happened?

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# Homework Help: QM: Sum of projection operators = identity operator?

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