(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

What are the conditions so that the matrix [itex]\hat{p}[/itex] describes the density operator of a pure state?

2. Relevant equations

[PLAIN]http://img846.imageshack.us/img846/2835/densitymatrix.png [Broken]

[itex]p=\sum p_{j}|\psi_{j}><\psi_{j}[/itex]

3. The attempt at a solution

I know that tr([itex]\rho[/itex])=1 for pure states.

But I do not know how to construct the density matrix. Or is it [itex]\hat{p}[/itex] already?

In my book, there is the example "hermitian, tr=1, [PLAIN]http://img89.imageshack.us/img89/4346/densitymatrixexample.png", [Broken] but I do not know how they constructed that.

Maybe I can just say a+d+e=1; c,b arbitrary?

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# Conditions for a density matrix; constructing a density matrix

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