There is something I do not understand. One way to define the current density operator is through the particle density operator Ï(r). From the fundamental interpretation of the wavefunction we have:(adsbygoogle = window.adsbygoogle || []).push({});

Ï(r)= lÏˆ(r)l^{2}

But my book takes this a step further by rewriting the equality above:

lÏˆ(r)l^{2}= âˆ«dr' Ïˆ*(r')Î´(r-r')Ïˆ(r')

And thus identifies the particle density operator as the delta function above. How does this make sense in any way?

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# Particle density operator

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