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I was reading

https://en.wikipedia.org/wiki/Fubini–Study_metric (qm section like always )

And can't figure out how to derive:

[tex]\gamma (\psi , \phi) = arccos \sqrt{\frac{<\psi|\phi><\phi|\psi>}{<\psi|\psi><\phi|\phi>}}[/tex]

I started with

[tex]\gamma (\psi , \phi) =|| |\psi> - |\phi>||= \sqrt{(<\psi|-<\phi|)(|\psi>-|\phi>)}=...[/tex]

as it is the distance between the two vectors (no?) but don't seem to get anywhere, help!!

NB: I assumed there the vectors are normalized + apologies for the dirac notation format.

Many thanks in advance!

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# I Fubini-Study metric of pure states

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