I read that states are positive operators of unit trace - not elements of a vector space.(adsbygoogle = window.adsbygoogle || []).push({});

Is it referring to quantum states or all classical states?

I know operators are like minus, plus, square root and vectors are like rays in Hilbert space.. but why can't quantum states be vectors when in fact quantum state is rays in Hilbert space or vectors of unit 1?

Please give a gentler reply (take note of the B in the thread). Thank you.

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# B States as positive operators of unit trace

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