Purity of a density operator
= Purity of a density operator
The purity of a density operator is $\operatorname{Tr}(\rho^2)$. It equals one exactly for a pure state; in finite dimension $d$ it lies between $1/d$ and $1$.
= Purity of a density operator
The purity of a density operator is $\operatorname{Tr}(\rho^2)$. It equals one exactly for a pure state; in finite dimension $d$ it lies between $1/d$ and $1$.