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-rw-r--r--content/know/concept/density-operator/index.pdc6
1 files changed, 5 insertions, 1 deletions
diff --git a/content/know/concept/density-operator/index.pdc b/content/know/concept/density-operator/index.pdc
index 84c2d74..39c2e85 100644
--- a/content/know/concept/density-operator/index.pdc
+++ b/content/know/concept/density-operator/index.pdc
@@ -45,11 +45,15 @@ $$\begin{aligned}
\end{aligned}$$
However, from the special case where $\ket{\Psi_n}$ are indeed basis vectors,
-we can conclude that $\hat{\rho}$ is Hermitian,
+we can conclude that $\hat{\rho}$ is positive semidefinite and Hermitian,
and that its trace (i.e. the total probability) is 100%:
$$\begin{gathered}
\boxed{
+ \hat{\rho} \ge 0
+ }
+ \qquad \qquad
+ \boxed{
\hat{\rho}^\dagger = \hat{\rho}
}
\qquad \qquad