Density Matrix & Purity — Bloch Ball
Pure states live on the sphere surface (purity=1); mixed states fill the interior
Channel:
Dephasing
Amplitude Damping
Depolarizing
Reset / Pure State
Rate γ:
0.30
Initial θ:
90°
Initial φ:
0°
Tr(ρ²)=1 → pure state
Tr(ρ²)=½ → maximally mixed
Dephasing: x,y decay → z stable
Amp.damp: relax to |0⟩
Depolar: shrink uniformly