|q⟩
Bad Qubits
Play
Quest
Questions
Learn
Playground
☕
← Question Bank
Multiple choice
A qubit has density matrix
ρ
=
[
0.75
0.25
0.25
0.25
]
\rho = \begin{bmatrix}0.75 & 0.25 \\ 0.25 & 0.25\end{bmatrix}
ρ
=
[
0.75
0.25
0.25
0.25
]
. Its purity is
T
r
(
ρ
2
)
\mathrm{Tr}(\rho^2)
Tr
(
ρ
2
)
. What is the purity?
🔬 try it before you answer
1.0 (would mean a pure state)
0.5 (maximally mixed)
0.75
0.625 (summed only the diagonal of
ρ
2
\rho^2
ρ
2
incorrectly)
Check answer