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Multiple choice
A qubit is in the mixed (classically random) state that is
∣
0
⟩
|0\rangle
∣0
⟩
with probability
0.7
0.7
0.7
and
∣
1
⟩
|1\rangle
∣1
⟩
with probability
0.3
0.3
0.3
, so
ρ
=
d
i
a
g
(
0.7
,
0.3
)
\rho = \mathrm{diag}(0.7, 0.3)
ρ
=
diag
(
0.7
,
0.3
)
. The purity is
T
r
(
ρ
2
)
=
0.7
2
+
0.3
2
\mathrm{Tr}(\rho^2) = 0.7^2 + 0.3^2
Tr
(
ρ
2
)
=
0.
7
2
+
0.
3
2
. What is the purity?
🔬 try it before you answer
0.58
1.0
0.5
0.42
Check answer