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Multiple choice
A depolarizing channel
E
(
ρ
)
=
(
1
−
p
)
ρ
+
p
(
I
/
2
)
E(\rho) = (1-p) \rho + p (I/2)
E
(
ρ
)
=
(
1
−
p
)
ρ
+
p
(
I
/2
)
with
p
=
0.4
p = 0.4
p
=
0.4
acts on
ρ
=
∣
0
⟩
⟨
0
∣
\rho = |0\rangle\langle 0|
ρ
=
∣0
⟩
⟨
0∣
. What is the purity
t
r
(
E
(
ρ
)
2
)
\mathrm{tr}(E(\rho)^2)
tr
(
E
(
ρ
)
2
)
of the output?
🔬 try it before you answer
1
0.6
0.5
0.68
Check answer