|q⟩
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A bit-flip channel acts on
∣
0
⟩
|0\rangle
∣0
⟩
as
ρ
′
=
(
1
−
p
)
∣
0
⟩
⟨
0
∣
+
p
∣
1
⟩
⟨
1
∣
\rho' = (1-p)|0\rangle\langle 0| + p|1\rangle\langle 1|
ρ
′
=
(
1
−
p
)
∣0
⟩
⟨
0∣
+
p
∣1
⟩
⟨
1∣
, applying
X
X
X
with probability
p
=
0.3
p = 0.3
p
=
0.3
. What is
P
(
measuring
∣
1
⟩
)
P(\text{measuring } |1\rangle)
P
(
measuring
∣1
⟩)
on the output?
🔬 try it before you answer
0.3
0.15
0.7
0.5
Check answer