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Multiple choice
A qubit starts in
∣
0
⟩
|0\rangle
∣0
⟩
and passes through two independent bit-flip channels, each flipping the state with probability
p
=
0.3
p = 0.3
p
=
0.3
. It ends in
∣
0
⟩
|0\rangle
∣0
⟩
only if neither or both flips fire:
P
(
0
)
=
(
1
−
p
)
2
+
p
2
P(0) = (1-p)^2 + p^2
P
(
0
)
=
(
1
−
p
)
2
+
p
2
. What is
P
(
measuring
∣
0
⟩
)
P(\text{measuring } |0\rangle)
P
(
measuring
∣0
⟩)
at the end?
🔬 try it before you answer
0.49
0.58
0.42
0.7
Check answer