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Multiple choice
A phase-damping channel with
L
=
0.5
L = 0.5
L
=
0.5
has Kraus operators
K
0
=
[
1
0
0
1
−
L
]
K_0 = \begin{bmatrix}1 & 0 \\ 0 & \sqrt{1-L}\end{bmatrix}
K
0
=
[
1
0
0
1
−
L
]
and
K
1
=
[
0
0
0
L
]
K_1 = \begin{bmatrix}0 & 0 \\ 0 & \sqrt{L}\end{bmatrix}
K
1
=
[
0
0
0
L
]
. It acts on
ρ
=
∣
+
⟩
⟨
+
∣
=
[
0.5
0.5
0.5
0.5
]
\rho = |+\rangle\langle +| = \begin{bmatrix}0.5 & 0.5 \\ 0.5 & 0.5\end{bmatrix}
ρ
=
∣
+
⟩
⟨
+
∣
=
[
0.5
0.5
0.5
0.5
]
. What is the survival probability
⟨
+
∣
E
(
ρ
)
∣
+
⟩
\langle +|E(\rho)|+\rangle
⟨
+
∣
E
(
ρ
)
∣
+
⟩
?
🔬 try it before you answer
0.854
0.75
0.5
1
Check answer