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Multiple choice
A two-qubit state is written as
c
00
∣
00
⟩
+
c
01
∣
01
⟩
+
c
10
∣
10
⟩
+
c
11
∣
11
⟩
c_{00}|00\rangle + c_{01}|01\rangle + c_{10}|10\rangle + c_{11}|11\rangle
c
00
∣00
⟩
+
c
01
∣01
⟩
+
c
10
∣10
⟩
+
c
11
∣11
⟩
with
c
00
=
1
/
2
c_{00} = 1/\sqrt{2}
c
00
=
1/
2
,
c
11
=
1
/
2
c_{11} = 1/\sqrt{2}
c
11
=
1/
2
, and
c
01
=
c
10
=
0
c_{01} = c_{10} = 0
c
01
=
c
10
=
0
. What is the marginal probability that qubit 0 is measured as 0,
P
(
q
0
=
0
)
=
∣
c
00
∣
2
+
∣
c
01
∣
2
P(q0=0) = |c_{00}|^2 + |c_{01}|^2
P
(
q
0
=
0
)
=
∣
c
00
∣
2
+
∣
c
01
∣
2
?
1
1
/
2
≈
0.707
1/\sqrt{2} \approx 0.707
1/
2
≈
0.707
0.25
0.5
Check answer