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Multiple choice
A spin-1/2 qubit is in state
∣
0
⟩
|0\rangle
∣0
⟩
. For the Pauli observable
σ
x
\sigma_x
σ
x
, the expectation values are
⟨
σ
x
⟩
=
0
\langle\sigma_x\rangle = 0
⟨
σ
x
⟩
=
0
and
⟨
σ
x
2
⟩
=
1
\langle\sigma_x^2\rangle = 1
⟨
σ
x
2
⟩
=
1
(since
σ
x
2
=
I
\sigma_x^2 = I
σ
x
2
=
I
). What is the uncertainty
Δ
σ
x
=
⟨
σ
x
2
⟩
−
⟨
σ
x
⟩
2
\Delta\sigma_x = \sqrt{\langle\sigma_x^2\rangle - \langle\sigma_x\rangle^2}
Δ
σ
x
=
⟨
σ
x
2
⟩
−
⟨
σ
x
⟩
2
?
🔬 try it before you answer
1
1/2
2
\sqrt{2}
2
0
Check answer