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A single-qubit density matrix is
ρ
=
[
0.5
0.25
0.25
0.5
]
\rho = \begin{bmatrix}0.5 & 0.25 \\ 0.25 & 0.5\end{bmatrix}
ρ
=
[
0.5
0.25
0.25
0.5
]
(real symmetric). What is its von Neumann entropy
S
=
−
∑
λ
log
2
(
λ
)
S = -\sum \lambda \log_2(\lambda)
S
=
−
∑
λ
lo
g
2
(
λ
)
, in bits?
0.5
0.918
0.811
1
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