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Can post-measurement states have entropy larger than the original state?

The stronger inequality holds if $\rho$ is a pure state. You can see it from the fact that $\sqrt M \rho \sqrt M$ has unit rank if $\rho$ does. Thus in all such cases you have $S(\rho)=S(\rho_i)=0$ (...
glS's user avatar
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3 votes

Why are all Rényi entropies equal for Clifford dynamics?

In stabilizer states (which are the states produced by clifford dynamics) the entanglement spectrum is flat, i.e., all the non-zero Schmidt coefficients are equal. Starting from there, it is ...
Norbert Schuch's user avatar
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Why are all Rényi entropies equal for Clifford dynamics?

Let me report here a brief demonstration that I used to convince myself. The R'enyi entropies are \begin{equation*} S_\mathrm{A}^\alpha = \frac{1}{1-\alpha} \log_2 \text{Tr} (\rho_\mathrm{A}^{\...
gcemin's user avatar
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1 vote

How to prove that the mutual information is subadditive?

Unlike entropy, mutual information can be either subadditive or superadditive. If $A$, $B$, $C$ are bits with equal probabilities and $A=B=C$, then $$ I(A,B:C) = 1,\\ I(A:C) + I(B:C) = 2, $$ ...
Adam's user avatar
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