  In the setup of isolated quantum systems, it is proved that the thermodynamic
entropy and the diagonal entropy must increase extensively in any nontrivial
quantum quench. The extensive increase of the thermodynamic entropy is shown
for any initial state (even for a pure state) that represents thermal
equilibrium. On the other hand, the extensive increase of the diagonal entropy
is shown for any stationary initial state under the condition that both the
pre-quench and the post-quench Hamiltonians satisfy the eigenstate
thermalization hypothesis.
