  We numerically investigate statistical ensembles for the occupations of
eigenstates of an isolated quantum system emerging as a result of quantum
quenches. The systems investigated are sparse random matrix Hamiltonians and
disordered lattices. In the former case, the quench consists of sudden
switching-on the off-diagonal elements of the Hamiltonian. In the latter case,
it is sudden switching-on of the hopping between adjacent lattice sites. The
quench-induced ensembles are compared with the so-called "quantum
micro-canonical" (QMC) ensemble describing quantum superpositions with fixed
energy expectation values. Our main finding is that quantum quenches with
sparse random matrices having one special diagonal element lead to the
condensation phenomenon predicted for the QMC ensemble. Away from the QMC
condensation regime, the overall agreement with the QMC predictions is only
qualitative for both random matrices and disordered lattices but with some
cases of a very good quantitative agreement. In the case of disordered
lattices, the QMC ensemble can be used to estimate the probability of finding a
particle in a localized or delocalized eigenstate.
