  We show that there are well separated families of quantum expanders with
asymptotically the maximal cardinality allowed by a known upper bound. This has
applications to the "growth" of certain operator spaces: It implies
asymptotically sharp estimates for the growth of the multiplicity of
$M_N$-spaces needed to represent (up to a constant $C>1$) the $M_N$-version of
the $n$-dimensional operator Hilbert space $OH_n$ as a direct sum of copies of
$M_N$. We show that, when $C$ is close to 1, this multiplicity grows as
$\exp{\beta n N^2}$ for some constant $\beta>0$. The main idea is to relate
quantum expanders with "smooth" points on the matricial analogue of the
Euclidean unit sphere. This generalizes to operator spaces a classical
geometric result on $n$-dimensional Hilbert space (corresponding to N=1). In an
appendix, we give a quick proof of an inequality (related to Hastings's
previous work) on random unitary matrices that is crucial for this paper.
