  We study the relation between isolated hypersurface singularities (e.g. ADE)
and the quantum cohomology ring by using spectral invariants, which are
symplectic invariants coming from Floer theory. We prove, under the assumption
that the quantum cohomology ring is semi-simple, that (1) if the smooth Fano
variety (or the symplectic manifold) degenerates to a Fano variety with an
isolated hypersurface singularity, then the singularity has to be an
$A_m$-singularity, (2) if the symplectic manifold contains an
$A_m$-configuration of Lagrangian spheres, then there are consequences on the
Hofer geometry, and that (3) the Dehn twist reduces spectral invariants.
