  Generic one-parameter billiards are studied both classically and quantally.
The classical dynamics for the billiards makes a transition from regular to
fully chaotic motion through intermediary soft chaotic system. The energy
spectra of the billiards are computed using finite element method which has not
been applied to the euclidean billiard. True generic quantum chaotic
transitional behavior and its sensitive dependence on classical dynamics are
uncovered for the first time. That is, this sensitive dependence of quantum
spectral measures on classical dynamics is a genuine manifestation of quantum
chaos.
