Classical and quantum chaos in a circular billiard with a straight cut

We study classical and quantum dynamics of a particle in a circular billiar d with a straight cut. Classically, this system can be integrable, noninteg rable with soft chaos, or nonintegrable with hard chaos as we vary the size of the cut. We plot Poincare surfaces of section to study chaos. Quantum m echanically, we look at Husimi plots, and also use the quantum web, the tec hnique primarily used in spin systems so far, to try to see differences in quantum manifestations of soft and hard chaos. [S1063-651X(99)06508-3].