In the two-dimensional isotropic parabolic potential barrier V(x,y)=V0−mγ2(x2+y2)/2, though it is a model of an unstable system in quantum
mechanics, we can obtain the stationary states corresponding to the real energy
eigenvalue V0. Further, they are infinitely degenerate. For the first few
eigenstates, we will find the stationary flows round a right angle that are
expressed by the complex velocity potentials W=±γz2/2.Comment: 12 pages, AmS-LaTeX, 4 figure