Quantum Chaos via the Quantum Action
  We discuss the concept of the quantum action with the purpose to characterize and quantitatively compute quantum chaos. As an example we consider in quantum mechanics a 2-D Hamiltonian system - harmonic oscillators with anharmonic coupling - which is classically a chaotic system. We compare Poincar\'e sections obtained from the quantum action with those from the classical action. 
H. Kr\"oger