Stability and instability in parametric resonance and quantum Zeno   effect
  A quantum mechanical version of a classical inverted pendulum is analyzed. The stabilization of the classical motion is reflected in the bounded evolution of the quantum mechanical operators in the Heisenberg picture. Interesting links with the quantum Zeno effect are discussed. 
P. Facchi, H. Nakazato, S. Pascazio, J. Perina, and J. Rehacek