Quantum state sensitivity to initial conditions
  The different time-dependent distances of two arbitrarily close quantum or classical-statistical states to a third fixed state are shown to imply an experimentally relevant notion of state sensitivity to initial conditions. A quantitative classification scheme of quantum states by their sensitivity and instability in state space is given that reduces to the one performed by classical-mechanical Lyapunov exponents in the classical limit 
Gonzalo Garcia de Polavieja