Sensitivity to measurement errors in the quantum kicked top

We address the problem of chaos in quantum systems in terms of the sensitivity of the evolution of individual quantum states to errors in measurements. Specifically, we generate quantum trajectories of the quantum kicked top by considering discrete measurements on individual states as they evolve. If an error occurs when recording the results of the measurements we can calculate the difference between the true quantum state and the state inferred from the measurement results. Not surprisingly, the results depend on the strength of the measurement back action and also on whether the initial state is centered in a regular or chaotic region of the corresponding classical phase space. For measurements with a strong back action we find that the initial chaotic state shows sensitivity to measurement errors, but an initial regular state does not. [S1050-2947(99)10002-7].