We study numerically the one-dimensional quantum evolution of a coherent state when the particle is bound by a nonlinear force. Snapshots of the Husimi function show that there exist times where the initial Gaussian distribution in phase space splits into chains of $2,3,\dots$ distributions of similar form. During their finite lifetime the members of such a string are equally distributed along the classical orbit which passes through the center of the initial distribution, and they move along this curve with the corresponding velocity. This effect, which is generic for integrable bounded motion, is explained in terms of the quantum analogs of action and angle variables.

• Received 24 March 1995

DOI:https://doi.org/10.1103/PhysRevLett.75.990