  The revival structure of wave packets is examined for quantum systems having
energies that depend on two nondegenerate quantum numbers. For such systems,
the evolution of the wave packet is controlled by two classical periods and
three revival times. These wave packets exhibit quantum beats in the initial
motion as well as new types of long-term revivals. The issue of whether
fractional revivals can form is addressed. We present an analytical proof
showing that at certain times equal to rational fractions of the revival times
the wave packet can reform as a sum of subsidiary waves and that both
conventional and new types of fractional revivals can occur.
