  In this article we present an exact and unified description of wave-packet
dynamics in various 2D systems in presence of a transverse magnetic field. We
consider an initial minimum-uncertainty Gaussian wave-packet, and find that its
long term dynamics displays the universal phenomena of spontaneous collapse and
quantum revival. We estimate the timescales associated with these phenomena
based on very general arguments for various materials, whose carrier dynamics
is described either by the Schr\"odinger equation or by the Dirac equation.
