  Quantum mechanical objects or nanoobjects have been proposed as bits for
information storage. While time-averaged properties of magnetic,
quantum-mechanical particles have been extensively studied experimentally and
theoretically, experimental investigations of the real time evolution of
magnetization in the quantum regime were not possible until recent developments
in pump-probe techniques. Here we investigate the quantum dynamics of effective
spin systems by means of analytical and numerical treatments. Particular
attention is paid to the quantum revival time and its relation to the
magnetization tunneling. The quantum revival time has been initially defined as
the recurrence time of a total wave-function. Here we show that the quantum
revivals of wave-functions and expectation values in spin systems may be quite
different which gives rise to a more sophisticated definition of the quantum
revival within the realm of experimental research. Particularly, the revival
times for integer spins coincide which is not the case for half-integer spins.
Furthermore, the quantum revival is found to be shortest for integer ratios
between the on-site anisotropy and an external magnetic field paving the way to
novel methods of anisotropy measurements. We show that the quantum tunneling of
magnetization at avoided level crossing is coherent to the quantum revival time
of expectation values, leading to a connection between these two fundamental
properties of quantum mechanical spins.
