  The control of open quantum systems has a fundamental relevance for fields
ranging from quantum information processing to nanotechnology. Typically, the
system whose coherent dynamics one wants to manipulate, interacts with an
environment that smoothly degrades its quantum dynamics. Thus, a precise
understanding of the inner mechanisms of this process, called "decoherence", is
critical to develop strategies to control the quantum dynamics. In this thesis
we solved the generalized Liouville-von Neumann quantum master equation to
obtain the dynamics of many-spin systems interacting with a spin bath. We also
solve the spin dynamics within the Keldysh formalism. Both methods lead to
identical solutions and together gave us the possibility to obtain numerous
physical predictions that contrast well with Nuclear Magnetic Resonance
experiments. We applied these tools for molecular characterizations,
development of new numerical methodologies and the control of quantum dynamics
in experimental implementations. But, more important, these results contributed
to fundamental physical interpretations of how quantum dynamics behaves in open
systems. In particular, we found a manifestation of an environmentally induced
quantum dynamical phase transition.
