  Much interest has been drawn in recent years to the concept and realization
of Nanoelectromechanical systems (NEMS). NEMS are nanoscale devices that
combine mechanical and electrical dynamics in a strong interplay. The shuttle
devices are a particular kind of Nanoelectromechanical systems. The
characteristic component that gives the name to these devices is an oscillating
quantum dot of nanometer size that transfers electrons one-by-one between a
source and a drain lead. The device represents the nano-scale analog of an
electromechanical bell in which a metallic ball placed between the plates of a
capacitor starts to oscillate when a high voltage is applied to the plates.
  This thesis contains the description and analysis of the dynamics of two
realizations of quantum shuttle devices. We describe the dynamics using the
Generalized Master Equation approach: a well-suited method to treat this kind
of open quantum systems. We also classify the operating modes in three
different regimes: the tunneling, the shuttling and the coexistence regime. The
characterization of these regimes is given in terms of three investigation
tools: Wigner distribution functions, current and current-noise. The essential
dynamics of these regimes is captured by three simplified models whose
derivation from the full description is possible due to the time scale
separation of the particular regime. We also obtain from these simplified
models a more intuitive picture of the variety of different dynamics exhibited
by the shuttle devices.
