Coherent versus noncoherent Bloch oscillations in the presence of direct and alternating fields

We first study noncoherent Bloch oscillations in ultrasmall-capacitance normal tunnel junctions using the semiclassical approach. We then study coherent Bloch oscillations in other systems showing an energy spectrum similar to the ``nearly-free-electron'' model in the extended--Brillouin-zone picture, and compare the two pictures. In the latter we calculate the response to a constant driving force, including both Zener tunneling and inelastic transitions between the energy bands. For both cases we also calculate the response of the system to an alternating driving force. In particular we calculate the size of the interference steps and show that a mesoscopic junction (either normal or Josephson) can be used as a phase-voltage converting element. Results are presented in a form suitable for comparison with experiment. We suggest specific experiments to verify our predictions.