  The transfer of charge between different regions of a phase-coherent
mesoscopic sample is investigated. Charge transfer from a side branch quantum
dot into a ring changes the persistent current through a sequence of plateaus
of diamagnetic and paramagnetic states. In contrast, a quantum dot embedded in
a ring exhibits sharp resonances in the persistent current, whose sign is
independent of the number of electrons in the dot if the total number of
electrons in the system is even. It is shown that such a mesoscopic system can
be polarized appreciably not only by the application of an external voltage,
but also via an Aharonov-Bohm flux.
