  In quantum Hall systems with two narrow constrictions, tunneling between
opposite edges can give rise to quantum interference and Aharonov-Bohm-like
oscillations of the conductance. When there is an integer quantized Hall state
within the constrictions, a region between them, with higher electron density,
may form a compressible island. Electron-tunneling through this island can lead
to residual transport, modulated by Coulomb-blockade type effects. We find that
the coupling between the fully occupied lower Landau levels and the
higher-partially occupied level gives rise to flux subperiods smaller than one
flux quantum. We generalize this scenario to other geometries and to fractional
quantum Hall systems, and compare our predictions to experiments.
