A 300-nm-diameter gate is used to introduce an antidot or artificial impurity into a quantum wire defined in an AlxGa1-xAs/GaAs two-dimensional electron gas. At low magnetic fields, geometry-induced quantum interference effects are observed, while at higher fields adiabatic edge-state transport is established. In the transitional regime, conductance resonances due to magnetically bound impurity states exhibit distinct characteristics including beating, sharp period changes, and spin splitting. An asymmetry is observed between the resonances observed as a function of magnetic field and gate voltage. The results are explained by a model based on an interedge-state coupling mechanism. © 1994 The American Physical Society.