A quantum-mechanical calculation of ballistic electron transport in a double-point-contact structure is presented. We include in our model structure the presence of side leads between opposite point contacts, a flared geometry around the corner of the intersection region, and a potential barrier in the constrictions. Nonadditivity of conductances is investigated for various geometries. When two constrictions are placed in close vicinity, the total transmission through the double quantum point contacts is determined by the narrower one. When the same number of channels are transmitted in both point contacts, the conductance takes a value between Ohmic addition and the adiabatic limit. A transmission resonance originating from bound states in the cavity region is observed when the side leads are pinched off, and is discussed in terms of the parity of the wave function.

• Received 27 January 1992

DOI:https://doi.org/10.1103/PhysRevB.45.13494