  We have investigated experimentally the magnetoresistance of strongly
asymmetric double-wells. The structures were prepared by inserting a thin
Al$_{0.3}$Ga$_{0.7}$As barrier into the GaAs buffer layer of a standard
modulation-doped GaAs/Al$_{0.3}$Ga$_{0.7}$As heterostructure. The resulting
double-well system consists of a nearly rectangular well and of a triangular
well coupled by tunneling through the thin barrier. With a proper choice of the
barrier parameters one can control the occupancy of the two wells and of the
two lowest (bonding and antibonding) subbands. The electron properties can be
further influenced by applying front- or back-gate voltage.
