We propose a novel electronic quantum interferometer which exhibits strong quantum interference effects in the ballistic regime. This behavior is produced without introducing additional barriers along the electronic path. Rather, by modulating the channel width of one of the arms in a multiply connected quantum nanoconstriction, one can produce an effect similar to that of an applied retarding gate potential. Strong conductance oscillations are then produced by quantum interference between phase‐lagged propagating subbands in the different channels. We present results for typical structures, and discuss the dependence of these effects on electron path length and temperature.