  Through a combination of experiment and theory we establish the possibility
of achieving strong tuning of Fano resonances (FRs), by allowing their usual
two-path geometry to interfere with an additional, 'intruder', continuum. As
the coupling strength to this intruder is varied, we predict strong modulations
of the resonance line shape that, in principle at least, may exceed the
amplitude of the original FR itself. For a proof-of-concept demonstration of
this phenomenon, we construct a nanoscale interferometer from nonlocally
coupled quantum point contacts and utilize the unique features of their density
of states to realize the intruder. External control of the intruder coupling is
enabled by means of an applied magnetic field, in the presence of which we
demonstrate the predicted distortions of the FR. This general scheme for
resonant control should be broadly applicable to a variety of wave-based
systems, opening up the possibility of new applications in areas such as
chemical and biological sensing and secure communications.
