Gate controlled resonant widths in double-bend waveguides: bound states in the continuum.

We consider quantum transmission through double-bend [Formula: see text]- and Z-shaped waveguides controlled by the finger gate potential. Using the effective non-Hermitian Hamiltonian approach we explain the resonances in transmission. We show a difference in transmission in the short waveguides that is the result of different chirality in Z and [Formula: see text] waveguides. We demonstrate that the potential selectively affects the resonant widths resulting in the occurrence of bound states in the continuum.