  Properties of the bound states of two quantum waveguides coupled via the
window of the width $s$ in their common boundary are calculated under the
assumption that the transverse electric field $\pmb{\mathscr{E}}$ is applied to
the structure. It is shown that the increase of the electric intensity brings
closer to each other fundamental propagation thresholds of the opening and the
arms. As a result, the ground state, which in the absence of the field exists
at any nonzero $s$, exhibits the energy $E_0$ decrease for the growing
$\mathscr{E}$ and in the high-field regime $E_0$ stays practically the same
regardless of the size of the connecting region. It is predicted that the
critical window widths $s_{cr_n}$, $n=1,2,\ldots$, at which new excited
localized orbitals emerge, strongly depend on the transverse voltage; in
particular, the field leads to the increase of $s_{cr_n}$, and, for quite
strong electric intensities, the critical width unrestrictedly diverges. This
remarkable feature of the electric-field-induced switching of the bound states
can be checked, for example, by the change of the optical properties of the
structure when the gate voltage is applied; namely, both the oscillator
strength and absorption spectrum exhibit a conspicuous maximum on their
$\mathscr{E}$ dependence and turn to zero when the electric intensity reaches
its critical value. Comparative analysis of the two-dimensional (2D) and 3D
geometries reveals their qualitative similarity and quantitative differences.
