  The quantum transport in a narrow channel (NC) is studied in the presence of
a time-dependent delta-profile electric field.
  The electric field is taken to be transversely polarized, with frequency
$\omega$, causing inter-subband and inter-sideband transitions. Suppression in
the dc conductance $G$ is found, which escalates with the chemical potential.
There are structures in $G$ which are related to the quasi-bound states (QBS)
features. Major dip, and dip-and-peak, structures occur when an incident
electron makes transition to a subband edge by absorbing or emitting one, and
two, $\hbar\omega$, respectively. Structures associated with three
$\hbar\omega$ processes are recognized. The QBS are closely associated with the
singular density of states (DOS) at subband bottoms. Our results indicate that,
due to this singular features of the DOS, the interaction of the electron with
the electric field has to be treated beyond finite order perturbation.
