  We present time-dependent results describing the current through a molecular
device, modeled as a complex with two active centers connected to leads under
bias. We show that, at a properly adjusted external voltage, a passing
terahertz electromagnetic pulse may cause a transition between states of finite
and negligible current, suggesting that the system might be useful as a
nanoscopic switch in the terahertz range. A phase diagram defining the bias
region in which the transition takes place within a short time is given. As
described, the physical processes involved are of an entirely different nature
than those in ordinary photodetectors.
