  We investigate the amplitude and phase effects of qubit dynamics and
excited-state population under the influence of a biharmonic control field. It
is demonstrated that the biharmonic driving field can have a significant effect
on the behavior of quasi-energy level crossing as well as on multiphoton
transitions. Also, the interference pattern for the populations of qubit
excited states is sensitive to the signal parameters. We discuss the
possibility of using these effects for manipulating qubit states and
calibrating nanosecond pulses.
