  We present a method for achieving complete population transfer in a two-state
quantum system via adiabatic time evolution in which, contrary to conventional
rapid adiabatic passage produced by chirped pulses, there occurs no crossing of
diabatic energy curves: there is no sign change of the detuning. Instead, we
use structured pulses, in which, in addition to satisfying conditions for
adiabatic evolution, there occurs a sign change of the Rabi frequency when the
detuning is zero. We present simulations that offer simple geometrical
interpretation of the two-dimensional motion of the Bloch vector for this
system, illustrating how both complete population inversion and complete
population return occur for different choices of structured pulses.
