  Two advantageous roles of the influence of measurement on a system subject to
coherent control are exposed using a five-level model system. In particular, a
continuous measurement of the population in a branch state in the Kobrak-Rice
extended stimulated Raman adiabatic passage scheme is shown to provide a
powerful means for controlling the population transfer branching ratio between
two degenerate target states. It is demonstrated that a measurement with a
large strength may be used to completely shut off the yield of one target state
and that the same measurement with a weak strength can dramatically enhance the
robustness of the controlled branching ratio against dephasing.
