  Dynamics of a state of interest coupled to a non-Markovian environment is
studied for the first time by concatenating the non-Markovian quantum state
diffusion (QSD) equation and the Feshbach projection operator partitioning
technique. An exact one-dimensional stochastic master equation is derived as a
general tool for controlling an arbitrary component of the system. We show that
the exact one-dimensional stochastic master equation can be efficiently solved
beyond the widely adapted second-order master equations. The generality and
applicability of this hybrid approach is justified and exemplified by several
coherence control problems concerning quantum state protection against leakage
and decoherence.
