  In this paper, we use the quantum state diffusion (QSD) equation to implement
the Uhrig dynamical decoupling (UDD) to a three-level quantum system coupled to
a non-Markovian reservoir comprising of infinite numbers of degrees of freedom.
For this purpose, we first reformulate the non-Markovian QSD to incorporate the
effect of the external control fields. With this stochastic QSD approach, we
demonstrate that an unknown state of the three-level quantum system can be
universally protected against both colored phase and amplitude noises when the
control-pulse sequences and control operators are properly designed. The
advantage of using non-Markovian quantum state diffusion equations is that the
control dynamics of open quantum systems can be treated exactly without using
Trotter product formula and be efficiently simulated even when the environment
comprise of infinite numbers of degrees of freedom. We also show how the
control efficacy depends on the environment memory time and the designed time
points of applied control pulses.
