  We study non-Markovian dynamics of a two level atom using pseudomode method.
Because of the memory effect of non-Markovian dynamics, the atom receives back
information and excited energy from the reservoir at a later time, which causes
more complicated behaviors than Markovian dynamics. With pseudomode method,
non-Markovian dynamics of the atom can be mapped into Markovian dynamics of the
atom and pseudomode. We show that by using pseudomode method and quantum jump
approach for Markovian dynamics, we get a physically intuitive insight into the
memory effect of non-Markovian dynamics. It suggests a simple physical meaning
of the memory time of a non-Markovian reservoir.
