  In this paper, we investigate coherence protection of a quantum system
coupled to a hierarchical environment by utilizing noise. As an example, we
solve the Jaynes-Cummings (J-C) model in presence of both a classical and a
quantized noise. The master equation is derived beyond the Markov
approximation, where the influence of memory effects from both noises is taken
into account. More importantly, we find that the performance of the coherence
protection sensitively depends on the non-Markovian properties of both noises.
By analyzing the mathematical mechanism of the coherence protection, we show
the decoherence caused by a non-Markovian noise with longer memory time can be
suppressed by another Markovian noise with shorter memory time. Last but not
least, as an outlook, we try to analyze the connection between the atom-cavity
entanglement and the atomic coherence, then discuss the possible clue to search
for the required noise. The results presented in this paper show the
possibility of protecting coherence by utilizing noise and may open a new path
to design noise-assisted coherence protection schemes.
