  We have studied the role of thermalization in lifetime reduction of quantum
memory based on multi-atomic ensembles. Herein, it is shown to be impossible to
remove the thermaization-caused decoherence in such systems using the methods
of dynamical decoupling. We have analyzed the existing models of the
thermalization and have proposed a new understanding of the thermalization as a
result of the internal processes which are not described in the unitary quantum
dynamics formalism. The possible ways for reducing the negative influence of
thermalization on the quantum memory lifetime are also discussed.
