  Exchange of information between a quantum system and its surrounding
environment plays a fundamental role in the study of the dynamics of open
quantum systems. Here we discuss the role of the information exchange in the
non-Markovian behavior of dynamical quantum processes following the decoherence
approach, where we consider a quantum system that is initially correlated with
its measurement apparatus, which in turn interacts with the environment. We
introduce a new way of looking at the information exchange between the system
and environment using the quantum loss, which is shown to be closely related to
the measure of non-Markovianity based on the quantum mutual information. We
also extend the results of [Phys. Rev. Lett. 112, 210402 (2014)] by Fanchini et
al. in several directions, providing a more detailed investigation of the use
of the accessible information for quantifying the backflow of information from
the environment to the system. Moreover, we reveal a clear conceptual relation
between the entanglement and mutual information based measures of
non-Markovianity in terms of the quantum loss and accessible information. We
compare different ways of studying the information flow in two theoretical
examples. We also present experimental results on the investigation of the
quantum loss and accessible information for a two-level system undergoing a
zero temperature amplitude damping process. We use an optical approach that
allows full access to the state of the environment.
