  We provide further characterization of non-Markovian quantum dynamics based
on the concept of divisible dynamical maps. In analogy to entanglement witness
we propose a non-Markovianity witness and introduce the corresponding measure
of non-Markovianity. We also provide characterization of non-Markovianity in
terms of entropic quantities, fidelity and Wigner-Yanase-Dyson skew
information.
