  The problem of recognizing (non-)Markovianity of a quantum dynamics is
revisited through analyzing quantum correlations. We argue that
instantaneously-vanishing quantum discord provides a necessary and sufficient
condition for Markovianity of a quantum map. This is used to introduce a
measure of non-Markovianity. This measure, however, requires demanding
knowledge about the system and the environment. By using a quantum correlation
monogamy property and an ancillary system, we propose a simplified measure with
less requirements. Non-Markovianity is thereby decided by quantum state
tomography of the system and the ancilla.
