Characterisation of Open Quantum System Dynamics based on Information Back-flow

Abstract: For unital dynamics, we show that a generalized trace distance measure offers no advantage over the trace distance measure for witnessing non-Markovianity. We determine the class of non-unital channels where the standard trace distance measure is insufficient here and the generalized measure is necessary. Finally, we assess the status of the GTD measure as an indicator of information flow between an open system and its environment.