Non-Markovianity criteria for open system dynamics

Understand

A universal definition of non-Markovianity for open systems dynamics is proposed.

• It is extended from the classical definition to the quantum realm by showing that a `transition' from the Markov to the non-Markov regime occurs when the correlations between the system and the environment, generated by their joint evolution, can no longer be neglected.
• The suggested definition is based on the comparison between measured correlation functions and those built by assuming that the system is in a Markov regime thus giving a figure of merit of the error coming from this assumption.
• It is shown that the knowledge of the dynamical map and initial condition of the system is not enough to fully characterise the non-Markovian dynamics of the reduced system.