Correlated and Critical Phenomena in Multipartite Quantum Non-Markovianity

We consider the problem of the general assessment of non-Markovianity in multipartite open quantum systems. To this end, we elaborate on a previously introduced non-Markovian measure to formulate a finite and additive quantifier with appropriate asymptotic behavior. We then study the dynamics of two two-level atoms in a resonant cavity as a function of their interatomic distance using an exact treatment. We observe a critical behavior in the non-Markovianity in the form of a Markovian to non-Markovian transition at a finite distance and a discontinuity in the limit of infinitely close atoms. Additionally, in this limit of highly correlated dynamics, non-Markovianity can emerge when the size of the system exceeds a critical threshold.