Environmental correlations and Markovian to non-Markovian transitions in   collisional models
  We investigate the smallest set of requirements for inducing non-Markovian dynamics in a collisional model of open quantum systems. This is done by introducing correlations in the state of the environment and analyzing the divisibility of the quantum maps from consecutive time steps. Our model and results serve as a platform for the microscopic study of non-Markovian behavior as well as an example of a simple scenario of non-Markovianity with purely contractive maps, i.e. with no back-flow of information between system and environment. 
N. K. Bernardes, A. R. R. Carvalho, C. H. Monken, and M. F. Santos
quant-ph