Collision models in quantum optics

Quantum collision models (CMs) provide ad- vantageous case studies for investigating major issues in open quantum systems theory, and especially quantum non-Markovianity. After reviewing their general de nition and distinctive features, we illustrate the emergence of a CM in a familiar quantum optics scenario. This task is carried out by highlighting the close connection between the well-known input-output formalism and CMs. Within this quantum optics framework, usual assumptions in the CMs’ literature – such as considering a bath of non- interacting yet initially correlated ancillas – have a clear physical origin.