  To facilitate the transition of quantum effects from the controlled
laboratory environment to practical real-world applications, there is a
pressing need for scalable platforms. One promising strategy involves
integrating thermal vapors with nanostructures designed to manipulate atomic
interactions. In this tutorial, we aim to gain deeper insights into this by
examining the behavior of thermal vapors that are confined within nanocavities
or waveguides and exposed to near-resonant light. We explore the interactions
between atoms in confined dense thermal vapors. Our investigation reveals
deviations from the predictions of continuous electrodynamics models, including
density-dependent line shifts and broadening effects. In particular, our
results demonstrate that by carefully controlling the saturation of single
atoms and the interactions among multiple atoms using nanostructures, along
with controlling the geometry of the atomic cloud, it becomes possible to
manipulate the effective optical nonlinearity of the entire atomic ensemble.
This capability renders the hybrid thermal atom-nanophotonic platform a
distinctive and valuable one for manipulating the collective effect and
achieving substantial optical nonlinearities.
