  The integration of neutral atoms with nanophotonic structures offer
significant potential as a versatile platform to explore fundamental
light-matter interactions as well as realizing novel quantum-optical devices.
Here, we investigate the possibility of creating low-threshold micro-scale
lasers in hybrid systems based on integrating room-temperature atomic gases
with both dielectric and metallic nanophotonic systems. We particularly focus
on studying two different devices resulting from incorporating an
optically-pumped Rb-ethane mixture in a dielectric ring resonator and a
plasmonic lattice. We show in both cases the combination of the optical gain
provided by the atomic vapor, along with the unique field-confinement
properties of nanophotonic structures, enables generating of coherent
radiation, i.e. laser light, at low power levels. In addition, we provide
general design guidelines for these hybrid nano-lasers and an efficient density
matrix-based formalism for studying these systems. Our results demonstrate a
unique route towards small foot-print, highly efficient, and fast lasers, which
paves the way towards the development of a whole new class of active
nanophotonic and metamaterial systems.
