  Hybrid quantum circuits combine two or more physical systems, with the goal
of harnessing the advantages and strengths of the different systems in order to
better explore new phenomena and potentially bring about novel quantum
technologies. This article presents a brief overview of the progress achieved
so far in the field of hybrid circuits involving atoms, spins and solid-state
devices (including superconducting and nanomechanical systems). How these
circuits combine elements from atomic physics, quantum optics, condensed matter
physics, and nanoscience is discussed, and different possible approaches for
integrating various systems into a single circuit are presented. In particular,
hybrid quantum circuits can be fabricated on a chip, facilitating their future
scalability, which is crucial for building future quantum technologies,
including quantum detectors, simulators, and computers.
