  Superconducting circuits based on Josephson junctions exhibit macroscopic
quantum coherence and can behave like artificial atoms. Recent technological
advances have made it possible to implement atomic-physics and quantum-optics
experiments on a chip using these artificial atoms. This review presents a
brief overview of the progress achieved so far in this rapidly advancing field.
We not only discuss phenomena analogous to those in atomic physics and quantum
optics with natural atoms, but also highlight those not occurring in natural
atoms. In addition, we summarize several prospective directions in this
emerging interdisciplinary field.
