Edited by: Gerard Milburn, Per Delsing, Tom Stace and Tim Duty
Advances in superconducting quantum circuits and microwave resonators now enable quantum optical experiments to be carried out at microwave frequencies. The ability to engineer very large dipole interactions enables one to achieve coupling regimes that are difficult if not impossible to achieve in atomic systems. The rapid modulation of microwave resonator SQUID devices enables strong parametric driving to be achieved giving access to very strong squeezing, and the ability to engineer arbitrary few-photon superposition states developed for quantum computing applications provides a powerful new resource in the microwave domain.