Over the last decade, astonishing progress in superconducting technology has lead to unprecedented control of macroscopic quantum effects in electronic circuits and a feasible route towards fully engineerable “on-chip” quantum systems. Recently, one specific area receiving great international interest and attention is the implementation of quantum optics in the microwave regime, eg, circuit quantum electrodynamics, where optical nonlinearities and light-atom couplings are orders of magnitude stronger than the near-visible equivalents. In this fellowship, we will address the limitations of current quantum detection techniques in this burgeoning, interdisciplinary field of circuit quantum optics. For example, single-photon detectors, which are invaluable off-the-shelf components in standard quantum optics, are not yet available at microwave frequencies, where photon energies are much lower (~200mK). We plan to build a single-photon detector using a novel cross-Kerr coupling, and use this system to develop quantum-nondemolition qubit readout, with a view to implementing quantum feedback and control. We will also explore other forms of nonlinearities accessible using similar devices, augmented by appropriately coupled qubits or SQUIDs. To achieve these goals, this interdisciplinary project will combine the candidate’s expertise in quantum optics & quantum information with the host’s extensive background in superconducting quantum devices.The candidate will be trained to carry out all aspects of superconducting circuit experiments, from design to fabrication & operation. Adding this complementary advanced research competence will provide him with the multidisciplinary expertise perfect for the interdisciplinary field of circuit quantum optics, thereby greatly enhancing his potential to contribute to its development. This fellowship will catalyse a significant development in the candidate’s career and enable him to attain a leading independent position in his new field.