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Content archived on 2024-06-18

Advanced Quantum Measurement and Detection for Superconducting Quantum Circuits

Final Report Summary - SQUDET (Advanced Quantum Measurement and Detection for Superconducting Quantum Circuits)

The principal aim of the Marie Curie Fellowship awarded to Dr Nathan Langford was to train Dr Langford in the techniques and practices of a relatively new area of physics, vis, Superconducting Quantum Circuits. Dr Langford's background is in quantum optics which relies on completely different experimental techniques, though the theoretical framework has strong analogous themes.
The main scientific objectives were to 1) fabricate and test cross-Kerr bifurcation detectors and 2) to demonstrate qubit readout using this type of detector.

The main training objectives were to provide Dr Langford with detailed training in all aspects of experimental research in the new field of superconducting circuit quantum optics, including device design, fabrication, cryogenic experiments, measurement and analysis, as well as complementary theoretical aspects, including specifically, device modelling, theoretical descriptions of real-world effects in superconducting devices and key analytical techniques for describing the devices.

The work performed since beginning the project has included:

* training the research fellow in almost all of the key technologies and technical knowledge required to perform superconducting quantum circuit experiments, including in circuit design, fabrication, cryogenics, measurement and analysis.

* conducting a comprehensive survey of literature in the field of superconducting quantum circuits for quantum computing, quantum optics and circuit QED and identifying new, open research opportunities.

* developing a full quantum model for the operation of the cross-Kerr coupled cavities which can be used to model the behaviour of a high-sensitivity superconducting microwave detector for applications in quantum circuits.

* establishing a collaboration with world-leading quantum optics theorists at the University of Queensland in Australia for developing quantum models of microwave cavity systems.

* a detailed theoretical study of errors in quantum tomography, in particular focussing on how to diagnose the presence of systematic noise in a situation where statistical noise is not necessarily the dominant source of noise.

* aiding in the commissioning the group’s Niobium sputtering machine, characterising the quality of the existing thin films and identifying and eradicating the underlying causes of poor quality films.

* exploring the source of a complex low-temperature Helium leak.

* aiding in the commissioning a new dilution refrigerator, including installing cryogenic wiring and designing and installing measurement and control electronics and a software control system.

* developing an introductory course in circuit QED which covers all key concepts required to attain a basic comprehension of research work in the field.

This body of work has substantially progressed the status of the research group towards the overall scientific objectives. A PhD student aided by Dr Langford is presently completing the fabrication of the next generation of cross-Kerr bifurcation detectors.

The second scientific objective remains a future ambition for the group. Publishable work arising from this project is and will be primarily aimed at scientists working in the field, though in addition Dr Langford has undertaken some scientific outreach work aimed at schoolchildren.