Superconducting Quantum Detector Group

Group Leaders:

Our research is primarily aimed at the development of ultra-sensitive cryogenic superconducting devices for astronomy and quantum computation. The two main research focuses of our current programme involves the development of high-quality Superconductor-Insulator-Superconductor (SIS) detectors and quantum-limited Superconducting Parametric Amplifiers (SPAs). Both topics are of high priority importance for fundamental physics, in particular the challenging millimetre (mm) and sub-mm astronomy and future development of quantum computers.

Coherent detectors based on photon-assisted tunnelling in SIS mixers below the superconducting gap of niobium (~700 GHz) is already approaching the quantum-limited sensitivity performance these days. They had been successfully deployed to many major telescopes in the world, in particular the Atacama Large Millimetre/Sub-Millimetre Array (ALMA), the largest mm/sub-mm telescope in the world, consisting of 66 12-m antennas installed at an altitude of 5000 m in the north of Chile. However, the current ALMA programme only includes receivers operating up to 950 GHz, due to the lack of convincing technologies above this limit. Our major project at present is therefore to develop THz SIS mixers above the niobium gap, operating beyond 1 THz. This works is challenging, yet plausible, due to recent development in high-gap superconductors such as niobium nitride and niobium titanium nitride. Another research focus of the group in this area is to develop technologies for building large pixel count focal plane SIS mixer array. We are currently working along with our collaborators to build a multi-beam dual-polarisation SIS demonstrator, with the aim to expand such design to large array for large single dish mm/sub-mm telescope such as James Clerk Maxwell Telescope, and interferometer like Smithsonian's Sub-Millimetre Array (SMA) and ALMA.

One major pillar of our long-term research programme is to develop ultra-broadband, quantum-noise-limited superconducting parametric amplifiers for astronomy and quantum information technologies. This is an emerging field that could potentially revolutionise how mm/sub-mm instrumentation can be performed in the future, enabling real prospect of building a practical multi-qubit quantum computers, due to the ability of SPAs to achieve quantum-limited (even below this limit in some circumstances) noise performance, ultra-broad operational bandwidth and extremely low heat dissipation compared to traditional semiconductor amplifier technologies. The research group is currently under a long-term funding to explore the underlying physics and develop these quantum amplifiers for fundamental physics.

All these research works require thorough understanding of the quantum physics of superconducting thin film, quantum detection physics, electromagnetism in superconducting structures, microwave engineering, cryogenic system handling, high-precision machining, quasi-optics etc. We make use of available commercial softwares, as well as developing in-house codes to design and understanding the behaviour of these quantum devices. Our superconducting quantum detector laboratory is equipped with state-of-the-art cryogenic systems for testing and characterization of their performance, along with supports from departmental-wide electronics and mechanical workshops. Apart from working on the two main topics listed above, we often encourage the group members to be ambitious and creative in exploring new sciences as well. We had since developed many new ideas, including the design of a novel type of smooth-walled feed horn that is easy to fabricate yet retain the same high quality as the conventional corrugated feed horn. These feed horns are now regularly deployed in many existing/up-coming cosmic microwave background (CMB) experiments. We also spin out our technologies to interested industrial partners, and working closely with them to ensure the successful deployment of our technologies to their applications, in particular the area of microwave components.

Current research projects:
Ultra-low-noise detectors for submillimetre astronomy (STFC Consortium grant)
Supra-THz SIS and HEB detectors (EU RadioNet project).
Interferometry Beyond 1 THz (STFC/ESO grant)
Superconducting Parametric Amplifiers (ERC)
High performance multiple flare-angled feed (ongoing-collaborations)
Phase modulation employing superconducting nano-switches