This project was organised into three key work packages:
1. Development of microwave travelling-wave parametric amplifiers (TWPAs)
2. Development of mm-wave TWPAs
3. Demonstration of TWPA-based parametric down-conversion
Despite pandemic-related delays, we achieved key milestones, including commissioning a 10 mK cryogenic system and constructing additional 300 mK and 4 K systems. We also collaborated on an industrially developed 300 mK system for rapid device screening. To enhance efficiency, we implemented an automated measurement system, enabling rapid SPA characterisation and optimising performance.
Work Package I: Microwave TWPAs:
We developed a novel theoretical framework to model and optimise both KI- and JJ-TWPAs, improving prediction accuracy and loss analysis. Using this, we successfully fabricated and tested high-gain, broadband KI-TWPAs, disseminating findings through academic publications and conferences. These amplifiers were deployed for quantum computing and astronomical applications.
For JJ-TWPAs, we doubled bandwidth while reducing the required Josephson junctions by fourfold, enhancing performance. We also developed high-power-handling JJ-TWPAs and unexpectedly innovated JSWPAs, which, though narrower in bandwidth, offer higher yield and stability. These findings contributed to a PhD thesis, career transitions into quantum research, and applications in axion dark matter searches.
Work Package II: Millimetre-Wave TWPAs:
SPAs' scalability makes them ideal for mm-wave systems, reducing noise at critical first-stage amplification. We designed, fabricated, and tested an SPA near 100 GHz, but pandemic-related disruptions slowed progress. To mitigate this, we collaborated with external institutions for testing. Though full high-gain operation was not achieved, we observed crucial nonlinear behaviour, laying the foundation for further development.
Work Package III: TWPA-Based Parametric Down-Converter:
This package aimed to develop a novel parametric mixer that amplifies while down-converting signals, a capability not previously demonstrated. Overcoming design challenges, we successfully implemented this functionality in KITWPAs, marking a likely first in the field. This has major implications for large-pixel mm/sub-mm heterodyne receiver systems.
Impact and Future Prospects:
This project advanced superconducting parametric amplification through theoretical and experimental breakthroughs, leading to multiple publications and a patent filing. The results will impact quantum science, high-frequency electronics, and fundamental physics. The project's success secured an ERC Consolidator Grant, starting in April 2025, to further develop mm-wave SPAs and expand their scientific applications, including quantum computing, neutrino mass measurements, and dark matter searches.
