Engineering control and readout of superconducting qubits

Superconducting qubits are a promising candidate for quantum computing and processing applications. Widely used in industry and academia is the transmon qubit, composed of a Josephson junction shunted by a large capacitor. These man-made atoms offer the benefit of being able to tune parameters via fabrication and offer ease of readout and control via coupling to a superconducting resonator. As the superconducting qubit community looks towards the future, a strong contender for an alternative is the fluxonium qubit, which is instead shunted by a large inductance and is resilient to charge fluctuations. As interest in the fluxonium continues to grow, the goal of this project is to first optimize readout parameters to achieve high performance measurement fidelity, and subsequently realize this experimentally. This project will be a continuation of the work I have completed during my Project B involving numerical and analytical optimization. The aim is to use the results from my Project B in order to identify the appropriate parameter regime to apply in the laboratory. Improved readout capabilities directly enable efficient characterization of the fluxonium which further improves the ability to calibrate the fluxonium gates as efficiently as possible. Thus, the future perspectives for the project will include efficient calibration of high fidelity gates and the implementation of both readout and gates in multi-qubit architectures. We ultimately want to answer the question: What is the best approach to implement high fidelity operations on fluxonium qubits? Additionally, superconducting qubits det ups require extensive shielding, attenuation, and filtering to protect against various sources of decoherence. Custom-made Eccosorb infrared filters are widely used in the superconducting qubit community, but little work has characterized their direct impact on qubit performance. We aim to build, characterize, and implement these filters to ultimately propose the optimal configuration to protect qubits against decoherence caused by high frequency photons. Other key learning objectives include, but are not limited to, learning how to design samples and understanding the control electronics and software required to run the experiments.

Our ambitions for the impact of the Quantum Engineering CDT are simple and clear: our PhD graduates will be the key talent that creates a new, thriving, globally-competitive quantum industry within the UK. In Bristol we will provide an entire ecosystem for innovation in quantum technologies (QT). Our strong and diverse research base includes strengths going from quantum foundations to algorithms, experimental quantum science to quantum hardware. What makes Bristol unique is our strong innovation and entrepreneurship focus that is deeply embedded in the entire culture of the CDT and beyond. This is reflected in our recent successful venture QTEC, the Quantum Technologies Enterprise Centre, and our Quantum Technologies Innovation Centre (QTIC), which are already enabling industry and entrepreneurs to set up their own QT activities in Bristol. This all occurs alongside internationally recognised incubators/accelerators SetSquared, EngineShed, and UnitDX.

At the centre of this ecosystem lies the CDT. We will not just be supplying existing industry with deeply trained talent, but they will become the CEOs and CTOs of new QT companies. We are already well along this path: 7 Bristol PhD students are currently involved in QT start-ups and 3 alumni have founded their own companies. We expect this number to rise significantly when the first CDT cohort graduates next year (2 students have already secured start-up positions). Equally, it is likely that our graduates will be the first quantum engineers to make new innovations in existing classical technology companies - this is an important aspect, as e.g. the existing photonics, aerospace and telecommunications industries will also need QT experts.

The portfolio of talent with which each CDT graduate will be equipped makes them uniquely suited to many roles in this future QT space. They will have a deep knowledge of their subject, having produced world-leading research, but will also understand how to turn basic science into a product. They will have worked with individuals in their cohort with very different skills background, making them invaluable to companies in the future who need these interdisciplinary team skills to bring about quantum innovations in their own companies. Such skills in teamworking, project management, and self-lead innovation are evidenced by the hugely successful Quantum Innovation Lab (QIL). The idea and development of QIL is entirely student-driven: it brings together diverse industrial partners such as Deutsche Bank, Hitachi, and MSquared Lasers, Airbus, BT, and Leonardo - the competition to take part in QIL shows the hunger by national industry for QT in general, and our students' skills and abilities specifically. With this in mind, our Programme has been co-developed with local, UK, and international companies which are presently investing in QT, such as Airbus, BT, Google, Heilbronn, Hitachi, HPE, IDQuantique, Keysight, Microsoft, Oxford Instruments, and Rigetti. The technologies we target should lead to products in the short and medium term, not just the longer term. The first UK-wide fibre-based quantum communication network will likely involve an academic-industrial partnership with our CDT graduates leading the way. Quantum sensing devices are likely to be the product of individual innovators within the CDT and supported by QTIC in the form of spin-outs. Our graduates will be well-positioned to contribute to the advancement of quantum simulation and computing hardware, as developed by e.g. our partners Google, Microsoft and Rigetti. New to the CDT will be enhanced training in quantum software: this is an area where the UK has a strong chance to play a key role. Our CDT graduates will be able to contribute to all aspects of the software stack required for first-generation quantum computers and simulators, the potential impact of which is shown by the current flurry of global activity in this area.