Colloquium: How to measure and tune quantum devices using machine learning
- Location: Ångströmlaboratoriet, Lägerhyddsvägen 1 Siegbahn hall
- Lecturer: Prof. Andrew Briggs, Department of Materials, University of Oxford, UK
- Contact person: Jan-Erik Rubensson
As the race to scale up reliable quantum computing accelerates, fault-tolerant error correction requires each logical qubit to be encoded in many physical qubits. A generic problem, common to all implementations, is device variability, whether in the gates of an ion trap or the electrostatic confinement of a solid state device. Electron spins in semiconducting devices offer a long-term platform for quantum computing, inspired by integrated circuits, with either the spin state or the relative spin alignment of two electrons representing the qubit. The elements of stabiliser codes (initialisation, one and two-qubit gates, single-shot readout) have been demonstrated, but a major obstacle to creating large circuits is variability due to trapped substrate charges. Tuning a single qubit requires searching a multi-dimensional gate voltage space, where device parameters vary non-monotonically and not always predictably with gate voltage. Tuning large multi-qubit circuits will require an automated approach. Advances in machine learning are becoming available for this purpose. Bayesian optimisation provides the basis for letting the machine decide what data to measure next in order to yield the greatest benefit in updating its knowledge of the device characteristics. This provides an automated pathway to converging in the shortest possible time on the configuration of parameters for the required performance. These methods are already being used to tune quantum dot devices, and they are applicable to a wide range of other platforms for quantum computing. I foresee that before too long, we shall be wondering how we ever managed without them!
Professor Andrew Briggs is the inaugural holder of the Chair in Nanomaterials at the University of Oxford. His research interests focus on nanomaterials for quantum technologies and their incorporation into practical devices. He uses similar techniques for experimental tests of the boundaries of non-classical behaviour in materials. He is Governing Body Fellow of St Anne’s College, Oxford, Emeritus Fellow of Wolfson College, Oxford, Honorary Fellow of the Royal Microscopical Society, Fellow of the Institute of Physics, Fellow of the International Society for Science and Religion, and Member of Academia Europaea. From 2002 – 2009 he was Director of the Interdisciplinary Research Collaboration in Quantum Information Processing, which served to create new experimental and theoretical capacity in the UK and has been followed by further UK government investment of £575M in Quantum Technologies. Since 2010 he has directed the services provided by the University of Oxford for Templeton World Charity Foundation. He has more than 600 publications, with over 24,000 citations. In 2016 Oxford University Press published his book with Roger Wagner, The Penultimate Curiosity: How science swims in the slipstream of ultimate questions; the documentary film is available at CuriosityStream; a series for children is published as The Curious Science Quest. His next book, It Keeps Me Seeking, with Hans Halvorson and Andrew Steane (Oxford University Press 2018) was selected by Times Higher Education as Book of the Week for the first issue of 2019.