Development of nanowire-based fluxonium devices

Abstract

This thesis presents the design, development and first spectroscopy measurements of nanowire-based fluxonium devices. We demonstrate the strong external flux and gate voltage tunability of their spectrum, which allows to accurately tune their first transition frequency over a range of more than 10 GHz. We also show the nanowire fluxonium resilience to magnetic fields up to 800 mT, demonstrating its compatibility with the creation of Majorana bound states (MBSs) at the junction ends, what would open the door to the exploration of new physics and new technological applications. First, the emergence of MBSs in a nanowire fluxonium would result in new Majorana signatures, obtained by radio-frequency spectroscopy techniques. This would complement the current experimental evidence for the creation of MBSs in semiconducting nanowires and would allow to characterize their coupling energy scales, that are, up to date, unknown. And second, the nanowire fluxonium devices presented here can be used for addressing a qubit whose state is topologically protected from local perturbations. Integrating topological qubits into a cQED platform would solve the currently existing problems of the lack of a universal set of quantum gates and reliable methods for qubit operation and readout, establishing a path for the development of topological quantum computing.