Quantum coherent manipulation and readout of superconducting vortex states

From the moment of its discovery, the antagonistic relation between superconductivity and a magnetic field has provided a complex playground for experimentalists and theorists alike. The measurement of the critical field and the Meissner effect 12 have anchored phase-transition theories 13 , 14 , and the trapping of quantized flux inside superconductors has provided direct evidence for the existence of Cooper pairs 15 . A hallmark of type II superconductivity in a magnetic field is the formation of Abrikosov vortices: regions of local gap suppression that interact to form lattices 1 . Vortex dynamics is detrimental for a wide range of applications 15 , causing heating, flux noise and magnetic hysteresis. However, pinned vortices enable quasiparticle trapping in their core, which enhances the critical current 16 of superconducting films, improves micro-cooler efficiency 17 , boosts resonator quality factors 18 and improves qubit coherence 19 , 20 . In all these cases, owing to the normal state core, vortices can be understood within semi-classical models. Gap suppression in the vortex core stems from the crowding of supercurrent at its centre, a consequence of continuity in the superconducting medium. …