Jeffrey Rable: Flux Channeling Induced Nanoconfinement and Enhancement of Microwaves Imaged by Rabi Oscillation Mapping

With advancements in quantum information science, there is an increasing need for techniques to generate large, localized, GHz-frequency microwave (MW) magnetic fields for qubit control. Here, we show that flux-channeling from a permalloy nanowire can be used to achieve precise, localized spatial modulation of a MW field generated by a nearby antenna, and characterize it using Rabi oscillations of nitrogen-vacancy (NV) centers in a diamond scanning probe. Rabi oscillation maps reveal that the wire locally alters the MW field amplitude, increasing and decreasing the field depending on the geometry of the wire, showing up to a 2.35x increase in Rabi frequency across a 20 dBm range of MW powers at an 84 nm NV center-surface separation. Furthermore, the proximal nanowire and field modulation have no impact on NV center T2 coherence time, and the decrease in T1 coherence is less than one would expect in other ferromagnet-based qubit driving schemes. Micromagnetic simulations confirm that the local MW modulation result from the nanowire's stray field interfering constructively or destructively with the incident waves. These measurements provide a basis for external-field free, wide bandwidth modulation of microwave fields, which has potential applications in quantum computing, quantum sensing, spintronics, and the engineering of nanoscale inductors.