Chiral microwave metasurface for controlling spins in diamond

Nitrogen-vacancy (NV) centers in diamond are versatile platforms for quantum technologies, for which engineering microwave magnetic-field confinement and polarization are key elements. However, current microwave devices lack the capability to flexibly manipulate both. In this study, we address this issue by investigating a spoof surface plasmon polariton (SSPP)-based metasurface for engineering strongly confined microwave magnetic fields. Within the propagating SSPP mode, we reveal a rich texture of three-dimensionally oriented polarization, including circular polarization. In addition, we demonstrate the generation of a circularly polarized microwave magnetic field for an NV-containing diamond nanostructure, evidenced by spin-resonance spectra probed via the SSPP. We further confirm the non-reciprocal behavior of spin excitation due to the magnetic spin-momentum locking of propagating SSPPs. Furthermore, the circularly polarized field can be engineered to align with NV axes, enabling spin- and axis-selective control. This architecture could potentially enable on-chip zero-field vector magnetometry, overcoming a significant hurdle in compact quantum device integration.