Coupling Nanostructured Plasmon–Strain Microwave Waveguide to Spin Defects in Hexagonal Boron Nitride for High‐Sensitivity Quantum Sensors

ABSTRACT Despite seamless integration of hexagonal boron nitride (hBN) with on‐chip devices, the intrinsically low optical quantum yield of spin‐active boron vacancy () defects remains a significant limitation to the sensitivity of hBN‐based quantum sensors. Here, we demonstrate an hBN quantum sensor with enhanced quantum yield and high DC magnetic field sensitivity (η DC ), achieved by coupling defects in hBN with a nanostructured plasmon‐strain microwave waveguide architecture.This platform is realized by fabricating arrays of alumina‐coated gold nanopillars, or plasmonic nanoresonators (PNRs), onto the constricted region of a microwave‐efficient, single‐port gold coplanar waveguide. The alumina coating acts as a dielectric barrier that suppresses photoluminescence (PL) quenching, while gold nanopillars enhance local electromagnetic fields and induce strain‐driven perturbations of the defect energy levels, causing accelerated photo‐emission. This synergistic effect results in a ∼tenfold enhancement in PL and improves optically detected magnetic resonance to −17% for on‐PNR regions, exceeding comparable prior works by over an order of magnitude. Consequently, we achieve an η DC of 9.4 µT/√Hz, approaching the highest reported values for defects. This research establishes a strategy for designing and fabricating highly sensitive quantum sensors that operate at room temperature without requiring extensive optimization of laser or microwave fields.