Continuous Heterodyne Microwave Sensing With van der Waals Spin Defects

Quantum sensing with solid‐state spin defects provides a powerful approach for microwave‐field detection, but conventional sensing protocols are often limited by narrow detection bandwidths. Here, we demonstrate continuous heterodyne microwave sensing using spin defects in hexagonal boron nitride, a van der Waals material with intrinsically broad spin resonances. By implementing a continuous heterodyne protocol that mixes a weak signal microwave field with a continuous auxiliary microwave field, we realize linear microwave‐field detection with a dynamic range from to . The large inhomogeneous linewidth of the defect ensemble enables a detection bandwidth of , while single‐frequency measurements achieve sub‐hertz spectral resolution. In addition, the scheme supports simultaneous detection of multiple microwave frequencies and wide‐field imaging. These results establish van der Waals spin defects as a promising platform for broadband continuous‐wave microwave sensing, with potential applications in microwave spectral analysis, spin dynamics, and quantum‐circuit diagnostics.