Extending the coherence of spin defects in hBN enables advanced qubit control and quantum sensing.

Negatively-charged boron vacancy centers ( V B − ) in hexagonal Boron Nitride (hBN) are attracting increasing interest since they represent optically-addressable qubits in a van der Waals material. In particular, these spin defects have shown promise as sensors for temperature, pressure, and static magnetic fields. However, their short spin coherence time limits their scope for quantum technology. Here, we apply dynamical decoupling techniques to suppress magnetic noise and extend the spin coherence time by two orders of magnitude, approaching the fundamental T₁ relaxation limit. Based on this improvement, we demonstrate advanced spin control and a set of quantum sensing protocols to detect radiofrequency signals with sub-Hz resolution. The corresponding sensitivity is benchmarked against that of state-of-the-art NV-diamond quantum sensors. This work lays the foundation for nanoscale sensing using spin defects in an exfoliable material and opens a promising path to quantum sensors and quantum networks integrated into ultra-thin structures. Negatively-charged boron vacancy centers in hBN have short coherence times, hindering their potential as quantum sensors. By employing dynamical decoupling, the authors achieve an ensemble coherence time approaching the fundamental relaxation limit, enabling sensitive detection of MHz range electromagnetic fields. [ABSTRACT FROM AUTHOR]