Quantum sensing with solid-state spin defects has transformed nanoscale metrology, offering sub-wavelength spatial resolution with exceptional sensitivity to multiple signal types. Maximizing these advantages requires minimizing both the sensor-target separation and the detectable signal threshold. However, leading platforms such as nitrogen-vacancy (NV) centers in diamond suffer from performance degradation near surfaces or in nanoscale volumes, motivating the search for optically addressable spin sensors in atomically thin, two-dimensional (2D) van der Waals materials. Here, we present a comprehensive experimental framework to probe a 2D spin ensemble, including its Hamiltonian, coherent sensing dynamics, and noise environment. Using a central spin system in a hexagonal boron nitride (hBN) crystal, we fully map the hyperfine interactions with proximal nuclear spins, demonstrate switchable magnetic and electric noise sensing, and introduce a method to accurately reconstruct the environmental noise spectrum while explicitly accounting for quantum control imperfections. We achieve a record coherence time of 80μs under dynamical decoupling, enabling sub-microtesla AC magnetic sensitivity at a 10nm target distance. Leveraging the broad opportunities for defect engineering in atomically thin hosts, these results lay the foundation for next-generation quantum sensors with ultrahigh sensitivity, tunable noise selectivity, and versatile functionalities.
@article{arxiv.2509.08984,
title = {Quantum sensing with a spin ensemble in a two-dimensional material},
author = {Souvik Biswas and Giovanni Scuri and Noah Huffman and Eric I. Rosenthal and Ruotian Gong and Thomas Poirier and Xingyu Gao and Sumukh Vaidya and Abigail J. Stein and Tsachy Weissman and James H. Edgar and Tongcang Li and Chong Zu and Jelena Vučković and Joonhee Choi},
journal= {arXiv preprint arXiv:2509.08984},
year = {2026}
}