Engineering Spin Coherence in Core-Shell Diamond Nanocrystals

Nitrogen vacancy (NV) centers in diamond nanocrystals have emerged as a promising platform for quantum-based sensing with nanoscale spatial resolution. However, applications beyond current proof-of-principle experiments require a substantial increase in sensitivity, which is generally limited by surface-noise-induced spin dephasing. In this work, we demonstrate a simple method to engineer the surface-dominated noise spectra and extend the spin bath correlation time with a core-shell design. Our work results in near bulk properties, with a 3.5-fold increase in both coherence and spin-lattice relaxation times, pointing to a broadband improvement across sensing relevant frequencies. We use our findings to investigate the noise spectrum and identify the addressable decoherence mechanisms in diamond nanocrystals, showing a shift from surface-dominated noise in bare particles to bulk-dominated noise in our core-shell design. This work opens a new path for improving sensing sensitivity using a capping layer to create engineered diamond interfaces.