Fault-Tolerant Quantum Metrology with High-Density Spin Ensembles: Experimental Results

High density solid-state spin ensembles have shown great promise as high-sensitivity magnetometers on the nanoscale. However, further increases in sensitivity require techniques to overcome the limits to coherence times imposed by spin-spin interactions. Here, using a dense ensemble of Nitrogen-Vacancy centers in diamond, we experimentally demonstrate fault-tolerant decoupling of spin-spin interactions, achieving a ten-fold enhancement of spin coherence times. This was made possible by introducing novel dynamical decoupling sequences that simultaneously suppress disorder, interactions, and imperfections in controls. We utilize the prolonged coherence time to perform quantum metrology, demonstrating an increase in sensitivity compared to conventional sensing protocols such as the XY-8 sequence. These results thus demonstrate a significant enhancement beyond the interaction limit, crucial for high-sensitivity magnetometers in high-density interacting spin ensembles.