2025/04/11 by Xiaofei Yu, Ernest Villafranca, Yu, Xiaofei +23 · 1 citation
Engineering · Materials Science · #Diamond and Carbon-based Materials Research #Electronic and Structural Properties of Oxides #FOS: Physical sciences #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #Quantum Physics (quant-ph) #Semiconductor materials and devices
paper · pdf · doi:10.48550/arxiv.2504.08883
openalex publication_date 2025/04/11 · openalex created_date 2025/10/14 · openalex updated_date 2026/08/02
Nitrogen-vacancy (NV) centers in diamond are extensively utilized as quantum sensors for imaging fields at the nanoscale. The ultra-high sensitivity of NV magnetometers has enabled the detection and spectroscopy of individual electron spins, with potentially far-reaching applications in condensed matter physics, spintronics, and molecular biology. However, the surfaces of these diamond sensors naturally contain electron spins, which create a background signal that can be hard to differentiate from the signal of the target spins. In this study, we develop a surface modification approach that eliminates the unwanted signal of these so-called dark electron spins. Our surface passivation technique, based on coating diamond surfaces with a thin titanium oxide (TiO2) layer, reduces the dark spin density. The observed reduction in dark spin density aligns with our findings on the electronic structure of the diamond-TiO2 interface. The reduction, from a typical value of 2,000~μm-2 to a value below that set by the detection limit of our NV sensors (200~μm-2), results in a two-fold increase in Hahn-echo coherence time of near surface NV centers. Furthermore, we derive a comprehensive spin model that connects dark spin relaxation with NV coherence, providing additional insights into the mechanisms behind the observed spin dynamics. Our findings are directly transferable to other quantum platforms, including nanoscale solid state qubits and superconducting qubits.