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Engineering diamond interfaces free of dark spins

Xiaofei Yu1,*, Evan J. Villafranca2,*, Stella Wang1, Jessica C. Jones3, Mouzhe Xie2,4, Jonah Nagura2, Ignacio Chi-Durán5, Nazar Delegan3,6, Alex B.F. Martinson3 et al.

Michael E. Flatté7,8, Denis R. Candido7,9, Giulia Galli2,3, and Peter C. Maurer2,3,10,†

  • *These authors contributed equally to this work.
  • †Contact author: pmaurer@uchicago.edu
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Phys. Rev. Applied 25, 034006 – Published 3 March, 2026

DOI: https://doi.org/10.1103/3j8r-2kt6

Abstract

Nitrogen-vacancy (NV) centers in diamond are utilized extensively as quantum sensors for imaging fields at the nanoscale. The ultrahigh 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 2000μm−2 to a value below that set by the detection limit of our NV sensors (200μm−2), results in a twofold 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.

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Phys. Rev. Applied 25, 034006– Published 3 March, 2026
  • Received 21 March 2025
  • Revised 14 November 2025
  • Accepted 15 December 2025
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