Long Spin Coherence Times of Nitrogen Vacancy Centres in Milled Nanodiamonds

Abstract

Nanodiamonds containing negatively charged nitrogen vacancy centres (${\text{NV}}^{-}$) have applications as localized sensors in biological material and have been proposed as a platform to probe the macroscopic limits of spatial superposition and the quantum nature of gravity. A key requirement for these applications is to obtain nanodiamonds containing ${\text{NV}}^{-}$ with long spin coherence times. Using milling to fabricate nanodiamonds processes the full 3D volume of the bulk material at once, unlike etching, but has, up to now, limited ${\text{NV}}^{-}$ spin coherence times. Here, we use natural isotopic abundance nanodiamonds produced by ${\text{Si}}_3{\text{N}}_4$ ball milling of bulk diamond grown by chemical vapour deposition with an average single substitutional nitrogen concentration of $121\text{ppb}$. We show that the electron spin coherence times of ${\text{NV}}^{-}$ centres in these nanodiamonds can exceed $400\mu \text{s}$ at room temperature with dynamical decoupling. Scanning electron microscopy provides images of the specific nanodiamonds containing ${\text{NV}}^{-}$ for which a spin coherence time was measured.

Vresion 1: 13 pages, 7 figures. Standalone paper containing the nanodiamond spin coherence time results that first appeared in the pre-print "Matter and spin superposition in vacuum experiment (MASSIVE)" arXiv:2105.02105v1, with additional details added. Version 2: 11 pages, 7 figures. Grammar edits and reformatting to match published version

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• Role of high nitrogen-vacancy concentration on the photoluminescence and Raman spectra of diamond
• Long Spin Relaxation Times in CVD-Grown Nanodiamonds
• ${}^{13}$C Hyperpolarization with Nitrogen-Vacancy Centers in Micro- and Nanodiamonds for Sensitive Magnetic Resonance Applications
• Heterogeneous integration of solid state quantum systems with a foundry photonics platform
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