Long Spin Coherence Times of Nitrogen Vacancy Centres in Milled Nanodiamonds

TL;DR

This study demonstrates that nanodiamonds produced by ball milling of bulk diamond can host nitrogen vacancy centers with spin coherence times exceeding 400 microseconds at room temperature, enhancing their potential for quantum sensing applications.

Contribution

The paper shows that milling-produced nanodiamonds can achieve long spin coherence times, surpassing previous limitations associated with this fabrication method.

Findings

Spin coherence times exceed 400 microseconds at room temperature.

Milling process preserves NV centers with long coherence.

Nanodiamonds suitable for quantum sensing applications.

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.