Long Spin Coherence and Relaxation Times in Nanodiamonds Milled from Polycrystalline $^{12}$C Diamond

TL;DR

This study reports long room-temperature spin coherence and relaxation times for NV$^-$ centers in polycrystalline nanodiamonds, enabling advanced sensing applications in complex environments.

Contribution

It demonstrates significantly long spin coherence and relaxation times in nanodiamonds, highlighting their potential for quantum sensing in biological and other environments.

Findings

Spin coherence times up to 786 μs observed.

T2* times up to 2.06 μs measured.

T1 times up to 4.32 ms recorded.

Abstract

The negatively charged nitrogen-vacancy centre (NV$^-$) in diamond has been utilized in a wide variety of sensing applications. The centre's long spin coherence and relaxation times ($T_2^*$, $T_2$ and $T_1$) at room temperature are crucial to this, as they often limit sensitivity. Using NV$^-$ centres in nanodiamonds allows for operations in environments inaccessible to bulk diamond, such as intracellular sensing. We report long spin coherence and relaxation times at room temperature for single NV$^-$ centres in isotopically-purified polycrystalline ball-milled nanodiamonds. Using a spin-locking pulse sequence, we observe spin coherence times, $T_2$, up 786 $\pm$ 200 $\mu$s. We also measure $T_2^*$ times up to 2.06 $\pm$ 0.24 $\mu$s and $T_1$ times up to 4.32 $\pm$ 0.60 ms. Scanning electron microscopy and atomic force microscopy measurements show that the diamond containing the NV$^{-}$ centre with the longest $T_1$ time is smaller than 100 nm. EPR measurements give an N$_{s}$$^{0}$ concentration of 0.15 $\pm$ 0.02 ppm for the nanodiamond sample.