Long spin coherence and relaxation times in nanodiamonds milled from polycrystalline 12C diamond

The negatively charged nitrogen-vacancy center (NVC) in diamond has been utilized in a wide variety of sensing applications. The long spin coherence and relaxation times (T2*, T2 and T1) of the center at room temperature are crucial to this, as they often limit sensitivity. Using NVCs 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 NVCs in isotopically purified polycrystalline ball-milled nanodiamonds. Using a spin-locking pulse sequence, we observe spin coherence times, T2, up to 786 +/- 200 mu s. We also measure T2* times up to 2.06 +/- 0.24 mu s and T1 times up to 4.32 +/- 0.60 ms. These results represent improvements on the leading literature values for T2 and T1 times in nano-and microdiamond and for T2* times in nanodiamond. Scanning-electron-microscopy and atomic force microscopy measurements show that the diamond containing the NVC with the longest T1 time is smaller than 100 nm. EPR measurements give an N0s concentration of 0.15 +/- 0.02 parts per million for the nanodiamond sample.

Automated summary

This study reports the long spin coherence and relaxation times of single NVCs in nanodiamonds. The results are significant for improving the applications of nanodiamonds in sensing and provide crucial parameters for sensitivity.