Reduction of surface spin-induced electron spin relaxations in nanodiamonds

TL;DR

This study investigates how surface spins affect electron spin relaxation times in nanodiamonds with NV centers, demonstrating that air annealing can effectively reduce surface spins and improve relaxation times for quantum sensing.

Contribution

It provides new insights into the relaxation mechanisms of NV centers in nanodiamonds and shows that air annealing reduces surface spins, enhancing spin coherence.

Findings

Air annealing removes surface spins effectively.

Reduced surface spins lead to longer $T_1$ relaxation times.

High-frequency EPR verifies surface spin reduction.

Abstract

Nanodiamonds (NDs) hosting nitrogen-vacancy (NV) centers are promising for applications of quantum sensing. Long spin relaxation times ($T_1$ and $T_2$) are critical for high sensitivity in quantum applications. It has been shown that fluctuations of magnetic fields due to surface spins strongly influences $T_1$ and $T_2$ in NDs. However, their relaxation mechanisms have yet to be fully understood. In this paper, we investigate the relation between surface spins and $T_1$ and $T_2$ of single-substitutional nitrogen impurity (P1) centers in NDs. The P1 centers located typically in the vicinity of NV centers are a great model system to study the spin relaxation processes of the NV centers. By employing high-frequency electron paramagnetic resonance (EPR) spectroscopy, we verify that air annealing removes surface spins efficiently and significantly reduces their contribution to $T_1$.