Increasing the coherence time of single electron spins in diamond by high temperature annealing

TL;DR

This study demonstrates that high-temperature annealing at 1200°C significantly enhances the electron spin coherence time of single NV$^-$ centers in diamond produced by ion implantation, reducing charge state switching and improving quantum properties.

Contribution

It introduces a high-temperature annealing method to increase the coherence time of ion-implanted NV$^-$ centers in diamond, addressing a key limitation in their quantum performance.

Findings

Annealing at 1200°C increases $T_2$ coherence times.

High-temperature annealing reduces NV charge state switching.

Implantation energy shows no effect on $T_2$ after annealing.

Abstract

Negatively charged Nitrogen-Vacancy (NV$^-$) centers in diamond produced by ion implantation often show properties different from NVs created during the crystal growth. We observe that NVs created from nitrogen ions with four different energies (30-300 keV) show much shorter electron spin coherence time $T_2$ compared to the "natural" NVs and we could find any dependence of $T_2$ on the implantation energy. Moreover, we also find out that about 10% of them show switching from NV$^-$to NV$^0$. We develop a method to increase $T_2$ of single NV$^-$ centers by annealing the sample at $t=1200 {\circ}$C whereas at the same time the fraction of the NVs showing discharging is greatly reduced.