Isotopic identification of engineered nitrogen-vacancy spin qubits in ultrapure diamond

TL;DR

This study investigates how nitrogen impurity levels affect the creation and coherence of NV$^-$ spin qubits in ultrapure diamond, using isotopic implantation and annealing to optimize qubit stability.

Contribution

It demonstrates a method to create stable NV$^-$ centers with high yield and long coherence times in ultrapure diamond through isotopic implantation and annealing.

Findings

High creation yield of NV$^-$ centers from $^{15}$N$^{3+}$ ions.

Significant yield from $^{14}$N impurities at low concentration.

Long coherence times achieved in dilute nitrogen impurity conditions.

Abstract

Nitrogen impurities help to stabilize the negatively-charged-state of NV$^-$ in diamond, whereas magnetic fluctuations from nitrogen spins lead to decoherence of NV$^-$ qubits. It is not known what donor concentration optimizes these conflicting requirements. Here we used 10-MeV $^{15}$N$^{3+}$ ion implantation to create NV$^-$ in ultrapure diamond. Optically detected magnetic resonance of single centers revealed a high creation yield of $40\pm3$% from $^{15}$N$^{3+}$ ions and an additional yield of $56\pm3$% from $^{14}$N impurities. High-temperature anneal was used to reduce residual defects, and charge stable NV$^-$, even in a dilute $^{14}$N impurity concentration of 0.06 ppb were created with long coherence times.