Impact of surface functionalisation on the quantum coherence of nitrogen vacancy centres in nanodiamond

TL;DR

This study demonstrates that surface functionalisation of nanodiamonds significantly enhances the quantum coherence of nitrogen-vacancy centres, improving their sensing capabilities by reducing surface-induced magnetic noise.

Contribution

It reveals that borane reduction of nanodiamond surfaces doubles NV centre spin relaxation times and identifies surface carbon bonds as key noise sources, advancing surface engineering for quantum sensors.

Findings

Borane-reduced surfaces double spin relaxation times.

Conversion of sp2 carbon to C-O and C-H bonds correlates with relaxation rates.

Surface engineering improves quantum properties of NV centres.

Abstract

Nanoscale quantum probes such as the nitrogen-vacancy centre in diamond have demonstrated remarkable sensing capabilities over the past decade as control over the fabrication and manipulation of these systems has evolved. However, as the size of these nanoscale quantum probes is reduced, the surface termination of the host material begins to play a prominent role as a source of magnetic and electric field noise. In this work, we show that borane-reduced nanodiamond surfaces can on average double the spin relaxation time of individual nitrogen-vacancy centres in nanodiamonds when compared to the thermally oxidised surfaces. Using a combination of infra-red and x-ray absorption spectroscopy techniques, we correlate the changes in quantum relaxation rates with the conversion of sp2 carbon to C-O and C-H bonds on the diamond surface. These findings implicate double-bonded carbon species as a dominant source of spin noise for near surface NV centres and show that through tailored engineering of the surface, we can improve the quantum properties and magnetic sensitivity of these nanoscale probes.