Prospects for nuclear spin hyperpolarisation of molecular samples using nitrogen-vacancy centres in diamond

TL;DR

This paper models the potential of nitrogen-vacancy centers in diamond to hyperpolarize nuclear spins in molecular samples, aiming to improve NMR sensitivity through theoretical analysis and practical considerations.

Contribution

It provides a theoretical evaluation of NV centers for nuclear spin hyperpolarisation, including performance estimates, fabrication challenges, and application prospects for macro and micro-NMR.

Findings

Potential to achieve >10% nuclear polarization over microliter volumes

Modest signal enhancements (1-2 orders of magnitude) in micro-NMR with current technology

No significant benefit for nano-NMR due to statistical polarization detection

Abstract

After initial proof-of-principle demonstrations, optically pumped nitrogen-vacancy (NV) centres in diamond have been proposed as a non-invasive platform to achieve hyperpolarisation of nuclear spins in molecular samples over macroscopic volumes and enhance the sensitivity in nuclear magnetic resonance (NMR) experiments. In this work, we model the process of polarisation of external samples by NV centres and theoretically evaluate their performance in a range of scenarios. We find that average nuclear spin polarisations exceeding 10% can in principle be generated over macroscopic sample volumes ($\gtrsim\mu$L) with a careful engineering of the system's geometry to maximise the diamond-sample contact area. The fabrication requirements and other practical challenges are discussed. We then explore the possibility of exploiting local polarisation enhancements in nano/micro-NMR experiments based on NV centres. For micro-NMR, we find that modest signal enhancements over thermal polarisation (by 1-2 orders of magnitude) can in essence be achieved with existing technology, with larger enhancements achievable via micro-structuring of the sample/substrate interface. However, there is generally no benefit for nano-NMR where the detection of statistical polarisation provides the largest signal-to-noise ratio. This work will guide future experimental efforts to integrate NV-based hyperpolarisation to NMR systems.