Optimal microwave control pulse for nuclear spin polarization and readout in dense nitrogen-vacancy ensembles in diamond

TL;DR

This paper develops optimized microwave control pulses to improve nuclear spin polarization and readout in dense nitrogen-vacancy ensembles in diamond, enhancing sensor performance especially at higher nitrogen concentrations.

Contribution

It introduces a method to optimize microwave pulse shapes for better nuclear spin polarization in dense NV ensembles, addressing limitations of narrowband pulses.

Findings

Optimized pulses improve target state population by 15% in dense NV ensembles.

Optimization effectiveness varies with nitrogen concentration and magnetic transition linewidth.

Simple square pulses are nearly as effective at low nitrogen concentrations.

Abstract

Nitrogen-vacancy centers possessing nuclear spins are promising candidates for a novel nuclear spin gyroscope. Preparation of a nuclear spin state is a crucial step to implement a sensor that utilizes a nuclear spin. In a low magnetic field, such a preparation utilizes population transfer, from polarized electronic spin to nuclear spin, using microwave pulses. The use of the narrowband microwave pulse proposed earlier is inefficient when magnetic transitions are not well resolved, particularly when applied to diamond with a natural abundance of carbon atoms or dense ensembles of nitrogen-vacancy centers. In this study, the authors performed optimization of the pulse shape for 3 relatively easily accessible pulse shapes. The optimization was done for a range of magnetic transition linewidths, corresponding to the practically important range of nitrogen concentrations (5-50 ppm). It was found that, while at low nitrogen concentrations, optimized pulse added very little to simple square shape pulse, and in the case of dense nitrogen-vacancy ensembles, with a rather wide magnetic transition width of 1.5 MHz optimal pulses, a factor of 15% improvement in the population of the target state was observed.