Picotesla magnetometry of microwave fields with diamond sensors

TL;DR

This paper introduces a heterodyne detection technique using diamond NV centers that significantly improves microwave field sensitivity, enabling practical, high-precision magnetometry without complex spin control pulses.

Contribution

The authors develop a continuous heterodyne detection method that enhances NV center-based microwave sensing sensitivity without requiring spin control, achieving record sensitivity levels.

Findings

Sensitivity of 8.9 pT/Hz^{1/2} at 2.9 GHz

Achieved 1/t frequency resolution scaling up to 10,000 seconds

Method removes the need for spin control pulses, simplifying practical applications

Abstract

Developing robust microwave-field sensors is both fundamentally and practically important with a wide range of applications from astronomy to communication engineering. The Nitrogen-Vacancy (NV) center in diamond is an attractive candidate for such purpose because of its magnetometric sensitivity, stability and compatibility with ambient conditions. However, the existing NV center-based magnetometers have limited sensitivity in the microwave band. Here we present a continuous heterodyne detection method that can enhance the sensor's response to weak microwaves, even in the absence of spin controls. Experimentally, we achieve a sensitivity of 8.9 pT$\cdot$Hz$^{-1/2}$ for microwaves of 2.9 GHz by simultaneously using an ensemble of $n_{\text{NV}} \sim 2.8\times10^{13}$ NV centers within a sensor volume of $4\times10^{-2}$ mm$^3$. Besides, we also achieve $1/t$ scaling of frequency resolution up to measurement time $t$ of 10000 s. Our method removes the control pulses and thus will greatly benefit the practical application of diamond-based microwave sensors.