A Highly Sensitive Diamond NV Magnetometer Using Ramsey Interferometry with a Short Sensor-to-Sample Distance

TL;DR

This paper presents a diamond NV magnetometer with enhanced sensitivity and minimal thermal issues, achieved through a novel light-trapping waveguide technique, enabling practical biomagnetic measurements at short sensor-to-sample distances.

Contribution

The study introduces a high-sensitivity diamond NV magnetometer using a light-trapping waveguide and Ramsey interferometry, reducing thermal effects and improving measurement accuracy at short distances.

Findings

Achieved a sensitivity of 2.93 pT/Hz^1/2 in 100-400 Hz range

Measured a 77.7 pT magnetic field without averaging

Maintained low thermal increase of 13 K at 210 mW laser power

Abstract

In this study, we developed a diamond quantum magnetometer based on Ramsey interferometry with a short sensor-to-sample distance. Conventional biomagnetic sensors with ensemble nitrogen-vacancy centers using continuous-wave optically detected magnetic resonance and Ramsey methods typically rely on watt-level lasers to achieve high sensitivity, resulting in thermal issues. In contrast, by employing the light-trapping diamond waveguide technique in a high-pressure and high-temperature diamond sample treated with electron beam irradiation, we obtained a high photon conversion efficiency of 9.5%, enabling us to simultaneously achieve a high sensitivity of 2.93(7) pT/Hz^1/2 in the 100-400 Hz frequency range and a minimal temperature increase of only approximately 13 K at a low laser power of 210 mW. Using a dry phantom designed to mimic magnetoencephalography signals, we measured a weak magnetic field of 77.7(2) pT without signal averaging at a sensor-to-sample distance of 2.5 mm. This short-distance measurement prevents severe spatial signal attenuation, yielding a high signal-to-noise ratio. The development here is crucial for practical biomagnetic applications based on Ramsey interferometry.