Avoiding power broadening in optically detected magnetic resonance of single NV defects for enhanced dc magnetic field sensitivity

TLDR

The study systematically investigates the magnetic‑field sensitivity of a single NV‑defect sensor using continuous optically detected ESR spectroscopy. The authors examine ESR contrast and linewidth dependence on microwave and optical power, model the NV spin dynamics, and employ a pulsed‑ESR scheme with resonant π‑pulses and optimized read‑out laser pulses to eliminate power broadening. The optimized continuous‑ESR sensitivity reaches ~2 μT/√Hz, and the pulsed‑ESR scheme improves sensitivity by an order of magnitude to match the Ramsey‑type optimal DC magnetic‑field sensitivity.

Abstract

We report a systematic study of the magnetic field sensitivity of a magnetic sensor based on a single Nitrogen-Vacancy (NV) defect in diamond, by using continuous optically detected electron spin resonance (ESR) spectroscopy. We first investigate the behavior of the ESR contrast and linewidth as a function of the microwave and optical pumping power. The experimental results are in good agreement with a simplified model of the NV defect spin dynamics, yielding to an optimized sensitivity around 2 \mu T/\sqrt{\rm Hz}. We then demonstrate an enhancement of the magnetic sensitivity by one order of magnitude by using a simple pulsed-ESR scheme. This technique is based on repetitive excitation of the NV defect with a resonant microwave \pi-pulse followed by an optimized read-out laser pulse, allowing to fully eliminate power broadening of the ESR linewidth. The achieved sensitivity is similar to the one obtained by using Ramsey-type sequences, which is the optimal magnetic field sensitivity for the detection of DC magnetic fields.