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arXiv:1212.1495 · Physical Review Letters

High-Sensitivity Magnetometry Based on Quantum Beats in Diamond Nitrogen-Vacancy Centers

Kejie Fang, Víctor M. Acosta, Charles Santori, Zhihong Huang, Kohei M. Itoh, Hideyuki Watanabe, Shinichi Shikata, Raymond G. Beausoleil

Published Mar 26, 2013• 162 citations
arXivHTMLPDF

Abstract

We demonstrate an absolute magnetometer based on quantum beats in the ground state of nitrogen-vacancy centers in diamond. We show that, by eliminating the dependence of spin evolution on the zero-field splitting D, the magnetometer is immune to temperature fluctuation and strain inhomogeneity. We apply this technique to measure low-frequency magnetic field noise by using a single nitrogen-vacancy center located within 500 nm of the surface of an isotopically pure (99.99% 12C) diamond. The photon-shot-noise limited sensitivity achieves 38 nT/sqrt[Hz] for 4.45 s acquisition time, a factor of sqrt[2] better than the implementation which uses only two spin levels. For long acquisition times (>10 s), we realize up to a factor of 15 improvement in magnetic sensitivity, which demonstrates the robustness of our technique against thermal drifts. Applying our technique to nitrogen-vacancy center ensembles, we eliminate dephasing from longitudinal strain inhomogeneity, resulting in a factor of 2.3 improvement in sensitivity.

DOI
10.1103/physrevlett.110.130802

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The negatively charged nitrogen vacancy center in diamond is widely used for quantum sensing due to the sensitivity of the spin triplet in the electronic ground state to external perturbations such as strain and electromagnetic fields, which makes it an excellent probe for changes in these perturbations.The spin state can be measured through optically detected magnetic resonance, which is most commonly achieved by detecting the photoluminescence after exciting the spin-triplet transition.Recently, methods have been proposed and demonstrated that use the absorption of the infrared singlet transition at 1042 nm instead.These methods, however, require cryogenic temperatures or external cavities to enhance the absorption signal.Here, we report on our efforts to optimize the magnetometer sensitivity at room temperature and without cavities.We reach a sensitivity of 18 pT/ √ Hz, surpassing previously reported values, and a calculated shot-noise limit of 5 pT/ √ Hz .We also report on a defect that is native to diamond grown by chemical vapor deposition and thus absent in high-pressure high-temperature diamond, the excitation of which impacts the measured singlet absorption signal.
Recent developments in magnetic field sensing with negatively charged nitrogen-vacancy centers (NV) in diamond employ magnetic-field (MF) dependent features in the photoluminescence (PL) and eliminate the need for microwaves (MW). Here, we study two approaches towards improving the magnetometric sensitivity using the ground-state level anti-crossing (GSLAC) feature of the NV center at a background MF of 102.4 mT. Following the first approach, we investigate the feature parameters for precise alignment in a dilute diamond sample; the second approach extends the sensing protocol into absorption via detection of the GSLAC in the diamond transmission of a 1042nm laser beam. This leads to an increase of GSLAC contrast and results in a magnetometer with a sensitivity of 0.45 nT/√Hz and a photon shot-noise limited sensitivity of 12.2 pT/√Hz.
Ensembles of nitrogen-vacancy (NV) centers in diamond are versatile quantum sensors with broad applications in the physical and life sciences. The concentration of neutral substitutional nitrogen ( [ N s 0 ]) strongly influences NV electronic spin coherence times, sensitivity, and optimal sensing strategies. Diamonds with [ N s 0 ] ∼ 1–10 ppm are a focus of recent material engineering efforts, with higher concentrations being favorable for continuous-wave optically detected magnetic resonance (CW-ODMR) and lower concentrations expected to benefit pulsed magnetometry techniques through extended NV spin coherence times and improved sensing duty cycles. In this work, we synthesize and characterize low- [ N s 0 ] ( ∼ 0.8 ppm), NV-enriched diamond material, engineered through low-strain chemical vapor deposition (CVD) growth on high-quality substrates, 12 C isotopic purification, and controlled electron irradiation and annealing. Our results demonstrate good strain homogeneity in diamonds grown on CVD substrates and spin-bath-limited NV dephasing times. By measuring NV spin and charge properties across a wide range of optical NV excitation intensity, we provide direct comparisons of photon-shot-noise-limited magnetic field sensitivity between the current low- [ N s 0 ] and previously studied higher- [ N s 0 ] ( ∼ 14 ppm) NV-diamond sensors. We show that low- [ N s 0 ] diamond can outperform higher- [ N s 0 ] diamond at moderate and low optical NV excitation intensity. Our results provide practical benchmarks and guidance for selecting NV-diamond sensors tailored to specific experimental constraints and sensing requirements.
The nitrogen vacancy (NV) center in diamond is a versatile color center used for magnetometry, quantum computing, and quantum communications. In this article, using a single laser beam as a pump and probe, we measure the spin states of the NV center using the Faraday effect and use such measurements to develop a novel magnetic field sensor. Using the spin-state-dependent effect on the left and right circularly polarized light, we probe and confirm the existence of spin-orbit coupling in the NV center at room temperature. The sensitivity of our magnetometer is 350 350~350 nT/Hz\sqrt{Hz}Hz​, limited by the background produced by the laser trapped inside the diamond. We argue that by using an optical cavity and a high-purity diamond, sensitivities in the femtotesla level can be achieved.