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Symposium Latsis on Diamond Photonics - Physics, Technologies and Applications

Microwave-free vector magnetometry based on nitrogen vacancy ensembles in diamond

Huijie Zheng, Zhiyin Sun, Georgios Chatzidrosos, Arne Wickenbrock, Dmitry Budker

Published Jan 1, 2019• 1 citation
Publisher

Abstract

We propose and demonstrate a microwave-free vector magnetometer using nitrogen- vacancy (NV) ensembles in diamond. This magnetometer leverages the level anti-crossing in the ground state. It exhibits rms noise floor of ≈300 pT/√Hz for all directions. This technique is broadly applicable to both ensemble sensors and potentially also to single-NV sensors.

DOI
10.1364/dp.2019.40

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We propose and demonstrate a microwave-free vector magnetometer using nitrogen- vacancy (NV) ensembles in diamond. This magnetometer leverages the level anti-crossing in the ground state. It exhibits rms noise floor of ≈300 pT/√Hz for all directions. This technique is broadly applicable to both ensemble sensors and potentially also to single-NV sensors.
Sensing vector magnetic fields is important to many applications in fundamental physics, bioimaging, and materials science. Sensors exploiting nitrogen-vacancy (N-VVV) centers typically interrogate N-VVV ensembles oriented in all directions, thwarting nanoscale spatial resolution. Utilizing the level anticrossing in the triplet ground state, the authors demonstrate a $m\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}w\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}v\phantom{\rule{0}{0ex}}e\ensuremath{-}f\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}e$ vector magnetometer that simultaneously measures all Cartesian components of the field, offering wide-band operation and high, equal sensitivity in all directions. This technique may work for single N-VVV centers as well as ensembles, extending vector measurements to the nanoscale, at ambient temperatures.
We demonstrate 4π4π4π-steradian vector magnetic field sensing using an ensemble of nitrogen-vacancy (NV) centers in a single-crystal diamond coupled to a microwave (MW) cavity. The MW cavity enhances the spin-photon coupling which enables efficient, high-contrast spin-state readout via MW interrogation and removes the need for bulky optical collection components. An applied AC bias magnetic field lifts the zero-field degeneracy of the four crystallographic NV orientations, allowing each orientation to be individually addressed and used for vector reconstruction of the magnetic field. The resulting magnetometer has a 40\% contrast (20x higher than typical for optical spin-ensemble readout) and achieves a single-axis sensitivity of 250 pT/Hz\sqrt{\mathrm{Hz}}Hz​ which is flat from DC to 1 kHz. Noise models of the composite spin-cavity system establish MW amplitude noise as the dominant noise source and predict a thermal noise limit of 2 pT/Hz\sqrt{\mathrm{Hz}}Hz​.
Nitrogen-vacancy (NV) centers in diamond provide a solid-state platform for quantum sensing. While optically detected magnetic resonance techniques offer high sensitivity, their reliance on microwaves introduces heating and stray electromagnetic fields that can perturb nearby samples. Optical approaches based on cross-relaxation between differently oriented NV centers remove this constraint but have so far required stringent alignment of the external field with crystallographic axes, restricting their practicality. Here we introduce a general framework for microwave-free vector magnetometry at near-zero field that leverages Bayesian inference to extract both the magnetic field vector and the NV orientation directly from photoluminescence maps. An analytical model of cross-relaxation resonances enables efficient inference under arbitrary field and orientation configurations, while naturally incorporating the discrete degeneracies of the NV symmetry. We experimentally demonstrate robust orientation determination and vector-field reconstruction, establishing a general route toward compact and alignment-free NV magnetometers for practical sensing applications.
Quantum sensing of low-frequency magnetic fields using nitrogen-vacancy (NV) center ensembles has been demonstrated in multiple experiments with sensitivities as low as $\sim1pT/1 pT/1pT/\sqrt{\text{Hz}}.Todate,however,demonstrationsofhigh−frequencymagnetometryintheGHzregimewithNVdiamondareordersofmagnitudelesssensitive,abovethenT/. To date, however, demonstrations of high-frequency magnetometry in the GHz regime with NV diamond are orders of magnitude less sensitive, above the nT/.Todate,however,demonstrationsofhigh−frequencymagnetometryintheGHzregimewithNVdiamondareordersofmagnitudelesssensitive,abovethenT/\sqrt{\text{Hz}}$ level. Here we adapt for microwave frequencies techniques that have enabled high-performance, low-frequency quantum sensors. Using a custom-grown NV-enriched diamond combined with a noise cancellation scheme designed for high-frequency sensing, we demonstrate a Rabi-sequence-based magnetometer able to detect microwave fields near 2.87 GHz with a record sensitivity of 3.4 pT/Hz\sqrt{\textrm{Hz}}Hz​. We demonstrate both amplitude and phase sensing and project tunability over a 300 MHz frequency range. This result increases the viability of NV ensembles to serve as microwave circuitry imagers and near-field probes of antennas.
Quantum sensors based on nitrogen vacancy (NV) centers in diamond have been a central topic in the sensing community for more than a decade. The extraordinary properties at room temperature of the spin system in diamond have made it one of the most prominent quantum platforms for the development of commercial quantum sensors. In particular, the sensitivity of the electronic spin in NV centers has made diamond-based magnetic sensors of special interest for their potential application in medical, industrial or navigation solutions. However, the use of these sensors for universal vector magnetometry was constrained by the need for previous knowledge on the field being measured to fully exploit their benefits. In this work, we show a method to perform unconditional vector magnetometry without the need of external information on the magnetic field, based only on the spatial arrangement of the diamond and the microwave antenna combination. While previous NV-based vector magnetometry methods require partial knowledge of the magnetic field (e.g. a calibrated bias field), we exploit the possibilities of selecting particular directions of the spins in the diamond with elliptically polarized microwave fields. We prove that our method allows to estimate both magnitude and direction of external magnetic fields without further assumptions or constraints.