Unconditional full vector magnetometry using spin selectivity in Nitrogen Vacancy centers in diamond

Abstract

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.

Figures (9)

• Figure 1: Schematic depiction of the protocol for bias-free vector magnetometry.$\boldsymbol{a)}$ Experimental setup showing the quadrature antenna with a diamond placed in the center and surrounded by Halbach arrays of permanent magnets. Laser excitation ($532$ nm) and fluorescence collection with a parabolic compound lens and analog detector are shown. The inset shows a schematic depiction of the spin-selective unconditional magnetometry method where elliptically polarized MW target a particular axis with circular polarization. $\boldsymbol{b)}$ Different peak ordering regions for magnetic field vectors in the surface of a sphere, showing the dynamic range limits of bias field magnetometry. Each color represents a distinct ordering of the directions producing the peaks in an ESR. The numbers labeling the colors correspond to each of the possible permutations of the four NV orientations ($4!$) when ordered from highest to lowest field projection, without distinguishing between positive and negative field projections. The 48 possible fields generating the ESR spectrum in c) are marked with dots over each colored region. $\boldsymbol{c)}$ Experimental measurement of an ESR with linear (black curve) and elliptically polarized (blue curve) MW showing peak attenuation from a single axis.
• Figure 2: Experimental proof of concept, where each row shows the optimizations of MW fields to target the individual NV directions NV2 (-), NV1(+) NV3(-) and NV4(+) from top to bottom. $\boldsymbol{a)}$ MW field ellipses generated by the AWG and optimized for each crystal direction after hardware imperfections. $\boldsymbol{b)}$ ESR spectra, under driving by the corresponding calibrated MW field to the left, showing attenuation of a single NV axis enabling the identification of the peak distribution in the ESR spectrum. $\boldsymbol{c)}$ Calibration of the MW fields showing great dependency of peak attenuation to MW phase. The configurations resulting in the highest contrast correspond to the results in a) and b).
• Figure 3: Unconditional Spin-Selective Vector Magnetometry. Measurement protocol based on 4 ESR measurements with pre-calibrated spin-selective MW configurations allowing exact unconditional identification of peak distribution.
• Figure 4: Unique solution of magnetic fields with similar ESR signature.$\boldsymbol{a)}$ ($\boldsymbol{b)}$) ESR measurement under magnetic field $\vec{B_1}$ ($\vec{B_2}$) with linear MW field (black line) and the optimized MW control field for NV3- (green line). $\boldsymbol{c)}$ Location of the resolved magnetic vectors in the configuration map of bulk NV centers, showing the calibration and protocol presented are sufficient to resolve magnetic fields generating arbitrary peak orientations with similar ESR signatures.
• Figure S1: Schematic representation of the crystal directions and reference frames.$\boldsymbol{a)}$ Axis orientations in diamond. $\boldsymbol{b)}$ Chosen coordinates for NV reference frame (blue) and laboratory frame of reference (black).