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arXiv:2309.12006 · PRX Quantum

High-Field Optical Cesium Magnetometer for Magnetic Resonance Imaging

Hans Stærkind, Kasper Jensen, Jörg Helge Müller, Vincent O. Boer, Eugene Simon Polzik, Esben Thade Petersen

Published Apr 24, 2024• 13 citations
arXivHTMLPDF

Abstract

We present a novel high-field optical quantum magnetometer based on saturated absorption spectroscopy on the extreme angular-momentum states of the cesium D2 line. With key features including continuous readout, high sampling rate, and sensitivity and accuracy in the ppm range, it represents a competitive alternative to conventional techniques for measuring magnetic fields of several teslas. The prototype has four small separate field probes, and all support electronics and optics are fitted into a single 19-inch rack to make it compact, mobile, and robust. The field probes are fiber coupled and made from nonmetallic components, allowing them to be easily and safely positioned inside a 7 T MRI scanner. We demonstrate the capabilities of this magnetometer by measuring two different MRI sequences, and we show how it can be used to reveal imperfections in the gradient coil system, to highlight the potential applications in medical MRI. We propose the term EXAAQ (EXtreme Angular-momentum Absorption-spectroscopy Quantum) magnetometry, for this novel method. Published by the American Physical Society 2024

DOI
10.1103/prxquantum.5.020320

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We present a novel high-field optical quantum magnetometer based on saturated absorption spectroscopy on the extreme angular-momentum states of the cesium D2 line. With key features including continuous readout, high sampling rate, and sensitivity and accuracy in the ppm range, it represents a competitive alternative to conventional techniques for measuring magnetic fields of several teslas. The prototype has four small separate field probes, and all support electronics and optics are fitted into a single 19-inch rack to make it compact, mobile, and robust. The field probes are fiber coupled and made from nonmetallic components, allowing them to be easily and safely positioned inside a 7 T MRI scanner. We demonstrate the capabilities of this magnetometer by measuring two different MRI sequences, and we show how it can be used to reveal imperfections in the gradient coil system, to highlight the potential applications in medical MRI. We propose the term EXAAQ (EXtreme Angular-momentum Absorption-spectroscopy Quantum) magnetometry, for this novel method. Published by the American Physical Society 2024
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Accurate measurement of strong magnetic fields in the Tesla range remains a persistent challenge due to calibration drift, nonlinearity, and spatial gradient sensitivity. Here, we present a compact magnetometry approach based on sideband-overlap Zeeman spectroscopy, enabled by a functionalized MEMS cesium vapor cell. The vapor cell features a dual-chamber glass–Si–glass structure with integrated microheaters on the optical window. A first-order electro-optic modulator produces optical sidebands aligned with the σ+ and σ−{{\rm{\sigma }}}^{-}σ− Zeeman-split components of the Cs D1 line under the hyperfine Paschen–Back regime. Magnetic field scanning from zero to Tesla-scale fields enables extraction of the frequency offset between reference and Zeeman-shifted spectra. This frequency shift is directly converted into magnetic field strength using Zeeman spectroscopy in the hyperfine Paschen–Back regime. The method resolves sixteen Zeeman transitions (eight σ+{{\rm{\sigma }}}^{+}σ+ and eight σ−{{\rm{\sigma }}}^{-}σ− ), allowing measurement of a field strength of 0.6694921 T, with a single-shot resolution of 6.4 μT and a cross-transition repeatability of σB = 8.9 μT (corresponding to 13 ppm at 0.6695 T). In a millimeter-scale sensing volume, the system achieves sub-10 μT repeatability without requiring a uniform bias field. These results indicate that the microfabricated high-field magnetometer can serve as a compact and practical approach for Tesla-range field measurement and pave the way for chip-scale quantum devices.
Abstract We develop a quantum precision measurement method for magnetic field at the Tesla level by utilizing a fiber diamond magnetometer. Central to our system is a micron-sized fiber diamond probe positioned on the surface of a coplanar waveguide made of nonmagnetic materials. Calibrated with a nuclear magnetic resonance magnetometer, this probe demonstrates a broad magnetic field range from 10 mT to 1.5 T with a nonlinear error better than 0.0028% under a standard magnetic field generator and stability better than 0.0012% at a 1.5 T magnetic field. Finally, we demonstrate quantitative mapping of the vector magnetic field on the surface of a permanent magnet using the diamond magnetometer.
The ability to measure magnetic fields with high sensitivity is a key requirement in many physical, biological and medical applications. Currently the most sensitive magnetometers are optical magnetometers, in which the polarization of an atomic sample responds to the field and is read out by an optical measurement. These instruments are limited by two fundamental sources of quantum noise: projection noise of the atoms and shot noise of the light. For magnetometers designed to have a high statistical sensitivity, contributions from both sources are comparable. Here we show that the sensitivity can be improved by the application of non-classical light.
We implement a scalable platform for quantum sensing comprising hundreds of sites capable of holding individual laser-cooled atoms and demonstrate the applicability of this single-quantum-system sensor array to magnetic field mapping on a two-dimensional grid. With each atom being confined in an optical tweezer within an area of 0.5 μ m 2 at mutual separations of 7.0 ( 2 ) μ m , we obtain micrometer-scale spatial resolution and highly parallelized operation. An additional steerable optical tweezer allows rearrangement of atoms within the grid and enables single-atom scanning microscopy with submicron resolution. This individual-atom sensor platform finds an immediate application in mapping an externally applied dc gradient magnetic field. In a Ramsey-type measurement, we obtain a field resolution of 98(29) nT. We estimate the sensitivity to be 25 μ T / Hz . Published by the American Physical Society 2024
Functional imaging equipment based on miniaturized atomic magnetometers with array arrangement exhibits promising prospects in biomagnetic scenarios. However, crosstalk from the modulated magnetic field between adjacent sensors degrades the imaging accuracy. To address this issue, this study proposes an all-optical dual-axis zero-field atomic magnetometer using light-shift modulation. We utilize an acousto-optic modulator to modulate a detuned circularly polarized beam for pumping the atomic spin ensembles. This beam allows for the optical modulation of spin polarization and meanwhile generates a light-shift modulation, effectively replacing the conventional magnetic field modulation. By using a probe beam to detect the optical rotation angle perpendicular to the direction of the pump beam, we construct an all-optical configuration of a longitudinally modulated atomic magnetometer, enabling dual-axis magnetic field measurements. Experimental results demonstrate dual-axis sensitivities of 29 and 15fT/Hz1/2, respectively. This method eliminates the need for conventional coil-based magnetic field modulation, thereby paving the way for potential applications in magnetocardiography and magnetoencephalography.Received 3 August 2023Revised 13 November 2023Accepted 4 December 2023DOI:https://doi.org/10.1103/PhysRevApplied.21.014023© 2024 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasMagneto-optical effectMagnetometryOptical pumpingStark effectPhysical SystemsAlkali metalsAtomic gasesTechniquesOptically detected magnetic resonancePrecision measurementsAtomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics