The n2EDM experiment at the Paul Scherrer Institute is a fundamental particle physics experiment which aims to measure the neutron electric dipole moment with a sensitivity below $1 \times 10^{-27}$โฏeยทcm. Achieving this level of sensitivity requires exact control of magnetic field uniformity to reduce systematic effects. To this end, an array of 112 optically pumped cesium vapor magnetometers...
Optically Pumped MagnetoEncephaloSpinography (OP-MSEG) offers a promising new avenue for concurrent non-invasive imaging of spinal cord and brain activity. However, the accuracy of source localisation in the cord critically depends on the quality of the forward model; particularly given the spinal cord's complex geometry, deep location, and conductive environment. In this study, we evaluate...
The n2EDM experiment at the Paul Scherrer Institut aims to probe the neutron electric dipole moment with a sensitivity below 10$^{-27}$ $e\cdot$$\mathrm{cm}$, requiring an exceptionally clean magnetic environment. To identify minuscule magnetic impurities that could introduce false EDM signals, we developed a mobile gradiometer based on optically pumped cesium magnetometers in the Mx...
This contribution reports on a new spray-coating approach for magnetic shielding materials aimed at improved low-frequency field measurements with optically pumped magnetometers. Building on earlier investigations, we have successfully spray coated pure iron and Invar onto Aluminum substrates, and ongoing work explores spray coating of mu-metal. A 3-axis Helmholtz coil setup in a magnetically...
Until now, highly sensitive optically pumped magnetometers (OPMs) have mainly been used in shielded environments under strictly controlled laboratory conditions. However, for a continuous dissemination of this technology and the development of additional areas of application and research, it will be essential to adapt it to more challenging environments.
In particular, the maritime domain...
Atomic magnetometers offer high sensitivity for measuring magnetic fields in areas such as biomagnetic monitoring, non-destructive testing, geological exploration, and fundamental physics research. Unlike superconducting quantum interference devices (SQUIDs), they do not require cryogenic operating temperatures, making them more practical for a range of real-world conditions. In addition, they...
Optically pumped magnetometers (OPMs) offer significant advantages for biomagnetic measurements such as magnetoencephalography (MEG), owing to their high sensitivity, room-temperature operation, and potential for wearable configurations. In these applications, gradiometric measurement serves as an effective method to suppress common-mode environmental noise. However, it is difficult to make...
Background: Magnetic Induction Tomography (MIT) is an electromagnetic imaging technique that maps a materialโs electrical conductivity by inducing eddy currents via a primary oscillating magnetic field. The resulting secondary magnetic fields from the eddy currents are measured for image reconstruction and object characterisation. Performing MIT on low-conductivity samples (e.g. human tissue,...
Sensitivity Improvement of a $^4$He Optically Pumped Magnetometer in the RF band
N. Umetani$^{1}$, Y. Fujimoto$^1$, K. Shinada$^1$, J. Saikawa$^1$, T. Munaka$^1$, and T. Kobayashi$^2$
$^1$Technology Research Laboratory, Shimadzu Corporation, Soraku-gun, Kyoto, Japan*
$^2$HBRC, Graduate School of Medicine, Kyoto University, Sakyo-ku, Kyoto, Japan***
High-sensitivity...
A key motivator for the adoption of OPMs for neural recordings is that they allow recordings from multiple different electrophysiological sources simultaneously. Simultaneous recording from the brain (MEG) and spinal cord (MSG) has recently garnered interest [1,2], as it has the potential to facilitate research into cortico-spinal connectivity, furthering our understanding of sensorimotor...
A novel approach for the fabrication of glass-based atomic vapor cells is presented, combining laser-assisted glass structuring and a hermetic glass joining technique. The structure of these glass-based cells includes three glass chips stacked on top of each other, with the central chip containing interconnected cavities. Glass structuring using selective laser-induced etching (SLE) process...
Enhancing the interaction strength between light and atoms amplifies the Faraday rotation effect, thereby improving the measurement sensitivity of optical rotation detection. This work integrates a multi-reflection cavity into the vapor cell of the SERF co-magnetometer for the first time, increasing the interaction strength between light and atoms. We establish a model that accounts for light...
Alkali vapor cells are at the heart of a variety of atomic systems and quantum sensors, including atomic clocks and gyroscopes, laser frequency references, Rydberg atom-based electric field sensors, and especially for this work, optically pumped magnetometers. In state-of-the-art, wafer-scale vapor cell fabrication technology, the alkali metal is often introduced as a chemical compound into...
Auditory Brainstem Response (ABR) testing is currently the only clinical method for objectively determining hearing thresholds by detecting wave V of Auditory Evoked Potentials (AEPs). Its magnetic counterpart, Auditory Evoked Fields (AEFs), offers a promising alternative by identifying the sound pressure level (SPL) at which auditory responses, such as the M100, are detectable.
Whilst...
Junlin Chen$^{a,b}$, Changhao Zhang$^{a,b}$, Jiaqi Yang$^{a,b}$, Zhenglong Lu$^{a,b}$, Haowen Tian$^{a,b}$, Yanchao Chai$^{a,b}$, Yuntian Zou$^{a,b}$, and Liwei Jiang$^{a,b,c}$
$^{a}$ Institute of Large-scale Scientific Facility and Centre for Zero Magnetic Field Science,
Beihang University, Beijing, 100191, China
$^{b}$ Hangzhou Innovation Institute, Beihang University, Hangzhou, 310051,...
Recently, Meta Platforms, Inc. reported that brain-machine interfaces (BMIs) based on magnetoencephalography (MEG) can achieve higher accuracy than those based on electroencephalography (EEG)$^1$. Optically pumped magnetometers (OPMs), which have been actively developed for miniaturization and shield-free measurements, offer a promising noninvasive sensing solution for BMIs. In this study, we...
This study investigates the effects of power broadening on nonlinear magneto-optical rotation (NMOR) magnetometers. As the laser power increases, the interference between two partially resolved transitions of 87Rb induced by velocity-changing collisions can be exacerbated by power broadening, resulting in a reduction
of the rotation rate, and the shift of the optimal laser frequency...
Optically Pumped Magnetometers (OPM) have been a promising technology for magnetometry. Zero-field OPMs have evidenced a capability to measure magnetic fields as small as 10 fT [1] with sensitivity levels ranging from 1 fT/โHz [2]. Moreover, the practical advantages of the OPM include its compact size and independence of the cryogenic environment, unlike SQUID-based magnetometers [3]. These...
Miniaturized high-sensitivity OPMs require โ simultaneously โ small volumes, temperature control, magnetic field control, and low magnetic noise. This presents interlinked challenges when designing vapor cells for OPMs. We report a dual-chamber ($4 \times 4 \times 1.5$ mm$^{3}$) low-noise functionalized vapor cell (FVC) and its use in a single-beam SERF OPM. The FVC, made at wafer scale by...
We present early results on the integration of a compact, hot-vapor based optically pumped magnetometer (OPM) onto a drone platform for unshielded airborne magnetic sensing. This work is part of a broader effort to develop quantum magnetometry solutions for field applications for geo-prospection and the detection of unexploded ordnance. The system employs an alkali vapour-based OPM operating...
Triaxial spin-exchange relaxation-free (SERF) atomic magnetometers (AMs) provide more comprehensive magnetic field information in bio-magnetic measurements, effectively improving the accuracy of magnetic source reconstruction. Typically, the triaxial AM is considered to be three independent orthogonal single-axis AMs, but the interaction of the triaxial modulation is ignored. This study...
For SERF atomic magnetometer, photo-elastic modulator (PEM) is a commonly-used optical polarimetry technique to detect the weak angle signal due to its high sensitivity. Magnetic field to be measured can be obtained by demodulating the first-harmonic response signal from the photoelectric detector (PD) based on the modulation frequency of PEM. The optical rotation angle contains essential...
Four wave mixing is a popular spectroscopic technique with limited examples of use for magnetometry. As an all optical, heterodyne technique, it allows for high sensitivity measurement, without the challenges associated with using RF.
All akali vapours could be used for four wave mixing, however we selected sodium due to having the vapour cell and dye laser readily available in our lab. A...
Optically pumped magnetometers (OPMs) utilizing entangled spins offer the promise of sensing performance beyond the standard quantum limit (SQL). Unfortunately, realizing this advantage has proven exceedingly difficult. Entangled states are inherently tricky to create and maintain. It is often better to simply use many unentangled atoms rather than entangling far fewer of them. Nevertheless,...
Changhao Zhang$^{1,2,3}$, Junlin Chen$^{1,2,3}$, Zhenglong Lu$^{1,2,3}$, Jiaqi Yang$^{1,2,3}$, Haowen Tian$^{1,2,3}$, Yanchao Chai$^{1,2,3}$, Yuntian Zou$^{1,2,3}$ and Liwei Jiang$^{1,2,3}$
$^1$ Institute of Large-scale Scientific Facility and Centre for Zero Magnetic Field Science, Beihang University, Beijing, 100191, China
$^2$ Hangzhou Innovation Institute, Beihang University, Hangzhou,...
Recording neuromagnetic fields from the spinal cord with Optically Pumped Magnetometers (OPMs) has the potential to offer new insights into spinal cord function. To realise the full potential of OPM based magnetospinography (OPM-MSG), accurate forward models incorporating subject-specific anatomy are required [1]. These models depend on torso and internal organ geometry (heart, lungs, etc.)...
The precision of magnetic field estimation using a scalar-mode optically pumped magnetometerใ(OPM) is significantly degraded in the presence of environmental magnetic noise. Spatial inhomogeneity in the noise magnetic field reduces the transverse relaxation time, resulting in a shorter, noisier free induction decay (FID) signal. To address this issue, we employ a spin echo technique using a...
We investigate the use of optically-addressable nuclear spins in the fermionic isotopes of Mercury (Hg199 and Hg201) for generating macroscopically entangled spin squeezed states [1,2] in hot atomic vapors. We calculate the Wineland spin squeezing parameter [3] under the influence of different atomic loss and spin decoherence sources as well as inhomogeneous atom-light coupling within the...
Unlike electrical signals, magnetic signals are not affected by the biological tissues because of the nearly homogeneous permeability. Therefore, magnetoencephalography (MEG) is more suitable for detecting biological phenomenon. In the past several decades, superconducting quantum interference device (SQUID) magnetometers are most commonly used for MEG. However, the SQUID magnetometers would...
In conventional magnetic field estimation using scalar-mode optically pumped magnetometers (OPMs), the goal is to estimate the frequency of a decaying sine curve that best fits a free induction decay (FID) signal. This approach assumes a constant magnetic field during each FID period, limiting its ability to track the temporal dynamics of fields oscillating at high frequencies.
ใTo overcome...
AbstractโSoft magnetic materials, characterized by high magnetic permeability, are typically utilized in the magnetic shields. Among these, a composite shielding system comprising outer layer Permalloy and inner layer manganese-zinc (Mn-Zn) ferrite has demonstrated exceptional performance in providing an extremely-low magnetic interference environment for spin-exchange relaxation-free (SERF)...
Abstract๏ผWith the rapid advancement of cutting-edge fields such as quantum precision measurement and biomagnetic sensing, increasingly stringent requirements are being placed on the suppression of ambient magnetic fields. The sensitivity improvement of atomic magnetometers is currently limited by the residual magnetization and intrinsic magnetic noise of conventional soft magnetic shielding...
Radio-frequency (rf) atomic magnetometers (AM) can measure oscillating magnetic fields (1 kHz-1 MHz range) with fT/โHz sensitivity and are 2D sensors. Magnetic induction tomography (MIT) measurements require sensitive magnetometers, e.g., for use in the non-destructive testing of pipework and defect detection. Experimental work, verified with COMSOL simulations, shows how changing rf field...
Magnetoencephalography (MEG) based on optically pumped magnetometers (OPM-MEG) is a relatively novel method to measure brain activity non-invasively in humans. It offers several advantages over traditional SQUID (superconducting quantum interference device) based MEG and EEG [1-3]. However, its properties, in particular test-retest reliability (stability of measurements in time) and construct...
Molecular Dynamics Optimization of Multilayer OTS SAMs Cells for Enhanced Performance in Single Beam SERF Magnetometers
*Yi-an XU1,2, Yuhao WANG1,2, Ziqian YUE1,2, Zhuangsheng ZHU1,2
1 School of Instrumentation Science and Opto-electronics Engineering,
Beihang University, Beijing, China
2 Hangzhou Innovation...
Spin-exchange relaxation-free (SERF) comagnetometer is significant in exploring fundamental physics and high-precision inertial sensing. However, traditional continuous measurement based on steady atomic spin polarization limits the suppression of long-term drifts, which is pivotal for inertial navigation and the search for new physics beyond standard model.We propose a SERF comagnetometer...
The modulated single-beam Spin-Exchange Relaxation-Free (SERF) optically pumped magnetometers (OPMs) hold significant promise for applications in biomagnetic measurements. Achieving the SERF regime requires a high atomic number density, which necessitates a stable thermal control system for the vapor cell. Conventionally, the vapor cell temperature is measured by the platinum resistance...
Auditory evoked responses, recorded using electroencephalography or magnetoencephalography (MEG), are commonly used to study cognitive processes related to hearing in humans. These responses have also been recorded in other species but mostly by using invasive techniques. Here, for the first time, we present non-invasive measurements of these responses in unanesthetized domestic cats (Felis...
Background:
Magnetoencephalography (MEG) systems using optically pumped magnetometers (OPMs) require magnetically shielded rooms (MSRs); typically built from 2โ5 layers of high-permeability material (e.g., MuMetal) and a conductive layer (e.g., copper) to block external magnetic fields. While effective, current MSRs are heavy (2,500โ13,000 kg) and difficult to install (>3 m high),...
We present the development of a compact and space compatible quantum wideband sensor for radio-frequency (RF) electric fields based on Rydberg atoms in thermal alkali vapor cells.
Rydberg-atom based sensors provide sensitivity to the electric component of RF fields thanks to the high polarizability of excited states.
Unlike traditional RF antennas, these sensors are self-calibrated via...
In SERF atomic magnetometers, the spin polarization of alkali-metal atoms is a critical parameter affecting the signal-to-noise ratio. The signal of the magnetometer is optimal for a particular spin polarization, and higher spatial uniformity of spin polarization enhances the signal. Hybrid optical pumping is a method to improve the spatial uniformity of spin polarization. The signal of the...
The miniaturization of optical pumping magnetometer became the focus of research, and the miniaturization of the alkali metal vapor cell is the key to the miniaturization of the atomic magnetometer. The development of micro-electromechanical systems (MEMS) provides the basis for miniaturization of alkali metal vapor cells. The sealing of MEMS vapor cells was mainly realized by anodic bonding,...
Atomic-optical magnetometers have reached sensitivities where quantum noise becomes a limiting factor. One fundamental quantum noise source is back-action noise, which arises from the coupling between quantum fluctuations in the probe lightโs polarization and the atomic spin ensemble being measured. This back-action can be circumvented by stroboscopically modulating the probe intensity at...
P. D. D. Schwindt$^1$, J. Iivanainen$^1$, J. Dhombridge$^1$, T. S. Read$^1$, D. M. Ridley$^1$, B. J. Little$^1$, T. R. Carter$^1$, J. McKay$^3$, J. Stephen$^4$, S. Taulu$^5$, and A. Borna$^1$
1 Sandia National Laboratories, Albuquerque, USA
2 University of New Mexico, Albuquerque, USA
3 Candoo Systems,
4 Mind Research Network
5 Institute for Learning and Brain Sciences, University of...
Nuclear spin-based OPMs offer a path toward advancing sensitive magnetometry by leveraging the long coherence times of nuclear spin ensembles. Mercury (Hg), particularly its odd isotopes, is a promising candidate due to its accessible 254 nm $^1S_0 \rightarrow\ ^3P_1$ optical transition and high vapor pressureโover $10^3$ times that of cesium at room temperatureโenabling large optical depths...
Magnetically shielded rooms (MSRs) significantly attenuate the ambient magnetic field, making it possible to perform measurements of very low signals. For measurements with optically pumped magnetometers (OPMs), such rooms are, in most cases, essential. In a two-layer magnetically shielded room at the Faculty of Mechatronics, Warsaw University of Technology, the QuSpin Zero-Field Magnetometer...
The current method for disseminating the unit Tesla relies on NMR measurements on field polarized proton spins, using water [1]. However, the relative measurement uncertainties are restricted to values between $10^{-4}$ and $10^{-6}$ by limited SNR at fields below 2ย mT and a rather insensitive absorption technique at fields above 10ย mT. To overcome these limitations, we explore the use of...
We report measurements of the bioelectricity of the electrically stimulated abductor digiti minimi (ADM) muscle of the right hand using three types of measurement modalities:
(1) by recording magnetic flux density with a state of the art zero field optically pumped magnetometer (OPM),
(2) by recording magnetic flux density with a superconducting quantum interference device (SQUID), and
(3)...
Optically pumped magnetometers (OPMs) are highly sensitive sensors that can detect minute biomagnetic fields. However, OPM signals are often degraded by ambient magnetic interference and motion artifacts. To address such noisy signals, we apply independent low-rank matrix analysis (ILRMA), a multichannel blind source separation (BSS) method that leverages the low-rank structure of source power...
Operating optically pumped magnetometers (OPMs) in unshielded environments is challenging. The sensors need a high dynamic range of at least several 100 nT to not be saturated by environmental noise (e.g. Mains noise), and a bandwidth of at least 1 kHz in order to avoid aliasing effects. Further, a multichannel system is often desired to allow for model-based spatial noise removal. We aim in...
Atomic magnetometry based on the spin-exchange relaxation-free (SERF) effect has emerged as a key technology for high-precision magnetic field measurements due to its ultrahigh sensitivity. A critical factor in enhancing the sensitivity of SERF magnetometers is achieving uniform spin polarization in high-density alkali-metal vapor. However, conventional narrow-linewidth optical pumping often...
We present a compact optical magnetic gradiometer based on laser-written vapor cells (LWVCs) with a dual-chamber design, aimed at high-sensitivity detection of magnetic field gradients. This system is built around an optically pumped magnetometer (OPM), which enables precise measurements of magnetic variations while rejecting common-mode noiseโan essential feature for operation in unshielded...
In recent work [1], we showed the efficacy of an intrinsic axial gradiometer for the detection of human biomagnetism. We now present the next generation of this sensor, which employs the nonlinear magneto-optical rotation effect. By using simplified integrated optics, printed circuit boards, and a modular design, we have improved the mechanical rigidity and decreased the standoff from the...
In the research of the interaction between light and atoms, optical ellipticity is a key parameter to characterize the pump and absorption process [1,2]. It was generally believed that ellipticity only originated from the the interaction between magnetic fields and polarized alkali metal atomic ensembles in previous researches [3,4,5]. In this research, a new mechanism of circular dichroism...
In mobile magnetoencephalography (MEG) systems, hundreds of atomic magnetometer sensor heads are typically deployed, making the miniaturization of atomic magnetometers essential. The coils used for spin modulation and magneticโfield control are critical components of these devices. Here, using microelectromechanical systems (MEMS) technology, we have designed and fabricated a threeโdimensional...
Strict magnetic field control is an integral part of quantum sensors such as optically pumped magnetometers (OPMs). OPMs are used in pioneering research including biomagnetic measurement, which utilises hybrid shielding to provide the low and stable field environment required for precise measurements. Further applications where controlled field environments are required include atom...
We demonstrate atomic spectroscopy and optical magnetometry with picotesla sensitivity using laser-written Rb vapor cells. The technology can be integrated with photonic structures and microfluidic channels in a single platform for lab-on-chip atomic quantum sensing.
We describe progress toward quantum enhancement of an optically pumped magnetometer (OPM), operating around Earth's magnetic field. We demonstrate back-action evading scheme with sub-pT/vHz quantum-noise-limited sensitivity, for frequency and amplitude modulation schemes. We also aim to demonstrate the quantum advantage of spin squeezing in highly polarized atomic ensembles within...
Optically pumped magnetometers (OPMs) have significantly advanced the field of biomagnetic sensing, particularly in wearable applications such as magnetoencephalography (MEG). Triaxial measurement techniques further enhance the localization accuracy of these systems by capturing full vector information. However, the precision of triaxial OPM measurements is still constrained by two major...
In magnetic resonance experiments, it is widely recognized that a nonuniform magnetic field can lead to an increase in the resonance line width, as well as a reduction in sensitivity and spectral resolution. However, a nonuniform magnetic field can also cause shifts in resonance frequency, which has received far less attention. In this work, we investigate the frequency shift caused by...
The Transient Electromagnetic Method (TEM) has attracted significant interest because of its non-destructive evaluation, rapid response, and environmentally adaptable. In traditional TEM systems, the signal acquisition module generally utilizes multi-turn induction coils. Based on Faradayโs law of electromagnetic induction, these coils detect the secondary eddy currents induced by the primary...
Miniature atomic vapor cells are a fundamental component in future-focused field-deployable quantum technology development. Here, we explore the physics of diffusive alkali metal-noble gas spin systems magnetization in a mm-sized wafer-fabricated vapor cell, engineered with an eye towards room temperature atomic magnetometry, co-magnetometry and gyroscope setups. Through a systematic survey of...
