Atomic Magnetometer Research Articles

Signal-enhanced high-sensitivity atomic magnetometer based on multi-pass cell

Signal-enhanced high-sensitivity atomic magnetometer based on multi-pass cell

A non-thermal method to maintain alkali vapor density of anti-relaxation coating cell in spin exchange relaxation-free magnetometer

The long-term stability of alkali metal vapor cell density is crucial for the performance of Spin Exchange Relaxation-Free (SERF) magnetometers. This paper addresses the issue of atomic density consistency commonly encountered with OTS and paraffin coatings in current quantum magnetometers. For the first time, the LIAD non-thermal method is applied to SERF magnetometers to maintain the long-term stability of alkali metal density. The study identifies the critical roles of desorption light luminous flux and integrating sphere uniformity in enhancing LIAD effectiveness. A new model based on the absorption spectrum of 85Rb and 87Rb was developed, achieving an R-square value of 0.989 and revealing a rubidium isotopic abundance ratio of 2.8:1, with OTS-coated cells showing the highest density retention. These findings contribute to the advancement of cryogenic SERF magnetometers by providing a deeper understanding of LIAD mechanisms and offering a viable alternative to thermal density control methods.

Bandwidth compensation for ultra-high-sensitivity SERF magnetometers in magnetocardiac sensing

The trade-off between sensitivity and bandwidth has limited the clinical application of spin exchange relaxation-free (SERF) atomic magnetometers in magnetocardiac measurements. This research addresses the issue by modeling the SERF magnetometer as a first-order inertial link and proposing a method that integrates transient response with tracking signals. The tracking-differential link enables the simultaneous acquisition of both transient and tracking signals, leading to effective noise suppression. Empirical mode decomposition is employed to extract features and filter out noise, ensuring high signal quality. This method extends the bandwidth of dual-beam magnetometers from 9.77 Hz to 240 Hz and single-beam magnetometers from 139 Hz to 289 Hz, while preserving sensitivities of 1 fT/Hz1/2 and 10 fT/Hz1/2, respectively. This research enables high-bandwidth measurements with sub-femtotesla magnetic field sensitivity, presenting promising application opportunities.

Time course of visual attention in rats by atomic magnetometer.

Atomic magnetometer (AM) is utilized to non-invasively detect event-related magnetic fields (ERMFs) evoked by visual stimuli in rats. The aim of this study was to investigate the relationship between N2-like amplitude and visual attention. To achieve this, we combined the AM with a visual stimulation system and employed the passive single-stimulus paradigm. By measuring the ERMFs at various inter-stimulus intervals (ISIs) with a sensitivity of 20 fT/[Formula: see text], we analyzed the effects of the ISI and the 'habituation' resulting from repeated stimuli on the N2-like amplitude. Our method serves as a valuable reference for studying the passive single-stimulus paradigm and the time course of mammalian attention.

Femtotesla atomic magnetometer with counter-propagating optical sideband pumping.

The ultrasensitive magnetometer has a vital importance in fundamental research and applications. Currently, the spin-exchange relaxation-free (SERF) atomic magnetometer has been reported with a sensitivity around the level of fT/Hz1/2. To enhance the sensitivity, a gradiometer configuration has usually been introduced to cancel the common-mode noise between two separate channels. However, the signal and response from different channels are not the same due to the attenuation of the pump beam. Here, we proposed a counter-propagating optical sideband pumping method to polarize the atoms, using the electro-optic modulator to modulate the single-pump beam, generating two symmetrically red- and blue-detuned sidebands of frequency. This scheme leads to a significant reduction of undesirable effects coming along with the optical pumping, such as light shifts and spatial inhomogeneity in atomic spin polarization. With the help of this pumping scheme, the two channels have the same magnetic response, and we have built a gradiometer atomic magnetometer with a sensitivity of 0.5 fT/Hz1/2 ranging from 5 to 40 Hz. Our results propose the possibility of creating larger arrays of atomic magnetometers (AMs) with high sensitivity and spatial resolution based on single-vapor cells for magnetocardiography and magnetoencephalography imaging or searching for exotic spin-dependent interactions.

Performance of a Radio-Frequency Two-Photon Atomic Magnetometer in Different Magnetic Induction Measurement Geometries.

Measurements monitoring the inductive coupling between oscillating radio-frequency magnetic fields and objects of interest create versatile platforms for non-destructive testing. The benefits of ultra-low-frequency measurements, i.e., below 3 kHz, are sometimes outweighed by the fundamental and technical difficulties related to operating pick-up coils or other field sensors in this frequency range. Inductive measurements with the detection based on a two-photon interaction in rf atomic magnetometers address some of these issues as the sensor gains an uplift in its operational frequency. The developments reported here integrate the fundamental and applied aspects of the two-photon process in magnetic induction measurements. In this paper, all the spectral components of the two-photon process are identified, which result from the non-linear interactions between the rf fields and atoms. For the first time, a method for the retrieval of the two-photon phase information, which is critical for inductive measurements, is also demonstrated. Furthermore, a self-compensation configuration is introduced, whereby high-contrast measurements of defects can be obtained due to its insensitivity to the primary field, including using simplified instrumentation for this configuration by producing two rf fields with a single rf coil.

Live magnetic observation of parahydrogen hyperpolarization dynamics

Hyperpolarized nuclear spins in molecules exhibit high magnetization that is unachievable by classical polarization techniques, making them widely used as sensors in physics, chemistry, and medicine. The state of a hyperpolarized material, however, is typically only studied indirectly and with partial destruction of magnetization, due to the nature of conventional detection by resonant-pickup NMR spectroscopy or imaging. Here, we establish atomic magnetometers with sub-pT sensitivity as an alternative modality to detect in real time the complex dynamics of hyperpolarized materials without disturbing or interrupting the magnetogenesis process. As an example of dynamics that are impossible to detect in real time by conventional means, we examine parahydrogen-induced 1H and 13C magnetization during adiabatic eigenbasis transformations at [Formula: see text]T-field avoided crossings. Continuous but nondestructive magnetometry reveals previously unseen spin dynamics, fidelity limits, and magnetization backaction effects. As a second example, we apply magnetometry to observe the chemical-exchange-driven 13C hyperpolarization of [1-13C]-pyruvate-the most important spin tracer for clinical metabolic imaging. The approach can be readily combined with other high-sensitivity magnetometers and is applicable to a broader range of general observation scenarios involving production, transport, and systems interaction of hyperpolarized compounds.

Frequency noise suppression of the high-power pumping laser in the SERF atomic magnetometer

Abstract A high-sensitivity SERF atomic magnetometer based on a noise-suppressed master oscillator power amplifier (MOPA) system is demonstrated. The spectrum and frequency noise of the laser are measured and it is proved that the frequency noise in the MOPA system is affected by the amplified spontaneous emission (ASE) stimulated from the power amplifier. The frequency noise of the MOPA system is decreased by filtering out the ASE background in the spectrum through a bandpass filter. The sensitivity of the SERF atomic magnetometer is improved by using the frequency noise-suppressed MOPA system as a pumping laser. This method can also be applied to other precision measurement fields based on the MOPA systems that have high requirement for frequency noise of laser.

Analysis and measurement of magnetic noise for tesla shielding based on superconducting coils applied to SERF magnetometer

Tesla Shielding (TS) is closed superconducting coils composed of superconducting tape, designed to resist changing magnetic fields, thereby achieving magnetic shielding. TS, optically transparent, is suitable for integration with spin exchange relaxation-Free (SERF) magnetometers, thereby improving the sensitivity of SERF magnetometers. However, no prior research has been conducted on the magnetic noise of TS. Noise source identification was conducted on the superconducting tapes used in the TS. We modeled the magnetic noise of superconducting coils, analyzed the the relationship between geometric parameters and magnetic noise of coils, and proposed methods to suppress magnetic noise. Finally, we established a measurement system to measure the magnetic noise of superconducting coils. The results confirm the feasibility of the magnetic noise calculation model and the effectiveness of the methods for suppressing magnetic noise. This study can guide the design of TS, which is important for improving the sensitivity of SERF magnetometers.

Subpicotesla Optomechanical Magnetometry.

High-sensitivity magnetometry has found important applications in fields ranging from basic science studies such as searching for dark matter and exotic particles to more practical tasks in geology, archaeology, navigation, and biomedicine. Currently, the performance of typical high-sensitivity magnetometers is limited by the required stringent operation environment, such as cryogenic conditions for superconducting quantum interference device magnetometers and near-zero-field environments for spin-exchange-relaxation-free atomic magnetometers. This Letter reports a high-sensitivity solid-state magnetometer based on a magnetostrictive gap-swing Fabry-Pérot cavity optomechanical system that is capable of benchmark performance at ambient environment conditions. Thanks to the strong resonance enhancement of the gap-swing mechanical mode, it achieves a sensitivity of 620 fT Hz^{-1/2} at room temperature and under the Earth's magnetic field, and is expected to approach the thermal-noise-limited sensitivity of 5.9 fT Hz^{-1/2} by controlling the optomechanical coupling. Our Letter opens the avenue toward the application of portable and low-maintenance high-sensitivity magnetometry in broad fields.

Suppression of the vapor cell temperature error in a spin-exchange relaxation-free comagnetometer

Abstract The fluctuation of the vapor cell temperature leads to the variations of the density of the alkali metal atoms, which seriously damages the long-term stability of the spin-exchange relaxation-free (SERF) comagnetometer. To address this problem, we propose a novel method for suppressing the cell temperature error by manipulating the probe laser frequency. A temperature coefficient model of the SERF comagnetometer is established based on the steady-state response, which indicates that the comagnetometer can be tuned to a working point where the output signal is insensitive to the cell temperature fluctuation, and the working point is determined by the relaxation rate of the alkali metal atoms. The method is verified in a K-Rb-21Ne comagnetometer, and the experimental results are consistent with the theory. The theory and method presented here lay a foundation for the practical applications of the SERF comagnetometer.

Realization of an Optimized Cylindrical Uniform Magnetic Field Coil via the Flexible Printed Circuit Technology

Abstract The design and fabrication method of magnetic field coils with high uniformity is essential for atomic magnetometers. In this paper, a novel design strategy for cylindrical uniform coils is first proposed, which combines the target-field method (TFM) with an optimized slime mold algorithm (SMA) to determine optimal structure parameters. Then, the realization method for the designed cylindrical coil by using the flexible printed circuit (FPC) technology is presented. Compared with traditional fabrication methods, this method has advantages in excellent flexibility and bending property, making the coils easier to be arranged in limited space. Moreover, the manufacturing process of the FPC technology via a specific cylindrical uniform magnetic field coil is discussed in detail, and the successfully realized coil is well tested in a verification system. By comparing the uniformity performance of the experimental coil with the simulation one, the effectiveness of the FPC technology in producing cylindrical coils has been well validated.

Ultra-compact and high-precision differential detection method based on liquid crystal polarization grating for miniature atomic magnetometer

Ultra-compact and high-precision differential detection method based on liquid crystal polarization grating for miniature atomic magnetometer

Phase-error-free atomic magnetometer and vector measurement method based on demodulated signal phase in geomagnetic environment

The performance of double-beam atomic magnetometer in the geomagnetic environment is greatly affected by the vectorial direction of magnetic field, which leads to the shift of the phase of the demodulation signal. We propose a phase-error-free scalar double-beam atomic magnetometer. When the RF field is along the direction of probe beam, the fluctuation of the phase of the demodulation signal can be avoided. For the practical measurement environment, we propose a phase extraction method for atomic magnetometer. Additionally, Based on the phase of the demodulated signal when the RF field is applied in the directions of pumping, probing, and perpendicular to the pumping-detection plane, we propose a method for vector magnetic field measurement. The measurement results indicate that under a 10 μT bias magnetic field, the deviations θ and φ are within 0.1°. The theory and method proposed are of great significance to the application of magnetometer in geomagnetic magnetic field.

Review on Grounds state Hanle effect on paraffin coated alkali atoms under condition EIT and EIA

IntroductionThis review is specifically aimed at a higher level of understanding of the ground-state Hanle effect through novel methods of atomic vapor interaction with resonant light. Electromagnetically Induced Transparency (EIT) and absorption (EIA) are the primary phenomena in this context. EIT is a process in which destructive interference at absorption frequencies within a medium is caused by a control laser and makes the medium clear to the probe laser light. It should be noted that this transparency is crucial for turning on/off the light pulses, slowing down or stopping in several cases, thus enhancing the effectiveness of atomic magnetometers. However, constructive interference that occurs in EIA raises the density of the medium, which is advantageous for profit-making precise measurements and the improvement of atomic clocks. ObjectiveThe objective of this study is to review the fundamental principles of the Hanle effect, EIT, EIA, and coating methods for alkali atoms. These principles and techniques are critical for improving the sensitivity and functionality of atomic magnetometers and other quantum devices. By understanding and leveraging these phenomena, significant progress has been made in the development of high-precision measurement tools and quantum technologies. ResultsAdvancements in atomic magnetometer sensitivity represent a rapidly growing area of interest, driving significant progress in the development of quantum devices. This review consolidates the existing knowledge and recent findings, offering a thorough understanding of the fundamental principles and practical applications of the Hanle effect, EIT, EIA, and coating methods for alkali atoms. This review highlights how advancements in EIT and EIA have contributed to the sensitivity improvements of atomic magnetometers, and underscores the importance of coating methods for maintaining system integrity and performance. These developments are essential to the evolution of modern quantum technologies and precision measurement devices.

Measurement of transverse and longitudinal relaxation rates of double-beam atomic magnetometers in geomagnetic environment

Longitudinal relaxation rate (R1) and transverse relaxation rate (R2) are crucial for evaluating the performance of atomic magnetometers. Unfortunately, to the best of our knowledge, methods for measuring R1 and R2 under arbitrary direction of magnetic field have been rarely studied. We propose, for the first time, measurement methods for R1 and R2 in magnetic fields with arbitrary direction. R1 is measured using the linewidth under three axis modulated magnetic field, while R2 is measured based on demodulated dispersive and absorptive curves of the magnetic resonance signal. The experimental results show that the relative mean deviation of R1 and R2 are 2.5% and 3.6%, respectively. The R1 and R2 measurement methods proposed in this paper has advantage of simple to implement and is validity for measurement in magnetic fields with arbitrary direction, which has significant importance for the application of atomic magnetometers in geomagnetic environments.

Suppressing Spatial Inhomogeneity in Spin Polarization and Light Shift in Atomic Magnetometer Array Using Frequency-Paired Counter-Propagating Pumps

Suppressing Spatial Inhomogeneity in Spin Polarization and Light Shift in Atomic Magnetometer Array Using Frequency-Paired Counter-Propagating Pumps

Integrated optical probing scheme enabled by localized-interference metasurface for chip-scale atomic magnetometer

Abstract Emerging miniaturized atomic sensors such as optically pumped magnetometers (OPMs) have attracted widespread interest due to their application in high-spatial-resolution biomagnetism imaging. While optical probing systems in conventional OPMs require bulk optical devices including linear polarizers and lenses for polarization conversion and wavefront shaping, which are challenging for chip-scale integration. In this study, an integrated optical probing scheme based on localized-interference metasurface for chip-scale OPM is developed. Our monolithic metasurface allows tailorable linear polarization conversion and wavefront manipulation. Two silicon-based metasurfaces namely meta-polarizer and meta-polarizer-lens are fabricated and characterized, with maximum transmission efficiency and extinction ratio (ER) of 86.29 % and 14.2 dB for the meta-polarizer as well as focusing efficiency and ER of 72.79 % and 6.4 dB for the meta-polarizer-lens, respectively. A miniaturized vapor cell with 4 × 4 × 4 mm3 dimension containing 87Rb and N2 is combined with the meta-polarizer to construct a compact zero-field resonance OPM for proof of concept. The sensitivity of this sensor reaches approximately 9 fT/Hz1/2 with a dynamic range near zero magnetic field of about ±2.3 nT. This study provides a promising solution for chip-scale optical probing, which holds potential for the development of chip-integrated OPMs as well as other advanced atomic devices where the integration of optical probing system is expected.

Synchronous achievement of laser frequency stabilization and tunability via modulation transfer spectroscopy on the rubidium D1 line

In the Spin Exchange Relaxation Free (SERF) magnetometer, the laser frequency must be stabilized at the alkali D1 line and tunable within a range of several gigahertz (GHz). We theoretically and experimentally analyzed the modulated sideband and resonant frequencies on the D1 transition line of rubidium (Rb) atoms using a modulation transfer spectroscopy (MTS) frequency stabilization system. The laser's self-estimated frequency stability shows the Allan deviation of 1.5 × 10−12/τ for resonance peak stabilization and 1.4 × 10−12/τ for sideband stabilization. The spectrum of the modulated laser interacting with the rubidium D1 line exhibits several absorption peaks and MTS signals across a 6 GHz scanning frequency range, which can be used to lock and tune the laser. This method enhances the application of distributed feedback semiconductor lasers in Rb atom-based magnetometers.

Single-Beam Atomic Magnetometer Enhanced With Elliptically Polarized Reflected Light

Single-Beam Atomic Magnetometer Enhanced With Elliptically Polarized Reflected Light