Abstract Atomic magnetometers (AMs) that use alkali vapors, such as rubidium, are among the most sensitive sensors for magnetic field measurement. They commonly use polarization differential detection to mitigate common‐mode noise. Nevertheless, traditional differential detection optics, including polarization beam splitters (PBS) and half‐wave plates, are typically bulky and large, which restricts further reductions in sensor dimensions. In this study, a combination of liquid crystal polarization grating (LCPG) and liquid crystal quarter‐wave plate is used for differential detection in AMs, with magnetic field strength determined by measuring the intensity of two diffracted beams from the LCPG. The experimental findings indicate that the fabricated LCPG exhibits a circularly polarized extinction ratio of 3,656 and achieves an average diffraction efficiency of 99 %. In addition, the differential detection method based on LCPG can achieve an angular resolution of 1.48 × 10 −7 rad. Subsequently, the method is employed in an AM to achieve an average magnetic sensitivity of 13.8 fT/Hz 1/2 . Compared to the PBS‐based differential detection method, this method enhances the magnetometer response coefficient by 13 % and achieves co‐side distribution of the two diffracted beams, thereby avoiding the need for additional vertical optical paths. The effective thickness of the detection optics is reduced to the micrometer scale, allowing for future integration as thin films onto microfabricated vapor cells. This study offers a practical solution for miniaturized AMs with exceptionally high sensitivity.
Abstract Atomic magnetometers (AMs) that use alkali vapors, such as rubidium, are among the most sensitive sensors for magnetic field measurement. They commonly use polarization differential detection to mitigate common‐mode noise. Nevertheless, traditional differential detection optics, including polarization beam splitters (PBS) and half‐wave plates, are typically bulky and large, which restricts further reductions in sensor dimensions. In this study, a combination of liquid crystal polarization grating (LCPG) and liquid crystal quarter‐wave plate is used for differential detection in AMs, with magnetic field strength determined by measuring the intensity of two diffracted beams from the LCPG. The experimental findings indicate that the fabricated LCPG exhibits a circularly polarized extinction ratio of 3,656 and achieves an average diffraction efficiency of 99 %. In addition, the differential detection method based on LCPG can achieve an angular resolution of 1.48 × 10 −7 rad. Subsequently, the method is employed in an AM to achieve an average magnetic sensitivity of 13.8 fT/Hz 1/2 . Compared to the PBS‐based differential detection method, this method enhances the magnetometer response coefficient by 13 % and achieves co‐side distribution of the two diffracted beams, thereby avoiding the need for additional vertical optical paths. The effective thickness of the detection optics is reduced to the micrometer scale, allowing for future integration as thin films onto microfabricated vapor cells. This study offers a practical solution for miniaturized AMs with exceptionally high sensitivity.
ABSTRACT Atomic magnetometers (AMs) are among the most sensitive magnetic field sensors, with uses in magnetic anomaly detection, geosciences, and fundamental physics research. Despite notable progress, developing highly integrated, miniaturized components with high resolution, sensitivity, and efficiency for chip‐scale AMs remains a significant challenge. Here, we present a novel integrated polarization detection scheme based on a bifocal liquid‐crystal polarization metalens (LCPM) for chip‐scale AMs. By leveraging geometric phase and holographic synthesis principles, the LCPM efficiently separates and focuses left‐ and right‐handed circularly polarized light at the rubidium D1 transition wavelength (795 nm), achieving a high focusing efficiency of up to 80% and extinction ratios of 104 and 134 for the two channels. We demonstrate a prototype AM operating in the spin‐exchange relaxation‐free regime, achieving a high magnetic‐field sensitivity of 17 fT/Hz 1/2 and a dynamic range of ±4.8 nT. The proposed LCPM‐based scheme reduces the optical‐path volume by 94% compared to traditional polarization detection systems. Importantly, our method is compatible with large‐scale, cost‐effective production through established liquid‐crystal manufacturing lines, paving the way for high‐throughput fabrication of chip‐scale AMs. This innovation enables compact, affordable polarization detection with enhanced sensitivity of atomic sensors, opening new opportunities for high‐resolution biomagnetic imaging and quantum precision measurements.
Optically pumped magnetometers (OPMs) enable high-resolution biomagnetic imaging, yet conventional single-beam designs are constrained by bulky, alignment-intensive polarization optics and susceptibility to laser-power noise. Here, we propose and demonstrate a compact, noise-suppressed OPM that uses a single planar liquid-crystal polarization grating (LCPG) functioning simultaneously as a high-efficiency polarization converter and a beam splitter. At the component level, the LCPG replaces multiple bulk elements, converts 795 nm light with 95% first-order diffraction efficiency and an ellipticity of ~44.6°, and exhibits robust performance against variations in incident-light polarization direction, ambient temperature, and angle of incidence. At the sensor level, a power-differential configuration effectively suppresses noise originating from pump-power fluctuations. We fabricated a probe with a total volume of 4 cm 3 and benchmarked it against a conventional OPM: the LCPG-enabled differential mode achieves a sensitivity of 8.6 fT/Hz 1/2 , representing an ~28% improvement over the conventional configuration. Importantly, the approach is compatible with mature, high-throughput, and cost-effective liquid-crystal manufacturing. These results demonstrate a scalable design strategy for OPMs that unites component-level efficiency, robustness, and cost-effectiveness with sensor-level compactness and noise suppression, paving the way for next-generation chip-scale quantum sensors.
We demonstrate a single-beam atomic magnetometer (AM) capable of measuring a three-axis magnetic field with high-sensitivity, achieved by applying a small DC offset field and a high frequency modulation field. To satisfy the miniaturization demand of AMs, an elliptically polarized light detuned by 50 GHz from the resonance transition center is employed. The circularly polarized component is used to polarize the alkali-metal atoms, while the linearly polarized light is used to detect the dynamics of the polarized spin under a magnetic field. Based on theoretical analysis, parameters that significantly affect the performance are optimized, and a sensitivity of 20 fT/Hz 1/2 in x -axis, 25 fT/Hz 1/2 in y -axis, 30 fT/Hz 1/2 in z -axis is achieved with a miniature 4 × 4 × 4 mm 87 Rb vapor cell. Moreover, we also verify that the operation principle of AMs can be used to null background magnetic fields in-situ with isotropic compensation resolution of 6.7 pT, which provides an effectively precise method for zeroing ambient magnetic field. The high-sensitivity operating of an elliptically-polarized-laser-based magnetometer provides prospective futures for constructing a compact, low-cost AM, which is particularly applicable for non-invasive bio-magnetic imaging such as array-based magnetoencephalography (MEG) and magnetocardiography (MCG).
Ultraweak magnetic field measurement, as one of the quantum precision measurement techniques, holds important significance in the forefront of explorations in physics and advanced medical technologies. The atomic magnetometer, serving as a typical instrument for measuring extremely weak magnetic fields, utilizes the Larmor precession frequency of electrons in alkali metal atoms to quantify magnetic field magnitudes at subfemtotesla levels. Additionally, atomic magnetometers boast advantages such as high sensitivity, miniaturization and high spatial resolution. Hence, arrays of atomic magnetometer sensors have become a reliable solution for measuring ultraweak magnetic fields in spatial dimensions. This paper proposes an ultracompact and highly sensitive atomic magnetometer array integrated structure via a highly stable polarization volume grating (PVG)-based waveguide structure for beam splitting. Instead of the traditional four polarizing beam splitters and polarizors, the structure integrates parallel beam splitting and polarization conversion functions using PVGs, which are then incorporated into an ultracompact atomic magnetometer array. This integration enables high sensitivity magnetic field measurements in four channels. The light separated by the structure exhibits power fluctuations along a single polarization axis below 0.2% during a 30 min period. The overall volume of the proposed integrated structure is approximately 0.6 cm 3, representing at least an order of magnitude reduction compared to other spatial optical atomic magnetometer array structures. The final validation demonstrates the system can measure magnetic fields on the order of femtotesla, with an average sensitivity of 16.1 fT/Hz 1/2 . This approach holds significant potential for applications in quantum precision sensing, high resolution medical imaging, and biological science exploration.
Abstract The powerful light field manipulation capability of metasurfaces offers a novel development perspective for the quantum precision measurement. By applying the phase-gradient metasurface (PGM) to atomic magnetometers (AMs), we have proposed and experimentally demonstrated a new type of compact single-beam elliptically polarized atomic magnetometers (EPAMs). Employing the fabricated chiral beam splitter PGM with high cross-polarization transmittance, a new atomic spin chirality detection method was devised, enabling the ultra-high sensitivity for extremely weak magnetic field measurement and achieving a high sensitivity of 2.67 pT/Hz1/2 under an external magnetic field of approximately 10,000 nT. The new AMs combine the pumping and probing polarized light, achieving a compact design. The fabricated PGM has a size of only 3 mm × 3 mm × 0.7 mm, which is beneficial for the miniaturization and integration of AMs. This work effectively expands the application of metasurfaces in the field of quantum precision measurement, and also provides a new viewpoint for the design and development of high-sensitivity and miniaturized AMs.
Sensitive and accurate magnetic-field measurements are essential in many applications, including geophysical studies, biomagnetic signal detection, navigation, event monitoring, and magnetic anomaly detection. In this context, atomic magnetometers are a particularly promising approach, combining high sensitivity and accuracy, and able to rival superconducting quantum interference devices (SQUIDs) without requiring cryogenic cooling. While the best sensitivity levels are achieved in the zero-field regime within magnetic shielding, scalar magnetometers operating in ambient fields also demonstrated remarkable sensitivities. Initiated in the 2000s, the miniaturization of atomic devices, and in particular alkali-vapor cells, paves the way for magnetometers that are both sensitive and compact, well suited to embedded measurements and field applications.This thesis contributes to the development of microfabricated vapor cells for atomic magnetometry. We propose a new filling and sealing method that overcomes some limitations of conventional approaches and could enable the fabrication of purer cells compatible with a wider range of chemical species. This strategy could also facilitate the integration of anti-relaxation coatings, which reduce relaxation caused by collisions with the cell walls. To date, no long-lasting anti-relaxation effects have been demonstrated in microfabricated cells, as traditional methods rely on high temperatures that are incompatible with these coatings.A cell design suited to the deposition of anti-relaxation coatings is presented. We then describe the fabrication and characterization of a multi-axis microfabricated cell, designed for compact atomic devices using multiple optical beams. This multi-axis cell was experimentally validated in a dual-beam magnetometry configuration using an experimental setup developed as part of this thesis.