ABSTRACT Nuclear magnetic resonance (NMR) co‐magnetometers are high‐precision atomic sensors, but their practical deployment is hindered by bulky free‐space optics. Here, we propose a circularly polarized light radiation scheme based on a silicon nitride photonic platform and develop a compact, chip‐scale integrated optical pumping module. Distinct from prior on‐chip schemes limited to electron spin polarization, our approach achieves polarization of alkali metal electron spins and noble gas nuclear spins. By integrating a spiral waveguide with angular gratings, the platform emits vertically propagating CPL with a 5.65° divergence angle, and the average degree of circular polarization exceeds 95%. Magnetic field‐dependent measurements reveal clear 129 Xe and 131 Xe precession responses. A 50% increase in SRC pumping power increases the relative nuclear spin polarization of 129 Xe by a factor of 1.72 and that of 131 Xe by a factor of 2.90, verifying efficient nuclear spin polarization. The SRC scheme yields electron and nuclear spin resonance responses in the vapor cell, while the SRC chip itself occupies a compact footprint of only 1 × 2 mm 2 . This work offers a highly integrated photonic solution for atomic polarization, facilitating the miniaturization and practical deployment of high‐performance NMR co‐magnetometers.
ABSTRACT Nuclear magnetic resonance (NMR) co‐magnetometers are high‐precision atomic sensors, but their practical deployment is hindered by bulky free‐space optics. Here, we propose a circularly polarized light radiation scheme based on a silicon nitride photonic platform and develop a compact, chip‐scale integrated optical pumping module. Distinct from prior on‐chip schemes limited to electron spin polarization, our approach achieves polarization of alkali metal electron spins and noble gas nuclear spins. By integrating a spiral waveguide with angular gratings, the platform emits vertically propagating CPL with a 5.65° divergence angle, and the average degree of circular polarization exceeds 95%. Magnetic field‐dependent measurements reveal clear 129 Xe and 131 Xe precession responses. A 50% increase in SRC pumping power increases the relative nuclear spin polarization of 129 Xe by a factor of 1.72 and that of 131 Xe by a factor of 2.90, verifying efficient nuclear spin polarization. The SRC scheme yields electron and nuclear spin resonance responses in the vapor cell, while the SRC chip itself occupies a compact footprint of only 1 × 2 mm 2 . This work offers a highly integrated photonic solution for atomic polarization, facilitating the miniaturization and practical deployment of high‐performance NMR co‐magnetometers.
Abstract Nuclear Magnetic Resonance (NMR) co‐magnetometers are advanced quantum sensors capable of measuring angular velocity for inertial navigation. Within the Rb‐Xe atomic ensemble, Rb atoms absorb polarized light, decreasing electron spin polarization as the light travels greater distances. This attenuation causes a gradient in Rb spin polarization that severely affects atomic relaxation characteristics and degrades NMR sensors’ performance. Considering atomic diffusion motion, a theoretical simulation model is developed and the spatial distribution of electron spin polarization under the encounter‐propagating dual‐beam configuration is simulated. The simulation results demonstrate that the proposed dual‐beam scheme achieves a more uniform distribution of electron polarization within the atomic vapor cell. Experiments reveal an 18% enhancement in 129 Xe nuclear spin polarization using the dual‐beam scheme compared to the conventional single‐beam. Through the Fermi contact interaction between optically pumped Rb and Xe atoms, a more uniform spatial distribution of Rb spin polarization reduces the gradient relaxation of Xe atoms and its depolarization effects, thereby significantly enhancing the macroscopic Xe spin polarization and the signal‐to‐noise ratio (SNR) of NMR sensors. This study presents a new method for improving atomic polarization, significantly enhancing the performance of quantum sensors.
Abstract Discrete optical system in optically pumped magnetometers (OPMs) presents a significant challenge to their integration into high‐spatial‐resolution magnetic field detection. Here, the electron spin polarization of atoms using a fiber‐coupled silicon nitride () photonic integrated circuit (PIC) is demonstrated, by the way of delivering arrayed elliptically polarized light (EPL) into a vapor cell. Specifically, the photonic integrated circuit (PIC) transforms fiber‐coupled 795 nm pump light via optical waveguides to eight divergent free‐space beams, simultaneously converting linear polarized light (LPL) into EPL with an average polarization conversion efficiency of 71%. The PIC‐enabled OPM has detected the weak magnetic field with an optimal sensitivity of 0.53 pT at 70Hz. This work presents an effective approach for manipulation of alkali atoms using a chip and, crucially, introduces a chip‐based pump solution for OPMs. This approach contributes to the integration of nanophotonics with atomic systems, paving the way for future advancements in quantum sensing.
ABSTRACT Optically pumped atomic magnetometers (AMs) have become powerful tools for biomagnetic sensing owing to their ultrahigh sensitivity. However, their broader deployment increasingly requires compact, scalable, and low‐cost free‐space photonic interfaces capable of delivering high quality beams for light‐atom interaction. Here, we present a photonic chip based on a silicon nitride (SiN) optical phased array (OPA) that serves as a free‐space optical interface for AMs, combining high radiation efficiency, low divergence, and compatibility with batch fabrication. The device generates a stable linearly polarized beam with long propagation capability, a polarization extinction ratio of 26.1 dB, and a degree of linear polarization of 99.5%, with a maximum overall radiation efficiency of 26.5%. In a dual beam atomic magnetometer, the chip emitted beam serves as the probe beam and enables differential detection with a sensitivity of 8 fT/Hz 1/2 . To assess fabrication reliability and reproducibility, we performed a statistical analysis of 168 devices fabricated by deep‐ultraviolet (DUV) lithography, with more than 50% exhibiting radiation efficiencies above 15%. These results demonstrate a low‐cost, scalable photonic interface for chip integrated AMs and highlight its potential for large scale implementation.
Emerging atomic magnetometers (AMs) are among the most advanced sensors for detecting and characterizing magnetic fields. Recently, there has been growing interest in the miniaturization and integration of AMs due to the urgent demand for portability and compactness in various fields such as biomagnetism imaging. While conventional AMs require a bulky setup of optical devices for the pumping and optical readout of atomic spin, here, a novel chip-scale single-beam AM scheme is proposed by leveraging extreme transmissive circular polarization dichroism (TCPD) and geometric phase manipulation of spin-selective interference meta-optics. This is achieved through silicon-based metasurfaces that enable the realization of arbitrary-to-circular polarization conversion and wavefront modulation within a monolithic chip at Rb D1 transition wavelength (λ = 795 nm). Two spin-selective interference metasurfaces, i.e., meta-circular-polarizer (MCP) and meta-circular-polarizer-lens (MCPL), are fabricated and characterized, with a measured TCPD of 0.68 for the MCP as well as focusing efficiency and TCPD of around 70.67% and 0.69 for the MCPL, respectively. As a proof of concept, a 4 × 4 × 4 mm 3 Rb vapor cell is combined with our metasurface to construct a miniaturized single-beam AM. The sensitivity of our compact metasurface-based system is about 15 fT/Hz 1/2, with a dynamic range near zero-field of ± 2.2 nT. We envision that this work could facilitate the development of burgeoning chip-scale quantum sensors, which hold great potential for high-spatial-resolution biomagnetic imaging, on-chip nuclear magnetic resonance, and so forth.
High-performance atomic magnetometers (AMs) rely on the measurement of optical rotation, which requires a set of bulky polarization optics that limit their applications in scenarios where portability and compactness are necessary. In this study, a miniaturized AM is constructed based on a cubic 87 Rb vapor cell and monolithic metalens, which provides an integrated scheme to achieve optical rotation detection induced by the circular birefringence of polarized atoms. The designed metalens achieves polarization splitting with deflection angles of ±10 ∘ and focusing with efficiencies of approximately 30% for orthogonal linear polarizations. The sensitivity of our compact device is ∼30 fT/Hz 1/2 with a dynamic range of around ±1.45 nT. We envision that the presented approach paves the way for the chip integration of emerging atomic devices, which are in demand for applications such as biomagnetic imaging and portable atomic gyroscopes.
Spin polarized atomic magnetometers involve the preparation of atomic spins and their detection for monitoring magnetic fields. Due to the fact that magnetic fields are ubiquitous in our world, spin polarized atomic magnetometers are used in a wide range of applications from the detection of magnetic fields generated by the human heart and brain to the detection of nuclear magnetic resonance. In this thesis we developed microfabricated spin polarized atomic magnetometers. These sensors are based on optical pumping and spin-exchange collisions between alkali atoms and noble gases contained in microfabricated millimeter-scale vapor cells. In the first part of the thesis, we improved different features of current microfabricated optical magnetometers. Specifically, we improved the bandwidth of these devices, without degrading their magnetic field sensitivity, by broadening their magnetic resonance through spin-exchange collisions between alkali atoms. We also implemented all-optical excitation techniques to avoid problems, such as the magnetic perturbation of the environment, induced by the radio-frequency fields used in some of these sensors. In the second part of the thesis we demonstrated a microfluidic chip for the optical production and detection of hyperpolarized Xe gas through spin-exchange collisions with optically pumped Rb atoms. These devices are critical for the widespread use of spin polarized atomic magnetometers in applications requiring simple, compact, low-cost, and portable instrumentation.