The miniaturization of quantum sensors is a popular trend for the development of quantum technology. One of the key components of these sensors is a coil which is used for spin modulation and manipulation. The bi-planar coils have the advantage of producing three-dimensional magnetic fields with only two planes of current confinement, whereas the traditional Helmholtz coils require three-dimensional current distribution. Thus, the bi-planar coils are compatible with the current micro-fabrication process and are quite suitable for the compact design of the chip-scale atomic devices that require stable or modulated magnetic fields. This paper presents a design of a miniature bi-planar coil. Both the magnetic fields produced by the coils and their inhomogeneities were designed theoretically. The magnetic field gradient is a crucial parameter for the coils, especially for generating magnetic fields in very small areas. We used a NMR (Nuclear Magnetic Resonance) method based on the relaxation of 131Xe nuclear spins to measure the magnetic field gradient in situ. This is the first time that the field inhomogeneities of the field of such small bi-planar coils have been measured. Our results indicate that the designed gradient caused error is 0.08 for the By and the Bx coils, and the measured gradient caused error using the nuclear spin relaxation method is 0.09±0.02, suggesting that our method is suitable for measuring gradients. Due to the poor sensitivity of our magnetometer under a large Bz bias field, we could not measure the Bz magnetic field gradient. Our method also helps to improve the gradients of the miniature bi-planar coil design, which is critical for chip-scale atomic devices.
The miniaturization of quantum sensors is a popular trend for the development of quantum technology. One of the key components of these sensors is a coil which is used for spin modulation and manipulation. The bi-planar coils have the advantage of producing three-dimensional magnetic fields with only two planes of current confinement, whereas the traditional Helmholtz coils require three-dimensional current distribution. Thus, the bi-planar coils are compatible with the current micro-fabrication process and are quite suitable for the compact design of the chip-scale atomic devices that require stable or modulated magnetic fields. This paper presents a design of a miniature bi-planar coil. Both the magnetic fields produced by the coils and their inhomogeneities were designed theoretically. The magnetic field gradient is a crucial parameter for the coils, especially for generating magnetic fields in very small areas. We used a NMR (Nuclear Magnetic Resonance) method based on the relaxation of 131Xe nuclear spins to measure the magnetic field gradient in situ. This is the first time that the field inhomogeneities of the field of such small bi-planar coils have been measured. Our results indicate that the designed gradient caused error is 0.08 for the By and the Bx coils, and the measured gradient caused error using the nuclear spin relaxation method is 0.09±0.02, suggesting that our method is suitable for measuring gradients. Due to the poor sensitivity of our magnetometer under a large Bz bias field, we could not measure the Bz magnetic field gradient. Our method also helps to improve the gradients of the miniature bi-planar coil design, which is critical for chip-scale atomic devices.
Inertial sensors that measure the acceleration of ultracold atoms promise unrivalled accuracy compared to classical equivalents. However, atomic systems are sensitive to various perturbations, including magnetic fields, which can introduce measurement inaccuracies. To address this challenge, we have designed, manufactured, and validated a magnetic field stabilisation system for a quantum sensor based on atom interferometry. We solve for the magnetic field generated by surface currents in-between a pair of bi-rectangular coils and approximate the surface current using discrete wires. The wires are wound by-hand onto machined panels which are retrofitted onto the existing mounting structure of the sensor without interfering with any experimental components. Along the central 60mm of the y-axis, which aligns with the trajectory of the atoms during interferometry, the coils are measured to generate an independent uniform axial magnetic field with a strength of Bz=22.81±0.01 μT/A [mean±2σstd. error] and an independent linear axial field gradient of strength dBz/dy=10.6±0.1 μT/Am. The uniform Bz field is measured to deviate by a maximum value of 1.3% in the same region, which is a factor of three times more uniform than the previously-used on-sensor rectangular Bz compensation set.
Magnetic field gradients affect numerous modern sensitive measurements and physics studies using atomic ensemble, resulting in the loss of coherence. In some cases, the presence of small gradients can reduce the performance significantly. In this study, we propose an effectivein situmethod to compensate the triaxial magnetic field gradient for atomic magnetometers, based on multichannel atomic signals in one vapor cell. We design two novel gradient coils by solving closed-form equations to improve the accuracy and efficiency of compensation. We demonstrate the performance of the compensation method in a spin-exchange relaxation-free atomic magnetometer, which reduces the magnetic linewidth by 4.2%–7.6% under the same conditions at a compensation resolution of 50 pT/cm. The proposed coils generate gradients only along two axes and achieve triaxial decoupling, which compensates for the gradient completely without iteration. Our results may aid in suppressing atomic spin relaxations due to magnetic field gradients in several modern measurements and improve their performance, such as the detection of electric dipole moments, ultralow-field nuclear magnetic resonance, and biomagnetism.
This paper presents a novel method to measure the magnetic gradient by an Mz atomic magnetometer using a micro-fabricated shaped rubidium vapor cell. The shaped vapor cell is fabricated by a chemical foaming process. Four micro radio frequency (RF) coils are mounted on the shaped rubidium vapor cell. Magnetic fields at the four points corresponding to the RF coils along the laser beam propagation are obtained by measuring Larmor frequency of the rubidium atoms inside the vapor cell. The magnetic gradients are also acquired with the measured magnetic fields. The measurement is performed in a magnetic shield environment. A dc electrical coil is taken to produce an existed magnetic field for the measurement and the theoretical magnetic field distribution is calculated. It is demonstrated that the measured magnetic fields and magnetic gradients correspond well with the calculated ones. Results show that the absolute error of the magnetic field is less than 0.1 μT, the relative error of the magnetic field is below 0.8%, and the relative error of the magnetic gradient is below 5.5%. Results also indicate that the atomic magnetometer has a sensitivity of 5 pT/Hz1/2from 1 to 2 Hz. The Mz atomic magnetometer is potentially useful for applications requiring gradient field information.
Abstract Atom chips provide flexible technologies for implementing modern concepts in quantum optics, quantum measurement, and quantum information processing. Atom chips are miniature devices that confine, control and manipulate cold atoms using electric, magnetic, and light fields. Due to the shrinkage of scale, arbitrary magnetic traps can be generated from current sources outside the chip’s vacuum compartment, in contrast to a traditional setup. This makes it easy to change trap configurations in an experiment that involves rapid prototyping of quantum states and quantum trajectory designs in free space. In this work, we show relevant parameters needed for transferring a cold atom cloud at the recoil limit from a magneto-optical trap (MOT) to an area close to the atom chip. To create a movable magnetic potential for this transfer, we used the MOT coils and an additional pair of coils in an anti-Helmholtz configuration. The properties of the movable potential were obtained by performing the Computer Simulation Tool (CST EM Studio suite®). Furthermore, an appropriate magnetic trap on a chip is developed, based on the simulation from COMSOL Multiphysics. We used a magnetic field gradient of around 20 G/cm to transport the cold atom with a distance over 20 mm with a temperature gain below 100 micro-Kelvin. The simulation results are based on an atom chip with a size of 2×2 cm2 and a copper wire thickness of 2 mm. The atom chip consists of Z, U and I-shaped wires that generate a quadrupole magnetic field. The resulting field minimum can be made at least 7 mm away from the chip surface.
Abstract Quantum sensors based on cold atoms are being developed which produce measurements of unprecedented accuracy. Due to shifts in atomic energy levels, quantum sensors often have stringent requirements on their internal magnetic field environment. Typically, background magnetic fields are attenuated using high permeability magnetic shielding, with the cancelling of residual and introduction of quantisation fields implemented with coils inside the shield. The high permeability shield, however, distorts all magnetic fields, including those generated inside the sensor. Here, we demonstrate a solution by designing multiple coils overlaid on a 3D-printed former to generate three uniform and three constant linear gradient magnetic fields inside the capped cylindrical magnetic shield of a cold atom interferometer. The fields are characterised in-situ and match their desired forms to high accuracy. For example, the uniform transverse field, Bx, deviates by less than 0.2% over more than 40% of the length of the shield. We also map the field directly using the cold atoms and investigate the potential of the coil system to reduce bias from the quadratic Zeeman effect. This coil design technology enables targeted field compensation over large spatial volumes and has the potential to reduce systematic shifts and noise in numerous cold atom systems.
As one of the fundamental properties of matter, magnetic fields have extensive application value in fields such as military, medical, and industrial sectors. High-sensitivity magnetic field measurement technology is crucial for exploring the physical world, ensuring national security, and promoting industrial development. Traditional magnetic sensors based on classical physics principles, such as fluxgate and Hall effect sensors, have become increasingly difficult to meet growing demands in terms of sensitivity, volume, and power consumption. In contrast, atomic magnetometers based on quantum effects utilize the interaction between atomic spins and external magnetic fields for measurement, offering advantages such as high sensitivity, no requirement for cryogenic cooling, and the capability for absolute measurement, making them a novel type of magnetic sensor that has received significant attention in recent years. In particular, the development of chip-scale atomic magnetometers, through technologies such as Micro-Electro-Mechanical Systems (MEMS), has significantly reduced the volume and power consumption of atomic magnetometers, enabling them to demonstrate tremendous application potential in fields such as ocean exploration, biomedical applications, and geological exploration. This paper will review the technological advances of high-sensitivity chip-scale atomic magnetometers, with a focus on discussing the latest achievements in their miniaturization and small-scale research.