Sensors are constant companions in our everyday lives and find countless applications in science. In this work we try to find sensors that are able to record magnetic field changes affecting trapped ions in our experiments. For this we assume that the magnetic field changes inside the vacuum chamber containing the trap in our experiment are the same as those measured by the sensor in the vicinity of the trap. To characterize three different sensors, we generate magnetic field offsets with a current-carrying wire, permanent magnet or a pair of coils. By isolating the sensors from the surroundings with a μ metal shield, we create a test environment under similar conditions. We showed that the fluxgate sensor is about a factor of 27500 more sensitive than the Hall sensor and a factor of 10 less sensitive than the atom itself as a sensor. We recognize that the noise of the electronics of the data acquisition system limits the performance of the fluxgate and Hall sensor. The fluxgate sensor, in contrast to the Hall sensor, turns out to be a suitable choice for monitoring magnetic field changes during experiments with ions.
Sensors are constant companions in our everyday lives and find countless applications in science. In this work we try to find sensors that are able to record magnetic field changes affecting trapped ions in our experiments. For this we assume that the magnetic field changes inside the vacuum chamber containing the trap in our experiment are the same as those measured by the sensor in the vicinity of the trap. To characterize three different sensors, we generate magnetic field offsets with a current-carrying wire, permanent magnet or a pair of coils. By isolating the sensors from the surroundings with a μ metal shield, we create a test environment under similar conditions. We showed that the fluxgate sensor is about a factor of 27500 more sensitive than the Hall sensor and a factor of 10 less sensitive than the atom itself as a sensor. We recognize that the noise of the electronics of the data acquisition system limits the performance of the fluxgate and Hall sensor. The fluxgate sensor, in contrast to the Hall sensor, turns out to be a suitable choice for monitoring magnetic field changes during experiments with ions.
We demonstrate a fully automated open-source magnetometer designed primarily for characterization of magnetic fields produced by coils, permanent magnets or by parasitic sources. It is based on an Arduino Mega microcontroller and a three-axis Hall sensor with a measurement range of ±8 G per axis and the RMS of the field readout below 0.3 mG. For all practical purposes, the sensor displacement during data acquisition is virtually unlimited, which can be particularly useful for characterizing large or extended coils like Helmholtz cages or Zeeman slowers. All components needed for the construction are cheap and widely available off-the-shelf elements or are 3D-printed. The operation of the magnetometer is controlled via a graphical user interface (GUI), which manages all essential functionalities, like data acquisition and plotting. The GUI also incorporates additional features, like data averaging, calibration of the displacement of the Hall sensor or real-time readout of the magnetic field, useful for monitoring magnetic field changes. We have used a pair of rectangular coils constructed for a potassium–cesium 2D magneto-optical trap to benchmark the performance of the magnetometer. We have obtained good agreement with both simulations and measurements acquired with a commercial gaussmeter.
We demonstrate a minimally-destructive in situ technique for measuring and stabilizing slowly-drifting magnetic fields in ultracold-atom experiments. While conventional magnetic-field sensors such as Hall, giant magnetoresistive, or fluxgate-based devices are broadly used, their accuracy, precision and dynamic range can be limited. In addition, these sensors are typically positioned at least several centimeters away from the in-vacuum atomic system, as their operation creates perturbing magnetic fields, and their placement is limited by geometric constraints imposed by the vacuum system. We overcome these issues by using the atomic system itself as a built-in magnetometer. To that end, we employ a pair of weak measurements to determine the Zeeman splitting -- and thereby the magnetic field -- of a magnetically sensitive atomic transition. We provide closed-form expressions quantifying the trade-offs between measurement noise, dynamic range, and atom loss. This procedure is demonstrated with ultracold Rb-87, weakly measured using partial-transfer absorption imaging. We then incorporate a Kalman filter to stabilize the magnetic field; this eliminated long-term drift in the ambient field (as high as ~70 nT/hr) in exchange for a modest increase in shot-to-shot variability from 1.8(2) nT to 2.0(2) nT.
Single-atom quantum sensors offer high spatial resolution and high sensitivity to electric and magnetic fields. Among them, trapped ions offer exceptional performance in sensing electric fields, which has been used in particular to probe these in the proximity of metallic surfaces. However, the flexibility of previous work was limited by the use of radio-frequency trapping fields, which has restricted spatial scanning to linear translations, and calls into question whether observed phenomena are connected to the presence of the radio-frequency fields. Here, using a Penning trap instead, we demonstrate a single ion probe which offers three-dimensional position scanning at distances between 50μm and 450μm from a metallic surface and above a 200×200μm2 area, allowing us to reconstruct static and time-varying electric as well as magnetic fields. We use this to map charge distributions on the metallic surface and noise stemming from it. The methods demonstrated here allow similar probing to be carried out on samples with a variety of materials, surface constitutions and geometries, providing a new tool for surface science.
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.
Surface based geometries of microfabricated wires or patterned magnetic films can be used to magnetically trap and manipulate ultracold neutral atoms or Bose-Einstein condensates. We investigate the magnetic properties of such atom chips using a scanning magnetoresistive (MR) microscope with high spatial resolution and high field sensitivity. By comparing MR scans of a permanent magnetic atom chip to field profiles obtained using ultracold atoms, we show that MR sensors are ideally suited to observe small variations of the magnetic field caused by imperfections in the wires or magnetic materials which ultimately lead to fragmentation of ultracold atom clouds. Measurements are also provided for the magnetic field produced by a thin current-carrying wire with small geometric modulations along the edge. Comparisons of our measurements with a full numeric calculation of the current flow in the wire and the subsequent magnetic field show excellent agreement. Our results highlight the use of scanning MR microscopy as a convenient and powerful technique for precisely characterizing the magnetic fields produced near the surface of atom chips.
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.