Exotic spin-spin-velocity-dependent interactions, predicted in extensions of the standard model involving new bosonic fields, could resolve fundamental puzzles from dark matter to cosmic asymmetry. However, exploring these weak potential interactions at centimeter scales presents formidable challenges, primarily due to the overwhelming dominance of electromagnetic backgrounds that can easily obscure the weak exotic signals. Here, we utilize a levitated magnet force sensor with ultrahigh electron spin density to probe these interactions. We constrain two interactions individually through a designed spin source and a multilayer magnetic shielding system that suppresses electromagnetic backgrounds. In this Letter, we constrain two types of interactions: the V_{6} potential at force ranges from 10^{-3} to 6×10^{-2}  m and the V_{14} potential at ranges greater than 10^{-3}  m. Our measurements establish 95% confidence-level bounds of |f_{6}|≤2.12×10^{-13} and |f_{14}|≤2.34×10^{-23} at λ=1.6×10^{-2}  m, improving prior limits by up to 12 and 13 orders of magnitude, respectively. Our result demonstrates the levitated magnet as a highly sensitive probe for detecting new bosonic fields in extensions of the standard model.

Frequency has always been one of the most significant parameters of mechanical oscillators in the field of weak signal sensing. Frequency tuning and stabilization are essential for enhancing precision and reliability during precision measurements. We propose and experimentally demonstrate a method to tune and stabilize the oscillator's frequency in the diamagnetic levitation system. In our method, a charged gold-foiled glass plate is positioned between the oscillator and the magnets, allowing for the modification of the electrical force between the oscillator and the gold foil. This adjustment enables fine-tuning of the frequency within a 10 mHz range and achieves a standard deviation of frequency of 60 μHz and a fractional frequency fluctuation of 2.7 ppm over a 16-h period. The compact design and rapid response of our device make it highly adaptable for a variety of applications. Our method paves the way for future ultra-precision measurements in diamagnetic levitation systems.

The precise measurement of the gravity of Earth plays a pivotal role in various fundamental research and application fields. Although a few gravimeters have been reported to achieve this goal, miniaturization of high-precision gravimetry remains a challenge. In this work, we have proposed and demonstrated a miniaturized gravimetry operating at room temperature based on a diamagnetic levitated micro-oscillator with a proof mass of only 215 mg. Compared with the latest reported miniaturized gravimeters based on microelectromechanical systems, the performance of our gravimetry has substantial improvements in that an acceleration sensitivity of 15  μGal/sqrt[Hz] and a drift as low as 61  μGal per day have been reached. Based on this diamagnetic levitation gravimetry, we observed Earth tides, and the correlation coefficient between the experimental data and theoretical data reached 0.97. Some moderate foreseeable improvements can develop this diamagnetic levitation gravimetry into a chip size device, making it suitable for mobile platforms such as drones. Our advancement in gravimetry is expected to facilitate a multitude of applications, including underground density surveying and the forecasting of natural hazards.

In this article, based on the magnetic levitation structure of superconducting gravity measurement, the design, adjustment, and fast measurement method of the weak magnetic force gradient are introduced. Based on the numerical simulation method of H-formulation, the weak magnetic force gradient of minimum −0.001 N·m is designed. The proposed “semiopen-loop magnetic force gradient adjustment method” can achieve the magnetic force gradient adjustment of less than −0.01 N·m. Aiming at the defect that the conventional solid earth tide observation method requires several or even tens of hours of long-term observation when measuring the magnetic force gradient, the proposed “closed-loop electromagnetic excitation method” can realize fast and accurate measurement in the process of force gradient adjustment, and evaluate the measurement accuracy of the gravity instrument at any time. The prototype is placed in the field observation station of the National Institute of Metrology where the environment is more stable to observe the solid earth tide signals. The force gradient of −0.00264 N·m was obtained using the method proposed in this article, and its correctness was verified by comparison with experimental results. This article is of great significance for improving the convenience of users, promoting the localization and commercialization of superconducting gravimeters, and promoting the in-depth research in the field of geodynamics.

Purpose This study aims to reveal the room-temperature effect of a superconducting gravimeter prototype, which will guide its subsequent optimization to improve its gravimetric measurement accuracy. Design/methodology/approach Without leveling, the prototype output signal, tilt data and room temperature were measured under steady operating conditions. After analyzing the correlations of the three data sets, the residuals of the prototype’s output signal were compensated using the tilt data and the geodynamic effects (ocean tide loading, atmospheric loading and the gravitational effect of polar motion) were then corrected. Findings The remaining residuals after correction may be caused by small tilt variations that are due to the sensor chamber temperature and radiation shield temperature changes. These small tilt variations were submerged in the tilt signal noise. Although the peak-to-peak noise of the tiltmeter does not exceed 15 µrad, it can still produce gravimetric deviations above 60 µGal when the prototype is significantly tilted. Originality/value This study analyzes in detail the room-temperature effect of a superconducting gravimeter prototype, introduces the tilt effect of the relative gravimeters to compensate for the gravimetric deviations and emphasizes that the improvement of fine leveling and the accuracy of the tiltmeter are key requirements for the prototype to perform high-accuracy gravity measurement tasks.

The annual drift of μ Gal level is an important indicator of superconducting gravimeters, which helps geophysicists to clarify the weak geophysical signals. In this paper, a finite element simulation model of the superconducting gravimeter sensor is developed based on the H formulation for evaluating the contribution of the excitation AC losses and the AC losses under operating conditions to the superconducting gravimeter’s drift. The model combines the H formulation and the heat transfer module of COMSOL Multiphysics software to calculate the AC losses of the superconducting gravimeter’s test mass and obtain the distribution images of the test mass’s temperature due to the AC losses-induced heating. The overall temperature rise of the test mass is obtained by assuming that it heats up uniformly and thus combines the temperature dependence factor (10 μ Gal mK −1 ) of the superconducting gravimeter to derive the instrument drift induced by AC losses. Then, the long-term drift due to excitation losses can reach 0.847 μ Gal yr −1 , while the operating losses can be 0.45 μ Gal yr −1 or even less, according to the simulation. In addition, this paper discusses the effects of the parameters (index number, critical electric field, and critical current density) in the E–J power law introduced by the H formulation on the AC loss evaluation. It is concluded that the AC losses are sensitive to the critical current density, and increasing the test mass’s critical current density helps enhance the stability of the superconducting gravimeter.

The superconducting gravimeter is currently the most accurate instrument in relative gravity measurement, so the high-precision calculation and analysis of superconducting magnetic levitation system is crucial to the development work of superconducting gravimeter. Shielding material can weaken the influence of external magnetic field source fluctuation on the internal levitation magnetic field and provide a stable electromagnetic environment for the magnetic levitation system. But at the same time, shielding material will also have an impact on the internal suspended magnetic field itself, which will lead to large deviations in the study of electromagnetic characteristics of the magnetic levitation system. This article establishes and optimizes the simulation calculation model of a superconducting gravimeter magnetic levitation system based on H method, and studies the effect of magnetic shielding on the magnetic field, levitation force, and magnetic force gradient of the internal levitation system. After that, the simulation calculation results are compared with the experimental results, and the simulation calculation error of superconducting levitation force and magnetic gradient is less than 1%, which verifies the correctness of the optimized simulation model. This study is an important guide for the accurate calculation of the electromagnetic properties of all superconducting systems containing magnetic shielding materials, such as superconducting gravimeter, superconducting gravity gradiometer, etc.

This paper presents a novel Nb superconducting joint with an ultralow resistance of 7.9 × 10 −16 Ω, fabricated using the electron beam welding (EBW) method. After the EBW process, the two Nb filaments formed a single joint with a much larger grain size and smaller grain misorientation. More importantly, the resistance of the EBW Nb joint was nearly one magnitude lower than that of most conventional pressing joint. The ultralow resistance is essential for superconducting gravimeters, which require an extremely low drift rate. The EBW Nb joint allowed the superconducting gravimeter to have a much better performance when applied in the field of structural geology, geodesy, microgravity, and metrology. We believe that the EBW method could be one of the most promising joint fabrication methods for achieving maximum stability (less than 1 μ gal yr −1 ).

To promote China’s research on fields related to high-accuracy gravity measurement, the Institute of Electrical Engineering, Chinese Academy of Sciences (IEECAS), is committed to developing superconducting gravimeters. A superconducting gravimeter prototype has been successfully designed, fabricated, and tested through continuous improvement and optimization design. This article describes the main components of the prototype: superconducting gravity sensor, magnetic shield, cryogenic system, and displacement detection and feedback system. The novel work improves the superconducting gravity sensor on the persistent current switch and superconducting joint. Furthermore, the method for testing the levitation stiffness is also introduced, and the result demonstrates that an electromagnetic force method is a feasible approach with fast and good linearity. Finally, experimental test results on the prototype are shown, where solid Earth tide, temperature effect, and parasitic mode are obtained in the prototype signal. Moreover, it is shown that the levitation stiffness obtained by the electromagnetic force method and the tidal observation method are close to each other.

High-resolution superconducting gravimeters (SGs) require μK-level temperature control. Passive isolation can increase the risk of quenching the superconducting gravity sensing unit. Also, the use of a vacuum chamber for passive isolation increases complexity and complicates the operation of the instrument. Therefore, to investigate how to avoid using passive isolation, we developed an analytical computation model based on the Maxwell-London (ML) equations for calculating the magnetic levitation forces of the SG, taking into account the penetration depth characteristics of type II superconducting sphere. The model can be used to calculate the independent contributions of the upper and lower superconducting coils to the superconducting sphere levitation force, the magnetic gradient of the SG, and most importantly, the temperature coefficient of the SG temperature effect. Calculations show that temperature variations change the penetration depth and levitation force of the superconducting sphere and that the penetration depth determined at 4.2 K corresponds to a unique temperature coefficient, which means that the effect of the same temperature on the levitation force of the superconducting sphere is definite for a certain penetration depth. Further studies find that the temperature coefficient depends linearly on the effective penetration depth of the superconducting sphere, and the greater temperature coefficient than that of the smooth superconductor depends on the surface preparation and surface oxidation of the superconducting sphere. After discussion, it is clear that Nb coating on the surface of superconducting spheres is an effective solution to avoid passive isolation in the future.

Measuring solar flux distribution (also called flux mapping) of a large receiver is quite challenging. Lunar flux mapping measures the illuminance distribution on the receiver aperture and the direct normal lunar illuminance during moonlight concentration experiments to determine the concentration ratio distribution (CRD). This paper presents a new lunar flux mapping model to extend the applicability to parts of the lunar cycle where the moon is not full. A dish concentrator with a similar concentration ratio to a tower concentrator was built in Beijing and used for lunar flux mapping experiments. A general method of backward ray tracing with effective sun/moon shapes for simulation of CRD is developed. The moonshape image and the normalized error image are convolved in two dimensions using the Fast Fourier Transform to give the effective moon shape image. Several optical simulations and moonlight concentration measurements on the concentrator show good similarity in the effects of changes in light source shape between solar and lunar CRD images. This model recognizes the potential of a solar concentrator to enhance the similarity between the solar CRD and a lunar CRD and that the residual differences can be compensated to some extent by using the smoothing filtering of the lunar CRD image to approximate the expected solar CRD image. The cosine similarity between lunar and solar CRDs is a function of the cosine similarity between the corresponding light source shapes, which can be derived from the dish concentrator and shows promise for application to a large solar tower system.

We have successfully reached the world record 32.35 T direct-current magnetic field by using a homemade all-superconducting magnet. The magnet has consisted of a 15 T low temperature superconductor outsert coil and two high temperature superconductor no-insulation (NI) insert coils using a conductor tape coated of REBCO (REBa2Cu3Ox, where RE = Y, Gd). This result proves the feasibility of reaching a strong magnetic field up to 32 T by using the NI process as well as the superconductor magnet with insulation. This magnet is one of the essential parts of the 'Synergetic Extreme Condition User Facility' project, which provides expertize, instrumentation, and infrastructure for investigating matter science under extreme physical conditions. We thought that such a strong superconductor magnet would bring the possibility to explore more mystery in physics, medicine, pharmacy, etc.

A high precision superconducting levitation system for gravity measurement has been developed, which used the levitation of a superconducting sphere by the magnetic field of two superconducting coils. The magnetic levitation is designed to provide independent adjustment of the levitating force and the force gradient. A Gifford-McMahon (GM) cryocooler is employed to cool down the system. This paper reviews the construction and operating characteristics of the system. The test results show that the earth tide signal was detected by the system.

Based on the Meissner effect a superconducting hollow sphere rotor is levitated in the vacuum housing. During the high speed rotation, the dynamic deformations caused by the centrifugal force will generate magnetic disturbing torque on the superconducting rotor. The deformations of the rotor are analyzed and simulated by finite-element method, and the deformation laws are obtained. The structure of spherical-like rotor is designed to compensate the centrifugal deformation at the high rotational velocity. It has significant theoretical value for the design and optimization of the rotor structure.

Due to the absence of friction, a superconducting rotor can achieve a very high speed to obtain a large angular momentum for high-precision measurement of the angular displacement and angular velocity. However, in practice, the superconducting rotor will do vibration and collide with the inner wall of the rotor cavity at a certain speed during startup, which will result in the failure of the rotor’s acceleration. In this paper, an improved starting strategy was proposed. This new method can avoid the peak of vibration amplitude by changing the bearing stiffness of the rotor quickly. The startup and shutdown process of the rotor was redesigned. Several experiments were carried out to verify its correctness. The results show that the superconducting rotor can be accelerated to the rated speed of 200 Hz (12 000 r/min) successfully by the proposed method. Furthermore, the start time of the rotor was greatly reduced to 20 minutes from more than one hour for the original method.

Superconducting quantum interference devices (SQUIDs) with 3D nano-bridge junctions can be miniaturized into nano-SQUIDs that are able to sense a few spins in a large magnetic field. Among all device parameters, the inductance is key to the performance of SQUIDs with 3D nano-bridge junctions. Here, we measured the critical-current magnetic flux modulation curves of 12 devices with three design types using a current strip-line directly coupled to the SQUID loop. A best flux modulation depth of 71% was achieved for our 3D Nb SQUID. From the modulation curves, we extracted the inductance values of the current stripe-line in each design and compared them with the corresponding simulation results of InductEX. In this way, London penetration depths of 110 and 420 nm were determined for our Nb (niobium) and NbN (niobium nitride) films, respectively. Furthermore, we showed that inductances of 11 and 119 pH for Nb and NbN 3D nano-bridge junctions, respectively, dominated the total inductance of our SQUID loops which are 23 pH for Nb and 255 pH for NbN. A screening parameter being equal to one suggests optimal critical currents of 89.6 and 8.1 mu A for Nb and NbN SQUIDs, respectively. Additionally, intrinsic flux noise of 110 +/- 40 n Phi(0)/(Hz)(1/2) is calculated for the Nb SQUIDs with 3D nano-bridge junctions by Langevin simulation.

We report here a correction to the listing order of the affiliations of the authors in the paper, “Fabrication and Characterization of Miniaturized NbN Superconducting Quantum Interference Devices With Nanobridge Junctions.”

Superconducting quantum interference filters (SQIFs) are arrays of superconducting quantum interference devices with various loop areas. In contrast to the SQIFs of conventional Josephson junctions, we propose a way for creating highly integrated SQIFs using 50 × 50 nm2 three-dimensional (3-D) nanobridge junctions. Here, we report the fabrication of arrays composed of a hundred 3-D nanobridge junctions. Current–voltage curves of single, 10, and 100 junctions in series were measured and analyzed. Measurements of single junctions revealed an average critical current of 104 μA with a standard deviation of 24 μA. Furthermore, the 10 junctions in series had randomly distributed switching events. The normal resistance as the function of the number of junctions in series showed a good linearity, indicating a good uniformity of the junctions. Therefore, we propose that the local differences in the thermal-dissipation conditions and random trapped vortices were likely responsible for the random switching of the nanobridge junctions in series.

The nano-superconducting quantum interference device (SQUID) is considered one of the most sensitive magnetic sensors for the characterization of mesoscopic and microscopic magnetic moments. Therefore, it is suitable for measuring the Meissner effect in small superconductors that cannot generate large enough signals for commercial magnetometers. To achieve an optimized coupling, the sample is usually placed directly on a SQUID chip and as close to the SQUID washer as possible. Therefore, a large working temperature range of the nano-SQUID is desirable to measure a wider range of samples. Here, we achieved the measurement of the Meissner effect in a 25 μm-sized Nb and a 40 μm × 120 μm-sized FeSe crystals using a niobium nitride (NbN) nano-SQUID. This nano-SQUID has a usable magnetic flux modulation for temperatures up to 9.5 K. The flux noise is around 50–60 μΦ0 Hz−1/2 for the entire measurement system. The diamagnetic branches induced by the Meissner effect below the lower critical field were observed for both Nb and FeSe crystals with the NbN nano-SQUID device. In addition, at various temperatures, strong magnetic hysteresis arising from vortices pinning was also observed and analyzed for both Nb and FeSe crystals.