arXiv subjects

Dong Sheng

Publications and source records attributed to Dong Sheng.

17 recordsLinked to original sources

arXiv2025

A high-sensitivity frequency counter for free-induction-decay signals

Real-time frequency readout of time-dependent pulsed signals with a high sensitivity are key elements in many applications using atomic devices, such as FID atomic magnetometers. In this paper, we propose a frequency measurement algorithm based on the Hilbert transform and implement such a scheme in a FPGA-based frequency counter. By testing pulsed exponential-decay oscillation signals in the frequency range of 10 to 500 kHz, this frequency counter shows a frequency sensitivity better than 0.1 mHz/Hz^(1/2) at 10 Hz, with an output rate of 200 Hz. When the output rate is increased to 1000 Hz, the sensitivity remains better than 0.4 mHz/Hz^(1/2) at 10 Hz. The performance on frequency sensitivity is comparable with results obtained by off-line nonlinear fitting processes. In addition, this frequency counter does not require the pre-knowledge of the analytic expression of the input signals. The realization of such a device paves the way for practical applications of highly-sensitive FID atomic magnetometers.

physics.ins-det↗

arXiv2025

Suppression of heading errors in Bell-Bloom optically pumped free-induction-decay alkali-metal atomic magnetometers

Heading errors of atomic magnetometers refer to the dependence of measurement results on the sensor orientation with respect to the external magnetic field. There are three main sources of such errors: the light shift effect, the linear nuclear-spin Zeeman effect, and the nonlinear Zeeman effect. In this work, we suppress the former two effects by using the Bell-Bloom optical pumping method and probe the atomic signals while the pumping beam is off, and focus on the heading error induced by nonlinear Zeeman effect while the sensor operates in the geomagnetic field range. We demonstrate several schemes to suppress this remaining heading error within 1 nT using a single magnetometer or a comagnetometer. In the magnetometer system, two schemes are developed to average out the horizontal atomic polarization in space or in time, respectively. In the comagnetometer system, we combine the simultaneously measured Larmor frequencies of two different kinds of alkali atoms to either suppress the heading error or extract the orientation of the pumping beam relative to the bias field.

physics.atom-ph↗

arXiv2024

Identifying Cocoa Pollinators: A Deep Learning Dataset

Cocoa is a multi-billion-dollar industry but research on improving yields through pollination remains limited. New embedded hardware and AI-based data analysis is advancing information on cocoa flower visitors, their identity and implications for yields. We present the first cocoa flower visitor dataset containing 5,792 images of Ceratopogonidae, Formicidae, Aphididae, Araneae, and Encyrtidae, and 1,082 background cocoa flower images. This dataset was curated from 23 million images collected over two years by embedded cameras in cocoa plantations in Hainan province, China. We exemplify the use of the dataset with different sizes of YOLOv8 models and by progressively increasing the background image ratio in the training set to identify the best-performing model. The medium-sized YOLOv8 model achieved the best results with 8% background images (F1 Score of 0.71, mAP50 of 0.70). Overall, this dataset is useful to compare the performance of deep learning model architectures on images with low contrast images and difficult detection targets. The data can support future efforts to advance sustainable cocoa production through pollination monitoring projects.

q-bio.QM↗

arXiv2024

Nano/micro-plastics effects in agricultural landscapes: an overlooked threat to pollination, biological pest control, and food security

Biodiversity-associated ecosystem services such as pollination and biocontrol may be severely affected by emerging nano/micro-plastics (NMP) pollution. We synthesized the little-explored effects of NMP on pollinators and biocontrol agents on the organismal, farm and landscape scale. For instance ingested NMP trigger organismal changes from gene expression, organ damage to behavior modifications. At the farm and landscape level, NMP will likely amplify synergistic effects with other threats such as pathogens and antibiotics, and may alter landscape properties such as floral resource distributions in high NMP concentration areas, what we call NMP islands. It is essential to understand the functional exposure pathways of NMP on pollinators and biocontrol agents to comprehensively evaluate the risks for agricultural ecosystems and global food security.

q-bio.OT↗

arXiv2023

Partial measurements of the total field gradient and the field gradient tensor using an atomic magnetic gradiometer

Magnetic gradiometers have wide practical and academic applications, and two important types of field gradient observables are the total field gradient and field gradient tensor. However, measurements of the field gradient tensor have not been the focus of previous researches on atomic magnetic gradiometers. In this work, we develop an atomic magnetic gradiometer based on two separately optically pumped atomic ensembles in a Herriott-cavity-assisted atomic cell. This gradiometer shows versatile operation modes and functions, and we demonstrate them in measurements of both types of field gradient observables.

physics.atom-ph↗

arXiv2023

Search for spin-dependent gravitational interactions at the Earth range

Among the four fundamental forces, only gravity does not couple to particle spins according to the general theory of relativity. We test this principle by searching for an anomalous scalar coupling between the neutron spin and the Earth gravity on the ground. We develop an atomic gas comagnetometer to measure the ratio of nuclear spin-precession frequencies between $^{129}$Xe and $^{131}$Xe, and search for a change of this ratio to the precision of 10$^{-9}$ as the sensor is flipped in the Earth gravitational field. The null results of this search set an upper limit on the coupling energy between the neutron spin and the gravity on the ground at 5.3$\times$10$^{-22}$~eV (95\% confidence level), resulting in a 17-fold improvement over the previous limit. The results can also be used to constrain several other anomalous interactions. In particular, the limit on the coupling strength of axion-mediated monopole-dipole interactions at the range of the Earth radius is improved by a factor of 17.

gr-qc↗

arXiv2023

A sensitive and stable atomic vector magnetometer for weak field detections using double orthogonal multipass cavities

This paper presents a compact low-temperature atomic vector magnetometer for weak field measurements, using an atomic cell containing two orthogonal multipass cavities. At the working temperature of 75 $^\circ$C, the magnetic field sensitivities at all three axes are better than 45 fT/Hz$^{1/2}$ at 10~Hz limited by photon noise, and 85 fT/Hz$^{1/2}$ at 0.1~Hz. This sensor also shows measurement stabilities better than 1.5~pT at three axes for an integration time of $10^4$ s, even with the laser frequency unlocked. The sensor response to a rotation is demonstrated, which is also developed to measure the effective gyromagnetic ratio of atoms in this sensor when the bias field is nulled. This magnetometer makes an important step towards long-term stable measurements and calibrations of ultra-low fields.

physics.atom-ph↗

arXiv2022

Search for monopole-dipole interactions at the sub-millimeter range with a $^{129}$Xe-$^{131}$Xe-Rb comagnetometer

Monopole-dipole interactions involving scalar couplings between a spin and a massive particle violate both P- and T-symmetry, and can be mediated by axions. We use a $^{129}$Xe-$^{131}$Xe-Rb atomic cell comagnetometer to measure the ratio of precession frequencies between the two xenon isotopes, and search for changes of the ratio correlated with the distance between the atomic cell and a non-magnetic bismuth germanate (BGO) crystal. A modulated Rb polarization scheme is used to suppress systematic effects by two orders of magnitude. The null results of this search improve the upper limit on the coupling strength $g_{s}^Ng_{p}^{n}$ over the interaction range 0.11 - 0.55 mm, and by a maximum improvement factor of 30 at 0.24 mm. The corresponding propagator mass range of this new excluded region covers 0.36 - 1.80 meV.

physics.atom-ph↗

arXiv2022

Light-shift-free and dead-zone-free atomic orientation based scalar magnetometry using a single amplitude-modulated beam

Detection dead zones and heading errors induced by light shifts are two important problems in optically pumped scalar magnetometry. We introduce an atomic orientation based single-beam magnetometry scheme to simultaneously solve these problems, using a polarization-reversing and path-bending Herriott cavity. Here, a reflection mirror is inserted into the cavity to bend the optical paths in the middle, and divide them into two separated orthogonal regions to avoid the detection dead zone. Moreover, half-wave plates are added in the center of each optical region, so that the light polarization is flipped each time it passes the wave plates and the light shift effects are spatially averaged out. This operation is demonstrated to eliminate the unnoticed heading errors induced by ac light shifts. The methods developed in this paper are robust to use, and easy to be applied in other atomic devices.

physics.atom-ph↗

arXiv2021

Search for topological defect dark matter with a global network of optical magnetometers

Ultralight bosons such as axion-like particles are viable candidates for dark matter. They can form stable, macroscopic field configurations in the form of topological defects that could concentrate the dark matter density into many distinct, compact spatial regions that are small compared to the galaxy but much larger than the Earth. Here, we report the results of a search for transient signals from axion-like particle domain walls with the Global Network of Optical Magnetometers for Exotic physics searches (GNOME). We search the data, consisting of correlated measurements from optical atomic magnetometers located in laboratories all over the world, for patterns of signals propagating through the network consistent with domain walls. The analysis of data from a continuous month-long operation of the GNOME finds no statistically significant signals, thus placing experimental constraints on such dark matter scenarios.

astro-ph.CO↗

arXiv2021

Herriott-Cavity-Assisted Closed-Loop Xe Isotope Comagnetometer

We present in this paper a Herriott-cavity-assisted closed-loop Xe isotope gas comagnetometer. In this system, $^{129}$Xe and $^{131}$Xe atoms are pumped and probed by polarized Rb atoms, and continuously driven by oscillating magnetic fields, whose frequencies are kept on resonance by phase-locked loops (PLLs). Different from other schemes, we use a Herriott cavity to improve the Rb magnetometer sensitivity instead of the parametric modulation method, and this passive method is aimed to improve the system stability while maintaining the sensitivity. This system has demonstrated an angle random walk (ARW) of 0.06 $^\circ$/h$^{1/2}$, and a bias instability of 0.2 $^\circ$/h (0.15 $μ$Hz) with a bandwidth of 1.5 Hz. By adding a closed-loop Rb isotope comagnetometer, we can extend this system to dual simultaneously working comagnetometers sharing the same cell. This extended system has wide applications in precision measurements, where we can simultaneously and independently measure the coupling of anomalous fields with proton spin and neutron spin.

physics.atom-ph↗

arXiv2020

Electric quadrupole shifts of the precession frequencies of $^{131}$Xe atoms in rectangular cells

We study an atomic comagnetometer design based on the spin precessions of $^{129}$Xe and $^{131}$Xe atoms in glass cells. The quadrupole splittings in the precession spectrum of $^{131}$Xe are fully resolved, allowing a precise determination of the magnetic-dipole precession frequency. The transverse asymmetry of quadrupole interactions, due to both the geometry and surface properties of the cell, characterized by a non-zero asymmetry parameter $η$, modifies the dependence of the quadrupole splittings on the relative orientation between the cell axes and the bias magnetic field, and lead to additional corrections in the precession frequencies of $^{131}$Xe atoms. We examine these effects both theoretically and experimentally, and develop methods to quantify and control such shifts.

physics.atom-ph↗

arXiv2020

Herriott-cavity-assisted all-optical atomic vector magnetometer

We report an all-optical atomic vector magnetometer using dual Bell-Bloom optical pumping beams in a Rb vapor cell. This vector magnetometer consists of two orthogonal optical pumping beams, with amplitude modulations at $^{85}$Rb and $^{87}$Rb Larmor frequencies respectively. We simultaneously detect atomic signals excited by these two pumping beams using a single probe beam in the third direction, and extract the field orientation information using the phase delays between the modulated atomic signals and the driving beams. By adding a Herriott cavity inside the vapor cell, we improve the magnetometer sensitivity. We study the performance of this vector magnetometer in a magnetic field ranging from 100~mG to 500~mG, and demonstrate a field angle sensitivity better than 10~$μ$rad/Hz$^{1/2}$ above 10~Hz.

physics.atom-ph↗

arXiv2019

Interactions between non-resonant rf fields and atoms with strong spin-exchange collisions

We study the interactions between oscillating non-resonant rf fields and atoms with strong spin-exchange collisions in the presence of a weak dc magnetic field. We find that the atomic Larmor precession frequency shows a new functional form to the rf field parameters when the spin-exchange collision rate is tuned. In the weak rf field amplitude regime, a strong modification of atomic Larmor frequency appears when the spin-exchange rate is comparable to the rf field frequency. This new effect has been neglected before due to its narrow observation window. We compare the experimental results with density matrix calculations, and explain the data by an underdamped oscillator model. When the rf field amplitude is large, there is a minimum atomic gyromagnetic ratio point due to the rf photon dressing, and we find that strong spin-exchange interactions modify the position of such a point.

physics.atom-ph↗

arXiv2017

A microfabricated optically-pumped magnetic gradiometer

We report on the development of a microfabricated atomic magnetic gradiometer based on optical spectroscopy of alkali atoms in the vapor phase. The gradiometer, which operates in the spin-exchange relaxation free regime, has a length of 60 mm and cross sectional diameter of 12 mm, and consists of two chip-scale atomic magnetometers which are interrogated by a common laser light. The sensor can measure differences in magnetic fields, over a 20 mm baseline, of 10 fT/Hz$^{1/2}$ at frequencies above 20 Hz. The maximum rejection of magnetic field noise is 1000 at 10 Hz. By use of a set of compensation coils wrapped around the sensor, we also measure the sensor sensitivity at several external bias field strengths up to 150 mG. This device is useful for applications that require both sensitive gradient field information and high common-mode noise cancellation.

physics.ins-det↗

arXiv2014

New classes of systematic effects in gas spin co-magnetometers

Atomic co-magnetometers are widely used in precision measurements searching for spin interactions beyond the Standard Model. We describe a new $^3$He-$^{129}$Xe co-magnetometer probed by Rb atoms and use it to identify two general classes of systematic effects in gas co-magnetometers, one associated with diffusion in second-order magnetic field gradients and another due to temperature gradients. We also develop a general and practical approach for calculating spin relaxation and frequency shifts due to arbitrary magnetic field gradients and confirm it experimentally.

physics.atom-ph↗

arXiv2012

Sensitivity test of a blue-detuned dipole trap designed for parity non-conservation measurements in Fr

A dynamic blue-detuned optical dipole trap with stable $^{87}Rb$ atoms produces a differential ac Stark shift of 18 Hz in the ground state hyperfine transition, and it preserves the ground state hyperfine superpositions for a long coherence time of 180 ms. The trapped atoms undergoing microwave Rabi oscillations are sensitive to a small signal, artificially generated with a second microwave source, phase locked to the first allow- ing a simple and effective method for determining signal-to-noise ratio limits through interference techniques. This provides an excellent means of calibrating sensitivity in experiments such as our ongoing Fr parity non-conservation measurement.

physics.atom-ph↗