Magnetic field regression using artificial neural networks for cold atom experiments

Accurately measuring magnetic fields is essential for magnetic-field sensitive experiments in areas like atomic,molecular,and optical physics,condensed matter experiments,and other areas.However,since many experiments are often conducted in an isolated environment that is inaccessible to experimentalists,it can be challenging to accurately determine the magnetic field at the target location.Here,we propose an efficient method for detecting magnetic fields with the assistance of an artificial neural network(NN).Instead of measuring the magnetic field directly at the desired location,we detect fields at several surrounding positions,and a trained NN can accurately predict the magnetic field at the target location.After training,we achieve a below 0.3%relative prediction error of magnetic field magnitude at the center of the vacuum chamber,and successfully apply this method to our erbium quantum gas apparatus for accurate calibration of magnetic field and long-term monitoring of environmental stray magnetic field.The demonstrated approach significantly simplifies the process of determining magnetic fields in isolated environments and can be applied to various research fields across a wide range of magnetic field magnitudes.

On-chip single-photon chirality encircling exceptional points

Exceptional points(EPs),which are typically defined as the degener-acy points of a non-Hermitian Hamiltonian,have been investigated in various physical systems such as photonic systems.In particular,the intriguing topological structures around EPs have given rise to novel strategies for manipulating photons and the underlying mechanism is especially useful for on-chip photonic applications.Although some on-chip experiments with the adoption of lasers have been reported,EP-based photonic chips working in the quantum regime largely re-main elusive.In the current work,a single-photon experiment was proposed to dynamically encircle an EP in on-chip photonic waveg-uides possessing passive anti-parity-time symmetry.Photon coinci-dences measurement reveals a chiral feature of transporting single photons,which can act as a building block for on-chip quantum de-vices that require asymmetric transmissions.The findings in the cur-rent work pave the way for on-chip experimental study on the physics of EPs as well as inspiring applications for on-chip non-Hermitian quantum devices.

Generation of time-varying orbital angular momentum beams with space-time-coding digital metasurface

The recently proposed extreme-ultraviolet beams with time-varying orbital angular momentum(OAM)realized by high-harmonic generation provide extraordinary tools for quantum excitation control and particle manipulation.However,such an approach is not easily scalable to other frequency regimes.We design a space-time-coding digital metasurface operating in the microwave regime to experimentally generate time-varying OAM beams.Due to the flexible programmability of the metasurface,a higher-order twist in the envelope wavefront structure of time-varying OAM beams can be further designed as an additional degree of freedom.The time-varying OAM field patterns are dynamically mapped by developing a two-probe measurement technique.Our approach in combining the programmability of space-time-coding digital metasurfaces and the two-probe measurement technique provides a versatile platform for generating and observing time-varying OAM and other spatiotemporal excitations in general.The proposed time-varying OAM beams have application potentials in particle manipulation,time-division multiplexing,and information encryption.

Ultra-broadband reflectionless Brewster absorber protected by reciprocity

The Brewster’s law predicts zero reflection of p-polarization on a dielectric surface at a particular angle.However,when loss is introduced into the permittivity of the dielectric,the Brewster condition breaks down and reflection unavoidably appears.In this work,we found an exception to this long-standing dilemma by creating a class of nonmagnetic anisotropic metamaterials,where anomalous Brewster effects with independently tunable absorption and refraction emerge.This loss-independent Brewster effect is bestowed by the extra degrees of freedoms introduced by anisotropy and strictly protected by the reciprocity principle.The bandwidth can cover an extremely wide spectrum from dc to optical frequencies.Two examples of reflectionless Brewster absorbers with different Brewster angles are both demonstrated to achieve large absorbance in a wide spectrum via microwave experiments.Our work extends the scope of Brewster effect to the horizon of nonmagnetic absorptive materials,which promises an unprecedented wide bandwidth for reflectionless absorption with high efficiency.

Non-Hermitian topological coupler for elastic waves

Non-Hermitian topological systems,by combining the advantages of topological robustness and sensitivity induced by nonHermiticity,have recently emerged and attracted much research interest.Here,we propose a device based on the topological coupler in elastic waves with non-Hermiticity,which contains two topological domain walls and four ports.In this device,topological robustness routes the transmission of waves,while non-Hermiticity controls the gain or loss of waves as they propagate.These mechanisms result in continuous and quantitative control of the energy distribution ratio of each port.A nonHermitian Hamiltonian is introduced to reveal the coupling mechanism of the topological coupler,and a scattering matrix is proposed to predict the energy distribution ratio of each port.The proposed topological coupler,which provides a new paradigm for the non-Hermitian topological systems,can be employed as a sensitive beam splitter or a coupler switch.Moreover,the topological coupler has potential applications in information processing and logic operation in elastic circuits or networks,and the paradigm also applies to other classical systems.