Nonlinear current response and electric quantum oscillations in the Dirac semimetal Cd_(3)As_(2)

Chiral anomaly is a distinct quantum anomaly associated with chiral fermions in Dirac or Weyl semimetals.The use of negative magnetoresistance(negative MR)as a signature for this anomaly remains contentious,as trivial mechanisms such as current jetting and weak localization can also induce negative MR.In this study,we report a novel nonlinear behavior of the chiral anomaly in the longitudinal direction,which we observed by applying parallel current and magnetic field to the Dirac semimetal Cd_(3)A_(s_(2)).This nonlinear characteristic peaks at an intermediate magnetic field of approximately5 T,displaying a resistance-increasing property concomitant with strengthening of the current source.Through angledependence experiments,we were able to rule out trivial factors,such as thermal effects,geometric artifacts,and anisotropy.Furthermore,additional electric quantum oscillations were observed when the direct current(DC)was applied as high as300μA.Such an unusual phenomenon is ascribed to the formation of quantized levels due to Bloch oscillation in the high DC regime,suggesting that an oscillatory density distribution may arise as the electric field increases.The non-Ohmic electric quantum oscillations open a new avenue for exploring chiral anomaly and other nontrivial topological properties,which is also one of the salient features of nonequilibrium steady states in condensed matter physics.

Electric modulation of the Fermi arc spin transport via three-terminal configuration in topological semimetal nanowires

Spin–momentum locking is a key feature of the topological surface state, which plays an important role in spintronics.The electrical detection of current-induced spin polarization protected by the spin–momentum locking in nonmagnetic systems provides a new platform for developing spintronics, while previous studies were mostly based on magnetic materials.In this study, the spin transport measurement of Dirac semimetal Cd_(3)As_(2) was studied by three-terminal geometry, and a hysteresis loop signal with high resistance and low resistance state was observed. The hysteresis was reversed by reversing the current direction, which illustrates the spin–momentum locking feature of Cd_(3)As_(2). Furthermore, we realized the on–off states of the spin signals through electric modulation of the Fermi arc via the three-terminal configuration, which enables the great potential of Cd_(3)As_(2) in spin field-effect transistors.

Evolution of pore systems in low-maturity oil shales during thermal upgrading--Quantified by dynamic SEM and machine learning

In-situ upgrading by heating is feasible for low-maturity shale oil,where the pore space dynamically evolves.We characterize this response for a heated substrate concurrently imaged by SEM.We systematically follow the evolution of pore quantity,size(length,width and cross-sectional area),orientation,shape(aspect ratio,roundness and solidity)and their anisotropy—interpreted by machine learning.Results indicate that heating generates new pores in both organic matter and inorganic minerals.However,the newly formed pores are smaller than the original pores and thus reduce average lengths and widths of the bedding-parallel pore system.Conversely,the average pore lengths and widths are increased in the bedding-perpendicular direction.Besides,heating increases the cross-sectional area of pores in low-maturity oil shales,where this growth tendency fluctuates at<300℃ but becomes steady at>300℃.In addition,the orientation and shape of the newly-formed heating-induced pores follow the habit of the original pores and follow the initial probability distributions of pore orientation and shape.Herein,limited anisotropy is detected in pore direction and shape,indicating similar modes of evolution both bedding-parallel and bedding-normal.We propose a straightforward but robust model to describe evolution of pore system in low-maturity oil shales during heating.

Experimental observation of Fermi-level flat band in novel kagome metal CeNi_(5)

Kagome materials are a class of material with a lattice structure composed of corner-sharing triangles that produce various exotic electronic phenomena,such as Dirac fermions,van Hove singularities,and flat bands.However,most of the known kagome materials have a flat band detached from the Fermi energy,which limits the investigation of the emergent flat band physics.In this work,by combining soft x-ray angle-resolved photoemission spectroscopy(ARPES)and the first-principles calculations,the electronic structure is investigated of a novel kagome metal CeNi_(5) with a clear dispersion along the kz direction and a Fermi level flat band in theΓ–K–M–Γplane.Besides,resonant ARPES experimental results indicate that the valence state of Ce ions is close to 4^(+),which is consistent with the transport measurement result.Our results demonstrate the unique electronic properties of CeNi_(5) as a new kagome metal and provide an ideal platform for exploring the flat band physics and the interactions between different types of flat bands by tuning the valence state of Ce ions.

Possible Superconductivity in Biphenylene

A new two-dimensional allotrope of carbon known as biphenylene has been synthesized.Building on previous research investigating the superconductivity of octagraphene with a square-octagon structure,we conduct a systematic study on possible superconductivity of biphenylene with partial square-octagon structure.First-principle calculations are used to fit the tight-binding model of the material and to estimate its superconductivity.We find that the conventional superconducting transition temperature Tc based on electron-phonon interaction is 3.02 K,while the unconventional Tc primarily caused by spin fluctuation is 1.7 K.We hypothesize that the remaining hexagonal C6structure of biphenylene may not be conducive to the formation of perfect Fermi nesting,leading to a lower Tc.The superconducting properties of this material fall between those of graphene and octagraphene,and it lays a foundation for achieving high-temperature superconductivity in carbon-based materials.

Negative magnetoresistance in Dirac semimetal Cd_(3)As_(2)with in-plane magnetic field perpendicular to current

Topological insulators and semimetals have exotic surface and bulk states with massless Dirac or Weyl fermions,demonstrating microscopic transport phenomenon based on relativistic theory.Chiral anomaly induced negative magnetoresistance(negative MR)under parallel magnetic field and current has been used as a probable evidence ofWeyl fermions in recent years.Here we report a novel negative MR result with mutually perpendicular in-plane magnetic field and current in Cd_(3)As_(2)nanowires.The negative MR has a considerable value of-16%around 1.5 K and could persist to room temperature of 300 K with value of-1%.The gate tuning and angle dependence of the negative MR demonstrate the mechanism of the observed negative MR is different from the chiral anomaly.Percolating current paths induced by charge puddles and disorder might be involved to produce such considerable negative MR.Our results indicate the negative MR effect in topological semimetals involves synergistic effects of many mechanisms besides chiral anomaly.

Prediction of Thermal Conductance of Complex Networks with Deep Learning

Predicting thermal conductance of complex networks poses a formidable challenge in the field of materials science and engineering. This challenge arises due to the intricate interplay between the parameters of network structure and thermal conductance, encompassing connectivity, network topology, network geometry, node inhomogeneity, and others. Our understanding of how these parameters specifically influence heat transfer performance remains limited. Deep learning offers a promising approach for addressing such complex problems. We find that the well-established convolutional neural network models AlexNet can predict the thermal conductance of complex network efficiently. Our approach further optimizes the calculation efficiency by reducing the image recognition in consideration that the thermal transfer is inherently encoded within the Laplacian matrix.Intriguingly, our findings reveal that adopting a simpler convolutional neural network architecture can achieve a comparable prediction accuracy while requiring less computational time. This result facilitates a more efficient solution for predicting the thermal conductance of complex networks and serves as a reference for machine learning algorithm in related domains.

Entanglement properties of superconducting qubits coupled to a semi-infinite transmission line

Quantum entanglement, a key resource in quantum information processing, is reduced by interaction between the quantum system concerned and its unavoidable noisy environment. Therefore it is of particular importance to study the dynamical properties of entanglement in open quantum systems. In this work, we mainly focus on two qubits coupled to an adjustable environment, namely a semi-infinite transmission line. The two qubits' relaxations, through individual channels or collective channel or both, can be adjusted by the qubits' transition frequencies. We examine entanglement dynamics in this model system with initial Werner state, and show that the phenomena of entanglement sudden death and revival can be observed. Due to the hardness of preparing the Werner state experimentally, we introduce a new type of entangled state called pseudo-Werner state, which preserves as much entangling property as the Werner state, and more importantly,it is experiment friendly. Furthermore, we provide detailed procedures for generating pseudo-Werner state and studying entanglement dynamics with it, which can be straightforwardly implemented in a superconducting waveguide quantum electrodynamics system.

Advances of phononics in 2012-2022

Due to its great potential applications in thermal management,heat control,and quantum information,phononics has gained increasing attentions since the first publication in Rev.Mod.Phys.841045(2012).Many theoretical and experimental progresses have been achieved in the past decade.In this paper,we first give a critical review of the progress in thermal diodes and transistors,especially in classical regime.Then,we give a brief introduction to the new developing research directions such as topological phononics and quantum phononics.In the third part,we discuss the potential applications.Last but not least,we point out the outlook and challenges ahead.

Nonlinear three-magnon scattering in low-damping La_(0.67)Sr_(0.33)MnO_(3)thin films

Three-magnon scattering,a nonlinear process in which a high-energy magnon splits into two low-energy magnons with energy and momentum conservation,has been widely studied in the magnonics community.Here,we report experimental observation of nonlinear three-magnon scattering in La_(0.67)Sr_(0.33)MnO_(3)thin films with low magnetic damping(~10^(-4))by all-electric and angle-resolved spin wave spectroscopy.The reflection spectra of the spin wave resonance with high-power excitation at Damon–Eshbach configuration demonstrate a scattering regime with gradual signal disappearance,where a magnon of Damon–Eshbach mode decays into two magnons of volume mode above the threshold power(-10 dBm)of the injected microwave.The nonlinear scattering is only allowed at low-field regime and the calculated dispersions of dipole-exchange spin wave claim the mechanism of allowed and forbidden three-magnon scattering.The films and heterostructures of La_(0.67)Sr_(0.33)MnO_(3)have been already demonstrated with rich physical phenomena and great versatility,in this work the nonlinear magnetic dynamics of La_(0.67)Sr_(0.33)MnO_(3)thin films is revealed,which offer more possibility for applications to oxide magnonics and nonlinear magnonic devices.

Hardware-efficient and fast three-qubit gate in superconducting quantum circuits

While the common practice of decomposing general quantum algorithms into a collection of single-and two-qubit gates is conceptually simple,in many cases it is possible to have more efficient solutions where quantum gates engaging multiple qubits are used.In the noisy intermediate-scale quantum(NISQ)era where a universal error correction is still unavailable,this strategy is particularly appealing since it can significantly reduce the computational resources required for executing quantum algorithms.In this work,we experimentally investigate a three-qubit ControlledCPHASE-SWAP(CCZS)gate on superconducting quantum circuits.By exploiting the higher energy levels of superconducting qubits,we are able to realize a Fredkin-like CCZS gate with a duration of 40 ns,which is comparable to typical single-and two-qubit gates realized on the same platform.By performing quantum process tomography for the two target qubits,we obtain a process fidelity of86.0%and 81.1%for the control qubit being prepared in|0>and|1>,respectively.We also show that our scheme can be readily extended to realize a general CCZS gate with an arbitrary swap angle.The results reported here provide valuable additions to the toolbox for achieving large-scale hardware-efficient quantum circuits.

Hardware-efficient quantum principal component analysis for medical image recognition

Principal component analysis(PCA)is a widely used tool in machine learning algorithms,but it can be computationally expensive.In 2014,Lloyd,Mohseni&Rebentrost proposed a quantum PCA(qPCA)algorithm[Nat.Phys.10,631(2014)]that has not yet been experimentally demonstrated due to challenges in preparing multiple quantum state copies and implementing quantum phase estimations.In this study,we presented a hardware-efficient approach for qPCA,utilizing an iterative approach that effectively resets the relevant qubits in a nuclear magnetic resonance(NMR)quantum processor.Additionally,we introduced a quantum scattering circuit that efficiently determines the eigenvalues and eigenvectors(principal components).As an important application of PCA,we focused on classifying thoracic CT images from COVID-19 patients and achieved high accuracy in image classification using the qPCA circuit implemented on the NMR system.Our experiment highlights the potential of near-term quantum devices to accelerate qPCA,opening up new avenues for practical applications of quantum machine learning algorithms.

Noisy intermediate-scale quantum computers

Quantum computers have made extraordinary progress over the past decade,and significant milestones have been achieved along the path of pursuing universal fault-tolerant quantum computers.Quantum advantage,the tipping point heralding the quantum era,has been accomplished along with several waves of breakthroughs.Quantum hardware has become more integrated and architectural compared to its toddler days.The controlling precision of various physical systems is pushed beyond the fault-tolerant threshold.Meanwhile,quantum computation research has established a new norm by embracing industrialization and commercialization.The joint power of governments,private investors,and tech companies has significantly shaped a new vibrant environment that accelerates the development of this field,now at the beginning of the noisy intermediate-scale quantum era.Here,we first discuss the progress achieved in the field of quantum computation by reviewing the most important algorithms and advances in the most promising technical routes,and then summarizing the next-stage challenges.Furthermore,we illustrate our confidence that solid foundations have been built for the fault-tolerant quantum computer and our optimism that the emergence of quantum killer applications essential for human society shall happen in the future.

Gapless quantum spin liquid and global phase diagram of the spin-1/2 J_(1)-J_(2) square antiferromagnetic Heisenberg model

The nature of the zero-temperature phase diagram of the spin-1/2 J_(1)-J_(2)Heisenberg model on a square lattice has been debated in the past three decades,and it remains one of the fundamental problems unsettled in the study of quantum many-body theory.By using the state-of-the-art tensor network method,specifically,the finite projected entangled pair state(PEPS)algorithm,to simulate the global phase diagram of the J_(1)-J_(2)Heisenberg model up to 24×24 sites,we provide very solid evidences to show that the nature of the intermediate nonmagnetic phase is a gapless quantum spin liquid(QSL),whose spin-spin and dimer-dimer correlations both decay with a power law behavior.There also exists a valence-bond solid(VBS)phase in a very narrow region 0.56■J_(2)/J_(1)≤0.61 before the system enters the well known collinear antiferromagnetic phase.We stress that we make the first detailed comparison between the results of PEPS and the well-established density matrix renormalization group(DMRG)method through one-to-one direct benchmark for small system sizes,and thus give rise to a very solid PEPS calculation beyond DMRG.Our numerical evidences explicitly demonstrate the huge power of PEPS for highly frustrated spin systems.Finally,an effective field theory is also proposed to understand the physical nature of the discovered gapless QSL and its relation to deconfined quantum critical point(DQCP).

Pair density wave facilitated by Bloch quantum geometry in nearly flat band multiorbital superconductors

Bloch electrons in multiorbital systems carry quantum geometric information characteristic of their wavevector-dependent interorbital mixing.The geometric nature impacts electromagnetic responses,and this effect carries over to the superconducting state,which receives a geometric contribution to the superfluid weight.In this paper,we show that this contribution could become negative under certain appropriate circumstances.This may facilitate the stabilization of Cooper pairings with real space phase modulation,i.e.,the pair density wave order,as we demonstrate through two-orbital model Bogoliubov de-Gennes mean-field calculations.The quantum geometric effect therefore constitutes an intrinsic mechanism for the formation of such a novel phase of matter in the absence of external magnetic field.

Rare-earth quantum memories: The experimental status quo

Rare-earth doped crystals carry great prospect in developing ensemble-based solid state quantum memories for remote quantum communication and fast quantum processing applications. In recent years, with this system, remarkable quantum storage performances have been realized, and more exciting applications have been exploited, while the technical challenges are also significant. In this paper, we outlined the status quo in the development of rare-earth-based quantum memories from the point of view of different storage protocols, with a focus on the experimental demonstrations. We also analyzed the challenges and provided feasible solutions.

Frequency-comb-linearized, widely tunable lasers for coherent ranging

Tunable lasers,with the ability to continuously vary their emission wavelengths,have found widespread applications across various fields such as biomedical imaging,coherent ranging,optical communications,and spectroscopy.In these applications,a wide chirp range is advantageous for large spectral coverage and high frequency resolution.Besides,the frequency accuracy and precision also depend critically on the chirp linearity of the laser.While extensive efforts have been made on the development of many kinds of frequency-agile,widely tunable,narrow-linewidth lasers,wideband yet precise methods to characterize and linearize laser chirp dynamics are also demanded.Here we present an approach to characterize laser chirp dynamics using an optical frequency comb.The instantaneous laser frequency is tracked over terahertz bandwidth at 1 MHz intervals.Using this approach we calibrate the chirp performance of 12 tunable lasers from Toptica,Santec,New Focus,EXFO,and NKT that are commonly used in fiber optics and integrated photonics.In addition,with acquired knowledge of laser chirp dynamics,we demonstrate a simple frequency-linearization scheme that enables coherent ranging without any optical or electronic linearization unit.Our approach not only presents novel wideband,highresolution laser spectroscopy,but is also critical for sensing applications with ever-increasing requirements on performance.

A wideband,high-resolution vector spectrum analyzer for integrated photonics

The analysis of optical spectra—emission or absorption—has been arguably the most powerful approach for discovering and understanding matter.The invention and development of many kinds of spectrometers have equipped us with versatile yet ultra-sensitive diagnostic tools for trace gas detection,isotope analysis,and resolving hyperfine structures of atoms and molecules.With proliferating data and information,urgent and demanding requirements have been placed today on spectrum analysis with ever-increasing spectral bandwidth and frequency resolution.These requirements are especially stringent for broadband laser sources that carry massive information and for dispersive devices used in information processing systems.In addition,spectrum analyzers are expected to probe the device’s phase response where extra information is encoded.Here we demonstrate a novel vector spectrum analyzer(VSA)that is capable of characterizing passive devices and active laser sources in one setup.Such a dual-mode VSA can measure loss,phase response,and dispersion properties of passive devices.It also can coherently map a broadband laser spectrum into the RF domain.The VSA features a bandwidth of 55.1 THz(1260–1640 nm),a frequency resolution of 471 kHz,and a dynamic range of 56 dB.Meanwhile,our fiber-based VSA is compact and robust.It requires neither high-speed modulators and photodetectors nor any active feedback control.Finally,we employ our VSA for applications including characterization of integrated dispersive waveguides,mapping frequency comb spectra,and coherent light detection and ranging(LiDAR).Our VSA presents an innovative approach for device analysis and laser spectroscopy,and can play a critical role in future photonic systems and applications for sensing,communication,imaging,and quantum information processing.

超越旋波近似的自旋轨道耦合拓扑费米子

The realization of spin-orbit-coupled ultracold gases has driven a wide range of research and is typically based on the rotating wave approximation(RWA).By neglecting the counter-rotating terms,RWA characterizes a single near-resonant spin-orbit(SO)coupling in a two-level system.Here,we propose and experimentally realize a new scheme for achieving a pair of two-dimensional(2D)SO couplings for ultracold fermions beyond RWA.This work not only realizes the first anomalous Floquet topological Fermi gas beyond RWA,but also significantly improves the lifetime of the 2D-SO-coupled Fermi gas.Based on pump-probe quench measurements,we observe a deterministic phase relation between two sets of SO couplings,which is characteristic of our beyond-RWA scheme and enables the two SO couplings to be simultaneously tuned to the optimum 2D configurations.We observe intriguing band topology by measuring two-ring band-inversion surfaces,quantitatively consistent with a Floquet topological Fermi gas in the regime of high Chern numbers.Our study can open an avenue to explore exotic SO physics and anomalous topological states based on long-lived SO-coupled ultracold fermions.

Perspectives on antiferromagnetic magnonics

Spin waves or magnons are the collective excitations in magnetic systems that have received considerable attention for lowpower logic and computation [1]. One key feature is their abilityto propagate over long distances without suffering from the Ohmicloss. This remarkable property positions them as a promising candidate as information carriers and addresses the energy consumption bottleneck due to Joule heating for data processing. Until now,the majority of studies have been focusing on magnons in ferromagnetic (FM) and ferrimagnetic (FiM) materials [2], where magnon resonance frequencies lie in the GHz regime and can beefficiently excited and detected using modern microwaveinstruments.