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The field-free spin-orbit torque (SOT) switching of perpendicular magnetization is a prerequisite for realizing fast, high-density, and low-power magnetic memories and logic devices. To date, field-free SOT switching of perpendicular magnetization has been realized through various asymmetric designs in the film structures, such as by adding additional functional layers or grow wedge shaped structures. Here we demonstrate a new strategy to realize field-free switching of perpe [Detail] ...
Download coverIn recent years, machine learning models have been introduced into the field of gravitational wave (GW) data processing. In this paper, we apply the convolutional neural network (CNN) to LIGO O1, O2, O3a data analysis to search the released 41 GW events which are emitted from binary black hole (BBH) mergers (here we exclude the events from binary neutron star (BNS) mergers, and the events that are not detected simultaneously by Hanford (H) and Livingston (L) detectors), and use time sliding method to reduce the false alarm rate (FAR). According to the results, the 41 confirmed GW events of BBH mergers can be classified successfully by our CNN model. Furthermore, through restricting the number of consecutive prewarning from sequential samples intercepted continuously in LIGO O2 real time-series and vetoing the coincidences of noise from H and L, the FAR is limited to be less than once in 2 months. It is helpful to promote LIGO real time data processing.
L10-FePt distinguishes itself for its ultrahigh perpendicular magnetic anisotropy (PMA), enabling thermally stabile memory cells to scale down to 3 nm. The recently discovered “bulk” spin−orbit torques inL10-FePt provide an efficient and scalable way to manipulate the L10-FePt magnetization. However, the existence of an external field during the switching limits its practical application, and therefore field-free switching of L10-FePt is highly demanded. In this manuscript, by growing the L10-FePt film on vicinal MgO (001) substrates, we realize the field-free switching of L10-FePt. This method is different from previously established strategies as it does not need to add other functional layers or create asymmetry in the film structure. The dependence on the vicinal angle, film thickness, and growth temperature demonstrates a wide operation window for the field-free switching of L10-FePt. We confirm the physical origin of the field-free switching is due to the tilted anisotropy of L10-FePt induced by the vicinal surface. We also quantitatively characterize the spin-orbit torques in the L10-FePt films. Our results extend beyond the established strategies to realize field-free switching, and potentially could be applied to mass production.
Due to the unique electronic structure of half-metals, characterized by the conductivity of majority-spin and the band gap of minority-spin, these materials have emerged as suitable alternatives for the design of efficient giant magnetoresistive (GMR) devices. Based on the first-principles calculations, an excellent GMR device has been designed by using two-dimensional (2D) half-metal Mn2NO2. The results show that Mn2NO2 has sandwiched between the Au/nMn2NO2 (n = 1, 2, 3)/Au heterojunction and maintains its half-metallic properties. Due to the half-metallic characteristics of Mn2NO2, the total current of the monolayer device can reach up to 1500 nA in the ferromagnetic state. At low voltage, the maximum GMR is observed to be 1.15 × 1031 %. Further, by increasing the number of layers, the ultra-high GMR at low voltage is still maintained. The developed device is a spintronic device exhibiting the highest magnetoresistive ratio reported theoretically so far. Simultaneously, a significant negative differential resistance (NDR) effect is also observed in the heterojunction. Owing to its excellent half-metallic properties and 2D structure, Mn2NO2 is an ideal energy-saving GMR material.
Improving the performance of generation, transport and injection of hot carriers within metal/semiconductor junctions is critical for promoting the hot-carrier applications. However, the conversion efficiency of hot carriers in the commonly used noble metals (e.g., Au) is extremely low. Herein, through a systematic study by first-principles calculation and Monte Carlo simulation, we show that TiN might be a promising plasmonic material for high-efficiency hot-carrier applications. Compared with Au, TiN shows obvious advantages in the generation (high density of low-energy hot electrons) and transport (long lifetime and mean free path) of hot carriers. We further performed a device-oriented study, which reveals that high hot-carrier injection efficiency can be achieved in core/shell cylindrical TiN/TiO2 junctions. Our findings provide a deep insight into the intrinsic processes of hot-carrier generation, transport and injection, which is helpful for the development of hot-carrier devices and applications.
Artificial synapse is one of the potential electronics for constructing neural network hardware. In this work, Pt/LiSiOx/TiN analog artificial synapse memristor is designed and investigated. With the increase of compliance current (C. C.) under 0.6 mA, 1 mA, and 3 mA, the current in the high resistance state (HRS) presents an increasing variation, which indicates lithium ions participates in the operation process for Pt/LiSiOx/TiN memristor. Moreover, depending on the movement of lithium ions in the functional layer, the memristor illustrates excellent conduction modulation property, so the long-term potentiation (LTP) or depression (LTD) and paired-pulse facilitation (PPF) synaptic functions are successfully achieved. The neural network simulation for pattern recognition is proposed with the recognition accuracy of 91.4%. These findings suggest the potential application of the LiSiOx memristor in the neuromorphic computing.
We investigate the thermal transport properties of three kinds of multilayer structures: a perfect superlattice (SL) structure, a quasi-periodic multilayer structure consisted of two superlattice (2SL) structures with different periods, and a random multilayer (RML) structure. Our simulation results show that there exists a large number of aperiodic multilayer structures that have effective thermal conductivity higher than that of the SL counterpart, showing enhancement ratio in the effective thermal conductivity up to 193%. Surprisingly, some RML structures also exhibit enhanced thermal transport than the SL counterpart even in the presence of phonon localization. The detailed analysis on the underlying mechanism reveals that such peculiar enhancement is caused by the synergistic effect of coherent and incoherent phonon transport, which can be tuned by the structural configuration. Combined with molecular dynamics simulations and the machine learning technique, we further reveal that the enhancement effect of the effective thermal conductivity by 2SL structure is more significant when the period of SL structure is close to the critical transition period between the coherent and incoherent phonon transport regimes. Our study proposes a novel strategy to enhance the thermal transport in multilayer structures by regulating the wave-particle duality of phonons via the structure optimization, which might provide valuable insights to the thermal management in devices with densely packed interfaces.
In this paper, we numerically studied the late-time evolutional mechanism of three-dimensional (3D) single-mode immiscible Rayleigh–Taylor instability (RTI) by using an improved lattice Boltzmann multiphase method implemented on graphics processing units. The influences of extensive dimensionless Reynolds numbers and Atwood numbers on phase interfacial dynamics, spike and bubble growth were investigated in details. The longtime numerical experiments indicate that the development of 3D singlemode RTI with a high Reynolds number can be summarized into four different stages: linear growth stage, saturated velocity growth stage, reacceleration stage and turbulent mixing stage. A series of complex interfacial structures with large topological changes can be observed at the turbulent mixing stage, which always preserve the symmetries with respect to the middle axis for a low Atwood number, and the lines of symmetry within spike and bubble are broken as the Atwood number is increased. Five statistical methods for computing the spike and bubble growth rates were then analyzed to reveal the growth law of 3D single-mode RTI in turbulent mixing stage. It is found that the spike late-time growth rate shows an overall increase with the Atwood number, while the bubble growth rate experiences a slight decrease with the Atwood number at first and then basically maintains a steady value of around 0.1. When the Reynolds number decreases, the later stages cannot be reached gradually and the evolution of phase interface presents a laminar flow state.
We propose an efficient scheme to implement a multiplex-controlled phase gate with multiple photonic qubits simultaneously controlling one target photonic qubit based on circuit quantum electrodynamics (QED). For convenience, we denote this multiqubit gate as MCP gate. The gate is realized by using a two-level coupler to couple multiple cavities. The coupler here is a superconducting qubit. This scheme is simple because the gate implementation requires only one step of operation. In addition, this scheme is quite general because the two logic states of each photonic qubit can be encoded with a vacuum state and an arbitrary non-vacuum state |φ> (e.g., a Fock state, a superposition of Fock states, a cat state, or a coherent state, etc.) which is orthogonal or quasi-orthogonal to the vacuum state. The scheme has some additional advantages: because only two levels of the coupler are used, i.e., no auxiliary levels are utilized, decoherence from higher energy levels of the coupler is avoided; the gate operation time does not depend on the number of qubits; and the gate is implemented deterministically because no measurement is applied. As an example, we numerically analyze the circuit-QED based experimental feasibility of implementing a three-qubit MCP gate with photonic qubits each encoded via a vacuum state and a cat state. The scheme can be applied to accomplish the same task in a wide range of physical system, which consists of multiple microwave or optical cavities coupled to a two-level coupler such as a natural or artificial atom.
By combining structural search and first-principles calculations, we predict a new stable two-dimensional PdSe monolayer, and systematically investigate its structural, electronic and optical properties. The calculated formation enthalpy, phonon spectra and molecular dynamic simulations confirm that PdSe monolayer possesses excellent thermodynamic and dynamic stability. PdSe monolayer is a semiconductor with an indirect band gap of ∼ 1.10 eV. The carrier transport of PdSe monolayer is dominated by hole and exhibits remarkable anisotropy due to the intrinsic structure anisotropy. The optical properties also show obvious anisotropic characteristic with considerable absorption coefficient and broad absorption from the visible to ultraviolet regions. Benefiting from these excellent physical properties, PdSe monolayer is expected to be a promising candidate as electronic and optoelectronic devices.
Topological edge solitons represent a significant research topic in the nonlinear topological photonics. They maintain their profiles during propagation, due to the joint action of lattice potential and nonlinearity, and at the same time are immune to defects or disorders, thanks to the topological protection. In the past few years topological edge solitons were reported in systems composed of helical waveguide arrays, in which the time-reversal symmetry is effectively broken. Very recently, topological valley Hall edge solitons have been demonstrated in straight waveguide arrays with the time-reversal symmetry preserved. However, these were scalar solitary structures. Here, for the first time, we report vector valley Hall edge solitons in straight waveguide arrays arranged according to the photonic lattice with innate type-II Dirac cones, which is different from the traditional photonic lattices with type-I Dirac cones such as honeycomb lattice. This comes about because the valley Hall edge state can possess both negative and positive dispersions, which allows the mixing of two different edge states into a vector soliton. Our results not only provide a novel avenue for manipulating topological edge states in the nonlinear regime, but also enlighten relevant research based on the lattices with type-II Dirac cones.
In view of the fact that most invisibility devices focus on linear polarization cloaking and that the characteristics of mid-infrared cloaking are rarely studied, we propose a cross-circularly polarized invisibility carpet cloaking device in the mid-infrared band. Based on the Pancharatnam–Berry phase principle, the unit cells with the cross-circular polarization gradient phase were carefully designed and constructed into a metasurface. In order to achieve tunable cross-circular polarization carpet cloaks, a phase change material is introduced into the design of the unit structure. When the phase change material is in amorphous and crystalline states, the proposed metasurface unit cells can achieve high-efficiency cross-polarization conversion, and reflection intensity can be tuned. According to the phase compensation principle of carpet cloaking, we construct a metasurface cloaking device with a phase gradient using the designed unit structure. From the near- and far-field distributions, the cross-circular polarization cloaking property is confirmed in the broadband wavelength range of 9.3–11.4 µm. The proposed cloaking device can effectively resist detection of cross-circular polarization.
Broadband, self-power, and polarization-sensitivity are desirable qualities for a photodetector. However, currently few photodetectors can fulfill these requirements simultaneously. Here, we propose a Ti3C2Tx (MXene) photodetector that is driven by the photogalvanic effect with impressive performances. A polarization-sensitive photocurrent is generated at zero bias under the illumination of linearly polarized laser light of 1064 nm, with an extinction ratio of 1.11. Meanwhile, a fast response with a 32/28 ms rise/decay time and a large on/off switching ratio of 120 are achieved. Besides, a robust zero-bias photocurrent is also generated in the photodetector under the illumination of 940 and 620 nm light, as well as the white light, showing a broadband photoresponse from the near-infrared to visible. Moreover, quantum transport simulations indicate that the photogalvanic effect plays an important role in the generation of the polarized photocurrent at zero bias due to the broken space inversion symmetry of the stacked few-layer Ti3C2Tx. Our results shed light on a potential application of the Ti3C2Tx–MXene in the low-power photodetection with high performances.
Two-dimensional (2D) WS2 films were deposited on SiO2 wafers, and the related interfacial properties were investigated by high-resolution X-ray photoelectron spectroscopy (XPS) and first-principles calculations. Using the direct (indirect) method, the valence band offset (VBO) at monolayer WS2/SiO2 interface was found to be 3.97 eV (3.86 eV), and the conduction band offset (CBO) was 2.70 eV (2.81 eV). Furthermore, the VBO (CBO) at bulk WS2/SiO2 interface is found to be about 0.48 eV (0.33 eV) larger due to the interlayer orbital coupling and splitting of valence and conduction band edges. Therefore, the WS2/SiO2 heterostructure has a Type I energy-band alignment. The band offsets obtained experimentally and theoretically are consistent except the narrower theoretical bandgap of SiO2. The theoretical calculations further reveal a binding energy of 75 meV per S atom and the totally separated partial density of states, indicating a weak interaction and negligible Fermi level pinning effect between WS2 monolayer and SiO2 surface. Our combined experimental and theoretical results provide proof of the sufficient VBOs and CBOs and weak interaction in 2D WS2/SiO2 heterostructures.
We theoretically present a scheme for nonreciprocal ground-state cooling in a double-cavity spinning optomechanical system which is consisted of an optomechanical resonator and a spinning optical harmonic resonator with directional driving. The optical Sagnac effect generated by the whispering-gallery cavity (WGC) rotation creates frequency difference between the WGC mode, we found that the mechanical resonator (MR) can be cooled to the ground state when the propagation direction of driving light is opposite to the spin direction of the WGC, but not from the other side, vice versa, so that the nonreciprocal cooling is achieved. By appropriately selecting the system parameters, the heating process can be completely suppressed due to the quantum interference effect. The proposed approach provides a platform for quantum manipulation of macroscopic mechanical devices beyond the resolved sideband limit.
Twist phase is a nontrivial statistical phase that only exists in partially coherent fields, which makes the beam carry orbital angular momentum (OAM). In this paper, we introduce a new kind of partially coherent beams carrying high-order twist phase, named generalized high-order twisted partially coherent beams (GHTPCBs). The propagation dynamics such as the spectral density and OAM flux density propagating in free space are investigated numerically with the help of mode superposition and fast Fourier transform (FFT) algorithm. Our results show that the GHTPCBs are capable of self-focusing, and the beam spot during propagation exhibits teardrop-like or the diamond-like shape in some certain cases. Moreover, the influences of the twist order and the twist factor on the OAM flux density during propagation are also illustrated in detail. Finally, we experimentally synthesize the GHTPCBs with controllable twist phase by means of pseudo-mode superposition and measure their spectral density during propagation. The experimental results agree well with the theoretical predictions. Our studies may find applications in nonlinear optics and particle trapping.
Three-dimensional (3D) driven optical lattices have attained great attention for their wide applications in the quest to engineer new and exotic quantum phases. Here we propose a 3D driven electric lattice (3D-DEL) for cold polar molecules as a natural extension. Our 3D electric lattice is composed of a series of thin metal plates in which two-dimensional square hole arrays are distributed. When suitable modulated voltages are applied to these metal plates, a 3D potential well array for polar molecules can be generated and can move smoothly back and forth in the lattice. Thus, it can drive cold polar molecules confined in the 3D electric lattice. Theoretical analyses and trajectory calculations using two types of molecules, ND3 and PbF, are performed to justify the possibility of our scheme. The 3D-DEL offers a platform for investigating cold molecules in periodic driven potentials, such as quantum computing science, quantum information processing, and some other possible applications amenable to the driven optical lattices.
Asymmetric mode transformation in waveguide is of great significance for on-chip integrated devices with one-way effect, while it is challenging to achieve asymmetric nonlinear-mode-conversion (NMC) due to the limitations imposed by phase-matching. In this work, we theoretically proposed a new scheme for realizing asymmetric NMC by combining frequency-doubling process and periodic PT symmetric modulation in an optical waveguide. By engineering the one-way momentum from PT symmetric modulation, we have demonstrated the unidirectional conversion from pump to second harmonic with desired guided modes. Our findings offer new opportunities for manipulating nonlinear optical fields with PT symmetry, which could further boost more exploration on on-chip nonlinear devices assisted by non-Hermitian optics.
The wavefront shaping based technique has been introduced to detect the edges of amplitude objects through complex media, but the extraction of the boundary information of invisible phase objects through complex media has not been demonstrated yet. Here, we present a phase contrast imaging technique to overcome the scattering, aiming to achieve the edge detection of the phase object through the complex media. An operator based on the experimentally measured transmission matrix is obtained by numerically adding a spiral phase in the Fourier domain. With the inverse of the filtered transmission matrix, we can directly reconstruct the edge enhanced images for both amplitude object and phase object beyond scattering. Experimentally, both digital and real objects are imaged, and the results verify that isotropic edge detection can be achieved with our technique. Our work could benefit the detection of invisible phase objects through complex media.
We theoretically investigate the Higgs oscillation in a one-dimensional Raman-type spin–orbit-coupled Fermi superfluid with the time-dependent Bogoliubov–de Gennes equations. By linearly ramping or abruptly changing the effective Zeeman field in both the Bardeen–Cooper–Schrieffer state and the topological superfluid state, we find the amplitude of the order parameter exhibits an oscillating behaviour over time with two different frequencies (i.e., two Higgs oscillations) in contrast to the single one in a conventional Fermi superfluid. The observed period of oscillations has a great agreement with the one calculated using the previous prediction [Volkov and Kogan, J. Exp. Theor. Phys. 38, 1018 (1974)], where the oscillating periods are now determined by the minimums of two quasi-particle spectrum in this system. We further verify the existence of two Higgs oscillations using a periodic ramp strategy with theoretically calculated driving frequency. Our predictions would be useful for further theoretical and experimental studies of these Higgs oscillations in spin–orbit-coupled systems.
We propose a protocol for detecting a single atom in a cavity with the help of the χ(2) nonlinear medium. When the χ(2) nonlinear medium is driven by an external laser field, the cavity mode will be squeezed, and thus one can obtain an exponentially enhanced light-matter coupling. Such a strong coupling between the atom and the cavity field can significantly change the output photon flux, the quantum fluctuations, the quantum statistical property, and the photon number distributions of the cavity field. This provides practical strategies to determine the presence or absence of an atom in a cavity. The proposed protocol exhibits some advantages, such as controllable squeezing strength and exponential increase of atom-cavity coupling strength, which make the experimental phenomenon more obvious. We hope that this protocol can supplement the existing intracavity single-atom detection protocols and provide a promise for quantum sensing in different quantum systems.
We present an error-detected hyperparallel Toffoli (hyper-Toffoli) gate for a three-photon system based on the interface between polarized photon and cavity-nitrogen-vacancy (NV) center system. This hyper-Toffoli gate can be used to perform double Toffoli gate operations simultaneously on both the polarization and spatial-mode degrees of freedom (DoFs) of a three-photon system with a low decoherence, shorten operation time, and less quantum resources required, in compared with those on two independent three-photon systems in one DoF only. As the imperfect cavity-NV-center interactions are transformed into the detectable failures rather than infidelity based on the heralding mechanism of detectors, a near-unit fidelity of the quantum hyper-Toffoli gate can be implemented. By recycling the procedures, the efficiency of our protocol for the hyper-Toffoli gate is improved further. Meanwhile, the evaluation of gate performance with achieved experiment parameters shows that it is feasible with current experimental technology and provides a promising building block for quantum compute.
In order to gain comprehensive knowledge of an arbitrary unknown quantum state, one feasible way is to reconstruct it, which can be realized by finding a series of quantum operations that can refactor the unitary evolution producing the unknown state. We design an adaptive framework that can reconstruct unknown quantum states at high fidelities, which utilizes SWAP test, parameterized quantum circuits (PQCs) and layerwise learning strategy. We conduct benchmarking on the framework using numerical simulations and reproduce states of up to six qubits at more than 96% overlaps with original states on average using PQCs trained by our framework, revealing its high applicability to quantum systems of different scales theoretically. Moreover, we perform experiments on a five-qubit IBM Quantum hardware to reconstruct random unknown single qubit states, illustrating the practical performance of our framework. For a certain reconstructing fidelity, our method can effectively construct a PQC of suitable length, avoiding barren plateaus of shadow circuits and overuse of quantum resources by deep circuits, which is of much significance when the scale of the target state is large and there is no a priori information on it. This advantage indicates that it can learn credible information of unknown states with limited quantum resources, giving a boost to quantum algorithms based on parameterized circuits on near-term quantum processors.
Hyperentangled Bell states analysis (HBSA) is an essential building block for certain hyper-parallel quantum information processing. We propose a complete and deterministic HBSA scheme encoded in spatial and polarization degrees of freedom (DOFs) of two-photon system assisted by a fixed frequency-based entanglement and a time interval DOF. The parity information the spatial-based and polarization-based hyper-entanglement can be distinguished by the distinct time intervals of the photon pairs, and the phase information can be distinguished by the detection signature. Compared with previous schemes, the number of the auxiliary entanglements is reduced from two to one by introducing time interval DOF. Moreover, the additional frequency and time interval DOFs suffer less from the collective channel noise.
