Information transmission through parallel multi-task-based recognition of high-resolution multiplexed orbital angular momentum

Orbital angular momentums(OAMs)greatly enhance the channel capacity in free-space optical communication.However,demodulation of superposed OAM to recognize them separately is always difficult,especially upon multiplexing more OAMs.In this work,we report a directly recognition of multiplexed fractional OAM modes,without separating them,at a resolution of 0.1 with high accuracy,using a multi-task deep learning(MTDL)model,which has not been reported before.Namely,two-mode,four-mode,and eight-mode superposed OAM beams,experimentally generated with a hologram carrying both phase and amplitude information,are well recognized by the suitable MTDL model.Two applications in information transmission are presented:the first is for 256-ary OAM shift keying via multiplexed fractional OAMs;the second is for OAM division multiplexed information transmission in an eightfold speed.The encouraging results will expand the capacity in future free-space optical communication.

Electronic properties of monolayer copper selenide with one-dimensional moirépatterns

Strain engineering is a vital way to manipulate the electronic properties of two-dimensional(2D)materials.As a typical representative of transition metal mono-chalcogenides(TMMs),a honeycomb CuSe monolayer features with one-dimensional(1D)moirépatterns owing to the uniaxial strain along one of three equivalent orientations of Cu(111)substrates.Here,by combining low-temperature scanning tunneling microscopy/spectroscopy(STM/S)experiments and density functional theory(DFT)calculations,we systematically investigate the electronic properties of the strained CuSe monolayer on the Cu(111)substrate.Our results show the semiconducting feature of CuSe monolayer with a band gap of 1.28 eV and the 1D periodical modulation of electronic properties by the 1D moirépatterns.Except for the uniaxially strained CuSe monolayer,we observed domain boundary and line defects in the CuSe monolayer,where the biaxial-strain and strain-free conditions can be investigated respectively.STS measurements for the three different strain regions show that the first peak in conduction band will move downward with the increasing strain.DFT calculations based on the three CuSe atomic models with different strain inside reproduced the peak movement.The present findings not only enrich the fundamental comprehension toward the influence of strain on electronic properties at 2D limit,but also offer the benchmark for the development of 2D semiconductor materials.

Review of the role of ionic liquids in two-dimensional materials

Ionic liquids(ILs)are expected to be used as readily available“designer”solvents,characterized by a number of tunable properties that can be obtained by modulating anion and cation combinations and ion chain lengths.Among them,its high ionicity is outstanding in the preparation and property modulation of two-dimensional(2D)materials.In this review,we mainly focus on the ILs-assisted exfoliation of 2D materials towards large-scale as well as functionalization.Meanwhile,electric-field controlled ILs-gating of 2D material systems have shown novel electronic,magnetic,optical and superconducting properties,attracting a broad range of scientific research activities.Moreover,ILs have also been extensively applied in various field practically.We summarize the recent developments of ILs modified 2D material systems from the electrochemical,solar cells and photocatalysis aspects,discuss their advantages and possibilities as“designer solvent”.It is believed that the design of ILs accompanying with diverse 2D materials will not only solve several scientific problems but also enrich materials design and engineer of 2D materials.

Theoretical investigation on optical properties of Möbius carbon nanobelts in one-and two-photon absorption

The first successful synthesis of fully fused and fully conjugated Möbius carbon nanobelts(CNBs)has attracted considerable attention.However,theoretical calculations based on suchπ-conjugated Möbius CNB are still insufficient.Herein,we theoretically investigated molecular spectroscopy of Möbius CNBs without and with n-butoxy groups via visualization methods.The results show that the presence of n-butoxy groups can significantly affect Möbius CNBs’optical performance,changing electron-hole coherence and enhancing two-photon absorption cross-sections.Our work provides a deeper understanding of photophysical mechanisms of Möbius CNBs in one-and two-photon absorption and reveals possible applications on optoelectronic devices.

Optimal gamma-ray selections for monochromatic line searches with DAMPE

The DArk Matter Particle Explorer (DAMPE) is a space high-energy cosmic-ray detector covering a wide energy band with a high energy resolution. One of the key scientific goals of DAMPE is to carry out indirect detection of dark matter by searching for high-energy gamma-ray line structure. To promote the sensitivity of gamma-ray line search with DAMPE, it is crucial to improve the acceptance and energy resolution of gamma-ray photons. In this paper, we quantitatively proved that the photon sample with the largest ratio of acceptance to energy resolution is optimal for line search. We therefore developed a line-search sample specifically optimized for the line-search. Meanwhile, in order to increase the statistics, we also selected the so-called BGO-only photons that convert into e^(+)e^(-) pairs only in the BGO calorimeter. The standard, the line-search, and the BGO-only photon samples are then tested for line-search individually and collectively. The results show that a significantly improved limit could be obtained from an appropriate combination of the date sets, and the increase is about 20% for the highest case compared with using the standard sample only.

Theoretical investigation of CoTa_(2)0_(6)/graphene heterojunctions for oxygen evolution reaction

Water electrolysis is to split water into hydrogen and oxygen using electricity as the driving force.To obtain low-cost hydrogen in a large scale,it is critical to develop electrocatalysts based on earth abundant elements with a high efficiency.This computational work started with Cobalt on CoTh_(2)C)_(6)surface as the active site,CoTa_(2)O_(6)/Graphene heterojunctions have been explored as potential oxygen evolution reaction(OER)catalysts through density functional theory(DFT).We demonstrated that the electron transfer(_(6))from CoTa_(2)C)_(6)to graphene substrate can be utilized to boost the reactivity of Co-site,leading to an OER overpotential as low as 0.30 V when N-doped graphene is employed.Our findings offer novel design of heterojunctions as high performance OER catalysts.

Fermion dynamical symmetry and strongly-correlated electrons:A comprehensive model of high-temperature superconductivity

We review application of the SU(4)model of strongly-correlated electrons to cuprate and iron-based superconductors.A minimal self-consistent generalization of BCS theory to incorporate antiferromag-netism on an equal footing with pairing and strong Coulomb repulsion is found to account system-atically for the major features of high-temperature superconductivity,with microscopic details of the parent compounds entering only parametrically.This provides a systematic procedure to separate es-sential from peripheral,suggesting that many features exhibited by the high-Te data set are of interest in their own right but are not central to the superconducting mechanism.More generally,we propose that the surprisingly broad range of conventional and unconventional superconducting and superfluid behavior observed across many fields of physics results from the systemnatic appearance of similar al-gebraic structures for the emergent ffoctive Harmiltonians,even though the microscopic Harmiltonians of the corresponding parent states may differ radically from each other.

Possible phase transition of anisotropic frustrated Heisenberg model at finite temperature

The frustrated spin-1/2 J1a-J1b-J2 antiforrornagnet with anisotropy on the two-diinonsional square lattice was investigated,where the parameters J1a and Ju,represent the nearest neighbor exchanges and along the x and y directions,respectively.J2 represents the next-nearest neighbor exchange.The anisotropy includes the spatial and exchange anisotropies.Using the double-time Green’s function method,the offects of the interplay of exchanges and anisotropy on the possible phase transition of the Neel state and stripe state were discussed.Our results indicated that,in the case of anisotropic parameter 0 ≤η< 1,the Neel and stripe states can exist and have the same critical temperature as long as J2 =J1b/2.Under such parameters,a first-order plia.se transformation between the Neel and stripe states can occur below the critical point.For J2≠J1b/2,our results indicate that the Neel and stripe states can also exist,while their critical temperatures differ.When J2 >J1b/2,a first-order phase transformation between the two states may also occur.However,for J2 < J1b/2,the Neel state is always more stable than the stripe state.

Evolution of individual quantum Hall edge states in the presence of disorder

By using the Bloch eigenmode matching approach, we numerically study the evolution of individual quantum Hall edge states with respect to disorder. As demonstrated by the two-parameter renormal- ization group flow of the Hall and Thouless conductances, quantum Hall edge states with high Chern number n are completely different from that of the n = 1 case. Two categories of individual edge modes are evaluated in a quantum Hall system with high Chern number. Edge states from the lowest Landau level have similar eigenfunctions that are well localized at the system edge and independent of the Fermi energy. On the other hand, at fixed Fermi energy, the edge state from higher Landau levels exhibit larger expansion, which results in less stable quantum Hall states at high Fermi energies. By presenting the local current density distribution, the effect of disorder on eigenmode-resolved edge states is distinctly demonstrated.

Cross-symmetry breaking of two-component discrete dipolar matter-wave solitons

We study the spontaneous symmetry breaking of dipolar Bose-Einstein condensates trapped in stacks of two-well systems, which may be effectively built as one-dimensional trapping lattices sliced by a repelling laser sheet. If the potential wells are sufficiently deep, the system is modeled by coupled discrete Gross-Pitaevskii equations with nonlocal self- and cross-interaction terms representing dipole-dipole interactions. When the dipoles are not polarized perpendicular or parallel to the lattice, the cross- interaction is asymmetric, replacing the familiar symmetric two-component solitons with a new species of cross-symmetric or -asymmetric ones. The orientation of the dipole moments and the interwell hopping rate strongly affect the shapes of the discrete two-component solitons as well as the characteristics of the cross-symmetry breaking and the associated phase transition. The sub- and super-critical types of cross-symmetry breaking can be controlled by either the hopping rate between the components or the total norm of the solitons. The effect of the interplay between the contact nonlinearity and the dipole angle on the cross-symmetry breaking is also discussed.

Spin filtering in transition-metal phthalocyanine molecules from first principles

Using first-principles calculations based on density functional theory and the nonequilibrium Green＇s function formalism, we studied the spin transport through metal-phthalocyanine （MPc, M=Ni, Fe, Co, Mn, Cr） molecules connected to aurum nanowire electrodes. We found that the MnPc, FePc, and CrPc molecular devices exhibit a perfect spin filtering effect compared to CoPc and NiPc. Moreover, negative differential resistance appears in FePc molecular devices. The transmission coefficients at different bias voltages were further presented to understand this phenomenon. These results would be useful in designing devices for future nanotechnology.

Design of diamond-shaped transient thermal cloaks with homogeneous isotropic materials

Transformation thermodynamics as a major extension of transformation optics has recently received considerable attention. In this paper, we present two-dimeusional （2D） and three-dimensional （3D） diamond-shaped transient thermal cloaks with non-singular homogeneous material parameters. The absence of singularity in the parameters results from the fact that the linear coordinate transformation is performed by expanding a line segment rather than a point into a region, while the mechanism behind the homogeneity is the homogeneous stretching and compression along orthogonal directions during the transformation. Although the derived parameters remain anisotropic, we further show that this can be circumvented by considering a layered structure composed of only four types of isotropic materials based on the effective medium theory. Numerical simulation results confirm the good performance of the proposed cloaks.

Subcycle electron emission in sequential double ionization by elliptical laser pulses

Using a classical ensemble method, we have investigated sequential double ionization (SDI) of Ar atoms driven by elliptical laser pulses. The results show that the ion momentum distribution of the Ar atoms depends strongly on the pulse duration. As the pulse duration increases, the ion momentum distribution changes from two bands to four bands and then to six bands and finally to an eight-band structure. Back analysis of double ionization trajectories shows that the variation of the band structure originates from pulse duration dependent multiple ionization bursts of the second electron. Our calculations indicate that the subcycle electron emission in the SDI could be more easily accessed by using elliptical laser pulses with a longer wavelength. Moreover, we show that there is good correspondence between the scaled radial momentum and the ionization time.

Enhanced phase sensitivity of an SU（1,1） interferometer with displaced squeezed vacuum light

We study the phase sensitivity of an SU（1,1） interferometer with two input beams in the displaced squeezed vacuum state and the coherent state, respectively. We find that there exists an optimal squeezing fraction of the displaced squeezed vacuum state that optimizes the phase sensitivity. We also examine the effects of some factors, including the loss, mean photon number of the input beams and amplitude gain of the opl;ical parameter amplifiers, on the optimal squeezing fraction so that we can choose the optimal values to enhance the phase sensitivity.

The role of microwaves in the enhancement of laser-induced plasma emission

We studied experimentally the effect of microwaves （MWs） on the enhancement of plasma emission achieved by laser-induced breakdown spectroscopy （LIBS）. A laser plasma was generated on a calcium oxide pellet by a Nd：YAG laser （5 m J, 532 nm, 8 ns） in reduced-pressure argon surrounding gas. A MW radiation （400 W） was injected into the laser plasma via a loop antenna placed immediately above the laser plasma to enhance the plasma emission. The results confirmed that when tile electromagnetic field was introduced into the laser plasma region by the MWs, the lifetime of the plasma was extended from 50 to 500 μs, similar to the MW duration. Furthermore, the plasma temperature and electron density increased to approximately 10900 K and 1.5×10^18 cm^-3, respectively and the size of the plasma emission was extended to 15 mm in diameter. As a result, the emission intensity of Ca lines obtained using LIBS with MWs was enhanced by approximately 200 times compared to the case of LIBS without MWs.

Institute of Atomic and Molecular Physics, Jilin University

OverviewEstablished in 1979 authorized by the State Ministry ot Education, China, the Institute of Atomic and Molecular Physics （lAMP） is the first institution for graduate（ education and research in atondc and molecular physic,, in China.

Black hole binaries and microquasars

This is a general review Oil the observations and physics of black hole X-ray binaries and microquasars, with the emphasize on recent developments in the high energy regime. The focus is put on understanding the accretion flows and measuring the parameters of black holes in them. It includes mainly two parts： i） Brief review of several recent review article on this subject; ii） Further development on several topics, including black hole spin measurements, hot accretion flows, corona formation, state transitions and thermal stability of standard think disk. This is thus not a regular bottom-up approach, which I feel not necessary at this stage. Major effort is made in making and incorporating from many sources useful plots and illustrations, in order to make this article more comprehensible to non-expert readers. In the end I attempt to make a unification scheme on the accretion-outflow （wind/jet） connections of all types of aecreting BHs of all accretion rates and all BH mass scales, and finally provide a brief outlook.

State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto- Electronics, Shanxi University~ China

Quantum information science is an advanced and sophisti- cated scientific and technologic field rapidly emerging fi＇om the interdisciplinary research between quantum physics and information science. Since it can provide, in principle, abso- lute secure communication and giant quantum parallel com- putation capability, many scientific communities around the world have been devoted to researching and exploring this new topic. Quantum optics is one of the important basic subjects in modern physics, and the system composed of light and atoms/molecules can be easily manipulated.

Transmission-reflection decoupling of non-Hermitian photonic doping epsilon-near-zero media

We present a novel method to achieve the decoupling between the transmission and reflection waves of non-Hermitian doped epsilon-near-zero(ENZ)media by inserting a dielectric slit into the structure.Our method also allows for independent control over the amplitude and the phase of both the transmission and reflection waves through few dopants,enabling us to achieve various optical effects,such as perfect absorption,high-gain reflection without transmission,reflectionless high-gain transmission and reflectionless total transmission with different phases.By manipulating the permittivity of dopants with extremely low loss or gain,we can realize these effects in the same configuration.We also extend this principle to multi-port doped ENZ structures and design a highly reconfigurable and reflectionless signal distributor and generator that can split,amplify,decay and phase-shift the input signal in any desired way.Our method overcomes limitations of optical manipulation in doped ENZ caused by the interdependent nature of the transmission and reflection,and has potential applications in novel photonic devices.

Recent developments in CVD growth and applications of 2D transition metal dichalcogenides

Two-dimensional(2D)transition metal dichalcogenides(TMDs)with fascinating electronic energy band structures,rich valley physical properties and strong spin–orbit coupling have attracted tremendous interest,and show great potential in electronic,optoelectronic,spintronic and valleytronic fields.Stacking 2D TMDs have provided unprecedented opportunities for constructing artificial functional structures.Due to the low cost,high yield and industrial compatibility,chemical vapor deposition(CVD)is regarded as one of the most promising growth strategies to obtain high-quality and large-area 2D TMDs and heterostructures.Here,state-of-the-art strategies for preparing TMDs details of growth control and related heterostructures construction via CVD method are reviewed and discussed,including wafer-scale synthesis,phase transition,doping,alloy and stacking engineering.Meanwhile,recent progress on the application of multi-functional devices is highlighted based on 2D TMDs.Finally,challenges and prospects are proposed for the practical device applications of 2D TMDs.