The entanglement evolution of two coupling two-level atoms interacting with a single-mode vacuum field in multiphoton Tavis-Cummings model

Using multipohton Tavis-Cummings model,the entanglement evolution of two coupling two-level atoms in Bell states interacting with a single-mode vacuum field is investigated by using negativity.The influences of coupling constants between atoms,the atomic initial states and the photon number of transition on the entanglement evolution of two coupling two-level atoms are discussed.The results obtained using the numerical method show that the entanglement of two atoms is related with coupling constants between atoms,the atomic initial states and the photon number of transition.The two-atom entanglement state will forever stay in the maximum entanglement state when the initial state is β11〉.When the initial state of two atoms is β01〉,the entanglement of two atoms displays periodic oscillation behavior.And its oscillation period decreases with increasing of coupling constant between atoms or the photon number of transition.On the other hand,when the initial state is β00〉 or β10〉,the entanglement of two atoms displays quasiperiodic oscillation behavior and its oscillation period decreases with increasing of coupling constant between atoms or the photon number of transition.

Oscillation of the spin-currents of cold atoms on a ring due to light-induced spin–orbit coupling

The evolution of two-component cold atoms on a ring with spin-orbit coupling has been studied analytically for the case with N noninteracting particles. Then, the effect of interaction is evaluated numerically via a two-body system. Two cases are considered： （i） Starting from a ground state the evolution is induced by a sudden change of the laser field, and （ii） the evolution starting from a superposition state. Oscillating persistent spin-currents have been found. A set of formulae have been derived to describe the period and amplitude of the oscillation. Based on these formulae the oscillation can be well controlled via adjusting the parameters of the laser beams. In particular, it is predicted that movable stripes might emerge on the ring.

Single photon transport properties in coupled cavity arrays nonlocally coupled to a two-level atom in the presence of dissipation

We discuss the effects of dissipation on the behavior of single photon transport in a system of coupled cavity arrays, with the two nearest cavities nonlocally coupled to a two-level atom. The single photon transmission amplitude is solved exactly by employing the quasi-boson picture. We investigate two different situations of local and nonlocal couplings, respectively. Comparing the dissipative case with the nondissipative one reveals that the dissipation of the system increases the middle dip and lowers the peak of the single photon transmission amplitudes, broadening the line width of the transport spectrum. It should be noted that the influence of the cavity dissipation to the single photon transport spectrum is asymmet- ric. By comparing the nonlocal coupling with the local one, one can find that the enhancement of the middle dip of single photon transmission amplitudes is mostly caused by the atom dissipation and that the reduced peak is mainly caused by the cavity dissipation, no matter whether it is a nonlocal or local coupling case. Whereas in the nonlocal coupling case, when the coupling strength gets stronger, the cavity dissipation has a greater effect on the single photon transport spectrum and the atom dissipation affection becomes weak, so it can be ignored.

Surface Electromechanical Coupling on DLC Film with Conductive Atomic Force Microscope

Diamond-like carbon (DLC) film composed of microscopically insulation but microscopically a mixture of conducting (sp2) and insulating (sp3) phases was discussed on the local modification with a conductive atomic force microscope (C-APM). Especially, a topographic change was observed when a direct current (DC) bias-voltage was applied to the DLC film. Experimental results show that a nanoscale pit on DLC surface was formed when applying a positive 25 V on DLC film. According to the interacting force between CoCr-coated microelectronic scanning probe (MESP) tip and DLC surface, as well as the Sondheimer oscillation theory, the 'scalewing effect' of the pit was explained. Electromechanical coupling on DLC film suggested that the depth of pits increased with an increase of load applied to surface when the cantilever-deflected signal was less than a certain threshold voltage.

Rapid synthesis of Pd single‐atom/cluster as highly active catalysts for Suzuki coupling reactions

Palladium(Pd)‐based catalysts are essential to drive high‐performance Suzuki coupling reactions,which are powerful tools for the synthesis of functional organic compounds.Herein,we developed a solution‐rapid‐annealing process to stabilize nitrogen‐mesoporous carbon supported Pd single‐atom/cluster(Pd/NMC)material,which provided a catalyst with superior performance for Suzuki coupling reactions.In comparison with commercial palladium/carbon(Pd/C)catalysts,the Pd/NMC catalyst exhibited significantly boosted activity(100%selectivity and 95%yield)and excellent stability(almost no decay in activity after 10 reuse cycles)for the Suzuki coupling reactions of chlorobenzenes,together with superior yield and excellent selectivity in the fields of the board scope of the reactants.Moreover,our newly developed rapid annealing process of precursor solutions is applied as a generalized method to stabilize metal clusters(e.g.Pd,Pt,Ru),opening new possibilities in the construction of efficient highly dispersed metal atom and sub‐nanometer cluster catalysts with high performance.

Edge Effects and Coupling Effects in Atomic Force Microscope Images

The AFM images were obtained by an atomic force microscope (AFM) and transformed from the deformation of AFM micro cantilever probe. However, due to the surface topography and surface forces applied on the AFM tip of sample, the deformation of AFM probe results in obvious edge effects and coupling effects in the AFM images.The deformation of AFM probe was analyzed,the mechanism of the edge effects and the coupling effects was investigated, and their results in the AFM images were studied. It is demonstrated by the theoretical analysis and AFM experiments that the edge effects make lateral force images more clear than the topography images,also make extraction of frictional force from lateral force images more complex and difficult. While the coupling effects make the comparison between topography images and lateral force images more advantage to acquire precise topography information by AFM.

Generalized Two-State Theory for an Atom Laser with Nonlinear Couplings

We present a generalized two-state theory to investigate the quantum dynamics and statistics of an atom laser with nonlinear couplings. The rotating wave approximate Hamiltonian of the system is proved to be analytically solvable. The fraction of output atoms is then showed to exhibit an interesting collapse and revival phenomenon with respect to the evolution time, a sign of nonlinear couplings. Several nonclassical effects, such as sub-Poissonian distribution, quadrature squeezing effects, second-order cross-correlation and accompanied violation of Cauchy-Schwartz inequality are also revealed for the output matter wave. The initial global phase of the trapped condensate, in weak nonlinear coupling limits, is found to exert an interesting impact on the quantum statistical properties of the propagating atom laser beam.

Electronic Coupling of Single Atom and FePS_3 Boosts Water Electrolysis

Engineering the electronic structure of surface active sites at the atomic level can be an efficient way to modulate the reactivity of catalysts.Herein,we report the rational tuning of surface electronic structure of FePS_(3) nanosheets(NSs)by anchoring atomically dispersed metal atom.Theoretical calculations predict that the strong electronic coupling effect in single-atom Ni-FePS_(3) facilitates electron aggregation from Fe atom to the nearby Ni-S bond and enhances the electron-transfer of Ni and S sites,which balances the oxygen species adsorption capacity,reinforces water adsorption and dissociation process to accelerate corresponding oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).The optimal Ni-FePS_(3)NSs/C exhibits outstanding electrochemical water-splitting activities,delivering an overpotential of 287 mV at the current density of 10 mA cm^(-2) and a Tafel slope of 41.1 mV dec^(-1) for OER;as well as an overpotential decrease of 219 mV for HER compared with pure FePS_(3)NSs/C.The concept of electronic coupling interaction between the substrate and implanted single active species offers an additional method for catalyst design and beyond.

Nonlinear coherent perfect photon absorber in asymmetrical atom–nanowires coupling system

Coherent perfect absorption provides a method of light-controlling-light and has practical applications in optical communications. Recently, a cavity-based nonlinear perfect photon absorption extends the coherent perfect absorber（CPA）beyond the linear regime. As nanowire-based system is a more competitive candidate for full-optical device, we introduce a nonlinear CPA in the single two-level atom–nanowires coupling system in this work. Nonlinear input–output relations are derived analytically, and three contributions of atomic saturation nonlinearity are explicit. The consociation of optical nonlinearity and destructive interference makes it feasible to fabricate a nonlinear monoatomic CPA. Our results also indicate that a nonlinear system may work linearly even when the incoming lights are not weak any more. Our findings show promising applications in full-optical devices.

Entanglement of two atoms in two-mode Raman coupled model with intrinsic decoherence

Considering intrinsic decoherence, the two-atom two-mode Raman coupled model is investigated in this paper. Utilizing the constants of motion in this model, we obtain the analytic expressions of the density operator of the system for investigating the entanglement of two atoms. The speed of entanglement decay increases with the increasing of the coupling coefficient of one atom. The difference between the oscillation periods when the initial state parameter of atomic subsystem belongs to two intervals becomes smaller with the increasing of the coupling coefficient of one atom. The increasing of the initial photon number of the second field can hasten the vanishing of entanglement of atomic subsystem. The robustness of atomic entanglement against decoherence depends on the interval of the initial state parameter of atomic subsystem.

Dynamic Behaviors of Coupled Three-Level Atom System Interactingwith Light Field in Cavity Filled with Kerr-Like Medium

The Hamiltonian of coupled three-level atoms interacting with light field in the cavity filled with Kerr-like medium is derived. A simplified analytic solution to the Schrodinger equation of the system is obtained. The case of A type atom with degenerate lower levels is discussed in detail. It is shown that the coupling strength between atoms and Kerr coefficient affect the system＇s dynamic behaviors, especially the modulation period and oscillation frequency of the squeezing parameters of the field and the collective dipole moment. Dynamic behaviors of the system are sensitive to the initial state of atoms.

Optimal entropy squeezing sudden generation and its control for an effective two-level moving atom entanglement with the two-mode coherent fields

From the viewpoint of quantum information, this paper proposes a concept and a definition of the atomic optimal entropy squeezing sudden generation （AOESSG） for the system of an effective two-level moving atom which entangles with the two-mode coherent fields. It also researches the relationship between the AOESSG and entanglement sudden death of the atom-fields, and discusses the influences of atomic initial state on the AOESSG and obtains the system parameter which controls the AOESSG.

Vacuum induced transparency and slow light phenomena in a two-level atomic ensemble controlled by a cavity

We study the optical properties of a two-level atomic ensemble controlled by a high-finesse cavity. Even though the cavity is initially in the vacuum state in the absence of external driving, the probe response of the atomic ensemble can be dramatically modified. When the collectively enhanced atom–cavity coupling is strong enough and the cavity decay rate is much smaller than the atomic damping rate, an electromagnetically induced transparency-like coherent phenomenon emerges with a dip absorption for the response of the two-level atoms in the cavity without driving, and thus is called vacuum induced transparency. We also show the slow light with very low group velocity in such an atomic ensemble.

Sustainable electrochemical cross‐dehydrogenative coupling of4‐quinolones and diorganyl diselenides

An environmentally friendly method for the synthesis of 3‐organylselenyl quinolones through theelectrochemical cross‐dehydrogenative coupling of 4‐quinolones and diorganyl diselenides wasdeveloped.As a green,atom economic and self‐separating process,the present reaction requiresneither external oxidants nor electrolytes,forming a recyclable catalytic system.

Insight into coupled Ni-Co dual-metal atom catalysts for efficient synergistic electrochemical CO_(2)reduction

The development of highly active,selective,and stable electrocatalysts can facilitate the effective implementation of electrocatalytic CO_(2)conversion into fuels or chemicals for mitigating the energy crisis and climate problems.Therefore,it is necessary to achieve the goal through reasonable material design based on the actuality of the operational active site at the molecular scale.Inspired by the stimulating synergistic effect of coupled heteronuclear metal atoms,a novel Ni-Co atomic pairs configuration(denoted as NiN_(3)?CoN_(3)-NC)active site was theoretically screened out for improving electrochemical CO_(2)reduction reaction(CO_(2)RR).The structure of NiN_(3)?CoN_(3)-NC was finely regulated by adjusting Zn content in the precursors Zn/Co/Ni-zeolite imidazolate frameworks(Zn/Co/Ni-ZIFs)and pyrolysis temperature.The structural features of NiN_(3)?CoN_(3)-NC were systematically confirmed by aberration-corrected HAADF-STEM coupled with 3D atom-overlapping Gaussian-function fitting mapping,XAFS,and XRD.The results of theoretical calculations reveal that the synergistic effect of Ni-Co atomic pairs can effectively promote the*COOH intermediate formation and thus the overall CO_(2)RR kinetic was improved,and also restrained the competitive hydrogen evolution reaction.Due to the attributes of Ni-Co atomic pairs configuration,the developed NiN_(3)?CoN_(3)-NC with superior catalytic activity,selectivity,and durability,with a high turnover frequency of 2265 h^(-1)at-1.1 V(vs.RHE)and maximum Faradaic efficiency of 97.7%for CO production.This work demonstrates the great potential of DACs as highly efficient catalysts for CO_(2)RR,provides a useful strategy to design heteronuclear DACs,exploits the synergistic effect of multiple metal sites to facilitate complex CO_(2)RR catalytic reactions,and inspires more efforts to develop the potential of DACs in various fields.

Melt metal sheet breaking mechanism of close-coupled gas atomization

The gas atomization is the process that a liquid mass is disintegrated into a collection of liquid melt droplets by the impact of high velocity gas stream and solidified into metal particles. However, the liquid melt sheet breaking mechanism has not been fully understood. So the experimental research was carried out under the condition of lower melt superheat. The results reveal that there are three approaches about melt metal sheet’s breakage: from the edges of sheets, from inner surface of sheets, and disrupted by other droplets and sheets. The approach of melt sheet breakage is dependent on its thickness. The thicker sheets (above 25μm) are disintegrated mainly by the way of droplet’s departing from edges, and the thinner sheets (below 10μm) are chiefly breaking from the inner surface.

Influence of melt superheat on breakup process of close-coupled gas atomization

In close-coupled gas atomization(CCGA), the influences of melt superheat on breakup process are fundamental to obtain desired or finer powder. Based on a series of Cu atomization experiment under different superheating conditions, the influences of melt superheat on breakup process were studied. Experimental results indicate that as the melt superheat is increased to 150, 200, 250 and 300 K, the mean particle size (D50) decreases consequently to 34.9, 32.3, 30.9 and 19.7 μm. Theoretical analysis reveals that the primary breakup and secondary breakup processes are close coupled, and the melt superheat radically influences the melt properties, and plays a crucial role on governing the filming process of primary breakup and the atomization modes of secondary breakup. There exists a strong nonlinear decrease of contact angle of melt to nozzle orifice wall when the superheat is increased from 250 K to 300 K, leading to a marked fall of the film thickness formed in primary breakup, and D50 of copper powders is therefore sharply reduced. However, the log-normal distribution feature of particle size has not been substantially improved.

Efficient Atomic One-Qubit Phase Gate Realized by a Cavity QED and Identical Atoms System

We present a scheme to implement a one-qubit phase gate with a two-level atom crossing an optical cavity in which some identical atoms are trapped. One can conveniently acquire an arbitrary phase shift of the gate by properly choosing the number of atoms trapped in the cavity and the velocity of the atom crossing the cavity. The present scheme provides a very simple and efficient way for implementing one-qubit phase gate.

Entropy of Field Interacting With Two Atoms in Bell State

In this paper, we investigate entropy properties of the single-mode coherent optical field interacting with the two two-level atoms initially in one of the four Bell states. It is found that the different initial states of the two atoms lead to different evolutions of field entropy and the intensity of the field plays an important role for the evolution properties of field entropy.

Trigger and control with different entanglement by atoms interaction times

The generation of the entanglement between two two-level atoms interacting with the third atom driven by white noise is investigated when the coupling between atoms is modulated by a pulse function. This paper finds that the initial triggering time and the width of the pulse can generate a peak in the entanglement. There is an optimal width of the pulse for which the entanglement can reach a maximum. The asymmetry of the coupling between atoms can generate different entanglement in the system. The multiple triggers can generate multiple peaks in the entanglement. The separation between two peaks is increased as the width of the pulse is increased.