具有三体相互作用海森堡自旋链模型的纠缠与几何失协

近年来有研究发现量子失协可以度量非纠缠的量子关联,而且非纠缠的量子关联在量子通信和量子计算中起到很重要的作用.本文研究了磁场,两种三体相互作用,各向异性参数,耦合常数,温度等参数对同时具有两种三体相互作用海森堡XXZ自旋链系统的量子纠缠,几何失协的影响以及与量子相变的关系.研究表明:量子纠缠和几何失协都可以清晰的表征本模型系统的量子相变现象;随着XZX+YZY型三体相互作用的增加量子纠缠和几何失协即使在高温时也可达到最大值;几何失协比量子纠缠更全面地描述了量子关联;XZY-YZX型三体相互作用的增加对量子纠缠有抑制作用;XZY-YZX型三体相互作用在一定区域内的增加对几何失协有抑制作用,在另一区域的增加可使几何失协增大到一个稳定的非零值.增大磁场和自旋耦合常数,减小各向异性参数会使纠缠的临界温度变大;调节自旋耦合常数可更有效的使量子纠缠和几何失协在高温时仍有一个较大的值.同时发现,在磁场0B5和各向异性参数-1J_Z10的区域两种量子关联都可以维持在最大值.     

具有三体相互作用海森堡自旋链模型的纠缠与几何失协

近年来有研究发现量子失协可以度量非纠缠的量子关联,而且非纠缠的量子关联在量子通信和量子计算中起到很重要的作用.研究了磁场,两种三体相互作用,各向异性参数,耦合常数,温度等参数对同时具有两种三体相互作用海森堡XXZ自旋链系统的量子纠缠,几何失协的影响以及与量子相变的关系.研究表明:量子纠缠和几何失协都可以清晰的表征本模型系统的量子相变现象; 随着XZX+YZY型三体相互作用的增加量子纠缠和几何失协即使在高温时也可达到最大值;几何失协比量子纠缠更全面地描述了量子关联; XZY-YZX型三体相互作用的增加对量子纠缠有抑制作用;XZY-YZX型三体相互作用在一定区域内的增加对几何失协有抑制作用,在另一区域的增加可使几何失协增大到一个稳定的非零值。增大磁场和自旋耦合常数,减小各向异性参数会使纠缠的临界温度变大; 调节自旋耦合常数可更有效的使量子纠缠和几何失协在高温时仍有一个较大的值.同时发现,在磁场 和各向异性参数 的区域两种量子关联都可以维持在最大值.     

Geometric discord for non-X states

The level surfaces of geometric discord for a class of two-qubit non-X states are investigated when the Bloch vectors are in arbitrary directions. The level surfaces of constant geometric discord are formed by three intersecting open tubes along three orthogc~nal directions. When Bloch vectors increase, the tubes along one or two directions shrink towards the center and may either totally disappear or the open tubes may become closed tubes when the Bloch vectors reach a critical value. In the generalized amplitude damping channel, the evolution of geometric discord shows double sudden changes when the parameter γ, increases. In the phase damping channel, the freezing phenomenon of geometric discord also exists.     

Modulation of entanglement and quantum discord for circuit cavity QED states

The paper investigates the dynamic evolution behaviors of entanglement and quantum discord of coupled superconducting qubits in circuit QED system. We put emphasis on the effects of cavity field quantum state on quantum entanglement and quantum correlations dynamic behaviors of coupling superconducting qubits. The results show that, (1) generally speaking, the entanglement will appear the death and new birth because of the interaction between qubits and cavity field, on the contrary, this phenomenon will not appear in quantum discord. (2) When the cavity field is in coherent state, the entanglement survival time is controlled by the average photon number. The more the average photon number is, the longer survival time of entanglement is prolonged. Thus it has the benefit of keeping quantum correlations. (3) When the cavity field is in squeezed state, the squeezed amplitude parameters have controlling effects on quantum correlations including entanglement and quantum discord. On the one hand, the increase of squeezed amplitude parameters can prolong the survival time of entanglement, on the other hand, with the increase of squeezed amplitude parameters, the robustness of quantum discord is more and more superior to concurrence and is more advantage to keep the system quantum correlations. The further study results show that the increase of the initial relative phase of coupling superconducting qubits can also keep the quantum correlations.     

One-norm geometric quantum discord and critical point estimation in the XY spin chain

In contrast with entanglement and quantum discord (QD), we investigate the thermal quantum correlation in terms of Schatten one-norm geometric quantum discord (GQD) in the XY spin chain, and analyze their capabilities in detecting the critical point of quantum phase transition. We show that the one-norm GQD can reveal more properties about quantum correlation between two spins, especially for the long-range quantum correlation at finite temperature. Under the influences of site distance, anisotropy and temperature, one-norm GQD and its first derivative make it possible to detect the critical point efficiently for a general XY spin chain.     

Dynamics control of geometric quantum discord for two coupling qubits in a squeezed vacuum reservoir

We investigate the dynamics of geometric quantum discord of coupled qubits in a squeezed vacuum reservoir. The results show that there is distinct difference between the dynamics of geometric quantum discord and that of quantum entanglement near (or away from) the decoherence free subspace. We also find that the squeezed vacuum reservoir with high squeezed amplitude is more suitable for geometric quantum discord to survive. The robustness of geometric quantum discord is stronger than that of quantum entanglement.     

Classical correlation, quantum discord and entanglement for two-qubit system subject to heat bath

Classical correlation (CC), quantum discord (QD) and entanglement (QE) of two qubits in one-side and two-side decoherence models are investigated. The sudden change of quantum discord (DSC) as well as classical correlation and sudden death of entanglement (ESD) are found. It is proved that QE (QD) presents no sudden change (sudden death). We prove that, for nonzero occupation number of the reservoir, QE must suffer sudden death; For zero occupation number and X-form initial states, we obtain the states which are robust and the states which experience sudden death. It is verified that if DSC and ESD occur under one-side decoherence, then it must appear in the two-side decoherence, while the reverse does not hold. We obtain the boundaries of CC-QE plane and QD-QE plane, and give the state possessing maximal amount of CC (QD) for a given amount of QE.     

The geometric potential of a double-frequency corrugated surface

For an electron confined to a surface reconstructed by double-frequency corrugations, we give the effective Hamiltonian by the formula of geometric influences, obtain an additive scalar potential induced by curvature that consists of attractive wells with different depth. The difference is generated by the multiple frequency of the double-frequency corrugation. Subsequently, we investigate the effects of geometric potential on the transmission probability, and find the resonant tunneling peaks becoming rapidly sharper and the transmission gaps being substantially widened with increasing the multiple frequency. As a potential application, double-frequency corrugations can be employed to select electrons with particular incident energy, as an electronic switch, which are more effective than a single-frequency ones.     

Activating MoS2 basal planes for hydrogen evolution through the As doping and strain

As a non-precious catalyst for the electrochemical hydrogen evolution reaction (HER), the two-dimensional MoS₂ has been widely studied. To activate the MoS₂ inert basal plane to enable optimal activity, high defect concentration of sulfur vacancies is needed. Herein, based on the first-principles calculations we demonstrate that the HER of MoS₂ can be greatly enhanced by As doping and biaxial strain. We show that the As-doping sites are new catalytic sites and the bonding of H can be greatly enhanced. Moreover, the relative hydrogen adsorption free energy ($\mathrm{\Delta }\mathrm{\Delta }{\mathrm{G}}_{\mathrm{H}}$) can be further manipulated by the strain effect, which efficiently adjusts the catalytic activity. With the synergy of the biaxial strain (2%–3%) and the uniform doping of the As atoms (3.125% concentration), the $\mathrm{\Delta }\mathrm{\Delta }{\mathrm{G}}_{\mathrm{H}}$ can be modulated to zero. Our findings provide a way to achieve the high intrinsic HER activity among molybdenum-sulfide-based catalysts.     

Sub-lattice polarization states in anti-ferroelectrics and their relaxation process

We report studies of quasi-remanent polarization states in Pb_0.99Nb_0.02[(Zr_0.57Sn_0.43)_0.94Ti_0.06]_0.98O₃ (PNZST) anti-ferroelectric ceramics and investigation of their relaxation effects using unique in-situ electrically activated time-resolved Synchrotron X-ray powder diffraction (SXPD) and ¹¹⁹Sn Mössbauer Spectroscopy (MS). The SXPD patterns are consistent with a phase transition from quasi-tetragonal perovskite in 0 V relaxed anti-ferroelectric state to rhombohedral distortion in ferroelectric state under saturating applied voltages of ±2 kV. The observed quasi-remanent polarization relaxation processes are due to the fact that tetragonal to rhombohedral distortion does not occur at the applied voltage required to access the quasi-remanent polarization states, and the tetragonal symmetry restored after the removal of the applied electric field is preserved. Since these quasi-remanent polarization states were seen as possibly suitable for memory applications, the implications of this study are that anti-ferroelectrics are more feasible for multi-state dynamic random access memories (DRAM), while their application to non-volatile memories requires development of more sophisticated “read-out” protocols, possibly involving dc electrical biasing.     

Impact of graphene nanoplatelet concentration and film thickness on vapor detection for polymer based chemiresistive sensors

Chemiresistive gas sensors utilizing graphene nanoplatelet (GNP)-polymer film coated electrodes have great promise for electronic nose applications. In this study GNP-polycaprolactone (PCL) based sensors fabricated using airbrush deposition are exposed to ethanol as an example target analyte to investigate ideal parameters for sensing performance maximization. The ratio of GNP to PCL was investigated from 3 to 21 wt% with sensing response maximized at 15 wt% and signal to noise ratio (SNR) maximized at 18 wt%. The effect of average coating thickness on the sensing performance was investigated by depositing 50–250 μL of 18 wt% GNP solution (852–2030 nm). The response was maximized at 150 μL (1370 nm) and the SNR was maximized at 200 μL (1680 nm). The results are consistent with previous studies of vapor sensors that employ carbon black-polymer films as sensing materials. The fabricated devices were robust and repeatable with respect to initial resistance, depth, roughness, sensor response, and SNR. Overall the results elucidate important parameters for fabrication and development of GNP-polymer gas sensors for detection and discrimination of target analytes with electronic nose systems.     

Pseudomagnetic fields and Landau levels for out-of-plane elastic waves in gradient snowflake-shaped crystals

The study of pseudomagnetic fields (PMF) in classical waves draws a growing attention due to the strength of PMF far higher than real magnetic fields. Here, we show that a giant PMF for out-of-plane elastic waves can be created in the snowflake-shaped crystals by introducing a gradient angle modulation along one direction. In particular, we demonstrate that the Landau energy levels for out-of-plane elastic waves can be formed near the Dirac cone region, as a hallmark of high-field physics induced by PMF. Moreover, the sublattice polarized bulk states similar to the behavior of graphene electron in magnetic fields are achieved in our elastic systems. Furthermore, the magnetic-induced edge state propagation along bend pathway is also demonstrated. Our study provides a new paradigm for manipulating the elastic waves in aspects of information processing and energy transport.     

Design and development of original WSN sensor for suspended particulate matter measurements

This paper comprehensively presents key issues in design of an original optoelectronic measurement device built to assess amount of suspended particulate matter. The paper is introduced with a short explanation of concerns with a suspended particulate matter, what role it has in the air quality and how it affects health of human population. Then, problems of construction of the measurement device supported by a theoretical explanation on the basis of Mie theory are discussed. Subsequently, it is followed by an analysis of the device operation both in laboratory and in real conditions. Results obtained with the presented device are compared with the professional measurement equipment and an expensive, outdoor measurement station. Paper is concluded with observations of differences in spatio-temporal PM change at very close but significantly different city locations.     

First-principles study of two-dimensional van der Waals heterostructure based on ZnO and Mg(OH)2: A potential photocatalyst for water splitting

In this study, the structural, electronic and optical properties of the two-dimensional heterostructure based on ZnO and Mg(OH)₂ are investigated by first-principle calculations. The ZnO/Mg(OH)₂ heterostructure, formed by van der Waals (vdW) interaction, possesses a type-II band structure, which can separate the photogenerated electron–holes constantly. The heterostructure has decent band edge positions for the redox reaction to decompose the water at pH 0 and 7. As for the interfacial properties of the heterostructure, the trend of band bending of the ZnO and Mg(OH)₂ layers in the heterostructure is addressed, which will result a built-in electric field. Besides, the charge-density difference and potential drop across the interface of the ZnO/Mg(OH)₂ vdW heterostructure are also calculated. Finally, the heterostructure is demonstrated that it not only has excellent ability to capture the light near the visible spectrum region, but also can improve the optical performance for the monolayered ZnO and Mg(OH)₂.     

Investigation of half-metallic ferromagnetism in hafnium and tantalum doped NiO for spintronic applications: A DFT study

Full Potential Linearised Augmented Plane Wave (FP-LAPW) method was used to investigate the electronic and magnetic properties of NiO doped with Hf and Ta within the frame work of density functional theory (DFT). NiO is found to be stable in rock salt structure. NiO shows conducting characteristics for the lattice constant of 4.155 Å. Doping Hf and Ta in the metallic super cell of NiO separately in the doping concentration of 12.5%, the compounds Hf_0.125Ni_0.875O and Ta_0.125Ni_0.875O are formed. These compounds of Hf_0.125Ni_0.875O and Ta_0.125Ni_0.875O are predicted to exhibit stability in the ferromagnetic phase. The density of states and band structure plots predict that these compounds exhibit half metallic character with formation of energy gap in one of the spins at the Fermi level. The total spin magnetic moments found in these compounds are 12.00689 μ_B and 10.97628 μ_B.     

Fabrication and characterization of dual-band organic/inorganic photodetector for optoelectronic applications

In this work, the optoelectronic performance of organic/inorganic heterojunction photodiode based on alpha-sexithiophene (α-6T/n-Si) is introduced. A thin film of α-6T was deposited on the n-type silicon substrate by a thermal evaporation technique. The topographical properties of the α-6T thin film grown on the n-Si substrate were investigated using a field emission scanning electron microscope (FESEM) technique. A network of nanocrystalline needles over the film surface was observed which give rise to an improvement in the electric charge transport. The optical properties of the prepared thin film were investigated using a spectrophotometric technique. The high absorption of α-6T in UV and visible region suggested the ability of this architecture for UV and visible light detection. The I-V characteristics of the fabricated photodiode were investigated in dark and under different illumination intensities and different wavelengths. The present architecture showed a good response to halogen lamb light, where the estimated values of rising and falling time at 160 mW/cm² were about 400 ms and 450 ms, respectively. The results show the possibility of using Au/α-6T/n-Si/Al structure as a photodetector for a wide range of the solar spectrum (UV–Visible).     

Persistent currents and induced magnetization in presence of external magnetic field and transition probabilities in presence of combined laser pulse and external magnetic field for a confined hydrogen atom

In this work we propose to study an atom confined in a potential which consists of a Hulthén potential plus a ring-shaped potential. The atom is further subjected to a spherical confinement. The time-independent Schrödinger equation (TISE) of the system is solved numerically. Exact energy levels are obtained. The persistent current and induced magnetic field of such a confined atom is evaluated. Finally, the atomic system in this potential and confinement is subjected to short electromagnetic pulses, which are shown to induce enormous currents.