Search

High-order harmonic generation of the cyclo[18]carbon (C18) molecule under few-cycle circularly polarized laser pulse is studied by time-dependent density functional theory. Compared with the harmonic emission of the ring molecule C6H6 having similar ionization potential, the C18 molecule has higher efficiency and cutoff energy than C6H6 with the same laser field parameters. Further researches indicate that the harmonic efficiency and cutoff energy of the C18 molecule increase gradually with the increase of the laser intensity of the driving laser or decrease of the wavelength, both are larger than those of the C6H6 molecule. Through the analysis of the time-dependent evolution of the electronic wave packets, it is also found that the higher efficiency of harmonic generation can be attributed to the larger spatial scale of the C18 molecule, which leads to a greater chance for the ionized electrons from one atom to recombine with others of the parent molecule. Selecting the suitable driving laser pulse, it is demonstrated that high-order harmonic generation in the C18 molecule has a wide range of applications in producing circularly polarized isolated attosecond pulse.

Proton-exchange membrane fuel cells (PEMFCs) have been widely used commercially to solve the energy crisis and environmental pollution. The oxygen reduction reaction (ORR) at the cathode is the rate-determining step in PEMFCs. Platinum (Pt) catalysts are used to accelerate the ORR kinetics. Pt’s scarcity, high cost, and instability in an acidic environment at high potentials seriously hinder the commercialization of PEMFCs. Therefore, studies should explore electrocatalysts with high catalytic activity, enhanced stability, and low-Pt loading. This review briefly introduces the research progress on Pt and Pt-based ORR electrocatalysts for PEMFCs, including anticorrosion catalyst supports, Pt, and Pt-based alloy electrocatalysts. Advanced preparation technology and material characterization of Pt-based ORR electrocatalysts are necessary to improve the performance and corresponding reaction mechanisms.

Diffractive lenses (DLs) can realize high-resolution imaging with light weight and compact size. Conventional DLs suffer large chromatic and off-axis aberrations, which significantly limits their practical applications. Although many achromatic methods have been proposed, most of them are used for designing small aperture DLs, which have low diffraction efficiencies. In the designing of diffractive achromatic lenses, increasing the aperture and improving the diffraction efficiency have become two of the most important design issues. Here, a novel phase-coded diffractive lens (PCDL) for achromatic imaging with a large aperture and high efficiency is proposed and demonstrated experimentally, and it also possesses wide field-of-view (FOV) imaging at the same time. The phase distribution of the conventional phase-type diffractive lens (DL) is coded with a cubic function to expand both the working bandwidth and the FOV of conventional DL. The proposed phase-type DL is fabricated by using the laser direct writing of grey-scale patterns for a PCDL of a diameter of 10 mm, a focal length of 100 mm, and a cubic phase coding parameter of 30π. Experimental results show that the working bandwidth and the FOV of the PCDL respectively reach 50 nm and 16° with over 8% focusing efficiency, which are in significant contrast to the counterparts of conventional DL and in good agreement with the theoretical predictions. This work provides a novel way for implementing the achromatic, wide FOV, and high-efficiency imaging with large aperture DL.

We investigate the properties of fundamental, multi-peak, and multi-peaked twisted solitons in three types of finitewaveguide lattices imprinted in photorefractive media with asymmetrical diffusion nonlinearity. Two opposite soliton self-bending signals are considered for different families of solitons. Power thresholdless fundamental and multi-peaked solitons are stable in the low power region. The existence domain of two-peaked twisted solitons can be changed by the soliton self-bending signals. When solitons tend to self-bend toward the waveguide lattice, stable two-peaked twisted solitons can be found in a larger region in the middle of their existence region. Three-peaked twisted solitons are stable in the lower (upper) cutoff region for a shallow (deep) lattice depth. Our results provide an effective guidance for revealing the soliton characteristics supported by a finite waveguide lattice with diffusive nonlocal nonlinearity.

Based on the two-dimensional (2D) tan-sin-cos-coupling (2D-TSCC), a new image protection method is designed, this method includes steganography and encryption. First, a 2D-TSCC system is designed. The 2D-TSCC has a large parameter space in a hyperchaotic state. The chaotic trajectory fills the entire window. The chaotic sequence generated by the 2D-TSCC has a good pseudorandomness, so it can be used in steganography and encryption. Then, the amount of information contained in each bit of the cover image is analyzed, and the three bits which carry the least amount of information are selected. The secret image is hidden in these three bits base on the 2D-TSCC. Finally, the carrier image is scrambled and diffused by the 2D-TSCC. The ciphertext is generated in this way. Send the ciphertext to the recipient through channel transmission, and the recipient obtains the secret image by decrypting twice.

We theoretically introduce two new photon-modulated atomic coherent states (ACSs) via using the Schwinger bosonic representation of the angular momentum operators (the sequential operations J ± n ) on an ACS, and investigate their nonclassicality using the Wigner distribution, photon number distribution, and entanglement entropy. It is found that photon-modulated ACSs possess more stronger nonclassicality than the original ACS in certain regions of τ, the nonclassicality enhances with increasing number n of the operations J ± and the operation J + ( − ) n enhances the entanglement in the region of small (large) τ.

The influence of transition metals (Sc, Ti, V, Cr, and Mn) doping at different distances on the magnetism of CdS is studied by using generalized gradient approximation combined with Hubbard U in the VASP package. The results show that the doping systems are more stable, easy to form, and the wurtzite structure of CdS is not changed. It is found that the systems are antiferromagnetic (AFM) when nearest neighbor doping, which is attributed to the direct charge transfers between two impurity ions. The systems are ferromagnetic (FM) when the doping distance increases further, since the double exchange interactions are observed among the 3d orbital of the transition metal, the Cd-5s and the S-3p orbitals are at conduction band minimum. We also found that the total magnetic moment of each ferromagnetic system increases with the order of SC to Mn-doping, the spin polarizability of Cr-doping system is 100%. The estimated Curie temperature indicates that the Cr- and Mn-doped CdS in this paper can achieve room-temperature ferromagnetic characteristics, especially the Cr doping is the most prominent. And TM-doping does not destroy the semiconductor characteristics of the system. Therefore, the TM-doped CdS can be used as an ideal dilute magnetic semiconductor functional material.

We arrange quantum mechanical operators (a † a) m in their normally ordered product forms by using Touchard polynomials. Moreover, we derive the anti-normally ordered forms of (a † a)± m by using special functions as well as Stirling-like numbers together with the general mutual transformation rule between normal and anti-normal orderings of operators. Further, the ℚ- and ℙ-ordered forms of (QP)±m are also obtained by using an analogy method.

By using the parameter differential method of operators, we recast the combination function of coordinate and momentum operators into its normal and anti-normal orderings, which is more ecumenical, simpler, and neater than the existing ways. These products are very useful in obtaining some new differential relations and useful mathematical integral formulas. Further, we derive the normally ordered form of the operator (fQ + gP)−n with n being an arbitrary positive integer by using the parameter tracing method of operators together with the intermediate coordinate–momentum representation. In addition, general mutual transformation rules of the normal and anti-normal orderings, which have good universality, are derived and hence the anti-normal ordering of (fQ + gP)−n is also obtained. Finally, the application of some new identities is given.

Electric quadrupole moments of low-lying excited states of Yb+ are calculated by relativistic coupled-cluster theory with perturbations from external fields. The field-dependent energy differentiation provides accurate values of the electric quadrupole moments of 2P3/2, 2D3/2,5/2, and 2F5/2,7/2 states which agree well with experimental values. The important role of the electronic correlation to the electric quadrupole moments is investigated. Our calculations indicate the early dispute of the electric quadrupole moment of the Yb+(2F7/2) state for which the measured and theoretical values have a large discrepancy. These electric quadrupole moment values can help us to determine the electric quadrupole shifts in start-of-the-art experiments of the Yb+ ion.

We study how can an angular momentum coherent state ∣ τ 〉 keeps its form-invariant during time evolution governed by the Hamiltonian H = f ( t ) J + + f * ( t ) J − + g ( t ) J z . We discuss this topic in the context of boson realization of ∣ τ 〉 . By employing the entangled state representation ∣ ζ 〉 and deriving a new binomial theorem involving two-subscript Hermite polynomials, we derive the wave function 〈 ζ ∣ τ 〉 , which turns out to be a single-subscript Hermite polynomial. Based on this result the maintenance of angular momentum coherent state during time evolution is examined, and the value of τ ( t ) is totally determined by the parameters involved in the Hamiltonian.

Using the thermal-entangled state representation and the operator-ordering method, we investigate Wigner function (WF) for the squeezed negative binomial state (SNBS) and the analytical evolution law of density operator in the amplitude decay channel. The results show that the analytical WF is related to the square of the module of single-variable Hermite polynomials, which leads to a new two-variable special function and its generating function, and the parameters s and γ play opposite roles in the WF distributions. Besides, after undergoing this channel, the initial pure SNBS evolves into a new mixed state related to two operator Hermite polynomials within normal ordering, and fully loses its nonclassicality and decays to vacuum at long decay time.

ZnO-based resistive switching device Ag/ZnO/TiN, and its modified structure Ag/ZnO/Zn/ZnO/TiN and Ag/graphene/ZnO/TiN, were prepared. The effects of inserted Zn layers in ZnO matrix and an interface graphene layer on resistive switching characteristics were studied. It is found that metal ions, oxygen vacancies, and interface are involved in the RS process. A thin inserted Zn layer can increase the resistance of HRS and enhance the resistance ratio. A graphene interface layer between ZnO layer and top electrode can block the carrier transport and enhance the resistance ratio to several times. The results suggest feasible routes to tailor the resistive switching performance of ZnO-based structure.

We theoretically analysed the linewidth of the probe absorption spectrum in a cold Cs atom–molecule system. The tunnelling coupling between the two excited molecular states, especially for the Cs atom–molecule system, plays an important role in obtaining the sub-natural linewidth of the probe absorption spectrum. For example, when the tunnelling couple strength fulfils σ12 = 10γab1, the linewidth is only about 0.66 MHz. Moreover, since the linewidth of interest is dominated by the tunnelling coupling, the absorption peak becomes very narrow even in the case of large pump laser intensities.

The surface dynamics of supercooled liquid-glycerol is studied by scanning the thickness of the glycerol film with single photon detection. Measurements are performed at room temperature well above the glycerol's glass transition temperature. It is shown that the surface dynamics of the glycerol film is very sensitive to the temperature. The linear relationship between the thickness of the film and the viscosity predicted by the Vogel–Fulcher–Tammann–Hesse (VFTH) law is also presented experimentally.

We construct four linear composite operators for a two-particle system and give common eigenvectors of those operators. The technique of integration within an ordered product (IWOP) of operators is employed to prove that those common eigenvectors are complete and orthonormal. Therefore, a new two-mode intermediate momentum-coordinate representation which involves quantum entanglement for a two-particle system is proposed and applied to some two-body dynamic problems. Moreover, the pure-state density matrix |ξ1, ξ2〉C,D C,D〈ξ1, ξ2| is a Radon transform of Wigner operator.

Using a numerical computational method, quasiprobability distributions of new kinds of even and odd nonlinear coherent states (EONLCS) are investigated. The results show that the distributions of the new even nonlinear coherent states (NLCS) are distinct from those of the new odd NLCS and imply that the new EONLCS always exhibit some different nonclassical effects. Finally, with the aid of newly introduced intermediate coordinate-momentum representation in quantum optics, the tomograms of the new EONLCS are calculated. This is a new way of obtaining the tomogram function.

This paper reports that ultracold atoms are populated into different nS and nD Rydberg states (n = 25~52) by two-photon excitation. The ionization spectrum of an ultracold Rydberg atom is acquired in a cesium magneto-optical trap by using the method of pulse field ionization. This denotes nS and nD states in the ionization spectrum and fits the data of energy levels of different Rydberg states to obtain quantum defects of nS and nD states.

This paper reports that the mesoscopic inductance and capacitance coupling LC circuit is quantized by means of the canonical quantization method. Using the 'invariant eigen-operator' method, it deduces the energy-level transition rule when the system is disturbed by an external electromagnetic field. At the same time, the quantum fluctuations for the system at finite temperature are examined by virtue of the generalized Hellmann–Feynman theorem.

Using the coherent state representation of Wigner operator and the technique of integration within an ordered product (IWOP) of operators, the Wigner functions of the even and odd binomial states (EOBSs) are obtained. The physical meaning of the Wigner functions for the EOBSs is given by means of their marginal distributions. Moreover, the tomograms of the EOBSs are calculated by virtue of intermediate coordinate-momentum representation in quantum optics.

This paper constructs the new common eigenvectors of n intermediate coordinate-momentum operators which are complete and orthonormal. The intermediate coordinate-momentum representation of a multi-particles system is proposed and applied to a generaln-mode quantum harmonic oscillators system with coordinate-momentum coupling.

In this paper a new class of finite-dimensional even and odd nonlinear pair coherent states (EONLPCSs), which can be realized via operating the superposed evolution operators D±(τ) on the state |q, 0), is constructed, then their orthonormalized property, completeness relations and some nonclassical properties are discussed. It is shown that the finite-dimensional EONLPCSs possess normalization and completeness relations. Moreover, the finite-dimensional EONLPCSs exhibit remarkably different sub-Poissonian distributions and phase probability distributions for different values of parameters q,η and ζ.