The European Physical Journal D最新文献

We propose a new quantum simulation method for a many-body quantum liquid of identical particles at finite (nonzero) temperature. The new scheme expands the high-temperature density matrix on the overcomplete set of single particles coherent states of John Rider Klauder instead of the usual plane waves as in conventional path integral methods. One is free to tune the elastic constant and/or the mass of the harmonic oscillator subtending the coherent states so as to maximize the computational efficiency of the algorithm. We prove that in the limit of an extremely stiff harmonic oscillator the results for the internal energy tend toward the correct expected values. Moreover, we suggest that a stiff harmonic oscillator could allow the use of larger (imaginary) timesteps. This additional degree of freedom is the characteristic feature of our new algorithm and is not available in more conventional path integral methods.

In this work, we present a comprehensive quantum-mechanical analysis of the spectral properties of the titanium atom, with emphasis on semi-forbidden (intercombination) electronic transitions. The calculations are performed within density-functional theory (DFT) including spin–orbit coupling, and the Kohn–Sham equations are solved numerically by a conjugate-gradient method, yielding high accuracy at moderate computational cost. Oscillator strengths and transition characteristics are obtained within time-dependent DFT using the Casida formalism, which enables a consistent treatment of correlation effects and multiplet structure. Particular attention is paid to the mechanisms of population inversion and to comparisons between theory and experiment. The results validate the proposed approach and demonstrate its potential for applications to complex atomic systems in astrophysics, materials science, and quantum optics.

Four-level system: optical pumping, laser emission, collisions, and spontaneous decays

The choice of basis functions plays a vital role in performing accurate calculations of atomic properties. An alternative to the commonly used Gaussian-type orbitals (GTOs) is the use of B-spline functions, which offer a highly flexible and efficient basis for representing atomic wave functions. The accuracy of an atomic property depends on the quality of the chosen basis functions used to construct single-particle wave functions. This work aims at revisiting the behavior of GTOs and B-spline functions to use them optimally in different atomic calculations so that it can help reduce computational cost. In this context, we analyze the magnetic-dipole hyperfine constants ((A_{fs})) for a number of atomic states in (^{133})Cs. We first analyze results obtained using GTOs and B-splines, which are often used in the literature, followed by redefining them to improve efficiency in the calculation of atomic properties. Our comparative study reveals that an adaptive distribution of GTOs delivers the best results for low- and intermediate-lying states, whereas a kinetically balanced B-spline basis becomes more reliable for high-lying states, especially when a large number of basis functions are employed.

Efficient basis choice improves accuracy and reduces computational cost in atomic property calculations

We investigate whether negative values of Wigner functions purely coming from correlations are sufficient for observing nonlocal correlations. We employ a simple model for superpositions of coherent states and examine how the corresponding Wigner negativity of correlations relates to the violation of a CHSH inequality based on pseudo-spins. We find that a critical amount of this negativity is necessary to violate the inequality, making a nonzero negativity not sufficient for observing nonlocal correlations.

Considering a combined Kappa–Cairns electron distribution, we have analytically explored the nonlinear dynamics of ion-acoustic solitary waves in a magnetized electron–ion–dusty plasma, encompassing both suprathermal and nonthermal aspects to provide a more realistic characterization. The Korteweg–de Vries–Zakharov–Kuznetsov (KdV–ZK) equation is developed by employing the reductive perturbation approach. The nonlinear coefficient of KdV–ZK equation disappears for certain parametric curves, resulting in modified KdV–ZK equation. The soliton solutions are derived for each case and the consequences of key physical parameters on soliton characteristics are numerically investigated. The small-k perturbation expansion approach is used to investigate the stability of solitary solutions. The numerical research on the impacts of the parameters associated with this system on the growth rate of instability predicts that the enhancements of the propagation angle and the ion gyro-frequency lead to the shrinkage of the maximum growth rate of instability. On the other hand, the enhancements of the suprathermal and nonthermal parameters associated with electron’s distribution lead to the shrinkage of the maximum growth rate of instability. Understanding wave propagation and stability in space and astrophysical dusty plasmas, such as the solar wind, magnetosheath, and wider heliospheric regions, may be improved by the present research.

Topological photonic crystals are innovative optical structures that leverage topological phases to achieve robust photonic bandgaps, exhibiting immunity to structural imperfections and disorder. However, a significant challenge in conventional topological photonic crystal designs has been the difficulty in precisely controlling the position of the transmission peak. To address this limitation, we present a modified topological photonic crystal composed of alternating (hbox {SiO}_2) and (hbox {TiO}_2) layers. This design incorporates a synergistic approach that integrates the transfer matrix method, quarter-wavelength thickness design principles, and iterative optimization of layer parameters to ensure precise wavelength alignment and enhanced spectral control. The proposed modified topological photonic crystal demonstrates superior performance, including wider photonic bandgaps, moderate transmission efficiency, and improved resistance to structural defects.

Top panel: Schematic diagrams of the proposed structure without modification (top) and with modification (bottom), together with the transmission spectra for the symmetric (red) and topological (blue) structures. Bottom panel: Transmission spectra (blue line), average transmission over perturbation (red line), and mean square error (gray shaded region) for the symmetric structure (left), topological structure (middle), and modified topological structure (right).