The European Physical Journal D最新文献

We use the Schur concavity of the von Neumann entropy and introduce a majorization-based entanglement criterion for the states of systems consisting of identical fermions. This criterion is in the form of an inequality between the von Neumann entropies of the total density matrix and the single-particle reduced density matrix which have to be satisfied by the separable states of such systems, and therefore, its violation indicates the entanglement. Our criterion is an improved version of the one introduced by Zander et al. (in Eur. Phys. J. D 66: 14, 2012). To illustrate its utility, we use the criterion to various illustrative instances of the families of mixed states and find that when the single-particle Hilbert spaces are of dimension four, the criterion indicates all the entangled states within the families under consideration.

Discovering hidden physical mechanisms of a system, such as underlying partial differential equations (PDEs), is an intriguing subject that has not yet been fully explored. In particular, how to go beyond the traditional method to obtain the PDEs of complex systems is currently under active debate. In this work, we propose a deep-learning approach to discover the underlying Gross-Pitaevskii equations (GPEs) of one-dimensional Bose–Einstein condensates (BECs). The results show that such method is markedly superior to the traditional method due to advantages of the deep neural network. The former possesses the ability to obtain a parsimonious model with high accuracy and insensitivity to data noise, and can successfully discover the underlying GPEs that BECs should obey directly from the data even in the absence of a knowledge structure. More importantly, we find that such method is able to work well even for data with (15%) noise. Although the cases studied are proof-of-concept, the method provides a promising technique for unveiling hidden novel physical mechanisms in quantum systems from observations.

We theoretically analyzed positron affinities (PAs) of acetaldehyde (CH₃CHO) and its deuterated (CD₃CDO) molecules at vibrational excited states with multi-component molecular orbital and vibrational quantum Monte Carlo methods. In the fundamental tone states, the PA value at the C=O stretching vibrational mode of acetaldehyde becomes increased by 9.8 meV (+ 12%) from the vibrational ground state of 84.5 meV, while that at the C-H (aldehyde group) stretching vibrational mode decreased by 2.8 meV ((-)3%). We also confirmed that each vibrational state has a different H/D isotope shift in PA values. Such non-uniformity in quantum vibrational influence on PA values and its H/D isotope shifts dominantly arise from the change in dipole moment by vibrational excitations.

In order to establish important reaction properties, such as rate coefficients, it is often necessary to know the number of reactants that are present in an interaction region. The absolute number densities of pulsed supersonic molecular (NH(_3)) and atomic (H) beams are reported using a laser-based detection method, under a range of experimental conditions including photolysis, Zeeman deceleration, and magnetic focusing. Time-averaged densities of (3.6 ± 2.7) (times ) 10(^4) cm(^{-3}) are reported for successfully Zeeman-decelerated and magnetically focused H atoms, generated by the photodissociation of precursor NH(_3) molecules. Without the magnetic guide components in the beamline, the density of the target radicals of interest is somewhat lower, at (2.5 ± 1.8) (times ) 10(^4) cm(^{-3}). The average density of the undecelerated H atom beam is approximately an order of magnitude higher (2.9 ± 1.9) (times ) 10(^5) cm(^{-3}), with the average density of the molecular ammonia beam over two orders of magnitude higher again (5.1 ± 2.9) (times ) 10(^7) cm(^{-3}). The average number densities measured for the two different species of interest in this work span more than three orders of magnitude. These findings highlight the need for accurate and precise experimental measurements of number densities—for each species of interest, under the appropriate experimental conditions—before doing absolute rate coefficient calculations.

Following up on a recent paper (Bharti et al. in Phys Rev A 109:023110, 2024), we compare the predictions from several R-matrix with time-dependence calculations for a modified three-sideband version of the “reconstruction of attosecond beating by interference of two-photon transitions” (RABBITT) configuration applied to helium. Except for the special case of the threshold sideband, which appears to be very sensitive to the details of coupling to the bound Rydberg states, increasing the number of coupled states in the close-coupling expansion used to describe the ejected-electron–residual-ion interaction hardly changes the results. Consequently, the remaining discrepancies between the experimental data and the theoretical predictions are likely due to uncertainties in the experimental parameters, particularly the detailed knowledge of the laser pulse.

This study is an overview of the atomic data and opacity computations performed by the Atomic Physics and Astrophysics Unit of Mons University in the context of kilonova emission following neutron star mergers, in both the photospheric and nebular phases. In this work, as a sample case, we focus on a specific lanthanide ion, namely Er III. As far as the LTE photospheric phase of the kilonova ejecta is concerned, we present our calculations using both a theoretical method (the pseudo-relativistic Hartree-Fock method, HFR) and a statistical approach (the Resolved Transition Array approach, RTA) to obtain the atomic data required to estimate the Er III expansion opacity for typical conditions expected in kilonova ejecta one day after the merger. In order to draw the limitations of both of our strategies, the results obtained using the latter are compared, and a calibration procedure of the HFR atomic data in this context is also discussed. Concerning the kilonova ejecta nebular phase, atomic parameters that characterize forbidden lines in Er III are calculated using HFR as well as another computational approach, namely the Multiconfiguration Dirac–Hartree–Fock (MCDHF) method. The potential detection of such lines in late-phase kilonova spectra is then discussed.