Highlights
Abstract +
With the advancement of synchrotron and free-electron laser, X-ray quantum optics has emerged as a novel frontier for exploring light-matter interactions at high photon energies. A significant challenge in this field is achieving well-defined two-level systems through atomic inner-shell transitions, which are often hindered by broad natural linewidths and local electronic structure effects. This study aims to explore the potential of tungsten disilicide (WSi2) as a two-level system for X-ray quantum optics applications. Utilizing high-resolution resonant inelastic X-ray scattering (RIXS) near the W-L3 edge, in this work, the white line of bulk WSi2 is experimentally distinguished, overcoming the spectral broadening caused by short core-hole lifetime. The measurements are conducted by using a von Hamos spectrometer at the GALAXIES beamline of the SOLEIL synchrotron. The results reveal a single resonant emission feature with a fixed energy transfer, confirming the presence of a discrete 2p-5d transition characteristic of a two-level system. Additional high-resolution XAS spectra, obtained via high energy resolution fluorescence detection method and reconstructed from off-resonant emission (free from self-absorption effect for bulk WSi2 sample) method, further support the identification of a sharp white line. These findings demonstrate the feasibility of using WSi2 as a model system in X-ray cavity quantum optics and establish RIXS as a powerful technique to resolve fine inner-shell structures.
SPECIAL TOPIC—AI + Physical Science
EDITOR'S SUGGESTION
2025, 74 (18): 188101.
doi: 10.7498/aps.74.20250497
Abstract +
EDITOR'S SUGGESTION
2025, 74 (18): 180401.
doi: 10.7498/aps.74.20250644
Abstract +
EDITOR'S SUGGESTION
2025, 74 (18): 183103.
doi: 10.7498/aps.74.20250812
Abstract +
EDITOR'S SUGGESTION
2025, 74 (18): 184204.
doi: 10.7498/aps.74.20250757
Abstract +
Photon localization is of great significance in both basic research and technical applications. Bound states in the continuum (BICs) in photonic crystal provide a new mechanism for effective photon localization. However, the imperfections and defects are inevitable in the process of fabricating photonic crystals. Momentum-space characterization is used as a powerful tool to analyze how such processing variations affect the photonic band structure, providing information for designing and fabricating photonic crystal devices. In this work, a photonic crystal in the visible light band is designed and its band structure is analyzed through FDTD simulation. The high symmetry at the point in momentum space Γ leads to a symmetry mismatch between the internal mode of the photonic crystal and the external propagation mode (radiation continuum), so that bound states with infinite lifetime appear above the light, thereby achieving the localization of photons in the vertical direction. At the same time, the angle-resolved photoluminescence (PL) spectrum of the photonic crystal is measured through the self-built angle-resolved optical path. The weak photoluminescence of the Si3N4 substrate is coupled with the photonic crystal mode for measuring the photonic crystal band. It can be observed that the band structure is consistent with the simulation results. At the same time, the intensity of the TE1 band near the Γ point is significantly weakened compared with the intensity at the position away from the Γ point, but it is not completely eliminated. This shows that errors and defects caused in fabrication process will destroy the symmetry of the structure, causing the BIC to evolve into the quasi-BIC. The quasi-BIC mode achieves effective localization of photons in the vertical direction near the Γ point. Furthermore, a heterostructure of photonic crystals with different periods is designed to achieve lateral photon localization by utilizing the band nesting between the photonic ctystals with different periods. Through this approach, this study ultimately develops a high-quality microcavity with a ratio of impressive quality factor to mode volume of $ 6\times {10}^{14} $ cm–3, and achieves characteristic regulation of the momentum space of photonic crystals by adjusting the structural parameters. This research is of great significance for designing photonic crystals and studying the interaction between light and matter.
EDITOR'S SUGGESTION
2025, 74 (18): 185203.
doi: 10.7498/aps.74.20250668
Abstract +
In this paper, the charge state evolution behavior of carbon ions interacting with hydrogen plasma is systematically investigated based on a cross-sectional model. First, the influence of introducing a “shifted” Maxwellian velocity distribution on the dielectronic recombination rate coefficients is investigated within the range of carbon ion incident energies from 1 keV/u to 100 MeV/u and hydrogen plasma electron temperatures of $k{T_{\text{e}}} = 1$–1000 eV. The rate coefficient data for this system are provided. On this basis, this research specifically solves the equilibrium rate equations by taking into account various ionization and recombination processes for projectile carbon ions with an energy of ${0}{\text{.5 MeV/u}}$, plasma electron temperatures of $k{T_{\text{e}}} = 3{\text{ eV}}$ and ${\text{8 eV}}$, and electron densities ranging from ${1}{{0}^{{18}}}{\text{ c}}{{\text{m}}^{{{ - 3}}}}$ to ${1}{{0}^{{20}}}{\text{ c}}{{\text{m}}^{{{ - 3}}}}$. The results show that the abundance of both non-equilibrium and equilibrium charge states of carbon ions passing through hydrogen plasma varies with plasma thickness, revealing how plasma conditions such as temperature and density, along with projectile ion energy and initial charge states, influence the evolution of the ion charge states. Furthermore, a comparison of the dynamic behaviors of carbon ions in hydrogen plasma and neutral gas (hydrogen) shows that the unique effects of the plasma environment on ion charge exchange are elucidated. The mean equilibrium charge state of projectile ions exhibits a positive correlation with electron temperature and a negative correlation with electron density. It is particularly important that the calculated equilibrium charge states in hydrogen gas targets are notably lower than those in plasma environments. As the initial charge state of projectile ions approaches its equilibrium value, the equilibrium thicknesses for all charge states demonstrate a decreasing trend, accompanied by a corresponding reduction in the mean equilibrium thickness. This phenomenon is consistently verified in both plasma and gas targets, with the mean equilibrium thickness values in gas targets being significantly smaller than those in plasma environments. Most importantly, when the initial charge state of projectile ions exceeds the equilibrium value, these ions display more pronounced energy loss characteristics in non-equilibrium regions. This study will provides important references for investigating the dynamic evolution and energy transport characteristics of ion-plasma interactions in the field of high-energy-density physics.
EDITOR'S SUGGESTION
2025, 74 (18): 187402.
doi: 10.7498/aps.74.20250795
Abstract +
Amorphous superconducting thin film materials have the advantages of high superconducting uniformity and good optical response sensitivity, which make them ideal materials for fabricating large-area and mid-infrared superconducting nanowire single-photon detectors (SNSPD). In this paper, three series of different amorphous superconducting films are deposited on Si wafers by room-temperature magnetron co-sputtering. For these films, the dependence of their physical properties, i.e. critical temperature Tc, Ginzburg-Landau coherence length ξ(0), normal-state electron diffusion coefficient De, magnetic penetration depth λ(0), and superconducting energy gap Δ(0), on film thickness is systematically investigated. Compared with amorphous tungsten silicide (WSi) and molybdenum germanide (MoGe) superconducting thin films, WGe alloys and WSi have similar superconducting properties, including critical temperature and coherence length, slightly lower normal-state electron diffusion coefficient and higher magnetic penetration depth. Compared with MoGe, both WGe and WSi alloys exhibit larger normal-state electron diffusion coefficient and higher magnetic penetration depths. By studying the superconducting properties of three different amorphous thin films, this research provides new material choices and experimental evidence for developing and optimizing the performance of large-area, high-sensitivity superconducting nanowire single-photon detectors.
EDITOR'S SUGGESTION
2025, 74 (18): 180302.
doi: 10.7498/aps.74.20250740
Abstract +
EDITOR'S SUGGESTION
2025, 74 (18): 182401.
doi: 10.7498/aps.74.20250633
Abstract +
To describe the projectile-target interaction in heavy-ion collision, the traditional optical model is improved and a corresponding optical model for heavy-ion collisions is established in this work The program APOMHI is developed accordingly. In heavy-ion collisions, the mass of the projectile is comparable to the mass of target nucleus. Therefore, the projectile and target nucleus must be treated equally. The potential field for their relative motion must arise from an equivalent contribution of both nuclei, not just from the target nucleus. Consequently, the angular momentum coupling scheme must adopt L - S coupling, instead of j - j coupling. The projectile spin i and target spin I first couple to form the projectile-target system spin S (which varies between $ \left| {I - i} \right| $ and $ i + I $). Then, the spin S of this system couples with the orbital angular momentum L of relative motion, forming a total angular momentum J . Thus, the radial wave function UlSJ (r) involves three quantum numbers: l , S , and J , while traditional optical model only involves l and j . Furthermore, since the mass of projectile is similar the mass of target, the form of the optical model potential is symmetrical relative to the projectile and target. The projectile nucleus and the target nucleus are still assumed to be spherical, and their excited states are not considered. The projectile may be lighter or heavier than the target, but they cannot be identical particles. By using this optical model program APOMHI, the elastic scattering angular distributions and compound nucleus absorption cross sections for heavy-ion collisions can be calculated. Taking for example a series of heavy-ion collision reactions with 18O as the projectile nucleus, a corresponding set of universal optical potential parameters is obtained by fitting experimental data. The comparisons show that the theoretical calculations generally accord well with the available experimental data. Here, the results for fusion cross-sections and elastic scattering angular distributions using several representative target nuclei (lighter, comparable in mass, heavier, and heavy compared to the projectile nucleus) are taken for example. Specifically, the fusion cross-section results correspond to targets 9Be, 27Al, 63Cu and 150Sm, while the elastic scattering angular distributions correspond to targets 16O, 24Mg, 58Ni, and 120Sn.
EDITOR'S SUGGESTION
2025, 74 (18): 183102.
doi: 10.7498/aps.74.20250684
Abstract +
The design of shaping pulse fields for controlling molecular orientation is of great importance in fields of stereochemical reactions, strong-field ionization, and quantum information processing. Traditional quantum optimal control algorithms typically solve the problem of molecular orientation in an infinite-dimensional rotational space, but they often overlook the constraints imposed by experimental limitations. In this work, a multi-objective and multi-constraint quantum optimal control algorithm is proposed to design a pulse field that conforms to the constraints of pulse area and energy. Specifically, the algorithm enforces a zero pulse area condition to eliminate the static field components and maintains constant pulse energy, ensuring compatibility with realistic experimental setups. Under these constraints, the algorithm optimizes the population and phase distribution of a selected number of low-lying rotational states in ultracold molecules to achieve maximum molecular orientation. The effectiveness of the proposed algorithm is demonstrated through numerical studies involving two- and three-state target subspaces, where the creation of a coherent superposition state with optimized population and phase distribution leads to the desired molecular orientation. Furthermore, its scalability is validated by applying it to a more complex 17-state subspace, where a maximum orientation value of 0.99055 is obtained, approaching the global optimal value of 1. Our findings demonstrate that by effectively managing these constraints, the influence of rotational states in the non-target state subspace can be substantially suppressed. The time-frequency analysis of the optimized pulses, combined with the Fourier transform spectrum of the time-dependent degree of orientation, indicates that the maximum molecular orientation is mainly achieved through ladder-climbing excitation of multi-color pulse fields, with the contributions from highly excited states being minimal. This work provides a valuable reference for designing experimentally feasible pulse fields using multi-constraint optimization algorithms, which helps to precisely control a limited number of rotational states to achieve maximum molecular orientation.
- 1
- 2
- 3
- 4
- 5
- ...
- 205
- 206
