Abstract In this study, we conduct a comprehensive exploration of the diatomic cation LiAs + , a species that has not yet been explored experimentally or computationally. Utilizing high-level ab initio calculations, we characterize the structural, electronic, and spectroscopic characteristics of the low-lying Λ–S states, correlating with the five lowest dissociation limits. Employing the icMRCI + Q approach, complemented by extended basis sets, we construct potential energy curves, extract spectroscopic constants, and derive vibrational energy levels. Our research indicates that the spin–orbit coupling effect has a relatively strong impact on the electronic structure of this species, resulting in the emergence of spin-forbidden transitions that are anticipated to be observable in spectroscopic detections. Additionally, we assess transition properties, including Einstein coefficients and radiative lifetimes, of interested transitions for the cation. Benchmark calculations conducted on neutral LiAs validate our theoretical framework, which further verifies the accuracy of our predictions for the cation. The simulated single photo-ionization process, represented as LiAs → LiAs + +e, serves as a guidance for spectroscopic detection. These results could illuminate future experimental or theoretical investigations of the diatomic LiAs + molecule.
Abstract Non-Gaussian noise is usually regarded as a limitation for precision measurements, something to be shielded against or eliminated. We take the opposite approach by injecting controllable random telegraph noise (RTN) into an optically pumped atomic magnetometer (OPAM), demonstrating that controlled colored noise can serve as a spectroscopic probe of spin-environment coupling. By independently tuning the RTN amplitude, switching rate, and carrier detuning, we resolve a stochastic-response crossover from fast-switching motional averaging to a slow-switching, configuration-resolved regime. Beyond noise-induced broadening, the spectral envelope reflects the finite residence time of the two values of the same RTN process. These results establish controlled RTN as a spectroscopic probe of spin-environment coupling in an OPAM. The measured spectra vary systematically with the applied RTN amplitude, switching rate, and carrier detuning.
Abstract Single- and double-electron capture processes in Si 4 + + He collisions are investigated using a semiclassical two-active-electron atomic orbital close-coupling method over the impact energy range of 0.1–100 keV u − 1 . A large 12 s 8 p 6 d 4 f expansion basis for Si 4 + is employed to account for electronic correlation and multi-channel coupling effects. The calculated results show that single-electron capture cross sections are about two orders of magnitude larger than double-electron capture cross sections throughout the considered energy region. The dominant single-electron capture into the 3 s state exhibits a pronounced oscillatory structure below 1 keV u − 1 , which originates from channel interference with the entrance channel. In contrast, the 3 p cross sections display a shoulder-like feature, reflecting the transition mechanism evolving from a quasi-molecular character at low energies to an atomic-orbital character at higher impact energies. Electronic correlation is found to have distinct effects on these two dominant capture channels, suppressing the 3 s cross sections at low energies while enhancing the 3 p cross sections over the entire energy range. This indicates that the two-active-electron model provides an improved description of both short-range nonadiabatic transitions and long-range polarization effects associated with the He target. Furthermore, weak channels, including high-lying single-electron capture and double-electron capture, also exhibit complex oscillatory structures at low energies, which arise from multi-channel coupling. These findings highlight the importance of explicit two-electron dynamics in accurately describing state-selective charge transfer in ion-atom collisions.
Abstract Despite extensive studies on the position-space electronic distributions for the ground state of the He atom trapped in an impenetrable spherical cavity, the corresponding momentum-space analysis has received little attention. The present article tries to bridge this gap by adopting an even-powered expansion of correlated coordinates in a Hylleraas basis consistent with the Dirichlet boundary condition. The corresponding momentum-space wavefunction is determined by the 3D Fourier transform of the explicitly correlated position-space wavefunctions. The analytic expression of the momentum-space wavefunction, and thereby the electronic density, allows us to examine the asymptotic limits of the same. With increased compression, the two-particle density distribution changes, and in the high compression regime, a crystalline-like structure in the contour map starts to appear. The corresponding topological complexity varies w.r.t. the cavity radius by maintaining symmetry along the equal momenta line. As a consequence, the one-particle momentum-space density and the derived Compton profile show oscillatory structure in the high-momentum regime. The evaluation of Shannon entropy provides further insights into the problem from the quantum information theoretic point of view. The estimation of position and momentum entanglement entropy measures is carried out here for the first time to exhibit the complete picture of the momentum correlation. Our investigation yields that despite showing all the contrasting differences in various density distributions and statistical information measures of the conjugate position and momentum spaces, the quantum correlation measure in terms of entanglement entropy remains invariant. Additionally, the Compton profiles are theoretically evaluated and subsequently compared with available theoretical and experimental results, demonstrating overall good agreement and consistency.
Abstract High-fidelity entangled-state generation in driven two-atom systems is often optimized at a nominal transition frequency, which can produce control pulses that are fragile against detuning errors and experimental imperfections. To address this limitation, we develop a sampled-detuning quantum optimal-control approach in which different detuning values are treated as control scenarios driven by a common laser field. Time-domain equality constraints, including zero pulse area and fixed fluence, are incorporated directly into the pulse update. The resulting constraint-projected update provides a common ascent direction for the sampled detuning objectives while preserving the imposed pulse constraints. Numerical simulations show that the optimized robust pulses maintain a high target-state population over a wider detuning interval than resonant Gaussian pulses and conventional single-objective optimal pulses. The results further reveal a fluence-bandwidth trade-off for robust plateau formation. Frequency-domain analysis indicates that the enhanced robustness is associated with optimized off-resonant spectral components, and the robustness window can be tuned by selecting the sampled-detuning training range.
Abstract Many light-emitting objects, such as gases, have free charges or ions, and atoms are building blocks of those objects. Therefore, there are charge-atom interactions in those objects. A better understanding of charge-atom interactions will help to understand such objects. Among those objects, many atoms are in excited states, which causes light to be emitted. Highly excited states are called Rydberg states. In this article, we study the few-body charge-atom interactions of two-dimensional configurations, or planar Rydberg-atom/charge geometries. Specifically, we study one positive charge and two atoms, three atoms, four atoms, and five atoms lying on the same plane. In addition, we assume those atoms are in excited states, Rydberg states. Moreover, we investigate the principal quantum number dependence of such interactions. It has been shown that the maximum frequency shift of the n s n s n s + states is proportional to n 6 for an energy level in a certain principal quantum number range. Furthermore, we study the 1 R 2 dependent charge-atom interactions, where R is the distance between one atom and the positive charge.
Abstract Photoionization of hydrogen and argon atoms is investigated under the simultaneous influence of endohedral confinement and Debye plasma screening. Confinement is modeled using a Gaussian annular square well potential representing a diffusive fullerene cage, while plasma effects are introduced through static Debye–Hückel screening of the atomic core. Bound and continuum states are obtained by solving the radial Schrödinger equation within a single-active-electron framework, including spin–orbit coupling to resolve the argon 3 p fine structure. Photoionization cross sections are calculated in the electric dipole approximation using energy-normalized continuum wavefunctions and channel-resolved analysis. In hydrogen, tuning the screening strength drives critical behavior near threshold, leading to quasibound and virtual-state-induced enhancements. In argon, interchannel competition and spin–orbit coupling produce pronounced near-threshold shape resonances governed primarily by the ϵ d continuum channels. The 3 p Cooper minimum exhibits systematic shifts with increasing screening strength, reflecting modifications to the radial dipole matrix element arising from changes in continuum phase accumulation and effective potential structure.
Abstract The scattering of electrons and positrons from neutral Zn atoms is studied in the incident energy range 1 eV to 1 MeV using a relativistic Dirac partial wave method combined with a complex optical-model potential. Within this framework, differential cross sections (DCS), angle-integrated cross sections, and the Sherman function are computed for both projectiles. The calculations reveal four pronounced critical minima (CM) in the electron DCS at ( 11.22 eV , 92.31 ∘ ) , ( 86.09 eV , 147.54 ∘ ) , ( 162.90 eV , 73.69 ∘ ) , and ( 347.10 eV , 124.00 ∘ ) , while no corresponding minima are observed for positron scattering. This difference is mainly due to the absence of exchange effects in the positron case. Analysis shows that the electron CM originate from relativistic interference between spin–orbit interaction channels, which strongly reduces the direct scattering amplitude. Consequently, very strong spin polarization occurs near these minima, with eight of the nine polarization maxima greater than 96 % , whereas positron polarization remains small across the whole energy range. Comparison with available measurements and previous theoretical results demonstrates reasonable agreement.
Abstract A numerical study is presented, based on single-particle collision dynamics, of positron ( e + ) capture in a two-stage buffer gas trapping (BGT) apparatus. The Penning–Malmberg type trap is simulated with a set of voltages (applied to cylindrical electrodes) typical of those used in e + trapping experiments and their applications. With molecular nitrogen as the standard capture gas, we find an overall capture efficiency, ϵ , of 19.3 ± 0.9% at a gas pressure of 2 × 10 − 3 mbar: this is in agreement with observations which find an efficiency of ∼ 20 % at this pressure. We have also investigated trapping at different gas pressures, which show a maximum ϵ of around 30 % ; additionally, we have studied the effects of varying the scattering cross section input to the collisional model. These data are presented and discussed herein, as are results for collision-induced radial expansion rates. Simulations of positron trapping using carbon tetrafluoride and carbon dioxide gases, which are commonly used as positron coolers, found maximum capture efficiencies similar to those observed, at ∼ 13 % and ∼ 6 % respectively. The numerical model was modified to investigate a new trapping geometry in which the two pressure stages of the BGT are no longer aligned coaxially (i.e. non-rotationally-symmetric with respect to the external solenoidal B -field). Without further modification, positrons experience significant magnetron-like E × B -induced losses at the interface of the two stages, but a ∼ 18 % trapping efficiency is found upon optimisation of trap electrode voltages.
Abstract The interaction of propene ( C 3 H 6 ) molecules with energetic projectiles, H + , N + and Ar 2 + , is studied using a recoil ion momentum spectrometer. The delayed dissociation of C 3 H 4 2 + ions, formed after emission of one or more neutral particles from the parent dication C 3 H 6 2 + , is observed. The population of metastable states of C 3 H 4 2 + is inferred, which decay by deprotonation. We observe that the decay of C 3 H 4 2 + ions follows a double exponential function, for experiments conducted with of N + and Ar 2 + projectiles. However, for the experiment conducted with H + projectile, the decay of C 3 H 4 2 + follows a power law. Furthermore, the formation of stable dications C 3 H n 2 + with 2 ⩽ n ⩽ 5 is reported. These dications are formed after emission of one or more neutral particles from the parent dication C 3 H 6 2 + .
The early-phase dynamics of laser-produced plasma (LPP) under nanosecond laser irradiation of aluminum have been investigated using time-resolved optical emission spectroscopy. This study elucidates for the first time the influence of silver nanoparticles (NPs) on the early evolution of LPP. Using a pre-trigger laser pulse, the emission signal is captured at the onset of the plasma, bypassing the internal delay of electronic components. This enables direct probing of the initial stage of plasma which is highly turbulent. The emission is found to be dominated by continuum radiation, primarily arising from bremsstrahlung processes. Electron temperature is estimated by fitting the bremsstrahlung model to the measured spectra, revealing high initial temperatures that decrease rapidly with plasma expansion. In the presence of silver NPs, a significant enhancement in continuum emission is observed, accompanied by an increase in electron number density and a slight decrease in electron temperature. This behavior is due to enhanced laser-target coupling as a result of localized surface plasmon resonance. High electron density leads to more collisional interactions, modifying the energy distribution and deposition within the plasma. These findings provide an insight into early plasma evolution in NP-assisted LPP.
Fractional-order extensions of quantum dynamical equations provide an effective framework for incorporating memory and non-Markovian effects into the description of open quantum systems. In this work we investigate a laser-driven two-level system governed by a fractional generalization of the optical Bloch equations based on Caputo derivatives. The resulting evolution is analyzed in phase space, where temporal memory manifests itself through systematic geometric modifications of the relaxation trajectories. In particular, decreasing the fractional order produces a rotation and contraction of the phase-space spirals, together with a displacement of their effective centers, revealing a consistent reorganization of the dissipative oscillatory dynamics. We further connect this time-domain behavior to experimentally accessible frequency-domain signatures by constructing the incoherent resonance-fluorescence power spectrum from the stationary dipole correlation function. The fractional spectra recover the classical three-peak (Mollow-type) structure in the limit alpha -> 1, while for alpha<1 they exhibit a redistribution of spectral weight accompanied by modified peak localization, sideband separation, and intensity ratios. These results demonstrate how fractional dynamics links the geometry of relaxation to measurable spectral morphology in non-Markovian quantum systems.
Abstract Our work (Ivanov and Kheifets 2025 J. Phys. B: At. Mol. Opt. Phys. 58 205601) contains a typographical error that was inherited from the draft used during the preliminary discussions of the work. This issue might cause confusion and therefore requires clarification.
Abstract In this paper we investigate theoretically Compton ionization of molecules by keV photons. H 2 + is considered here as a test case, at the equilibrium internuclear distance. We consider situations where the A 2 nondipole term dominates over the dipole coupling A . P (where P is the electron momentum operator and A is the vector potential of the field). We investigate various approximative forms for the initial and final continuum states, in particular we focus on the representation of the final continuum states in view of developing a simple and versatile scheme to calculate the differential ionization cross section. In this context, the photoelectron angular distributions are calculated and discussed for various geometries of the Compton process and for different ionization regimes, varying the photon momentum transfer magnitude | Q → | from 1.1 a.u. to 0.01 a.u.
Abstract High-precision time–frequency standards play vital roles in fundamental physics, geodesy, navigation, and communication. This paper reports experimental progress on an optical frequency standard (OFS) based on the 5S 1/2 → 5D 5/2 two-photon transition in 87 Rb. A 1556 nm communication-band laser is frequency-doubled to generate a 778.1 nm clock laser, which excites Rb atoms via counter-propagating beams. The 420 nm fluorescence is collected to obtain a high signal-to-noise-ratio transition spectrum. The effects of laser power and vapor cell temperature on the fluorescence intensity were systematically investigated. The impact of laser beam waist and atomic collisions on frequency shifts was analyzed. Results show that replacing a tightly focused beam with a large collimated one reduced the laser power-induced frequency shift by two orders of magnitude. Furthermore, increasing the vapor temperature enhances collision-induced frequency shifts, adversely affecting long-term stability. Under optimized conditions, the system achieved a short-term fractional frequency stability of 2.6 × 10 −13 at 1 s, reaching 5.3 × 10 −15 at 10 000 s. This work lays a critical technical foundation for the development of compact and high-performance OFSs.
Optomechanics has become a very active area of research in recent years and has attracted significant interest in both theoretical and experimental studies. In this work, we theoretically investigate optomechanically induced transparency (OMIT) using a hybrid system consisting of two coupled optical cavities, each interacting with a spin ensemble. The cavities are coherently driven by a strong control field and a weak probe field. We analytically calculate the transmission spectrum of the coupled spin-cavity system and analyze the dynamics of the system. The obtained transmission response shows clear signatures of multi-window OMIT, which arises from coherent interference between the hybridized normal modes. Our results indicate that the presence of spin ensembles in both cavities significantly enhances the transparency behavior and provides additional tunable parameters to control the OMIT windows. In particular, the transmission spectrum and the shape of the transparency profile can be controlled by the spin-cavity interaction and the inter-cavity coupling strength J. Furthermore, the inter-cavity tunneling rate, spin decoherence, and spin-cavity coupling strength strongly influence the transparency properties. Overall, this study highlights the potential of spin-based multi-cavity optomechanical systems for coherent optical control and tunable quantum interference.
Optimal molecular orientation is achieved through a hybrid scheme comprising a non-resonant slow turn-on and rapid turn-off (STRT) laser pulse and time-delayed resonant THz pulses. The adiabatic pre-excitation via a non-resonant STRT laser pulse provides a broad rotational population distribution and a uniform relative phase distribution. The influence of both laser and molecular parameters on the realization of the adiabatic process is discussed in detail. Within this combined framework, the subsequent resonant excitation process can be simplified to a set of independent two-level systems. This allows for the analytical determination of the required THz pulse peak amplitude based on the target population distribution, ensuring a robust and optimized control strategy.
