Excited Atomic States Research Articles

Relativistic hyperpolarizabilities for atomic H, Li, and Be+ systems

Abstract For atoms in external electric fields, the hyperpolarizabilities are the coefficients describing the nonlinear interactions contributing to the induced energies at the fourth power of the applied electric fields. Accurate evaluations of these coefficients for various systems are crucial for improving precision in advanced atom-based optical lattice clocks and for estimating field-induced effects in atoms for quantum information applications. However, there is a notable scarcity of research on atomic hyperpolarizabilities, especially for the relativistic realm. Our work addresses this gap by establishing a novel set of alternative formulas for the hyperpolarizability based on fourth-order perturbation theory. These formulas offer a more reasonable regrouping of scalar and tensor components compared to previous formulas, thereby enhancing their correctness and applicability. To validate our formulas, we perform the calculations for the ground and low-lying excited pure states of few-electron atoms H, Li, and Be+. The highly accurate results obtained for the H atom could serve as benchmarks for further development of other theoretical methods.

Functionality enhancement of pea protein isolate through cold plasma modification for 3D printing application

Pea protein isolate (PPI) is a valued sustainable protein source, but its relatively poor functional properties limit its applications. This study reports on the effects of cold argon plasma (CP) treatment of a 15 % (w/w) PPI solution on the functionality, structure, and oxidative characteristics of PPI, as well as its application in 3D-printed plant-based meat. Results indicate that hydroxyl radicals and high-energy excited-state argon atoms are the primary active substances. A decrease in free sulfhydryl content and an increase in carbonyl content were observed in treated PPI, indicating oxidative modification. Compared to the control group, the gel strength of PPI was increased by 62.5 % and the storage modulus was significantly improved after 6 min treatment, forming a more ordered and highly cross-linked 3D gel network. Additionally, CP significantly improved the water-holding capacity, oil-holding capacity, emulsifying activity, and emulsion stability of PPI. The α-helix and random coil content in PPI decreased, while the β-sheet content increased, resulting in a more ordered secondary structure after CP treatment. Compared to untreated PPI, the consistency coefficient (K) increased from 36.00 to 47.68 Pa·sn. The treated PPI exhibited higher apparent viscosity and storage modulus and demonstrated better 3D printing performance and self-supporting ability. This study demonstrates that CP can significantly enhance the functional properties of PPI, providing great potential and prospects for improving the printability of 3D printing materials and developing plant protein foods with low-allergenicity.

Finite Nuclear Size Effect on the Relativistic Hyperfine Splittings of 2s and 2p Excited States of Hydrogen-like Atoms

Hyperfine splittings play an important role in quantum information and spintronics applications. They allow for the readout of the spin qubits, while at the same time providing the dominant mechanism for the detrimental spin decoherence. Their exact knowledge is thus of prior relevance. In this work, we analytically investigate the relativistic effects on the hyperfine splittings of hydrogen-like atoms, including finite-size effects of the nucleis’ structure. We start from exact solutions of Dirac’s equation using different nuclear models, where the nucleus is approximated by (i) a point charge (Coulomb potential), (ii) a homogeneously charged full sphere, and (iii) a homogeneously charged spherical shell. Equivalent modelling has been done for the distribution of the nuclear magnetic moment. For the 1s ground state and 2s excited state of the one-electron systems H1, H2, H3, and He+3, the calculated finite-size related hyperfine shifts are quite similar for the different structure models and in excellent agreement with those estimated by comparing QED and experiment. This holds also in a simplified approach where relativistic wave functions from a Coulomb potential combined with spherical-shell distributed nuclear magnetic moments promises an improved treatment without the need for an explicit solution of Dirac’s equation within the nuclear core. Larger differences between different nuclear structure models are found in the case of the anisotropic 2p3/2 orbitals of hydrogen, rendering these excited states as promising reference systems for exploring the proton structure.

Exploration of a vapor cell optical frequency standard scheme implemented using Doppler-free spectroscopy.

We implement a compact optical frequency standard scheme with laser frequency locked to the 5S1/2 (F = 2) - 6P3/2 (F' = 3) transition of the second excited state of 87Rb atoms in a 3 mm cubic glass cell, using a Doppler-free saturated absorption spectroscopy. The experimental results show the frequency stability at the level of 2.2 × 10-12 at 1 s. Furthermore, we conduct an experimental study on the effect of a repump laser on the frequency performance of the saturated absorption spectroscopy optical frequency standard, providing valuable experimental results with reference values for implementing this type of optical atomic clock.

Magnetically induced perfect absorption and slow light trapping in a double-cavity structure with strontium atoms.

Photon manipulation using quantum interference is crucial for understanding the physical meaning of optical phenomena and promoting photonic quantum technologies. Here, two fundamentally optical phenomena, including coherent perfect absorption (CPA) and slow light trapping, are proposed simultaneously in a double-cavity structure with strontium atoms. When two counterpropagating probe fields are injected into the coupled atom-cavity system, we demonstrate that double-cavity-mediated interference assisted by the atomic Zeeman effect can be utilized to control multiple mode splitting in the transmission light. According to the analytical CPA criterion, we report that these splitting modes in the output spectra can be completely absorbed, forming multiple perfect or nearly perfect absorption. More importantly, we illustrate that sizable intracavity field localization can be found at the multiple CPA points, as an amount of system energy stores in the intracavity fields and the atomic excited states. In this case, the dispersion property of the system enables the localized intracavity fields to operate in the long-lived slow-light regime, whose group delay is tuned to be in the order of microseconds.

Geometric properties of the first singlet S-wave excited state of two-electron atoms near the critical nuclear charge

Abstract In this work the geometric structure parameters and radial density distribution of 1s2s 1 S excited state of the two-electron atomic system near the critical nuclear charge Z c were calculated in detail under tripled Hylleraas basis set. Contrary to the localized behavior observed in the ground and the doubly excited 2p 2 3 P e states, for this state our results identify that while the behavior of the inner electron increasingly resembles that of a hydrogen-like atomic system, the outer electron in the excited state exhibits diffused hydrogen-like character and becomes perpendicular to the inner electron as nuclear charge Z approaches Z c. This study provides insights into the electronic structure and stability of the two-electron system in the vicinity of the critical nuclear charge.

Properties of the ionization region in a magnetron plasma at gas-aggregation-source-relevant pressure regime explored using a global model

A global (volume averaged) model is developed for the ionization region (IR) of a gas aggregation source (GAS) plasma. The case of using argon gas and a copper target is considered. The model describes the densities of thermal and hot electrons, argon and copper ions, copper atoms and argon atoms in different excited states, the temperature of thermal electrons, the kinetic energies of the ions with which they bombard the target, the sheath width near the target cathode and the energy fluxes by different plasma species to a planar probe in the IR. Also, the fraction of input power is estimated which is dissipated to energize the thermal electrons in the IR. The gas discharge properties are analyzed for different pressures and discharge currents under conditions corresponding to the experimental conditions (Gauter et al 2018 J. Appl. Phys. 124 073301). The calculated pressure- and current-dependences for the GAS properties are used to explain the measured dependences for the deposition rate and the energy flux. It is found that the deposition rate increases with increasing discharge current because of the growth of currents of copper atoms and ions. With increasing pressure, the rate decreases due to drop of the densities of copper atoms and ions because of decreasing the kinetic energies of the ions with which they bombard the target. The model indicates that in the gas-aggregation-source relevant pressure regime, the energy flux by ions dominates over the energy fluxes of other plasma species.

Effect of relaxation on the transfer of orbital angular momentum via four-wave mixing process in the four-level double lambda atomic system

In this work, we have theoretically studied the resonant four-wave mixing (FWM) in a four-level double Lambda (Λ) atomic system in connection with orbital angular momentum (OAM) transfer from probe to generated signal beam. The effect of the relaxation process is studied in the forward as well as backward FWM. Based on the semiclassical model, our analysis shows a strong dependence of conversion efficiency on spontaneous decay and decoherence rates. From the intensity and phase profile, we have confirmed the OAM nature of the generated signal beam. The physical explanation is given for the dependence of efficiency on the decay rate of the excited atomic state. We have shown that decoherence present in the system always leads to a deleterious effect on conversion efficiency. Our presentation treats forward and backward FWM in a unified way in the context of OAM transfer and sheds light on the parameter dependence of conversion efficiency.

Photoionization cross sections measurements of the excited states of lutetium and ytterbium in the near threshold region.

In this work, the threshold photoionization cross sections from the excited states of lutetium and ytterbium atoms were investigated by the laser pump-probe scheme under the condition of saturated resonant excitation. We obtained the resonance enhanced multiphoton ionization spectra of the lutetium and ytterbium atoms of the lanthanide metals in the range of 307.50-312.50nm and 265.00-269.00nm, respectively; the photoionization cross sections of the 5d6s(1D)6p(2D05/2) and 5d6s(3D)6p(2P01/2) states of lutetium and the 4f13(2F0)5d6s2(J = 1) states of ytterbium above threshold regions (0.4-1.6eV) were measured, and measured values ranged from 2.3 ± 0.2 to 17.7 ± 1.5 Mb.

Dipolar focusing in laser-assisted positronium formation

We consider positronium formation in collisions of positrons with excited hydrogen atoms H(n) in an infrared laser field theoretically. This process is assisted by the dipolar focusing effect: a positron moving in a superposition of a laser field and the dipolar field can approach the atomic target even if its trajectory starts with a very large impact parameter, leading to a significant enhancement of the Ps formation cross section. The classical trajectory Monte Carlo method, which is justified for n⩾3 , allows efficient calculation of this enhancement. A similar effect can occur in collisions of positrons with other atoms in excited states, which can lead to improvements in the efficiency of positronium formation.

Ultrafast quantum control of atomic excited states via interferometric two-photon Rabi oscillations

Quantum-state manipulation through coherent interaction with a radiation field is a fundamental process with broad implications in quantum optics and quantum information processing. However, current quantum control methods are limited by their operation at Rabi frequencies below the gigahertz range, which restricts their applicability to systems with long coherence times. To overcome this limitation, alternative approaches utilizing ultrafast driving lasers have garnered great interest. In this work, we demonstrate two-photon Rabi oscillations in the excited states of argon operating at terahertz frequencies driven by ultrafast laser pulses. Leveraging quantum-path interferometry, we are able to measure and manipulate both the amplitudes and phases of the transition dipoles by exploiting the intensity and polarization state of the driving laser. This precise control enables femtosecond population transfer and coherent accumulation of geometric phase. Our findings provide valuable insights into the all-optical manipulation of extreme-ultraviolet radiations and demonstrate the possibility of ultrafast quantum control through interferometric multiphoton transitions.

Coherent interface between optical and microwave photons on an integrated superconducting atom chip

Sub-wavelength arrays of atoms exhibit remarkable optical properties, analogous to those of phased array antennas, such as collimated directional emission or nearly perfect reflection of light near the collective resonance frequency. We propose to use a single-sheet sub-wavelength array of atoms as a switchable mirror to achieve a coherent interface between propagating optical photons and microwave photons in a superconducting coplanar waveguide resonator. In the proposed setup, the atomic array is located near the surface of the integrated superconducting chip containing the microwave cavity and optical waveguide. A driving laser couples the excited atomic state to Rydberg states with strong microwave transition. Then the presence or absence of a microwave photon in the superconducting cavity makes the atomic array transparent or reflective to the incoming optical pulses of proper frequency and finite bandwidth.

Gailitis–Damburg Oscillations in the Three-Body e–e+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar {p}$$\\end{document} System

We study the near threshold behavior of cross sections of low-energy antiproton scattering off the ground and excited states of positronium with zero total orbital momentum L = 0. In our computational experiment, the existence of singularities called the Gailitis–Damburg oscillations above the thresholds of excited states of positronium and antihydrogen atoms is confirmed. In the future the obtained results can be useful for developing proposals for improving the conditions of experiments with antimatter.

Investigation on plasma ionization process of a micro-cathode arc thruster

Micro-cathode arc thrusters (μCATs) are space propulsion options suitable for microspacecraft, and have recently attracted much attention because of their low electrical power requirements and simple, compact propellant systems. The plasma ionization process, however, is not currently well understood. In this study, a μCAT prototype was designed with the use of different specific materials for each component, enabling the study of the ionization process from the emissive light of excited and ionized states from different elements. ICCD emission spectroscopy and scanning monochromator measurements are conducted inside the electrode channel of a μCAT with a coaxial configuration. The excited state atomic spectral results and ionization state spectral results give us a comprehensive understanding of the behavior of neutral particles and ions during the discharge process of the μCAT. The ionization sequence follows in the order of C+, Al+, Ti+, Cu+, and Ti2+. From the duration of the spectral lines, C I has the shortest duration (16.9 μs), which shows that the ablation of the conductive film is mainly concentrated during the first half of the discharge, while anode and cathode ionization occur over the entire discharge duration. Additionally, Al+ ionization is observed during the discharge process, showing that part of the discharge energy is expended in ionizing the thruster outer shell, resulting in efficiency loss. An ionization ratio of k is proposed in this work to represent the relative ionization of the conductive film and cathode material, aiding us in determining the optimal operation conditions for lifetime extension.

Generating a Sustained Oxygen-Stable Atomic Concentration in a High-Temperature Gas Effect Investigation.

Modulated laser absorption spectroscopy is an ideal technique for evaluating flow-field parameters and determining flow-field quality by measuring the atoms dissociated in high-temperature environments. However, to obtain the absolute number density of atoms in the flow field, it is necessary to compare the measured modulated absorption spectroscopy signal with a known atomic concentration and establish a quantitative relationship through concentration calibration. Nevertheless, it remains a challenging task to prepare transient atomic samples with known concentrations that meet the calibration requirements. This study utilized the alternating-current glow discharge technique to dissociate oxygen in the air flow, resulting in the continuous generation of oxygen atoms. The absolute number densities of the generated oxygen atoms were determined by measuring the direct absorption spectra of centered on 777 nm for oxygen atoms. The number densities of the generated atoms were finely tuned by adjusting the discharge parameters. Throughout the 120-min continuous operation of the discharge system, the concentration of excited-state oxygen atoms remained stable within the range of (2.51 ± 0.02) × 108 cm-3, demonstrating the remarkable stability of the transient atomic concentration generated by the glow discharge plasma. This observation suggests that the generated atoms can be utilized as a standardized atomic sample of known concentration for absolute concentration calibration purposes.

A superradiant two-level laser with intrinsic light force generated gain

The implementation of a superradiant laser as an active frequency standard is predicted to provide better short-term stability and robustness to thermal and mechanical fluctuations when compared to standard passive optical clocks. However, despite significant recent progress, the experimental realization of continuous wave superradiant lasing still remains an open challenge as it requires continuous loading, cooling, and pumping of active atoms within an optical resonator. Here we propose a new scenario for creating continuous gain by using optical forces acting on the states of a two-level atom via bichromatic coherent pumping of a cold atomic gas trapped inside a single-mode cavity. Analogous to atomic maser setups, tailored state-dependent forces are used to gather and concentrate excited-state atoms in regions of strong atom-cavity coupling while ground-state atoms are repelled. To facilitate numerical simulations of a sufficiently large atomic ensemble, we rely on a second-order cumulant expansion and describe the atomic motion in a semi-classical point-particle approximation subject to position-dependent light shifts which induce optical gradient forces along the cavity axis. We study minimal conditions on pump laser intensities and detunings required for collective superradiant emission. Balancing Doppler cooling and gain-induced heating we identify a parameter regime of a continuous narrow-band laser operation close to the bare atomic frequency.

The synergistic effect of radical and non-radical processes on the dephosphorization of dimethoate by vacuum ultraviolet: The overlooked roles of singlet oxygen atom and high-energy excited state

Organophosphorus pesticides are extensively utilized worldwide, but their incomplete dephosphorization poses significant environmental risks. This study investigates the dephosphorization of dimethoate (DMT), a representative organophosphorus pesticide, using a vacuum ultraviolet system. Surprisingly, in addition to hydroxyl radicals (•OH), non-radical processes such as photoexcitation and singlet oxygen atoms (O(1D)) exert more significant effects on DMT dephosphorization. The degradation kinetics of DMT demonstrate a perfect linear correlation with the radical yield in both UV-based and VUV-based advanced oxidation processes (AOPs), with greater efficacy of radical attack observed in the VUV system. This heightened efficiency is attributed to the excitation of DMT to a high-energy excited state induced by UV185 radiation. Additionally, •OH alone is inadequate for achieving complete dephosphorization of DMT. The Fukui index and singly occupied orbital (SOMO) analysis reveal that the O(1D) generated by UV185-induced photolysis of O2 exhibits exceptional selectivity towards P=S bonds, thereby playing an indispensable role in the dephosphorization process of DMT. This study highlights the significant contribution of non-radical pathways in DMT dephosphorization by VUV, which holds great implications for the advancement of photochemical-based AOPs.

Nonlocal Static and Dynamical Vacuum Field Correlations and Casimir-Polder Interactions.

In this review, we investigate several aspects and features of spatial field correlations for the massless scalar field and the electromagnetic field, both in stationary and nonstationary conditions, and show how they manifest in two- and many-body static and dynamic dispersion interactions (van der Waals and Casimir-Polder). We initially analyze the spatial field correlations for noninteracting fields, stressing their nonlocal behavior, and their relation to two-body dispersion interactions. We then consider how field correlations are modified by the presence of a field source, such as an atom or in general a polarizable body, firstly in a stationary condition and then in a dynamical condition, starting from a nonstationary state. We first evaluate the spatial field correlation for the electric field in the stationary case, in the presence of a ground-state or excited-state atom, and then we consider its time evolution in the case of an initially nonstationary state. We discuss in detail their nonlocal features, in both stationary and nonstationary conditions. We then explicitly show how the nonlocality of field correlations can manifest itself in van der Waals and Casimir-Polder interactions between atoms, both in static and dynamic situations. We discuss how this can allow us to indirectly probe the existence and the properties of nonlocal vacuum field correlations of the electromagnetic field, a research subject of strong actual interest, also in consequence of recent measurements of spatial field correlations exploiting electro-optical sampling techniques. The subtle and intriguing relation between nonlocality and causality is also discussed.

Faraday polarization rotation control of 1529 nm wavelength between excited states of Rb atoms

Faraday polarization rotation control of 1529 nm wavelength has been obtained using the 5S1/2→5P3/2→4D5/2 transition of rubidium. The traditional off-resonant polarization rotation method commonly used in the Faraday effect for direct transitions of atoms is not applicable to the transitions between excited states. In this study, we proposed a near-resonant polarization rotation method using the Faraday effect between excited states of atoms, by which the polarization rotation of the rubidium 5P3/2→4D5/2 transition can be controlled from 0° to 90° with low distortion. The 780 nm pump light corresponding to the 5S1/2→5P3/2 transition can also be used simultaneously as a control source to manipulate the polarization state of the 1529 nm optical signal.

Ultrafast Dynamics of the Medicinal Pigment Curcumin inside the Imidazolium Surface Active Ionic Liquid Containing Giant Vesicles and White Light Generation via Triple-FRET Technique.

The naturally occurring yellow polyphenolic medicinal pigment curcumin shows ultrafast dynamics in the excited states. These ultrafast dynamics are strongly influenced by the rigidity of the environments of the systems. The present investigation unveils the ultrafast excited-state intramolecular hydrogen atom transfer (ESIHT) (which is involved in the antioxidant mechanism) and the solvation dynamics of curcumin inside the imidazolium surface active ionic liquid (SAIL), 1-hexadecyl-3-methylimidazolium chloride ([C16mim]Cl) micelle, and giant vesicles after introducing sorbitan monoesters (Span 20 and Span 80) in the aqueous medium. Interestingly, the short hydrocarbon chain containing Span 20 forms smaller, less rigid vesicles, and the long hydrocarbon chain containing Span 80 forms larger, more rigid giant vesicles after being assembled with [C16mim]Cl. The ESIHT and the solvation dynamics are slower in Span 80, containing rigid vesicles, than that in Span 20, comprising less rigid vesicles. Finally, we have established a three-component fluorescence resonance energy transfer (Triple-FRET) system to generate white light (WL) in the micelle and giant vesicles. Here the hydrophobic dye 1,6-diphenyl-1,3,5-hexatriene (DPH) acts as the donor, and the hydrophilic anticancer drug doxorubicin hydrochloride (DOX) serves as the acceptor along with the intermediate donor, curcumin. At a specific combination of the concentrations of these dyes in a particular self-assembled system, WL is generated due to the triple-FRET phenomena.