Quantum Electrodynamic Effects Research Articles

Light Concentration by Metal-Dielectric Micro-Resonators for SERS Sensing.

Metal-dielectric micro/nano-composites have surface plasmon resonances in visible and near-infrared domains. Excitation of coupled metal-dielectric resonances is also important. These different resonances can allow enhancement of the electromagnetic field at a subwavelength scale. Hybrid plasmonic structures act as optical antennae by concentrating large electromagnetic energy in micro- and nano-scales. Plasmonic structures are proposed for various applications such as optical filters, investigation of quantum electrodynamics effects, solar energy concentration, magnetic recording, nanolasing, medical imaging and biodetection, surface-enhanced Raman scattering (SERS), and optical super-resolution microscopy. We present the review of recent achievements in experimental and theoretical studies of metal-dielectric micro and nano antennae that are important for fundamental and applied research. The main impact is application of metal-dielectric optical antennae for the efficient SERS sensing.

Universal behavior of diatomic halo states and the mass sensitivity of their properties

The scattering and spectroscopic properties of molecular halo states can serve as sensitive probes of the constancy of the electron-to-proton mass ratio . Since halo states are formed by resonant s-wave interactions, their properties exhibit universal correlations that are fairly independent of the interactions at short distances. For diatomic molecules, these properties depend on a single-parameter only, and so this ‘universality’ means that all the characteristics of a diatomic halo state can be determined with high precision if only one-parameter is accurately known. Furthermore, this knowledge can be used to establish the respective property mass sensitivities for investigating the stability of β. Here, we show for the halo states of the helium dimers that the relationship between the probed properties and their mass sensitivity can be derived from numerically exact solutions of suitable radial Schrödinger equations for a set of effective potential energy curves. The resulting relations exhibit a weak dependence on the short-range part of the used potentials and a near-negligible dependence on the ‘higher-order’ nonadiabatic, relativistic, quantum electrodynamical and residual retardation effects. The presented approach is thus a robust alternative to other literature approaches, particularly in cases where a lack of experimental data prevents an accurate interaction potential from being determined.

Interacting fermions in an expanding spacetime

We evaluate the effect of quantum electrodynamics on the correlations between Dirac field modes corresponding electron-positron pairs of opposite momenta generated by expansion of an asymptotically flat Friedmann-Robertson-Walker (FRW) universe. The mutual information of out-going electron-positron pairs is evaluated to leading order in the coupling strength and compared with the free case. It is shown a decrease in the mutual information between the electron and positron. In addition, it is found that the change in the electron-positron mutual information depends on how the momentum is distributed between the positron and photon modes.

A study for hydrogen-like lawrencium

Studying hydrogenic ions with high Z is an occasion to understand atomic structure. It also provides a reliable test of methods used to determine atomic structures. Many fields and applications require precise atomic data. For this reason, a hydrogen-like study is performed for lawrencium (Lr102+, Z = 103). The energy levels of hydrogen-like lawrencium are calculated with both multiconfiguration Hartree–Fock (MCHF) and multiconfiguration Dirac–Fock (MCDF) methods. The calculations contain Breit–Pauli relativistic corrections in MCHF calculation and the transverse photon and quantum electrodynamics (QED) effects in MCDF calculation along with electron correlations. In addition, some transition parameters (wavelengths, λ, logarithmic weighted oscillator strengths, log(gf) value, and transition probabilities, Aki) for allowed (E1) and forbidden (E2 and M1) transitions are investigated. The results from this study are compared with only a few theoretical works, but there is no available experimental data yet for Lr102+.

Relativistic calculations on the x-ray satellites of platinum with multiply ionized L shell

The energies, electric dipole rates and oscillator strengths of Kα x-ray satellites from 1s–2p transitions in platinum with a single vacancy in the K shell and variously ionized L shell are calculated using multi-configuration Dirac Fock wavefunctions with the inclusion of Breit interaction and quantum electrodynamics effects. The computations have been performed for low ionized (Pt1+–Pt6+) and also for highly ionized (Pt69+–Pt77+) Pt. As Kα x-ray satellites with spectator vacancies only in the L shell, to the best of our knowledge, have been studied for the first time, to check the accuracy of the present work, calculations have also been performed for H-, He-, Li-, Be-, B- and F-like Pt for which theoretical data for comparison exist. The purpose of choosing a high Z element is that the detailed decay properties of heavy ions due to systematic 1s–2p transitions with spectator vacancies in the L shell using fully relativistic treatment are unexplored and the increasing need for reliable data from such ions in various applications that are under investigations in recent years. Also, for heavy ions like Pt, the contribution from the competing non-radiative transitions is less and hence the atomic properties are largely due to radiative transitions. The K X ray satellite energies, rates and resonance photo- ionization cross sections from H-, He-, Li-, Be-, B- and F-like Pt are compared with available data.

In My Element: How did I land in a gold mine?

The In My Element series celebrates the personal accounts from Chemistry – A European Journal Editorial Board members for the 2019 International Year of the Periodic Table. In this contribution, Pekka Pyykkö gives his story on gold. In late 1975 Jean-Paul Desclaux and I had developed a fully relativistic (or non-relativistic) quantum chemical approach for hydride molecules, MHn. It converged well at short M−H bond lengths so we needed a molecule in which that was indeed the case. It turned out that AuH was one, so we tried it and it worked. There was a sizable relativistic contraction of the Au−H bond length. Moreover, relativistic effects explained most of the differences from AgH to AuH. We had the audacity to say that “the chemical difference between silver and gold may mainly be a relativistic effect”1 (see Figure 1). Earlier band-structure studies on Au metal had indicated large relativistic effects2 but in a germ, there may have been a trace of originality in our coupling of chemical periodicity to relativity. That turned out to be a scientific gold mine. Because the shell structure of gold has a local maximum of valence-shell relativistic effects, which normally scale as Z2, that was a lucky start. The relativistic (R) and non-relativistic (NR) orbital energies of the diatomic AgH and AuH (a.u. is atomic units). Data from Ref. 1. Figure from Ref. 17. A decade later, when lecturing at the Technical University of Munich, I learned from Hubert Schmidbaur about a strange attraction between two or more closed-shell AuI cations.3 They had both crystallographic and NMR evidence for it. Both cations carried a positive charge and had no open-shell electrons to make covalent bonds with. Yet they enjoyed an “aurophilic attraction” comparable in strength with a good hydrogen bond. Our explanation for it was a dispersion-type van der Waals interaction.4 Although other mechanisms also may contribute, for example electrostatic multipole interactions or induction,5-7 this is at least a partial explanation. That dispersion-type interaction is also comparable for silver,8, 9 and thus not specific for gold. We are not aware of a known case in which a suggested 6s–6p–5d hybridization10 would be sufficient to yield an observable attraction. Moreover, certain main-group elements also show it. Not only is gold a laboratory of relativistic quantum chemistry. Also, quantum electrodynamic (QED) effects can be seen in the ionization potential and electron affinity of the Au atom by pushing the current theories to their limits.11 Predicting new species with Au was a third aspect. Two examples were the first noble-metal−noble-gas bond12 in AuXe+, observed in mass-spectroscopy, or the predicted nanocluster WAu12,13 also subsequently made.14 Among novel covalent bonds, take the newly prepared unbridged AuII−AuII bonds.15 Both homogeneous and heterogeneous catalysis involving gold have become vast fields. Partially inspired by this application, the studies of both naked and ligand-covered gold nanoclusters are being intensively studied.16 Thus, keeping an eye on the theoretical chemistry of gold is a very good idea.17-20 Position Professor Emeritus of Chemistry E-mail [email protected] Homepage www.chem.helsinki.fi/∼pyykko ORCID 0000-0003-1395-8712 Education University of Turku, Finland, M.Sc. 1964, Ph.D. 1967. Post-doc at Aarhus, Denmark 1968–69 Post-doc at Gothenburg, Sweden 1969–70 Awards A.I. Virtanen Prize 1997, E.J. Nyström Prize 1998 decorated by President of Finland (FVR R I, 1995) Humboldt Prize 2002, Palmes Académiques (France) 2009 Schrödinger medal 2012 Honorary Fellow of Chinese Chemical Society 2012 Research interests Quantum chemistry of heavy elements Recently: simple models for eutectics

The g factor of highly charged ions

Recent years have witnessed a remarkable improvement in the theoretical description of bound-electron g factors, paralleled with a quantum jump in the experimental accuracy in the investigation of these quantities. In the present article we give a brief summary of the latest developments, with emphasis on the influence of quantum electrodynamic and nuclear effects on the g factor of few-electron highly charged ions, and on the possible determination of fundamental constants.

Energies, wavelengths, transition probabilities, and oscillator strengths for electric dipole transitions of Na-like and Mg-like mercury

We have reported atomic data including energies and electric dipole (E1) transition parameters, such as wavelengths, transition probabilities (or rates), and weighted oscillator strengths, for Na-like and Mg-like mercury (Hg69+ and Hg68+) using the AUTOSTRUCTURE atomic code, which includes Breit and quantum electrodynamics effects as well as correlation developed by Badnell. We have compared our results with the available theoretical results in the literature. Also, we have presented new results where no other theoretical and experimental results are available.

Collimated ultrabright gamma rays from electron wiggling along a petawatt laser-irradiated wire in the QED regime

Even though high-quality X- and gamma rays with photon energy below mega-electron volt (MeV) are available from large-scale X-ray free electron lasers and synchrotron radiation facilities, it remains a great challenge to generate bright gamma rays over 10 MeV. Recently, gamma rays with energies up to the MeV level were observed in Compton scattering experiments based on laser wakefield accelerators, but the yield efficiency was as low as [Formula: see text], owing to low charge of the electron beam. Here, we propose a scheme to efficiently generate gamma rays of hundreds of MeV from submicrometer wires irradiated by petawatt lasers, where electron accelerating and wiggling are achieved simultaneously. The wiggling is caused by the quasistatic electric and magnetic fields induced around the wire surface, and these are so high that even quantum electrodynamics (QED) effects become significant for gamma-ray generation, although the driving lasers are only at the petawatt level. Our full 3D simulations show that directional, ultrabright gamma rays are generated, containing [Formula: see text] photons between 5 and 500 MeV within a 10-fs duration. The brilliance, up to [Formula: see text] photons [Formula: see text] per 0.1% bandwidth at an average photon energy of 20 MeV, is second only to X-ray free electron lasers, while the photon energy is 3 orders of magnitude higher than the latter. In addition, the gamma ray yield efficiency approaches 10%-that is, 5 orders of magnitude higher than the Compton scattering based on laser wakefield accelerators. Such high-energy, ultrabright, femtosecond-duration gamma rays may find applications in nuclear photonics, radiotherapy, and laboratory astrophysics.

Testing atomic wave functions in the nuclear vicinity: The hyperfine structure with empirically deduced nuclear and quantum electrodynamic effects

Calculations of the magnetic hyperfine structure rely on the input of nuclear properties -- nuclear magnetic moments and nuclear magnetization distributions -- as well as quantum electrodynamic (QED) radiative corrections for high-accuracy evaluation in heavy atoms. The uncertainties associated with assumed values of these properties limit the accuracy of hyperfine calculations. For example, for the heavy alkali-metal atoms Cs and Fr, these uncertainties may amount collectively to almost 1\% or 2\%, respectively. In this paper we propose a method for removing the dependence of hyperfine structure calculations on assumed values of nuclear magnetic moments and nuclear magnetization distributions by determining these effects empirically from measurements of the hyperfine structure for high states. The method is valid for $s$, $p_{1/2}$, and $p_{3/2}$ states of alkali-metal atoms and alkali-metal-like ions. We have shown that for $s$ states the dependence on QED effects may also be removed to high accuracy. The ability to probe the electronic wave functions, through hyperfine comparisons, with significantly increased accuracy is important for the analysis of atomic parity violation measurements and may enable the accuracy of atomic parity violation calculations to be improved. More broadly, it opens the way for further development of high-precision atomic many-body methods.

Breit and QED Effects in Spectra of the 4s2 1S0−4s4p 3P1,1P1 Transitions in the Zn Sequence

The 4s2–4s4p E1 transitions for Zn-like ions from Z in the range 30–92 are calculated using the multiconfi guration Dirac–Hartree–Fock (MCDHF) method. The results obtained are in good agreement with other theoretical and experimental data and demonstrate the applicability of this method to high-precision atomic structure calculations of both few-electron systems and large atomic systems, such as Zn-like ions, along the entire isoelectronic sequence. We also report herein the calculations of many-electron quantum electrodynamic (QED) and Breit effects for the 3P0, 3P1, 3P2, and 1P1 states for all Zn-like ions in the range 30 ≤ Z ≤ 100.

Accurate evaluation of the conditions for generation of quantum effects in relativistic interactions between laser and electron beams

AbstractThe quantum behavior of the system composed of an electron in an electromagnetic field is described by the Dirac equation, whose solution is a wave function represented by a column matrix with four components. We prove, without using any approximation, that these components can be put in a form which reveals directly the values of the electron energy, laser beam intensity, or amplitude of the electric field intensity, for which the quantum electrodynamics effects are generated. Our results are in good agreement with the experimental data reported in the literature. We prove that the four components of the wave function verify the continuity equation of quantum electrodynamics. Our treatment is in good agreement with the Compton relation. We show that the interaction of electrons with laser beams could be modeled using classical approaches regardless of the laser beam intensity as long as the electrons are non-relativistic, in agreement with published experimental data.

Energy Levels, Radiative Rates, and Lifetimes for Transitions in Fe XIV

Energy levels, transition rates, and lifetimes are reported for the low-lying 129 levels of Fe XIV, belonging to the n = 3 states (1s22s22p6)3s23p, 3s3p2, 3s23d, 3p3, 3s3p3d, 3p23d, 3s3d2, and 3p3d2. High-accuracy calculations have been performed as benchmarks in the request for accurate treatments of relativity, electron correlation and quantum electrodynamic (QED) effects in multi-valence-electron systems. The calculated energy levels are in excellent agreement with the experimental results and the experimentally compiled energy values, of the National Institute for Standards and Technology wherever available. The calculated values including core–valence correlation are found to be in good agreement with other theoretical and experimental values.

Proposal of highly accurate tests of Breit and QED effects in the ground state 2p5 of the F-like isoelectronic sequence

We propose that the ground term transition, 2p5P3/22-P1/22, for ions in the F-like isoelectronic sequence could be used to accurately test current methods to compute Breit and quantum-electrodynamic (QED) effects. These systems are of interest since correlation is small due to what we will label Layzer quenching. Using the multiconfiguration Dirac-Hartee-Fock method, we investigate how correlation, Breit and QED corrections vary along the sequence and show that QED dominates over correlation already for Z≈20. We also investigate the behavior of different QED effects as a function of the nuclear charge and find that the self-energy dominates for the mid-Z range (40-80), but then decreases to change sign for Z≈90. For a few elements between Z=85 and 90 the vacuum polarization is the leading term, while for higher Z the two QED contributions cancel. This opens up the possibility for these ions to carefully test the frequency-dependent transverse photon correction. The uncertainties of the treatment of the well-understood frequency-independent Breit correction and correlation are expected to be at least three orders of magnitude smaller than the QED and frequency-dependent transverse photon corrections for high Z. In this work we also compare and evaluate the results from three different methods to compute self-energies. (Less)

Testing Quantum Electrodynamics in the Lowest Singlet State of Neutral Beryllium-9.

We report spectroscopic results on the 2s2p^{1}P_{1} state in neutral atomic beryllium-9. The absolute frequency for the center of gravity is determined to be 42 565.4501(13) cm^{-1}, a factor of 130 more precise than the previous experimental measurement. The result is in agreement with and a factor of 8 more precise than the current best theoretical estimate of 42 565.441(11) cm^{-1}, which was calculated including the effects of quantum electrodynamics. Because of the large natural linewidth of the transition, the hyperfine constants were not able to be extracted to high precision.

Multiconfiguration Dirac–Hartree–Fock energy levels, weighted oscillator strengths, transitions probabilities, lifetimes, hyperfine constants, Landé [formula omitted]-factors and isotope shifts of [formula omitted][formula omitted

Energy levels, weighted oscillator strengths and transition probabilities, lifetimes, hyperfine interaction constants, Landé gJ factors and isotope shifts are calculated for all levels of 1s2 and 1snl (n=2−7) configurations of He-like xenon ion (XeLIII). Multiconfigurational Dirac–Hartree–Fock (MCDHF) method is adopted for calculating these spectroscopic data. Comparisons are made with similar data obtained with FAC (Flexible Atomic Code) to assess the accuracy of the results. Transition probabilities are reported for all E1, E2, M1 and M2 transitions from the ground level. Breit interactions and quantum electrodynamics effects are estimated in extensive Relativistic Configuration Interaction (RCI) calculations. Comparisons were made with the available data in the literature and good agreement was found which confirms the reliability of our results. The accuracy of the present calculations is high enough to facilitate identification of many observed spectral lines. Almost all atomic data of He-like xenon ion presented in this paper are calculated for the first time.

Enhanced electron-positron pair production by two obliquely incident lasers interacting with a solid target

Enhanced electron-positron (e−e+) pair production using two obliquely incident lasers interacting with a solid target is investigated through multi-dimensional particle-in-cell (PIC) simulations. Two obliquely incident lasers can strengthen the laser-hole boring effect, which enhances the reflected focusing laser field and the consequent quantum electrodynamics effects. PIC simulations show that by using two 10 PW-scale lasers, a high-yield (3 × 1010) overdense (∼1022 cm−3) positron beam can be generated and laser to pair energy conversion efficiency can be increased up to one percent. Such positron yield is fifty times higher than that produced from a single laser with the same peak power. The robustness of such a scheme is confirmed by numerically studying parametric influences of the oblique incident angle, temporal asynchrony and phase difference between the two lasers. It is found that the temporal asynchrony and the phase difference have minor effects on the pair production. The proposed scheme may provide great potential for high dense pair plasma generation in experiments with coming approachable high power laser facilities.

Forbidden transition properties of fine-structure 2p3 4S3/2−2p3 2D3/2,5/2 for nitrogen-like ions**Project supported by the National Natural Science Foundation of China (Grant Nos. 11604385 and 91436103).

Based on relativistic wave functions from multiconfiguration Dirac–Hartree–Fock and configuration interaction calculations, E2 and M1 transition probabilities of 2p3 4S3/2–2p3 2D3/2,5/2 are investigated in the nitrogen-like sequence with 7 ≤ Z ≤ 16. The contributions of the electron correlations, Breit interaction, and the quantum electrodynamic (QED) effects on the transition properties are analyzed. The present results can be used for diagnosing plasma. In addition, several N-like ions can also be recommended as a promising candidate for a highly charged ion (HCI) clock with a quality factor (Q) of transition as high as 1020.

Superconducting Qubit Systems as a Platform for Studying Effects of Nonstationary Electrodynamics in a Cavity

It has been shown that superconducting qubit systems, having high tunability, can be used as a platform for the experimental study of various effects of nonstationary quantum electrodynamics in a cavity. In particular, the dynamic Lamb effect can be implemented owing to a nonadiabatic change in the effective coupling between the subsystem of qubits and a cavity. This effect is manifested in the excitation of a qubit (atom) at the change in the Lamb shift of its levels. It is remarkable that the effect of energy dissipation in such parametrically excited systems can be very nontrivial: dissipation in one of the subsystems of the hybrid system can enhance quantum effects in the other subsystem. This refers to various phenomena such as parametric qubit excitation, generation of photons from vacuum, and creation and confinement of finite entanglement of qubits.

Exploration of Strong Field Physics with Multi-PW Lasers

At the Center for Relativistic Laser Science (CoReLS) petawatt (PW) lasers have been developed for the investigations of strong field physics. The CoReLS has successfully upgraded one of the existing PW laser beamlines to a 4 PW laser at 20 fs. From laser-driven charged-particle acceleration experiments, multi-GeV electrons and 90-MeV protons can be generated using the laser wakefield acceleration and the radiation pressure acceleration schemes, respectively. The GeV electron beam can be, in turn, used for Compton backscattering with another PW laser. Such a Compton scattering process can be examined for other quantum electrodynamics (QED) effects, including the radiation reaction effect and the Breit-Wheeler pair production process. PW lasers have, thus, offered new opportunities to pursue novel physics research in relativistic plasma physics, strong field quantum electrodynamics, nuclear physics and laboratory astrophysics.