Ground-state Atoms Research Articles

On density distribution of Ti atom and ion ground states near the target in HiPIMS discharge using cavity ring-down spectroscopy and laser induced fluorescence

Cavity ring-down spectroscopy combined with laser induced fluorescence was applied during a high-power impulse magnetron sputtering of Ti target to determine the time evolutions and spatial distributions of Ti atom and ion densities of levels belonging to the ground state multiplets (GSM) near the sputtered target. From these densities, an estimate of the time evolution and spatial distribution of the ionization degree near the target was calculated. It was found that the densities (number of particles per unit volume) of levels in GSM of Ti atom and ion increases with their level energies and the highest levels in GSMs show an inversion in their populations (the density of level divided by its statistical weight) during a voltage pulse. The population inversion (a higher population of levels with a higher energy than those with lower ones) is distinct for the highest level in GSM of Ti+ ion and it persists even at 40 μs after the voltage pulse end. The sum of ground state level densities reaches values up to 8.3 × 1011 cm−3 for Ti+ ions above the target racetrack and up to 4.8 × 1011 cm−3 for Ti atoms above the target center for the regime with the peak power density of 498 W cm−2. A frequent ionization of Ti atoms above the target racetrack is manifested by distinct drops in the Ti atom spatial distribution. This leads to a very high ionization degree up to 94% at the racetrack position and the ionization degree stays also high 40 μs after the voltage pulse termination.

Dynamical Casimir effects with atoms: From the emission of photon pairs to geometric phases

The coupling between a moving ground-state atom and the quantum electromagnetic field is at the origin of several intriguing phenomena ranging from the dynamical Casimir emission of photons to Sagnac-like geometric phase shifts in atom interferometers. Recent progress in this emerging field reveals unprecedented connections between non-trivial aspects of modern physics such as electrodynamic retardation, non-unitary evolution in open quantum systems, geometric phases, non-locality and inertia.

Angle-Dependent Magic Optical Trap for the 6S1/2↔nP3/2 Rydberg Transition of Cesium Atoms

The existence of an anisotropic tensor part of atomic states with an angular momentum greater than 1/2 causes their dynamic polarizabilities to be very sensitive to the polarization direction of the laser field. Therefore, the magic wavelength of the transition between two atomic states also depends on the polarization angle between the quantized axis and the polarization vector. We perform a calculation of the magic conditions of the 6S1/2↔nP3/2 (n = 50–90) Rydberg transition of cesium atoms by introducing an auxiliary electric diople transition connected to the target Rydberg state and a low-excited state. The magic condition is determined by the intersection of dynamic polarizabilities of the 6S1/2 ground state and the nP3/2 Rydberg state. The dynamic polarizability is calculated by using the sum-over-states method. Furthermore, we analyze the dependence of magic detuning on the polarization angle for a linearly polarized trapping laser and establish the relationship between magic detuning and a principal quantum number of the Rydberg state at the magic angle. The magic optical dipole trap can confine the ground-state and Rydberg-state atoms simultaneously, and the differential light shift in the 6S1/2↔nP3/2 transition can be canceled under the magic condition. It is of great significance for the application of long-lifetime high-repetition-rate accurate manipulation of Rydberg atoms on high-fidelity entanglement and quantum logic gate operation.

Atomic shell structure from Born probabilities: Comparison to other shell descriptors and persistence in molecules.

Real space chemical bonding descriptors, such as the electron localization function or the Laplacian of the electron density, have been widely used in electronic structure theory thanks to their power to provide chemically intuitive spatial images of bonded and non-bonded interactions. This capacity stems from their ability to display the shell structure of atoms and its distortion upon molecular formation. Here, we examine the spatial position of the N electrons of an atom at the maximum of the square of the wavefunction, the so-called Born maximum, as a shell structure descriptor for ground state atoms with Z = 1-36, comparing it to other available indices. The maximization is performed with the help of variational quantum Monte Carlo calculations. We show that many electron effects (mainly Pauli driven) are non-negligible, that Born shells are closer to the nucleus than any other of the examined descriptors, and that these shells are very well preserved in simple molecules.

Photoionization of Electrons in Degenerate Energy Level of Hydrogen Atom Induced by Strong Laser Pulses

Photoionization dynamics of bounded electrons in the ground state, the first and second excited states of a hydrogen atom, triggered by ultrashort near-infrared laser pulses, have been investigated in a transition regime (γ∼1) that offers both multiphoton and tunneling features. Significant differences in spectral characteristics are found between the three low-energy states. The H(2s) ionization probability is larger than the H(2p) value with a special oscillating structure, but both are much greater than the ground state H(1s) in a wide range of laser intensities. By comparing the momentum spectrum and angular distributions of low-energy photoelectrons released from these degenerate states, we find the H(2p) state shows a stronger long-range Coulomb attraction force than the H(2s) state on account of the difference in the initial electron wave packet. Furthermore, analysis of the photoelectron momentum distributions sheds light on both the first and second excited states with a symmetrical intercycle interference structure in a multicycle field but an intracycle interference of an asymmetric left-handed or right-handed rotating spectrum in a few-cycle field. By analyzing photoelectron spectroscopy, we identify the parity characteristics of photoelectrons in different energy intervals and their corresponding above-threshold single-photon ionization (ATSI) or above-threshold double-photon ionization (ATDI) processes. We finally present the momentum distributions of the electrons ionized by laser pulses with different profiles and find the carrier-envelope phase (CEP) is a strong factor in deciding the rotating structure of the emission spectrum, which provides a new method to distinguish the CEP of few-cycle pulses.

Spatially strongly confined atomic excitation via a two dimensional stimulated Raman adiabatic passage.

We consider a method of sub-wavelength superlocalization and patterning of atomic matter waves via a two dimensional stimulated Raman adiabatic passage (2D STIRAP) process. An atom initially prepared in its ground level interacts with a doughnut-shaped optical vortex pump beam and a traveling wave Stokes laser beam with a constant (top-hat) intensity profile in space. The beams are sent in a counter-intuitive temporal sequence, in which the Stokes pulse precedes the pump pulse. The atoms interacting with both the traveling wave and the vortex beam are transferred to a final state through the 2D STIRAP, while those located at the core of the vortex beam remain in the initial state, creating a super-narrow nanometer scale atomic spot in the spatial distribution of ground state atoms. By numerical simulations we show that the 2D STIRAP approach outperforms the established method of coherent population trapping, yielding much stronger confinement of atomic excitation. Numerical simulations of the Gross-Pitaevskii equation show that using such a method one can create 2D bright and dark solitonic structures in trapped Bose-Einstein condensates (BECs). The method allows one to circumvent the restriction set by the diffraction limit inherent to conventional methods for formation of localized solitons, with a full control over the position and size of nanometer resolution defects.

Noble-gas atoms characterized by hyperfine frequency shift of lithium atom.

We report an experimental and theoretical study on the shift of the hyperfine splitting frequency of ground-state Li atoms in noble gases, He, Ne, Ar, and Xe. The frequency shift is due to the change in the electron-spin density at the Li nuclei induced by collisions to the noble-gas atoms. The electron density is calculated along the interatomic distance in a pseudopotential and a dispersion potential. Based on the measured and the calculated frequency shifts, we find the importance of attractive force in collisions to helium as well as heavy noble-gas atoms. Taking advantage of the simple energy structure of the Li atom, we obtain the s wave scattering length for free electrons on noble-gas atoms by using the hyperfine splitting frequency as a precise measure.

Nonreciprocal photonic devices based onwhispering-gallery-modes microcavities

<p indent="0mm">Because the nonreciprocity has both theoretical and applicable prospects, it is desired to break through the restriction of the reciprocity principle for nonreciprocity optical transmission. Theoretically, the reciprocity principle is equivalent to the limited time reversal symmetry. To break the symmetry, the system should include nonlinearity, magneto-optical effects, or modulation in time. Some key components in the optical circuits, such as isolators, circulators, and phase shifters, are typical nonreciprocal devices. They are realized based on the Faraday effect of magneto-optical materials in traditional free-space optics. However, the magneto-optical materials are not naturally compatible with the integrated optics. Therefore, while pursuing the magneto-optical integration on a chip, people also devote to developing nonreciprocal theories and devices without magnetic materials. Whispering-gallery-modes (WGMs) optical microcavity has the advantages of small mode volume and high-quality factor. Therefore, many nonreciprocal strategies in photonic integration are based on optical microcavities. Similar to the nonreciprocal principle of the magneto-optical effect, the external bias fields (such as magnetic field, angular momentum, linear momentum, etc.) are necessary to break the time reversal symmetry. In this paper, we review the research on nonreciprocal optics in WGMs optical microcavities, and summarize recent research achievements in the following interaction categories: Magneto-optical effect, chiral coupling of atoms with energy level distribution bias, macroscopic Doppler effect with angular momentum bias, optomechanical driving, acousto-optic oscillation and nonlinear driving. Firstly, even on the chip, the magneto-optical effect is an important way to realize nonreciprocity. Nonreciprocity can be achieved by depositing/bonding magneto-optical materials on a silicon chip or using the spin-orbit interaction of WGMs in the YIG microsphere with the help of an external magnetic field. Secondly, preparing the atom to a specific Zeeman energy level can also lead to the polarization concerned interaction between the atoms and the photons, so that the nonreciprocity of the photon can be realized based on the control of the atomic ground state population. Thirdly, the Doppler effect can make the moving dielectric medium produce an additional refractive index related to the speed. Then the effective refractive index is different between the light propagating in the opposite directions. The reciprocity of the system is destroyed, thereby achieving nonreciprocity. Finally, the nonreciprocity of optomechanical systems, acousto-optic modulation, and nonlinear effects can be explained by the conservation of angular momentum of photon-phonon interactions. As a summary, some representative parameters of isolators obtained in related experiments are listed in the table. The existing solutions for nonreciprocity have also be classified in terms of angular momentum and interactions, which is beneficial to deeply understanding the existing solutions and to developing potential solutions. The research of nonreciprocity is also discussed by listing problems to be studied.

For some atomic ground state energy and the connection between the interaction of speculation

For some atomic ground state energy and the connection between the interaction of speculation

N–H collision integrals with study of repulsive interactions

Abstract Collision integrals are calculated and analyzed for the ground state nitrogen N ( S 4 ) and hydrogen H ( S 2 ) atoms involving the 3Σ and 5Σ electronic states in the temperature range of 1000–30 000 K. Influence of the quality of different known potential energy functions on the collision integrals was also studied and compared with the available data. Based on our analysis, the repulsive potential and its description beyond simple exponential also at small interatomic distances is necessary to obtain reliable collision integrals. Besides the ground state atoms, for the first time the collision integrals for excited nitrogen atoms (N ( D 2 ) and N ( P 2 ) ) with ground state hydrogen H ( S 2 ) were also calculated. The corresponding potential energy curves are also computed by using multireference configuration interaction (MRCI) method of electronic structure theory with aug-cc-pV6Z basis set. The resulting collision integrals were fitted to simple functional forms.

The implication of the atomic effects in neutrinoless double beta decay

In the planned ton-scale neutrinoless double beta [Formula: see text] decay experiments, the used [Formula: see text] value is the mass-energy difference between the ground states of mother and daughter atoms, without correcting the atomic energy difference due to the alteration in the nuclear charge before and after the decay process. We show that the atomic energy change between the two ground states can potentially reduce the [Formula: see text] value by 5.502, 12.103, and 12.372 keV for the decays from [Formula: see text], [Formula: see text], and [Formula: see text], respectively. The available kinetic energy for two electrons can be 2033.51 keV for [Formula: see text] decay, 2515.41 keV for [Formula: see text] decay, and 2445.45 keV for [Formula: see text] decay after correcting for atomic effects. This implies that the planned experiments could potentially miss the decay signature if a narrow energy window is designated to reduce background events including [Formula: see text] decay events.

Determination of quadrupole polarizabilities of the excited states of alkali-metal atoms

The scalar and tensor components of the electric quadrupole (E2) polarizabilities of the first two excited states of all the alkali-metal atoms are determined. To validate the calculations, we have evaluated the ground state E2 polarizabilities of these atoms and compared them with the literature values. We could not find the ground state E2 polarizability value for Fr in the literature to compare with our result. The dominant parts of these quantities are estimated by combining the precisely calculated E2 transition matrix elements of many low-lying transitions with the experimental energies, while the other contributions are estimated using lower-order methods. Our estimated values for the ground states of the above atoms are in good agreement with the literature values suggesting that our estimated E2 polarizabilities for the excited states of the alkali atoms, which were not known earlier except for the Li atom, are also quite accurate. These reported E2 polarizabilities could be useful in guiding many precision measurements in the alkali atoms.

Distinctive Features of Charge Exchange Involving the Second Flavor of Hydrogen Atoms—The Candidates for Dark Matter

The second flavor of hydrogen atoms (SFHA) refers to the kind of hydrogen atoms that have only the states of the zero orbital angular momentum (the S-states), both in the discrete and continuous spectra. They were first discovered theoretically in one of my earlier papers, where a proof of their existence was also provided by analyzing atomic experiments concerning the high-energy tail of the linear momentum distribution in the ground state of hydrogen atoms. From a theoretical point of view, the discovery was based on the standard Dirac equation for hydrogen atoms without changing the existing physical laws. Recently, the existence of the SFHA was seemingly also confirmed by two types of astrophysical observations: the allowance for the SFHA explained the puzzling results concerning both the anomalous absorption of the redshifted 21 cm spectral line from the early Universe, and the observations by the Dark Energy Survey (DES) team where it was found that the distribution of dark matter in the Universe is noticeably smoother than predictions employing Einstein’s relativity. In the present review, we exhibit results from two recent papers where attention was brought to a visible difference in the cross-sections of the resonant charge exchange for collisions of the SFHA with incoming protons, compared to collisions of the usual hydrogen atoms with incoming protons. It was shown that, after taking into account the SFHA, there is a better agreement with the corresponding experimental cross-section. Coupled with the previous evidence of the existence of the SFHA, deduced from the analysis of the other kind of atomic experiments, and evidenced by two different kinds of astrophysical observations, this strengthens the standing of the SFHA as the most probable candidate for all or a part of dark matter.

Associative detachment in anion-atom reactions involving a dipole-bound electron

Associative electronic detachment (AED) between anions and neutral atoms leads to the detachment of the anion’s electron resulting in the formation of a neutral molecule. It plays a key role in chemical reaction networks, like the interstellar medium, the Earth’s ionosphere and biochemical processes. Here, a class of AED involving a closed-shell anion (OH−) and alkali atoms (rubidium) is investigated by precisely controlling the fraction of electronically excited rubidium. Reaction with the ground state atom gives rise to a stable intermediate complex with an electron solely bound via dipolar forces. The stability of the complex is governed by the subtle interplay of diabatic and adiabatic couplings into the autodetachment manifold. The measured rate coefficients are in good agreement with ab initio calculations, revealing pronounced steric effects. For excited state rubidium, however, a lower reaction rate is observed, indicating dynamical stabilization processes suppressing the coupling into the autodetachment region. Our work provides a stringent test of ab initio calculations on anion-neutral collisions and constitutes a generic, conceptual framework for understanding electronic state dependent dynamics in AEDs.

Evidence for the association of triatomic molecules in ultracold 23Na40K + 40K mixtures.

Ultracold assembly of diatomic molecules has enabled great advances in controlled chemistry, ultracold chemical physics and quantum simulation with molecules1-3. Extending the ultracold association to triatomic molecules will offer many new research opportunities and challenges in these fields. A possible approach is to form triatomic molecules in a mixture of ultracold atoms and diatomic molecules by using a Feshbach resonance between them4,5. Although ultracold atom-diatomic-molecule Feshbach resonances have been observed recently6,7, using these resonances to form triatomic molecules remains challenging. Here we report on evidence of the association of triatomic molecules near the Feshbach resonance between 23Na40K molecules in the rovibrational ground state and 40K atoms. We apply a radio-frequency pulse to drive the free-bound transition in ultracold mixtures of 23Na40K and 40K and monitor the loss of 23Na40K molecules. The association of triatomic molecules manifests itself as an additional loss feature in the radio-frequency spectra, which can be distinguished from the atomic loss feature. The observation that the distance between the association feature and the atomic transition changes with the magnetic field provides strong evidence for the formation of triatomic molecules. The binding energy of the triatomic molecules is estimated from the measurements. Our work contributes to the understanding of the complex ultracold atom-molecule Feshbach resonances and may open up an avenue towards the preparation and control of ultracold triatomic molecules.

Ion and Electron Momentum Distributions from Single and Double Ionization of Helium Induced by Compton Scattering.

We present the momentum distributions of the nucleus and of the electrons from double ionization of the helium atom by Compton scattering of photons with hν=40 keV. We find that the doubly charged ion momentum distribution is very close to the Compton profile of the nucleus in the ground state of the helium atom, and the momentum distribution of the singly charged ion to give a precise image of the electron Compton profile. To reproduce these results, nonrelativistic calculations require the use of highly correlated initial- and final-state wave functions.

Trapping Alkaline Earth Rydberg Atoms Optical Tweezer Arrays.

Neutral atom qubits with Rydberg-mediated interactions are a leading platform for developing large-scale coherent quantum systems. In the majority of experiments to date, the Rydberg states are not trapped by the same potential that confines ground state atoms, resulting in atom loss and constraints on the achievable interaction time. In this Letter, we demonstrate that the Rydberg states of an alkaline earth atom, ytterbium, can be stably trapped by the same red-detuned optical tweezer that also confines the ground state, by leveraging the polarizability of the Yb^{+} ion core. Using the previously unobserved ^{3}S_{1} series, we demonstrate trapped Rydberg atom lifetimes exceeding 100 μs, and observe no evidence of auto- or photoionization from the trap light for these states. We measure a coherence time of T_{2}=59 μs between two Rydberg levels, exceeding the 28 μs lifetime of untrapped Rydberg atoms under the same conditions. These results are promising for extending the interaction time of Rydberg atom arrays for quantum simulation and computing, and are vital to capitalize on the extended Rydberg lifetimes in circular states or cryogenic environments.

Time-Dependent Quantum Dynamics Study of the Interaction between Helium Atom and Synchrotron Radiation

For the first time, excitation and ionization of helium atom (He) induced by synchrotron radiation(SR) is simulated in the present work. It is found that electrons can tunnel through the ground state of helium atom and leave from the atomic region caused by subsequent SR field. Therefore, the ionization of He atom can happen. Additionally, some electrons can be captured by a higher electronic state, which leads to the tunneling excitation from the ground state to a specific excited state.

Magnetic nature and hyperfine interactions of transition metal atoms adsorbed on ultrathin insulating films: a challenge for DFT.

The magnetic ground state and the hyperfine coupling parameters of some first-row transition metal (TM) atoms (Ti, Cr, Mn, Fe, Co, and Ni) adsorbed on ultrathin insulating oxide films are studied by means of DFT calculations. The results obtained using GGA, screened hybrid, and GGA+U functionals are compared for TMs adsorbed on free-standing MgO(100). Then, the case of adsorption on MgO mono- and bilayers supported on Ag(100) is studied using GGA+U. Along with the problematic aspects inherent to the calculation of hyperfine coupling constants, a critical dependence on the magnetic state and electron configuration of the TM is reported, which implies a real challenge for the state-of-the-art DFT methods. In the cases where all functionals considered provide a coherent magnetic and electron configuration, however, the calculated hyperfine parameters do not depend significantly on the choice of the functional. In this respect, the role of the metal support in the hyperfine coupling constants is highly system-dependent and becomes crucial in all cases where the support modifies the oxidation state of the adatom, induces a change in the bonding site or simply induces a rearrangement of the orbital energy diagram. This has important implications for the modelling of single TM atoms deposited on insulating ultrathin films supported on metals for application in quantum technologies or as memory devices.

Spectroscopic characterization of two boron heterocyclic radicals in the solid neon matrix.

Two novel boron heterocyclic radicals, a 3,4,5-trihydroborinine radical and a 1-methyl-2-dihydro-1H-borole radical, were observed in the reaction of boron atom with cyclopentene. These radicals were trapped in solid neon and identified using matrix isolation infrared spectroscopy as well as quantum chemical calculations. The ground-state boron atom selectively inserts into the CC double bond of cyclopentene forming a 3,4,5-trihydroborinine radical (A). This radical can further isomerize to a 1-methyl-2-dihydro-1H-borole radical (B) under UV light irradiation via multiple hydrogen-atom transfer and rearrangement reactions. The observation of species A and further photo-isomerization to species B is consistent with theoretical predictions that these reactions are thermodynamically exothermic and kinetically facile. This is an exciting example of the synthesis of borole derivatives through multiple hydrogen-atom transfer and rearrangement reactions of borinine compounds induced by light irradiation. The present findings provide new insight into the future design and synthesis of the corresponding boron heterocyclic compounds.