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The variations of exchange Slater integrals with respect to their order k are not well known. While direct Slater integrals Fk are positive and decreasing when the order increases, this is not stricto sensu the case for exchange integrals Gk. However, two inequalities were published by Racah in his seminal article 'Theory of complex spectra. II'. In this article, we show that the technique used by Racah can be generalized, albeit with cumbersome calculations, to derive further relations, and provide two of them, involving respectively three and four exchange integrals. Such relations can prove useful to detect regularities in complex atomic spectra and classify energy levels. [ABSTRACT FROM AUTHOR]

Network science provides a universal framework for modeling complex systems, contrasting the reductionist approach generally adopted in physics. In a prototypical study, we utilize network models created from spectroscopic data of atoms to predict microscopic properties of the underlying physical system. For simple atoms such as helium, an a posteriori inspection of spectroscopic network communities reveals the emergence of quantum numbers and symmetries. For more complex atoms such as thorium, finer network hierarchies suggest additional microscopic symmetries or configurations. Furthermore, link prediction in spectroscopic networks yields a quantitative ranking of yet unknown atomic transitions, offering opportunities to discover new spectral lines in a well-controlled manner. Our work promotes a genuine bi-directional exchange of methodology between network science and physics, and presents new perspectives for the study of atomic spectra.

Because of the unquestionable presence of magnetic fields in stars, their role in the structure of stellar atmospheres has for a long time been a subject of speculation. In our contribution to this discussion we present spectropolarimetric evidence of the decrease of the radial component of the magnetic field with altitude in the atmosphere of HD 58260, a B-type magnetic star on the main sequence. We show that the Stokes V profiles of metal lines in emission of the outer atmosphere are evidence for a field three times weaker than absorption lines from inner layers. The extra flow of energetic particles due to the magnetic-gradient pumping mechanism could be at the origin of the magnetospheres surrounding this class of stars and at the basis of the high-energy phenomena observed. We also list a series of spectral lines useful for measuring the surface field of early-type stars. [ABSTRACT FROM AUTHOR]

We studied photoelectron angular distributions (PADs) and energy spectra of sodium atoms photo-ionized with intense short laser pulses in the near-infrared region. Energy spectra of photoelectrons due to multistep ionization of sodium atoms through intermediate levels 5p, 6p, 7p, and 4f were observed in above threshold ionization (ATI) at laser intensities of 2 × 1013 W cm−2 and 1 × 1013 W cm−2. The PADs from the 5p(4f) state for zero, first, second and third order ATI peaks were measured. We observed that for the two selected laser intensities the angular distribution of photoelectrons showed only slight variations. The PADs exhibit main lobes within ∼60° degrees from the laser polarization and additional lobes that become more pronounced with the increasing ATI peak number. Besides a general analytical representation of the observed angular dependences, the experimental PADs for each ATI peak were fitted with Legendre polynomials accounting for different ionization channels. The good agreement between the experimental data and fitting functions allowed to evaluate the contributions of the ionization channels to the observed ATI orders. The calculations of the photoelectron spectra by numerically solving the time-dependent Schrödinger equation in a single active electron approximation produced agreement with the experiment in the main features of the spectra, while differences in more subtle details were observed. [ABSTRACT FROM AUTHOR]

Rotational bands are commonplace in the spectra of atomic nuclei. Inspired by early descriptions of these bands by quadrupole deformations of a liquid drop, Elliott constructed discrete nucleon representations of SU(3) from fermionic creation and annihilation operators. Ever since, Elliott's model has been foundational to descriptions of rotation in nuclei. Later work, however, suggested the symplectic extension Sp(3, R) provides a more unified picture. We decompose no-core shell-model nuclear wave functions into symmetry-defined subspaces for several beryllium isotopes, as well as 20Ne, using the quadratic Casimirs of both Elliott's SU(3) and Sp(3, R). The band structure, delineated by strong B(E2) values, has a more consistent description in Sp(3, R) rather than SU(3). In particular, we confirm previous work finding in some nuclides strongly connected upper and lower bands with the same underlying symplectic structure. [ABSTRACT FROM AUTHOR]

The identifications of Fe vii emission lines in the wavelength range 193–197 Å are discussed in the light of new measurements of laboratory spectra and atomic data calculations. This region is of importance to studies of solar spectra from the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft, which has its peak sensitivity at these wavelengths. Ten lines are measured, arising from seven fine structure levels in the 3p53d3 configuration. Two lines have not previously been reported and lead to new experimental energies for the levels. Updated experimental energies are obtained for the remaining levels. The new atomic model is used to compute theoretical values for the two density diagnostic ratios λ196.21/λ195.39 and λ196.21/λ196.06, and densities are derived from EIS spectra of coronal loop footpoints. [ABSTRACT FROM AUTHOR]

We develop a method of synthetic frequency generation to construct an atomic clock with blackbody radiation (BBR) shift uncertainties below 10−19 at environmental conditions with a very low level of temperature control. The proposed method can be implemented for atoms and ions, which have two different clock transitions with frequencies ν1 and ν2 allowing to form a synthetic reference frequency νsyn = (ν1 − ɛν2)/(1 − ɛ), which is absent in the spectrum of the involved atoms or ions. Calibration coefficient ɛ can be chosen such that the temperature dependence of the BBR shift for the synthetic frequency νsyn has a local extremum at an arbitrary operating temperature T0. This leads to a weak sensitivity of BBR shift with respect to the temperature variations near operating temperature T0. As a specific example, the Yb+ ion is studied in detail, where the utilized optical clock transitions are of electric quadrupole (S → D) and octupole (S → F) type. In this case, temperature variations of ±7 K lead to BBR shift uncertainties of less than 10−19, showing the possibility to construct ultra-precise combined atomic clocks (including portable ones) without the use of cryogenic techniques. [ABSTRACT FROM AUTHOR]

We present the first measurements of photoelectron spectra of atomic clusters embedded in superfluid helium (He) nanodroplets. Owing to the large absorption cross section of xenon (Xe) around 100 eV photon energy (4d inner-shell ionization), direct dopant photoionization exceeds charge transfer ionization via the ionized He droplets. Despite the predominant creation of Xe2+ and Xe3+ by subsequent Auger decay of free Xe atoms, for Xe embedded in He droplets only singly charged , k = 1, 2, 3 fragments are observed. Broad Xe+ ion kinetic-energy distributions indicate Coulomb explosion of the ions due to electron transfer to the primary Auger ions from surrounding neutral atoms. The electron spectra correlated with Xe ions emitted from the He nanodroplets contain a low-energy feature and nearly unshifted Xe photolines. These results pave the way to extreme ultraviolet and x-ray photoelectron spectroscopy of clusters and molecular complexes embedded in He nanodroplets. [ABSTRACT FROM AUTHOR]

Semiconductor CdSe/CdS core–shell nanoplatelets exhibit narrow and intense absorption and photoluminescence spectra in the visible range, which makes them suitable for numerous applications in optoelectronics. Of particular interest is the preparation and optical characterization of thin films with an accurately controlled amount of nanoplatelets. Here we report on the use of spectroscopic ellipsometry for investigating the optical properties of ultrathin films composed of a single layer of negatively charged CdSe/CdS core–shell nanoplatelets prepared by the electrostatic layer-by-layer deposition on SiO2/Si substrates. Combining the ellipsometric spectra with atomic force microscopy measurements, we were able to infer the nanoplatelet film extinction spectra which was found to exhibit the two characteristic exciton peaks albeit blueshifted relative to the colloidal nanoplatelets. [ABSTRACT FROM AUTHOR]

The interference fringes of above-threshold ionization (ATI) spectrum from atoms or molecules have been extensively studied. In this paper, we investigate the ATI of the polyatomic molecule SF6 in IR + XUV two-color laser fields, and find that some interference fringes on the spectrum are from the molecular structure, which is independent of the parameters of the laser field. Based on the frequency-domain theory, we analyze the interference fringes for different orbitals of SF6 molecules in detail. It is found that the orbital of SF6 can be simplified by several terms in the region of high value of momentum, where the destructive interference fringes from these terms may carry the information of the molecular structure. Furthermore, we obtain destructive interference formulas from these simplified orbitals, which may predict the interference fringes on the ATI spectrum. Additionally, we may obtain the information about the bond length of molecules. It will be useful for the study of the ionization spectrum of polyatomic molecules. [ABSTRACT FROM AUTHOR]

In this paper we show that the second derivative (SD) technique of the absorption spectra of Rb atomic vapours, confined in a nanocell with a thickness ℓ = λ/2 = 398 nm, allows us to achieve close to Doppler-free spectroscopy. The narrow linewidth and linearity of the SD signal response with respect to transition probabilities allows us to study separately, in an external transverse magnetic field (0.6 to 4 kG), a large number of the atomic transitions of 85Rb and 87Rb atoms. Atomic transitions |Fg, 0⟩ → |Fe = Fg, 0′⟩, for which the dipole moment is null in a zero magnetic field (so-called magnetically-induced transitions), show a gigantic increase in probability with an increasing magnetic field. When a magnetic field is applied to the vapour, we show the possibility of forming a dark resonance on these transitions by adding a coupling laser. We are therefore able to demonstrate a five-fold increase in the transmission of the probe radiation when the coupling laser is on. Theoretical calculations are in very good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Cooperative atomic emission spectrum as a key probe of entanglement dynamics of an independent and a classically-pumped qubits pair is showed and investigated. The qubits are initially maximally-entangled while they penetrate a detuned, single-photon and coherent cavity embedded in nonlinear media. The system Hamiltonian; that is a nonlinear and a time-dependent system, is diagonalized and the time evolution unitary operator in an exact form is derived. Various characteristics are monitored while observations are theoretically documented—via tracing the field state tomography—and experimentally calibrated. Cooperation and decoherence as well as the statistics of the emitted radiation are discussed and analyzed in terms of the other phenomena. We show that, a measurement of the spectrum outputs represent a highly effective key calibration for entanglement attributes, where complete time dynamics may be predicted with a high considerable accuracy. The most striking feature realized is that, on high detuned interaction, a full matching of these phenomena outputs can be achieved regardless of the absence or presence or pumping. Once the pumping starts, a partial dephasing is encouraged, thus, the spectrum is inversely but slightly affected, nevertheless, matching remains highly closed. Within various surroundings of Kerr materials of different Kerr constants, that is an additional source of an effective dephasing, spectrum rapidly oscillates and so also entanglement that shows rapid Rabi oscillations during its fast degradation depending on the detuning width. However, on measuring the intracavity field state tomography, measurements confirm such a matching, that is, calibration is well documented. [ABSTRACT FROM AUTHOR]

We demonstrate that the present superaccurate measurements of transition processes between atomic states in a hydrogen atom reached the limit of accuracy when transition the frequency could not be defined anymore in a unique way. This was predicted earlier and is due to the necessity to include the nonresonant corrections in the description of resonant processes. The observed spectral line profile becomes asymmetric, and it becomes impossible to extract the value of transition frequency from this profile in a unique way. Nonresonant corrections depend on the type of experiment and on the experimental arrangement. However, the line profile itself for any resonant process can be defined with any desired level of accuracy. A popular trend in the modern search for atomic frequency standards and atomic clocks is the search for transitions where the nonresonant corrections are negligible. In this paper we present closed expressions for the resonant photon scattering cross sections on an atomic level with dependence on all atomic quantum numbers including fine and hyperfine structures. These expressions are given for different types of experiments with fixing of the incident (outgoing) photon propagation directions and incident (outgoing) photon polarization. Using these expressions we demonstrate that the transition frequencies in particular cases cannot be derived uniquely if the accuracy of measurement reaches the level quoted in Beyer et al (2017 Science 358 79). The definition of transition frequency suggested in Beyer et al may become unique with additional requirements to the process of measurement: the use of the 'magic angle' in an experimental arrangement and summation over all possible final states including the hyperfine sublevels. Our interpretation of the results of this experiment is alternative to the interpretation given by Beyer et al. [ABSTRACT FROM AUTHOR]

Electron affinities (EA) of most lanthanide elements still remain unknown owing to their relatively lower EA values and the fairly complicated electronic structures. In the present work, we report the high-resolution photoelectron spectra of atomic cerium anion Ce− using the slow electron velocity-map imaging method in combination with a cold ion trap. The electron affinity of Ce is determined to be 4840.62(21) cm−1 or 0.600160(26) eV. Moreover, several excited states of Ce− (4H9/2, 4I9/2, 2H9/2, 2G9/2, 2G7/2, 4H13/2, 2F5/2, and 4I13/2) are observed. [ABSTRACT FROM AUTHOR]

An extremely-high field nuclear magnetic resonance (NMR) spectrometer has the potential to significantly augment the resolution and sensitivity of the atomic resonance spectrum, which will significantly boost the development of a range of scientific areas. The success of an extremely-high field NMR spectrometer depends to a great extent on the development of a superconducting magnet system. A high-temperature superconducting (HTS) insert magnet and low-temperature superconducting (LTS) shim coils design scheme for a 27 T NMR spectrometer is proposed in this work. A LTS background magnet was used to generate a 15 T magnetic field in the central area and the designed HTS insert magnet contributed the remaining 12 T magnetic field. The HTS insert magnet adopted notch double-pancake (DP) optimization to improve the rough magnetic field distribution in the central area to a highly-homogeneous level, and shim compensation schemes were proposed for the hybrid magnet to eliminate the inhomogeneous magnetic field components in the practical fabrication. The HTS insert magnet design had a current margin of 45.64% in terms of the perpendicular magnetic field intensity and the maximum hoop stress was reduced to 260 MPa with binding. There were in total eight shim coils, including two Nb3Sn zonal coils located between the insert magnet and the background magnet and six NbTi tesseral coils placed outside the background magnet. The magnet system will be fabricated in the near future. [ABSTRACT FROM AUTHOR]

There are theoretical frameworks, such as the large extra dimension models, which predict the strengthening of the gravitational field in short distances. Here we obtain new empiric constraints for deviations of standard gravity in the atomic length scale from analyses of recent and accurate data of hydrogen spectroscopy. The new bounds, extracted from transition, are compared with previous limits given by antiprotonic Helium spectroscopy. Independent constraints are also determined by investigating the effects of gravitational spin–orbit coupling on the atomic spectrum. We show that the analysis of the influence of that interaction, which is responsible for the spin precession phenomena, on the fine structure of the states can be employed as a test of a post-Newtonian potential in the atomic domain. The constraints obtained here from transition in hydrogen are tighter than previous bounds determined from measurements of the spin precession in an electron-nucleus scattering. [ABSTRACT FROM AUTHOR]

According to the frequency-domain theory, we investigate the asymmetric structure of above-threshold ionization (ATI) spectrum of an atom in two-color elliptically polarized (EP) laser fields. When both laser fields are linearly polarized (LP), the spectrum shows that the multi-plateau structure is symmetric about the emitted angle of electron at π/2, while the spectrum becomes asymmetric and shifts rightwards with the increase of the EP degree of the IR laser field. Since the total ATI process is regarded as including direct ATI and the rescattering ATI, we analyze the spectrum structure of direct ATI and rescattering ATI separately. Using the saddle-point approximation, we find that for direct ATI, the fringes on the spectrum are mainly attributed to the fact that the ionization probability becomes very small when the direction of emitted electrons is perpendicular to the direction of the XUV laser polarization; while for the rescattering ATI, the interference fringes on the spectrum mainly come from the superposition of the waist structures on the spectra of all sub-channels. [ABSTRACT FROM AUTHOR]

Motivated by recent progress in the experimental manipulation of cold atoms in optical lattices, we study three different protocols for non-adiabatic quantum state preparation and state transport in chains of Rydberg atoms. The protocols we discuss are based on the blockade mechanism between atoms which, when excited to a Rydberg state, interact through a van der Waals potential, and rely on single-site addressing. Specifically, we discuss protocols for efficient creation of an antiferromagnetic GHZ state, a class of matrix product states including a so-called Rydberg crystal and for the state transport of a single-qubit quantum state between two ends of a chain of atoms.Weidentify system parameters allowing for the operation of the protocols on timescales shorter than the lifetime of the Rydberg states while yielding high fidelity output states.Wediscuss the effect of positional disorder on the resulting states and comment on limitations due to other sources of noise such as radiative decay of the Rydberg states. The proposed protocols provide a testbed for benchmarking the performance of quantum information processing platforms based on Rydberg atoms. [ABSTRACT FROM AUTHOR]

We investigate the effects of spontaneously generated coherence (SGC) on both the steady and transient gain properties in a four-level inverted-Y-type atomic system in the presence of a weak probe, two strong coherent fields, and an incoherent pump. For the steady process, we find that the inversionless gain mainly origins from SGC. In particular, we can modulate the inversionless gain by changing the relative phase between the two fields. Moreover, the amplitude of the gain peak can be enhanced and the additional gain peak can appear by changing the detuning of the coupling field. As for the transient process, the transient gain properties can also be dramatically affected by the SGC. Compared to the case without SGC, the transient gain can be greatly enhanced with completely eliminated transient absorption by choosing the proper relative phase between the two fields. And the inverted-Y-type system with SGC can be simulated in both atomic and semiconductor quantum well systems avoiding the conditions of SGC. [ABSTRACT FROM AUTHOR]

We provide an accurate calculation of the energy spectrum of three atoms interacting through a contact force in a one-dimensional harmonic trap, considering both spinful fermions and spinless bosons. We use fermionic energies as a benchmark for the exact-diagonalization technique (also known as full configuration interaction), which is found to slowly converge in the case of strong inter-atomic attraction. [ABSTRACT FROM AUTHOR]

In the emission spectrum of six 12C16O, 13C16O, 12C18O, 14C16O, 13C18O and 14C18O isotopologues of the carbon monoxide molecule, new recordings and analyses or new reanalyses of the selected and strongest bands belonging to the Ångström (B1Σ+ − A1Π) system were carried out. Under high resolution, emission spectra of the 0–1 and 1–1 bands were recorded and reanalysed, representing both the 0 − v″ and 1 − v″ progressions of this system. Unobserved so far, new spectral lines were identified, and for the 12C16O, 13C16O, 12C18O, 14C16O and 14C18O molecules new parameters of the rovibronic structure B0, B1, D0 and D1 of the v = 0 and v = 1 levels of the B1Σ+ state and band origins ν0 of the 0–1 and 1–1 bands of the B − A transition were determined. A detailed analysis included the predissociation regions of the spectra observed in all analysed bands and isotopologues. The values of rotational quantum numbers and rovibronic terms of the highest nonpredissociated Jh as well as the first, already predissociated Jf levels were determined. On that basis, a new and more precise value of dissociation energy of the CO molecule was determined: cm−1. Also, atomic states of the dissociation products of this molecule, which correspond to this energy, were identified as C(3P0) + O(3P2) i.e. as both triplet ground atomic sublevels. [ABSTRACT FROM AUTHOR]

Using numerical simulations, we show that atomic high order harmonic generation (HHG) with a circularly polarized laser field offers an ideal framework for quantum-classical correspondence in strong field physics. With an appropriate initialization of the system, corresponding to a superposition of ground and excited state(s), simulated HHG spectra display a narrow strip of strong harmonic radiation preceded by a gap of missing harmonics in the lower part of the spectrum. In specific regions of the spectra, HHG tends to lock to circularly polarized harmonic emission. All these properties are shown to be closely related to a set of key classical periodic orbits that organize the recollision dynamics in an intense, circularly polarized field. [ABSTRACT FROM AUTHOR]

Branching fractions of 13 levels in Gd I and 12 levels in Gd II were experimentally determined based on the emission spectrum of a hollow cathode lamp. In addition, transition probabilities and oscillator strengths for 66 lines of Gd I and 74 lines of Gd II were derived from a combination of the radiative lifetimes reported in the earlier literature and the branching fractions obtained in the present paper. [ABSTRACT FROM AUTHOR]

High resolution crossed atomic beam laser spectroscopy has been used to measure isotope shifts and hyperfine structures in 12 transitions in naturally occurring ruthenium isotopes. Improved values for the changes in mean square charge radii have been deduced from a combined analysis of optical isotope shift and muonic x-ray data. [ABSTRACT FROM AUTHOR]

The excited states of a HeH molecule for an n of up to 4 are studied using the multi-reference configuration–interaction method and Kaufmann's Rydberg basis functions. The advantages of using two different ways of locating Rydberg orbitals, either on the atomic nucleus or at the charge centre of molecules, are exploited by limiting their application to different ranges of R. Using this method, the difference between the experimental binding energies of the lower Rydberg states obtained by Ketterle and the ab initio results obtained by van Hemert and Peyerimhoff is reduced from a few hundreds of wave numbers to a few tens of wave numbers. A substantial improvement in the accuracy allows us to obtain quantum defect curves characterized by the correct behaviour. We obtain several Rydberg series that have more than one member, such as the ns series (n = 2, 3 and 4), npσ series (n = 3 and 4), npπ (n = 2, 3, 4) series and ndπ (n = 3, 4) series. These quantum defect curves are compared to the quantum defect curves obtained by the R-matrix or the multichannel quantum defect theory methods. [ABSTRACT FROM AUTHOR]

The arbitrary ℓ-wave solutions to the Schrödinger equation for the deformed hyperbolic Eckart potential is investigated analytically by using the Nikiforov—Uvarov method. The centrifugal term is treated with the improved Greene and Aldrich approximation scheme. The wave functions are expressed in terms of the Jacobi polynomial or the hypergeometric function. The discrete spectrum is obtained and it is shown that the deformed hyperbolic Eckart potential is a shape-invariant potential and the bound state energy is independent of the deformation parameter q. [ABSTRACT FROM AUTHOR]

In this work we present the Stark widths (W) of 22 neutral (Cu I) and 100 singly ionized (Cu II) copper spectral lines that have been measured at 18 400K and 19 300 K electron temperatures and 6.3 × 1022 m-3 and 2.1 × 1023 m-3 electron densities, respectively. The experiment is conducted in the laser-induced plasma--the Nd:YAG laser, operating at 532 nm, was used to produce plasma from the copper sample in the residual air atmosphere at a pressure of 8 Pa. The electron temperature and density were estimated by the Boltzmann-plot method and from the Saha equation. The investigated Cu I lines belong to the 4s-4p', 4s²-4p'' and 4p'-4d' transitions while Cu II spectral lines belong to the 4s-4p, 4p-5s, 4p-4d, 4p-4s², 4d-4f and 4d-v transitions. Comparison with existing experimental data was possible only in the case of 17 Cu II lines due to a lack of experimental and theoretical values. The rest of the data, Stark widths of 22 Cu I and 83 Cu II lines are published for the first time. [ABSTRACT FROM AUTHOR]

We study the dynamics of a coupled cavity system composed of three cavities, and propose a scheme for the coherent manipulation of two collective atomic modes by a control atom. In the scheme, the control atom and two atomic ensembles interact with the local cavity mode, while the control atom is externally driven by a laser field. We show that under certain conditions, the dynamics of the whole system are reduced to an effective coherent coupling between the control atom and two collective atomic modes, while the cavity fields are only virtually excited. We also study the dynamics of the entanglement generation of the two distant collective atomic modes. The scheme provides a potential application for quantum-state engineering and quantum control. [ABSTRACT FROM AUTHOR]

We demonstrate theoretically that the high-order harmonic of an atom can be generated by a circularly polarized laser pulse. The harmonic spectrum shows a clear cutoff with an energy Ip +2Up. In particular, the high-order harmonic generation comes from the multiple recombination of the ionized electron with non-zero initial velocity. These results are verified by the classical model theory and the time-frequency analysis of a harmonic spectrum. [ABSTRACT FROM AUTHOR]

In hot plasmas, a temperature of a few tens of eV is sufficient for producing highly stripped ions where multipole transitions become important. At low density, the transitions from tightly bound inner shells lead to electric-quadrupole (E2) lines which are comparable in strength with electric-dipole ones. In this work, we propose analytical formulas for the estimation of the number of E2 lines in a transition array. Such expressions rely on statistical descriptions of electron states and J-levels. A generalized 'J-file' sum rule for E2 lines and the strength-weighted shift and variance of the line energies of a transition array nlN+1→ nlNńĺ of inter-configuration E2 lines are also presented [ABSTRACT FROM AUTHOR]

We study modulation spectroscopy of the potassium D2 transitions at 766.7 nm. The vapour pressure, controlled by heating a commercial reference cell, is first optimized using conventional saturated absorption spectroscopy. Heterodyne detection then yields sub-Doppler frequency discriminants suitable for stabilizing lasers in experiments with cold atoms. Comparisons are made between spectra obtained by direct modulation of the probe beam and those using modulation transfer from the pump via nonlinear mixing. Finally, suggestions are made for further optimization of the signals. [ABSTRACT FROM AUTHOR]

We propose the realization of linear crystals of cold ions that contain different atomic species for investigating quantum phase transitions and frustration effects in spin systems beyond the commonly considered case of s = ½ . Mutual spin-spin interactions between ions can be tailored via the Zeeman effect by applying oscillating magnetic fields with strong gradients. Further, collective vibrational modes in the mixed ion crystal can be used to enhance and to vary the strength of spin-spin interactions and even to switch the nature of the interacting forces from a ferro- to an antiferromagnetic character. We consider the behavior of the effective spin-spin couplings in an ion crystal of spin-1/2 ions doped with high-magnetic-moment ions with spin S = 3. We analyze the ground state phase diagram and find regions with different spin orders including ferrimagnetic states. In the most simple nontrivial example, we deal with a linear {Ca+,Mn+, Ca+} crystal with spins of {½ , 3, ½ }. To demonstrate feasibility with current state-of-the-art experiments, we discuss how quantum phases might be detected using a collective Stern-Gerlach effect of the ion crystal and highresolution spectroscopy. Here, the state-dependent laser-induced fluorescence of the indicator spin-1/2 ion, of species 40Ca+, is used to reveal also the spin state of the simulator spin-3 ions, 50Mn+, which does not possess suitable levels for optical excitation and detection. [ABSTRACT FROM AUTHOR]

We analyzed absorption features arising from interstellar neutral carbon that appeared in the UV spectra of 89 stars recorded in the highest resolution echelle modes of the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope so that we could determine the relative populations of collisionally excited fine-structure levels in the atom's electronic ground state. From this information, in combination with molecular hydrogen rotation temperatures, we derive the distribution of thermal pressures in the diffuse, cold neutral medium (CNM). We find a lognormal pressure distribution (weighted by mass) with a mean in log(p/k) equal to 3.58 and an rms dispersion of at least 0.175 dex that plausibly arises from turbulence with a characteristic Mach number in the range 1 < M < 4. The extreme tails in the distribution are, however, above the lognormal function. Overall, pressures are well correlated with local starlight intensities and extreme kinematics, and they show some anticorrelation with kinetic temperatures. A subsample restricted to low ambient UV intensities reveals a mode in the distribution of log(p/k) that is nearly the same as the complete sample, but with a strong negative skewness created by a near absence of a tail at high pressures. Approximately 23% of this gas is at a pressure that is below that which is allowed for a static CNM. Accompanying nearly all of the gas is a small fraction (~0.05%) that has an extraordinarily large pressure, log(p/k) > 5.5, and this condition is more prevalent at high velocities or for regions with enhanced starlight densities. This survey suggests that the dispersion of thermal pressures in the CNM is predominantly governed by microscopic turbulence driven by star-forming regions, with some additional effects from macroscopic events (e.g., supernova explosions), and these measurements provide constraints for future studies of the broader impact of turbulence on the ISM and star formation. [ABSTRACT FROM AUTHOR]

We investigate the propagation of wave packets on graphene in a perpendicular magnetic field and the appearance of collapses and revivals in the time evolution of an initially localized wave packet. The wave-packet evolution in graphene differs drastically from the one in an electron gas and shows a rich revival structure similar to the dynamics of highly excited Rydberg states. We present a novel numerical wave-packet propagation scheme in order to solve the effective single-particle Dirac--Hamiltonian of graphene and show how the collapse and revival dynamics is affected by the presence of disorder. Our effective numerical method is of general interest for the solution of the Dirac equation in the presence of potentials and magnetic fields. [ABSTRACT FROM AUTHOR]

We propose a scheme for implementing conditional quantum phase gates for two four-state atoms trapped in a cavity. The two ground states of the atoms are coupled through two Raman processes induced by the cavity mode and two classical fields. Under certain conditions nonresonant Raman processes lead to two-atom coupling and can be used to produce conditional phase gates. The scheme is insensitive to cavity decay, thermal photons, and atomic spontaneous emission. The scheme does not require individual addressing of the atoms. [ABSTRACT FROM AUTHOR]

This paper studies the interaction of a L-type three-level atom with a single mode field. It discusses the emission spectrum characteristics of the L-type three-level atom driven by the photon-added coherent field. By means of the second-order degree of coherence, it shows some nonclassical properties of the cavity field, such as sub-Poissonian photon-number distribution and the two-time intensity-intensity correlation which violates the Cauchy-Schwarz inequality. [ABSTRACT FROM AUTHOR]

This paper studies the isotopic effect of Cl2+ rovibronic spectra in the A2IIu (O = 1/2) - X2IIg (O = 1/2) system. Based on the experimental results of the molecular constants of 35Cl2+, it calculates the vibrational isotope shifts of the (2, 7) and (3, 7) band between the isotopic species 35Cl2+, 35Cl37Cl+ and 37Cl2+, and estimates the rotational constants of both A2IIu and X2IIg states for the minor isotopic species 35Cl37Cl+ and 37Cl2+. The experimental results of the spectrum of 35Cl37Cl+ (3, 7) band proves the above mentioned theoretical calculation. The molecular constants and thus resultant rovibronic spectrum for 37Cl2+ were predicted, which will be helpful for further experimental investigation. [ABSTRACT FROM AUTHOR]

Using the isolated-core-excitation scheme and three-step laser resonance ionization spectroscopy approach, this paper, for the first time, has systematically investigated the autoionization spectra of atomic Sm, belonging to the 4f66pnl and 4f55d6snl (l = 0,2) configurations. In the experiment, the first two tunable dye lasers are employed to excite the Sm atom from its initial state to the different 4f66snl bound Rydberg states, then the third dye laser is scanned to drive the atom to the doubly-excited autoionizing states. With the above excitation scheme, the measured transition profiles of the autoionizing states are nearly symmetric, from which the level energies and widths can be easily obtained. [ABSTRACT FROM AUTHOR]

In order to understand the recycling and emission processes of hydrogen atoms in HT-7, spectral profiles of the Da(Ha) line emitted in front of the limiter have been observed with a high-resolution spectrometer and simulated by using the neutral particle transport code DEGAS 2. The results show that four processes are necessary to interpret the Da(Ha) line shape: 1) atom desorption, 2) molecular dissociation, 3) particle reflection, and 4) charge-exchange. The products of the first two processes are cold atoms which emit photons near the peak of Da(Ha) line shape, and those from the last two are warm atoms contributing to the blue side of the spectrum. For a typical ohmic discharge (shot 68520 ne(0) [?]3× 1019 m-3), these components contribute 32%, 15%, 32% and 21%, respectively. Da(Ha) line shapes under different plasma parameters are also discussed in this paper. [ABSTRACT FROM AUTHOR]

The state-selective dissociation pathways for ionic and excited neutral fragments of gaseous and condensed CCl4 following Cl 2p core-level excitation have been characterized by combining photon-induced ionic dissociation, x-ray absorption, resonant photoemission and UV/visible dispersed fluorescence measurements. The Cl 2p→7a*1 excitation of CCl4 induces significant enhancement of the Cl+ desorption yield in the condensed phase and the CCl+ yields in the gaseous phase. Based on the resonant photoemission studies, excitations of Cl 2p electrons to valence orbitals and Rydberg states decay predominantly via the spectator Auger transitions. The transitions of Cl 2p electrons to the Rydberg state of gaseous CCl4 lead to a noteworthy production of excited atomic neutral fragments (C*) and excited diatomic neutral fragments (CCl*). These results provide insight into the state-selective ionic and neutral fragmentation processes of molecules via core-level excitation. [ABSTRACT FROM AUTHOR]

Using the time-dependent multilevel approach, we have calculated the coherent population transfer between the quantum states of potassium atom by a single frequency-chirped laser pulse. The result shows that a pair of sequential 'broadband' frequency-chirped laser pulses can efficiently transfer population from the initial state of the ladder system to the target state. It is also found that the population can be efficiently transferred to a target state and trapped there by using an 'intuitive' or a 'counterintuitive' frequency sweep laser pulse in the case of 'narrowband' frequency-chirped laser pulse. Our research shows that the complete population transfer is related to the pulse duration, chirp rate, and amplitude of the laser pulse. [ABSTRACT FROM AUTHOR]

We consider a two-dimensional Bose gas formed in a planar atomic trap in conditions where the two-dimensional scattering length exceeds all other microscopic length scales in the system and, accordingly, the gas parameter assumes relatively high values. We show that, unlike in the three-dimensional case, for sufficiently low areal densities the two-dimensional gas remains stable against collapse even in the resonant regime. Furthermore, we evaluate the three-body recombination rate that sets the upper limit for the lifetime of the two-dimensional resonant atomic condensate. [ABSTRACT FROM AUTHOR]

By taking full account of the non-orthogonality of the orbitals between the low-lying doubly excited states 1Poand the singly excited states 1Seand 1Deof He, the corresponding radiative decay rates have been investigated theoretically via analytic generalized Laguerre-type atomic orbitals at a nearly numerical multi-configuration self-consistent field accuracy in a general non-orthogonal configuration interaction scheme. From these rates, we calculate the VUV photon emission and metastable atom spectra, and both are found to be in good qualitative agreement with recent excellent measurements. We obtain, successfully, the enhancement of the VUV photon spectrum, experimentally observed at the energy of (2s4p-4s2p)/(2p,3d) 1Poas compared with other nearby lying states. The mechanism proposed by Odling-Smee et alis verified, implying that taking appropriate account of the overlap existing between orbitals of the low-lying doubly excited and singly excited states (especially important for the compact orbitals) can reveal basic physical dominant mechanism and is crucial in understanding these spectra. [ABSTRACT FROM AUTHOR]

The laser properties of the Nd:YGG crystal are investigated. The absorption spectrum from 500 to 900 nm and emission spectrum from 850 to 1400nm of Nd:YGG are measured. As much as 1.35 W output power of fundamental laser operating at 935 and 938 nm with a slope efficiency of 15.7% and 105 mW output power of frequency doubled blue laser are successfully obtained. [ABSTRACT FROM AUTHOR]

The spontaneous evolution from ultracold Rydberg atoms to plasma is investigated in a caesium MOT by using the method of field ionization. The plasma transferred from atoms in different Rydberg states (n = 22-32) are obtained experimentally. Dependence of the threshold time of evolving to plasma and the threshold number of initial Rydberg atoms on the principal quantum number of initial Rydberg states is studied. The experimental results are in agreement with hot-cold Rydberg-Rydberg atom collision ionization theory. [ABSTRACT FROM AUTHOR]

We develop a nondirect product discrete variable representation (npDVR) for treating quantum dynamical problems which involve nonseparable angular variables. The npDVR basis is constructed on spherical functions orthogonalized on the grids of the Lebedev or Popov 2D quadratures for the unit sphere instead of the direct product of 1D quadrature rules. We compare our computational scheme with the old one that used the product of 1D Gaussian quadratures in terms of their convergence and efficiency by calculating, as an example, the spectrum of a hydrogen atom in the magnetic and electric fields arbitrarily oriented to one another. The use of the npDVR based on the Lebedev or Popov 2D quadratures substantially accelerates the convergence of the computational scheme. Moreover, we get the fastest convergence with the npDVR based on the Popov quadratures, which has the largest efficiency coefficient. [ABSTRACT FROM AUTHOR]

Efforts to detect low-mass exoplanets using stellar radial velocities (RVs) are currently limited by magnetic photospheric activity. Suppression of convective blueshift is the dominant magnetic contribution to RV variability in low-activity Sun-like stars. Due to convective plasma motion, the magnitude of RV contributions from the suppression of convective blueshift is related to the depth of formation of photospheric spectral lines for a given species used to compute the RV time series. Meunier et al. used this relation to demonstrate a method for spectroscopic extraction of the suppression of convective blueshift in order to isolate RV contributions, including planetary RVs, that contribute equally to the time series for each spectral line. Here, we extract disk-integrated solar RVs from observations over a 2.5 yr time span made with the solar telescope integrated with the HARPS-N spectrograph at the Telescopio Nazionale Galileo (La Palma, Canary Islands, Spain). We apply the methods outlined by Meunier et al. We are not, however, able to isolate physically meaningful contributions due to the suppression of convective blueshift from this solar data set, potentially because our data set is taken during solar minimum when the suppression of convective blueshift may not sufficiently dominate activity contributions to RVs. This result indicates that, for low-activity Sun-like stars, one must include additional RV contributions from activity sources not considered in the Meunier et al. model at different timescales, as well as instrumental variation, in order to reach the submeter per second RV sensitivity necessary to detect low-mass planets in orbit around Sun-like stars. [ABSTRACT FROM AUTHOR]

Fluorescence loss spectrum for detecting cold Rydberg atoms with high sensitivity has been obtained based on lock-in detection of fluorescence of 6P3/2 state when cooling lasers of the magneto-optical trap are modulated. The experiment results show that the signal to noise ratio has been improved by 32.64 dB when the modulation depth (converted to laser frequency) and frequency are optimized to 4 MHz and 6 kHz, respectively. This technique enables us to perform a highly sensitive non-destructive detection of Rydberg atoms. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is a widely used tool for the characterization of insulating or semiconducting materials of various kinds. The Raman shift is related to vibrationals modes of the probed sample and, as such, can be related to the atomic scale structure of the materials. However, when Raman spectrometry is used to probe materials featuring disorder, radiation damage or simply a large enough concentration of point defects, the relationship between the spectrum and the atomic structure cannot be easily unraveled. In this paper we present a method to extend the scale of the ab initio calculation of first order Raman spectra, based on density functional perturbation theory (DFPT), to cope with larger systems, in order to be able to describe point defects in the limit of low concentration. The goal is to provide a quantitative basis for the interpretation of experimental Raman spectra. The procedure consists in embedding force constant matrices, Born effective charges, and Raman tensor, calculated with DFPT for a supercell with a point defect, into a corresponding perfect bulk matrix to simulate a larger system. After describing in detail the procedure, we present benchmark applications to three quite different materials, containing defects of various kinds: silicon carbide with an intrinsic defect (a carbon antisite), boron carbide with helium impurities—also in combination with vacancies-, and cesium lead iodide with two different alloying impurities. Strengths and limitations of the approach are discussed in the light of the three examples. [ABSTRACT FROM AUTHOR]

The photoionization of a hydrogen atom from its ground state with ultra-fast chirped pulses is investigated by numerically solving the time-dependent Schrödinger equation within length, velocity, and Kramers–Henneberger gauges. Converged results for all gauges for chirp-free pulses agree with the prediction of dynamic interference for ground state hydrogen atoms predicted recently by Jiang and Burgdörfer [Opt. Express 26, 19921 (2018)]. In addition, we investigated photoelectron spectra of hydrogen atoms by chirped laser pulses, and showed that dynamic interference effect will be weaken for pulses with increasing linear chirp. Our numerical results can be understood and discussed in terms of an interplay of photoelectron wavepackets from first and second halves of laser enevelop, including the ac Stark energy level shift of the photoelectron final state and atomic stabilization effect at ultra-high intensities. [ABSTRACT FROM AUTHOR]