Jun Jiang

Tune-out wavelengths for potassium

The five longest tune-out wavelengths for the potassium atom are determined using a relativistic structure model which treats the atom as consisting of a single valence electron moving outside a closed shell core. The importance of various terms in the dynamic polarizability in the vicinity of the 4p(J), 5p(J), and 6p(J) transitions are discussed. DOI: 10.1103/PhysRevA.87.032518

Computational investigation of static multipole polarizabilities and sum rules for ground-state hydrogenlike ions

High-precision multipole polarizabilities, alpha(l) for l <= 4 of the 1s ground state of the hydrogen isoelectronic series, are obtained from the Dirac equation using the B-spline method with Notre Dame boundary conditions. Compact analytic expressions for the polarizabilities as a function of Z with a relative accuracy of 10(-6) up to Z = 100 are determined by fitting to the calculated polarizabilities. The oscillator strengths satisfy the sum rules Sigma(i) f(gi)((l)) = 0 for all multipoles from l = 1 to l = 4. The dispersion coefficients for the long-range H-H and H-He+ interactions are given.

Effective oscillator strength distributions of spherically symmetric atoms for calculating polarizabilities and long-range atom–atom interactions

Effective oscillator strength distributions are systematically generated and tabulated for the alkali atoms, the alkaline-earth atoms, the alkaline-earth ions, the rare gases and some miscellaneous atoms. These effective distributions are used to compute the dipole, quadrupole and octupole static polarizabilities, and are then applied to the calculation of the dynamic polarizabilities at imaginary frequencies. These polarizabilities can be used to determine the long-range C6, C8 and C10 atom–atom interactions for the dimers formed from any of these atoms and ions, and we present tables covering all of these combinations.

Tune-out wavelengths for the alkaline-earth-metal atoms

The lowest three tune-out wavelengths of the four alkaline-earth-metal atoms Be, Mg, Ca, and Sr are determined from tabulations of matrix elements produced from large first-principles calculations. The tune-out wavelengths are located near the wavelengths for the 3P1o and 1P1o excitations. The measurement of the tune-out wavelengths could be used to establish a quantitative relationship between the oscillator strength of the transition leading to existence of the tune-out wavelength and the dynamic polarizability of the atom at the tune-out frequency. The longest tune-out wavelengths for Be, Mg, Ca, Sr, Ba, and Yb are 454.9813, 457.2372, 657.446, 689.200, 788.875, and 553.00 nm, respectively.

Hyperfine effects on potassium tune-out wavelengths and polarizabilities

The influence of hyperfine interactions on the tune-out wavelengths of the 39K, 40K, and 41K isotopes of the potassium atom was investigated. The hyperfine interaction of the 4s1/2 ground state results in a shift and splitting of the primary tune-out wavelength near 769 nm. The 4s1/2 state hyperfine splittings of the primary tune-out wavelength were almost equal to the hyperfine splittings of the ground states. The splittings in the wavelengths were 0.0009, 0.0026, and 0.0005 nm for 39K, 40K, and 41K, respectively. The hyperfine splitting of the npJ levels leads to the creation of additional tune-out wavelengths. The additional tune-out wavelengths could be difficult to detect due to very small differences from the transition wavelengths to the 4pJ,F states. The hyperfine Stark shift for the ground states of all three isotopes was also computed, and the value for 39K was found to be compatible with the previous experiments and the most recent calculation using relativistic many-body perturbation theory.

Convergence of the multipole expansions of the polarization and dispersion interactions for atoms under confinement

The multipole expansion of the polarization interaction between a charged particle and an electrically neutral object has long been known to be asymptotic in nature, i.e., the multiple expansion diverges at any finite distance from the atom. However, the multipole expansion of the polarization potential of a confined hydrogen atom is shown to be absolutely convergent at a distance outside the confinement radius, R(0), of the atom. The multipole expansion of the dispersion potential between two confined hydrogen atoms is also shown to be absolutely convergent provided the two atoms satisfy R > 2R(0), where R is the inter-nuclear separation. These results were established analytically using oscillator strength sum rules and verified numerically using a B-spline description of the hydrogen ground state and its excitation spectrum.

Relativistic semiempirical-core-potential calculations of Sr+ using Laguerre and Slater spinors

A relativistic description of the structure of heavy alkali atoms and alkali-like ions using S-spinors and L-spinors has been developed. The core wavefunction is defined by a Dirac-Fock calculation using an S-spinors basis. The S-spinor basis is then supplemented by a large set of L-spinors for the calculation of the valence wavefunction in a frozen-core model. The numerical stability of the L-spinor approach is demonstrated by computing the energies and decay rates of several low-lying hydrogen eigenstates, along with the polarizabilities of a Z = 60 hydrogenic ion. The approach is then applied to calculate the dynamic polarizabilities of the 5s, 4d and 5p states of Sr. The magic wavelengths at which the Stark shifts between different pairs of transitions are zero are computed. Determination of the magic wavelengths for the 5s → 4d 3 2 and 5s → 4d 5 2 transitions near 417 nm (near the wavelength for the 5s → 5pj transitions) would allow a determination of the oscillator strength ratio for the 5s → 5p 1 2 and 5s → 5p 3 2 transitions.

Long-range interactions between alkali and alkaline-earth atoms

Dispersion coefficients between the alkali metal atoms (Li–Rb) and alkaline-earth metal atoms (Be–Sr) are evaluated using matrix elements computed from frozen core configuration interaction calculations. Besides dispersion coefficients with both atoms in their respective ground states, dispersion coefficients are also given for the case where one atom is in its ground state and the other atom is in a low-lying excited state.

Complex polarisabilities and hyperpolarisabilities of atoms

The complex dipole polarisabilities of alkali atoms are computed for low-lying eigenstates. We present a unified method of calculation of the real part of the polarisability as well as two different imaginary contributions to the polarisability. One imaginary polarisability is related to the resonant damping of the cross-section both below and above threshold, whilst the other imaginary polarisability describes the photoionisation cross-section above threshold. We also present preliminary calculations of the complex hyperpolarisabilities of atomic clocks and how they are impacted by the linear and non-linear photon-atom interactions.