arXiv subjects

Li-Yan Tang

Publications and source records attributed to Li-Yan Tang.

29 records · Page 2Linked to original sources

arXiv2016

Calculations of long-range three-body interactions for Li($2\,^2S$)-Li($2\,^2S$)-Li($2\,^2P$)

General formulas for calculating the several leading long-range interactions among three identical atoms where two atoms are in identical $S$ states and the other atom is in a $P$ state are obtained using perturbation theory for the energies up to second order. The first order (dipolar) interactions depend on the geometrical configurations of the three atoms. In second order, additive and nonadditive dispersion interactions are obtained. The nonadditive interactions depend on the geometrical configurations in marked contrast to the case where all three atoms are in identical $S$ states, for which the nonadditive (also known as triple-dipole or as Axilrod-Muto-Teller) dispersion interactions appear at the third order. The formalism is demonstrated by the calculation of the coefficients for the Li($2\,^2S$)-Li($2\,^2S$)-Li($2\,^{2}P$) system using variationally-generated atomic lithium wave functions in Hylleraas coordinates. The present dipolar coefficients and additive and nonadditive dispersion coefficients may be useful in constructing precise potential energy surfaces for this three lithium atom system.

physics.atom-ph↗

arXiv2015

Precision Measurement for Metastable Helium Atoms of the 413 nm Tune-Out Wavelength at Which the Atomic Polarizability Vanishes

We present the first measurement for helium atoms of the tune-out wavelength at which the atomic polarizability vanishes. We utilise a novel, highly sensitive technique for precisely measuring the effect of variations in the trapping potential of confined metastable ($2^{3}S_{1}$) helium atoms illuminated by a perturbing laser light field. The measured tune-out wavelength of 413.0938($9_{Stat.}$)($20_{Syst.}$) nm compares well with the value predicted by a theoretical calculation (413.02(9) nm) which is sensitive to finite nuclear mass, relativistic, and quantum electro-dynamic (QED) effects. This provides motivation for more detailed theoretical investigations to test QED.

physics.atom-ph↗

arXiv2015

Dynamic dipole polarizabilities for the low-lying triplet states of helium

The dynamic dipole polarizabilities for the four lowest triplet states ($2\,^3S$, $3\,^3S$, $2\,^3P$ and $3\,^3P$) of helium are calculated using the B-spline configuration interaction method. Present values of the static dipole polarizabilities in the length, velocity and acceleration gauges are in good agreement with the best Hylleraas results. Also the tune-out wavelengths in the range from 400 nm to 4.2~$μ$m for the four lowest triplet states are identified, and the magic wavelengths in the range from 460~nm to 3.5~$μ$m for the $2\,^3S \to 3\,^3S$, $2\,^3S \to 2\,^3P$, and $2\,^3S \to 3\,^3P$ transitions are determined. We show that the tune-out wavelength of $2\,^3S$ state is 413.038 28(3) nm, which corroborates the value of Mitroy and Tang (Phys. Rev. A 88, 052515 (2013)), and the magic wavelength around 1066 nm for the $2\,^3S \to 3\,^3P$ transition can be expected for precision measurement to determine the ratio of transition matrix elements $(2\,^3S \to 2\,^3P) / (3\,^3P\to 6\,^3S)$.

physics.atom-ph↗

arXiv2014

High-precision nonadiabatic calculations of dynamic polarizabilities and hyperpolarizabilities for the lowlying vibrational-rotational states of hydrogen molecular ions

The static and dynamic electric multipolar polarizabilities and second hyperpolarizabilities of the H$_2^+$, D$_2^+$, and HD$^+$ molecular ions in the ground and first excited states are calculated nonrelativistically using explicitly correlated Hylleraas basis sets. The calculations are fully nonadiabatic; the Born-Oppenheimer approximation is not used. Comparisons are made with published theoretical and experimental results, where available. In our approach, no derivatives of energy functions nor derivatives of response functions are needed. In particular, we make contact with earlier calculations in the Born-Oppenheimer calculation where polarizabilities were decomposed into electronic, vibrational, and rotational contributions and where hyperpolarizabilities were determined from derivatives of energy functions. We find that the static hyperpolarizability for the ground state of HD$^+$ is seven orders of magnitude larger than the corresponding dipole polarizability. For the dipole polarizability of HD$^+$ in the first excited-state the high precision of the present method facilitates treatment of a near cancellation between two terms. For applications to laser spectroscopy of trapped ions we find tune-out and magic wavelengths for the HD$^+$ ion in a laser field. In addition, we also calculate the first few leading terms for long-range interactions of a hydrogen molecular ion interacting with a ground-state H, He, and Li atoms.

physics.atom-ph↗

arXiv2013

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.

physics.atom-ph↗

arXiv2012

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

High precision multipole polarizabilities, $α_{\ell}$ for $\ell \le 4$ 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 $\sum_i f^{(\ell)}_{0i} = 0$ for all multipoles from $\ell = 1$ to $\ell = 4$. The dispersion coefficients for the long-range H-H and H-He$^+$ interactions are given.

physics.atom-ph↗

arXiv2012

The long-range non-additive three-body dispersion interactions for the rare gases, alkali and alkaline-earth atoms

The long-range non-additive three-body dispersion interaction coefficients $Z_{111}$, $Z_{112}$, $Z_{113}$, and $Z_{122}$ are computed for many atomic combinations using standard expressions. The atoms considered include hydrogen, the rare gases, the alkali atoms (up to Rb) and the alkaline-earth atoms (up to Sr). The term $Z_{111}$, arising from three mutual dipole interactions is known as the Axilrod-Teller-Muto coefficient or the DDD (dipole-dipole-dipole) coefficient. Similarly, the terms $Z_{112}$, $Z_{113}$, and $Z_{122}$ arise from the mutual combinations of dipole (1), quadrupole (2), and octupole (3) interactions between atoms and they are sometimes known, respectively, as DDQ, DDO, and DQQ coefficients. Results for the four $Z$ coefficients are given for the homonuclear trimers, for the trimers involving two like-rare-gas atoms, and for the trimers with all combinations of the H, He, Li atoms. An exhaustive compilation of all coefficients between all possible atomic combinations is presented as supplementary data.

physics.atom-ph↗

arXiv2011

Convergence of the multipole expansion of the polarization interaction

The multipole expansion of the polarization interaction between a charged particle and an electrically charged particle has long been known to be asymptotic in nature, i.e. the multiple expansion diverges at any finite distance from the atom. However, it is shown that the multipole expansion of the polarization potential of a confined hydrogen atom is absolutely convergent at a distance outside the atoms confinement radius. It is likely that the multipole expansion of the dispersion interaction of two confined atoms will also be absolutely convergent provided the internuclear separation of the two atoms is sufficiency large to exclude any overlap between the electron charge clouds of the two atoms.

physics.atom-ph↗

arXiv2010

The dynamic dipole polarizabilities of the Li atom and the Be+ ion

The dynamic dipole polarizabilities for the Li atom and the Be+ ion in the 2s and 2p states are calculated using the variational method with a Hylleraas basis. The present polarizabilities represent the definitive values in the non-relativistic limit. Corrections due to relativistic effects are also estimated. Analytic representations of the polarizabilities for frequency ranges encompassing the n=3 excitations are presented. The recommended polarizabilities for ^7Li and ^9Be+ were 164.11 \pm 0.03 a.u. and 24.489 \pm 0.004 a.u..

physics.atom-ph↗

arXiv2009

Calculations of polarizabilities and hyperpolarizabilities for the Be$^+$ ion

The polarizabilities and hyperpolarizabilities of the Be$^+$ ion in the $2^2S$ state and the $2^2P$ state are determined. Calculations are performed using two independent methods: i) variationally determined wave functions using Hylleraas basis set expansions and ii) single electron calculations utilizing a frozen-core Hamiltonian. The first few parameters in the long-range interaction potential between a Be$^+$ ion and a H, He, or Li atom, and the leading parameters of the effective potential for the high-$L$ Rydberg states of beryllium were also computed. All the values reported are the results of calculations close to convergence. Comparisons are made with published results where available.

physics.atom-ph↗

arXiv2009

Non-relativistic ab initio calculations for $2^2S$, $2^2P$ and $3^2D$ lithium isotopes: Applications to polarizabilities and dispersion interactions

The electric dipole polarizabilities and hyperpolarizabilities for the lithium isotopes $^6$Li and $^7$Li in the ground state $2^2S$ and the excited states $2^2P$ and $3^2D$, as well as the leading resonance and dispersion long-range coefficients for the Li($2^2S$)--Li($2^2S$) and Li($2^2S$)--Li($2^2P$) systems, are calculated nonrelativistically using variational wave functions in Hylleraas basis sets. Comparisons are made with published results, where available. We find that the value of the second hyperpolarizability of the $2^2S$ state is sensitive to the isotopic mass due to a near cancellation between two terms. For the $3^2D$ state polarizability tensor the calculated components disagree with those measured in the sole experiment and with those calculated semi-empirically.

physics.atom-ph↗