Atomic swelling upon compression

The hydrogen atom under the pressure of a spherical penetrable confinement potential of a decreasing radius $r_{0}$ is explored, as a case study. A novel counter-intuitive effect of atomic swelling rather than shrinking with decreasing $r_{0}$ is unraveled, when $r_{0}$ reaches, and remains smaller than, a certain critical value. Upon swelling, the size of the atom is shown to increase by an order of magnitude, or more, compared to the size of the free atom. Examples of changes of photoabsorption properties of confined hydrogen atom upon its swelling are uncovered and demonstrated.Comment: 5 pages, 4 figure

`C60_{60} spin-charging' with an eye on a quantum computer

A question whether there exists an interaction between the spins of the endohedral atom $A$@C$_{60}$ and the properties of the confining shell which might affect the alignment of, or manipulation by, the spins for building a register for a quantum computer is discussed. It is argued that an effect, termed the `C$_{60}$ spin-charging' effect, can occur in endohedral atoms and would affect the operation of a quantum register. The effect is exemplified by choosing the $\rm 3d$ (Cr and Mn) and $\rm 4d$ (Mo and Tc) transition metal atoms as well as a rare-earth Eu atom as the case study. A class of high-spin atoms which are less suitable for building a quantum register is, thus, identified.Comment: 5 pages, 1 figure, submitted to J. Phys. B: At. Mol. Opt. Phy

Ground state properties of a confined simple atom by C60_{60} fullerene

We numerically study the ground state properties of endohedrally confined hydrogen (H) or helium (He) atom by a molecule of C$_{60}$. Our study is based on Diffusion Monte Carlo method. We calculate the effects of centered and small off-centered H- or He-atom on the ground state properties of the systems and describe the variation of ground state energies due to the C$_{60}$ parameters and the confined atomic nuclei positions. Finally, we calculate the electron distributions in $x-z$ plane in a wide range of C$_{60}$ parameters.Comment: 23 pages, 9 figures. To appear in J.Phys. B: Atom. Mol. Op

Term-dependent hybridization of the 5 f-wave functions of Ba and Ba++

It is shown that, unlike in neutral Ba, the 4d→5f transitions cannot be neglected in the interpretation of the 4d spectrum of Ba++. A term-dependent hybridization of the 5f wave functions occurs, the effects of which reverse between Ba and Ba++, and oscillator strength reappears in the 4d→nf (n>~5) transitions. A second kind of wave-function collapse is identified and its effects are described

On the photoionization of the outer electrons in noble gas endohedral atoms

We demonstrate the prominent modification of the outer shell photoionization cross-section in noble gas (NG) endohedral atoms NG@F under the action of the fullerene F electron shell. This shell leads to two important effects, namely to strong enhancement of the cross-section due to fullerenes shell polarization under the action of the incoming electromagnetic wave and to prominent oscillation of this cross-section due to the reflection of the photoelectron from NG by the F shell. All but He noble gas atoms are considered. The polarization of the fullerene shell is expressed via the total photoabsorption cross-section of F. The reflection of the photoelectron is taken into account in the frame of the so-called bubble potential that is a spherical zero --thickness potential. It is assumed in the derivations that NG is centrally located in the fullerene. It is assumed also, in accord with the existing experimental data, that the fullerenes radius R is much bigger than the atomic radius and the thickness of the fullerenes shell . These assumptions permit, as it was demonstrated recently, to present the NG@F photoionization cross-section as a product of the NG cross-section and two well defined calculated factors.Comment: 19 pages, 9 figure

Magneto-optical rotation of spectrally impure fields and its nonlinear dependence on optical density

We calculate magneto-optical rptation of spectrally impure fileds in an optically thick cold atmic medium. We show that the spectral impurity leads to non-linear dependence of the rotation angle on optical density. Using our calculations, we provide a quanttative analysis of the recent experimental results of G. Labeyrie et al. [Phys. Rev. A 64, 033402 (2001)] using cold Rb$^{85}$ atoms.Comment: 6 pages, 5 Figures, ReVTeX4, Submitted to PR

Statistics of electromagnetic transitions as a signature of chaos in many-electron atoms

Using a configuration interaction approach we study statistics of the dipole matrix elements (E1 amplitudes) between the 14 lower odd states with J=4 and 21st to 100th even states with J=4 in the Ce atom (1120 lines). We show that the distribution of the matrix elements is close to Gaussian, although the width of the Gaussian distribution, i.e. the root-mean-square matrix element, changes with the excitation energy. The corresponding line strengths are distributed according to the Porter-Thomas law which describes statistics of transition strengths between chaotic states in compound nuclei. We also show how to use a statistical theory to calculate mean squared values of the matrix elements or transition amplitudes between chaotic many-body states. We draw some support for our conclusions from the analysis of the 228 experimental line strengths in Ce [J. Opt. Soc. Am. v. 8, p. 1545 (1991)], although direct comparison with the calculations is impeded by incompleteness of the experimental data. Nevertheless, the statistics observed evidence that highly excited many-electron states in atoms are indeed chaotic.Comment: 16 pages, REVTEX, 4 PostScript figures (submitted to Phys Rev A

Reducing multiphoton ionization in a linearly polarized microwave field by local control

We present a control procedure to reduce the stochastic ionization of hydrogen atom in a strong microwave field by adding to the original Hamiltonian a comparatively small control term which might consist of an additional set of microwave fields. This modification restores select invariant tori in the dynamics and prevents ionization. We demonstrate the procedure on the one-dimensional model of microwave ionization.Comment: 8 page

Confinement resonances in photoionization of endohedral atoms: a myth or reality?

We demonstrate that the structure of confinement resonances in the photoionization cross section of an endohedral atom is very sensitive to the mean displacement of the atom from the cage center. The resonances are strongly suppressed if 2 exceeds the photoelectron half-wavelength. We explain the results of recent experiments which contradict the earlier theoretical predictions on the existence of confinement resonances in particular endohedral systems.Comment: 4 pages, 5 figures, RevTe