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Using potential models, we analyze range corrections to the universal law dictated by the Efimov theory of three bosons. In the case of finite-range interactions, we have observed that at first order, it is necessary to supplement the theory with one finite-range parameter Γn3 for each specific n level [A. Kievsky and M. Gattobigio, Phys. Rev. A 87, 052719 (2013)]. The value of Γn3 depends on the way the potentials are changed to tune the scattering length toward the unitary limit. In this work, we analyze a particular path in which the length rB = a - aB, measuring the difference between the two-body scattering length a and the energy-scattering length aB, is almost constant. Analyzing systems with very different scales, such as atomic or nuclear systems, we observe that the finite-range parameter remains almost constant along the path with a numerical value of Γn3 ≈ 0.87 for the ground-state level. This observation suggests the possibility of constructing a single universal function that incorporates finite-range effects for this class of paths. The result is used to estimate the three-body parameter κ*, in the case of real atomic systems brought to the unitary limit through broad Feshbach resonances. Furthermore, we show that the finite-range parameter can be put in relation to the two-body contact C2 at the unitary limit. [ABSTRACT FROM AUTHOR]

We demonstrate Feshbach optimized photoassociation (FOPA) into the 0g- (5S1/2 + 5P1/2) state in 85Rb2. FOPA uses the enhancement of the amplitude of the initial atomic scattering wave function due to a Feshbach resonance to increase the molecular formation rate from photoassociation. We observe three vibrational levels, ν = 127, 140, and 150, with previously unmeasured binding energies of 256, 154, and 96 cm-1. We measure the frequency, central magnetic field position, and magnetic field width of each Feshbach resonance. Our findings experimentally confirm that this technique can measure vibrational levels lower than those accessible to traditional photoassociative spectroscopy. [ABSTRACT FROM AUTHOR]

The standard perturbative expansion of the S matrix cannot generally be used in the treatment of atomic scattering processes, involving atomic bound states, due to the special type of singularity that can appear here. It is demonstrated in the present paper that as a consequence of the optical theorem for free particles the effective Hamiltonian is closely related to the total cross section, a relation that is valid also when bound states are present. This implies that methods designed for structure calculations also can be used in dynamical processes. We have found that the covariant-evolution-operator technique that we have developed for structure calculations is here particularly useful. This is a consequence of the fact that the regular part of this operator (the Green's operator), running over all times, is essentially equal to the effective Hamiltonian and therefore directly related to the scattering cross section. In this paper the procedure is demonstrated for the case of radiative recombination. [ABSTRACT FROM AUTHOR]

A variational R-matrix approach combined with multichannel quantum defect theory is used for a computational study of triplet gerade states of H2. Electron-ion reaction (quantum defect) matrices are calculated as functions of internuclear distance and energy for the bound and continuum ranges including singly and doubly excited configurations built on the 1σg (X+²Σg+) and 1σu (A+²Σu+) core states of the H2+ shown how these matrices can be reduced to effective quantum defect functions adapted to the analysis of high-resolution spectra in the bound range. These R-matrix effective quantum defects are finally adjusted to the available experimental data [Sprecher et al., J. Phys. Chem. A 117, 9462 (2013)], producing agreement with experiment to within 0.5 cm-1, nearly as good as obtained by Sprecher et al. In addition, the Ä-matrix calculations predict the evolution of the quantum defects for higher energies, in a range extending far into the electronic continuum. [ABSTRACT FROM AUTHOR]

We investigate topological aspects of subnanometer electron vortex beams upon elastic propagation through atomic scattering potentials. Two main aspects can be distinguished: (i) significantly reduced derealization compared to a similar nonvortex beam if the beam centers on an atomic column and (ii) site symmetry dependent splitting of higher-order vortex beams. Furthermore, the results provide insight into the complex vortex line fabric within the elastically scattered wave containing characteristic vortex loops predominantly attached to atomic columns and characteristic twists of vortex lines around atomic columns. [ABSTRACT FROM AUTHOR]

We use the equivalence of positron scattering on atomic hydrogen, and positronium-proton scattering, to provide benchmark results for (anti)hydrogen formation in positronium (Ps) scattering on (anti)protons in a low-energy region. Using the two-center e+-H convergent close-coupling approach convergence to a few percent accuracy is demonstrated, in the only required zeroth partial wave, by substantial variation in the .treatment of the two centers. A simple relation for the cross section at low Ps energies (k2) is given, with the I/k behavior demonstrated to strictly hold only at threshold [ABSTRACT FROM AUTHOR]