Bound States and Scattering Processes in the ^4He_3 Atomic System

Feshbach resonances in ultracold atomic and molecular collisions: threshold behaviour and suppression of poles in scattering lengths

In the absence of inelastic scattering, Feshbach resonances produce poles in scattering lengths and very large peaks in elastic cross sections. However, inelastic scattering removes the poles. Whenever the resonant state is coupled comparably to the elastic and inelastic channels, the scattering length exhibits only a small oscillation and peaks in cross sections are dramatically suppressed. A resonant scattering length is defined to characterize the amplitude of the oscillation, and is shown to be small for many collisions of ultracold molecules. The results suggest that cross sections for ul…

Atomic Scattering For Chemical Analysis Of Surfaces

The study explores machine learning methods for revealing chemical sensitivity in Helium spin-echo spectroscopy, in order to obtain ultra-sensitive surface analytic technique. We model bi-species co-adsorbed systems and demonstrate that by using deep-learning neural-networks partial surface concentrations are obtainable. An example system of particles with mass 50 and 100 a.m.u was tested with characteristic inter-adsorbate and adsorbate-substrate interactions, with partial surface concentrations being resolvable up to 20% occupancy of adsorption sites, and with modestly high noise level of 4%…

Binding Energies and Scattering Observables in the 4^He_3 Atomic System

The ^4He_3 bound states and the scattering of a ^4He atom off a ^4He dimer at ultra-low energies are investigated using a hard-core version of the Faddeev differential equations. Various realistic ^4He-^4He interactions were employed, amomg them the LM2M2 potential by Aziz and Slaman and the recent TTY potential by Tang, Toennies and Yiu. The ground state and the excited (Efimov) state obtained are compared with other results. The scattering lengths and the atom-diatom phase shifts were calculated for center of mass energies up to 2.45 mK. It was found that the LM2M2 and TTY potentials, althou…

Coherent and stochastic contributions of compound resonances in atomic processes: Electron recombination, photoionization and scattering

In open-shell atoms and ions, processes such as photoionization, combination (Raman) scattering, electron scattering and recombination, are often mediated by many-electron compound resonances. We show that their interference (neglected in the independent-resonance approximation) leads to a coherent contribution, which determines the energy-averaged total cross sections of electron- and photon-induced reactions obtained using the optical theorem. In contrast, the partial cross sections (e.g., electron recombination, or photon Raman scattering) are dominated by the stochastic contributions. Thus…

Multichannel quantum-defect theory for slow atomic collisions

We present a multichannel quantum-defect theory for slow atomic collisions that takes advantages of the analytic solutions for the long-range potential, and both the energy and the angular-momentum insensitivities of the short-range parameters. The theory provides an accurate and complete account of scattering processes, including shape and Feshbach resonances, in terms of a few parameters such as the singlet and the triplet scattering lengths. As an example, results for $^{23}$Na-$^{23}$Na scattering are presented and compared close-coupling calculations.

Multiple scattering of matter waves: an analytic model of the refractive index for atomic and molecular gases

We present an analytic model of the refractive index for matter waves propagating through atomic or molecular gases. The model, which combines a WKB treatment of the long range attraction with the Fraunhofer model treatment of the short range repulsion, furnishes a refractive index in compelling agreement with recent experiments of Jacquey et al. [Phys. Rev. Lett. 98, 240405 (2007)] on Li atom matter waves passing through dilute noble gases. We show that the diffractive contribution, which arises from scattering by a two dimensional "hard core" of the potential, is essential for obtaining a co…

冷原子碰撞中Fano共振轮廓的散射角依赖性分析：基于复值$ w $参数

Scattering Angle Dependence of Fano Resonance Profiles in Cold Atomic Collisions Analyzed with the Complex Valued $w$ Parameter

通过复值$ w $参数分析冷原子碰撞中Fano共振轮廓的散射角依赖性，揭示了共振轮廓不对称性与原子间相互作用势能的关系。

Editorial: Special Issue on the Atomic and Molecular Processes in the Ultracold Regime, the Chemical Regime, and Astrophysics

This editorial introduces the J. Phys. B: Atomic, Molecular and Optical Physics Special Issue "Atomic and Molecular Processes in the Ultracold Regime, the Chemical Regime and Astrophysics" dedicated to Professor Alexander Dalgarno (1928-2015). After a brief biographical review, short summaries of the contributed papers and their relations to some of Prof. Dalgarno's work are given.

Steerable Wavelet Scattering for 3D Atomic Systems with Application to Li-Si Energy Prediction

A general machine learning architecture is introduced that uses wavelet scattering coefficients of an inputted three dimensional signal as features. Solid harmonic wavelet scattering transforms of three dimensional signals were previously introduced in a machine learning framework for the regression of properties of small organic molecules. Here this approach is extended for general steerable wavelets which are equivariant to translations and rotations, resulting in a sparse model of the target function. The scattering coefficients inherit from the wavelets invariance to translations and rotat…