Taking the ultracold 85Rb–87Rb collision system as an example, we investigated the Feshbach resonances of nonzero partial waves above the threshold. The self-energy at the threshold, which represents the coupling strength between open and closed channels, is considered a critical parameter to quantitatively describe the properties of Feshbach resonances. The total elastic and inelastic cross sections are calculated as functions of the magnetic field B and collision energy E col, ranging from 0.1 to 600 μK. For a large absolute value of the self-energy at the threshold, the resonance decays rapidly with increasing collision energy, and narrow resonances of nonzero partial waves can be clearly resolved in the contour plot of the inelastic cross section versus the collision energy and magnetic field. It was found that the resonance tail appeared at the given magnetic field when the cross section decreased from the maximal value of the resonance peak to the minimum value, where a long resonance tail indicates an appreciable resonance in a relatively large region of collision energy. This relationship between the self-energy and the properties of Feshbach resonances still exists in the thermally averaged inelastic rate coefficient. The bound-state energies for nonzero partial waves split owing to the spin–spin interaction, which results in multiple nearly-overlapping resonances. Both the spin–spin and second-order spin–orbit effects are included. However, multiple nearly-overlapping resonances for nonzero partial waves are difficult to resolve in thermally averaged rate coefficients.

No abstract

We investigate the modulating action of an external electric field on the magnetically tuned Feshbach resonance in ultracold heteronuclear atomic collision by using the multichannel quantum-defect theory (MQDT). The coupling between different partial wave states induced by an electric field is included into the singlet and triplet quantum defect matrices y(0) and y(1). By taking the truncated −C6/R6 − C8/R8 − C10/R10 potential as the reference potential, the threshold behaviors of four quantum-defect parameters for the lowest three partial waves are described. The results calculated by using the MQDT agree with those calculated using the coupled channel method. Moreover, we present an analytical expression used for describing the variation of the position and width of the magnetically tuned Feshbach resonance modulated by an electric field.

A Feshbach optimized photoassociation (FOPA) process for preparing ultracold excited-state 39K133Cs molecules is studied theoretically. Under the joint action of the magnetic field and short laser pulse, the colliding atoms in a superposition state composed of eight hyperfine components are converted into a molecule in the vibrational level of the excited state via two transition processes, the transition between singlet states and the transition between triplet states. The association efficiency can be significantly enhanced by taking advantage of Feshbach resonance. At different resonance positions, different hyperfine components of the superposition state dominate over the FOPA process, and the quantum interference displays different behaviors. Compared with the FOPA process only including a single hyperfine component, the quantum interference in the FOPA process containing all hyperfine components has a visible effect on the association efficiency.

Electron beam welding (EBW) with multiple beams is a new technology simultaneous with preheating or postheating, which contributes to reducing residual stresses. To improve corrosion resistance in marine, EBW with multiple beams is employed on AF1410 steel. The weld is uniform, with a width of 7.3-8.4 mm, which is wider than that of conventional welding. To evaluate susceptibility to stress corrosion cracking (SCC), the welding stresses and slow strain rate tests (SSRT) are studied. The longitudinal stresses on the front weld with preheating and postheating are 25% and 15% lower than conventional welding. The transversal stresses also, respectively, decreased by 15% and 6%. The tensile properties of EBW from SSRT present a susceptibility to SCC. Compared with conventional welding, the loss of elongation I δ with preheating and postheating decreases to 0.9-1.5%, and the area reduction rate I R lowers to 7-10%. EBW with multiple beams presents a low susceptibility, attributed to reducing welding stresses related to a temperature gradient.