Efficient three-body calculations with a two-body mapped grid method

Abstract

We investigate the prospects of combining a standard momentum space approach for ultracold three-body scattering with efficient coordinate space schemes to solve the underlying two-body problem. In many of those schemes the two-body problem is numerically restricted up to a finite interparticle distance rb. We analyze effects of this two-body restriction on the two- and three-body level using pairwise square-well potentials that allow for analytic two-body solutions and more realistic Lennard-Jones van der Waals potentials to model atomic interactions. We find that the two-body t-operator converges exponentially in rb for the square-well interaction. Setting rb to 2000 times the range of the interaction, the three-body recombination rate can be determined accurately up to a few percent when the magnitude of the scattering length is small compared to rb, while the position of the lowest Efimov features is accurate up to the percent level. In addition we find that with the introduction of a momentum cut-off, it is possible to determine the three-body parameter in good approximation even for deep van der Waals potentials