An optimized absorbing potential for ultrafast, strong-field problems

Theoretical treatments of strong-field physics have long relied on the numerical solution of the time-dependent Schr\"odinger equation. The most effective such treatments utilize a discrete spatial representation---a grid. Since most strong-field observables relate to the continuum portion of the wave function, the boundaries of the grid---which act as hard walls and thus cause reflection---can substantially impact the observables. Special care thus needs to be taken. While there exist a number of attempts to solve this problem---e.g., complex absorbing potentials and masking functions, exterior complex scaling, and coordinate scaling---none of them are completely satisfactory. The first of these is arguably the most popular, but it consumes a substantial fraction of the computing resources in any given calculation. Worse, this fraction grows with the dimensionality of the problem. And, no systematic way to design such a potential has been used in the strong-field community. In this work, we address these issues and find a much better solution. By comparing with previous widely used absorbing potentials, we find a factor of 3--4 reduction in the absorption range, given the same level of absorption over a specified energy interval

Mass Dependence of Ultracold Three-Body Collision Rates

We show that many aspects of ultracold three-body collisions can be controlled by choosing the mass ratio between the collision partners. In the ultracold regime, the scattering length dependence of the three-body rates can be substantially modified from the equal mass results. We demonstrate that the only non-trivial mass dependence is due solely to Efimov physics. We have determined the mass dependence of the three-body collision rates for all heteronuclear systems relevant for two-component atomic gases with resonant s-wave interspecies interactions, which includes only three-body systems with two identical bosons or two identical fermions

Suppression of molecular decay in ultracold gases without Fermi statistics

We study inelastic processes for ultracold three-body systems in which only one interaction is resonant. We have found that the decay rates for weakly bound molecules due to collisions with other atoms can be suppressed not only without fermionic statistics but also when bosonic statistics applies. In addition, we show that at ultracold temperatures three-body recombination involving a single resonant pair of atoms leads mainly to formation of weakly bound molecules which, in turn, are stable against decay. These results indicate that recombination in three-component atomic gases can be used as an efficient mechanism for molecular formation, allowing the achievement of high molecular densities

Ultracold three-body collisions near narrow Feshbach resonances

We study ultracold three-body collisions of bosons and fermions when the interatomic interaction is tuned near a narrow Feshbach resonance. We show that the width of the resonance has a substantial impact on the collisional properties of ultracold gases in the strongly interacting regime. We obtain numerical and analytical results that allow us to identify universal features related to the resonance width. For narrow resonances, we have found a suppression of all inelastic processes in boson systems leading to deeply bound states and an enhancement for fermion systems.Comment: 5 pages, 3 figure

Efimov Trimer Formation via Ultracold Four-body Recombination

We discuss the collisional formation of Efimov trimers via ultracold four-body recombination. In particular, we consider the reaction A+A+A+B->A3+B with A and B ultracold atoms. We obtain expressions for the four-body recombination rate and show that it reflects the three-body Efimov physics either as a function of collision energy or as a function of the two-body s-wave scattering length between A atoms. In addition, we briefly discuss issues important for experimentally observing this interesting and relatively unexplored process.Comment: 5 pages, 3 figure