Hyperfine structure modifications of collisional losses from light-force atom traps

Abstract

Inelastic atomic collisions constitote loss mechanihms for neutral atom traps. and the study of trap-loss rates may provide detailed information on the long-range interaction behueen atoms and on the dynamics of very slow collisions. Gallagher and Pritchard have given a simple two-state model for such collisions which includes a radiative transition or a single curve crossing at short range representing, for example. fine-structurechanging collisions. In order to better describe the more complicated case found in alkali metals, we have extended this model to include several excited hypefine structure levels with curve crossings at long range.We find that collisions in a laser field that are capable of expelling atoms from the trap can be suppressed in some laser frequency regions and enhanced in others, in comparison with the predictions of the simple two-state model. Using this model to represent radiative escape via the 2, potential of alkali dimer molecules we are able to geatly improve agreement between theory and experiment, including new measuremeals an sSRb reported here.

Optical cooling and trapping of highly magnetic atoms: the benefits of a spontaneous spin polarization

“…We model this phenomenon using a simple description of molecular dynamics, inspired from [36,40,39]. The large electron spin of Dysprosium leads to an intricate structure of 2(2J + 1)(2J + 1) = 646 molecular potential curves that we calculated numerically.…”

Theories for cold atomic collisions in light fields

“…where τ is a constant. Lett et al [54] have derived an improved but more complicated expression for S, but they also ignored E. A comparison with fully quantum numerical simulations, however, indicates that E does play a role, and it should not be disregarded too lightly [39]. Of course, the integral can be easily evaluated numerically [12,55], but for comparisons with experimental data it is useful to have simple analytic expressions, especially if the actual values for some parameters are not completely known.…”

“…In the weak field limit it is usually easy to extend the above two-state models to cover multistate cases, because most of the curve crossing situations are isolated and can thus be treated independently, as a sequence of multiple crossings. This has been utilized in [46,53,54]. With the complex potential model this is especially simple, and it is not even necessary to assume that we have isolated crossings.…”

Time-Resolved Studies of Ultracold Ionizing Collisions

“…As shielding affects only 6s 1 6s collisions, this indicates that the formation of molecular ions is due only to atom pairs which survive in and collide on the excited-state potentials (EAI). We thus observe the excited-state survival which has long been thought to play an important role in the enhancement of ultracold collisions [13][14][15]. Excitedstate survival in this system does not involve the population of long-lived states (such as the 1u and 2u states in alkali systems), which have been considered in previous work [6,14,15].…”

“…We thus observe the excited-state survival which has long been thought to play an important role in the enhancement of ultracold collisions [13][14][15]. Excitedstate survival in this system does not involve the population of long-lived states (such as the 1u and 2u states in alkali systems), which have been considered in previous work [6,14,15]. There is no attractive molecular potential from the 6s 1 6p asymptote with a lifetime more than 20% longer than the 34 ns atomic lifetime [16].…”