Long-range states in collisions of ultracold molecules

TL;DR

This paper investigates long-range bound states in ultracold molecule collisions, revealing states with long lifetimes and potential for narrow Feshbach resonances due to their weak short-range coupling.

Contribution

It demonstrates the existence of long-range states near threshold that are weakly coupled to chaotic short-range states, impacting ultracold molecule control.

Findings

Long-range states exist close to threshold and persist below thresholds.

These states are weakly coupled to short-range chaotic states.

They can cause narrow Feshbach resonances with long lifetimes.

Abstract

We use coupled-channel calculations to explore the nature of near-threshold bound states in a simplified model of Rb+KRb. This is a prototype for systems with very strong coupling at short range and chaotic behavior for the short-range states. We find that there are states with strong long-range character that exist close to threshold and probably persist to depths at least 100 GHz below each threshold. These states are only weakly coupled to the short-range states and do not form part of the chaotic manifold. Since they spend little time at short range, they are relatively insensitive to destruction by laser light. They can thus have long lifetimes that are unrelated to the density of states and can cause narrow Feshbach resonances when the states are shifted across thresholds by external fields.