Rotational-state dependence of interactions between polar molecules

TL;DR

This paper explores how the rotational states of polar molecules influence their long-range electrostatic interactions, revealing state-dependent behaviors that can impact ultracold molecular physics and quantum applications.

Contribution

It demonstrates that molecules in rotational states differing by more than one quantum exhibit repulsive van der Waals interactions, a novel insight into molecular interaction control.

Findings

Repulsive van der Waals interactions occur for rotational states differing by more than one quantum.

At sub-millikelvin temperatures, these interactions significantly reduce collisional losses.

The results enable new approaches in quantum simulation and impurity physics with ultracold polar molecules.

Abstract

The long-range electrostatic interactions between molecules depend strongly on their relative orientation, which manifests as a rotational state dependence. Interactions between molecules in the same rotational quantum state are well-known attractive rotational van der Waals interactions. Interactions in rotational states that differ by one quantum show resonant dipole-dipole interactions. We show that where molecules are in rotational states that differ by more than one quantum, they exhibit repulsive van der Waals interactions. At temperatures below a millikelvin, this effect can reduce collisional loss by multiple orders of magnitude. These repulsive interactions lead to applications in quantum simulation and impurity physics with ultracold polar molecules.