Tuning of dipolar interactions and evaporative cooling in a three-dimensional molecular quantum gas

TL;DR

This paper demonstrates the control of dipolar interactions and successful evaporative cooling in a three-dimensional ultracold molecular gas, enabling exploration of complex quantum many-body phenomena.

Contribution

It introduces a method to tune elastic dipolar interactions in 3D ultracold molecules using electric field-induced shielding resonance, overcoming previous limitations.

Findings

Achieved a thirtyfold suppression of reactive loss.

Demonstrated thermalization dependent on dipole orientation.

Realized evaporative cooling in a 3D molecular quantum gas.

Abstract

Ultracold polar molecules possess long-range, anisotropic, and tunable dipolar interactions, providing the opportunities to probe quantum phenomena inaccessible with existing cold gas platforms. However, experimental progress has been hindered by the dominance of two-body loss over elastic interactions, which prevents efficient evaporative cooling. Though recent work has demonstrated controlled interactions by confining molecules to a two-dimensional geometry, a general approach for tuning molecular interactions in a three-dimensional (3D), stable system has been lacking. Here, we demonstrate tunable elastic dipolar interactions in a bulk gas of ultracold 40K87Rb molecules in 3D, facilitated by an electric field-induced shielding resonance which suppresses the reactive loss by a factor of thirty. This improvement in the ratio of elastic to inelastic collisions enables direct thermalization. The thermalization rate depends on the angle between the collisional axis and the dipole orientation controlled by an external electric field, a direct manifestation of the anisotropic dipolar interaction. We achieve evaporative cooling mediated by the dipolar interactions in three dimensions. This work demonstrates full control of a long-lived bulk quantum gas system with tunable long-range interactions, paving the way for the study of collective quantum many-body physics.