Observation of Self-Bound Droplets of Ultracold Dipolar Molecules

TL;DR

This paper reports the creation of self-bound droplets in ultracold dipolar sodium-cesium molecules, demonstrating controllable dipole interactions and transitions from 1D arrays to 2D structures, paving the way for exploring novel quantum phases.

Contribution

It demonstrates the formation of self-bound molecular droplets with tunable dipole interactions, a significant step towards realizing strongly dipolar quantum matter.

Findings

Formation of self-bound droplets from molecular BECs

Controlled transition from 1D arrays to 2D structures

Densities up to 100 times higher than initial BEC

Abstract

Ultracold gases of dipolar molecules have long been envisioned as a platform for the realization of novel quantum phases. Recent advances in collisional shielding, protecting molecules from inelastic losses, have enabled the creation of degenerate Fermi gases and, more recently, Bose-Einstein condensation of dipolar molecules. However, the observation of quantum phases in ultracold molecular gases that are driven by dipole-dipole interactions has so far remained elusive. In this work, we report the formation of self-bound droplets and droplet arrays in an ultracold gas of strongly dipolar sodium-cesium molecules. Starting from a molecular Bose-Einstein condensate (BEC), microwave dressing fields are used to induce dipole-dipole interactions with controllable strength and anisotropy. By varying the speed at which interactions are induced, covering a dynamic range of four orders of magnitude, we prepare droplets under equilibrium and non-equilibrium conditions, observing a transition from robust one-dimensional (1D) arrays to fluctuating two-dimensional (2D) structures. The droplets exhibit densities up to 100 times higher than the initial BEC, reaching the strongly interacting regime, and suggesting the possibility of a quantum-liquid or crystalline state. This work establishes ultracold molecules as a system for the exploration of strongly dipolar quantum matter and opens the door to the realization of self-organized crystal phases and dipolar spin liquids in optical lattices.