Ultracold dense gas of deeply bound heteronuclear molecules

TL;DR

This paper demonstrates a method to produce ultracold, densely packed heteronuclear molecules with significantly increased binding energy and potential dipole moments, advancing the development of quantum gases with long-range interactions.

Contribution

The authors coherently transfer Feshbach molecules into deeply bound vibrational states, significantly increasing their binding energy and dipole moment in a single step.

Findings

Achieved 84% transfer efficiency from Feshbach to ground vibrational state.

Increased binding energy and dipole moment by over four orders of magnitude.

Technique can be extended to produce molecules with observable dipolar effects.

Abstract

Recently, the quest for an ultracold and dense ensemble of polar molecules has attracted strong interest. Polar molecules have bright prospects for novel quantum gases with long-range and anisotropic interactions, for quantum information science, and for precision measurements. However, high-density clouds of ultracold polar molecules have so far not been produced. Here, we report a key step towards this goal. Starting from an ultracold dense gas of heteronuclear 40K-87Rb Feshbach molecules with typical binding energies of a few hundred kHz and a negligible dipole moment, we coherently transfer these molecules into a vibrational level of the ground-state molecular potential bound by >10 GHz. We thereby increase the binding energy and the expected dipole moment of the 40K-87Rb molecules by more than four orders of magnitude in a single transfer step. Starting with a single initial state prepared with Feshbach association, we achieve a transfer efficiency of 84%. While dipolar effects are not yet observable, the presented technique can be extended to access much more deeply bound vibrational levels and ultimately those exhibiting a significant dipole moment. The preparation of an ultracold quantum gas of polar molecules might therefore come within experimental reach.