Ultracold field-linked tetratomic molecules

TL;DR

This paper demonstrates a novel method to create ultracold tetratomic molecules from diatomic molecules using electroassociation in a degenerate Fermi gas, achieving high phase space density and stability, paving the way for advanced quantum applications.

Contribution

It introduces a new approach to produce ultracold polyatomic molecules via field-linked resonances, enabling the formation of stable tetratomic molecules with high phase space density from diatomic precursors.

Findings

Created approximately 1100 tetratomic molecules with high phase space density.

Observed a maximum tetramer lifetime of 8 ms, indicating collision stability.

Measured binding energy and wave function anisotropy, aligning with theoretical predictions.

Abstract

Ultracold polyatomic molecules offer intriguing new opportunities in cold chemistry, precision measurements, and quantum information processing, thanks to their rich internal structure. However, their increased complexity compared to diatomic molecules presents a formidable challenge to employ conventional cooling techniques. Here, we demonstrate a new approach to create ultracold polyatomic molecules by electroassociation in a degenerate Fermi gas of microwave-dressed polar molecules through a field-linked resonance. Starting from ground state NaK molecules, we create around $1.1\times 10^3$ tetratomic (NaK)$_2$ molecules, with a phase space density of $0.040(3)$ at a temperature of $134(3)\,\text{nK}$, more than $3000$ times colder than previously realized tetratomic molecules. We observe a maximum tetramer lifetime of $8(2)\,\text{ms}$ in free space without a notable change in the presence of an optical dipole trap, indicating these tetramers are collisionally stable. The measured binding energy and lifetime agree well with parameter-free calculations, which outlines pathways to further increase the lifetime of the tetramers. Moreover, we directly image the dissociated tetramers through microwave-field modulation to probe the anisotropy of their wave function in momentum space. Our result demonstrates a universal tool for assembling ultracold polyatomic molecules from smaller polar molecules, which is a crucial step towards Bose--Einstein condensation (BEC) of polyatomic molecules and towards a new crossover from a dipolar Bardeen-Cooper-Schrieffer (BCS) superfluid to a BEC of tetramers. Additionally, the long-lived FL state provides an ideal starting point for deterministic optical transfer to deeply bound tetramer states.