This work sits at the periphery: few neighbors nearby, the closest at a distance of 0.517. Surrounding research covers laser cooling, quantum squeezing of molecules, chips combining light and sound, and atomic optical switches. The main stream among neighbors is manipulating light and sound at the microscale, as well as cooling to quantum regimes. This paper stands out by working with a bulk gas of bosonic molecules and using a static electric field to suppress collisions, whereas neighboring studies focus on laser methods or are limited to fermionic systems.
Molecules of 23Na87Rb were prepared from ultracold sodium and rubidium atoms via magnetoassociation followed by STIRAP transfer to the absolute ground rotational state. Eight electrodes surrounding the molecular cloud generated a uniform static electric field. The field was tuned near a Förster resonance, where two paired rotational states are nearly degenerate. The dipole-dipole coupling between them produces a repulsive barrier at short range, preventing molecules from approaching and undergoing inelastic processes. Losses were measured by holding the gas in an optical dipole trap and tracking molecule number and temperature over time using time-of-flight imaging. Path-integral Monte Carlo simulations modeled droplet formation.
Applying a field above the Förster resonance suppressed two-body losses by four orders of magnitude: the loss coefficient dropped from 3.8×10⁻¹⁰ to below 3×10⁻¹⁴ cm³/s. In a region without bound states, three-body losses were also strongly suppressed. Evaporation with an efficiency of 2.09(9) increased phase-space density by two orders of magnitude, reaching quantum degeneracy with 7200(1000) molecules at a temperature of 44(4) nK. At the end of evaporation, a compact droplet of 230(80) molecules emerged. Its size remained constant during expansion, indicating self-binding. Droplets appeared over a wide range of fields, and at large Förster detunings they formed even from a non-degenerate parent gas. Simulations showed that the droplets have a filamentary structure elongated along the field.
Unlike neighboring studies that focus on laser methods or fermionic systems, this work is the first to demonstrate static shielding for bosonic molecules in a three-dimensional volume. It shows that a single field suffices to simultaneously suppress two- and three-body losses, which was previously thought to require two microwave fields. This opens a simpler path to quantum-degenerate molecular gases. Moreover, observing self-bound droplets from a non-degenerate gas points to a new stabilization mechanism distinct from Lee-Huang-Yang quantum fluctuations.
The topic could evolve toward combining the static field with a single microwave field for additional tuning of interactions. Transferring molecules to a quasi-two-dimensional geometry at temperatures above the droplet formation temperature could stabilize the gas phase and allow exploring transitions between superfluid, crystalline, and potential supersolid phases. The quasi-2D geometry is also compatible with quantum gas microscopy, opening the way to microscopic studies of the extended Bose-Hubbard model with long-range dipolar interactions.
The results will impact ultracold molecule physics, many-body quantum simulation, and studies of dipolar quantum matter.
Immediate next steps include verifying the predicted filamentary structure of the droplets, for example by rotating the electric field direction perpendicular to the imaging axis, and investigating the finite-temperature phase diagram.
This work addresses the unresolved problem of achieving quantum degeneracy in bosonic molecular gases while maintaining control over dipolar interactions. It also touches on the question of stabilization mechanisms for self-bound dipolar droplets beyond the quantum fluctuation regime.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The work demonstrates the use of a static electric field near a Förster resonance to suppress inelastic losses in a gas of bosonic NaRb molecules, achieving quantum degeneracy and observing self-bound droplets.
Where its strength is
The key strength is the simultaneous suppression of two- and three-body losses by a single static field, which simplifies the path to degenerate molecular gases and opens a new mechanism for stabilizing droplets.
Where it could go next
Worth trying
Why this may matter
This result could serve as a foundation for simpler and more scalable experiments with quantum-degenerate molecular gases, which is important for quantum simulation, precision measurements, and exploring new many-body physics with long-range interactions.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.55, against a usual 0.64. It looks like few have drilled nearby.
A droplet of 230 molecules has a density of about 6.3×10¹³ cm⁻³, thousands of times denser than a typical ultracold molecular gas, and lives for just 260 milliseconds.
Self-bound filamentary structures of ultracold molecules evoke exotic forms of matter from science fiction, such as the 'filamentary crystals' in Greg Egan's novel 'Schild's Ladder'.