Interactions between ultracold molecules controlled by physicists

Amazing stuff! Controlling chemical reactions down to the level of a single molecule! Mind boggling!

"A way of colliding ultracold molecules while controlling the rate at which they react has been developed by physicists at the Massachusetts Institute of Technology (MIT) in the US. Researchers at Germany’s Max Planck Institute for Quantum Optics have made a similar discovery using an different experimental technique. Their research opens new pathways for enhanced control of chemical reactions. ..."

From the abstract of the first research article:

"Collisional resonances are important tools that have been used to modify interactions in ultracold gases, for realizing previously unknown Hamiltonians in quantum simulations, for creating molecules from atomic gases and for controlling chemical reactions. So far, such resonances have been observed for atom–atom collisions, atom–molecule collisions and collisions between Feshbach molecules, which are very weakly bound. Whether such resonances exist for ultracold ground-state molecules has been debated owing to the possibly high density of states and/or rapid decay of the resonant complex. Here we report a very pronounced and narrow (25 mG) Feshbach resonance in collisions between two triplet ground-state NaLi molecules. This molecular Feshbach resonance has two special characteristics. First, the collisional loss rate is enhanced by more than two orders of magnitude above the background loss rate, which is saturated at the p-wave universal value, owing to strong chemical reactivity. Second, the resonance is located at a magnetic field where two open channels become nearly degenerate. This implies that the intermediate complex predominantly decays to the second open channel. We describe the resonant loss feature using a model with coupled modes that is analogous to a Fabry–Pérot cavity. Our observations provide strong evidence for the existence of long-lived coherent intermediate complexes even in systems without reaction barriers and open up the possibility of coherent control of chemical reactions."

From the abstract of the second research article:

"Scattering resonances are an essential tool for controlling the interactions of ultracold atoms and molecules. However, conventional Feshbach scattering resonances, which have been extensively studied in various platforms, are not expected to exist in most ultracold polar molecules because of the fast loss that occurs when two molecules approach at a close distance. Here we demonstrate a new type of scattering resonance that is universal for a wide range of polar molecules. The so-called field-linked resonances occur in the scattering of microwave-dressed molecules because of stable macroscopic tetramer states in the intermolecular potential. We identify two resonances between ultracold ground-state sodium–potassium molecules and use the microwave frequencies and polarizations to tune the inelastic collision rate by three orders of magnitude, from the unitary limit to well below the universal regime. The field-linked resonance provides a tuning knob to independently control the elastic contact interaction and the dipole–dipole interaction, which we observe as a modification in the thermalization rate. Our result provides a general strategy for resonant scattering between ultracold polar molecules, which paves the way for realizing dipolar superfluids and molecular supersolids, as well as assembling ultracold polyatomic molecules."

Interactions between ultracold molecules controlled by physicists – Physics World

A Feshbach resonance in collisions between triplet ground-state molecules (no public access, but article above contains a link to the PDF file)

Field-linked resonances of polar molecules (open access)

Fig. 1: Interaction potentials and bound states of microwave-dressed ground-state molecules

Ultracold environment offers a first look at a chemical reaction

Amazing stuff! This could be a breakthrough!

"In such intense cold — 500 nanokelvin, or just a few millionths of a degree above absolute zero — the molecules slowed to such sluggish speeds that Ni and her team saw something no one has ever seen before: the moment when two molecules meet to form two new molecules. In essence, they captured a chemical reaction in its most critical and elusive act."

"In her previous work, Ni used colder and colder temperatures to forge molecules from atoms that would otherwise never react. Cooled to such extremes, atoms and molecules slow to a quantum crawl, their lowest possible energy state. There, Ni can manipulate molecular interactions with utmost precision. But even she could only see the start of her reactions: Two molecules go in, but then what? What happened in the middle and the end was a black hole only theories could try to explain."

"Chemical reactions occur in just a thousandth of a billionth of a second, better known in the scientific world as a picosecond"

"the phase when bonds break and form — in essence, how one molecule turns into another"


Ultracold environment offers a first look at a chemical reaction – Harvard Gazette: Harvard researchers have performed the coldest reaction in the known universe by capturing a chemical reaction in its most critical and elusive act.