Quantum-State Controlled Chemical Reactions of Ultracold Potassium-Rubidium Molecules

By S. Ospelkaus, Kang-kuen Ni, Dajun Wang, M. Miranda, B. Neyenhuis, G. Quéméner, P. Julienne, J. Bohn, D. Jin, J. Ye. Science, 2009

691 citations recorded by the source corpus.

Colliding in the Cold Chemical reactions occur through molecular collisions, which, in turn, are governed by the distributions of energy in each colliding partner. What happens when molecules are cooled so that they no longer have sufficient energy to collide? Ospelkaus et al. (p. 853; see the Perspective by Hutson) explored this question by preparing a laser-cooled sample of potassium rubidium (KRb) diatomics with barely any residual energy in any form (translational, rotational, vibrational, or electronic). By monitoring heat release over time, evidence was gathered for exothermic atom exchange reactivity through quantum mechanical tunneling. As predicted by theory, these reactions were exquisitely sensitive to the molecular states, with rates changing by orders of magnitude on varying minor factors such as nuclear spin orientation. Reactions mediated by quantum mechanical tunneling are observed, even in a sample of molecules cooled almost to a standstill. How does a chemical reaction proceed at ultralow temperatures? Can simple quantum mechanical rules such as quantum statistics, single partial-wave scattering, and quantum threshold laws provide a clear understanding of the molecular reactivity under a vanishing collision energy? Starting with an optically trapped near–quantum-degenerate gas of polar 40K87Rb molecules prepared in their absolute ground state, we report experimental evidence for exothermic atom-exchange chemical reactions. When these fermionic molecules were prepared in a single quantum state at a temperature of a few hundred nanokelvin, we observed p-wave–dominated quantum threshold collisions arising from tunneling through an angular momentum barrier followed by a short-range chemical reaction with a probability near unity. When these molecules were prepared in two different internal states or when molecules and atoms were brought together, the reaction rates were enhanced by a factor of 10 to 100 as a result of s-wave scattering, which does not have a centrifugal barrier. The measured rates agree with predicted universal loss rates related to the two-body van der Waals length.

Subfields: Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/b4effd57fe5c8340378de6149d57987d1df404e4

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In Atomic and Molecular Physics, and Optics

Citations in the corpus

Roadmap on STIRAP applications (2019, background): “enhancement of the reaction rate by one to two orders of magnitude has been observed (see figure 9(a) and [44]).”
Controlling the quantum stereodynamics of ultracold bimolecular reactions (2010, background): “Atom-exchange reactions observed in a recent experiment with an ultracold gas of KRb molecules proceed with a single partial wave in the quantum threshold regim”