Journal
SCIENCE
Volume 327, Issue 5967, Pages 853-857Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.1184121
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Funding
- NIST Innovations in Measurement Science-Ultracold Stable Molecules
- NSF Physics Frontier Center
- U.S. Department of Energy
- Air Force Office of Scientific Research MURI on Ultracold Molecules
- NSF
- Office of Naval Research [N0001409IP20041]
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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 (KRb)-K-40-Rb-87 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.
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