Quantum-state controlled chemical reactions of ultracold potassium-rubidium molecules.
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.
Ospelkaus
S
S
JILA, NIST and University of Colorado, Department of Physics, University of Colorado, Boulder, CO 80309, USA.
Ni
K-K
KK
Wang
D
D
de Miranda
M H G
MH
Neyenhuis
B
B
Quéméner
G
G
Julienne
P S
PS
Bohn
J L
JL
Jin
D S
DS
Ye
J
J