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Controlling the quantum stereodynamics of ultracold bimolecular reactions


Molecular collisions in the quantum regime represent a new opportunity to explore chemical reactions. Recently, atom-exchangereactions were observed in a trapped ultracold gas of KRb molecules. In an external electric field, these polar molecules can easily be oriented and the exothermic and barrierless bimolecular reactions, KRb+KRb→K2+Rb2, occur at a rate that rises steeply with increasing dipole moment. Here we demonstrate the suppression of the bimolecular chemical reaction rate by nearly two orders of magnitude when we use an optical lattice trap to confine the fermionic polar molecules in a quasi-two-dimensional, pancake-like geometry, with the dipoles oriented along the tight confinement direction. With the combination of sufficiently tight confinement and Fermi statistics of the molecules, two polar molecules can approach each other only in a ‘side-by-side’ collision under repulsive dipole–dipole interactions. The suppression of chemical reactions is a prerequisite for the realization of new molecule-based quantum systems.

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Figure 1: Quantized stereodynamics of ultracold chemical reactions in quasi-two dimensions.
Figure 2: Relative population of molecules in the lattice vibrational levels.
Figure 3: Measurements of 2D loss rates and comparison with theory.
Figure 4: Loss rates from three dimensions to two dimensions.

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We thank P. Julienne, P. Zoller, G. Pupillo and A. Micheli for stimulating discussions and S. Moses for technical contributions. We gratefully acknowledge financial support for this work from NIST, NSF, AFOSR-MURI, DOE and DARPA.

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The experimental work and data analysis were carried out by M.H.G.d.M., A.C., B.N., D.W., S.O., J.Y. and D.S.J. Theoretical calculations of the inelastic loss rates in the 2D trap were done by G.Q. and J.L.B.

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Correspondence to J. Ye or D. S. Jin.

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The authors declare no competing financial interests.

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de Miranda, M., Chotia, A., Neyenhuis, B. et al. Controlling the quantum stereodynamics of ultracold bimolecular reactions. Nature Phys 7, 502–507 (2011).

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