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Phys Rev Lett. 2018 Aug 17;121(7):073202. doi: 10.1103/PhysRevLett.121.073202.

Observation of Quantum Interference and Coherent Control in a Photochemical Reaction.

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Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA.
School of Materials Sciences and Technology, Universidad del Turabo, Gurabo, Puerto Rico 00778, USA.
Department of Physics, Indian Institute of Science Education and Research, Bhopal 462066, India.
School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA.
Purdue Quantum Center, Purdue University, West Lafayette, Indiana 47907, USA.


Coherent control of reactants remains a long-standing challenge in quantum chemistry. In particular, we have studied laser-induced molecular formation (photoassociation) in a Raman-dressed spin-orbit-coupled ^{87}Rb Bose-Einstein condensate, whose spin quantum state is a superposition of multiple bare spin components. In contrast to the notably different photoassociation-induced fractional atom losses observed for the bare spin components of a statistical mixture, a superposition state with a comparable spin composition displays the same fractional loss on every spin component. We interpret this as the superposition state itself undergoing photoassociation. For superposition states induced by a large Raman coupling and zero Raman detuning, we observe a nearly complete suppression of the photoassociation rate. This suppression is consistent with a model based upon quantum destructive interference between two photoassociation pathways for colliding atoms with different spin combinations. This model also explains the measured dependence of the photoassociation rate on the Raman detuning at a moderate Raman coupling. Our work thus suggests that preparing atoms in quantum superpositions may represent a powerful new technique to coherently control photochemical reactions.

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