Observation of Quantum Interference and Coherent Control in a Photochemical Reaction

TL;DR

This study demonstrates quantum interference effects in a Bose-Einstein condensate, showing that superposition states can suppress or modify photoassociation rates, revealing a new method for coherent control of photochemical reactions.

Contribution

It provides experimental evidence of quantum interference controlling photoassociation in a spin-orbit-coupled BEC, introducing superposition states as a tool for photochemical reaction control.

Findings

Superposition states exhibit uniform fractional atom loss across spin components.

Large Raman coupling and zero detuning suppress photoassociation rate.

Quantum destructive interference explains the dependence on Raman detuning.

Abstract

Coherent control of reactants remains a longstanding challenge in quantum chemistry. In particular, we have studied laser-induced molecular formation (photoassociation) in a Raman-dressed spin-orbit-coupled 87Rb 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.