State-to-state control of ultracold molecular reactions

TL;DR

This paper demonstrates quantum state control of ultracold molecular reactions by manipulating nuclear spins, enabling precise control over reaction outcomes and opening new avenues for studying quantum reaction dynamics.

Contribution

It introduces a method to control reaction product states via nuclear spin manipulation, a novel approach in ultracold chemistry.

Findings

Nuclear spins are conserved throughout the reaction.

Reaction products retain a strong memory of reactant nuclear spins.

External magnetic fields can alter the occupation of product states.

Abstract

Quantum control of reactive systems has enabled microscopic probes of underlying interaction potentials, the opening of novel reaction pathways, and the alteration of reaction rates using quantum statistics. However, extending such control to the quantum states of reaction outcomes remains challenging. In this work, we realize this goal through the nuclear spin degree of freedom, a result which relies on the conservation of nuclear spins throughout the reaction. Using resonance-enhanced multiphoton ionization spectroscopy to investigate the products formed in bimolecular reactions between ultracold KRb molecules, we find that the system retains a near-perfect memory of the reactants' nuclear spins, manifested as a strong parity preference for the rotational states of the products. We leverage this effect to alter the occupation of these product states by changing the coherent superposition of initial nuclear spin states with an external magnetic field. In this way, we are able to control both the inputs and outputs of a bimolecular reaction with quantum state resolution. The techniques demonstrated here open up the possibilities to study quantum interference between reaction pathways, quantum entanglement between reaction products, and ultracold reaction dynamics at the state-to-state level.