Using Machine Learning to Understand the Causes of Quantum Decoherence in Solution-Phase Bond-Breaking Reactions

Abstract

Decoherence is a fundamental phenomenon that occurs when an entangled quantum state interacts with its environment, leading to collapse of the wave function. The inevitability of decoherence provides one of the most intrinsic limits of quantum computing. However, there has been little study of the precise chemical motions from the environment that cause decoherence. Here, we use quantum molecular dynamics simulations to explore the photodissociation of Na 2 + in liquid Ar, in which solvent fluctuations induce decoherence and thus determine the products of chemical bond breaking. We use machine learning to characterize the solute−solvent environment as a high-dimensional feature space that allows us to predict when and onto which photofragment the bonding electron will localize. We find that reaching a requisite photofragment separation and experiencing out-of-phase solvent collisions underlie decoherence during chemical bond breaking. Our work highlights the utility of machine learning for interpreting complex solution-phase chemical processes as well as identifies the molecular underpinnings of decoherence.

How Solvation Alters the Thermodynamics of Asymmetric Bond-Breaking: Quantum Simulation of NaK+ in Liquid Tetrahydrofuran

“…In previous work, we investigated the effect of solvation on the PESs and reactivity of simple diatomic solutes like Na 2 and Na 2 + . − In weakly interacting, nonpolar solvents like liquid argon, the solvent compresses the density of the bonding electron(s), altering the PES by decreasing the equilibrium bond distance and increasing the bond vibrational frequency. ,, Even though both Ar and Na 2 are nonpolar, collisions between the solvent and solute can induce instantaneous solute dipoles due to Pauli repulsive interactions that displace the bonding electron density, changing vibrational selection rules. ,, We also saw that during photodissociation of Na 2 + , asynchronous collisions between Ar solvent atoms and the Na + photofragments induce decoherence of the bonding electron, localizing it onto a single Na + and thus breaking the symmetry and determining the dissociation products …”

“…To date, the most detailed investigations of solvent effects on small molecules have explored symmetric diatomics, where there is only a single set of possible reaction products. − ,− This leads to the question of what happens when solvents interact with small molecules that are asymmetric: can the local asymmetry of a solvent environment enhance or even reverse the inherent asymmetry of a solute? To address this question, we extend our previous simulation studies to examine the behavior of NaK + in THF solution.…”