Decoherence in Molecular Electron Spin Qubits: Insights from Quantum Many-Body Simulations

TL;DR

This paper investigates the fundamental decoherence mechanisms in molecular electron spin qubits through quantum many-body simulations, revealing how environmental interactions influence quantum coherence.

Contribution

It provides a microscopic understanding of decoherence in isolated molecules and introduces residual coherence as a practical descriptor for molecular spin qubit coherence.

Findings

Decoherence occurs even in isolated molecules due to nuclear spin interactions.

Residual coherence varies with molecular environment and can predict coherence times.

Nearby molecules influence decoherence non-trivially depending on their separation.

Abstract

Quantum states are described by wave functions whose phases cannot be directly measured, but which play a vital role in quantum effects such as interference and entanglement. The loss of the relative phase information, termed decoherence, arises from the interactions between a quantum system and its environment. Decoherence is perhaps the biggest obstacle on the path to reliable quantum computing. Here we show that decoherence occurs even in an isolated molecule although not all phase information is lost via a theoretical study of a central electron spin qubit interacting with nearby nuclear spins in prototypical magnetic molecules. The residual coherence, which is molecule-dependent, provides a microscopic rationalization for the nuclear spin diffusion barrier proposed to explain experiments. The contribution of nearby molecules to the decoherence has a non-trivial dependence on separation, peaking at intermediate distances. Molecules that are far away only affect the long-time behavior. Because the residual coherence is simple to calculate and correlates well with the coherence time, it can be used as a descriptor for coherence in magnetic molecules. This work will help establish design principles for enhancing coherence in molecular spin qubits and serve to motivate further theoretical work.