A quantum information approach to material science simulations

Thesis

Despite its ubiquity, many-body dispersion remains poorly understood. There have been numerous studies confirming the importance of many-body effects in dispersive forces. These often play a decisive role in determining properties and functionalities of physical, chemical and biological systems, ranging from condensed phases in noble gases to biomolecules and nanomaterials. Still, a general understanding of their behavior is lacking.

In this thesis we study many-body dispersion with quantum Drude oscillator assemblies — minimal models for dispersion bound systems. We show how Gaussian states provides an efficient and comprehensive framework for understanding many-body forces, within the quantum Drude model. In doing so, we analytically and rigorously establish how the distribution of entanglement in the QDO model governs many-body dispersive bond energies. We further show how the monogamy of entanglement can be used to predict whether many-body corrections to the bond energy are repulsive or attractive.

The work in this thesis does not aim to study a specific physical system or experiment. Instead, we use model systems and analytical results to characterize and discuss how entanglement properties affect dispersive bonds. Importantly, our method is applicable to arbitrary arrangements of dipoles and hence to a wide range of systems.

Gaussian state quantum information tools bring important insights and understanding of dipolar forces from a new angle. In addition the Gaussian state approach allows us to construct efficient symplectic optimization algorithms for variationally solving the coupled quantum Drude model. Our symplectic optimization algorithm provides a novel route towards including many-body dispersive forces in material simulations. We further show how our symplectic optimization algorithm can in principle be turned into a variational quantum algorithm. Our methods and results provide a path toward fully understanding the nature of quantum effects in large biomolecules and complex crystal structures.

Authors: Willby, C

• DOI: 10.5287/ora-yrw2qd4w6
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: quantum information; approximation methods for many-body systems; chemical bonds; entanglement; many-body dispersion; crystal lattices; Gaussian states
• Subjects: Quantum computing; Quantum chemistry