In this dissertation, I describe my work investigating quantum entanglement in a variety of contexts, with the aim of making concrete technical progress towards answering deep physical questions about the quantum nature of the world around us. Part One discusses work that broadly falls under quantum information science—with some motivations fromcosmology—while the work in Part Two is mainly cosmological.

The research presented in Part One of this dissertation involves developing and utilizing the adapted Caldeira-Leggett (ACL) model, a toy model that describes a harmonic oscillator coupled to an idealized environment. The model has allowed my collaborators and me to explore novel quantum entanglement phenomena. In Part One I introduce the model and demonstrate its robustness (as done in [1]). I then present a derivation and investigation of behavior that occurs in the early stages of entanglement between a system initially in a quantum superposition and its environment (as done in [2]). Part One concludes with an investigation of entanglement phenomena in equilibrium, to see if the emergence of classicality requires an arrow of time, and what that might imply for deep questions about our Universe (as done in [3]).

Part Two considers entanglement in another cosmological context. In a series of papers [4, 5, 6] my collaborators and I investigated the influence entanglement may have on the period of inflation in the very early universe. Specifically, we calculated how entanglement can be generated between the quantum perturbations in the inflaton field—which drives inflation—and those in another spectator field. In Part Two I begin by deriving and demonstrating how entanglement is naturally and inevitably generated during inflation (as done in [4]). I then present results from a full parameter estimation using Monte Carlo techniques to determine what amount of entanglement is allowed by current cosmological data, and what that might imply for our Universe’s quantum origins (as done in [5]). Finally, I present results that explore whether signatures of entanglement during inflation can be used to answer other questions about the history of the early universe—via distinguishing features of phase transitions and/or the inflationary energy scale that may be imprinted on cosmological observables due to entanglement (as explored in [6]).