The Enemy of my Enemy: How Disorder and Dissipation Can Be Your Friend in Quantum Systems

Author: O'Brien, Liam Christopher

Year: 2025

Degree: Dissertation (Ph.D.)

Advisor: Refael, Gil

Committee Members: Motrunich, Olexei I.; Refael, Gil; Alicea, Jason F.; Nadj-Perge, Stevan

Option: Physics

Abstract

In many physical quantum systems, disorder and dissipation are a nuisance that must be actively countered or minimized, or something that the utility of the system must otherwise survive. In this thesis, we study how these typically harmful concepts can actually be helpful in the right circumstances.

We first study disorder-induced localization in quantum systems---so-called \textit{many-body localization}, or MBL. MBL suppresses the spreading of information, an otherwise ubiquitous phenomenon, and thus can be leveraged to preserve information and realize new types of protected quantum order. We discuss a novel mathematical technique to measure a localization length in MBL systems and connect this length scale to the conventional picture of the MBL-thermal transition. In doing so, we are able to probe the probability distribution of the coupling between distant degrees of freedom near the transition, which contains valuable information about the nature of the MBL phase and the transition to thermalization.

We then switch gears and study how to harness dissipation for autonomous quantum error correction of Gottesman-Kitaev Preskill (GKP) qubits in superconducting circuits. Typically, dissipation destroys quantum information via decoherence, but we show how, by appropriately constraining the dissipative dynamics, dissipation can actually \textit{prevent} decoherence and counteract the effects of noise. As a result, our proposed GKP qubit enjoys exponential robustness to extrinsic noise and imperfections in the circuit/protocol. We also demonstrate how to realize robust non-Clifford gates on our proposed qubit, granting our device universal, self-correcting single qubit logic. The experimental realization of such a setup, which we discuss in detail, would represent a major step forward for the field of quantum computation.