Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item QUANTUM INFORMATION SCRAMBLING AND PROTECTION IN MANY-BODY SYSTEM(2023) Cheng, Gong; Swingle, Brian; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work is focused on two main topics in quantum information theory: the scramblingof quantum information and the preservation of quantum information in many-body system. In terms of information scrambling, the main focus of this work is on the Out-of-time-order corre- lator (OTOC), which is used to probe the dynamics of quantum information as it spreads from localized degrees of freedom to those that are distributed throughout the system. On the other hand, the aim of the study of quantum information protection is to construct a system that can preserve quantum information for a sufficiently long time when coupled to a finite-temperature environment. The many-body systems analyzed in this work belong or are related to a class of stronglyinteracting systems known as holographic quantum models. The standard examples in this class are believed to be equivalent to gravitational theory in spacetime that is one-dimensional higher than that the quantum model lives in. Therefore, the results may also provide insights into topics in quantum gravity. The first part of the thesis explores the scrambling dynamics close to a critical point whereconformal symmetry emerges. The second case deals with the scrambling dynamics with con- servation law constraints in holographic quantum field theory. The result also clarifies how con- served charges influence the dynamics in the bulk dual. The third part of the thesis presents a matrix model with a large matrix rank N that belongs to the class of approximate quantum error correction codes. We investigate its thermal stability by coupling it to a thermal bath and demonstrate that it behaves as a self-correcting quantum memory at finite temperature. The coherent memory time scales polynomially with the system size N.Item Holographic Cosmological Models and the AdS/CFT Correspondence(2023) Antonini, Stefano; Swingle, Brian; Jacobson, Theodore; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The formulation of a quantum theory of gravity is a central open problem in theoretical physics. In recent years, the development of holography---and in particular the Anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence---provided a new framework to investigate quantum gravity and led to consistent advancement. However, how to describe cosmology within holography remains an unanswered question whose solution could determine whether holography is able to capture physics in our universe. This dissertation describes a new proposal for embedding cosmological physics in the holographic paradigm. This is articulated in two different but related approaches, both involving time-symmetric Big Bang-Big Crunch cosmologies with negative cosmological constant $\Lambda$.In the first approach, the cosmological universe is given by a four-dimensional end-of-the-world brane moving in a five-dimensional AdS black hole spacetime. The proposed holographic dual description is given by a boundary conformal field theory. Under specific conditions, gravity is localized on the brane and effectively four-dimensional: an observer living on the brane is unaware of the existence of the extra dimension. In this dissertation, I show how these conditions can be met in an AdS-Reissner-Nordstr\"om background while retaining a holographic dual description. The second approach focuses on spatially flat $\Lambda<0$ cosmologies which analytically continue to Euclidean wormholes connecting two asymptotic AdS boundaries. The proposed dual theory is given by two holographic 3D CFTs coupled by non-holographic 4D degrees of freedom on a strip. A different analytic continuation of the Euclidean wormhole leads to a Lorentzian traversable wormhole. After discussing the general features of these holographic cosmologies, I describe how the traversable wormhole can be reconstructed from the dual theory and how the existence of the former constrains the latter. Finally, I show that these $\Lambda<0$ cosmologies can undergo phases of accelerated expansion and match observational data for the scale factor evolution. The results presented in this dissertation should be regarded as the initial steps on a new line of research which will hopefully lead to a description of quantum gravity in a cosmological universe via holography. Achieving this goal would render holography a viable candidate to describe quantum gravity in our universe.Item Microscopy of elongated superfluids(2020) Salces Carcoba, Francisco; Spielman, Ian; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis covers three experiments with cold and ultracold (Bose-Einstein condensate based) alkali Rb-87 gases for quantum simulation. In the first experiment, we quantum simulate Abelian and non-Abelian gauge fields in the parameter space of a four-level quantum system. Then, we describe the experimental framework to perform optimal in-situ microscopy of elongated quantum gases. We then study the thermodynamics of individual one-dimensional Bose gases using in-situ resonant absorption imaging. Finally, we combine holographic microscopy and impulse correlations to digitally enhance our absorption images.Item The Dilaton, the Radion and Duality(2013) Mishra, Rashmish; Chacko, Zackaria; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation, scenarios where strong conformal dynamics constitutes the ultraviolet completion of the physics that drives electroweak symmetry breaking are considered. It is shown that in theories where the operator responsible for the breaking of conformal symmetry is close to marginal at the breaking scale, the dilaton mass can naturally lie below the scale of the strong dynamics. However, in general this condition is not satisfied in the scenarios of interest for electroweak symmetry breaking, and so the presence of a light dilaton in these theories is associated with mild tuning. The effective theory of the light dilaton is constructed in this framework, and the form of its couplings to Standard Model states are determined. It is shown that corrections to the form of the dilaton interactions arising from conformal symmetry violating effects are suppressed by the square of the ratio of the dilaton mass to the strong coupling scale, and are under good theoretical control. These corrections are generally subleading, except in the case of dilaton couplings to marginal operators, when symmetry violating effects can sometimes dominate. Phenomenological implications of these results are investigated for models of technicolor, and for models of the Higgs as a pseudo-Nambu-Goldstone boson, that involve strong conformal dynamics in the ultraviolet. Using AdS/CFT correspondence, a holographic realization of this scenario is obtained by constructing the effective theory of the graviscalar radion in the Randall-Sundrum models, taking stabilization into account. The conditions under which the radion can remain light are explored, and the corrections to its couplings to Standard Model (SM) states localized on the visible brane are determined. It is shown that in the theories of interest for electroweak symmetry breaking that have a holographic dual, the presence of a light radion requires mild tuning. Corrections to the form of the radion coupling to SM states arising from effects associated with brane stabilization are also calculated. These corrections scale as the square of the ratio of the radion mass to the Kaluza-Klein scale, and are generally subleading, except in the case of gluons and photon, when they can sometimes dominate. These results are in agreement with and lend robustness to the conclusions for the dilaton.