Magic-angle twisted graphene systems, including bilayer (MATBG) and trilayer (MATTG) structures, constitute a highly tunable platform for exploring strongly correlated electronic phenomena and unconventional superconductivity. Despite extensive studies, the local electronic structure, symmetry-breaking transitions, and their interplay with superconductivity remain elusive. In this thesis, we employ high-resolution scanning tunneling microscopy and spectroscopy, to investigate the evolution, and hierarchy of correlated phases in twisted multilayer graphene as functions of doping, temperature, magnetic field, and twist angle.
\r\n\r\nIn twisted bilayer graphene, we map the evolution of flat electronic bands and detect filling-dependent band flattening, which drives cascades of symmetry-breaking transitions and the emergence of correlated gaps. Correlated gaps that occur at high magnetic fields are identified as Chern insulators, driven by interaction induced degeneracy breaking. In twisted trilayer graphene, we identify a sequence of correlated gaps at the Fermi level, including a robust outer gap associated with intervalley coherence and a more fragile inner gap linked to superconductivity. Atomic-scale reconstruction reveals Kekul\u00e9 reconstruction indicative of inter-valley coherence, which coexists with moir\u00e9-scale translation symmetry breaking.
\r\n\r\nOur results demonstrate that superconductivity in twisted multilayer graphene emerges from a hierarchy of correlated states, starting from cascade physics, to formation of Kondo resonance, flavor symmetry breaking to superconductivity. Our findings provide an insightful microscopic framework that is relevant to many moir\\'e systems and offer guiding principles for engineering correlated and topological states in designer quantum materials.
", "doi": "10.7907/2rk8-2q20", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17732", "collection": "thesis", "collection_id": "17732", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10262025-132142523", "type": "thesis", "title": "Engineering Quantum Resources for Quantum Networking Using Single Rare-Earth Ions Inside Crystals", "author": [ { "family_name": "Wu", "given_name": "Chun-Ju", "orcid": "0009-0007-0882-4812", "clpid": "Wu-Chun-Ju" } ], "thesis_advisor": [ { "family_name": "Faraon", "given_name": "Andrei", "orcid": "0000-0002-8141-391X", "clpid": "Faraon-A" } ], "thesis_committee": [ { "family_name": "Endres", "given_name": "Manuel A.", "orcid": "0000-0002-4461-224X", "clpid": "Endres-M" }, { "family_name": "Painter", "given_name": "Oskar J.", "orcid": "0000-0002-1581-9209", "clpid": "Painter-O" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Faraon", "given_name": "Andrei", "orcid": "0000-0002-8141-391X", "clpid": "Faraon-A" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Quantum networks are foundational components of quantum technology, enabling transformative applications in secure communication, distributed quantum computation, and enhanced sensing. Rare-earth ions in solid-state hosts represent a leading platform for building such networks due to their exceptional optical and spin coherence properties. This thesis details the experimental realization of a quantum network node using single \u00b9\u2077\u00b9Yb\u00b3\u207a ions in YVO\u2084 coupled to nanophotonic crystal cavities. We demonstrate the fundamental building blocks of quantum networks and develop multiple advanced capabilities, including multiplexing, protected nuclear spin storage, and high-dimensional qudit control, to expand the platform's power and versatility.
\r\n\r\nUsing this platform, we demonstrate heralded remote entanglement between two physically separate devices. A key innovation is a novel entanglement distribution protocol that employs real-time feedforward to cancel spectral diffusion on timescales slower than a single experiment by rephasing the optical transition based on photon arrival time. We also apply real-time phase compensations to entangle \u00b9\u2077\u00b9Yb ions with different optical frequencies. By combining this novel protocol with multiple spectrally distinguishable ions, we demonstrate heralding of a three-ion W state and implement multiplexed remote entanglement. This multiplexing approach increases the entanglement rate by nearly a factor of two, showcasing a scalable pathway to mitigate network overhead.
\r\n\r\nBeyond establishing remote entanglement, we explore the local nuclear spin environment of \u00b9\u2077\u00b9Yb as an integrated quantum resource. We harness the four symmetrically located \u2075\u00b9V nuclear spins to generate multi-qubit Greenberger\u2013Horne\u2013Zeilinger states. Critically, we identify and experimentally verify a decoherence-protected subspace within these states that exhibits insensitivity to common-mode magnetic field noise. By developing a sequence to transfer quantum information into this protected subspace, we establish the \u2075\u00b9VV nuclear ensemble as an integrated, noise-resilient quantum memory.
\r\n\r\nTo further expand the platform's capabilities, we demonstrate coherent control over the four-level ground state of the \u00b9\u2077\u00b9Yb ion, operating it as a qudit. Through development of a new device architecture that enables microwave driving of all transitions and comprehensive characterization of their coherence properties, this work establishes the foundation for higher-dimensional quantum communication protocols that offer significant advantages in network capacity and efficiency.
\r\n\r\nCollectively, these results establish the \u00b9\u2077\u00b9Yb:YVO\u2084 system as a uniquely versatile platform and demonstrate the feasibility of building scalable quantum networks using single rare-earth ions in crystals.
", "doi": "10.7907/kgjp-xe35", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17581", "collection": "thesis", "collection_id": "17581", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07312025-212004631", "type": "thesis", "title": "Probing Quantum States in Low-Dimensional Materials via Laser-Assisted Scanning Tunneling Microscopy and Structured Light", "author": [ { "family_name": "Park", "given_name": "Akiyoshi", "orcid": "0000-0003-2383-1088", "clpid": "Park-Akiyoshi" } ], "thesis_advisor": [ { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" }, { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "This dissertation presents the development and application of a laser-assisted scanning tunneling microscope (STM) to probe and control emergent quantum phenomena in two-dimensional (2D) and topological materials. A custom-built STM system was designed to operate under ultra-high vacuum and cryogenic conditions, integrating electronic, mechanical, and optical subsystems to enable high-resolution tunneling spectroscopy with in situ optical excitation. This platform allows for the detection of light-induced tunneling photocurrents with polarization control, facilitating direct investigations of light\u2013matter interactions at the atomic scale.
\r\n\r\nUsing this instrument, we first investigate the dynamics of photoexcited quasiparticles in strained monolayer (ML) transition metal dichalcogenides (TMDs), specifically ML-MoS$_2$ grown on corrugated Au(111). Nanoscale strain induces local bandstructure modulation, which acts as a trapping potential for excitons, trions, and electron-hole plasmas. Optical excitation in these strained regions leads to strongly enhanced band renormalization effects, which we interpret through a tight-binding model that incorporates non-uniform strain and many-body interactions. These results establish a framework for manipulating quasiparticle interactions and optoelectronic properties in 2D materials via strain and light.
\r\n\r\nMoreover, we utilize STM/STS to explore magnetically doped topological insulators exhibiting the quantum anomalous Hall (QAH) effect. Scanning tunneling spectroscopy (STS) measurements on six-quintuple-layer films reveal a topologically non-trivial energy gap at low temperature. However, spatially inhomogeneous band alignment driven by many-body interactions, including electron-defect and electron-phonon coupling results in local band overlap and a breakdown of the insulating QAH state into a metallic phase, even below the Curie temperature. These findings highlight the role of microscopic disorder and finite-temperature renormalization in destabilizing topological phases.
\r\n\r\nFinally, we demonstrate angular momentum transfer from structured light to Rydberg excitons in monolayer MoSe\u2082. Optical vortex beams carrying orbital angular momentum (OAM) selectively couple to exciton degrees of freedom. At low light intensity, photonic OAM modifies the center-of-mass motion of excitons, while at higher light intensities, exchange-mediated processes transfer angular momentum of light to the internal excitonic orbitals. Photoluminescence measurements under Laguerre-Gaussian beam excitation reveal fingerprints of higher orbital Rydberg exciton states, providing a new pathway for controlling exciton orbital structure in solid-state systems.
\r\n\r\nTogether, these studies showcase how laser-assisted STM and structured light can be harnessed to probe, engineer, and control quantum states in low-dimensional materials, with implications for topological electronics, nanoscale optoelectronics, and quantum excitonic devices.
", "doi": "10.7907/p17k-3619", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17311", "collection": "thesis", "collection_id": "17311", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302025-180056920", "type": "thesis", "title": "The Enemy of my Enemy: How Disorder and Dissipation Can Be Your Friend in Quantum Systems", "author": [ { "family_name": "O'Brien", "given_name": "Liam Christopher", "orcid": "0000-0002-8603-1347", "clpid": "O'Brien-Liam-Christopher" } ], "thesis_advisor": [ { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" } ], "thesis_committee": [ { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" }, { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "local_group": [ { "literal": "div_pma" } ], "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.
\r\n\r\nWe 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.
\r\n\r\nWe 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.
", "doi": "10.7907/mz8m-an97", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17305", "collection": "thesis", "collection_id": "17305", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302025-053900946", "type": "thesis", "title": "Novel Electronic and Optoelectronic Interactions in Two-Dimensional Materials", "author": [ { "family_name": "Hao", "given_name": "Duxing", "orcid": "0000-0002-8907-9776", "clpid": "Hao-Duxing" } ], "thesis_advisor": [ { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" } ], "thesis_committee": [ { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" }, { "family_name": "Patrick", "given_name": "Lee A.", "orcid": "0000-0001-7809-8157", "clpid": "Lee-Patrick-A" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Two-dimensional (2D) materials host a rich set of emerging physical phenomena such as superconductivity, ferroelectricity, quantum magnetism, and circular dichroism. Moreover, these phenomena are highly tunable by crystalline composition variations and crystalline structural phase modifications and are sensitive to external conditions such as temperature, magnetic field and optical excitation, substrate and gate tuning. Therefore, 2D material-based devices are highly desirable for modern electronic and optoelectronic devices applications. In this thesis, we employed a fully scalable approach to synthesize materials and fabricate 2D material-based devices such as those based on graphene and 1H-Molybdenum disulfide (1H-MoS2), and explore their electronic and optoelectronic properties in cryogenic conditions under various excitation sources, such as external magnetic field and structured light.
\r\n\r\nIn the first part of the thesis (Chapters 2 and 3), we provide experimental details for achieving nanoscale strain engineering of monolayer (ML)-graphene and demonstrate that periodic patterns of nanoscale strain distributions in ML-graphene can lead to local giant pseudomagnetic fields as well as global modifications to the electronic properties of ML-graphene, including strain-induced valley Hall and anomalous Hall effects in the absence of external magnetic fields, nonlocal valley-polarized currents and evidence of quantum valley Hall effect under external magnetic field. These findings suggest new approaches towards developing emerging quantum states with tunable electronic correlation based on graphene straintronics.
\r\n\r\nThe second part of the thesis (Chapters 4 and 5) focus more on the semiconducting monolayer transition metal dichalcogenides (ML-TMDs), whose broken inversion symmetry and strong spin-orbit coupling result in spin-valley lock-in effects so that the valley degeneracy may be lifted by external magnetic fields, potentially leading to real-space structural transformation.
\r\n\r\nIn Chapter 4, we report magnetic field (B)-induced giant electric hysteretic responses to back-gate voltages in ML-MoS\u2082 field-effect transistors (FETs) on SiO\u2082/Si at temperatures < 20 K. The observed hysteresis increases with |B| up to 12 T and is tunable by varying the temperature. Raman spectroscopic and scanning tunneling microscopic studies reveal significant lattice expansion with increasing |B| at 4.2 K, and this lattice expansion becomes asymmetric in ML-MoS\u2082 FETs on rigid SiO\u2082/Si substrates, leading to out-of-plane mirror symmetry breaking and the emergence of a tunable out-of-plane ferroelectric-like polar order. This broken symmetry-induced polarization in ML-MoS\u2082 shows typical ferroelectric butterfly hysteresis in piezo-response force microscopy, adding ML-MoS\u2082 to the single-layer material family that exhibit out-of-plane polar order-induced ferroelectricity, which is promising for such technological applications as cryo-temperature ultracompact non-volatile memories, memtransistors, and ultrasensitive magnetic field sensors. Moreover, the polar effect induced by asymmetric lattice expansion may be further generalized to other ML-TMDs and achieved by nanoscale strain engineering of the substrate without magnetic fields.
\r\n\r\nIn Chapter 5, we further demonstrate the design and application of a novel instrument that integrates scanning spectroscopic photocurrent measurements with structured light of controlled spin and orbital angular momentum. For structured photons with wavelengths between 500 nm to 700 nm, this instrument can perform spatially resolved photocurrent measurements of 2D materials or thin crystals under magnetic fields up to \u00b114 Tesla, at temperatures from 300 K down to 3 K, with either spin angular momentum (SAM) \u2113\u0127 or orbital angular momentum (OAM) \u00b1 \u2113\u0127 (where \u2113 = 1, 2, 3\u2026 is the topological charge), and over a (35x25) \u00b5m\u00b2 area with ~ 1 \u00b5m spatial resolution. These capabilities of the instrument are exemplified by magneto-photocurrent spectroscopic measurements of monolayer 2H-MoS\u2082 field-effect transistors, which not only reveal the excitonic spectra but also demonstrate monotonically increasing photocurrents with increasing |\u2113| as well as excitonic Zeeman splitting and an enhanced Land\u00e9 g-factor due to the enhanced formation of intervalley dark excitons under magnetic field. These studies thus demonstrate the versatility of the scanning photocurrent spectrometry for investigating excitonic physics, optical selection rules, and optoelectronic responses of novel quantum materials and engineered quantum devices to structured light.
\r\n\r\nFinally, we summarize the research accomplishments of this thesis work in Chapter 6 and discuss the outlook for new research directions associated with these 2D quantum materials.
", "doi": "10.7907/wegr-tg72", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17216", "collection": "thesis", "collection_id": "17216", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05092025-211543101", "primary_object_url": { "basename": "Zongyuan_Wang_PhD_thesis_2025.pdf", "content": "final", "filesize": 16910661, "license": "other", "mime_type": "application/pdf", "url": "/17216/1/Zongyuan_Wang_PhD_thesis_2025.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Type-I Fractons -- Foliation in Non-Abelian Models", "author": [ { "family_name": "Wang", "given_name": "Zongyuan", "orcid": "0000-0003-0813-6247", "clpid": "Wang-Zongyuan" } ], "thesis_advisor": [ { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "In this thesis, we present recent contributions to the study of Type-I non-abelian fracton models, which led us to propose the notion of generalized foliated fracton orders that captures the universal properties of both abelian and non-abelian Type-I fracton models.
\r\n\r\nFracton models are known for their exotic properties such as point-like excitations with restricted mobilities and robust topological ground state degeneracy that grows sub-extensively with the system size. A multitude of Type-I fracton models whose excitations obey either abelian or non-abelian fusion rules have recently been constructed. Among them, a large number of the abelian fracton models have been shown to possess foliation structures, where models of different system sizes can be related through the addition / removal of an entire piece of topologically ordered system on a sub-dimensional manifold via the action of a finite-depth local unitary circuit. In this thesis, this is referred to as the original foliation renormalization group (RG) scheme, which leads us to the notion of original foliation fracton orders. The Ising cage-net model and other similar non-abelian models are closely related to these abelian models in terms of their excitation structures and coupled layers construction etc. However, it was not known whether their fracton orders can also be understood within the original foliation framework. We address this problem in this thesis.
\r\n \r\nIn Chapter 2, we show that the Ising cage-net model does not fit into the original definition of foliated fracton orders, by calculating its ground state degeneracy. We realize that there exists naturally a more general way to define foliation -- the generalized foliation scheme (Chapter 3). The Ising cage-net and other similar non-abelian fracton models are foliated according to this generalized scheme. In the generalized foliation scheme, the RG transformation is defined by, from the excitation perspective, the condensation of planons / gauging subsystem symmetries. In terms of quantum circuits, this RG transformation is equivalent to a sequential linear-depth circuit that acts near a sub-dimensional manifold. With this definition, we can study phase relation of the Ising cage-net with other known fracton models. In Chapter 4, via gauging composite subsystem symmetries, we further show that the Ising cage-net belongs to the same generalized foliated fracton phases as the prototypical X-cube model. Furthermore, gauging composite subsystem symmetries opens up a new route to constructing non-abelian fracton models hosting exotic non-abelian fractons. An example is the tri-Ising-fracton model (Sec. 4.5).
", "doi": "10.7907/2x8m-j581", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17150", "collection": "thesis", "collection_id": "17150", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04112025-180844471", "primary_object_url": { "basename": "Christopher_Yang_Thesis-2.pdf", "content": "final", "filesize": 20240940, "license": "other", "mime_type": "application/pdf", "url": "/17150/1/Christopher_Yang_Thesis-2.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Dynamical Control of Many-Body Interactions in Driven Quantum Matter", "author": [ { "family_name": "Yang", "given_name": "Christopher Kai-Chen", "orcid": "0000-0002-9462-9074", "clpid": "Yang-Christopher-Kai-Chen" } ], "thesis_advisor": [ { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" } ], "thesis_committee": [ { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Strongly driven Floquet systems have emerged as promising platforms for exotic non-equilibrium physics, but their instability to heating motivates practical questions about how Floquet engineering can be useful. Although drive-induced heating is often attributed to interactions, this thesis adopts a different perspective, identifying regimes where dissipative many-body dynamics can stabilize Floquet physics and define remarkable new drive-tunable properties. This principle enables highly tunable many-body steady states with minimal heating, leading to a novel regime where drive control over single-particle Floquet states can extend to many-body interactions. Our theoretical and experimental results in Parts II and III center around two themes. The first theme focuses on discovering controllable and stable many-body Floquet states. The second explores further into what the future holds--envisioning the prospects for unconventional Floquet physics with nontraditional driving fields and three-dimensional materials.
\r\n\r\nPart II of this thesis leverages kinematic constraints on low-dimensional many-body scattering as new principles for tuning and stabilizing Floquet phases. First, we predict that a circularly polarized laser can drive slow electrons of moir\u00e9 systems into a subsonic regime where they decouple from the intrinsic 2D acoustic phonons of the system. This \"slow-electron regime\" enables optical control over the steady-state occupation of topological Floquet states and the resulting anomalous Hall conductivity. Second, we present experimental transport signatures of steady Floquet physics in graphene irradiated by a continuous-wave laser. Our experiment, performed at 3-4 K lattice temperatures with lasers off-resonant to optical phonons, creates electron-phonon scattering bottlenecks that stabilize persistent low-temperature phases with light-induced longitudinal transport characteristics. The long-lived many-body phase represents the first experimental signatures of steady Floquet physics in a metallic solid.
\r\n\r\nPart III presents emerging opportunities for many-body Floquet engineering beyond traditional optically-driven, low-dimensional materials. We first explore beyond-optical driving fields, revealing the emergence of quantized charge transport in 1D systems driven by coherent phonons. Incoherent phonons relax electrons into a topological spatiotemporal Floquet state with quantized group velocity set by the coherent phonon, realizing topological charge pumping in a highly non-adiabatic setting. Finally, we address the topological effects of time-periodic drives beyond low-dimensional systems, revealing that THz-frequency, circularly polarized light can induce topological chiral plasmons in Weyl semimetals with band anisotropy, broken time-reversal symmetry, and broken inversion symmetry.
\r\n\r\nThe theoretical and experimental work in this thesis represent key progress towards realizing persistent Floquet physics for diverse applications in quantum device engineering.
", "doi": "10.7907/fh52-tw61", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16642", "collection": "thesis", "collection_id": "16642", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08152024-222635476", "primary_object_url": { "basename": "Yiran_Zhang_2024_thesis.pdf", "content": "final", "filesize": 106668206, "license": "other", "mime_type": "application/pdf", "url": "/16642/1/Yiran_Zhang_2024_thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Spin-Orbit Enhanced Superconductivity in Graphene Heterostructures", "author": [ { "family_name": "Zhang", "given_name": "Yiran", "orcid": "0000-0002-8477-0074", "clpid": "Zhang-Yiran" } ], "thesis_advisor": [ { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Flat electronic bands in moire and crystalline graphene multilayers showcase emergent correlated phenomena including correlated insulators, superconductivity, topological orders, etc. This thesis focuses on the electrical transport characterization of superconductivity in moire and crystalline graphene, with the proximity of a layer of tungsten diselenide (WSe\u2082) that induces spin-orbit coupling (SOC). The interplay between spontaneous symmetry-breaking and explicit spin-orbit interactions emerges various unconventional superconducting pairing.
\r\n\r\nIn the case of moire graphene multilayers, superconductivity in twisted bilayer graphene persists much far away from the magic angle at which electronic correlations dominate. At the lowest twist angle 0.79\u00b0, superconductivity appears despite the absence of any insulating states. By changing the moire twist angle, the ratio between Coulomb interactions and kinetic energy is reduced, and we thus established a hierarchy of various symmetry-breaking orders. Importantly, superconductivity is tightly related to the half-filling symmetry-breaking reconstructions. We further generalize the twisted moire graphene to trilayer, quadrilayer and pentalayer cases. Characterizations around their respective magic angle show that superconductivity is more prominent in filling phase space when the number of layers is increased.
\r\n\r\nWe then investigated the effect of SOC on correlated phases in crystalline Bernal-stacked bilayer graphene. Surprisingly, placing monolayer WSe\u2082 on bilayer graphene promotes Cooper pairing to an extraordinary degree: field-induced superconductivity is stabilized at zero magnetic field, exhibits an order of magnitude enhancement in critical temperature and occurs over a density range that is wider by a factor of eight. The superconductivity descends from a broken-symmetry parent state with two out of the four spin-valley flavors being predominantly populated. Moreover, the superconductivity arises only for perpendicular electric fields that push hole wavefunctions toward WSe\u2082, indicating that proximity-induced Ising spin-orbit coupling plays a key role in stabilizing the pairing.
\r\n\r\nThe last part of the thesis focuses on a new degree of freedom: interfacial twisting between graphene and WSe\u2082. We experimentally demonstrate the \"moireless\" tuning of superconductivity in Bernal bilayer graphene proximitized by WSe\u2082. The precise alignment between the two materials systematically controls the strength of the induced Ising SOC, profoundly altering the phase diagram. As Ising SOC is increased, superconductivity onsets at a higher displacement field and features a higher critical temperature, reaching up to 0.5K. Within the main superconducting dome and in the strong Ising SOC limit, we find an unusual phase transition characterized by a nematic redistribution of holes among trigonally warped Fermi pockets and enhanced resilience to in-plane magnetic fields. Moreover, we identify two additional superconducting regions, one of which descends from an inter-valley coherent normal state and exhibits a Pauli-limit violation ratio exceeding 40, among the highest for all known superconductors.
", "doi": "10.7907/nfyx-3565", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17332", "collection": "thesis", "collection_id": "17332", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012025-033851773", "primary_object_url": { "basename": "Armstrong_Thesis_Final.pdf", "content": "final", "filesize": 2872510, "license": "other", "mime_type": "application/pdf", "url": "/17332/1/Armstrong_Thesis_Final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Effects of Disorder on Quantum Phase Transitions and Quantum Dynamics", "author": [ { "family_name": "Armstrong", "given_name": "Stephen Lowell", "orcid": "0000-0001-7325-4763", "clpid": "Armstrong-Stephen-Lowell" } ], "thesis_advisor": [ { "family_name": "Rosenbaum", "given_name": "Thomas F.", "orcid": "0009-0008-6152-666X", "clpid": "Rosenbaum-T-F" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Jackson", "given_name": "Jennifer M.", "orcid": "0000-0002-8256-6336", "clpid": "Jackson-J-M" }, { "family_name": "Rosenbaum", "given_name": "Thomas F.", "orcid": "0009-0008-6152-666X", "clpid": "Rosenbaum-T-F" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "We present experimental studies of the effects of disorder on the quantum phase transitions of antiferromagnetic LiErF\u2084 and of the dynamic behavior of LiHo0.2Y0.8F\u2084, which hosts a spin glass ground state due to the combination of substitutional disorder and magnetic frustration. Both compounds are insulating dipolar-coupled magnets that can be effectively treated as spin \u00bd systems.
\r\n\r\nTwo distinct quantum phase transitions can be induced in the easy-plane antiferromagnet LiErF\u2084, applying a magnetic field in the plane or perpendicular to it. The isotopic distribution of natural Er permits us to probe these transitions in the clean and dirty regimes. 167Er has a natural abundance of 23% and is the only stable isotope with a non-zero nuclear spin. At low temperatures, the nuclear spin slaves to the electronic spin and reduces the effective field felt by the electronic spin, thereby inducing random mass disorder in the dirty (low-temperature) regime. We use specific heat measurements to identify the temperature scale of the crossover between the dirty and clean regime as T=150 mK, and make ac magnetic susceptibility measurements to characterize the effects of disorder on the two quantum phase transitions. When the field is applied along the c-axis, the critical behavior is consistent with a violation of the Harris criterion in the clean regime and a change of universality class in the dirty regime. When the field is applied along the a-axis, the critical behavior is unchanged by the crossover between clean and dirty regimes.
\r\n\r\nWe use ac susceptibility measurements to conduct thermal memory dip experiments on the spin glass state of LiHo0.2Y0.8F\u2084 in zero magnetic field and find no apparent rejuvenation or memory. We perform an analogous \u201cquantum memory dip\u201d measurement which uses a transverse magnetic field rather than temperature to enter the spin glass state, and we find strong rejuvenation. The relaxation rate of the susceptibility decreases as the transverse field increases. This counterintuitive result is attributed to an increase in the variance of the random longitudinal field associated with increasing the transverse field and is supported by simulations. Finally, we perform a \"negative field cycle\" experiment which finds erasure of memory in the spin glass state. We establish a theoretical framework of quantum resonant tunneling to explain our results, rather than the conventional picture of a hierarchical free energy landscape associated with classical spin glasses.
", "doi": "10.7907/yeaq-w360", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17445", "collection": "thesis", "collection_id": "17445", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06112025-032822492", "primary_object_url": { "basename": "Senior_Thesis___Correct_Format-1.pdf", "content": "final", "filesize": 7615911, "license": "other", "mime_type": "application/pdf", "url": "/17445/1/Senior_Thesis___Correct_Format-1.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "The Assembly and Testing of the Spin Dressing Magnet for the Neutron Electric Dipole Experiment", "author": [ { "family_name": "Fox", "given_name": "Jessica Lauren", "orcid": "0000-0001-5053-229X", "clpid": "Fox-Jessica-Lauren" } ], "thesis_advisor": [ { "family_name": "Filippone", "given_name": "Bradley W.", "orcid": "0000-0002-2618-2688", "clpid": "Filippone-B-W" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Filippone", "given_name": "Bradley W.", "orcid": "0000-0002-2618-2688", "clpid": "Filippone-B-W" }, { "family_name": "Politzer", "given_name": "Hugh David", "orcid": "0000-0002-4983-6621", "clpid": "Politzer-H-D" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Hutzler", "given_name": "Nicholas R.", "orcid": "0000-0002-5203-3635", "clpid": "Hutzler-N-R" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "The discrepancy between the quantity of matter and anitmatter in the universe is something that can likely be attributed to violations in the fundamental symmetries of the universe; however, much like the antimatter itself, there is a discrepancy between the required versus obeserved magnitude of these violations. One theory states that, to account for these violations in symmetry, the neutron must have an electric dipole moment. One such method to find the existence and magnitude of the neutron electric dipole moment (nEDM) is the critical dressing method. Such a method requires the use of two superconducting magnets with perpendicular magnetic fields. This specific method of critical dressing uses superfluid Helium-4, polarized Helium-3, and ultracold polarized neutrons, with critical dressing occurring when the Helium-3 precession rates are equivalent. This method is used to determine the existence of an nEDM, if there is critical dressing with an electric field, there is no nEDM, but if there is a precession rate difference with the electric field, there is an EDM that can thus be measured. Over the past several months, the assembly of the spin dressing magnet used in the critical dressing portion of the nEDM experiment has begun. This has included assembling the boss rings, constructing the magnet frame, placing the story sticks and wire guides, and winding the superconducting wire around the coil skeleton. Data was also taken using this wire. Furthermore, simulations have been run on COMSOL Multiphysics to compare the theoretical predictions with the measurements of the magnetic field and B-field gradients produced by the spin dressing magnet.", "doi": "10.7907/rjne-gy68", "publication_date": "2025", "thesis_type": "senior_major", "thesis_year": "2025" }, { "id": "thesis:16750", "collection": "thesis", "collection_id": "16750", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09222024-203253433", "primary_object_url": { "basename": "Dhruv_Desai_Caltech_Thesis_proofread_sept16 (1).pdf", "content": "final", "filesize": 23028559, "license": "other", "mime_type": "application/pdf", "url": "/16750/2/Dhruv_Desai_Caltech_Thesis_proofread_sept16 (1).pdf", "version": "v7.0.0" }, "type": "thesis", "title": "First-Principles Calculations of Magnetotransport and Electron-Phonon Interactions in Semiconductors and Topological Materials", "author": [ { "family_name": "Desai", "given_name": "Dhruv Chimanbhai", "orcid": "0009-0008-2898-9750", "clpid": "Desai-Dhruv Chimanbhai" } ], "thesis_advisor": [ { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-Marco" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-Marco" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Understanding and predicting electron transport in novel materials is crucial to develop practical applications and accelerate materials discovery. Electron-phonon (e-ph) interactions are a key source of electron scattering and therefore play a dominant role in limiting electron transport under applied external fields. These interactions and the resulting phonon-limited charge transport can be calculated very accurately using ab-initio methods based on the semiclassical Boltzmann transport equation (BTE), where electron and phonon properties are obtained using density functional theory (DFT) and density functional perturbation theory (DFPT) techniques. Despite these advances, first-principles calculations of magnetotransport are still in their infancy, primarily due to technical challenges associated with solving the BTE in the presence of a magnetic field. Additionally, calculations of electrical charge transport and magnetotransport in topological materials are lacking because of various technical challenges, including computational cost and the absence of a unified formalism combining electron scattering and band topology in the BTE. In this work, we develop a framework that incorporates these effects into the BTE to compute charge transport, magnetotransport and topological transport regimes in several classes of conventional and quantum materials. Our magnetotransport calculations achieve excellent agreement with experiments, and we uncover an interplay of strong e-ph interactions and magnetic fields in graphene through a microsopic analysis of steady-state electron distributions. As a first step toward including band topology, we compute e-ph interactions and charge transport in the Dirac semimetal Na\u2083Bi and find that specific two-dimensional phonons control charge transport near room temperature. These lattice vibrations induce a dynamic phase transition to a Weyl semimetal, providing a platform for ultrafast control of dynamical phases in Na\u2083Bi. Expanding into more advanced phenomena, we incorporate the electron Berry curvature in the BTE formalism and study topological transport effects such as the chiral anomaly and nonlinear Hall effect (NLHE). Our calculations provide an accurate quantitative framework and demonstrate the importance of e-ph interactions in accurately describing topological transport in quantum materials. Lastly, we compute e-ph interactions in a novel correlated metal, RuO\u2082 which has been widely studied for its unconventional magnetism. We uncover various interesting properties such as phonon softening, strong e-ph band renormalization and a high superconducting Tc upon application of strain in RuO\u2082. Finally, we show a method to significantly accelerate all these calculations by compressing the matrices representing e-ph interactions. In summary, this work expands the scope of first-principles transport calculations to include magnetic fields and band topology. This enables future studies of electron dynamics in broad classes of novel quantum materials.", "doi": "10.7907/s0ca-dg17", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16460", "collection": "thesis", "collection_id": "16460", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012024-155841744", "primary_object_url": { "basename": "Caltech_Thesis_Chen_Li_2023.pdf", "content": "final", "filesize": 20241306, "license": "other", "mime_type": "application/pdf", "url": "/16460/1/Caltech_Thesis_Chen_Li_2023.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Ultrafast Optical Studies of Pressure-Tuned Spin-Orbit Materials", "author": [ { "family_name": "Li", "given_name": "Chen", "orcid": "0000-0001-6750-5925", "clpid": "Li-Chen" } ], "thesis_advisor": [ { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Rosenbaum", "given_name": "Thomas F.", "orcid": "0009-0008-6152-666X", "clpid": "Rosenbaum-T-F" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "The advent of quantum materials has provided researchers with a remarkable opportunity to delve into the intricate interplay among various degrees of freedom, encompassing charge, orbital, spin, and lattice dynamics. Transition metal compounds, possessing distinct characteristics, exemplify the captivating competition between interactions arising from different degrees of freedom, each with comparable strength. These interactions encompass the on-site Coulomb interaction, kinetic hopping, spin-orbit coupling (SOC), crystal electric field splitting, and Hunds exchange coupling. In correlated electron systems of this nature, the intricate interplay of these complex interactions gives rise to a plethora of exotic phenomena, rendering the understanding of each variable a daunting task. Hence, it becomes imperative to explore their responses to external stimuli, and in this regard, hydrostatic pressure emerges as a versatile tool capable of tuning the strength of competing interactions and shifting the delicate balance between coexisting and competing ground states. This engenders a rich diversity of quantum phases and holds the potential to decouple these intertwined variables in phase transitions, thus unveiling the distinctive roles played by each constituent.
\r\n\r\nIn Chapter I, a comprehensive discussion on pressure-induced phase transitions will ensue, encompassing phenomena such as insulator-metal transitions, spin-crossover transitions, structural transformations, and the fervent search for elusive quantum spin liquid and topological superconductive states. Chapter II shall delve into the experimental techniques that have been extensively employed throughout my research endeavors. This will encompass a synergistic combination of a high-pressure environment and cutting-edge ultrafast optical probing techniques, including optical second harmonic generation (SHG), harnessed by the high peak power of femtosecond lasers, as well as time-resolved reflectivity, capitalizing on the exceedingly short time duration of laser pulses. Moreover, a wide-field microscopy approach based on the magneto-optical Kerr effect shall be expounded upon, enabling direct observations of intricate domain structures. In subsequent chapters, three projects shall be elucidated, encompassing Weyl semimetals, with a specific focus on TaAs in Chapter III, Co3Sn2S2 in Chapter V, and an investigation into the spin-orbit-coupled Mott insulator Sr2IrO4 in Chapter IV.
\r\n\r\nThe transition metal monopnictide family of Weyl semimetals recently has been shown to exhibit anomalously strong second-order optical nonlinearity, which is theoretically attributed to a highly asymmetric polarization distribution induced by their polar structure. We experimentally test this hypothesis by measuring optical SHG from TaAs across a pressure-tuned polar to non-polar structural phase transition. Despite the high-pressure structure remaining non-centrosymmetric, the SHG yield is reduced by more than 60% by 20 GPa as compared to the ambient pressure value. By examining the pressure dependence of distinct groups of SHG susceptibility tensor elements, we find that the yield is primarily controlled by a single element that governs the response along the polar axis. Our results confirm a connection between the polar axis and the giant optical nonlinearity of Weyl semimetals and demonstrate pressure as a means to tune this effect in situ.
\r\n\r\nSr2IrO4 stands as an archetypal SOC-mediated Mott insulator, where the electronic and magnetic structures are highly sensitive to the intricacies of the crystallographic structure, particularly the rotation and tilting of the IrO6 cages. External pressure serves as a direct means to manipulate these characteristics. Under high pressure, fascinating phenomena have emerged, including the persistence of the insulating state up to an extreme pressure of 185 GPa, a sequence of magnetic transitions culminating in a quantum paramagnetic phase around 20 GPa. However, a dearth of information exists concerning the low-energy electronic band structure. To address this gap, we conducted time-resolved reflectivity measurements under pressures up to 14 GPa. Within the low-pressure range below 10 GPa, anomalies in the temperature-dependent reflectivity transients exhibit a trend akin to the Neel temperature. Yet, as pressure increases further, the temperature associated with these anomalies rises and deviates from the monotonically decreasing magnetic ordering temperature, thereby unveiling a mysterious underlying mechanism governing the relaxation dynamics.
\r\n\r\nIn addition to the breaking of inversion symmetry, Weyl topology can also arise from the breaking of time reversal symmetry in magnetic systems, offering a fertile ground for investigating the intricate relationship between magnetism and topological order. Endeavors have been undertaken to manipulate magnetism as a means to tune the topological electronic band structure. Notably, the well-established ferromagnetic Weyl semimetal, Co3Sn2S2, has garnered significant attention due to its intriguing magnetic anomalies persisting below the Curie temperature. Further investigations have revealed that the distribution of magnetic domains and domain walls plays a pivotal role in elucidating these anomalies. Herein, we report the observation of domain structures using a wide-field Kerr microscope and the manipulation of said structures employing a mid-infrared laser and magnetic field. This study not only sheds light on domain-related properties but also holds promise for uncovering exotic topological phenomena exhibited at domain boundaries.
", "doi": "10.7907/79g4-4392", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16388", "collection": "thesis", "collection_id": "16388", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05172024-212658426", "primary_object_url": { "basename": "Gu_Shouzhen_2024.pdf", "content": "final", "filesize": 3702205, "license": "other", "mime_type": "application/pdf", "url": "/16388/1/Gu_Shouzhen_2024.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Quantum Error Correction Using Low-Density Parity-Check Codes and Erasure Qubits", "author": [ { "family_name": "Gu", "given_name": "Shouzhen", "orcid": "0000-0003-2560-4209", "clpid": "Gu-Shouzhen" } ], "thesis_advisor": [ { "family_name": "Preskill", "given_name": "John P.", "orcid": "0000-0002-2421-4762", "clpid": "Preskill-J" } ], "thesis_committee": [ { "family_name": "Kitaev", "given_name": "Alexei", "orcid": "0000-0002-5777-642X", "clpid": "Kitaev-A" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Preskill", "given_name": "John P.", "orcid": "0000-0002-2421-4762", "clpid": "Preskill-J" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_pma" } ], "abstract": "Quantum error correction is a method to reduce the effective error rate on quantum computers so that they can be used to carry out useful computation. In this thesis, we study two main problems: decoding quantum low-density parity-check codes and using erasure qubits to implement error correction protocols.
\r\n\r\nIn the first part of this thesis, we focus on quantum low-density parity-check codes, which are a promising approach to reducing the spacetime overhead associated with error correction. We show that certain families of codes with constant rate and linear distance can be decoded efficiently. In particular, we propose a linear-time algorithm that will correct any error affecting at most a constant fraction of the qubits.
\r\n\r\nWe also analyze the setting where the measurement outcomes given to the decoder can be corrupted. In this more realistic scenario, the decoder is shown to have the single-shot property. Using one round of noisy syndrome data, it can output a correction that is close to the data error as long as at most a constant fraction of the data qubits and syndrome bits are flipped. As a consequence, the decoder can operate under a stochastic noise model where errors occur with sufficiently small but constant probability.
\r\n\r\nIn the second part of the thesis, we analyze quantum error-correcting codes implemented using erasure qubits. The idea behind erasure qubits is to bias the noise into a form where likely locations of errors are known, for example, by converting the dominant noise source into detectable leakage from the computational subspace. We provide a formalism for simulating and decoding stabilizer circuits with erasures, erasure checks, and resets. Using this formalism, we study the performance of Floquet codes and show that the benefits of knowing error locations outweigh the cost of extra noise due to erasure checks.
\r\n\r\nLastly, we optimize erasure check schedules in the context of the surface code. By performing simulations with one, two, or four erasure checks per syndrome extraction round, we find different error parameter regimes where it is optimal to use each schedule. Additionally, we provide a simplified way of decoding erasure circuits suitable for circuits with infrequent erasure checks.
", "doi": "10.7907/5pj8-wv34", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:15230", "collection": "thesis", "collection_id": "15230", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302023-084739008", "type": "thesis", "title": "A Deep Dive into the Connections Between the Renormalization Group and Deep Learning in the Ising Model", "author": [ { "family_name": "Taylor", "given_name": "Kelsie", "orcid": "0009-0001-7510-2306", "clpid": "Taylor-Kelsie-Reed" } ], "thesis_advisor": [ { "family_name": "Spiropulu", "given_name": "Maria", "orcid": "0000-0001-8172-7081", "clpid": "Spiropulu-M" }, { "family_name": "Lykken", "given_name": "Joseph", "orcid": "0000-0002-0090-9439", "clpid": "Lykken-J" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Politzer", "given_name": "Hugh David", "orcid": "0000-0002-4983-6621", "clpid": "Politzer-H-D" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Filippone", "given_name": "Bradley W.", "orcid": "0000-0002-2618-2688", "clpid": "Filippone-B-W" }, { "family_name": "Frautschi", "given_name": "Steven C.", "clpid": "Frautschi-S-C" }, { "family_name": "Hutzler", "given_name": "Nicholas R.", "orcid": "0000-0002-5203-3635", "clpid": "Hutzler-N-R" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Spiropulu", "given_name": "Maria", "orcid": "0000-0001-8172-7081", "clpid": "Spiropulu-M" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "The renormalization group (RG) is an essential technique in statistical physics and quantum field theory, which considers scale-invariant properties of physical theories and how these theories\u2019 parameters change with scaling. Deep learning is a powerful computational technique that uses multi-layered neural networks to solve a myriad of complicated problems. Previous research suggests the possibility that unsupervised deep learning may be a form of RG flow, by being a layer-by-layer coarse graining of the original data. We examined this connection on a more rigorous basis for the simple example of Kadanoff block renormalization of the 2D nearest-neighbor Ising model, with our deep learning accomplished via Restricted Boltzmann Machines (RBMs). We developed extensive renormalization techniques for the 1D and 2D Ising model to provide a baseline for comparison. For the 1D Ising model, we successfully used Adam optimization on a correlation length loss function to learn the group flow; yielding results consistent with the analytical model for infinite N. For the 2D Ising model, we successfully generated Ising model samples using the Wolff algorithm, and performed the group flow using a quasi-deterministic method, validating these results by calculating the critical exponent \\nu. We then examined RBM learning of the Ising model layer by layer, finding a blocking structure in the learning that is qualitatively similar to RG. Lastly, we directly compared the weights of each layer from the learning to Ising spin renormalization, but found quantitative inconsistencies for the simple case of nearest-neighbor Ising models.", "doi": "10.7907/ztpg-z092", "publication_date": "2023", "thesis_type": "senior_major", "thesis_year": "2023" }, { "id": "thesis:15213", "collection": "thesis", "collection_id": "15213", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05262023-213514916", "primary_object_url": { "basename": "Main_ChaoJungLee_PhDThesis_2023_0526.pdf", "content": "final", "filesize": 3276887, "license": "other", "mime_type": "application/pdf", "url": "/15213/1/Main_ChaoJungLee_PhDThesis_2023_0526.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "The Effects of Disorder and Interaction in Metallic Systems", "author": [ { "family_name": "Lee", "given_name": "Chao-Jung", "orcid": "0000-0003-3339-1522", "clpid": "Lee-Chao-Jung" } ], "thesis_advisor": [ { "family_name": "Mulligan", "given_name": "Michael", "orcid": "0009-0001-8457-986X", "clpid": "Mulligan-Michael" } ], "thesis_committee": [ { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" }, { "family_name": "Mulligan", "given_name": "Michael", "orcid": "0009-0001-8457-986X", "clpid": "Mulligan-Michael" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Metallic states in two-dimensional quantum matter have a long history and pose extremely challenging problems. A generic metallic state is described by a gapless system with a finite density of particles, along with disorders and interactions. Such correlated many-body systems are usually difficult to study, both analytically and numerically. In this thesis, we are dedicated to certain simplified cases which enable us to study via analytical approaches. Firstly, we study the effects of quenched disorder and a dissipative Coulomb interaction in the Dirac composite fermion theory describing the quantum phase transition of integer quantum Hall plateau and magnetic-field tuned 2D supercondutor\r\nThe renormalization group study is presented, by considering the quantum effect of disorder and gauge fluctuation. Secondly, we present a study of integer quantum Hall plateau transition using a mean-field theory of composite fermions with a gyromagnetic ratio equal to two. We investigate the stability problem in terms of semi-classical approach and derive the corresponding nonlinear sigma model. Thirdly, we study a single 2D Dirac fermion at finite density, subjected to a quenched random magnetic field. The low-energy theory can be mapped onto an infinite collection of 1D chiral fermions coupled by a random vector potential matrix. The theory is exactly solvable, and the electrical response is computed non-perturbatively. Lastly, we shift our focus to a disorder-free system formed by a collection of 1D wires. We provide an example of an Ersatz Fermi liquid by deforming the chiral Wess-Zumino-Witten model with level k greater than unity.", "doi": "10.7907/p4b6-y780", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15273", "collection": "thesis", "collection_id": "15273", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-010804337", "type": "thesis", "title": "Fractonic Orders from Lattice Models and Field Theories", "author": [ { "family_name": "Ma", "given_name": "Xiuqi", "orcid": "000-0001-8294-2277", "clpid": "Ma-Xiuqi" } ], "thesis_advisor": [ { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Ni", "given_name": "Yi", "orcid": "0000-0002-5287-4258", "clpid": "Ni-Yi" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Fracton models are characterized by exotic features such as point-like excitations with restricted mobility, sub-extensive ground state degeneracy and UV/IR mixing. They have been studied previously using exactly solvable lattice models, higher rank gauge theories, etc. In an effort to classify fracton models into phases (i.e., fractonic orders), the so-called foliation structure has been introduced and shown to exist in many previously known models. A natural question then arises concerning the feasibility of the foliation paradigm in general. In this thesis, I study fracton models beyond the foliation paradigm and give simple diagnostics for the absence of a foliation structure. New notions of fractonic orders therefore need to be conceived, and I present such a conception which is a generalization of the foliation RG.
\r\n\r\nIn Chapters 2 - 4, I introduce new fracton models obtained from infinite-component Chern-Simons (CS\u221e) theories. By calculating observables such as ground state degeneracy and planon braiding statistics, I prove that most CS\u221e theories are not foliated. A CS\u221e theory can also be gapless with certain choices of parameters, and I show that such a theory is a stable gapless fracton model. Furthermore, I discuss topological features of a large subclass of gapless CS\u221e theories and present fully continuous effective field theories for this subclass.
\r\n\r\nIn Chapters 5 - 6, I discuss a new notion of fractonic orders by studying the example of the Ising cage-net model. I begin by calculating the ground state degeneracy of the model, which shows that the model is not foliated. The calculation uses an operator algebra approach which relies only on intrinsic physical properties of the model rather than microscopic details, and I establish the framework of this approach conceptually and via examples. I then argue why this intrinsic approach, despite being a tool for calculation initially, may be a useful characterization of a fractonic order. Finally, I present a generalized foliation RG scheme, apply it to the Ising cage-net model, and discuss its limitations.
", "doi": "10.7907/g80m-dy31", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15081", "collection": "thesis", "collection_id": "15081", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01052023-230400021", "type": "thesis", "title": "Electronic Correlations and Topology in Graphene Moir\u00e9 Multilayers and InAs/GaSb-Derivative Systems", "author": [ { "family_name": "Polski", "given_name": "Robert Michael", "orcid": "0000-0003-0887-8099", "clpid": "Polski-Robert-Michael" } ], "thesis_advisor": [ { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Twisted bilayer graphene (TBG) near the magic angle exhibits a wide variety of correlated and topological phases such as superconductivity, correlated insulators, and orbital ferromagnetism. We show using electrical transport measurements that adding a layer of tungsten diselenide in proximity to twisted bilayer graphene stabilizes superconductivity to twist angles significantly below the magic angle despite the disappearance of correlated insulators and insulators at full moir\u00e9 filling. These findings--along with our report of a relationship between superconductivity and symmetry breaking Fermi surface reconstruction--suggest constraints on theories of the origin of superconductivity in TBG. In the context of this TBG-tungsten diselenide system, we study how the correlated phases evolve over a wide twist angle range and classify them into a hierarchy based on where they occur relative to the magic angle (or where bands have been maximally flattened). While effects such as orbital ferromagnetism near one electron per moir\u00e9 unit cell and gapped correlated insulators only exist in close proximity to the magic angle, superconductivity and high-temperature cascade transitions survive in a wider twist angle range.
\r\n\r\nWe also analyze the structures of twisted trilayer, quadrilayer, and pentalayer graphene (and all proximitized to tungsten diselenide) near their respective theoretical magic angles, revealing robust electron- and hole-side superconductivity in each heterostructure. We additionally find previously unreported insulating states in twisted trilayer and quadrilayer graphene along with an enlarged filling range of superconductivity in pentalayer. Our studies on twisted graphene multilayers beyond two layers allow us to generalize the correlated physics found in TBG and consider the role of the additional bands introduced.
\r\n\r\nIn the last part of this thesis, we measure the two-dimensional topological insulator candidate system InAs/GaSb with added stoichiometric impurities. Previous studies in pure InAs/GaSb structures have revealed low bulk resistivity and edge states that arise from trivial effects which can be easily mistaken for topological effects. Due, in part, to the strain effects of Indium impurities added to GaSb, our results show high bulk resistivity. We also, due to the wide gate-tunability in our devices, are able to measure the expected spin-orbit-split valence band structure. Our development of highly tunable InAs/GaSb-derivative structures paves the way for another look at two-dimensional topological insulator behavior in these systems and for their integration into superconducting devices.
", "doi": "10.7907/yhws-0f08", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14372", "collection": "thesis", "collection_id": "14372", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09242021-222116257", "primary_object_url": { "basename": "Youngjoon_Choi_PhD_Thesis_Final.pdf", "content": "final", "filesize": 49417580, "license": "other", "mime_type": "application/pdf", "url": "/14372/1/Youngjoon_Choi_PhD_Thesis_Final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "A Spectroscopic Study of Electronic Correlations in Twisted Bilayer Graphene by Scanning Tunneling Microscopy", "author": [ { "family_name": "Choi", "given_name": "Youngjoon", "orcid": "0000-0001-9783-5992", "clpid": "Choi-Youngjoon" } ], "thesis_advisor": [ { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "thesis_committee": [ { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Lee", "given_name": "Patrick A.", "orcid": "0000-0001-7809-8157", "clpid": "Lee-Patrick-A" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Twisted bilayer graphene around the magic angle has shown variety of correlated phases such as superconductivity, correlated insulators, and magnetism due to its flat band structure. The unconventional nature of the superconductivity and its pos- sible relation to high temperature superconductors have sparked a lot of theoretical and experimental efforts to understand the properties of the magic angle twisted bilayer graphene. While electrical transport measurements revealed the interesting phases, spectroscopic understanding is strongly needed to connect the phases with theoretical calculations. We present the spectroscopic studies of gate-tunable magic angle twisted bilayer graphene using scanning tunneling microscopy. We report that the band structure is significantly modified even at charge neutrality due to exchange interaction. We apply a perpendicular magnetic field and develop a novel method that enables scanning tunneling microscopy to reveal Landau fan diagrams. We discover topologically non-trivial states appearing at finite magnetic field, and from spectroscopy we are able to identify the mechanism. Finally, we verify inter- action driven band flattening experimentally in twisted bilayer graphene, which is responsible for creating strong correlations.
", "doi": "10.7907/ajgk-7246", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14944", "collection": "thesis", "collection_id": "14944", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06052022-215214933", "primary_object_url": { "basename": "park_jinsoo_2022.pdf", "content": "final", "filesize": 11000317, "license": "other", "mime_type": "application/pdf", "url": "/14944/2/park_jinsoo_2022.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Spin-Phonon Interactions and Spin Decoherence from First Principles", "author": [ { "family_name": "Park", "given_name": "Jinsoo", "orcid": "0000-0002-1763-5788", "clpid": "Park-Jinsoo" } ], "thesis_advisor": [ { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-Marco" } ], "thesis_committee": [ { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" }, { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-Marco" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Developing a microscopic understanding of spin decoherence is essential to advancing quantum technologies. Electron spin decoherence due to atomic vibrations (phonons) plays a special role as it sets an intrinsic limit to the performance of spin-based quantum devices. Two main sources of phonon-induced spin decoherence, the Elliott-Yafet (EY) and Dyakonov-Perel (DP) mechanisms, have distinct physical origins and theoretical treatments. First-principles calculations of electron-phonon (e-ph) interactions combined with many-body perturbation theory are promising to study phonon-induced spin decoherence. However, predicting the spin response in materials remains an open challenge; methods for quantifying spin-dependent e-ph interactions in materials, as well as a linear response framework for spins in the presence of e-ph interaction is missing. In this thesis, we provide a first-principles framework for computing the relativistic spin-dependent electron-phonon interactions. We develop a formalism that unifies the modeling of EY and DP spin decoherence, and provide a rigorous many-body perturbation theory for obtaining the spin-spin correlation function including the vertex corrections due to e-ph interactions. We compute the phonon-dressed vertex of the spin-spin correlation function with a treatment analogous to the calculation of the anomalous electron magnetic moment in QED. We find that the vertex correction provides a giant renormalization of the electron spin dynamics in solids, greater by many orders of magnitude than the corresponding correction from photons in vacuum. We further identify the long-range quadrupole e-ph interaction in materials, and demonstrate its importance in the description of phonon-induced spin decoherence. We show first-principle calculations of spin-dependent e-ph interactions in correlated electron systems, using the framework of Hubbard-corrected density functional theory. Lastly, we provide technical details in the implementation of ab-initio e-ph interaction in PERTURBO, a software package for first-principles calculations of charge transport, spin dynamics, and ultrafast carrier dynamics in materials. In summary, the thesis demonstrates a general approach for quantitative analysis of spin decoherence in materials, advancing the quest for spin-based quantum technologies.
", "doi": "10.7907/80bd-x991", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14962", "collection": "thesis", "collection_id": "14962", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06192022-010740124", "primary_object_url": { "basename": "Senior_Thesis_Shubh_Agrawal.pdf", "content": "final", "filesize": 5897362, "license": "other", "mime_type": "application/pdf", "url": "/14962/1/Senior_Thesis_Shubh_Agrawal.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Direct Imaging of Exoplanets Closer to Stars", "author": [ { "family_name": "Agrawal", "given_name": "Shubh", "orcid": "0000-0003-2429-5811", "clpid": "Agrawal-Shubh" } ], "thesis_advisor": [ { "family_name": "Mawet", "given_name": "Dimitri", "orcid": "0000-0002-8895-4735", "clpid": "Mawet-D" }, { "family_name": "Ruffio", "given_name": "Jean-Baptiste", "orcid": "0000-0003-2233-4821", "clpid": "Ruffio-Jean-Baptiste" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Politzer", "given_name": "Hugh David", "orcid": "0000-0002-4983-6621", "clpid": "Politzer-H-D" }, { "family_name": "Filippone", "given_name": "Bradley W.", "orcid": "0000-0002-2618-2688", "clpid": "Filippone-B-W" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Mawet", "given_name": "Dimitri", "orcid": "0000-0002-8895-4735", "clpid": "Mawet-D" }, { "family_name": "Ruffio", "given_name": "Jean-Baptiste", "orcid": "0000-0003-2233-4821", "clpid": "Ruffio-Jean-Baptiste" } ], "local_group": [ { "literal": "Keck Institute for Space Studies" }, { "literal": "div_pma" } ], "abstract": "Detecting exoplanets through direct imaging at lower angular separations, where more planets are expected to be, is limited by the variability of the stellar point spread function. Integral field spectrographs like OSIRIS at the Keck Observatory can leverage high spectral resolution to search for new planets at smaller separations (< 0.3 arcseconds) by detecting their distinct spectral signature compared to the diffracted starlight. In this thesis, we present the mid-survey results of a search for planets around 23 targets in the Ophiuchus and Taurus star-forming regions.
\r\n\r\nWe use this pathfinder survey with Keck/OSIRIS to demonstrate our technique and compare the final sensitivities to other classical imaging techniques, particularly at separations of 0.05-0.3 arcseconds. We detect an M dwarf companion around HD 148352 at a \u2248 34\u03c3 significance level. We measure this binary star companion to be at an angular separation of roughly $0.11$ milliarcseconds, with a contrast of $0.38\\%$, effective temperature Teff \u2248 3200 K, and radial velocity RV \u2248 12 km/s. We also present other low-significance objects, along with detection maps and sensitivity limits around these 23 targets.
\r\n\r\nWe use our open-source data analysis pipeline, called the Broad Repository for Exoplanet Analysis, Detection, and Spectroscopy (breads), as the framework for this planet search. breads operates on high spectral resolution data from existing and in-development instruments. Our code is based on a forward-modeling framework, which is statistically more accurate than classical cross-correlation techniques. It includes a built-in optimization and analytical marginalization of linear parameters in the forward model, therefore limiting the number of parameters to be explored by the posterior sampling method. We allow users to select forward models, parameters to detect and analyze, and fitting methods like Markov Chain Monte Carlo sampling, grid optimization, and gradient descent. breads provides a flexible framework to retrieve radial velocity, spin, and atmospheric parameters of high-contrast companions. We also describe wavelength and resolution calibration, transmission and spectra calculation, and bad pixel identification techniques.
\r\n\r\nOur work will be applicable to future integral field spectrographs like NIRSpec on the James Webb Space Telescope and other first light instruments on the future Extremely Large Telescopes, which are poised to become the next generation of exoplanet detection facilities.
", "doi": "10.7907/17sv-vf40", "publication_date": "2022", "thesis_type": "senior_major", "thesis_year": "2022" }, { "id": "thesis:14250", "collection": "thesis", "collection_id": "14250", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06072021-061251562", "primary_object_url": { "basename": "Swati_ThesisJune8.pdf", "content": "final", "filesize": 85448266, "license": "other", "mime_type": "application/pdf", "url": "/14250/1/Swati_ThesisJune8.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Light Induced Dynamics in Quantum Matter", "author": [ { "family_name": "Chaudhary", "given_name": "Swati", "clpid": "Swati Chaudhary" } ], "thesis_advisor": [ { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" } ], "thesis_committee": [ { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Endres", "given_name": "Manuel A.", "orcid": "0000-0002-4461-224X", "clpid": "Endres-M" }, { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "This thesis presents studies of different schemes to probe and manipulate quantum matter using light with an aim to discover novel routes to efficiently control the properties of quantum materials. A special focus is placed on developing new schemes utilizing light-matter interactions (1) to modify exchange interactions in magnetic insulators, and (2) to probe and modify band topology in quantum matter.
\r\n\r\nIn part II, new schemes are presented to probe local band topology of Bloch bands. First, we study the effects of time-dependent band topology on adiabatic evolution of a Bloch wavepacket. We find that it results in an electric-field analog in semi-classical equation of motion, and can be demonstrated in a honeycomb lattice by varying the sublattice offset energy. We then extend these methods to include non-adiabatic processes, and found interesting connections between the anomalous drift during band excitation and a quantum geometric quantity known as shift-vector. We generalize the concept of shift-vector to include different kinds of band transition protocols beyond light-induced dipole transitions. The idea of electric-field analog and the shift-vector are then combined to develop a novel charge pumping scheme. Motivated by these interesting consequences of band topology in non-adiabatic processes, we study shift-current response in moir\u00e9 materials, and find that the highly topological nature of flat bands along with their very large unit cells significantly enhances these shift-vector related effects. This response also displays a strong dependence on interaction-induced changes in the band structure and quantum geometric quantities. These results suggest that shift-current response can possibly serve as a very reliable probe for interactions in twisted bilayer graphene. In addition to studying consequences of band topology on single-particle transport, we also consider Berry curvature effects on exciton transport. We find that the non-trivial band topology of underlying electron and hole bands allows us to manipulate excitons with a uniform electric field. We examine the conditions necessary to observe such transport and propose that transition metal dichalcogenide heterobilayers with moir\u00e9 structure can prove an ideal platform for these effects.
\r\n\r\nIn part III, we propose novel drive protocols based on manipulating orbital and lattice degrees of freedom in quantum materials with light. We found that light induced changes in orbital hybridization and their electronic energies results in a significant change in exchange interactions in quantum magnets. We also accounted for the role of ligands in periodically driven quantum magnets, and found that the predictions made by the minimal model based on direct-hopping can be wrong in certain regimes of drive parameters. This understanding of light induced modifications in ligand-mediated exchange interactions was used to explain the phase shift observed in coherent phonon oscillations of CrSiTe\u2083 upon the onset of short-range spin correlations. We also demonstrate that light induced coherent lattice vibrations can provide a new route to realize space-time symmetry protected topological phases. Our results suggest that manipulating additional degrees of freedom (not included in commonly employed minimal models of periodically driven systems) with light can provide novel routes for ultrafast control of quantum materials.
", "doi": "10.7907/a8z1-5c40", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14279", "collection": "thesis", "collection_id": "14279", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06162021-230506010", "primary_object_url": { "basename": "Senior Thesis mk5.pdf", "content": "final", "filesize": 1759771, "license": "other", "mime_type": "application/pdf", "url": "/14279/1/Senior Thesis mk5.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Liquid-Induced Discharge of Polypropylene Microfiber Electret Filters", "author": [ { "family_name": "Nazeeri", "given_name": "Albert Isaac", "orcid": "0000-0003-0000-9841", "clpid": "Nazeeri-Albert-Isaac" } ], "thesis_advisor": [ { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Politzer", "given_name": "Hugh David", "orcid": "0000-0002-4983-6621", "clpid": "Politzer-H-D" }, { "family_name": "Frautschi", "given_name": "Steven C.", "clpid": "Frautschi-S-C" }, { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" }, { "family_name": "Kapustin", "given_name": "Anton N.", "orcid": "0000-0003-3903-5158", "clpid": "Kapustin-A" }, { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Polymer microfiber electret filters are the technology behind N95 and equivalent type respirators. Understanding how liquids interact with and discharge these filters would allow for the development of non-damaging liquid decontamination protocols. Previous work on liquid/filter interactions has been largely empirical with articles reporting the effect a specific liquid has on the filtration efficiency of a particular filter. This thesis proposes a theoretical model of liquid induced discharge of polymer microfiber electret filters via the ideas of surface wetting and electrical conductivity. This model was tested, and validated, on commercially available polypropylene microfiber electret filters through wetting, thermally stimulated discharge (TSD), and filtration experiments.
", "doi": "10.7907/f88b-x760", "publication_date": "2021", "thesis_type": "senior_major", "thesis_year": "2021" }, { "id": "thesis:14438", "collection": "thesis", "collection_id": "14438", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12012021-011312125", "primary_object_url": { "basename": "Mudide_Thesis_2021.pdf", "content": "final", "filesize": 5179437, "license": "other", "mime_type": "application/pdf", "url": "/14438/1/Mudide_Thesis_2021.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Limits of The Quasi-Harmonic Approximation: Anharmonicity in Germanium and the Entropy of Melting", "author": [ { "family_name": "Mudide", "given_name": "Shiva", "clpid": "Mudide-Shiva" } ], "thesis_advisor": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Politzer", "given_name": "Hugh David", "orcid": "0000-0002-4983-6621", "clpid": "Politzer-H-D" }, { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Inelastic Neutron Scattering (INS) measurements were made at the Wide Angular-Range Chopper Spectrometer (ARCS) on Germanium at temperatures higher than what has been done before, from 296 K to 1203 K. Raw data was used to calculate the dynamic structure factor. Multi-phonon and multiple scattering events were accounted for and subtracted. These dynamic structure factors were then used to calculate single phonon density of states (DOS) for temperatures throughout the said temperature range. Thermal softening of the phonon modes was observed. The softening was quantitatively characterized with several Gruneisen parameters to better understand the effects phonon anharmonicity in Germanium. We find the quasi-harmonic approximation alone cannot explain the large phonon softening. The vibrational entropy contribution to the total entropy was also determined. We find that the vibrational entropy makes up almost all of the total entropy in Germanium, even at elevated temperatures.
\r\n\r\nWe also conduct melting experiments to ensure containment of Si, Bi, and Pb in quartz ampules. These metals will be heated through their melting points at ARCS in the near future in order to determine the vibrational entropy contribution to the latent heat of melting. Furthermore, we write an algorithm based on the work of Sivia to determine the number of phonon modes there is the maximum evidence for in any given phonon DOS.
", "doi": "10.7907/9mn0-y471", "publication_date": "2021", "thesis_type": "senior_major", "thesis_year": "2021" }, { "id": "thesis:15035", "collection": "thesis", "collection_id": "15035", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09272022-143825909", "primary_object_url": { "basename": "Senior_thesis.pdf", "content": "final", "filesize": 4758015, "license": "other", "mime_type": "application/pdf", "url": "/15035/1/Senior_thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Quantum Computing for Machine Learning and Physics Simulation", "author": [ { "family_name": "Zlokapa", "given_name": "Alexander", "orcid": "0000-0002-4153-8646", "clpid": "Zlokapa-Alexander" } ], "thesis_advisor": [ { "family_name": "Spiropulu", "given_name": "Maria", "orcid": "0000-0001-8172-7081", "clpid": "Spiropulu-M" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Kapustin", "given_name": "Anton N.", "orcid": "0000-0003-3903-5158", "clpid": "Kapustin-A" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" }, { "family_name": "Spiropulu", "given_name": "Maria", "orcid": "0000-0001-8172-7081", "clpid": "Spiropulu-M" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Quantum computing is widely thought to provide exponential speedups over classical algorithms for a variety of computational tasks. In classical computing, methods in artificial intelligence such as neural networks and adversarial learning have enabled drastic improvements in state-of-the-art performance for a variety of tasks. We consider the intersection of quantum computing with machine learning, including the quantum algorithms for deep learning on classical datasets, quantum adversarial learning for quantum states, and variational quantum machine learning for improved physics simulation.
\r\n \r\nWe consider a standard deep neural network architecture and show that conditions amenable to trainability by gradient descent coincide with those necessary for an efficient quantum algorithm. Considering the neural network in the infinite-width limit using the neural tangent kernel formalism, we propose a quantum algorithm to train the neural network with vanishing error as the training dataset size increases. Under a sparse approximation of the neural tangent kernel, the training time scales logarithmically with the number of training examples, providing the first known exponential quantum speedup for feedforward neural networks. Related approximations to the neural tangent kernel are discussed, with numerical studies showing successful convergence beyond the proven regime. Our work suggests the applicability of the quantum computing to additional neural network architectures and common datasets such as MNIST, as well as kernel methods beyond the neural tangent kernel.
\r\n \r\nGenerative adversarial networks (GANs) are one of the most widely adopted machine learning methods for data generation. We propose an entangling quantum GAN (EQ-GAN) that overcomes some limitations of previously proposed quantum GANs. EQ-GAN guarantees the convergence to a Nash equilibrium under minimax optimization of the discriminator and generator circuits by performing entangling operations between both the generator output and true quantum data. We show that EQ-GAN has additional robustness against coherent errors and demonstrate the effectiveness of EQ-GAN experimentally in a Google Sycamore superconducting quantum processor. By adversarially learning efficient representations of quantum states, we prepare an approximate quantum random access memory and demonstrate its use in applications including the training of near-term quantum neural networks.
\r\n \r\nWith quantum computers providing a natural platform for physics simulation, we investigate the use of variational quantum circuits to simulate many-body systems with high fidelity in the near future. In particular, recent work shows that teleportation caused by introducing a weak coupling between two entangled SYK models is dual to a particle traversing an AdS-Schwarzschild wormhole, providing a mechanism to probe quantum gravity theories in the lab. To simulate such a system, we propose the process of compressed Trotterization to improve the fidelity of time evolution on noisy devices. The task of learning approximate time evolution circuits is shown to have a favorable training landscape, and numerical experiments demonstrate its relevance to simulating other many-body systems such as a Fermi-Hubbard model. For the SYK model in particular, we demonstrate the construction of a low-rank approximation that favors a shallower Trotterization. Finally, classical simulations of finite-N SYK models suggest that teleportation via a traversable wormhole instead of random unitary scrambling is achievable with O(20) qubits, providing further indication that such quantum gravity experiments may realizable with near-term quantum hardware.
", "doi": "10.7907/q75q-zm20", "publication_date": "2021", "thesis_type": "senior_major", "thesis_year": "2021" }, { "id": "thesis:14145", "collection": "thesis", "collection_id": "14145", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05122021-000037101", "type": "thesis", "title": "New Tensor Network Methods and Studies of Criticality in Low-Dimensional Quantum Systems", "author": [ { "family_name": "Roberts", "given_name": "Brenden Carlisle", "orcid": "0000-0002-3107-1878", "clpid": "Roberts-Brenden-Carlisle" } ], "thesis_advisor": [ { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" }, { "family_name": "Simmons-Duffin", "given_name": "David", "orcid": "0000-0002-2937-9515", "clpid": "Simmons-Duffin-D" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Several investigations are presented around the general topic of the ground state and low-energy behavior of models for many-body quantum physics in one dimension (1d). We develop a novel numerical method for the ground and low-energy sectors of local Hamiltonians in 1d which is based on proofs from quantum information theory. This method, the rigorous renormalization group (RRG), enjoys the benefits of explicit global information from the Hamiltonian in its local step, allowing it to avoid spurious convergence in systems with challenging energy landscapes. We apply RRG to the random XYZ spin chain in an unbiased numerical study evaluating infinite-randomness fixed point physics and continuously varying critical exponents in the ground state, finding evidence for both. In a related effective model with correlations preventing the exact solution of the strong-disorder renormalization group equations, we use the framework of random walks to rigorously establish continuously varying critical exponents. We also perform detailed studies of deconfined quantum critical points (DQCP) in 1d, providing strong evidence for phase transitions which display similar phenomenology to the canonical examples in 2d. A family of DQCP phase transitions in 1d is exhibited which appears to controlled by complex fixed points corresponding to a walking scenario for renormalization group flows.", "doi": "10.7907/vhwq-gz88", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14006", "collection": "thesis", "collection_id": "14006", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11252020-093720107", "primary_object_url": { "basename": "Lee_Nien-En_2021_Thesis.pdf", "content": "final", "filesize": 5768170, "license": "other", "mime_type": "application/pdf", "url": "/14006/1/Lee_Nien-En_2021_Thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Electron-Phonon Interactions and Charge Transport from First-Principles Calculations: Complex Crystals, Higher Order Coupling, and Steps Toward the Small Polaron Regime", "author": [ { "family_name": "Lee", "given_name": "Nien-En", "orcid": "0000-0002-3172-7750", "clpid": "Lee-Nien-En" } ], "thesis_advisor": [ { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-M" } ], "thesis_committee": [ { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Minnich", "given_name": "Austin J.", "orcid": "0000-0002-9671-9540", "clpid": "Minnich-A-J" }, { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-Marco" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Electron-phonon (e-ph) interactions quantify the strength of interplay between charge carriers and lattice vibrations and critically determine the transport properties in materials near room temperature. Depending on the coupling strength, charge carriers can exhibit behaviors ranging from propagating waves extending across crystals to trapped particles localized in space. Therefore, accurately describing e-ph interactions plays a central role in quantitative transport studies on real materials. Over the last few years, first-principles methods combining density functional theory (DFT) and related techniques with the Boltzmann transport equation (BTE) have rapidly risen and reached maturity for investigating transport in various metals, semiconductors, and insulators with weak e-ph coupling. The lowest-order e-ph scattering process can be investigated starting from e-ph interactions from DFT calculations; this first-principles approach provides unambiguous quantitative prediction of transport properties such as the conductivity and mobility in common semiconductors and metals over a wide temperature range without using any empirical parameter. Encouraged by the agreement of the computed transport properties with experiment for many simple materials, this thesis aims to extend the applicability of this first-principles methodology and to further our understanding of microscopic transport mechanisms, especially in the wide temperature window near room temperature where transport is governed by e-ph scattering. We present research that expands the state of the art in three distinct ways, focusing on three research directions we pursue in this work. First, we employ the BTE to calculate the hole carrier mobility of naphthalene, an organic molecular crystal containing 36 atoms in a unit cell, the record largest system for first-principles charge transport calculations to date. The results are in excellent agreement with experiments, demonstrating that transport in some high-mobility organic semiconductors can still be explained within the band theory framework, and show that low-frequency rigid molecular motions control the electrical transport in organic molecular semiconductors in the bandlike regime. The second topic is an attempt to go beyond the lowest-order theory of e-ph interactions and quantify the importance of higher-order e-ph processes. We derive the electron-two-phonon scattering rates using many-body perturbation theory, compute them in GaAs, and quantify their impact on the electron mobility. We show that these next-to-leading order e-ph scattering rates, although smaller than the lowest-order contribution, are not negligible, and can compensate the overestimation of mobility generally made by the lowest-order BTE calculation in weakly-polar semiconductors. In the third part of the thesis, we explore the opposite extreme case in which e-ph interactions are strong and lead to the formation of localized (so-called \"polaron\") electronic states that become self-trapped by the interactions with the atomic vibrations. We derive a rigorous approach based on canonical transformations to compute the energetics of self-localized (small) polarons in materials with strong e-ph interactions. With the aid of \\textit{ab initio} e-ph interactions, we carry out the corresponding numerical calculations to investigate the formation energy of small polaron and determine whether the charge carriers favor localized states over the Bloch waves. Due to the low computational cost of our approach, we are able to apply these calculations to various compounds, focusing on oxides, predicting the presence of small polaron in agreement with experiments in various materials. Our work paves the way to understanding small polaron formation and extending these calculations to predict transport in the polaron hopping mechanism in materials with strong e-ph coupling.", "doi": "10.7907/b040-2y98", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14061", "collection": "thesis", "collection_id": "14061", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01292021-001639979", "type": "thesis", "title": "Entangling, Controlling, and Detecting Individual Strontium Atoms in Optical Tweezer Arrays", "author": [ { "family_name": "Madjarov", "given_name": "Ivaylo Sashkov", "clpid": "Madjarov-Ivaylo-Sashkov" } ], "thesis_advisor": [ { "family_name": "Endres", "given_name": "Manuel A.", "orcid": "0000-0002-4461-224X", "clpid": "Endres-M" } ], "thesis_committee": [ { "family_name": "Hutzler", "given_name": "Nicholas R.", "orcid": "0000-0002-5203-3635", "clpid": "Hutzler-N-R" }, { "family_name": "Endres", "given_name": "Manuel A.", "orcid": "0000-0002-4461-224X", "clpid": "Endres-M" }, { "family_name": "Painter", "given_name": "Oskar J.", "orcid": "0000-0002-1581-9209", "clpid": "Painter-O" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "We present a novel experimental platform for quantum and precision science: single strontium atoms trapped in arrays of optical tweezers. We demonstrate development of this platform along three important fronts: single-atom trapping, imaging, and cooling; coherent control of the ultra-narrow clock transition; and inter-atom entanglement via Rydberg interactions.
\r\n\r\nIn the context of single-atom physics, we demonstrate trapping in tweezer arrays of one- and two-dimensions as well as cooling to the motional ground state. We furthermore show high-fidelity single-atom imaging with extremely low loss, allowing us to image the same atoms thousands of times before losing them and in principle allowing for the assembly of defect-free atom arrays of several hundred sites.
\r\n\r\nNotably, we show these results in tweezers that are at a magic wavelength for strontium's clock transition. This feature allows us to perform high-fidelity state rotations on the clock transition. We also demonstrate operation of a single-site resolved atomic-array optical clock -- a new atomic clock platform that combines several benefits of optical lattice and single-ion clocks.
\r\n\r\nFrom the metastable clock state, we drive the atoms to highly-excited Rydberg states to introduce interactions between nearby atoms. Using a Rydberg blockade in an assembled array of atom pairs, we demonstrate generation of two-atom entangled Bell states with a fidelity of >98%, or >99% with correction for state preparation and measurement errors. Furthermore, we demonstrate an auto-ionization state-detection scheme for Rydberg atoms which improves on the infidelity of previous Rydberg state-detection schemes by over an order of magnitude.
\r\n\r\nWe conclude with several outlooks, including preliminary data on light-cone correlation spreading in a system of 17 interacting atoms. We also discuss prospects for implementing quantum gates, operating a spin-squeezed clock, increasing system size, quantifying many-body state fidelity, and reducing sources of infidelity.
", "doi": "10.7907/d1em-dt34", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:13812", "collection": "thesis", "collection_id": "13812", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06092020-162351992", "primary_object_url": { "basename": "Senior_Thesis__Anant_Kale_v_1_5.pdf", "content": "final", "filesize": 15146256, "license": "other", "mime_type": "application/pdf", "url": "/13812/1/Senior_Thesis__Anant_Kale_v_1_5.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Towards High Fidelity Quantum Computation and Simulation with Rydberg Atoms", "author": [ { "family_name": "Kale", "given_name": "Anant M.", "orcid": "0000-0002-7049-5630", "clpid": "Kae-Anant-M" } ], "thesis_advisor": [ { "family_name": "Endres", "given_name": "Manuel A.", "orcid": "0000-0002-4461-224X", "clpid": "Endres-M" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" }, { "family_name": "Roukes", "given_name": "Michael Lee", "orcid": "0000-0002-2916-6026", "clpid": "Roukes-M-L" }, { "family_name": "Politzer", "given_name": "Hugh David", "orcid": "0000-0002-4983-6621", "clpid": "Politzer-H-D" }, { "family_name": "Frautschi", "given_name": "Steven C.", "clpid": "Frautschi-S-C" }, { "family_name": "Endres", "given_name": "Manuel A.", "orcid": "0000-0002-4461-224X", "clpid": "Endres-M" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Individually trapped neutral atoms are a promising candidate for use in quantum computing and simulation applications. They are highly scalable, have long coherence times and can be entangled via strong dipole-dipole interactions by driving to highly excited Rydberg states. However, the fidelity of single atom operations as well as two-atom entangling operations is limited by intrinsic sources of decoherence such as atomic motion, as well as technical sources of noise such as laser intensity fluctuations and phase/frequency fluctuations. We study the effect of these factors on single atom Rabi oscillations and two-atom Rydberg blockaded Rabi oscillations, using perturbation theory and numerical simulation. We develop a window function approach which helps us qualitatively understand the significance of the different spectral components of the noise as well as quantitatively understand the dependence of the Rabi oscillation fidelity on Rabi frequency. This allows us to predict the maximum experimentally achievable fidelities using independent measurements of experimental parameters such as noise spectra and atomic temperature. Turning to the question of near-term scalability of the experimental system, we prototype and test a method of generating a \u2019ladder\u2019 configuration of optical tweezers utilizing two independent lasers. Our setup allows us to fully tune the geometry of the ladder, namely the separation between the two rows, the angle between them, and their relative position along the axis of the ladder. This pseudo-2D configuration enables us to reach larger system sizes in the near future and allows us to access beyond 1D physics.", "doi": "10.7907/8mee-md98", "publication_date": "2020", "thesis_type": "senior_major", "thesis_year": "2020" }, { "id": "thesis:13788", "collection": "thesis", "collection_id": "13788", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06082020-083409184", "primary_object_url": { "basename": "Chen_Yu_An_2020_thesis.pdf", "content": "final", "filesize": 1945057, "license": "other", "mime_type": "application/pdf", "url": "/13788/8/Chen_Yu_An_2020_thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Exact Bosonization in All Dimensions: the Duality Between Fermionic and Bosonic Phases of Matter", "author": [ { "family_name": "Chen", "given_name": "Yu-An", "orcid": "0000-0002-8810-9355", "clpid": "Chen-Yu-An" } ], "thesis_advisor": [ { "family_name": "Kapustin", "given_name": "Anton N.", "orcid": "0000-0003-3903-5158", "clpid": "Kapustin-A" } ], "thesis_committee": [ { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Kapustin", "given_name": "Anton N.", "orcid": "0000-0003-3903-5158", "clpid": "Kapustin-A" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "We describe an n-dimensional (n\u22652) analog of the Jordan-Wigner transformation, which maps an arbitrary fermionic system to Pauli matrices while preserving the locality of the Hamiltonian. When the space is simply-connected, this bosonization gives a duality between any fermionic system in arbitrary n spatial dimensions and a new class of (n-1)-form Z\u2082 gauge theories in n dimensions with a modified Gauss\u2019s law. We describe several examples of 2d bosonization, including free fermions on square and honeycomb lattices and the Hubbard model, and 3d bosonization, including a solvable Z\u2082 lattice gauge theory with Dirac cones in the spectrum. This bosonization formalism has an explicit dependence on the second Stiefel-Whitney class and a choice of spin structure on the manifold, a key feature for defining fermions. A new formula for Stiefel-Whitney homology classes on lattices is derived. We also derive the Euclidean actions for the corresponding lattice gauge theories from the bosonization. The topological actions contain Chern-Simons terms for (2+1)D or Steenrod Square terms for general dimensions. Finally, we apply the bosonization to construct various bosonic or fermionic symmetry-protectedtopological (SPT) phases. It has been shown that supercohomology fermionic SPT phases are dual to bosonic higher-group SPT phases.", "doi": "10.7907/593v-5r52", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13705", "collection": "thesis", "collection_id": "13705", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05142020-114820618", "type": "thesis", "title": "Enriching Majorana Zero Modes", "author": [ { "family_name": "Chew", "given_name": "Aaron", "orcid": "0000-0003-0448-6215", "clpid": "Chew-Aaron" } ], "thesis_advisor": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "thesis_committee": [ { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "My various projects in graduate school have centered around a common theme: harnessing relatively well-understood phases of matter and combining them to create exotic physics. They also involve Majoranas, or more accurately, defects that bind Majorana zero modes and are the centerpiece for topological quantum computation. We exploit and enrich this Majorana zero mode by employing topological superconductors, time crystals, and quantum dots and combining them together. Our first project involved joining Majorana nanowires and quantum dots to simulate the SYK model, a zero-dimensional strongly interacting phase with connections to black holes and holography. We follow by explaining how to combine spontaneous symmetry-breaking with topological superconductivity to recover parafermion physics in one dimension. We explain an exact mapping that relates fermions to parafermions, illustrating a deep connection between different one-dimensional phases of matter. We finally show that enhancing the topological superconductor with a time crystal, a phase of matter that spontaneously breaks time-translation symmetry, creates an anomalous zero mode that displays 4Tperiodicity in the Floquet drive. By combining these different phases in judicious ways we achieve exotic physics unattainable by the constituent parts. Our work thus illustrates profitable directions for harnessing Majorana zero modes to study the physics of exotic matter.
", "doi": "10.7907/91q9-9606", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13660", "collection": "thesis", "collection_id": "13660", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03172020-153749505", "primary_object_url": { "basename": "Thesis_Final_Chen-Chih Hsu.pdf", "content": "final", "filesize": 6521176, "license": "other", "mime_type": "application/pdf", "url": "/13660/13/Thesis_Final_Chen-Chih Hsu.pdf", "version": "v13.0.0" }, "type": "thesis", "title": "Physics and Applications of Graphene-Based Nanostructures and Nano-Meta Materials", "author": [ { "family_name": "Hsu", "given_name": "Chen-Chih", "orcid": "0000-0003-1130-5240", "clpid": "Hsu-Chen-Chih" } ], "thesis_advisor": [ { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" } ], "thesis_committee": [ { "family_name": "Roukes", "given_name": "Michael Lee", "orcid": "0000-0002-2916-6026", "clpid": "Roukes-M-L" }, { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Graphene, a single layer of carbon atoms forming a honeycomb lattice structure, has been considered a wonder material for both scientific research and technological applications. Structural distortions in nano-materials can induce dramatic changes in their electronic properties. In particular, strained graphene can result in both charging effects and pseudo-magnetic fields, so that controlled strain on a perfect graphene lattice can be tailored to yield desirable electronic properties.
\r\n\r\nIn the first part of this thesis (Chapter 2 to 5), we explore a new approach to manipulating the topological states in monolayer graphene via nanoscale strain engineering. By placing strain-free monolayer graphene on architected nanostructures to induce global inversion symmetry breaking, we demonstrate the development of giant pseudo-magnetic fields, global valley polarization, and periodic one-dimensional topological channels for protected propagation of chiral modes in strained graphene. We have also observed pseudo-magnetic field-induced quantum oscillations and valley Hall signals, including quantum valley Hall effect, by transport measurements at 1.8K.
\r\n\r\nThe second part of this thesis focuses on the development and applications of other graphene-based nanostructures. We report PECVD techniques for the synthesis of various graphene and graphene-based nanostructures, including horizontal growth of graphene sheets, vertical growth of graphene nanostructures such as graphene nanostripes with large aspect ratios, and direct and selective deposition of multi-layer graphene on nanostructured substrates. By properly controlling the gas environment of the plasma, it is found that no active heating is necessary for the PECVD growth processes and that high-yield growth can take place in a single step on a variety of surfaces, including metallic, semiconducting, and insulating materials.
", "doi": "10.7907/6T02-4X35", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13768", "collection": "thesis", "collection_id": "13768", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022020-110730808", "type": "thesis", "title": "Development of Tools for Probing Order in Single Crystals Using Electron and Photon Spectroscopy", "author": [ { "family_name": "Deshpande", "given_name": "Tejas Makarand", "orcid": "0000-0003-0326-1372", "clpid": "Deshpande-Tejas-Makarand" } ], "thesis_advisor": [ { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "thesis_committee": [ { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" }, { "family_name": "Eisenstein", "given_name": "James P.", "orcid": "0000-0001-5460-0464", "clpid": "Eisenstein-J-P" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Discovering novel quantum phases of matter\u2013from emergent behavior of strongly-correlated electrons in solid-state systems to superfluidity in quantum degenerate liquids\u2013has been a cornerstone of condensed matter physics for many decades. In the most recent decades, however, the discovery of topological phases has emphasized the importance of symmetry, in addition to the conventional paradigm of symmetry breaking, in the definition of the order parameter, \u03a8, and hence the quantum phase it represents. Naturally, novel experimental tools, capable of coupling to said order parameter, directly or indirectly, are required to discover conventionally elusive quantum phases. In this thesis, I will discuss experimental techniques, using both photon and electron spectroscopy, to study exotic electronic phases in single crystals. The thesis will be divided into two unequal parts: (a) the development of a high-energy-resolution sub-Kelvin angle-resolved photoemission spectroscopy apparatus to study 3D time-reversal invariant topological superconductors, and (b) the experiments exploiting the non-linear and time-resolved aspects of femtosecond lasers to study a broad class of many-body systems.
", "doi": "10.7907/tt7b-fm83", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13851", "collection": "thesis", "collection_id": "13851", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08062020-222003579", "type": "thesis", "title": "Gravitational Wave Polarizations: A Test of General Relativity Using Binary Black Hole Mergers", "author": [ { "family_name": "Mathur", "given_name": "Sudhi", "orcid": "0000-0003-4891-0567", "clpid": "Mathur-Sudhi" } ], "thesis_advisor": [ { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" }, { "family_name": "Roukes", "given_name": "Michael Lee", "orcid": "0000-0002-2916-6026", "clpid": "Roukes-M-L" }, { "family_name": "Politzer", "given_name": "Hugh David", "orcid": "0000-0002-4983-6621", "clpid": "Politzer-H-D" }, { "family_name": "Frautschi", "given_name": "Steven C.", "clpid": "Frautschi-S-C" }, { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "General Relativity predicts that gravitational radiation is purely tensor polarized and thus, gravitational waves are composed of linear combinations of two transverse polarization modes, referred to as plus (+) and cross (\u00d7) tensor modes. However, alternate gravitational theories predict the existence of up to four additional vector and scalar longitudinal GW polarization modes.
\r\n\r\nIn this thesis, we develop a test of the gravitational wave (GW) polarization prediction of general relativity by searching for small admixtures of vector and/or scalar polarization components in transient GWs from binary black hole mergers. We use a network of five non-co-oriented GW detectors available in the near future, Bayesian inference parameter estimation, and nested sampling to quantify the detection sensitivity for such non-tensor GW polarization components.
", "doi": "10.7907/q9qa-7770", "publication_date": "2020", "thesis_type": "senior_major", "thesis_year": "2020" }, { "id": "thesis:13644", "collection": "thesis", "collection_id": "13644", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02262020-182938837", "type": "thesis", "title": "Information Scrambling in Quantum Many-Body Systems", "author": [ { "family_name": "Zhang", "given_name": "Yongliang", "orcid": "0000-0002-8246-3759", "clpid": "Zhang-Yongliang" } ], "thesis_advisor": [ { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" } ], "thesis_committee": [ { "family_name": "Brandao", "given_name": "Fernando", "orcid": "0000-0003-3866-9378", "clpid": "Brand\u00e3o-F-G-S-L" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Endres", "given_name": "Manuel A.", "orcid": "0000-0002-4461-224X", "clpid": "Endres-M" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "Walter Burke Institute for Theoretical Physics" }, { "literal": "div_pma" } ], "abstract": "A closed quantum system never forgets its initial state, but the encoded information can get scrambled and become inaccessible without measuring a large fraction of all the system degrees of freedom. This scrambling can be diagnosed by studying the spatial spreading of initially local operators under the Heisenberg time evolution, and the decay of the out-of-time-ordered correlators (OTOC). What insights can OTOCs provide to understand the dynamics of quantum many-body systems? What are the characteristic behaviors of OTOCs during the time evolution? How is information scrambling affected by the dissipation in open quantum many-body systems?
\r\n\r\nWe first study slow scrambling in many-body localized systems via calculating various correlators, two-point retarded correlators and OTOCs. Comparing with retarded correlators, OTOCs provide more information about the dynamics. We find that disorder slows and partially halts the onset of information scrambling. Instead of ballistic spreading, propagation of information forms a logarithmic light cone.
\r\n\r\nNext, we study the finite-size scaling of OTOCs at late times in generic thermalizing quantum many-body systems. When energy is conserved, the late-time saturation value of the OTOC of generic traceless local operators scales as an inverse polynomial in the system size. This is in contrast to the inverse exponential scaling expected for chaotic dynamics without energy conservation.
\r\n\r\nWe also study information scrambling in open quantum many-body systems. We define a dissipative version of OTOC and study its behaviors in a prototypical chaotic quantum chain with dissipation. We find that dissipation leads to not only the overall decay of the scrambled information due to leaking, but also structural changes so that the information light cone can only reach a finite distance even when the effect of overall decay is removed.
\r\n\r\nFinally, we construct a family of local Hamiltonians for understanding the asymmetric information scrambling. Our models live on a one-dimensional lattice and exhibit asymmetric butterfly light cone between the left and right spatial directions.
", "doi": "10.7907/GDZ1-0G66", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:11147", "collection": "thesis", "collection_id": "11147", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08162018-100820958", "type": "thesis", "title": "Transport Signatures of Spin-Orbit Coupling in Graphene-Based Materials", "author": [ { "family_name": "Tu", "given_name": "Min-Feng", "orcid": "0000-0001-6292-627X", "clpid": "Tu-Min-Feng" } ], "thesis_advisor": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Mong", "given_name": "Roger S.", "orcid": "0009-0000-7182-5681", "clpid": "Mong-Roger-S" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Topological materials have been a fastest growing research topic in the recent decade. Out of the numerous new phases proposed and/or discovered, \"topological insulators\" (TIs) are one of the most promising materials that could lead to further advances in high-performance electronics and to applications in quantum computing. Similar to the ordinary semiconductors, TIs have a bulk gap; yet they host robust edge/surface states which are protected from non-magnetic disorder and interactions while the gap remains open. This feature is a manifestation of the non-trivial topology of TIs, the crucial feature that distinguishes them from ordinary semiconductors. Although the search for more topological materials continues, discovered TI currently are limited by practical difficulties that prevent industrialization.
\r\n\r\nIn this thesis, we study graphene, which is the first proposed TI candidate in the history, and its derivatives. With the intrinsic spin-orbital coupling (SOC) on graphene, one can open a topologically nontrivial band gap at the Dirac cones, although the SOC of the carbon atoms is exceedingly small for topological insulation to be observed in experiments. Many proposals exist to enhance the SOC on graphene by doping with adatoms, changing the functionality of the surface, placing graphene on top of other strong SOC materials, etc. However, few proposed TI signatures have been found experimentally. Furthermore, measuring these intrinsic SOCs through magnetoconductance is challenging due to their relatively weak signatures in transport. This work addresses the challenges in transport measurements from both analytical and numerical approaches on various graphene-based materials. Graphene\u2019s Dirac band structure and open geometry underlie its exciting prospects for engineering new physics via impurity-induced spin-orbit coupling. As a tantalizing example, previous theory works predicted a robust quantum-spin-Hall phase in graphene covered with dilute heavy adatoms such as In, Tl, and Os, although experiments to date have not detected the required enhancement of spin-orbit coupling. Motivated by these experiments, we explore the consequences of adatom-generated spin-orbit couplings on magneto-transport in graphene. We attack the problem using diagrammatic techniques and the Landauer-Buttiker transport simulation informed by microscopics, and study various coverages, chemical potentials, and disorder types. We find that the induced spin-orbit couplings can contribute to magneto-conductance differently from conventional intrinsic and Rasbha spin-orbit couplings. Our results provide a possible rationale for the absence of spin-orbit signatures in recent experiments, and also highlight a roadmap for their discovery\r\nin future work.
\r\n\r\nIn addition to the adatom-dedoped graphene, we also study graphene placing on top of strong SOC substrate, WS2, by jointing theory, numerics, and experiment. We demonstrate, in experiment, a clear weak anti-localization (WAL) effect arising from induced Rashba spin\u2013orbit coupling (SOC) in WS2-covered single-layer and bilayer graphene devices. Contrary to the uncovered region of a shared single layer graphene flake, WAL in WS2-covered graphene occurs over a wide range of carrier densities on both the electron and hole sides.
", "doi": "10.7907/KCPE-1F36", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11554", "collection": "thesis", "collection_id": "11554", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282019-145954923", "primary_object_url": { "basename": "main.pdf", "content": "final", "filesize": 39853578, "license": "other", "mime_type": "application/pdf", "url": "/11554/1/main.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Clocked Atom Delivery to a Photonic Crystal Waveguide: Simulations and Experiments", "author": [ { "family_name": "Peng", "given_name": "Lucas Sky", "orcid": "0000-0002-8053-0372", "clpid": "Peng-Lucas-Sky" } ], "thesis_advisor": [ { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" } ], "thesis_committee": [ { "family_name": "Vahala", "given_name": "Kerry J.", "orcid": "0000-0003-1783-1380", "clpid": "Vahala-K-J" }, { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" }, { "family_name": "Hutzler", "given_name": "Nicholas R.", "orcid": "0000-0002-5203-3635", "clpid": "Hutzler-N-R" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Integrating atomic physics with nanophotonics devices provides a new research platform for quantum optics and many-body physics. The robustness and scalability of advanced lithographic fabrication technology provide powerful tools to enhance and control atom-photon interaction. Dispersion engineered photonic crystal waveguides (PCWs), such as the alligator photonic crystal waveguides (APCWs) described in this thesis, allow stable trapping and probing of atoms via guided modes (GMs). By tuning the photonic band-edges of the PCWs, the photon-mediated interactions between atoms can be modified. This thesis describes simulations and experiments that develop a quantitative understanding of atomic motion near the surfaces of APCWs. The atoms are delivered to APCWs using optical lattice. Synchronous with the moving lattice, transmission spectra for a guided-mode probe field are recorded as functions of lattice transport time and frequency detuning of the probe beam. With these 2D \"clocked\" spectra, we have been able to validate quantitatively our numerical simulations, which are based upon a detailed understanding of atomic trajectories that pass around and through nanoscopic regions of the APCW under the influence of optical and surface forces. By introducing auxiliary GMs of various polarizations and intensities, we have begun to control the atomic trajectories to some degree. For example, atoms can be guided to the central vacuum gap of the APCW at predetermined times and with known AC-Stark shifts. The applications of combining clocked atom delivery and numerical simulation include enabling high fractional filling of optical trap sites within PCWs, calibration of optical fields within PCWs, and utilization of the time-dependent, optically dense atomic medium for novel nonlinear optical experiments.", "doi": "10.7907/KDQ6-3S79", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11554", "collection": "thesis", "collection_id": "11554", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282019-145954923", "primary_object_url": { "basename": "main.pdf", "content": "final", "filesize": 39853578, "license": "other", "mime_type": "application/pdf", "url": "/11554/1/main.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Clocked Atom Delivery to a Photonic Crystal Waveguide: Simulations and Experiments", "author": [ { "family_name": "Peng", "given_name": "Lucas Sky", "orcid": "0000-0002-8053-0372", "clpid": "Peng-Lucas-Sky" } ], "thesis_advisor": [ { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" } ], "thesis_committee": [ { "family_name": "Vahala", "given_name": "Kerry J.", "orcid": "0000-0003-1783-1380", "clpid": "Vahala-K-J" }, { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" }, { "family_name": "Hutzler", "given_name": "Nicholas R.", "orcid": "0000-0002-5203-3635", "clpid": "Hutzler-N-R" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Integrating atomic physics with nanophotonics devices provides a new research platform for quantum optics and many-body physics. The robustness and scalability of advanced lithographic fabrication technology provide powerful tools to enhance and control atom-photon interaction. Dispersion engineered photonic crystal waveguides (PCWs), such as the alligator photonic crystal waveguides (APCWs) described in this thesis, allow stable trapping and probing of atoms via guided modes (GMs). By tuning the photonic band-edges of the PCWs, the photon-mediated interactions between atoms can be modified. This thesis describes simulations and experiments that develop a quantitative understanding of atomic motion near the surfaces of APCWs. The atoms are delivered to APCWs using optical lattice. Synchronous with the moving lattice, transmission spectra for a guided-mode probe field are recorded as functions of lattice transport time and frequency detuning of the probe beam. With these 2D \"clocked\" spectra, we have been able to validate quantitatively our numerical simulations, which are based upon a detailed understanding of atomic trajectories that pass around and through nanoscopic regions of the APCW under the influence of optical and surface forces. By introducing auxiliary GMs of various polarizations and intensities, we have begun to control the atomic trajectories to some degree. For example, atoms can be guided to the central vacuum gap of the APCW at predetermined times and with known AC-Stark shifts. The applications of combining clocked atom delivery and numerical simulation include enabling high fractional filling of optical trap sites within PCWs, calibration of optical fields within PCWs, and utilization of the time-dependent, optically dense atomic medium for novel nonlinear optical experiments.", "doi": "10.7907/KDQ6-3S79", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11538", "collection": "thesis", "collection_id": "11538", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05232019-192004916", "primary_object_url": { "basename": "Lin__Cheng_Ju__2019.pdf", "content": "final", "filesize": 18638108, "license": "other", "mime_type": "application/pdf", "url": "/11538/1/Lin__Cheng_Ju__2019.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Surviving Quantum Chaos: Weak Thermalization, Prethermalization and Quantum Many-Body Scar States", "author": [ { "family_name": "Lin", "given_name": "Cheng-Ju", "orcid": "0000-0001-7898-0211", "clpid": "Lin-Cheng-Ju" } ], "thesis_advisor": [ { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Quantum chaos and the eigenstate thermalization hypothesis are based on the assumption of the validity of random matrix theory description on the spectrum and eigenstates. They provide the foundation and descriptions for the typical dynamics and thermalization in generic closed quantum systems. In this thesis, we investigate situations where the systems show atypical dynamics or anomalous thermalization, conflicting with the usual expectations from quantum chaos and eigenstate thermalization hypothesis.\r\nWe first examine weak thermalization in a nonintegrable spin chain. The system shows long-lived strong oscillations and relaxes to the thermal equilibrium weakly. We identify the dynamics describable by quasiparticles and recognize the oscillation frequency to be the quasiparticle mass gap. We also estimate the damping time for the oscillations.\r\nNext, we study prethermalization, a phenomenon where a system relaxes to an intermediate almost-equilibrium stage before reaching the true thermal equilibrium. We study a nonintegrable spin chain in the strong coupling limit, where an almost-conserved quantity emerges and gives rise to the prethermalization.\r\nWe also study a newly proposed diagnostic for quantum chaos: out-of-time-ordered correlators. Contrasting to the chaotic systems, we inspect their behaviors in various noninteracting integrable models.\r\nFinally, we dig into the quantum many-body scar states in the PXP model which describes a Rydberg atom chain. These special states do not satisfy the random matrix theory description nor the eigenstate thermalization hypothesis, therefore defying quantum chaos.", "doi": "10.7907/DKYP-PH92", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11488", "collection": "thesis", "collection_id": "11488", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04242019-205929726", "type": "thesis", "title": "Topological Phases of Matter: Exactly Solvable Models and Classification", "author": [ { "family_name": "Wang", "given_name": "Zitao", "orcid": "0000-0002-2326-2674", "clpid": "Wang-Zitao" } ], "thesis_advisor": [ { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" } ], "thesis_committee": [ { "family_name": "Kapustin", "given_name": "Anton N.", "orcid": "0000-0003-3903-5158", "clpid": "Kapustin-A" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Endres", "given_name": "Manuel A.", "orcid": "0000-0002-4461-224X", "clpid": "Endres-M" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "Walter Burke Institute for Theoretical Physics" }, { "literal": "div_pma" } ], "abstract": "In this thesis, we study gapped topological phases of matter in systems with strong inter-particle interaction. They are challenging to analyze theoretically, because interaction not only gives rise to a plethora of phases that are otherwise absent, but also renders methods used to analyze non-interacting systems inadequate. By now, people have had a relatively systematic understanding of topological orders in two spatial dimensions. However, less is known about the higher dimensional cases. In Chapter 2, we will explore three dimensional long-range entangled topological orders in the framework of Walker-Wang models, which are a class of exactly solvable models for three-dimensional topological phases that are not known previously to be able to capture these phases. We find that they can represent a class of twisted discrete gauge theories, which were discovered using a different formalism. Meanwhile, a systematic theory of bosonic symmetry protected topological (SPT) phases in all spatial dimensions have been developed based on group cohomology. A generalization of the theory to group supercohomology has been proposed to classify and characterize fermionic SPT phases in all dimensions. However, it can only handle cases where the symmetry group of the system is a product of discrete unitary symmetries. Furthermore, the classification is known to be incomplete for certain symmetries. In Chapter 3, we will construct an exactly solvable model for the two-dimensional time-reversal-invariant topological superconductors, which could be valuable as a first attempt to a systematic understanding of strongly interacting fermionic SPT phases with anti-unitary symmetries in terms of exactly solvable models. In Chapter 4, we will propose an alternative classification of fermionic SPT phases using the spin cobordism theory, which hopefully can capture all the phases missing in the supercohomology classification. We test this proposal in the case of fermionic SPT phases with Z2 symmetry, where Z2 is either time-reversal or an internal symmetry. We find that cobordism classification correctly describes all known fermionic SPT phases in space dimensions less than or equal to 3.
", "doi": "10.7907/BXJR-1M62", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:10955", "collection": "thesis", "collection_id": "10955", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282018-173928314", "primary_object_url": { "basename": "Kubica2018.pdf", "content": "final", "filesize": 6379501, "license": "other", "mime_type": "application/pdf", "url": "/10955/1/Kubica2018.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "The ABCs of the Color Code: A Study of Topological Quantum Codes as Toy Models for Fault-Tolerant Quantum Computation and Quantum Phases Of Matter", "author": [ { "family_name": "Kubica", "given_name": "Aleksander Marek", "orcid": "0000-0001-8213-8190", "clpid": "Kubica-Aleksander-Marek" } ], "thesis_advisor": [ { "family_name": "Preskill", "given_name": "John P.", "orcid": "0000-0002-2421-4762", "clpid": "Preskill-J" } ], "thesis_committee": [ { "family_name": "Preskill", "given_name": "John P.", "orcid": "0000-0002-2421-4762", "clpid": "Preskill-J" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Brandao", "given_name": "Fernando", "orcid": "0000-0003-3866-9378", "clpid": "Brand\u00e3o-F-G-S-L" }, { "family_name": "Kitaev", "given_name": "Alexei", "orcid": "0000-0002-5777-642X", "clpid": "Kitaev-A" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_pma" } ], "abstract": "This thesis is devoted to studying a class of quantum error-correcting codes \u2014 topological quantum codes. We explore the question of how one can achieve fault- tolerant quantum computation with topological codes. We treat quantum error-correcting codes not only as a compelling ingredient needed to build a quantum computer, but also as a useful theoretical tool in other areas of physics. In particular, we explore what insights topological codes can provide into challenging questions, such as the classification of quantum phases of matter.
\r\n\r\nIn this thesis, we focus on a family of topological codes \u2014 color codes, which are particularly intriguing due to the rich physics they display and their computational power. We start by introducing color codes and explaining their basic properties. Then, we show how to perform fault-tolerant universal quantum computation with three-dimensional color codes by transverse gates and code switching. We later compare the resource overhead of the code-switching approach with that of a state distillation scheme. We discuss how to perform error correction with the toric and color codes, as well as introduce local decoders for those two families of codes. By exploiting a connection between error correction and statistical mechanics we estimate the storage threshold error rates for bit-flip and phase-flip noise in the three-dimensional color code. We finish by showing that the color and toric code families in d dimensions are equivalent in a sense of local unitary transformations and explore implications of this equivalence.
", "doi": "10.7907/059V-MG69", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:11032", "collection": "thesis", "collection_id": "11032", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06062018-171256773", "type": "thesis", "title": "Thermalization in Periodically-Driven Interacting Quantum Systems", "author": [ { "family_name": "Seetharam", "given_name": "Karthik Iyengar", "orcid": "0000-0003-1928-8019", "clpid": "Seetharam-Karthik-Iyengar" } ], "thesis_advisor": [ { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" } ], "thesis_committee": [ { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_eng" } ], "abstract": "Periodically-driven (Floquet) quantum systems are ubiquitous in science and technology. For example, when a laser illuminates a material or an AC voltage is applied to a device, the system is well-described by a time-periodic Hamiltonian. In recent years, periodic driving has been proposed, not just as a tool to excite and probe devices, but actually as a mechanism of engineering new phases of matter, some of which have no equilibrium analog. However, with this promise comes a serious problem. Intuitively, if energy is injected into and distributed throughout a system, it is no surprise that it tends to heat up indefinitely to infinite temperature.
\r\n\r\nIn this thesis, we study the mechanisms of heating, i.e. the process of thermalization, in Floquet systems and propose methods to control them. Specifically, for non-interacting Floquet systems that are coupled to external bosonic and fermionic baths (e.g. laser-driven electrons in a semiconductor that interact with phonons and an external lead), we classify the relevant scattering processes that contribute to cooling/heating in the Floquet bands and suggest methods to suppress heating via bandwidth-restrictions on the baths. We find that is possible, with appropriate dissipative engineering, to stabilize a controlled incompressible nonequilibrium steady-state resembling a ground state - a state we term the \"Floquet insulator.\" We extend this analysis to include short-range interactions that contribute additional heating processes and show, under the same framework, that heating can be controlled with dissipation. In the process, we develop a simple effective model for the Floquet band densities that captures the essence of all the Floquet scattering processes and that is useful for ballparking experimentally-relevant estimates of heating. Next, we turn our attention to strongly-interacting closed Floquet systems and study how heating emerges through a proliferation of resonances. We find a novel integrable point governing the strong-interaction limit of the Floquet system and examine the breakdown of integrability via the proliferation of resonances. We observe two distinct scaling regimes, attributed to non-thermal and thermal behavior, and discover a power-law scaling of the crossover between them as a function of system size. The lingering ergodicity-breaking effects of the conserved quantities in the vicinity (in parameter space) of the integrable point at finite size is a phenomena we term \"near-integrability.\" These results suggest that small quantum systems, which are accessible currently in many platforms (e.g. trapped ions, cold atoms, superconducting devices), intrinsically host non-thermal states that one may be able to utilize to avoid heating. Furthermore, our results suggest a \"dual\" interpretation, in the thermodynamic limit, that a periodically-driven system exhibits prethermalization as a power-law in interaction strength.
", "doi": "10.7907/3G0V-TW52", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:11008", "collection": "thesis", "collection_id": "11008", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012018-180443792", "type": "thesis", "title": "Spin in Conformal Field Theory", "author": [ { "family_name": "Kravchuk", "given_name": "Petr", "orcid": "0000-0003-0977-3686", "clpid": "Kravchuk-Petr" } ], "thesis_advisor": [ { "family_name": "Ooguri", "given_name": "Hirosi", "orcid": "0000-0001-6021-3778", "clpid": "Ooguri-H" } ], "thesis_committee": [ { "family_name": "Ooguri", "given_name": "Hirosi", "orcid": "0000-0001-6021-3778", "clpid": "Ooguri-H" }, { "family_name": "Simmons-Duffin", "given_name": "David", "orcid": "0000-0002-2937-9515", "clpid": "Simmons-Duffin-D" }, { "family_name": "Kapustin", "given_name": "Anton N.", "orcid": "0000-0003-3903-5158", "clpid": "Kapustin-A" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "local_group": [ { "literal": "Walter Burke Institute for Theoretical Physics" }, { "literal": "div_pma" } ], "abstract": "We study various questions related to operators with spin in quantum conformal field theory in dimensions higher than two. In particular, we classify conformally-invariant tensor structures which appear in correlation functions of local operators and develop tools for computation of conformal blocks which contribute to these functions. We study the crossing equations for four-point functions using numerical and analytical techniques. Finally, we explore the question of analytic continuation of local operators in spin, which leads us to a simple proof of a generalized Lorentzian inversion formula.
", "doi": "10.7907/54MW-WY30", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10982", "collection": "thesis", "collection_id": "10982", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-132922155", "type": "thesis", "title": "Super Pivotal Categories, Fermion Condensation, and Fermionic Topological Phases", "author": [ { "family_name": "Aasen", "given_name": "David", "orcid": "0000-0002-6552-488X", "clpid": "Aasen-David" } ], "thesis_advisor": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_eng" } ], "abstract": "We describe a systematic way of producing fermionic topological phases using the technique of fermion condensation. We give a prescription for performing fermion condensation in bosonic topological phases which contain an emergent fermion. Our approach to fermion condensation can roughly be understood as coupling the parent bosonic topological phase to a phase of physical fermions, and condensing pairs of physical and emergent fermions. There are two distinct types of objects in fermionic theories, which we call “m-type” and “q-type” particles. The endomorphism algebras of q-type particles are complex Clifford algebras, and they have no analogues in bosonic theories. We construct a fermionic generalization of the tube category, which allows us to compute the quasiparticle excitations in fermionic topological phases. We then prove a series of results relating data in condensed theories to data in their parent theories; for example, if C is a modular tensor category containing a fermion, then the tube category of the condensed theory satisfies Tube(C/ψ) ≅ C × C/ψ. We also study how modular transformations, fusion rules, and coherence relations are modified in the fermionic setting, prove a fermionic version of the Verlinde dimension formula, construct a commuting projector lattice Hamiltonian for fermionic theories, and write down a fermionic version of the Turaev-Viro-Barrett-Westbury state sum.
", "doi": "10.7907/P9A4-MH26", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10872", "collection": "thesis", "collection_id": "10872", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05102018-115838454", "primary_object_url": { "basename": "Wang-2018-Thesis.pdf", "content": "final", "filesize": 11832256, "license": "other", "mime_type": "application/pdf", "url": "/10872/15/Wang-2018-Thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Antiferromagnetic Quantum Phase Transitions: Continuous Tuning and Direct Probes of Competing States", "author": [ { "family_name": "Wang", "given_name": "Yishu", "orcid": "0000-0003-1259-8073", "clpid": "Wang-Yishu" } ], "thesis_advisor": [ { "family_name": "Rosenbaum", "given_name": "Thomas F.", "orcid": "0009-0008-6152-666X", "clpid": "Rosenbaum-T-F" } ], "thesis_committee": [ { "family_name": "Rosenbaum", "given_name": "Thomas F.", "orcid": "0009-0008-6152-666X", "clpid": "Rosenbaum-T-F" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_pma" } ], "abstract": "Antiferromagnets are choice systems to study quantum critical behavior. Unlike ferromagnets, they can experience continuous quantum phase transitions when tuned by pressure. However, the lack of a net magnetization renders experimental approaches difficult and often indirect. Here I demonstrate that both non-resonant and resonant x-ray magnetic diffraction under pressure provide the highly-desired direct probe for microscopic insights into the disappearance of the magnetic order, as well as the evolution of the charge and structural degrees of freedom. In Mo3Sb7, where spins are itinerant with small magnetic moments, we have discovered the doubling of the superconducting transition temperature under pressure and relate it to a lattice change from tetragonal to cubic structure. In MnP, a spiral magnetic order with tightened pitch was revealed in the high-pressure phase near a superconducting state at \u223c7 GPa. As the spiral pitch changes, fluctuations move from antiferromagnetic to ferromagnetic at long and short wavelengths, respectively, thereby potentially pro- moting spin-fluctuation-mediated superconductivity of different symmetries. In the all-in-all-out (AIAO) pyrochlore antiferromagnet Cd2Os2O7, we discovered an anti- ferromagnetic quantum critical point at 35.8 GPa using new techniques for resonant x-ray magnetic diffraction under pressure. The continuous suppression of AIAO antiferromagnetic order to zero temperature is accompanied by inversion symmetry breaking of the lattice, dividing the P \u2212 T phase space into three regions of different time reversal and spatial inversion symmetries. While phase lines of opposite curvature indicate a striking departure from a mean-field form at high pressure, the intertwined spin, charge, and phonon fluctuation modes point to a strong-coupled scenario of quantum criticality.
", "doi": "10.7907/VTHP-7645", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10318", "collection": "thesis", "collection_id": "10318", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06082017-134311664", "primary_object_url": { "basename": "mcclung_andrew_2017_thesis_final.pdf", "content": "final", "filesize": 18389506, "license": "other", "mime_type": "application/pdf", "url": "/10318/9/mcclung_andrew_2017_thesis_final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Photonic Crystal Waveguides for Integration into an Atomic Physics Experiment", "author": [ { "family_name": "McClung", "given_name": "Andrew Corby", "orcid": "0000-0001-6995-3289", "clpid": "McClung-Andrew-Corby" } ], "thesis_advisor": [ { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" } ], "thesis_committee": [ { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Painter", "given_name": "Oskar J.", "orcid": "0000-0002-1581-9209", "clpid": "Painter-O" }, { "family_name": "Vahala", "given_name": "Kerry J.", "orcid": "0000-0003-1783-1380", "clpid": "Vahala-K-J" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_pma" } ], "abstract": "Strongly interacting systems of atoms and photons are an important resource in many active areas of research, including quantum information science, quantum simulation, and metrology. Frequently, the strength of these interactions is enhanced by using an optical resonator to confine light to a small volume. In recent years, there have been efforts to replace traditional Fabry\u2013P\u00e9rot resonators, formed from macroscopic mirrors, with micro- and nano-fabricated systems, leveraging techniques and infrastructure from semiconductor manufacture to scalably produce high-quality, small mode volume waveguides and resonators. Of particular interest are nano-fabricated photonic crystals, in which very fine control over modal and dispersion properties is possible. Here I describe our efforts to reliably produce photonic crystal waveguides with guided modes designed to trap and interrogate an array of ultracold cesium atoms. Specifically, I present models capturing band placement, modal structure, finite photonic crystal effects, and waveguide input and output coupling; I discuss the techniques we use to fabricate our photonic crystal waveguides; and I describe our characterization capabilities and the packaging and installation of the waveguides into the atomic physics system.
", "doi": "10.7907/Z9154F3G", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:10318", "collection": "thesis", "collection_id": "10318", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06082017-134311664", "primary_object_url": { "basename": "mcclung_andrew_2017_thesis_final.pdf", "content": "final", "filesize": 18389506, "license": "other", "mime_type": "application/pdf", "url": "/10318/9/mcclung_andrew_2017_thesis_final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Photonic Crystal Waveguides for Integration into an Atomic Physics Experiment", "author": [ { "family_name": "McClung", "given_name": "Andrew Corby", "orcid": "0000-0001-6995-3289", "clpid": "McClung-Andrew-Corby" } ], "thesis_advisor": [ { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" } ], "thesis_committee": [ { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Painter", "given_name": "Oskar J.", "orcid": "0000-0002-1581-9209", "clpid": "Painter-O" }, { "family_name": "Vahala", "given_name": "Kerry J.", "orcid": "0000-0003-1783-1380", "clpid": "Vahala-K-J" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_pma" } ], "abstract": "Strongly interacting systems of atoms and photons are an important resource in many active areas of research, including quantum information science, quantum simulation, and metrology. Frequently, the strength of these interactions is enhanced by using an optical resonator to confine light to a small volume. In recent years, there have been efforts to replace traditional Fabry\u2013P\u00e9rot resonators, formed from macroscopic mirrors, with micro- and nano-fabricated systems, leveraging techniques and infrastructure from semiconductor manufacture to scalably produce high-quality, small mode volume waveguides and resonators. Of particular interest are nano-fabricated photonic crystals, in which very fine control over modal and dispersion properties is possible. Here I describe our efforts to reliably produce photonic crystal waveguides with guided modes designed to trap and interrogate an array of ultracold cesium atoms. Specifically, I present models capturing band placement, modal structure, finite photonic crystal effects, and waveguide input and output coupling; I discuss the techniques we use to fabricate our photonic crystal waveguides; and I describe our characterization capabilities and the packaging and installation of the waveguides into the atomic physics system.
", "doi": "10.7907/Z9154F3G", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:9763", "collection": "thesis", "collection_id": "9763", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05262016-092645359", "primary_object_url": { "basename": "Titum_Paraj_2016_thesis.pdf", "content": "final", "filesize": 9149970, "license": "other", "mime_type": "application/pdf", "url": "/9763/1/Titum_Paraj_2016_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Disorder Driven Transitions in Non-Equilibrium Quantum Systems", "author": [ { "family_name": "Titum", "given_name": "Paraj", "orcid": "0000-0002-7792-1532", "clpid": "Titum-Paraj" } ], "thesis_advisor": [ { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" } ], "thesis_committee": [ { "family_name": "Refael", "given_name": "Gil", "orcid": "0009-0007-4566-8441", "clpid": "Refael-G" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" }, { "family_name": "Lindner", "given_name": "Netanel H.", "orcid": "0000-0003-1879-3902", "clpid": "Lindner-N-H" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_pma" } ], "abstract": "This thesis presents studies of the role of disorder in non-equilibrium quantum systems. The quantum states relevant to dynamics in these systems are very different from the ground state of the Hamiltonian. Two distinct systems are studied, (i) periodically driven Hamiltonians in two dimensions, and (ii) electrons in a one-dimensional lattice with power-law decaying hopping amplitudes. In the first system, the novel phases that are induced from the interplay of periodic driving, topology and disorder are studied. In the second system, the Anderson transition in all the eigenstates of the Hamiltonian are studied, as a function of the power-law exponent of the hopping amplitude.
\r\n\r\nIn periodically driven systems the study focuses on the effect of disorder in the nature of the topology of the steady states. First, we investigate the robustness to disorder of Floquet topological insulators (FTIs) occurring in semiconductor quantum wells. Such FTIs are generated by resonantly driving a transition between the valence and conduction band. We show that when disorder is added, the topological nature of such FTIs persists as long as there is a gap at the resonant quasienergy. For strong enough disorder, this gap closes and all the states become localized as the system undergoes a transition to a trivial insulator.
\r\n \r\nInterestingly, the effects of disorder are not necessarily adverse, disorder can also induce a transition from a trivial to a topological system, thereby establishing a Floquet Topological Anderson Insulator (FTAI). Such a state would be a dynamical realization of the topological Anderson insulator. We identify the conditions on the driving field necessary for observing such a transition. We realize such a disorder induced topological Floquet spectrum in the driven honeycomb lattice and quantum well models.
\r\n \r\nFinally, we show that two-dimensional periodically driven quantum systems with spatial disorder admit a unique topological phase, which we call the anomalous Floquet-Anderson insulator (AFAI). The AFAI is characterized by a quasienergy spectrum featuring chiral edge modes coexisting with a fully localized bulk. Such a spectrum is impossible for a time-independent, local Hamiltonian. These unique characteristics of the AFAI give rise to a new topologically protected nonequilibrium transport phenomenon: quantized, yet nonadiabatic, charge pumping. We identify the topological invariants that distinguish the AFAI from a trivial, fully localized phase, and show that the two phases are separated by a phase transition.
\r\n \r\nThe thesis also present the study of disordered systems using Wegner's Flow equations. The Flow Equation Method was proposed as a technique for studying excited states in an interacting system in one dimension. We apply this method to a one-dimensional tight binding problem with power-law decaying hoppings. This model presents a transition as a function of the exponent of the decay. It is shown that the the entire phase diagram, i.e. the delocalized, critical and localized phases in these systems can be studied using this technique. Based on this technique, we develop a strong-bond renormalization group that procedure where we solve the Flow Equations iteratively. This renormalization group approach\r\nprovides a new framework to study the transition in this system.
", "doi": "10.7907/Z9MK69VV", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9172", "collection": "thesis", "collection_id": "9172", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09232015-145320310", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 13477843, "license": "other", "mime_type": "application/pdf", "url": "/9172/1/thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Coulomb Drag and Tunneling Studies in Quantum Hall Bilayers", "author": [ { "family_name": "Nandi", "given_name": "Debaleena", "clpid": "Nandi-Debaleena" } ], "thesis_advisor": [ { "family_name": "Eisenstein", "given_name": "James P.", "orcid": "0000-0001-5460-0464", "clpid": "Eisenstein-J-P" } ], "thesis_committee": [ { "family_name": "Eisenstein", "given_name": "James P.", "orcid": "0000-0001-5460-0464", "clpid": "Eisenstein-J-P" }, { "family_name": "Schwab", "given_name": "Keith C.", "orcid": "0000-0001-8216-4815", "clpid": "Schwab-K-C" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_pma" } ], "abstract": "The bilayer quantum Hall state at total filling factor \u03bdT=1, where the total electron density matches the degeneracy of the lowest Landau level, is a prominent example of Bose-Einstein condensation of excitons. A macroscopically ordered state is realized where an electron in one layer is tightly bound to a \"hole\" in the other layer. If exciton transport were the only bulk transportmechanism, a current driven in one layer would spontaneously generate a current of equal magnitude and opposite sign in the other layer. The Corbino Coulomb drag measurements presented in this thesis demonstrate precisely this phenomenon.
\r\n\r\nExcitonic superfluidity has been long sought in the \u03bdT=1 state. The tunneling between the two electron gas layers exihibit a dc Josephson-like effect. A simple model of an overdamped voltage biased Josephson junction is in reasonable agreement with the observed tunneling I-V. At small tunneling biases, it exhibits a tunneling \"supercurrent\". The dissipation is carefully studied in this tunneling \"supercurrent\" and found to remain small but finite.
", "doi": "10.7907/Z97H1GG0", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:10337", "collection": "thesis", "collection_id": "10337", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06072015-223040119", "primary_object_url": { "basename": "ShuPingLeeThesisv2.pdf", "content": "final", "filesize": 4200459, "license": "other", "mime_type": "application/pdf", "url": "/10337/1/ShuPingLeeThesisv2.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Signatures of Topological Superconductors", "author": [ { "family_name": "Lee", "given_name": "Shu-Ping", "orcid": "0000-0002-6199-2408", "clpid": "Lee-Shu-Ping" } ], "thesis_advisor": [ { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "thesis_committee": [ { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Eisenstein", "given_name": "James P.", "orcid": "0000-0001-5460-0464", "clpid": "Eisenstein-J-P" }, { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_pma" } ], "abstract": "Topological superconductors are particularly interesting in light of the active ongoing experimental efforts for realizing exotic physics such as Majorana zero modes. These systems have excitations with non-Abelian exchange statistics, which provides a path towards topological quantum information processing. Intrinsic topological superconductors are quite rare in nature. However, one can engineer topological superconductivity by inducing effective p-wave pairing in materials which can be grown in the laboratory. One possibility is to induce the proximity effect in topological insulators; another is to use hybrid structures of superconductors and semiconductors.
\r\n\r\nThe proposal of interfacing s-wave superconductors with quantum spin Hall systems provides a promising route to engineered topological superconductivity. Given the exciting recent progress on the fabrication side, identifying experiments that definitively expose the topological superconducting phase (and clearly distinguish it from a trivial state) raises an increasingly important problem. With this goal in mind, we proposed a detection scheme to get an unambiguous signature of topological superconductivity, even in the presence of ordinarily detrimental effects such as thermal fluctuations and quasiparticle poisoning. We considered a Josephson junction built on top of a quantum spin Hall material. This system allows the proximity effect to turn edge states in effective topological superconductors. Such a setup is promising because experimentalists have demonstrated that supercurrents indeed flow through quantum spin Hall edges. To demonstrate the topological nature of the superconducting quantum spin Hall edges, theorists have proposed examining the periodicity of Josephson currents respect to the phase across a Josephson junction. The periodicity of tunneling currents of ground states in a topological superconductor Josephson junction is double that of a conventional Josephson junction. In practice, this modification of periodicity is extremely difficult to observe because noise sources, such as quasiparticle poisoning, wash out the signature of topological superconductors. For this reason, We propose a new, relatively simple DC measurement that can compellingly reveal topological superconductivity in such quantum spin Hall/superconductor heterostructures. More specifically, We develop a general framework for capturing the junction's current-voltage characteristics as a function of applied magnetic flux. Our analysis reveals sharp signatures of topological superconductivity in the field-dependent critical current. These signatures include the presence of multiple critical currents and a non-vanishing critical current for all magnetic field strengths as a reliable identification scheme for topological superconductivity.
\r\n\r\nThis system becomes more interesting as interactions between electrons are involved. By modeling edge states as a Luttinger liquid, we find conductance provides universal signatures to distinguish between normal and topological superconductors. More specifically, we use renormalization group methods to extract universal transport characteristics of superconductor/quantum spin Hall heterostructures where the native edge states serve as a lead. Interestingly, arbitrarily weak interactions induce qualitative changes in the behavior relative to the free-fermion limit, leading to a sharp dichotomy in conductance for the trivial (narrow superconductor) and topological (wide superconductor) cases. Furthermore, we find that strong interactions can in principle induce parafermion excitations at a superconductor/quantum spin Hall junction.
\r\n\r\nAs we identify the existence of topological superconductor, we can take a step further. One can use topological superconductor for realizing Majorana modes by breaking time reversal symmetry. An advantage of 2D topological insulator is that networks required for braiding Majoranas along the edge channels can be obtained by adjoining 2D topological insulator to form corner junctions. Physically cutting quantum wells for this purpose, however, presents technical challenges. For this reason, I propose a more accessible means of forming networks that rely on dynamically manipulating the location of edge states inside of a single 2D topological insulator sheet. In particular, I show that edge states can effectively be dragged into the system's interior by gating a region near the edge into a metallic regime and then removing the resulting gapless carriers via proximity-induced superconductivity. This method allows one to construct rather general quasi-1D networks along which Majorana modes can be exchanged by electrostatic means.
\r\n\r\nApart from 2D topological insulators, Majorana fermions can also be generated in other more accessible materials such as semiconductors. Following up on a suggestion by experimentalist Charlie Marcus, I proposed a novel geometry to create Majorana fermions by placing a 2D electron gas in proximity to an interdigitated superconductor-ferromagnet structure. This architecture evades several manufacturing challenges by allowing single-side fabrication and widening the class of 2D electron gas that may be used, such as the surface states of bulk semiconductors. Furthermore, it naturally allows one to trap and manipulate Majorana fermions through the application of currents. Thus, this structure may lead to the development of a circuit that enables fully electrical manipulation of topologically-protected quantum memory. To reveal these exotic Majorana zero modes, I also proposed an interference scheme to detect Majorana fermions that is broadly applicable to any 2D topological superconductor platform.
\r\n", "doi": "10.7907/Z90R9MB4", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:8872", "collection": "thesis", "collection_id": "8872", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05202015-155217795", "primary_object_url": { "basename": "AGoban_thesis.pdf", "content": "final", "filesize": 65110077, "license": "other", "mime_type": "application/pdf", "url": "/8872/1/AGoban_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Strong Atom-Light Interactions Along Nanostructures: Transition from Free-space to Nanophotonic Interfaces", "author": [ { "family_name": "Goban", "given_name": "Akihisa", "orcid": "0000-0002-1766-6779", "clpid": "Goban-Akihisa" } ], "thesis_advisor": [ { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" } ], "thesis_committee": [ { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" }, { "family_name": "Painter", "given_name": "Oskar J.", "orcid": "0000-0002-1581-9209", "clpid": "Painter-O" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_pma" } ], "abstract": "An exciting frontier in quantum information science is the integration of otherwise \"simple\" quantum elements into complex quantum networks. The laboratory realization of even small quantum networks enables the exploration of physical systems that have not heretofore existed in the natural world. Within this context, there is active research to achieve nanoscale quantum optical circuits, for which atoms are trapped near nano-scopic dielectric structures and \"wired\" together by photons propagating through the circuit elements. Single atoms and atomic ensembles endow quantum functionality for otherwise linear optical circuits and thereby enable the capability of building quantum networks component by component. Toward these goals, we have experimentally investigated three different systems, from conventional to rather exotic systems : free-space atomic ensembles, optical nano fibers, and photonics crystal waveguides. First, we demonstrate measurement-induced quadripartite entanglement among four quantum memories. Next, following the landmark realization of a nanofiber trap, we demonstrate the implementation of a state-insensitive, compensated nanofiber trap. Finally, we reach more exotic systems based on photonics crystal devices. Beyond conventional topologies of resonators and waveguides, new opportunities emerge from the powerful capabilities of dispersion and modal engineering in photonic crystal waveguides. We have implemented an integrated optical circuit with a photonics crystal waveguide capable of both trapping and interfacing atoms with guided photons, and have observed the collective effect, superradiance, mediated by the guided photons. These advances provide an important capability for engineered light-matter interactions, enabling explorations of novel quantum transport and quantum many-body phenomena.", "doi": "10.7907/Z9T151KX", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:8872", "collection": "thesis", "collection_id": "8872", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05202015-155217795", "primary_object_url": { "basename": "AGoban_thesis.pdf", "content": "final", "filesize": 65110077, "license": "other", "mime_type": "application/pdf", "url": "/8872/1/AGoban_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Strong Atom-Light Interactions Along Nanostructures: Transition from Free-space to Nanophotonic Interfaces", "author": [ { "family_name": "Goban", "given_name": "Akihisa", "orcid": "0000-0002-1766-6779", "clpid": "Goban-Akihisa" } ], "thesis_advisor": [ { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" } ], "thesis_committee": [ { "family_name": "Kimble", "given_name": "H. Jeff", "clpid": "Kimble-H-J" }, { "family_name": "Painter", "given_name": "Oskar J.", "orcid": "0000-0002-1581-9209", "clpid": "Painter-O" }, { "family_name": "Hsieh", "given_name": "David", "orcid": "0000-0002-0812-955X", "clpid": "Hsieh-David" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_pma" } ], "abstract": "An exciting frontier in quantum information science is the integration of otherwise \"simple\" quantum elements into complex quantum networks. The laboratory realization of even small quantum networks enables the exploration of physical systems that have not heretofore existed in the natural world. Within this context, there is active research to achieve nanoscale quantum optical circuits, for which atoms are trapped near nano-scopic dielectric structures and \"wired\" together by photons propagating through the circuit elements. Single atoms and atomic ensembles endow quantum functionality for otherwise linear optical circuits and thereby enable the capability of building quantum networks component by component. Toward these goals, we have experimentally investigated three different systems, from conventional to rather exotic systems : free-space atomic ensembles, optical nano fibers, and photonics crystal waveguides. First, we demonstrate measurement-induced quadripartite entanglement among four quantum memories. Next, following the landmark realization of a nanofiber trap, we demonstrate the implementation of a state-insensitive, compensated nanofiber trap. Finally, we reach more exotic systems based on photonics crystal devices. Beyond conventional topologies of resonators and waveguides, new opportunities emerge from the powerful capabilities of dispersion and modal engineering in photonic crystal waveguides. We have implemented an integrated optical circuit with a photonics crystal waveguide capable of both trapping and interfacing atoms with guided photons, and have observed the collective effect, superradiance, mediated by the guided photons. These advances provide an important capability for engineered light-matter interactions, enabling explorations of novel quantum transport and quantum many-body phenomena.", "doi": "10.7907/Z9T151KX", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:8909", "collection": "thesis", "collection_id": "8909", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282015-205532544", "primary_object_url": { "basename": "master.pdf", "content": "final", "filesize": 2124134, "license": "other", "mime_type": "application/pdf", "url": "/8909/1/master.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Numerical Studies of Topological Phases", "author": [ { "family_name": "Geraedts", "given_name": "Scott D.", "clpid": "Geraedts-Scott-D" } ], "thesis_advisor": [ { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" } ], "thesis_committee": [ { "family_name": "Motrunich", "given_name": "Olexei I.", "orcid": "0000-0001-8031-0022", "clpid": "Motrunich-Olexei" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Mong", "given_name": "Roger S.", "orcid": "0009-0000-7182-5681", "clpid": "Mong-Roger-S" }, { "family_name": "Eisenstein", "given_name": "James P.", "orcid": "0000-0001-5460-0464", "clpid": "Eisenstein-J-P" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_pma" } ], "abstract": "The topological phases of matter have been a major part of condensed matter physics research since the discovery of the quantum Hall effect in the 1980s. Recently, much of this research has focused on the study of systems of free fermions, such as the integer quantum Hall effect, quantum spin Hall effect, and topological insulator. Though these free fermion systems can play host to a variety of interesting phenomena, the physics of interacting topological phases is even richer. Unfortunately, there is a shortage of theoretical tools that can be used to approach interacting problems. In this thesis I will discuss progress in using two different numerical techniques to study topological phases.
\r\n\r\nRecently much research in topological phases has focused on phases made up of bosons. Unlike fermions, free bosons form a condensate and so interactions are vital if the bosons are to realize a topological phase. Since these phases are difficult to study, much of our understanding comes from exactly solvable models, such as Kitaev's toric code, as well as Levin-Wen and Walker-Wang models. We may want to study systems for which such exactly solvable models are not available. In this thesis I present a series of models which are not solvable exactly, but which can be studied in sign-free Monte Carlo simulations. The models work by binding charges to point topological defects. They can be used to realize bosonic interacting versions of the quantum Hall effect in 2D and topological insulator in 3D. Effective field theories of \"integer\" (non-fractionalized) versions of these phases were available in the literature, but our models also allow for the construction of fractional phases. We can measure a number of properties of the bulk and surface of these phases.
\r\n\r\nFew interacting topological phases have been realized experimentally, but there is one very important exception: the fractional quantum Hall effect (FQHE). Though the fractional quantum Hall effect we discovered over 30 years ago, it can still produce novel phenomena. Of much recent interest is the existence of non-Abelian anyons in FQHE systems. Though it is possible to construct wave functions that realize such particles, whether these wavefunctions are the ground state is a difficult quantitative question that must be answered numerically. In this thesis I describe progress using a density-matrix renormalization group algorithm to study a bilayer system thought to host non-Abelian anyons. We find phase diagrams in terms of experimentally relevant parameters, and also find evidence for a non-Abelian phase known as the \"interlayer Pfaffian\".
\r\n", "doi": "10.7907/Z9668B3N", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:7774", "collection": "thesis", "collection_id": "7774", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302013-143644943", "primary_object_url": { "basename": "pbrooks-thesis.pdf", "content": "final", "filesize": 5261910, "license": "other", "mime_type": "application/pdf", "url": "/7774/1/pbrooks-thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Quantum Error Correction with Biased Noise", "author": [ { "family_name": "Brooks", "given_name": "Peter Bernard", "clpid": "Brooks-Peter-Bernard" } ], "thesis_advisor": [ { "family_name": "Preskill", "given_name": "John P.", "orcid": "0000-0002-2421-4762", "clpid": "Preskill-J" } ], "thesis_committee": [ { "family_name": "Preskill", "given_name": "John P.", "orcid": "0000-0002-2421-4762", "clpid": "Preskill-J" }, { "family_name": "Kitaev", "given_name": "Alexei", "orcid": "0000-0002-5777-642X", "clpid": "Kitaev-A" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Brun", "given_name": "Todd A.", "orcid": "0000-0002-8807-3495", "clpid": "Brun-T-A" } ], "local_group": [ { "literal": "Institute for Quantum Information and Matter" }, { "literal": "div_pma" } ], "abstract": "Quantum computing offers powerful new techniques for speeding up the calculation of many classically intractable problems. Quantum algorithms can allow for the efficient simulation of physical systems, with applications to basic research, chemical modeling, and drug discovery; other algorithms have important implications for cryptography and internet security.
\r\n\r\nAt the same time, building a quantum computer is a daunting task, requiring the coherent manipulation of systems with many quantum degrees of freedom while preventing environmental noise from interacting too strongly with the system. Fortunately, we know that, under reasonable assumptions, we can use the techniques of quantum error correction and fault tolerance to achieve an arbitrary reduction in the noise level.
\r\n\r\nIn this thesis, we look at how additional information about the structure of noise, or \"noise bias,\" can improve or alter the performance of techniques in quantum error correction and fault tolerance. In Chapter 2, we explore the possibility of designing certain quantum gates to be extremely robust with respect to errors in their operation. This naturally leads to structured noise where certain gates can be implemented in a protected manner, allowing the user to focus their protection on the noisier unprotected operations.
\r\n\r\nIn Chapter 3, we examine how to tailor error-correcting codes and fault-tolerant quantum circuits in the presence of dephasing biased noise, where dephasing errors are far more common than bit-flip errors. By using an appropriately asymmetric code, we demonstrate the ability to improve the amount of error reduction and decrease the physical resources required for error correction.
\r\n\r\nIn Chapter 4, we analyze a variety of protocols for distilling magic states, which enable universal quantum computation, in the presence of faulty Clifford operations. Here again there is a hierarchy of noise levels, with a fixed error rate for faulty gates, and a second rate for errors in the distilled states which decreases as the states are distilled to better quality. The interplay of of these different rates sets limits on the achievable distillation and how quickly states converge to that limit.
", "doi": "10.7907/1TVT-J780", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" } ]