Physics Theses and Dissertations

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Unifying Searches for New Physics with Precision Measurements of the W Boson Mass
(2024) Sathyan, Deepak; Agashe, Kaustubh; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The Standard Model (SM) of particle physics has been extremely successful in describing the interactions of electromagnetic, weak nuclear, and strong nuclear forces. Yet, there are both unexplained phenomena and experimentally observed tensions with the SM, motivating searches for new physics (NP). Collider experiments typically perform two kinds of analyses: direct searches for new physics and precision measurements of SM observables. For example, experimental collaborations use collider data to search for NP particles like the heavy superpartners of the SM particles, whose observation would be clear evidence of supersymmetry (SUSY). These direct searches often consider kinematic regions where the SM background is small. This strategy is unable to probe regions of the NP parameter space where the SM background is dominant. The same collaborations also measure the masses of SM particles, which not only serve as consistency tests of the SM, but can also probe effects of NP. In 2022, the Collider Detector at Fermilab (CDF) collaboration published the most precise measurement of the $W$ boson mass: $m_W$ = 80433.5 $\pm$ 9.4 MeV. This measurement is in $7\sigma$ significance tension with the SM prediction via the electroweak (EW) fit, $m_W^{\rm pred.}$ = 80354 $\pm$ 7 MeV. Many extensions to the SM can affect the prediction of $m_W$ with indirect effects of heavy NP. However, in 2023, the ATLAS re-measurement of the $W$ boson mass, $m_W$ = 80360 $\pm$ 16 MeV, was found to be consistent with the SM prediction. Both collaborations found a high-precision agreement between the measured kinematic distributions and the SM prediction of the kinematic distributions for their corresponding extracted $m_W$. We propose using the precision measurements of $m_W$ to directly probe NP contributing to the same final state used to measure $m_W$: a single charged lepton $\ell$ and missing transverse energy $\met$. This strategy is independent of modifying the EW fit, which tests indirect effects of NP on the predicted value of $m_W$. Any NP producing $\ell+\met$ which modifies the kinematic distributions used to extract $m_W$ can be probed with this method. With this strategy, since these distributions are used to search for NP while measuring $m_W$, a simultaneous fit of NP and SM parameters is required, thus unifying searches and measurements. This simultaneous fitting can induce a bias in the measured $m_W$, but only to a limited extent for our considered models. We consider three categories of NP which can be probed: ($i$) modified decay of $W$ bosons; ($ii$) modified production of $W$ bosons; and ($iii$) $\ell+\met$ scenarios without an on-shell $W$ boson. We also show that models whose signals extend beyond the kinematic region used to measure $m_W$ can be probed in an intermediate kinematic region. Our results highlight that new physics can still be discovered at the LHC, including light new physics, via SM precision measurements. Additionally, anticipated improvements in precision SM measurements at the High Luminosity LHC further enables new searches for physics Beyond the Standard Model (BSM).
EXCURSION IN THE QUANTUM LOSS LANDSCAPE: LEARNING, GENERATING AND SIMULATING IN THE QUANTUM WORLD
(2024) Rad, Ali; Hafezi, Mohammad; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Statistical learning is emerging as a new paradigm in science. This has ignited interestwithin our inherently quantum world in exploring quantum machines for their advantages in learning, generating, and predicting various aspects of our universe by processing both quantum and classical data. In parallel, the pursuit of scalable science through physical simulations using both digital and analog quantum computers is rising on the horizon. In the first part, we investigate how physics can help classical Artificial Intelligence (AI) by studying hybrid classical-quantum algorithms. We focus on quantum generative models and address challenges like barren plateaus during the training of quantum machines. We further examine the generalization capabilities of quantum machine learning models, phase transitions in the over-parameterized regime using random matrix theory, and their effective behavior approximated by Gaussian processes. In the second part, we explore how AI can benefit physics. We demonstrate how classical Machine Learning (ML) models can assist in state recognition in qubit systems within solid-state devices. Additionally, we show how ML-inspired optimization methods can enhance the efficiency of digital quantum simulations with ion-trap setups Finally, in the third part, we focus on how physics can help physics by using quantum systems to simulate other quantum systems. We propose native fermionic analog quantum systems with fermion-spin systems in silicon to explore non-perturbative phenomena in quantum field theory, offering early applications for lattice gauge theory models.
Constraining Higgs Boson Self-coupling with VHH Production and Combination, and Searching for Wgamma Resonance using the CMS Detector at the LHC
(2024) Lai, Yihui; Palmer, Christopher; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Since the discovery of the Higgs boson (H) with a mass of 125 GeV by the ATLAS and CMS collaborations at the CERN LHC in 2012, the focus of the particle physics community has expanded to include precise measurements of its properties, and so far the measurements align with the Standard Model (SM) predictions. Of particular interest among these properties is the Higgs boson self-coupling, which can be directly probed by measuring the cross section for the production of Higgs boson pair (HH). This thesis presents three analyses using proton- proton collision data at \sqrt{s} = 13TeV with an integrated luminosity of 138 fb−1: a search for SM Higgs boson pair production with one associated vector boson (VHH), a combination of H measurements and HH searches, and a search for a new particle decaying to a W boson and a photon (\gamma). The VHH search focuses on Higgs bosons decaying to bottom quarks, and vector boson decaying to electrons, muons, neutrinos, or hadrons, with a novel background estimation approach. An observed (expected) upper limit on the VHH production cross section is set at 294 (124) times the SM predicted value. The combination of H measurements and HH searches aims to constrain the Higgs self-coupling with the best possible precision. The search for Wgamma resonance focuses on leptonic W boson decays, achieving the world’s best sensitivity for this resonance in the mass ranges considered.
EXCITED DYONIC STATES OF MONOPOLES AND ASTRONOMICAL BOUNDS ON AN AXION-PHOTON-DARK PHOTON INTERACTION
(2024) Ristow, Clayton James; Hook, Anson; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The study of beyond the standard model physics can largely be broken into twocategories: theoretical and phenomenological. In the former, we study theories in depth to better understand their implications while in the latter, we hold models of our physical world to scrutiny against experimental evidence. Both are crucial to understanding physics beyond the standard model. To reflect this dichotomy, this thesis is broken into two acts, one covering theoretic research and the other discussing progress made on the phenomenological front. Chapter 2, comprising the entirety of Act 1 of this thesis, concerns the theory of magnetic monopoles. In the mid-1970’s t’Hooft and Polyakov discovered magnetic monopoles exist as generic solutions in spontaneously broken gauge theories. Since then much progress has been made in understanding these monopoles, most notably by Callan who argued that the fermion vacuum is non-trivial around the core of the magnetic monopole. These non-trivial vacuua can be interpreted as bound states of fermions with fractional fermion number. In this work, we explicitly compute these fermion bound states in an SU (2) gauge theory coupled to Nf fermions. We demonstrate there are two unique ways to grant mass to the fermions in the SU (2) theory which, after symmetry breaking, give the same UEM (1) theory of fermions. Despite this low energy equivalence, we show that the two theories exhibit very different physics at low energy scales around a magnetic monopole. We show that there may exist stable excited dyonic states with differing charges and energies between the two theories. We find the ground states can also differ in energy and charge between the two theories. We demonstrate the monopole can inherit a mass correction and charge distribution that depends on the topological θ angle even if one of the fermions is massless. This effect is present in one of the theories and is completely absent in the other. Finally, we discuss the implications of these effects on the SU (5) GUT monopole. Act two, comprising of chapters 3 and 4, focuses on the phenomoenological side of beyond the standard model physics. In these chapters, we consider two highly motivated beyond the standard model particles, the axion, φ, and the dark photon AD which are coupled to the standard model photon via a coupling φF ̃FD. In some models, this coupling can provide the leading order coupling between our sector and the dark sector containing the axion and dark photon. In chapter 2, we demonstrate the effect this coupling has on the Cosmic Microwave Background (CMB) in the scenario where either the axion or the dark photon constitutes dark matter. Depending on which we choose to be dark matter, we show that this interaction leads to the conversion of the CMB photons into the other dark sector particle, leading to a distortion in the CMB spectrum. We present the details of these unique distortion signatures and the resulting constraints on the φF ̃FD coupling. In particular, we find that for a wide range of masses, the constraints from this effect are stronger than on the more widely studied axion-photon-photon coupling. We also demonstrate that CMB distortions of this type can a exhibit unique, non-thermal frequency profile which could be detected by future experiments. In chapter 3, we consider the astrophysical effects of the φF ̃FD coupling, in particular, its effect on supernova cooling rates. We show that the bound on this interaction due to supernova cooling exhibits two unusual features. If there is a large mass difference between the axion and dark photon, we show both production and scattering become suppressed and the bounds from bulk (volume) emission and trapped (area) emission both weaken exponentially. We show that these bounds do not intersect leading to a larger area of excluded parameter space than may have otherwise been expected. The other unusual feature occurs because the longitudinal modes of light dark photons couple more weakly than their transverse modes. As a consequence, the longitudinal modes can still cause excessive cooling even if the transverse modes are trapped. Thus, the supernova constraints for massive dark photons look like two independent supernova bounds super-imposed on top of each other. We also briefly consider the effect of this interaction on white dwarf cooling and Big Bang Nucleosynthesis.
Ultracold Gases in a Two-Frequency Breathing Lattice
(2024) Dewan, Aftaab; Rolston, Steven L; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Driven systems have been of particular interest in the field of ultracold atomic gases. Theprecise control and relative purity allows for construction of many novel Hamiltonians. One such system is the ‘breathing’ lattice, where both the frequency and amplitude is modulated in time, much like an accordion. We present the results of a phenomenological investigation of a proposed experiment, one where we apply a two-frequency breathing lattice to an atomic system. The results are surprising, as they indicate the possibility of a phase-dependent transition between nearest-neighbour and beyond nearest-neighbour interactions.
PHENOMENOLOGY OF ULTRALIGHT FIELDS
(2024) Brzeminski, Dawid; Hook, Anson; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Standard Model is an amazing success of particle physics, a success further cemented by the discovery of the Higgs boson. While its picture is incredibly satisfying, there are still a few mysteries it cannot address, one of which is the nature of dark matter. While we have overwhelming evidence for its existence, we still do not know its basic properties such as mass or spin. Ultralight fields are among the most exciting dark matter candidates. Their large occupation number allows us to treat them as classical fields, while their non-relativistic velocities ensure that the field oscillates at an angular frequency equal to its mass with a long coherence time. In this dissertation, we discuss some challenges associated with constructing successful models of ultralight dark matter and discuss new detection strategies. In the first part of this dissertation, we address the underlying issue with ultralight scalars, namely the naturalness problem. Generally, requiring the scalar to couple to the Standard Model introduces radiative corrections to its mass, which conflicts with the requirement of a small mass. We present an ultraviolet-complete model that avoids this issue by employing $Z_N$ symmetry, which suppresses corrections to the mass while retaining relatively large couplings to photons, making the model testable by current and future experiments looking for the time-variation of the fine structure constant. In the second part of this dissertation, we focus on the experimental aspects of ultralight scalars. The general experimental landscape is divided into two categories: experiments assuming a dark matter background, and experiments measuring the fifth force associated with the new scalar.The former provides strong constraints for the lightest scalars due to their large abundance, while the latter provides more conservative but robust limits on scalar interactions across many decades in scalar mass. We propose a novel approach based on measuring scalar potential using atomic and nuclear clocks, which complements fifth force measurements and offers significant improvements over current bounds. In the third part of the dissertation, we shift our attention to vector dark matter. Specifically, we consider a scenario where some of the lepton generations are charged under a new gauge field. In this case, neutrino decays in the early universe impose strong constraints on their couplings, particularly for the lightest vectors. At higher masses, neutrino oscillations become a leading constraint due to the sourcing of the field by electrons affecting their oscillations. We demonstrate that in the presence of vector dark matter, the influence of the background field on neutrinos is even more pronounced, significantly enhancing constraints on the lightest vectors by several orders of magnitude.
Chiral light-matter interaction in fermionic quantum Hall systems
(2024) Session, Deric Weston; Hafezi, Mohammad; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Achieving control over light-matter interactions is crucial for developing quantum technologies. This dissertation discusses two novel demonstrations where chiral light was used to control light-matter interaction in fermionic quantum Hall systems. In the first work, we demonstrated the transfer of orbital angular momentum from vortex light to itinerant electrons in quantum Hall graphene. In the latter, we demonstrated circular-polarization-dependent strong coupling in a 2D gas in the quantum Hall regime coupled to a microcavity. Our findings demonstrate the potential of chiral light to control light-matter interactions in quantum Hall systems. In the first part of this dissertation, we review our experimental demonstration of light-matter interaction beyond the dipole-approximation between electronic quantum Hall states and vortex light where the orbital angular momentum of light was transferred to electrons. Specifically, we identified a robust contribution to the radial photocurrent, in an annular graphene sample within the quantum Hall regime, that depends on the vorticity of light. This phenomenon can be interpreted as an optical pumping scheme, where the angular momentum of photons is transferred to electrons, generating a radial current, where the current direction is determined by the vorticity of the light. Our findings offer fundamental insights into the optical probing and manipulation of quantum coherence, with wide-ranging implications for advancing quantum coherent optoelectronics. In the second part of this dissertation, we review our experimental demonstration of a selective strong light-matter interaction by harnessing a 2D gas in the quantum Hall regime coupled to a microcavity. Specifically, we demonstrated circular-polarization dependence of the vacuum Rabi splitting, as a function of magnetic field and hole density. We provide a quantitative understanding of the phenomenon by modeling the coupling of optical transitions between Landau levels to the microcavity. This method introduces a control tool over the spin degree of freedom in polaritonic semiconductor systems, paving the way for new experimental possibilities in light-matter hybrids.
Collective dynamics of astrocyte and cytoskeletal systems
(2024) Mennona, Nicholas John; Losert, Wolfgang; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Advances in imaging and biological sample preparations now allow researchersto study collective behavior in cellular networks with unprecedented detail. Imaging the electrical signaling of neuronal networks at the cellular level has generated exciting insights into the multiscale interactions within the brain. This thesis aims at a complementary view of the general information processing of the brain, focusing on other modes of non-electrical information. The modes discussed are the collective, dynamical characteristics of non-electrically active, non-neuronal brain cells, and mechanical systems. Astrocytes are the studied non-neuronal brain cells, and the cytoskeleton is the studied dynamic, mechanical system consisting of various filamentous networks. The two filamentous networks studied herein are the actin cytoskeleton and the microtubule network. Techniques from calcium imaging and cell mechanics are adapted to measure these often overlooked information channels, which operate at length scales and timescales distinct from electrical information transmission. Structural, astrocyte actin images, microtubule structural image sequences, and the calcium signals of collections of astrocytes are analyzed using computer vision and information theory. Filamentous alignment of actin with nearby boundaries reveals that stellate astrocytes have more perpendicularly oriented actin than undifferentiated astrocytes. Harnessing the larger length scale and slower dynamical time scale of microtubule filaments relative to actin filaments led to the creation of a computer vision tool to measure lateral filamentous fluctuations. Finally, we adapt information theory to the analog calcium (Ca2+) signals within astrocyte networks classified according to subtype. We find that, despite multiple physiological differences between immature and injured astrocytes, stellate (healthy) astrocytes have the same speed of information transport as these other astrocyte subtypes. This uniformity in speed persists when either the cytoskeleton (Latrunculin B) or energy state (ATP) is perturbed. Astrocytes, regardless of physiological subtype, tend to behave similarly when active under normal conditions. However, these healthy astrocytes respond most significantly to energy perturbation, relative to immature and injured astrocytes, as viewed through cross-correlation, mutual information, and partitioned entropy. These results indicate the value of drawing information from structure and dynamics. We developed and adapted tools across scales from nanometer scale alignment of actin filaments to hundreds of microns scale information dynamics in astrocyte networks. Including all potential modalities of information within complex biological systems, such as the collective dynamics of astrocytes and the cytoskeleton in brain networks is a step toward a fuller characterization of brain functioning and cognition.
Quantization of causal diamonds in (2+1)-gravity
(2024) Andrade e Silva, Rodrigo; Jacobson, Theodore A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
We develop the non-perturbative reduced phase space quantization of causal diamondsin (2+1)-dimensional gravity with a nonpositive cosmological constant. The system is defined as the domain of dependence of a spacelike topological disk with fixed boundary metric. By solving the constraints in a constant-mean-curvature time gauge and removing all the spatial gauge redundancy, we find that the phase space is the cotangent bundle of Diff+(S1)/PSL(2,R). Classically, the states correspond to causal diamonds embedded in AdS3 (or Mink3 if Λ = 0), with fixed corner length, and whose Cauchy surfaces have the topology of a disc. Because the phase space does not have a natural linear structure, a generalization of the standard canonical (coordinate) quantization is required. As the configuration space is a homogeneous space for the Diff+(S1) group, we apply Isham’s group-theoretic quantization scheme. We propose a quantization based on (projective) unitary irreducible representations of the BMS3 group. We find a class of suitable quantum theories labelled by a choice of a coadjoint orbit of the Virasoro group and an irreducible unitary representation of the corresponding little group. The most natural choice, justified by a Casimir matching principle, corresponds to a Hilbert space realized by wavefunctions on Diff+(S1)/PSL(2,R) valued in some unitary irreducible representation of SL(2,R). A surprising result is that the twist of the diamond corner loop is quantized in terms of the ratio of the Planck length to the corner perimeter.
Analyzing the Dynamics of Biological and Artificial Neural Networks with Applications to Machine Learning
(2024) Srinivasan, Keshav; Girvan, Michelle; Biophysics (BIPH); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The study of the brain has profoundly shaped the evolution of computational learning models and the history of neural networks. This journey began in the 1940s with Warren McCulloch and Walter Pitts’ groundbreaking work on the first mathematical model of a neuron, laying the foundation for artificial neural networks. The 1950s and 60s witnessed a significant milestone with Frank Rosenblatt’s development of the perceptron, showcasing the potential of neural networks for complex computational tasks. Since then, the field of neural networks has witnessed explosive growth, and terms like “Artificial Intelligence” and “Machine Learning” have become commonplace across diverse fields, including finance,medicine, and science. This dissertation explores the symbiotic parallels between neuroscience and machine learning, focusing on the dynamics of biological and artificial neural networks. We begin by examining artificial neural networks, particularly in predicting the dynamics of large, complex networks—a paradigm where traditional machine learning algorithms often struggle. To address this, we propose a novel approach utilizing a parallel architecture that mimics the network’s structure, achieving scalable and accurate predictions. Shifting our focus to biological neuronal networks, we delve into the theory of critical systems. This theory posits that the brain, when viewed as a complex dynamical system, operates near a critical point, a state ideal for efficient information processing. A key experimental observation of this type of criticality is neuronal avalanches—scale-free cascades of neuronal activity—which have been documented both in vitro (in neuronal cultures and acute brain slices) and in vivo (in the brains of awake animals). Recent advancements in experimental techniques, such as multi-photon imaging and genetically encoded fluorescent markers, allow for the measurement of activity in living organisms with unparalleled single-cell resolution. Despite these advances, significant challenges remain when only a fraction of neurons can be recorded with sufficient resolution, leading to inaccurate estimations of power-law relationships in size, duration, and scaling of neuronal avalanches. We demonstrate that by analyzing simulated critical neuronal networks alongside real 2-photon imaging data, temporal coarse-graining can recover the critical value of the mean size vs. duration scaling of neuronal avalanches, allowing for more accurate estimations of critical brain dynamics even from subsampled data. Finally, we bridge the gap between machine learning and neuroscience by exploring the concept of excitatory-inhibitory balance, a crucial feature of neuronal networks in the brain, within the framework of reservoir computing. We emphasize the stabilizing role of inhibition in reservoir computers (RCs), mirroring its function in the brain. We propose a novel inhibitory adaptation mechanism that allows RCs to autonomously adjust inhibitory connections to achieve a specific firing rate target, motivated by the firing rate homeostasis observed in biological neurons. Overall, this dissertation strives to deepen the ongoing collaboration between neuroscience and machine learning, fostering advancements that will benefit both fields.
EXPLORING QUANTUM MANY-BODY SYSTEMS IN PROGRAMMABLE TRAPPED ION QUANTUM SIMULATORS
(2024) De, Arinjoy; Monroe, Christopher R; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Quantum simulation is perhaps the most natural application of a quantum computer, where a precisely controllable quantum system is designed to emulate a more complex or less accessible quantum system. Significant research efforts over the last decade have advanced quantum technology to the point where it is foreseeable to achieve `quantum advantage' over classical computers, to enable the exploration of complex phenomena in condensed-matter physics, high-energy physics, atomic physics, quantum chemistry, and cosmology. While the realization of a universal fault-tolerant quantum computer remains a future goal, analog quantum simulators -- featuring continuous unitary evolution of many-body Hamiltonians -- have been developed across several experimental platforms. A key challenge in this field is balancing the control of these systems with the need to scale them up to address more complex problems. Trapped-ion platforms, with exceptionally high levels of control enabled by laser-cooled and electromagnetically confined ions, and all-to-all entangling capabilities through precise control over their collective motional modes, have emerged as a strong candidate for quantum simulation and provide a promising avenue for scaling up the systems. In this dissertation, I present my research work, emphasizing both the scalability and controllability aspects of \ion based trapped-ion platforms, with an underlying theme of analog quantum simulation. The initial part of my research involves utilizing a trapped ion apparatus operating within a cryogenic vacuum environment, suitable for scaling up to hundreds of ions. We address various challenges associated with this approach, particularly the impact of mechanical vibrations originating from the cryostat, which can induce phase errors during coherent operations. Subsequently, we detail the implementation of a scheme to generate phase-stable spin-spin interactions that are robust to vibration noise. In the second part, we use a trapped-ion quantum simulator operating at room temperature, to investigate the non-equilibrium dynamics of critical fluctuations following a quantum quench to the critical point. Employing systems with up to 50 spins, we show that the amplitude and timescale of post-quench fluctuations scale with system size, exhibiting distinct universal critical exponents. While a generic quench can lead to thermal critical behavior, a second quench from one critical state to another (i.e., double quench) results in unique critical behavior not seen in equilibrium. Our results highlight the potential of quantum simulators to explore universal scaling beyond the equilibrium paradigm. In the final part of the thesis, we investigate an analog of the paradigmatic string-breaking phenomena using a quantum spin simulator. We employ an integrated trapped-ion apparatus with $13$ spins that utilizes the individual controllability of laser beams to program a uniform spin-spin interaction profile across the chain, alongside 3-dimensional control of the local magnetic fields. We introduce two static probe charges, realized through local longitudinal magnetic fields, that create string tension. By implementing quantum quenches across the string-breaking point, we monitor non-equilibrium charge evolution with spatio-temporal resolution that elucidates the dynamical string breaking. Furthermore, by initializing the charges away from the string boundary, we generate isolated charges and observe localization effects that arise from the interplay between confinement and lattice effects.
NONEQUILIBRIUM STATISTICAL PHYSICS OF FEEDBACK-CONTROLLED AND AUTONOMOUS INFORMATION-THERMODYNAMIC SYSTEMS
(2024) Bhattacharyya, Debankur; Jarzynski, Christopher; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This thesis investigates the nonequilibrium dynamics of a variety of systems evolving under control protocols. A control protocol can involve feedback based on measurements performed by an external agent, or it can be a predefined protocol that does not rely on explicit measurements of the system’s state. In the context of information thermodynamics, the former setup belongs to the paradigm of non-autonomous or feedback-controlled Maxwell's demons, and the latter to the paradigm of autonomous demons. The thesis begins with a framework for analyzing non-autonomous feedback control, when the control protocol is applied by an agent making continuous measurements on the system. A multiple-timescales perturbation theory, applicable when there exists an appropriate separation of timescales, is developed. This framework is applied to a classical two-state toy model of an information engine – a device that uses feedback control of thermal fluctuations to convert heat into work. Additionally, quantum trajectory simulations are used to study a feedback-controlled model of Maxwell's demon in a double quantum dot system. Next, a modeling scheme for converting feedback-controlled Maxwell's demons to autonomous (non-feedback) systems is developed. This scheme explicitly accounts for the thermodynamic costs of information processing, by incorporating an information reservoir, modeled as a sequence of bits. This modeling scheme is then applied for converting the classical analogue of the non-autonomous double quantum dot Maxwell's demon, discussed previously, to an autonomous model. Using analytical, semi-analytical and stochastic simulation-based approaches, it is shown that the obtained model can act either as an information engine, or as a “Landauer eraser”, and then the phase diagrams that identify these regimes of behavior are constructed. Finally, fast-forward shortcuts to adiabaticity for classical Floquet-Hamiltonian systems is developed, and applied to a periodically driven asymmetric double well (without feedback control). Tools from dynamical systems theory are then used to characterize the system’s angle-variable dynamics.
Quantum Circuits for Chiral Topological Order
(2024) Chu, Su-Kuan; Hafezi, Mohammad; Gorshkov, Alexey; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Quantum simulation stands as an important application of quantum computing, offering insights into quantum many-body systems that are beyond the reach of classical computational methods. For many quantum simulation applications, accurate initial state preparation is typically the first step for subsequent computational processes. This dissertation specifically focuses on state preparation procedures for quantum states with chiral topological order, states that are notable for their robust edge modes and topological properties. These states are interesting due to their profound connections to the behavior of electrons and spins in real-world solid-state materials. In this dissertation, we explore a type of state preparation procedure known as entanglement renormalization circuits. This class of quantum circuits is characterized by its hierarchical arrangement of quantum gates (or quantum operations in general), which systematically organize and prepare the entanglement of the target states across various length scales. In the first part of the dissertation, we present an entanglement renormalization circuit for a non-interacting chiral topological system. The non-interacting chiral topological system we consider is a continuous Chern insulator model, which can serve as a toy model for the integer quantum Hall effect. The entanglement renormalization circuit for the continuous Chern insulator is the continuous multiscale entanglement renormalization ansatz (cMERA). The cMERA circuit, adapted for field theories, provides a natural framework for quantum systems that are continuous in momentum space. One of the key findings of this work is that we find a scale-invariant cMERA for which the continuous Chern insulator is a fixed-point wavefunction, a property that is believed to be impossible within the traditional lattice multiscale entanglement renormalization ansatz (MERA) framework. Furthermore, we provide an experimental proposal to realize the cMERA circuit using cold atoms. In the second part of this dissertation, we shift our focus to entanglement renormalization circuits for interacting chiral topologically ordered states. We analytically derive a class of exactly solvable chiral spin liquids, classified under Kitaev's 16-fold way. Some of these chiral spin liquids share universal properties with certain fractional quantum Hall states. We then construct entanglement renormalization circuits for these chiral spin liquids by combining traditional MERA circuits with time-dependent quasi-local Hamiltonians. We refer to this class of circuits as the multiscale entanglement renormalization ansatz with quasi-local evolution (MERAQLE).
NEXT-GENERATION SUPERCONDUCTING METAMATERIALS: CHARACTERIZATION OF SUPERCONDUCTING RESONATORS AND STUDY OF STRONGLY COUPLED SUPERCONDUCTING QUANTUM INTERFERENCE META-ATOMS
(2024) Cai, Jingnan; Anlage, Steven SMA; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Metamaterials are artificial structures consisting of sub-wavelength ‘atoms’ with engineered electromagnetic properties that create exotic light-matter interactions through the effective medium approximation. Since the early 2000s, superconductors have been incorporated into a variety of structures to achieve tunable, low-loss, and nonlinear metamaterials, and have enabled applications such as negative index of refraction, near zero permittivity, and parametric amplification. We have designed, fabricated and characterized two types of superconducting metamaterials based on the quantum three-junction flux qubits and classical radio frequency superconducting quantum interference devices (rf SQUIDs). The coplanar waveguide resonators hosting the qubit meta-atoms exhibit anomalous reduction in loss in microwave transmission measurements at low rf excitation levels upon decreasing temperature below 40 mK. In contrast, the well-known standard tunneling model (STM) of the two-level system (TLS), believed to be the dominant source of loss at low temperatures, predicts a loss increasing then saturating with lowering temperatures. This anomalous loss reduction is attributed to the discrete nature of an ensemble of TLSs in the resonator. As temperature decreases, the individual TLS response bandwidth reduces with their coherence rate Γ2 ∼ T, creating less overlap between neighboring TLSs in the energy spectrum. This effective reduction in the density of states around the probe frequency is responsible for the observed lower loss at low rf excitation levels and low temperatures as compared to the STM prediction. We also incorporate the discrete TLS ansatz with the generalized tunneling model proposed by Faoro and Ioffe [PRL 2012, 109, 157005 and PRB 2015, 91, 014201] to fit the experimental data over a wide range of temperatures and rf excitation powers. The resulting goodness of fit is better than all common alternative explanations for the observed phenomenon. Metamaterials made of large arrays of hysteretic (βrf= Lgeo/LJJ > 1) classical rf SQUIDs are also designed and characterized in microwave transmission measurements, where we observed the SQUID self-resonances tuning with applied dc and rf magnetic flux, as well as temperature. The resonance features are tuned with dc flux in integers of the flux quantum, as expected. Due to the phenomenon of multistability present in the large system, the resonance bands can cross those from adjacent dc flux periodicities resulting in hysteresis in dc flux sweeps, which is observed in the experiment. Furthermore, we developed a new three-dimensional architecture of rf SQUID metamaterials where the nearest-neighbor SQUID loops overlap. The resulting capacitive coupling dramatically changes the response by introducing many more resonance bands that spread over a broad range of frequencies, the upper limit of which is much higher than the single-layer counterparts. A resistively and capacitively shunted junction (RCSJ) model with additional capacitive coupling between SQUIDs is proposed and successfully attributes the high frequency bands to the displacement current loops formed between the overlapping wiring of neighboring SQUIDs. The capacitively-coupled rf SQUID metamaterial is relevant to the design of single-flux-quantum-based superconducting digital electronic circuits, which has adopted three-dimensional wiring to reduce the circuit footprint.
Multi-messenger search for galactic PeVatron with HAWC and IceCube
(2024) Fan, Kwok Lung; Goodman, Jordan A; Sullivan, Gregory W; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
In recent years, many advancements in astrophysics have brought astrophysicists new tools to study the universe. Specifically, the discovery of astrophysical neutrinos by the IceCube Neutrino Observatory and Gravitational waves by the LIGO/Virgo collaboration has started the era of multi-messenger astronomy. Scientists can finally use messengers other than electromagnetic waves to study astrophysical phenomena. With the addition of new messengers, it is crucial that data from multiple instruments and messengers can be jointly analyzed through a unified framework using one physics model. Many efforts have been put into jointly analyzing electromagnetic waves of different wavelengths from different instruments, but the ability to jointly fit other messengers to a single physics model is still missing. In this work, we present a method to jointly analyze data from HAWC Gamma-ray Observatory and IceCube Neutrino Observatory by using a newly developed IceCube likelihood software called i3mla and the existing HAWC likelihood software called HAL. Together with the Multi-Mission Maximum Likelihood framework (3ML), we are able to jointly fit the gamma-ray emission model and neutrino emission model simultaneously with the HAWC gamma-ray and IceCube neutrino data. We apply the method to search for Galactic PeVatrons. Galactic PeVatrons are sources of PeV galactic cosmic rays. When the cosmic ray interacts with nearby material, it will produce both gamma rays and neutrinos with the same morphology and spectral shape. While gamma rays could also be produced from other interactions, neutrinos can only be produced by hadronic interactions of the cosmic ray. Therefore, it is natural to search for neutrino emissions from gamma-ray sources. We first perform a search for neutrino emissions from the 12 known gamma-ray sources detected by LHAASO. No significant detection was found and we put constraints on the neutrino emission on the sources. Second, a more detailed multimessenger search of Galactic PeVatrons candidates using simultaneously the HAWC data and IceCube neutrino data is conducted. We model the gamma-ray emission using the HAWC data and jointly fit a unified model to both the gamma-ray and neutrino data. No significant detection was found and we put constraints on the fraction of the gamma rays due to hadronic interactions.
Constructing an ergodic theory of quantum information dynamics
(2024) Anand, Amit Vikram; Galitski, Victor; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The ergodic theory of classical dynamical systems, originating in Boltzmann's ergodic hypothesis, provides an idealized description of how the flow of information within energy surfaces of a classical phase space justifies the use of equilibrium statistical mechanics. While it is an extremely successful mathematical theory that establishes rigorous foundations for classical chaos and thermalization, its basic assumptions do not directly generalize to quantum mechanics. Consequently, previous approaches to quantum ergodicity have generally been limited to model-specific studies of thermalization, or well-motivated but imprecise general conjectures. In this Dissertation, we develop a general theoretical framework for understanding how the energy levels of a quantum system drive the flow of quantum information and constrain the applicability of statistical mechanics, guided by two prominent conjectures. The first of these, the Quantum Chaos Conjecture (QCC), aims to characterize which quantum systems may thermalize, by postulating a connection between ergodicity or chaos and the statistical properties of random matrices. The second, the Fast Scrambling Conjecture (FSC), is concerned with how fast a quantum system may thermalize, and posits a maximum speed of thermalization in a sufficiently “local” many-body system. This Dissertation is divided into three main parts. In the first part, Theory of Quantum Dynamics and the Energy Spectrum, we tackle these conjectures for a general isolated quantum system through results that may be understood as new formulations of the energy-time uncertainty principle. For QCC, we introduce precise quantum dynamical concepts of ergodicity and quantitatively establish their connections to the statistics of energy levels, deriving random matrix statistics as a special consequence of these dynamical notions. We subsequently build on one of these connections to derive an energy-time uncertainty principle that accounts for the full structure of the spectrum, introducing sufficient sensitivity for many-body systems. The resulting quantum speed limit allows us to prove a precise formulation of FSC from the mathematical properties of the energy spectrum. In doing so, we generalize QCC beyond the statistics of random matrices alone, and FSC beyond requirements of locality, establishing precise versions of these statements for the most general quantum mechanical Hamiltonian. In the second part, Quantum Systems Beyond the Chaotic-Integrable Dichotomy, we demonstrate the need for the aforementioned precise formulations of these conjectures, by showing that looser formulations can be readily violated in “maximally” chaotic or integrable systems that would be most expected to satisfy them. Finally, in the third part, Experimental Probes of Many-Body Quantum Ergodicity, we develop tools to experimentally probe the structure of energy levels associated with ergodic dynamics, and demonstrate a generalization of these probes to open systems in an experiment with trapped ions.
ENGINEERING OPTICAL LATTICES FOR ULTRACOLD ATOMS WITH SPATIAL FEATURES AND PERIODICITY BELOW THE DIFFRACTION LIMIT and DUAL-SPECIES OPTICAL TWEEZER ARRAYS FOR RUBIDIUM AND YTTERBIUM FOR RYDBERG-INTERACTION-MEDIATED QUANTUM SIMULATIONS
(2024) Subhankar, Sarthak; Rolston, Steven; Porto, Trey; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This dissertation is based on two independent projects and is therefore divided into two parts. The first half of this dissertation summarizes a series of investigations, both experimental and theoretical, that culminates in the realization of an optical lattice with a subwavelength spacing of $\lambda/4$, where $\lambda$ is the wavelength of light used to create the lattice. The second half of this thesis presents details on the design andconstruction of an apparatus for dual-species optical tweezer arrays of Rb and Yb for Rydberg-interaction-mediated quantum computation and simulation. Ultracold atoms trapped in optical lattices have proven to be a versatile, highly controllable, and pristine platform for studying quantum many-body physics. However, the characteristic single-particle energy scale in these systems is set by the recoil energy $E_R=h^2 /\left(8 m d^2\right)$. Here, $m$ is the mass of the atom, and $d$, the spatial period of the optical lattice, is limited by diffraction to ${\lambda}/{2}$, where $\lambda$ is the wavelength of light used to create the optical lattice. Although the temperatures in these systems can be exceedingly low, the energy scales relevant for investigating many-body physics phenomena, such as superexchange or magnetic dipole interactions, can be lower yet. This limitation can be overcome by raising the relevant energy scales of the system ($E_R^{\mathrm{eff}}=h^2 /\left(8 m d_{\mathrm{eff}}^2\right)$) by engineering optical lattices with spatial periodicities below the diffraction limit ($d_{\mathrm{eff}} < \lambda/2$). To realize this subwavelength-spaced lattice, we first generated a Kronig-Penney-like optical lattice using the nonlinear optical response of three-level atoms in spatially varying dark states. This conservative Kronig-Penney-like optical potential has strongly subwavelength barriers that can be less than 10 nm ($\equiv\lambda/50$) wide and are spaced $\lambda/2$ apart, where $\lambda$ is the wavelength of light used to generate the optical lattice. Using the same nonlinear optical response, we developed a microscopy technique that allowed the probability density of atoms in optical lattices to be measured with a subwavelength resolution of $\lambda/50$. We theoretically investigated the feasibility of stroboscopically pulsing spatially shifted 1D Kronig-Penney-like optical lattices to create lattices with subwavelength spacings. We applied the lattice pulsing techniques developed in this theoretical investigation to realize a $\lambda/4$-spaced optical lattice. We used the subwavelength resolution microscopy technique to confirm the existence of this $\lambda/4$-spaced optical lattice by measuring the probability density of the atoms in the ground band of the $\lambda/4$-spaced optical lattice. Single neutral atoms trapped in optical tweezer arrays with Rydberg interaction-mediated entangling gate operations have recently emerged as a promising platform for quantum computation and quantum simulation. These systems were first realized using atoms of a single species, with alkali atoms being the first to be trapped in optical tweezers, followed by alkaline-earth (like) atoms, and magnetic lanthanides. Recently, dual-species (alkali-alkali) optical tweezer arrays were also realized. Dual-species Rydberg arrays are a promising candidate for large-scale quantum computation due to their capability for multi-qubit gate operations and crosstalk-free measurements for mid-circuit readouts. However, a dual-species optical tweezer array of an alkali atom and an alkaline-earth (like) atom, which combines the beneficial properties of both types of atoms, has yet to be realized. In this half of the thesis, I present details on the design and construction of an apparatus for dual-species Rydberg tweezer arrays of Rb (alkali) and Yb (alkaline-earth like).
TENSOR NETWORK APPROACHES IN NON-EQUILIBRIUM QUANTUM MANY-BODY DYNAMICS
(2024) Yoo, Yongchan; Swingle, Brian; Sau, Jay D; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Understanding the dynamics of non-equilibrium quantum systems has been a longstanding challenge in a wide range of physical phenomena. Recent advancements in various quantum technologies have driven theoretical investigations of non-equilibrium quantum many-body dynamics. A crucial aspect of the theory is the development of computational methods, which have led to significant results and show promising directions for further development. However, simulating these complex systems using classical algorithms remains extremely difficult, primarily due to the challenge of identifying physically principled and efficient approximations capable of reducing their computational complexity.This thesis discusses theoretical and numerical studies on the non-equilibrium dynamics of quantum many-body systems, particularly focusing on the steady-state transport of conserved quantities in various one-dimensional spin systems. We study transport phenomena employing boundary-driven open quantum setups and investigate various aspects of the non-equilibrium dynamics induced by these systems. Our goal is to understand steady-state phenomena and to push the boundaries of simulation capacity using state-of-the-art technologies. In the first part, we examine the non-equilibrium steady-state (NESS) phases of an interacting Aubry-Andr´e-Harper model. This model involves a quasiperiodic potential, leading to interesting emergent collective phenomena. The observed spin transport and quantum correlation structure suggest the presence of multiple dynamical phases between the well-studied thermal and many-body-localized phases. In the second part, we study the impact of operator weight dissipation on the scaling behavior of transport in various spin models. Our findings suggest that dissipation’s effect on transport depends on the system’s conserved quantities. When dissipation preserves these symmetries, it maintains the scaling of the system’s transport properties. However, when it disrupts these conserved quantities, it leads the system towards diffusive scaling of transport. In the third part, we investigate energy transport within the non-integrable regime of the Z3 chiral clock model, utilizing Lindblad operators with adjustable size and temperature. Through scaling analysis, we extract the model’s transport coefficients at relatively high temperatures, both above its gapless and gapped low-temperature phases. Furthermore, we calculate the temperature dependence of the energy diffusion constant across various model parameters, including the regime where the model exhibits quantum critical behavior at low temperatures.
Spectral Statistics, Hyrodynamics, and Quantum Chaos
(2024) Winer, Michael Hofmann; Swingle, Brian; Galitski, Victor; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
One of the central problems in many-body physics, both classical and quantum, is the relations between different notions of chaos. Ergodicity, mixing, operator growth, the eigenstate thermalization hypothesis, and spectral chaos are defined in terms of completely different objects in different contexts, don't necessarily co-occur, but still seem to be manifestations of closely related phenomena. In this dissertation, we study the relation between two notions of chaos: thermalization and spectral chaos. We define a quantity called the Total Return Probability (TRP) which measures how a system forgets its initial state after time $T$, and show that it is closely connected to the Spectral Form Factor (SFF), a measure of chaos deriving from the energy level spectrum of a quantum system. The main thrust of this work concerns hydrodynamic systems- systems where locality prevents charge or energy from spreading quickly, this putting a throttle on thermalization. We show that the detailed spacings of energy levels closely capture the dynamics of these locally conserved charges. We also study spin glasses, a phase of matter where the obstacle to thermalization comes not from locality but from the presence of too many neighbors. Changing one region requires changing nearby regions which requires changing nearby-to-nearby regions, until only catastrophic realignments of the whole system can fully explore phase space. In spin glasses we find our clearest analytic link between thermalization and spectral statistics. We analytically calculate the spectral form factor in the limit of large system size and show it is equal to the TRP. Finally, in the conclusion, we discuss some ideas for the future of both the SFF and the TRP.
Harnessing Quantum Systems for Sensing, Simulation, and Optimization
(2024) Bringewatt, Jacob Allen; Gorshkov, Alexey V; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Quantum information science offers a remarkable promise: by thinking practically about how quantum systems can be put to work to solve computational and information processing tasks, we gain novel insights into the foundations of quantum theory and computer science. Or, conversely, by (re)considering the fundamental physical building blocks of computers and sensors, we enable new technologies, with major impacts for computational and experimental physics. In this dissertation, we explore these ideas through the lens of three different types of quantum hardware, each with a particular application primarily in mind: (1) networks of quantum sensors for measuring global properties of local field(s); (2) analog quantum computers for solving combinatorial optimization problems; and (3) digital quantum computers for simulating lattice (gauge) theories. For the setting of quantum sensor networks, we derive the fundamental performance limits for the sensing task of measuring global properties of local field(s) in a variety of physical settings (qubit sensors, Mach-Zehnder interferometers, quadrature displacements) and present explicit protocols that achieve these limits. In the process, we reveal the geometric structure of the fundamental bounds and the associated algebraic structure of the corresponding protocols. We also find limits on the resources (e.g. entanglement or number of control operations) required by such protocols. For analog quantum computers, we focus on the possible origins of quantum advantage for solving combinatorial optimization problems with an emphasis on investigating the power of adiabatic quantum computation with so-called stoquastic Hamiltonians. Such Hamiltonians do not exhibit a sign problem when classically simulated via quantum Monte Carlo algorithms, suggesting deep connections between the sign problem, the locality of interactions, and the origins of quantum advantage. We explore these connections in detail. Finally, for digital quantum computers, we consider the optimization of two tasks relevant for simulating lattice (gauge) theories. First, we investigate how to map fermionic systems to qubit systems in a hardware-aware manner that consequently enables an improved parallelization of Trotter-based time evolution algorithms on the qubitized Hamiltonian. Second, we investigate how to take advantage of known symmetries in lattice gauge theories to construct more efficient randomized measurement protocols for extracting purities and entanglement entropies from simulated states. We demonstrate how these protocols can be used to detect a phase transition between a trivial and a topologically ordered phase in $Z_2$ lattice gauge theory. Detecting this transition via these randomized methods would not otherwise be possible without relearning all symmetries.

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