## Alexander Chernoglazov - August 19, 2024

Dissertation Title: **Radiative Plasmas in Pulsar Magnetospheres**

Date and Time:** Monday, August 19, 11:00 am**

Location:** 1207 ERF**

Dissertation Committee Chair:** Alexander Philippov**

Committee:

James Drake

Michael Coleman Miller (Dean Representative)

Anatoly Spitkovsky

Marc Swisdak

Abstract:

Pulsars are highly magnetized rotating neutron stars known for their periodic bursts of radio emission. Decades of astronomical observations revealed that pulsars produce non-thermal radiation in all energy bands, from radio to gamma rays, covering more than 20 decades in photon energy. Modern theories consider strongly magnetized relativistic electron-positron plasmas to be the source of the observed emission. In my Thesis, I investigate physical processes that can be responsible for plasma production and the observed high-energy emission in the wide range of photon energies, from eV to TeV.

In the first Chapter of my Thesis, I investigate relativistic magnetic reconnection with strong synchrotron cooling using three-dimensional particle-in-cell kinetic plasma simulations. I characterize the spectrum of accelerated particles and emitted synchrotron photons for varying strengths of synchrotron cooling. I show that the cutoff energy of the synchrotron spectrum can significantly exceed the theoretical limit of 16 MeV if the plasma magnetization parameter exceeds the radiation reaction limit. Additionally, I demonstrate that a small fraction of ions present in the current sheet can be accelerated to the highest energies, making relativistic radiative reconnection a promising mechanism for the acceleration of high-energy cosmic rays.

In the second Chapter, I present the first multi-dimensional simulations of the QED pair production discharge that occurs in the polar region of the neutron star. This process is believed to be the primary source of the pair plasma in pulsar magnetospheres and also the source of the radio emission. In this work, I focus on the self-consistently emerging synchronization of the discharges in different parts of the polar region. I find that pair discharges on neighboring magnetic field lines synchronize on a scale comparable to the height of the pair production region. I also demonstrate that the popular “spark” model of pair discharges is incompatible with the universally adopted force-free magnetospheric model: intermittent discharges fill the entire polar region that allows pair production, leaving no space for discharge-free regions. My findings disprove the key assumption of the spark model about the existence of distinct discharge columns.

In the third Chapter, I demonstrate how the key findings of two previous chapters can provide a self-consistent explanation of the recently discovered very-high-energy, reaching 20TeV, pulsed emission in Vela pulsar. Motivated by the results of recent global simulations of pulsar magnetospheres, I propose that this radiation is produced in the magnetospheric current sheet undergoing radiative relativistic reconnection. I show that high-energy synchrotron photons emitted by reconnection-accelerated particles efficiently produce electron-positron pairs. The density of secondary pairs exceeds the supply from the polar cap and results in a self-regulated plasma magnetization parameter of ~10^7. Electrons and positrons accelerate to Lorentz factors comparable to ~10^7 and emit the observed GeV radiation via the synchrotron process and ~10 TeV photons by Compton scattering of the soft synchrotron photons emitted by secondary pairs. My model self-consistently accounts for the ratio of the gamma-ray and TeV luminosities.

## Christopher J. Flower - August 15, 2024

Dissertation Title: **Topological Photonics: Nested Frequency Combs and Edge Mode Tapering**

Date and Time:** Thursday, August 15, 4:00 pm **

Location:** PSC 2136 ****and Zoom**

Dissertation Committee Chair:** Prof. Mohammad Hafezi**

Committee:

Professor Kartik Srinivasan

Professor Yanne Chembo

Professor Carlos A. Rios Ocampo

Professor Miao Yu (Dean’s Representative)

Abstract:

Topological photonics has emerged in recent years as a powerful paradigm for the design of photonic devices with novel functionalities. These systems exhibit chiral or helical edge states that are confined to the boundary and are remarkably robust against certain defects and imperfections. While several applications of topological photonics have been demonstrated, such as robust optical delay lines, quantum optical interfaces, lasers, waveguides, and routers, these have largely been proof-of-principle demonstrations. In this dissertation, we present the design and generation of the first topological frequency comb. While on-chip generation of optical frequency combs using nonlinear ring resonators has led to numerous applications of combs in recent years, they have predominantly relied on the use of single-ring resonators. Here, we combine the fields of linear topological photonics and frequency microcombs and experimentally demonstrate the first frequency comb of a new class in an array of hundreds of ring resonators. Through high-resolution spectrum analysis and out-of-plane imaging we confirm the unique nested spectral structure of the comb, as well as the confinement of the parametrically generated light. Additionally, we present a theoretical study of a new kind of valley-Hall topological photonic crystal that utilizes a position dependent perturbation (or “mass-term”) to manipulate the width of the topological edge modes. We show that this approach, due to the inherent topological robustness of the system, can result in dramatic changes in mode width over short distances with minimal losses. Additionally, by using a topological edge mode as a waveguide mode, we decouple the number of supported modes from the waveguide width, circumventing challenges faced by more conventional waveguide tapers.

## Jingnan Cai - July 30, 2024

Dissertation Title: **Next-Generation Superconducting Metamaterials: Characterization of Superconducting Resonators and Study of Strongly Coupled Superconducting Quantum Interference Meta-Atoms**

Date and Time:** Tuesday, July 30, 2:00 pm**

Location:** John S Toll Physics Building, Room 2219 ****and Zoom**

Dissertation Committee Chair:** Steven M. Anlage**

Committee:

Kevin D. Osborn

Benjamin S. Palmer

Aaron Sternbach

Thomas M. Antonsen

Ichiro Takeuchi (Dean’s representative)

Abstract:

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 systems (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 the TLS ensemble in the resonator. As temperature decreases, the individual TLS response bandwidth reduces with their coherence rate Γ_{2 }~ T, creating less overlap between neighboring TLS 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.

Large metamaterial arrays of hysteretic (β_{rf}=L_{geo}/L_{JJ }> 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.

## Deepak Sathyan - July 22, 2024

Dissertation Title: **Unifying Searches for New Physics with Precision Measurements of the W Boson Mass**

Date and Time:** Monday, July 22, 3:00 pm**

Location:** PSC Room 3150**** and Zoom**

Dissertation Committee Chair:** Kaustubh Agashe**

Committee:

Tom Cohen

Sarah Eno

Raman Sundrum

Richard Wentworth

Abstract:

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 ± 9.4 MeV. This measurement is in 7𝜎 significance tension with the SM prediction via the electroweak (EW) fit, m_{W}^{pred.} = 80354 ± 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 ± 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 (l) 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 l+MET which modifies the kinematic distributions used to extract m_{W} can be probed with this method. An important point of this strategy is that since these distributions are used to search for NP while measuring m_{W}, a simultaneous fit of NP and SM parameters, 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) l+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 directly 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).

## Ali Rad - July 19, 2024

Dissertation Title: **Excursion in the Quantum Loss Landscape: Learning, Generating and Simulating in the Quantum World**

Date and Time:** Friday, July 19, 2:00 pm**

Location:** ATL 3100A (QuICS Conference Room) and Zoom**

Dissertation Committee Chair:** Mohammad Hafezi**

Committee:

Michael Gullans

Zohreh Davoudi

Victor Albert

Christopher Jarzynski

Abstract:

Statistical learning is emerging as a new paradigm in science.

This has ignited interest within 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.

## Yihui Lai - July 18, 2024

Dissertation Title:** Constraining Higgs Boson Self-coupling with VHH Production and Combination, and Searching for Wγ Resonance using the CMS Detector at the LHC**

Date and Time:** Thursday, July 18, 11:00 am**

Location:** PSC 3150 and Zoom**

Dissertation Committee Chair:** Professor Christopher Palmer, Chair/Advisor**

Committee:

Professor Sarah Eno, Co-chair

Professor Kaustubh Agashe

Professor Manuel Franco Sevilla

Professor Mihai Pop, Dean’s Representative

Abstract:

Since the discovery of the Higgs boson (H) with a mass of 125 GeV by the ATLAS and CMS collaborations at CERN LHC in 2012, the focus of the particle physics community has shifted towards precise measurements of its properties and so far the measurements align with the standard model (SM) predictions. Among the properties, of particular interest is the Higgs trilinear self-coupling, which can be directly measured through the production of the Higgs boson pair (HH).

This thesis presents three analyses using proton-proton collision data at sqrt(s) = 13 TeV 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 (γ).

The VHH search focuses on Higgs bosons decay to bottom quarks with a novel background estimation approach. The combination of H measurements and HH searches aims to constrain the trilinear self-coupling with the best possible precision. The Wγ resonance search focuses on leptonic W decays, achieving the best sensitivity in the mass ranges considered compared to other searches for this resonance.

## Deric Session - July 15, 2024

Dissertation Title:** Chiral light-matter interaction in fermionic quantum Hall systems**

Date and Time:** Monday, July 15, 11:30 AM**

Location:** PSC 3150 and Zoom**

Dissertation Committee Chair:** Mohammad Hafezi**

Committee:

Glenn Solomon

Jay Sau

Nathan Schine

You Zhou

Ichiro Takeuchi (Dean’s representative)

Abstract:

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.

## Aftaab Dewan - July 15, 2024

Dissertation Title:** Ultracold Gases in a Two-Frequency Breathing Lattice**

Date and Time:** Monday, July 15, 11:30 AM**

Location:** PSC 2136 and Zoom**

Dissertation Committee Chair:** Prof. Steve Rolston**

Committee:

Prof. Gretchen Campbell

Prof. Nathan Schine

Prof. Ron Walsworth

Prof. Ki-yong Kim

Abstract:

Driven systems have been of particular interest in the field of ultracold atomic gases. The precise control and relative purity allow 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. Our results show a shift in the tunneling Hamiltonian away from nearest neighbour couplings.

## Huayu Zhang - July 10, 2024

Dissertation Title:** DEVELOPMENT OF COST-EFFECTIVE AND HIGHLY INTEGRATED NV CENTER SCANNING PROBES FOR QUANTUM SENSING AND IMAGING APPLICATIONS**

Date and Time:** Wednesday, July 10, 10:30 am**

Location:** John S. Toll Physics Building room 2219**

Dissertation Committee Chair:** Prof. Min Ouyang**

Committee:

Prof. Yuhuang Wang (Dean’s Representative)

Prof. Steven Mark Anlage

Prof. Ki-yong Kim

Prof. Cheng Gong

Abstract:

The nitrogen-vacancy (NV) center is a photostable fluorescent atomic defect in diamond, exhibiting unique magneto-optic effects. Its Hamiltonian is sensitive to the local magnetic, electric field, temperature, and strain, making NV centers ideal for atomic-scale quantum sensing and various scientific and technological applications. In this thesis, we first briefly introduce the properties and applications of nitrogen-vacancy centers, then we present a cost-effective method for fabricating and characterizing a new class of durable, highly integrated scanning quantum sensors using both fiber-based and cantilever-based nitrogen-vacancy center scanning probes using nanodiamonds.

The fiber-based NV center scanning probe is compatible with any tuning fork-based scanning probe microscope and supports multiple operational modes, including near-field excitation with far-field detection, far-field excitation with near-field detection, near-field excitation with near-field detection and far-field excitation with far-field detection. These diverse functional modes enable high-sensitivity and high-resolution quantum imaging and sensing applications, such as magnetic field imaging, electric field imaging, and thermal imaging at the nanoscale.

The cantilever-based nitrogen-vacancy centers scanning probe is suitable for use with any commercial cantilever-based scanning probe microscopes and it allows highly integrated microwave manipulation through metal coating. Additionally, we have developed a methodology to accurately determine the orientation of NV centers beneath the tip, establishing a foundation for utilizing these unique NV scanning probe for quantum sensing. Compared to existing fabrication methods, our method is reproducible, low-cost, and robust, offering significant advancements in NV center scanning probe technology.

## Nicholas John Mennona - July 2, 2024

Dissertation Title:** Collective Dynamics of Astrocyte and Cytoskeletal Systems**

Date and Time:** Tuesday, July 2, 11:00 AM**

Location:** PSC 1136**

Dissertation Committee Chair:** Professor Wolfgang Losert**

Committee:

Professor Pratyush Tiwary (Dean’s Representative)

Professor Arpita Upadhyaya

Professor Ronald Walsworth

Dr. Ibtissam Echchgadda (Special Member)

Abstract:

Advances in imaging and biological sample preparations now allow researchers to 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. Detailing such interactions reveals the specifically electrical information processing performed by the brain. This thesis aims at a complementary view of the general information processing of the brain, focusing on other modes of information. The modes discussed are the collective, dynamical characteristics of non-electrically active, non-neuronal brain cells, and mechanical systems. Astrocytes are such brain cells, and the cytoskeleton is a dynamic, mechanical system 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 and timescales distinct from electrical information transmission. Inclusion of the collective dynamics of both astrocytes and the cytoskeleton into brain networks is a step toward a fuller characterization of brain functioning and cognition.

Computer vision and information theory are used on structural, astrocyte actin images, microtubule structural image sequences, and the calcium signals of collections of astrocytes. 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 slow calcium Ca^{2+} signals within astrocyte networks classified according to subtype. Despite multiple physiological differences with 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 cytoskeletal and energy perturbation, relative to immature and injured astrocytes, as seen within their pairwise interactions and individual calcium fluctuations as measured by mutual information and cross correlation, and partitioned entropy, respectively.

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. This work highlights the importance of investigating all potential modalities of information within complex biological systems.

## Kwok Lung Fan - July 1, 2024

Dissertation Title:** Multi-messenger search for galactic PeVatron with HAWC and IceCube**

Date and Time:** Monday, July 1, 2:00 pm**

Location:** PSC 2136 and Zoom**

Dissertation Committee Chair:** Jordan Goodman, Gregory Sullivan (co-chair)**

Committee:

Kara Hoffman

Michael Larson

M. Coleman Miller (Dean’s Representative)

Abstract:

In recent years, many advancements in astrophysics have brought astrophysicists new tools to study the universe. Specifically, the discovery of astrophysical neutrino by IceCube Neutrino Observatory and Gravitational wave by 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. 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 can jointly fit the gamma-ray emission model and neutrino emission model simultaneously with the HAWC gamma-ray data 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 produces both gamma and neutrinos with a fixed relation between gamma-ray and neutrinos. We first perform a search for neutrino emissions from the 12 known gamma-ray sources detected by LHAASO. A more detailed multimessenger search on Galactic PeVatrons candidates using the HAWC gamma-ray data and IceCube neutrino data is then conducted. We model the gamma-ray emission using the HAWC data and jointly fit a unified model on the gamma-ray and neutrino data. No significant detection was found and we can put constraints on the fraction of the gamma rays due to hadronic interactions.

## Dawid Brzeminski - June 28, 2024

Dissertation Title:** Phenomenology of ultralight fields**

Date and Time:** Friday, June 28, 12:00pm**

Location:** PSC 3150**

Dissertation Committee Chair:** Anson Hook**

Committee:

Zackaria Chacko

Raman Sundrum

Peter Shawhan

Richard Wentworth (Dean's Representative)

Abstract:

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, making the model testable by current and future experiments.

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.

## Clayton Ristow - June 12, 2024

Dissertation Title:** Stable Excited Dyonic States of Magnetic Monopoles**

Date and Time:** Thursday, June 27, 12:00 PM**

Location:** PSC 3150**

Dissertation Committee Chair:** Anson Hook**

Committee:

Zackaria Chacko

Kaustubh Agashe

Thomas Cohen

Richard Wentworth (Dean's Representative)

Abstract:

Advancements in our understanding of new physics can be largely divided into two areas of study: phenomenology and theory with the former concerning the formulation of new theories and holding them to scrutiny against experimental evidence while the latter involves the in-depth study of these theories to better understand the scope of their implications. To reflect this dichotomy, this thesis is broken into two acts: one covering progress made on the phenomenological front and the other covering progress made on the theoretical front. This defense will focus on the latter by detailing advancements made in our understanding of the structure 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 a magnetic monopole and 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 N_{f } fermions. We demonstrate there are two unique ways to grant mass to the fermions in the SU(2) theory which, after symmetry breaking, both give a theory of QED with N_{f} massive fermions. Despite this seeming equivalence of the two theories at low energies, we demonstrate that the structure of the fermion bound states differ drastically between them and as a consequence can encode information about the high-energy theory, which is accessible at low-energy scales. We find that each theory exhibits a different number of stable excited dyonic states of the monopole with differing charges and energies. 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 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.

## Sarthak Subhankar - June 12, 2024

Dissertation Titles: **Engineering optical lattices for ultracold atoms with spatial features and periodicity below the diffraction limit **

**&**

**Dual-species optical tweezer arrays for Rubidium and Ytterbium for Rydberg-interaction-mediated quantum simulations**

Date and Time:** Wednesday, June 12, 11:00 am**

Location:

**PSC 2136 and Zoom**

Dissertation Committee Chair:

**Prof. Steven Rolston (co-advisor)**

Committee:

Prof. Trey Porto (co-chair/co-advisor)

Prof. Ian Spielman

Prof. Nathan Schine

Prof. Ronald Walsworth

Abstract:

This dissertation is based on two independent projects.

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}

*/*(8

*md*

^{2}). Here,

*m*is the mass of the atom, and

*d*, the spatial period of the optical lattice, is limited by diffraction to

*λ/*2, where

*λ*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}^{eff}*h*

^{2}

*/*(8

*md*

_{eff}

^{2})) by engineering optical lattices with spatial periodicities below the diffraction limit (

*d*

_{eff}

*< λ/*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 (*≡ **λ/*50) wide and are spaced *λ/*2 apart, where *λ *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 *λ/*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 *λ/*4-spaced optical lattice. We used the subwavelength resolution microscopy technique to confirm the existence of this *λ/*4-spaced optical lattice by measuring the probability density of the atoms in the ground band of the *λ/*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).

## Yongchan Yoo - June 11, 2024

Dissertation Title:** Tensor Network Approaches in Non-equilibrium Quantum Many-body Dynamics**

Date and Time:** Tuesday, June 11, 2:00 pm**

Location:** PSC 3150 **

Dissertation Committee Chair:

**Brian Swingle, Jay Sau**

Committee:

Maissam Barkeshli

Michael Gullans

Christopher Jarzynski

Abstract:

Understanding the dynamics of non-equilibrium quantum systems has long been a challenge across a wide range of physical phenomena. Recent advancements in various quantum technologies have propelled theoretical investigations of non-equilibrium quantum many-body dynamics. A key part of the theory is the development of computational methods, leading to significant results and a promising direction for further development. Nevertheless, simulating these complex systems using classical algorithms remains notoriously difficult, primarily due to the challenge of identifying physically principled and efficient approximations capable of reducing their computational complexity.

This thesis presents a collection of theoretical and numerical studies focusing on non-equilibrium dynamics of quantum many-body systems, with a particular emphasis on the steady-state transport of conserved quantities in various one-dimensional spin systems. In these systems, transport phenomena can be effectively captured by utilizing boundary-driven open quantum setups. Our investigations focus on various aspects of the non-equilibrium dynamics induced by novel boundary-driven systems. The aim is to comprehend a range of steady-state phenomena and to push the boundaries of simulation capacity using current state-of-the-art technologies.

In the first part, we delve into the non-equilibrium steady-state (NESS) phases of an interacting Aubry-André-Harper model, where a quasiperiodic potential gives rise to intriguing emergent collective phenomena. The peculiar spin transport and quantum correlation structure observed suggest the existence of multiple dynamical phases lying between the extensively studied thermal and many-body-localized phases.

Moving on to the second part, we explore the impact of operator weight dissipation on the scaling behavior of transport in various spin models. Our findings indicate that the effect of dissipation on transport is influenced by its impact on the system's conserved quantities. When dissipation preserves these symmetries, it maintains the scaling of the system's transport properties; however, when it breaks 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, employing Lindblad operators with adjustable size and temperature. Through scaling analysis, we extract the transport coefficients of the model 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.

## Arinjoy De - June 11, 2024

Dissertation Title:** Exploring Quantum Many-body Systems in Programmable Trapped Ion Quantum Simulators**

Date and Time:** Tuesday, June 11, 11:00 am**

Location:** Zoom **

Dissertation Committee Chair:** Professor Christopher R. Monroe**

Committee:

Professor Alexey V. Gorshkov

Professor Zohreh Davoudi

Professor Norbert M. Linke

Professor Christopher Jarzynski

Abstract:

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 can achieve `quantum advantage' over classical computers, enabling 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 evolutions with 50 to 100 qubits--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.

In this dissertation, I present my research work, emphasizing both the scalability and controllability aspects of a ^{171}Yb^{+} based trapped-ion platform, 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. I 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, I detail the implementation of a scheme to generate phase-stable spin-spin interactions that are robust to vibration noise.

In the second part, using a trapped-ion quantum simulator operating at room temperature, we 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 of Quantum Chromodynamics using a quantum spin simulator. For this purpose, we employ an integrated trapped ion apparatus with 13 spins. This setup utilizes the individual controllability of laser beams to program a uniform spin-spin interaction profile across the chain, alongside 3D 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 elucidate the patterns of dynamical string breaking, monitoring non-equilibrium charge evolution with spatio-temporal resolution. 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.

## Su-Kuan Chu - June 10, 2024

Dissertation Title:** Quantum Circuits for Chiral Topological Order**

Date and Time:** Monday, June 10, 1:00-3:00 pm**

Location:

**ATL 3100A and Zoom**

Dissertation Committee Chair:

**Mohammad Hafezi**

Committee:

Alexey Gorshkov

Maissam Barkeshli

Ian Spielman

Andrew Childs

Abstract:

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).

## Michael Winer - June 10, 2024

Dissertation Title:** Spectral Statistics, Hydrodynamics, and Quantum Chaos**

Date and Time:** Monday, June 10, 10:00 am**

Location: **PSC 2136**

Dissertation Committee Chair:** Brian Swingle, Victor Galitski**

Committee:

Maissam Barkeshli

Jay Sau

Jonathan Rosenberg (Dean’s representative)

Abstract:

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.

## Amit Vikram Anand - June 7, 2024

Dissertation Title:** Constructing an ergodic theory of quantum information dynamics**

Date and Time:** Friday, June 7, 4:00 pm**

Location:** PSC 2136**

Dissertation Committee Chair:** Victor Galitski**

Committee:

Paulo Bedaque

Alexey Gorshkov

Christopher Jarzynski

Nicole Yunger Halpern

Abstract:

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.

## Jacob Bringewatt - May 23, 2024

Dissertation Title:** Harnessing Quantum Systems for Sensing, Simulation, and Optimization**

Date and Time:** Thursday, May 23 at 2:00 pm**

Location:** ATL 3100A**

Dissertation Committee Chair:** Zohreh Davoudi**

Committee:

Alexey Gorshkov

Andrew Childs (Dean’s Representative)

Yi-Kai Liu

Ronald Walsworth

Abstract:

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 the symmetries.

## Hanyu Liu - May 22, 2024

Dissertation Title:** Understanding and Controlling Nanoscale Chirality: Materials Synthesis, Characterizations, Modeling and Applications**

Date and Time:** Wednesday, May 22, 10:30 am**

Location:** PHYS 2219 **

Dissertation Committee Chair:** Min Ouyang**

Committee:

Gregory Jenkins

Thomas Murphy

Taylor Woehl

Lourdes Salamanca-Riba (Dean’s Representative)

Abstract:

Chirality, the property of objects possessing non-superimposable mirror images, initially identified and explored in organic and biological molecules, has gained growing interests in the realm of inorganic nanomaterials due to its foreseeable applications in the fields such as Enantiochemistry, Nanophotonics, Spintronics.

In the first segment of this dissertation, we demonstrate a bottom-up synthetic strategy to induce chirality in plasmonic nanoparticles and hybrid plasmonic-semiconductor nanostructures. Subsequently, we detail a simplified analytical coupled-oscillators model to facilitate the understanding of plasmonic-chiral coupling and predict various chiroptical responses based on different coupling strengths, validated through finite element method simulations. Furthermore, advancements in characterizing nanoscale chirality with high spatial resolution at the single nanoparticle level are explored using a novel polarization-dependent optical atomic force microscopy technique, overcoming resolution limits in far field measurements. Finally, we demonstrate the employment of nanoscale chirality to induce spin polarization and enable unique nanoscale chiral Floquet engineering.

## Adam Ehrenberg - May 1, 2024

Dissertation Title:** Quantum Advantage in Sensing and Simulation**

Date and Time:** Wednesday, May 1, 11:00 am**

Location:** Atlantic 3332 and Zoom **

Dissertation Committee Chair:** Steven Rolston**

Committee:

Alexey Gorshkov (co-chair)

Andrew Childs (Dean’s Representative)

Nathan Schine

Michael Gullans

Abstract:

Since the discovery of Shor’s factoring algorithm, there has been a sustained interest in finding more such examples of *quantum advantage*, that is, tasks where a quantum device can outperform its classical counterpart. While the universal, programmable quantum computers that can run Shor’s algorithm represent one direction in which to search for quantum advantage, they are certainly not the only one. In this dissertation, we study the theory of quantum advantage along two alternative avenues: sensing and simulation.

Sensing refers to the task of measuring some unknown quantity with the smallest possible error. In many cases, when the sensing apparatus is a quantum device, this ultimate achievable precision, as well as specific protocols achieving this precision, are unknown. In this dissertation, we help close this gap for both qubit-based and photonic quantum sensors for the specific task of measuring a linear function of unknown parameters. We use quantum Fisher information and the quantum Cramér-Rao bound to derive limits on their ultimate precision. We further develop an algebraic framework that allows us to derive protocols saturating these bounds and also better understand the quantum resources, such as entanglement, that are necessary to implement these protocols. In doing so, we help clarify how quantum resources like entanglement lead to more precise sensing.

We also study a specific form of simulation called Gaussian Boson Sampling, which is a member of a broad framework of random sampling tasks that have become a popular method for demonstrating quantum advantage. While many of the theoretical underpinnings of these random sampling tasks, including Gaussian Boson Sampling, are well understood, many questions remain. Anticoncentration, which is strongly related to the moments of the output distribution, is a particularly relevant property when it comes to formally proving the existence of quantum advantage. We develop a graph-theoretic framework to calculate these moments, and we show that there is a transition in the strength of anticoncentration as a function of how many of the photonic modes were initially squeezed. We therefore demonstrate a transition in the evidence for the so-called approximate average-case hardness of Gaussian Boson Sampling, hence clarifying in what regimes we have the strongest evidence for quantum advantage.## Rodrigo Andrade e Silva - April 26, 2024

Dissertation Title:** Quantization of Causal Diamonds in (2+1)-Dimensional Gravity**

Date and Time:** Friday, April 26, 2:00 pm**

Location:** PSC 3150**

Dissertation Committee Chair: **Ted Jacobson**

Committee:

Maissam Barkeshli

Steven Carlip

William Goldman (Dean’s Representative)

Raman Sundrum

Abstract:

## Dhruvit Patel - April 12, 2024

Dissertation Title: **Machine Learning for Predicting Non-Stationary Dynamical Systems, and Global Subseasonal-To-Seasonal Weather Phenomenon**

Date and Time:** Friday, April 12, 3:00 PM**

Location:

**ERF1207 (IREAP Large Conference Room)**

Dissertation Committee Chair:

**Prof. Edward Ott**Committee:

Prof. Brian Hunt

Prof. Michelle Girvan

Prof. Rajarshi Roy

Prof. Thomas Antonsen

Abstract:

In this thesis, we are interested in modeling (1) the long-term statistical behavior of non-stationary dynamical systems, and (2) global weather patterns on the Subseasonal-to-Seasonal (S2S) time scale (2 weeks - 6 months). The first part of this thesis is primarily concerned with the situation where we have available to us measured time series data of the past states of the system of interest, and in some cases, a (perhaps inaccurate) scientific-knowledge-based model of the system. The central problem here lies in predicting a future behavior of the system that may be fundamentally different than that observed in the measured time series of its past. We develop machine learning -based methods for accomplishing this task and test it in various challenging scenarios (e.g., predicting future abrupt changes in dynamics mediated by bifurcations encountered that were not included in the training data). We also investigate the effects of dynamical noise in the training data on the predictability of such systems. For the second part of this thesis, we modify a machine learning -based global climate model to predict various weather phenomenon on the S2S time scale. The model is a hybrid between a purely data-driven machine learning component and an atmospheric general circulation model.

We begin by formulating a purely machine learning approach that utilizes the measured time series of the past states of the target non-stationary system, as well as knowledge of the time-dependence of the non-stationarity inducing time-dependent system parameter. We demonstrate that this method can enable the prediction of the future behavior of the non-stationary system even in situations where the future behavior is qualitatively and quantitatively different from the behavior in the training data. For situations where the training data contains dynamical noise, we develop a scheme to enable the trained machine learning model to predict trajectories which mimic the effects of dynamical noise on typical trajectories of the target system. We test our methods on the discrete time logistic map, the continuous time Lorenz system, and the spatiotemporal Kuramoto-Sivashinsky system, and for a variety of non-stationary scenarios.

Next, we study the ability of our approach to not only extrapolate to previously unseen dynamics, but also to regions previously unexplored by the training data of the target system's state space. We find that while machine learning models can exhibit some capabilities to extrapolate in state space, they fail quickly as the amount of extrapolation required increases (as expected of any purely data-driven extrapolation method). We explore ways in which such failures can be mitigated. For instance, we show that a hybrid model which combines machine learning with a knowledge-based component can provide substantial improvements in extrapolation. We test our methods on the Ikeda map, the Lorenz system, and the Kuramoto-Sivashinsky system, under challenging scenarios (e.g., predicting future hysteretic transitions in dynamical behavior).

Finally, we modify a machine learning -based hybrid global climate model to forecast global weather patterns on the S2S time scale. Predicting on this time scale is crucial for many domains (e.g., land, water, and energy management), yet it remains a difficult period to obtain useful predictions for. We demonstrate that our model has useful skill in predicting a number of phenomenon including global precipitation anomalies, the El Nino Southern Oscillation and its related teleconnections, and various equatorial waves.

## Edgar Perez- April 5, 2024

Dissertation Title: **High Performance Nanophotonic Cavities and Interconnects for Optical Parametric Oscillators and Quantum Emitters**

Date and Time:** Friday, April 5, 10:00 am**

Location:** PSC 2136**

Dissertation Committee Chair:** Mohammad Hafezi and Kartik Srinivasan**

Committee:

Yanne Chemo

Efrain Rodriguez

Edo Waks

Xiyuan Lu

Abstract:

Integrated photonic devices like photonic crystals, microring resonators, and quantum emitters produce useful states of light, like solitons or single photons, through carefully engineered light-matter interactions. However, practical devices demand advanced integration techniques to meet the needs of cutting-edge technologies. High performance nanophotonic cavities and interconnects present opportunities to solve outstanding issues in the integration of nanophotonic devices. In this dissertation I develop three core tools required for the comprehensive integration of quantum emitters: wavelength-flexible excitation sources with enough pump power to drive down stream systems, photonic interconnects to spatially link the excitation sources to emitters, and cavities that can Purcell enhance quantum emitters without sacrificing other performance metrics.

To create wavelength-flexible excitation sources, high performance χ(3) microring Optical Parametric Oscillation (OPO) is realized in silicon nitride. Microring OPOs are nonlinear frequency conversion devices that can extend the range of a high quality on-chip (or off-chip) laser source to new wavelengths. However, parasitic effects normally limit the output power and conversion efficiency of χ(3) microring OPOs. This issue is resolved by using a microring geometry with very strongly normal dispersion, that uses multiple spatial mode families to satisfy the phase and frequency matching conditions. Our OPO achieves world-class performance with a conversion efficiency of up to 29% and an on-chip output power of over 18 mW.

To create photonic interconnects, Direct Laser Writing (DLW) is used to fabricate 3-dimensional (3D) nanophotonic devices that can couple light into and out of photonic chips. In particular, polymer microlenses of 20 µm diameter are fabricated on the facet of photonic chips that increase the tolerance of the chips to misaligned input fibers by a factor of approximately 4. DLW is also used to fabricate Polymer Nanowires (PNWs) with diameters smaller than 1 µm that can directly couple photons from quantum emitters into Gaussian-like optical modes. Comparing the same quantum emitter system before and after the fabrication of a PNW, a (3±0.7)× increase in the fiber-coupled collection efficiency is measured in the system with the PNW.

To refine the design of quantum emitter cavities, a toy model is used to understand the underlying mechanisms that shape the emission profiles of Circular Bragg Gratings (CBGs). Insights from the toy model are used to guide the Bayesian optimization of high performance CBG cavities suitable for coupling to single mode fibers. I also demonstrate cavity designs with Qs on the order of 105 that can be used in future experiments in cavity quantum electrodynamics or nonlinear optics. Finally, I show that these cavities can be optimized for extraction to a cladded PNW while producing a Purcell enhancement factor of 100 with efficient extraction into the fundamental PNW mode.

The tools developed in this dissertation can be used to integrate individual quantum emitter systems or to build more complex systems, like quantum networks, that require the integration of multiple quantum emitters with multiple photonic devices.

## Shiyi Sheng - April 3, 2024

Dissertation Title: **Quantum Computing and Machine Learning Approaches to Many-Body Physics**

Date and Time:** Wednesday, April 3, 10:00 AM**

Location:** PSC 3150**

Dissertation Committee Chair:** Professor Paulo F. Bedaque**

Committee:

Professor Thomas Cohen

Professor Zackaria Chacko

Professor Manuel Franco Sevilla

Professor Mohammad Hafezi

Abstract:

Lattice field theory provides a framework for which to explore properties of quantum field theories non-perturbatively. However for certain lattice calculations, for example when considering real-time dynamics or fermionic systems at finite density, sign problems occur which render those calculations intractable. One approach to solving the sign problem is to avoid it altogether by instead considering a simulation of the field theory on a quantum computer. For bosonic field theories, a procedure of qubitizing the bosonic fields is a necessary first step. The infinite-dimensional Hilbert space of the bosonic fields must be properly truncated as to encode those fields on a finite-dimensional Hilbert space spanned by the qubits on the quantum computer.

This thesis first discusses various strategies of making such a truncation. Ideally, the truncation yields a discrete spin system that contains a critical point in the same universality class as the untruncated field theory. That way, the physics of the original field theory is reproduced in the continuum limit of the truncated theory without needing to take a second limit of removing the truncation. Simulations of different models arising from various truncation strategies of the (1+1)-dimensional O(3) nonlinear sigma model are performed and different qubitizations for SU(2) gauge fields are considered and proposed. Due to a lack of an efficient method for solving many-body systems in more than one dimension, numerical simulations of these SU(2) qubitizations are unavailable.

The second half of the thesis explores the use of machine learning techniques in providing effective ways to solve quantum many-body problems. Neural network structures, such as feed-forward networks and restricted Boltzmann machines are universal approximators for continuous and discrete functions respectively. Therefore, they can be used as flexible wavefunction ansatze. Gradient descent algorithms can be applied to variationally search the general functional space spanned by neural-network-based ansatze for ground states of interacting, many-body systems. An ansatz is constructed explicitly for a system of indistinguishable bosons in one dimension and tested by comparing numerical results with analytic solutions of several exactly-solvable models. An extension of these neural-network ansatze to systems of identical bosons and fermions and discrete spin systems in higher dimensions would allow for concrete simulations of systems ranging from nuclei and qubitization models.

## Hong Nhung Nguyen - April 3, 2024

Dissertation Title: **Quantum Simulation of High-Energy Physics with Trapped Ions**

Date and Time:** Wednesday, April 3, 1:00 pm**

Location:** PSC 2136 and Zoom **

Dissertation Committee Chair:** Professor Alicia Kollár**

Committee:

Professor Norbert Linke, Advisor and Co-Chair

Professor Zohreh Davoudi

Professor Ian Spielman

Professor Xiaodi Wu

Abstract:

Trapped ions stand out as a leading platform for quantum computing due to their long coherence times, high-fidelity quantum gates, and the ability to precisely control individual qubits, enabling scalable and precise quantum computations. This dissertation reports advances in quantum computing with trapped ions, focusing on robust and high-fidelity entanglement generation, logical qubit encoding, and applications in quantum simulations of high-energy physics.

In particular, we report the implementation of a novel pulse optimization scheme for

achieving high-fidelity entangling gates in our setup. The scheme enables a balanced trade-

off between robustness to experimental drift, laser power, and gate duration, without the

need for expensive optimization. We also demonstrate the implementation of the Shor code with different code distances on our trapped-ion quantum computer, highlighting the fault-tolerant preparation of a logical qubit with high fidelity and showcasing the potential for reliable quantum computing.

Finally, we detail an experimental quantum simulation of the Schwinger model, a quantum electrodynamics theory in 1+1 dimensions, using two, four, and six qubits, demonstrating non-perturbative effects such as pair creation over extended periods of time. We study the gate requirement for two formulations of the model using a quantum simulation algorithm, considering the trade-offs between Hamiltonian term ordering, the number of time steps, and experimental errors. We employ a symmetry-protection protocol with random unitaries and a symmetry based post-selection technique to minimize errors. This work emphasizes the importance of the integrated approach between theory, algorithms, and experiments for efficient simulation of complex physical systems like lattice gauge theories.

## Elijah Willox - April 2, 2024

Dissertation Title: **The Search for Coincident Gamma-Ray Emission From Fast Radio Bursts with the HAWC Observatory**

Date and Time:** Tuesday, April 2, 3:00 PM**

Location:** PSC 3150**

Dissertation Committee Chair:** Jordan Goodman**

Committee:

Andrew Smith

Gregory Sullivan

Brian Clark

M. Coleman Miller

Abstract:

In 2007 a new class of radio transients was discovered, coming from outside of our galaxy with high fluence emitted in the radio band on millisecond timescales, emitting within an order of magnitude of the power of a gamma-ray burst or supernova. These fast radio bursts (FRBs) have since become the target of many searches across radio observatories and multiwavelength follow-up campaigns, but their origin remains unknown. In order to understand more about these fascinating events, a complete multiwavelength understanding in necessary to get a complete picture of what is creating such powerful bursts. The High Altitude Water Cherenkov (HAWC) observatory is a very-high-energy gamma-ray detector covering the range of 100 GeV to 300 TeV that is well suited to the detection of transient phenomena due its high live-time and wide field of view, and in particular for a follow-up search on FRBs to determine possible very high energy gamma-ray coincidences. The search for gamma-ray signals from FRBs consists of two searches: first is a persistent source search to identify if FRB emission ever comes from TeV gamma-ray emitting galaxies, and a transient search centered on the reported burst time and location. The results of the FRB search within the HAWC data sets the most constraining limits on the widest population ever searched in the VHE band.

## Maya Amouzegar - March 29, 2024

Dissertation Title: **Photon-Mediated Interactions in Lattices of Coplanar Waveguide Resonators**

Date and Time:** Friday, March 29, 1:30 PM**

Location:** PSC 3150**

Dissertation Committee Chair:** Professor Alicia Kollár**

Committee:

Professor Mohammad Hafezi (Dean’s Representative)

Professor Steven Rolston

Professor Trey Porto

Professor Sarah Eno

Abstract:

Circuit quantum electrodynamics (circuit QED) has become one of the main platforms for quantum simulation and computation. One of its notable advantages is its ability to facilitate the study of new regimes of light-matter interactions. This is achieved due to the native strong coupling between superconducting qubits and microwave resonators, and the ability to lithographically define a large variety of resonant microwave structures, for example, photonic crystals. Such geometries allow the implementation of novel forms of photon-mediated qubit-qubit interaction, cross-Kerr qubit-mediated interactions, and studies of many-body physics. In this dissertation, I will show how coplanar waveguide (CPW) lattices can be used to create engineered photon-mediated interactions between superconducting qubits. I will discuss the design and fabrication of a quasi one-dimensional lattice of CPW resonators with unconventional bands, such as gapped and ungapped flat bands. I will then present experimental data characterizing photon-mediated interactions between tunable transmon qubits and qubit-mediated non-linear photon-photon interactions in the said lattice. Our results indicate the realization of unconventional photon-photon interactions and qubit-qubit interactions, therefore, demonstrating the utility of this platform for probing novel interactions between qubits and photons. In future design iterations, one can extend the study of these interactions to two-dimensional flat and hyperbolic lattices.

## Eli Mizrachi - March 29, 2024

Dissertation Title: **Studies of Ionization Backgrounds in Noble Liquid Detectors For Dark Matter Searches**

Date and Time:** Friday, March 29, 1:00 pm**

Location:** PSC 2136**

Dissertation Committee Chair:** Professor Carter Hall **

Committee:

Research Professor Anwar Bhatti

Assistant Professor Brian Clark

Professor Sarah Penniston-Dorland

Dr. Jinkge Xu

Abstract:

Dark matter is believed to make up almost 85% of the total mass of the universe, yet its identity remains unclear. Weakly Interacting Massive Particles (WIMPs) have historically been a favored dark matter candidate, and dual-phase noble liquid time projection chambers (TPCs) have set the strongest interaction limits to date on WIMPs with a mass greater than several GeV. However, because no definitive interactions have been observed, the parameter space for conventional WIMPs is highly constrained. This has sparked greater interest in new sub-GeV dark matter models. At this mass scale, dark matter interactions with xenon or argon target media may still produce detectable signals at or near the single electron limit. However, these signals are currently obscured by delayed ionization backgrounds (“electron-trains”) which persist for seconds after an ionization event occurs. Electron-trains have been observed in many different experiments and exhibit similar characteristics, but their cause is only partially understood.

This work examines the nature of electron-trains in various contexts, as well as possible strategies to mitigate them. First, a characterization of electron-trains in the LZ experiment is presented, including new evidence of a dependence on detector conditions. The characterization also informed the development of an electron-train veto for LZ’s first WIMP search, which set world-leading limits on the spin-independent and spin-dependent WIMP-nucleon cross-sections for medium and high-mass WIMPs.

Next, to complement the analysis of LZ data, hardware upgrades were performed in XeNu, a small xenon TPC at Lawrence Livermore National Lab. These included replacing plastics with low-outgassing metal and machinable ceramic components, as well as a replacement of XeNu’s photomultiplier tube array with silicon photomultipliers. The resulting reduction in the intensity of electron-trains and better position resolution from the respective upgrades will improve future studies of low energy interactions and phenomena. Concurrent with this work, XeNu was used to perform a nuclear recoil calibration and a search for the Migdal effect, the latter of which can substantially enhance an experiment's low-mass dark matter sensitivity.

Finally, the development of CoHerent Ionization Limits in Liquid Argon and Xenon (CHILLAX), is reported. CHILLAX is a new xenon-doped, dual-phase argon test stand that has the potential to have a higher sensitivity to low-mass dark matter interactions and lower backgrounds than current liquid xenon TPCs. The system is designed to handle high (percent level) xenon concentrations in liquid argon that can enable a range of ionization signal production and collection benefits. CHILLAX demonstrated the feasibility of such concepts by achieving a world record xenon doping concentration with stable operation.

## Robert Dalka - March 11, 2024

Dissertation Title: **Developing Methods and Theories for Modeling Student Leadership Development and Student’s Experiences of Academic Support**

Date and Time:** Monday, March 11, 1:00 pm**

Location:** Atlantic Building 3332 and Zoom**

Dissertation Committee Chair:** Dr. Chandra Turpen **

Committee:

Dr. Justyna P. Zwolak

Dr. Diana Sachmpazidi

Dr. Andrew Elby

Dr. Michelle Girvan

Dr. Christopher Palmer

Abstract:

This dissertation brings together two research strands that study: (a) the ways in which physics and STEM students contribute to growing capacity for institutional change within collaborative teams and (b) the support structures of graduate programs through an innovative methodology grounded in network science.

The first research strand is explored within two different team environments, one of a student-centric interinstitutional team and a second of departmental change teams. Across both of these contexts, I identify how by engaging in an interaction-based agency, students are able to jointly define their own roles and the projects they pursue. In comparing across these contexts, we identify how students navigate different leadership structures and how this can support or limit student contributions in these teams. A central contribution of this work is a model for cultivating capacity for change through shared leadership and relational agency. This model captures how capacity can be built in different domains tied to the activity systems of the work. I show how this model can help practitioners and facilitators better partner with students as well as how researchers can use this model to capture how students contribute to the work of the team.

The second research strand focuses on developing and applying an innovative methodology for network analysis of Likert-style surveys. This methodology generates a meaningful network based on survey item response similarity. I show how researchers can use modular analysis of the network to identify larger themes built from the connections of particular aspects. Additionally, I apply this methodology to provide a unique interpretation of responses to the Aspects of Student Experience Scale instrument for well-defined demographic groups to show how thematic clusters identified in the full data set re-emerge or change for different groups of respondents. These results are important for practitioners who seek to make targeted changes to their physics graduate programs in hopes of seeing particular benefits for particular groups.

This dissertation opens up lines for future work within both strands. The model for building capacity for change draws attention to the mediating processes that emerge on a team and in students’ interactions with others. This model can be developed further to include additional constructs and leadership structures, as well as explore the relevance to other academic contexts. For quantitative researchers, the network analysis for Likert-style surveys methodology is widely applicable and provides a new way to investigate the wide range of phenomena assessed by Likert-style surveys.

## Evan Dowling - March 5, 2024

Dissertation Title: **Feedback experiments using entangled photons for polarization control in future quantum networks**

Date and Time:** Tuesday, March 5, 9:00 AM**

Location:** ERF (IREAP) 1207**

Dissertation Committee Chair:** Professor Thomas E. Murphy **

Committee:

Professor Rajarshi Roy, Co-Advisor

Professor Julius Goldhar

Professor Yanne Chembo

Professor Wendell T. Hill

Abstract:

Control of the measurement frames that project on polarization entangled photons is an important experimental task for near term fiber-based quantum networks. Because of the changing birefringence in optical fiber arising from temperature fluctuations or external vibrations, the polarization projection direction at the end of a fiber channel is unpredictable and varies with time. This polarization drift can cause errors in quantum information protocols, like quantum key distribution, that rely on the alignment of measurement bases between users sharing a quantum state. Polarization control within fiber is typically accomplished using feedback measurements from classical power alignment signals, multiplexed in time or wavelength with the quantum signal that coexist in the same fiber. This thesis explores ways to use only measurements on the entangled photons for polarization control and perform entanglement measures without multiplexing alignment signals. This approach is experimentally less complex and can reduce the noise within the quantum channel arising from the alignment signals. In the first part of this dissertation, we study how to use distributed measurements on polarization entangled photons for polarization drift correction in a 7.1 km deployed fiber between the University of Maryland and the Laboratory of Telecommunication Sciences for two individuals sharing a near maximally entangled Bell state, $\hat \rho = |\Psi^-\rangle\langle\Psi^-|$. In the second part of the dissertation, we examine how to use feedback measurements to maximize the violation of a Bell's inequality used as an entanglement measure. Both polarization drift correction and the maximization of a Bell's inequality violation use iterative optimization algorithms to actuate upstream polarization controllers. In the Bell's inequality investigation, three numerical methods: Bayesian optimization, Nelder-Mead simplex optimization, and stochastic gradient descent are implemented and compared against each other. For complete polarization control and Bell's inequality violation experiments, we developed a polarization and time multiplexed detection system that reduced the number of photon detectors needed and mitigates the demand on the coincidence counting electronics for real-time feedback and control.

## Mingshu Zhao - March 1, 2024

Dissertation Title: **Turbulence and superfluidity in atomic Bose-Einstein condensates**

Date and Time:** Friday, March 1, 12:00 PM**

Location:** PSC 3150**

Dissertation Committee Chair:** Daniel Lathrop**

Committee:

Ian Spielman

Nathan Schine

Thomas Antonsen

Johan Larsson (Dean’s Rep)

Abstract:

In this dissertation, I investigate superfluid properties of atomic Bose-Einstein condensates (BECs) including laminar flow experiments that probe the superfluid density and turbulent flow experiments that explore connections to Kolmogorov theory. In this presentations, I focus on a novel technique to measure the BECs velocity field and apply it to turbulence. While turbulence in classical fluids has been extensively studied, there are many open questions in atomic superfluids, particularly regarding the existence of an inertial scale and the applicability of Kolmogorov scaling laws. I developed a velocimetry method, similar to particle image velocimetry using spinor impurities as tracers to measure the velocity field in a spatially resolved way. This enables the first observation of velocity structure functions (VSFs) in BECs, turbulent or otherwise. The observed VSFs reveal that superfluid turbulence in BECs conforms to Kolmogorov theory, including the so-called intermittency evident in both higher-order VSFs and the distribution of velocity increments.

## Henry Elder - January 17, 2024

Dissertation Title: **Nonlinear Propagation of Orbital Angular Momentum Light in Turbulence and Fiber**

Date and Time:** Wednesday, January 17, 3:00 PM**

Location:** AVW 2460**

Dissertation Committee Chair:** Phillip Sprangle**

Committee:

Thomas Murphy

Howard Milchberg

Thomas Antonsen

Wendel Hill (Dean’s Rep)

Abstract:

Light that carries orbital angular momentum (OAM), also referred to as optical vortices or twisted light, is characterized by a helical or twisted wavefront ∝exp[*imφ*]. In contrast to spin angular momentum (SAM), where photons are limited to two states, OAM allows for, in principle, an infinite set of spatially orthogonal states. OAM-carrying light has found applications ranging from quantum key distribution in free space and guided-wave communication systems, particle trapping and optical tweezers, nanoscopy, and remote sensing. Understanding how OAM light propagates through complex environments, and how to efficiently generate particular OAM states, is critical for any such application.

In the first part of this dissertation, we describe how OAM light propagates through a turbulent atmosphere. We build analytic models which describe (1) the OAM mode mixing caused by turbulence, (2) the evolution of short, high-power OAM pulses undergoing the effects of self-phase modulation (SPM) and group velocity dispersion (GVD), and (3) the evolution of high-power Gaussian pulses including SPM, GVD, and turbulence. The models are compared to experimental data and nonlinear, turbulent pulse propagation simulation programs, which we have made freely available. We also explore how self-focusing can minimize certain deleterious effects of turbulence for OAM light.

The second part of this dissertation considers nonlinear effects of OAM light propagating in azimuthally symmetric waveguides. Such waveguides have so-called spin-orbit (SO) modes, which are quantized based on their total angular momentum (TAM). We develop a generalized theory of four wave mixing-based parametric amplification of SO modes and show that these processes conserve TAM, but under certain circumstances can be taken to conserve SAM and OAM independently. Our theory is validated against a nonlinear multimode beam propagation simulation program which we developed and, again, have made freely available.

## Huan-Kuang Wu - January 8, 2024

Dissertation Title: **Aspects of Unconventional Transport and Quasiparticle in Condensed Matter Systems**

Date and Time:** Monday, January 8, 1:00pm**

Location:** ATL 4402**

Dissertation Committee Chair:** Jay Sau**

Committee:

Steven Anlage

Christopher Jarzynski

Johnpierre Paglione

Victor Yakovenko

Abstract:

The Boltzmann transport equation (BTE) is a successful framework for describing transport in condensed matter systems. The assumption of BTE is the localized energy excitations, or quasiparticles, and it is applicable to length scales above the mean free path of the quasiparticles. In this dissertation defense, I will cover two example systems where the assumptions of BTE fail. One is a new proposed system for Majorana zero mode whose topological phase is controlled by the phases of three s-wave superconductors. When the time reversal symmetry is restored, it can be tuned to a class DIII topological superconductor, which exhibits helical Majorana edge states. The second system I will talk about is the Josephson junction chain in the insulating regime, whose high-frequency plasmon remains coherent while the low energy excitations are Anderson-localized due to charge disorder.

## Sara Nabili - January 4, 2024

Dissertation Title: **Search for boosted semi-visible jets in all hadronic final states with the CMS experiment at CERN**

Date and Time:** Thursday, January 4, 10:30 am**

Location:** PSC 3150**

Dissertation Committee Chair:** Sarah Eno**

Committee:

Thomas Cohen

Christopher Palmer

Peter Shawhan

Mohamad Al-Sheikhly

Abstract:

This dissertation represents the search for the dark sector beyond the standard model using the Compact Muon Solenoid experiment simulated Monte Carlo data of the Large Hadron Collider at CERN. The search is focused on the strongly coupled Hidden Valley models that couple with the standard model via a leptophobic (fully hadronic) Z′ mediator. The final state of resonant production consists of one large jet composed of both visible and invisible particles. This search focuses on the lower mediator mass range (mZ′ ≤ 550 GeV) with the boosted topology that recoils against the initial state radiation (ISR) jet such that its decay products are contained within a single large-diameter “semi-visible” jet. The main parameters of our model are the mediator mass, the mass of the dark mesons, and the fraction of invisible stable particles. In the event of no discovery, the exclusion limits for mediator mass of 275 to 550 GeV are expected.