Physics and Astronomy

Permanent URI for this collectionhttps://uwspace.uwaterloo.ca/handle/10012/9949

This is the collection for the University of Waterloo's Department of Physics and Astronomy.

Research outputs are organized by type (eg. Master Thesis, Article, Conference Paper).

Waterloo faculty, students, and staff can contact us or visit the UWSpace guide to learn more about depositing their research.

Browse

Now showing 1 - 20 of 852

Field-Theoretic Simulations of Binary Blends of Complementary Diblock Copolymers
(University of Waterloo, 2026-01-21) Willis, James
The phase behavior of binary blends of AB diblock copolymers of compositions f and 1 − f is examined using field-theoretic simulations. Highly asymmetric compositions (i.e., f ≈ 0) behave like homopolymer blends macrophase separating into coexisting A- and B- rich phases as the segregation is increased, whereas more symmetric diblocks (i.e., f ≈ 0.5) microphase separate into an ordered lamellar phase. In self-consistent field theory, these behaviors are separated by a Lifshitz critical point at f = 0.2113. However, its lower critical dimension is believed to be four, which implies that the Lifshitz point should be destroyed by fluctuations. Consistent with this, it is found to transform into a tricritical point. Furthermore, the highly swollen lamellar phase near the mean-field Lifshitz point disorders into a bicontinuous microemulsion (BμE), consisting of large, interpenetrating A- and B-rich microdomains. A BμE has been previously reported in ternary blends of AB diblock copolymers with its parent A- and B-type homopolymers, but in that system the homopolymers have a tendency to macrophase separate. Our alternative system for creating BμE is free of this macrophase separation.
Progress towards FrAg molecules for nuclear CP violation
(University of Waterloo, 2026-01-21) Lagno, Andrew
Ultracold francium silver is a promising experiment that has the potential to set a new upper bound on nucleon electric dipole moments. In working towards making francium sil- ver molecules, our short term goal is to develop the knowledge and ability to evaporatively cool francium and silver. This entails finding the scattering properties of francium and silver using photoassociation spectroscopy and developing the ability to sub-Doppler cool silver. In this thesis, I talk about my work towards this goal, including attempting pho- toassociation at TRIUMF during francium beam time, work at the University of Chicago towards photoassociation and gray molasses in silver. Even though these efforts weren’t successful, the next steps are clear. Additionally, I talk about what I’ve accomplished at Waterloo when I’m not working on the francium silver project. This includes working to- wards better control over and stabilization of lasers and experimental optics and beginning optimization of the Cs Zeeman slower.
A proof-technique-independent framework for detector imperfections in QKD
(University of Waterloo, 2026-01-14) Nahar, Shlok
The security of Quantum Key Distribution (QKD) protocols is theoretically established using idealised device models. However, the physical implementations upon which practical security relies inevitably deviate from these ideals. This thesis develops a rigorous and versatile framework to address a subclass of such deviations: detector imperfections. This framework, termed ’noise channels’, is independent of security proof technique. This approach recasts imperfections as a quantum channel preceding an idealised measurement process. By granting the eavesdropper control over this channel, the security analysis is simplified to an ideal scenario, with the effects of the imperfections mathematically contained within a well-defined parameter. The utility and versatility of the framework are demonstrated through applying it to the postselection technique, and for phase error estimation. The application to phase error estimation is an improvement over past analyses which either assumed qubit detection setups, IID attacks, or required hardware modifications. We observe a remarkably high tolerance to imperfections when using the postselection technique. Finally, we extend the framework to address cross-round correlations, providing a methodology to prove security against detector memory effects such as afterpulsing and dead times. This work thus establishes a structured and powerful toolkit for analysing detector imperfections in practical QKD systems, unifying their treatment across different security proof techniques and advancing the development of robust implementation security.
Systems and Control Protocols for Neutral-Atom-Array Quantum Processors
(University of Waterloo, 2026-01-12) Zhutov, Artem
Neutral atom arrays are a leading platform for programmable quantum processors, offering individual qubit addressability, long-lived hyperfine ground states, and strong Rydberg interactions. Recent progress has demonstrated coherent control over thousands of atoms. However, achieving scalable control requires precise mitigation of environmental and hardware imperfections that degrade gate performance. This thesis presents an integrated neutral-atom array platform built from the ground up that incorporates quantum sensing directly into the processor. Each atom functions both as a qubit and a local magnetometer. We design, build, and characterize from first principles three subsystems: 1) a microwave control system for driving hyperfine transitions in ground-state rubidium atoms; 2) a Raman laser system for site-selective single-qubit gates; and 3) a Rydberg laser system with quantum optimal control for robust two-qubit gates. This work provides a universal gate set and quantifies which error sources limit performance. First, we develop an in-situ magnetic field imaging technique using the atom array as a quantum sensor. Through site-resolved Ramsey spectroscopy, we image magnetic fields across a 260 μm × 160 μm region with 3 μm spatial resolution. We then apply computed corrections that compensate for the bias magnetic fields, producing uniform global microwave single-qubit rotations. Second, we introduce a hardware-aware simulation framework to evaluate Raman laser systems for hyperfine qubit manipulation. Simulations predict a single-qubit gate infidelity of 4.4 × 10⁻⁴ using BB1 composite pulses to mitigate thermal motion errors. We validate the Raman laser system by building and characterizing its phase noise. Third, we develop a Rydberg laser system for high-fidelity entangling gates. We apply linear response theory to map laser phase noise to single-atom Rydberg excitation fidelity. We then demonstrate fast phase-noise engineering by optimizing laser servo parameters. We employ hardware-aware quantum optimal control to design both Rydberg excitation and two-qubit gate pulses with built-in robustness against physical and control parameter fluctuations, outperforming analytical benchmarks. This integrated platform demonstrates high-fidelity universal control of neutral-atom registers with hundreds of qubits. By systematically addressing environmental inhomogeneities through integrated sensing and hardware-aware control design, this work provides a validated path for scaling quantum processors while maintaining gate fidelity.
Micro-Calorimeter X-Ray Spectroscopy of Galaxy Clusters using the XRISM X-Ray Observatory
(University of Waterloo, 2026-01-07) Meunier, Julian
Galaxy clusters are some of the most massive objects in the universe, yet the evolution of these objects, particularly with regards to the heating and cooling of the intracluster medium, still has many unknowns. With the launch of the new X-ray imaging and spectroscopy mission, XRISM, galaxy clusters can now be studied with higher precision. This data can reveal a plethora of new information about the dynamics of the atmospheres of these clusters, which can be used to develop a better understanding of the evolution of galaxy clusters. In this thesis, I present analysis of X-ray spectroscopic data of the Perseus, Hydra A, and Cygnus A clusters obtained with XRISM Resolve. We apply spectral modeling techniques to the data to derive gas temperature, metal abundance, velocity dispersion, and bulk velocity to develop a further understanding of the dynamics of the intracluster medium in these galaxy clusters. I present spectral analysis of the five XRISM Resolve pointings of the Perseus cluster, binned into a radial profile. We measure radial profiles of temperature, metal abundances, velocity dispersion, and bulk velocities up to $\sim250$ kpc from the cluster center with single temperature models. While the temperature and abundance profiles are consistent with typical cool core clusters, the velocity dispersions suggest a relatively quiescent state for the intracluster medium, with only up to $\sim175$ km s$^{-1}$ dispersion in the central $\sim 60$ kpc. We interpret this velocity dispersion to be due to turbulence. The dispersion profile suggests that the jets and bubbles may be driving turbulence in the core, but also that the core may be under-heated. We find evidence for a second temperature component in the inner $\sim60$ kpc, that is cooler ($\sim2-2.4$ keV) and has a significantly higher velocity dispersion of $\sim300-400$ km s$^{-1}$. We interpret the cooler component to be sloshing gas from a merger or gas being churned by the jets and bubbles. I present spectral analysis of the full-FOV XRISM Resolve data of the Hydra A cluster, measuring temperature, velocity dispersion, and bulk velocity with a single temperature model. Despite Hydra A's high jet power, we find a remarkably low velocity dispersion of $164^{+10}_{-10}$ km s$^{-1}$, and a small velocity offset of $-37^{+20}_{-17}$ km s$^{-1}$ between the gas and the central galaxy. We interpret this velocity dispersion to be due to turbulence, which may suggest that the relationship between the jet power and the velocity structure of the intracluster medium is less significant than expected. However, further analysis of the outer regions of the cluster is needed to fully understand the dynamics of the gas in Hydra A. Finally, I present spectral analysis of the full-FOV XRISM Resolve data of the Cygnus A cluster, measuring temperature, metal abundances, velocity dispersion, and bulk velocity with a single temperature model. We measure a relatively higher velocity dispersion of $272^{+14}_{-13}$ km s$^{-1}$ with a bulk velocity of $101\pm26$ km s$^{-1}$ with respect to the central galaxy. These velocities likely reflect a combination of both turbulence in the gas and motion of the cocoon shock. We find some evidence for a second temperature component, that is cooler ($2.06^{+0.43}_{-0.20}$ keV) and broader ($333^{+127}_{-129}$ km s$^{-1}$), with a bulk velocity of $-311\pm118$ km s$^{-1}$. The second component may be necessary for fitting asymmetric features in the prominent emission lines of the spectrum. However, the large uncertainties of the model fit along with other uncertainties suggest that this component may not be significant.
Studies on the Characterization and Measurement Optimization of Superconducting Microwave Resonators
(University of Waterloo, 2025-12-22) Chen, Mengyang
This work presents a study aimed at improving the accuracy and efficiency of low-temperature loss-tangent measurements in superconducting resonators. Measurements were performed on aluminum and niobium devices, where a plateau in the internal quality factor at the single-photon level was observed, consistent with prior reports. By truncating the acquired resonance data, it was shown that the loss tangent experienced no systematic shift even when only four points spanned the resonance linewidth; the resulting increase in uncertainty was attributed to reduced effective averaging. Based on this result, an optimized data acquisition scheme was developed, reducing measurement time by a factor of four while maintaining approximately 1% accuracy. Further improvements were achieved through the use of a lower-noise HEMT amplifier, which reduced measurement noise and decreased acquisition time to 60% of the original. Additional circuit modifications showed that improved infrared shielding reduced total resonator loss, while the nonlinear behavior at high RF power was attributed to intrinsic device nonlinearity rather than external circuitry. Finally, crossover temperature measurements showed agreement with BCS theory at high temperatures, although its accuracy could be limited by not fully saturated TLS-loss, indicating the need for improved device designs.
Revisiting the ‘Lensing is Low’ Problem With UNIONS
(University of Waterloo, 2025-12-22) Campbell, Martine
In this thesis, we present new measurements of the galaxy–galaxy lensing (GGL) signal around Baryon Oscillation Spectroscopic Survey (BOSS) CMASS galaxies using background sources from the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS). With an overlap of approximately 2650 square degrees between CMASS lenses and background source galaxies—the largest to date—we obtain precise large-scale GGL measurements. With these new measurements, we revisit the so-called ‘lensing is low’ problem, wherein galaxy–halo connection models calibrated on clustering data over-predict the GGL signal by 20–40% under cosmic microwave background (CMB)-based cosmologies. We model the galaxy–halo connection using a halo occupation distribution (HOD), and perform joint fits to both GGL and clustering signals across a wide range of scales, as well as a clustering-only fit. Similar to previous work, we find a lensing–is–low effect in the CMASS sample, although our GGL and clustering predictions are less inconsistent with each other. The best joint fits are achieved by lowering the amplitude of the matter power spectrum relative to Planck 2018, driven by the precision of our large-scale GGL measurements. Once a lower matter power spectrum amplitude is adopted, feedback is the only HOD extension that further improves the joint fit. Our feedback model redistributes matter within a halo, modifying the halo–matter cross–power spectrum. Overall, we find that two models describe our observables equally well: one where HOD and cosmological parameters are free, and one where HOD, cosmological, and feedback parameters are free. Importantly, we emphasize the role of large scales in driving the lensing–is–low effect, shifting the narrative away from a purely small-scale issue.
A Neural-network-based Solver for the Three Dimensional Shape of Vesicle Membranes
(University of Waterloo, 2025-12-17) Rohanizadegan, Yousef
A neural-network-based numerical solver is developed for computing three-dimensional (3D) equilibrium shapes of deformable biomembranes, specifically phospholipid vesicles modeled by Helfrich's curvature elasticity theory. The solver represents vesicle morphology using a phase-field formulation, in which a scalar field distinguishes the interior and exterior of the vesicle through a diffuse interface. The phase field is parameterized by a compact feedforward neural network, and the equilibrium shape is obtained by direct minimization of the Helfrich bending energy subject to global surface-area and volume constraints, enforced via Lagrange multipliers. Automatic differentiation is used to evaluate all spatial derivatives, thereby avoiding finite-difference truncation errors and explicit surface discretization. This framework produces both axisymmetric and fully non-axisymmetric vesicle shapes without imposing symmetry assumptions. Canonical free-space branches, namely prolates, oblates, and stomatocytes, are reproduced, and the classical bending-energy–reduced-volume diagram is recovered in close quantitative agreement with established results in the literature. In addition, a phase-field expression for the bilayer area-difference constraint is derived and incorporated into the solver, providing a numerical setting for the computation of non-axisymmetric equilibrium morphologies in free space. A major contribution of this work is a systematic investigation of vesicle morphology under confinement. Vesicles are studied within a range of hard-wall geometries, including cylindrical (tube), slit, spherical, and cubic confinements. By varying confinement size and reduced volume, the solver captures a rich spectrum of deformations, including biaxial squeezed states, bent prolates, squeezed stomatocytes, and cubic and clam-like morphologies. Stability diagrams, bending-energy curves, and phase diagrams are constructed for each confinement, revealing both discontinuous (first-order) and continuous (second-order) shape transitions, as well as hysteresis and metastable branches. These results extend existing confinement studies by providing fully three-dimensional, non-axisymmetric solutions across multiple geometries and different regimes of confinement (free space to weak to strong) within a unified computational framework. Overall, this work establishes a versatile and scalable neural-network-based phase-field approach for vesicle shape modeling. By unifying classical membrane elasticity theory with modern machine-learning optimization, the solver facilitates a structured exploration of equilibrium morphologies, phase transitions, and confinement effects beyond the reach of traditional axisymmetric or surface-discretization methods. The framework provides a foundation for future extensions to more complex membrane models, dynamic processes, and biologically relevant geometries in soft-matter and biophysical systems.
Quantum Fields in Curved Spacetimes: From Detector Entanglement to Black Hole Thermodynamics
(University of Waterloo, 2025-12-05) Bhattacharya, Dyuman
This thesis presents two independent investigations into quantum field theory in curved spacetime. The first concerns relativistic quantum information, with a focus on entanglement harvesting and detector-based probes of quantum fields in curved spacetimes. The second addresses semiclassical aspects of black hole thermodynamics in AdS braneworld settings, incorporating the backreaction of quantum fields to all orders of perturbation theory, and extending previous studies of quantum black holes to include both charge and spin. In Part I, we study the entanglement of quantum fields in curved spacetime, using localized particle detectors interacting with a scalar field. We analyze scenarios involving both flat and curved backgrounds, including gravitational shock waves, the BTZ black hole, and general dimensional anti–de Sitter and de Sitter spacetimes. For the case of initially entangled detectors, we find that interactions with the field can lead to either degradation or amplification of entanglement, depending on the initial state and spacetime geometry. We further derive exact expressions for density matrix elements, at the lowest perturbative order, in the form of infinite analytical series, for detectors on static worldlines in various spacetimes. The transition rate of an in-falling detector in the BTZ black hole spacetime is also derived as an infinite series. These analytic results allow for exact evaluation of quantities, namely the entanglement measures of concurrence and negativity, which are typically computed numerically. In addition, we provide a new example of the ability of detectors to distinguish topologically distinct spacetimes which are locally identical outside of horizons, focusing on the ℝP² and Swedish geons built from the BTZ spacetime. Our results show that localized measurements are sensitive not only to curvature but also to topological features of the underlying geometry. Part II is concerned with the construction and thermodynamic analysis of quantum-corrected black holes in a doubly holographic braneworld model. We obtain a charged and rotating solution localized on an AdS₃ brane embedded in an AdS₄ bulk, incorporating the full backreaction from conformal fields to all orders of perturbation theory. We compute the thermodynamic properties of these black holes, and examine their behavior in extended thermodynamic phase space where the cosmological constant is a variable. We find that the inclusion of charge or spin removes re-entrant phase transitions present in the neutral-static case, and that the critical exponents of these objects match those predicted by classical mean-field theory. The re-entrant phase transitions of the neutral-static quantum black hole has critical exponents which differ from the mean-field values
Control and Characterization of the Central Spin System
(University of Waterloo, 2025-11-18) Chen, Jiahui
Precise, coherent, robust quantum control and characterization of quantum systems play important roles in the development of applications of quantum technologies. In particular, advancing the quality of control requires precise characterization, which, in turn, depends on the quality of control. In the first part of the thesis, we introduce a general framework for designing efficient, precise, and robust quantum control strategies using effective Hamiltonian engineering. The methods enable designs that are robust to systematic control errors and variations in the Hamiltonian. The efficiency benefit of achieving control at zeroth order in the Magnus expansion is highlighted. Design tools, such as methods that identify the space of achievable effective Hamiltonians at each order from the Magnus expansion, are introduced. Objective functions for engineering arbitrary effective Hamiltonians are provided and can be used by numerical optimizers for control sequence design. The second part of the thesis explores the characterization of general noise models based on experiments on a central spin system. The noise is probed through stimulated echo experiments, multi-dimensional correlation spectroscopy, and multi-quantum experiments to characterize system/environment correlation and environmental memory effects. Combined with Bayesian inference, these experiments provide quantitative measures of correlation growth, environmental mixing, and deviations from stochastic noise models. Measures that influence the choice of control schemes include non-Gaussianity, non-stationarity, and non-Markovianity. The multi-quantum experiments can also reveal an extended environment and show how the environmental mixing propagates quantum information throughout the environment.
Machine learning for quantum sensing
(University of Waterloo, 2025-11-18) MacLellan, Benjamin
Precisely measuring the natural world around us underpins new scientific discoveries and technological innovation. Quantum sensors, which harness quantum effects such as superposition and entanglement, represent the frontier of precision measurement and are capable of surpassing conventional limits on measurement sensitivity, precision, and resolution. Such instruments have myriad applications in, e.g., astronomical observations, biological imaging, material science, and geophysical surveys, among many others, and provide new opportunities in the search for new physics, including in gravitational wave detection, searches for dark matter and physics beyond the Standard Model, and probing many-body phenomena such as superconductivity. In recent years, artificial intelligence and machine learning have emerged as a promising paradigm for quantum physics, providing computational tools to extract insights from large scientific datasets, discover structure in complex models, and automate scientific processes. In this thesis, we present novel numerical techniques for the study, design, and implementation of quantum sensing protocols by leveraging machine learning and optimization techniques. First, we propose and demonstrate an end-to-end variational quantum sensing framework, in which parameterized quantum circuits and neural networks form adaptive, trainable ansätze for the quantum dynamics and estimator, respectively. Extending this machine-learning design perspective, we study quantum-enhanced very-long baseline imaging, which uses entanglement distributed through a quantum network to increase the achievable angular resolution of optical telescope arrays. We develop differentiable simulation and optimization techniques to identify optimal resource states and measurements in realistic regimes. Next, we propose and demonstrate a simulation-based inference technique for quantum sensing protocols, which maps observed data to estimated values without the need for explicit likelihood functions. Finally, we investigate the generation of quantum graph states using hybrid photon-emitter platforms, and present a framework for optimizing the generation of large, noise-robust entangled probe states for quantum sensing protocols.
Structured Wavefunctions for Precision Quantum Metrology
(University of Waterloo, 2025-10-20) Kapahi, Connor
In this thesis, several projects from biomedical optics measurements of the retina to precision gravimetric designs with neutron interferometers are presented, united by the common theme of applied quantum information techniques to develop next-generation precision metrological instruments. In particular, we introduce theoretical tools for analyzing neutron optical experiments and highlight parallels between neutron and light optics. These tools are applied to a new neutron prism design, demonstrating significantly higher transmission than traditional designs. Designs for devices applying these techniques, including a neutron Fresnel prism, spectrum analyzer, and spin collimator, are discussed. Potential advantages in neutron flux and spectrum resolution are quantified for these designs. The isometry between neutron spin and the polarization of light is exploited to validate the neutron spin collimator experimentally. Applications of structured states of light and experiments applying spin-orbit states to create patterns in the human visual system are described. Results demonstrate an increase in the perceived extent of these patterns, from 3° for Haidinger's Brush to 10° for a spin-orbit state. Work demonstrating a new method of generating a lattice of spin-orbit states in light is applied to neutron optics. Throughout the preceding experiments, methods of modeling neutron optics experiments with light and a semi-classical path-integral approximation have been developed. These methods are then applied to design an experiment that measures the gravitational constant using a neutron interferometer. A three-phase grating moiré interferometer (3-PGMI) design is first tested with infrared light. The deflection caused by a wafer sample is measured with the 3-PGMI and found to match direct measurements. The path-integral model is then applied to determine the uncertainty in the gravitational constant that can be achieved with a near-term measurement with a neutron 3-PGMI. An experiment to measure the gravitational constant is described, with an uncertainty budget, resulting in a measurement to 150 ppm. Potential corrections to previous experiments measuring the gravitational constant, due to lunar gravitational forces are quantified. Future applications of the tools and techniques described in this thesis are then discussed.
Translocation-Induced Shape Transitions in Vesicles using a Neural Network-Based Solver for the Helfrich Model
(University of Waterloo, 2025-10-16) Choheili, Soorna
This thesis discusses our efforts to model the translocation of an enclosed lipid bilayer membrane (vesicle) through a circular pore. First, we will discuss the study of lipid bilayers, introduce the standard model for representing the energy of a membrane, and provide background on the many theoretical and experimental efforts in the field of membrane modeling. We then review the relevant theoretical and practical considerations regarding the simulation of vesicles and translocation, and implement a neural network-based solver for a scalar phase field. We will proceed to detail our efforts to characterize each constraint imposed on the vesicle throughout the translocation and model them within the context of the solver. Following this, we provide a variety of visual snapshots of the translocation process showing different classes of translocation and the resulting behavior of each. Equally important is the quantitative analysis of the energy landscape traversed by the vesicle, where we chart the induced bending energy imposed upon it by the narrow pore. Additionally, we introduce two types of external effects that modify the energy landscape and illustrate their impact on the total vesicle energy throughout its passage. We then map the results out onto the relevant parameter space to give a picture of where the thresholds between qualitatively different behaviors lie. As a final demonstration of our model’s capabilities, we estimate the time of passage of the vesicle by modeling it diffusively using the energy landscape to calculate the effect of narrower pores on the time to translocate. This model successfully demonstrates explicit phase transitions between stable vesicle states and maps out the energy landscape throughout the unstable regime under the effects of translocation.
The Dependence of Halo Mass on Galaxy Size at Fixed Stellar Mass and Colour using Galaxy-Galaxy Lensing
(University of Waterloo, 2025-10-16) Patel, Darshak
To advance our holistic understanding of galaxy formation physics, we must examine the relationship between baryonic matter and dark matter (DM) within the universe. In this thesis, we investigate the correlation between dark matter halo mass and galaxy size at fixed stellar mass and colour. Using galaxy-galaxy lensing, we measure excess surface density (ESD) profiles for red, early-type galaxies from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging survey, with shape measurements from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS). We model the lensing signal using a conditional stellar mass function (CSMF) halo occupation distribution (HOD) calibrated on the AbacusSummit simulations and adopt a power-law relation between halo mass and galaxy size at fixed stellar mass: Mh ∝ r^ηeff . To fit the HOD parameters to the observationally measured ESD vectors, we train and utilize neural-network emulators, a form of non-linear interpolators. The analysis performed in this work follows a two-step process. First, we fit the HOD parameters to the ESD vectors corresponding to three stellar mass bins, not split further into two size bins. We freeze the best-fit HOD parameters and generate the corresponding best-fit mock catalogue. Using this best-fit mock catalogue, we apply our halo mass-size model and fit to the size-split observational ESD measurements. For central galaxies with stellar mass 10.5 ≤ log10(M⋆/M⊙) < 11.2, we find no significant correlation. At higher stellar masses, 11.2 ≤ log10(M⋆/M⊙) < 11.78, we detect a positive correlation with ηcent = 0.51 ± 0.14. A linear fit as a function of the logarithm of stellar mass yields a slope of sηcent = 0.66 ± 0.28, indicating that the halo mass-size correlation strengthens with increasing stellar mass. For satellite galaxies, we observe a negative correlation at low and intermediate stellar masses for the host halo mass-galaxy size relation of ηsat = −0.19 ± 0.05 and ηsat = −0.09 ± 0.05, respectively. The correlation is consistent with zero within the stellar mass range of 11.2 ≤ log10(M⋆/M⊙) < 11.78.
From Spin Vorticity Models to Spin Liquids on the Octochlore Lattice
(University of Waterloo, 2025-09-23) Burke, Michael
Nearest-neighbour spin ice has been central to the study of frustrated magnetism for nearly three decades, providing a framework that reveals emergent gauge fields and monopole excitations within geometrically frustrated spins on the pyrochlore lattice. The geometry of corner-sharing tetrahedra admits only a single symmetry-equivalent nearest-neighbour bond, strongly constraining the range of allowed interactions. Recently, a new frustrated lattice of corner sharing octahedra, dubbed the octochlore lattice, has emerged as a promising platform for novel spin liquid phases. Unlike the pyrochlore, the octahedra permit distinct intra-octahedral interactions, greatly expanding the variety of realizable models. Building on the work of Szabó et al., where the spin-ice analogue was studied in a restricted region of parameter space, this thesis pursues two complementary directions. First, we investigate the spin vorticity model, in which the monopole excitations of spin ice are replaced with string-like excitations analogous to closed current loops. Second, we identify all the long-range ordered phases at the second nearest-neighbour level, fully elucidating the intra-octahedra model of Szabó et al. through an irreducible representation analysis. In doing so, we discover a novel classical U(1) analog to the celebrated X-cube model of fracton topological order. Overall, this work demonstrates that the octochlore lattice of corner-sharing octahedra constitutes a next-generation platform for three dimensional frustrated magnetism, uniquely capable of hosting exotic spin liquid phases with potential realizations in rare-earth based antiperovskites and potassium rare-earth fluorides.
Information-Theoretic Tools for Analyzing Non-IID Structures in Quantum Key Distribution
(University of Waterloo, 2025-09-23) Arqand, Amir
Quantum key distribution (QKD) is the task of establishing an information-theoretically secure key between two parties (Alice and Bob) by exploiting the rules of quantum mechanics. A central goal in QKD is to provide finite-size security proofs against the most general class of attacks—namely, coherent attacks. One approach for obtaining such proofs is through the original entropy accumulation theorem (EAT) and the generalized entropy accumulation theorem (GEAT). In this thesis, we improve and extend these EAT-style techniques in several aspects. We begin by presenting techniques for applying the GEAT in the finite-size analysis of generic prepare-and-measure protocols. We then improve the statistical analysis in these EAT-style techniques, yielding a significant improvement in the key rates obtained by these methods. In addition, these improvements can be applied directly at the level of Rényi entropies if desired, yielding fully-Rényi security proofs. Beyond this, we develop an EAT-style framework that can accommodate specific forms of marginal-state constraints ``compatible'' with the source-replacement scheme. This allows us to overcome the repetition-rate restriction previously imposed on the GEAT when analyzing prepare-and-measure protocols. Furthermore, it yields ``fully adaptive'' protocols that can, in principle, update the entropy estimation procedure during the protocol itself. Finally, we investigate the effect of imperfections in QKD by deriving a number of chain rules for mutual information suited for analyzing protocols involving information leakage from imperfect devices. In particular, we derive chain rules between smooth min-entropy and smooth max-information for characterizing one-shot information leakage caused by an additional conditioning register. Furthermore, we introduce an EAT-style theorem for mutual information to simplify the evaluation of leakage measured by smooth max-information. In addition, we derive suitable chain rules to incorporate the leakage process into the GEAT framework.
Vacuum assembly, atomic source development, and micromotion studies for a trapped Ba+ based quantum processor
(University of Waterloo, 2025-09-22) Khatai, Ali
Trapped-ions are one of the leading platforms for quantum information processing, due to their long coherence times and high-fidelity State Preparation and Measurement (SPAM) and gate operations. However, implementing a trapped-ion system with many desirable features such as Ultra-High-Vacuum (UHV), High-Optical-Access (HOA), and a high trapping probability presents significant technical challenges. These features are critical for enabling complex quantum simulation experiments, including simulations of spin-1/2 systems and beyond, by leveraging the multiple internal states of barium and tunable spin–spin interactions. High optical access is required to deliver tightly focused beams for site-resolved control and inter-ion coupling, while UHV conditions are essential for achieving long ion lifetimes necessary for stable, large-scale simulations. Achieving such optical access, which is vital for both coherent gate operations and high numerical aperture fluorescence collection, whilst maintaining vacuum integrity presents substantial engineering challenges. This thesis presents the construction of a vacuum chamber system intended for an individually addressable 16-qubit quantum processor based on barium-133 ions confined in a microfabricated surface-electrode ion trap. Although the complete processor has not yet been realized, the chamber has been assembled to support its future implementation. The microfabricated surface-electrode ion trap features ∼ 100 electrodes that require independent control of static voltages for precise tailoring of the confining electric potential. The experimental setup was designed to provide high optical access and to reach base pressures in the low 10^(−11) mbar range, thereby minimizing ion–background gas collisions. This is achieved by centrally mounting the trap within the vacuum chamber, a departure from conventional flange-mounted designs. To bring in-vacuum electrical connections to ∼ 100 trap electrodes, a custom implementation of an in-vacuum wire harness is described that enables reliable electrical connectivity to the centrally mounted surface electrode ion trap. The development of this wire harness enabled us to reach UHV with a pressure of ≈ 3 × 10^(−11) mbar. The successful development of this wire harness demonstrates that it is possible to create a UHV compatible wiring solution using commercially available components for a surface-electrode ion trap suspended at the center of the vacuum chamber. This centrally mounted design provides both high optical access and high conductance to vacuum pumps, enabling individual ion addressing and long ion lifetimes, which in turn facilitate more complex quantum simulation experiments. In addition, a multispecies ablation target was developed that incorporates both radioactive barium-133 and metallic barium to enable ion loading at lower trap depths, addressing a common challenge in surface-electrode ion traps. The velocity of the atomic plume generated from barium metal ablation targets was measured and compared to that of BaCl_2 targets. Although we were unable to definitively measure the effective temperature and peak velocity of the atomic plume generated from barium metal, the neutral fluorescence measurements from the barium metal targets indicate a larger number of slower moving atoms compared to BaCl_2 targets. The lower speeds of the atoms generated from metal targets is also plausible due to the low bond energy of metallic bonds compared to covalent bonds in salts. Barium has recently become a popular choice for high-fidelity trapped-ion experiments due to its favorable atomic structure. The larger number of slower moving atoms from barium metal demonstrates that metallic barium could be a much more promising atomic source for barium-based trapped-ion experiments, as the slower plume enables higher loading rates in surface-electrode ion trap systems. Finally, excess micromotion, caused by stray electric fields in RF traps, can lead to undesirable effects such as heating and frequency modulation of atomic transitions. This work evaluates the micromotion compensation capabilities of the Phoenix ion trap used in our system through numerical simulations of single ion trajectories. Through these simulations, it was determined that stray fields of Ex ≈ 3000 V/m, Ey ≈ 3800 V/m, and Ez ≈ 600 V/m can be effectively compensated for with the Phoenix ion trap. With typical stray electric fields in trapped-ion systems ranging from tens to a few hundred V/m, this demonstrates that the Phoenix trap should be well capable of compensating any stray fields expected in our system.
Temperature Dependence of 1/f Charge Noise Coupled to a Quantum Dot Confined in a 2DHG
(University of Waterloo, 2025-09-22) Nademi, Cody
Reliable operation of semiconductor quantum dot-based qubits relies on a stable electrostatic environment. However, charge noise stemming from the randomized motion of trapped charge carriers poses a significant challenge to qubit coherence. This thesis presents experimental results acquired from a quantum dot confined within a 2DHG formed at the interface of a cs-GoS heterostructure, with the motivation of characterizing the 1/f charge noise coupled to the dot. Charge stability diagrams reveal irregularities in transition between adjacent stable charge states, motivating the investigation into the behavior of charge noise in cs-GoS lateral quantum dot devices. Charge noise likely originates within the amorphous dielectric layer or at the dielectric-semiconductor interface where bonding mismatch serves as charge trapping sites, each with their own characteristic activation energy. To characterize the spectral and temperature-dependent behavior of the charge noise, current fluctuations across the quantum dot sensor were measured and analyzed to compare with the Dutta-Horn model for 1/f noise. During the process, a novel technique was developed to mitigate the effects of charge noise induced device drift and account for the quantum dot’s changing transfer function. To precisely characterize the behavior of the charge noise, the quantum dot sensor needs to maintain a constant sensitivity to surrounding electrostatic fluctuations. However, while studying charge noise, the operating point of the quantum dot sensor is inherently prone to changes. Thus, the technique involved implementing an AC modulation on a nearby gate to determine a time-averaged transfer function. Using the AC modulation technique, an ensemble of current spectra revealed an average frequency exponent value of 1.06±0.19, consistent with Dutta-Horn’s model for 1/f noise arising from a uniform distribution of two-level systems. Additionally, analysis incorporating the time-averaged transfer function showed that the charge noise increased nearly linearly with temperature. Across the ensemble of experiments, the average temperature exponent value was 1.01±0.19, also consistent with the model’s prediction for thermally activated two-level systems with a uniform distribution of activation energies. Furthermore, at 1 Hz and 100 mK, the average noise magnitude was determined to be √(S_E )=0.94 μeV/√Hz, with a significant spread likely stemming from thermal cycling and abrupt gate voltage changes, leading to a redistribution of trapped charges within the quantum dot’s environment. These results highlight the sensitivity of charge noise to device history and operating conditions, suggesting it is not entirely intrinsic. While the exact source of charge noise has not been identified, future work focused on dielectric engineering and improved gate control may open pathways towards reduced chare noise and eventually improved qubit coherence.
Explorations in Generalized Quasi-topological Gravities
(University of Waterloo, 2025-09-22) Mengqi, Lu
This thesis presents a comprehensive study of Generalized Quasi-Topological Gravities (GQTGs), a broad class of higher-curvature extensions of Einstein gravity in arbitrary spacetime dimensions. These theories are distinguished by possessing second-order lin- earized field equations around maximally symmetric backgrounds and admitting static, spherically symmetric black hole solutions characterized by a single metric function f (r) obeying a second-order differential equation. We rigorously demonstrate that, at order n in curvature, exactly n − 1 inequivalent GQTG densities exist in dimensions D ≥ 5, among which only one belongs to the Quasi-topological subclass for which the field equa- tions reduce to an algebraic equation for f (r). In contrast, we find strong evidence that only a unique such density exists for each order in four dimensions, which is not of the Quasi-topological kind. We analyze the thermodynamic properties of black holes in these theories and confirm that the first law of thermodynamics is satisfied. Moreover, we provide evidence that the black hole thermodynamics is fully encoded in the same embedding function that determines the maximally symmetric vacua of the theory, offering a unified and simplified framework for studying solutions with arbitrary higher-curvature corrections. Building on this foundation, we explore the multi-critical thermodynamic behavior of uncharged AdS black holes in GQTGs. Utilizing a reformulated version of Maxwell’s equal area law, we identify a geometric criterion for the existence of multicritical (or N -tuple) points in the black hole phase diagram. Applying this criterion, we explicitly construct black hole solutions exhibiting quadruple and quintuple critical points supported by genuine GQTG densities. Finally, we uncover a novel class of traversable wormhole solutions in four-dimensional Einsteinian Cubic Gravity—a specific GQTG—including examples that are entirely vac- uum configurations with no need for exotic matter. These wormholes connect asymptoti- cally AdS regions with a geometric deficit at infinity, interpretable as a global monopole. We demonstrate that these configurations satisfy standard traversability conditions and exhibit a variety of geometries depending on the parameter space.
Towards satellite-assisted quantum communication with reconfigurable networks and frequency-bin qubits
(University of Waterloo, 2025-09-22) Vinet, Stéphane
The development of quantum networks will enable advanced applications in quantum cryptography, quantum-enhanced metrology, and quantum computing. Central to this vision is the ability to reliably distribute quantum entanglement between distant nodes. To date, quantum networks have been largely confined to metropolitan scales and a small number of nodes with predominantly static implementations, constraining their scalability and adaptability for broader deployment. Satellites provide a promising platform for distributing entanglement over global distances. However, the integration of satellites into terrestrial quantum networks poses significant challenges, including intermittent connectivity and high link attenuation during orbital passes. In this thesis, we first propose a reconfigurable quantum network architecture that dynamically adapts its topology according to satellite availability. This reconfiguration ensures efficient and continuous operation while accommodating satellite links within a metropolitan quantum network. We demonstrate this network architecture, using a correlated photon source specifically designed for Canada’s Quantum Encryption and Science Satellite (QEYSSat) mission. Using both frequency and time multiplexing, we demonstrate a linear performance improvement with minimal resource overhead. Moreover, we propose an integrated source design to facilitate deployment in realistic scenarios. Second, we investigate frequency-encoded quantum communication over free-space channels. We propose a novel approach that leverages linear interferometry and time-resolved detectors to decode frequency-bins without any adaptive optics or modal filtering. Furthermore, we investigate the phase stability requirements so that frequency-bin encoding could be feasible for satellite to ground quantum links. A proof-of-concept experiment is conducted over a turbulent free-space channel. Third, we distribute frequency-bin entangled photons over multi-mode channels and test their non-local correlations. We report, to the best of our knowledge, the first measurement of the joint temporal intensity between frequency-bin entangled photons revealing a rich temporal structure. By combining time-resolved detection with energy-correlation measurements, we perform full quantum state tomography and further certify our source's non-classicality via a violation of the time-energy entropic uncertainty relations. We extend this scheme to higher-dimensional frequency-bin states, opening new possibilities for high-capacity robust quantum communication and quantum information processing. The concepts, protocols, and experimental demonstrations presented in this thesis establish new approaches to utilize frequency-bin entanglement and contribute to the development of satellite-assisted quantum networks thus paving the way towards the realization of a global quantum network.

Browse

Recent Submissions