Add to Calendar 2026-04-07T09:30:00 2026-04-07T11:00:00 Understanding Correlated Phases in Twisted Multilayer Graphene Event Information: Abstract: Recent advances in experimental techniques have helped establish unprecedented control over the electronic structure and properties of 2D materials. Moiré materials are created by producing a small lattice mismatch between two superimposed lattices by introducing a small twist or superimposing lattices with different lattice constants. Moiré graphene structures have been shown to host a variety of interesting phases, like superconductivity and strongly-correlated topological insulators. The quantum devices group at UBC assembled a 5-layer moiré graphene structure with a relative twist between a bilayer and a trilayer stack (t2+3). They measured the Longitudinal and Hall resistivity while varying an out-of-plane electric field (D) through the stack and the electron density (n) in the layers. They showed that in the presence of a non-zero electric field and a small magnetic field, spontaneously symmetry broken correlated topological insulators are obtained at integer fillings with respect to charge neutrality. Many non-trivial metallic phases (halos) have also been observed in the vicinity of the insulators in the D vs. n phase diagram.  The goal of this thesis is to gain a theoretical understanding of these insulators and phases surrounding these insulators through a mean field approach. This is achieved by starting with the phenomenological Bistritzer-MacDonald model of t2+3 and adding correlations through a Hartree-Fock decoupling of Coulomb interactions. The nature of the symmetry broken insulators is characterized through Spin-Valley order parameter calculations. In addition, layer polarization and screening in the graphene stack is accounted for self-consistently and discussed in context of the halos.  All results have been contextualized with experimental parameters and assumptions of the theory.  Event Location: Brimacombe 288

Add to Calendar 2026-04-07T12:30:00 2026-04-07T13:30:00 Dynamic Respiratory Tracking in the Presence of Cardiac Motion for Stereotactic Arrhythmia Radioablation (STAR) Event Information: Dear PHAS community, our MSc student, Katja Nell, will present her current research next Tuesday, April 7, at 12:30pm. Bring your packed lunch and learn more about cutting-edge radiation treatments!   Abstract: Stereotactic arrhythmia radioablation (STAR) is a novel treatment employing single high dose radiation beam treatment for ventricular tachycardia. STAR is a non-invasive alternative to catheter ablation, both of which aim to ablate arrhythmogenic myocardial scar tissue driving reentry. Radiation treatment of moving targets necessitates utilization of motion management methods in order to minimize healthy tissue irradiation and maximize target tissue irradiation up to the intended dose. For STAR, the radiation target is affected by cardiac and respiratory motion, introducing errors in both treatment planning and delivery. Dynamic tracking is a motion management method which adjusts radiation delivery in real time throughout treatment delivery, based on a respiratory correlation model between internal and external surrogate motion generated prior to treatment. This thesis investigates the efficacy of dynamic tracking using a correlation model trained on cardiorespiratory motion, and additionally determines the potential benefits of filtering out the cardiac component of motion prior to training the correlation model. A cardiac phantom was successfully designed and constructed to simulate the 1D motion of a cardiac target.annel. An original version (without interpretation) will also be available here. Event Location: HENN 318

Add to Calendar 2026-04-13T09:30:00 2026-04-13T11:00:00 Measurements in quantum topological phases of matter and quantum computing Event Information: Abstract: Contrary to classical computing, quantum information is stored on quantum devices that can be in a superposition of states. Moreover, entanglement is an intrinsic property of quantum systems that can be used to protect and process quantum information. My thesis focuses on the utility of measurements in such a framework, notably by studying measurement-based quantum computation. A first goal is to improve a process in which a three-dimensional quantum state—known as a cluster state—is locally measured to perform computations on information encoded on a topological lattice while preserving it. Secondly, this thesis aims at understanding the fundamental reasons why quantum measurements can create long-range entanglement from a short-range entangled state, from a mathematical perspective. Indeed, long-range entangled states are of great interest from the perspective of quantum computing and quantum information protection, but are hard to create. Thanks to local measurements, however, this is much easier. Event Location: HENN 318