Theoretical Physics - From Outer Space to Plasma

Nonlinear dynamics of active particles

Dr Rahil Valani provides an introduction to active matter (a field focusing on active particles' nonlinear dynamical behaviors) exploring the active system of superwalking droplets that can exhibit hydrodynamic quantum analogs. Active particles are non-equilibrium entities that consume energy from their environment and convert it into directed motion. They can be living organisms such as cells, bacteria, animals and birds, or inanimate entities such as colloidal particles or robots. A large collection of active particles, known as active matter, exhibits emergent collective phenomena such as bird flocks, mammalian herds, bacterial colonies and swarming robots. In this talk, I will provide an introduction to active particles and active matter -- a rapidly growing field of physics, focusing on the nonlinear dynamical behaviors of such particles. We will explore in particular the active system of superwalking droplets that can exhibit hydrodynamic quantum analogs.

The physics of “flat” electrons

Dr Dumitru Călugăru explores the main strategies for engineering flat band materials, discusses band topology concepts and their relevance to flat band physics, and highlights the role of strong interactions in these materials. Landau’s Fermi liquid theory, a cornerstone of condensed matter physics, explains why electrons in most metallic crystalline solids behave as free fermions with renormalized parameters at low enough temperatures. However, the most exotic phases of quantum matter emerge when this framework breaks down—typically when electron-electron interactions become strong enough to surpass the perturbative regime. Such interactions are naturally enhanced in flat band materials, where suppressed kinetic energy allows electron-electron repulsion to dominate. In this talk, I will explore the main strategies for engineering flat band materials, with an emphasis on conventional crystalline systems while briefly touching on engineered heterostructures. I will also introduce key concepts from band topology in an intuitive manner and discuss their relevance to flat band physics. Finally, I will highlight the role of strong interactions in these materials and survey recent experimental realizations.

How to program a quantum computer

Dr Dominik Hahn explains how a quantum computer is built, discusses how quantum operations are programmed in a way similar to classical computing, and showcases examples of quantum programs running on superconducting devices. Quantum computers have the potential to solve certain problems much faster than classical computers, including simulating quantum systems and optimizing complex processes. In this talk, I will explain how a quantum computer is built, using superconducting quantum processors as an example. I will discuss how quantum operations are programmed in a way similar to classical computing, and how these instructions are executed on real hardware. Finally, I will showcase practical examples of quantum programs running on superconducting devices, illustrating how theory translates into real-world computation.

A New Twist on Topology: The Rise of “Moiré Materials”

Prof Sid Parameswaran discusses how quantum condensed matter physics has been revolutionized by “moiré materials”, made by stacking individual atomically thin layers such as graphene with a relative twist/offset between layers. The world of quantum condensed matter physics has recently been revolutionized by the advent of “moiré materials”, made by stacking individual atomically thin layers such as graphene (a two dimensional form of carbon) with a relative twist or offset between the layers. Electrons see a long-wavelength potential as they scatter from the positive ions in the different layers, leading to the formation of a new type of two-dimensional electron gas. In certain circumstances, the resulting electronic states are analogous to the Landau levels that lie at the heart of the quantum Hall effect, but form without an external magnetic field. This has led to the experimental realisation of the long-sought “fractional Chern insulator” state of matter, and has triggered an ongoing worldwide effort to explore other effects of the interplay of topology and interactions in this new setting. I’ll discuss the origins of the moiré phenomenon, and survey the exciting developments in the field, including some with links to Oxford.

Anyons: New Types of Particles in Quantum Physics

While it was originally believed that only bosons and fermions were allowed by quantum mechanics, in fact, when objects are restricted to move on a two-dimensional plane, new types of particles called "anyons" can emerge. For much of the last century it was believed that the only types of particles allowed by quantum mechanics are bosons (such as photons, phonons, pions, Higgs, etc.) and fermions (such as electrons, muons, quarks, etc.). This rule of only two particle types turns out to be a reflection of the dimensionality of space. When objects are restricted to move on a two-dimensional plane, new types of particles, called "anyons" can emerge. While originally just a theoretical fantasy, such particles have recently been observed in several different types of experiments. I will discuss the history of this field, why it is viewed as important, and recent progress.