Theoretical Physics - From Outer Space to Plasma

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.

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.

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.

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.

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.

Prof Shivaji Sondhi explains how topology is applied to understanding properties of condensed matter systems, providing an introduction to topics including defects & solitons, the quantum Hall effect, and topological insulators. The mathematics of topology has been applied with increasing success to understanding the properties of condensed matter systems. Indeed, it is fair to say that over the past couple of decades, it has revolutionized our understanding of what forms of order are possible in quantum matter. In this talk, I will provide a brief, pedagogical introduction to some of the most well-known applications of topological ideas. These will include topics such as defects & solitons, the quantum Hall effect, and topological insulators.

Professor Prateek Agrawal discusses the ongoing crisis in cosmology regarding the measurement of the Hubble parameter by two separate probes in this Morning of Theoretical Physics talk from 9th November, 2024 Professor Prateek Agrawal discusses the Hubble tension. Cosmology has matured into a precision science over the last couple of decades. We are now in a position to test cosmological models to percent level precision, and cracks in our understanding of the universe have emerged. I will show how the measurement of the Hubble parameter by two separate probes has become an ongoing crisis in cosmology, and discuss some of the proposed solutions.

Professor Edward Hardy discusses how the network of cosmic strings that occurs in some theories of the early Universe evolves and emits gravitational waves in this Morning of Theoretical Physics talk from 9th November, 2024. Professor Edward Hardy discusses cosmic strings and gravitational waves from the early Universe. Cosmic strings are one-dimensional objects that often arise if a symmetry is spontaneously broken, as occurs in the early Universe in many theories of physics beyond the standard model. I will describe how the resulting network of strings evolves and in the process emits gravitational waves. These gravitational waves might be detectable in spectacularly precise searches today, and if discovered could give us information about physics at extremely high energies, far beyond any that could be explored directly e.g. in particle colliders.

Prof Alexander Mietke discusses recent findings in this field that have linked chirality in living systems to the formation of a left-right body axis in organisms and to a new kind of elasticity that is found in crystals formed by starfish embryos. Chirality describes objects and features that are distinct from their mirror image, a property that can be found in many biological systems ranging from spiral patterns of seashells over helical swimming paths of sperm cells to the shape of our hands and feet. This is rather surprising, given that most organisms develop from a single, round cell which shows no obvious signs of chirality. The physics of chirality in biological systems is a research area within the modern field of living matter that aims to identify the physical principals that underlie how chirality emerges during organism development and how the chiral nature of biological materials contributes to their highly unconventional mechanical properties

Dr Adrien Hallou presents a new methodology called 'spatial mechano-transcriptomics', which allows the simultaneous measurement of the mechanical and transcriptional states of cells in a multicellular tissue at single cell resolution. Over the last 10 years, advances in microscopy and genome sequencing have revolutionised our understanding of how molecular programmes contained in the genome control cellular behaviours such as cell division, differentiation or death, and how these behaviours are influenced by biochemical and mechanical signals from the cell environment. In this talk, I will present a new methodology called 'spatial mechano-transcriptomics', which allows the simultaneous measurement of the mechanical and transcriptional states of cells in a multicellular tissue at single cell resolution. This new framework provides a generic scheme for exploring the interplay of biomolecular and mechanical cues in tissues in a variety of contexts, such as embryonic development, tissue homeostasis and regeneration, but also in diseases such as cancer.