Talks

CondMat for Dummies: Basic statistics of diffusive and subdiffusive random walks

Diffusion emerges naturally as the scaling description for dynamics in a large class of physical systems, and random walks are the simplest stochastic toy models to study the basic statistics. We will see how microscopic random motion is coarse grained to obtain the diffusion equation, and then discover displacement and first-passage-time statistics and their peculiar dependence on dimensionality. Things become even more interesting in cases where random walks manage to avoid the fate of diffusive scaling: When a scale-free structure dominates either space (as for example in fractal environments) or time (in some continuous time random walks) the scaling becomes anomalous, and in the latter case even ergodicity is broken.

Cavity Quantum Electrodynamics with Antiferromagnets — Quantum Light as a Probe and Driver of Antiferromagnetic Matter

Quantum electrodynamic (QED) cavities confine electromagnetic fields to small mode volumes, enabling coherent coupling between photons and collective excitations in solid-state systems. Magnons — the quanta of spin waves — are a particularly versatile target: they span the GHz–THz range, couple to microwave, terahertz, and optical photons through distinct mechanisms, and naturally interface with superconducting, mechanical, and photonic degrees of freedom. Within this framework, antiferromagnets (AFMs) provide a distinctive platform. Their multi-sublattice order gives rise to intrinsically multimode excitations, their near-zero net magnetisation suppresses stray-field cross-talk and facilitates on-chip integration, and their exchange-dominated dynamics enable regimes of light–matter interaction without ferromagnetic analogue. I present a theoretical framework for cavity QED with AFMs across optical and microwave regimes. In the first-order Raman regime, optical cavities couple coherently to single-magnon modes; sublattice symmetry produces optically bright and dark states, magnetically tunable photon–magnon coupling, and distinctive multimode signatures in the cavity response. In the second-order Raman regime, exchange-mediated processes generate correlated magnon pairs; mapping the dynamics onto an SU(1,1) algebraic structure shows how cavity driving yields steady-state magnon-pair squeezing below the vacuum level, and how the same system enters nonlinear regimes including limit cycles and chaos under stronger driving. For bilayer cuprate AFMs, a gapless Goldstone mode provides a natural microwave interface while higher-frequency branches extend into the sub-THz and THz regimes; cavity-mediated interactions enable tunable hybridisation, radiatively protected dark modes, and controllable avoided crossings, realising a programmable multimode architecture that positions bilayer cuprate AFMs as a candidate platform for GHz–THz quantum transduction within a single material. These results extend naturally toward altermagnets, frustrated and topological magnets, and quantum spin liquids, where cavity photons can become symmetry-selective probes of chirality, fractionalization, and emergent gauge structure.

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Perfect Adaptation in Biological Networks

A distinctive feature of many biological systems is their ability to adapt to persistent stimuli or disturbances that would otherwise drive them away from a desirable steady state. This resulting stasis enables reliable function across a wide range of external environments. We focus on a stringent form of this behavior—robust perfect adaptation (RPA)—which remains resilient to certain network and parameter perturbations. As in engineered control systems, RPA is not incidental: it requires the regulating network to satisfy specific, unavoidable structural constraints. Using examples from systems biology and synthetic biology, we show how these constraints arise in natural and engineered circuits. We argue that identifying the structural basis of RPA allows us to move beyond implementation details and provides a principled lens for understanding regulatory complexity and information processing in biological systems

Colloquium

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Emergent Gauge Fields in Quantum Condensed Matter

It has long been understood that the exact (“fundamental”) gauge symmetry of the electromagnetic fields plays an important role in the theory of quantum materials. What has come into focus more recently is that there exist essential properties of quantum phases of matter that are best understood in terms of an effective field theory with emergent gauge fields, rather than (or in addition to) in terms of broken symmetries. Here, gauge invariance is not a symmetry of the microscopic problem but is rather an efficient representation of the low energy physics. As time permits, I will discuss recent theoretical results that suggest that exotic “resonating valence-bond” fluids, describable by emergent gauge theories, might exist in a much broader range of experimentally accessible platforms than has been previously appreciated.

The emergent "graviton" in the fractional quantum Hall effect

In fractional quantum Hall states, electrons self-organize into a strongly interacting fluid with nontrivial emergent properties. It has recently been understood that fractional quantum Hall fluids accommodate one or several spin-2 excitations, which have been argued to be condensed-matter analogues of the graviton. In this talk we will review the origin of the idea of the graviton and the basic physics of the fractional quantum Hall effect. We then discuss a recent experiment claiming observation of a graviton-like mode in fractional quantum Hall effect and its broader implications.

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Colloquium

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