Talks

CMD SEMINARS: First-Detection Probability in the Deterministic Floquet Quantum East Model

First-Detection Probability in the Deterministic Floquet Quantum East Model Kinetically Constrained Models (KCMs) are governed by local dynamical rules which, unlike conservation laws, do not affect thermodynamic properties, typically described by featureless stationary states. However, they exhibit rich out-of-equilibrium dynamics at the level of trajectories. In quantum systems, an interesting problem is the interplay between dynamical constraints and repeated measurements. In this talk, I will explore this interplay in the Floquet Quantum East model, focusing on first-detection probabilities under stroboscopic local measurements. This setting provides access to analytically tractable dynamics for certain target states and makes it possible to study the relaxation of the system under repeated measurements.

Strong Disorder Renormalization Group Method for Bond Disordered Quantum Spin Chains with Long Range Interactions

We introduce and implement a reformulation of the strong disorder renormalization group (SDRG) method in real space, which is well suited to study bond disordered power law long range coupled quantum spin chains. We apply the method to derive the entanglement entropy growth after a global quench and find at a critical power law exponent a transition from logarithmic to subvolume law growth with time. We trace that transition to the emergence of rainbow states. https://arxiv.org/abs/2501.07298

Microwave studies of complex systems

A review is given on the microwave studies performed in the Marburg quantum chaos group starting from the very beginning about 1990 up to the shut-down two years ago. This includes test of random matrix theory and periodic orbit theory in chaotic microwave resonators, the emission patterns of distorted dielectric resonators, studies of microwave equivalents of graphene-like structures, or the generation of freak waves in a lab size version of the ocean.

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Colloquium

Critical gauge theories on the fuzzy sphere: a Monte Carlo perspective

The deconfined quantum critical point (DQCP) is an example of phase transitions beyond the Landau symmetry breaking paradigm that attracts wide interest. However, its nature has not been settled after decades of study. In this talk, we apply the recently proposed fuzzy sphere regularisation to study the SO(5) non-linear sigma model (NL

Quantum Dynamics Seminar: tba

Tunable Matter -- Many More is More Different

In 1972 Phil Andersen articulated the motto of condensed matter physics as “More is different.” However, for most many-body systems the behavior of a trillion bodies is nearly the same as that of a thousand. Here I argue for a class of condensed matter, “tunable matter," in which many more is different. The ultimate example of tunable matter is the brain, whose cognitive capabilities increase as size increases from 302 neurons (C. Elegans) to a million neurons (honeybees) to 100 billion neurons (humans). I propose that tunable matter provides a unifying conceptual framework for understanding not only a wide range of systems that perform biological functions, but also physical systems capable of being trained to develop special collective behaviors without using a processor.

Effect of interaction softness on the collective properties of active Brownian particles

Colloquium

Specificity and tolerance of the immune T cell repertoire

The adaptive immune system protects the body from an ever-changing landscape of foreign pathogens. The two arms of the adaptive immune system, T cells and B cells, mount specific responses to pathogens by utilizing the diversity of their receptors, generated through hypermutation. T cells recognize and clear infected hosts when their highly variable receptors bind sufficiently strongly to antigen-derived peptides displayed on a cell surface. To avoid auto-immune responses, randomly generated receptors that bind strongly to self-peptides are eliminated in the “central" process of thymic selection, ensuring a mostly self-tolerant repertoire of mature T cells. “Peripheral” tolerance, including a quorum mechanism further protects against self-targeting T cells that escape thymic selection. We discuss how these mechanisms can still fail during persistent infections.

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Colloquium SPEQED25

Colloquium

Colloquium