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A new theory developed in Hei­del­berg connects the Anderson orthogonality catastrophe for static impurities with the quasiparticle picture of mobile impurities.

When a single particle moves inside a sea of many others, their mutual interactions can give rise to new collective behaviours, such as the formation of so-called quasiparticles. These emergent forms of matter display properties of individual particles even though they arise from the coordinated motion of many particles, acting together as if they were a single one. An important example is the Fermi polaron, which forms when an impurity is introduced into a sea of fermions – particles such as electrons that obey what is known as Pauli exclusion principle. Like a pebble dropped into calm water, the impurity perturbs its surrounding, forming a particle-like pattern: the polaron. These polarons serve as a cornerstone for understanding novel quan­tum materials and ultracold atomic gases.

For years, however, physicists have faced a fundamental puzzle about the formation of Fermi polarons: how can their familiar quasiparticle nature coexist with a phenomenon known as the Anderson orthogonality catastrophe? The latter is a theo­re­ti­cal prediction stating that if the impurity is made so heavy that it becomes effectively immobile, it should instead completely disrupt its environment.

A new study by Xin Chen, Eugen Dizer, Emilio Ramos Rodríguez, and Richard Schmidt – three of whom are members of STRUC­TURES – resolved this long-standing question. The researchers developed a unified theory that smoothly connects the two seemingly contradictory regimes. The key insight lies in the impurity's unavoidable response to changes in the environment, which softens the disturbance it causes. In particular, when the surrounding medium adjusts, an impurity with finite mass cannot remain at rest: even if its net momentum is zero, it must recoil as the medium reorganizes. This creates what physicists refer to as an “energy gap” – a small energy cost for disturbing the medium. As a result of this gap, the impurity and its neighbouring particles can develop a smooth, coordinated motion, forming a well-defined quasiparticle. In contrast, if the impurity becomes heavier, it can respond less to its surrounding, and the medium reacts more strongly – until, in the extreme limit of an immobile impurity, the quasiparticle nature ultimately breaks down. 

This mechanism explains how quasiparticles emerge from an otherwise “gapless” medium and reveals the microscopic origin of the observed transition between polarons and molecules. The new theory provides a simple yet powerful description of interacting quan­tum systems, with broad implications for ultracold-atom experiments, novel atomically thin semiconductors, and future studies of strongly correlated matter.

The new study has been published in the Physical Review Letters.

Further information:

• Quan­tum Matter Theory - Schmidt Group
• Original Publication in Physical Review Letters

We are pleased to announce the 2026 Les Houches Summer School on Quan­tum Theory on All Scales, taking place August 03-28, 2026 in the idyllic location of Les Houches in the French Alps. The school, which is supported by STRUC­TURES, aims to highlight recent significant progress on the mathematical analysis of complex quan­tum systems, and to discuss interesting open questions for the future. Six lectures, along with numerous short courses and talks, will focus on interacting and correlated systems, as well as random systems – with methods drawn from analysis and probability to algebra and topology. 

The main topics of the school will be:

• Topological Quan­tum Matter
• Open Quan­tum Systems
• Integral Representations for Quan­tum Theory and the Renormalization Group
• Quan­tum Physics and Randomness
• Macroscopic Quan­tum Systems: Beyond Mean-Field Descriptions
• Entanglement, Entropy and Spacetime

The last Les Houches school with this focus took place in 2010 under the title Quan­tum theory from small to large scales. It brought together many of the best doctoral students and postdoctoral researchers in the field and from all over the world and gave them a perspective beyond their specific thesis and re­search work. It further led to lasting re­search connections, friendships and a sense of community. Many of those that attended the 2010 school as PhD students and postdoctoral fellows have since been appointed as faculty at major re­search universities.

The summer school is organized by Sven Bachmann (University of British Columbia, Canada), Serena Cenatiempo (Gran Sasso Science Institute, L’Aquila, Italy), Alain Joye (Université Grenoble Alpes, Institut Fourier, France) and Manfred Salmhofer ( STRUC­TURES, Universität Hei­del­berg, Germany).

Les Houches School of Physics is proud to have been welcoming physicists from around the world since 1951. Founded by French physicist Cécile DeWitt-Morette, the school has trained generations of early-career researchers, some of whom have since won Nobel prizes.

Application is open until December 8, 2025.

Further information:

• Summer School 2026: Quan­tum Theory on All Scales
• Les Houches School of Physics

The GTML 2025 workshop brought together a wide community of researchers for a full week of exchange at the intersection of geometry, topology, and ma­chine learning. With overwhelming interest, the event highlighted the growing momentum of this rapidly evolving re­search field.

The Workshop on Geometry, Topology, and Ma­chine Learning (GTML 2025), jointly organized by the Max Planck Institute for Mathematics in the Sciences (Leipzig) and the STRUC­TURES Cluster of Excellence (Heidelberg) took place recently in Leipzig. It marked the first event of this scale to unite the re­search communities of geometry, topology, and ma­chine learning. The workshop attracted 132 participants, with registration reaching full capacity within only two weeks – a clear evidence of the strong interest within the scientific community.

GTML 2025 provided a unique platform for researchers to explore the fundamental role of geometric and topological methods in understanding data structures and developing rigorous frameworks for ma­chine learning. The workshop format fostered deep scientific exchange and created valuable opportunities to identify new connections and build bridges between traditionally separate fields.

The scientific programme featured 10 keynote lectures and 20 expert presentations from leading researchers worldwide. A number of renowned speakers contributed to the programme, including industry experts Hartmut Maennel (DeepMind), Robert Lilow (Deepshore), and Vincent Stimper (Isomorphic Labs). Short papers will be published as a special edition of the PMLR (Proceedings of Ma­chine Learning Research) series, ensuring continued visibility of the scientific contributions beyond the event itself.

A special highlight of the workshop were the Lightning Sessions, designed specifically for early-career researchers. These rapid-format presentations created a dynamic space for young scientists to share ideas, showcase ongoing work, and expand their professional networks.

The programme covered a broad spectrum of topics, including Mathematical foundations of ma­chine learning, geometric ma­chine learning (geometric deep learning, graph neural networks, geometry processing), topological ma­chine learning (topological deep learning, TDA, shape analysis), and applications in the life sciences and complex systems.

Please visit the conference website for detailed information on the scientific topics.

With its strong scientific programme, interdisciplinary focus, and outstanding level of engagement, GTML 2025 has set a promising precedent for future meetings at the intersection of geometry, topology, and ma­chine learning.

Further information:

• Conference Website GTML 2025
• Max Planck Institute for Mathematics in the Sciences
• Organizers: Michael Bleher, Freya Jensen, Levin Maier, Diaaeldin Taha, Anna Wienhard

We are delighted to announce the next event in our Ma­chine Learning Galore! series, focusing on Scientific Ma­chine Learning, which will take place on Thursday, November 13, from 4:30 to 6:00 pm at INF 205 Mathematikon (5th floor). The event features lab presentations by principal investigators, followed by brief presentations from junior scientists showcasing their latest work. Extended discussions will offer ample opportunity for in-depth exchanges.

Event Details:

• Lab presentations: 
  • Lukas Balles
  • Jürgen Hesser
  • Wolfgang Huber
• Science Talks:
  • Constantin Ahlmann-Eltze (Huber lab): ML in Single Cell and Spatial Omics for Tissue Biology and Biomedical Research
  • Pit Neitemeier (Balles lab): Learnt splitting and the influence of compression ratios in end-to-end hierarchical language modeling
  • Marcus Buchwald (Hesser lab): Reaching for Causal Image Generation using deep conditioning

Registration is free but required via the ML-AI portal:
https://www.mlai.uni-heidelberg.de/en/machine-learning-talks-on-campus

About Scientific Ma­chine Learning
Scientific Ma­chine Learning is a collaborative initiative by the Interdisciplinary Center for Scientific Computing (IWR) and the STRUC­TURES Cluster of Excellence. Its mission is to foster interaction and exchange within the local ma­chine learning community, and to support its development by consolidating activities and resources that might otherwise remain scattered across individual institutions or disciplines. The initiative aligns closely with the objectives of STRUC­TURES, which aims to advance fundamental research, and with IWR’s focus on applying ma­chine learning to address long-standing challenges in the natural and life sciences, engineering, and the humanities.

Further information:

• Scientific Ma­chine Learning Hei­del­berg
• Ma­chine Learning Talks on Campus – Information service and mailing list
• Interdisciplinary Center for Scientific Computing (IWR)

From September 1 to 5, 2025, Hei­del­berg Uni­ver­si­ty welcomed the international numerical mathematics community to the Neuenheimer Feld campus for 2025's Eu­ro­pean Conference on Numerical Mathematics and Advanced Applications (ENUMATH). The event, supported by the STRUC­TURES Cluster of Excellence, brought together more than 750 participants from over 30 countries and six continents, including leading experts as well as early-career researchers. Over the course of five days, mathematicians and computational scientists from all backgrounds shared their latest results, exchanged ideas, and explored new directions for applying numerical mathematics in science and industry.

Alongside invited plenary lectures by leading international experts, the scientific program consisted of over 600 talks in mini-symposia and contributed sessions, as well as a large poster session. Vibrant discussions spanned from advances in discretization schemes and multi-scale modelling to questions on uncertainty quantification, optimisation, and scientific ma­chine learning – reflecting the broad scope and growing role of numerical mathematics in solving complex scientific and industrial challenges.

This year's conference was chaired by STRUC­TURES member Robert Scheichl. The local organization committee included Peter Bastian, Roland Herzog, Vincent Heuveline, Guido Kanschat, Ekaterina Kostina, and Jakob Zech – members of STRUC­TURES, IWR and IMa. The Programme Committee consisted of nine international experts from various countries across Europe. Their efforts, supported by numerous colleagues, institutions, and partners, made the conference a big success.

Since its launch in 1995, ENUMATH has established itself as a central forum for the exchange of ideas in numerical mathematics. The Hei­del­berg meeting continued this tradition by fostering international collaboration and providing a platform for early-career researchers to present their work alongside established experts. Proceedings of the conference will appear with Springer, extending the impact of the lively discussions in Hei­del­berg to the wider mathematical community.

For STRUC­TURES, supporting ENUMATH was a way of underlining the importance of numerical mathematics for our mission to connect disciplines and methods across the natural sciences. It was a great pleasure to welcome the international numerical mathematics community to Hei­del­berg, a vibrant hub for mathematics and computational science in Europe.

Further information:

• ENUMATH Conference Page 2025
• Interdisciplinary Center for Scientific Computing (IWR)
• Institute for Mathematics (IMa)

We are pleased to announce that our member Victor Ksoll will establish a new re­search group at the Institute of Theo­re­ti­cal Astrophysics (ITA), one of the participating institutes in STRUC­TURES, starting in early 2026. Supported by funding from the Carl Zeiss Foundation, the group – titled “Ma­chine Learning Solutions for Star Formation” (StarForML) – will develop innovative ma­chine learning algorithms for the efficient analysis of astrophysical observational data.

The group’s re­search will focus in particular on star formation, a complex process spanning a vast range of sclaes from molecular clouds to individual protostars. Comparing theo­re­ti­cal predictions to observations requires solving so-called inverse problems, which are computationally intensive. Given the massive data volumes produced by modern telescopes, ma­chine learning has become an indispensable tool for tackling this challenge in an automated fashion. Dr. Ksoll’s goal is to design ma­chine learning methods for such inverse problems in astronomy to enhance our understanding of star formation while increasing the transparency and interpretability of these computational approaches. The group will also employ transfer learning techniques to bridge the gap between simulations and real observational data.

About Victor Ksoll
Victor Ksoll studied physics at the Uni­ver­si­ty of Hei­del­berg, where he also earned his doctorate in astronomy. His re­search included stays at the Institute of Planetology and Astrophysics in Grenoble, France, and the Space Telescope Science Institute in Baltimore, USA. Within STRUC­TURES, he is involved in projects CP 1 (Cosmic Structure Formation) and CP 2 (From Dust to Planets) in addition to various Exploratory Projects. He is also a member of STRUCTURES' Young Researchers Convent (YRC).

Further information:

• Victor Ksoll's website
• Carl Zeiss Foundation: project overview 
• Press release of Hei­del­berg Uni­ver­si­ty