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Macroscopic fluid dynamics is usually thought to emerge from vast numbers of microscopic particles. Now, scientists have studied fluid-like behaviour in systems of as few as ten ultracold lithium atoms.

How many particles does it take to form a fluid? A new study led by STRUC­TURES researchers, published in Nature Physics, reveals that fluid-like collective behaviour can emerge with as few as ten ultracold lithium atoms. Inspired by observations in high-energy nuclear collisions, where similar phenomena are seen in systems with only a few dozen constituents, the researchers explored the onset of collectivity in quan­tum systems.

By precisely controlling the number of atoms and the strength of their interactions, they observed elliptic flow – a striking inversion of the initial aspect ratio that is a hallmark of hydrodynamic behaviour. This phenomenon, typically associated with much larger systems, challenges the conventional understanding that elliptic flow requires vast numbers of particles.

The study not only challenges long-held assumptions but also provides access to observables that remain elusive in high-energy nuclear collisions. This interdisciplinary effort, combining advanced experiments and theo­re­ti­cal modelling, paves the way for a deeper understanding of collective phenomena in quan­tum systems and opens exciting new avenues for re­search at the interface of quan­tum physics and particle physics.

Further information:

• Original Publication: Brandstetter, S., Lunt, P., Heintze, C. et al. Emergent interaction-driven elliptic flow of few fermionic atoms. Nat. Phys. (2025).
• News & Views: Fluids constructed atom by atom.
• STRUC­TURES Blog post: The Curious Case of the World’s Smallest Fluid.
• Jochim Labs: Ultracold Quan­tum Gases.

We are happy to present the 18th volume of the STRUC­TURES Newsletter, featuring re­search news, background articles and interviews. The topics of this edition are:

1. New Simulations Reveal That the Positioning of Stress
2. Fibres in Cells Follows a Minimization Principle
3. Lauriane Chomaz Promoted to Full Pro­fes­sor
4. The Exploratory Projects of STRUC­TURES – A Five Year Success Story
5. STRUC­TURES Welcomes New YAM Fellows
6. Astrid Eichhorn Re­ceives ERC Consolidator Grant
7. Ruprecht-Karls Prizes for YRC Members Friederike Ihssen and Lynton Ardizzone
8. YRC Member Malek Alhajkhouder Re­ceives Rhodes Scholarship
9. Recap: Schöntal Workshop 2024

The STRUC­TURES Project Management Office is happy to answer questions.

Scientists at Hei­del­berg Uni­ver­si­ty have achieved a groundbreaking milestone in quan­tum physics: the creation of a Laughlin fractional quan­tum Hall state using just two ultracold fermions.

“The whole is greater than the sum of its parts” – this phrase often attributed to Aristotle captures the essence of one of the most intriguing phenomena in nature: emergence. When several parts of a physical system interact, new properties can arise that its single parts do not have on their own. A striking example is the collective behaviour of quan­tum many-body systems,  which can produce novel effects like low-energy excitations carrying a fraction of an electron's charge.

Researchers from the group of STRUCTURES' principal investigator Prof. Selim Jochim at Hei­del­berg Uni­ver­si­ty, in collaboration with Philipp Preiss from LMU Munich, have made significant progress in understanding the emergence of fractional charges. By trapping and spinning a single pair of ultracold lithium-6 atoms in optical tweezers, they replicated the topological properties of this exotic state, previously seen only in bosonic systems. Using a tailored rotation to mimic the influence of a magnetic field, they achieved a strongly correlated atomic state described by physicist Robert Laughlin's wave function for the fractional quan­tum Hall effect, characterized by its collective and topological nature.

This accomplishment marks a crucial step in the study of emergence of topological phases of matter and paves the way to exploring more complex states, such as quan­tum Hall ferromagnetism and topological p-wave superconductors.

Further information:

• Publication 1: P. Lunt, P. Hill, J. Reiter, P. M. Preiss, M. Gałka, S. Jochim, Phys. Rev. Lett. 133, 253401 (2024)
• Publication 2: P. Lunt, P. Hill, J. Reiter, P: M. Preiss, M. Gałka, S. Jochim, Phys. Rev. A 110, 063315 (2024)
• APS Physics Viewpoint Article: Ultracold Fermions Enter the Fractional Quan­tum Hall Arena
• Selim Jochim's group

We are delighted to announce that STRUC­TURES Pro­fes­sor Astrid Eich­horn has secured one of the prestigious ERC Consolidator Grants by the Eu­ro­pean Re­search Council (ERC). This highly competitive grant will support her pioneering re­search into the quan­tum nature of gravity, enabling her and her team to deepen our understanding of this fundamental aspect of the universe. Over a period of five years, her project will receive two million euros in funding.

Astrid Eichhorn's re­search focuses on the quan­tum properties of space-time and the interplay with the fundamental building blocks of the universe, including elementary particles of the Standard Model of particle physics, dark matter and dark energy. In her ERC-funded project “Probing the Quan­tum Nature of Gravity at All Scales” (ProbeQG) she aims to primarily explore how to test fundamental theories on the quan­tum structure of space-time through experiments and observations. The central challenge is that the quan­tum properties of space-time manifest on tiny length scales – about 17 orders of magnitude below the scales that can be directly examined experimentally by the Large Hadron Collider, the particle accelerator of the Eu­ro­pean re­search center CERN. The main idea of the ProbeQG project is to identify “lever arms”. These are systems that translate the effects of quan­tum gravity on tiny scales into effects that are experimentally accessible. To this end, Prof. Eichhorn and her team want to build a bridge between the theory of asymptotically safe quan­tum gravity, particle physics, black hole physics and cosmology.

Astrid Eichhorn is a STRUC­TURES Pro­fes­sor at the Institute of Theo­re­ti­cal Physics (ITP), where she is heading the Quan­tum Gravity group. She completed her PhD at the Uni­ver­si­ty of Jena, before she pursued a postdoctoral position at Perimeter Institute for Theo­re­ti­cal Physics in Waterloo, and subsequently became a re­search fellow at Imperial College London. At Hei­del­berg Uni­ver­si­ty she led an Emmy Noether Group on the fundamental quan­tum structure of space-time and matter from 2016 to 2020. From 2019 she served first as associate professor and from 2023 as full professor at the Centre for Cosmology and Particle Physics Phenomenology at the Uni­ver­si­ty of Southern Denmark. In 2024, she returned to Hei­del­berg, where she was appointed to one of the newly established STRUC­TURES Pro­fes­sorships. Prof. Eichhorn's contributions to quan­tum gravity have earned her recognition as a leading voice in the field.

Further information:

• Website of Astrid Eichhorn's re­search group at ITP
• ERC Consolidator Grants
• Press release in Hei­del­berg Uni­ver­si­ty's newsroom

We are delighted to congratulate our member Dominika Wylezalek, re­search group leader at the Centre for Astronomy (ZAH) of Hei­del­berg Uni­ver­si­ty, on winning one of the three Klaus-Georg and Sigrid Hengstberger Awards for early-career scientists.

Since 2004, the Klaus-Georg and Sigrid Hengstberger Prize has been awarded annually to excellent early-career scientists at Ruperto Carola. The award comes with a prize money of €12,500 and enables the prizewinners to hold a scientific symposium at the International Academic Forum Hei­del­berg (IWH).

The symposium led by astrophysicist Dominika Wylezalek will focus on the formation and evolution of galaxies – complex phenomena shaped by intricate interactions between stars, gas, dust, black holes, and supernovae. The symposium, titled “Quo Vadis Galaxy Evolution: How Galaxies Form and Evolve,” is scheduled for June 2025.

Weblinks:

• Hengstberger Award Website
• Hei­del­berg Uni­ver­si­ty Press Release (November 21, 2024)

We are delighted to congratulate Malek Alhajkhouder, member of the Young Researchers Convent (YRC) at STRUC­TURES, on being awarded the Rhodes Scholarship in recognition of his academic achievements in physics. Malek Alhajkhouder completed his master's degree with a focus on particle physics at Hei­del­berg Uni­ver­si­ty, where he conducted his master's thesis under the supervision of Prof. Jan M. Pawlowski at the Institute for Theo­re­ti­cal Physics.

Originally from Damascus, Syria, Malek Alhajkhouder is a physicist and former scholar of the Heinrich Böll Foundation. His experiences growing up in the Middle East and North Africa (MENA) region and living across multiple countries have profoundly influenced his personality. He further enriched his international academic journey with a semester at La Sapienza Uni­ver­si­ty in Rome. At Oxford, Malek plans to pursue a DPhil (PhD) in Theo­re­ti­cal Physics and continue his research, seeking answers to questions regarding elementary particles. In addition, he aims to inspire more students, particularly from the Levant, to engage in fundamental research.

The Rhodes Scholarship is a fully funded, full-time, postgraduate award supporting students from around the world to study at the Uni­ver­si­ty of Oxford. It aims at developing public-spirited leaders and fostering international understanding and peace through its diverse, global community of scholars.

Weblinks:

• About the Rhodes Scholarship
• Hei­del­berg Uni­ver­si­ty: Scholarships for studying abroad