Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2509.05049 · The European Physical Journal A

Few is different: deciphering many-body dynamics in mesoscopic quantum gases

J. Berges, Sandra Brandstetter, Jasmine Brewer, Georg M. Bruun, Tilman Enss, Stefan Floerchinger, Keisuke Fujii, Maciej Gałka, Giuliano Giacalone, Qingze Guan, Carl Heintze, Lars Helge Heyen, Ilya Selyuzhenkov, Selim Jochim, Jesper Levinsen, Philipp Lunt, S. Masciocchi, Aleksas Mazeliauskas, Nir Navon, A. Ohlson, Meera M. Parish, S. M. Reimann, Francesco Scazza, Thomas Schäfer, Derek A. Teaney, Joseph H. Thywissen, Raju Venugopalan B, Yangqian Yan, Matteo Zaccanti, Torsten V. Zache

Published Jun 12, 2026• 0 citations
arXivHTMLPDF

Abstract

Abstract Emergent macroscopic descriptions of matter, such as hydrodynamics, are central to our description of complex physical systems across a wide spectrum of energy scales. The conventional understanding of these many-body phenomena has recently been shaken by a number of experimental findings. Collective behavior of matter has been observed in mesoscopic systems, such as high-energy hadron–hadron collisions, or ultracold gases with only a few strongly interacting fermions. In such systems, the separation of scales between macroscopic and microscopic dynamics (at the heart of any effective theory) is inapplicable. To address the conceptual challenges that arise from these observations and explore the universality of emergent descriptions of matter, the EMMI Rapid Reaction Task Force was assembled. This document summarizes the RRTF discussions on recent theoretical and experimental advances in this rapidly developing field. Leveraging technological breakthroughs in the control of quantum systems, we can now quantitatively explore what it means for a system to exhibit behavior beyond the sum of its individual parts. In particular, the report highlights how the (in)applicability of hydrodynamics and other effective theories can be probed across three principal frontiers: the size frontier, the equilibrium frontier, and the interaction frontier.

DOI
10.1140/epja/s10050-026-01843-2

Related papers

Qualifying collective behavior in expanding ultracold gases as a function of particle number

Stefan Floerchinger, Giuliano Giacalone, Lars Helge Heyen +1 more

The collective behavior of strongly interacting subatomic particles produced in high-energy proton and nuclear collisions is often interpreted using fluid dynamics. This paper considers systems of interacting cold atoms to explore the emergence of hydrodynamic behavior as a function of particle number. It proposes methods that have the potential to connect results of experiments performed with mesoscopic atomic systems with those performed at the Large Hadron Collider.

Physical Review C•Apr 26, 2022•8 citations

How many particles do make a fluid? Qualifying collective behavior in expanding ultracold gases

Stefan Floerchinger, Giuliano Giacalone, Lars Helge Heyen +1 more

Collective phenomena in quantum many-body systems are often described in terms of hydrodynamics, an appropriate framework when the involved particle numbers are effectively macroscopic. We propose to use experiments on expanding clouds of few and many interacting cold atoms to investigate the emergence of hydrodynamics as a function of particle number. We consider gases confined in two-dimensional elliptically-deformed traps, and we employ the manifestation of elliptic flow as an indicator of collective behavior. We quantify the response of the gas to the deformation of the trapping potential, and show how such information can be used to establish how many atoms are needed for the system to develop a degree of collectivity comparable to that expected in the hydrodynamic limit. This method permits one, in particular, to exploit observations made in expanding atomic gases to shed light on the apparent hydrodynamic behaviour of mesoscopic systems of quarks and gluons formed in the scattering of light ions in high-energy collider experiments.

arXiv:2111.13591•Nov 26, 2021•4 citations

Complex quantum systems

Irène Burghardt, Andreas Buchleitner

What is “complex”? A question which stimulates a panoply of often quite diverse associations and answers. While in condensed matter and also (macro-) molecular physics we are used to be forced into effective descriptions of large, multicomponent, interacting quantum systems, complexity is “(re-) constructed” in modern quantum optical experiments. In learning how “complexity” emerges from strongly coupling few degrees of freedom (or particles) we start to contemplate how to control complex systems, and learn to distinguish what is just complicated from what is truly complex. This special issue of Annalen der Physik collects expertise and perspectives on complex (quantum) systems from very diverse areas of research: disordered quantum systems, molecular dynamics and interactions, mesoscopic physics, quantum many body physics, open quantum systems, network and scattering theory, quantum information and control – which all share the same interest in getting a better grasp of complexity on the quantum level. Disorder physics with its long-standing history in the condensed matter context nowadays merges with the physics of ultracold atomic gases in highly controlled potential landscapes, and finds applications in “big data”. Mesoscopic transport theory finds novel playgrounds in graphene or in coupled quantum circuits. The coupling of electronic and nuclear degrees of freedom determines chemical reactions, as well as energy flow and directionality in large molecular complexes, with an intricate interplay of coherent and incoherent effects. Today's “femtochemistry” and “femtobiology” experiments reveal these ultrafast molecular pathways in detail and make the border between quantum and classical regimes directly observable. Indeed, this research area has become a test bed for quantum transport and control theory applied to realistic, truly complex, finite quantum systems. Given the generically highly structured spectral densities which underlie molecular systems, novel strategies are called for to characterize complex open quantum systems exhibiting structured, “active” environments. Well-controlled non- equilibrium many-particle quantum dynamics becomes accessible with ultracold quantum gases loaded into engineered potential landscapes, or in photonic circuitry. This challenges theory to develop novel tools for the efficient characterization of many-particle non-equilibrium dynamics and transport, and possibly for their control, e.g. through robust design principles. Furthermore, controlled many-body quantum systems allow for enhanced sensing, and give room for the creation of highly complex many-particle states. The latter may serve, e.g., as resources for quantum computation – which, in turn, may be used to characterize such states’ complexity. This collection of various contributions either on complex molecular structures which are ever better resolved, or on novel composite quantum systems or materials which are ever better controlled, provide a snapshot of current trends in the science of complex quantum systems. Our authors’ diverse specializations highlight the research field's interdisciplinary appeal, and the broad relevance of many of the unveiled structures – and of those phenomena which remain to be understood. We thus hope that this collection will inspire future work connecting concepts of complexity across disciplines. Irene Burghardt received her Ph.D. in chemistry in 1992 from the University of Lausanne. She carried out postdoctoral research at the Center for Nonlinear Phenomena and Complex Systems in Brussels in 1992–1995, followed by research fellowships at the Universities of Bonn and Heidelberg in 1996–1998. From 1999–2011, she held a CNRS research position at ENS Paris, and was appointed CNRS Research Director in 2007. In 2011, she moved to Goethe University Frankfurt where she holds a full professorship in Theoretical Chemistry. Her research addresses quantum molecular dynamics and nonequilibrium phenomena, with a focus on materials and biological systems. Andreas Buchleitner studied Physics at the Ludwig Maximilians University of Munich and received his diploma in 1989, upon research in experimental quantum optics. In 1993, he obtained his PhD, with theoretical research at Laboratoire de Spectroscopie Hertzienne (today Laboratoire Kastler Brossel) of Universite Pierre et Marie Curie and Ecole Normale Supérieure in Paris. Afterwards, he was a PostDoc at the Max Planck Institute for Quantum Optics, Garching, and a visiting researcher at the Queen's University of Belfast and at the Weizmann Institute of Science, Revohot. In 1999, he received his Habilitation from the Ludwig Maximilians University of Munich. From 1999 to 2007, he led the research group “Nonlinear Dynamics in Quantum Systems” at the Max Planck Institute for the Physics of Complex Systems in Dresden. Since 2007, he holds the Chair for “Quantum Optics and Statistics” at the Albert Ludwigs University of Freiburg. His main research interests are Quantum Chaos, Quantum Information and Quantum Transport. From October 2014 to 2015, he was a Senior Fellow, and Speaker of the Research Focus “Designed Quantum Transport in Complex Materials”, at the Freiburg Institute for Advanced Studies. He serves in different honorary capacities, e.g., for the German Physical Society and for the German National Academic Foundation.

Annalen der Physik•Oct 1, 2015•1 citation

Emergent Hydrodynamics in Integrable Quantum Systems Out of Equilibrium

Olalla A. Castro-Alvaredo, Benjamin Doyon, Takato Yoshimura

Understanding the general principles underlying strongly interacting quantum states out of equilibrium is one of the most important tasks of current theoretical physics.With experiments accessing the intricate dynamics of many-body quantum systems, it is paramount to develop powerful methods that encode the emergent physics.Up to now, the strong dichotomy observed between integrable and nonintegrable evolutions made an overarching theory difficult to build, especially for transport phenomena where spacetime profiles are drastically different.We present a novel framework for studying transport in integrable systems: hydrodynamics with infinitely many conservation laws.This bridges the conceptual gap between integrable and nonintegrable quantum dynamics, and gives powerful tools for accurate studies of spacetime profiles.We apply it to the description of energy transport between heat baths, and provide a full description of the current-carrying nonequilibrium steady state and the transition regions in a family of models including the Lieb-Liniger model of interacting Bose gases, realized in experiments.

arXiv:1605.07331•Physical Review X•Dec 27, 2016•897 citations

Many-Body Physics: Unnished Revolution

Piers Coleman

The study of many-body physics has provided a scientic playground of surprise and continuing revolution over the past half century. The serendipitous discovery of new states and properties of matter, phenomena such as superfluidity, the Meissner, the Kondo and the fractional quantum hall eects, have driven the development of new conceptual frameworks for our understanding about collective behavior, the ramications of which have spread far beyond the connes of terres- trial condensed matter physics- to cosmology, nuclear and particle physics. Here I shall selectively review some of the developments in this eld, from the cold-war period, until the present day. I describe how, with the discovery of new classes of collective order, the unfolding puzzles of high temperature superconductivity and quantum criticality, the prospects for major conceptual discoveries remain as bright today as they were more than half a century ago. 1 Emergent Matter: a new Frontier Since the time of the Greeks, scholars have pondered over the principles that govern the universe on its tiniest and most vast scales. The icons that exemplify these frontiers are very well known - the swirling galaxy denoting the cosmos and the massive accelerators used to probe matter at successively smaller scales- from the atom down to the quark and beyond. These traditional frontiers of physics are largely concerned with reductionism: the notion that once we know the laws of nature that operate on the smallest possible scales, the mysteries of the universe will nally be revealed to us(1). Over the last century and a half, a period that stretches back to Darwin and Boltzmann- scientists have also become fascinated by another notion: the idea that to understand nature, one also needs to understand and study the princi- ples that govern collective behavior of vast assemblies of matter. For a wide range of purposes, we already know the microscopic laws that govern matter on the tiniest scales. For example, a gold atom can be completely understood with the Schrodinger equation and the laws of quantum mechanics established more than seventy years ago. Yet, a gold atom is spherical and featureless- quite unlike the lustrous malleable and conducting metal which human society so prizes. To under- stand how crystalline assemblies of gold atoms acquire the properties of metallic gold, we need new principles{ principles that describe the collective behavior of matter when humungous numbers of gold atoms congregate to form a metallic crystal. It is the search for these new principles that denes the frontiers of many- body physics in the realms of condensed matter physics and its closely related

•Jan 1, 2003•2 citations

Out-of-equilibrium dynamics of quantum many-body systems with long-range interactions

Nicolò Defenu, Alessio Lerose, Silvia Pappalardi

Experimental progress in atomic, molecular, and optical platforms in the last decade has stimulated strong and broad interest in the quantum coherent dynamics of many long-range interacting particles. The prominent collective character of these systems enables novel non-equilibrium phenomena with no counterpart in conventional quantum systems with local interactions. Much of the theory work in this area either focussed on the impact of variable-range interaction tails on the physics of local interactions or relied on mean-field-like descriptions based on the opposite limit of all-to-all infinite-range interactions. In this Report, we present a systematic and organic review of recent advances in the field. Working with prototypical interacting quantum spin lattices without disorder, our presentation hinges upon a versatile theoretical formalism that interpolates between the few-body mean-field physics and the many-body physics of quasi-local interactions. Such a formalism allows us to connect these two regimes, providing both a formal quantitative tool and basic physical intuition. We leverage this unifying framework to review several findings of the last decade, including the peculiar non-ballistic spreading of quantum correlations, counter-intuitive slowdown of entanglement dynamics, suppression of thermalization and equilibration, anomalous scaling of defects upon traversing criticality, dynamical phase transitions, and genuinely non-equilibrium phases stabilized by periodic driving. The style of this Report is on the pedagogical side, which makes it accessible to readers without previous experience in the subject matter.

arXiv:2307.04802•Physics Reports•May 9, 2024•69 citations
Abstract Emergent macroscopic descriptions of matter, such as hydrodynamics, are central to our description of complex physical systems across a wide spectrum of energy scales. The conventional understanding of these many-body phenomena has recently been shaken by a number of experimental findings. Collective behavior of matter has been observed in mesoscopic systems, such as high-energy hadron–hadron collisions, or ultracold gases with only a few strongly interacting fermions. In such systems, the separation of scales between macroscopic and microscopic dynamics (at the heart of any effective theory) is inapplicable. To address the conceptual challenges that arise from these observations and explore the universality of emergent descriptions of matter, the EMMI Rapid Reaction Task Force was assembled. This document summarizes the RRTF discussions on recent theoretical and experimental advances in this rapidly developing field. Leveraging technological breakthroughs in the control of quantum systems, we can now quantitatively explore what it means for a system to exhibit behavior beyond the sum of its individual parts. In particular, the report highlights how the (in)applicability of hydrodynamics and other effective theories can be probed across three principal frontiers: the size frontier, the equilibrium frontier, and the interaction frontier.
Collective phenomena in quantum many-body systems are often described in terms of hydrodynamics, an appropriate framework when the involved particle numbers are effectively macroscopic. We propose to use experiments on expanding clouds of few and many interacting cold atoms to investigate the emergence of hydrodynamics as a function of particle number. We consider gases confined in two-dimensional elliptically-deformed traps, and we employ the manifestation of elliptic flow as an indicator of collective behavior. We quantify the response of the gas to the deformation of the trapping potential, and show how such information can be used to establish how many atoms are needed for the system to develop a degree of collectivity comparable to that expected in the hydrodynamic limit. This method permits one, in particular, to exploit observations made in expanding atomic gases to shed light on the apparent hydrodynamic behaviour of mesoscopic systems of quarks and gluons formed in the scattering of light ions in high-energy collider experiments.
What is “complex”? A question which stimulates a panoply of often quite diverse associations and answers. While in condensed matter and also (macro-) molecular physics we are used to be forced into effective descriptions of large, multicomponent, interacting quantum systems, complexity is “(re-) constructed” in modern quantum optical experiments. In learning how “complexity” emerges from strongly coupling few degrees of freedom (or particles) we start to contemplate how to control complex systems, and learn to distinguish what is just complicated from what is truly complex. This special issue of Annalen der Physik collects expertise and perspectives on complex (quantum) systems from very diverse areas of research: disordered quantum systems, molecular dynamics and interactions, mesoscopic physics, quantum many body physics, open quantum systems, network and scattering theory, quantum information and control – which all share the same interest in getting a better grasp of complexity on the quantum level. Disorder physics with its long-standing history in the condensed matter context nowadays merges with the physics of ultracold atomic gases in highly controlled potential landscapes, and finds applications in “big data”. Mesoscopic transport theory finds novel playgrounds in graphene or in coupled quantum circuits. The coupling of electronic and nuclear degrees of freedom determines chemical reactions, as well as energy flow and directionality in large molecular complexes, with an intricate interplay of coherent and incoherent effects. Today's “femtochemistry” and “femtobiology” experiments reveal these ultrafast molecular pathways in detail and make the border between quantum and classical regimes directly observable. Indeed, this research area has become a test bed for quantum transport and control theory applied to realistic, truly complex, finite quantum systems. Given the generically highly structured spectral densities which underlie molecular systems, novel strategies are called for to characterize complex open quantum systems exhibiting structured, “active” environments. Well-controlled non- equilibrium many-particle quantum dynamics becomes accessible with ultracold quantum gases loaded into engineered potential landscapes, or in photonic circuitry. This challenges theory to develop novel tools for the efficient characterization of many-particle non-equilibrium dynamics and transport, and possibly for their control, e.g. through robust design principles. Furthermore, controlled many-body quantum systems allow for enhanced sensing, and give room for the creation of highly complex many-particle states. The latter may serve, e.g., as resources for quantum computation – which, in turn, may be used to characterize such states’ complexity. This collection of various contributions either on complex molecular structures which are ever better resolved, or on novel composite quantum systems or materials which are ever better controlled, provide a snapshot of current trends in the science of complex quantum systems. Our authors’ diverse specializations highlight the research field's interdisciplinary appeal, and the broad relevance of many of the unveiled structures – and of those phenomena which remain to be understood. We thus hope that this collection will inspire future work connecting concepts of complexity across disciplines. Irene Burghardt received her Ph.D. in chemistry in 1992 from the University of Lausanne. She carried out postdoctoral research at the Center for Nonlinear Phenomena and Complex Systems in Brussels in 1992–1995, followed by research fellowships at the Universities of Bonn and Heidelberg in 1996–1998. From 1999–2011, she held a CNRS research position at ENS Paris, and was appointed CNRS Research Director in 2007. In 2011, she moved to Goethe University Frankfurt where she holds a full professorship in Theoretical Chemistry. Her research addresses quantum molecular dynamics and nonequilibrium phenomena, with a focus on materials and biological systems. Andreas Buchleitner studied Physics at the Ludwig Maximilians University of Munich and received his diploma in 1989, upon research in experimental quantum optics. In 1993, he obtained his PhD, with theoretical research at Laboratoire de Spectroscopie Hertzienne (today Laboratoire Kastler Brossel) of Universite Pierre et Marie Curie and Ecole Normale Supérieure in Paris. Afterwards, he was a PostDoc at the Max Planck Institute for Quantum Optics, Garching, and a visiting researcher at the Queen's University of Belfast and at the Weizmann Institute of Science, Revohot. In 1999, he received his Habilitation from the Ludwig Maximilians University of Munich. From 1999 to 2007, he led the research group “Nonlinear Dynamics in Quantum Systems” at the Max Planck Institute for the Physics of Complex Systems in Dresden. Since 2007, he holds the Chair for “Quantum Optics and Statistics” at the Albert Ludwigs University of Freiburg. His main research interests are Quantum Chaos, Quantum Information and Quantum Transport. From October 2014 to 2015, he was a Senior Fellow, and Speaker of the Research Focus “Designed Quantum Transport in Complex Materials”, at the Freiburg Institute for Advanced Studies. He serves in different honorary capacities, e.g., for the German Physical Society and for the German National Academic Foundation.
Understanding the general principles underlying strongly interacting quantum states out of equilibrium is one of the most important tasks of current theoretical physics.With experiments accessing the intricate dynamics of many-body quantum systems, it is paramount to develop powerful methods that encode the emergent physics.Up to now, the strong dichotomy observed between integrable and nonintegrable evolutions made an overarching theory difficult to build, especially for transport phenomena where spacetime profiles are drastically different.We present a novel framework for studying transport in integrable systems: hydrodynamics with infinitely many conservation laws.This bridges the conceptual gap between integrable and nonintegrable quantum dynamics, and gives powerful tools for accurate studies of spacetime profiles.We apply it to the description of energy transport between heat baths, and provide a full description of the current-carrying nonequilibrium steady state and the transition regions in a family of models including the Lieb-Liniger model of interacting Bose gases, realized in experiments.
The study of many-body physics has provided a scientic playground of surprise and continuing revolution over the past half century. The serendipitous discovery of new states and properties of matter, phenomena such as superfluidity, the Meissner, the Kondo and the fractional quantum hall eects, have driven the development of new conceptual frameworks for our understanding about collective behavior, the ramications of which have spread far beyond the connes of terres- trial condensed matter physics- to cosmology, nuclear and particle physics. Here I shall selectively review some of the developments in this eld, from the cold-war period, until the present day. I describe how, with the discovery of new classes of collective order, the unfolding puzzles of high temperature superconductivity and quantum criticality, the prospects for major conceptual discoveries remain as bright today as they were more than half a century ago. 1 Emergent Matter: a new Frontier Since the time of the Greeks, scholars have pondered over the principles that govern the universe on its tiniest and most vast scales. The icons that exemplify these frontiers are very well known - the swirling galaxy denoting the cosmos and the massive accelerators used to probe matter at successively smaller scales- from the atom down to the quark and beyond. These traditional frontiers of physics are largely concerned with reductionism: the notion that once we know the laws of nature that operate on the smallest possible scales, the mysteries of the universe will nally be revealed to us(1). Over the last century and a half, a period that stretches back to Darwin and Boltzmann- scientists have also become fascinated by another notion: the idea that to understand nature, one also needs to understand and study the princi- ples that govern collective behavior of vast assemblies of matter. For a wide range of purposes, we already know the microscopic laws that govern matter on the tiniest scales. For example, a gold atom can be completely understood with the Schrodinger equation and the laws of quantum mechanics established more than seventy years ago. Yet, a gold atom is spherical and featureless- quite unlike the lustrous malleable and conducting metal which human society so prizes. To under- stand how crystalline assemblies of gold atoms acquire the properties of metallic gold, we need new principles{ principles that describe the collective behavior of matter when humungous numbers of gold atoms congregate to form a metallic crystal. It is the search for these new principles that denes the frontiers of many- body physics in the realms of condensed matter physics and its closely related
Experimental progress in atomic, molecular, and optical platforms in the last decade has stimulated strong and broad interest in the quantum coherent dynamics of many long-range interacting particles. The prominent collective character of these systems enables novel non-equilibrium phenomena with no counterpart in conventional quantum systems with local interactions. Much of the theory work in this area either focussed on the impact of variable-range interaction tails on the physics of local interactions or relied on mean-field-like descriptions based on the opposite limit of all-to-all infinite-range interactions. In this Report, we present a systematic and organic review of recent advances in the field. Working with prototypical interacting quantum spin lattices without disorder, our presentation hinges upon a versatile theoretical formalism that interpolates between the few-body mean-field physics and the many-body physics of quasi-local interactions. Such a formalism allows us to connect these two regimes, providing both a formal quantitative tool and basic physical intuition. We leverage this unifying framework to review several findings of the last decade, including the peculiar non-ballistic spreading of quantum correlations, counter-intuitive slowdown of entanglement dynamics, suppression of thermalization and equilibration, anomalous scaling of defects upon traversing criticality, dynamical phase transitions, and genuinely non-equilibrium phases stabilized by periodic driving. The style of this Report is on the pedagogical side, which makes it accessible to readers without previous experience in the subject matter.