Highlights of Max Planck Institute for the Physics of Complex Systems https://www.pks.mpg.de/ here are the highlights of Max Planck Institute for the Physics of Complex Systems en_GB Max Planck Institute for the Physics of Complex Systems Wed, 04 Oct 2023 09:33:40 +0200 Wed, 04 Oct 2023 09:33:40 +0200 TYPO3 EXT:news news-748 Tue, 12 Sep 2023 22:00:00 +0200 Cell Lineage Statistics with Incomplete Population Trees https://journals.aps.org/prxlife/abstract/10.1103/PRXLife.1.013014 Cell lineage statistics is a powerful tool for inferring cellular parameters, such as division rate, death rate, fitness landscape and selection. Yet, in practice such an analysis suffers from a basic problem: how should we treat incomplete lineages that do not survive until the end of the experiment? Examples of such lineages are found in experiments in which cells can die (antibiotic experiments, ...) and in experiments in which cells are diluted to maintain the population constant (microchannels, cytometers, ...). Arthur Genthon of the Max Planck Institute for the Physics of Complex Systems, Takashi Nozoe (U. Tokyo, Japan), Luca Peliti (Santa Marinella Research Institute, Italy), and David Lacoste (Gulliver, Paris) have now developed a model-independent theoretical framework to address this issue. They show how to quantify fitness landscape, survivor bias, and selection for arbitrary cell traits from cell lineage statistics in the presence of death, and they test this method using an experimental data set in which a cell population is exposed to a drug that kills a large fraction of the population. This analysis reveals that failing to properly account for dead lineages can lead to misleading fitness estimations. For simple trait dynamics, they prove and illustrate numerically that the fitness landscape and the survivor bias can in addition be used for the nonparametric estimation of the division and death rates, using only lineage histories. Their framework provides universal bounds on the population growth rate, and a fluctuation-response relation that quantifies the change in population growth rate due to the variability in death rate. Further, in the context of cell size control, they obtain generalizations of Powell's relation that link the distributions of generation times with the population growth rate, and they show that the survivor bias can sometimes conceal the adder property, namely the constant increment of volume between birth and division. Arthur Genthon, Takashi Nozoe, Luca Peliti, and David Lacoste, PRX Life 1, 013014 (2023) Publication Highlights news-747 Tue, 05 Sep 2023 14:05:00 +0200 Two ERC Starting Grants awarded to group leaders at MPI-PKS https://erc.europa.eu/news-events/news/erc-2023-starting-grants-results The European Research Council (ERC) has announced early-career top researchers across Europe who will receive a starting grant. The prestigious grants enable the best young researchers in Europe to build their own teams and to conduct pioneering research across all disciplines. This year, two of these grants were awarded to research group leaders at the MPI-PKS: Marin Bukov for his proposal "Nonequilibrium Many Body Control of Quantum Simulators" and Ricard Alert for his proposal "The Spectrum of Fluctuations in Living Matter". Congratulations!!  

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Awards and Honors
news-746 Wed, 23 Aug 2023 22:00:00 +0200 Anderson localization of a Rydberg electron https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.033032 The hydrogen atom is one of the few exactly solvable quantum systems. Its well-known properties are shared by highly excited Rydberg atoms, albeit to such an exaggerated degree that their behavior is often wholly unexpected. Scientists at the Max Planck Institute for the Physics of Complex Systems have now investigated a Rydberg atom perturbed by ground state atoms, exploiting hydrogen's infinite spectrum and high degeneracy to show that the Rydberg electron localizes in the same fashion as electrons in a disordered solid. This unexpected manifestation of Anderson localization is enabled by the existence of a well-defined thermodynamic limit of the single Rydberg electron as its principle quantum number and the number of ground state atoms increase in tandem. Myriad localization regimes can be realized as a function of the geometry of the system. Matthew T. Eiles, Alexander Eisfeld, and Jan M. Rost, Phys. Rev. Research 5, 033032 (2023) Publication Highlights news-745 Thu, 10 Aug 2023 11:04:00 +0200 ELBE Postdoctoral Fellowships call is open! https://www.csbdresden.de/join-us/as-a-postdoc/ Application deadline: 25 September 2023. The ELBE postdoctoral fellows program addresses independent researchers on the postdoctoral level, who come with their own research proposal and freely choose which groups to affiliate with. The program provides an ideal springboard to an independent research career in systems biology, theoretical biophysics, computational biology, mathematics in the life sciences, computer science and machine learning with application to biological systems, and related areas. Please click on the link- button for more info and application instructions!  

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Institute's News
news-744 Wed, 26 Jul 2023 22:00:00 +0200 An artificial intelligence agent manipulates many interacting quantum bits of information https://doi.org/10.1038/s42256-023-00687-5 In recent years, quantum technologies have experienced significant growth, offering immense potential in various areas. Quantum computers are expected to revolutionise optimisation and search algorithms; quantum simulators help explore new quantum phases of matter; quantum sensors can achieve unparalleled precision in measurements, and quantum cryptography provides robust security for communication protocols. The advantage of these new technologies over their classical counterparts lies in quantum correlations (called by physicists quantum entanglement), and realises phenomena beyond the scope of classical physics. However, the successful implementation of most quantum technologies relies heavily on the ability to manipulate the underlying quantum systems. This task is already challenging in classical dynamics, but quantum physics adds an extra layer of complexity. The issue arises from the difficulty in simulating quantum systems with many interacting qubits, as the memory requirements exceed the capabilities of even the best classical supercomputers.Physicists refer to this challenge as the "curse of dimensionality", rendering it infeasible to simulate the behavior of large quantum many-body systems using classical computers and devising optimal control strategies for them. Addressing this problem, Friederike Metz (OIST and EPFL) and Marin Bukov (Max Planck Institute for the Physics of Complex Systems and Sofia University) introduced a new approach: they applied deep reinforcement learning (RL), a subfield of machine learning, to design an artificial intelligent agent capable of controlling quantum many-body systems effectively. To overcome the curse of dimensionality, they employed tensor networks–mathematical structures that allow for an approximate representation of large quantum states on classical computers. Leveraging tensor networks, Metz and Bukov developed a novel deep learning architecture that empowers RL agents to process and interpret quantum many-body states seamlessly. The trained RL agent demonstrated remarkable performance in preparing ordered ground states in the quantum Ising chain, a fundamental model for studying quantum magnetism. This new framework surpassed the limitations of standard neural-network-only architectures, enabling the control of significantly larger systems while retaining the benefits of deep learning algorithms, such as generalizability and trainable robustness to noise. Notably, the RL agent exhibited the ability to find universal controls in few-qubit systems, learn to steer previously unseen many-qubit states optimally, and adapt control protocols in real-time when faced with stochastic perturbations in quantum dynamics. Additionally, the authors propose a way to map their RL framework to a hybrid quantum-classical algorithm that can be executed on noisy intermediate-scale quantum devices. This research has profound implications, paving the way for applying deep RL to efficiently control large quantum systems–a crucial requirement for advancing modern quantum technologies. With these techniques, researchers expect to explore novel quantum phases, design complex molecules, achieve unprecedented measurement precision, and build secure networks using quantum communication, among other groundbreaking applications. An earlier version of this text was improved using ChatGPT. The image accompanying the text was created with the assistance of DALL·E 2 using the prompt "A robot manipulating atoms in a quantum computer, Surrealism". Friederike Metz and Marin Bukov, Nat. Mach. Intell. 5, 780 (2023) Publication Highlights news-743 Tue, 18 Jul 2023 22:00:00 +0200 Understanding 3D Active Fluids Through Mathematical Supercomputing https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.L022061 Active matter physics is a cornerstone theory to understand biological phenomena across multiple scales, ranging from cellular movement to tissue morphogenesis and the flocking behavior of animals. One such fascinating class of active matter are active fluids. These are densely packed, soft substances whose component parts can flow independently and operate by dissipating energy at the microscopic scale to perform directed motion. Although this offers a general framework that can be applied to practically all of biology, active fluids are incredibly challenging to understand in three dimensions due to increased mathematical and computational complexity. Given the technical obstacles and a lack of the necessary supercomputing scientific software for 3D investigations, only two-dimensional models of active fluids were investigated in the previous decade. In a current study, Frank Jülicher, director at the Max Planck Institute of the Complex Systems, investigates, together with the research group of Ivo Sbalzarini, TU Dresden Professor in the Center for Systems Biology Dresden (CSBD), Research Group Leader at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG), and Dean of the Faculty of Computer Science at the TU Dresden, how an active fluid behaves in a three-dimensional environment. Recent experiments that directly correspond to the three-dimensional world we live in, have observed that microtubules and kinesin motor protein mixtures can flow on their own in different directions, but a comprehensive theoretical model explaining these observations and how to control them was missing. Abhinav Singh, the first author of the study, explains: “Our most important discovery is that boundary conditions, which are frequently overlooked in ideal physical models, are crucial in the formation of instabilities in active matter. In simple terms, this means that the active material can latch onto and interact with the boundary or surface it is against, and then move in two ways: in the direction of alignment (in-plane) or perpendicular to the alignment of polymers (out-of-plane). Whether it is pulled or pushed by its internal motors, and the way molecules orient at the edges, dictate the movement. Interestingly, we discovered a unique 3D 'rippling' or 'wrinkling' effect that corresponds directly to the observed puzzling behavior of microtubules when they are under a stretching force created by motors called kinesins. These results were confirmed through rigorous mathematical analysis and unprecedented supercomputing codes of novel numerical techniques, marking a significant leap in our understanding of active biological processes.” “These findings expand our understanding of the behavior of active matter and move us one step closer to unraveling the beautiful complexity of morphogenesis,” concludes Ivo Sbalzarini, who supervised the study. “Our findings and software contributions in OpenFPM will be instrumental for physicists, biologists, and materials scientists who are looking into the behavior of active fluids made up of living materials. This new understanding can enhance the manipulation and control of active fluids, paving the way for a range of applications, from microfluidic devices to drug delivery systems and novel material designs. However, further research is necessary to validate our findings in various real-world scenarios.” (Highlight text by Katrin Boes, MPI-CBG) Abhinav Singh, Quentin Vagne, Frank Jülicher, and Ivo F. Sbalzarini, Phys. Rev. Research 5, L022061 (2023) Publication Highlights news-742 Wed, 12 Jul 2023 11:49:00 +0200 "Physik-Preis Dresden 2023" awarded to Professor Jörg Schmalian On July 11, 2023, Prof. Jörg Schmalian from the Karlsruhe Institute of Technology received the "Physik-Preis Dresden 2023" (Dresden Physics Prize), jointly awarded by the TU Dresden and the Max Planck Institute for the Physics of Complex Systems (MPI-PKS). The "Physik-Preis Dresden" has been established, with a generous donation by Prof. Peter Fulde, to promote cooperation between the Max Planck Institute for the Physics of Complex Systems and the Faculty of Physics of TU Dresden. It is geared towards outstanding researchers whose research is of particular interest to scientists in Dresden. This year's recipient, Prof. Jörg Schmalian, fits this condition perfectly. Jörg Schmalian studied physics in Leipzig and Merseburg and graduated from the Technische Hochschule Merseburg in 1990. The German reunification made it possible for him to obtain a doctorate in physics in 1993 from Freie Universität Berlin under the supervision of Karl Bennemann. He stayed at FU Berlin as a postdoc before joining the group of David Pines at the University of Illinois at Urbana-Champaign in 1997. In 1999, Jörg Schmalian moved back to Europe and became a fellow of St. Catherine's College at the University of Oxford. In the same year, he accepted an offer for a tenure-track faculty position at Iowa State University, in connection with a researcher position at Ames National Lab. Jörg Schmalian quickly moved up through the ranks to become full professor in 2007. In 2011, he moved to the Karlsruhe Institute of Technology as a professor. Currently, he is the Dean of the Faculty of Physics of KIT. Jörg Schmalian has been a visiting professor at Royal Holloway University, University of Paris Diderot, and Stanford University. He has received multiple honors, among them a fellowship of the American Physical Society and the 2022 John Bardeen Prize for Theory of Superconductivity. Jörg Schmalian is an internationally highly visible theoretical physicist with a broad range of interests. He has published over 200 research papers with over 10.000 citations. Jörg Schmalian started to work on strongly correlated electrons and superconductivity during his doctoral studies, at that time with a focus on cuprate high-temperature superconductors. He later made significant contributions to superconductivity and other ordering phenomena in iron-based and organic compounds as well as more generally on the physics of coupled order parameters. It is characteristic for Jörg Schmalian's work that he has both established conceptual foundations and modeled and predicted specific phenomena, working close to experiments. Jörg Schmalian's papers on spin-fluctuation-mediated superconductivity and on nematic order have become standard references in these fields. Moreover, Jörg Schmalian's works on quantum criticality and transport in graphene have strongly advanced the hydrodynamics of electron liquids. They were essential for identifying graphene as a readily available system in which many aspects of hydrodynamical transport can be studied experimentally. Last but not least, Jörg Schmalian has made significant contributions to the field of disordered systems. He has worked on electronic glasses and disordered magnets as well as on novel superconducting phases in models with strong disorder. Jörg Schmalian has multiple connections to Dresden, not only to theoretical physics groups at MPI-PKS and TUD. There is also strong overlap with experimental work done at IFW Dresden, at the Helmholtz-Zentrum Dresden-Rossendorf, and by Andrew Mackenzie's group at the Max Planck Institute for Chemical Physics of Solids. This is exemplified by a new paper on strontium ruthenate with Jörg Schmalian and Andrew Mackenzie as two of the authors. The Physik-Preis Dresden for the year 2023 honors Jörg Schmalian as an outstanding theoretical condensed-matter physicist with strong connections to Dresden and will hopefully help to strengthen these connections further. On July 11, 2023, Prof. Jörg Schmalian from the Karlsruhe Institute of Technology received the "Physik-Preis Dresden 2023" (Dresden Physics Prize), jointly awarded by the TU Dresden and the Max Planck Institute for the Physics of Complex Systems (MPI-PKS).

The "Physik-Preis Dresden" has been established, with a generous donation by Prof. Peter Fulde, to promote cooperation between the Max Planck Institute for the Physics of Complex Systems and the Faculty of Physics of TU Dresden. It is geared towards outstanding researchers whose research is of particular interest to scientists in Dresden. This year's recipient, Prof. Jörg Schmalian, fits this condition perfectly.

Jörg Schmalian studied physics in Leipzig and Merseburg and graduated from the Technische Hochschule Merseburg in 1990. The German reunification made it possible for him to obtain a doctorate in physics in 1993 from Freie Universität Berlin under the supervision of Karl Bennemann. He stayed at FU Berlin as a postdoc before joining the group of David Pines at the University of Illinois at Urbana-Champaign in 1997. In 1999, Jörg Schmalian moved back to Europe and became a fellow of St. Catherine's College at the University of Oxford. In the same year, he accepted an offer for a tenure-track faculty position at Iowa State University, in connection with a researcher position at Ames National Lab. Jörg Schmalian quickly moved up through the ranks to become full professor in 2007. In 2011, he moved to the Karlsruhe Institute of Technology as a professor. Currently, he is the Dean of the Faculty of Physics of KIT. Jörg Schmalian has been a visiting professor at Royal Holloway University, University of Paris Diderot, and Stanford University. He has received multiple honors, among them a fellowship of the American Physical Society and the 2022 John Bardeen Prize for Theory of Superconductivity.

Jörg Schmalian is an internationally highly visible theoretical physicist with a broad range of interests. He has published over 200 research papers with over 10.000 citations. Jörg Schmalian started to work on strongly correlated electrons and superconductivity during his doctoral studies, at that time with a focus on cuprate high-temperature superconductors. He later made significant contributions to superconductivity and other ordering phenomena in iron-based and organic compounds as well as more generally on the physics of coupled order parameters. It is characteristic for Jörg Schmalian's work that he has both established conceptual foundations and modeled and predicted specific phenomena, working close to experiments. Jörg Schmalian's papers on spin-fluctuation-mediated superconductivity and on nematic order have become standard references in these fields. Moreover, Jörg Schmalian's works on quantum criticality and transport in graphene have strongly advanced the hydrodynamics of electron liquids. They were essential for identifying graphene as a readily available system in which many aspects of hydrodynamical transport can be studied experimentally. Last but not least, Jörg Schmalian has made significant contributions to the field of disordered systems. He has worked on electronic glasses and disordered magnets as well as on novel superconducting phases in models with strong disorder.

Jörg Schmalian has multiple connections to Dresden, not only to theoretical physics groups at MPI-PKS and TUD. There is also strong overlap with experimental work done at IFW Dresden, at the Helmholtz-Zentrum Dresden-Rossendorf, and by Andrew Mackenzie's group at the Max Planck Institute for Chemical Physics of Solids. This is exemplified by a new paper on strontium ruthenate with Jörg Schmalian and Andrew Mackenzie as two of the authors.

The Physik-Preis Dresden for the year 2023 honors Jörg Schmalian as an outstanding theoretical condensed-matter physicist with strong connections to Dresden and will hopefully help to strengthen these connections further.

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Awards and Honors
news-740 Sun, 21 May 2023 22:00:00 +0200 Towards the realisation of chiral spin liquids and non-Abelian anyons in quantum simulators https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.4.020329 Chiral spin liquids are one of the most fascinating phases of matter ever imagined by physicists. These exotic liquids exhibit quasi-particles known as non-Abelian anyons that are neither bosons nor fermions, the manipulation of which could allow for the realisation of a universal quantum computer. Despite intense efforts in condensed matter physics, discovering such a phase in Nature remains an outstanding challenge at the forefront of modern research. From a theoretical point of view, chiral spin liquids emerge in a simple model that was imagined by Kitaev in 2006, and which allows revealing their properties using analytical tools. Remarkably, recent advances in the design of quantum simulators open a possible path for the first experimental realisation of the original Kitaev model, hence suggesting that chiral spin liquids (including their exotic quasi-particles) can be studied and manipulated in a highly-controlled experimental environment. Recent work by an international collaboration involving BoYe Sun and Nathan Goldman (ULB, Brussels), Monika Aidelsburger (LMU, Munich), and Marin Bukov (Max Planck Institute for the Physics of Complex Systems and Sofia University) proposes a realistic implementation of the Kitaev model in quantum simulators. Based on a precise pulse sequence, their system is shown to host a chiral spin liquid with non-Abelian anyons. The authors describe practical methods to probe the striking properties of these exotic states. In particular, their methods unambiguously reveal the topological heat current that flows on the edge of the system: a hallmark signature of the non-Abelian anyons that emerge on the edge of chiral spin liquids. This work paves the way for the quantum simulation of chiral spin liquids, offering an appealing alternative to their experimental investigation in quantum materials. Bo-Ye Sun, Nathan Goldman, Monika Aidelsburger, and Marin Bukov, Phys. Rev. X Quantum 4, 020329 (2023). Publication Highlights news-739 Tue, 02 May 2023 22:00:00 +0200 The tissue collider https://www.nature.com/articles/s41467-022-31459-1 Physics has a long tradition of learning about fundamental interactions by making particles collide against each other. Could a similar approach be applied to biological systems? Work by Ricard Alert of the Max Planck Institute for the Physics of Complex Systems and collaborators shows what can be learnt about the mechanics of living tissues by making them collide against each other. In experiments, the researchers placed cell monolayers on a substrate and allowed them to expand and collide. The work first characterised how two tissues change shape upon collision. The researchers discovered that denser tissues, with more cells per unit area, can mechanically displace less dense tissues. Based on their calculations, the team proposes that this displacement arises because denser tissues have a higher pressure, which allows them to push on other tissues. This theory enables measurements of the elastic properties of the tissues just from their displacements upon collision. The researchers then analyzed collisions between three tissues. Surprisingly, they found that these three-tissue events are not simply a superposition of two-tissue collisions. Instead, some cells speed up as if trying to squeeze between the two other tissues. Finally, they used all these collision principles to design and assemble specific tissue patterns, similar to tile patterns, like the diamond pattern in the image. Ultimately, these results might help engineering tissue composites for implants, as well as understanding and controlling tissue interactions during embryonic development or wound healing. In all these situations, tissues grow and collide, either merging into a single tissue or establishing clear boundaries between different tissues and organs. Matthew A. Heinrich*, Ricard Alert*, Abraham E. Wolf*, Andrej Košmrlj, and Daniel J. Cohen, Nat. Commun. 13, 4026 (2022). Publication Highlights news-736 Tue, 04 Apr 2023 22:00:00 +0200 From Dual Unitarity to Generic Quantum Operator Spreading https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.130.130402 Chaotic quantum many-body systems hide information non-locally in many degrees of freedom via a dynamical process called scrambling. Understanding the capacity of quantum systems to scramble information is a crucial requirement for the design and control of quantum computing platforms as well as being intimately related to questions of thermalisation and quantum chaos. In recent years, dual-unitary circuits have emerged as minimal models for quantum many-body dynamics in which the dynamics are chaotic yet analytically tractable. However, despite their chaoticity these circuits display behaviour that is in many respects non-generic. Michael Rampp, Roderich Moessner, and Pieter Claeys from the Max Planck Institute for the Physics of Complex Systems have investigated the effect of weakly broken dual-unitarity on the spreading of local operators, a particular probe of information scrambling. They recover two universal features of ergodic quantum spin chains absent in dual-unitary circuit dynamics: a butterfly velocity smaller than the light-cone velocity and a diffusively broadening operator front. They present a physical picture for these effects through a discrete path-integral formalism, allowing for a quantitative connection between the microscopic properties of these gates and the macroscopic butterfly velocity and diffusion constant. M. A. Rampp, R. Moessner, P. W. Claeys, Phys. Rev. Lett. 130, 130402 (2023). Publication Highlights news-735 Wed, 29 Mar 2023 12:05:00 +0200 IUPAP Medal for Frank Jülicher https://iupap.org/who-we-are/internal-organization/commissions/biological-physics/c6-news/ Frank Jülicher shares the inaugural 2023 IUPAP Medal for the Physics of Life The International Union of Pure and Applied Physics (IUPAP) has awarded the 2023 IUPAP Medal for the Physics of Life jointly to John J. Hopfield and to Frank Jülicher, director at the Max Planck Institute for the Physics of Complex Systems. The citation reads “For his key contributions to biological active matter physics, shedding light on the physical mechanisms that underlie cellular processes, including cooperative molecular motors; hearing; flagellar beat; active gels, fluids, and droplets; the active cell cortex; tissue growth and patterning; protein phase separation in cells; and self-organization of active surfaces.” The IUPAP Medal for the Physics of Life is a new award of the International Union for Pure and Applied Physics (IUPAP), presented by its C6 Commission on Biological Physics every three years, at the IUPAP International Conference on Biological Physics (ICBP). The Award, consisting of a gilded medal and a certificate, recognizes outstanding achievements in Biological Physics, regardless of the country where the research has been done, the age, or the employment status of the nominee. Congratulations, Frank!  

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Awards and Honors
news-734 Fri, 24 Mar 2023 22:00:00 +0100 Cancer cells move to stiff environments as living droplets https://www.nature.com/articles/s41567-022-01835-1 Recent work by Ricard Alert of the Max Planck Institute for the Physics of Complex Systems and his collaborators uncovered a similarity between liquid droplets and cell groups, revealing that surface tension helps cells to migrate towards stiffer environments. The new work proposes that this process, called durotaxis and which was defined in the field of cell biology, can be accounted for quite precisely with the physics of wetting. This new insight could help us to understand how cancer cells disseminate across tissues with different rigidity in our body. M. E. Pallarès*, I. Pi-Jaumà*, I. C. Fortunato, V. Grazu, M. Gómez-González, P. Roca-Cusachs, J. M. de la Fuente, R. Alert, R. Sunyer, J. Casademunt, and X. Trepat. Nat. Phys. 19, 279 (2023). Publication Highlights news-733 Fri, 24 Mar 2023 12:05:00 +0100 IUPAP Early Career Prize for Ricard Alert https://iupap.org/who-we-are/internal-organization/commissions/biological-physics/c6-news/ Ricard Alert receives the IUPAP Early Career Scientist Prize in Biological Physics (C6) 2023 The International Union of Pure and Applied Physics (IUPAP) has awarded the 2023 Early Career Prize 2023 in Biological Physics to Ricard Alert, research group leader at the Max Planck Institute for the Physics of Complex Systems and the Center for Systems Biology Dresden for "revealing how new phenomena in active matter underlie a wide range of biological processes, from the spreading of epithelial tissues, to turbulent-like flows in cytoskeletal networks, to the formation of fruiting bodies in bacterial colonies". The IUPAP C6 Early Career Scientist Prize recognizes exceptional achievements of scientists in the field of Biological Physics at a relatively early stage of their career. The recipients must be no more than eight years past the award of their PhDs (excluding career interruptions), and they are expected to have demonstrated significant scientific achievements and display exceptional promise for future achievements in Biological Physics. Congratulations, Ricard!  

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Awards and Honors
news-728 Thu, 23 Feb 2023 22:00:00 +0100 Non-Fermi-Liquid Behavior from Cavity Electromagnetic Vacuum Fluctuations https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.130.083603 In a number of different behaviour, so-called non-Fermi-liquid behaviour appears due to strong correlations between electrons. The standard theoretical scenario relies on emergent collective bosonic modes with strong critical fluctuations that destroy the electronic quasiparticles. Due to the complexity of the actual material, it is difficult to determine the microscopic origin of the relevant bosonic modes systematically. Peng Rao and Francesco Piazza of the Max Planck institute for the Physics of Complex Systems have now shown that cavity quantum electrodynamics within two-dimensional materials is ideal to implement non-Fermi-liquid behaviour. The emergent bosonic modes belong here to the vacuum electromagnetic field, a microscopic degree of freedom of which the dynamics and coupling with electrons can be controlled by cavity engineering. P. Rao and F. Piazza, Phys. Rev. Lett. 130, 083603 (2023) Publication Highlights news-727 Mon, 06 Feb 2023 22:00:00 +0100 Symmetry-induced decoherence-free subspaces https://doi.org/10.1103/PhysRevResearch.5.L012003 Preservation of coherence is a fundamental, yet subtle, phenomenon in open systems. We uncover its relation to symmetries respected by the system Hamiltonian and its coupling to the environment. We discriminate between local and global classes of decoherence-free subspaces for many-body systems through the introduction of “ghost variables”. The latter are orthogonal to the symmetry and the coupling to the environment depends solely on them. Constructing them is facilitated in classical phase space and can be transferred to quantum mechanics through the equivalent role that Poisson and Lie algebras play for symmetries in classical and quantum mechanics, respectively. Examples are given for an interacting spin system. J. Dubois, U.Saalmann, and J.M. Rost, Phys. Rev. Research 5, L012003 (2023) Publication Highlights news-726 Thu, 02 Feb 2023 10:00:00 +0100 New Research Group: Superconductivity and Magnetic Correlations https://www.pks.mpg.de/smc We cordially welcome the arrival of our new group at the institute, headed by Alexander Wietek, who joins us from the Flatiron Institute. Alex's group is interested in the way quantum particles, like electrons or atoms, organize themselves while interacting with one another. This way, Alex and his colleagues aim at understanding how the macroscopic behavior of materials, like various forms of magnetism or superconductivity, emerges. Besides trying to explain existing experimental phenomena in solid-state physics, they investigate under which circumstances entirely new states of matter, like quantum spin liquids, can occur. To solve these questions, the new group is developing numerical technology to simulate quantum many-body systems. The quantum many-body problem is considered to be exponentially hard in the number of particles. One approach Alex is pursuing is to push the limits of exact simulations by developing high-performance computing software and distributed parallel algorithms for quantum many-body systems. Furthermore, the team is also embracing tensor network methods to reduce computational complexity by representing data efficiently. Welcome at MPI-PKS!! Institute's News news-725 Sat, 14 Jan 2023 22:00:00 +0100 Discrete time crystal created by two-frequency external driving https://www.nature.com/articles/s41567-022-01891-7 Time crystals are a freshly discovered nonequilibrium phase of matter without an equilibrium counterpart, stabilized by external periodic drives and characterized by broken spatiotemporal symmetry. Scientists from the Nonequilibrium Quantum Dynamics group at the Max Planck Institute for the Physics of Complex Systems, together with collaborators at the KTH Royal Institute of Technology and at UC Berkeley, created a critical time crystal in a system of long-range interacting nuclear spins. Designing a novel two-frequency external driving protocol allowed the scientists to monitor the time-crystalline behavior continuously (avoiding the wave function collapse), and take real-time movies displaying the formation, lifetime, and meltdown of this exotic phase of matter. The experimental platform used offers unprecedented clarity and measurement throughput, which turned out fundamental for determining the boundaries of the time-crystalline phase, and investigating in detail the melting dynamics of the time crystal as it gradually heats up. W. Beatrez et al., Nat. Phys. (2023) Publication Highlights news-723 Mon, 19 Dec 2022 22:00:00 +0100 Dynamical fractal discovered in clean magnetic crystal https://www.science.org/doi/10.1126/science.add1644 A new type of fractal has been discovered in a class of materials called spin ices—famous, among other reasons, for their emergent magnetic monopole excitations. Spin ice materials are some of the most researched and best understood topological magnets. Nevertheless, the unusual dynamical properties of spin ice have been puzzling scientists for almost two decades. An international research team, including Jonathan N. Hallén and Roderich Moessner of the Max Planck Institute for the Physics of Complex Systems, has now shown that the dynamical rules governing the motion of the magnetic monopoles constrain these to move on fractal structures. By hosting the monopole motion, the fractals cause the peculiar dynamical behaviours observed in spin ice materials. The discovery was surprising because the fractals were seen in a clean three-dimensional crystal, where they would not be expected conventionally. Even more remarkably, the fractals are visible in dynamical properties of the crystal, and hidden in static ones. The capacity of spin ice to exhibit such striking phenomena makes the team hopeful that spin ice will allow further surprising discoveries in the cooperative dynamics of even simple topological many-body systems. More details can be found in a press release (PDF). J. N. Hallén et al., Science 378, 1218 (2022) See also the related Science Perspective article by F. Flicker. Publication Highlights news-720 Mon, 12 Dec 2022 22:00:00 +0100 Recipe for a spin-orbital liquid https://www.nature.com/articles/s41567-022-01816-4 An international team of scientists including Roderich Moessner of the Max Planck Institute for the Physics of Complex Systems has observed an exotic quantum state of matter: a spin-orbital liquid formed on the pyrochlore oxide Pr2Zr2O7. Here, both spin and orbital degrees of freedom remain dynamic down to extremely low temperature. It is known from the long history of condensed matter physics that suppressing orbital order down to low temperatures is extremely difficult, a precondition for the next tricky step of obtaining a spin-orbital liquid state. Pr2Zr2O7 serves as a rare counterexample in which spins and orbitals are interlocked, so that fluctuation of one necessitates fluctuation of the other. More details can be found in a press release (PDF). N. Tang, Y. Grisenko, K. Kimura et al., Nat. Phys. (2022) See also the related Nat. Phys. News & Views article by V. S. Zapf, M. Lee, and P. F. S. Rosa. Publication Highlights news-718 Mon, 28 Nov 2022 22:00:00 +0100 Scaling Description of Creep Flow in Amorphous Solids https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.208001 Amorphous solids, which include colloidal glasses, dense emulsions, foams, and granular materials, are ubiquitous and important in both engineering and industry. When subjected to a suddenly imposed stress, they can exhibit a transient flow known as creep during which the flow rate decays as a power law over time. This power law is characterized by a quantity called the creep exponent. If the stress inducing the creep flow is low, the material eventually stops moving. But if this stress is sufficiently high, the power-law decay can be followed by sudden fluidization. Together with colleagues from École polytechnique fédérale de Lausanne (EPFL) and Université Paris-Saclay, Marko Popović of the Max Planck Institute for Physics of Complex Systems developed a theory of creep flow that can predict both the creep exponent and the time at which sudden fluidization occurs, as well as the temperature dependence of these two quantities. These predictions have been tested in numerical simulations and are consistent with previously published experimental observations. The key ingredient of the proposed theory is the new concept of a transient yield stress, which reflects the dynamics of the maximal stress that the material could sustain without flowing while it undergoes creep flow. Remarkably, the scaling of the creep exponent and the time of fluidization then follow from generic properties of the transient yield stress for both athermal and thermal systems. The success of the transient yield stress concept opens new exciting questions: What is the origin of the transient yield stress and what controls its dynamics? Can the concept of a transient yield stress be employed to describe other characteristic behaviours associated with the yielding of amorphous solids, such as shear banding instabilities? Marko Popović, et al., Phys. Rev. Lett. 129, 208001 (2022), Editors' Suggestion Selected for a Synopsis in Physics Publication Highlights