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 Sat, 20 Jul 2024 03:39:15 +0200 Sat, 20 Jul 2024 03:39:15 +0200 TYPO3 EXT:news news-784 Tue, 16 Jul 2024 22:00:00 +0200 Moving together despite turning away https://journals.aps.org/prx/abstract/10.1103/PhysRevX.14.031008 Self-propelled agents such as birds, cells, and active colloidal particles often move collectively in flocks. In the paradigmatic Vicsek model, flocking emerges due to alignment interactions between the active agents, which align much in the same way as spins do. Suchismita Das, Matteo Ciarchi, Ricard Alert of the Max Planck Institute for the Physics of Complex Systems and their collaborators have now discovered that flocking can emerge even if the agents turn away from each other. The researchers made this surprising discovery in experiments with self-propelled colloidal particles that repel more strongly in their front half than in their rear half, in such a way that they turn away from each other. They then used simulations and two types of kinetic theory to explain how these particles end up flocking. Their theory revealed that repulsion between the particles is key: When two particles interact, repulsion pushes them apart before they can turn away too much, thus producing effective alignment, as shown in the figure. This crucial role of repulsion is surprising as repulsion is not even an ingredient in the paradigmatic models of flocking, such as the Vicsek model, where collective motion emerges just from alignment interactions between particle orientations. The new work also showed that, via repulsion, the particles can form flocking crystals, which are active counterparts of Wigner crystals formed through electrostatic repulsion in electron gases. In conclusion, these active particles move in the same direction as a compromise between turning away from left and right neighbors. This mechanism of flocking could potentially be relevant for certain cells, which also turn away from each other upon collision via a process known as contact inhibition of locomotion. Whether these findings can explain how cells flock remains an open question for future work. Suchismita Das, Matteo Ciarchi, Ziqi Zhou, Jing Yan, Jie Zhang, and Ricard Alert, Phys. Rev. X 14, 031008 (2024) Publication Highlights news-783 Wed, 19 Jun 2024 11:49:00 +0200 Prof. Matthieu Wyart awarded the "Physik Preis Dresden 2024" On 18 June 2024, the French physicist Prof. Matthieu Wyart (EPFL, École Polytechnique Fédérale de Lausanne) was awarded the Physik Preis Dresden 2024. The theoretical physicist is being honoured for his pioneering contributions to various problems of complex systems, in particular the theory of financial markets, the physics of disordered and glassy systems as well as the theory of neural networks and machine learning. The Physik Preis Dresden is awarded annually jointly by the Dresden University of Technology and the Max Planck Institute for the Physics of Complex Systems (MPI-PKS). Matthieu Wyart completed his PhD in Paris in 2005, where he worked together with J.-P. Bouchaud. During this time, he developed a model of price response functions in electronic markets, which became a standard in the industry. In the field of physics of disordered systems, he made an important breakthrough very early on by explaining how the surplus of soft modes in closely-packed systems of particles is controlled by their disordered geometry. This work elegantly solved the long-standing problem of the origin of the so-called boson peak in glasses with repulsive interactions. As a postdoc, he moved to Harvard and then Princeton before becoming an assistant and associate professor at New York University. He has been a professor at EPF Lausanne since 2015. In recent years, Matthieu Wyart's original approaches and way of reasoning have had a strong impact and brought new insights into the physics of disordered systems. More recently, he has made significant contributions to the problem of the nature of the glass transition. In particular, his work suggests that increasing local energy barriers control the slowing down of dynamics in supercooled liquids, as opposed to co-operative effects. The numerous original approaches to solving problems in different fields and disciplines are testimony to his extraordinary scientific excellence. In recognition of his outstanding contributions to the physics of complex and disordered systems, the Dean of the Faculty of Physics at Dresden University of Technology, Prof. Gesche Pospiech, together with Prof. Frank Jülicher, Director at the MPI-PKS, awarded the Physik Preis Dresden 2024 to Matthieu Wyart on 18 June 2024 as part of the Physics Colloquium. The Physik Preis Dresden, endowed with 5,000 euros, was founded in 2015 by the Dresden physicist Prof Peter Fulde (1936-2024), the founding director of the MPI-PKS, and has been awarded annually to renowned scientists since 2017. The award winners are selected by a joint commission of the Dresden University of Technology and the MPI-PKS. In addition to the central criterion of scientific excellence, it is particularly important for the decision that the work of the award winners is of particular importance for the cooperation between the two DRESDEN-concept partners MPI-PKS and TUD and that their connection has been further strengthened in the long term. Prof. Matthieu Wyart awarded the Physik Preis Dresden 2024

On 18 June 2024, the French physicist Prof. Matthieu Wyart (EPFL, École Polytechnique Fédérale de Lausanne) was awarded the Physik Preis Dresden 2024. The theoretical physicist is being honoured for his pioneering contributions to various problems of complex systems, in particular the theory of financial markets, the physics of disordered and glassy systems as well as the theory of neural networks and machine learning. The Physik Preis Dresden is awarded annually jointly by the Dresden University of Technology and the Max Planck Institute for the Physics of Complex Systems (MPI-PKS).

Matthieu Wyart completed his PhD in Paris in 2005, where he worked together with J.-P. Bouchaud. During this time, he developed a model of price response functions in electronic markets, which became a standard in the industry. In the field of physics of disordered systems, he made an important breakthrough very early on by explaining how the surplus of soft modes in closely-packed systems of particles is controlled by their disordered geometry. This work elegantly solved the long-standing problem of the origin of the so-called boson peak in glasses with repulsive interactions. As a postdoc, he moved to Harvard and then Princeton before becoming an assistant and associate professor at New York University. He has been a professor at EPF Lausanne since 2015.

In recent years, Matthieu Wyart's original approaches and way of reasoning have had a strong impact and brought new insights into the physics of disordered systems. More recently, he has made significant contributions to the problem of the nature of the glass transition. In particular, his work suggests that increasing local energy barriers control the slowing down of dynamics in supercooled liquids, as opposed to co-operative effects.

The numerous original approaches to solving problems in different fields and disciplines are testimony to his extraordinary scientific excellence. In recognition of his outstanding contributions to the physics of complex and disordered systems, the Dean of the Faculty of Physics at Dresden University of Technology, Prof. Gesche Pospiech, together with Prof. Frank Jülicher, Director at the MPI-PKS, awarded the Physik Preis Dresden 2024 to Matthieu Wyart on 18 June 2024 as part of the Physics Colloquium.

About the Physik Preis Dresden

The Physik Preis Dresden, endowed with 5,000 euros, was founded in 2015 by the Dresden physicist Prof Peter Fulde (1936-2024), the founding director of the MPI-PKS, and has been awarded annually to renowned scientists since 2017. The award winners are selected by a joint commission of the Dresden University of Technology and the MPI-PKS. In addition to the central criterion of scientific excellence, it is particularly important for the decision that the work of the award winners is of particular importance for the cooperation between the two DRESDEN-concept partners MPI-PKS and TUD and that their connection has been further strengthened in the long term.

More about the Physik Preis Dresden

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Awards and Honors
news-782 Mon, 10 Jun 2024 22:00:00 +0200 Quantum skyrmion Hall effect https://journals.aps.org/prb/abstract/10.1103/PhysRevB.109.155123 The framework of the quantum Hall effect has been extended to a framework of a quantum skyrmion Hall effect by Ashley Cook of the Max Planck Institute for the Physics of Complex Systems and the Max Planck Institute for Chemical Physics of Solids, by generalizing the notion of a particle to include compactified p-dimensional charged objects. This is consistent with three sets of topologically non-trivial phases of matter previously discovered by Cook and collaborators: the topological skyrmion phases of matter, the multiplicative topological phases of matter, and the finite-size topological phases of matter. These findings indicate that topological states of D-dimensions can persist after compactification and yield previously unidentified generalizations of particles, a finding of relevance to many areas of physics, and particularly string theory, with great potential for rapid experimental confirmation. Ashley Cook, Phys. Rev. B 109, 155123 (2024) Publication Highlights news-777 Fri, 26 Apr 2024 22:00:00 +0200 Quantum Electrodynamics in 2+1 Dimensions as the Organising Principle of a Triangular Lattice Antiferromagnet https://journals.aps.org/prx/abstract/10.1103/PhysRevX.14.021010 Quantum electrodynamics (QED) is the fundamental theory that describes the interactions between electrons and photons. Its success has led some to wonder whether quantum field theories, like QED, can describe quasiparticles in a solid. These collective excitations include phonons, which describe lattice vibrations, and magnons, which are waves in a magnetic material, but might also be of a more exotic nature. In a recent study, Alexander Wietek of the Max Planck Institute for the Physics of Complex Systems and his collaborators show that QED in two spatial dimensions can be observed in frustrated antiferromagnets. An antiferromagnet is a material in which neighbouring electron spins in the crystal lattice would like to point in opposite directions. However, in certain geometries, such as a triangular lattice, it is impossible to have all neighbouring spins align in precisely the opposite way. This is called geometric frustration and can lead to strong disorder in the system. This disorder is not featureless, however. In fact, it is shown that the quasiparticles of such a spin soup, known as a quantum spin liquid, are related one-to-one to excitations of QED. Importantly, even the elusive magnetic monopoles, among a wide variety of other particle-hole excitations, are observed. The precise understanding of the spin-liquid state with magnetic monopoles as elementary excitations is a key step to discovering these exotic quasiparticles in antiferromagnetic materials. It is unlikely that the founders of QED would have predicted such a surprising emergence in condensed matter. Alexander Wietek, Sylvain Capponi, and Andreas M. Läuchli, Phys. Rev. X 14, 021010 (2024) Selected for a Viewpoint in Physics. Publication Highlights news-773 Wed, 28 Feb 2024 22:00:00 +0100 Bioenergetic costs and the evolution of noise regulation by microRNAs https://www.pnas.org/doi/10.1073/pnas.2308796121 MicroRNAs (miRNAs) are short strands of genetic material that regulate various cellular functions and developmental processes. One of the regulatory functions of miRNAs is noise control that confers robustness in gene expression. The interaction with their target messenger RNA (mRNA) requires a specific binding sequence of 6-8 nucleotide pairs in length. There are a variety of open questions about the evolution of miRNA regulation regarding their functional efficiency and binding specificity. Efe Ilker of the Max Planck Institute for the Physics of Complex Systems and Michael Hinczewski (Case Western Reserve University) show that this regulation incurs a steep energetic price, so that natural selection may have driven such systems towards greater energy efficiency. This involves tuning the interaction strength between miRNAs and their target messenger RNAs, which is controlled by the length of a miRNA seed region that pairs with a complementary region on the target. They show for the first time that microRNAs lie in an evolutionary sweet spot that may explain why 7 nucleotide pair interactions are prevalent: sequences that are much longer or shorter would not have the right binding properties to reduce noise optimally. To achieve this, they develop a stochastic model of miRNA noise regulation, coupled with a detailed analysis of the associated metabolic costs and binding free energies for a wide range of miRNA seeds. Moreover, the behaviour of the optimal miRNA network mimicks the best possible linear noise filter, a classic concept in engineered communication systems. These results illustrate how selective pressure toward metabolic efficiency has potentially shaped a crucial regulatory pathway in eukaryotes. Efe Ilker and Michael Hinczewski, Proc. Natl. Acad. Sci. USA 121, e2308796121 (2024) Publication Highlights news-772 Thu, 01 Feb 2024 22:00:00 +0100 Characterising the gait of swimming microorganisms https://physics.aps.org/articles/v17/s8 The survival strategies of Escherichia Coli are controlled by their run-and-tumble "gait". While much is known about the molecular mechanisms of the bacterial motor, quantifying the motion of these microorganisms in three dimensions has remained challenging. Christina Kurzthaler of the Max Planck Institute for the Physics of Complex Systems and her collaborators have now proposed a high-throughput method, using differential dynamic microscopy and a renewal theory, for measuring the run-and-tumble behavior of a population of E. Coli cells. Besides providing a full spatiotemporal characterisation of their swimming gait, this new method allowed relating, for the first time, molecular properties of the motor to the dynamics of engineered E. coli cells. It therefore lays the foundation for future studies on gait-related phenomena in different microorganisms and has the potential of becoming a standard tool for rapidly determining motility parameters of swimming cells. More details can be found in a press release (PDF). C. Kurzthaler*, Y. Zhao*, N. Zhou, J. Schwarz-Linek, C. Devailly, J. Arlt, J.-D. Huang, W. C. K. Poon, T. Franosch, J. Tailleur, and V. A. Martinez, Phys. Rev. Lett. 132, 038302 (2024) Y. Zhao*, C. Kurzthaler*, N. Zhou, J. Schwarz-Linek, C. Devailly, J. Arlt, J.-D. Huang, W. C. K. Poon, T. Franosch, V. A. Martinez, and J. Tailleur, Phys. Rev. E 109, 014612 (2024) Selected for a Synposis in Physics. Publication Highlights news-771 Mon, 22 Jan 2024 22:00:00 +0100 Exotic fractons constraining electron motion to one dimension https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.016701 Fractons are the latest addition to the set of exotic quasiparticles in condensed matter, and models exhibiting fracton phenomenology are highly sought after. Alexander Wietek of the Max Planck Institute for the Physics of Complex Systems and his collaborators have now proposed a model that shows this phenomenology. They studied a simple "doped" Ising magnet on the two-dimensional honeycomb lattice with anisotropic Ising couplings that exhibits a dipolar symmetry. This peculiar property leads to the complete localization of one hole, whereas a pair of two holes is localized only in one spatial dimension. The emergent dipole symmetry is found to be remarkably precise, being present up to the 15th order of perturbation theory and to numerically accurate precision away from the perturbative limit. The proposed model captures the very essence of subdimensional mobility constraints and could become a prime example of how new and exotic fracton-like quasiparticles can be implemented in a condensed matter setting. Sambuddha Sanyal, Alexander Wietek, and John Sous, Phys. Rev. Lett. 132, 016701 (2024) Publication Highlights news-764 Fri, 17 Nov 2023 22:00:00 +0100 Using quantum computers to test Jarzynski’s equality for many interacting particles https://doi.org/10.1103/PhysRevX.13.041023 Statistical mechanics is a branch of physics that uses statistical and probabilistic methods to understand the behaviour of large numbers of microscopic particles, such as atoms and molecules, in a system. Instead of focusing on the individual motion of each particle, statistical mechanics analyses the collective properties of the system. It provides a bridge between the microscopic world of particles and the macroscopic world that we can observe, explaining phenomena like the behaviour of liquids and gases, phase transitions, and the thermodynamic properties of materials. Through the statistical distribution of particle properties, such as energy and velocity, statistical mechanics helps us make predictions about how physical systems behave on a larger scale, contributing to our understanding of fundamental principles in physics and chemistry. One of the most remarkable relations in statistical mechanics is Jarzynski's equality, connecting the irreversible work performed in an arbitrary thermodynamic process with the energy and entropy of the system in thermodynamic equilibrium. Because the system is free to leave the equilibrium state during its evolution, Jarzynski’s equality is a prime example of how equilibrium physics can constrain the outcome of nonequilibrium processes. Remarkably, the familiar Second Law of Thermodynamics – a fundamental principle of physics – follows directly from Jarzynski’s equality. The Second Law is a statement about the average properties of particles in a system undergoing a thermodynamic process, and postulates that heat always flows spontaneously from hotter to colder regions of the system. Intriguingly, Jarzynski’s equality shows that this fundamental law of Thermodynamics can be “violated” in individual realizations of a process (but never on average!). Despite its fundamental importance, experimental tests of Jarzynski’s equality for classical and quantum systems are extremely challenging, since they require complete control in manipulating and measuring the system. Even more so, a test for many quantum interacting particles was until recently completely missing. In a new joint study, an international team from the Max Planck Institute for the Physics of Complex Systems, the University of California at Berkeley, the Lawrence Berkeley National Laboratory, the German Cluster of Excellence ML4Q and the Universities of Cologne, Bonn, and Sofia identified quantum computers as a natural platform to test the validity of Jarzynski’s equality for many interacting quantum particles. (A quantum computer is a computing device that uses the principles of Quantum Mechanics to perform certain types of calculations at speeds and efficiency levels that are unattainable by classical computers. Quantum computers use quantum bits, or qubits, as the basic unit of information. Hence, any quantum computer is, at its core, a system of interacting quantum particles.) The researchers used the quantum bits of the quantum processor to simulate the behaviour of many quantum particles undergoing nonequilibrium processes, as is desired for an experimental verification of Jarzynski’s equality. They tested this fundamental principle of nature on multiple devices and using different quantum computing platforms. To their surprise, they found that the agreement between theory and quantum simulation was more accurate than originally expected due to the presence of computational errors, which are omnipresent in current quantum computers. The results demonstrate a direct link between certain types of errors that can occur in quantum computations and violations of Jarzynski’s equality, revealing a fascinating connection between quantum computing technology and this fundamental principle of physics. Dominik Hahn, Maxime Dupont, Markus Schmitt, David J. Luitz, and Marin Bukov, Physical Review X 13, 041023 (2023) Publication Highlights news-763 Fri, 10 Nov 2023 22:00:00 +0100 Investigating the impact of a defect basepair on DNA melting https://pubs.aip.org/aip/jcp/article/159/14/145102/2916016/Equilibrium-melting-probabilities-of-a-DNA As temperature is increased, the two strands of DNA separate. This DNA melting is described by a powerful model of statistical physics, the Poland–Scheraga model. It is exactly solvable for homogeneous DNA (with only one type of basepairs), and predicts a first-order phase transition. Arthur Genthon of the Max Planck Institute for the Physics of Complex Systems, Albertas Dvirnas and Tobias Ambjörnsson (Lund University, Sweden) have now derived an exact equilibrium solution of an extended Poland–Scheraga model that describes DNA with a defect site that could, for instance, result from DNA basepair mismatching, cross-linking, or the chemical modifications from attaching fluorescent labels, such as fluorescent-quencher pairs, to DNA. This defect was characterized by a change in the Watson–Crick basepair energy of the defect basepair, and in the associated two stacking (nearest-neighbour) energies for the defect compared to the remaining parts of the DNA. The exact solution yields the probability that the defect basepair and its neighbors are separated at different temperatures. In particular, the authors investigated the impact of the defect on the phase transition, and the number of base pairs away from the defect at which its impact is felt. This work has implications for studies in which fluorophore-quencher pairs are used to analyse single-basepair fluctuations of designed DNA molecules. Arthur Genthon, Albertas Dvirnas, and Tobias Ambjörnsson, J, Chem. Phys. 159, 145102 (2023) Publication Highlights news-761 Sun, 29 Oct 2023 22:00:00 +0100 A Quantum Root of Time for Interacting Systems https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.140202 In 1983, the two physicists Page and Wootters postulated a timeless entangled quantum state of the universe in which time emerges for a subsystem in relation to the rest of the universe. This radical perspective of one quantum system serving as the other’s temporal reference resembles our traditional use of celestial bodies’ relative motion to track time. However, a vital piece has been missing: the inevitable interaction of physical systems. Forty years later, Sebastian Gemsheim and Jan M. Rost from the Max Planck Institute for the Physics of Complex Systems have finally shown how a static global state, a solution of the time-independent Schrödinger equation, gives rise to the time-dependent Schrödinger equation for the state of the subsystem once it is separated from its environment to which it retains arbitrary static couplings. Exposing a twofold role, the environment additionally provides a time-dependent effective potential governing the system dynamics, which is intricately encoded in the entanglement of the global state. Since no approximation is required, intriguing applications beyond the question of time are within reach for heavily entangled quantum systems, which are elusive but relevant for processing quantum information. Sebastian Gemsheim and Jan M. Rost, Phys. Rev. Lett. 131, 140202 (2023) Publication Highlights news-755 Thu, 19 Oct 2023 10:00:00 +0200 New Max Planck Fellow group established at the institute https://www.pks.mpg.de/research/divisions-and-groups The Max Planck Fellows Programme promotes cooperation between universities and Max Planck institutes and enables a university professor to install a research group at an MPI. We are glad to announce that Prof. Jan Budich from TU Dresden has started a new Max Planck Fellow group "Dissipative Quantum Matter" at MPI-PKS. The research group will explore quantum many-body systems in which dissipation plays a crucial role, for example inducing novel phases of topological matter or enabling the controlled preparation of complex quantum states in the context of quantum simulators. Regarding physical platforms, the spectrum of interest ranges from quantum condensed matter to atomic and quantum-optical many-body systems. Welcome at the institute, Jan! Institute's News news-754 Wed, 18 Oct 2023 22:00:00 +0200 Unraveling the mysteries of glassy liquids https://journals.aps.org/prx/abstract/10.1103/PhysRevX.13.031034 When a liquid is cooled to form a glass, its dynamic slows down significantly, resulting in its unique properties. This process, known as “glass transition”, has puzzled scientists for decades. One of its intriguing aspects is the emergence of “dynamical heterogeneities”, when the dynamics become increasingly correlated and intermittent as the liquid cools down and approaches the glass transition temperature. In a new collaborative study, Ali Tahaei and Marko Popovic from the Max Planck Institute for the Physics of Complex Systems, with colleagues from EPFL Lausanne, ENS Paris, and Université Grenoble Alpes, propose a new theoretical framework to explain the origin of the dynamical heterogeneities in glass-forming liquids. Based on the premise that relaxation in these materials occurs occurs through local rearrangements of particles that interact via elastic interactions, the researchers formulated a scaling theory that predicts a growing length-scale of dynamical heterogeneties upon decreasing temperature. The proposed mechanism is an example of extremal dynamics that leads to self-organised critical behavior. The proposed scaling theory also accounts for the Stokes-Einstein breakdown, which is a phenomenon observed in glass-forming liquids in which the viscosity becomes uncoupled from the diffusion coefficient. To validate their theoretical predictions, the researchers conducted extensive numerical simulations that confirmed the predictions of the scaling theory. Ali Tahaei, Giulio Biroli, Misaki Ozawa, Marko Popovic, and Matthieu Wyart, Phys. Rev. X 13, 031034 (2023). Publication Highlights news-753 Mon, 16 Oct 2023 12:05:00 +0200 Marin Bukov receives John Atanasoff Award https://m.president.bg/en/cat37/5/About-award-John-Atanasov.html The John Atanasoff Award, named after the creator of the first electronic computer - the famous scholar of Bulgarian descent, John Atanasoff, was first awarded in 2003 in support of the personal achievements of young Bulgarian researchers working in the fields of informatics and information technology. Marin Bukov, group leader at MPI-PKS, is among this year's awardees ”for his outstanding contributions to the field of artificial intelligence applied to quantum technologies, and for his role in the development of efficient innovative research and education tools used worldwide”. Congratulations, Marin!  

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Awards and Honors
news-751 Fri, 06 Oct 2023 10:04:00 +0200 Call for Distinguished PKS Postdoctoral Fellowship 2024 open! https://www.mpipks-dresden.mpg.de/fileadmin/user_upload/MPIPKS/Contact/Work_with_us/PKS_Fellow24.pdf Application deadline: 10 November 2023. Distinguished PKS postdoctoral fellows appear personally along with the departments and groups on the main research page of the institute and are expected to have at least one year of postdoctoral experience at an institution other than the one at which their PhD was awarded. Applications for this fellowship directly after completion of the PhD might be considered in exceptional cases. Please click on the link- button to see the full advertisement!  

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Institute's 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