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, 10 Jun 2023 02:30:30 +0200 Sat, 10 Jun 2023 02:30:30 +0200 TYPO3 EXT:news news-740 Sun, 21 May 2023 22:00:00 +0200 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 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 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 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!  

]]> Awards and Honors news-734 Fri, 24 Mar 2023 22:00:00 +0100 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 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!  

]]> Awards and Honors news-728 Thu, 23 Feb 2023 22:00:00 +0100 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 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 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 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 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 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 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 news-715 Tue, 18 Oct 2022 22:00:00 +0200 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.177001 The mechanism behind high-temperature superconductors has long been a great mystery to physicists. Even though the fundamental physical equations of interacting electrons in these materials are well-known, their solution has proved challenging. Whether or not superconductivity or the so-called "stripe order", where the density of electrons forms regular waves called "stripes", is realized has been an open question and these two states of matter have been considered in competition to one another. This study now shows that stripe order and superconductivity can, in fact, get along with one another quite well. By performing exact numerical simulations on a minimal model for cuprate superconductors, the author demonstrates that there exist states of matter with exactly one superconducting condensate per stripe. Since there are multiple stripes in the systems, there are also multiple condensates, a phenomenon called "fragmentation". The physical picture proposed in this study agrees well with experimental observations and demonstrates the predictive power of modern numerical techniques to study quantum many-body systems. A. Wietek, Phys. Rev. Lett. 129, 177001 (2022) Publication Highlights news-713 Thu, 29 Sep 2022 11:04:00 +0200 https://www.pks.mpg.de/fileadmin/user_upload/MPIPKS/Contact/Work_with_us/BMO-28026090-MPI-Physik-komplexer-Systeme_3_.pdf Application deadline: 17 November 2022. 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!  

]]> Institute's News news-712 Tue, 20 Sep 2022 22:00:00 +0200 https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.4.033224 The different microbial species in complex ecological communities like the human microbiome often have different subpopulations called phenotypes, between which they can switch stochastically or in response to environmental cues, such as toxins released by competitors or antibiotics. Pierre Haas of the Max Planck Institute for the Physics of Complex Systems and the Max Planck Institute of Molecular Cell Biology and Genetics and collaborators at the University of Cambridge have analysed the ecological implications of such responsive switching. They combined a statistical analysis of many-species systems, a numerical study of a minimal two-species model, and analytical results for still simpler mathematical models. While responsive switching to a rare phenotype is destabilising on average, they could show that responsive switching to a rare "attack" phenotype is stabilising on average. A similar "attack" subpopulation was recently observed experimentally, which underlines the importance of responsive switching for ecological stability. P. A. Haas, M. A. Gutierrez, N. M. Oliveira, and R. E. Goldstein, Phys. Rev. Research 4, 033224 (2022) Publication Highlights news-710 Fri, 02 Sep 2022 22:00:00 +0200 https://doi.org/10.1016/j.cels.2022.08.002 Biological systems fascinate scientists across disciplines because of the highly complex structures that emerge from these systems, from cells to organisms and societies. While biological systems fulfil highly specialised tasks despite noisy signals, they can also rapidly break up these structures and perform entirely different tasks when the right signals are present. A new study in Cell Systems published by Adolfo Alsina and Steffen Rulands from MPI-PKS, Wolf Reik from the Babraham Institute in Cambridge and Solenn Patalano from the BBSRC Alexander Fleming in Athens used paper wasps as a paradigmatic example. Paper wasps are social insects that display societal division of labor between workers and a queen. While this division of labor remains stable for the entire lifetime of the queen, when the queen is removed from the nest or dies the remaining workers can rapidly change their behavior and establish a new queen. Due to this behavior the paper wasps serve an experimental testing ground to study biological plasticity. Rulands and colleagues carried out a unique set of experiments in Panama where they removed the queen from paper wasp nests and then followed the reorganization process back to the intact society simultaneously on different scales of biological organization: from time-resolved profiling of brains using multi-omics of the brains to colony-level video recordings. Using theory, they showed that by balancing antagonistic molecular and colony-level processes these societies are able to distinguish between different kinds of perturbations affecting the nest: intrinsic perturbations, such as molecular noise, affect insects independently of each other and these perturbations are actively suppressed by the society. By contrast, extrinsic perturbations affect the entire society and the society reacts plasticly. Given the above, the authors conclude that by employing a self-organised multi-scale mechanism Polistes manages to overcome the seeming paradox between specialisation and plasticity. S. Patalano et al., Cell Systems 13, 1–12 (2022) Publication Highlights news-709 Thu, 01 Sep 2022 14:00:00 +0200 https://www.pks.mpg.de/nqd The research in our new group "Nonequlibrium Quantum Dynamics" lies at the intersection of many-body dynamics, quantum simulation, quantum control, and applications of machine learning in physics. It is headed by Marin Bukov, who joins MPI-PKS from the University of Sofia. Marin and his coworkers are interested in problems of both fundamental nature and immediate applications. They develop approximate analytical methods, and design numerical techniques in order to investigate different problems in quantum dynamics, and collaborate with theory groups and experimental labs to test the theoretical predictions against experiment. Welcome to the institute, Marin!  

]]> Institute's News news-708 Tue, 02 Aug 2022 22:00:00 +0200 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.066401 Quantum excited states underpin new states of matter, support biological processes such as vision, and determine opto-electronic properties of photovoltaic devices. Yet, while ground-state properties can be determined by rather accurate computational methods, there remains a need for theoretical and computational developments to target excited states efficiently. Inspired by the duplication of the Hilbert space used to study black-hole entanglement and the electronic pairing of conventional superconductivity, researchers from the Max Planck Institute for the Physics of Complex Systems and their collaborators from Munich and Modena have developed a new scheme to compute the full spectrum of a quantum many-body Hamiltonian, rather than only its ground or lowest-excited states. An important feature of their proposed scheme is that these spectra can be computed in a one-shot calculation. The scheme thus provides a novel variational platform to excited-state physics. It is also suitable for efficient implementation on quantum computers, so has the potential to enable unprecedented calculations of excited-state processes of quantum many-body systems. C. L. Benavides-Riveros et al., Phys. Rev. Lett. 129, 066401 (2022), Editors' Suggestion Publication Highlights news-707 Mon, 04 Jul 2022 22:00:00 +0200 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.148101 Much like animals can trace odors, cells also move toward certain chemicals. In fact, cells often do this in groups, which can be up to millions of individuals strong. But how do these cell populations manage to move together as a cohesive unit while following chemical cues? New work by Ricard Alert of the Max Planck Institute for the Physics of Complex Systems and collaborators shows that the answer lies in limitations in the ability of cells to sense chemicals at high concentrations. Thus, the work bridges scales by connecting the sensing of tiny molecules by individual cells to the shape and motion of an entire cell population, which can be centimeters or even larger in size. The work is important because it reveals a potentially general principle: Sensing—a distinguishing feature of living systems—governs the ability of cells to migrate in groups. This principle could operate in many other examples of collective migration, as cells and other living creatures can sense and follow a variety of stimuli, such as electric fields, temperature, and light intensity. Finally, the new results open a tantalizing question for future work: Has evolution pushed the sensing limitations of cells to ensure that they can follow chemical cues as a cohesive group? (Image credit: Mariona Esquerda Ciutat.) R. Alert, A. Martínez-Calvo, and S. S. Datta, Phys. Rev. Lett. 128, 148101 (2022) Publication Highlights