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, 28 May 2022 15:01:11 +0200 Sat, 28 May 2022 15:01:11 +0200 TYPO3 EXT:news news-700 Wed, 25 May 2022 11:00:00 +0200 Left-right symmetry of zebrafish embryos requires surface tension https://www.nature.com/articles/s41586-022-04646-9 Bilateral symmetry of the vertebrate musculoskeletal system is necessary for proper function and its defects are associated with debilitating conditions, such as scoliosis. In a collaboration with biologists from the École polytechnique fédérale de Lausanne (EPFL) in Switzerland, Marko Popovic of the Max Planck Institute for Physics of Complex Systems has studied the early stage of body segmentation using zebrafish as a model organism. They discovered that biochemical signalling and transcriptional processes that drive segmentation are not sufficient to explain the precision and symmetry of tissue shapes and sizes. However, they found that surface tension forces of the newly formed segments are a crucial component of the mechanism that is responsible for recovery and maintenance of the symmetric body plan. This discovery highlights the importance of physical interactions for precise and robust development of living beings. S. R. Naganthan, M. Popovic, and A. C. Oates, Nature 605, 516-521 (2022) Publication Highlights news-698 Thu, 05 May 2022 18:00:00 +0200 New Research Group: Transport and flows in complex environments https://www.pks.mpg.de/de/tfce We cordially welcome Christina Kurzthaler at the institute! Christina joins MPI-PKS from Princeton University and establishes the research group "Transport and flows in complex environments“. The group aims to unravel physical phenomena arising in soft and active matter, with emphasis on the role of transport and flows for biological systems and microfluidics. Its research topics range from the hydrodynamics of swimming bacteria and their interactions with their environments to the statistical physics of active transport in porous materials to the motion of colloidal suspensions in microfluidic settings. While the group's work is theoretical, it seeks to establish collaborations with experimentalists of the Dresden research community.  

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Institute's News
news-697 Mon, 18 Apr 2022 11:00:00 +0200 Novel quantum phases of droplets https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.103201 Attractive forces are ubiquitous in nature: they glue very different objects ranging from atomic nuclei, droplets of water, to stars, galaxies, and black holes. Peter Karpov and Francesco Piazza of the Max Planck Institute for the Physics of Complex Systems have now demonstrated that highly tuneable attractive interactions can be engineered artificially using optical cavities, leading to various novel phases of quantum droplets of ultracold atoms. Upon tuning the cavity-mediated interactions it is possible to switch between superfluid droplets and incompressible water-like droplets, as well as to realise crystalline and even more exotic supersolid droplets combining superfluid and solid properties. P. Karpov and F. Piazza, Phys. Rev. Lett. 128, 103201 (2022) Publication Highlights news-696 Wed, 30 Mar 2022 11:00:00 +0200 Molecular Assembly Lines in Active Droplets https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.108102 A fundamental question in biology is how complexes of several molecules can assemble reliably. Tyler Harmon and Frank Jülicher of the Max Planck Institute for the Physics of Complex Systems have now shown that a molecular assembly line can be self-organized by active droplets where it can form spontaneously. This assembly line arranges different assembly steps spatially so that a specific order of assembly is achieved and incorrect assembly is suppressed. They have shown how assembly bands are positioned and controlled and discuss the rate and fidelity of assembly as compared to other assembly scenarios. T. S. Harmon and F. Jülicher, Phys. Rev. Lett. 128, 108102 (2022) Publication Highlights news-695 Thu, 17 Mar 2022 12:05:00 +0100 Funding to understand emergent physical properties of chromatin using synthetic nuclei https://erc.europa.eu/news/erc-2021-consolidator-grants-results ERC Consolidator Grant for Jan Brugués Today, the European Research Council (ERC) announced the winners of its latest  Consolidator Grant competition for ambitious mid-career researchers. Jan Brugués, research group leader both at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) and the Max Planck Institute for the Physics of Complex Systems (MPI-PKS) is one of the 313 laureates who were awarded the 2022 ERC Consolidator Grants. The funding is part of the EU’s Horizon Europe programme, and the winners will receive in total 632 million Euros to tackle big scientific questions. In total, 2,652 applicants submitted proposals and 12% of them will receive the funding. Male and female applicants were equally successful in winning the grants. The future grantees will carry out their projects at universities and research centers across 24 EU Member States and associated countries. This new round of grants will create an estimated 1,900 jobs for postdoctoral fellows, PhD students and other staff at 189 host institutions. Jan receives the grant for his project “Understanding emergent physical properties of chromatin using synthetic nuclei.” The main goal of this project is to resolve how the physics of molecular-scale activities result in the material properties of chromatin and how those contribute to chromatin organization and function. Jan Brugués explains: “With my project, I hope to provide a physical description of the material state of chromatin across different scales and contribute to reveal the basic physical principles that govern nuclear organization and function.” Congratulations Jan!  

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Awards and Honors
news-694 Wed, 16 Mar 2022 11:00:00 +0100 Dirac Magnons, Nodal Lines, and Nodal Plane in Elemental Gadolinium https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.097201 The exploration of band topology in crystalline solids has been at the forefront of condensed matter physics for many years in efforts tying together theoretical physics, materials science and powerful spectroscopic techniques. One relatively new avenue is the exploration of band topology in the spin wave, or magnon, excitations of magnetic materials. Spin wave topology is connected to novel magnetic transport properties, little explored symmetries and surface magnetism and offers a new platform to study interactions. One of the main current directions is to find new materials with topologically interesting band structures and this new study does exactly this by establishing the existence of Dirac nodal lines and a nodal plane in the magnons of elemental gadolinium. Gadolinium is a hexagonal closed packed magnetic metal in which, at around room temperature, the magnetic moments order into a simple ferromagnetic structure. In this new study, a team of experimentalists at Oakridge National Lab in the US together with theory collaborators explored the magnetic excitations of gadolinium in the ordered phase in unprecedented detail using inelastic neutron scattering. They found that gadolinium hosts Dirac magnons in the form of nodal lines extending along the zone corners. The existence of the nodal lines can be seen to arise from the presence of combined spin rotation and crystalline symmetries providing a first experimental example of the importance of such symmetries for band topology. In the vicinity of the nodal lines, the neutron scattering intensity can be seen to wind around the lines from strong to weak and in antiphase between the two bands (as shown in the figure). This intensity signature is a robust prediction connected to the nontrivial topology of these points. From the existence of the nodal lines one may infer the existence of magnon surface states $-$ a challenging target for future experiments. Furthermore, the nonsymmorphic crystal symmetries together with spin rotation enforce the presence of a degenerate plane of magnon excitations. Just as the nodal lines exhibit winding of the neutron intensity in their vicinity, the nodal plane is linked to a sharp flip in the intensity on paths crossing through the plane. Both the nodal plane and the intensity jump are clearly observed in the data. Phys. Rev. Lett. 128, 097201 (2022) Publication Highlights news-693 Mon, 07 Mar 2022 11:04:00 +0100 Emergency Fellowships for Scientists in Ukraine https://www.pks.mpg.de/de/work-with-us We offer Emergency Fellowships to researchers at all career stages in Ukraine. Applications are considered continuously.  

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Institute's News
news-692 Mon, 14 Feb 2022 17:00:00 +0100 Flowing by gelating - gelation enables the correct architecture of the mitotic spindle. https://www.nature.com/articles/s41567-021-01467-x In the cell, the mitotic spindle is a structure that forms during cell division and segregates the chromosomes into the two future daughter cells. Spindles are made of dynamic filaments called microtubules that are continuously transported towards the two opposite poles of the spindle by molecular motors. However, scientists still do not understand how these poleward flows are generated and how they lead to spindle self-organization. Researchers in the group led by Jan Brugués at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG), the Max Planck Institute for the Physics of Complex Systems (MPI-PKS) and the Center for Systems Biology Dresden (CSBD), worked together with Frank Jülicher’s research group at the MPI-PKS to understand how such poleward flows are generated in spindles. In 2018, the Brugués lab was able to show that the size of spindles is controlled by microtubule branching: In the vicinity of DNA, new microtubules branch off from mother microtubules like branches in a tree. However, such a branching process naturally leads to microtubules branching outwards from chromosomes, whereas in real spindles they branch inwards to interact with chromosomes during segregation. In the current study, published in the journal Nature Physics, the scientists combined in vitro experiments with physical models to show that the poleward flows together with a gelation process driven by motor crosslinking, allows for the correct microtubule inward branching observed in spindles. Benjamin Dalton an author in the study, explains, “The spindle is a highly dynamic structure where its building blocks are constantly created, transported and destroyed within seconds. Still, the spindle can survive for as long as an hour and the microtubule flows are remarkably constant throughout the structure. It’s difficult to reconcile these things.” David Oriola, another author in the study explains, “By tracking the movement of single microtubules using fluorescent microscopy, we found that the spindle did not behave as a simple fluid, but rather as a gel.” Combining large-scale simulations with experimental data, the researchers found that gelation is necessary for the generation of the poleward flows, and in turn, such flows are in charge of organizing the microtubule network such that microtubules point inwards rather than outwards. Dalton et al.: A gelation transition enables the self-organization of bipolar metaphase spindles. Nature Physics, 10 February 2022, doi: 10.1038/s41567-021-01467-x Publication Highlights news-691 Wed, 09 Feb 2022 12:05:00 +0100 Artificial intelligence and stochastic models to guide personalized cancer therapy https://medienservice.sachsen.de/medien/news/1037047 Steffen Rulands receives funding within the REDESIGN consortium to bring personalized cancer therapy to patients using organoids and predictive models. The Saxon Ministry for Science, Arts and Tourism is funding four research projects for individualized cancer therapy with around 2.3 million euros. The projects will start this year and run for three years. One of the projects is the REDESIGN consortium with the goal to develope personalized medical therapy of Gastric Cancer. This type of cancer is difficult to treat once resistance to standard chemotherapy develops. Therefore, there is a need to tailor the therapy to each patient. The REDESIGN consortium is led by Daniel E. Stange (University Hospital Carl Gustav Carus Dresden), in collaboration with Steffen Rulands, Bon-Kyoung Koo (Institute of Molecular Biotechnology of the Austrian Academy of Sciences), and Mette N. Svendsen (University of Copenhagen). Steffen Rulands will use functional drug response data generated from patient-derived organoids to predict the efficacy of different regimines of chemotherapy. These organoids are initially grown by clinical research labs from patient tumor tissue samples’and then exposed to varying cocktails of chemotherapy. Organoids are sequenced before and after treatment to detect mutations that may affect the outcome of therapy. Moreover, organoid growth speed, among other parameters, are measured during the treatment. These datasets will be used by Steffen's group to develop quantitative predictions of treatment efficiency using two complementary approaches, stochastic models and deep neural networks. The combination of the two methods will allow for high predictive and explanatory power while tackling the complexity of the data. This complexity arises from the presence of mixed populations of cells in the tumor and different constellations of mutations between tumors from different patients. Eventually, the developed model will help understand how resistance to therapy develops. More importantly, it will predict how any given patient would respond to chemotherapy based on the constellation of mutations found in the tumor. It will also assess the likelihood of tumor relapse in patients for each possible therapeutic approach and recommend the therapy that targets the tumor cells carrying mutations that make the tumor more aggressive and relapsing.  

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Awards and Honors
news-690 Thu, 03 Feb 2022 17:00:00 +0100 Reading DNA is team work https://www.nature.com/articles/s41567-021-01462-2 Life starts with one cell. When an organism develops, dividing cells specialize to form the variety of tissues and organs that build up the adult body, while keeping the same genetic material – contained in our DNA. In a process known as transcription, parts of the DNA – the genes ¬– are copied into a messenger molecule -the ribonucleic acid (RNA) – that carries the information needed to produce proteins, the building blocks of life. The parts of our DNA that are read and transcribed determine the fate of our cells. The readers of the DNA are proteins called transcription factors: they bind to specific sites on the DNA and activate the transcription process. How they recognize which location on the DNA they need to bind to and how these are distinguished from other random binding sites in the genome remains an open question. Scientists at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) and the Max Planck Institute for the Physics of Complex Systems (MPI-PKS), both located in Dresden, show that thousands of individual transcription factors team up and interact with each other. They collectively wet the DNA surface by forming liquid droplets that can identify clusters of binding sites on the DNA surface. Jose A. Morin et al: Sequence dependent surface condensation of a pioneer transcription factor on DNA. Nature Physics. 03. February 2022, doi: 10.1038/s41567-021-01462-2 Publication Highlights news-689 Thu, 03 Feb 2022 11:04:00 +0100 Call for ELBE postdoctoral Fellowships now open! https://www.pks.mpg.de/fileadmin/user_upload/MPIPKS/Research/Highlights/Highlights/ElbePostDocAd_spring_2022_final_comp.pdf Application deadline: 13 March 2022. 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, and related areas. Please click on the link- button to see the full advertisement!  

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Institute's News
news-688 Thu, 23 Dec 2021 10:49:52 +0100 How do our organs know when to stop growing? https://doi.org/10.1038/s41586-021-04346-w The smallest fish in the world, the Paedocypris, measures only 7 millimeters. This is nothing compared to the 9 meters of the whale shark. The small fish shares many of the same genes and the same anatomy with the shark, but the dorsal and caudal fins, gills, stomach and heart, are thousands of times smaller! How do organs and tissues of this miniature fish stop growing very quickly, unlike those of their giant cousin? A multidisciplinary team led by scientists from the University of Geneva (UNIGE), Switzerland, and the Max Planck Institute for the Physics of Complex Systems (MPIPKS) was able to answer this fundamental question by studying its physics and using mathematical equations, as revealed by their work published in the journal Nature. M. R. Michaelidi et al., Nature (2021) Publication Highlights news-684 Tue, 09 Nov 2021 20:31:26 +0100 Long-Range Photon Fluctuations Enhance Photon-Mediated Electron Pairing and Superconductivity https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.177002 Recently, the possibility of inducing superconductivity for electrons in two-dimensional materials has been proposed via cavity-mediated pairing. The cavity-mediated electron-electron interactions are long range, which has two main effects: firstly, within the standard BCS-type pairing mediated by adiabatic photons, the superconducting critical temperature depends polynomially on the coupling strength, instead of the exponential dependence characterizing the phonon-mediated pairing; secondly, as we show here, the effect of photon fluctuations is significantly enhanced. These mediate novel non-BCS-type pairing processes, via nonadiabatic photons, which are not sensitive to the electron occupation but rather to the electron dispersion and lifetime at the Fermi surface. Therefore, while the leading temperature dependence of BCS pairing comes from the smoothening of the Fermi-Dirac distribution, the temperature dependence of the fluctuation-induced pairing comes from the electron lifetime. For realistic parameters, also including cavity loss, this results in a critical temperature which can be more than 1 order of magnitude larger than the BCS prediction. Moreover, a finite average number of photons (as can be achieved by incoherently pumping the cavity) adds to the fluctuations and leads to a further enhancement of the critical temperature. A. Chakraborty and F. Piazza, Phys. Rev. Lett. 127, 177002 (2021) Publication Highlights news-683 Tue, 02 Nov 2021 08:28:48 +0100 Cavity QED with quantum gases: new paradigms in many-body physics https://www.tandfonline.com/doi/full/10.1080/00018732.2021.1969727 We review the recent developments and the current status in the field of quantum-gas cavity QED. Since the first experimental demonstration of atomic self-ordering in a system composed of a Bose–Einstein condensate coupled to a quantized electromagnetic mode of a high-Q optical cavity, the field has rapidly evolved over the past decade. The composite quantum-gas-cavity systems offer the opportunity to implement, simulate, and experimentally test fundamental solid-state Hamiltonians, as well as to realize non-equilibrium many-body phenomena beyond conventional condensed-matter scenarios. This hinges on the unique possibility to design and control in open quantum environments photon-induced tunable-range interaction potentials for the atoms using tailored pump lasers and dynamic cavity fields. Notable examples range from Hubbard-like models with long-range interactions exhibiting a lattice-supersolid phase, over emergent magnetic orderings and quasicrystalline symmetries, to the appearance of dynamic gauge potentials and non-equilibrium topological phases. Experiments have managed to load spin-polarized as well as spinful quantum gases into various cavity geometries and engineer versatile tunable-range atomic interactions. This led to the experimental observation of spontaneous discrete and continuous symmetry breaking with the appearance of soft-modes as well as supersolidity, density and spin self-ordering, dynamic spin-orbit coupling, and non-equilibrium dynamical self-ordered phases among others. In addition, quantum-gas-cavity setups offer new platforms for quantum-enhanced measurements. In this review, starting from an introduction to basic models, we pedagogically summarize a broad range of theoretical developments and put them in perspective with the current and near future state-of-art experiments. F. Mivehvar et al. Adv. Phys. 70, 1 (2021) Publication Highlights news-682 Tue, 02 Nov 2021 08:25:52 +0100 Signatures of Quantum Phase Transitions after Quenches in Quantum Chaotic One-Dimensional Systems https://journals.aps.org/prx/abstract/10.1103/PhysRevX.11.031062#fulltext Quantum phase transitions are central to our understanding of why matter at very low temperatures can exhibit starkly different properties upon small changes of microscopic parameters. Accurately locating those transitions is challenging experimentally and theoretically. Here, we show that the antithetic strategy of forcing systems out of equilibrium via sudden quenches provides a route to locate quantum phase transitions. Specifically, we show that such transitions imprint distinctive features in the intermediate-time dynamics, and results after equilibration, of local observables in quantum chaotic spin chains. Furthermore, we show that the effective temperature in the expected thermal-like states after equilibration can exhibit minima in the vicinity of the quantum critical points. We discuss how to test our results in experiments with Rydberg atoms and explore nonequilibrium signatures of quantum critical points in models with topological transitions. A. Haldar et al. Phys. Rev. X 11, 031062 (2021) Publication Highlights news-681 Tue, 02 Nov 2021 08:11:41 +0100 Cavity-induced quantum spin liquids https://www.nature.com/articles/s41467-021-26076-3 Quantum spin liquids provide paradigmatic examples of highly entangled quantum states of matter. Frustration is the key mechanism to favor spin liquids over more conventional magnetically ordered states. Here we propose to engineer frustration by exploiting the coupling of quantum magnets to the quantized light of an optical cavity. The interplay between the quantum fluctuations of the electro-magnetic field and the strongly correlated electrons results in a tunable long-range interaction between localized spins. This cavity-induced frustration robustly stabilizes spin liquid states, which occupy an extensive region in the phase diagram spanned by the range and strength of the tailored interaction. This occurs even in originally unfrustrated systems, as we showcase for the Heisenberg model on the square lattice. A. Chiocchetta et al. Nat. Commun. 12, 5901 (2021) Publication Highlights news-680 Mon, 01 Nov 2021 15:39:19 +0100 Carrier transport theory for twisted bilayer graphene in the metallic regime https://www.nature.com/articles/s41467-021-25864-1 Understanding the normal-metal state transport in twisted bilayer graphene near magic angle is of fundamental importance as it provides insights into the mechanisms responsible for the observed strongly correlated insulating and superconducting phases. Here we provide a rigorous theory for phonon-dominated transport in twisted bilayer graphene describing its unusual signatures in the resistivity (including the variation with electron density, temperature, and twist angle) showing good quantitative agreement with recent experiments. We contrast this with the alternative Planckian dissipation mechanism that we show is incompatible with available experimental data. An accurate treatment of the electron-phonon scattering requires us to go well beyond the usual treatment, including both intraband and interband processes, considering the finite-temperature dynamical screening of the electron-phonon matrix element, and going beyond the linear Dirac dispersion. In addition to explaining the observations in currently available experimental data, we make concrete predictions that can be tested in ongoing experiments. G. Sharma et al. Nature Commun. 12, 5737 (2021) Publication Highlights news-679 Tue, 12 Oct 2021 11:04:00 +0200 Call for Distinguished PKS Postdoctoral Fellowship 2022 now open! https://www.pks.mpg.de/fileadmin/user_upload/MPIPKS/Research/Highlights/Distinguished_PKSFellow_2022.pdf Application deadline: 24 November 2021. 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-678 Tue, 05 Oct 2021 10:38:00 +0200 New Research Group - The Physics of Living Matter https://www.pks.mpg.de/de/forschung/abteilungen-und-gruppen We cordially welcome Ricard Alert at the institute! Ricard joins MPI-PKS from Princeton University and establishes the research group "The Physics of Living Matter". The group aims at uncovering physical principles of living matter. In particular, it will develop the physics of active matter to understand collective behaviors in cells and tissues. The group's research topics include collective cell migration, self-organization in bacterial colonies, active turbulence, mechanochemical patterns in tissues, mechanically-regulated tissue growth, and active fluctuations in cells. Ricard is also a member of the Center for Systems Biology Dresden and strengthens the collaboration of MPI-PKS with experimental groups at MPI-CBG.  

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Institute's News
news-677 Thu, 16 Sep 2021 10:13:49 +0200 Reinforcement Learning for Digital Quantum Simulation https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.110502 Digital quantum simulation on quantum computers provides the potential to simulate the unitary evolution of any many-body Hamiltonian with bounded spectrum by discretizing the time evolution operator through a sequence of elementary quantum gates. A fundamental challenge in this context originates from experimental imperfections, which critically limits the number of attainable gates within a reasonable accuracy and therefore the achievable system sizes and simulation times. In this work, we introduce a reinforcement learning algorithm to systematically build optimized quantum circuits for digital quantum simulation upon imposing a strong constraint on the number of quantum gates. With this we consistently obtain quantum circuits that reproduce physical observables with as little as three entangling gates for long times and large system sizes up to 16 qubits. As concrete examples we apply our formalism to a long-range Ising chain and the lattice Schwinger model. Our method demonstrates that digital quantum simulation on noisy intermediate scale quantum devices can be pushed to much larger scale within the current experimental technology by a suitable engineering of quantum circuits using reinforcement learning. A. Bolens et al., Phys. Rev. Lett. 127, 110502 (2021). Publication Highlights