Department of Physics • University of Cologne

In physics, we are used to describing the world around us in terms of particles, or quasiparticles, with defined properties and interactions. Even when the particles have substructure, this description remains useful, for as long as the particles remain intact. Living matter consists of very complex “particles”, with internal states that are often hidden to the observer. Inferring the quantitative properties and interactions of these biological particles from targeted experiments is an exciting endeavor for physicists. I will try to demonstrate this for the case where the particles are micron-sized bacterial cells, using examples from our own and other groups work.

Lipid Nanoparticles (LNPs) represent the most advanced technology for delivery of nucleic acid. The particles exhibit a well-designed core-shell structure containing ordered lipid mesophases that encapsulate nucleic acid. We discuss distinct pH dependent structural transitions in bulk phases of cationic ionizable lipids (CILs) and their role in nucleic acid transfer. Using high resolution small angle X-ray scattering we elucidate the distinct role of a pH-driven transitions from inverse cubic Fd3m to inverse hexagonal HII phases. These structural transitions are related to gene delivery activity. Gene expression time courses, taken by live cell imaging on single cell arrays (LISCA), yield delivery delay times, mRNA translation efficiency and mRNA stability. We show that understanding the content and release kinetics of lipid nanoparticles that contain multiple nucleic acid species, allows for the design of regulatory motives, e.g. feed forward loops, resulting in tailored expression kinetics.

Neutron excess in atomic nuclei have challenged our understanding of nuclear structure and the properties of nuclear matter for decades: the existence of neutron droplets have been looked for 60 years, the discovery of neutron halos in neutron drip line nuclei have impulsed radioactive beam physics, nucleus with neutron excess show a shell structure different from the one of stable nuclei, while the spatial distribution of the neutron excess directly connects to the nuclear equation of state at saturation density. Rare isotope facilities have given access to the neutron-rich side of the nuclear landscape. This colloquium will focus on few of the most recent experiment results in the field: the first observation of an interacting free four-neutron system, the discovery of the 28O unbound system (8 protons, 20 neutrons), as well as the description of the new experiment PUMA (antiproton Unstable Matter Annihilation) at CERN aiming at using antimatter to investigate neutron skins at the nuclear surface.

One of the major challenges for future quantum information technology is to establish a global quantum network, where different quantum systems are coupled via fiber-based single-photon channels. In such a quantum network, the analog of a bit in a classical computer, the quantum bit, has to be transferred to its optical counterpart, which is a single photon. In my talk, I will describe the main components and interfaces before discussing two-dimensional (2D) materials as a promising material platform for a quantum network. I will discuss different promising two-dimensional (2D) materials: (i) Bilayer graphene has a high potential as a host material for so-called spin or valley qubits. In this direction, we realized the first few-electron quantum dots based on bilayer graphene, where we observed important requirements for a qubit, such as spin and valley blockade. (ii) Hexagonal boron nitride or transition metal dichalcogenides can be used as platforms for single photon emitters, promising highly coherent and indistinguishable photons, as previously shown for self-assembled quantum dots.

Understanding how thermal equilibrium and irreversibility arise from unitary quantum evolution is a theme as old as quantum mechanics. This question has recently been the focus of great attention due to the great experimental progress in quantum simulations, which now allow us to probe dynamics at unprecedented time scales in condensed matter physics. The current framework for understanding quantum dynamics is given by the Eigenstate-Thermalization Hypothesis (ETH). This is a simple assumption on the structure of local observables in the energy eigenbasis, that has proved to be extremely successful in describing some dynamical properties of physical Hamiltonian systems. In this colloquium, I will discuss the recent developments in the field going beyond the standard framework. First, if one is interested in correlations of multiple times (relevant beyond linear response or to account for chaos), it becomes clear that ETH as was known is incomplete. I will introduce the full version of ETH and the emergence of Free Probability as the right tool to describe it. Secondly, I will describe the different mechanisms leading to violations of ETH and I will present long-range interacting systems as a remarkable example.

The past 25 years have revealed a diversity of exoplanets far beyond what was imagined from the limited sample in the Solar System. With new and upcoming observing facilities and a rapidly growing number of nearby planets, we are beginning to bring this diversity into focus, with detailed follow-up characterization of the planets’ atmospheres. In this talk, I will focus on two key questions in exoplanet atmosphere studies: (1) what can we learn about giant planets' origins from their present-day atmospheres? And (2) what can we learn about habitability from “Earth cousins”, planets that are a little bigger or a little hotter than the Earth? I will provide some historical context on these two questions, share a few preliminary results from the first JWST observations of transiting planets, and conclude with a long-term perspective on exoplanet atmosphere characterization through the 2040s, including the search for biosignatures in the atmospheres of potentially inhabited planets.

Remarkable experimental progress in quantum simulation enabled studies of non-equilibrium phenomena in interacting quantum systems. Bringing quantum matter out-of-equilibrium is a tool to engineer desired properties, but theoretically poses a major challenge, due to the exponential growth of computational complexity. I will overview theoretical progress in describing non-equilibrium quantum matter, based on quantum entanglement. In particular, I will describe mechanisms to avoid thermalisation, which lead to coherence protection and enable non-equilibrium phenomena not envisioned within statistical mechanics. Understanding spatial and temporal entanglement out-of-equilibrium suggests new efficient computational methods and provides a unifying principle for classification of non-equilibrium phases.

Physical law imposes important constraints for virus structure, replication and spread. Here we discuss how it can help to better understand the different stages of the viral life cycle. Most viruses use a spherical protein shell to protect their genome; its assembly has to avoid kinetic trapping and malformed structures, a process that can be analyzed with statistical models for self-assembly. Many viruses, including SARS-CoV-2, influenza A and Ebola, are in addition wrapped by a membrane which anchors the glycoproteins attaching them to the host cells. Continuum models can be used to identify the physical limits of the entry process, including the minimal size and typical time required for entry. For enveloped viruses, the most critical step in the life cycle is the opening of a fusion pore, to release the genome into the host cell. Continuum models can be used to calculate the corresponding free energy landscape and to identify strategies to prevent this last step of the infection.

An elegant concept for the creation of entangled electrons in a solid state device is to split Cooper pairs by coupling a superconductor to two parallel quantum dots in a Y junction geometry Cooper pair splitting (was investigated in recent years in devices based on semiconducting nanowires and carbon nanotubes I will first review these experiments and demonstrate that high splitting efficiencies 90 can be achieved. A high CPS efficiency is a prerequisite for Bell state measurements, a clear way of proving that Cooper pairs can be extracted coherently, leading to spatially separated entangled electron pairs My aim is to present a journey in research that started around 12 years ago in my lab It shows how scientific research evolves, where one often takes detours and where one constantly must reflect the finding in the lab based on either physical intuition (simple minded models) or, if available, good theory.

The four fundamental interactions and their symmetries, the fundamental constants as well as the properties of elementary particles like masses and moments, determine the basic structure of the universe and are the basis for our so well tested Standard Model (SM) of physics. Performing stringent tests on these interactions and symmetries in extreme conditions at lowest energies and with highest precision by comparing e.g. the properties of particles and their counterpart, the antiparticles, will allow us to search for physics beyond the SM. Any improvement of these tests beyond their present limits requires novel experimental techniques. An overview is given on recent mass and g-factor measurements with extreme precision on single or few cooled ions stored in Penning traps. On the one hand, mass measurements provide crucial information for atomic, nuclear and neutrino physics as well as for testing fundamental interactions and their symmetries. On the other hand, g-factor measurements of the bound electron in highly charged hydrogen-like ions allow for the determination of fundamental constants and for constraining Quantum Electrodynamics. For example, the most stringent test of CPT symmetry in the baryonic sector could be performed by mass comparison of the antiproton with the H- ion and the knowledge of the electron atomic mass could be improved by a factor of 13. Our latest results on precision measurements with exotic ions in Penning traps will be presented.

Until the 19th century, classical astronomical research was based on measuring stellar and planetary positions for compiling star catalogues, in addition, since Newton's gravitational theory also celestial mechanics, and astronomers were mathematicians. Around 1860, astronomy underwent a revolution. Instead of only studying the direction of star light, the quantity and quality of radiation were studied for the first time. This was the beginning of modern (observational) "astrophysics". The astrophysicists began to investigate the properties of the celestial bodies with physical and chemical methods. The new topics were photometry, photography, spectroscopy/spectralanalysis, and solar physics. The next step was the introduction of theoretical astrophysics around 1900. Karl Schwarzschild (1873-1916), born 150 years ago, started with observational astrophysics by introducing photographic photometry. With his pioneering research as director of Göttingen and Potsdam observatories, he introduced new theoretical topics like solar physics, theory of stellar atmospheres, stellar structure, and Einstein's General Theory of Relativity. He achieved the breakthrough of the Hertzsprung-Russell-Diagram (HRD), developed independently by Ejnar Hertzsprung (1873-1967) in 1905, and Henry Norris Russell (1877- 1957) in 1910/12. The HRD is essential for the discussion of stellar evolution. Modern theoretical astrophysics began through the inclusion of the important new physics in astronomy.

The first deep images with the James Webb Space Telescope (JWST) have transformed our view of the Universe. With its unparalleled imaging and spectroscopic capabilities, JWST finally provides deep restframe optical observations to z=10 -- a huge leap from the current z=3. Additionally, JWST immediately extended our cosmic horizon into uncharted territory, with galaxy candidates now identified out to z~14-16, only ~250-300 Myr after the Big Bang. We are thus at the brink of finding the first galaxies that ended the cosmic Dark Ages and started the reionization of the Universe. In this talk, I will show how far we have come in understanding early galaxy build-up over the last years. I will start with the state of knowledge from three decades of Hubble and Spitzer Space Telescope datasets before JWST, and will then present an overview of our current understanding of early galaxies based on early results from the first JWST images that have become available since last summer.

Antibiotics are a mainstay of modern medicine, but there is huge global concern about the emergence of antibiotic resistant infections. Despite their importance, we understand surprisingly little about how antibiotics actually inhibit bacterial infections. This is a complex problem because of the interplay between antibiotic action and bacterial growth, which connects with physics via nonlinear dynamics, mechanics and stochasticity. I will discuss, with examples, how bacteria grow in different scenarios. I will further discuss how statistical physics approaches can provide new understanding of how antibiotics work in the context of growing bacteria, with implications for antibiotic resistance evolution.

In solid-state matter, topological properties of the band structure can enforce the appearance of conducting one-dimensional edge states at the boundaries of the material, while the bulk remains insulating. These states are a fascinating playground to study the physics of one-dimensional quantum coherent conductors. They also provide a support system for ‘topological quantum bits’, robust against local perturbations, and envisioned to solve decoherence problems in the realization of quantum computers. I will discuss how one can utilize GHz excitations and current correlations to generate, manipulate and study excitations in these systems down to the elementary level of single electrons.

We are all made from nuclear matter, with carbon, nitrogen and oxygen being among the most essential to form all life on earth. Although Earth’s complex organic life is dictated by the rules of biology and organic chemistry, the fact that these elements are available in large quantities is a direct consequence of their nuclear properties. Nuclear astrophysicists have a detailed understanding about how lighter elements are formed by nuclear fusion reactions in dying stars. Thus, Carl Sagan was correct when he famously said, “We are made of starstuff.” Fusion reactions are however not able to explain the creation of heavier elements, whose exact origin is a complex puzzle with many open questions. In this presentation I will provide an overview about current experimental efforts in the field of explosive nucleosynthesis. I will discuss the origin of the rare 60Fe isotope detected via Accelerated Mass Spectrometry at the University of Cologne, as well as our efforts to enhance the sensitivity for detection of this key isotope in the future. I will also show recent results from Radioactive Ion Beam facilities which enable us to study neutron-rich nuclear matter, playing a pivotal role in neutron star merger events.

Unconventional superconductivity with high critical temperatures, topologically non-trivial phases, frustrated magnetism, spin-liquids or the intensively discussed Kitaev phases are a few examples of exotic states in quantum materials. One of the big challenges in quantum physics is the microscopic description of such systems. Moreover, being able to understand them implies the possibility of predicting compounds with desirable properties. In this talk, I will present and discuss strategies for designing quantum materials from first principles and by using statistical methods, and will motivate their possible use for present technological applications.

Since its birth roughly 60 years ago, the field of Nuclear Astrophysics strives to provide a comprehensive description of element synthesis in the Universe. While parts of stellar nucleosynthesis are well understood, others remain elusive to this day. Especially, the production of elements heavier than iron has been one of the major open questions in the field. Multiple processes and stellar sites contribute to the complex puzzle of heavy element production. Interpreting the astronomical observations requires the understanding of the nuclear processes that drive stellar explosions. This colloquium will focus on the critical nuclear properties needed to explain heavy element nucleosynthesis. I will discuss recent experimental results, as well as new initiatives and future plans at the next generation rare isotope facility, the Facility for Rare Isotope Beams (FRIB) at Michigan State University.

The mitigation of climate change requires a comprehensive transformation of our energy system. Power plants based on fossil fuel must be replaced by renewable energy sources, which challenges the operation and stability of the electric power system. In my talk, I will review the key challenges and discuss how methods and ideas from theoretical physics can contribute to their solution. I will focus on two topics: (i) Renewable power fluctuates on many time scales, making it increasingly difficult to balance generation and load. Methods from stochastic time series analysis are essential to quantify these fluctuations and to understand their impact on power system operation. (ii) Damages of transmission and generation infrastructures are the biggest threat for system stability. Network science helps to understand how failures spread and enables the design of resilient grid structures.

Workshop MENTAL HEALTH IN MASTER/PHD STUDIES - CHALLENGES AND COPING STRATEGIE

(Antrittsvorlesung) Remote attendance possible via: https://uni-koeln.zoom.us/j/7641714854 Kennwort: 209699

(Antrittsvorlesung) Remote attendance possible via: https://uni-koeln.zoom.us/j/7641714854 Kennwort: 209699

Remote attendance possible via: https://uni-koeln.zoom.us/j/7641714854 Kennwort: 209699

Remote attendance possible via: https://uni-koeln.zoom.us/j/7641714854 Kennwort: 209699

The SARS-CoV-2 pandemic has resulted in unprecedented genomic and epidemiological surveillance as well as virological characterization in record time. The volume of data and requirement for rapid feedback to decision makers required continuous data analysis and method development to make sense of the data. Multiple variants of SARS-CoV-2 have arisen independently from each other and swept the globe over the course of two years. In contrast, endemic RNA viruses we often see co-circulation of variants and gradual emergence of one variant from another. This endemic circulation is characterized by an approximate equilibrium between the build-up and decay of immunity. I will discuss models of the transition from pandemic to endemic circulation, the possibility of speciation, and the drivers of antigenic evolution in SARS-CoV-2 and other viruses. Remote attendance possible via: https://uni-koeln.zoom.us/j/7641714854 Kennwort: 209699

Antrittsvorlesung.

Quantum computers offer important speed-ups in the solution of a variety of problems. One of them is the simulation of quantum many-body systems, as they appear in atomic, condensed matter or high-energy physics, or quantum chemistry. Other, like SAT, are related to classical optimization problems. In this talk I will first review some of the quantum algorithms to simulate the equilibrium and dynamics of quantum many-body systems. Then I will present a hybrid quantum-classical algorithm to solve SAT problems with (relatively) small quantum devices.

All animals and plants are associated to a huge number of microbes that live together with them or even within them. These microbes often have fundamental roles in the functioning of their hosts, from metabolic functions to defense against diseases. In many cases, a disease microbiome seems distinct from a healthy one. This multi-stability of microbiomes can be understood in terms of game theoretical models that describe the interactions between microbes, but it is challenging to assess the associated parameters from experimental data. On the other hand, many microbes will randomly vary in their abundance, such that stochastic models are more appropriate to describe them. In the most extreme case of neutral models, it is assumed that all microbes are identical. Such neutral models are widely used in theoretical ecology and they can be directly applied to the microbiomes of a wide variety of host organisms. Neutral models allow to identify key microbial types, which are not necessarily those that are found in particularly high abundance.

Isolated systems tend to evolve towards thermal equilibrium, a special state that has been a research focus in physics for more than a century. By contrast, most processes studied in biological systems are far from equilibrium. A fundamental overarching hallmark of all these processes is the emergence of structure, order, and information, and we are facing the major challenge to identify the underlying physical principles. Two particular exciting problems are the self-organised formation of spatio-temporal patterns and the robust self-assembly of complex structures. In both fields there are recent advances in understanding the underlying physics that will be reviewed in this talk.

Granular materials are characterized by an additional degree of freedom, rotations, which become particularly relevant for spherical particles. They allow for soft modes under shear which do find realizations for instance in tectonic faults. A packing of spheres is called bi-chromatic if every loop formed by contacts is even. In three dimensions, bi-chromatic bearings have many different sliding-free configurations, so called bearing states. If all loops have length four the system exhibits four continuous degrees of freedom and a systematic way of constructing such bearing states can be devised. By considering spheres of different size, packings with bearing states can even be made space-filling. The construction and mechanical properties of such space-filling bearings will be discussed. Their bearing states can be viewed as a realization of solid turbulence exhibiting Kolmogorov scaling and anomalous heat conduction. In three dimensions a continuum of such configurations can be obtained as cuts through four-dimensional space-filling bearing states. Bearings states can be perceived as physical realizations of networks of oscillators with asymmetrically weighted couplings. These networks can exhibit optimal synchronization properties through tuning of the local interaction strength as a function of node degree or the inertia of their constituting rotor disks through a power-law mass-radius relation . Under this condition, the average participation per disk is maximized and the energy dissipation rate is homogeneously distributed among elementary rotors. The synchronization of rotations occurs in avalanches following a broad size distribution.

Starting from examples of experimental systems which exhibit growth and pinning I will give an introduction into the physics of elastic systems with quenched disorder in non-equilibrium situations. We review developments in the description of depinning and avalanches, as well as in the study of the Kardar-Parisi-Zhang (KPZ) class of stochastic growth. We introduce some of the analytical methods which lead to predictions testable (and sometimes tested) in experiments. Our last example is the calculation of memory effects in the KPZ class in expanding geometries which illustrates the remarkable connections between growth and disordered systems.

The celebrated KPZ equation (Kardar, Parisi, Zhang, 1986) is an important milestone in statistical physics, originally introduced to describe the late time dynamics in two dimensional growth models. Over the last 30 years, the KPZ story has evolved in various interesting directions, making links on the way to different areas of physics and mathematics. This includes in particular the link to the famous Tracy-Widom distribution in random matrix theory. The story of KPZ is a very successful one, involving theoretical physics, mathematics and experiments--a fertile playground for interdisciplinary science. In this talk, I will review the evolution of the KPZ story, pointing out the important landmarks as I go along. At the very end, I will discuss some recent developments establishing a nice link between the KPZ height fluctuations and the edge physics in cold atom systems.

The conceptual basis for a classical nonlocal generalization of Einstein's theory of gravitation is presented. The framework of general relativity is enlarged by the introduction of a preferred frame field; then, history dependence is introduced. Nonlocality --- in the sense of an influence ("memory") from the past that endures --- could be a natural feature of the universal gravitational interaction. Nonlocal gravity is formally analogous to the nonlocal electrodynamics of media. The nonlocal aspect of gravity can simulate dark matter. The implications of nonlocal gravity theory for the problem of dark matter in galaxies, clusters of galaxies, and cosmology are discussed. Special Colloquium honoring Friedrich Hehl's 80th birthday.

Warum und zu welchem Ende ist es lohnenswert, sich mit den Beziehungen zwischen Physik und Literatur zu beschäftigen? Das soll im Vortrag anhand von historischen Beispielen und systematischen Analysen skizziert werden. So ist z.B. zur Zeit Johannes Keplers die Synthese wissenschaftlicher und literarischer Schreibweisen in einem Text noch denkbar: Kepler entwirft 1609 in seinem Somnium eine fiktive Mondreise, die den Kampf zwischen den miteinander konfligierenden Weltbildern inszeniert und durch allegorische, optische, narrative und wissenschaftliche Schreibverfahren der neuen astronomischen Auffassung zur Verbreitung verhilft. Mit Kepler als Vorbild reflektieren auch heute literarische Texte den Beitrag der Physik zur Kultur des 20. und 21. Jahrhunderts, so z.B. Thomas Lehrs Roman '42' und Raoul Schrotts Epos 'Erste Erde'. Das Erlanger Zentrum für Literatur und Naturwissenschaft (ELINAS) widmet sich diesem interdisziplinären Austausch durch Tandemprojekte: dieses zusammen mit der Literaturwissenschaftlerin Aura Heydenreich.

Comets with their coma and tail are a spectacular sight on the night sky; they are important objects to understand the origin of our solar system. Comets are pristine and thus carry information on how they initially formed 4.5 billion years ago. 67P/Churyumov-Gerasimenko is the first comet studied in detail with a spacecraft in its vicinity for more than two years along its orbit around the sun. The Rosetta mission of the European Space Agency arrived on August 6, 2014, at the target comet 67P. Onboard the Rosetta spacecraft, the two scientific cameras, the OSIRIS narrow- and the wide-angle camera, are observing the cometary nucleus, its activity, as well as the dust and gas environment. The presentation will give an overview on what OSIRIS observed. The scientific results reveal a nucleus with two lobes and varied morphology. Active regions are located at steep cliffs and collapsed pits which form collimated gas jets. Dust is accelerated by the gas, forming bright jet filaments and the large scale, diffuse coma of the comet.

The world we live in is made of 81 stable chemical elements and another dozen of radioactive species all coming in different abundances. How were these elements synthesized in nature? What are the cosmic sites for their formation? Despite considerable progress in our understanding, the sites for the nucleosynthesis of heavy elements are still unclear. Neutron-star mergers are the strongest candidates. Yet, scientists are lacking quantitative information on properties of neutron-rich nuclei for deeper insight. New research infrastructures for addressing the open questions are under construction or have even started operation. At Darmstadt the international Facility for Antiproton and Ion Research (FAIR) is under construction, with considerable arsenal of novel instruments being already partly ready for use. We will motivate some experimental routes, give an overview of the FAIR project, in particular with respect to its pillar on Nuclear Structure, Nuclear Astrophysics and Reactions (NU STAR), and address recent scientific successes and progress.

Der Hauptvorteil der Mikroskopie mit Röntgenstrahlung ist die Möglichkeit, auch das Innere von Objekten zerstörungsfrei abbilden zu können. Aber obwohl die Wellenlänge von Röntgenstrahlung im Bereich atomarer Abstände liegt, gelingt es heute nicht, Atome aufzulösen. Das liegt vor allem an den heutigen Röntgenoptiken, die aufgrund der schwachen Wechselwirkung von Röntgenstrahlung mit Materie eine stark beschränkte numerische Apertur haben, und so ihr Auflösungsvermögen begrenzt wird. Ein Ausweg ist der Verzicht auf eine abbildende Röntgenoptik und die Beleuchtung der Probe mit kohärenter Röntgenstrahlung. Das von der Probe gestreute Licht wird von einem Flächendetektor aufgezeichnet. Dabei geht die Information über die Phase der gestreuten elektromagnetischen Welle verloren. Diese kann mit Hilfe numerischer Methoden und zusätzlichen Informationen rekonstruiert werden, so dass sich ein Bild der Probe errechnen lässt. Dabei sind heute höchste Auflösungen im Bereich von ca. 5 nm möglich. In diesem Vortrag wird ein Überblick über die Bildgebung mit kohärenter Röntgenstrahlung an modernen Synchrotronstrahlungsquellen und dem Röntgen-Freie-Elektronen-Laser gegeben.

Astronomical observations have shown that carbonaceous matter is ubiquitous in our own as well as distant galaxies and a significant number of molecules that are used in contemporary biochemistry on Earth are found in interstellar and circumstellar regions as well as solar system environments. Understanding the evolution of organic molecules and their voyage from molecular clouds to the early solar system and Earth provides important constraints on the emergence of life on Earth and possibly elsewhere. The spectacular touch-down of the Philae lander on the comet 67/P allowed the first measurements of organic molecules on a cometary surface. These results contribute new insights into impact delivered material that may have provided significant raw material for the origin of life. In-depth understanding of the organic reservoir in different space environments as well as data on the stability of organic and prebiotic material in solar system environments are vital to assess the sources of prebiotic material available to the young planets and the search for life in our solar system. This lecture will review the evolution of organic matter in space including recent observations, space experiments and laboratory research and discuss the science and technology preparation necessary for robotic and human exploration efforts investigating habitability and biosignatures in our solar system.

Viele Menschen halten sich für unmusikalisch. Sie mögen ihre Stimme nicht und singen nicht mit, wenn in Gesellschaft Lieder angestimmt werden. Aber neue Erkenntnisse der Hirnforschung zeigen, dass bis auf eine kleine Minderheit praktisch jeder Mensch musikalische Fähigkeiten besitzt. Wir kommen mit einem fest verdrahteten musikalischen Sinn auf die Welt. Der Vortrag zeigt anhand von überzeugenden Tonbeispielen, wie viel Musikalität in jedem Menschen steckt, auch wenn er nie ein virtuoser Musiker werden wird.

Die Übertragung von Bildern und Videos im Internet ist nur möglich, da solche Datensätze hochgradig komprimierbar sind. Bei der Aufnahme der Daten wurde diese Eigenschaft jedoch bisher nicht benutzt: Eine Digitalkamera z.B. tastet das Bild Pixel für Pixel ab und reduziert es erst danach auf seine wesentlichen Komponenten. Seit etwa zehn Jahren zeigt die viel beachtete Theorie des compressed sensing, dass dem nicht so sein muss. In vielen Situationen kann man Datensätze fehlerfrei aus einer Menge von Messungen rekonstruieren, deren Anzahl lediglich proportional zur komprimierten Größe der Daten ist. Physiker waren von Anfang an an der Entwicklung der Theorie beteiligt. Ich werde eine Reihe von Anwendungen vorstellen, die auf mathematischen Methoden aus der Quantenmechanik aufbauen. Die Beispiele umfassen Aufgaben der Bildverarbeitung, der Mobilkommunikation, aber auch der experimentellen Rekonstruktion quantenmechanischer Dichtematrizen. Alle bekannten Beweismethoden beruhen auf randomisierten Konstruktionen, bei denen die Messungen zumindest teilweise zufällig gewählt werden müssen. Ein Schwerpunkt des Vortrags wird die Rolle des Zufalls und Ansätze zur Derandomisierung sein.

Topological insulators and superconductors are new quantum states of matter that are characterized by nontrivial topological structures of the Hilbert space. Recently, they attract a lot of attention because of the appearance of exotic quasiparticles such as spin-helical Dirac fermions or Majorana fermions on their surfaces, which hold promise for various novel applications. In this colloquium, I will introduce the basics of those materials and present some of the key contributions we have made in this new frontier.

Planets are expected to form in circumstellar disks around young stellar objects - a common by-product of the star-formation process. Consequently, these disks provide the key to evaluate and to refine existing hypotheses for the various phases of the planet formation process. Currently, various instruments/observatories go into operation which will provide the required angular resolution and sensitivity over a broad wavelength range which are ideal for investigating the potential planet- forming region in circumstellar disks. I will discuss the feasibility to study the various stages of the planet formation process observationally - from the growth of submicron-sized dust grains in young, gas-rich circum-stellar disks to the stage of long-term stable planetary systems embedded in debris disks. In this context, a special focus will be on protoplanets which represent the major missing link on the way from dust to planets.

Theoretical Nuclear Physics has entered a new era. Using the powerful machinery of chiral effective Lagrangians, the forces between two, three and four nucleons can now be calculated with unprecedented precision and with serious uncertainties. Furthermore, Monte Carlo methods can be adopted to serve as a new and powerful approach to exactly solve nuclear structure and reactions. I discuss the foundations of these new methods and illustrate them with a variety of intriguing examples. Variations of the fundamental constants of Nature can also be investigated and the consequences for the element generation in the Big Bang and in stars are considered. This sheds new light on our anthropic view of the Universe.

In 1964 the theoretical work of Higgs, Guralnik, Hagen, Kibble, Brout, and Englert led to the prediction that, as a consequence of the coupling bet- ween matter currents and gauge particles, the gauge particles can acquire a non-zero mass. As Higgs phrased it, „this phenomenon is just the relati- vistic analog of the plasmon phenomenon to which Anderson has drawn attention: that the scalar zero-mass excitations of a superconducting neu- tral Fermi gas become longitudinal plasmon modes of finite mass when the gas is charged.“ A superconducting gap has collective oscillations of its amplitude –equi- valent to the Higgs particle- and of its phase. As shown by Anderson in 1958, the longitudinal and transverse oscillations of the superconducting condensate coupled to the electromagnetic field now acquire a finite mass, which is seen experimentally in the energy-momentum dispersion. In cer- tain superconductors two or more condensates coexist. Weak coupling bet- ween the condensates then gives rise to the so-called Leggett-exciton, and the coupling to the electromagnetic field makes that two or more massive photon-branches coexist. These and many other phe- nomena in elementary par- ticles and condensed matter are marvelous by the beau- ty and simplicity of the prin- ciples uniting them, despite conditions and energy sca- les being so vastly different.

The goal of my group‘s research is to prepare and chemically functionalize layered materials and then to characterize them in-situ using a novel combination of photoelectron and optical spectroscopies. This approach provides a solution to the intense research efforts in trying to engineer, probe and unravel many-body physics and the superconducting coupling mechanism in layered solids. Regarding the materials under investigation, I will show results from the growing family of 2D materials such as graphene, hexagonal boron nitride, transition metal dichalcogenides and phosphorene. Chemical functionalization using dopants allows for an unprecedented control over their physical properties. The proposed material systems provide a new arena to explore diverse condensed matter phenomena such as electron correlation, electron-phonon coupling and superconductivity.

While most current biological research focuses on molecular, biochemical aspects of cell and their functioning, we are interested in their global physical properties. I will discuss our recent findings that the mechanical properties of cells determine the physical limits of cell function, for example in cell migration. Cell mechanics can therefore be used to characterize cells, to monitor physiological changes and to diagnose pathological alterations, such as cancer progression. Another example for the importance of physics in biology are the optical properties of cells, specifically in the retina. We have shown that there are cells in the retina that act as optical fibers and that photoreceptor cells even invert their usual nuclear chromatin arrangement to turn them into micro-lenses. Both aspects improve the light transmission through the retina and help to mitigate the disadvantage of its inverted structure. These results provide novel insight into the importance of physics for biological function and even offer new diagnostic and therapeutic avenues for further exploration.

Twenty years ago the first Jupiter-mass planet was found orbiting a sunlike star. With a 4-day orbital period 51 Peg b was the first indication that planetary systems could be far more diverse than what we expected from the properties of our own solar system. Early exoplanet discoveries consisted mostly of giant planets in single systems. We now know of thousands of multi-planet systems and have detected planets with the mass of earth, albeit with short orbital periods. The field has also moved into an era where exoplanets are being characterized in terms of their true mass, radius, density, surface temperature, and atmospheric features. I will discuss the early history of exoplanet research but will focus largely on two space missions CoRoT and Kepler, that have been at the forefront of these characterization studies. Almost 20 years after the discovery of 51 Peg, a giant planet in a 4-day orbit, the field of extrasolar planets continues to produce unexpected discoveries.

How turbulence arises in simple shear flows, such as pipes and channels has been an open question for over a century. In these flows turbulence is found despite the linear stability of the laminar flow and transition is caused by finite amplitude perturbations. Despite numerous experimental and theoretical studies it has not been possible to determine a well defined critical point nor to clarify the nature of the transition. It will be shown for the examples of pipe and Couette flow that the onset of sustained turbulence is a nonequilibrium phase transition. The critical point is determined by resolving the extremely long time scales of the underlying growth and decay processes. By detailed numerical simulations and experimental measurements close to the transition point we also determine the critical exponents and show that this transition falls into the directed percolation universality class.

A chemical element is characterised by the total number of positively charged protons in the atomic nucleus. The interplay between the attractive short range strong force and the repulsive long range Coulomb force leads to a limit in the number of protons and neutrons that can be bound in a nucleus. Today single atoms of elements up to Z=118 have been created in the laboratory. [...]

How turbulence arises in simple shear flows, such as pipes and channels has been an open question for over a century. In these flows turbulence is found despite the linear stability of the laminar flow and transition is caused by finite amplitude perturbations. Despite numerous experimental and theoretical studies it has not been possible to determine a well defined critical point nor to clarify the nature of the transition. It will be shown for the examples of pipe and Couette flow that the onset of sustained turbulence is a nonequilibrium phase transition. The critical point is determined by resolving the extremely long time scales of the underlying growth and decay processes. By detailed numerical simulations and experimental measurements close to the transition point we also determine the critical exponents and show that this transition falls into the directed percolation universality class.

Magnetische Datenspeicher und Logikelemente auf atomarer Skala: was heute noch Vision ist, könnte eines Tages Wirklichkeit werden. Neue Methoden der atomar auflösenden Mikroskopie erlauben den direkten Zugang zu magnetischen Strukturen und dynamischen Prozessen auf atomarer Skala. Dabei werden nicht nur neue magnetische Zustände entdeckt, sondern auch die fundamentalen magnetischen Wechselwirkungen zwischen einzelnen magnetischen Atomen erforscht. Mit Hilfe der gezielten Manipulation einzelner magnetischer Atome und Nanostrukturen auf Oberflächen lassen sich bereits heute funktionale Bauelemente maßschneidern. Dies könnte die Informations- und Kommunikationstechnologie in gleicher Weise revolutionieren, wie wir dies in den vergangenen dreißig Jahren erlebt haben.

The origin of life is one of the fundamental, unsolved riddles of modern science. Life as we know it is a stunningly complex non-equilibrium process, keeping its entropy low against the second law of thermo­dynamics. Therefore it is straightforward to argue that first living systems had to start in a natural non-equilibrium settings. Recent experiments with non-equilibrium microsystems suggest that geological conditions should be able to drive molecular evolution, i.e. the combined replication and selection of genetic molecules towards ever increasing complexity. As a start, we explored the non-equilibrium setting of natural thermal gradients. Temperature differences across rock fissures accumulate small monomers more than millionfold by thermo­phoresis and convection. Longer molecules are exponentially better accumulated, hyperexponentially shifting the polymerization equilibrium towards long RNA strands. The same setting implements convective temperature oscillations which overcome template poisoning and yield length-insensitive, exponential replication kinetics. Accumulation and thermally driven replication was demonstrated in the same chamber, driven by the same temperature gradient. Protein-free, non-ligating replication schemes can be driven by thermal convection. For example, the hairpins of tRNA can be used for reversible codon-sequence replication, bridging from replication of genes to the translation of proteins. Non-templated polymerization and hybridization-dependent degradation leads to replication-like information transmission. Replication and trapping of DNA persist over long time in a constant influx of monomers, closely approaching the criteria for an autonomous Darwin process. Besides temperature gradients, many more non-equilibrium settings can be imagined and become increasingly accessible to experimentation. For example, geological pH gradients, geological redox potentials or the optical excitation of geological nanoparticles should drive metabolic reactions in a very peculiar way.

Developments in string theory and black hole physics indicate that gravity should be viewed as an emergent phenomenon that is derived from an underlying microscopic description. Following these insights I illuminate the basic mechanisms responsible for the emergence of gravity. I will argue that space time, matter and gravity originate from a highly entangled quantum mechanical system, whose energy contains the dark energy. Gravity, or rather inertia, appears as an adiabatic reaction force, while non-adiabatic corrections due to slow relaxation processes lead to the phenomena attributed to dark matter. These considerations lead to a universal formula for the dark matter distribution which explains the observed velocity profiles for all types of galaxies and galaxy clusters and agrees with the cosmic dark matter density obtained from the WMAP and Planck-data.

Die Quantenmechanik hält viele Überraschungen bereit – eine immer wiederkehrende Erfahrung, die nicht nur Physik-Studierende in den ersten Semestern machen, sondern auch eine, die der aktuellen Forschung immer wieder neuen Antrieb verleiht. Etwa dann, wenn das Zusammenspiel einer großen Zahl quantenmechanischer Freiheitsgrade in subtiler Weise konspiriert und zu qualitativ völlig neuen Effekten und Materialeigenschaften führt. Ein besonders faszinierendes emergentes Phänomen dieser Art ist die Entstehung topologischer Ordnung. In diesem Kolloquium werde ich berichten von der aktuellen Suche nach topologischer Ordnung in einer Vielzahl von physikalischen Systemen, den Hoffnungen auf den Einsatz topologischer Materie in Quantencomputern, sowie all den kleinen und großen Hürden auf dem Weg dorthin – etwa in Form all jener Instabilitäten topologischer Ordnung, die durch Unordnung hervorgerufen werden, und dabei neuer Quell eben jener Faszination der Quantenmechanik sind.

At the microscopic level the correct working of our organism vitally depends on chemical and physical signals. It was shown recently that signals of mechanical nature result in very profound effects on animal cells. Here, concepts and techniques from physics are profoundly changing the understanding of biological phenomena. We have developed methods to apply defined mechanical stimuli to cells and quantify their mechanical responses and activity. Using such techniques we, and others, are approaching the principles underlying the intricate interplay of cells and forces.

Magnets and superfluids provide the simplest examples of symmetry breaking and correlations in interacting quantum systems. When disorder is thrown into the mix, particularly in low-dimensional quantum systems, novel and universal behavior often emerges. In my talk I will first explore some surprising effects of disorder in systems of non-interacting electrons, and magnetic chains. I will then focus on the superfluid-insulator transition for interacting bosons in a disordered environment. Recent research on this system has brought about a new understanding of superfluidity and its demise in low-dimensional disordered bosonic systems

Ultrakalte Gase bieten bemerkenswerte Möglichkeiten um das Verhalten stark korrelierter Quantensysteme zu erforschen. In diesem Vortrag zeige ich, wie es möglich ist solche Gase in optischen Gittern auf der Ebene einzelner Atome abzubilden und zu manipulieren. Diese Techniken haben uns erlaubt Higgs-artige Anregungen in Vielteilchensystemen zu beobachten. Weitere Themen sind künstliche Eichfelder in ultrakalten Gasen, mit denen magnetische Felder von mehreren tausend Tesla erzeugt werden können und Bose-Einstein Kondensate bei negativen Temperaturen.

A key step to reducing power consumption of mobile devices is to replace volatile memory by fast non-volatile spintronic memory. Novel low power memories with switching by spin-polarized currents have been proposed. We study the rich physics of the interaction between magnetization and spin currents as well as photons, and we use these to excite spin dynamics and manipulate the magnetization on ultrafast timescales. We are probing the magnetization dynamics to gauge the ultimate speed limits of spin angular momentum transfer that governs device switching speed.

Wie beeinflusst die globale Klimaerwärmung die Häufigkeit von Wärmerekorden? Diese Frage wird oft auch in der Öffentlichkeit diskutiert. Dabei sind Rekorde nicht nur für die Medien interessant, sondern auch wissenschaftlich eine besonders dankbare Art der Extreme, da über Rekorde einige statistische Aussagen möglich sind ohne die Verteilungsfunktion zu kennen. Das unterscheidet Rekorde von Extremen, die z.B. als Überschreitung eines vorgegebenen Temperaturwertes definiert sind. Wir haben das Auftreten von Rekorden in der globalen Durchschnittstemperatur analysiert ebenso wie in lokalen Monatsmitteltemperaturen. Dabei zeigt sich, dass weltweit die Häufigkeit von Wärmerekorden in lokalen Monatstemperaturen heute rund fünf mal so hoch ist, wie sie in einem stationären Klima (also ohne Klimaerwärmung) wäre.

To understand the emergence of spatiotemporal structures in biological systems remains a major challenge to this day. Self-organization of a limited number of different agents has been found to account for structure formation in sea shells, slime mold aggregation, and bee colonies. On a subcellular level, however, the importance of self-organization of proteins and other molecules for forming vital structures is still debated. In this talk, I will discuss recent experimental and theoretical advances that indicate that self-organization plays an important role in cellular processes like cell division and cell locomotion. Specifically, I will discuss patterns formed by the Min proteins in the bacterium Escherichia coli as well as cytoskeletal polymerization waves in animal cells. Together these results show how physical concepts and methods can help us to understand life.

In dem Vortrag "Mathematische Experimente" führt Professor Beutelspacher mit Hilfe einfachster Materialien faszinierende Experimente vor und erläutert deren mathematische Bedeutung. All diese Experimente können von den Zuhörern zu Hause direkt nachgemacht werden. Professor Beutelspacher ist Professor für Geometrie und Diskrete Mathematik am Mathematischen Institut der Justus-Liebig-Universität Gießen und Leiter des Mathematikums in Gießen. Dort hat auch die bekannte Wanderausstellung "Mathematik zum Anfassen" ihren Ausgangspunkt. Professor Beutelspacher wurde mehrfach ausgezeichnet, unter anderem mit dem Communicator Preis für herausragende Leistungen in der Vermittlung seiner Wissenschaft in die Öffentlichkeit.

The basic principles of quantum computation were enunciated twenty years ago, and within ten years there was good motivation to build one, and a basic idea of the physical challenges that would need to be overcome to achieving working quantum computation in the lab. Since then there has been steady progress in achieving this goal, involving striking advances in the solid state control of single quanta. I will give my overview of the status of spin qubits and superconducting qubits, and indicate where they may be going in the future.

Bacteria are the smallest free-living organisms, but they are not isolated. Bacteria communicate by exchanging chemical signals and DNA in a process called gene transfer. They can actively control the transition from a lifestyle as individual motile cells to a lifestyle in large and structured clusters. The type IV pilus is an extracellular polymer which is essential for gene transfer, cluster formation, motility, and adhesion in many bacterial species. When it depolymerizes, it generates force exceeding 100pN, making it the strongest molecular motor characterized so far. Using a combination between nanotechnological and genetic tools we address the molecular mechanism of force generation, its regulation, and its biological function.

Es werden die physikalischen Grundlagen, die den Problemen in Fukushima zu Grunde liegen besprochen. Es gibt auch interessante Gemeinsamkeiten mit den Unfällen in Harrisburg (Three Mile Island), sowie (erstaunlicherweise) auch mit Tschernobyl. Dazu werden einige Experimente live vorgefuehrt.

Sehzellen können ein einziges Photon detektieren und in ein elektrisches Signal umwandeln. Spermien navigieren in einem chemischen Gradienten von Lockstoffen. Sie können ein einziges Lockstoffmolekül, das von der Eizelle ausgesendet wird, registrieren und dadurch ihr Schwimmverhalten verändern. In meiner Vortrag werde ich die zellulären Signalwege erläutern, die diese Empfindlichkeit an der physikalischen Grenze ermöglichen. Während der Evolution haben sich verschiedene Signalwege entwickelt, die Variationen eines zellulären Verarbeitungsmoduls darstellen. Wahrscheinlich können viele andere Zelltypen, beispielsweise Riechzellen, die auf Pheromone spezialisiert sind, einzelne Moleküle detektieren und in ein elektrisches Signal umwandeln.

Fractionalisation is a counterintuitive phenomenon, in which an 'elementary' particle appears to break into two independent entities. A celebrated example of this is spin-charge separation, in which an electron's magnetic (spin) and electric (charge) degrees of freedom appear to become independent. Spin ice materials such as Dy2Ti2O7 and Ho2Ti2O7 provide a rare instance of fractionalisation in three dimensions: their elementary excitations carry a fraction of the magnetic moment of the microscopic spin degrees of freedom, and they can be thought of as magnetic monopoles. The peculiar nature of these excitations leads to unique signatures in the equilibrium and response properties of spin ice materials. These include unusual neutron scattering structure factors, dynamical arrest and long lived non-equilibrium metastable states, as well as a response to external magnetic fields that promotes spin ice as a magnetic analogue of an electrolyte. This talk reviews several of these striking phenomena, and discusses open questions and future perspectives.

Kernfusions-Reaktionen in Sternen und in Supernova-Explosionen bringen die Vielfalt der chemischen Elemente hervor, die wir im Universum vorfinden. In diesen Prozessen entstehen auch Beimischungen instabiler Atomkerne. Deren radioaktiver Zerfall im interstellaren Raum geht meist einher mit Aussendung charakteristischer Linienstrahlung bei Gammastrahlen-Energien. Astronomische Teleskope im Weltraum können so einen Blick auf kosmische Nukleosynthese erhalten. Die ESA-Mission INTEGRAL liefert seit 2002 Beobachtungsdaten von verschiedenen Regionen in unserer Milchstrasse. Insbesondere langlebige Isotope wie 44Ti, 26Al und 60Fe wurden gemessen, aber auch Annihilations- strahlung von interstellaren Positronen. Die Technik der Gammastrahlenteleskope wird im Vortrag vorgestellt, bevor die astrophysikalischen Prozesse, die bisherigen Erkenntnisse und offene Fragen diskutiert werden. Hierbei werden insbesondere Kernfusionsprozesse in kosmischer Umgebung, Supernova-Explosionen und das interstellare Medium behandelt.

All eukaryotic cells including those of our body contain a large variety of molecular machines that convert the chemical energy released from nucleotide hydrolysis into mechanical work. This talk focusses on molecular stepping motors such as kinesin, which use their two motor domains or "heads" to walk along very thin filaments. Our theory for these motors starts from their enzymatic activity during ATP hydrolysis and from the corresponding nucleotide states. This approach provides a general classification scheme for the different motor cycles, each of which can be characterized in terms of its free energy transduction and entropy production arbitrarily far from chemical and/or mechanical equilibrium. The properties of single motors are then used to describe the cooperative behavior of many motors. The latter behavior includes cargo transport by one or two (antagonistic) team of motors. Systems consisting of many motors and cargo particles can undergo traffic phase transitions.