Collage of all research fields
© Composing: Anke Heinzelmann

Research Fields

Research towards the degree Dr. rer. nat. can be performed in one of several fields, offered at the Department of Physics and Astronomy.

Research encompasses core areas of fundamental physics as well as inter­disciplinary border areas. In the core areas, research focuses on elementary particle physics, the structure and evolution of the universe, and the properties of complex classical and quantum systems. The interdisciplinary border areas include environmental physics, bio- and medical physics as well as technical computer science.

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Condensed matter

Condensed matter physics deals with all aspects of the macroscopic and microscopic physical properties of matter. Research at Heidelberg University includes a wide range of physical phenomena and mathematical concepts in both quantum and classical systems and ranges from fundamental many-body physics and quantum materials to materials science and modern technology. It covers fundamental questions central to our understanding of quantum mechanics, such as unconventional ordering phenomena and how complex multi-body quantum systems can be understood as well as aspects of surface science and nanomaterials.

Condensed matter at low temperatures

The presence of disorder strongly influences the dynamics of non-equilibrium quantum systems and leads to a multitude of unique phenomena which are investigated at extremely low temperatures with new methods. The focus is on physical realizations of such systems like amorphous solids, disordered crystals and spin glasses. Fundamental questions regarding the interplay of disorder and many-particle interaction, the microscopic nature of low-lying states, the relaxation and decoherence channels, the dissipative dynamics, as well as the occurrence of complex collective modes are studied. Current projects focus on the surprising influence of nuclear degrees of freedom on the dynamics of atomic tunneling systems in structural disordered system like multicomponent glasses and polymers. In particular, the non-linear response and phase coherence of such systems are investigated.

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Quantum Sensors and Superconducting Electronics

Quantum sensors based on cryogenic microcalorimeters have reached a state of development in recent years that makes them a key technology for the detection of single photons and particles in many fields of physics and for a variety of applications. Metallic magnetic calorimeters (MMCs) are a special variant of such detectors that are able to measure the energy of single X-ray and gamma-ray photons with an accuracy better than one part per four thousand, while maintaining good quantum efficiency and spectral linearity. This makes them an ideal tool for ultra-high precision spectroscopy in a very wide energy range. Applications include X-ray astronomy, measurement of Lamb shifts of highly charged ions, nuclear forensics and quantum metrology. In addition, the MMCs developed in Heidelberg play a key role in particle physics experiments, such as the ECHo project, which aims to determine the neutrino mass via the electron capture spectrum of 163Ho, and AMoRE, which is searching for the neutrino-less double-beta decay of 100Mo.

Work on MMCs includes detector design, development of the necessary microfabrication processes, design of the cryogenic environment, detector fabrication and characterization, and development of the necessary readout electronics. For the latter, superconducting electronics is a key component designed and produced for optimal adaptation to MMCs. In order to meet the demands for high spectral resolution, SQUID amplifiers with noise temperatures close to the quantum limit are necessary. Microwave SQUID multiplexers are developed for reading out large MMC detector arrays with several hundred pixels.

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Electron correlations and magnetism

Novel magnetic materials exhibit a plethora of fascinating features and aspects rendering them relevant for basic research as well as for applications. The group applies a materials-based approach to investigate fundamental aspects of magnetic interactions and electronic correlations mainly in the field of basic research. Particular focus is set on quantum ground states like unconventional superconductivity, electronic nemantic order or quantum magnetism which challenge standard theory and hence enable extending our understanding of quantum many-body systems. Basic building blocks in several of these materials are low-dimensional and/or geometrically frustrated magnetic substructures, in which quantum effects are particularly pronounced. Applied materials research on battery materials and in the biomedical field illustrates how fundamental science is directly linked to application.

Research topics include unconventional superconductivity, low-dimensional quantum magnets, molecular magnetism, functional magnetic oxides, and carbon-based hybride nanomaterials.

Smart nanoplasmonics

The optical properties of metal nanoparticles have been an object of fascination since ancient times. When light interacts with a metal nanoparticle (for example a gold colloid in a stained church window), collective oscillations of conduction electrons known as particle plasmons are excited. Functionalized metallic nanoparticle assemblies with well-designed configurations enable intriguing optical properties and offer a helpful hand for understanding profound biochemical behavior. Our group focuses on developing sophisticated and smart nanomaterials for (I) answering structural biology questions and (II) answering catalytic chemistry questions in local environments.

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Surface science and infrared spectroscopy of nanostructures

Our research focuses on nanostructures (ultrathin layers and nanoparticles from atomic size up to several 100 nm on well-defined surfaces) with emphasis on the relationship between structure formation, surface, and interface properties and excitation spectra in the infrared (IR) range. Surface and interface properties become increasingly important with the decreasing size of nanostructures.

Our main experimental tools are IR spectroscopy (including IR micro-spectroscopy, IR spectroscopic ellipsometry) under ambient and ultra-high vacuum conditions at various temperatures. Studies have been performed within a variety of research projects ranging from astronomy and high-energy physics to plasmonics and organic electronics. Materials in organic electronics show rich vibrational fingerprint spectra that are unique for a molecular species in a certain environment. For this reason, IR spectral characterization becomes a powerful tool for the study of changes in the geometric and electronic structure of organic semiconductors.

Theory of spectroscopy, dynamics and numerical methods for complex materials

We aim at advancing the fundamental understanding of many body quantum materials. We not only focus on the description of the groundstate of these systems, but also treat the dynamical properties and excitations. We focus on extending our capabilities of performing quantitative calculations of excitations by light ranging from terahertz to x-ray spectroscopy. The calculations are done for bulk crystals, (topological) surfaces, interfaces, thin films, impurity centres, or the active centres in many of the known enzymes and catalysts. Of particular interest are the interaction between local entangled electronic states and multiplets as one sees in transition metal and rare earth centers interacting with delocalized states. Often such systems possess a large number of low energy electronic degrees of freedom, which are responsible for their rich physical behavior. This behavior does not only make these materials interesting, it also makes them involved to understand. In our group we use a manifold of different methods.

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Biomolecular assemblies and cellular biophysics

The elementary unit of life is the cell. Biological cells come in many different sizes and shapes, but they all use the same molecules (mainly nucleic acids and proteins) because they all have a common evolutionary origin. These molecules then self-assembly into larger structures due to the laws of physics, without which one cannot understand structure formation in biological systems. The same holds true on the cellular level: the size and shape of cells is strongly determined by the physical properties of their environment, which range from fluid environment such as blood flow through viscous environment such as the mucus in the gut to elastic environments such as the extracellular matrix of connective tissue. During recent years, mechanics has emerged as a central element of cell and tissue dynamics, complementing more traditional biochemical approaches. Using physics tools, such as lithography, micropatterning and microfluidics, today one can design cellular environments to understand and control cell function. An important research direction at Heidelberg is also the attempt to build synthetic cells from scratch, using physics tools such as microfluidics. Such approaches result in quantitative data which are an ideal starting point for quantitative data analysis and modelling. Cellular studies have to be anchored in an understanding of the underlying molecular processes. At Heidelberg, we push the limits of methods to characterize biomolecules, including X-ray diffraction and the free electron laser, electron cryo microscopy and phase plates, and super-resolution microscopy (e.g. STED and MINFLUX).

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Theoretical physics of complex biosystems

Our research encompasses soft matter and biological physics. In particular, we are interested in concepts and methods to understand the adhesion and mechanics of cells. Our interest on the cellular level also branches out to the sub-cellular level (assembly of supra-molecular complexes in cells) and to the multi-cellular context (model tissue, collective migration). The group uses methods from statistical physics, computational physics, continuum mechanics, non-linear dynamics and stochastic dynamics.

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Medical Physics

Medical physics (also called biomedical physics, medical biophysics or applied physics in medicine) is, generally speaking, the application of physics concepts, theories and methods to medicine or healthcare. Medical physics departments may be found in hospitals or universities. There are 4 main areas of medical physics speciality 1) radiation therapeutic physics, 2) medical imaging physics, 3) nuclear medicine physics and 4) health physics, which cover more than 90% of all medical physics activities.

Radiation therapeutic physics

Radiation therapeutic physicists work primarily in radiation oncology hospital departments, which specialize in cancer care. Radiation therapy (RT) is the most common treatment for cancer, being used in approximately 70% of all cancers either alone or combined with surgery or chemotherapy. It uses high-energy particles or waves, such as x-rays, gamma rays, electron beams, protons, carbon ions, to "kill" or "damage" cancer cells. There is a growing interest in the use of ion-beams (protons, carbon ions) for cancer therapy. The principal benefit of ion-beams are there finite range (or depth) in tissue, known as Bragg peak, where a significant amount of the radiation is deposited at the end of the track where the ions stop. The Bragg peak guarantees that healthy organs distal (deeper) to this peak receive very little or NO radiation, reducing significantly side effects. However, due to treatment and beam delivery uncertainties, it is not possible to accurately place the Bragg peak on the distal edge of the tumor. Thus, we voluntarily irradiate healthy surrounding organs to guarantee the tumor receives the needed radiation dose to sterilize the cancer. The Bragg peak 'uncertainty' reduces the clinical benefit of ion-beam radiotherapy.

Ongoing radiation oncology medical physics research in Heidelberg focuses on 1) developing novel imaging technologies to reduce the Bragg positioning uncertainty in patients using prompt gamma spectroscopy and Helium beam imaging for carbon ion therapy; 2) motion management technology for reducing effects during patient treatments, 3) incorporation of physical and mathematical models into the decision making process for radiotherapy, and 4) exploitation of the capabilities of the pixelized semiconductor detector Timepix for Helium and Carbon ion therapy. In addition, the molecular mechanism of DNA damage due to radiation is poorly understood. Thus, the field of radiation biology focuses on studying the biological effect on tissues of ionizing radiation.

Ion-Beam Therapy

Group J. Seco: In principle, ion-beam therapy offers a substantial clinical advantage over conventional photon therapy. This is because of the unique Bragg peak depth-dose characteristics, which can be exploited to achieve significant reductions in normal tissue doses proximal and distal to the target volume. These may, in turn, allow escalation of tumor doses and greater sparing of normal tissues, thus potentially improving local control and survival while at the same time reducing toxicity and improving quality of life. In the future, a more widespread use of ion-beam radiotherapy will make it possible to significantly improve cancer survival with minimal side effects. However, in order to take full advantage of ion-beam radiotherapy a better control is needed of the Bragg peak within the patient (cancer) and a better understanding of the radiation triggered DNA damage is required. Once we can control very accurately the positioning of the Bragg peak within the cancer to within 1mm, then it will be possible to reduce radiation side-effects, while simultaneously boosting the cancer with more radiation.

Our aims are to develop novel imaging technologies to reduce the Bragg peak positioning "uncertainties" for ion-beam radiotherapy, using Helium beam imaging and prompt gamma spectroscopy and to investigate the mechanism of radiation triggered DNA damage via reactive oxygen species (ROS). We are currently developing an high energy resolution detector system to perform spectroscopy of the prompt gamma radiation emitted during proton, Helium and Carbon ion therapy. We perform Monte Carlo radiation transport simulations to investigate the nuclear excited states produced by the different ion beams and to optimize the detection of the Prompt Gamma. Our aim is to perform online monitoring of the delivered Bragg peak during therapy.

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Medical imaging physics

Medical imaging physicists work primarily in radiology departments within an hospital, and specialize in early detection, tumor characterization, treatment guidance and response monitoring using morphological, functional, metabolic and molecular imaging. The enormous advances in the understanding of human anatomy, physiology and pathology in recent decades have led to ever-improving methods of disease prevention, diagnosis and treatment. Many of these achievements have been enabled, at least in part, by advances in 1) multi-slice computed tomography (CT), 2) magnetic resonance imaging (MRI), 3) positron emission tomography (PET) and 4) single photon emission tomography (SPECT). Major achievements in Heidelberg have centered on the development and evaluation of novel techniques in high- and ultrahigh-field MRI, dual-energy/spectral CT, contrast-enhanced ultrasound and dynamic PET.

Ongoing medical imaging research in Heidelberg focuses on evaluation of novel techniques in high- and ultrahigh-field MRI, dual energy/spectral CT, contrast-enhanced ultrasound and dynamic PET including hybrid imaging using new radiotracers. Ongoing research centers on 1) development of ultrahigh-field imaging devices, 2) photon-counting CT detectors, 3) simultaneous optical imaging and tomography with MRI, PET, SPECT and ultrasound, 4) chemical exchange saturation transfer (CEST) and NMR spectroscopy (MRS) with 1H and X nuclei, 5) diffusion weighted imaging (DWI) to gain insights into the structure of biological structures and 6) quantitative susceptibility mapping (QSM).

MRI

Group M. Ladd: In MRI, a significant difference encountered at ultra-high magnetic fields (= 7 Tesla) is that the RF wavelength inside the tissue can be shorter than the cross-sectional dimension of the human body, which implies that phase effects and wave propagation have to be accounted for. We are developing new RF technology based on multi-channel excitation coils to provide precise control over the RF field distribution. A 32-channel RF array for whole-body excitation at 7 Tesla has been developed, see illustration

Group L. Schad: We are working on several aspects of improved oncological radiotherapy treatment planning and monitoring by using physiological and functional imaging of CT, MRI and PET. One of our main research aspects lies in developing new MR techniques (23Na imaging, dynamic MRT, diffusion, perfusion, blood bolus tagging, BOLD MRI) for clinical use in therapy planning and monitoring. Another main aspect denotes imaging of hyperpolarized 3He in the human lung, as well as T2*- and T1-techniques for non-invasive measurement of tissue oxygenation and perfusion in the myocardium which is of general interest in radiology.

Physics Faculty: Prof. Peter Bachert Medical Faculty: Prof. Marc Kachelrieß
In both physics and medical faculties:
Prof. Mark Ladd, Prof. Lothar Schad

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Atmospheric Physics

Atmospheric physics explores the gaseous and particulate composition of the Earth's atmosphere through observations and models. We study the biogeochemical cycling of greenhouse gases, the water cycle, radiative transfer processes, chemically reactive species, and volcanic processes. To this end, we develop spectroscopic sensors and isotope tools that enable highly accurate measurements from ground, from mobile and airborne platforms, and from satellites. We develop numerical methods and models to examine the observational data and to gain insights into the climate system, into anthropogenic climate change and air pollution, as well as into stratospheric ozone photochemistry.

Atmospheric Physics
Aquatic Physics

Aquatic Systems

Water is a key player in global environments, its transport of heat and substances is crucial to the climate system, the ecosystems, and global biogeochemical cycles, as well as to our societies. We study water in all its compartments from rivers, lakes, and groundwater to the global ocean and including the cryosphere and atmosphere. Central tools are the use and development of trace isotope methods, and numerical models to quantify transport and residence times in the studied system compartments as well as at their interfaces (air sea gas exchange). Our studies include anthropogenic changes of the water cycle as well as past climate induced changes of precipitation and flow.

Terrestrial Systems and Chaotic, Complex and Evolving Environmental Systems

Terrestrial systems are by nature highly non-linear and scale sensitive in the processes at play. Central questions concern soil hydrology and solute transport using methods that cover the spectrum from experiments through modeling and simulation to data assimilation and knowledge fusion. Departing from the non-linear system behavior we explore the characteristics of environmental chaotic, complex, and evolving behavior of systems along example numerical models of geomorphological processes, population dynamics, and evolution. The aim is to approach the fundamental operations of complex bi-furcating systems through both experiments and numerical simulation.

Atmospheric Physics
Ocean

Image Processing and Air-Sea Interaction

Boundary layer physical processes such as air-sea heat and gas exchange are of major relevance in the climate system and very difficult to measure. But they are approachable through imaging techniques. Hence, uncovering the nature of such processes requires the development of dedicated imaging techniques, time resolved image processing techniques and data retrievement tools that have numerous applications in other scientific and industrial domains. They give insight into the highly complex and non-linear mechanisms of small-scale air-sea interaction processes in the vicinity of the air-sea interface. In addition, visual, machine and deep learning algorithms and application are developed in cooperation with the HCI and IWR.

Paleoclimate Physics

Physics of past climates

Past climate messages are left in the isotope and element composition of various geological archives such as corals, secondary carbonates, and marine sediments. To extract past climate system properties, dynamics, and statistical variance the timing of information storage is studied through chronometers such as radiocarbon and other natural radioactive isotopes (U-series nuclides), while trace elements and isotopes serve to fingerprint past climate change. To use such tools and develop new once, modern local to global cycles of elements and isotopes (including carbon and water) need to be quantified. Moreover, we contribute the the development of numerical models of biogeochemical cycles today and in the past climate system and we explore in depth the statistical analysis of climate proxy data and model ensembles to determine the local, regional, and seasonal relevance of past climate information

Application specific computing

Research focuses on significant improvements of performance and accuracy in application specific computing through a global optimization across the entire spectrum of numerical methods, algorithm design, software implementation and hardware acceleration.

These layers typically have contradictory requirements and their integration poses many challenges. For example, numerically superior methods expose little parallelism, bandwidth efficient algorithms convolve the processing of space and time into unmanageable software patterns, high level language abstractions create data layout and composition barriers, and high performance on today's hardware poses strict requirements on parallel execution and data access. High performance and accuracy for the entire application can only be achieved by balancing these requirements across all layers.
The following topics are given particular attention: Mixed precision methods, Multigrid methods, Adaptive data structures, Data representation, Bandwidth optimization, Reconfigurable computing.

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Circuit design

Circuit design

Microelectronic circuits are developed, tested and applied. These microchips often contain extremely sensitive, low noise amplifiers for capturing sensor data and modules for further analog and digital signal processing. The crucial parts of such chips are designed completely manually. They are simulated on the analog level to achieve a maximal performance. The designs are fabricated in state-of-the-art CMOS technologies and are put into operation here at the group. A typical use case consists not only of designing the chip, but also includes building suitable control and data acquisition systems, the control and synchronisation of all components and the analysis of the measured data.

Recent developments include highly integrated circuits for positron emission tomography, readout electronics for DEPFET sensors for the future ILC detector, chips for detecting X-rays with hybrid pixel sensors, novel monolithic pixel sensors, development of front-end electronics for the CBM experiment at FAIR at the GSI, high-speed microscopy within the Viroquant project, detectors for synchrotron experiments at DESY, ESRF and the future XFEL, and circuit design techniques for generation of secret keys for cryptography.

Visual learning and image analysis

In the group of Prof. Hamprecht, the topics of research include learning algorithms for image analysis, and its applications to the segmentation of biological images and beyond and tracking.

Prof. Rother's interests also lie in the field of computer vision and machine learning - ranging from deep learning and graphical models to smart data generation. A broad range of applications are investigated, such as image editing, image matching, scene understanding and bio-imaging.

3D understanding

Cosmic structure formation

The formation and evolution of cosmic structures and the large-scale distribution of galaxies is a phenomenon of nonlinear 'fluid' mechanics driven by gravity, but its statistics also reflects properties of elementary particles that make up the dark matter content of the universe. Apart from being an interesting non-perturbative system on its own, cosmic structures ultimately harbour galaxies and set the boundary conditions for their formation, evolution and gravitational interaction.

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Weak Gravitational lensing

Gravitational light deflection is a way of mapping out the matter distribution in the universe and to investigate objects that are not directly interacting with light, for instance primordial black holes or cosmic structures made up of dark matter. The many regimes and methods of gravitational lensing provide insight into a large range of physical phenomena: the search for primordial black holes, extrasolar planets or even exomoons in microlensing, the matter distribution inside clusters of galaxies by strong lensing and the cosmic matter distribution with weak lensing.

Structure of the Milky Way and galactic archaeology

The Milky Way and the Local Group of galaxies is the best-studied system of galaxy formation and evolution, and provides an insight into the formation history of grand-design spiral galaxies: These systems bring together theories of dynamics of dark matter streams inside the Milky Way, the history of mass accretion and star formation in different environments, and lastly processes of chemical enrichment. Observations combine methods from astrometry with multi-object spectroscopy.

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Formation of stars and planets

Physical processes that lead to the formation of stars inside galaxies and ultimately of planetary systems around these stars encompass a large range of scales and are very complex. Understanding aspects of star or planet formation requires numerical simulations on supercomputers and thorough understanding of the contributing physical processes. Now that submillimeter-observations can map protoplanetary discs around stars in the Milky Way and reveal their dynamical structure and that the number of detected exoplanets has reached a few thousand, a new era of quantitative theories for planet formation is beginning.

High-energy and non-thermal astrophysics

Astrophysical objects and phenomena such as active galactic nuclei and supernovae are rapidly time-evolving physical systems, where radiation, including gravitational waves and neutrinos, are produced out of thermal equilibrium. In Heidelberg, researchers study the late stages of stellar evolution and the processes in a supernova explosion by means of numerical simulations, and they survey the sky for objects emitting radiation at GeV and TeV-scales.

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Barred Spiral Galaxy

Galaxy Formation and large-scale astronomical surveys

The cosmic large-scale structure sets the boundary conditions for the formation and evolution of galaxies, in which matter cools and condenses to form stars. A multitude of not yet fully understood physical processes shapes galaxies and determines their physical properties. Surveying huge cosmic volumes with newly developed instruments allow insights into the chemical and dynamical properties of galaxies, with their implication on models for galaxy evolution.

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Mathematical Physics

Research in Mathematical Physics in Heidelberg takes place at a variety of interfaces between the two disciplines, ranging from the analysis of functional renormalization and statistical mechanics to applications of ideas from quantum field theory in topology and algebraic geometry. We aim both to develop mathematical theories as required and inspired by physical considerations, and to achieve mathematically rigorous treatments of relevant physical phenomena.

The fruitful interaction of mathematics and physics is at the very heart of the cluster of excellence STRUCTURES at Heidelberg University.

Many-Body Physics

The activities center on many-body theory, quantum field theory and statistical mechanics. A main interest is the mathematical construction of correlated-fermion models by multi-scale methods, with applications in the theory of unconventional superconductivity and other symmetry-broken phases of matter.

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Geometry and String Theory

The activities derive from the interaction between geometry and high-energy physics that have arisen in string theory since the 1980's. Research builds on supersymmetric and topological field theories, and supergravity. A central topic is mirror symmetry in its various formulations, and the mathematical theory of BPS invariants.

Structures

Synthetic quantum systems

Correlations in space and time: In the lab, we can prepare and control quantum systems nearly perfectly and thus study these correlation functions in engineered model systems. The ability to resolve the dynamical response function in highly tunable systems allows us to study the transition from regular to chaotic behavior. An additional twist is added by the fact that we can also time-reverse the dynamics.

Dynamical gauge fields: Within the Standard Model of Particle Physics, the interaction between fundamental particles is described by gauge theories. These theories have an enormous predictive power, but to compute the dynamics they generate is an extremely hard task. As a consequence, high-energy physics contains many unsolved problems such as quark confinement or the dynamics of quarks and gluons during heavy-ion collisions. Instead of computing them in classical devices or investigating them in enormous accelerator facilities, we aim at implementing lattice gauge theories on the optical table by having atomic gases in optical lattices mimic the interplay between particles, anti-particles, and gauge bosons. In this way, experiments at temperatures just above absolute zero could give insights into unsolved phenomena that in Nature appear at very high energies.

Entanglement: We use perfectly controlled gases of ultracold atoms to explore both the fundamental aspects and applications of entanglement. For example, we observed the 'spooky action' between two spatially separated parts of an atomic cloud and generated entanglement that can help improving the precision of atomic clocks and magnetometers.

Structures

Quantum dynamics of atomic and molecular systems

We study atomic and molecular quantum systems with respect to their interactions on different levels of complexity. Of special importance is the application and extension of modern methods for the manipulation and quantum control to many-body quantum systems, in particular using coherent light. The systems under investigation range from highly excited Rydberg atoms over atomic and molecular quantum gases to molecular aggregates. The group develops technologies for trapping and cooling of neutral atoms as well as quantum-state sensitive diagnostics.

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Ultra-cold quantum gases

Our research group performs fundamental research in the fields of quantum and atomic physics. In our experiments, we use ultracold atom clouds to understand how complex quantum systems behave. In particular, we are interested in questions related to how strong interactions, reduced dimensionality (1D and 2D) and finite system size affects the physical properties of a quantum system. More information on current research projects and the experimental setups can be found here.

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Heavy-ion physics at the LHC

ALICE is one of the four big experiments at the CERN Large Hadron Collider (LHC), which is dedicated to the investigation of the nucleus-nucleus collisions. The aim of ALICE Collaboration is to study the physics of strongly interacting matter at extreme energy densities, where the formation of a new phase of matter, the quark-gluon plasma, is expected.
The ALICE group at Heidelberg and GSI has made significant contribution to the design and construction of the two key detectors subsystems of ALICE, the Time Projection Chamber (TPC) and the Transition Radiation Detector (TRD). Today, the group is strongly involved in the operation and calibration of the TPC and TRD subsystems, as well as in the physics analysis of the ALICE data.

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Heavy-ion physics at FAIR

The Compressed Baryonic Matter (CBM) experiment will be one of the major scientific pillars of the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. The goal of the CBM research program is to explore the QCD phase diagram in the region of high baryon densities using high-energy nucleus-nucleus collisions. This includes the study of the equation-of-state of nuclear matter at neutron star core densities, and the search for phase transitions, chiral symmetry restoration, and exotic forms of (strange) QCD matter. The CBM detector is designed to measure the collective behavior of hadrons, together with rare diagnostic probes such as multi-strange hyperons, charmed particles and vector mesons decaying into lepton pairs with unprecedented precision and statistics. Most of these particles will be studied for the first time in the FAIR energy range. In order to achieve the required precision, the measurements will be performed at reaction rates up to 10 MHz. This requires very fast and radiation hard detectors, a novel data read-out and analysis concept including free streaming front-end electronics, and a high performance computing cluster for online event selection.

Particle physics at ATLAS

The Heidelberg group a member of the ATLAS collaboration since its founding in 1992. The Heidelberg group, together with five other groups from England, Germany and Sweden, has designed and built the ATLAS level-1 calorimeter trigger. The design and the construction of the Calorimeter Trigger Preprocessor (PPr) which digitises and processes 8000 channels of calorimetric energy measurements 40 million times per second was undertaken here in Heidelberg. The PPr is a crucial component for ATLAS operation.

In the analysis of physics processes the group dedicates its efforts to both precision measurement of the Standard Model and the search for new physics beyond that model. Current work-in-progress includes tests of Quantum Chromodynamics (QCD) at extremely high momentum transfers, investigation of missing transverse momentum from undetectable particles and the search for dark matter particles. In addition the group works on calibration of hadronic jets, developing new analysis approaches such as New Physics searches at the trigger level and improving analysis methods by incorporating Machine Learning.

Structures

Particle physics at the LHCb

The Heidelberg group is a member of the LHCb collaboration. We cover a broad field of activities: We were one of the groups to design and construct the OuterTracker (OT) - the main tracking device of the LHCb experiment - and to develop readout electronics. Since the construction and installation of this subdetector is nearly finished, the LHCb group Heidelberg turns its focus on physics analysis. The activities of our group include measurement of the mixing frequency Δms, measurement of particle multiplicities, and upgrading the system.

Event at LHCb

Particle physics at mu3e

The μ3e experiment is a new search for the lepton-flavour violating decay of a positive muon into two positrons and one electron and is operated at the Paul Scherrer Institute (PSI) in Switzerland. Since this decay is suppressed to unobservable levels in the Standard Model of particle physics, any measurement of this decay would be a clear sign of new physics. The Heidelberg groups play a strong role in the developing and building of the detector as well as analysis of data. To achieve the precision vertexing and timing necessary for this experiment, the groups work on pixel detectors and a detector consists out of small scintillating tiles, which are read out by Silicon Photomultipliers.

mu3e

Theory beyond the Standard Model

This research field explores the most fundamental, microscopic laws of nature. These laws rest on Quantum Field Theory (the quantized version of, e.g., electromagnetism) and Einstein's General Relativity. On this theory foundation, the so-called "Standard Model of Particle Physics" describes, through a lagrangian of just a few lines, all that we know about the microscopic world. This lagrangian is coupled in a unique way to gravity as a low-energy effective (quantum) field theory. But many pressing questions remain unanswered: How do Dark Matter and Cosmological Inflation in the very early Universe fit into this framework? What sets the energy scale of the Higgs mechanism? How does full-fledged quantum gravity, which becomes relevant at very high energies, change the picture? Are there new particles accessible at the LHC, possibly explaining some of the puzzles hidden in the Standard Model lagrangian? We struggle with these questions using ideas from quantum field-theoretic model building to 10-dimensional Superstring Theory and its compactifications, employing analytical methods, numerical simulations and machine learning. We also consider ultra-light particles, like axions, and more general approaches to quantum gravity together with its possible relations to low-energy observables.

Tilman

Astroparticle Physics: Neutrinos and Dark Matter

Astroparticle Physics is a relatively new research field at the interfaces of particle physics, cosmology and astrophysics. Central to this field are investigations of dark matter and of neutrinos. Deciphering the nature of dark matter is one of the most important problems in particle physics and cosmology. A promising method to find dark matter is via its scattering with nuclei in direct detection experiments. Here the current XENONnT and the future DARWIN projects, all located in deep underground labs, are leading the world-wide effort to search for Dark Matter.

Neutrinos remain the only physics beyond the Standard Model that is testable in the lab. With GERDA and LEGEND searches for neutrinoless double beta decay are pursued, an observation of which would demonstrate the Majorana nature of the neutrinos, and which would test many models beyond the Standard Model. Coherent elastic neutrino-nucleus scattering is a process that allows one to test neutrino properties precisely in and beyond the standard paradigm. CONUS aims at measuring this process with reactor neutrinos. Searches for sterile neutrinos, which are motivated by several experimental anomalies, are performed in the STEREO project. Detector development and low background techniques to suppress the various sources of contamination are common for all projects.

The experimental activities are complemented with theoretical work. This includes general model building beyond the Standard Model, interpreting the various observational results, putting them in broader context, and making additional predictions for a variety of searches.

Xenon Experiment

Dark energy and modified gravity

The expansion of the universe and the formation of cosmic structures are a testbed for the properties of gravity on the largest scales, where new and unexpected gravitational phenomena might arise and deviations from general relativity can be observed. Dark energy can drive the late-time accelerated expansion of the universe and be a viable alternative to the cosmological constant, and alternative theories of gravity can challenge our understanding of the construction principles of field theories. We aim to test these theories with data of the European Euclid satellite mission, which will carry out a 3-dimensional survey of the cosmic matter distribution and is capable of testing cosmological models beyond the standard picture.

StrangeUniverse

Physics of the early universe and particle cosmology

Physical processes in the universe probe the laws of nature on a very high energy scale and link the physics of gravity and of inflation to particle physics and the standard model. We investigate inflationary models, their relation very light elementary particles such as neutrinos and axions, the genesis of baryons and leptons in the early universe, deduce observable consequences of processes near the Planck-scale and describe early universe-physics in different frames. In particular, methods of renormalisation allow us to compute the running of fundamental constants of nature in their cosmological evolution.

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