Lunch Seminars

Winter semester 2021/2022

CRC 1225 – YRC Lunch Seminar 14.02.2022 – Online
Speaker: Lukas Kades (PostDoc at Institut für Theoretische Physik,, Heidelberg)
Title: “Machine learning in physics – A (very) short introduction”
Abstract: I will give a very short overview of different classes of problems in physics that can be tackled by machine learning/deep learning algorithms. Thereby, I will focus on the nature of the problem and the means that the algorithms provide for solving the given problem. This should provide a good basis for discussing potential applications in everybody’s specific area of research.

CRC 1225 Lunch Seminar 07.02.2021 – Golden Box, Physikalisches Intitute, INF, 226/ Online via Zoom
Prof. Dr. Jan M. Pawlowski (Institut für Theoretische Physik, Heidelberg)
Project A02
Title of Talk: Can we unravel strongly correlated QCD from heavy ion collisions?
Abstract: At large temperatures and energies, QCD is a weakly interacting system of deconfined quarks and gluons thanks to asymptotic freedom. In turn, at low temperatures and energies, QCD is well-described by a (weakly interacting) gas or liquid of hadrons, with confined and heavier quark and gluon constituents. This transition is governed by spontaneous strong chiral symmetry breaking and the confinement dynamics. In this talk I discuss the programme of how to unfold the experimental heavy ion data towards unravelling the underlying QCD dynamics in the vicinity of the transition. This information is contained in the QCD transport coefficients such as QCD pressure, viscosities, relaxation time and heavy quark diffusion coefficients. These observables are (timelike) correlation functions of the energy-momentum tensor as well as of currents in QCD. I discuss their first principles computation within QCD, their use in QCD transport and the unfolding procedure.
Download the slides of the talk here:

CRC 1225 – YRC Lunch Seminar 17.01.2022 – Online
Speaker: Tobias Pozdszus (PhD at Max Planck Institute for Nuclear Physics, Heidelberg)
Title: “First-order strong-field QED processes including the damping of particle states”
Abstract: Strong field QED considers electrodynamic processes in the presence of an electromagnetic background field. Here “strong” refers to the intensity of the background field, which is so high that the interactions of electrons and positrons with the background field have to be taken into account exactly in the calculations. This is done by implementing the background field in the quantization procedure of the fermion field. Exact solutions of the corresponding Dirac equation in the presence of an arbitrary plane wave field are the so called Volkov states. However, Volkov states, as well as free photon states, are not stable in the presence of the background plane-wave field but “decay” as electrons/positrons can emit photons and photons can transform into electron-positron pairs. By using the solutions of the corresponding Schwinger-Dyson equations within the locally constant field approximation, we compute the probabilities of nonlinear single Compton scattering and nonlinear Breit-Wheeler pair production by including the effects of the decay of electron, positron, and photon states. As a result, we find that the probabilities of these processes can be expressed as the integral over the light-cone time of the known probabilities valid for stable states per unit of light-cone time times a light-cone time-dependent exponential damping function for each interacting particle. Here the exponential damping functions describe the decay of the corresponding initial or final particle state before or after the interaction, respectively.
Download the slides of the talk here:

CRC 1225 Lunch Seminar 22.11.2021 – Golden Box, Physikalisches Intitute, INF, 226/ Online
Prof. Dr. Peter Braun-Munzinger (Physikalisches Institut, Heidelberg/ GSI Darmstadt)
Project C05
Title of Talk: Fluctuations and correlations of conserved charges in relativistic nuclear collisions
Download the slides of the talk here:

CRC 1225 – YRC Lunch Seminar 06.12.2021 – Golden Box, Physikalisches Intitute, INF, 226
Speaker: Federica Capellino (PhD at GSI, Darmstadt)
Title: “Hydrodynamic approach to heavy-quark diffusion in the quark-gluon plasma”
Abstract: Exciting experimental results on the flow of charmonia and bottomonia, which have nowadays an unprecedented level of precision, pose the important physics question about the possible heavy-quark thermalization in the QGP. In this work, a new hydrodynamic approach to the transport of heavy quarks in the quark-gluon plasma (QGP) is presented. We exploit the conservation of the number of heavy quark–antiquark pairs within the evolution of the QGP to construct causal second-order hydrodynamic equations of motion. The hydrodynamic transport coefficients associated with the heavy-quark diffusion current are then compared with the momentum-diffusion coefficients obtained in transport theory (Fokker-Planck equation). By investigating the relation between the two approaches, we provide new insights concerning the level of local thermalization of charm and bottom quarks inside the expanding QGP.
Download the slides of the talk here:

CRC 1225 Lunch Seminar 25.10.2021– Golden Box, Physikalisches Intitute, INF, 226/ Online
Dr. Antonino Di Piazza (Max Planck Institute for Nuclear Physics, Heidelberg)
Project B02
Title of Talk: Recent progresses in strong-field QED in intense laser beams
Download the slides of the talk here:

Summer semester 2021

CRC 1225 Lunch Seminar 13.07.2021 – Online
Speaker: Jun.-Prof. Dr. Lauriane Chomaz (Physikalisches Institut, Heidelberg University)
Title of Talk: Ultracold gases with dipolar interactions
Abstract: Ultracold quantum gases realize a pristine platform to study few- and many-body quantum phenomena with an exquisite level of control. The achievement of quantum degeneracy in gases of atoms possessing large magnetic dipole moments has opened up new research directions where long-range anisotropic dipole-dipole interactions are competing with the conventional short-range contact interactions. Within the last few years, thanks to a fine control of this interaction competition and the subsequent discovery of a unique stabilization mechanism based on quantum fluctuations, experiments using magnetic lanthanide atoms proved novel self-organized many-body quantum states. These include liquid-like droplets, roton excitations, and, most recently, supersolids, a paradoxical phase of matter where both solid and superfluid orders coexists. In my talk, I will present some of the latest results that we achieved with my former group in Innsbruck, and discuss prospects for the future research that I want to develop in Heidelberg.

CRC 1225 Lunch Seminar 15.06.2021 – Online
Speaker: Prof. Dr. Tilman Enss (Institute for Theoretical Physics, Heidelberg University)
Project C02, C03
Title of Talk: Impurity dynamics and transport in strongly correlated quantum gases
Abstract: In this talk, I will discuss recent theoretical progress on transport in strongly interacting Fermi gases (CRC1225 project C02) and on Fermi and Bose polarons (CRC1225 project C03). 

CRC 1225 Lunch Seminar 11.05.2021 – Online
Jun.-Prof. Dr. Fred Jendrzejewski (KIP)
Project B04
Title of Talk: Engineering local U(1) symmetry in artificial systems
Abstract: In this talk, I will present our work on analog simulators of a U(1) gauge theory in one spatial dimension. To engineer the local gauge symmetry, we employ inter-species spin-changing collisions in an atomic mixture. We demonstrate the experimental realization of the elementary building block and discuss how it can be scaled to a U(1) gauge theory in one spatial dimension. Finally, I will discuss our more recent studies on realizations in classical electric circuits.

CRC 1225 Lunch Seminar 13.04.2021 – Online
Speaker: Prof. Dr. Christoph Keitel (MPIK Heidelberg)
Project B02
Title of Talk: Nonperturbative quantum electrodynamic theory in strong electromagnetic fields
Abstract: Challenges in the quantum electrodynamic theory and ever increasing precision of ion trap and laser experiments call for new improved and adapted theoretical methods. An overview is given on activities of my division including g factor calculations and nuclear quantum optics mostly in close local cooperation with partner at MPIK and the SFB. As following talks by the two other project leaders will focus on high-precision atomic theory and nonperturbative strong field QED most focus of this talk will be placed on a general overview of extreme field laser physics.
Download the slides of the talk here:

Winter semester 2020/2021

CRC 1225 Lunch Seminar 09.02.2021 – Online
Speaker: Prof. Dr. Anna Wienhard (Mathematisches Institut, Heidelberg)
Project B03
Title of Talk: Applying methods from geometry and topology to analyse data
Abstract: Data sets can be treated as point clouds in a metric space, or also as a network or graph. These different representations of data make them amenable to an analysis by topological and geometric methods. I will explain some of the standard methods and describe ideas to go beyond them.

CRC 1225 Lunch Seminar 12.01.2021 – Online
Speaker: Dr. Sebastian Erne (TU Wien)
Project A03
Title of Talk: Cold atom systems as analogue quantum simulators: From many-body relaxation to fundamental physics
Abstract: Ultracold atoms and their non-equilibrium evolution present an ideal platform to study fundamental processes of quantum field theory and the relaxation dynamics of quantum many-body systems. Transfer of results is often based on either functional equivalence of an effective description based on perturbative expansion or universal aspects independent of the microscopic details of the system. Here we present recent results and future prospects for analogue quantum simulators based on these concepts. In particular, we present results on (i) the relaxation in an inhomogeneous extended bosonic Josephson junction and show that nonlinear dynamics leads to the breakdown of the effective description based on the sine-Gordon model and the fast relaxation of the system to a phase locked state and (ii) the Kibble-Zurek mechanism in cooling quenched one-dimensional Bose gases and show that correlation measurements enable to test the KZ scaling predictions up to very fast quench-rates. We give an outlook on how the regimes of validity for these analogue simulators can be extended through tailored experimental trapping potentials realized by potential painting using a DMD device. Finally we present recent results on the possibility of analogue cold-atom simulators to measure the analogue Unruh effect, which is one of the fundamental and yet still untested predictions of quantum field theory that a uniformly accelerated observer in the Minkowski vacuum observes a thermal state whose temperature is proportional to the acceleration.
Download slides here:

CRC 1225 Lunch Seminar 01.12.2021 – Online
Speaker: Prof. Dr. Michael Klasen (Westfälische Wilhelms-Universität Münster)
Project C05
Title of Talk: Probing the QCD phase structure with heavy quarks: Nuclear PDFs
Abstract: The nuclear structure at high energies is an important research topic not only for our understanding of the fundamental quark and gluon dynamics in protons and neutrons bound in nuclei, but also for determining the initial conditions in the creation of a new state of matter, the quark-gluon plasma (QGP). While the evolution of parton distribution functions (PDFs) with the squared energy scale can be calculated in perturbative QCD, their dependence on the longitudinal momentum fraction must be fitted to experimental data. We review the current status of the nCTEQ project and discuss the impact of quarkonium and heavy-quark production data from the LHC on nuclear PDFs and on the description of the QGP phase structure within the Statistical Hadronization Model.
Download slides here:

CRC 1225 Lunch Seminar 10.11.2021 – Online
Speaker: Dr. Sven Sturm (Max-Planck-Institut für Kernphysik, Heidelberg)
Project B01
Title of Talk: Precision tests of atomic physics with isolated ions in Penning traps
Abstract: The simple structure of few- or single electron ions gives us the unique opportunity to probe the validity of Quantum Electrodynamics (QED) via a comparison of measured observables with precise predictions by theory. Single ions in Penning traps have proven to be a versatile test system for such precision measurements. The extremely good vacuum conditions we can achieve in cryogenic traps allows for very long storage of even highly charged ions, so that they can be precisely studied by measuring their motional and internal frequencies. Furthermore, in heavy highly charged ions the binding field of the nucleus can reach values up to 1016 V/cm, enabling a unique test in such extreme conditions. One prominent example is the ultra-precise determination of the g-factor of highly charged ions. While the weak-field regime has been already exquisitely tested, in the presence of strong fields higher-order contributions beyond the Standard Model might become significant. It is possible to sensitively search for such effects by measuring the Larmor- and cyclotron frequencies of single, highly charged ions in a cryogenic Penning trap with high precision. This way, by measuring the g-factor of medium heavy hydrogenlike ions with previously unprecedented precision, we have been able to perform the most stringent test of QED in strong fields. Particularly the effect of the nucleus on the g-factor of the electron is a novel and unique access to nuclear size and structure information.
To push these tests far into the strong-field, heavy ion regime we have developed and commissioned the ALPHATRAP experiment at the MPIK in Heidelberg. ALPHATRAP has recently performed the first high-precision measurement of the g-factor of a boronlike highly charged ion, 40Ar13+. This not only enables a sensitive test of multi-electron QED, but also paves the way towards a determination of the finestructure constant α. Furthermore, using a novel detection scheme also the internal atomic structure can be probed. This way, the finestructure splitting in 40Ar13+ has been measured by means of laser spectroscopy. Recent results of ALPHATRAP and future projects will be presented.
Download slides here:

Summer semester 2020

CRC 1225 Breakfast Seminar 14.07.2020 – Online
Speaker: Dr. Martin Gärttner (KIP, Heidelberg)
Project A05, A06
Title of Talk: Entanglement detection
Abstract: Quantum entanglement is a key concept enabling quantum technologies but also plays an important role in fundamental physics, for example for the understanding of the approach to thermal equilibrium in quantum many-body systems. The efficient detection and quantification of entanglement is a challenge which obstructs quantum simulation experiments. I will report on recent progress towards using entropic uncertainty relations for constructing experimentally accessible bounds on entanglement measures.
Materials: Slides (pdf)

CRC 1225 Lunch Seminar 18.06.2020 – Online
Speaker: Dr. Ilya Selyuzhenkov (GSI Darmstadt)
Project C06
Title of Talk: Collective QCD dynamics in relativistic collisions
Abstract: Ongoing and planned experiments worldwide with relativistic collisions of hadrons and nuclei allow to explore the hot and dense QCD matter at extreme temperatures of about 10^12K and/or baryon densities a few
times that of a nuclei. Extracting the equilibrium properties of the QCD matter requires detailed understanding of the QCD dynamics during the collision process which lasts only for a few 10^(-23) seconds and has a tiny scale of a few femtometers. Theoretically this demands to build a model of a quantum system beyond equilibrium which describes (collective) multiparticle production in relativistic collisions.

CRC 1225 Breakfast Seminar 20.05.2020 – Online
Speaker: Dr. Adriana Pállfy-Buß (MPIK, Heidelberg)
Project B02
Title of Talk: Coherent light interacting with nuclei: from ultraviolet to gamma rays
Abstract: In the past decades, the interaction of optical coherent light (laser light) with atoms and molecules has revolutionized atomic physics. Nuclear systems proved to be less easy to tame due to the partial lack of coherent sources for the frequency regime of interest and their weaker coupling to the radiation field. However, appealing potential applications  in coherent light interacting with nuclei exist along a broad range of parameters, from vacuum ultraviolet radiation to gamma rays. Three examples covering this range are addressed. The talk will introduce current efforts to develop a novel ultra-precise clock based on a nuclear transition in 229Th driven with a vacuum ultraviolet laser.  Moving towards higher energies, we show how the cooperative effects occurring when x-ray radiation interacts with nuclei in a crystal lattice offer the possibility to put single x-ray photons on hold. Finally, the formation of compound nuclei in a parameter regime never available so far by coherent MeV photons as the ones envisaged at upcoming petawatt laser facilities is discussed.  Such applications speak for the potential that coherent radiation may bring for controlling atomic nuclei.

CRC 1225 Lunch Seminar 21.04.2020 – Online
Prof. Dr. Selim Jochim (Physikalisches Institut, Heidelberg)
Project C01, C02
Title of Talk: Emergence of Many Body Physics – Shell by Shell
Abstract: When we think of many body physics, we typically assume the thermodynamic limit where the exact number of particles does not matter, and macroscopic behavior is characterized by quantities like pressure or temperature. Quantum physics can have a dramatic effect on such quantities, such as magnetization or the resistance, that might suddenly drop at a phase transition. We will give you an introduction into our quest trying to understand the emergence of such quantum many body effects by increasing the size of a well-controlled few-body system atom by atom. To this end we developed techniques to determine correlation functions and excitation spectra of isolated, tunable few-body systems. We will present the first results observing the emergence of a quantum phase transition in systems with filled shells.

Special Seminars

CRC 1225 Special Seminar 18.05.2021 – Online
Prof. Dr. John Martinis (Google and UCSB)
Topic: Quantum supremacy using a programmable superconducting processor
Abstract: The promise of quantum computers is that certain computational tasks might be executed exponentially faster on a quantum processor than on a classical processor.  We have used a programmable superconducting processor to create quantum states on 53 qubits, corresponding to a “parallel computation” of 10 million trillion states.  For a simple algorithm, our Sycamore processor takes about 200 seconds to run a quantum circuit a million times – the equivalent task for a state-of-the-art classical supercomputer would take approximately 10,000 years. This dramatic increase in speed compared to all known classical algorithms is an experimental realization of quantum supremacy, heralding a much-anticipated computing paradigm.

This talk is part of the official program of the Online Retreat of Young Researchers within CRC1225 : “Quantum Computation  – Solving Problems on Quantum Hardware”, 17-19, May 2021.

CRC 1225 Special Seminar 08.06.2021 – Online
Dr. Torsten Zache (University of Innsbruck)
Title of Talk: Quantum Variational Learning of the Entanglement Hamiltonian
The experimental capabilities of quantum simulation platforms, such as ultracold atoms, Rydberg tweezer arrays and trapped ions, already allow to realise and probe a variety of model Hamiltonians. However, the development of efficient and scalable protocols to measure the entanglement properties of quantum many-body systems – as encoded in the Entanglement Hamiltonian (EH) and its eigenvalues, the Entanglement spectrum (ES) – remains an outstanding challenge.
In this talk, I will present recent progress towards learning the EH in quantum simulations using a variational quantum-classical hybrid algorithm. Our protocol is enabled by the approximate locality of the EH, which is motivated by the Bisognano-Wichmann theorem of quantum field theory. For the example of a Fermi-Hubbard model on a ladder geometry our results demonstrate the experimental feasibility of the proposed algorithm. I will further discuss the application of such protocols to topological states, where it will allow to test with existing quantum simulators the Li-Haldane conjecture that the low-lying ES is related to the conformal field theory of edge excitations.

CRC 1225 Special Seminar 04.06.2020 – Online
Speaker: Mari Carmen Bañuls (MPI for Quantum Optics, Garching)
Title of Talk: Spectral properties and thermalization with matrix product operators
Abstract: Matrix product states, and operators, are powerful tools for the description of low energy eigenstates and thermal equilibrium states of quantum many-body systems in one spatial dimension. But in out-of-equilibrium scenarios, and for high energy eigenstates of generic systems, the scaling of entanglement with time and system size makes a direct application often impossible. However, MPS and more general TNS techniques can still be used to explore some of the most interesting dynamical properties.
We have recently introduced a method in which MPO techniques are combined with Chebyshev polynomial expansions to explore spectral properties of quantum many-body Hamiltonians. In particular, we show how this method can be used to probe thermalization of large spin chains without explicitly simulating their time evolution, as well as to compute full and local densities of states.
(Reference: arXiv:1909.01398)


YRC retreat 2021, 17-19.05.2021 – Online
Topic: Quantum Computation – Solving Problems on Quantum Hardware
Goal: The main intention of this event is to provide a platform for cross-project collaboration and the opportunity to intensify exchanges and networking between young researchers (bachelor, master and PhD students & young postdocs) within the IsoQuant collaboration. Due to the current Covid-19 situation, we decided to turn the retreat into a fully online event.
Prof. Fred Jendrzejewski (IsoQuant), Prof. John Martinis (Silicon Quantum Computing, Sydney, formerly at Google), Dr. Juris Ulmanis (Quantum Alpine Technology, Innsbruck) and Dr. Christian Gogolin (Covestro, Germany) will join this online workshop contributing with lectures, talks and a panel discussion.
The plan is to develop small group projects focussing on current research topics ranging from gauge theories to quantum chemistry. You will get a glimpse at the current state of quantum technologies, run your own algorithm (eg. using Qiskit) on real quantum computers and hear leading experts on the future of quantum computation.
Link to the registration form and preliminary schedule here

YRC retreat 2020, 5-8.04.2020 – Kurhaus Trifels in Annweiler  – cancelled due to Covid19
Data Science and Analysis

YRC retreat 2019, 24-27.03.2019 – Kurhaus Trifels in Annweiler
Machine Learning – Regression, Classification and Clustering
Goal: The main intention of our retreat is to provide a platform for cross-project collaboration on interesting topics and as well as the opportunity to intensify exchange and networking between young researchers within the SFB 1225. Working sessions will be organized in groups, where you will have the time to learn about your chosen topic’s background, try out already existing implementations and connect what you learned with your own research area. On the last day, all groups present their results such that everybody also has the opportunity to learn about the basics of the other topics.