Programm Wintersemester 2023/2024
Montag, 22.01.2024, 16:30 Uhr Physik Hörsaal
Philippe Grangier (CNRS, Université Paris Saclay)
Experimental tests of Bell’s inequalities at Institut d’Optique (1980-82): past achievements and future directions
We will review the motivations and history of the experiments that lead to the Nobel Prize in Physics 2022, attributed to Alain Aspect, John Clauser and Anton Zeilinger. We will then discuss some future perspectives, both on the side of quantum technologies, and on the side of the more philosophical issues that motivated initially these experiments.
Host: Julien Lesgourgues
Montag, 08.01.2024, 16:30 Uhr Physik Hörsaal
Jim Hinton (MPI Heidelberg)
The Southern Wide-field Gamma-ray Observatory
Over the last few decades ground-based gamma-ray astronomy has become an established astronomical discipline, exploring the extreme phenomena of the high energy universe. More recently, very wide field detectors, based on detecting particles from gamma-ray initiated electro-magnetic cascades at ground level, have emerged as a powerful tool to search for transient phenomena and search for emission at the ultra-high-energy limit of the electromagnetic radiation from the universe (around 10^15 electronVolts). I will discuss the motivations for, and progress towards, a new observatory of this type: SWGO; to be constructed high in the Andes in South America and offering not only unprecedented performance, but also the very first wide-field view of the inner part of the Milky Way at high energies.
Host: Christopher Wiebusch
Montag, 11.12.2023, 16:30 Uhr Physik Hörsaal
Ronald Hanson (TU Delft)
From Einstein’s Spooky Action to a Quantum Internet
Entanglement – the property that particles can share a single quantum state - is arguably the most counterintuitive yet potentially most powerful element in quantum theory. The non-local features of quantum theory are highlighted by the conflict between entanglement and local causality discovered by John Bell. Decades of Bell inequality tests, culminating in a series of loophole-free tests in 2015, have confirmed the non-locality of nature .
Future quantum networks  may harness these unique features of entanglement in a range of exciting applications, such as blind quantum computation, secure communication, enhanced metrology for astronomy and time-keeping as well as fundamental investigations. To fulfill these promises, a strong worldwide effort is ongoing to gain precise control over the full quantum dynamics of multi-particle nodes and to wire them up using quantum-photonic channels.
Here I will briefly introduce the field of quantum networks. I will then discuss our most recent work, demonstrating the realization of the first multi-node network wired by quantum entanglement, based on optically connected solid-state chips, including first primitive network protocols, Also I will discuss new results on entanglement distribution over deployed fiber on metropolitan scale. I will finally touch upon some aspects for scaling these technologies.
 For a popular account of these experiments, see e.g. Ronald Hanson and Krister Shalm, Scientific American 319, 58-65 (2018).
 Quantum internet: A vision for the road ahead, S Wehner, D Elkouss, R Hanson, Science 362 (6412), eaam9288 (2018).
Host: David DiVincenzo
Montag, 27.11.2023, 16:30 Uhr Physik Hörsaal
Benjamin Sacepe (CNRS Grenoble)
Quantum Hall physics in graphene
The quantum Hall (QH) effect is a fascinating playground that harbors a variety of correlated and symmetry protected phases, but also a peculiar, chiral charge transport via edge channels. Graphene enables to probe these phenomena down to the atomic scale by scanning tunneling microscopy. In this talk I will first review the physics of QH edge channels and present an original scanning tunneling spectroscopy performed at the crystal edge of a graphene flake. I will show that the exact real-space structure of those QH edge channels challenges the commonly accepted picture. In a second part I will focus on the graphene zeroth Landau level, a particularly interesting flat band in which interelectron interactions are predicted to induce several broken-symmetry states with distinct topological and lattice-scale orders. I will describe three distinct broken-symmetry phases that we have identified in transport and imaged using scanning tunneling spectroscopy.
Host: Markus Morgenstern
Montag, 30.10.2023, 16:30 Uhr Physik Hörsaal
Mario Berta (RWTH Aachen University)
Quantum Algorithm Development
Information technologies based on components governed by the laws of quantum physics have long promised a transformative impact on computing. Most famously, this includes quantum computers running dramatically faster algorithms than those available for computers based on classical physics. In my talk, I will discuss the current state of quantum hardware and present a critical assessment of the landscape of quantum algorithms from an application driven perspective. Looking forward—and as improvements in quantum hardware increase the number and quality of qubits—we seek quantum algorithms that are able to showcase practical quantum advantage against state-of-the-art classical methods. Towards this goal and motivated by applications in scientific computing for condensed matter physics and computational chemistry, I will present a selection of our recently developed qubit efficient, hybrid quantum algorithms. These allow for a flexible trading between quantum circuit depth and sample complexity — while outsourcing all but the critical quantum sub-routines to classical pre- and post-processing.
Host: Hendrik Bluhm
Montag, 16.10.2023, 16:30 Uhr Physik Hörsaal
Philip Mertsch (RWTH Aachen University)
The Galaxy under a high-energy microscope
The fate of the Milky Way is in the hands of high-energy, charged particles, so-called cosmic rays. Discovered over a hundred years ago, their origin is still shrouded in mystery. In the past, progress had been hampered by the scarcity of experimental data. Today, however, we are in a position to unravel the origin of cosmic rays thanks to new multi-messenger data. I will argue that experimental efforts must be guided by state-of-the-art modelling and highlight some examples of recent progress by our group on a variety of physical scales: We have found surprising features in the microscopic interactions of charged cosmic rays with turbulent magnetic fields, making use of methods from quantum field theory and modern computational paradigms like GPUs. On the intermediate scales of individual sources, cosmic rays can regulate their own transport, and we are employing machine learning to accelerate our numerical models. On the large scales, that is the size of the Galaxy, better spatial information on gas, magnetic fields and star light is needed, and I will review recent progress in reconstructing 3D maps using Bayesian variational inference.
Host: Stefan Schael