Programm für das Sommersemester 2021
Thursdays, 14 Uhr c.t.
Institut für Physik
live at
Zoom
15.04.21  Prof. Dr. Peter Hommelhoff, FriedrichAlexanderUniversität ErlangenNürnberg  
Free electrons are used in a plethora of instruments, ranging from electron microscopes to particle accelerators and modern light sources for decades. Yet, fundamentally new concepts are surfacing, taking advantage of electrons in an entirely new way, mainly based on quantum mechanical and nanophotonics concepts. In this talk, I will show recent results towards interactionlean imaging with electrons and onchip control of electrons. These results bring us closer to a quantum electron microscope and to a particle accelerator on a chip.  
14:00 Uhr s.t., at Zoom  

22.04.21  Prof. Dr. Konrad Lehnert, JILA, University of Colorado, Boulder, USA  
Can emerging quantum information technologies, in some way, improve or enhance searches for fundamental physical phenomena? Indeed, the use of optical squeezing in gravitational wave observatories is a beautiful example that they can. In addition to this one prominent example, the search for dark matter may offer several other nearterm experiments that can, and perhaps must, use enhanced quantum sensing methods. In particular detail, I’ll discuss the case of searching for a hypothetical dark matter particle known as the axion and accelerating the search using quantum squeezing approaches.  
14:00 Uhr s.t., at Zoom  

zukünftige Termine
29.04.21  Prof. Dr. Andreas Hemmerich, Institut für LaserPhysik, Universität Hamburg  
I will review our recent research on time crystal dynamics in an atomcavity system. In contrast to discrete time crystals in driven closed systems, where dissipation constitutes an undesired obstacle, I will discuss an ansatz, where tailored dissipation and fluctuations, induced via controlled coupling to a suitable environment, stabilize time crystal dynamics. The central signature in our implementation in a driven open atomcavity system is a period doubled switching between distinct chequerboard density wave patterns, induced by the interplay between controlled cavitydissipation, cavitymediated interactions and external driving. We demonstrate the robustness of this dynamical phase against system parameter changes and temporal perturbations of the driving.  
14:00 Uhr s.t., at Zoom  

06.05.21  Prof. Dr. Ignacio Cirac, MaxPlanckInstitut für Quantenoptik, Garching  
Quantum manybody systems are very hard to simulate, as computational resources (time and memory) typically grow exponentially with system size. However, quantum computers or analog quantum simulators may perform that task in a much more efficient way.
In this talk, I will first review some of the quantum algorithms that have been proposed for this task and then explain the advantages and disadvantages of analog quantum simulators. I will also describe theoretical proposals to solve different quantum simulation problems with cold atoms in optical lattices.  
14:00 Uhr s.t., at Zoom  

20.05.21  Prof. Dr. Ralf Röhlsberger, Helmholtz Institut Jena/FriedrichSchiller Universität Jena  
The remarkable development of acceleratordriven light sources such as synchrotrons and Xray lasers with their highly brilliant Xrays has brought quantum and nonlinear phenomena at Xray energies within reach. Xray photonic structures like cavities and superlattices are employed as new laboratory to realize quantum optical concepts at xray energies. The prime candidates to be chosen as atomic emitters in this field are Mössbauer isotopes. Their extremely small resonance bandwidth facilitates to probe fundamental phenomena of the lightmatter interaction like the observation of singlephoton superradiance and the collective Lamb shift as well as electromagnetically induced transparency with nuclei. Employing higherorder coherences of xray fields in the spirit of Glauber could even lead to novel concepts for quantum imaging at xray energies.  
14:00 Uhr s.t., at Zoom  

27.05.21  Dr. Christian Sanner, JILA, University of Colorado, Boulder, USA  
Can Fermi quantum statistics be used to manipulate the radiative properties of atomic emitters? Is it possible to extend the natural lifetime of an electronically excited atom by placing it inside a bath of quantumdegenerate groundstate atoms? I will report on an experiment that demonstrates how a Fermi sea can block the spontaneous decay of an excited atom. This striking manifestation of Fermi statistics connects for the first time the fundamental radiative property of atoms to their motional degrees of freedom subject to quantum statistics. Quantum engineering the atomphoton coupling opens up new perspectives for optical clocks, which face spontaneous decay as a fundamental decoherence mechanism.  
14:00 Uhr s.t., at Zoom  

10.06.21  Dr. Ana Maria Rey, JILA, NIST and University of Colorado, Boulder, USA  
I will discuss recent progress on the use of planar crystals with hundreds of ions as a platform for quantum simulation of spin and spinboson models. The key idea is the use of a pair of lasers to couple two internal levels of the ions, that act as a spin½ degree of freedom, to the vibrational modes, phonons, of the crystal. In the regime when phonons do not play an active role in the dynamics and instead mediate spinspin interactions we have been able to simulate Ising models with tunablerange spin couplings, and a manybody echo sequence, which we used to measure outoftimeorder correlations (OTOCs), a type of correlations that quantify the scrambling of quantum information across the system’s manybody degrees of freedom. In the regime when phonons actively participate we have been able to simulate the Dicke model, an iconic model in quantum optics which describes the coupling of a (large) spin to an oscillator and more recently realize a manybody quantumenhanced sensor that can detect weak displacements and electric fields. Our system is the first to demonstrate an enhanced sensitivity resulting from quantum entanglement in a mesoscopic ion crystal with an improvement by a factor of 300 over prior classical protocols in trapped ions and more than an order of magnitude compared to stateoftheart electrometers based on Rydberg atoms. Overall my talk plans to illustrate the great potential offered by trapped ion crystals not only as quantum simulators but also as feasible nearterm detectors of dark matter.  
14:00 Uhr s.t., at Zoom  

17.06.21  Dr. Silvia ViolaKusminskiy, MaxPlanckInstitute for the Science of Light, Erlangen  
In the last few years, a new field has emerged at the intersection between Condensed Matter and Quantum Optics, denominated “Quantum Magnonics”. This field strives to control the elementary excitations of magnetic materials, denominated magnons, to the level of the single quanta, and to interface them coherently to other elementary excitations such as photons or phonons. The recent developments in this field, with proof of concept experiments such as a singlemagnon detector, have opened the door for hybrid quantum systems based on magnetic materials. This can allow us to explore magnetism in new ways and regimes, has the potential of unraveling quantum phenomena at unprecedented scales, and could lead to breakthroughs for quantum technologies. A predominant role in these developments is played by cavity magnonic systems, where an electromagnetic cavity, either in the optical or microwave regime, is used to enhance and control the interaction between photons and magnons. In this talk, I will introduce the field and present some theoretical results from our group which aim to push the boundaries of the current state of the art.  
14:00 Uhr s.t., at Zoom  

24.06.21  Prof. Dr. Georg von Freymann, Technische Universität Kaiserslautern  
Terahertz spectroscopy has evolved over recent years from an interesting but technologically hard to address tool for fundamental studies to a technology with industrial applications. Closing the socalled terahertz gap is nowadays possible with ultrafast lasers from the optical side as well as with millimeterwavetechnology from the electronic side. After a brief review of the stateoftheart I will focus on recent progress on terahertz crosscorrelationspectroscopy driven by a superluminescent light emitting diode and terahertz spectroscopy with undetected photons for which all terahertz spectral information is gained from visible photons.  
14:00 Uhr s.t., at Zoom  

01.07.21  Dr. Sven Herrmann, ZARM, Universität Bremen  
TBA  
14:00 Uhr s.t., at Zoom  

08.07.21  Prof. Dr. Hiroshi Kawarada, School of Fundamental Science and Engineering, Waseda University, Japan  
TBA  
14:00 Uhr s.t., at Zoom  

15.07.21  Prof. Dr. Stefan Filipp, WaltherMeißnerInstitut, Bayerische Akademie der Wissenschaften  
The rapid development of quantum technologies in the recent past has brought us a step closer to operational quantum computers that hold promise to outperform conventional computers in certain types of problems. While a large number of qubits is necessary to run complex algorithms, fast and highfidelity gate operations of different types are as important. We utilize a system based on fixedfrequency superconducting qubits that are characterized by their stability, relatively long coherence times and scalability. On this platform we explore different ways to increase the performance of future quantum processors. We demonstrate that optimal control techniques allow us to shape microwave control pulses and realize fast singlequbit pulses without sacrificing their fidelity. Furthermore, we explore measurement techniques with a high duty cycle to overcome the challenge of timeconsuming optimization sequences. For the generation of entangled twoqubit states we make use of a parametrically driven tunable coupler and implement different types of gates. Since exchangetype gates preserve the number of qubit excitations these are particularly well suited for quantum chemistry algorithms in which the number of electrons in the molecule is typically fixed. With this choice of gates we can make best use of the available hardware and realize short algorithms that finish within the coherence time of the system. With gate fidelities around 95% we compute the eigenstates within an accuracy of 50 mHartree on average, a good starting point for nearterm applications with scientific and commercial relevance.  
14:00 Uhr s.t., at Zoom  

Koordination:  Kontakt: 
Dr. Arne Wickenbrock Dr. Laatiaoui Mustapha  Andrea Graham 