QUANTUM-Seminar

Programm für das Sommersemester 2021

Thursdays, 14 Uhr c.t.

Institut für Physik
live at Zoom

15.04.21Prof. Dr. Peter Hommelhoff, Friedrich-Alexander-Universität Erlangen-Nürnberg
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 interaction-lean imaging with electrons and on-chip 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

22.04.21Prof. 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 near-term 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
29.04.21Prof. Dr. Andreas Hemmerich, Institut für Laser-Physik, Universität Hamburg
I will review our recent research on time crystal dynamics in an atom-cavity 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 atom-cavity system is a period doubled switching between distinct chequerboard density wave patterns, induced by the interplay between controlled cavity-dissipation, cavity-mediated 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

06.05.21Prof. Dr. Ignacio Cirac, Max-Planck-Institut für Quantenoptik, Garching
Quantum many-body 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

20.05.21Prof. Dr. Ralf Röhlsberger, Helmholtz Institut Jena/Friedrich-Schiller Universität Jena
The remarkable development of accelerator-driven light sources such as synchrotrons and X-ray lasers with their highly brilliant X-rays has brought quantum and nonlinear phenomena at X-ray energies within reach. X-ray photonic structures like cavities and superlattices are employed as new laboratory to realize quantum optical concepts at x-ray 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 light-matter interaction like the observation of single-photon superradiance and the collective Lamb shift as well as electromagnetically induced transparency with nuclei. Employing higher-order coherences of x-ray fields in the spirit of Glauber could even lead to novel concepts for quantum imaging at x-ray energies.
14:00 Uhr s.t., at Zoom

27.05.21Dr. 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 quantum-degenerate ground-state 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 atom-photon coupling opens up new perspectives for optical clocks, which face spontaneous decay as a fundamental decoherence mechanism.
14:00 Uhr s.t., at Zoom

10.06.21Dr. 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 spin-boson 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 spin-spin interactions we have been able to simulate Ising models with tunable-range spin couplings, and a many-body echo sequence, which we used to measure out-of-time-order correlations (OTOCs), a type of correlations that quantify the scrambling of quantum information across the system’s many-body 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 many-body quantum-enhanced 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 state-of-the-art 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 near-term detectors of dark matter.
14:00 Uhr s.t., at Zoom

17.06.21Dr. Silvia Viola-Kusminskiy, Max-Planck-Institute 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 single-magnon 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

24.06.21Prof. 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 so-called terahertz gap is nowadays possible with ultrafast lasers from the optical side as well as with millimeter-wave-technology from the electronic side. After a brief review of the state-of-the-art I will focus on recent progress on terahertz cross-correlation-spectroscopy 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

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

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

15.07.21Prof. Dr. Stefan Filipp, Walther-Meißner-Institut, 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 high-fidelity gate operations of different types are as important. We utilize a system based on fixed-frequency 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 single-qubit pulses without sacrificing their fidelity. Furthermore, we explore measurement techniques with a high duty cycle to overcome the challenge of time-consuming optimization sequences. For the generation of entangled two-qubit states we make use of a parametrically driven tunable coupler and implement different types of gates. Since exchange-type 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 near-term applications with scientific and commercial relevance.
14:00 Uhr s.t., at Zoom

Koordination: Kontakt:

Dr. Arne Wickenbrock
Institut für Physik und HIM Mainz
wickenbr@uni-mainz.de

Dr. Laatiaoui Mustapha
Department Chemie und HIM Mainz
laatiaoui@uni-mainz.de

Andrea Graham
Institut für Physik
graham@uni-mainz.de