Programm für das Wintersemester 2020/2021

Thursdays, 14 Uhr c.t.

Institut für Physik
live at Zoom

22.10.20Prof. Dr. Simon Stellmer, Rheinische Friedrich-Wilhelms-Universität Bonn
Our quantum metrology research group has recently been established at the University of Bonn. The overarching goal of our various projects is the improvement of precision measurements in an interdisciplinary context. In my talk, I will present two of our projects. In the first project, we address one of the most pressing fundamental questions in contemporary physics: Why does the Universe contain matter, but almost no antimatter? This matter-to-antimatter asymmetry is understood as massive CP violation, which in turn would show up as a permanent electric dipole moment (EDM) in fundamental particles. I will show how ultracold and even quantum-degenerate Fermi gases of mercury can be used to measure the neutron EDM with a sensitivity that might exceed state-of-the-art limits. The second project is related to geodesy: the rotation of Earth is not as constant as it may seem. On the contrary, it is an amazingly sensitive probe of all kinds of phenomena, ranging from rotational coupling to other celestial objects all the way to mantle/crust coupling and the anthropogenic climate change. We have started to develop novel gyroscopes to measure, via the Sagnac effect, variations in the Earth rotation rate at an unprecedented sensitivity.
14 Uhr c.t., at Zoom

29.10.20Prof. William D. Phillips (Nobel Prize in Physics), National Institute of Standards and Technology (NIST), USA
On 20 May 2019 the International System of Units (the SI) experienced its most revolutionary change since the French revolution produced the metric system. Today, all of the base units of the SI are defined by fixing the values of constants of nature, resulting in a fundamentally quantum system of measurement units. This talk will discuss why such a reform was needed and how it is implemented.
14 Uhr c.t., at Zoom

05.11.20Prof. Dr. Arno Rauschenbeutel, Humboldt-Universität zu Berlin
Correlating photons using the collective nonlinear response of atoms weakly coupled to an optical mode Typical schemes for generating correlated states of light require a highly nonlinear medium that is strongly coupled to an optical mode. However, unavoidable dissipative processes, which cause photon loss and blur nonlinear quantum effects, often impede such methods. In this talk, I will report on our recent experimental demonstration of a proposal that takes the opposite approach [1]. Using a strongly dissipative, weakly coupled medium, we generate and study strongly correlated states of light [2]. Specifically, we study the transmission of resonant light through an ensemble of non-interacting atoms that weakly couple to a guided optical mode. Dissipation removes uncorrelated photons while preferentially transmitting highly correlated photons created through collectively enhanced nonlinear interactions. As a result, the transmitted light constitutes a strongly correlated many-body state of light, revealed in the second-order correlation function. The latter exhibits strong antibunching or bunching, depending on the optical depth of the atomic ensemble. The demonstrated mechanism opens a new avenue for generating nonclassical states of light and for exploring correlations of photons in non-equilibrium systems using a mix of nonlinear and dissipative processes. Furthermore, our scheme may turn out useful in quantum information science. For example, it offers a fundamentally new approach to realizing single photon sources, which may outperform sources based on single quantum emitters with comparable coupling strength [3]. [1] S. Mahmoodian, M. Čepulkovskis, S. Das, P. Lodahl, K. Hammerer, A. S. Sørensen, Phys. Rev. Lett. 121, 143601 (2018). [2] A. Prasad, J. Hinney, S. Mahmoodian, K. Hammerer, S. Rind, P. Schneeweiss, A. S. Sørensen, J. Volz, A. Rauschenbeutel, Nat. Photonics (2020). https://doi.org/10.1038/s41566-020-0692-z [3] European patent pending (PCT/EP2019/075386)
14 Uhr c.t., at Zoom

12.11.20Univ.-Prof. Dr. Tracy E. Northup, Universität Innsbruck
Future quantum networks offer a route to quantum-secure communication, distributed quantum computing, and quantum-enhanced sensing. A current challenge across all experimental platforms is how to move beyond proof-of-principle realizations to the efficient, faithful distribution of quantum states over scalable networks. I will present ongoing work on nodes for quantum networks based on trapped ions in optical cavities, focusing in particular on a connection between remote trapped-ion systems in Innsbruck and the development of fiber-cavity-based interfaces. To conclude, we will consider another role for ions coupled to optical cavities, namely, how they may enable the preparation of macroscopic quantum states of motion, in this case, of levitated nanoparticles. A common theme in this talk will be how an optical cavity can serve as an interface between quantum states encoded in light, in motion, and in the electronic states of an ion.
14 Uhr c.t., at Zoom

19.11.20Prof. Dr. Anastasia Borschevsky, University of Groningen, NL
The Van Swinderen Institute for Particle Physics and Gravity, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands Search for variation of fundamental constants and for violation of fundamental symmetries provides a unique opportunity for observing new physics and for testing various extensions of the Standard Model. Atomic and molecular experiments offer a low energy and comparatively inexpensive alternative to high energy accelerator research in this field. As the observable effects are expected to be very small, highly sensitive systems and extremely precise measurements are required in order to detect any manifestations of the physical phenomena beyond the Standard Model. An important task of theoretical research is to identify optimal molecular and atomic systems for measurements and to understand the mechanisms behind the enhanced sensitivity, which is strongly dependent on the electronic structure. Thus, accurate computational methods are needed in order to provide reliable predictions rather than estimates, and to obtain the various parameters that are required for the interpretation of the experiments. I will present the results of our recent investigations of atoms and molecules in the context of search for variation of fundamental constants and for parity violating effects. A short overview of the theoretical methods will be provided, but the talk will focus on showcasing the different types of systems (highly-charged ions, diatomic and chiral molecules) that are promising candidates for experiments that aim to detect new physical phenomena.
14 Uhr c.t., only via ZOOM

26.11.20Dr. James Millen, King's College London, UK
Nanoparticles suspended and cooled in vacuum are seen as ideal candidates for testing the limits of quantum mechanics, beyond state-of-the-art sensing, and tabletop detection of gravitational waves and dark matter. The standard technology involves optical trapping and levitation, though this comes with issues of optical absorption and photon scattering. Away from the optical regime, electromechanics concerns the control of mechanical motion via its coupling to an electrical circuit. Chip-based electromechanical systems are leading quantum technologies, allowing entanglement between different circuit-signals, quantum squeezing, and the coherent conversion of signals between different frequency regimes. I will present our preliminary results in the field of Levitated Electromechanics, where particles are levitated, detected and controlled all-electrically. I will introduce the concept of bath engineering in this system with a preliminary study of non-equilibrium dynamics, and our work towards miniaturization. For more information see www.levi-nano.com
14 Uhr c.t., at Zoom

03.12.20Prof. Dr. Andrey Surzhykov, Physikalisch-Technische Bundesanstalt Braunschweig
The Gamma Factory (GF) is a novel research tool, currently considered by CERN as part of its Physics Beyond Colliders initiative. While the main goal of the GF is the generation of high-intensity beams of gamma rays, it will also open up many opportunities in atomic, nuclear and particle physics. In my presentation, I will focus especially on the planned atomic physics activities. In particular, we will discuss how the GF can enable a wide range of ground-breaking studies, from the high-precision spectroscopy of partially stripped ions to testing Special Relativity and fundamental symmetries of Nature. Joint seminar with the MITP workshop on Physics Opportunities with the Gamma Factory: https://www.hi-mainz.de/de/news-events/detail/news/physics-opportunities-with-the-gamma-factory/ Prof. Dr. Andrey Surzhykov, Physikalisch-Technische Bundesanstalt Braunschweig
14 Uhr c.t., at Zoom

10.12.20Dr. Lars von der Wense, JILA, University of Colorado, Boulder, USA
A nuclear optical clock based on ^229Th ions is expected to achieve a higher accuracy than the best atomic clocks operational today [1]. Although proposed back in 2003 [2], such a nuclear frequency standard has not yet become reality. The main obstacle that has so far hindered the development of a nuclear clock was an imprecise knowledge of the energy value of a nuclear excited state of the ^229Th nucleus, generally known as the ^229Th isomer. This metastable nuclear excited state is the one of lowest energy in the whole nuclear landscape and - with an energy of less than 10 eV - offers the potential for nuclear laser spectroscopy, which poses a central requirement for the development of a nuclear clock [3]. Recently, a couple of new experiments have led to an improved knowledge about the isomer’s excitation energy [4, 5, 6], thereby constraining the isomeric energy to a value of 8.12 0.11 eV. This new knowledge offers great potential for future laser spectroscopy experiments and the development of a nuclear optical clock. With a wavelength equivalent of 152.7 2.1 nm, the energy is very well accessible by the 7th harmonic of a high-power Yb:doped-fiber frequency-comb [7] and a corresponding spectroscopy experiment is already in preparation [8]. If successful, the experiment would provide the first laser spectroscopy of a nuclear transition, thereby improving our current constraints of the isomer’s energy by six orders of magnitude. In addition, the stabilization of an individual comb-mode to the nuclear transition would result in the immediate development of a nuclear frequency standard. In this presentation I will give an overview over the current status of the nuclear clock development, with a particular focus on the most recent progress. Also the next required steps will be detailed and future perspectives will be given. References [1] C.J. Campbell et al., Phys. Rev. Lett. 108, 120802 (2012). [2] E. Peik and C. Tamm, Eur. Phys. Lett. 61, 181 (2003). [3] L. von der Wense and B. Seiferle, arXiv:2009.13633 (2020). [4] B. Seiferle et al., Nature 573, 243 (2019). [5] A. Yamaguchi et al., Phys. Rev. Lett. 123, 222501 (2019). [6] T. Sikorsky et al., Phys. Rev. Lett. 125, 142503 (2020). [7] C. Zhang et al., Phys. Rev. Lett. 125, 093902 (2020). [8] L. von der Wense and C. Zhang, Eur. Phys. J D 74, 126 (2020).
14 Uhr c.t., at Zoom

17.12.20Univ.-Prof. Dr. Markus Arndt, Universität Wien
Physics is currently in a state where many would say, the essential laws of nature are well understood. And it is true that quantum physics has matured for more than a century and has become the basis of a stunning range of modern technologies. And yet, fundamental questions of quantum physics have remained unsolved until today such as its transition into classical phenomenology or its relation to gravity theory. More recently a growing evidence has also suggested that we may actually know only a few percent of the world, missing the entire dark sector in matter and energy. Here I will focus on how to set up universal matter - wave interferometers that can demonstrate and utilize the quantum wave nature of matter. I will present experiments to explore the interface between quantum physics and classical phenomena and shine light on the question of objective wave function collapse. I will discuss how gravity influences all matter-wave interferometry, and many conceivable ways for it may to modify the dynamics of very massive superpositions. Finally, matter-wave interferometers built for that purpose will also mature into sensors for dark matter in a specific energy range. Ideas and prospects are briefly discussed.
14 Uhr c.t., at Zoom

07.01.21Prof. Dr. Antoine Browaeys, Laboratoire Charles Fabry, Palaiseau, France
This talk will present our effort to control and use the dipole-dipole interactions between cold atoms in order to implement spin Hamiltonians useful for quantum simulation of condensed matter or quantum optics situations. We trap individual atoms in arrays of optical tweezers separated by a few micrometers. We create almost arbitrary geometries of the atomic arrays in two and three dimensions up to about 200 atoms. To make the atoms interact, we either excite them to Rydberg states or induce optical dipoles with a near-resonance laser. Using this platform, we have in particular explored quantum magnetism, topological synthetic quantum matter, and a new light-matter interface.
14 Uhr c.t., at Zoom

14.01.21Tanya S. Roussy, M.A., JILA (University of Colorado Boulder & NIST)
Over the past few decades, accelerators have been the traditional venue for new particle discoveries – but the paradigm is shifting. Accelerator energies are likely to remain on a plateau for some time, while atomic physics & precision measurement are in a remarkable period of progress. Some limits have advanced by a factor of 100 in less than 10 years, and laser technologies are being refined to exquisite levels. New Physics searches are already an established avenue in the atomic physics field; from atomic parity violation, to EDM searches, to equivalence principle tests. Happily, many of these platforms are well-suited to do double-duty as broadband dark matter searches. In this talk, I will explain the basics of our unique trapped-ion electron EDM search, how we used our recent data to constrain the gluon to axion-like particle coupling over seven mass decades, and how we solved some important methodological issues along the way.
14 Uhr c.t., at Zoom

21.01.21Prof. Dr. Hatice Altug, EPFL Lausanne, CH
New health initiatives with global healthcare, precision medicine and point-of-care diagnostics are demanding breakthrough developments in biosensing and bioanalytical tools. Current biosensors are lacking precision, bulky, and costly, as well as they require long detection times, sophisticated infrastructure and trained personnel, which limit their application areas. My laboratory is focused on to address these challenges by exploiting novel optical phenomena at nanoscale and engineering toolkits such as nanophotonics, nanofabrication, microfluidics and data science. In particular, we use photonic nanostructures based on plasmonics and dielectric metasurfaces that can confine light below the fundamental diffraction limit and generate strong electromagnetic fields in nanometric volumes. In this talk I will present how we exploit nanophotonics and combine it with imaging, biology, chemistry and data science techniques to achieve high performance biosensors. I will introduce ultra-sensitive Mid-IR biosensors based on surface enhanced infrared spectroscopy for chemical specific detection of molecules, large-area chemical imaging and real-time monitoring of protein conformations in aqueous environment. Next, I will describe our effort to develop ultra-compact, portable, rapid and low-cost microarrays and their use for early disease diagnostics in real-world settings. Finally, I will highlight label-free optofluidic biosensors that can perform one-of-a-kind measurements on live cells down to the single cell level, and provide their prospects in biomedical and clinical applications.
14 Uhr c.t., at Zoom

28.01.21Univ.-Prof. Dr. Tanja Mehlstäubler, Physikalisch-Technische Bundesanstalt, Braunschweig
Single trapped and laser-cooled ions in Paul traps allow for a high degree of control of atomic quantum systems. They are the basis for modern atomic clocks, quantum computers and quantum simulators. Our research aims to use ion Coulomb crystals, i.e. many-body systems with complex dynamics, for precision spectroscopy. This paves the way to novel quantum clocks for applications such as relativistic geodesy and improved navigation. The high-level of control of self-organized Coulomb crystals also opens up a fascinating insight into the non-equilibrium dynamics of coupled many-body systems, displaying atomic friction and symmetry-breaking phase transitions. We discuss the creation of topological defects in 2D crystals and present recent results on the study of tribology and transport mediated by the topological defect.
14 Uhr c.t., at Zoom

04.02.21Prof. David Cassidy, University College London, UK
Positronium (Ps) is a hydrogenic atom composed of an electron bound to a positron. Since it contains only leptons Ps is, for all practical purposes, a pure QED system, unaffected by nuclear structure effects. Also, being composed of a particle-antiparticle pair, Ps atoms are metastable, and may decay via self-annihilation, as well as through the usual radiative decay channels seen in regular atoms. The energy levels of Ps can be calculated to arbitrary precision (in principle), and precision spectroscopy of Ps can therefore be used to perform rigorous tests of bound-state QED theory. Moreover, since the theoretical description is limited only by the order of the calculations performed, rather than unknown physical constants or incalculable terms, any observed (and confirmed) disagreement with theory could indicate the existence of “new physics” such as particles or fields not currently included in the Standard Model. In this talk I will describe some new measurements of the Ps n = 2 fine structure, specifically 2 ^3S_1--> 2 ^3P_J (J = 0,1,2) transitions. The experiments were performed using a radioactive isotope-based positron beam coupled to a buffer gas/Penning trap. This allows positron pulses to be generated, which are converted into a dilute Ps gas with in vacuum an initial number density on the order of 10^6 cm^-3. A pulsed dye laser was used to optically excite atoms to the 2 ^3S_1 level, and microwave radiation was used to drive transitions to the 2 ^3P_J levels, which decay radiatively to the ground state before annihilation. The different annihilation decay rates of the ground and excited (S) states allows the fine structure transitions to be monitored via the time spectrum of the Ps annihilation radiation. We found that the measured J = 1 and J = 2 lineshapes exhibited significant asymmetries, whereas a symmetric lineshape was observed for the J = 0 transition. The observed asymmetries are not consistent with the most obvious quantum interference or line-pulling phenomena arising from nearby (off-resonant) transitions, and in the absence of a complete lineshape model we are therefore unable to determine the fine structure intervals for these transtions. Since the J = 0 lineshape did not exhibit any significant asymmetry it was possible to extract a value for the centre frequency: however, the obtained interval was found to disagree with theory by 2.77 MHz, which amounts to 4.5 standard deviations. No mechanism for a line shift of this magnitude has so far been identified.
14 Uhr c.t., at Zoom

11.02.21Dr. Stefan Ulmer, Ulmer Fundamental Symmetries Laboratory, RIKEN, Japan & CERN
The Standard Model of particle physics is both incredibly successful and glaringly incomplete. Among the questions left open is the striking imbalance of matter and antimatter in our universe, which inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision. The BASE collaboration at the antiproton decelerator of CERN is performing such high-precision comparisons with protons and antiprotons. Using advanced, ultra-stable, cryogenic particle traps and superconducting detectors with single particle sensitivity, we have performed the most precise measurement of the proton-to-antiproton charge-to-mass ratio with a fractional uncertainty of 69 parts per trillion [1]. In another measurement, we have invented a novel spectroscopy method, which allowed for the first ultra-high precision measurement of the antiproton magnetic moment with a fractional precision of 1.5 parts in a billion [2]. Together with our recent measurement of the proton magnetic moment [3] this improves the precision of previous experiments [4] by more than a factor of 3000. A time series analysis of this recent magnetic moment measurement furthermore enabled us to set first direct constraints on the interaction of antiprotons with axion-like particles (ALPs) [5], and most recently, we have used our ultra-sensitive single particle detection systems to derive narrow-band constraints on the conversion of ALPs into photons [6]. In my talk I will review the recent achievements of BASE and will outline strategies to further improve our high-precision studies of matter-antimatter symmetry. This outlook will involve the implementation of sympathetic cooling of antiprotons using quantum logic methods, the development of the transportable antiproton trap BASE-STEP, and will also review recent experimental progress towards 10-fold improved measurements of the antiproton properties. [1] S. Ulmer et al., Nature 524, 196 (2015). [2] C. Smorra et al., Nature 550, 371 (2017). [3] G. Schneider et al., Science 358, 1081 (2017). [4] J. DiSciacca et al., Phys. Rev. Lett. 110, 130801 (2013). [5] C. Smorra et al., Nature 575, 310 (2019). [6] J. A. Devlin et al., Phys. Rev. Lett., accepted (2021). S. Ulmer1, K. Blaum2, M. Bohman1,2, M. Borchert1,3, J. A. Devlin1,4, S. Erlewein1,2,4, M. Fleck1,5, C. Smorra1, M. Wiesinger1,2, C. Will2, E. Wursten5, Y. Matsuda6, C. Ospelkaus3, W. Quint6, J. Walz7,8, Y. Yamazaki1 1RIKEN, Ulmer Fundamental Symmetries Laboratory, Saitama, Japan; 2Max-Planck-Institut für Kernphysik, Heidelberg, Germany; 3Leibnitz University, Hannover, Germany; 4CERN, Geneva, Switzerland; 5The University of Tokyo, Tokyo, Japan; 6GSI - Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany; 7Johannes Gutenberg-Universität, Mainz, Germany; 8Helmholtz-Institut Mainz, Germany;
14 Uhr c.t., at Zoom

Koordination: Kontakt:

Dr. Arne Wickenbrock
Institut für Physik und HIM Mainz

Dr. Laatiaoui Mustapha
Department Chemie und HIM Mainz

Andrea Graham
Institut für Physik