Colloquia

Our past events

• 2024

  24 April:

  12:30 - 12:50  Frank Cozijn - PhD Candidate, Quantum Metrology & Laser Applications, Vrije Universiteit Amsterdam
  
  Lamb Dip of a Quadrupole Transition in H2
  Abstract: The saturated absorption spectrum of the hyperfineless S(0) quadrupole line in the (2-0) band of H2 is measured at λ = 1189 nm, using the NICE-OHMS technique under cryogenic conditions (72 K). It is for the first time that a Lamb dip of a molecular quadrupole transition is recorded. At low (150-200 W) saturation powers a single narrow Lamb dip is observed, ruling out an underlying recoil doublet of 140 kHz. Studies of Doppler detuned resonances show that the red-shifted recoil component can be made visible for low pressures and powers, and prove that the narrow Lamb dip must be interpreted as the blue recoil component. A transition frequency of 252 016 361 164 (8) kHz is extracted, which is off by -2.6 (1.6) MHz from molecular quantum electrodynamical calculations therewith providing a challenge to theory.

  12:50 -13:45 - Prof. Dr. Daniela Kraft, Leiden University
  
  Designing reconfigurable colloidal structures: from powerful model systems to autonomous microscopic robots
  Abstract: Many biological structures such as proteins and ion channels as well as machines and robots rely on changes in their shape to do useful work. Key to these shape changes is the presence of hinging elements that enable a reconfiguration of their conformation and the ability to consume energy. In this talk I will show how we realize flexible structures at the micrometer scale using micrometer-sized analogues of joints and hinges [1]. I will demonstrate their powerful model system character using micrometer-sized flexible chains [2,3], rings [4], and floppy lattices [5]. We find that thermal fluctuations, and thus entropy, together with their topology play a crucial role in shaping their conformations as well as their soft and stiff modes. I will demonstrate that we can realize unusual properties into colloidal structures by designing reconfiguration modes and in this way obtain the first colloidal versions of auxetic mechanical metamaterials. Finally, I will discuss how we can control and activate conformational changes to pave the way towards truly functional microstructures and autonomous microrobots.

  14 March:

  12:30 - 12:50   Pim America - PhD Candidate (Physics of Living Systems, Vrije Universiteit Amsterdam)        Two coronavirus helicases bind the polymerase sequentially and the second speeds up RNA synthesis

  Abstract: The SARS-CoV-2 pandemic has had a profound impact on humanity, underscoring the urgent need for therapeutics against this class of viruses. To address this, a deep understanding of coronavirus molecular biology and biochemistry is essential. In this study, we focused on exploring the role of nsp13-helicase in the dynamics of SARS-CoV-2 RNA synthesis within the functional complex of the replication-transcription complex (RTC). Nsp13-helicase is essential for the virus to replicate, but its functional role remains unknown. The nsp13-helicase has an opposite polarity to nsp12-polymerase, and whether nsp13-helicase supports RTC RNA synthesis, how it provides such supports remain unclear. To shed light on nsp13-helicase functional role in RNA synthesis, we employed a high-throughput magnetic tweezers assay to monitor CoV RTC RNA synthesis at the single-molecule level under a constant force. We found that, in the presence of nsp13-helicase, the RTC exhibits bursts of very fast nucleotide addition and fewer pausing compared to the core RTC (consisting of nsp12-polymerase with co-factors nsp7 and nsp8). Furthermore, we show that nsp13-helicase association with the CoV polymerase is specific, and support replication through RNA secondary structures by unwinding the template strand from the complementary non-template strand. We obtained the energy landscape of nsp13-helicase association with the RTC and derived a precise model of the nucleotide addition dynamics in the presence of nsp13-helicase. We tested this model for nsp13-helicase concentration and the applied force sweeps. Our work is the first functional characterization of the role of nsp13-helicace in CoV replication.  

  12:50 -13:45 - Jun. Prof. Dr. Elina Fuchs (CERN and Leibniz Universität Hannover)
  Searching for physics beyond the Standard Model with atoms and colliders
  Abstract: The observed matter-antimatter asymmetry of the Universe and the existence of Dark Matter are among the most compelling evidences for the necessity of physics beyond the Standard Model. As these puzzles do not predict at which energy scale to expect a discovery, a variety of observables at different energies is needed to explore viable scenarios of heavy and light new particles. I will present two such avenues.

  First, I will discuss the interplay between the Large Hadron Collider at high energy and electric dipole moments at low energy to investigate the potential role of the discovered Higgs boson in explaining the baryon asymmetry. The focus will be on improving the sensitivity to the CP structure of the Higgs interactions, also with Machine Learning.

  In a complementary way, I will present how high-precision frequency measurements in atoms, ions and a nucleus open up a novel window to search for light Dark Matter and high-frequency Gravitational Waves. In particular, I will discuss the implications of recent spectroscopic data from atomic clock transition in ytterbium and calcium on new, light dark bosons.

  17 January:
  
  12:30 - 12:50   Eduard Elias - PhD Candidate, Vrije Universiteit Amsterdam
  The Ultrafast Excitation Energy Equilibration Dynamics in the Plant Photoynthetic LHCII-CP24-CP29 Assembly

  Abstract: In photosynthesis light is primarily captured by Photosystem I and II. The photosystems consist of a modular assembly of pigment-protein complexes, commonly referred to as the light-harvesting complexes (LHCs), which absorb light and shuttle excitation energy via their vast network of pigments to the photosystem reaction center where the energy is used for charge separation. In order to outcompete the natural excited-state decay processes, it is vital that the LHCs very rapidly transfer the excitation energy to the reaction center (on the order of ~10-11 - 10-10  s). Ultrafast transient absorption measurements on isolated LHC complexes have yielded detailed pictures of the intra-LHC energy transfer pathways, yet the inter-LHC pathways remain elusive. This is mainly because the photosystem contain a large number of pigments, many iso-energetic, meaning that the energy equilibration between them is not always directly observable as a spectral evolution in the ultrafast measurements. To circumvent this problem, we have performed transient absorption measurements providing high excitation densities to our samples. In this way, excitations that combine in the assemblies annihilate and show up as a detectable quenching signal, which corresponds to the inter-LHC energy equilibration time. We have applied this method to a sub-complex of Photosystem II, which is an assembly of the LHCs CP24, CP29 and LHCII and is composed of 5 subunits. By combining annihilation measurements on the complex and its constituents and by leveraging structural modelling, we have shed light on the inter-LHC energy transfer pathways between these complexes.

  12:50 -13:45 - Prof. Dr. Andreas Freise (Vrije Universiteit Amsterdam and Nikhef)
  
  Abstract: Gravitational wave observatories have started to make significant contributions to physics and astronomy. Now the gravitational wave community has the responsibility to provide adequate observational capability for gravitational waves for 2030 and beyond. The ‘Einstein Telescope’ (ET) is our vision to build a new gravitational wave observatory in Europe, possibly near Maastricht. In this talk he will give a brief overview of the vision behind this plan and the current status of the project. He will then highlight the challenges in realising such an ambitious project, including organisational and political aspects. Of course he will also present recent research results from our people at the VU and Nikhef.

• 2023

  6 December:
  
  12:30 - 12:50   Pan Li - PhD candidate, Vrije Universiteit Amsterdam
  
  Nanoscale thermometry of plasmonic structures via Raman shifts in copper phthalocyanine
  Abstract: Temperature measurements at the nanoscale are vital for the application of plasmonic structures in medical photothermal therapy and materials science, but very challenging to realize in practice. In this work, we exploit a combination of surface enhanced Raman spectroscopy together with the characteristic temperature dependence of the Raman peak maxima observed in β-phase copper phthalocyanine (β-CuPc) to measure the surface temperature of plasmonic gold nanoparticles (NPs) under laser irradiation. We begin by measuring the temperature dependent Raman shifts of the three most prominent modes of β-CuPc films coated on an array of Au nanodisks over a temperature range of 100 K to 500 K. We then use these calibration curves to determine the temperature of an array of Au nanodisks irradiated with varying laser powers. The extracted temperatures agree quantitatively with the ones obtained via numerical modelling of the electromagnetic and thermodynamic properties of the irradiated array. Thin films of β-CuPc display low extinction coefficients in the blue-green region of the visible spectrum as well as exceptional thermal stability, allowing a wide temperature range of operation of our Raman thermometer, with minimal optical distortion of the underlying structures. Thanks to the strong thermal response of the Raman shifts in β-CuPc, our work opens the opportunity to investigate photothermal effects at the nanoscale in real-time and over single-nanoparticles.

  12:50 -13:45 - Dr. Eliska Greplova, Department Quantum Nanoscience - Kavli Institute of Nanoscience, TU-Delft, Faculty of Applied Sciences
  
  Exploring human creativity and AI for engineered quantum matter
  Abstract: In research labs worldwide, quantum physics is making unprecedented strides. The realization of robust quantum systems holds tremendous promise for applications in secure communication and computing. Yet, as physicists, our most exciting pursuit lies in experimentally testing quantum phenomena predicted over the past century within highly controlled environments. In this colloquium, I will explore two distinct approaches to engineering quantum matter: one fueled by human creativity and the other driven by artificial intelligence. Throughout the colloquium, we will uncover how these approaches can be effectively deployed in contemporary quantum experiments, paving the way for advancements in our understanding and control of quantum phenomena.

  
  25 October:
  
  12:30 - 12:50    Dr. Suzanne Klaver, Vrije Universiteit, Natuur- en Sterrenkunde - Nikhef 

  Searching for a new force of nature in LHCb and its upgrade
  Abstract: A crucial foundation of particle physics is that the building blocks of the universe appear in three generations. These differ in mass, but interact identically. Recent experiments, however, question the fundamental principle of identical interactions, which could imply a new force of nature. I will present what types of measurements we perform in LHCb to either confirm or rule out these results. Moreover, I will discuss the new LHCb upgrade detector, which is currently being commissioned, and the prospects for these measurements.

  12:50 -13:45 - Dr. Peter Kraus, Vrije Universiteit, Natuur- en Sterrenkunde - ARCNL

  New routes for label-free super-resolution microscopy and attosecond science via transient high-harmonic generation
  Abstract: While the upconversion of infrared driving lasers into soft-X-ray pulses by high-harmonic generation (HHG) in gases has become an established technique for attosecond science and nanoscale imaging [1-3], HHG in solids is less explored. Gas-phase HHG is highly sensitive and thus controllable with regards to the microscopic generation mechanism, and the macroscopic buildup of emission via phase matching [4,5]. Parallels between solid and gas-phase HHG suggest that solid-state HHG may be controlled in similar manners, which would enable a generally applicable all-optical light switch with wide application potential.

  13 September:

  12:50-13:45 - Ewine van Dishoeck, Professor of Molecular Astrophysics
  Molecules from clouds to planets: new insights from ALMA and Webb
  
  Abstract: The space between the stars is not empty but filled with a very dilute gas. In spite of the extremely low temperatures and densities, these clouds contain a surprisingly rich chemistry, as evidenced by the detection of more than 240 different molecules, from simple to complex and from gas to solid-state ices. These clouds are also the birthplaces of stars and planets. New powerful facilities such as the Atacama Large Millimeter Array (ALMA) and the James Webb Space Telescope (Webb) have found water and a surprisingly rich variety of organic materials near forming stars, including simple sugars, ethers and alcohols. How are these molecules formed in space? Which molecular processes play a role? How common are they and can they be delivered to new planets?

  Biography: Ewine van Dishoeck stood and still stands at the cradle of the most powerful telescopes in the world. She studies icy, thin clouds of gas between the stars near our own solar system. Including in the Orion Nebula - so often beautifully imaged with the Hubble telescope. These clouds contain all kinds of molecules that are interesting in their own right: due to the special conditions in space, molecules are found there that do not or hardly occur on earth. But something fascinating is happening in many of those gas clouds: new stars and planets are being born. Van Dishoeck examines the formation process of these celestial bodies and investigates which molecules from the clouds could eventually end up on such a new planet.

  Van Dishoeck has won many prizes and awards, including the Kavli Prize for astrophysics in 2018, the highest award in this field. In 2000 she also received the Spinoza Prize, the most important scientific award in the Netherlands - and won numerous research grants. With the Leiden Observatory, its field of activity, Leiden University has one of the world's most renowned astronomical institutes. In addition to Van Dishoeck, her colleagues, the Leiden astronomers Marijn Franx and Xander Tielens, also received the Spinoza Prize. Van Dishoeck is also known for her contributions to the construction of various telescopes. These are almost always international collaborative projects where Van Dishoeck acts as a bridge builder. It brings people, resources and organizations together. Personal Homepage: https://home.strw.leidenuniv.nl/~ewine/
  

  Gijs Buist
  PhD Candidate, Biophotonics and Medical Imaging, Vrije Universiteit

  13:45-14:15 - Monte Carlo simulations of OCT and Rayleigh range detection in scattering media

  Abstract: Optical Coherence Tomography is a light based imaging technique that uses coherence properties of light to measure depth resolved backscatter intensity in scattering media. OCT is a widely used technique to diagnose pathologies through morphological changes in tissue structure. However, current standards provide qualitative images that are not quantitatively related to tissue optical properties, such as the attenuation coefficient. During this talk I will present a Monte Carlo simulation framework for OCT developed with the aim to aid in the development of robust and accurate attenuation coefficient extraction algorithms, as well as increase understanding of signals generated via OCT.

  10 May:

  12:50-13:45 Renate Loll, Professor - High Energy Physics, Radboud University - Quantum Gravity Reloaded

  Abstract: Quantum Gravity Reloaded - Quantum gravity is the art of showing that quantum theory and general relativity are not fundamentally incompatible, all the way to the Planck scale. It turns out that a highly fruitful strategy is to use nothing but good old quantum field theory, without any exotic ingredients, and adapt it to the situation where spacetime geometry is dynamical. It has taken us a while to address the underlying technical and conceptual challenges, but the good news is that we now have charted a path toward a theory of quantum gravity which is unitary, essentially unique and can produce "numbers" beyond perturbation theory.

   I will introduce the approach of Causal Dynamical Triangulations (CDT), which is to quantum gravity what lattice QCD is to nonabelian gauge theory. Its nonperturbative toolbox has allowed us to go where other approaches cannot (yet) and to extract quantitative results on quantum observables at or near the Planck scale. They reveal promising evidence for both genuine quantum effects and the existence of a classical limit, reflecting the mathematical richness of the underlying "random geometry". A breakthrough result of CDT quantum gravity in four dimensions is the emergence, from first principles, of a nonperturbative quantum spacetime with de Sitter-like properties. I will summarize these findings, highlight some structural challenges and discuss the future prospects of quantum gravity.

  13:45-14:15 -  Tom Brandstaetter (group of Chase Broedersz, Theoretical Physics of Living Systems)
  Title: Life in curved space

  31 March: 

  12:30-12:50 Prof. Dr. Randall Goldsmith

  Title: Photonics technologies for chemical and biophysical measurements
  Abstract: how my group uses whispering gallery mode microresonators, microFabry-Perot cavities, plasmonic nanostructures, and topological photonic structures to develop new instrumentation for making measurements on single molecules and biomolecules.
  Biography: Randall Goldsmith is the Helfaer Professor of Chemistry and an affiliate of the Department of Electrical and Computer Engineering. He completed undergraduate degrees in chemistry and biology (2002) at Cornell University. He received his Ph.D at Northwestern University (2008) studying photoinduced electron transfer under the direction of Professors Michael Wasielewski and Mark Ratner, and performed postdoctoral work at Stanford University with Professor W.E. Moerner, where he became profoundly convinced that molecules deserve to be looked at one at a time. He has been a faculty member in the Department of Chemistry at the University of Wisconsin Madison since 2011 where his research interests span single-molecule spectroscopy, micro and nanophotonics, chemical catalysis, photochemistry, and biophysics. His work has been recognized with a DARPA young faculty award, NSF CAREER award, Alzheimer’s Association Young Faculty Award, Dreyfus Teacher-Scholar Award, and Journal of Physical Chemistry Lectureship Award. He was recently designated a Schmidt Futures Polymath.
  
  12:50-13:45 Elmer Gründeman PhD Candidate, Faculty of Science, Atoms, Molecules, Lasers

  Title: First observation of the 1S - 2S transition of singly-ionized helium

  Abstract: Precision spectroscopy of simple, calculable atomic and molecular systems is an important tool for tests of bound-state quantum electrodynamics (QED), the determination of fundamental constants, and searches for physics beyond the standard model. Singly-ionized helium (He+) is a promising alternative system to atomic hydrogen, the current standard for experimental tests of QED in neutral atoms, as high-order QED corrections scale with high powers of the nuclear charge. Since He+ is charged, it can be confined in a Paul trap and sympathetically cooled down close to absolute zero. To excite the 1S - 2S electronic transition, which is of interest for QED tests, laser light at extreme ultraviolet (XUV) wavelengths is required along with a high-precision spectroscopy method available in this spectral range. We aim to measure this transition with an accuracy better than 1 kHz (10-13) using high-harmonic generation (HHG) combined with Ramsey-comb spectroscopy (RCS). RCS allows us to drive this two-photon transition with unequal photons, one at 790 nm (the fundamental of our frequency comb laser) and one at 32 nm (the 25th harmonic). We recently demonstrated the first laser excitation of the 1S-2S transition in He+, based on an atomic beam of helium. This paves the way to high-precision 1S - 2S laser spectroscopy of He+ in an ion trap using Ramsey-Comb spectroscopy.

  
  
  1 February: 

  12:30-12:50  Dr. Sven H.C. Askes, VU Amsterdam: “Light-pulsed nanoscale heating for catalyst control”

  12:50-13:40  Prof. Sera Markoff, University of Amsterdam: “A tale of two black holes: Sgr A* and M87*"

  Black holes are one of the most exotic consequences of Einstein’s General Relativity, yet they are also very common, ranging from stellar remnants up to beasts billions of times more massive than our sun. Despite their reputation as cosmic vacuum cleaners, they actually drive extremely complicated astrophysical systems that can majorly influence their surroundings. Via their powerful outflows in particular, black holes shape the way the Universe looks today...but not at all times. Black holes undergo cycles of activity, so to understand their role over cosmological timescales we need to understand not only how they power these outflows from just outside their event horizons, but also what drives their cyclic behavior. Thanks to the Event Horizon Telescope (EHT) we have now directly imaged the event horizon region for two nearby supermassive black holes: Sgr A* in our own Galactic center, and M87* in the Virgo cluster of galaxies. After a brief review of the key results so far, I will put them into the context of our greater understanding of black hole activity, with emphasis on the gains made by combining EHT observations with those from other multi-wavelength facilities. I will also discuss the near- and longterm outlook for the studies of black hole astrophysics and their cosmic impact.

• 2013

  17.01: Colloquium    Simon Scheuring, U1006 INSERM, Univesite Aix-Marseille

  24.01: Colloquium    Henry Kapteyn, Department of Physics, JILA, and NSF ERC in EUV Science and Technology, University of Colorado and NIST, Boulder

  07.02: Colloquium    Pierre Clade, Ecole Normale Superieure, Paris, France 

  28.03: Colloquium    Jeroen Koelemeij, LaserLaB, Vrije Universiteit Amsterdam, Amsterdam

  25.04: Colloquium    Martin Plenio, Institute of Theoretical Physics, Ulm University, Ulm, Germany

  30.05: Colloquium    Jeff Gore, Massachusetts Institute of Technology, Cambridge

• 2012

  07.07 : Colloquium  Claudiu Gradinaru, Department of Physics and  Institute for Optical Sciences, University of Toronto, Canada

  11.09 : Colloquium  Michael Murphy, Swinburne University of Technology, Centre for Astrophysics & Supercomputing, Hawthorn, Victoria, Australia

  11.10 : Colloquium  Niek van Hulst, ICFO – the Institute of Photonic Sciences, Barcelona, Spain

  25.10 : Colloquium  Peter Hommelhoff, Max-Planck-Institut für Quantenoptik, Garching, Germany

  08.11 : ColloquiumAdela Ben-Yakar, N. Doug Williams Memorial Centennial Endowed Faculty, The University of Texas at Austin, USA

  20.12 : Colloquium  Andreas Buchleitner, Institute of Physics, Albert-Ludwigs University of Freiburg, Freiburg, Germany 

• 2011

  07.12: Colloquium  Alexandra Olaya-Castro, University College London

  18.05: Colloquium  Laurens Siebbels, TU Delft

  16.05: Colloquium  Kevin Sivula, École Polytechnique Fédérale de Lausanne

  12.05: Colloquium  Greg Stephens, Princeton Uniersity

  26.04: Colloquium  Martin Depken, Vrije Universiteit

  20.04: Colloquium  Eleni Katifori, Rockefeller University

  06.04: Colloquium  Matthias Kaschube, Princeton University

  16.03: Colloquium  Erik Verlinde, UvA

• 2010

  22.01: Colloquium Quantum-coherent solar energy capture by marine algae, Gregory D. Scholes, Department of Chemistry, Institute for Optical Sciences and Centre for Quantum Information and Quantum Control, University of Toronto

  18.06: Colloquium; Using Adaptive Optics to Probe the Limits of Foveal Vision, Austin Roorda, Associate Professor of Optometry and Vision Science, University of California, Berkeley

• 2009

  9.10: Fysisch Colloquium; Excited-State Proton Transfer: From "super" photoacids to the green fluorescent protein

  28.10: Colloqium Elisabeth Charlaix Lyon University

  26:11: Fysisch Colloqium Thomas Rockmann, Utrecht University