Physikalische Kolloquien im Winterersemester 2019/20

Gastvorträge für Hochschulmitarbeiter und Studierende ab dem Masterstudium. Gelegenheit zum gemeinsamen Austausch.
Foto: Dekanat PAF
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Das Physikalische Kolloquium findet, wenn nicht anders angegeben,  jeweils um 16:15 Uhr im Hörsaal 1 Abbeanum, Fröbelstieg 1 statt.

Termine im Wintersemester 2019/20

11.11.2019 Eintrag erweitern
Dr. Gopalakrishnan Balasubranian Dr. Gopalakrishnan Balasubranian Foto: privat

Dr. Gopalakrishnan Balasubramanian
Max-Planck-Institut für Biophysikalische Chemie Göttingen

Understanding physical quantities at the nanoscale is a frontier research topic that has profound and broad impact covering fundamental physics to emerging technologies. In nanoscale, the material properties manifest their quantum nature; hence a quantum sensor could be advantageous to effectively harness these quantum effects for sensing and precision measurements. In this talk, I will discuss the prospects of spins associated with Nitrogen-Vacancy (NV) centres in diamond for quantum sensing1. This solid-state sensor offers unique advantages for precision measurement of magnetic field2,3, electric field4, temperature and strain under ambient conditions1.

The first part of my talk will focus on applications pertaining to single NV spins. I will outline the developments of an NV spin microscope to probe molecular structure and dynamics of single biomolecules1,2,5. Followed by this, I will present some results on using single NV sensors to probe phase transition at the nanoscale in a liquid-crystalline material6. Here we used a single NV as a dual-mode sensor to probe the nuclear spin fluctuations and temperature simultaneously to obtain information about controlled phase transition of the soft-matter as a function of temperature. Finally, I will detail our approach on a Hybrid quantum sensor that enhances the static-field sensitivity 102 times and reaching nT/√Hz. This scheme could be scaled to achieve another 103 improvements thus being able to detect bio-magnetic fields from cardiac activities in real-time on par with vapour-cell magnetometers. In the second part of my talk, I will discuss our research focus on fibre-based NV sensor for non-local and multiplexed sensing in a highly flexible environment. I will include some key possibilities and proof-of-principle results. These include enhancing the excitation/collection efficiencies of NV rich diamond micro-crystals7, NV defects as a precision optical micro-heater8 and also NV sensor operated in a dual-mode to study demagnetization of micro-magnets9.

  1. Balasubramanian, A. Lazariev, S.R. Arumugam, and D.-W. Duan. Nitrogen- vacancy color center in diamond-emerging nanoscale applications in bioimaging and biosensing. Current Opinion in Chemical Biology, 20(1):69–77, 2014.

  2. Balasubramanian, I.Y. Chan, R. Kolesov, M. Al-Hmoud, J. Tisler, C. Shin, C. Kim, A. Wojcik, P.R. Hemmer, A. Krueger, T. Hanke, A. Leitenstorfer, R. Bratschitsch, F. Jelezko, and J. Wrachtrup. Nanoscale imaging magnetometry with diamond spins under ambient conditions. Nature, 455(7213):648–651, 2008.

  3. Balasubramanian, P. Neumann, D. Twitchen, M. Markham, R. Kolesov, N. Mizuochi, J. Isoya, J. Achard, J. Beck, J. Tissler, V. Jacques, P.R. Hemmer, F. Jelezko, and J. Wrachtrup. Ultralong spin coherence time in isotopically engineered diamond. Nature Materials, 8(5):383–387, 2009.

  4. Dolde, H. Fedder, M.W. Doherty, T. Nöbauer, F. Rempp, G. Balasubramanian, T. Wolf, F. Reinhard, L.C.L. Hollenberg, F. Jelezko, and J. Wrachtrup. Electric-field sensing using single diamond spins. Nature Physics, 7(6):459–463, 2011.

  5. Lazariev, S. Arroyo-Camejo, G. Rahane, V.K. Kavatamane, and G. Balasubramanian. Dynamical sensitivity control of a single-spin quantum sensor. Scientific Reports, 7(1), 2017.

  6. K. Kavatamane, D. Duan, S. Arumugam, N. Raatz, S. Pezzagna, J. Meijer, G. Balasubramanian, “Probing phase transitions in a soft matter system using a single spin quantum sensor.”, New Journal of Physics, 2019.

  7. Duan, G.X. Du, V.K. Kavatamane, S. Arumugam, Y.-K. Tzeng, H.-C. Chang, and G. Balasubramanian. Efficient nitrogen-vacancy centers’ fluorescence excitation and collection from micrometer-sized diamond by a tapered optical fiber in endoscope- type configuration. Optics Express, 27(5):6734–6745, 2019.

  8. Duan, V.K. Kavatamane, S.R. Arumugam, G. Rahane, G.-X. Du, Y.-K. Tzeng, H.-C. Chang, and G. Balasubramanian. Laser-induced heating in a high-density ensemble of nitrogen-vacancy centers in diamond and its effects on quantum sensing. Optics Letters, 44(11):2851–2854, 2019.

  9. Duan, V.K. Kavatamane, S. Arumugam, G. Balasubramanian, “Nitrogen-Vacancy centers as a self-gauged micro-scale heater and its application for multi-modal sensing of demagnetization in micro-magnets.”, Optics Express (submitted).

18.11.2019 Eintrag erweitern
Jo van den Brand, Sprecher der Virgo Collaboration Jo van den Brand, Sprecher der Virgo Collaboration Foto: privat

Prof. Dr. Jo van den Brand
Spokesman of the Virgo Collaboration, National Institute for Subatomic Physics (Nikhef), Amsterdam

Gravitational Waves: Physics at the Extreme

The LIGO Virgo Consortium achieved the first detection of gravitational waves.  A century after the fundamental predictions of Einstein, we report the first direct observations of binary black hole systems merging to form single black holes. The detected waveforms match the predictions of general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. Our observations provide unique access to the properties of space-time at extreme curvatures: the strong-field, and high velocity regime. It allows unprecedented tests of general relativity for the nonlinear dynamics of highly disturbed black holes. In 2017 the gravitational waves from the merger of a binary neutron star was observed. This discovery marks the start of multi-messenger astronomy and the aftermath of this merger was studied with 70 observatories on seven continents and in space, across the electromagnetic spectrum.

The scientific impact of the recent detections will be explained. In addition key technological aspects will be addressed, such as the interferometric detection principle, optics, sensors and actuators. Attention is paid to Advanced Virgo, the European detector near Pisa. The presentation will close with a discussion of the largest challenges in the field, including plans for a detector in space (LISA), and Einstein Telescope, an underground observatory for gravitational waves science. 


02.12.2019 Eintrag erweitern
Prof. Dr. Dr. h. c. Henry Chapman, Center for Free-Electron Laser Science, DESY, Hamburg Prof. Dr. Dr. h. c. Henry Chapman, Center for Free-Electron Laser Science, DESY, Hamburg Foto: privat

Prof. Dr. Dr. h.c. Henry Chapman
Center for Free-Electron Laser Science, DESY, Hamburg

Imaging Macromolecules with X-ray laser pulses

Free-electron lasers produce X-ray pulses with a peak brightness a billion times that of beams at a modern synchrotron radiation facility.  This has provided a disruptive new technology, in several senses of the word.  A single focused X-ray FEL pulse completely destroys a small protein crystal placed in the beam, but not before that pulse has passed through the sample and given rise to a diffraction pattern.  This principle of diffraction before destruction has given the methodology of serial femtosecond crystallography for the determination of macromolecular structures from tiny crystals without the need for cryogenic cooling.   Consequently, it is possible to carry out high-resolution diffraction studies of dynamic protein systems with time resolutions ranging from below 1 ps to milliseconds, from samples under physiological temperatures and other conditions.  The high intensity and coherence of the X-ray beam can also be exploited for novel phasing approaches, ranging from preferential ionisation of elements to the use of intensity measurements between Bragg peaks.  Even now, a decade after the first experiment at LCLS, we have not fully explored the limits of the technique, nor developed it to its full potential.  I will discuss some of those potentials. 

09.12.2019 Eintrag erweitern
Dr. Jörg Körner Dr. Jörg Körner Foto: privat

Dr. Jörg Körner
Institut für Optik und Quantenelektronik, FSU Jena

Exploring novel concepts and laser media for diode-pumped bulk lasers to tap new applications

Many novel industrial applications and laser matter interaction sciences are relying on high energy class lasers. Therefore, scaling the performance of such systems with respect to energy, repetition rate, and availability at other wavelengths is an essential point in laser development.

Over the last decades, diode pumped lasers based on neodymium doped active media became the state of the art for commercially available lasers. For further scaling of their performance, ytterbium doped active media are very attractive, due to their lower quantum defect, longer excited state lifetime and high quantum efficiency. Nevertheless, actually using these materials in such systems requires novel approaches for the laser architecture due to their relatively low cross sections. This includes simplified imaging multi-pass extraction schemes and modifications in resonator design to enable the use of unstable cavities for the direct generation of high energy pulses.

Materials doped with threefold positive thulium ions are a candidate to realize diode pumped high energy class laser systems in the wavelength range from 1.8 µm to 2 µm. So far detailed spectroscopic studies and first testbed systems are under development to define promising architectures for high energy short pulse systems.


16.12.2019 Eintrag erweitern
Prof. Dr. Klaus Hentschel Prof. Dr. Klaus Hentschel Foto: privat


Prof. Dr. Klaus Hentschel
Universität Stuttgart

Entstehung und Veränderung des mentalen Modells von Lichtquanten

Anhand des komplexen Konzepts von Photonen, das bis heute diskutiert wird, präsentiert Klaus Hentschel sein Modell für Begriffsentwicklung als schichtweise Anreicherung und Überlagerung von Bedeutungsebenen. Die ältesten im Vortrag diskutierten stammen noch aus der Zeit des Newtonianischen Projektilmodells des Lichtes. Der Bogen wird im Vortrag bis zur QED geschlagen.

20.01.2020 Eintrag erweitern
Prof. Dr. Christian_Schroer, DESY Hamburg Prof. Dr. Christian_Schroer, DESY Hamburg Foto: privat

Prof. Dr. Christian Schroer
DESY, Hamburg

Mikroskopie mit kohärenter Röntgenstrahlung: Kristallographie des Nichtkristallinen

Der Hauptvorteil der Mikroskopie mit Röntgenstrahlung ist die Möglichkeit, auch das Innere von Objekten zerstörungsfrei abbilden zu können. Aber obwohl die Wellenlänge von Röntgenstrahlung im Bereich atomarer Abstände liegt, gelingt es heute nicht, Atome aufzulösen. Das liegt vor allem an den heutigen Röntgenoptiken, die aufgrund der schwachen Wechselwirkung von Röntgenstrahlung mit Materie eine stark beschränkte numerische Apertur haben, und so ihr Auflösungsvermögen begrenzt wird. Ein Ausweg ist der Verzicht auf eine abbildende Röntgenoptik und die Beleuchtung der Probe mit kohärenter Röntgenstrahlung. Das von der Probe gestreute Licht wird von einem Flächendetektor aufgezeichnet. Dabei geht die Information über die Phase der gestreuten elektromagnetischen Welle verloren. Unter geeigneten Bedingungen kann diese mit Hilfe numerischer Methoden rekonstruiert werden, so dass sich ein Bild der Probe errechnen lässt. Dabei sind heute höchste Auflösungen im Bereich von ca. 5 nm möglich. Mit der zukünftigen Synchrotronstrahlungsquelle PETRA IV könnten mit diesen Methoden physikalische, chemische und biologische Prozesse bis in den sub-Nanometerbereich verfolgt werden.

03.02.2020 Eintrag erweitern
Prof. Dr. Andrea Santangelo Prof. Dr. Andrea Santangelo Foto: privat

Prof. Dr. Andrea Santangelo
Eberhard Karls Universität Tübingen

Fundamental physics studies with high energy missions

Spectral, timing, and polarimetric observations at high energies allow us to address scientific questions in fundamental physics. In this seminar I will address three specific topics:

  1. Which is the state of baryonic matter at extreme densities, larger than several times the ones in the atomic nuclei, and expected in the cores of neutron stars?
  2. How can we constrain the properties of the dark matter particle candidate through high energy observations?
  3. Which is the behavior of light in the presence of ultra-strong magnetic fields, almost a billion of times stronger that what achievable on earth (i.e., in magnetars)? The matter inside neutron stars, the extremely magnetized vacuum close to magnetars, the objects in which dark matter clusters, are among the uncharted territories of fundamental physics.

    In this talk, after having discussed the science case at the base of these three questions, I will review briefly future missions that could help us to answers those questions, such as the enhanced X-ray Timing and Polarimetry, an innovative space mission that will observationally address those fundamental questions.