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Belgian Physical Society
General Scientific Meeting 2008
Université Libre de Bruxelles
May 21 2008
SCIENTIFIC PROGRAM
MORNING SESSION – FORUM B
8:00 Registration & Coffee
9:00 Welcome
9:10 Plenary Lecture: Pr Dr Hartmut Zabel (Ruhr-Universität Bochum)
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Recent progress on spintronics |
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Abstract: Since the discovery of the giant magneto-resistance (GMR) effect by Albert Fert and Peter Grünberg in 1988 and awarded with the Nobel Prize for Physics in 2007, much progress has been made in the field of spintronics. Spin valves were introduced, switching via spin torque was proposed and confirmed, the tunneling magneto-resistance effect has matured to marketability, and magnetic domain walls and their propagation are being developed for memory storage devices with enhanced density. Simultaneously advanced nanofabrication and characterization techniques and novel spintronic materials promise further progress in spintronics in the future. An overview will be presented on these recent developments. |
10:00 Plenary Lecture: Pr Dr Reinhard Genzel (MPE, Garching)
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The massive black hole at the Center of the Milky Way |
Abstract: Evidence has been accumulating for several decades that many galaxies harbor central mass concentrations that may be in the form of black holes with masses between a few million to a few billion time the mass of the Sun. I will discuss measurements over the last decade, employing adaptive optics imaging and spectroscopy on large ground-based telescopes that prove the existence of such a massive black hole in the Center of our Milky Way, beyond any reasonable doubt. These data also provide key insights into its properties and environment. Future interferometric studies of the Galactic Center black hole promise to be able to test gravity in its strong field limit. I will also briefly discuss the cosmological evolution of massive black holes. |
10:50 Coffee break & Poster session
11:20 Young Lecturer Contest (three lectures)
11:20 Benoit FAMAY
Université Libre de Bruxelles
Brussels, Belgium
The bullet cluster of galaxies: a proof of the existence of dark matter?
Abstract
We review the arguments against and in favour of the existence of Dark Matter (DM) in the Universe. We also present the main phenomenological contender to the DM paradigm, known as Modified Newtonian Dynamics (MOND). We confront both paradigms with the weak lensing observations of 1E0657-56, an extremely interesting object, known as the bullet cluster, in which the collisionless component and the fluid-like X-ray emitting plasma are spatially segregated due to the collision of two galaxy clusters. We fit this lensing map in General Relativity (GR) and in MOND, so to infer the nature and amount of collisionless matter with less dependence on the validity of GR on galaxy cluster scales. We prove that 1E0657-56 is dominated by a collisionless component of DM - in GR as well as in MOND – but show that this DM could be made of ordinary neutrinos or cold gas clouds in the context of MOND.
11:40 Philippe SMET
Universiteit Gent
Cathodoluminescence mapping with an energy-dispersive x-ray detector: principle, simulation and application
Abstract
The observation of cathodoluminescent (CL) emission in a scanning electron microscope (SEM) offers a wealth of information as it allows to study the luminescence of materials on a nanoscale. In combination with elemental analysis (e.g. EDX), even more information can be extracted. Here we report on the use of the silicon detector, normally used for the energy-dispersive analysis of the characteristic x-rays, for the detection of (CL) light. Based on the working principle of an EDX detector we explain why this detector is sensitive to visible radiation. The response of the detector to the intensity of the CL light is highly non-linear. By using a purposely written software program, the detector behaviour was correctly simulated. We show that the signal in the low energy part of the EDX spectrum can readily be used to obtain CL mappings along with simultaneously recorded elemental mappings. This is illustrated on both powders and thin films. The main advantage of this method is that no additional software or hardware is required to obtain the mappings. Results are compared with CL mappings obtained by measuring the light output with a CCD-based spectrometer.
12:00 Evi VINCK
Universiteit Antwerpen
Probing the electronic structure of transition-metal-ion complexes using EPR techniques
Abstract
Electron paramagnetic resonance (EPR) techniques form the ideal tool to analyze paramagnetic molecules. The potential of EPR techniques has increased enormously in the past years, due to the development of pulsed-EPR techniques, and due to recent advances in quantum-chemical computations. Therefore, many aspects of the technique remain largely unexplored. Especially the use of the HYSCORE (Hyperfine Sublevel Correlation) technique, combined with spectral simulations is relatively new. In this work, we have tested the performance of the latter technique to analyze different paramagnetic transition-metal-ion complexes. The EPR analyses were compared with density functional theory (DFT) computations, which enhances the interpretation of the spectra.
The techniques were applied to study the electronic structure of the cobalt Jacobsen catalyst, which is widely used in the pharmaceutical industry, for the hydrolytic kinetic resolution of terminal epoxides, an important step in the production of several medicines. Despite its widespread use, the active catalytic species is unknown. In this work, the structural changes that occur upon activation of the catalyst were mapped in detail, using EPR techniques. These analyses revealed the different molecules that are formed upon activation and allowed to probe their electronic structure. The analyses show the formation of a cobalt-bound phenoxyl radical, situated on the Jacobsen ligand. It is the first time that such a species is observed. In the second part of this work, it is shown how pulsed-EPR techniques can be applied to obtain information on both the electronic and geometrical structure of newly discovered globins, which are iron-containing proteins.
12:20 Lunch
AFTERNOON SESSIONS – PLENARY TALK IN FORUM B
14:00 Plenary Lecture: Pr Nicolas Gisin (Université de Genêve)
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Quantum Teleportation and Nonlocality |
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Abstract: Quantum communication is the art of transferring quantum states from one place to another. The most fascinating example is Quantum Teleportation: an object dissolves here and reappears there without ever existing at any intermediate location. In the first half of this presentation we present the experimental challenges that had to be overcome in order to demonstrate teleportation from our lab to a Swisscom center downtown Geneva. In the second half we discuss some conceptual issues of quantum nonlocality. We consider it both from the point of view of the resources required to simulate it and as a resource enabling one to achieve tasks otherwise impossible. |
14:50 Coffee break
15:20 Parallel sessions (topics and conveners - see next page)
17:30 Poster session & Coffee
18:15 Proclamation – Drink
PARALLEL SESSIONS
15:20-17:30
1. Physics and education (Room H)
Invited speaker: Raffaella TONCELLI
Université Libre de Bruxelles,Brussels, Belgium
A different approach to the General Relativity
Abstract
The classical approach to the General Relativity (GR) consists in presenting this theory as extension of Special Relativity (SR) theory, and as a research of generally covariant field equations. This is one of possible approaches, but it is not the only one and the research of generally covariant field equations is not the only criterion chosen by Einstein. During the formulation of GR (eight years, from 1907 to 1915) three principles actually guide Einstein, i.e. the equivalence principle, the general covariance principle and the Mach’s principle. The recent publication of the Einstein's "Zurich Notebook" [1], that turned out to contain Einstein's private calculations for the crucial period of the making of his greatest discovery, enable a reconstruction of Einstein's path and suggest a different approach to the GR.
In this talk I want to disentangle these three principles which, as Einstein said [2], correspond to three different points of view. The first step of my talk will be the analysis of the Equivalence Principle and of its formulation given by Einstein in 1907. We will see that this formulation is frequently misunderstood. The second step will be the discussion of the “hole argument”, which is a key point in Einstein’s research of GR, for it lead Einstein far of the right path during two years (1913-1915). Finally, we will see how Einstein realized that there was a mistaken assumption about the nature of spacetime and how he came back to general covariance and, as we will see, to Mach’s Principle.
Conveners: Jacky Hellemans (KUL), Pasquale Nardone (ULB)
2. Biophysics (Forum E)
Invited speaker: Michael MERTIG
Max Bergmann Center of Biomaterials and Institute of Materials Science, Dresden University of Technology, Germany
Biomimetic materials synthesis: From DNA arrays to metallic super lattices
Abstract
Modern principles for the controlled bottom-up assembly of advanced nanostructures by making use of the unique molecular recognition and self-assembly capabilities of biomolecules will be discussed. Fundamental issues of biomolecular templating will be addressed to demonstrate the advantage of using biomolecules in an engineering context for future technological applications, including (i) site-specific integration of DNA duplexes into microelectronic systems, (ii) manipulation of DNA by molecular motors, (iii) assembly of artificially designed biomolecular structures with the aim to tailor the complexity of desired biomolecular templates, and (iv) growth of metallic clusters at biomolecular structures promoted and controlled by the template itself with the goal to transform the template into a stable, artificial nanostructure. We will discuss the multifunctional use of selective properties intrinsic to biomolecules and important for a controlled bottom-up processing for two particular examples: engineering of nano-scaled electronic circuits when DNA is used as the biomolecular template, and growth of metallic super lattices on bacterial surface layer proteins.
Conveners: Marianne Rooman (ULB), Patrick Wagner (UHasselt)
3. Statistical Physics & fluid dynamics (Room G)
Invited speaker: Joachim SAUER
Institute of Geophysics and Meteorology, Koln U., Germany
Satellite Plasma Interaction and the Search for Liquid Water in Our Solar System
Abstract
Magnetic field measurements near Jupiter's satellite Europa provide strong evidence for a currently liquid ocean under its icy surface. Europa also possesses a thin oxygen atmosphere and orbits in the magnetosphere of Jupiter. Both, the interaction of Jupiter's magnetosphere with Europa's atmosphere, as well as electromagnetic induction in an electrolytically conducting ocean due to the time-varying component of Jupiter's magnetospheric field create measurable magnetic field perturbations. Here we will present models to describe these interactions in order to constrain properties of the potential ocean and its atmosphere. We will also discuss similar interactions at other satellites of Jupiter and Saturn.
Conveners: Bernard Knaepen (ULB), Stefaan Poedts (KUL)
4. Astrophysics (Forum B)
Invited speaker: Tom THEUNS
Institute for Computational Cosmology, Durham U.,UK
The first stars and the nature of dark matter
Abstract
The first stars in the Universe form when gas cools in small dark matter potential wells. In Cold Dark Matter, these potential wells are small spherical haloes, and each halo forms a single, very massive star. However the observed abundance pattern of extremely low metallicity stars does not exhibit the signature of such very massive stars. In contrast, when the dark matter is warm, stars form in a gigantic burst in a large filament, and both low and high mass stars form. The massive stars may have contaminated the low-mass stars with metals, and these could be the low-metallicity stars detected in the Milky Way. The eventual collapse of the filament may produce the seed for a supermassive black hole. I will also briefly review current constraints on the nature of the dark matter from Large Scale Structure observations.
Conveners: Jean Surdej (Ulg), Sophie Van Eck (ULB)
5. Fundamental Interactions (Room F)
Invited speaker: Michel HERQUET
CP3, UCL, Belgium
The hunt is on: strategies, challenges and prospects for Brout-Englert-Higgs (BEH) boson(s) searches at the dawn of the LHC era
Abstract
The Large Hadron Collider (LHC) is now entering its final phase of commissioning. One of its most important goal will be to assess (or disprove) the existence of the elusive scalar boson(s) predicted by the BEH mechanism for the electroweak symmetry breaking. In this talk, I will first briefly review the main strategies and expected difficulties associated with the Standard Model BEH boson searches, from both phenomenological and experimental points of view. I will then provide examples of scenarios going beyond the "minimal" SM hypothesis (i.e. a single complex weak doublet) which can be justified by theoretical and/or phenomenological arguments. In particular, I will focus on the possibility for exotic signatures involving scalars which may help to disentangle between these scenarios, and on the theoretical and experimental challenges associated with their observation. Taking up these challenges will certainly imply a fair amount of collaborative work, involving theorists, Monte-Carlo experts and experimentalists, and I will end by discussing this generic aspect of New Physics discoveries at the LHC."
Conveners: Catherine de Clercq (VUB), Michel Tytgat (ULB)
6. Atomic &Molecular physics, Optics (Forum C)
Invited
speaker: Andreas BUCHLEITNER
Institute
of Physics, Quantum Optics and Statistics, Albert Ludwigs University
of Freiburg, Germany
Order from disorder: quantum chaos and its potential for robust quantum control
Abstract
Controlling the time evolution of ever more complex quantum systems is of fundamental as well as of practical interest: understanding the dynamics of complex quantum systems has the potential to improve our intuition for "complexity", and quantum systems with high spectral densities (Rydberg systems, complex molecules, (ultra-)cold atoms, quantum registers) move into focus in atomic physics and quantum optics labs, where they can be studied with hitherto unknown precision, and finally open novel perspectives for technological applications. The traditional approach of quantum state engineering, which essentially relies on "tailoring" a Hamiltonian such as to execute a predefined task, tends to be fragile against perturbations, which abound as the system size increases. The theory of deterministic quantum systems with complex dynamics - quantum chaos - provides an alternative, topological perspective on the control issue, and offers, e.g., nondispersive wave packets as a very generic phenomenon to achieve robust quantum control. The lecture will elaborate on the essential pillars of this point of view, and discuss examples of this universal phenomenon in various physical settings.
Conveners: Michel Godefroid (ULB), Xavier Urbain (UCL)
7. Nuclear & Hadron Physics (Forum A)
Invited speaker: Pierre CAPEL
Service de Physique Nucléaire Théorique et Physique Mathématique, Université Libre de Bruxelles, Belgium
Extracting the rate of radiative-capture 7Be(p,gamma)8B in the sun from Coulomb-breakup measurements
Abstract
The 7Be(p,γ)8B radiative capture is one of the key reactions in the study of solar-neutrino. Unfortunately, this reaction is difficult to measure directly at stellar energies. To circumvent this difficulty, it has been proposed to infer the radiative-capture rate from the measurement of Coulomb breakup of 8B. In this indirect method, the time reversed reaction is simulated by virtual photons in the Coulomb field of a heavy target. Unfortunately, this can be done only if one assumes that the breakup is purely Coulomb, due to E1 virtual photons, and occurs in a single step. Using the recently developed Dynamical Eikonal Approximation, we study various measurements of the Coulomb breakup of 8B with the aim of checking these assumptions.
Conveners: Jean-Marc Sparenberg, Pierre Descouvemont (ULB), Jan Ryckebusch (UGent)
8. Condensed matter & nanophysics (Forum D)
Invited speaker: Lieven VANDERSYPEN
Technische Universiteit Delft, The Netherlands
Coherence and control of a single electron spin in a quantum dot
Abstract:
As part of our work on quantum computation with electron spins in quantum dots, we demonstrate coherent control of a single spin. First, we manipulate the spin using conventional magnetic resonance (detection is done using a second spin in a neighbouring dot). Next, we show that we can also rotate the spin using electric fields instead of magnetic fields. In both cases, 90 rotations can be realized in about 50 ns or less. We use these control techniques to probe decoherence of an isolated electron spin. The spin dephases in about 30 ns, due to the hyperfine interaction with the uncontrolled nuclear spin bath in the host material of the dot. However, since the nuclear spin dynamics is very slow, this dephasing can be largely reversed using a spin-echo pulse. Echo decay times of about 0.5 us are obtained at 70 mT. In parallel, we have started work on quantum dots in graphene, which is expected to offer superior coherence times. As a first step, we have succeeded in opening a bandgap in bilayer graphene, necessary for electrostatic confinement of carriers.
Conveners: François Peeters (UA), Michele Sferrazza (ULB)