Department of Physics John Anderson Research Colloquia

Wednesday's at 3.00pm (unless otherwise stated) 

Colloquia will usually be held in JA3.14
John Anderson Building 
107 Rottenrow, Glasgow

Coffee and Tea served at 4.00 pm.

All Welcome

Coordinated with the Colloquia at the Department of Physics and Astronomy of the University of Glasgow. (They may have donuts but we have free chocolate covered biscuits and coffee!)

Colloquia Schedule 2018-2019

Semester I

Semester II

  • 16/1/19 - Mark Hughes Joule Physics Laboratory, University of Salford
  • 30/1/19 - Maria Dienerowitz, Jena
  • 27/2/19 - Anna Minguzzi , Grenoble
  • 13/3/19 - Henning Reichert, Paul Drude Institute
  • 27/3/19 - TBC

* Note: Outside of regular schedule.

Physics of Ultrashort Long-Wave Infrared TeraWatt Pulse Atmospheric Propagation and Interactions

Jerome V Moloney (College of Optical Sciences, University of Arizona) 27 August 2018, JA3.14, 11am

We predict that new physics paradigms emerge when long wave high power, high energy ultrashort pulses are propagated in the atmosphere. Specifically, optical carrier shock waves and many-body excitation induced dephasing emerge as key players at progressively longer wavelengths. Mathematically, the canonical description of propagation is described by a full field resolved modified Kadomtsev – Petviashili (mKP) equation. The latter encompasses two important singularities, namely blow-up or critical self-focusing and optical carrier self-steepening – the former is also described by nonlinear envelope equations. While ionization induced defocusing and losses tend to dominate at near-IR wavelengths, dispersive waves generated by shocks tend to limit the growth in filament intensity at longer wavelengths in the mid-IR.

From the Sun to controlled fusion: plasma diagnostics and spectroscopic techniques

Alessandra Giunta (STFC RAL Space) 3 October 2018, JA3.14, 3pm

The emission of photons and all spectral lines have encoded information to diagnose the physical and chemical status of the emitting source, carrying the signature of the underlying plasma parameters.

This approach is appropriate not only in an astrophysical context, but also for laboratory fusion plasmas. Atomic physics provides the link that enables the observed spectra to be interpreted in terms of the properties of the source from which they arise, whether they originate in an experiment on Earth, such as a laser or tokamak device, or in an astronomical object, ranging from the Sun and stars to planetary nebulae and interstellar medium.

The increasing capabilities of the current and new space-borne instrumentation (e.g. Interface Region Imaging Spectrometer, Solar Orbiter, Parker Solar Probe) and controlled fusion devices (e.g. Mega Ampère Spherical Tokamak Super-X upgrade divertor, International Thermonuclear Experimental Reactor, DEMOnstration Power Station), require atomic modelling and the derived spectroscopic techniques to be regularly revised and upgraded.

The present work will strongly exploit this interdisciplinary link between laboratory and astrophysics plasma environments. Atomic data requirements and their accuracy will be discussed, concentrating on the applications to the analysis of the solar upper atmosphere emission and the investigation of controlled fusion plasmas in a tokamak divertor. An example of the exploitation of a common methodology for the detection and assessment of non-equilibrium processes will be described. This will show that the derived atomic data allow equivalent prediction in non-stationary transport regimes and dynamic conditions of both the solar atmosphere and tokamak 

Atoms and Lasers for Space-Time Referencing

Leo Hollberg (Department. of Physics, Stanford University) 10 October 2018 JA5.05, 3pm

With precision laser spectroscopy, laser-cooling and –trapping of atoms, and femtosecond optical frequency combs we now have the necessary science and technology to measure Time and Space with unprecedented precision. To date, as a result of various constraints and bottlenecks, the capabilities of the high-performance systems have not yet found their way into real-world applications.  With the recent introduction of commercial instruments based on laser-cooled atoms perhaps that landscape is beginning to change. One limitation of the highest performance clocks is in transferring “Time” and even frequency from one location to another. Cold atom clocks and sensors in space could enable future scientific missions (such as tests of General Relativity, and searches for physics beyond the Standard Model and Dark Matter). These capabilities could also enhance the performance of existing global navigation systems as well as precision measurements in earth sciences such as geodesy and sea level determinations.

In contrast, Atomic Molecular Optical (AMO) science is making a significant impact at relatively low performance levels with Chip Scale Atomic Devices. Taking advantage of semiconductor MEMS and microfabrication technologies it is feasible to make laser-based atomic/molecular instruments that are small and robust while delivering surprisingly good performance.

Chaos and Complexity

Celso Grebogi (Institute for Complex Systems and Mathematical Biology, King’s College, University of Aberdeen) 17 October 2018, JA3.14, 3pm

Many simple nonlinear deterministic systems can behave in an apparently unpredictable and chaotic manner. This realisation has broad implications for many fields of science. Some basic concepts and properties in the field of chaotic dynamics of dissipative systems will be reviewed in this talk, including strange nonchaotic attractors, chaos-induced intermittency, and fractal basin boundaries. I will use some of these properties in application topics, including the control of chaos in the brain. I will then go a step further by arguing that a complex system is made up of many states that are interrelated in a complicated manner. The ability of a complex system to access those different states, combined with its sensitivity, offers great flexibility in manipulating the system’s dynamics to select a desired behaviour. Another important issue is the question of mathematical modelling of chaotic and complex systems. Mathematical modellers of such systems need to understand and take seriously the question of their own limitations.

  • Chaos, strange attractors, and fractal basin boundaries in nonlinear dynamics, C. Grebogi, E. Ott, and J. A. Yorke, Science 238, 632 (1987)
  • Strange attractors that are nonchaotic, C. Grebogi, E. Ott, S. Pelikan, and J. A. Yorke, Physica D 13, 261 (1984)
  • Controlling complexity, L. Poon and C. Grebogi, Phys. Rev. Lett. 75, 4023 (1995)
  • Controlling Chaotic Dynamical Systems, C. Grebogi and Y. C. Lai, Systems Control Lett. 31, 307 (1997)
  • Modelling of deterministic chaotic systems, Y.-C. Lai and C. Grebogi, Phys. Rev. Lett. 82, 4803 (1999)
  • Data Based Identification and Prediction of Nonlinear and Complex Dynamical Systems, W.-X. Wang, Y.-C. Lai, and C. Grebogi, Phys. Reports. 644, 1-76 (2016)
  • Relativistic quantum chaos – An emergent interdisciplinary field, Y.-C. Lai, H.-Y Xu, L. Huang, and C. Grebogi, AIP CHAOS 28, 052101 (2018)

Seeing and believing at super-resolution

Susan Cox (Fellow in the Randall Division of Cell & Molecular Biophysics, King's College London) 31st October 2018, 3pm in JA3.14 

Conventional localisation microscopy relies on sparse activation of flurophores to allow accurate data fitting, meaning acquisition is slow and live cell experiments difficult or impossible. Several algorithms have been developed to cope with high emitter density. However, these produce significant image artefacts as the density is increased, which are easily mistaken for high resolution. By examining known biological structures it is shown that artefacts can be largely eliminated by pre-processing the image sequence with a succession of Haar wavelet kernels (HAWK), improving the resolving power and ensuring that the image reflects the structure of the sample. The ability to produce images without sharpening artefacts has important implications for super-resolution image assessment and evaluation.

Electron Diffraction in the Scanning Electron Microscope: An Atom's Perspective

Aimo Winkelmann (Laser Zentrum Hannover, Germany) 7th November 2018 3pm, in JA3.14

The Scanning Electron Microscope (SEM) is a powerful tool to investigate a wide variety of samples on length scales ranging from centimeters down to the nanometer region. The polycrystalline microstructure of many technological, geological, and even biological materials calls for suitable microcrystallographic analysis methods in the SEM. Application examples include steels, metal alloys and semiconductors, but also meteorites, chiral quartz crystals, and egg-shells of dinosaurs and birds.

In this talk, the two main sources of crystallographic information in the SEM will be discussed:

Diffraction effects of electrons in the primary SEM beam lead to the formation of the "electron channelling patterns" (ECP), while diffraction of inelastically backscattered electrons is used in the method of "electron backscatter diffraction" (EBSD).

In both methods, very characteristic diffraction patterns play a central role, the so-called "Kikuchi patterns". By adopting the perspective of an atom in a crystal, the beautiful geometry and the instructive physics of Kikuchi pattern formation will be explained.

The Measure of All Things

JT Janssen (National Physical Laboratory) 14th November 2018, 3pm in JA3.14

Measurement is at the heart of all science and engineering. Progress in science and engineering is often linked to progress in metrology- the science of measurement. In this talk I will explain how the International System of Units works and why, from May 2019 scientists are planning subtle but profound changes in the definitions of four of the SI base units- the kilogram, ampere kelvin and mole. I will discuss some of the experiments which underpinned these changes and highlight their impact.

Squeezing Forty Orders of Magnitude in Four Squared Meters

Maria Luisa Chiofalo (Department of Physics "Enrico Fermi", University of Pisa and INFN, Italy) Wednesday 28th November 2018, 3pm JA3.14

Physics is in an era of unprecedented cross-fertilization: the length and energy scales characterizing the physics of quantum atomic gases cooled down to tens of nK, have fostered connections of ideas born in condensed matter with crucial concepts in fundamental interactions and cosmology. Spontaneous symmetry breaking is a striking example of the former case, and superfluid analogues of gravity of the second. More than forty orders of magnitude in length from quarks to the estimatedsize of the universe, passing through condensed matter systems, can in principle be investigated in table-top experimental settled in a few squared meters.

In fact, quantum gases represent a formidable analogue quantum simulation platform, which can be used in different setups like atoms in optical lattices, superfluids, trapped ions, dipolar or Rydberg atoms or molecules. All these systems share extreme quantum degeneracy by tuning temperature, interactions strength and range, dimensionality, and disorder. They can be investigated under highly controllable experimental conditions and theoretical modelling, bridging between atomic and condensed matter physics, quantum optics and quantum information science. In fact, the whole concept represents an exciting implementation of the seminal Feynman idea of a quantum simulator: in essence, coding in a controllable (quantum) system the analogue (quantum) simulation of the (quantum) system under study.

In the colloquium, I will discuss this general idea via examples selected from different contexts. In particular, I will show how quantum gases may ease the understanding of quantum transport, one-dimensional quantum liquids or high-temperature superconductivity in the realm of condensed matter, and allow to perform precision measurements with a modern version of Galileo's pendulum experiment in the context of fundamental physics. I will finally discuss contemporary perspectives in using quantum gases as quantum simulators of open problems in cosmology and fundamental interactions.

Optically modulated electron paramagnetic resonance of erbium implanted silicon.  

Mark Hughes  (Joule Physics Laboratory, School of Computing Science and Engineering, University of Salford)  16 January  2019, JA3.14, 3pm

There are currently no quantum technology (QT) platforms with telecommunications and integrated circuit (IC) processing compatibility, and long coherence times. Er transitions can be optically addressed at telecoms wavelengths, which allows transfer of quantum information over distance. Er and O co-implanted Si (Er:Si) is compatible with both telecoms and IC processing and produces electron paramagnetic resonance (EPR) lines and 1.5 μm photoluminescence (PL) lines. It is believed that several different Er centers are involved in both PL and EPR. However, the exact nature and the relationship between the PL and EPR centers is not currently known. We swept a tuneable 1.5 μm laser to modulate the EPR signal from Er:Si and generate optical modulated EPR (OMEPR) spectra at various magnetic fields, see Fig. 1. We fitted crystal field parameters (CFPs) to PL lines associated with a cubic Si coordinated Er centre and a monoclinic O coordinated Er centre. These CFPs were then used to calculate the expected splitting of the first excited state in the cubic and monoclinic centre, which had a good agreement with the observed OMEPR spectra at ~ 800 G and 900 G, respectively.


Figure 1 Contour plot showing OMEPR spectra of Er:Si at various magnetic fields

Confining Brownian motion of molecules and nano particles

Maria Dienerowitz (University of Jena) 30 January 2019, 3pm JA3.14 

Observing the Brownian motion of individual nanoscopic objects in solution is key to investigate the interaction with their close environment. Confining Brownian motion within the microscopic detection volume increases the length of the observation time, enabling us to study dynamic behaviour of single molecules for seconds. Most techniques rely on surface attachment, transient diffusion through a confocal laser focus or application of external forces. 

This talk concentrates on optical and electrokinetic trapping. We present an *A*nti-*B*rownian *EL*ectrokinetic trap (ABELtrap) to trap nanoparticles, DNA origami and individual proteoliposomes labeled with a single fluorophore. The ABELtrap is an active feedback system using electric fields that act on the surface charge of the particle to trap. We show how the induced electrokinetic force confines the motion of nanoparticles and molecules to the centre of the trap. We are particularly interested in the conformational dynamics of individual F_o F_1 -ATP synthase proteins. Monitoring sequential distance changes between two specifically attached dyes using single-molecule FRET allows us to observe this membrane-bound rotary protein in real time.