John Anderson Research Colloquia
Wednesday's at 3.00pm (unless otherwise stated)
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!)
Dr Andrew Daley (Pittsburgh)
Exploring non-equilibrium many-body dynamics with cold atoms
Over the last ten years, experiments with ultracold atoms have begun to explore many-body physics in regimes where the particles are strongly interacting. These systems can be constructed from the "ground up", with atoms trapped in highly controllable light fields, where we have exceptional understanding and control over the microscopic physics. This provides unique opportunities to study many-body quantum dynamics, e.g., allowing us to construct and explore model hamiltonians that were previously the domain of solid state theorists. The experiments also offer a range of new detection techniques, ranging from measurements of momentum and quasi-momentum distributions to in-situ imaging of atoms in individual sites of an optical lattice.
In addition to the study of equilibrium physics and quantum phases of matter, these experiments open possibilities to address fundamental questions in non-equilibrium dynamics. These range from the mechanisms behind thermalization in closed quantum systems to the behaviour of entanglement in many-body systems. I will give an introduction to these systems, discussing current experimental and theoretical possibilities. I will illustrate this with examples from our recent theoretical work, including studies of decoherence and thermalization in many-body systems, as well as proposals for the measurement of many-body quantum entanglement.
Prof David A. B. Miller (Carnegie Centenary Visiting Professor at Strathclyde, Stanford)
How to design any linear optical component and how to avoid it
Though we can readily understand any particular linear optical device, we have not in general known how to design one to do just what we want. At worst, we have to resort to blind, trial-and-error iterative processes, with no guarantee that the device is even possible. For example, current challenging practical devices include efficient arbitrary spatial mode splitters and converters for communications through free-space or in multimode fibers, especially avoiding any fundamental power splitting loss. Here we show a new constructive, progressive, non-iterative method to design any arbitrary linear optical device or, indeed, any linear operation on waves, including microwaves, acoustics and quantum mechanical superpositions. We propose practical approaches for spatial optical devices that could be implemented, for example, in silicon photonics. The existence of this design approach also proves, in the spirit of a universal machine, that any linear wave device is possible in principle. Surprisingly, we show that all these designs can be completed without performing any calculations at all.
Prof B.S. Sathyaprakash (Cardiff)
Gravitational Astronomy: A New Window for Observing the Universe
Exploding stars, merging black holes, colliding galaxies and the early Universe are all intense sources of gravitational waves. There is worldwide effort to detect gravitational radiation using a variety of different techniques. The coming years will see the dawn of gravitational astronomy that will be critical to answering some of the most puzzling questions in astrophysics, cosmology and fundamental physics. In this talk I will describe what gravitational waves are, how we might detect them and how they will help understand internal structure of neutron stars, measure the geometry of black hole spacetimes and reveal what triggered the formation of galaxies and large scale structure in the Universe.
PK Das (IISc Bangalore)
Application of second harmonic light scattering from molecules and materials in solution
When light of sufficiently high intensity falls on randomly oriented non-centrosymmetric molecules in solution, incoherent second harmonic light from the centrosymmetric medium is scattered. This is possible because of the instantaneous orientational fluctuation of molecules in the timescale of interaction. The incoherently scattered second harmonic is weak but can be easily detected in an experiment. We have shown that by detecting second harmonic scattering from solution it is possible to measure dissociation constant of a weak organic acid, partition coefficient of an analyte distributed in a binary solvent mixture, supramolecular structure formation and its stoichiometry, critical micelle concentration of a surfactant, multiple binding constants of a small molecule to a large biological molecule, equilibrium geometry of a charge transfer complex, etc.
Metal nanoparticles dispersed in solution, show large second harmonic scattered light intensity. The origin of nonlinearity in small size nanoparticles is ascribed to surface polarization properties. However, we have shown that the surface polarization mechanism becomes less important when bulk polarization contribution grows in large size metal nanoparticles. For gold and copper nanoparticles ,“the small particle limit” starts at a diameter to wavelength ratio (d/l) of 1/15. For silver this ratio is larger. The advantages of applying this nonlinear optical technique to a variety of problems described above will be discussed.
G.W. Collins, Lawrence Livermore National Laboratory
Matter at extreme energy density: exotic solids to inertial fusion
A breakthrough in exploring matter at high compression, to 1000-fold initial density, is underway thanks to experimental developments associated with achieving inertially confined fusion in the laboratory. High-energy lasers can now manipulate the energy density of matter to atomic pressures, i.e. the pressure required to significantly distort core electron orbitals. Improvements in controlling dynamic compression paths enable the exploration of solids and fluids to >10 of TPa (> 100 million atmospheres pressure), and the incipient stages of inertial fusion. I will describe recent experimental results revealing quite exotic behavior of matter at extreme compression and our effort to understand and control material microphysics and gradients on the way to inertial fusion.
* This work was performed under the auspices of the U.S. Dept. of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Dr Daniele Faccio (Heriot-Watt)
Light in moving media
Light propagates following laws that depend on the "optical length'' of the medium. Hence, by changing the refractive index spatial profile, one may create an effectively distorted space in which light propagates. This is the basic idea behind so-called transformation optics. On the other hand, if one changes the refractive index in time, then an effective distorted time or, more generically, spacetime is created. I will overview a very simple and accessible mechanism by which effective spacetimes of different kinds may be created using nonlinear optics. This technique allows to create strongly distorted media that may simulate and test a range of fundamental predictions that are still lacking an experimental demonstration. Examples are Hawking radiation from event horizons, dynamical Casimir emission from oscillating media and amplification from rotating media. I will overview the basic theory and ideas behind these examples and describe ongoing experiments together with some preliminary experimental results.
Prof Andrew Huxley (Edinburgh)
Superconductivity on the dark side of magnetism
The talk will look at how superconductivity and other states can be brought about in itinerant ferromagnets when quantum fluctuations are amplified close to quantum critical points. Although the observed superconductivity can survive in spectacularly high magnetic fields, it is restricted to low temperatures. However, the richer structure of the superconducting order parameter compared with conventional superconductivity opens up new possibilities. This includes the potential for hosting topologically protected states that may be entangled to make quantum computations.
Prof Thorsten Ackemann (Strathclyde)
Nonlinear Photonics in semiconductors and cold atoms
The talk will review some experiments on fundamental and applicative aspects of the complex dynamics of nonlinear optical systems. Laser solitons, vortices, self-oscillations and spintronics in vertical-cavity surface-emitting lasers (VCSELs) will be discussed as well as the recent observation of the spontaneous emergence of two-dimensional density patterns in cold atoms due to optomechanical coupling.
Prof Christophe Salomon (ENS, Laboratoire Kastler Brossel)
From Ultracold Fermi Gases to Neutron Stars
Ultracold dilute atomic gases can be considered as model systems to address some pending problems in Many-Body physics that occur in condensed matter systems, nuclear physics, and astrophysics. We have developed a general method to probe with high precision the thermodynamics of locally homogeneous ultracold Bose and Fermi gases [1,2,3]. This method allows stringent tests of recent many-body theories. For attractive spin 1/2 fermions with tunable interaction, we will show that the gas thermodynamic properties can continuously change from those of weakly interacting Cooper pairs described by Bardeen-Cooper-Schrieffer theory to those of strongly bound molecules undergoing Bose-Einstein condensation. First, we focus on the finite-temperature Equation of State (EoS) of the unpolarized unitary gas above and below the superfluid transition. Detailed comparisons with theories including Monte-Carlo calculations initially revealed some surprises but excellent agreement is found with a recent bold diagrammatic Monte-Carlo technique. Surprisingly, the low-temperature properties of the strongly interacting normal phase are well described by Fermi liquid theory. The Lee-Huang-Yang corrections for low-density bosonic and fermionic superfluids are also directly measured for the first time. Despite orders of magnitude difference in density and temperature, our equation of state can be used to describe low density neutron matter such as the outer core of neutron stars.
[1] S. Nascimbène, N. Navon, K. Jiang, F. Chevy, and C. Salomon, Nature 463, 1057 (2010)
[2] N. Navon, S. Nascimbène, F. Chevy, and C. Salomon, Science 328, 729 (2010)
[3] N. Navon, S. Piatecki, K. Günter, B. Rem, T. C Nguyen, F. Chevy, W. Krauth, and C. Salomon, Phys. Rev. Lett., 107, 135301 (2011)
Prof Ian A. Walmsley (University of Oxford)
Entangbling – quantum correlations in diamond
The familiar world of everyday objects has at its heart a fitful, counter-intuitive microworld in which things may be in two places at once and may be tied more closely than identical twins. Yet, as Schrodinger noted in his famous cat gedanken experiment, this is not something that seems to translate into common experience in the “normal” world. Perhaps the most enigmatic quantum phenomena are correlations, such as entanglement, between separate entities that underpin phenomena running counter to our classical intuition of usual macroscopic objects. Such correlations also provide an important resource for quantum communication and quantum computing. I shall report experiments in which we demonstrate entanglement between the vibrations of two macroscopic, spatially-separated diamonds at room temperature by means of off-resonant Raman scattering of ultrashort optical pulses and quantum erasure. This shows that it possible to generate non-classical states of solids under ambient laboratory conditions, and thus suggests new possibilities for robust quantum machines.
Prof Mark Newton (University of Warwick)
Diamond: An engineering material for the 21st Century?
This talk will review the properties of diamond and investigate the potential for its exploitation. It has long been recognized that, aside from its extreme hardness, diamond is a remarkable material with many properties – optical, thermal, electrochemical, chemical, and electronic – that outclass competing materials. When combined, these properties offer the designer an engineering material with tremendous potential to create solutions that can shift performance to new levels or enable completely new approaches to challenging problems. Components routinely fabricated by Chemical Vapour Deposition (CVD) of diamond now span tweeters for loudspeakers, radiation detectors and sensors, optical components for lasers, windows for radio frequency and microwave transmission, a range of blades and cutting tools, and electrodes for electrochemical sensing, ozone generation and direct oxidation of organic matter. Developments in material synthesis and processing are leading to high purity and low defect grades of the material, such as an ultra-low birefringence single crystal CVD diamond. This material provides a step forward for all photonics applications of diamond.
A major task for 21st century technology is to complete the quantum revolution that began with transistors and integrated circuits in the 20th century. Foremost among the challenges are the implementation of devices that work in the quantum regime, i.e. one photon, one atom, or a few quantized modes of oscillation. Although some truly quantum devices have been demonstrated in laboratory settings, there are very few examples of practical commercial devices. The construction of platforms and architectures to harness the full power of quantum mechanics through coherent control for practical applications is a major technological challenge. Creating a practical solid-state quantum computer is seriously hard. Getting such a computer to operate at room temperature is even more challenging. It will be explained why colour centres in diamond are now amongst the most attractive building blocks for a quantum computer, but it will be shown that the diamond science and technologies being developed should impact long before a useful quantum computer is built in many different and diverse fields.
Acknowledgements
This research is supported by EPSRC, the European Commission, Advantage West Midlands, Birmingham Science City, De Beers and the Gemolocial Institute of America (GIA). Much of the experimental work reported is only possible because of highly skilled sample preparation, and we are indebted to Element Six Ltd., King's Ride Park, Ascot, Berkshire, SL5 8BP, United Kingdom and DTC Research Centre, Belmont Road, Maidenhead, Berkshire SL6 6JW, United Kingdom
Dr Jens Reichardt (German Meteorological Service (DWD))
Cloud studies with Raman LIDAR
Lidar (Light detection and ranging) instruments have evolved into powerful tools in many fields of research. Especially, in the atmospheric sciences lidars contribute significantly to our understanding of the role clouds play in the Earth's climate system. Similarly to the more commonly known radars, lidars emit intense radiation (here: light) pulses into the atmosphere, and analyze the return signal as a function of propagation time to yield height-resolved measurements of atmospheric constituents. From the large variety of lidars one type of lidar stands out in cloud research because of its versatility, the Raman lidar. As its name implies, it utilizes the Raman effect to obtain information on temperature, humidity, and cloud optical and microphysical parameters. In this colloquium, an introduction to the principles of lidar is given, and the capabilities of high-performance Raman lidars in cloud studies are discussed.
Prof Ernesto Estrada (University of Strathclyde)
Complex Networks. A Tour d' Horizon
The field of complex networks is gently introduced. The classical concepts of 'small-world' and 'scale-freeness' are briefly discussed. Then, the problem of communicability in complex networks is motivated and analyzed by considering the use of matrix functions. The concept of network communicability is then applied to a few real-world situations. It motivates a new Euclidean metric for networks, which allows embedding every network into a hypersphere of certain radius. Finally I discuss dynamical processes on networks. In particular I show how to extend these concepts to the consideration of long-range interactions among the agents in complex networks. The consequences of these extensions for real-world situations are briefly discussed.
Dr Sonja Franke-Arnold (University of Glasgow)
The world through a rotating window
For at least a century, researchers have been concerned with the question whether light may be dragged along by a medium (be it water, glass or ether). A spinning medium rotates the polarisation (by typically a microradian), but the same mechanism has been predicted to also rotate an image. By slowing light down to about the speed of sound we managed to observe a macroscopic rotation of light - and recently also of darkness.
Image rotation is also described as the "mechanical Faraday effect," whereas the true Faraday effect induces only polarisation but not image rotation - at least for light. For (TEM) electron beams however we predict a Faraday rotation affecting both polarisation and images.
And for those of you who think light and electrons are not matter enough I will also report on how to use Rubidium atoms in order to translate OAM from infrared to blue frequencies.
Dr Paul Soler (University of Glasgow)
Matter-antimatter asymmetry: the quest for CP violation in quarks and neutrinos
The matter-antimatter asymmetry of the universe, or why we live in a universe filled with matter and not antimatter, is one of the outstanding questions in physics. In 1967, the Soviet physicist Andrei Sakharov suggested three conditions to create a universe filled with matter (baryogenesis):
- Baryon number must be violated
- Charge (C) and charge-parity (CP) violation
- The early universe must have had a condition of non-thermal equilibrium
These conditions can arise in the Standard Model but the experimentally observed asymmetry of one part in 10^9 cannot be explained, so we expect new mechanisms in CP violation to account for the matter-antimatter problem. Experimental particle physics aims to address this question by testing CP violation of quarks in experiments at the so-called B-factories (the Belle and Babar experiments) and at CERN (the LHCb experiment). However, a more promising avenue seems to be to search for CP violation in neutrinos, which might offer an explanation to the matter-antimatter puzzle through a process called leptogenesis.
In this talk I will review our knowledge of CP violation and its impact on the matter-antimatter problem, I will describe some of the most important experimental results in CP violation, how the LHC at CERN is improving the picture with unparalleled precision and ideas for future experiments that will aim to discover CP violation in neutrinos, which may potentially solve the matter-antimatter puzzle. The talk is at an introductory level, so will not require any specialist knowledge.
