Colloquiums and Public Lectures

2021

Title:	Diamond Nanophotonics and Electronics for Bright Single-Photon Emission
Speaker:	Professor Mario Agio
Date:	1 April 2021
Time:	5.00pm
Venue:	Zoom (ID and PW will be given upon registration)
Host:	Associate Professor Cesare Soci
Abstract:	Solid-state single-photon sources play an important role in the implementation of photonics quantum technologies. Color centers in diamond have gained much attention in this context for their unique optical properties. However, a substantial basic research effort in materials science, nanophotonics and electronics is still required. In my talk I will introduce single-photon emission and its applications. Next, I will discuss color centers in diamond and present nano-optical concepts to largely improve their optical properties. I will also present results pertaining to diamond implantation and characterization as well as on the design of antenna configurations that can significantly improve the out-coupling efficiency. Finally, I will discuss some ideas on the possibility of electrical pumping and the expected performances.

Title:	From Dust Grains to Planets: Building New Worlds in Protoplanetary Disks around Nearby Stars
Speaker:	Dr Hui LI
Date:	5 March 2021
Time:	10.00am
Venue:	Zoom (ID and PW will be given upon registration)
Host:	Associate Professor Elbert Chia
Abstract:	The last two decades saw the detection of more than 4400 confirmed exoplanets (planets around other stars) in > 3000 systems. An amazing amount of diversity in their planetary mass, orbital radius and eccentricity has raised a number of important questions, including the formation processes of exoplanets. Using the planets in our solar system as a guide, some of the detected exoplanets are also gas-rich, similar to Jupiter, whereas the majority of exoplanets is super-Earth sized, which are made mostly of dust/rocks. To understand the hydrodynamic processes that caused the gas and dust grains to concentrate and form objects, we are getting some answers from the Atacama Large Millimeter/submillimeter Array (ALMA, https://almascience.nrao.edu/), the most sensitive ground-based telescope in detecting the dust and gas in protoplanetary disks (PPDs) around young stars. As nurseries of planet formation, the high-resolution images of PPDs reveal how planets which are still forming can disturb their environment, producing rings, gaps, and vortices. We present theoretical and numerical studies of these systems to reproduce such complexity in their formation and evolution processes. This in turn allows us to infer the properties of forming planets and their likely future. View Colloquium Recording

Archives (2005–2020)

Title:	Why the world is simple
Speaker:	Professor Ard A. Louis
Date:	23 September 2020
Time:	5.00pm
Venue:	Zoom (ID and PW will be given upon registration)
Host:	Division seminar committee
Abstract:	The coding theorem from algorithmic information theory (AIT) -- which should be much more widely taught in Physics! -- suggests that many processes in nature are highly biased towards simple outputs. Here simple means highly compressible, or more formally, outputs with relatively lower Kolmogorov complexity. Two applications will be explored in two related problems: 1) In biological evolution, the AIT coding theorem implies an exponential bias towards structures with higher symmetry even when they are not favored by natural selection. Evidence for this trend can be found in protein quaternary structure and RNA secondary structure. 2) For deep learning neural networks, the coding theorem predicts an Occam's razor bias that helps explain why these systems work so well in the highly over-parametrized regime where we would otherwise expect overfitting. View Colloquium Recording

Title:	Testing Gravity with Cold Atoms
Speaker:	Professor Guglielmo M. Tino
Date:	15 January 2020
Time:	4.00pm - 5.00pm
Venue:	SPMS-LT3 (SPMS-03-02)
Host:	Division seminar committee
Abstract:	The ability to control the quantum degrees of freedom of atoms using laser light opened the way to precision measurements of fundamental physical quantities. I will describe experiments for precision tests of gravitational physics using new quantum devices based on ultracold atoms, namely, atom interferometers and optical clocks. I will report on the measurement of the gravitational constant G with a Rb Raman interferometer, on experiments based on Bloch oscillations of Sr atoms confined in an optical lattice for gravity measurements at small spatial scales, and on new tests of the Einstein equivalence principle. I will also discuss prospects to use atoms as new detectors for gravitational waves and for experiments in space.

Title:	On systems with and without excess energy in environment ICD and other interatomic mechanisms
Speaker:	Professor Lorenz S. Cederbaum
Date:	24 September 2019
Time:	4.00pm - 5.00pm
Venue:	SPMS-LT4 (SPMS-03-09)
Host:	Division seminar committee
Abstract:	How does a microscopic system like an atom or a small molecule get rid of the excess electronic energy it has acquired, for instance, by absorbing a photon? If this microscopic system is isolated, the issue has been much investigated and the answer to this question is more or less well known. But what happens if our system has neighbors as is usually the case in nature or in the laboratory? In a human society, if our stress is large, we would like to pass it over to our neighbors. Indeed, this is in brief what happens also to the sufficiently excited microscopic system. A new mechanism of energy transfer has been theoretically predicted and verified in several exciting experiments. This mechanism seems to prevail “everywhere” from the extreme quantum system of the He dimer to water and even to quantum dots. The transfer is ultrafast and typically dominates other relaxation pathways. Can there be interatomic/intermolecular processes in environment when the system itself (again, an atom or small molecule) does not possess excess energy? The answer to this intriguing question is yes. The possible processes are introduced and discussed. Examples and arguments are presented which make clear that the processes in question play a substantial role in nature and laboratory. Work on the interatomic processes discussed can be found in the Bibliography: http://www.pci.uni-heidelberg.de/tc/usr/icd/ICD.refbase.html

Title:	Technological innovation in photonics: from the Institute of Photonics to Fraunhofer and from mLED to Oculus
Speaker:	Professor Martin D. Dawson
Date:	25 June 2019
Time:	11.00am - 12.00pm
Venue:	SPMS-LT3 (SPMS-03-02)
Host:	Division seminar committee
Abstract:	Photonics is a key enabling technology with a very broad range of applications across multiple research and market sectors. We justify much of our research funding and research outputs in photonics in terms of the field’s potential for innovation – when, for example, did you last read a research proposal or research paper which did not highlight the prospective applications of the work? Furthermore, it is often the prospects for commercialisation that most excite our students and post-docs. But what is innovation exactly? The presenter will use his 35 year research career to illustrate how technological innovation works in practice – from the laboratory bench to commercial exploitation. This talk will unpick the elements that combine in innovative developments using examples from his own work in semiconductor optoelectronics and lasers. This will include work on ultrafast dye lasers, semiconductor materials science, VECSELs and micro-LEDs.

Title:	Light Matter Interaction at TeraHertz frequencies: Nonlinear optics and functional control
Speaker:	Professor Andrea Cavalleri
Date:	17 April 2019
Time:	11.00am - 12.00pm
Venue:	SPMS-LT5 (SPMS-03-08)
Host:	PAP Seminar committee
Abstract:	I will discuss how coherent electromagnetic radiation at infrared and TeraHertz frequencies can be used to drive collective excitations in solids nonlinearly. The driven cooperative response can yield new types functional control. I will for example discuss experiments in which superconducting fluctuations can be amplified by light at temperatures higher than the thermodynamic transition temperature. I will also discuss the physics of superconducting plasmons in layered superconductors and how these reveal new nonlinear THz phenomena.

Title:	Cooperative and Ultrastrong Light-Matter Coupling: Dicke Phenomena in Condensed Matter
Speaker:	Professor Junichiro Kono
Date:	4 April 2018
Time:	3.00pm - 4.00pm
Venue:	MAS Executive Classroom 2 (SPMS-MAS-03-07)
Host:	PAP Seminar committee
Abstract:	Recent advances in optical studies of condensed matter systems have led to the emergence of a variety of phenomena that have conventionally been studied in the realm of quantum optics. These studies have not only deepened our understanding of light-matter interactions but also introduced aspects of many-body correlations inherent in optical processes in condensed matter systems. This talk will describe our recent studies of cooperative light-matter coupling, first studied by Dicke in 1954, in solids. In one type of experiment, electron-hole pairs were incoherently prepared, but a macroscopic polarization spontaneously emerged and cooperatively decayed, emitting a giant pulse of coherent light, i.e., a superfluorescent burst . In another type of experiment, we placed an ultrahigh-mobility 2D electron gas in a photonic-crystal cavity in a magnetic field and achieved ultrastrong light-matter coupling, which suppressed superradiance, leading to ultrahigh cooperativity and a vacuum Bloch-Siegert shift due to the breakdown of the rotating-wave approximation. Finally, we studied microcavity exciton polaritons in a film of aligned carbon nanotubes embedded in a Fabry-Perot cavity, exhibiting ultrastrong light-matter coupling with continuous controllability over the coupling strength through polarization rotation. These results show that cooperative effects in solidstate systems are not just small corrections that require exotic conditions to be observed; rather, they dominate the nonequilibrium dynamics and light emission processes of interacting electrons.

Title:	Taming active nematics
Speaker:	Professor Francesc Sagues
Date:	16 March 2018
Time:	11.00am - 12.00pm
Venue:	MAS Executive Classroom 2 (SPMS-03-07)
Host:	PAP Seminar committee
Abstract:	Motor-proteins are responsible for transport inside cells. Harnessing their activity is key towards developing new nanotechnologies or functional biomaterials. Cytoskeleton-like networks, recently tailored in vitro, result from the selfassembly of subcellular autonomous units. Taming this biological activity bottom-up may thus require molecular level alterations compromising protein integrity. We have taken a top-down perspective consisting on tuning the anisotropic viscosity of a contacting thermotropic liquid crystal oil. We show that the seemingly chaotic flows of a tubulin-kinesin aqueous active gel with nematic-like order [1] can be forced to adopt well-defined spatial directions that correlate with the structure of the responsive oil/water interface. Different configurations of the active material are realized, when the passive liquid crystal is either unforced [2] or commanded by a magnetic field [3]. The inherent instability of the extensile active fluid (active turbulence) is thus spatially regularized, leading to organized flow patterns, endowed with characteristic length and time scales whose role is redefined under the imposed geometrical confinements. Other control strategies, based in the preparation of active nematic droplets emulsified in liquid crystals, will be discussed. [1] T. Sanchez, D. T. Chen, S. J. De Camp, M. Heymann, Z. Dogic. Nature, 491, 431 (2012). [2] P. Guillamat, J. Ignés-Mullol, F. Sagués, Nat. Comm. 8, 564 (2017) [3] P. Guillamat, J. Ignés-Mullol, F. Sagués, PNAS 113, 5498-5502 (2016).

Title:	Quantum frequency combs: generation, characterization and applications to scalable quantum information processing
Speaker:	Professor Claude Fabre
Date:	1 February 2018
Time:	10.00am - 11.00am
Venue:	SPMS-LT2 (SPMS-03-03)
Host:	PAP Seminar committee
Abstract:	The development of Wavelength Division Multiplexing has been at the origin of a revolution in communication, that has even changed our everyday life. It is natural to investigate now whether this way of encoding and processing classical information can be extended to the domain of quantum information. We show that parametrically generated optical frequency combs, spanning over more than one million wavelength components, exhibit highly multipartite entanglement between the quantum fluctuations of its frequency modes. We introduce the tools that are needed to completely characterize such highly multimode quantum states of light and discuss the ways to utilize them in Measurement Based Quantum Computing. We finally show how to produce, by mode-selective photon subtraction, frequency comd quantum states exhibiting non-Gaussian statistics that are needed to provide a quantum advantage in Quantum Computing tasks.

Title:	Topological Quantum Matter and Entanglement
Speaker:	Professor F. Duncan Haldane
Date:	26 January 2018
Time:	4.00pm - 5.00pm
Venue:	SPMS-LT1 (SPMS-04-07)
Host:	PAP Seminar committee
Abstract:	Long-range "entanglement" was initially pointed out by Einstein as a strange property predicted by quantum mechanics that he felt was so contrary to common-sense that experiments to test it would surely undermine the quantum theory. But when experimental tests eventually became possible, quantum mechanics was vindicated. In recent years, it has been realized that, instead of merely being an abstract and obscure philosophical issue in the interpretation of the quantum theory, entanglement is in fact perhaps its central feature, and in particular, plays an important role in the new "topological (quantum) states of matter” which have unexpected properties that have given rise to much recent excitement in condensed matter physics. I will describe some examples of this and how ideas from quantum information theory and condensed matter physics have fruitfully joined together.

Title:	Unknowns of energy concentrating phenomena
Speaker:	Professor Seth Putterman
Date:	17 November 2016
Time:	4.00pm - 5.00pm
Venue:	MAS Executive Classroom 1 (SPMS-MAS-03-06)
Host:	Associate Professor Claus-Dieter Ohl
Abstract:	The path to equilibrium is not controlled by entropy production. Although entropy increases with every time step, dynamical motion can be dominated by nonlinear physical process which spontaneously concentrate energy density. In sonoluminescence a bubble concentrates the energy of a traveling sound wave by 12 orders of magnitude to create picoseconds flashes of blackbody radiation that originate in a new state of matter. When surfaces are brought into and out of contact they exchange charge: a process call triboelectrification. This phenomenon can be so strong that the power applied to peel sticky tape is efficiently transduced into a flux of high energy electrons, and x-ray photons that can expose an image in a few seconds. For a ferroelectric crystal, instabilities in the phonon spectrum lead to a spontaneous polarization that for Lithium Niobate reaches 15.million volts per cm. The temperature dependence of this field can be used to build a neutron generator based on the fusion of deuterium nuclei. These phenomena challenge a reductionist approach to the theoretical physics of emergent phenomena. The degree to which the energy density of a continuous system can be concentrated by off-equilibrium motion has not been determined by theory. For sonoluminescence we do not know if the parameter space includes a region where an extra factor of 100 in energy density makes it possible to realize thermonuclear fusion. For triboelectrification we do not have an ab-initio theory of charge transfer. And for ferroelectrics we do not have an ab-initio theory of the limits of spontaneous polarization which can be designed.

Title:	The maggot in the apple: peaceful coexistence of incompatible theories
Speaker:	Professor Sir Michael Berry
Date:	12 April 2016
Time:	3.15pm - 4.15pm
Venue:	NTU, LT23, Block SS2 SS2-B2-05
Host:	The Photonics Institute
Abstract:	In physics, as in science generally, most phenomena can be understood in more than one way: the gas in an engine obeys the laws of thermodynamics and also those of the motion of its molecules. The different theories correspond to different levels of description. These must overlap, but understanding their consilience is far from straightforward because they are usually based on seemingly incompatible concepts. The discordance arises from the fact, unappreciated until recently, that the limit in which the more general theory reduces to the less general (usually older) theory is mathematically singular. One consequence is a range of phenomena, of intense current interest, inhabiting the borderlands between the theories. I will explore this theme with examples from the physics of fluids, light and the quantum world.

Title:	Enriching the Standard Model: What if the Higgs has many brothers?
Speaker:	Professor Chang Ngee Pong
Date:	22 August 2013
Time:	4.00pm
Venue:	Hilbert Space (SPMS-PAP-02-02)
Host:	The Institute of Advanced Studies and the School of Physical and Mathematical Sciences
Abstract:	With the discovery at CERN of the Higgs particle, there is great excitement in the world of high-energy physics because it ‘confirms’ the Standard Model. The origin of all constituent quark and lepton masses may be attributed to this one Higgs. But few people will admit that the Standard Model is pretty, because the Yukawa coupling matrices are the most complex one possible. In this talk, Prof Chang will explore the consequences with simplifying the fundamental Yukawa coupling, and let instead the complexity be associated with a rich family of Higgs bosons. Remarkably, it is even possible to make a prediction on the masses of some of this rich family.

Title:	Experimental Detection of the He-McKellar-Wilkens Phase
Speaker:	Professor Bruce McKellar
Date:	23 April 2013
Time:	4.00pm
Venue:	Hilbert Space (SPMS-PAP-02-02)
Host:	The Institute of Advanced Studies and the School of Physical and Mathematical Sciences
Abstract:	In the late 80s and early 90s, Xiao-Gang He and I calculated the electric dipole moments of the neutron, electron and other particles in many models of CP violation. With electric dipole moments on our mind, we realised that the dual of the Aharonov-Casher phase (acquired when a magnetic dipole moves around a line of charges) was the phase acquired when an electric dipole moves around a line of magnetic monopoles. We devised a consistent theoretical model and published the result in 1993. In 1994, Wilkens independently reached the same conclusion. This phase has become known as the He-McKellar-Wilikens (HMW) phase. In September 2012, S. Lepoutre, A. Gauguet, G. Trenec, M. Buchner, and J. Vigue published a Physics Review Letter with the title “He-McKellar-Wilkens Topological Phase in Atom Interferometry”, reporting an observation of the HMW phase of about 30 mrad. After reviewing the original He-McKellar proposal, I describe how it turned out to be possible to observe the HMW phase without having monopoles to hand. I go on to discuss the topological nature of phases and to suggest alternative experimental arrangements, developed in collaboration with Xiao-Gang He and Tony Klein.

Title:	Holography, Graviton, and High Energy Scattering at LHC
Speaker:	Professor Tan Chung-I
Date:	7 January 2013
Time:	3.00pm - 4.00pm
Venue:	Level 2, Hilbert Space, School of Physical and Mathematical Sciences
Host:	The Institute of Advanced Studies and the School of Physical and Mathematical Sciences
Abstract:	Exploration of Gauge-String Duality, also known as AdS/CFT Correspondence, or, more broadly, Holography, has exploded in recent years, from heavy ion collisions to condensed matter physics. Here we focus on high-energy hadron collision at LHC and beyond. In particular, the crucial role of “graviton” in an AdS-like space will be explained. Applications to Deep Inelastic Scattering at Small-x and the detection of diffractively produced Higgs particle will also be discussed.

Title:	What can we learn about non-standard model CP violation from Hadrons?
Speaker:	Professor Bruce Mckellar
Date:	20 February 2012
Time:	2.00pm
Venue:	Hilbert Space (PAP-02-01), School of Physical and Mathematical Sciences
Host:	The Institute of Advanced Studies and School of Physical and Mathematical Sciences
Abstract:

Title:	The Turbulent Cosmos: Dark Energy and Other Mysteries
Speaker:	Professor Kerson Huang
Date:	15 December 2010
Time:	10.30am
Venue:	SPMS-MAS Executive Classroom 1 (MAS-03-06)
Host:	Institute of Advanced Studies and School of Physical and Mathematical Sciences
Abstract:	This is a popular lecture on some outstanding mysteries of the universe, and a theory being developed at the Institute of Advanced Studies, NTU, that offers explanations. The phenomena include dark energy, which propels accelerated expansion of the universe; dark mass, an obscure constituent of galaxies; cosmic inflation, which underlies the uniformity of the universe, and the large voids in galactic distributions. The theory is base on a vacuum field, which is derived from quantum field theory. It supplies dark energy, and makes the universe a superfluid. In the early epoch, it was densely laced with vortices, generating quantum turbulence, and all the matter that later became galaxies.

Title:	Fundamental Constants in Physics and their Time Dependence
Speaker:	Professor Harald Fritzsch
Date:	8 December 2010
Time:	10.30am
Venue:	SPMS-MAS Executive Classroom 1 (MAS-03-06)
Host:	Institute of Advanced Studies and School of Physical and Mathematical Sciences
Abstract:	In the Standard Model of Particle Physics there are 32 fundamental constants. In the experiments these constants can be measured, but theoretically they are not understood. I will discuss these constants, which are mostly mass parameters. Astrophysical measurements indicate that the finestructure constant depends on time. Grand unification implies a time variation of the QCD scale. Thus the masses of the atomic nuclei and the magnetic moments of the nuclei will depend on time. I proposed an experiment, which is currently done by Prof. Haensch in Munich and his group. The first results indicate a time dependence of the QCD scale. I will discuss the theoretical implications.

Title:	Global Warming & Energy Policy For the 21st Century
Speaker:	Professor Douglas Osheroff
Date:	20 September 2005
Time:	2.30pm - 3.45pm
Venue:	LT19A North Spine Level 1
Host:	Institute of Advanced Studies and the School of Physical and Mathematical Sciences
Abstract:	Based on the analysis of trapped gas in ice cores from Greenland and Antarctica, it is clear that the CO2 levels in our atmosphere now exceed the levels seen in the previous 400,000 years. The level has risen sharply over the past 100 years, and correlates strongly with the burning of fossil fuels and destruction of our forests. At the same time, average ocean temperatures have risen about 1 degree Celsius, and there is growing evidence that this is having a profound impact on our environment, including the melting of much of the Antarctic ice shelf, ground water percolation through the Greenland ice cap, the melting of glaciers around the world at an accelerating rate, and the wide destruction of coral colonies. In the next 50 years, largely due to development in India and China, we expect that the CO2 level in our atmosphere will again double, unless a concerted effort world wide is undertaken to limit our production of CO2 through conservation and a shift to alternate energy sources. While it is not easy to predict through the highly non-linear models the consequences of such high levels of CO2, it is clear that the time required to remove the gas from our atmosphere is long, and that whatever changes occur, they will not be easily reversed. Probable changes include a rise in ocean levels as a result of the melting of fossil ice, shifts in climate, and stress and possible extinction of native species unable to adapt to the rapid changes. It is essential that we begin to confront this technological and economic challenge now