IPS Meeting 2018 - Institute of Physics Singapore

Asst. Prof. Huanqian Loh Centre for Quantum Technologies and Department of Physics, National University of Singapore	Plenary 1: Quantum Control of Ultracold Dipolar Molecules
	Wednesday, 7 March, 9:30am
	Polar molecules offer long-range anisotropic interactions, which are fundamental to a wide variety of phenomena, from ferrofluid behavior to the folding of proteins. Recent demonstrations of cooling and trapping polar molecules have made it possible to study these particles in the quantum regime, making them highly attractive for applications such as quantum information storage and exploring novel condensed matter phases. In this talk, I will discuss the creation and quantum control of dipolar fermionic NaK molecules in the ground rovibronic state and at ultracold temperatures as low as 300 nK. Using microwaves, we have coherently manipulated not only the rotational states of the molecules, but also the nuclear spin degree of freedom. I will present our observation of nuclear spin coherence times on the scale of 1 second, and discuss its implications for quantum memory and probing new physics via Hertz-level precision spectroscopy.

Asst. Prof. Shengyuan Yang Engineering Product Development, Singapore University of Technology and Design	Plenary 2: 2D and 3D Nonsymmorphic Topological Metals
	Wednesday, 7 March, 10:15am
	Nonsymmorphic symmetries, i.e. symmetry operations involving fractional lattice translations, can produce nontrivial band-crossings in the band structure. Importantly, these crossings could Hourbe intrinsically stable under spin-orbit coupling (SOC). For example, the previously discussed Dirac points in 2D systems, such as in graphene, are all vulnerable against SOC. In contrast, nonsymmorphic symmetries may give rise to 2D spin-orbit Dirac points, which are truly stable under SOC. We identify the first realistic material example (2D HfGeTe family) that hosts such points at Fermi level, and we show that it is also the first identified 2D Z2 topological metal. We also discuss nonsymmorphic-symmetry-protected hourglass Dirac loops, which are fourfold degenerate and robust against SOC. These loops each enclose a pair of drumhead surface bands on the sample surface. Connecting two such loops can make an extended Dirac chain in the momentum space. We propose for the first time such hourglass Dirac chain metal phase, and find its realization in ReO₂.

Asst. Prof. Robert E. Simpson Engineering Product Development Singapore University of Technology and Design	Plenary 3: Active electronic and photonic materials by nanostructural design
	Thursday, 8 March February, 9:30am
	Francis Crick famously remarked "If you want to understand function, study structure". The properties and functions of all materials result from their atomic arrangements. Here I will discuss new ways to design the nanostructure of chalcogenide materials to achieve bespoke functional properties. The properties of chalcogenides are often optimised by inefficient Edison-style methodologies, where interesting attributes are occasional serendipitous discoveries rather than designed to specification. In contrast, a generalisable approach to optimise the design of materials for application in data storage, photonics, and electronics will be discussed. In particular, strain engineering and evolutionary approaches will be used to optimise chalcogenide superlattices. I will show how these methods have allowed us to introduce atomic switching into van der Waals heterostructure superlattices that are composed of two different two-dimensional chalcogenide crystals. Finally I will demonstrate that when "designed" phase change materials are incorporated into prototype memory cells, the memory characteristics exhibit substantial improvements over unstructured alloys of the same composition.

A/Prof. KOH Wee Shing Institute of High Performance Computing (IHPC), A*STAR and Department of Physics, National University of Singapore	Plenary 4: Environmental Modelling for Urban Cities
	Thursday, 8 March, 10:15am
	Urbanization has resulted to an increasing population density in many cities similar to Singapore. An increasing amount of forested land is converted to public housing to cater for the demands from the residents and industries as economic activities pick up. Therefore, in the place of forested land, are more and more concrete surfaces that trap heat in the urban environment by day and dissipate heat much more slowly at night. This results in the urban heat island (UHI) effect, where the ambient temperature of an urban town can be as high as 30 °C even at high. Another issue with high density living is the annoyance due to noise. Noise can come from many different sources, but the most prevalent noise source in many places including Singapore is traffic noise. Therefore, the liveability of the city is greatly dependent on (1) how much lesser solar energy can the city absorb; (2) how to maximize passive ventilation or natural wind flow to take heat away; (3) how to reduce the noise to the residents? Before addressing needs to improve city’s liveability, we must be able to model the physics with real virtual geometries of the city so that our urban planners can design a better environment for all. In this talk, I will briefly present an integrated environmental modeller (IEM) to simulate the solar radiation, wind and noise in the urban cities. The physics involved will be discussed. Some simulation results involving common urban features will be illustrated.

Assoc. Prof.
Cheong Siew Ann
Complexity institute and School of Physical and Mathematical Sciences,
Nanyang Technological University

Plenary 5: From the Knowledge of Physics to the Physics of Knowledge

Friday, 9 March, 9:00am

We physicists pride ourselves as the pioneers of human knowledge. Indeed, starting with Gallileo, Newton, and Maxwell in the 16th, 17th, and 18th centuries, we have amassed a vast knowledge of physics that is unthinkable in the times of Newton. We now understand pretty well the birth of our universe, the elementary particles, nucleosynthesis in stars, nuclei, atoms, and molecules, and condensed matter. But do we know how our knowledge of physics grows and evolves? Reflecting on the scientific enterprise, Karl Popper clarified the logic behind coming up with hypotheses, design experiments to test these hypotheses, refine our hypotheses, and test again. In Popper’s view, scientific progress is incremental, and the nature of our knowledge is tentative. Studying the birth of special relativity and quantum physics, Thomas Kuhn believed that scientific truth is a social construct born of consensus between scientists. Whenever scientists change their mind, dropping an old theory for a new one, we see a paradigm shift. In this talk, I will describe our attempts to better understand knowledge evolution, by mining the American Physical Society publication data sets, which consists of about 500,000 publications between 1893 and 2013. For each year, we construct a bibliographic coupling network (BCN), and perform community detection. We show that the BCN communities represent research topics that can be treated as mesoscopic units of knowledge. We then visualize how these knowledge units evolve from year to year, to show that this time evolution is a Popperian process dominated by weak mixing between topics. However, we also see strongly-mixing Kuhnian processes where two or more knowledge units merge to become one, or where one knowledge unit split into two or more knowledge units. We show that these Kuhnian processes strongly impact our knowledge of the topics involved, and so these can be considered paradigm shifts at scales smaller than the special relativity or quantum physics revolutions. Finally, I will describe ongoing work to combine bibliographic analysis with linguistic analysis of the APS publication data, to understand how scientific concepts evolve through Popperian and Kuhnian changes in the citation structure. Another ongoing work involves identifying features in the citation structure that allow us to most accuratey predict Kuhnian processes. Ultimately, we hope to understand knowledge evolution itself as a physical process as well.

[1]	W. Liu, A. Nanetti, and S. A. Cheong: Knowledge evolution in physics research: An analysis of bibliographic coupling networks, PLoS ONE 12, 0184821 (2017).

Assoc. Prof. Subramaniam Ramanathan National Institute of Education, Nanyang Technological University	Plenary 6: Making the teaching of physics fun and interesting
	Friday, 9 March, 9:45am
	Research has shown that physics is a difficult subject for students. A number of concepts in physics is counter-intuitive to real life experience, and this makes the subject especially prone to misconceptions. Creating a fun and interesting learning environment can make the subject more appealing and engaging for students. Some of these approaches include the use of demonstrations, thinking questions, everyday contexts, and class-based enrichment activities. These and other approaches are discussed during this presentation.