Seminars 2018

Title: Publishing in Nature Communications
Speaker:Dr Liu Bo
Date:20 December 2018
Time:2pm – 3pm
Venue:MAS Executive Classroom 2 (MAS-03-08)
Host:Associate Professor Fan Hongjin
Abstract: In this talk, I will introduce the Nature Communications journals, the editorial office in Shanghai, the editorial process and insiders’ view on the Nature Communications.


Title: SQM Seminar S​eries​​
Speaker:Daniele Vella and Xiaoye Chen
Date:14 December 2018
Time:11am - 12.30pm 
Venue:MAS Executive Classroom 1 (MAS-03-06)
Host:Assistance Professor Justin Song 

Title: Spectrally and spatially resolved scattering of exciton-carrier dynamics in WSe2single layer
Speaker: Daniele Vella

Atomically thin layers of transition metal dichalcogenides (TMDs) host strongly bound excitons and exhibit extraordinary lightmatter interactions. This exceptional behavior is corroborated by a variety of intriguing many-body effects such as exciton complex formation, cavity polariton at room temperature, as well as tightly bound trions. Therefore, TMDs are predicted to exhibit various exciton-mediated electro-optical phenomena such as excitonic Stark and Pockels effect and hold promise for high performance electro-optical modulator. Here, we report on electroabsorption (EA) and electroreflectance (ER) spectroscopy of encapsulated monolayer WSe2 in a contact-less device geometry and subject to modulated in-plane electric field. Our results reveal that both the real and imaginary part of the complex dielectric function are modulated. Both EA and ER spectra are dominated by linewidth broadening of the ground state and 2s excitons for an electric field perturbation up to 9 V/um. By spatially mapping EA signal we show how the electric field induces a modulation of the intrinsic carrier density creating a region of accumulation and depletion near opposite edges of the semiconducting monolayer. Contrary to the well known Stark and Pockels effect the electro-optical response is dominated by the scattering of the excitons with the free carriers that results in modulation of the homogeneous exciton linewidth. The extracted linewidth can be used to retrieve the intrinsic free carrier density. The modulation signal is as large as 2%, comparable to the theoretical limit of graphene, suggests an efficient scattering

Title: Emergence of magnetic skyrmions in Co/Pt-based multilayers with strong interfacial chiral interactions
Speaker: Xiaoye Chen (Spin Technologies for Electronic Devices Group, IMRE, A*STAR) [see abstract below]

Magnetic skyrmions with sub-100 nm sizes can be stabilized at room temperature in multilayer thin films . They are promising candidates for next-generation in-memory computing applications. The stability of these small skyrmions derives from the interplay of the chiral Dzyaloshinskii–Moriya interaction (DMI) generated at the ferromagnet/heavy metal interfaces with conventional magnetic anisotropy and exchange interactions. While nominally symmetric multilayers (e.g. Pt/Co/Pt) have negligible DMI, asymmetric structures (e.g. Ir/Fe/Co/Pt or Pt/Co/MgO) can acquire large DMI, stabilizing skyrmions down to 20 nm sizes. These stacks also offer a large latitude of tunability – one can access a wide phase-space of magnetic textures, manipulating their size, density and thermodynamic stability by varying the thickness of individual layers. To understand the role of these various interactions in generating magnetic textures, we used a series of complementary magnetic microscopy techniques – magnetic force microscopy, magnetic transmission x- ray microscopy and Lorentz transmission electron microscopy. Combined with previous theoretical work and micromagnetic simulations, we differentiate between domain walls of Bloch and Néel character and between skyrmions and chiral bubbles. In addition, we elucidate their stability by studying their low-lying resonant excitations, and their thermodynamic signatures through first-order reversal curve magnetometry. We have thus established a platform for investigating functional room temperature skyrmions, paving the way for the development of skyrmion-based devices.


Title: From Cold Molecules to Tests of Physics beyond Standard Model
Speaker:Mr Xing Wu
Date:11 December 2018
Time:10.30am - 11.30am 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Associate Professor Rainer Dumke
Abstract: Ultracold molecules represent a fascinating research frontier in physics and chemistry, but it has proven challenging to produce cold molecules with both high densities and low velocities. This talk covers two topics. First, I present a nonconventional approach to produce cold (<1K) polyatomic molecules with densities exceeding 109 cm-3[1], allowing observation of cold dipolar scattering in samples of fluoromethane (CH3F) and deuterated ammonia (ND3) [2]. Second, to demonstrate one of the many applications with cold molecules, I report our recent measurement on electron electric dipole moment using a cold beam of thorium monoxide (ThO). Our measurement places an upper limit of |de| < 1.1×10-29 e·cm [3], and sets the most stringent test on the supersymmety extension to the Standard Model of particle physics.

[1] Phys. Rev. Lett., (2014), 112, 013001
[2] Science, (2017), 358, 645-648
[3] Nature, (2018), 562, 355-360


Title: Quantum chaos of hydrogen-like atoms in a solid-state environment
Speaker:Professor Zhanghai Chen
Date:10 December 2018
Time:10.30am – 11.30am
Venue:MAS Executive Classroom 1 (MAS-03-06)
Host:Professor Xiong Qihua
Abstract: The motion of electrons, as well as their manipulation in external fields, has been a fundamental problem in all modern scientific and technological endeavors. Electron dynamics in external fields can be much more complicated than the familiar linear or weakly nonlinear behavior. It can even be chaotic. Indeed, the problem of chaotic electron dynamics in the quantum regime has been studied by many physicists for decades. It remains a scientific challenge that plays a crucial role in the understanding of quantum physics. In recent decades, progress in understanding nonlinear behavior of electron orbital motion has been achieved by investigating isotropic atoms in vacuum. As one of the most important examples, nonlinear motion of electrons in a Rydberg atom under external magnetic fields, i.e., the diamagnetic Kepler problem, gives rise to striking and measurable features such as the quasi-Landau resonance (QLR), manifesting the notion of quantum chaotic dynamics of electrons in atomic physics. On the other hand, such a nonlinear behavior of electron motion has not yet been examined in an anisotropic solid-state environment, though it is clearly of great importance. In this talk, I will present the first experimental realization of anisotropic diamagnetic Kepler problem in a solid-state environment. In particular, we investigate highly excited states of a phosphorus shallow donor in ultrapure silicon in magnetic fields using infrared thermal ionization spectroscopy. The experimental data clearly show a coherent interference of electron wave packets traveling along semiclassical closed orbits of hydrogenlike states, resulting in a series of quasi-Landau resonances. The experimental data can be well understood by analyzing semiclassical closed orbits that manifest chaotic motion of electrons with different effective masses in different crystalline directions. For the first time, our experiment provides direct evidence of the anisotropic diamagnetic Kepler problem achieved by the hydrogenlike impurities in an anisotropic crystal field.


Title: Laser cooling in semiconductors: A look through a prism of time
Speaker:Dr Denis Seletskiy
Date:3 December 2018
Time:10.30am - 11.30am  
Venue:Hilbert space (PAP-02-02)
Host:Professor Xiong Qihua
Abstract: A process of light amplification by stimulated emission of radiation necessarily involves generation of heat, which accompanies the lasing action. On the contrary, a laser running in reverse should operate as a refrigerator! Well before the invention of the laser, the concept of optical refrigeration was first postulated by P. Pringsheim in 1929, which in modern language involves excitation of a material resonance with a low-entropy red-detuned laser, which is followed by high-entropy spontaneous emission at an average photon energy which is higher than the excitation. Cooling of the material commences following annihilation of vibrational quanta of the material’s crystalline lattice. First demonstrated in 1995 by R. Epstein et al., optical refrigeration has seen a remarkable progress with recent demonstration of cooling to cryogenic temperatures as well as first demonstration of a cryocooler with a realistic payload by a team lead by M. Sheik-Bahae. These success is largely based on the utilization of a trivalent ions of ytterbium doped into an yttrium lithium fluoride crystal. In parallel, laser cooling of semiconductors has been theoretically analyzed. In 2013, Q. Xiong’s team at NTU has demonstrated first signatures of laser cooling in II-VI semiconductor CdS. This result caught the scientific community by surprise, as at that time III-V GaAs-based doubleheterostructures were deemed the best candidates for observation of laser cooling, possessing ultrahigh quantum efficiencies well in excess of 99%. While the community slowly is zooming in onto the potential culprits which prevented laser cooling, the puzzle of GaAs still remains unsolved. In this talk I will review our approach of investigating laser cooling cycle directly in the time domain and highlight its direct benefits. After the introduction, I will present two sets of measurements performed on GaAs samples at room temperature. First, transient absorption spectroscopy has been carried out to reveal novel excitation mechanism in the absorption tail of the semiconductor, which proceeds via the thermally ionized bound exciton transitions. Close analysis of the signal demonstrates observation of laser cooling in GaAs on few picosecond timescales. In the second set of measurements, we track evolution of GaAs temperature on nanosecond timescale and with 30 ps temporal resolution. We confirm observation of transient cooling in GaAs, which is masked by a heating signal on a timescale of approximately 100 ps, providing a hint of parasitic absorption processes occurring in the cladding of the GaAs epilayer. These combined measurements demonstrate novel insight into temporal dynamics of the laser cooling cycle, uncovering transient laser cooling of GaAs semiconductor on short timescales.


Title: Many-Body Invariants for Multipolar Higher-Order Topological Insulators
Speaker:Dr Gil Young Cho
Date:29 November 2018
Time:11am – 12pm
Venue:Hilbert Space ( PAP-02-02)
Host:Assistant Professor Justin Song
Abstract: In this talk, we will propose many-body invariants for multipolar higher-order topological insulators by generalizing Resta's pioneering work on polarizations. The many-body invariants are designed to measure the distribution of electron charge in unit cells and thus can detect quantized multipole moments purely from the bulk ground state wave functions. Using the invariants, we prove the bulk-boundary correspondence of the higher-order topological insulators. We will also discuss application of our invariants to spin systems as well as various other aspects of these many-body invariants.


Title: Emerging superconducting materials for high field applications: activities @ CNR-SPIN
Speaker:Professor Carlo Federghini
Date:28 November 2018
Time:11am – 12pm
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Associate Professor Massimo Pica Ciamarra
Abstract: Many applications in the field of high energy, nuclear magnetic resonance and laboratory high field magnets, require superconducting materials with increasingly high current characteristics at high fields. The material that has been developed most for these needs is the YBCO in the form of coated conductors which has numerous advantages but also problems in its use of not easy solution. For this reason, other alternative superconducting materials have attracted interest, some discovered in the new millennium, which offer particular characteristics for their use, albeit in niche sectors. After a brief presentation of the SPIN Institute of the Italian National Research Council, this seminar will briefly present the activities, projects and the most interesting results of the SPIN institute in this field in particular for Fe-based materials, for Magnesium Diboride and for some oxides more neglected by current international research.


Title: Ultrastrong coupling physics and its implications, latest developments in quantum computing and quantum physics
Speaker:Dr Thi Ha Kyaw
Date:14 November 2018
Time:11am – 12pm
Venue:Hilbert Space (PAP-02-02)
Host:Assistant Professor Ranjan Singh
Abstract: Superconducting circuits architecture is one of the promising quantum computing platforms to date, due to its good scalability and outstanding controllability. Besides these amazing attributes, the circuit architecture allows us to explore physics beyond the usual quantum optics experiments. In particular, the light-matter coupling stregnth g/ω in the superconducting circuit has reached to 1.34, while in standard quantum optics experiment, the coupling strength is of 10^{-6}. In this so-called ultrastrong coupling (USC) regime. the Jaynes-Cummings model with rotating wave approximation, obtained from the minimal coupling Hamiltonian between a two-level atom and a quantized electromagnetic field, is not valid. More general quantum Rabi model is required, which was proposed by Isidor Rabi 80 years ago. Its recent analytical integrability and experimental realizations in the superconducting circuit, metamaterial THz cavities, carbon nanotube microcavity exciton-polaritons, etc, are timely. In this talk, without assuming any familarity with the superconducting circuit and the quantum Rabi model, the basics of the two will be discussed in the first part, followed by some quantum computing applications such as quantum memory and quantum error correction, due to its built-in ℤ_2 parity symmetry. In the second part, the long-lasting controversies arising from gauge ambiguities in the quantum Rabi model will then be discussed.


Title: Observing Novel Electronic/Magnetic States in Transition-metal Compounds by using Soft X-Ray
Speaker:Associate Professor Hiroki Wadati
Date:12 November 2018
Time:4pm - 5pm
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Assistant Professor WANG Xiao, Renshaw

Control of charge/spin states by optical excitations in magnetically ordered materials has attracted considerable attention since the demonstration of ultrafast demagnetization in Ni within 1 ps, explored by time-resolved magneto optical Kerr effect studies[1] . For this study, we chose time-resolved x-ray measurements to study ultrafast charge/spin dynamics in transition-metal compounds. We performed a time-resolved x-ray study in a pump-probe setup by using our experimental setup at BL07LSU in SPring-8 [2] . This system is for time-resolved x-ray magnetic circular dichroism and resonant soft x-ray scattering measurements. The femtosecond Ti:sapphire laser with a wavelength of ~ 800 nm is introduced into the chamber. Photoinduced dynamics of the electronic and structural evolutions are examined by means of a pump-probed technique. The pulse width of the Ti:sapphire laser is ~ 50 fs. > The single bunch width of the x-rays at SPring-8 is ~ 50 ps, which limits the experimental time-resolution. For example, we observed spin dynamics of the FePt thin film, demonstrating photoinduced demagnetization.

[1] E. Beaurepaire et al., Phys. Rev. Lett. 76, 4250 (1996).
[2] K. Takubo, H. Wadati et al., Appl. Phys. Lett. 110, 162401 (2017).


Title: Purcell brightening of single-wall carbon nanotubes for efficient and tunable single-photon generation
Speaker:Professor Christophe Voisin
Date:9 November 2018
Time:1.30pm – 2.30pm
Venue:MAS Executive classroom 1 (MAS-03-06)
Host:Professor Xiong Qihua
Abstract: Single-photon sources (showing a vanishing probability to emit more than one photon at a time) are a key building block for secured quantum telecommunications or for future quantum optical information processing. In most protocols, this source is required to be on-demand and to show a large anti-bunching purity. For the sake of high speed communications, it also needs to show high brightness. In addition, technological integration in long range telecommunication networks requires near infrared operation. Room temperature operation together with electrical injection would also be highly valuable for large scale integration. Carbon nanotubes have strong assets in this perspective since they were shown to be excellent single-photon emitters (both at low-temperature and room temperature for chemically grafted nanotubes) and high polarization purity. In addition, their emission wavelength can be chosen over a wide range, including the telecom O and C bands, by selecting appropriate nanotube species. Finally, electro-luminescence has been reported by several teams. Nevertheless, whatever the excitation scheme, the reported luminescence quantum efficiency is consistently small and the linewidth may be strongly broadened by interactions with phonons or by local environment electrical fluctuations. In this talk I will show how these key properties can be drastically improved by coupling a nanotube to a small volume, highfinesse micro cavity, through the so-called Purcell effect. In order to tackle the so-called spatial and spectral mode matching issues (that become especially critical in high Q applications), we used a tunable cavity designed at the apex of an optical fiber for further integration in telecom networks. We show that the emission rate of the nanotube can be enhanced by a factor 60 leading to an effective luminescence quantum yield of about 40% and a coupling factor close to 100%. In addition, the original tuning capability of our open cavity, allows us to exploit the spectral broadening of the nanotube excitonic line and to achieve a widely tunable single-photon source. This new feature is possibly valuable for multiplexing applications in telecommunications or for indistinguishability engineering from remote nano-sources for quantum computing. We show how an original asymmetric energy exchange between a localized emitter, a 1D phonon bath and a photonic cavity can serve as a new handle to bypass the intrinsic spectral efficiency limit of a symmetrically broadened emitter.


Title: There are still spots on the sun. Some problems to be solved in fundamental physics
Speaker:Professor Lars Brink
Date:2 November 2018
Time:1.30pm – 3pm
Venue:SPMS – LT1 (SPMS-04-07)
Host:Dr Ho Shen Yong
Abstract: Fundamental physics has progressed enormously in the last fifty years. We have a Standard Model for Particle Physics that seemingly describe all the experimental results from the big accelerators. We have a Standard Model of Cosmology that describe the universe extremely well. However, they are not the ultimate models of the world. There are both theoretical, observational and experimental evidence that they are not complete and that there must be more fundamental theories underneath. I will describe these and tell what some possible solutions could be.


Title: SQM Seminar Series
Speaker:Xingyu Gu and Gou Jian
Date:19 October 2018
Time:11am - 12.30pm 
Venue:Hilbert Space (PAP-02-02)
Host:Assistant Professor Justin Song Chien Wen 
Abstract: Talk 1: Insulating phase and unconventional superconductivity in twisted bilayer graphene
Xingyu Gu (Shaffique Adam Group, NUS)
Recently a phase diagram similar to High Tc superconductors is found in twisted bilayer graphene(tBG) system: an insulating phase is observed at half filling and it becomes superconducting after slight electron or hole doping. Based on the continuum model developed by Bistritzer and MacDonald, we use random phase approximation(RPA) to study the study the competition between spin, charge, and superconducting order in twisted bilayer graphene. Depending on the details of the Fermi surface, we find various possibilities of density wave and superconducting phases. We find our result is consistent with the intuition from the phenomenological spin-fermion model. I will also briefly introduce some ongoing research on tBG, mainly on the nature of insulating phase.

Talk 2: Synthesization of 2D honeycomb structure based on group IV and V elements and their properties
Gou Jian (Andrew Wee Group, NUS)

The discovery of graphene has opened a new era for physics and materials research. Inspired by graphene, many novel physical properties in two-dimensional (2D) materials, such as linear dispersion (Dirac fermion), valley polarization and quantum spin Hall effect were discovered. Though graphene is versatile in fundamental physics research, however applications in electronic devices are restricted due to its gapless band structure. 2D honeycomb structures made up of other elements in group IV or V are predicted to have similar exotic properties and a larger band gap. In our works, we use molecular beam epitaxy (MBE) method to explore the synthesization of 2D honeycomb structure (Germanene, Stanene, Bismuthene, Sn2Bi) based on group IV and V elements. With in-situ measurements, we found their single-layer structures were accessible and stable. Besides, some interesting quantum properties were also found


Title: The Artful Application of Machine Learning to Accelerate Invention, Discovery, and Development of Novel Materials
Speaker:Professor Tonio Buonassisi
Date:11 October 2018
Time:10.30am – 12pm
Venue:MAS Executive Classroom 2 (MAS-03-07)
Host:Professor Sum Tze Chien
Abstract: Most can imagine how machine learning will shape the future of transportation and medical diagnosis. But how will machine learning shape our research laboratories focused on chemistry, materials, and hardware development? How can one apply ML to fields with sparse data sets, expensive experiments, and partially understood property-process-structure relationships? By way of background, I’ll describe how the combination of high-throughput experimentation (HTE) and machine learning (ML) has evolved in recent years, and promises to accelerate the rate of scientific learning without sacrificing quality of information. Early applications to the tasks of diagnosis and process optimization are presented. “Diagnosis” in this context refers to the purposeful application of characterization to identify underlying performance-limiting physics, an essential step toward improving early-stage prototypes. In one example, an advanced statistical approach known as “Bayesian inference” is applied to identify underlying bulk and interface properties limiting the performance of early-stage photovoltaic devices, ten times faster than traditional spectroscopy methods. With more accurate diagnosis, “process optimization” is more effective. In one example, ML is applied to optimize solarcell processing, exceeding the performance of a constrained “design of experiments.” In another example, the design of a villagescale solar-powered desalination system is presented; this system was recently deployed in India. The combination of HTE + ML saves the human researcher time in the lab by estimating the performance limits of novel candidate materials and system designs, identifying pathways for their rapid improvement, and/or deciding if an unpromising candidate should be quickly abandoned. I’ll illustrate how these principles generalize to other systems (through the recently-launched A*STAR “Accelerated Materials Development” Programme), and promise to accelerate the cycle of learning by ≥10x across a range of chemistry and materials disciplines. Opportunities for collaboration will be highlighted. Within the next five years, as “self-driving laboratories” embodying HTE+ML become commonplace, it is useful to bear in mind their limitations — humans still define the research sandbox, and automation performs tasks within this sandbox, ranging from straightforward optimization to inverse design. Further afield, there is nascent clarity for how ML may provide cognitive assistance to humans performing the entire scientific method, from invention and discovery of new science to dissemination. (Credit to discussions with Rob Simpson (SUTD), Ely Sachs and Elsa Olivetti (MIT) for seeding and shaping these ideas.) I’ll provide one example, of how an ML-augmented high-throughput experimentation platform can result in novel materials “discovery,” illustrating the case of novel lead-free perovskite-inspired photovoltaic materials with promising optoelectronic properties. To realize this vision in its entirety, various sub-disciplines within science, engineering, and the humanities will be developed and integrated, softening traditional inter-disciplinary boundaries and re-defining educational needs.


Title: Quantum experiments with massive, mechanical oscillators
Speaker:Simon Gröblacher
Date:10 October 2018
Time:11am - 12pm 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Assistant Professor Mile Gu 
Abstract: Mechanical oscillators coupled to light via the radiation pressure force have attracted significant attention over the past years for their potential in testing quantum physics with massive objects, in gravitational wave detection and in quantum information processing. Early experiments included ground-state cooling of the mechanical motion and squeezing of the optical field. Recent advances have allowed to obtain coherent control over the mechanical degrees of freedom, with experiments involving non-classical state preparation, entanglement between two oscillators, as well as violation of Bell's inequality. Here, we would like to discuss the latest results and highlight a promising route towards using mechanical systems as quantum memories, as light-matter quantum interfaces and for fundamental tests of quantum mechanics.


Title: Mechanical Motion
Speaker:Professor Junichiro Kono
Date:10 October 2018
Time:2.30pm - 3.30pm
Venue:SPMS-LT3 (SPMS-03-02)
Host:Associate Professor Ranjan Singh 
Abstract: In this lecture for first year undergraduate students as a part of course PH 1105: Optics, Vibrations and Waves, Prof. Junichiro Kono will introduce the concept of mechanical motion that causes different types of vibrations and mechanical waves such as longitudinal and transverse periodic waves. He will teach the mathematical description of a general wave phenomena and describe the intensity of wave along with discussion on the inverse square law. He will also discuss the concept of superposition of waves and the conditions that lead to the formation of standing waves on a string.


Title: Macroscopic One-Dimensional Dynamics in Aligned Carbon Nanotubes
Speaker:Professor Junichiro Kono
Date:8  October 2018
Time:2pm - 3pm 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Professor Yu Ting 

Single-wall carbon nanotubes (SWCNTs) provide a unique one-dimensional (1D) environment in which to examine the physics of interplay between multivalley Dirac band structure and strong Coulomb interactions. Semiconducting SWCNTs exhibit extremely stable 1D excitons, whereas metallic SWCNTs host massless 1D carriers that show Tomonaga-Luttinger liquid behaviors. Although the 1D nature of individual SWCNTs has stimulated much interest, its macroscopic manifestation has been difficult to observe. We have recently developed a controlled vacuum filtration technique to fabricate wafer-scale films of highly aligned and densely packed SWCNTs [1] . In this talk, we summarize our recent accomplishments using these unique samples. We have made the first observation of intersubband plasmons – quantum plasmons whose excitation energy is comparable to the quantum confinement energy – in gated and aligned SWCNT films [2] . We have also made the first observation of cross-polarized excitons in absorption spectra for an aligned undoped (6,5) film [3] , which allowed us to estimate the oscillator strength of this transition as well as the effective dielectric constant. We further built an excitonpolariton architecture by incorporating an aligned single-chirality SWCNT film inside a Fabry-Pérot microcavity. This system displayed a continuous transition from the ultrastrong-coupling regime to the weak-coupling regime through facile polarization control [4] . The vacuum Rabi splitting exhibited cooperative enhancement when the number of excitons was increased by increasing the SWCNT film thickness.

1 X. He, W. Gao, L. Xie, B. Li, Q. Zhang, S. Lei, J. M. Robinson, E. H. Hároz, S. K. Doorn, R. Vajtai, P. M. Ajayan, W. W. Adams, R. H. Hauge, and J. Kono, Nature Nanotechnology 11, 633 (2016).
2 K. Yanagi, R. Okada, Y. Ichinose, Y. Yomogida, F. Katsutani, W. Gao, and J. Kono, Nature Communications 9, 1121 (2018).
3 F. Katsutani, W. Gao, X. Li, Y. Ichinose, Y. Yomogida, K. Yanagi, and J. Kono, arXiv:1808.08602.
4 W. Gao, X. Li, M. Bamba, and J. Kono, Nature Photonics 12, 362 (2018).


Title: Start-Up by Proxy - A Second Hand Account of High Tech and Quantum Start Ups
Speaker:Dr Andrew Collins
Date:3 October 2018
Time:4pm - 5pm 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Assistant Professor Tomasz Paterek 
Abstract: Working in research is a joy and a privilege where, after years of exams and hard work, you can explore your ideas and ideally become a world expert in something. At the outset of a research career it's arguably the goal to go for tenure, or something like it, and the dream to make a big impact with your discoveries. However, impact can be so much more than just papers, talks and grant money. A scientific discovery can rapidly become a daily influence or disruptive change in everyday life. For an increasing number of scientists there is a passion to see something they have created making a difference in society. I manage a programme aimed at commercialising Quantum Technology and have seen up close the early part of the journey from scientist to entrepreneur. In this talk I will present case studies and observations of the talented people building an industry that, until very recently, did not exist.


Title: Medical Physicist and Radiation Medicine
Speaker:Professor David Huang
Date:2 October 2018,
Time:10am - 11am 
Venue:SPMS-LT4 (SPMS-03-09)
Host:Adjunct Associate Professor Lee Cheow Lei James 
Abstract: Radiation has been applied to our daily life as well as to medical field for over 100 years. There are three basic physical principles applied in radiation medicine, respectively are Photoelectric Effect, Compton Scattering, and Pair Production. W. Roentgen opened the door of Radiology and M. Cures opened the door for radiotherapy. Medical Physics is a sub-field of Medicine and a hybrid of physics and medicine. Medical Physics applies the physical concepts and knowledge to Radiology, Nuclear Medicine, Radiotherapy and Health Physics fields. Medical Physicist is a professional who specializes in the application of the concepts and methods of physics to the diagnose and treatment of disease. They build the bridge between Physics and Medicine. In the talk, Prof. Huang will briefly go over the radiotherapy process and radiological process in clinical setting. Also he will go over the important roles of medical physicists in clinic as well as in radiation protection.


Title: Magnetic Skyrmions in Confined Geometries
Speaker:Professor Mingliang Tian
Date:2 October 2018, Tuesday 
Time:11am - 12pm 
Venue:Hilbert Space 9SPMS-PAP-02-02) 
Host:Professor Xiong Qihua 
Abstract: Magnetic skyrmions are topologically stable whirlpool-like spin textures that offer great promise as information carriers for future ultra-dense memory and logic devices. To enable such applications, particular attention has been focused on the skyrmions in highly confined geometry such as nanodisks or one dimensional nanostripes or wires. Here, we systematically report the real space visualization and manipulation of individual magnetic skyrmion in FeGe nanostripes or nanodisks by high resolution Lorentz TEM and electron holography. We observed the high flexibilities of the shape of individual skyrmion tuned by the width and a unique field-driven helix-to-skyrmion cluster states transition directly. Also, new state, called target skyrmion consisting of a central skyrmion surrounded by one or more concentric helical stripes and the magnetic bobbers are also identified. These findings demonstrate that the geometry defects can be used to control the formation of topologically nontrivial magnetic objects.


Title: Towards Universal Quantum Computation with Bosonic Qubits
Speaker:Dr. Yvonne
Date:27 September 2018
Time:4pm - 5pm 
Venue:MAS Executive Classroom1 (SPMS-MAS-03-06)
Host:Associate Professor Rainer Dumke
Abstract: The realisation of robust universal quantum computation with any platform ultimately requires both the coherent storage of quantum information and (at least) one entangling operation between individual elements. The use of multiphoton states encoded in superconducting microwave cavities as quantum memories is a promising route to preserve the coherence of quantum information against naturally-occurring errors. However, operations between such encoded qubits can be challenging due to the lack of intrinsic coupling between them. In this talk, I will discuss the recent experimental work on engineering a coherent and tunable bilinear coupling between two otherwise isolated microwave quantum memories in a three-dimensional circuit QED architecture. Building upon this coupling, we also demonstrate programmable interference between stationary quantum modes and realise robust entangling operations between two encoded qubits. Our results provide a crucial primitive necessary for universal quantum computation using bosonic modes.


Title: How to Synchronize the World to One Atomic Transition: An Overview of Atomic Clocks and Global Timekeeping
Speaker:Assistant Professor Travis Nicholson 
Date:14 September 2018 
Time:11am - 12pm 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Associate Professor David Wilkowski 
Abstract: Atomic clocks are at the heart of international commerce, long-range data synchronization, global positioning, cutting edge metrology, and more. Despite that most countries maintain national atomic clocks that neither gain nor lose a second in several million years, there are excellent reasons to push clocks further. This is because the best atomic clocks have a surprising range of applications, such as clock-based dark matter searches, quantum manybody physics, and new geophysical technologies. Have you ever wondered how physicists and engineers synchronize the entire world to one atomic resonance frequency? In this seminar I will provide an overview of how atomic clocks work, how international timekeeping works, and how advances in low-noise lasers and ultracold atoms have led to a new generation of atomic clocks that have raised fundamental questions about what it means to measure time.


Title: Structural Properties of Multiplex Networks
Speaker:Professor José Fernando F. Mendes
Date:10 September 2018
Time:3pm - 4pm 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Associate Professor Chew Lock Yue 
Abstract: Many complex systems, both natural, and man-made, can be represented as multiplex or interdependent networks. Multiple dependencies make a system more fragile: damage to one element can lead to avalanches of failures throughout the system. In this talk I will present recent developments about the structural properties of multiplex networks. What kind of transition will we find? A complete understanding of the transition cannot therefore be had without first understanding this critical behavior. I will discuss and describe the nature of such hybrid phase transitions. I will also present a theory that enables us to find the giant mutually connected component in a two-layer multiplex network with arbitrary correlations between connections of different types. I will show that the correlations between the overlapping and non-over lapping links markedly change the phase diagram of the system, leading to multiple hybrid phase transitions. For assortative correlations we observe recurrent hybrid phase transitions.


Title: Stochastic Coherence Theory for Qubits
Speaker:Professor Alexander Streltsov
Date:4 September 2018
Time:3pm - 4pm 
Venue:Hilbert Space (SPMS-PAP-02-02) 
Host:Assistant Professor Tomasz Peterk 
Abstract: The resource theory of coherence studies the operational value of superpositions in quantum technologies. A key question in this theory concerns the efficiency of manipulation and interconversion of this resource. We solve this question completely for mixed states of qubits by determining the optimal probabilities for mixed state conversions via stochastic incoherent operations. This implies new lower bounds on the asymptotic state conversion rate between mixed single-qubit states which in some cases is proven to be tight. Furthermore, we obtain the minimal distillable coherence for given coherence cost among all single-qubit states, which sheds new light on the irreversibility of coherence theory.


Title: Femtosecond Spin Dynamics in Molecular Magnets
Speaker:Dr J. Olof Johansson
Date:3 September 2018
Time:3pm - 4pm 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Nanyang Assistant Professor Marco Battiato 
Abstract: Despite the rapid expansion of femtomagnetism, molecular magnets have so far been under-explored using ultrafast techniques. These materials offer interesting possibilities because it is possible to systematically tune the nature of the magnetic interactions due to the vast library of structures available with synthetic chemistry, which is not as trivial in conventional magnets. We report the first ultrafast magneto-optical (MO) study of a molecule-based magnet. We found a fast magnetic response on a femtosecond timescale, which was attributed to the super-exchange interaction between the metal ions.Femtosecond pump-probe spectroscopy was used to measure the MO dynamics of thin films of the V-Cr Prussian blue analogue (PBA), which is a room-temperature molecule-based magnet. The MO measurements could detect a change in the super-exchange interaction taking place as a result of a spin flip occurring in less than 250 fs after the absorption of a pump photon. We have more recently explored the initially excited state by comparing femtosecond transient absorption spectroscopy with spectroelectrochemistry and also developed coloured magnetic heterostructures. These results demonstrate the powerful combination of transient absorption spectroscopy, magneto-optics, and spectroelectrochemistry in understanding photoinduced magnetisation dynamics in magnetic functional materials. We will also present recent results on femtosecond vibrational coherences in a single-molecule magnet, enabling the possibility to optically modulate the magnetic anisotropy in these interesting molecular systems.


Title: Ab Inito Based Multi-Model to Understand Structures and Vibrational Spectra of Molecular Systems
Speaker:Professor Jer-Lai Kuo
Date:21 August 2018
Time:11am - 12pm 
Venue:MAS Executive Classroom 1 (SPMS-MAS-03-06)
Host:Associate Professor Mu Yuguang 
Abstract: Modeling the structures and properties of molecular systems has been a challenging task for Physics, Chemistry and Material Science. The relatively weak interaction and intrinsic structural flexibility has given rise to a rich phases and properties. In our group, we have been working on developing a framework of computational algorithms to engage different models (ranging from empirical model, semi-empirical methods, DFT to high-level quantum chemistry methods) for molecular modeling. To search for structures, we have build an array for structural searching schemes to utilize the efficiency of empirical and semi-empirical methods to explore the configurational space. Structural info. obtained will further been refined using high-level methods. Furthermore, different molecular properties require different level of quantum mechanical theories. As a example, we will present our recent effort to understand the vibrational motion of proton in various molecules using the computational algorithms we developed including both types of proton (Zundel and Eigen) under different solvation environments. If time permits, we will also access the performance of a few approximate treatments on vibrational coupling and anharmonicity to treat larger hydrogen-bonded molecular (water, alcohols and amines) clusters.


Title: The Cosmological Constant: How Big Is The Problem?
Speaker:Professor Ngee-Pong Chang
Date:6 August 2018
Time:4pm - 5pm 
Venue:MAS Executive Classroom 2 (SPMS-MAS-03-07)
Host:Associate Professor David Wilkowski 
Abstract: Ever since Einstein pronounced it to be the greatest mistake in his life, the cosmological constant has continued to be a puzzle and a challenge to physicists of the day. In this talk, I will give an introduction to the issues involved, and see how today it has become the central cause of dark energy and expansion of the universe. How does this impact on the Theory of Everything and LHC ? Come and see.


Title: Tunable Phenomena in Graphene: From Quantum Critical Dirac Fluid to Engineered Mott Insulator
Speaker:Professor Feng Wang
Date:3 August 2018
Time:11am - 12pm 
Venue:MAS Executive Classroom 1 (SPMS-MAS-03-06)
Host:Assistant Professor Gao Weibo 
Abstract: The electronic structure of graphene depends sensitively on the layer number and stacking. Monolayer graphene is famously known to have massless Dirac electrons, while ABC stacked trilayer can have a remarkably large electron mass at low energy. In this seminar I will discuss unique phenomena that emerge in these two very different systems. Using an on-chip terahertz spectroscopy, we directly probe the quantum critical electrodynamics of massless Dirac fluid in boron nitride-encapsulated monolayer graphene. In ABC trilayer graphene, we exploit the Moire superlattice between graphene and boron nitride to realize strongly correlated behavior such as a tunable Mott insulator.


Title: Accelerated Discovery and Design of Perovskite-Based Advanced Functional Materials
Speaker:Dr. Kesong YANG
Date:24 July 2018
Time:3pm - 4pm 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Assistant Professor Wang Xiao, Renshaw
Abstract: As a rapidly growing area of materials science, high-throughput computational materials design is playing a crucial role in accelerating the discovery and development of novel functional materials. In this talk, I will introduce the strategy of high-throughput first-principles computational materials design, and take several research examples to show the usage of this approach in the accelerated design of functional materials. In particularly, I will talk about our recent research progress on the perovskite-based functional materials: perovskite-based two-dimensional electron gas (2DEG) and hybrid organic-inorganic double perovskites for optoelectronics. For more information, a brief research summary can be found below.

i) The two-dimensional electron gas (2DEG) formed at the interface between two wide-band-gap perovskite insulators such as LaAlO3 and SrTiO3 has attracted intense interests because of their potential applications in the next-generation nanoelectronic devices. In this talk, I will show that, by introducing a group of combinatorial materials descriptors, we are able to realize a high-throughput design of perovskite-oxide-based 2DEG systems based on the polar catastrophe and polarization discontinuity mechanism, respectively.

ii) Hybrid organohalide perovskites have emerged as one class of most promising light-harvesting materials for the next-generation solar cells because of their exceptional properties such as an appropriate band gap, high absorption coefficient, long carrier diffusion length, and high carrier mobility. Despite of their promising applications, the large-scale industrial applications of hybrid halide perovskites are limited by several major challenges, such as poor stability of perovskites and the demand for lead-free perovskites. Here I will show that we are able to identify a series of candidate halide perovskites for photovoltaic applications using high-throughput first-principles electronic structure calculations.


Title: Complex Variables and Their Application in Theoretical/ Mathematical Physics
Speaker:Dr. Ehsan Hatefi
Date:18 July 2018
Time:3pm - 4pm 
Venue:MAS Executive Classroom 2 (SPMS-MAS-03-07)
Host:Dr. Tan Hai Siong
Abstract: We start to introduce complex variables and their analytic properties, including Cauchy-Riemann conditions and its integral theorem. To illustrate their importance, during the course we also provide various examples about these variables, in particular, we show that how these variables can be algebraically used to be able to derive all the singularities of various non-trivial integrations on upper half plane. If we have enough time, we would be pleased to talk about some infinite series, Gamma and Beta functions because they play crucial role in various contexts. Finally making use of simple techniques we mention the value of 𝜍 −1 or σ𝑛=1 ∞ 𝑛 and its correspondence in fixing the number of spacetime dimensions in string theory.


Title: The Fundamental Theory of The Universe and Universality in String Theory
Speaker:Dr. Ehsan Hatefi
Date:17 July 2018
Time:3pm - 4pm 
Venue:MAS Executive Classroom 2 (SPMS-MAS-03-07)
Host:Dr. Tan Hai Siong
Abstract: In this seminar, we talk about the search for the fundamental theory of the universe as well as unification. We would like to introduce to you the fundamental objects, "D-branes" in String Theory. The main goal of our talk is to convey to you the importance of these objects not only in String Theory and fundamental physics but also in the other fields such as Mathematical Physics and Geometry. We also highlight their roles in exploring further symmetries and unification. We try to talk about all kinds of effective actions in String Theory, involving DBI, Chern-Simons and more importantly new Wess-Zumino actions. We would also like to provide a comprehensive explanation not only for BPS branes but also for D-brane-anti D-brane systems. Along those actions, we also introduce various new techniques for mathematicians/string theorists for which getting the exact and final form of the world-sheet integrals to all orders will be presented. Eventually, we make various remarks on how to derive without any ambiguity all order α’ corrections to some of the effective actions. We then mention several applications related to those effective actions for Black Holes and Cosmology as well as other related areas.


Title: Substrate-Induced Curvature Effects and Charge Localization in Monolayer MoS2
Speaker:Dr. Bong Gyu Shin
Date:21 June 2018
Time:3pm - 4pm 
Venue:Hilbert Space (PAP-02-02)
Host:Assistant Professor Bent Weber 
Abstract: Monolayer transition metal dichalcogenides (TMdCs) have attracted considerable attention due to their rigorous electronic and optical properties with spin and valley. For applications with TMdCs, environmental factors such as substrates or adsorbates are critical due to their low-dimensionality as a layered structure which are mostly exposed to the environment. Inevitably, the quasiparticle (or electronic) bandgap in monolayer MoS2 exhibits variety due to dielectric screening or external strain effects from external factors. If we want to achieve the benefits of ideal monolayer TMdCs in applications, understanding the basic phenomena triggered by the extrinsic factors it is important to control and manipulate those. Here, we report an unusually large quasiparticle bandgap modulation of 1.23-2.65 eV from monolayer MoS2 on Si substrate, which is induced by a substrate. By reduction of the quasiparticle bandgap due to substrate-induced bending strain or curvature in monolayer MoS2 , the direct bandgap in monolayer MoS2 was eventually converted to an indirect bandgap above a bending strain of approximately 1.5%. Even for the small range of surface roughness of ~1 nm, curvature can be critical depending on the aspect ratio between height and width of hill or valley in MoS2 . The observed bending strain in the top sulfur-layer was ranged from -6 to 6 %, which is within the observed linear elastic limit of 6-11%. By the bending strain, approximately 80% of the surface area revealed an indirect bandgap in contrast with the general belief of a direct bandgap in monolayer MoS2 . Such a remarkable change in quasiparticle bandgap of MoS2 was not observed in a flat substrate like HOPG. In addition, charge localization was observed along the curvature in monolayer MoS2 . DFT results support charge localization by curvature of MoS2 and Fermi-level pinning-like behavior when MoS2 are doped as shown in STS results. Photoluminescence and Raman spectroscopy were performed on MoS2 /SiO2 with a cavity to investigate further in comparison with suspended MoS2 , which confirmed large variation in supported MoS2 from those in suspended MoS2 due to the surface roughness of substrate. It confirmed that substrate-induced curvature effects in atomic scale can be probed quickly and macroscopically by the optical methods. We, therefore, can easily qualify the flatness and modified electronic structures of monolayer MoS2 over micrometer-scale, elucidating a strain-engineering of MoS2 or other semiconducting 2D materials for future applications.


Title: Combing for New Quantum Sensors
Speaker:Professor Andre Luiten
Date:20 June 2018
Time:11am - 12pm 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Assistant Professor Lan Shau-yu 
Abstract: The subject of the 2005 Nobel Prize, the optical frequency comb, is driving a revolution in spectroscopy, optical frequency synthesis and optical frequency measurement. What was once very difficult has now become routine. We are using frequency combs to simultaneously obtain high-resolution spectral and temporal information in a single measurement. This is highly useful in providing a deep understanding of complex phenomena where such complete information can be indispensable. I will provide a few examples in which we have used a mode-locked laser comb to deliver measurements of molecular and atomic gases to obtain quantitive measurements of composition, or use it an accurate sensor of some other property of interest (temperature, magnetic field). We have also built combs based on electro-optical modulation of continuous-wave lasers and used heterodyne detection to measure the complex transmittance in atomic gases that are evolving in time. This allows us to see the complex dynamics of saturation spectroscopy and precession in magnetic fields of Rb gas.


Title: Increasing The Appeal Of Mathematics And Sciences In Children - What Can Universities Do?
Speaker:Dr Riikka Lahtinen
Date:14 June 2018
Time:2pm - 3pm 
Venue:Hilbert Space (PAP-02-02)
Host:Dr Ho Shen Yong 
Abstract: Inspiring and motivating children and youth into mathematics, science and technology through the latest methods and activities of science and technology education has become increasingly important in Finland and worldwide. It is also important to support the life-long learning of teachers working on levels of education from early childhood to universities, and strengthen the development of researchbased teaching.: These aims have been put into practice in LUMA centres, which are part of almost all Universities in Finland (LU=luonnontieteet, sciences in Finnish, MA mathematics). LUMA Centre Finland was established in 2013 as the umbrella organization for local LUMA Centres to strengthen and promote their collaboration on national and international level. This presentation will discuss the organization of this work in Finland and the practical functions the individual LUMA centres and LUMA centre Finland have.


Title: Kinetics of Phase Separation in Ternary Fluid Mixtures with One Polymeric Component
Speaker:Dr. Amrita Singh
Date:5 June 2018
Time:3pm - 4pm 
Venue:Hilbert Space (PAP-02-02)
Host:Associate Professor Cheong Siew Ann 
Abstract: We present Dissipative Particle Dynamics (DPD) simulation studies for the segregation kinetics in three dimensional ternary fluids mixture, mainly for two cases: (i) segregation of simple ternary (ABC) fluids with symmetric and asymmetric compositions and (ii) segregation of ternary (ABC) mixture with one polymeric fluid component, where we explored, how some parameters such as, concentration of polymers, polymer chain-length, and stiffness of the polymers affect the coarsening dynamics. We show that the domain growth law, in both the cases, is consistent with Lifshitz-Slyozov growth law and also observe that off-criticality (asymmetric compositions) leads to more segregated domains. By comparing our results for various morphologies, we notice that the coarsening is affected more significantly by changing the composition of the component beads. We have also accessed the crossover from viscous hydrodynamic regime to inertial hydrodynamic regime for simple ternary, as well as for the polymeric fluid mixtures. To the best of our knowledge, this is the first such significant observation for the phase separation dynamics in three dimensional ternary fluids.


Title: SQM Seminar Series
Speaker:Thorin Jake Duffin and Jia Ning Leaw
Date:25 May 2018
Time:11am - 2pm 
Venue:Hilbert Space (PAP-02-02)
Host:Assistant Professor Justin Song Chien Wen
Abstract: Talk 1: Exploring Light Emission from Metal-Insulator-Metal Quantum Tunnelling Junctions Presented By Thorin Jake Duffin (Nijhuis group, NUS)

Talk 2: The Role of Electron-Electron Interactions in Dirac Fermions Presented By Jia Ning Leaw (Shaffique Adam group, NUS)


Title: Workshop on Incorporating computational thinking in a Physics Curriculum
Speaker:Professor Duncan Carlsmith
Date:17 May, 18 May, 21 May 2018
Venue:SPMS -PAP-Year 1 Physics Lab 
Host:Dr Ho Shen Yong 
Abstract: Duncan Carlsmith_workshop


Title: Quantum vortex limitations to ultracold neutron extraction
Speaker:Professor Jeffery Martin
Date:27 April 2018
Time:3pm - 4pm 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Associate Professor Rainer Dumke 
Abstract: Free neutrons that are moving very slowly have an amazing property: they bounce off walls. Neutrons with this property are called ultracold neutrons (UCN), and they can be stored for long periods of time (hundreds of seconds) in bottles. This makes UCN perfect for measurements of the fundamental properties of the neutron, for example the neutron electric dipole moment (nEDM). If the nEDM were found to be nonzero, it would signify a violation of CP (particle-antiparticle) symmetry beyond the standard model. Ultimately, it could lead to an explanation of the predominance of matter over antimatter in the universe. The TRIUMF Ultracold Advanced Neutron (TUCAN) collaboration uses a UCN source based on superfluid helium. Superfluids are usually thought of as having infinite thermal conductivity. But at the operating temperature and heat flux for our source, the normal and superfluid components (in the two-fluid model) are expected to be turbulent with friction between the normal component and quantum vortices limiting the conduction of heat. This could result in unacceptably large losses of UCN, if the superfluid heats up too much. In this talk I will discuss our recent experimental progress on UCN production and the thermal properties of superfluid helium, and our plans to measure the nEDM.


Title: The Cobra Wave
Speaker:Professor Frédéric Chevy
Date:20 April 2018
Time:4pm - 5pm 
Venue:Hilbert Space (SPMS-PAP-02-02)
Host:Associate Professor David Wilkowski
Abstract: The cobra wave is a popular physical phenomenon illustrated online by many spectacular videos. It arises from the explosion of a metastable grillage made of popsicle sticks and for a physicist, this system provides a non-trivial example of structural dynamics that is nevertheless amenable to an in-depth understanding. Using a joint experimental and theoretical analysis, we have studied the interplay between the dynamics of single sticks and that of the whole structure and we have shown that the cobra wave could only exist in a narrow range of parameters constrained by gravity and material fracture.


Title: Nanostructures for Green Photonics
Speaker:Professor Dieter Bimberg
Date:20 April 2018
Time:11am - 12pm 
Venue:MAS Executive Classroom 1 (SPMS-MAS-03-06)
Host:Associate Professor Cesare Soci
Abstract: Universal self-organization and self-ordering effects at surfaces of semiconductors lead to the formation of coherent zero-dimensional clusters, quantum dots (QDs). The electronic and optical properties of QDs, being smaller than the de-Broglie-wavelength in all three directions of space are close to those of atoms in a dielectric cage than of solids. Their delta-function-like energy eigenstates are only twofold (spin) degenerate. All few particle excitonic states are strongly Coulomb correlated due to the strong carrier localisation. Their energies depend on shape and size of the dots, such that positive, zero or negative biexciton binding energies and finestructure splitting (caused by exchange interaction) appear. Consequently, single QDs present the most practical possible basis of emitters of single polarized photons (Q-bit emitters) on demand or entangled photons via the biexciton-exciton cascade for future quantum cryptography, repeaters and communication systems. Embedding them in electrically pumped resonant cavity structures, they can emit single photons at rates beyond 1 Gbit/s. Using GaN-based structures room temperature operation is possible.
Multiple QD layers, as active materials for nano-optoelectronic devices like edge and surface emitting lasers, or semiconductor optical amplifiers, are extremely promising. Their properties, in particular their energy efficiency, are outperforming those of photonic devices based on higher dimensional systems. Semiconductor nanotechnologies transform presently to enabling technologies for new economies. The commercialization of nano-devices and systems has started. High bit rate and secure quantum cryptographic systems, nano-flash memories, ultra-high speed nano-photonic devices for metropolitan area networks, the 400 Gbit/s ethernet, etc. present some of the first fields of applications of nano-devices.


Title: Non-linear Optics and THz generation in semiconductor microcavities
Speaker:Professor Jérôme Tignon
Date:23 March 2018
Time:11am - 12pm 
Venue:MAS Executive Classroom 2 (MAS-03-07)
Host:Professor Xiong Qihua
Abstract: Semiconductor microcavities with embedded quantum wells in the strong light-matter coupling regime host quasiparticles called microcavity exciton-polaritons. Their hybrid light-matter nature, half-electronic, half-photonic, brings about remarkable nonlinear optical properties. Here, we will focus on multiple microcavities that allows to achieve optical parametric scattering in a nanostructure. Further, in the elastic Rayleigh scattering regime, the TE-TM splitting induces a spatial and angular separation of polaritons with different pseudospins. We show that this phenomenon, called "Optical Spin Hall Effect", can be controlled by a strong optical pump beam. In the OPO regime, the light self-organizes to form patterns in the far field. These studies pave the way for the realization of microscopic devices such as ultrafast all-optical switches. Last, we will show how these multiple microcavites can be used to generate or detect tera-Hertz waves.


Title: Charge regulation - not an upgrade but rather a game changer
Speaker:Professor Rudolf Podgornik
Date:15 March 2018
Time:3pm - 4pm 
Venue:MAS Executive Classroom 2 (SPMS-MAS-03-07)
Host:Dr Lu Bing Sui 
Abstract: Charge regulation, implying a variable response of dissociable charge groups on solvent exposed surfaces of macromolecules, is a quintessential feature of polyelectrolytes in biological systems. This in particular applies to bulk protein solutions and such proteinaceous aggregates as viral shells and enzymatic nanocontainers, that can provide scaffolding and compartmentalization for chemical engineering on the nano-scale. While it is known and sometimes appreciated that charge regulation modifies the behavior of chargeable colloidal systems, I will specifically address such features that are not only modifications of the standard PB (Poisson-Boltzmann) paradigm, but fall completely outside of that toolbox. I will choose two examples: (i) spontaneous symmetry breaking of charge-regulated surfaces whose consequences contradict one of the fundamental assumptions commonly made in the application of the PB theory to chemically identical surfaces; (ii) charge regulation of complex fluids with mobile macro-ions having internal non-electrostatic degrees of freedom, that leads to positional dependence of the effective charge of the macro-ions and a non-monotonic dependence of the effective Debye screening length. These new developments embed the PB paradigm into an entirely new perspective.


Title: Even less of an engineer: A random walk from physics research to engineering leadership
Speaker:Professor Richard J Parker
Date:19 January 2018
Time:3.30pm - 5pm 
Venue:SPMS-LT3 (SPMS-03-02)
Host:Dr Koh Teck Seng
Abstract: Ric Parker retired in 2016 after 37 years with Rolls-Royce, the last 15 as Director of Research and Technology (the longest serving Chief Technology Officer in the FTSE 100). His is now a Special Advisor working with various companies and institutions, including A-Star, Singapore. After he graduated in Physics from Imperial College and completed laser applications research jointly at Imperial and the National Physical Laboratory, Ric joined Rolls-Royce to apply lasers to measurement in harsh environments. He went on to lead Advanced Materials Research (Composites, Ceramics, etc.) and then became a leader in Compressor Design. In his last 15 years he was responsible for the entire technology portfolio of this major British engineering company, now with global reach. He enhanced and supported the Rolls-Royce UTC model which has the Company working closely with 31 University Technology Centres worldwide (including the Rolls-Royce Corporate Lab@NTU). He will review the technologies he has been close to, but also look forward to those technological developments which those who follow must bring to the market. The cryptic title will also be explained, so do come along.