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Seminars 2015
| Title: | From Smartphones to Diagnostics: programmable droplet microfluidics |
| Speaker: | Professor Hywel Morgan |
| Date: | 14 December 2015 |
| Time: | 2pm - 4pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Associate Professor Lew Wen Siang |
| Abstract: | Our group is developing integrated analytical systems for healthcare and medicine that utilize inexpensive electronics for sample detection and manipulation. Such systems will find applications as tools for life science and in new diagnostics for molecular and cellular analysis. This talk describes the development of a new generation of programmable miniature microfluidic systems, based on digital microfluidics. Unlike conventional microfluidic systems that require pumps and valves to control liquids, digital microfluidics (DMF) employs Electro Wetting on Dielectric (EWOD) to manipulate and process nanolitre droplets of liquid using electric fields. The chips contain thousands of electrodes, manufactured using active matrix Thin Film Transistor (TFT) technology; the same low cost electronics that are used in mobile phone displays. The devices are the size of microscope slides and contain thousands of individual electrodes, each of which can be programmed separately. Each electrode can be switched on and off independently allowing many droplets to be manipulated in parallel, providing an extremely flexible platform that enables the development of automated custom diagnostic assays. The DMF chips include sensors to measure droplet position and droplet volume, providing feedback control to automatically verify and validate successful operation. The systems support a wide range of different chemical and biochemical assays, for example immuno-assays and DNA analysis. Further examples of low-cost electronic systems for analyte and cell detection will be given, including microfluidic impedance cytometry for label free cell analysis and Si nano-wire biosensors made using simple fabrication methods. |
| Title: | Low Cost Soft Magnets for Power Transformers, Electric Motors, and Current Sensors |
| Speaker: | Dr Michael Kurniawan |
| Date: | 11 December 2015 |
| Time: | 2pm - 3pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Associate Professor Sum Tze Chien |
| Abstract: | Over several decades, soft magnets have been studied for various applications ranging from power transformers, electric motors and current sensors. The types of soft magnets investigated include amorphous, crystalline, and also nanocrystalline ones. Various soft magnets with wide range of properties have been developed using different synthesis techniques such as melt spinning and in-water rotating wheel. Progress has also been made on the processing and post-synthesis treatments (e.g. field annealing, strain annealing) to tailor the soft magnetic properties for different engineering applications. This seminar will review the basics of soft magnets from the perspective of synthesis, structure, properties, and performance. The roles of soft magnets in power transformers, electric motors, and current sensors will be discussed in detail. The last part of the talk will cover the most recent developments and future of power transformers, electric motors, and current sensors. |
| Title: | Cavity opto-mechanics with ultra cold atoms in synthetic gauge field |
| Speaker: | Professor Sankalpa Ghosh |
| Date: | 10 December 2015 |
| Time: | 4pm - 5.30pm |
| Venue: | MAS Executive Classroom 2 (MAS-03-07) |
| Host: | Associate Professor Pinaki Sengupta |
| Abstract: | In this talk we discuss the properties of ultra cold atoms in synthetic abelian and non-abelian
gauge field placed inside a single mode Fabry-Perot cavity. Due to strong atom-photon coupling
the resultant phases of ultra cold atoms in such ambiance shows interesting features. As specific
cases we shall consider the cavity optomechanics of ultra cold fermionic atoms placed in a
synthetic magnetic field ( abelian) and the cavity induced phase-diagram of spin-orbit coupled ultra
cold bosonic atoms ( non-abelian case). We shall particularly emphasize how the bistable features
in the transmission spectrum from the cavity can be used to detect the interesting properties of
ultra cold atoms in such cavity. The talk is primarily based on following two references:
1. Bikash Padhi and Sankalpa Ghosh, Physical Review Letters, Vol 111, 043603 (2013) 2. Bikash Padhi and Sankalpa Ghosh, Physical Review A, Vol. 90, 023627 (2014) |
| Title: | Dark mode meta surfaces and applications |
| Speaker: | Dr Anatole Lupu |
| Date: | 7 December 2015 |
| Time: | 11am – 12pm |
| Venue: | MAS Executive Classroom 1 (PAP-03-06) |
| Host: | Assistant Professor Ranjan Singh |
| Abstract: | The concept of dark states, initially introduced in atomic physics, was borrowed and intensively
developed during the last decades in the fields of photonics, plasmonics and metamaterials. The
interest to the concept of dark states was driven mainly by the ability to obtain sharp spectral features
with steep intensity variation, which are highly desirable for sensing applications. Despite the great
variety of studied designs, most of them are based on the same principle. It consists in associating a
superradiant element bearing an electric dipolar momentum and acting as a radiative or bright mode,
with a subradiant element bearing an electric quadripolar or magnetic dipolar momentum and playing
the role of the dark (or trapped) mode. The mode hybridization induced by a strong coupling between
bright and dark elements leads to the opening of a narrow electromagnetically induced transparency
(EIT) window inside the absorption band.
However the last theoretical advances lead to revisit this commonly shared interpretation. In particular it was evidenced that no dark mode excitation is necessary for the excitation of Fano resonances. They can be described by the interference of bright modes only. In our recent studies we bring further evidence for direct dark mode excitation that is neither relying on hybridization mechanism nor interference effects, and is thus distinctly different from EIT. We experimentally investigated the concept of dark modes and EIT metamaterials in the microwave and optical domains and demonstrate its implementation for both the case of free space and guided wave light propagation configurations. |
| Title: | Biomorphism and electromagnetic signaling in biological structures |
| Speaker: | Professor Eugenio Fazio |
| Date: | 2 December 2015 |
| Time: | 2pm - 3pm |
| Venue: | MAS Executive Classroom 1 (SPMS-MAS-03-06) |
| Host: | Professor N. Zheludev |
| Abstract: | In 1959 A.G. Gurvich and L.D. Gurvich reported the first experimental observation of photon emission during cellular mitosis. Such emission was reported to be originated by both free-radical reactions and organized morphogenetic field at the basic of life. After this pioneering work, biophoton emission by many biological systems was reported in literature. In plants (as well as animals and humans) specific emissions were correlated to stresses and injuries. Moreover, statistical analysis of biophoton temporal distributions revealed incoherent as well as coherent correlations between them, as a signature of the organized quantum states of the emitters. Biophoton emission by germinating seeds was also recorded: recently, it was determined that such emission is partially produced by the bean coat, which acts as a sensor of the environmental conditions. According to the oxygen-carbon dioxide-humidity-temperature levels, the seed coat emits light at specific chromatic bands for internal signaling. In dicotyledon seeds, the shape acts like an optical resonator, whose asymmetric morphology is optimized to focus such emitted light onto the embryo plumula. Even if biophotons are usually reported as an “ultraweak emission”, the light refocusing from the bean shape might generate quite intense fluxes. Beans seem to use such emission to transmit the germination information to the plant embryo. Consequently, electromagnetic signaling could play an important role in nature, and biomorphism could take into account it. Light in nature has three main functionalities: it transmits information, transmits energy and acts like a clock, i.e. a temporal trigger for all biological activities. In germinating seeds (at least in dicotyledon ones) all such functionalities seem to be present, as it should be for isolated systems |
| Title: | The perfect lens and manipulating light on the nanoscale |
| Speaker: | Professor Sir John Pendry |
| Date: | 1 December 2015 |
| Time: | 2.30pm - 3.30pm |
| Venue: | SPMS Lecture Theatre 2 (SPMS-03-03) |
| Host: | Professor N. Zheludev |
| Abstract: | Increasingly we need to control light on a scale much less than the wavelength where concepts such as ray optics are of no assistance. This is particularly true for plasmonic systems where the surface plasmons excited on the surfaces of metals can be compressed into less than a square nanometre. I shall show how transformation optics can be deployed to design sub wavelength optical elements and bring new understanding to the structures that create huge enhancements to the energy density of radiation. |
| Title: | Quasi-stationary states in particle systems with power law interactions |
| Speaker: | Dr Michael Joyce |
| Date: | 30 November 2015 |
| Time: | 4pm – 5pm |
| Venue: | SPMS – LT5 (03-08) |
| Host: | Associate Professor David Wilkowski |
| Abstract: | “Quasi-stationary states” are very long lived non-equilibrium stationary states which
have been observed in various classical many body systems with long-range
interactions. In the first part of my talk I will review the nature of these states - of which
the most notable example are galaxies - and their theoretical interpretation within
the framework of the Vlasov equation. In the second part I will address the question of
how their existence is tied to the nature of the underlying interaction, and in particular
to its properties at large and small scales. Two quite different approaches to the
question lead to the conclusion, born out by numerical study, that the existence of these
states is a robust property only for interactions for which the pair force is non-integrable
at large separation. This motivates a natural classification of interactions into
“"dynamically" long/short range which is distinct from the usual thermodynamic
classification
|
| Title: | Large Quantum and Reactive Molecular Dynamics Simulations of Materials |
| Speaker: | Aiichiro Nakano |
| Date: | 27 November 2015 |
| Time: | 11am – 12pm |
| Venue: | SPMS-LT5 (SPMS-03-08) |
| Host: | Associate Professor Sun Handong |
| Abstract: | We have developed a divide-conquer-recombine algorithmic framework for large quantum molecular dynamics (QMD) and reactive molecular dynamics (RMD) simulations. The algorithms have achieved parallel efficiency over 0.98 on 786,432 IBM Blue Gene/Q processors for 39.8 trillion electronic degrees-of-freedom QMD in the framework of density functional theory and 67.6 billion-atom RMD. We will discuss several applications including (1) 16,616-atom QMD simulation of rapid hydrogen production from water using metallic alloy nanoparticles, (2) 6,400- atom nonadiabatic QMD simulation of exciton dynamics for efficient solar cells, and (3) 112 million-atom RMD simulation of nanocarbon synthesis by high temperature oxidation of SiC nanoparticles. |
| Title: | Towards a new generation of high-performance operational quantum sensors |
| Speaker: | Mr Jean Lautier-Gaud |
| Date: | 3 November 2015 |
| Time: | 4pm – 5pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Associate Professor David Wilkowski |
| Abstract: | After 30 years of academic research in cold atom sciences, intensive developments are being conducted to improve the compactness and the reliability of experimental set-ups in order to transfer such devices from laboratory-based research to an operational utilization.This seminar will be dedicated to the presentation of the Absolute Quantum Gravimeter and the atomic clock that are being developed by Muquans. We will present in detail the principles of operation and the main features of our instruments. Their performances in terms of sensitivity, stability and accuracy and the latest results they achieved will be reviewed. We will then discuss their use to support other research activities (Geodynamics and hydrology, geodesy). |
| Title: | The Compton-Schwarzschild correspondence from extended de Broglie relations |
| Speaker: | Dr Matthew J. Lake |
| Date: | 2 November 2015 |
| Time: | 3pm – 4pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Assistant Professor Tomasz Paterek |
| Abstract: | The Compton wavelength gives the minimum radius within which the mass of a particle may be localized due to quantum effects, while the Schwarzschild radius gives the maximum radius within which the mass of a black hole may be localized due to classical gravity. In a mass-radius diagram, the two lines intersect near the Planck point $(l_P,m_P)$, where quantum gravity effects become significant. Since canonical (non-gravitational) quantum mechanics is based on the concept of wave-particle duality, encapsulated in the de Broglie relations, these relations should break down near $(l_P, m_P)$. It is unclear what physical interpretation can be given to quantum particles with energy $E \gg m_Pc^2$, since they correspond to wavelengths $\lambda \ll l_P$ or time periods $\tau \ll t_P$ in the standard theory. We therefore propose a correction to the standard de Broglie relations, which gives rise to a modified Schr{\" o}dinger equation and a modified expression for the Compton wavelength, which may be extended into the region $E \gg m_Pc^2$. For the proposed modification, we recover the expression for the Schwarzschild radius for $E \gg m_Pc^2$ and the usual Compton formula for $E \ll m_Pc^2$. The sign of the inequality obtained from the uncertainty principle reverses at $m \approx m_P$, so that the Compton wavelength and event horizon size may be interpreted as minimum and maximum radii, respectively. We interpret the additional terms in the modified de Broglie relations as representing the self-gravitation of the wave packet. |
| Title: | Strong acoustic vibrations of bubbles within microfluidic devices or trees |
| Speaker: | Dr Philippe Marmottant |
| Date: | 30 October 2015 |
| Time: | 10.30am – 11.30am |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Associate Professor Claus Dieter Ohl |
| Abstract: | In this talk we will present unusual phenomena occurring in microfluidic bubbles and trees, linked to bubble vibrations. First, we will present the vibration mode of bubbles flattened in microfluidic channel. Bubbles exhibit parametric shape modes that we can carefully investigate under ultrasound. A strong associated streaming occurs near vibrating bubbles, especially when bubbles are close to each other. This streaming would prove helpful to mix liquids. Second we will present our investigations on the nucleation of bubbles in tree vessels, by showing experiments on wood and on leaves. Such explosive bubbles occur by cavitation, since the liquid sap in trees is under extreme negative pressure. They form an emboly that can affect the hydraulic circulation of sap. |
| Title: | Counterterms in Gravity and N=8 Supergravity |
| Speaker: | Professor Lars Brink |
| Date: | 29 October 2015 |
| Time: | 3.30pm – 4.30pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Associate Professor Pinaki Sengupta |
| Abstract: | The vital issue in quantum gravity is how far one can go with ordinary gravity theories in order to have a unitary quantum gravity theory. In the talk I will discuss what kind of quantum corrections that will occur in Einstein gravity and extended gravity theories, especially the so-called N=8 gravity. I will do it in a very special formalism, called the light-cone gauge, in which we only keep the real degrees of freedom, in the simple gravity case the two helicities. I will argue that the reparametrization invariance restricts the possible terms even though it is broken by gauge fixing. |
| Title: | Probing the quantum-classical boundary with compression software |
| Speaker: | Professor Pawel Kurzynski |
| Date: | 27 October 2015 |
| Time: | 11am – 12pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Assistant Professor Tomasz Paterek |
| Abstract: | We recast the problem of the existence of a local-realistic description of quantum measurements using an
algorithmic approach. First, we revisit the information-theoretic Bell inequality due to Braunstein and Caves
[Phys. Rev. Lett. 61, 662 (1988)] that is based on Shannon entropies. Then, we ask if a similar inequality can
be formulated in an algorithmic way. We assume that outcomes in a bipartite Bell scenario are locally
simulated by Turing machines. In particular, each party has a universal Turing machine that outputs local
measurement outcomes. These outcomes are calculated from inputs that encode information about a local
measurement setting and a description of the bipartite system that was sent to both parties. In general, the
system description can encode some additional information that is not available in quantum theory, i.e., local
hidden variables. However, we later show that an analysis of the Kolmogorov complexity of this data allows
us to derive an inequality, similar to the one due to Braunstein and Caves, that must be obeyed by any
theory in which such data exists. Since the Kolmogorov complexity is in general uncomputable, we show that
the inequality can be expressed in terms of compressability of the data generated in such experiments and
that quantum mechanical predictions lead to its violation if one applies known compression algorithms.
Finally, we experimentally demonstrate that compressed outcomes of measurements on photonic pairs do
not satisfy our inequality. We argue that our approach allows us to relax the i.i.d. assumption, namely that
individual bits in the outcome bit-strings are independent identically distributed.
In collaboration with: Hou Shun Poh, Marcin Markiewicz, Alessandro Cere, Dagomir Kaszlikowski and Christian Kurtsiefer Affiliation: 1) Centre for Quantum Technologies, NUS 2) Faculty of Physics, Adam Mickiewicz University, Poznan, Poland |
| Title: | Control and Dynamics of Temporal Localized Structures in Semiconductor Lasers |
| Speaker: | Professor Massimo Giudici |
| Date: | 22 October 2015 |
| Time: | 2pm - 3pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Associate Professor Sun Handong |
| Abstract: | In this presentation I will describe recent experimental results on the control and on the dynamics of temporal localized structures in a passively mode-locked VCSEL. Localized pulses have been proposed as information bits and the possibility of their manipulation opens interesting perspectives for information processing. I will show that a modulation of the pumping current leads to control the position and the speed of the localized pulses within the cavity. In addition to pin the pulses at well defined positions, which enables clocking the bit flow, the pulses can be driven to collide one against the other, thus unveiling the purely repulsive mutual interaction. |
| Title: | Quantum phase estimation using a class of entangled states: NOON-type states |
| Speaker: | Dr Su-Yong Lee |
| Date: | 19 October 2015 |
| Time: | 3pm – 4pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Assistant Professor Tomasz Paterek |
| Abstract: | We address how a quantum phase estimation using a NOON-type state can be controllable by photon counting statistics of a single-mode component. From a simple form of the quantum Fisher information, we show that quantum Cramer-Rao bound (QCRB) can be enhanced with super-Poissonianity of the single-mode component. By introducing a superposition of single-photon and N-photon states as a component state, we particularly show that an unlimited phase sensitivity can be achieved even with a finite energy under an ideal situation. For practical measurement schemes, we consider parity measurement and Fisher information schemes for the NOON-type states. Without photon loss, the latter scheme achieves the QCRB over the entire range of unknown phase shift whereas the former does so in a certain confined range of phase shift. In the presence of loss, we find a robust NOON-type state over the whole range of input photon numbers. Finally, we also propose experimental schemes to generate the NOON-type states. |
| Title: | The reasonable effectiveness of mathematical deformation theory in physics, especially quantum mechanics and maybe elementary particle symmetries |
| Speaker: | Dr Daniel Sternheimer |
| Date: | 16 October 2015 |
| Time: | 4pm – 5pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Associate Professor Pinaki Sengupta |
| Abstract: | In 1960 Wigner marveled about ``the unreasonable effectiveness of mathematics in the natural sciences," referring mainly to physics. In that spirit we shall first explain how a posteriori relativity and quantum mechanics can be obtained from previously known theories using the mathematical theory of deformations. After a tachyonic overview of how the standard model of elementary particles arose from empirically guessed symmetries we indicate how these symmetries could (very reasonably) be obtained from those of relativity using deformations (including quantization). This poses difficult and interesting mathematical problems with potentially challenging applications to physics.” |
| Title: | Mean-field theory for random close packings of non-spherical particles |
| Speaker: | Dr Adrian Baule |
| Date: | 16 September 2015 |
| Time: | 3pm – 4pm |
| Venue: | MAS Executive Classroom 2 (MAS-03-07) |
| Host: | Associate Professor Massimo Pica Ciamarra |
| Abstract: | The question of how densely objects can pack in a given volume is probably one of the most
ancient problems in science and engineering. Previous studies have traditionally focused on
understanding packings of spheres - the shape with the highest symmetry - despite the fact that
practically all shapes in nature exhibit anisotropies. Non-spherical shapes indeed achieve much
denser packing densities than the random close packing of spheres at 64%, as shown in recent
experiments and simulations. However, any systematic theoretical treatment has been elusive so
far due to the strong positional and orientational correlations involved. Here, a mean field theory
based on a statistical treatment of the Voronoi tessellation is discussed, which allows for the
prediction of the random close packing densities of non-spherical particles in good agreement with
empirical data [1]. A phase diagram is presented that describes packings of elongated shapes such
as spherocylinders and dimers in terms of an analytic continuation from the spherical random close
packing [2].
[1] A. Baule, R. Mari, L. Bo, L. Portal, and H. A. Makse, Nature Commun. 4, 2194 (2013) [2] A. Baule and H. A. Makse, Soft Matter 10, 4423 (2014) |
| Title: | Quantum Physics with Ultra-Cold Atoms: from Bose-Einstein Condensation to Quantum Simulation |
| Speaker: | Dr Gerhard Birkl |
| Date: | 10 September 2015 |
| Time: | 11am – 12pm |
| Venue: | MAS Executive Classroom 2 (MAS-03-07) |
| Host: | Associate Professor Rainer Dumke |
| Abstract: | Research on ultra-cold atomic systems has developed an important role in the investigation of fundamental quantum principles and the quantum physical behavior of matter. Two important fields of research can be identified in the study of quantum degenerate gases, such as Bose-Einstein condensates, as well as in quantum simulation and quantum information processing. In this presentation, recent developments in our work towards these objectives are presented: we generate samples of BECs and of single ultracold atoms and apply external potential structures created by optical fields for the manipulation of atomic matter waves and for the development of a scalable architecture for quantum computing with ultra-cold atoms. I show the experimental investigation of Bose-Einstein condensates in external guiding potentials, such as a novel optical storage ring based on the application of conical refraction as a new technique for creation of toroidal potentials and review the experimental progress towards quantum information processing and quantum simulation using neutral atoms in two-dimensional (2D) arrays of optical microtraps as 2D registers of qubits. We describe a scalable quantum information architecture based on micro-fabricated optical elements, simultaneously targeting the important issues of single-site addressability and scalability. |
| Title: | Recent Advances in Organic Optoelectronics |
| Speaker: | Professor Huang Wei |
| Date: | 8 September 2015 |
| Time: | 9am to 10am |
| Venue: | SPMS-LT5 (SPMS-03-08) |
| Host: | Associate Professor Yu Ting |
| Abstract: | In the past few decades, organic optoelectronics has made great progress both in fundamental studies and commercial applications because of their excellent properties, such as solution processable, printable, flexible, low-cost and able to be made at large area. Our recent work is devoted to the development of high-performance organic semiconductors for organic optoelectronics. We will present our recent advancement on rational molecular design of organic semiconductors for organic light-emitting diodes, lasers, memories, chemo-/biosensors, latest research results about ultralong organic phosphorescence and color display technologies. |
| Title: | Controlling and probing weak colloidal interactions from the nano to the micro scale |
| Speaker: | Professor Dr Frank Scheffold |
| Date: | 31 August 2015 |
| Time: | 3pm – 4pm |
| Venue: | Hilbert Space (SPMS-PAP-02-02) |
| Host: | Associate Professor Massimo Pica Ciamarra |
| Abstract: | I will discuss a few examples how we can manipulate and probe soft interactions between small colloidal spheres ranging
from 200nm to several microns. The control and understanding of these interactions is of fundamental interest in
condensed matter physics but also of great importance for the design of new materials. I will mainly focus on three types
of colloids – charge stabilized polymer beads, emulsion droplets and microgels. These three popular model systems are
rather well defined and the properties can be analyzed and tuned by different means. I will first speak about strongly
screened charge stabilized polymer beads with a solid polymer core. These systems essentially behave as hard spheres. I
will present an experiment on a pair of particles where we demonstrate that the interaction potential can be tuned
externally by inducing ‘artifical van-der Waals’ attractive forces by embedding the particles in a very intense diffuse light
cloud [1]. I will then proceed to discuss two colloidal systems where the particles are deformable. First I will discuss the
popular microgel particles where the swelling can be tuned by changing the solvent properties. These ‘smart colloids’ with
tunable size and elasticity have attracted much attention because of their potential use as drug delivery agent or for tuning
the flow properties of complex fluids. Here I will present a novel experiment where we have used STORM superresolution
microscopy (nanoscopy) to study the swelling of individual microgel particles on the nanoscale [2]. Finally I will conclude
by presenting recent results on dense suspensions of nano- and micron sized emulsion droplets where we study the glass
and the jamming transition from the fluid to the highly compressed regime using a combination of confocal microscopy,
low-coherence light scattering and diffusing wave spectroscopy [3,4].
[1] G. Brügger, L.S. Froufe-Pérez, F. Scheffold, and J.J. Saenz, Nature Communications 6, 7460 (2015) [2] G. M. Conley, S. Nöjd, M. Braibanti, P. Schurtenberger, and F. Scheffold,in preparation [3] T. G. Mason and F. Scheffold, Soft Matter, 2014, 10, 7109; M. Braibanti, T. G. Mason and F. Scheffold, in preparation [4] C. Zhang, C.B. O’Donovan, E.I. Corwin, F. Cardinaux, T.G. Mason, M.E. Möbius, F. Scheffold, Phys. Rev. E 91, 032302 (2015) |
| Title: | Processing Information with Small Quantum Devices |
| Speaker: | Dr Marco Tomamichel |
| Date: | 28 August 2015 |
| Time: | 2pm – 3pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Associate Professor Rainer Dumke |
| Abstract: | One of the predominant challenges when engineering future quantum information processors is that complex quantum states are notoriously hard to prepare, maintain and control. Hence, there will be severe limitations on the size of quantum computers for the foreseeable future. On the other hand, most proposals for applications of quantum information processing require very large quantum computers. Here I report on progress on a simple question: Can even a small quantum device offer significant advantages over classical information processing in the context of noisy channel coding? I will also briefly discuss quantum cryptography, where such an advantage has already been demonstrated, and conclude with remarks on the mathematical framework required to tackle such questions. |
| Title: | Topological valley currents in gapped Dirac materials |
| Speaker: | Dr Justin Song |
| Date: | 25 August 2015 |
| Time: | 2pm – 3pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Assistant Professor Chong Yidong |
| Abstract: | Charge carriers in materials are often described as quasiparticles similar to free electrons and can be characterized by effective quantities such as an effective mass. However, electrons in topological materials acquire an additional quantum mechanical property - Berry curvature - that can result in anomalous transport phenomena. I will discus how Berry curvature radically affects carrier dynamics in gapped Dirac systems, such as graphene on hexagonal-boron-nitride (G/h-BN), giving rise to transverse valley currents even in the absence of a magnetic field. Crucially, these valley currents do not depend on the presence of edge states, and persist even in the gapped system bulk. These anomalous carrier dynamics manifest naturally in G/h-BN, displaying large non-local resistances mediated by valley currents in G/h-BN devices. Importantly, topological currents in G/h-BN grant control over the valley index (an internal quantum degree of freedom), and provides a new platform/scheme to access topological characteristics in layered 2D stacks of materials. |
| Title: | Dynamics and Thermodynamics in Many-Body Quantum Systems |
| Speaker: | Professor Dario Poletti |
| Date: | 20 August 2015 |
| Time: | 4pm – 5pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Assistant Professor Pinaki Sengupta |
| Abstract: | I am going to present a personal selection of topics in Many-Body Quantum Dynamics and Thermodynamics. The talk will be divided in two parts: in the first part I will discuss open systems, that is systems in contact with an environment. I will discuss the possible emergence of interesting steady states and of complex dynamical behaviors; in the second part I will discuss how the quantum statistics of particles can strongly affect the functioning of a quantum heat engine showing in which regimes it would be better to use a bosonic or a fermionic gas. |
| Title: | Publishing in Nature Journals |
| Speaker: | Dr. Elisa De Ranieri |
| Date: | 6 August 2015 |
| Time: | 10am to 11am |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Associate Professor Fan Hongjin |
| Abstract: | Nature-branded journals strive to publish papers that report significant advances in research areas
within their respective scopes, with an emphasis on quality rather than quantity. Manuscripts are
handled by in-house, professional editors who are responsible for conducting a rigorous and fair
peer-review process and for each decision up to acceptance of the work for publication. Beside
original research articles, Nature journals publish also review and commentary articles authored by
experts in the field.
This talk aims at providing insight into the editorial process at Nature journals, helping authors in the preparation of their manuscript for submission to Nature journals and reviewers in clarifying how their valuable input enters the editorial decision. In particular, I will discuss the editorial criteria for the different journals within the Nature family, and how the external peer review is handled up to publication. I will give information on frequently asked topics such as embargo policies and the possibility to transfer manuscripts across journals. I will also briefly discuss the evolving publishing landscape in which our journals operate, and mention innovative initiatives run by the Nature publishing Group. |
| Title: | Gravitationally Induced Decoherence |
| Speaker: | Dr Vlatko Vedral |
| Date: | 5 August 2015 |
| Time: | 2.30pm to 3.30pm |
| Venue: | Hilbert Space (PAP-02-02) |
| Host: | Associate Professor David Wilkowski |
| Abstract: | There are numerous speculations as to whether the quantum and the classical domain are separated by a
boundary that might depend (among other things) on the mass and spatial extent of quantum
superpositions. Due to the amazing rate of progress of quantum technologies, experiments in quantum
physics are currently able to manipulate, control and observe superpositions of ever increasing sizes of
objects. We are perhaps for the first time in the position to experimentally ask probing questions regarding
the universality of the superposition principle at the micro to macro boundary. One of the foremost
candidates to “collapse” quantum physics is gravity, since this is the only known force that has not (yet?)
been quantized. I will go through some proposals of gravitationally-induced collapse and show how they could be probed experimentally in a simple interferometric setup. Some induced decoherence proposals are of purely classical gravitational origin (such as the dephasing due to time dilation in different field strengths) while others are possibly a genuine (quantum) form of decoherence due to entanglements with a quantized gravitational field (here, in the absence of the full theory of quantum gravity, we can at least use some heuristic arguments based on linearized gravity). Two key questions are: can we discriminate “gravitational noise” from other sources of noise and can we tell apart the effects of classical and (presumed) quantum gravity on massive superpositions? |
| Title: | Can quantum theory reduce the complexity of classical models? |
| Speaker: | Dr Mile Gu |
| Date: | 3 August 2015 |
| Time: | 9.30am to 10.30am |
| Venue: | CBC Conference Room |
| Host: | Associate Professor Chew Lock Yue |
| Abstract: | We understand complex phenomena around us though predictive models – algorithms that generate future
predictions when given relevant past information. Each model encapsulates a way of understanding future
expectations through past observations. In the spirit of Occam’s razor, the better we can isolate potential
indicators of future behaviour, the greater our understanding. This philosophy privileges simpler models; should
two models make identical predictions, the one that requires less input information is preferred.
Yet, for almost all stochastic processes, even the provably optimal classical models waste information. The amount of input information they demand exceeds the amount of predictive information they output. In this presentation, I outline how we can systematically construct quantum models that break classical bounds, and that the system of minimal entropy that simulates such processes must necessarily harness quantum information. Thus many observed phenomena could be significantly simpler than classically possible should quantum effects be involved, and existing notions of structure and complexity may ultimately depend on the type of information theory we use. This talk is designed to be accessible to non-specialists, and will assume minimal prior knowledge in complexity or quantum theory. References: · Nature Communications 3, 762 · Eur. Phys. J. Plus 129, 191 · `Quantum Logic, its Simpler to be two things at Once.' New Scientist, Issue 2995 |