Aalto Physics Colloquium

Aalto Physics Colloquium is a high-level colloquium series covering all branches of physics at Aalto University. We invite physicists of the highest level from all around the world to tell about their research. The lectures should be on a general level accessible to all physicists. 

2018

15.02.2018 Stefan A. Maier (Imperial College London) Plasmonic and dielectric nanocavities for enhancing light/matter interactions and nanolocalized chemistry

07.02.2018 Hans-Jürgen Butt (MPI for Polymer Research, Germany) Wetting -- a multiscale phenomenon

 

Previous colloquia

Click on the presenter and title to read the abstract.

2016

7.10.2016 Michael Roukes Single-Molecule Analysis with Nanomechanical Systems

3.2.2016 John Clarke The SQUID at 50: From Cosmology to Medicine

2015

24.9.2015 William Phillips Synthetic electromagnetic fields for cold neutral atoms

8.5.2015 Tomasz Dietl Functionalities of ferromagnetic semiconductors

19.3.2015 Hiroshi Amano Illuminating the World by LEDs

3.2.2015 Katherine Freese The Dark Side of the Universe

2014

9.10.2014 Sumio Iijima Carbon nanotubes and related nanomaterials

14.3.2014 Jacqueline Bloch Polariton Condendsates: A Photonic Platform for Quantum Simulation

2013

29.11.2013 Markus Aspelmeyer Schrödinger's Mirrors: Towards Table-Top Experiments at the Interface between Quantum Physics and Gravity

2012

30.11.2012 Ali Yazdani Visualizing Helical Metals on the Surface of Topological Insulators

9.11.2012 Christofer Hierold Carbon nanotube sensors

5.10.2012 Ken Dill How the physics of proteins and proteomes limits the behavior of cells

14.9.2012 Tom Fennell Coulomb phase and emergent magnetic monopoles in spin ice

11.5.2012 Andrew Cleland Mechanical resonators in the quantum regime

23.3.2012 Stefano Liberati Black holes, history and mysteries

24.2.2012 Mikhail Katsnelson Graphene: CERN on the desk

15.2.2012 Jascha Repp Individual Molecules on Thin Insulating Films

20.1.2012 Nicolas Gisin Quantum communications

2011

11.11.2011 Ludwik Leibler Discovery of strong organic liquids

6.10.2011 Bernard Huberman Social media and attention

13.5.2011 Stuart Parkin The Spin on Electronics! - Science and Technology of spin currents in nano-materials and nano-devices

8.4.2011 Marc Mezard Glassy Phase Transitions in Hard Computer Science Problems

11.3.2011 John Pendry Invisible Cloaks & a Perfect Lens

11.2.2011 Andrei Varlamov Superconductivity: approaching the century jubilee

2010

12.11.2010 Katherine Richardson Redefining the Human-Earth Relationship: A Scientist’s view on climate change

8.10.2010 Charlie Marcus Using Spin as a Quantum Bit

10.9.2010 Kurt Binder Computer simulations of critical phenomena and phase behavior of fluids

2.6.2010 Steve Girvin ‘Circuit QED’: Quantum Electrodynamics of Superconducting Circuits and Qubits

16.4.2010 Jaw-Shen Tsai Quantum Coherent Behavior in Macroscopic Objects via Superconducting Devices

5.3.2010 Tilman Esslinger Factories for Quantum Physics

2009

22.10.2009 Carlo Beenakker What is special about graphene?

 

List of abstracts:

Single-Molecule Analysis with Nanomechanical Systems

Michael Roukes, Caltech

NEMS (nanoelectromechanical systems) now enable ultrasensitive measurement of the inertial mass of individual atoms and molecules [1]. We have employed NEMS devices to realize a new form of mass spectrometry (MS) enabling single-molecule analysis, and with it have analyzed individual large-mass biomolecular complexes, one-by-one, in real-time [2]. Recently, we developed an approach that enhances our previously demonstrated capabilities of NEMS-MS by resolving the spatial mass distribution of the individual analytes – in real time with molecular-scale resolution – upon their adsorption onto the NEMS sensor [3]. This new approach, which we term inertial imaging, employs the ensemble of discrete time-correlated perturbations, resulting from each molecular adsorption event, to yield the spatial moments of the mass distribution in real time for each analyte. The lowest moment yields the analyte’s total mass; higher moments reveal its center-of-mass position of adsorption, the analyte’s average diameter, and its spatial skew and kurtosis, etc. Once acquired, these moments can be employed to reconstruct the analyte’s “inertial image”. Unlike conventional imaging, the precision of inertial imaging is not set by wavelength-dependent diffraction phenomena; instead frequency fluctuation processes determine the ultimate limits of spatial resolution. I will describe the ultimate limits of sensitivity expected for NEMS-based analysis. Today’s advanced NEMS devices are already capable of resolving molecular-scale analytes. I will describe current fields of application that can be enabled by this technology including the analysis of intact protein complexes – such as membrane proteins, antibody isoforms, organelles, and viruses, and the pursuit of frontiers in single-cell proteomics and subcellular proteomic imaging.

[1] Naik, A. K., Hanay, M. S., Hiebert, W. K., Feng, X. L. & Roukes, M. L., Towards Single-molecule Nanomechanical Mass Spectrometry. Nature Nanotechnology 4, 445–450 (2009).

[2] Hanay, M. S., Kelber, S. I., Naik, A. K., Chi, D., Hentz, S., Bullard, E. C., Colinet, E., Duraffoug, L. & Roukes, M. L., Single-protein Nanomechanical Mass Spectrometry in Real Time. Nature Nanotechnology, 7, 602-608 (2012).

[3] Hanay, M. S., Kelber, S. I., O'Connell, C. D., Mulvaney, P., Sader, J. E. & Roukes, M. L., Inertial Imaging with Nanomechanical Systems. Nature Nanotechnology 10, 339-344 (2015).

 


The SQUID at 50: From Cosmology to Medicine

John Clarke, Department of Physics, University of California, Berkeley

Following Brian Josephson’s prediction in 1962, Josephson tunneling through an oxide barrier separating two superconducting films was first observed in 1963. Quantum interference in a superconducting ring containing two Josephson junctions was demonstrated in 1964. The first practical SQUIDs (Superconducting QUantum Interference Devices) included a blob of solder frozen around a length of niobium wire. Today’s SQUIDs, fabricated from patterned, multilayer thin films on silicon wafers, offer extraordinary sensitivity to magnetic flux. These SQUIDs can be configured for a wide range of applications, including magnetometers and quantum-limited amplifiers. I describe experiments to search for the axion—a candidate particle for cold dark matter—and to perform magnetic resonance imaging (MRI) in microtesla magnetic fields, four orders of magnitude lower than in clinical MRI systems.

 


Synthetic electromagnetic fields for cold neutral atoms

William D. Phillips, NIST

While cold neutral atoms have acted as quantum simulators for a number  of important quantum many-body problems, one  difficulty is in having  the neutral atoms mimic the behavior of charged particles.  One  approach to this issue is to use optical Raman fields to alter the  atom's energy-momentum dispersion curve to mimic that of a charged  particle in a magnetic vector potential.  By introducing temporal and  spatial variation of that effective vector potential, we have  demonstrated the effects of synthetic electric and magnetic fields on  "synthetically charged" neutral atoms.

 


Functionalities of ferromagnetic semiconductors

Tomasz Dietl, Laboratory of Cryogenic and Spintronic Research, Institute of Physics, Polish Academy of Sciences; also at Institute of Theoretical  Physics, University of Warsaw, Poland and WPI Advanced Institute of Materials Research, Tohoku University, Sendai, Japan

Over the past years, synthesis of epitaxial films combining properties and functionalities of semiconductors, topological insulators, and ferromagnets has evolved into an important field of materials science. Here, I survey recent experimental and theoretical developments in studies of semiconductors and topological insulators containing magnetic ions [1], emphasizing that they not only disentangle many puzzles accumulated over the past decade but have also resulted in discoveries of important functionalities. In particular, I discuss exchange mechanisms accounting for spin ordering in various families of magnetically doped semiconductors and insulators, emphasizing the role of specific nanocharacterization tools in determining charge and spin states, location in the lattice, and distribution of magnetic ions in particular hosts. Furthermore, I present experimental demonstrations and theoretical understanding of magnetization manipulations by electric field and current in structures of ferromagnetic semiconductors. The role of interplay between exchange interactions, spin-orbit coupling, strain, and non-random distributions of magnetic ions is discussed together with examples of fruitful flows of ideas between communities studying different families of ferromagnets.  

[1] T. Dietl and H. Ohno, Rev. Mod. Phys. 86 (2014) 187; T. Dietl et al., arXiv:1412.8062 [Rev. Mod. Phys., to be published].

 


Illuminating the World by LEDs

Hiroshi AMANO, Department of Electrical Engineering and Computer Science, Nagoya University

Worldwide research on the fabrication of GaN-based MIS-type blue LEDs using the HVPE method had almost been completed by the late 1970’s. For compound semiconductor researchers in the early 1980’s, the main research subject was high-frequency wireless communication systems using high-electron-mobility transistors based on AlGaAs/GaAs heterostructure grown by MBE or MOVPE. It was fortunate for us that very few people had started to investigate the MOVPE growth of GaN. So, we could concentrate on improving the quality of GaN and also to control its conductivity. InGaN-based blue LEDs have been commercialized in 1993 and the white LEDs composed of blue LEDs with phosphors have been commercialized in 1999 by the Japanese company. In this presentation, I would like to explain the early stage of research on the growth of GaN and InGaN by MOVPE in the ’80’s and the very important technology developed ‘90s. I would also like to discuss the present status and future prospects for the applications of GaN to optoelectronic and power electronics.

 


The Dark Side of the Universe

Katherine Freese, Director of NORDITA, Stockholm Sweden and George E. Uhlenbeck Professor of Physics, University of Michigan, Ann Arbor, MI 48109

“What is the Universe made of?” This question is the longest outstanding problem in all of modern physics, and it is the most important research topic in cosmology and particle physics today. The reason for the excitement is clear: the bulk of the mass in the Universe consists of a new kind of dark matter particle, and most of us believe its discovery is imminent.  I'll start by discussing the evidence for the existence of dark matter in galaxies, and then show how it fits into a big picture of the Universe containing 5% atoms, 25% dark matter, and 70% dark energy.

Probably the best dark matter candidates are WIMPs (Weakly Interacting Massive Particles).  There are three approaches to experimental searches for WIMPS: at the Large Hadron Collider at CERN in Geneva; in underground laboratory experiments; and with astrophysical searches for dark matter annihilation products. Currently there are claimed detections in multiple experiments --- but they cannot possibly all be right.   Excitement is building but the answer is still unclear. At the end of the talk I'll turn to dark energy and its effect on the fate of the Universe.

 


Carbon nanotubes and related nanomaterials

Sumio Iijima, Graduate School of Science and Technology, Meijo University, National Institute of Advanced Industrial Science and Technology / Nanotube Research Center, and NEC

Atomic structures of carbon nanotubes (CNT) werefirst disclosed by high-resolution electron microscopy(HRTEM)[1].Many unique properties of CNTscome from their cylindrical form withnanometer size diameter, which has brought a new concept of matters into material research community.

Generally modern electron optical technologysuch HRTEM, electron energy loss spectroscopy (EELS) [2] and energy dispersive X-ray analysis (EDX) [3] has supported widely innovative research on nano-materials. Some of typical examples of atomiccharacterizations of nanocarbon materialslike CNTs, graphene sheets and layered nanomaterials will be presented[4].

The second example of nanostructured materials is concerned with the aluminum monohydroxide febrilepsuedoboehmite AlO(OH) [4]. Claymineral boehmiteis a stable crystalline form in nature but pseudoboehmite (PB) is synthesizedas solbut its crystal structure has not been clarified. The basic structure of boehmite is a layer of two staggered edge-shared Al-O octahedraheld together by hydrogen bonds.Based on electron diffractionstudyof PB a crystal structure and morphology of the PB will be proposed for the first time, which seems to be similar to the nanosheet of titania[5].

[1] S. Iijima, Nature 345, 56 (1991).

[2] K. Suenaga et al., Nature 468, 1088 (2010).

[3] K. Suenaga et al., Nature Photonics 6, 503 (2012).

[4] Z. Liu et al., Nature Commnications 5, 4055 (2014).

[5] T. Sasaki et at., J. Phys. Chem. 108, 13088 (2004).

 


Polariton Condendsates: A Photonic Platform for Quantum Simulation

Jacqueline Bloch, Laboratoire de Photonique et de Nanostructures, LPN/CNRS

Optical properties of semiconductor microcavities are governed by bosonic quasi-particles named cavity polaritons, which are light-matter mixed states. Cavity polaritons propagate like photons, but interact strongly with their environment via their matter component. They are bosonic quasi-particles with dissipation due to their finite lifetime. Their quantum state can be fully accessed by optical spectroscopy technics. Moreover the geometry of the cavity can be sculpted using electron beam lithography and etching and allows implementing complex hamiltonians.

After a general introduction on cavity polaritons, I will review recent experimental works performed on polariton condensates confined in microstructures. The aim of the talk is to illustrate the great potential of semiconductor cavities as a new platform to investigate the physics of interacting bosons in a dissipative system and realize quantum simulations.

I will show how we can generate, in one-dimensional cavities, polariton flows which propagate over macroscopic distances (mm), while preserving their spontaneous coherence [1-3]. These propagation properties can be used to implement a variety of optically controlled polariton devices: a non-linear resonant tunneling polariton diode will be addressed, a device very promising to reach the quantum regime of polariton blockade[4].

The second part of the talk will be devoted to the physics of polaritons in lattices. I will discuss polariton condensation in a 1D periodic potential and dynamical formation of gap solitons [5]. I will show how we can sculpt a Fibonacci quasi-periodic potential and observe specific properties of the resulting fractal polariton spectrum [6]. Finally I will show how we can generate polaritons in a 2D honeycomb lattice and directly reveal experimentally not only well resolved Dirac cones but also a flat band [7]. This opens unique avenues to explore the physics of mass-less and of infinitely massive quasi-particles.

[1] Spontaneous formation and optical manipulation of extended polariton condensates, E. Wertz, et al., Nat. Phys. 6, 860 (2010)

[2] Backscattering suppression in supersonic 1D polariton condensates , D. Tanese, et al., Phys. Rev. Lett. 108, 036405 (2012)

[3] Propagation and Amplification Dynamics of 1D Polariton Condensates, E. Wertz et al., Phys. Rev. Lett. 109, 216404 (2012)

[4] Realization of a double barrier resonant tunneling diode for cavity polaritons, H-.S. Nguyen et al., Phys. Rev. Lett. 110, 236601 (2013)

[5] Polariton condensation in solitonic gap states in a one-dimensional periodic potential, D. Tanese et al., Nature Communications 4, 1749 (2013)

[6] Fractal energy spectrum of a polariton gas in a Fibonacci quasi-periodic potential, D. Tanese, arXiv:1311.3453

[7] Direct observation of Dirac cones and a flatband in a honeycomb lattice for polaritons, T. Jacqmin et al., Phys Rev Lett to appear (arXiv:1310.8105)

 


Schrödinger's Mirrors: Towards Table-Top Experiments at the Interface between Quantum Physics and Gravity

Markus Aspelmeyer, University of Vienna (http://aspelmeyer.quantum.at/)

Massive mechanical objects are now becoming available as new systems for quantum science. Devices currently under investigation cover a mass range of more than 17 orders of magnitude - from nanomechanical waveguides of some picogram to macroscopic, kilogram-weight mirrors of gravitational wave detectors. This has fascinating perspectives for quantum foundations: the mass of available mechanical resonators provides access to a hitherto untested parameter regime of macroscopic quantum physics, eventually enabling novel tests at the interface between quantum physics and gravity.

 


Visualizing Topological States of Matter

Ali Yazdani, Princeton University

Soon after the discovery of quantum mechanics it was realized why some solids are insulating (like diamond) and others are highly conducting (like graphite),even though they could be comprised of the same element. Now, 80 years later, the concept of insulators and metals is again being fundamentally revised. During the last few years, it has become apparent that there can be a distinct type of insulator, which can occur because of the topology of electronic wavefunctions in materials comprised of heavier elements. Strong interaction between the spin and the orbital angular momentum of electrons in these compounds alters the sequence in energy of their electronic states. The key consequence of this topological characteristic (and the way to distinguish a topological insulator from an ordinary one) is the presence of metallic electrons with helical spin texture at their surfaces. I will describe experiments that directly visualize these novel quantum states of matter and demonstrate their unusual properties through spectroscopic mapping with the scanning tunneling microscope (STM). These experiments show that the spin texture of these states protects them against backscattering and localization. These states appear to penetrate through barriers that stop other electronic states. I will describe these experiments and our most recent attempts to create and visualize other topological states such as creation of Majorana fermions, which are another instance of boundary state associated with topological order.

 


Carbon Nanotube Sensors

Christofer Hierold, ETH

Carbon nanotubes exhibit a number of excellent mechanical and electronic properties as functional materials in sensors. In particular single walled carbon nanotubes (SWNT) are known for their band gap modulation due to mechanical strain, or electronic property-changes due to interaction with surrounding molecules, but also for their ultra-low power consumption. However, successful technology transfer to production and development of affordable products based on CNTs is threatened by the lack of solutions for fabrication and integration of these materials. We present results on individual SWNTs as functional material in field effect transistors, mechanical and chemical sensors. We discuss the influence of process variations on the properties of SWNT devices, and options for sensor fabrication.

 


How does protein physics limit the behaviors and evolution of cells?

Ken Dill, Stony Brook University

Biological cells have many behaviors, developed through evolution. These behaviors must obey the laws of physics. We combine the knowledge of the physical properties of proteins that are now contained in databases with simple physical models, to make predictions about various physical limits of cells. We consider why cells are so sensitive to temperature, why their internal protein densities are so high, and what are the various speed limits imposed by protein folding, diffusion, and synthesis, for example.

 


Coulomb phase and emergent magnetic monopoles in spin ice

Tom Fennell, Paul Scherrer Institut, Switzerland

Fennell

A frustrated magnet is one in which all pair-wise interactions cannot be minimized due to competing interactions or geometry (e.g. antiferromagnetically coupled spins on a triangular lattice). Ground states are typically constructed by enforcing a local constraint on every sub-unit of the lattice, usually resulting in an extensively degenerate manifold of ground states. In the case of spin ices, the local constraint is known as the ice rule, and is a magnetic analogue of the Bernal-Fowler ice rules, which originally described degenerate hydrogen bonding configurations in ice crystals. As a consequence of the topological properties of the ice rules, a spin ice can be described by an effective theory in which the ice rule obeying ground states map to a free magnetic field. Then, the excitations (or ice rule defects) are emergent quasiparticles which take the role of magnetic monopoles. These emergent monopoles are deconfined, because the macroscopic ground state degeneracy allows them to diffuse across the lattice with local ground state configurations reestablished in their wake, while the particular interaction scheme of real spin ices such as Ho2Ti2O7 and Dy2Ti2O7 gives them a magnetic Coulomb interaction. I will discuss the origins and extent of the analogies between ice and spin ice, and “emergent” and “fundamental” magnetic monopoles; neutron scattering experiments demonstrating the required form of underlying spin correlations (or monopole vacuum); the role of the monopoles in controlling the dynamics of spin ices at low temperature (by which means they can also be investigated); and the possibility of “quantum spin ice” in Tb2Ti2O7.

 


Mechanical resonators in the quantum regime

Andrew Cleland, University of CaliforniaCleland

The superconducting quantum circuits group at UC Santa Barbara has spent the past ten years developing superconducting and nanomechanical systems for fundamental experiments in quantum mechanics; our ultimate goal is to build a superconducting quantum computer. The Josephson junction, a fundamental superconducting device analogous to a transistor, provides an extremely nonlinear electrical circuit element that can be used as an “electronic atom”, enabling the detection and manipulation of single quanta of energy, as well as demonstrations of simple quantum algorithms. We have used this device to demonstrate full quantum control over microwave-frequency photons in electromagnetic resonators, and more recently demonstrate ground-state cooling of a macroscopic mechanical resonator as well as manipulate individual phonons, the quanta of mechanical vibrations.

Cleland

“Generation of Fock states in a superconducting quantum circuit “, M. Hofheinz et al., Nature 454, 310-314 (2008)
“Synthesizing arbitrary quantum states in a superconducting resonator”, M. Hofheinz et al., Nature 459, 546-549 (2009)
“Quantum ground state and single-phonon control of a mechanical resonator”, A.D. O'Connell et al., Nature 464, 697-703 (2010)
“Implementing the Quantum von Neumann Architecture with Superconducting Circuits”, M. Mariantoni et al., Science 334, 61 (2011)

 


Black holes, history and mysteries

Stefano Liberati, SISSA, TriesteLiberati

Black holes, regions of spacetime where the curvature is so strong that even light is not able to escape, are among the most extreme and mysterious manifestations of nature. As the famous astrophysicists Chandrasekhar said they are "the most perfect macroscopic object there are in the universe: the only elements in their construction are our concepts of space and time." Black holes are implicated in a wide range of astrophysical phenomena, including many of the most energetic events in the Universe but they also represent the most striking bridge between classical General relativity and quantum physics. In this colloquium I will review the long history that lead to the discovery and understanding of these extreme spacetimes and discuss how condensed matter physics is now playing a role in further exploring their nature and possibly the very essence of the fabric of reality.

 

 

 

 


Graphene: CERN on the desk

Mikhail Katsnelson, Radboud University NijmegenKatsnelson

Graphene, a recently (2004) discovered two-dimensional allotrope of carbon (this discovery was awarded by Nobel Prize in physics 2010), has initiated a huge activity in physics, chemistry and materials science, mainly, for three reasons. First, a peculiar character of charge carriers in this material makes it a “CERN on the desk” allowing us to simulate subtle and hardly achievable effects of high energy physics. Second, it is the simplest possible membrane, an ideal testbed for statistical physics in two dimensions. Last not least, being the first truly two-dimensional material (just one atom thick) it promises brilliant perspectives for the next generation of electronics which uses mainly only surface of materials. I will tell about the first aspect of the graphene physics, some unexpected relations between materials science and quantum field theory and high-energy physics.

Electrons and holes in this material have properties similar to ultrarelativistic particles (two-dimensional analog of massless Dirac fermions). This leads to some unusual and even counterintuitive phenomena, such as finite conductivity in the limit of zero charge carrier concentration (quantum transport by evanescent waves) or transmission of electrons through high and broad potential barriers with a high probability (Klein tunneling). This allows us to study subtle effects of relativistic quantum mechanics and quantum field theory in condensed-matter experiments, without accelerators and colliders. Some of these effects were considered as practically unreachable. Apart from the Klein tunneling, this is, for example, a vacuum reconstruction near supercritical charges predicted many years ago for collisions of ultra-heavy ions. Another interesting class of quantum-relativistic phenomena is related with corrugations of graphene, which are unavoidable for any two-dimensional systems at finite temperature. As a result, one has not just massless Dirac fermions but massless Dirac fermions in curved space. Gauge fields, of the central concepts of modern physics, are quite real in graphene and one can manipulate them just applying mechanical stress.

 


Individual Molecules on Thin Insulating Films

Jascha Repp, University of Regensburg

Scanning probe microscopy is an ideal tool to study the properties of individual molecules on the atomic length-scale in a well-defined environment. However, if a molecule is adsorbed onto a metal surface, its molecular identity is partially lost because of the hybridization of its electronic states with the ones of the support. The use of ultra-thin insulating films on metal substrates allows for the almost unperturbed electronic properties of molecules to be studied by means of the scanning probe microscopy techniques as it facilitates an electronic decoupling from the substrate. We investigated different kind of π–conjugated molecules in a combined scanning tunneling (STM) and atomic force microscope (AFM). Whereas both measurement channels show features with sub-molecular resolution, the information they can provide is truly complementary. For example, STM allows the direct imaging of the unperturbed molecular orbitals, whereas the AFM channel directly reveals the bonding geometry in artificial molecular structures and configurational changes in molecular switches.

 


Quantum Non-locality

Nicolas Gisin, University of Geneva Gisin

Quantum communications is the art of transferring a quantum state from one location to a distant one. On the application side, quantum communication is already relatively advanced with Quantum Random Number Generators and Quantum Key Distribution (QKD) systems having found niche markets. However, on the academic research side quantum communication has still a long way to go until a functional quantum repeater can extend the distances to continental scales. Quantum repeaters are based on quantum teleportation, the most fascinating application of entanglement. Additionally, quantum repeaters require quantum memories with memory times close to a second; this represents one grand challenge for quantum communication. Another grand challenge is the demonstration of device independent QKD.

 

 

 


Discovery of strong organic liquids

Ludwik Leibler, ESPCI ParisTech Leibler

Many aspects of glass formation remain deeply puzzling. During cooling, silica, and a few other inorganic compounds called strong liquids gradually increase their viscosity over a wide temperature range and become so viscous that for all practical purposes they behave like hard solids, glasses. Yet, silica, the archetype of glass, is quite unique. In striking contrast to silica, all organic and polymer glass forming liquids increase their viscosity and rigidify abruptly when cooled. In silica, atoms are linked into a disordered network by chemical bonds. We have designed and synthesized organic networks able to rearrange their topology by exchange reactions without link breaking. Unlike organic compounds and polymers whose viscosity varies abruptly near glass transition, these networks show Arrhenius-like gradual viscosity variations just like vitreous silica. The expansion coefficient studies confirm that topology freezing leads to a glass transition. From materials science point of view, permanently cross-linked polymers, either thermosets or rubbers, have outstanding mechanical properties and solvent resistance, but they cannot be processed and reshaped once synthesized. Non-cross-linked polymers and those with reversible cross-links are processable, but they are soluble. Our materials made by epoxy chemistry can be soft and elastic like rubbers or hard like thermosets. Yet, they are insoluble and processable and thus represent a new class of polymers. Like silica, they can be wrought and welded to make complex objects by local heating without the use of molds. The concept of a glass, made by reversible topology freezing in epoxy networks can be readily scaled up for applications and generalized to other chemistries.

 


Social media and attention

Bernardo Huberman, HP ResearchHuberman

We are witnessing a momentous transformation in the way people interact and exchange information with each other. Content is now co-produced, shared, classified, and rated on the Web by millions of people, while attention is becoming the ephemeral and valuable resource that everyone seeks to acquire. This talk will describe how social attention determines the production and consumption of content within social media, how it can be used to predict future trends, and its role in determining the public agenda.

 

 

 

 


The Spin on Electronics! - Science and Technology of spin currents in nano-materials and nano-devices

Stuart Parkin, IBM Almaden Research CenterParkin

Recent advances in manipulating spin-polarized electron currents in atomically engineered magnetic heterostructures make possible entirely new classes of sensor, memory and logic devices - a research field generally referred to as spintronics [1]. A magnetic recording read head, initially formed from a spin-valve, and more recently by a magnetic tunnel junction, has enabled a 1,000-fold increase in the storage capacity of hard disk drives since 1997. The very low cost of disk drives and the high performance and reliability of solid state memories, may be combined in the Racetrack Memory [2]. The Racetrack Memory is a novel three dimensional technology which stores information as a series of magnetic domain walls in nanowires, manipulated by spin polarized currents. Spintronic devices may even allow for “plastic” devices that mimic synaptic switches in the brain, thereby allowing for the possibility of very low power computing architectures.

[1] S.S.P. Parkin et al. Proc. IEEE 91, 661-680 (2003)
[2] Science 320, 190 (2008)Scientific American (June, 2009).

 


Glassy Phase Transitions in Hard Computer Science Problems

Marc Mézard, CNRS - Université Paris SudMezard

Given a large set of discrete variables, and some constraints between them, is there a way to choose the variables so that all constraints are satisfied? This "satisfiability" problem is one of the most fundamental complex optimization problems. It also has very concrete applications, for instance in computer chip testing or in error correcting codes.

There exist deep connections between this fundamental problem in computer science and structural glasses. By increasing the density of constraints in random satisfiability, one meets a phase transition to a glass phase, associated with a structural change in the satisfiability problem at the origin of computational hardness.

This talk will give an introduction to the recent progress, both conceptual and algorithmic, obtained in hard computer science problems using statistical physics concepts and methods.

 


Invisible Cloaks & a Perfect Lens

John Pendry, Imperial College LondonPendry

Electromagnetism encompasses much of modern technology. Its influence rests on our ability to deploy materials that can control the component electric and magnetic fields. A new class of materials has created some extraordinary possibilities such as a negative refractive index, and lenses whose resolution is limited only by the precision with which we can manufacture them. Cloaks have been designed and built that hide objects within them, but remain completely invisible to external observers. The new materials, named metamaterials, have properties determined as much by their internal physical structure as by their chemical composition and the radical new properties to which they give access promise to transform our ability to control much of the electromagnetic spectrum.

 


Superconductivity: approaching the century jubilee

Andrei Varlamov, Institute of Superconductivity and Innovative Materials, Italian National Research Council Varlamov

The lecture is devoted to discussion of one of the most bright and unusual discoveries of XX century Physics: superconductivity. First we discuss the story of discovery of this phenomenon, hopes and delusions followed it, speak about a long half-century of the search for new superconductors and accumulation of the experimental facts. Then we pass to the remarkable phenomenological theory of superconductivity created by Russian physicists Vitaly Ginzburg and Lev Landau. In those times when this theory was developed, the microscopic origin of this quantum phenomenon still could not be recognized, but even being phenomenological in its nature the Ginzburg-Landau theory allowed to systemize and predict a lot of superconductor’s properties. Basing on it A.A.Abrikosov discovered soon the fundamentally new class of superconductors: superconductors of the second type. At the end of this part of lecture I will present the basic ideas of the microscopic theory of superconductivity, created in 1957 by three American scientists J.Bardeen, L. Cooper and R.Schriffer. This, first period of studies of superconductivity was superseded by the second one: the period of the chase for high critical temperatures and magnetic fields, proposals of the theoretical concepts for alternative to the BCS mechanisms of superconductivity and development first practical applications. At the same time English physicist Brian Josephson predicted the phenomenon of a weak superconductivity, which opened the new fields of applicability of superconductivity. The third period in development of superconductivity started in 1986 with the discovery by Swiss scientists Alex Muller and George Bednortz of the new class of oxide superconductors which critical temperatures in short time overcame crucial for practical applications the “nitrogen limit” - 77 К. The author tells about this last, fascinating, period being its immediate participant.

 


Redefining the Human-Earth Relationship: A Scientist’s view on climate change

Katherine Richardson, University of CopenhagenRichardson

It is seldom that advances in scientific understanding cause the reverberations in society as a whole as is the case with climate change. Possibly the last time that this happened to such a degree was when Darwin introduced the concept of evolution in 1859. As in the case of evolution, the recognition of human-induced climate change challenges society’s perception of the role of humans in nature. The Bible teaches us that humans are above nature and should dominate nature but Darwin showed us we are a part of nature: a species like all others. Now, science is telling us that that the combined activities of that species influence the way the Earth System functions. This is difficult for many non-scientists to accept but the evidence that humans are influencing the Earth System is overwhelming and it is not only the climate system which is affected. The knowledge that our species is influencing the Earth System brings with it the responsibility to manage our relationship with the planet. In this talk, some of the evidence for human influence on the climate system is reviewed and suggestions as to how management of the human-Earth relationship might be developed are presented.

 


Using Spin as a Quantum Bit

Charles Marcus, Harvard UniversityMarcus

Over the last two decades, our understanding of the uses and limitations of quantum entanglement for efficient information processing and computation has developed remarkably quickly. Theoretically, it appears possible to build machines that remain coherent in a quantum mechanical sense throughout a computation, including error correction, and that in some instances this gives the machine computational power. Despite great progress in our understanding, however, the challenge of building machines (electrical, optical, or mechanical) that can demonstrate these principles remains a profound challenge.

This talk will review recent progress of one approach, which is using electron spin in semiconductor quantum dots as the holder of quantum information. This approach combines semiconductor nanofabrication, electrical measurements at temperatures below 0.1 kelvin, and microwave manipulation of spin and charge. And so far, this is all needed to get a mere one or two quantum bits to work. Extending this approach to several, and ultimately thousands or millions of devices, working together appears almost unimaginably difficult. However, the effort seems justified by the promise, or hope, of building fully controllable quantum "chips."

Work supported by the US DoD, IARPA, DARPA and Harvard University.MarcusMarcus

 

 

 

 

 

 

 

 


Computer simulations of critical phenomena and phase behavior of fluids

Kurt Binder, University of MainzBinder

Computer simulation techniques such as Monte Carlo (MC) and Molecular Dynamics (MD) methods yield numerically exact information (apart from statistical errors) on model systems of classical statistical mechanics. However, a systematic limitation is the restriction to a finite (and often rather small) particle number N (or box linear dimension L, respectively). This limitation is particularly restrictive near critical points (due to the divergence of the correlation length of the order parameter) and for the study of phase equilibria (possibly involving interfaces, droplets, etc.). Starting out with simple lattice gas (Ising) models, finite size scaling analysis have been developed to overcome this limitation. These techniques work for both simple Lennard-Jones fluids and their mixtures, including generalizations to approximate models for quadrupolar fluids such as carbon dioxide, benzene etc. and various mixtures, whose phase behaviour can be predicted. A combination of MC and MD allows the study of dynamic critical phenomena, and specialised techniques (umbrella sampling plus thermodynamic integration) yield the surface free energy of droplets as function of droplet size. Thus, computer simulation has become a versatile and widely applicable tool for the study of fluids.

 


‘Circuit QED’: Quantum Electrodynamics of Superconducting Circuits and Qubits

Steven M. Girvin, Yale UniversityGirvin

‘Circuit QED’ [1] explores quantum optics and cavity quantum electrodynamics in electrical circuits. Josephson junction ‘atoms’ placed inside an on-chip resonant cavity can interact with microwave photons with extremely strong coupling. Even though microwave photons have times less energy than visible photons, very rapid recent experimental progress has led to the ability to see the particle nature of microwaves and create arbitrary superposition states of different numbers of photons. In addition to being a new test bed for quantum mechanics and quantum optics in the ultra-strong coupling regime, the circuit QED paradigm has many promising features for quantum computation. It is now possible to routinely entangle two qubits with high fidelity, and perform simple quantum algorithms on small quantum processors.

[1] ‘Wiring up quantum systems,’ R.J. Schoelkopf and S.M. Girvin, Nature 451, 664 (2008).

 


Quantum Coherent Behavior in Macroscopic Objects via Superconducting Devices

Jaw-Shen Tsai, NEC Nano Electronics Research Laboratories & Riken Advanced Science InstituteTsai

Can macroscopic object such as a Josephson junction behave like a quantum object with full quantum coherence, and where is the boundary between classical and quantum worlds? The secondary macroscopic quantum effect associated with the Josephson junction produces band structures in the energy spectrum, so in such system, besides the usual BCS solitary ground state associated with superconductivity, there are multiple numbers of macroscopic quantum states with aharmonic energy separations. A concrete demonstration of quantum coherence in such system can be realized by creation of a coherent superposition state involving two of these states. We demonstrated a quantum coherent oscillation between two lowest-energy states in a small Josephson junction system, demonstrating the creation of such coherent state with controls in amplitude and phase [1]. Such object can be considered as an artificial atom. We have been utilizing it to pursue the prospect of quantum information processing. I this direction, dynamical creation of quantum entangled states [2]; quantum controlled-NOT logic gate [3]; simple quantum information manipulation [4] were demonstrated. The Josephson artificial atom can also be used to realize the concept of quantum optics that initially developed for the natural atoms. In this direction, single artificial atom lasing [5], as well as macroscopic quantum scatterings [6] were demonstrated.

[1] Y. Nakamura, Yu. A. Pashkin, J. S. Tsai, Nature, 398, 786, 1999 
[2] Yu. A. Pashkin, T. Yamamoto, O. Astafiev, Y. Nakamura, D. V. Averin and J. S. Tsai, Nature, 421, 823, 2003 
[3] T. Yamamoto, Yu. Y. Pashkin, O. Astafiev, Y. Nakamura, and J. S. Tsai, Nature 425, 941, 2003
[4] A. O. Niskanen, K. Harrabi, F. Yoshihara, Y. Nakamura, S. Lloyd and J. S. Tsai, Science, 316, 723, 2007 
[5] O. Astafiev, K. Inomata, A. O. Niskanen, T. Yamamoto, Yu. A. Pashkin, Y. Nakamura & J. S. Tsai, Nature, 449, 588, 2007
[6] O. Astafiev, A. M. Zagoskin, A. A. Abdumalikov, Jr., Yu. A. Pashkin, T. Yamamoto, K. Inomata, Y. Nakamura, J. S. Tsai, Science, to be published

 


Factories for Quantum Physics

Tilman Esslinger, ETH ZurichEsslinger

In a cloud of atoms which is cooled to almost zero temperature the particles come practically to a standstill and one may wonder whether anything interesting can happen in such a collection of resting atoms. Yet it turns out that these ultralow temperatures provide an exceptionally clear view on macroscopic quantum phenomena and fascinating quantum effects. Indeed, a large variety of different Hamiltonians can be engineered with quantum gases making their physics accessible. This includes fundamental concepts of statistical physics, condensed matter physics and quantum optics. In my talk I will report on intriguing breakthroughs and address major challenges lying ahead.

 

 


What is special about graphene?

Carlo Beenakker, University of LeidenBeenakker

Page content by: communications-phys [at] aalto [dot] fi (Department of Physics) | Last updated: 06.02.2018.