This will be an unusual sort of talk. What I will do is tell you a little bit about these two great men, who they were and what they did. My aim will to give you an impression of their place in the history of science and why what they did was important. However, at the same time I will describe a thought experiment that will illustrate the gravitational theories of the two men.
Ultra sensitive nanomechanical sensing platforms for label-free qualitative and quantitative bio-analytical measurements will change the way we perform diagnostics. Mechanical sensors oscillating in a liquid pose a challenge since they are highly dampened, we will show approaches to overcome this. The assays require minimal sample preparation and provide highly-sensitive, fast and specific bio-assays results in a miniaturized format. The expression profile of noncoding RNAs (miRNAs) can be used as circulating bio-markers and has been linked to the diagnosis and prognosis of a number of human cancers and other diseases. siRNA are designed to regulate gene expression in specific tissues. The molecules we are investigating are enabling the temporal opening of the blood-brain barrier for drug treatment. We demonstrate that cantilever array sensors are capable to directly track the pharmacokinetics of therapeutic siRNA molecules in tissues and the early detection of miRNA biomarker molecules, which indicate organ pathology induced by adverse drug effects measured from blood serum. Further measurements in the field of cell growth analysis and protein detection will be shown. These new platforms pave the way for fast ultra sensitive, multiplexed, selective, portable nanomechanical diagnostic devices.
Modern computer technology is based on the very large scale integration of digital logic circuits onto semiconductor wafers. The circuits are based on complementary arrangements of MOSFETs (metal-oxide-semiconductor field effect transistors) to implement the Boolean logic gates required for data processing - the so called CMOS technology. Over the last decades, the miniaturization of these transistor circuits has followed Moore's law, with the number of transistors per unit area doubling roughly every 18 months. Today, a typical CPU contains over two billion transistors. Silicon has long been the semiconductor of choice for CMOS applications. Better tailoring of the material properties is often achieved through alloying and Silicon-Germanium (SiGe) systems have also been introduced. More recently, alloying SiGe with dilute quantities of carbon has also been explored. The carbon helps to compensate for the biaxial strain suffered by SiGe layers grown on Si and is also known to suppress the diffusion of p-type dopants during wafer growth. In order to maintain the efficiency of such devices, it is important that the charge transport properties of the material are not unduly degraded. For carbon in SiGe there are likely to be conflicting effects: on the one hand, the modification of the band structure due to the tensile biaxial strain introduced by the carbon atoms ought to improve the transport properties of electrons, which would see a smaller effective mass. On the other, the perturbation to the crystal lattice due to carbon substitution will also introduce 'alloy scattering', which would be detrimental to the electron mobility. Moreover, due to the much small size and larger electronegativity of the carbon atom relative to Si or Ge, it is possible that the carbon may form a localised state. A method of calculating the alloy scattering potential of substitutional atoms based on first-principles band structure calculations has been developed. This has been applied to the problem of substitutional carbon in silicon. The effect of alloy scattering on the electron (n-type) transport properties has been calculated and compared to experiment. We find that, although this effect is large compared to alloy scattering in SiGe, it is not large enough to account for the observed degradation of the mobility. Evidence is offered that the reduction in mobility is actually due to electrically active interstitials. Deeper exploration has also been pursed into " The effect of biaxial strain on the alloy scattering potential for electrons (n-type carriers) " The contributions of chemical substitution and ionic relaxation to the alloy scattering potential " Models of the virtual crystal approximation implemented for band structure calculations " Application of the method to hole (p-type) transport [1] Tyndall National Institute, Cork, Ireland [2] Dept. of Physics, UCC, Cork, Ireland
For a period, 30 - 50 years ago, the favoured way of constructing quantum gravity was the canonical quantization programme. One wrote down G.R. in canonical form, replaced the momenta by operators, and one had a quantum theory. This does not work. The gauge group of G.R. is too complicated. The problem is the arbitrariness of the time. Allowing all possible times is equivalent to allowing no time at all. One needs to make a particular choice of time to construct a Schroedinger equation. How to pick one? I will argue that an `intrinsic' time, one that is proportional to the log of the 3-volume, works wonderfully well. This will be a `no-tech' talk and I will try and make it as general as possible. I will only assume some understanding of Hamiltonian mechanics.
Our Galaxy is largely empty. By terrestrial standards the space between the stars can be considered a perfect vacuum: the average particle density in the solar neighborhood is roughly a factor of 1019 less than in the terrestrial atmosphere at sea level. However the highly diluted material present between the stars, the so-called InterStellar Medium (ISM), plays a central role in the chemical evolution of the Galaxy. Today, more than 160 species have been identified in space, and are evidence of a rich and exotic chemistry. Identifying the molecular fingerprints of interstellar candidates has proved a large challenge in the laboratory, simulating the cold harsh conditions of the interstellar medium, in combination with sensitive spectroscopic techniques. Examples of these techniques will be presented. Particular attention will be placed on the enigmatic Diffuse Interstellar Bands, a series of broad absorption lines on the interstellar extinction curve and one of the oldest mysteries in astronomy.
Nonlinear optical conversions of femtosecond pulses are both of great interest from the fundamental point of view as well as a very versatile tool. In particular optical parametric amplifiers (OPA) allow the generation of tailored pulses from the deep UV to the middle IR. If the OPA is not seeded by a weak signal, it still generates output light due to the amplification of the vacuum fluctuations of the electromagnetic field. We were recently able to "count" the modes of these fluctuations. Advanced OPAs rely on seeding with continua generated in bulk material. These continua not only allow the generation of pulses down to the 5 fs regime, but are also an unprecedented coherent light source for the probing of the ultrafast and not so fast dynamics and kinetics in physical and chemical processes. I will present the fundamentals and operation of our transient spectrometer that covers three octaves in spectrum and eleven orders of magnitude in time. Dynamic processes can be observed with their specific signatures ranging from 225 to 1700 nm, from few femtoseconds to one millisecond. To illustrate this potential, I will use examples from elementary chemical processes.
Optical techniques for probing surface and interface nanostructure are introduced and recent developments in the field will be discussed. These techniques offer significant advantages over conventional surface probes: all pressure ranges of gas–condensed matter interfaces are accessible and liquid–liquid, liquid–solid and solid–solid interfaces can be probed, due to the large penetration depth of the optical radiation. Sensitivity and discrimination from the bulk are the two challenges facing optical techniques in probing surface and interface structure. Where instrumental improvements have resulted in enhanced sensitivity, conventional optical techniques can be used to characterize heterogeneous adsorbed nanostructures on a substrate, often with sub-monolayer resolution. A separate class of techniques, which includes reflection anisotropy spectroscopy, and various nonlinear optical probes, uses the difference in symmetry between the bulk and the surface or interface to suppress the bulk contribution. State-of-the-art examples will be presented and recent developments in ab initio calculations of the linear optical response of nanostructures outlined.
We are living at the dawn of the quantum information revolution. Quantum communication and quantum cryptography provide fundamentally higher speeds and greater security than their conventional counterparts. Furthermore quantum computation offers immense computing power well beyond current computing capabilities. However the fragility of quantum information presents a serious challenge. Topological protection of quantum information against errors circumvents demanding engineering approaches to fault-tolerance. It comes as an intrinsic property of certain quantum materials where quantum information is stored and processed in a way that is sensitive only to their global, topological structure. I will briefly introduce topological quantum computation and information processing and then review relevant recent theoretical and experimental developments, naturally with emphasis on our own achievements.
The lack of a significant spin-orbit and hyperfine interaction makes spins long-living in organic materials [1]. This however also means that they cannot be easily manipulated. As such organic molecules appear as a system for spin-electronic conceptually different from standard metals and semiconductors [2]. This means that new strategies for reading, writing and manipulating spins need to be designed. In particular there is a growing expectation on the possibility of addressing spins with electric fields and currents, via manipulation of either the charge state of a molecule [3] or its geometry [4]. In this lecture I will overview recent ideas in the field of molecular spintronics, in particular highlighting the various new emerging concepts in relation with the available materials sets.
The development of a technique is presented for the measurement of accurate temperature in low pressure laminar sooting flames. Thus far, few experimental attempts have managed to measure temperature with sufficient accuracy in these environments. Here, we present for the first time the application of blue diode lasers in conjunction with indium Two Line Atomic Fluorescence (TLAF) to achieve this goal. The results presented here are deemed of quantitative utility and have been used in a model flame to study the chemical kinetics of soot formation.
All stars, low mass and high, young and extremely old, appear to eject matter from their surfaces. The physics behind this ubiquitous mass-loss must depend, however, on the mass and age of the star, and changes with the star's position in the colour-magnitude (Hertzsrpung-Russell) Diagram. For stars burning hydrogen in their cores astronomers have a good idea of the mechanisms that drive mass loss, however, once stars exhaust this hydrogen things are not so clear. For the evolved red giants and red supergiants, like Betelgeuse, we simply do not have a good idea of what is happening and thus we have no predictive models. I will describe the parts we think we understand and the highlight the problems with the "plan B" theories for evolved red stars that require magnetic fields. New observations, hopefully, will shed light on the physics and at least eliminate some hypotheses.
We present new methods to speed-up manipulations of cold atoms in a harmonic trap: a shortcut to adiabatic expansion of the trap and a shortcut to adiabatic transport of the trap. In both cases, the final atomic state is the same as in the adiabatic process, but the state is achieved with fidelity one in arbitrarily short time, keeping the same populations of vibrational levels in the initial and final trap. These methods can also be generalized to condensates and we are examining their stability concerning different types of errors like noise errors and systematic errors. Moreover, we present shortcuts to adiabatic passage from one internal atomic state to another. Again we especially examine and compare the stability of different schemes concerning different types of errors.
Biophotonics is a new multidisciplinary area that use light based technologies in medicine and the life sciences. The seminar will briefly introduce vibrational spectroscopic techniques such as Raman and InfraRed spectroscopy and will focus on the use of vibrational spectroscopy for biomedical applications such as cervical cancer screening and diagnosis.
Energy band gaps are observed to increase with decreasing diameter due to quantum confinement in quasi-one-dimensional (1D) semiconductor nanostructures or nanowires. A similar effect is observed in semimetal nanowires and for sufficiently small wire diameters a bandgap is induced: the semimetal nanowire becomes a semiconductor. It is demonstrated that on the length scale on which the semimetal-semiconductor transition occurs, the use of bandgap engineering allows for the design of a field effect transistor operating near atomic dimensions and eliminates the need for introducing impurity atoms or doping to modify the materials electrical properties. By removing the requirement to supply free carriers through doping, quantum confinement allows for a materials engineering to overcome one of the fundamental physical challenges to making sub-5 nm transistors, thereby allowing a new option for scaling electronic devices to near atomic limits. As the dimensions of nanowires are scaled further until the wire consists of a chain of atoms, electron correlations become dominant and the idea of single charge carriers or quasi-particles breaks down. This effect for metal atomic chains is presented.
Quantum Chromodynamics is the theory of the strong interaction, responsible for binding fundamental particles inextricably inside the nucleus of hadrons. I will discuss this theory and its role in the Standard Model of particle physics and describe how numerical simulations of the theory are crucial to make predictions of confinement phenomenology.
Gamma-ray bursts (GRBs), flashes of gamma ray that release as much as 10^{53} erg in few seconds, are the most violent explosions known in the universe. I will describe our current state of knowledge on some key aspects of the physics of GRBs, by following the history of the field, in particular the revolution in the 90's and the 2000's made possible by the CGRO, Beppo-SAX and Swift satellites. I will then describe the most recent results obtained by the Fermi satellite. In the second part of my talk, I will focus on some key, unsolved questions raised by recent Fermi data. I will particularly address the current debate about the origin of the prompt emission. I will describe theoretical efforts aimed at understanding the observed spectra, that led to a 'paradigm shift' in recent years. ------------ For further read, see Nature news http://www.nature.com/news/cosmic-blasts-powered-by-a-hot-glow-1.10598
When a dilute gas of bosonic atoms is cooled to degeneracy it passes through a quantum phase transition to form a Bose-Einstein condensate (BEC). Beyond this point the properties and dynamics of the BEC can frequently be very well described by a nonlinear classical field equation, the so-called Gross-Pitaevskii equation, which is capable of supporting a variety of excitations, including solitons and vortices.
Bright solitons (non-dispersive waves that are robust to collisions) are of particular interest because they have attractive stability properties for potential applications in metrology and interferometry. Formally, such solitons exist as solutions to a 1D nonlinear Schrodinger equation with a focusing (attractive) cubic nonlinearity, in the absence of any confining potential. In my talk I will discuss such questions as:
*How 1D is 1D?
*How soliton-like is a trapped soliton?
*How classical-like is the (fundamentally quantum) system?
*How can solitons be used in interferometry?
Among the large variety of different detection methods direct spectroscopic absorption techniques based on high finesse optical cavities appear to be very promising for highly sensitive in situ trace gas detection in real time with high spatial resolution. In recent years a powerful new approach, incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS), has been developed at University College Cork, Ireland. In IBBCEAS, the light from a bright incoherent source (e.g. a short-arc lamp) is transmitted through an optically stable cavity and dispersed with a grating monochromator and detected by a sensitive charged coupled device (CCD) detector. The measurement principle combines the simplicity and robustness of conventional optical absorption spectroscopy with the enhancement concepts developed in so-called cavity ring-down spectroscopy. The broad simultaneous spectral coverage allows multiple species to be detected and interfering atmospheric constituents to be accounted for. The 20 m long SAPHIR (=simulation of atmospheric photochemistry in a large reaction) chamber at Forschungszentrum Jülich (FZJ), Germany, is designed to operate at low concentration levels of trace species that are typical for true conditions in the troposphere. The possibility to setup a long optical resonator (increasing the sensitivity of the instrument) together with the availability of other already standardized detection methods such as DOAS, chemoluminescence and LOPAP makes the SAPHIR chamber an ideal platform to further develop and validate the IBBCEAS approach especially for open path in situ field applications. For the past year an IBBCEA instrument has been commissioned at the SAPHIR chamber for near-UV kinetics measurements of nitrous acid (HONO) and glyoxal (CHOCHO), two trace species playing a significant role in the polluted troposphere. The instrument implementation and the comparison between the first concentrations retrieved from IBBCEAS and from other standardized techniques available at SAPHIR will be presented and discussed.
Currently there is considerable interest in cooling nano and micro mechanical oscillators to their motional quantum mechanical ground state. A dielectric particle trapped by an optical tweezer in vacuum forms a high-Q oscillator that is well isolated from environmental disturbances. This system has good prospects for cooling to its ground state and promises to be a unique platform for making highly sensitive measurements of weak forces at the quantum limit. The most important step towards reaching this regime is the development of methods to cool the trapped particles. One method we have developed uses cavity cooling to damp the motion of trapped nanoparticles. These interact strongly with an optical cavity field, and cooling occurs when the input field is red detuned from resonance. The cavity damps the motion of the trapped sphere by preferentially scattering blue-shifted photons out of the cavity. Microspheres, however, cannot be cooled by an external cavity. For these particles we are currently implementing a type of Doppler cooling that is analogous to laser cooling of atoms. Here the whispering gallery modes (WGM) of the sphere serve the same function as the electronic resonances in an atomic system, such that when illuminated by light that is red detuned from the WGM resonances, the particle's motion is damped. In this presentation I will outline the theoretical development of these two methods as well as their experimental implementation for both nanospheres and microspheres held in a two beam optical trap in a vacuum.
High resolution LC-based spatial light modulators (SLM) can be used to advance the performance of a light microscope in many ways: Using the SLM as a programmable Fourier-filter, one can emulate classic techniques for contrast enhancement, such as dark-field microscopy, Zernike phase contrast, or spiral phase contrast. In shearing microscopy, e.g. differential interference contrast (DIC), SLM-based techniques provide unparalleled flexibility, since the shearing parameters can be computer-controlled at video-rate. The SLM enables also depth-of-focus multiplexing for thick transparent samples. Moreover, SLM-tailored illumination may be employed for artifact reduction in linear microscopy or for the fine-tuning of phase-matching in nonlinear CARS-microscopy.
Polymer nanocomposites have attracted substantial interest from both the academia and industries over the past two decades mainly because additions of a small amount of nanofiller may provide significant enhancements in mechanical, thermal and barrier properties of polymers. This talk will present the preparation, structure and properties of cellular and non-cellular polymer nanocomposites with particular emphasis on polymer/graphen?e oxide nanocomposites. The effects of nanofiller on the structure, mechanical and thermal properties and bioactivity of polymers and the reinforcement mechanisms in polymer nanocomposites will be discussed.
Electron motion and light waves form the basis of life: the microscopic motion of electrons creates light, which supplies our globe with life-giving energy from the sun; electrons transform light into biological energy during photosynthesis and into biological signal endowing us with the capability of seeing the world around us. Upon their motion inside and between atoms, electrons emit light, carry and process information in biological systems and man-made devices; create, destroy, or modify molecules, affecting thereby biological function. Consequently, they are key players in physical, chemical, and life sciences; information, industrial, and medical technologies likewise. During the past ten years (2001-2011), advances in laser science opened to door to watching and controlling these hitherto inaccessible dynamics: the motion of electrons at the atomic scale and light wave oscillations (being mutually the cause of each other) evolving on attosecond time scales. Key tools include waveform-controlled few-cycle laser light and attosecond pulses of extreme ultraviolet and soft-X-ray light. They provide a force capable of steering electrons inside and between atoms and a probe for tracking their motion. Insight into and control over microscopic electron motion are likely to be important for developing brilliant sources of X-rays, understanding molecular processes relevant to the curing effects of drugs, the transport of bioinformation, or the damage and repair mechanisms of DNA, at the most fundamental level, where the borders between physics, chemistry and biology disappear. Once implemented in condensed matter, the new technology will be instrumental in advancing electronics and electron-based information technologies to their ultimate speed: from microwave towards lightwave frequencies.
III-N semiconductors are known for their potential in producing visible and ultraviolet light emitting diodes and lasers, and for high power, or high frequency electronics. These applications and their importance will be briefly described. Most of these applications use either AlGaN or InGaN alloys within the device. The use of InAlN is less well explored due to the challenges in producing the material and as a result is less well understood. In the presentation we will look at the potential advantages and issues in employing this system such device applications.
While many extrasolar planets have now been detected using indirect techniques, the problem of detecting an exoplanet in images remains very challenging. This is due to the extreme brightness ratio between the parent star and the planet, and the small angular separations involved. Diffraction-lim?ited images from large telescope are required, and this can be provided using ‘extreme’ adaptive optics. However, even tiny residual aberrations will give rise to speckles in the images and these can easily be confused with planets. In this talk I will review techniques that have been proposed to circumvent these problems. I will present the results of work on the application of optimal statistical approaches. I will also introduce a technique which relies on analysing images obtained at several wavelengths in order to discriminate planets from speckles.
For the past 150 years weather measurements have been made at Valentia. This talk will briefly explain why Valentia Observatory was established where it is and why it remains one of the most strategic atmospheric monitoring stations in Europe. The talk will focus mainly on how modern technology is currently being used in the national monitoring of solar radiation, ozone, upper air meteorology, pollution, phenology, geomagnetics, seismology and more.
In a decade, the international fusion experiment ITER will start operating in the south of France. This historic experiment will generate up to 500 megawatts of fusion power and provide a proof of principle for fusion energy. Fusion has the potential to provide a large fraction of our energy for millions of years. I will describe the scientific progress in fusion -- from Sir Arthur Stanley Eddington's prophetic predictions in 1920 to the remarkable results that have led to ITER. There are challenging problems that must be solved to make fusion power a commercial option. I will outline these problems and worldwide efforts to find their solution.
Water ice is a very strange and beautiful substance - not only in the shapes it forms around us (snowflakes, icicles...), but also in the microscopic details of its chemistry.The nature of chemical bonding in ice was established by Bernal, Fowler and Pauling in the early 1930's [1,2]. However their theory hides a puzzle - chemical bonding alone does not select a unique orientation of the water molecules. As a result each water molecule has a finite ground state entropy, in violation of the third law of thermodynamics.In fact water is not the only "ice", and exactly the same contradiction arises in problems of frustrated charge order on the pyrochlore lattice, and in ''spin ice'' materials, recently the cause of great excitement for their magnetic monopole excitiations.
The talk will discuss pursuing a career in applied physics in both an industrial and academic setting. Dr. O'Neill will outline the current work of CIT's Centre for Advanced Photonics & Process Analysis (CAPPA) where a group of 20 post graduate and post doctoral researchers carry out research at the industrial-acad?emic interface. CAPPA explores new applications for existing and emerging photonic technologies in collaboration with companies in sectors such as medical devices, diagnostics, pharmaceuticals?, electronics, food technology, environmental sciences and photonics itself. In addition he will discuss the challenges to pursuing and maintaining a technical career path for researchers with a background in physical sciences.
The use of magnets in surgery was proposed in diverse contexts over the last century. However, it is the development of advanced, minimally-invasive intervention methods such as single-port laparoscopy and endovascular procedures that has propelled the use of high-strength, permanent magnetic components to the forefront of surgical innovation. The use of magnetic components to improve clinician access and manoeuvrability in vivo has been demonstrated by multiple groups in a variety of advanced minimally-invasive procedures. However, these passive magnetic devices are necessarily limited in size for laparoscopic or endoscopic delivery. A novel solution to this shortcoming is the use of self-deployed magnetic components that can assembly into larger macro-magnets in vivo but are still suitable for delivery through a small access port. The Bioelectromagnetics group at UCC has designed, constructed and tested a number of these self-deployed systems. Early iterations have been successfully tested in live animal studies. This seminar will present (i) a brief context for the use of magnets in surgery, (ii) a theory for self-deployed magnetic microsystems, (iii) the simulated and experimental testing procedures employed and, (iv) results of in vivo animal testing using a prototype device.
A feature of wave superposition is that one plus one does not necessarily equal two. The interference of two equivalent waves can result in a zero intensity - e.g. Young's double slits. However, the waves fill 3D space not just a 2D screen and Young's dark fringes map out planes. But two waves are a special case. In general, when three or more waves interfere, complete destructive interference occurs on lines (phase singularities) around which the phase advances or retards by 2?. This azimuthal phase gradient means that the Poynting vector, and associated energy flow, circulates too - hence the lines are also called "optical vortices". Despite their appearance in all natural light fields, it was not until the early 1990's that it was recognized that the light surrounding a single line phase singularity carried an angular momentum, completely independent of the photon spin. This orbital angular momentum can be created using simple lens systems, or holograms - made from 35mm film or encoded onto liquid crystal displays. Both whole beams, and single photons can carry this information, or transfer it to particles to create an optical spanner. In this talk I hope to introduce the underlying physical properties and discuss a number of manifestations of orbital angular momentum, which highlight how optics still contains surprises and opportunities for both the classical and quantum worlds.
Astrophysical jets associated with supermassive black holes in active galaxies rank among the most energetic known phenomena in nature, and are one of the few direct probes we have of the extreme distant universe. We are able to study these jets in great detail with radio interferometers, and more recently, with NASA's Chandra X-ray and Fermi Gamma-Ray orbiting observatories. For the first time, these and other facilities are being used together to provide a true multi-wavelength picture of what occurs deep in the nuclei of distant galaxies. The MOJAVE program is a large project to investigate nearly three hundred of the brightest jets in the northern sky, whose light is highly Doppler beamed toward us. These 'blazars' flicker rapidly in intensity at all wave-bands, and dominate the gamma-ray sky outside the galactic plane. With regular radio wavelength images from the world's highest resolution telescope, the Very Long Baseline Array, we are studying detailed total intensity and polarimetric changes in blazar jets on lightyear-scales. I will describe some of the recent findings of the MOJAVE program regarding long term jet kinematics, including accelerations, apparent superluminal speeds, possible jet nozzle precession, and the links seen between lightyear-scale jet activity and high-energy gamma-ray emission detected by the Fermi observatory.
The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is an array of four 12 m imaging atmospheric Cherenkov imaging telescopes for gamma-ray astronomy above 100 GeV, that entered full scientific operation in Autumn 2007. The VERITAS collaboration maintains a strong and varied science program that has resulted in the detection, to date, of 33 sources including active galactic nuclei, supernova remnants & pulsar wind nebulae, a binary system, and a starburst galaxy. In this talk I will give an update on the status and performance of the array, and discuss the main science results from VERITAS so far.
Recent research shows that security of communication can be guaranteed by peculiar "non-local" correlations, no matter whether they are of quantum origin or not. Bell's inequality alone makes seemingly insane scenario possible --- devices of unknown or dubious provenance, even those that are manufactured by our enemies, can be safely used for secure communication, including key distribution. This is a truly remarkable feat, also referred to as the "device independent cryptography". All that is needed to implement such a bizarre form of cryptography is a loophole-free violation of Bell's inequalities. It is on the edge of being technologically feasible. I will provide a brief overview of the intriguing connections between Bell's inequality and cryptography and describe how studies of entanglement and the foundations of quantum theory influenced the way we may soon protect information. Recommended reading: Semi-popular article titled "Less reality, more security" available at http://www.arturekert.org/Site/Varia.html - abbreviated version published in Physics World, September 2009.
This talk will explore how room-temperature semiconductor surfaces can manipulate atoms cooled to nK temperatures and, conversely, be probed by the atoms themselves. Quantum-mechanical reflection can shield the ultracold atoms from the disruptive influence of a nearby room-temperature surface. By considering experiments performed at MIT [1], it will be shown that inter-atomic interactions and the aspect ratio of the condensate both strongly affect the reflection process [2]. Next, the interaction between atomic condensates and surfaces that are patterned on the nanometre and micrometre scales will be considered. Strong focusing of the condensate by a transmission zone plate suggests a route towards re-writable matter-wave lithography of quantum electronic devices [2]. Finally, I will present calculations, which predict that current through a two-dimensional electron gas (2DEG) can trap ultracold atoms < 1 micron away with orders of magnitude less spatial noise than a more usual metal trapping wire [3]. This may enable the creation of hybrid systems, which integrate ultracold atoms with quantum electronic devices to give high sensitivity and control: for example, activating a single quantised conductance channel in the 2DEG can split a Bose-Einstein condensate (BEC) for atom interferometry. In turn, the BEC itself offers structural and functional imaging of quantum devices and transport. [1] T.A. Pasquini, Y. Shin, C. Sanner, M. Saba, A. Schirotzek, D.E. Pritchard, and W. Ketterle, Phys. Rev. Lett. 93, 223201 (2004). [2] R.G. Scott, A.M. Martin, T.M. Fromhold, and F.W. Sheard, Phys. Rev. Lett. 95, 073201 (2005); T.E. Judd, R.G. Scott, G. Sinuco, T.W.A. Montgomery, A.M. Martin, P. Krüger, and T.M. Fromhold, New J. Phys. 12, 063033 (2010). [3] G. Sinuco-León, B. Kaczmarek, P. Krüger, T.M. Fromhold, arXiv:1007.5339
Laser and discharge produced plasmas have been used for many years as intense sources of extreme ultraviolet (EUV) and soft x-ray radiation. Depending on the choice and composition of the target the EUV spectra can be dominated by line, unresolved transition array or continuum emission. Nowadays, volume microchip manufacturing is performed using 193 nm excimer laser radiation with which feature sizes of 32 nm can be attained. However Moore's Law requires the doubling of processor speed every eighteen months and is predicated on a 40% reduction in feature size. To begin manufacturing at feature sizes of 22 nm and below requires the introduction of a new technological step, namely EUV Lithography, which is based on the availability of mirrors with high reflectivity in a 2% bandwidth at 13.5 nm wavelength. Much effort is being expended on the development of suitable sources because of the power requirement for high volume manufacturing. After early work on Xe plasmas it was found that the emission from plasmas using tin provides a better solution. The results of recent experimental measurements of absolute in-band and out of band intensity, ion distribution and debris will be presented. It has been shown that, because of opacity effects, the conversion efficiency is sensitive to ion density and laser wavelength. Various schemes to improve the conversion efficiency will be discussed. The results of recent plasma modelling calculations will also be presented and compared with experiment. In addition, recent advances in EUV mirror development at other wavelengths has led to the adoption of 6.x nm as the wavelength of choice for lithography past the 13.5 nm manufacturing step. Laser produced plasmas of some high Z elements emit intensely at these wavelengths. Some recent results on these new developments will be discussed.
Since it was first proposed in 1975, the laser cooling of vapour-phase atoms has become a workhorse of experimental atomic physics. After further developments, it now allows direct optical cooling of atoms to microkelvin temperatures, as well as the cooling of molecules, microstructures, and bulk fluids. In this talk, I shall briefly review established techniques of laser cooling, and then consider various possibilities for its extension to a wider range of atoms, molecules, structures and particles.
Laser and discharge produced plasmas have been used for many years as intense sources of extreme ultraviolet (EUV) and soft x-ray radiation. Depending on the choice and composition of the target the EUV spectra can be dominated by line, unresolved transition array or continuum emission. Nowadays, volume microchip manufacturing is performed using 193 nm excimer laser radiation with which feature sizes of 32 nm can be attained. However Moore's Law requires the doubling of processor speed every eighteen months and is predicated on a 40% reduction in feature size. To begin manufacturing at feature sizes of 22 nm and below requires the introduction of a new technological step, namely EUV Lithography, which is based on the availability of mirrors with high reflectivity in a 2% bandwidth at 13.5 nm wavelength. Much effort is being expended on the development of suitable sources because of the power requirement for high volume manufacturing. After early work on Xe plasmas it was found that the emission from plasmas using tin provides a better solution. The results of recent experimental measurements of absolute in-band and out of band intensity, ion distribution and debris will be presented. It has been shown that, because of opacity effects, the conversion efficiency is sensitive to ion density and laser wavelength. Various schemes to improve the conversion efficiency will be discussed. The results of recent plasma modelling calculations will also be presented and compared with experiment. In addition, recent advances in EUV mirror development at other wavelengths has led to the adoption of 6.x nm as the wavelength of choice for lithography past the 13.5 nm manufacturing step. Laser produced plasmas of some high Z elements emit intensely at these wavelengths. Some recent results on these new developments will be discussed.
In a standard theoretical picture of the formation and launching of astrophysical jets, the jets should acquire helical magnetic fields, due essentially to the combination of the rotation of the central black hole and accretion disk and the jet outflow. As was pointed out by Roger Blandford in the early 1990's, one way such helical fields may be manifest is through their tendency to give rise to gradients in the observed local Faraday rotation across the jet, due to the systematic variation of the line-of-sight component of the helical magnetic field across the jet. Indeed, transverse Faraday rotation gradients have been observed across a number of AGN jets, providing direct evidence that they carry toroidal or helical magnetic fields. The directions of the observed transverse Faraday rotation gradients provide statistical evidence for the operation of a cosmic "battery" in the accretion disks of AGN, which couples the direction of rotation and the direction of the poloidal (axial) field of the jet. If this "battery" is indeed operating, we have detected the presence of ordered currents and magnetic fields on a grand scale.
Owing to the rich diversity in settings encountered in the Solar System, a cross-body comparison is of great relevance for deepening our understanding of processes occurring on different planets and moons. We will apply this approach to study upper atmospheres, focusing on the deposition of energy sources in these regions. We will in particular discuss the deposition of solar radiation in the upper atmosphere of Titan, the largest moon of Saturn, which has been sampled in situ by the Cassini-Huygens spacecraft since 2004, and compare our findings with those obtained at other Solar System bodies. We will also briefly discuss auroral emissions in the Solar System and the energy crisis at the giant planets.
From the enormity of super massive black holes to the minuteness of asteroids, both inform us of their very nature by their brightness. Using specific techniques and instrumentation, measuring and understanding these different objects like never before is now possible.
Since the invention of frequency comb lasers, now 10 years ago, these devices have made a profound impact in many fields of physics. Comb lasers are based on mode-locked lasers, which produce a repetitive train of ultrafast pulses. With these devices it has become possible to control the electromagnetic waves of optical pulses, and to perform extremely precise frequency measurements over a wide range of the electromagnetic spectrum. This has e.g. resulted in the emergence of attosecond science, and made atomic clocks and tests of the basic laws of physics possible with unprecedented precision. Up to now, application of frequency combs has been limited to wavelengths in the (far) infrared to ultraviolet range. In the lecture, after an introduction on comb lasers, it will be shown that the frequency comb principle can be extended to much shorter wavelengths in the extreme ultraviolet (XUV, wavelengths below 100 nm). Phase-coherent amplification and carefully controlled high-harmonic generation techniques enable comb generation over a wide range of wavelengths in the XUV. To illustrate the versatility of the method, XUV frequency comb excitation of helium at 51 nm will be discussed. With this experiment a nearly 10-fold improved ground state ionization energy was determined, challenging the accuracy of the most recent QED calculations in helium.
During the past decade, keeping pace with conventional CMOS device scaling has required the semiconductor manufacturing industry to transition from the traditional role of consistently achieving aggressive photolithography pitch and thin film dimensional requirements at the rapid pace of Moore's Law to an unprecedented role of introducing and optimizing new materials systems designed to supplant such touchstone components as the SiO2 gate dielectric and doped poly-Si electrode layers. In particular, La and Al cap layer doping of high-k gate dielectrics has been introduced to increase the dielectric layer permittivity and tune the effective work function (EWF) of n and p-type metal nitride electrodes, respectively. In addition, engineered high mobility substrates of strained Si, SiGe and III-V channel materials have been introduced. In spite of significant integration progress, the limit of conventional planar CMOS scaling is inevitable and new architectures, currently under intense competitive development, are being characterized and evaluated. Recognizing the critical need for advanced energy and spatial resolution physical characterization techniques to identify subtle microstructure variation in buried layers, Lysaght launched the SEMATECH High Resolution Initiative (HRI) in 2002. The HRI program has been focused on active utilization of US National User Facilities to elucidate mechanistic pathways that give rise to the limits of electrical performance. This presentation will include detailed explanations of several advanced high-k/metal gate transistor materials and interface characterization techniques including small angle neutron scattering (SANS), synchrotron x-ray photoemission spectroscopy (XPS), and extended x-ray absorption fine structure (EXAFS) measurements that have yielded breakthrough results in understanding that have impacted the global semiconductor industry. In addition to achievements and challenges associated with the extension of planar CMOS, novel FinFET device structures and resistive random access memory (RRAM) systems will be presented. Finally, the exciting potential of functionalizing graphene, a single carbon atom layer hexagonal lattice sheet structure, will be discussed in the context of RF and hydrogen sensor applications with respect to recent polarized near edge x-ray absorption fine structure (NEXAFS) experiments conducted at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory in New York.
This seminar deals with the basic principles and practice of holography. The applications of holographic photopolymers in sensing , holographic data storage and optical device fabrication will be discussed. Holographic sensors are of two types. In the first the spacing of the recorded fringes in a holographic diffraction grating, changes in the presence of an analyte so that the direction of the diffracted laser light changes, or, in the case of a white light reflection grating, the wavelength of the diffracted light changes. An example is a reflection grating which swells in the presence of atmospheric moisture to indicate relative humidity by a change in the colour of the diffracted light. In a more versatile approach one can add inorganic nanoparticles to the photopolymer composition. During recording of diffraction gratings, the polymerisation and accompanying diffusion processes cause redistribution of the nanoparticles. Zeolite nanoparticles have the form of hollow cages enabling them to trap analyte molecules of appropriate sizes. The refractive index of the nanoparticle-analyte combination is normally different from that of the nanoparticles alone and this alters the refractive index modulation of the recorded grating, leading to a change in diffraction efficiency and intensity of the diffracted light. The second type makes use of a principle called dye deposition holography. The analyte is labelled using a dye which acts as a photosensitiser for the polymerisation process. If the analyte then is deposited on a layer containing the other photopolymer components, photopolymerisation can take place. If the illumination is in the form of an interference pattern, a diffraction grating is formed but only in the region where dye has been deposited. In this way the formation of a holographic diffraction grating itself becomes a sensing action with the potential for extremely high signal to noise ratio. The method also allows fabrication of photonic devices by direct writing, using photosensitising dye, of structures such as Fresnel zone plate lenses and waveguides in the photopolymer layer followed by exposure to spatially uniform light. Our work on holographic data storage (HDS) is concerned with enhancing the diffraction efficiency of user selected, very weak diffraction gratings by illumination with a single beam at the Bragg angle. Light in the illuminating beam is coupled into the diffracted beam and the two interfere to enhance the grating strength. In this way grating diffraction efficiency can be raised above a threshold so that a binary zero can be changed to binary one. A large number of identical weak holographic gratings may be multiplexed into the recording medium at the manufacturing stage, for user selection at the data recording stage. In this way consumer HDS systems could be made much more simply and cheaply than at present.
The topic of antimatter will be introduced by recalling its prediction and discovery in the 1930's, and a brief history of the subject will be given. Positrons have since found numerous applications in material science, engineering and medicine based upon their annihilation with electrons, their matter equivalent particle. A few examples will be described. Recently, physicists have learnt how to create atoms of antihydrogen under controlled conditions in vacuum. These experiments will be described as well as the motivation for undertaking them. The latter will involve one of nature's great conundrums: the absence of bulk antimatter in the current epoch of the Universe.
Quantum teleportation has proved to be one of the most striking applications of entanglement (quantum correlations) as a resource in quantum information processing. By means of a shared entangled channel and a conditional local operation, Bob is able to reconstruct perfectly an unknown state given to Alice, after she performs a measurement on her system and communicates classically her result to him. I will introduce the original idea and describe the advances that have been recently made in experimentally demonstrating quantum teleportation. In the standard protocol, it is assumed that Bob is able to perform ideal operations on his system. I will analyse the case where some of these operations are more reliable than others. I will show that the average fidelity of teleportation can be maximised by choosing properly the basis in which Alice performs her measurement.
The human eye, like the eyes of other species, is optimized for its visual tasks. The cornea and the crystalline lens projects an image of the outside world onto the retina where a high density of pigment-containing photoreceptors sample the image and transmits it to the visual cortex triggering our sensation of sight. The spectral and temporal properties of the visual pigments, the structure, arrangement and densities of the cone and rod photoreceptors all play a role for our visual system. The Stiles-Crawford effect (SCE), known since 1933 [1], is an inherent directional sensitivity of the photoreceptors that reduce the visual sensitivity to obliquely incident and intra-ocular scattered light. The SCE appears in a variety of situations: as a psychophysical visibility dependence of the incident light, in the backscattering of light from the retina, and in a minor hue change when observing quasi-monochromatic light. The SCE is believed to have its origin in wave-guiding by the elongated photoreceptors as well as in the visual pigments themselves. In this presentation, I will show experimental results for the SCE and compare these to elementary calculations of wave-guiding by individual fibre-like photoreceptors. I show that the match between the model and the experimental observations is remarkably good across the visible spectrum with important implications for vision [2, 3]. This knowledge may also be used to optimize high-resolution diagnostic retinal imaging techniques including scanning laser ophthalmoscopy [4] and optical coherence tomography [5]. The degradation of the images may be reduced with adaptive optics that cancels the time-varying aberrations of the eye during imaging. Finally, our recent work on multi-photon imaging of the cornea structure [6] will be discussed in relation to the development of clinically- relevant ophthalmic diagnostic tools for patients suffering reduced visual acuity. *Our research is funded by SFI (07/SK/B1239a and 08/IN.1/B2053) and Enterprise Ireland (PC/2008/0125). [1] Stiles, W.S.; Crawford, B.H. "The luminous efficiency of rays entering the eye pupil at different points," Proc. Roy. Soc. B 1933, 112, 428-450. [2] Vohnsen, B.; Iglesias, I.; Artal, P. "Guided light and diffraction model of human-eye photoreceptors," J. Opt. Soc. Am. A 2005, 22, 2318-2328. [3] Vohnsen, B. "On the spectral relation between the first and second Stiles-Crawford effect," J. Mod. Optics 2009, in press. [4] Vohnsen, B.; Iglesias, I.; Artal, P. "Directional imaging of the retinal cone mosaic," Opt. Lett. 2004, 29, 968-970. [5] Gao, W.; Cense, B.; Zhang, Y.; Jonnal, R.S.; Miller, D.T. "Measuring retinal contributions to the optical Stiles-Crawford effect with optical coherence tomography," Opt. Express 2008, 16, 6486-6501. [6] Vohnsen, B; Artal, P. "Second-harmonic microscopy of ex-vivo porcine corneas," Journal of Microscopy-Oxford 2008, 232, 158-163.
Global climate change resulting from increasing concentrations of "greenhouse gases" in the atmosphere threatens to alter radically the conditions for human habitation on our planet. Over the next 100 years, the average global air temperature is expected to increase by several degrees (~1.8-4.0 °C) bringing with it associated increases in sea level (~20-60 cm) and changes to ecosystems all over the world. In direct contrast to this global warming in the troposphere (sea-level to 15 km altitude), the atmosphere at higher altitudes (stratosphere (15-50 km altitude) and mesosphere (50-90 km)) is experiencing a cooling effect. The magnitude of this cooling effect could be several times larger than the changes seen at the surface, because the very tenuous nature of the upper atmosphere makes it much more sensitive to change. The mesopause (80-100 km altitude) is the coldest layer in the Earth's atmosphere and is the region about which the least is known due to its inherent complexity and because of the difficulty of making measurements at this altitude. In recent years, a number of dedicated satellites, TIMED and AURA (USA) and ACE (Canada), have begun to address the dearth of measurements in this region, but considerable work remains before the complex interplay of chemistry, dynamics and radiation balance is understood satisfactorily. The seminar will present results of ground-based measurements of mesopause temperature made at Maynooth, and highlight some recent reports which illustrate the sensitivity of this atmospheric region to anthropogenic activities.
The big bang model of the origin and evolution of the universe has been highly successful in explaining many features of the cosmos, from the expansion of the universe to the cosmic microwave background. However, many puzzles remain, such as the horizon, flatness and singularity problems. These problems have led to a modification of big bang theory known as cosmic inflation. The inflationary model of the universe will be reviewed in this seminar and contemporary evidence supporting the model will be discussed.
The ocean takes up a significant fraction of greenhouse gases from the atmosphere. Our ability to accurately quantify and model air-sea fluxes requires (i) we can measure the fluxes under all conditions (ii) we can understand the processes controlling the fluxes. We have not yet achieved this. One of the key processes controlling air-sea exchange is upper ocean turbulence. Here I will present the scientific background to ocean turbulence and some data from the Indian Ocean acquired with the Air-Sea Interaction Profiler (ASIP). I will also present some background on the eddy correlation technique for measuring air-sea fluxes directly and discuss the limitations with currently available technology. I will describe some of the recent research we are doing to develop new technology using photoacoustic spectroscopy.
Gravity explains the world on scales from apples to satellites to planets to stars to the entire universe and has been measured to extreme precision. Quantum mechanics describes the world on the smallest scales: solids, molecules, atoms, sub-atomic particles and has resulted in most of the technology of the twentieth century. These two theory have been experimentally tested to exceptional accuracy and yet they are incompatible: they both cannot be correct! Unifying these competing theories is one of the most important problems in theoretical physics. In this talk I will review the reasons why Gravity cannot be quantised in the standard way, discuss the regimes where this is important and explain why this leads to important conceptual problems for our understanding of the universe. I will explain how these problems are being tackled (but not yet solved) via String Theory and Loop Quantum Gravity, before discussing why Cosmology is a fruitful place to explore these problems.
X-ray and gamma-ray flares are a common occurrence in blazars, active galactic nuclei with relativistic plasma jets that are pointing almost directly at us. This talk will present the results of a comprehensive multi-waveband monitoring program of blazars with gamma-ray flares observed by the Fermi Gamma-ray Space Telescope. The relative timing of the flares at different wavebands and the emergence of bright radio knots moving down the jet at apparent superluminal speeds allows us to locate where in the jet the high-energy emission arises. This information provides strong clues for determining the physics behind the gamma-ray emission.
The presentation first provides an introduction to the method of wind profiling with lidar. Next some measurement examples will illustrate the capabilities and possible applications of wind lidar measurements. The measurements presented in this contribution were made at Leipzig, Germany, in the framework of the COPS campaign (southern Germany), and during the SAMUM campaign in the Cape Verde islands (North Atlantic).
First, we describe how we measure vertically resolved aerosol properties with Raman lidar. We introduce the European Aerosol Research Lidar Network EARLINET. Measurement examples illustrate, how multiwavelength Raman lidar can provide characteristical optical properties of different aerosol types. This kind of information is required to combine the data from the first satellite lidar CALIPSO (operating at 532 and 1064 nm wavelength);NASA, and the data from future ESA-led lidar-in-space missions operating at 355 nm into a long-term, global dataset of vertically resolved aerosol distributions.
Quantum gas experiments are witnessing rapid progress in attaining control over interactions, dimensionality, statistics and geometry. As a result the synthetic engineering of an increasing number of central models of quantum many-body physics is now within sight. I will discuss this development in the context of our recent experiments with fermionic quantum gases in optical lattices where we access the physics of the repulsive Hubbard model. We investigate the cross-over from a metallic to a Mott-insulating phase and quantify the approach to magnetic order. I will further report on a study of a Bose-Einstein condensate in an ultrahigh-finesse optical cavity where we observe that the superfluid self-organizes into an emergent checkerboard pattern above a critical pump power. When entering this self organized phase, the gas initially maintains phase coherence and can thus be regarded as a supersolid. The underlying quantum phase transition is described by the Dicke model. Over a wide range of parameters, the phase boundary is mapped out.
The human eye, like the eyes of other species, is optimized for its visual tasks. The cornea and the crystalline lens projects an image of the outside world onto the retina where a high density of pigment-containing photoreceptors sample the image and transmits it to the visual cortex triggering our sensation of sight. The spectral and temporal properties of the visual pigments, the structure, arrangement and densities of the cone and rod photoreceptors all play a role for our visual system. The Stiles-Crawford effect (SCE), known since 1933 [1], is an inherent directional sensitivity of the photoreceptors that reduce the visual sensitivity to obliquely incident and intra-ocular scattered light. The SCE appears in a variety of situations: as a psychophysical visibility dependence of the incident light, in the backscattering of light from the retina, and in a minor hue change when observing quasi-monochromatic light. The SCE is believed to have its origin in wave-guiding by the elongated photoreceptors as well as in the visual pigments themselves. In this presentation, I will show experimental results for the SCE and compare these to elementary calculations of wave-guiding by individual fibre-like photoreceptors. I show that the match between the model and the experimental observations is remarkably good across the visible spectrum with important implications for vision [2, 3]. This knowledge may also be used to optimize high-resolution diagnostic retinal imaging techniques including scanning laser ophthalmoscopy [4] and optical coherence tomography [5]. The degradation of the images may be reduced with adaptive optics that cancels the time-varying aberrations of the eye during imaging. Finally, our recent work on multi-photon imaging of the cornea structure [6] will be discussed in relation to the development of clinically- relevant ophthalmic diagnostic tools for patients suffering reduced visual acuity. *Our research is funded by SFI (07/SK/B1239a and 08/IN.1/B2053) and Enterprise Ireland (PC/2008/0125). [1] Stiles, W.S.; Crawford, B.H. "The luminous efficiency of rays entering the eye pupil at different points," Proc. Roy. Soc. B 1933, 112, 428-450. [2] Vohnsen, B.; Iglesias, I.; Artal, P. "Guided light and diffraction model of human-eye photoreceptors," J. Opt. Soc. Am. A 2005, 22, 2318-2328. [3] Vohnsen, B. "On the spectral relation between the first and second Stiles-Crawford effect," J. Mod. Optics 2009, in press. [4] Vohnsen, B.; Iglesias, I.; Artal, P. "Directional imaging of the retinal cone mosaic," Opt. Lett. 2004, 29, 968-970. [5] Gao, W.; Cense, B.; Zhang, Y.; Jonnal, R.S.; Miller, D.T. "Measuring retinal contributions to the optical Stiles-Crawford effect with optical coherence tomography," Opt. Express 2008, 16, 6486-6501. [6] Vohnsen, B; Artal, P. "Second-harmonic microscopy of ex-vivo porcine corneas," Journal of Microscopy-Oxford 2008, 232, 158-163.
One might think that quantum physics has come of age: First introduced by Planck in 1900 and embedded into a sound theoretical framework by Heisenberg and Schrödinger in 1926, quantum physics might have obtained a status comparable to that of Newtonian mechanics and other scientific models, by now. Quantum physics has, indeed, developed into a corner stone of modern science and it is often seen as the quantitatively most precisely confirmed theory of nature. Quantum effects have been the basis for a plethora of technological innovations, devices and scientific studies over many decades. And still: genuine quantum phenomena are and remain puzzling mind-bogglers, since they simply don't fit to our common notions of reality and/or locality. The lecture aims at giving an introduction to some puzzles, that were already established in the days of Schrödinger and that have yet remained the cause of scientific debate and interpretation, even until today. Most puzzles are rooted in the quantum superposition principle, which allows even massive individual particles to be delocalized over macroscopic distances and pairs of particles to seemingly "know" of each other, without any obvious means of communication. We will discuss how we observe such quantum effects, why we usually don't see them in our everyday world and why modern quantum science still holds many promises for future technologies.
Topological Quantum Computation (TQC) is an approach to quantum computing which aims to produce quantum "hardware" with dramatically reduced intrinsic error rates (before active error correction). This can be achieved in principle by storing quantum information in non-local quantum numbers associated with anyons. Anyons are a type of (quasi)particles that can occur only in two-dimensional systems and which have topological exchange interactions different from those of the more familiar bosons and fermions. There is currently a lot of excitement over experiments which may have detected a particularly interesting type of anyon in one of the electron liquids of the fractional quantum Hall effect. I will try and give a short introduction to topologically fault tolerant media for quantum information storage, introduce anyons and sketch how to manipulate quantum information by "braiding" their worldlines. I also hope to say something about the phenomena found recently in fractional quantum Hall systems, which may well be due to the presence of anyons suitable for quantum computing applications.
Low dimensional quantum gases have rapidly evolved from a being a solely theoretical concept towards being experimentally accessible systems in the laboratories. Since restricted geometry are known to introduce strong correlations, these systems show very involved and interesting physics while still being largely analytically treatable. In the first part of this talk I will give a comprehensive account of the ground state properties and correlation functions of such a gas confined in a potential split by a point-like barrier. This model can be used to approximate a realistic double well situation where the height of the barrier is related to the area of a physical potential. Alternatively, a point like potential can be a good approximation to describe a strongly localised impurity. I will explain how an ionic impurity inside a gas of neutral atoms can be described and compare the results with the above mentioned split trap model. The second part of the talk will focus on entanglement in two-particle bosonic systems. Entanglement is not only one of the defining characteristics of quantum mechanics but it is also at the heart of many current quantum information processing protocols. It is therefore of fundamental importance to develop a toolbox for its detection and quantification. The analytic accessibility of the realistic dimer model I will describe makes it an ideal system for testing such ideas. I will describe how different types of entanglement may arise in such models and outline detection and quantification techniques.
Tremendous progress has been achieved in the preparation of strongly correlated quantum systems using ultra-cold quantum gases in the past years. Due to their exceptional degree of controllability, not present in typical condensed matter systems, cold atomic gases realize an "Experimental Quantum Simulator" in the sense initially proposed by Feynman to tackle the problem of strongly correlated quantum systems. Both in fermionic and bosonic quantum systems cold atomic gases have advanced the understanding of correlated matter. In particular when atoms are studied in the periodic potential of an optical lattice, access to various quantum many-body regimes including superfluids, Mott-insulators, and Luttinger liquids has been achieved. We will present recent experiments with cold atomic quantum gases in optical lattices.
The wave properties of material particles are one of the most widely known features of quantum physics. Wave properties become apparent in diffraction and perhaps most strikingly in interference phenomena. In this lecture I will present experiments where we trap and control small groups of neutral atoms by means of optical dipole forces. I will show how to distinguish individual atoms, how to transport and sort them, and how to store and retrieve information from the atoms. Recently, we have have taken the atoms to the full quantum regime, i.e. to the observation of atomic matter wave interferences at the single trapped atom level. Moreover, we have realized the quantum analogue of Brownian motion, the quantum walk, a concept of relevance in quantum information science. In future research, the methodological approaches should allow to study the transition from the single atom to the few to the many atom worlds.
The final merger of two black holes releases a tremendous amount of energy and is one of the brightest sources in the gravitational wave sky. Observing these sources with gravitational wave detectors requires that we know the radiation waveforms they emit. Since these mergers take place in regions of very strong gravitational fields, we need to solve Einstein's equations of general relativity on a computer in order to calculate these waveforms. For more than 30 years, scientists have tried to compute these waveforms using the methods of numerical relativity. The resulting computer codes have been plagued by instabilities, causing them to crash well before the black holes in the binary could complete even a single orbit. Recently this situation has changed dramatically, with a series of amazing breakthroughs. This talk will take you on this quest for the holy grail of numerical relativity, showing how a spacetime is constructed on a computer to build a simulation laboratory for binary black hole mergers. We will focus on the recent advances that are revealing these waveforms, and the dramatic new potential for discoveries that arises when these sources will be observed by LIGO and LISA.
Since the 1994 discovery by Peter Shor, that a quantum computer may factor large numbers more efficiently than any known classical computing strategy, research in quantum computing has been studied by a large number of research communities and its potential has been recognized by a variety of national, international, strategic, and commercial funding initiatives. Quantum computers may be built from physical quantum systems that are already studied extensively in the laboratory: trapped ions, cold atoms, superconducting circuits, liquid and solid state spin ensembles, etc., and numerous experiments have now demonstrated precise elementary gate operations. The lecture will review the progress within the field with emphasis on the status of physical implementation in laboratory experiments. By taking a look at a few experiments, we will show that, some times, progress has happened due to rather simple theory ideas which have led to significant improvements of the original theoretical proposals, and some times quantum systems just behave better in the laboratory than we expect. We conclude the presentation by discussing a few novel theoretical ideas and proposals, showing that this research is still as diverse as ever, and that we may still have only a vague image of the appearance of the first real quantum computer.
In 1967, a graduate student named Jocelyn Bell, working at the time under Antony Hewish at the Mullard Radio Astronomy Observatory in Cambridge, serendipitously discovered pulsars while undertaking some reasonably ordinary observations with an antenna, to survey the sky for scintillating sources. After a number of possible explanations for the objects were dismissed, to include "Little green men", pulsars were finally identified to be highly-magnetised, rapidly rotating neutron stars. These objects are surrounded by plasma-filled magnetospheres, containing immense electromagnetic fields, with magnetic field strengths exceeding 1014G in many cases and rotational periods as low as 1.5ms. They are observed across the spectrum from radio to gamma-ray emission and are often likened to galactic light-houses, as they sweep highly-directional beams of intense radiation across the cosmos. Remarkably, after some 40 years of intensive research, a number of the most fundamental questions regarding pulsars remain unanswered. Given the shear distances to these objects, rendering observations unlikely to resolve the magnetospheric scales in the foreseeable future, our only avenue for in-depth scrutiny at present is computational modelling. With this goal in mind, we have developed a three-dimensional, fully electromagnetic, relativistic, fully parallel and modular Particle-In-Cell plasma simulation code, as a tool to allow us to probe the secret lives of these exotic objects. We have successfully applied the developed code to the investigation of the plasma distribution in the vicinity of a pulsar, with some interesting results.
The thermosphere links the space environment to the terrestrial atmosphere and plays an important role in understanding the interactions between these very different regimes. It remains a region which is poorly observed compared to the lower atmosphere yet can have important consequences for satellite operations and radio communications. The extremes of thermospheric behaviour are found at the poles and the instruments and techniques used at present in the Arctic will be introduced. The coordinated development of measurement techniques and global models of the thermosphere will be demonstrated, in particular the influence of impulsive events such as the "Halloween" geomagnetic storms in 2003. One aspect of thermospheric research which has only recently been developed is the possible influence of auroral activity on climate and the significance in terms of the wider debate on global warming will be discussed. Finally the prospects for the next generation of thermospheric research, and the important role to be played by EU-funded infrastructure, will be shown.
In this seminar we will discuss the Large Hadron Collider (LHC) at CERN, starting with an introduction to the complexities of the machine and the experiments built to exploit it. We then look at the exciting physics goals and aspirations of the LHC, focusing on the extensive program planned for proton-proton collisions. Finally, we present a more personal view on the potential of the LHC to answer some of the most vexing questions in high-energy physics.
The synchronisation of self-sustained oscillators has been part of science since at least the seventeenth century. Since then, entrainment phenomena have been described in many areas of physics, engineering, social science and biology. Any long-distance airline traveller will be familiar with the transient where internal circadian rhythms (slave oscillator) are required to re-synchronise with local time (master oscillator). In engineering, synchronisation allows one to separate the functions of precision and power, and indeed to generate them at distinct locations. In laser physics, these phenomena have been used to generate multiple coherent emitters, but the innate instability of semiconductor lasers has hampered their deployment. Recently, a new class of semiconductor materials has reached sufficient maturity where reliable devices are available in communications bands. Quantum-dots represent an effort by materials scientists to deliver new materials by exploiting nano-structures with dimension similar to the electron de Broglie wavelength. I will describe the behaviour of quantum-dot laser devices under the influence of an external forcing, including stable locking, excitable pulsations, multistability and chaos.
Total Internal Reflection Fluorescence (TIRF) Microscopy and Optical tweezers enable individual biological molecules to be visualised and manipulated using laser light. A conventional light microscope can be readily adapted to allow single fluorophores to be viewed using a video camera or to allow objects to be captured and manipulated using photon pressure. Single molecule techniques are now accessible to most biologists and we are able to measure the biophysics and biochemistry of molecules with millisecond time-resolution and nanometre spatial precision. Single molecule studies can provide new insights into how biological molecules work as they allow the sequential steps that make up a biochemical pathway to be observed directly. Furthermore, since the chemical trajectory of an individual molecule can be followed in space and time its biochemical kinetics are revealed simply as "dwell-times" and changes in molecular structure can sometimes be measured directly from the optical signals. Data analysis can present new challenges in terms of the volume of data and the methods of data interpretation. The statistical approaches used are perhaps more familiar to ecologists than biochemists. Work within the Division of Physical Biochemistry at MRC NIMR aims to increase our understanding of the molecular mechanism of force generation by molecular motors such as the proteins that make our muscles contract. Our goal is to understand how biochemical change is coupled to mechanical work by these energy transducing enzymes. We use a combination of single molecule technologies to address this problem: Optical tweezers enable us to measure the force produced as a single motor molecule breaks down a single molecule of fuel (ATP) and single fluorophore imaging enables us to observe the movement of molecular motors within living cells.
Quantum memories are an important ingredient for the realization of quantum information processing and scalable, long-distance quantum communication. While light is a natural choice for transmitting quantum states, the storage of such states requires non-volatile objects as carriers of quantum information. Alkali atoms are a possible choice for such carriers, as their electronic ground state manifolds provide long coherence times. Interfacing them to transmitted light pulses however, is non-trivial. I will show how room temperature ensembles of alkali atoms can be used to perform this task with relatively little experimental overhead. I will discuss recent experiments, which employed optically pumped Cesium vapour to map the quantum variables of coherent and squeezed states of light onto collective spin components of the atomic ensemble.
In this talk the problem of doping-induced variations in the physical properties of carbon nanotubes is addressed. In particular, transport and magnetic properties are considered. Regarding the transport properties, nanotube-based sensors depend on sizable conductivity changes induced by impurities. Predictions of which impurity/nanotube combination provides good sensor characteristics are usually made on a case-by-case basis, following the study of how a particular nanotube responds to the presence of a specific doping agent. With a multitude of possible combinations, this so-called forward modeling approach is unable to address questions of general nature, like, for instance, the necessary features the components must have to produce certain physical properties on the device. Questions of this nature call for an inverse modeling scheme in which information about the sensor components can be extracted from the knowledge of a few physical quantities demanded for the device. Here we make use of a mathematically transparent formalism that works in both the forward and the inverse directions. We argue that this method can provide general guidelines on the absorption process and is a first step to narrow down the universe of combinations of tube and doping agents capable of producing efficient nano-scale sensors.
Regarding the magnetic properties, we are interested in establishing the nature of the indirect coupling that arises when magnetic impurities are present. This coupling is known to play a central role in determining the magnetic order in systems composed of adsorbed magnetic moments in metallic hosts. For low-dimensional metallic structures, such as nanotubes, this interaction is predicted to decay rather slowly. Ab-initio calculations have nevertheless been unable to reproduce this prediction. To clarify this matter, we make use of a simple analytical expression for the indirect coupling that, on the one hand, confirms the long ranged nature of this interaction, and, on the other hand, points to situations in which the coupling may display unexpectedly shorter ranges. We show that the interaction range depends rather sensitively on the location of the magnetic moments, which explains the difficulty in probing the long range character of the indirect coupling from standard ab-initio calculations.