Upcoming Physics Conferences

[To add an upcoming physics conference to this list, please send an email to 2Physics@gmail.com ]

Nov 29-Dec 04: Intl Conference on Hadron Spectroscopy (Tallahassee, FL, USA)
Nov 30-Dec 03: International Symposium on Computational Mechanics (Hong Kong and Macau, China)
Dec 01-04: Workshop on Quantum Chaos: Theory and Applications. Dedicated to the 65th birthday of Marcos Saraceno (Buenos Aires, Argentina)
Dec 15-20: Topical Conference on Elementary Particles, Astrophysics, and Cosmology (Fort Lauderdale, Florida, USA)
Jan 04-08: 3rd Intl Workshop On High Energy Physics in the LHC Era (Valparaiso, Chile)
Jan 05-08: 39th Winter Meeting on Statistical Physics (Taxco, Guerrero, Mexico)
Jan 11-15: Essential Cosmology for the Next Generation (Playa del Carmen, Mexico)
Jan 15-17: Axions 2010 (Gainesville, Florida)
Jan 26-29: GWDAW14: Gravitational Wave Data Analysis Workshop (Rome, Italy)
Feb 08-13: 46th Winter School of Theoretical Physics: Quantum Dynamics and Information: Theory and Experiment (Ladek Zdroj, Poland)
Feb 23-26: Gravitational Wave Symposium (John Hopkins U., USA)
Apr 05-09: PDEs, Relativity and Nonlinear Waves (Granada, Spain)
May 23-29: Workshop on Advances in Foundations of Quantum Mechanics and Quantum Information with atoms and photons ad memoriam of Carlo Novero (Turin, Italy)
Jun 14-17: Advances in Quantum Theory (Vaxjo, Sweden)
Jun 20-26: Theory Meets Data Analysis at Comparable and Extreme Mass Ratios (Waterloo, ON, Canada)
Jun 23-Jul 03: Quantum Gravity summer school (Morelia, Mexico)
Jun 28-Jul 02: LISA 8 (Stanford University, USA)
Jul 05-09: GR19 (Mexico City, Mexico)

Observation of Magnetic Monopoles in Spin Ice

Hiroaki Kadowaki, Yuji Aoki and Naohiro Doi of Tokyo Metropolitan University


[This is an invited article based on recently published work of the authors -- 2Physics.com]






Authors: H. Kadowaki¹, Y. Aoki¹, T. J. Sato², J. W. Lynn³

Affiliations: ¹Department of Physics, Tokyo Metropolitan University, Tokyo, Japan,
²NSL, Institute for Solid State Physics, University of Tokyo, Tokai, Japan,
³NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, USA

From the symmetry of Maxwell's equations of electromagnetism, magnetic charges or monopoles would be expected to exist in parallel with electric charges. About 80 years ago, a quantum mechanical hypothesis of the existence of magnetic monopoles was proposed by Dirac [1]. Since then, many experimental searches have been performed, ranging from a monopole search in rocks of the moon to experiments using high energy accelerators [2]. But none of them was successful, and the monopole is an open question in experimental physics. Theoretically, monopoles are predicted in grand unified theories as topological defects in the energy range of the order 10¹⁶ GeV [2]. However these enormous energies preclude all hope of creating them in laboratory experiments.

Taku J. Sato of University of Tokyo

Alternatively, recent theories predict that tractable analogs of the magnetic monopole might be found in condensed matter systems [3,4,5]. One prediction [4] is for an emergent elementary excitation in the spin ice compound Dy₂Ti₂O₇ [6], where the strongly competing magnetic interactions exhibit the same type of frustration as water ice [7]. In addition to macroscopically degenerate ground states [6], the excitations from these states are topological in nature and mathematically equivalent to the Dirac monopoles [1,4]. We have successfully observed [8] the signature of magnetic monopoles in the spin ice Dy₂Ti₂O₇ using neutron scattering, and find that they interact via the magnetic inverse-square Coulomb force. In addition, specific heat measurements show that the density of monopoles can be controlled by temperature and magnetic field, with the density following the expected Arrhenius law.

Jeffrey W. Lynn of NIST, USA

In Fig. 1 we illustrate creation of a magnetic monopole and antimonopole pair in spin ice under applied magnetic field along a [111] direction. This excitation is generated by flipping a spin, which results in ice-rule-breaking "3-in, 1-out" and "1-in, 3-out" tetrahedral neighbors, simulating magnetic monopoles, with net positive and negative charges sitting on the centers of tetrahedra. The monopoles can move and separate by consecutively flipping spins in the kagome lattice.

Fig. 1. Spins of Dy₂Ti₂O₇ occupy a cubic pyrochlore lattice, which is a corner -sharing network of tetrahedra, and consists of a stacking of triangular and kagome lattices. The competing magnetic interaction brings about a geometrical constraint where the lowest energy spin configurations on each tetrahedron follow the ice rule, in which two spins point inward and two point outward on each tetrahedron. (A) By applying a small magnetic field along a [111] direction, the spins on the triangular lattices are parallel to the field, while those on the kagome lattices retain disorder under the same ice rules. This is referred to as the kagome ice state [9]. (B) Creation of a magnetic monopole (blue sphere) and antimonopole (red sphere) pair in the kagome ice state.

A straightforward signature of monopole-pair creation is an Arrhenius law in the temperature (T) dependence of the specific heat (C). This Arrhenius law of C(T) is clearly seen in Fig. 2 at low temperatures, indicating that monopole-antimonopole pairs are thermally activated from the ground state, and that the number of monopoles can be tuned by changing temperature and magnetic field.

Fig. 2. Specific heat of Dy₂Ti₂O₇ under [111] magnetic fields is plotted as a function of 1/T. In intermediate temperature ranges these data are well represented by the Arrhenius law denoted by solid lines.

A microscopic experimental method of observing monopoles is to perform magnetic neutron scattering using the neutron's dipole moment as the probe. One challenge to the experiments is to distinguish the relatively weak scattering from the monopoles from the very strong magnetic scattering of the ground state. By choosing appropriate field-temperature values, we have successfully observed scattering by magnetic monopoles, diffuse scattering close to the (2,-2,0) reflections, and that by the ground state (Fig. 3) [8].

Fig. 3. Intensity maps of neutron scattering at T = T_c + 0.05 K in the scattering plane perpendicular to the [111] field are shown for H = 0.5 T and H = H_c. The kagome ice state at H = 0.5 T (A) compared with the MC simulation (C). The weakened kagome-ice state scattering plus the diffuse monopole scattering (B) at H = H_c agree with the MC simulation (D).

Typical elementary excitations in condensed matter, such as acoustic phonons and (gapless) magnons, are Nambu-Goldstone modes where a continuous symmetry is spontaneously broken when the ordered state is formed. This contrasts with the monopoles in spin ice, which are point defects that can be fractionalized in the frustrated ground states. Such excitations are unprecedented in condensed matter, and now enable conceptually new emergent phenomena to be explored experimentally [10].

References:
[1] "Quantised singularities in the electromagnetic field",
P. A. M. Dirac, Proc. R. Soc. A 133, 60 (1931). Article.
[2] "Theoretical and experimental status of magnetic monopoles",
K. A. Milton, Rep. Prog. Phys. 69, 1637 (2006). Abstract.
[3] "The anomalous Hall effect and magnetic monopoles in momentum space", Zhong Fang, Naoto Nagaosa, Kei S. Takahashi, Atsushi Asamitsu, Roland Mathieu, Takeshi Ogasawara, Hiroyuki Yamada, Masashi Kawasaki, Yoshinori Tokura, Kiyoyuki Terakura, Science 302, 92 (2003). Abstract.
[4] "Magnetic monopoles in spin ice"
C. Castelnovo, R. Moessner, S. L. Sondhi, Nature 451, 42 (2008). Abstract.
[5] "Inducing a magnetic monopole with topological surface states"
X-L. Qi, R. Li, J. Zang, S-C. Zhang, Science 323, 1184 (2009). Abstract.
[6] "Spin ice state in frustrated magnetic pyrochlore materials"
S. T. Bramwell, M. J. P. Gingras, Science 294, 1495 (2001). Abstract.
[7] "The structure and entropy of ice and of other crystals with some randomness of atomic arrangement" , L. Pauling, J. Am. Chem. Soc. 57, 2680 (1935). Abstract.
[8] "Observation of Magnetic Monopoles in Spin Ice", H. Kadowaki, N. Doi, Y. Aoki, Y. Tabata, T. J. Sato, J. W. Lynn, K. Matsuhira, Z. Hiroi, J. Phys. Soc. Jpn. 78, 103706 (2009). Abstract.
[9] "A new macroscopically degenerate ground state in the spin ice compound Dy2Ti2O7 under a magnetic field" K. Matsuhira, Z. Hiroi, T. Tayama, S. Takagi and T. Sakakibara, J. Phys. Condens. Matter 14, L559 (2002). Article; "Kagome ice State in the dipolar spin ice Dy2Ti2O7" Y. Tabata, H. Kadowaki, K. Matsuhira, Z. Hiroi, N. Aso, E. Ressouche, and B. Fåk, Phys. Rev. Lett. 97, 257205 (2006). Abstract.
[10] In Oct. 2009, in addition to [8], three experimental papers on the magnetic monopoles in spin ice have been published: "Measurement of the charge and current of magnetic monopoles in spin ice" S. T. Bramwell, S. R. Giblin, S. Calder, R. Aldus, D. Prabhakaran & T. Fennell, Nature 461, 956 (2009), Abstract; "Dirac Strings and Magnetic Monopoles in the Spin Ice Dy2Ti2O7" D. J. P. Morris, D. A. Tennant, S. A. Grigera, B. Klemke, C. Castelnovo, R. Moessner, C. Czternasty, M. Meissner, K. C. Rule, J.-U. Hoffmann, K. Kiefer, S. Gerischer, D. Slobinsky, R. S. Perry, Science 326, 411 (2009) Abstract; "Magnetic Coulomb Phase in the Spin Ice Ho2Ti2O7" T. Fennell, P. P. Deen, A. R. Wildes, K. Schmalzl, D. Prabhakaran, A. T. Boothroyd, R. J. Aldus, D. F. McMorrow, S. T. Bramwell, Science 326, 415 (2009). Abstract.

Finer Atomic Matchmaking by Radio Frequency Tuning

The image shows, in the sequence of green arrows, how a pair of ultracold gas atoms collides, briefly forms a molecule, and flies apart, in the presence of an external magnetic field (not shown) that influences this process. By adding RF radiation (lightning bolts) of the right frequency, the atoms can experience being in many different molecular states (red arrows), providing even more extensive and detailed control of the collision. The size of the yellow bursts indicate the amount of absorption/emission of RF radiation. [Image Credit: Eite Tiesinga, Joint Quantum Institute, University of Maryland/ National Institute of Standards and Technology]

In a paper accepted for publication in Physical Review A, a team of scientists at the Joint Quantum Institute (JQI) of the National Institute of Standards and Technology (NIST) and the University of Maryland have reported that properly tuned radio-frequency waves can influence how much the atoms attract or repel one another, opening up new ways to control their interactions.

While investigating mysterious data in ultracold gases of rubidium atoms, they found that the radio-frequency (RF) radiation could serve as a second "knob," in addition to the more traditionally used magnetic fields, for controlling how atoms in an ultracold gas interact. Just as it is easier to improve reception on a home radio by both electronically tuning the frequency on the receiver and mechanically moving the antenna, having two independent knobs for influencing the interactions in atomic gases could produce richer and more exotic arrangements of ultracold atoms than ever before.

Previous experiments with ultracold gases, including the creation of Bose-Einstein condensates, have controlled atoms by using a single knob—traditionally, magnetic fields. These fields can tune atoms to interact strongly or weakly with their neighbors, pair up into molecules, or even switch the interactions from attractive to repulsive. Adding a second control makes it possible to independently tune the interactions between atoms in different states or even between different types of atoms.

Such greater control could lead to even more exotic states of matter. A second knob, for example, may make it easier to create a weird three-atom arrangement known as an Efimov state, whereby two neutral atoms that ordinarily do not interact strongly with one another join together with a third atom under the right conditions [Read past 2Physics report on Efimov state]

For many years, researchers had hoped to use RF radiation as a second knob for atoms, but were limited by the high power required. The new work shows that, near magnetic field values that have a big effect on the interactions, significantly less RF power is required, and useful control is possible.

In the new work, the JQI/NIST team examined intriguing experimental data of trapped rubidium atoms taken by the group of David Hall at Amherst College in Massachusetts. This data showed that the RF radiation was an important factor in tuning the atomic collisions. To explain the complicated way in which the collisions varied with RF frequency and magnetic field, NIST theorist Thomas Hanna developed a simple model of the experimental arrangement.

"The model reconstructed the energy landscape of the rubidium atoms and explained how RF radiation was changing the atoms' interactions with one another. In addition to providing a roadmap for rubidium, this simplified theoretical approach could reveal how to use RF to control ultracold gases consisting of other atomic elements", Hanna says.

Reference
"Radio-frequency dressing of multiple Feshbach resonances"
A.M. Kaufman, R.P. Anderson, T.M. Hanna, E. Tiesinga, P.S. Julienne, and D.S. Hall,
To appear in Physical Review A.
Abstract: We demonstrate and theoretically analyze the dressing of several proximate Feshbach resonances in 87Rb using radiofrequency radiation (rf). We present accurate measurements and characterizations of the resonances, and the dramatic changes in scattering properties that can arise through the rf dressing. Our scattering theory analysis yields quantitative agreement with the experimental data. We also present a simple interpretation of our results in terms of rf-coupled bound states interacting with the collision threshold.

[We thank NIST for materials used in this posting]

Quantum Fingerprints of Chaos

Poul Jessen [photo courtesy: College of Optical Sciences, University of Arizona]

In a recent article in the journal Nature, Prof. Poul Jessen and his group in the College of Optical Sciences at the University of Arizona have reported some interesting outcomes of a series of experiments showing clear fingerprints of classical-world chaos in a quantum system designed to mimic a textbook example of chaos known as the "kicked top."

Chaotic behavior is the rule, not the exception, in the world we experience through our senses, the world governed by the laws of classical physics. Even tiny, easily overlooked events can completely change the behavior of a complex system, to the point where there is no apparent order to most natural systems we deal with in everyday life.

The weather is one familiar case, but other well-studied examples can be found in chemical reactions, population dynamics, neural networks and even the stock market. Scientists who study "chaos" - which they define as extreme sensitivity to infinitesimally small tweaks in the initial conditions - have observed this kind of behavior only in the deterministic world described by classical physics.

The University of Arizona team (front row, L to R) Worawarong Rakreungdet, Souma Chaudhury, Brian Anderson and (back, L to R) Aaron Smith, Enrique Montano, Jae Hoon Lee, and Poul Jessen [photo courtesy: College of Optical Sciences, University of Arizona]

Until now, no one has produced experimental evidence that chaos occurs in the quantum world, the world of photons, atoms, molecules and their building blocks. This is a world ruled by uncertainty: An atom is both a particle and a wave, and it's impossible to determine its position and velocity simultaneously.

And that presents a major problem. If the starting point for a quantum particle cannot be precisely known, then there is no way to construct a theory that is sensitive to initial conditions in the way of classical chaos.

Yet quantum mechanics is the most complete theory of the physical world, and therefore should be able to account for all naturally occurring phenomena.

"The problem is that people don't see [classical] chaos in quantum systems," said Poul Jessen. "And we believe quantum mechanics is the fundamental theory, the theory that describes everything, and that we should be able to understand how classical physics follows as a limiting case of quantum physics."

Now, however, Jessen and his group in UA's College of Optical Sciences have performed a series of experiments that show just how classical chaos spills over into the quantum world. They studied the quantum version of a spinning top with this laboratory apparatus.

The quantum version of the top is the "spin" of individual laser-cooled cesium atoms that Jessen's team manipulate with magnetic fields and laser light, using tools and techniques developed over a decade of painstaking laboratory work.

"Think of an atom as a microscopic top that spins on its axis at a constant rate of speed," Jessen said. He and his students repeatedly changed the direction of the axis of spin, in a series of cycles that each consisted of a "kick" and a "twist". Because spinning atoms are tiny magnets, the "kicks" were delivered by a pulsed magnetic field. The "twists" were more challenging, and were achieved by subjecting the atom to an optical-frequency electric field in a precisely tuned laser beam.

They imaged the quantum mechanical state of the atomic spin at the end of each kick-and-twist cycle with a tomographic technique that is conceptually similar to the methods used in medical ultrasound and CAT scans. The end results were pictures and stop-motion movies of the evolving quantum state, showing that it behaves like the equivalent classical system in some significant ways.

One of the most dramatic quantum signatures the team saw in their experiments was directly visible in their images: They saw that the quantum spinning top observes the same boundaries between stability and chaos that characterize the motion of the classical spinning top. That is, both quantum and classical systems were dynamically stable in the same areas, and dynamically erratic outside those areas.

Jessen's experiment revealed a new signature of chaos for the first time. It is related to the uniquely quantum mechanical property known as "entanglement" which is best known from a famous thought experiment proposed by Albert Einstein, in which two light particles, or photons, are emitted with polarizations that are fundamentally undefined but nevertheless perfectly correlated. Later, when the photons have traveled far apart in space, their polarizations are both measured at the same instant in time and found to be completely random but always at right angles to each other.

"It's as though one photon instantly knows the result for the other and adjusts its own polarization accordingly," Jessen said. By itself, Einstein's thought experiment is not directly related to quantum chaos, but the idea of entanglement has proven useful, Jessen added.

Theorists have speculated that the onset of chaos will greatly increase the degree to which different parts of a quantum system become entangled. Jessen took advantage of atomic physics to test this hypothesis in his laboratory experiments. The total spin of a cesium atom is the sum of the spin of its valence electron and the spin of its nucleus, and those spins can become quantum correlated exactly as the photon polarizations in Einstein's example. In Jessen's experiment, the electron and nuclear spins remained unentangled as a result of stable quantum dynamics, but rapidly became entangled if the dynamics were chaotic.

Entanglement is a buzzword in the science community because it is the foundation for quantum cryptography and quantum computing. However, Jessen clarified,"Our work is not directly related to quantum computing and communications. It just shows that this concept of entanglement has tendrils in all sorts of areas of quantum physics because entanglement is actually common as soon as the system gets complicated enough."

Reference
"Quantum signatures of chaos in a kicked top"
S. Chaudhury, A. Smith, B. E. Anderson, S. Ghose & P. S. Jessen,
Nature 461, 768-771 (2009). Abstract.

Colorful Quantum Entanglement

Paulo Nussenzveig (left) and Marcelo Martinelli in their lab, in Brazil.



[This is an invited article based on recently published works of the authors and their collaborators -- 2Physics.com]




Authors: Paulo Nussenzveig and Marcelo Martinelli

Affiliation: Experimental Physics Department, Instituto de Fisica -- USP,
Sao Paulo, Brazil
Link to the Laboratory of Coherent Manipulation of Atoms and Light (LMCAL) >>

Quantum entanglement has just become more colorful. In a recent experiment, three bright beams of light, all of different wavelengths, were entangled [1]. Physicists have been playing around with this mind-boggling concept since 1935, but recently they have acquired enormous control over quantum systems. Entanglement is now viewed as a valuable resource to enable sophisticated information tasks. Indeed, the field of quantum information science relies heavily on entanglement in order to perform quantum computing, teleportation, and communication. A quantum internet is envisaged as a dream to be pursued, with information being conveyed among its nodes via quantum teleportation [2].

Since quantum hardware is still composed of different physical systems, which do not always share common resonances for interaction with light, one faces challenges to exchange quantum information among them. By entangling light beams of different wavelengths, this is no longer a problem. This is what was achieved, with one beam in the visible portion of the spectrum (532.251 nm) and two in the near infrared (1062.102 nm and 1066.915 nm). Research was performed by a group at the University of São Paulo, in Brazil, with participation of two researchers (former students in Brazil) from the new Max Planck Institute for the Science of Light, in Germany.

Entanglement in continuous variable (CV) systems, such as bright beams of light, is generated by means of nonlinear optical processes [3]. The lowest nonlinear order is two, corresponding to processes in which three fields are coupled. Examples are second harmonic generation, sum- and difference-frequency generation, and parametric down-conversion. This latter process is used for the generation of twin photons, a well-known way of producing entangled qubits (e.g. polarization-entangled photons). A nonlinear crystal is pumped by a laser, generating spontaneously emitted pairs of photons. In each fundamental process, a pump photon is annihilated and a pair of lower-frequency photons is created. If the crystal is placed inside a cavity, resonant for all three fields involved, photons are emitted in occupied modes (stimulated emission). The resulting gain can overcome losses and the system oscillates, similarly to a laser. This optical parametric oscillator (OPO), as sketched in Fig. 1, was used by the researchers to generate the three-color entanglement.

Fig. 1 : Sketch of an OPO. A nonlinear optical crystal is placed within two mirrors, forming a cavity. Green incident light is down-converted into twin beams of infrared light.

In order to measure entanglement, researchers had to cool the crystal, to reduce thermal vibrations (phonons), which were responsible for generating unwelcome phase noise in the optical fields. In a tripartite Gaussian state, there is a necessary and sufficient criterion to check for entanglement, due to Simon [4] and extended by Werner and Wolf [5]. By measuring the full covariance matrix of the three-field system, researchers could check that the lowest symplectic eigenvalue under partial transposition with respect to each beam was smaller than one, demonstrating full inseparability (Fig. 2).

Fig. 2: Full tripartite inseparability. Symplectic eigenvalues corresponding to transposition by the pump (green), signal (red) and idler (blue) are lower than one for a broad range of values of the pump power relative to the threshold power (from ref. [1]).

Three-color entangled beams can be useful for communications. Since quantum resources are in general very fragile, the robustness of the entanglement against losses was studied. The researchers observed a subtle quantum property hitherto only witnessed in few-particle systems, called entanglement sudden death [6]. Entanglement was lost for partial attenuation, in certain situations. However, in others the researchers showed that entanglement can be kept alive. The states that were generated have different sensitivity to losses, warranting further investigations.

Entanglement implies a certain “familiarity” among the constituents of a system composed of different parts. The Brazilian experiment generates entanglement among the pump and the twins to which it gives birth: one can think of it as “quantum genealogy”, since it is shown that the twins are entangled to their “mother”.

References
[1] "Three-Color Entanglement", A. S. Coelho, F. A. S. Barbosa, K. N. Cassemiro, A. S. Villar, M. Martinelli, and P. Nussenzveig, Science Express, DOI: 10.1126/science.1178683 (September 17, 2009). Abstract.
[2] "The Quantum Internet", H. J. Kimble, Nature 453, 1023 (2008). Abstract.
[3] "Quantum information with continuous variables", S. L. Braunstein and P. van Loock, Rev. Mod. Phys. 77, 513 (2005). Abstract.
[4] "Peres-Horodecki Separability Criterion for Continuous Variable Systems", R. Simon, Phys. Rev. Lett. 84, 2726 (2000). Abstract.
[5] "Bound Entangled Gaussian States", R. F. Werner and M. M. Wolf, Phys. Rev. Lett. 86, 3658 (2001). Abstract.
[6] "Environment-Induced Sudden Death of Entanglement", M. P. Almeida, F. de Melo, M. Hor-Meyll, A. Salles, S. P. Walborn, P. H. Souto Ribeiro, and L. Davidovich, Science 316, 579 (2007). Abstract.

Physics Nobel 2009 : The Masters of Light

Charles K. Kao [photo courtesy: Chinese University of Hong Kong]

This year's Nobel Prize in Physics is awarded for two scientific achievements that have helped to shape the foundations of today’s networked societies. They have created many practical innovations for everyday life and provided new tools for scientific exploration.

The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 2009 with one half to Charles K. Kao of Standard Telecommunication Laboratories, Harlow, UK, and Chinese University of Hong Kong "for groundbreaking achievements concerning the transmission of light in fibers for optical communication", and the other half jointly to Willard S. Boyle and George E. Smith of Bell Laboratories, Murray Hill, NJ, USA "for the invention of an imaging semiconductor circuit – the CCD sensor".

In 1966, Charles K. Kao made a discovery that led to a breakthrough in fiber optics. He carefully calculated how to transmit light over long distances via optical glass fibers. With a fiber of purest glass it would be possible to transmit light signals over 100 kilometers, compared to only 20 meters for the fibers available in the 1960s. Kao's enthusiasm inspired other researchers to share his vision of the future potential of fiber optics. The first ultrapure fiber was successfully fabricated just four years later, in 1970.

Willard S Boyle [photo courtesy: RMC Club of Canada]

Today optical fibers make up the circulatory system that nourishes our communication society. These low-loss glass fibers facilitate global broadband communication such as the Internet. Light flows in thin threads of glass, and it carries almost all of the telephony and data traffic in each and every direction. Text, music, images and video can be transferred around the globe in a split second.

If we were to unravel all of the glass fibers that wind around the globe, we would get a single thread over one billion kilometers long – which is enough to encircle the globe more than 25 000 times – and is increasing by thousands of kilometers every hour.

A large share of the traffic is made up of digital images, which constitute the second part of the award. In 1969 Willard S. Boyle and George E. Smith invented the first successful imaging technology using a digital sensor, a CCD (Charge-Coupled Device). The CCD technology makes use of the photoelectric effect, as theorized by Albert Einstein and for which he was awarded the 1921 year's Nobel Prize. By this effect, light is transformed into electric signals. The challenge when designing an image sensor was to gather and read out the signals in a large number of image points, pixels, in a short time.

George E. Smith [photo courtesy: IEEE]

The CCD is the digital camera's electronic eye. It revolutionized photography, as light could now be captured electronically instead of on film. The digital form facilitates the processing and distribution of these images. CCD technology is also used in many medical applications, e.g. imaging the inside of the human body, both for diagnostics and for microsurgery.

Digital photography has become an irreplaceable tool in many fields of research. The CCD has provided new possibilities to visualize the previously unseen. It has given us crystal clear images of distant places in our universe as well as the depths of the oceans.