Highlights

Every year, a committee of experts sits down with a tough job to do: from among all ICREA publications, they must find a handful that stand out from all the others. This is indeed a challenge. The debates are sometimes heated and always difficult but, in the end, a shortlist of  the most outstanding publications of the year is produced. No prize is awarded, and the only additional acknowledge is the honour of being chosen and highlighted by ICREA. Each piece has something unique about it, whether it be a particularly elegant solution, the huge impact it has in the media or the sheer fascination it generates as a truly new idea. For whatever the reason, these are the best of the best and, as such, we are proud to share them here.

LIST OF SCIENTIFIC HIGHLIGHTS

Format: yyyy

  • Experimental estimation of the dimension of classical and quantum systems (2012)

    Acín Dal Maschio, Antonio (ICFO)

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    Experimental estimation of the dimension of classical and quantum systems

    Dimensionality is one of the most basic and essential concepts in science, inherent to any theory aiming at explaining and predicting experimental observations. In building up a theoretical model, one makes some general and plausible assumptions about the nature and the behavior of the system under study. The dimension of this system, that is, the number of relevant and independent parameters needed to describe it, represents one of these initial assumptions. In general, the failure of a theoretical model in predicting experimental data does not necessarily imply that the assumption on the dimensionality is incorrect, since there might exist a different model assuming the same dimension that is able to reproduce the observed data. A natural question is whether this approach can be reversed and whether the dimension of an unknown system, classical or quantum, can be estimated experimentally. That is, is the standard initial assumption on the dimension unavoidable? If not, what can be said about the dimension of an unknown system only from the observed measurement data and without making any assumption about the detailed functioning of the devices used in the experiment? The concept of a dimension witness answers this question, as it allows bounding the dimension of an unknown system only from measurement statistics. In a recent work, we report the first experimental demonstration of a dimension witnesses. We use photon pairs entangled in polarization and orbital angular momentum to generate ensembles of classical and quantum states of dimensions up to four. We then use a dimension witness to certify their dimensionality as well as their quantum nature. Proving that the dimension of an unknown system is an experimentally accessible quantity is a fundamental result. Besides its fundamental interest, our work opens new avenues in quantum information science, where dimension represents a powerful resource, especially for device-independent estimation of quantum systems and quantum communications.

  • Redirecting the design of high temperature superconductors by using a "Gruyère cheese"-type nanostructure. (2012)

    Arbiol Cobos, Jordi (CSIC - ICMAB)

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    Redirecting the design of high temperature superconductors by using a "Gruyère cheese"-type nanostructure.

    A new and easy mechanism for the design of high temperature superconducting materials has been developed. The technique is based on the alteration of the superconducting material, creating special regions in its structure, where superconductivity breaks. These regions could resemble the holes in Swiss cheese at the nanoscale. Superconducting materials are capable of carrying electric currents up to 100 times higher than copper thanks to their quantum mechanical properties. For this, the material must exhibit nanometric dimensions where quantum coherence is broken and the superconducting magnetic vortices are stored. Until now, these regions were obtained by creating defects and overlapping in the structure of a non-conductive secondary phase that created the voids. The present work shows that by creating a strained structure of the crystal lattice at the nanoscale extraordinary electrical currents, governed by a new physical mechanism, are generated. The main advantage of this mechanism is that it allows designing a new generation of high-temperature superconductors able to provide unsuspected benefits for the most demanding applications.
    Up to date high temperature superconductors are the most efficient. This entails a great advantage from the practical point of view because the used cooling temperature has a ten-times lower cost than their low temperature counterparts. Thanks to the high current volume produced by superconducting materials, they are able to generate magnetic fields much higher than conventional metals. The large particle accelerators like CERN in Geneva (Switzerland) and the large fusion reactor ITER in Marseille (France) are nowadays based on low-temperature superconductors. With these new nanotechnology superconductors the barriers of magnetic fields accessible to humanity will be broken. In addition, the mechanism developed significantly reduces the operating costs of the magnets.
    Applications that can take advantages of this discovery cover engines and power generators for boats, wind power or different industries, and cables and current limiters to achieve a smarter and safer electrical power network. It is estimated that this nascent industry will have a global market estimated at over 3,000 million euros annually in ten years. Superconducting systems will be more efficient, lighter and safer, generating an environmental friendlier electrical system. Given this increase in efficiency, the development of a new superconductor technology will result in significant savings in energy and, th

  • Worldrecord broadband and coherent light source (2012)

    Biegert, Jens (ICFO)

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    Worldrecord broadband and coherent light source

    An energy and coherent supercontinuum light source was demonstrated by the group of Prof. Biegert from ICFO with theoretical support from Ecole Polytechnique in France and Heriot-Watt University in the UK. The results are published in Nature Communications and highlight a source spanning a continuous wavelength range between 450 nm to 4500 nm.

    Supercontinuum light sources are similar to a very intense rainbow of light, containing a continuum of wavelengths, finding widespread applications in optical spectroscopy, optical coherence tomography, optical microscopy, frequency metrology, fluorescence lifetime imaging, optical communications, gas sensing and many others. In fluorescence microcopy, for instance, alleviates a supercontinuum light source the microscopist from using many individual laser sources or to tune a laser to excite a specific fluorescing dye.
    A supercontinua is generated during the nonlinear propagation of intense laser light in optical fibers, gases or solid state materials. The standing issue with such processes had been the increasing loss of coherence and energy with increasing bandwidth which was now resolved.

  • Large scale brain activations predict reasoning profiles (2012)

    Bonatti, Luca (UPF)

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    Large scale brain activations predict reasoning profiles

    For many centuries, philosophers and scientists have been fascinated by a form of reasoning that allows us to draw necessary conclusions from some premises. For example, if we hear that All men are mortals, and that Socrates is a man, we know that Socrates is mortal, by simply reasoning from these premises. This way to draw novel knowledge by means of necessary inferences is so ubiquitous in human reasoning that we often do not even realize that we are making logical inferences. However its neural bases are poorly understood. Furthermore, notoriously, different individuals follow different strategies to find solutions. In our study, we propose a new approach to understand the neural basis of deductive reasoning and explore in detail the inter-individual variability.

    In general, when studying the neural basis of behavior, researchers start from a certain behavior and try to identify the underlying patterns of brain activity. We reverse this strategy and show that specific patterns of brain activity can predict what strategy an individual will use when reasoning about elementary deductive problems. We also show that the predictive power of the activity profiles is distributed in a non-uniform way across the areas activated during the corresponding cognitive operation. Thus, the activation of left ventro-lateral and occipital cortex (BA47 and BA9) predicts if participants will draw logically valid solutions. By contrast, the activations of the left lateral and superior frontal cortex ((BA44/45 and BA6/8) predict if participants will be consistent in their responses, even when they make mistakes.

    We conclude that deductive reasoning can best be described as a cascade of cognitive processes that require the concerted operation of several, functionally different brain areas. In general, the activation of some areas of the left brain are essential to reason logically. Potentially, this discovery may allow future research to better characterize some cognitive deficits that attain patients with brain injuries, and set up better rehabilitation therapies. This research may also help creating novel and more efficient educational tools inspired by how the brain actually processes problems.

    The work, realized in collaboration with Carlo Reverberi, Paolo Cherubini and Eraldo Paulesu (University of Milano-Bicocca), Richard Frackowiak (Centre Hospitalier Universitaire Vaudois, Lausanne) and Emiliano Macaluso (Fondazione Santa Lucia, Rome), won the Editor's Choice Award at the 18th World Congress of the Human Brain Mappin

  • The smallest typewriter in the world (2012)

    Catalán Bernabé, Gustau (ICN2)

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    The smallest typewriter in the world

    The search for more compact ways to store information is a running theme in nanotechnology. The basic concept is simple: one needs materials that can be in two different states (that become the 1's and 0's in binary code), and an efficient way to change between them so as to write the information. A good example is magnetic memories, which are based on tiny magnets that can be oriented with their north pole up or down. An alternative are ferroelectric memories based on the property of some materials to have a reorientable electric dipole, i.e. a molecular structure where the centers' positive charge and negative charge are separated and can be inverted by an electric field. Like magnets, ferroelectrics also have a north pole and a south pole that define a 1 and a 0. Unlike magnets, however, ferroelectrics are written with voltage rather than current, and are therefore more energy-efficient in theory. In practice, however, although in thin films the writing voltage can be only a couple of volts, the electric field (voltage divided by thickness) is still huge, and this causes problems: materials may fatigue or degrade over time, or even have dielectric breakdown. It is therefore desirable to find an alternative writing method. In a collaboration involving groups in Catalonia and the US, we have just discovered a simple alternative: pushing.

    Although mechanical pressure (stress) cannot in theory invert polarization, stress differences can, thanks to a phenomenon known as flexoelectricity, which is the ability of all materials to polarize when subject to a deformation gradient. Although it is a universal property, it is small at the macroscale. At the nanoscale, however, gradients can be huge and so is therefore flexoelectricity. Big enough, in fact, to invert the polarization of a ferroelectric memory. We have demonstrated this by using the sharp tip of an atomic force microscope (a needle with a radius of only 30nm) and pushing gently (a millionth of a Newton of force) onto the surface of a ferroelectric thin film. Because of the sharpness of the tip, the force is concentrated, leading to large but very localized deformation gradients. In the places where the tip pushes, therefore, large flexoelectricity is realized, which inverts the ferroelectric dipole from the up state to the down state -between 1 and 0 in information terms. Thus, by converting mechanical pressure into nanoscopic information, flexoelectricity brings up to date a very old memory storage device: the typewriter.

  • Understanding how malaria parasites adapt to changes in their environment: the role of epigenetic variation (2012)

    Cortés Closas, Alfred (ISGlobal)

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    Understanding how malaria parasites adapt to changes in their environment: the role of epigenetic variation

    Asexual blood stages of malaria parasites live inside red blood cells, a relatively stable environment. However, there are still exogenous changes to which they need to adapt. The majority of organisms respond to environmental fluctuations by sensing the environment and activating distinct transcriptional programs that allow survival under the different conditions, but malaria parasites are largely unable to do this. We predicted that this limited capacity is compensated by the ability of the parasite to use alternative strategies for rapid adaptation. To test this hypothesis, we took "transcriptional snapshots" of clonal populations of parasites, where all parasites have the same genes, and found that individual parasites within the populations have different combinations of expressed and repressed genes. Genes that can be found in different transcriptional states represent about 10% of the genes in the parasite's genome, and their expression patterns are clonally transmitted by epigenetic mechanisms. The majority of these genes (clonally variant genes) are involved in host-parasite interactions. They include genes involved in immune evasion but also genes involved in many other processes for which alternative conditions exist. The characteristics of these genes indicate that changes in their expression result not only in antigenic variation but also in functional variation.

    Spontaneous transcriptional and phenotypic heterogeneity within isogenic parasite populations has a clear adaptive potential. When an environmental challenge occurs, heterogeneity allows selection of pre-existing parasites with transcriptional patterns that confer fitness under the new conditions. We demonstrated experimentally that malaria parasites use this bet-hedging (risk spreading) strategy for adaptation to periodical heat-shock mimicking cyclical malaria fevers. We also found that the mechanism that mediates repression of clonally variant genes is similar for all gene families, involving formation of a conserved type of heterochromatin that can be transmitted from one generation to the next by epigenetic mechanism. The active or repressed states are heritable but spontaneously reversible, to confer the necessary flexibility to the process.

    Malaria parasites have a remarkable ability to adapt to any challenge, including adaptation to human interventions such as drugs or vaccines. Our findings bring light into the adaptive mechanisms used by malaria parasites and open the way to identify the specific genes that mediate adaptation

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