ERC FUNDED PROJECTS

Some of the most fascinating physical phenomena are experimentally observed in strongly correlated electron systems and, on the theoretical side, only poorly understood hitherto. The aim of the ERC project AbinitioDGA is the development, implementation and application of a new, 21th century method for the ab initio calculation of materials with such strong electronic correlations. AbinitioDGA includes strong electronic correlations on all time and length scales and hence is a big step beyond the state-of-the-art methods, such as the local density approximation, dynamical mean field theory, and the GW approach (Green function G times screened interaction W). It has the potential for an extraordinary high impact not only in the field of computational materials science but also for a better understanding of quantum critical heavy fermion systems, high-temperature superconductors, and transport through nano- and heterostructures. These four physical problems and related materials will be studied within the ERC project, besides the methodological development. On the technical side, AbinitioDGA realizes Hedin's idea to include vertex corrections beyond the GW approximation. All vertex corrections which can be traced back to a fully irreducible local vertex and the bare non-local Coulomb interaction are included. This way, AbinitioDGA does not only contain the GW physics of screened exchange and the strong local correlations of dynamical mean field theory but also non-local correlations beyond on all length scales. Through the latter, AbinitioDGA can prospectively describe phenomena such as quantum criticality, spin-fluctuation mediated superconductivity, and weak localization corrections to the conductivity. Nonetheless, the computational effort is still manageable even for realistic materials calculations, making the considerable effort to implement AbinitioDGA worthwhile.

1 491 090 €

Start date: 2013-01-01, End date: 2018-07-31

The overall goal of this project is to develop new concepts and techniques in geometric and asymptotic group theory for a systematic study of the analytic properties of discrete groups. These are properties depending on the unitary representation theory of the group. The fundamental examples are amenability, discovered by von Neumann in 1929, and property (T), introduced by Kazhdan in 1967. My main objective is to establish the precise relations between groups recently appeared in K-theory and topology such as C*-exact groups and groups coarsely embeddable into a Hilbert space, versus those discovered in ergodic theory and operator algebra, for example, sofic and hyperlinear groups. This is a first ever attempt to confront the analytic behavior of so different nature. I plan to work on crucial open questions: Is every coarsely embeddable group C*-exact? Is every group sofic? Is every hyperlinear group sofic? My motivation is two-fold: - Many outstanding conjectures were recently solved for these groups, e.g. the Novikov conjecture (1965) for coarsely embeddable groups by Yu in 2000 and the Gottschalk surjunctivity conjecture (1973) for sofic groups by Gromov in 1999. However, their group-theoretical structure remains mysterious. - In recent years, geometric group theory has undergone significant changes, mainly due to the growing impact of this theory on other branches of mathematics. However, the interplay between geometric, asymptotic, and analytic group properties has not yet been fully understood. The main innovative contribution of this proposal lies in the interaction between 3 axes: (i) limits of groups, in the space of marked groups or metric ultralimits; (ii) analytic properties of groups with curvature, of lacunary or relatively hyperbolic groups; (iii) random groups, in a topological or statistical meaning. As a result, I will describe the above apparently unrelated classes of groups in a unified way and will detail their algebraic behavior.

1 065 500 €

Start date: 2011-04-01, End date: 2016-03-31

AQSuS aims at experimentally implementing analogue quantum simulation of interacting spin models in two-dimensional geometries. The proposed experimental approach paves the way to investigate a broad range of currently inaccessible quantum phenomena, for which existing analytical and numerical methods reach their limitations. Developing precisely controlled interacting quantum systems in 2D is an important current goal well beyond the field of quantum simulation and has applications in e.g. solid state physics, computing and metrology. To access these models, I propose to develop a novel circuit quantum-electrodynamics (cQED) platform based on the 3D transmon qubit architecture. This platform utilizes the highly engineerable properties and long coherence times of these qubits. A central novel idea behind AQSuS is to exploit the spatial dependence of the naturally occurring dipolar interactions between the qubits to engineer the desired spin-spin interactions. This approach avoids the complicated wiring, typical for other cQED experiments and reduces the complexity of the experimental setup. The scheme is therefore directly scalable to larger systems. The experimental goals are: 1) Demonstrate analogue quantum simulation of an interacting spin system in 1D & 2D. 2) Establish methods to precisely initialize the state of the system, control the interactions and readout single qubit states and multi-qubit correlations. 3) Investigate unobserved quantum phenomena on 2D geometries e.g. kagome and triangular lattices. 4) Study open system dynamics with interacting spin systems. AQSuS builds on my backgrounds in both superconducting qubits and quantum simulation with trapped-ions. With theory collaborators my young research group and I have recently published an article in PRB [9] describing and analysing the proposed platform. The ERC starting grant would allow me to open a big new research direction and capitalize on the foundations established over the last two years.

1 498 515 €

Start date: 2017-04-01, End date: 2022-03-31

Computational simulations of natural phenomena are essential in science, engineering, product design, architecture, and computer graphics applications. However, despite progress in numerical algorithms and computational power, it is still unfeasible to compute detailed simulations at large scales. To make matters worse, important phenomena like turbulent splashing liquids and fracturing solids rely on delicate coupling between small-scale details and large-scale behavior. Brute-force computation of such phenomena is intractable, and current adaptive techniques are too fragile, too costly, or too crude to capture subtle instabilities at small scales. Increases in computational power and parallel algorithms will improve the situation, but progress will only be incremental until we address the problem at its source. I propose two main approaches to this problem of efficiently simulating large-scale liquid and solid dynamics. My first avenue of research combines numerics and shape: I will investigate a careful de-coupling of dynamics from geometry, allowing essential shape details to be preserved and retrieved without wasting computation. I will also develop methods for merging small-scale analytical solutions with large-scale numerical algorithms. (These ideas show particular promise for phenomena like splashing liquids and fracturing solids, whose small-scale behaviors are poorly captured by standard finite element methods.) My second main research direction is the manipulation of large-scale simulation data: Given the redundant and parallel nature of physics computation, we will drastically speed up computation with novel dimension reduction and data compression approaches. We can also minimize unnecessary computation by re-using existing simulation data. The novel approaches resulting from this work will undoubtedly synergize to enable the simulation and understanding of complicated natural and biological processes that are presently unfeasible to compute.

1 500 000 €

Start date: 2015-03-01, End date: 2020-02-29

This project aims at the development of a novel toolbox of ab-initio methods that approximate the true many-electron wavefunction using systematically improvable perturbation and coupled-cluster theories. The demand and prospects for these methods are excellent given that the highly-accurate coupled-cluster theories can predict atomization- and reaction energies in a wide range of solids and molecules with chemical accuracy (≈43 meV). However, the computational cost involved inhibits their widespread use in the field of materials science so far. A multitude of suggested developments in the present proposal hold the promise to reduce the computational cost beyond what is currently considered possible by the community. These include explicit correlation methods that augment the conventional wavefunction expansion with terms that depend on the electron pair correlation factors. In contrast to the widely-used homogeneous correlation factors, this proposal aims at the investigation of inhomogeneous correlation factors that can also capture van der Waals interactions. Furthermore this proposal seeks to employ a recently developed combination of atom-centered basis functions and plane wave basis sets, maximizing the compactness in the wavefunction expansion. The combination of these ideas bears the potential to reduce the computational cost of coupled-cluster calculations in solids by three orders of magnitude, leading to a breakthrough in the field of highly-accurate ab-initio simulations. As such the study of challenging solid state physics and chemistry problems forms an important part of this proposal. We seek to investigate molecular adsorption and reactions in zeolites and on surfaces, pressure-driven solid-solid phase transitions of two dimensional layered materials and defects in solids. These problems are paradigmatic for van der Waals interactions and strong correlation, and methods that describe their electronic structure accurately are highly sought after.

1 460 826 €

Start date: 2017-07-01, End date: 2022-06-30

In photovoltaics (PVs), a significant scientific and technological attention has been given to technologies that have the potential to boost the solar-to-electricity conversion efficiency and to power recently unpowerable devices and objects. The research of various solar cell concepts for diversified applications (building integrated PVs, powering mobile devices) has recently resulted in many innovations. However, designs and concepts of solar cells fulfilling stringent criteria of efficiency, stability, low prize, flexibility, transparency, tunable cell size, esthetics, are still lacking. Herein, the research focus is given to a new physical concept of a solar cell that explores extremely promising materials, yet unseen and unexplored in a joint device, whose combination may solve traditional solar cells drawbacks (carrier recombination, narrow light absorption). It features a high surface area interface (higher than any other known PVs concept) based on ordered anodic TiO2 nanotube arrays, homogenously infilled with nanolayers of high absorption coefficient crystalline chalcogenide or organic chromophores using different techniques, yet unexplored for this purpose. After addition of supporting constituents, a solid-state solar cell with an extremely large incident area for the solar light absorption and optimized electron pathways will be created. The CHROMTISOL solar cell concept bears a large potential to outperform existing thin film photovoltaic technologies and concepts due to unique combination of materials and their complementary properties. The project aims towards important scientific findings in highly interdisciplinary fields. Being extremely challenging and in the same time risky, it is based on feasible ideas and steps, that will result in exciting achievements. The principal investigator, Jan Macak, has an outstanding research profile in the field of self-organized anodic nanostructures and is an experienced researcher in the photovoltaic field

1 644 380 €

Start date: 2015-03-01, End date: 2020-02-29

The widespread adoption of the Internet and its influence on our daily life is unquestioned. Global Zettabyte traffic has rendered photonics as indispensable for the communication infrastructure. While direct signal detection has been dismissed in radio communications decades ago, it prevails in short- and medium-reach optics in virtue of its simplicity. In such an environment photonics can only rely on incremental improvements, whereas it desperately seeks for disruptive concepts. COYOTE envisions a novel coherent homodyne transceiver concept for analogue signals and access to higher-order formats with efficiencies of 10 bits/symbol. On top of this, high-fidelity transport of multi-band 5G radio signals in the millimetre-wave range up to 100 GHz will be enabled by analogue coherent photonics while mitigating energy-hungry digital signal processing. COYOTE takes one more leap and dares the contradictory full-duplex data transmission in virtue of its novel reception engine to ultimately guarantee a lean solution with greatly simplified yet flexible “hardware”. The key asset of COYOTE’s coherent engine will be a locked laser with improved coherence characteristics together with a flexible modulator-detector element, which is capable to emulate direct-detection systems in a transparent way while giving birth to novel networking concepts. Exploration of the 3D Stokes and 2D quadrature spaces through a segmented receiver architecture will boost the spectral efficiency to >10 bits/s/Hz. It is the lean and yet efficient coherent transceiver methodology of COYOTE that will remove the currently existing boundary between direct-detection and coherent systems in the midst of network reaches. By coherently “reviving” these telecom segments of integrated wireline-wireless access networks, optical interconnects for intra-datacentre connectivity and even quantum communication, an order-of-magnitude improvement in terms of spectral efficiency x reach product will be gained.

1 500 000 €

Start date: 2019-01-01, End date: 2023-12-31

At the interface between quantum optics and semiconductors we find a rich field of investigation with huge potential for quantum information processing communication technologies. Entanglement is one of the most fascinating concepts in quantum physics research as well as an important resource for quantum information processing. This project will develop novel sources of entangled photon pairs with semiconductor nanostructures. In particular, we will use the scattering of microcavity exciton-polaritons as an extremely strong optical nonlinearity for the generation of entanglement with properties that are difficult to achieve with the traditional methods. Further we will work with individual semiconductor quantum dots to create controlled single entangled pairs and explore the interfacing of quantum dots to flying qubits. The long term vision of this research is to create integrated sources of entanglement that can be combined with laser sources, passive optical elements, and even detectors in order to realize the quantum optics lab on a chip.

1 259 726 €

Start date: 2011-01-01, End date: 2015-12-31

"The stereoselective preparation of enantioenriched organic compounds of high structural complexity and synthetic value, in an economically viable and expeditious manner, is one of the most important goals in contemporary Organic Synthesis. In this proposal, I present a unified and conceptually novel approach for the conversion of flat, aromatic heterocycles into highly valuable compounds for a variety of applications. This approach hinges upon a synergistic combination of the dramatic power of organic photochemical transformations combined with the exceedingly high selectivity and atom-economy of efficient catalytic processes. Indeed, the use of probably the cheapest reagent (light) combined with a catalytic transformation ensures near perfect atom-economy in this journey from flat and inexpensive substructures to chiral added-value products. Conceptually, the photochemical operation is envisaged as a energy-loading step whereas the catalytic transformation functions as an energy-release where asymmetric information is inscribed into the products. The chemistry proposed herein will open up new vistas in enantioselective synthesis. Furthermore, groundbreaking and unprecedented methodology in the field of catalytic allylic alkylation is proposed that significantly expands (and goes beyond) the currently accepted “dogmas” for these textbook reactions. These include (but are not limited to) systematic violations of well-established rules “by design”, new contexts for application, new activation modes and innovative leaving groups. Finally, the comprehensive body of synthetic technology presented will be applied to pressing target-oriented problems in Organic Synthesis. It shall result in a landmark, highly efficient total synthesis of Tamiflu, as well as in application to an environmentally important target (Fomannosin), allowing the easy production of analogues for biological testing."

1 487 000 €

Start date: 2012-01-01, End date: 2016-12-31