ERC FUNDED PROJECTS

This project focuses on developing quantum field theory methods and applying them to the phenomenology of elementary particles. At the Large Hadron Collider (LHC) our current best theoretical understanding of particle physics is being tested against experiment by measuring e.g. properties of the recently discovered Higgs boson. With run two of the LHC, currently underway, the experimental accuracy will further increase. Theoretical predictions matching the latter are urgently needed. Obtaining these requires extremely difficult calculations of scattering amplitudes and cross sections in quantum field theory, including calculations to correctly describe large contributions due to long-distance physics in the latter. Major obstacles in such computations are the large number of Feynman diagrams that are difficult to handle, even with the help of modern computers, and the computation of Feynman loop integrals. To address these issues, we will develop innovative methods that are inspired by new structures found in supersymmetric field theories. We will extend the scope of the differential equations method for computing Feynman integrals, and apply it to scattering processes that are needed for phenomenology, but too complicated to analyze using current methods. Our results will help measure fundamental parameters of Nature, such as, for example, couplings of the Higgs boson, with unprecedented precision. Moreover, by accurately predicting backgrounds from known physics, our results will also be invaluable for searches of new particles.

2 000 000 €

Start date: 2017-10-01, End date: 2022-09-30

Electronics is rapidly speeding up. Ultimately, miniaturization will reach atomic dimensions and the switching speed will reach optical frequencies. This ultimate regime of lightwave electronics, where atomic-scale charges are controlled by few-cycle laser fields, holds promise to advance information processing technology from today’s microwave frequencies to the thousand times faster regime of optical light fields. All materials, including dielectrics, semiconductors and molecular crystals, react to such field oscillations with an intricate interplay between atomic-scale charge displacements (polarizations) and collective carrier motion on the nanometer scale (currents). This entanglement provides a rich set of potential mechanisms for switching and control. However, our ability to eventually realize lightwave electronics, or even to make first steps, will critically depend on our ability to actually measure electronic motion in the relevant environment: within/around atoms. The most fundamental approach would be a direct visualization in space and time. This project, if realized, will offer that: a spatiotemporal recording of electronic motion with sub-atomic spatial resolution and sub-optical-cycle time resolution, i.e. picometers and few-femtoseconds/attoseconds. Drawing on our unique combination of expertise covering electron diffraction and few-cycle laser optics likewise, we will replace the photon pulses of conventional attosecond spectroscopy with freely propagating single-electron pulses at picometer de Broglie wavelength, compressed in time by sculpted laser fields. Stroboscopic diffraction/microscopy will provide, after playback of the image sequence, a direct visualization of fundamental electronic activity in space and time. Profound study of atomic-scale light-matter interaction in simple and complex materials will provide a comprehensive picture of the fundamental physics allowing or limiting the high-speed electronics of the future.

1 992 083 €

Start date: 2015-08-01, End date: 2020-07-31

In the recent couple of years, we have achieved an incredibly deep understanding of N=4 maximally supersymmetric gauge theory and the AdS/CFT correspondence which relates this model to string theory. The main reason for this progress consists in the apparent exact integrability of the models in the planar limit. Integrability is a hidden symmetry which allows to establish very efficient tools for performing calculations. Remarkably, these tools not only conveniently compute observables at very high orders in the coupling constant, both at weak and at strong coupling, but they also make quantitative predictions at finite coupling strength. A similar amount of progress is due to the development of novel on-shell techniques which allow to construct scattering amplitudes at several loop orders. They become especially powerful when combined with the extended symmetries related to integrability. The aim of the project is to put the recent rapid progress in integrability and scattering amplitudes on a solid foundation. By enhancing the encountered symmetries and applications towards more realistic gauge and gravity theories we hope to obtain new tools for QFT in general as well as new clues for the problem of quantum gravity. More concretely, we will work out a precise formulation for the algebra underlying integrability. This is a crucial step towards proving integrability in AdS/CFT and to justify and develop efficient methods. Furthermore, we plan to develop applications of integrability away from the planar limit and for non-integrable gauge theories. Finally, we will extend these methods and considerations to gravity models. We will also take a fresh look at alternative models with a view to solving the puzzle of quantum gravity. We plan to address these important objectives with the common framework of extended symmetries and powerful calculational techniques for scattering amplitudes.

1 660 804 €

Start date: 2014-06-01, End date: 2019-05-31

In the standard model of particle physics (SM), the Higgs boson explains the existence of mass of the elementary particles. However, the model suffers from severe weaknesses: radiative corrections drive the theoretical mass of the Higgs boson to extremely high, unnatural values, while the observed mass is rather low (the famous hierarchy problem). Unknown mechanisms of physics beyond the standard model (BSM) must exist to avoid this unnatural situation. Such BSM mechanisms modify the predicted properties and decay patterns of the Higgs boson. The experimental collaborations at the LHC are measuring these decay patterns as precisely as possible. The decay of the Higgs boson into bottom quarks is dominant with a predicted decay fraction of 57%. Neither this nor the subdominant decay into charm quarks of 2.9% have ever been observed. The small decay fraction into charm quarks makes it susceptible to BSM modifications, if they exist. A measurement of this charm decay fraction would either unravel new physics that has been sought for more than 60 years, or constrain BSM scenarios to enhance the understanding of the fundamental theory of matter. However, the decay of the Higgs boson into charm quarks has been considered to be experimentally inaccessible at the LHC, because of the difficulties to distinguish charm quarks from other quarks. In this proposal I will show how to overcome these experimental obstacles with new methods for the detection of charm quarks in the CMS detector. The new methods will be based on decay vertex reconstruction algorithms that make use of modern pattern recognition concepts. In combination with new techniques for data analysis and interpretation, this will facilitate the first observation of the Higgs to charm decay, and the measurement of its branching fraction, if it is anomalously enhanced through BSM contributions. With this strategy the first indication for physics beyond the standard model may be found.

1 973 875 €

Start date: 2017-09-01, End date: 2022-08-31

This project will develop a new platform for quantum computation and quantum simulation based on scalable two-dimensional arrays of ions in micro-fabricated Penning traps. It builds upon the rapid advances demonstrating high precision quantum control in micro-fabricated radio-frequency ion traps while eliminating the most problematic element - the radio-frequency potential - using a uniform magnetic field. This offers a significant advantage: since the magnetic field is uniform it provides confinement at any position for which a suitable static quadrupole can be generated. By contrast, r.f. potentials only provide good working conditions along a line. This changed perspective provides access to dense two-dimensional strongly interacting ion lattices, with the possibility to re-configure these lattices in real time. By combining closely-spaced static two-dimensional ion arrays with standard laser control methods, the project will demonstrate previously inaccessible many-body interacting spin Hamiltonians at ion numbers which are out of the reach of classical computers, providing a scalable quantum simulator with the potential to provide new insights into the links between microscopic physics and emergent behavior. Through dynamic control of electrode voltages, reconfigurable two-dimensional arrays will be used to realize a scalable quantum computing architecture, which will be benchmarked through landmark experiments on measurement-based quantum computation and high error-threshold surface codes which are natural to this configuration. Realizing multi-dimensional connectivity between qubits is a major problem facing a number of leading quantum computing architectures including trapped ions. By solving this problem, the proposed project will pave the way to large-scale universal quantum computing with impacts from fundamental physics through to chemistry, materials science and cryptography.

1 999 375 €

Start date: 2019-04-01, End date: 2024-03-31

This project aims at developing a novel method of optical spectroscopy to study the wholly unexplored atomic structure of the superheavy transition metals, starting with element 103, lawrencium (Lr). My team will experimentally identify optical spectral lines that will serve as fingerprints in the search for superheavy elements in the universe. The spectral lines are strongly influenced by relativistic and quantum electrodynamic effects and thus will constitute powerful benchmarks for atomic modeling incorporated within this project. Furthermore, since the nuclear charge distribution influences the atomic structure, our experimental data will advance our understanding of the effects of nuclear shells and deformations on the stability of radionuclides at the top of the Segré chart. While I recently opened up the atomic structure of element 102, nobelium, the new challenges faced are the refractory nature of the elements, which lay ahead, coupled with shorter half-lives and decreasing production yields. I propose to overcome these by developing an ultra-sensitive and fast Laser Resonance Chromatography (LRC) to set the new standard in optical spectroscopy. The LRC method combines the element selectivity and spectral precision of laser spectroscopy with cutting-edge technology of ion-mobility mass spectrometry. Based on high-accuracy atomic calculations, my team will optically probe the 1S0-3P1 ground-state transition in singly-charged 255Lr ions and record the distinct arrival times of the ions after passing a drift tube to identify the laser resonance signal. We will perform the experiments at leading in-flight facilities such as the GSI velocity filter SHIP and the new GANIL separator S3. Crucially, the LRC method will be insensitive to physicochemical properties and tolerant of the decreasing yields with increasing atomic number. This paves the way for atomic structure studies of the superheavy elements, in particular, those of refractory nature beyond lawrencium.

1 999 750 €

Start date: 2019-06-01, End date: 2024-05-31

This project proposes to use modern Machine Learning (ML), particularly Deep Learning (DL), as a breakthrough solution to address the scientific, technological, and financial challenges that High Energy Physics (HEP) will face in the decade ahead. The quest for new physics is increasing the complexity of the experiments and, consequently, the human and financial costs to operate these detectors, with experiments facing at best flat budgets. ML offers a way out of this impasse. With the development of DL, ML has successfully addressed tasks such as image recognition and text understanding, which eventually opened the way to automatizing complex tasks. These progresses have the potential to revolutionize HEP experimental techniques. We propose to apply cutting-edge ML technologies to HEP problems, paving the way to self-operating detectors, capable of visually inspecting events and identifying the physics process generating them, while monitoring the goodness of the data, the correct functioning of the detector components and, if any, the occurrence of anomalous events caused by unspecified new physics processes. We structure the work in a set of working packages, representing intermediate steps towards this final goal. We propose to apply ML to data taking, event identification, data-taking monitoring, and event reconstruction as intermediate steps toward using these techniques for unsupervised physics searches. The project resources will by used to create a team of computer scientists, who will carry on a systematic R&D program to apply cutting-edge ML technology to HEP: reinforced learning, generative models, event indexing, data mining, anomaly and outliers detection, etc. Being hosted at CERN, the project will benefit from existing computing infrastructures, large datasets availability, the presence of local experts of each aspect of HEP, and established collaborations with private companies on hardware and software R&D.

1 703 750 €

Start date: 2018-04-01, End date: 2023-03-31

"NAUTILUS will investigate the nucleosynthesis of the chemical elements during the evolution of stars, which is the basis for understanding the chemical history of the Universe. The vast majority of the elements heavier than iron are produced by neutron capture reactions. The precise knowledge of the involved neutron capture cross sections for certain isotopes sets tight limits for stellar parameters and puts strong constraints on the age of the Universe. Accurate measurements of the key nuclear reactions in the mass region around the radioactive 85Kr will lead to the improvements needed to characterize the production processes of the elements in stars. The respective high-accuracy abundance patterns in single stars can then be interpreted as diagnostic tools for the deep stellar interior and the isobaric 87Sr/87Rb chronometer constraints the history of the Universe. The neutron capture cross section of radioactive isotopes for neutron energies in the keV region will be measured by a time-of-flight (TOF) experiment. NAUTILUS will provide a unique facility realizing the TOF technique with an ultra-short flight path at the FRANZ setup at Goethe University Frankfurt am Main, Germany. A highly optimized spherical photon calorimeter will be built and installed at an ultra-short flight path. NAUTILUS opens new horizons in the area of neutron-induced reaction research, as smallest samples like of 85Kr - which will be produced as an isotopically pure radioactive sample - will become measureable in reasonable times. Future applications include the study of neutron capture cross sections important for next generation nuclear reactors: For the first time the high neutron fluxes needed to study the mass region of interest in the keV energy range will be available."

1 871 596 €

Start date: 2014-04-01, End date: 2019-03-31

The discovery of cosmic neutrinos is one of the major breakthroughs in science in the year 2013. These neutrinos are expected to point back to the origin of the cosmic rays, which are produced in the most powerful accelerators in the universe. In order to solve the puzzle where the highest energetic neutrinos and cosmic rays come from, the key information could be the composition of the observed cosmic ray flux. The question critical for the future development of high-energy astrophysics is especially how heavier nuclei can be accelerated and escape from the sources, such as gamma-ray bursts or active galactic nuclei, without disintegration, or what the consequences for the neutrino fluxes and cosmic ray compositions at the sources are. Neutrinos, on the other hand, may be good for surprises, such as new physics only detectable at extreme energies, distances, or densities. In addition, the possibility to measure neutrino properties in neutrino telescopes has been emerging, either using astrophysical or atmospheric neutrino fluxes, which means that the border line between neutrino physics and astrophysics applications in these experiments fades. The key idea of this proposal is therefore to combine the expertise from astrophysics and particle physics in a multi-disciplinary working group 1) to study the effect of heavy nuclei on the source fluxes from multiple messengers, such as a neutrinos, cosmic rays, and gamma-rays, using efficient descriptions for the radiation processes and particle interactions, and 2) to optimize future experiment infrastructure in ice and sea water for both astro- and particle physics applications. The key goals are to eventually identify the origin of the cosmic rays and cosmic neutrinos, and to solve the open questions in particle physics, such as neutrino mass hierarchy and leptonic CP violation.

1 746 000 €

Start date: 2015-09-01, End date: 2020-08-31

One of our dreams for the future is to control and manipulate complex materials and devices at will. This progress would revolutionize technology and influence many aspects of our everyday life. A promising direction is the control of material properties by electromagnetic radiation leading to photo-induced phase transitions. An example of such a transition is the reported dynamically induced superconductivity via a laser pulse. Whereas the theoretical description of the coupling of fermions to bosonic modes in equilibrium has seen enormous progress and explains highly non-trivial phenomena as the phonon-induced superconductivity, driven systems pose many puzzles. In addition to the inherent time-dependence of the external driving field, a multitude of possible excitation and relaxation mechanisms challenge the theoretical understanding. Recently in the field of quantum optics, a much cleaner realization of a photo-induced phase transition, the Dicke transition, has been observed for bosonic quantum gases loaded in an optical cavity. Above a critical pump strength of an external laser field, the ensemble undergoes a transition to an ordered phase. We aim to advance the general theoretical understanding of photo-induced phase transitions both in the field of solid state physics and quantum optics. In particular, we will focus on the design and investigation of photo-induced transitions to unconventional superconductivity and non-trivial topological phases. Our insights will be applied to fermonic quantum gases in optical cavities and solid state materials. In order to treat these systems efficiently, we will develop new variants of the numerical density matrix renormalization group (or also called matrix product state) methods and combine these with analytical approaches.

1 486 973 €

Start date: 2015-09-01, End date: 2021-08-31

One of the most fascinating quantum phenomena in nuclear physics is the occurrence of neutron halos and neutron skins in very neutron rich atomic nuclei. Thick neutron skins and halos, not yet evidenced in medium mass nuclei, would be unique low-density neutron matter accessible in the laboratory. Nuclear shell structure is also known to change with the number of protons and neutrons. The nuclear structure of very heavy nuclei at and above Z=100 is barely known, and the existence of new long-lived heavy isotopes is still an open question. The above fundamental phenomena related to the unbalance of neutron and protons in unstable nuclei are essential to understand the complex nature of nuclei and related astrophysical processes. We propose a new physics program to determine the neutron over proton densities at the nuclear surface for the most exotic nuclei that can be produced today, to evidence and to characterize neutron halos and skins in medium and heavy mass regions. PUMA will also allow the spectroscopy of single-particle states in heavy-nuclei above Z=100 will offer a new insight into the unknown shell structure at the top of the nuclear landscape. To address these questions, PUMA explores a new way to study radioactive nuclei produced at very low kinetic energy: the interaction of antiprotons with unstable nuclei. PUMA is based on a new apparatus: a transportable magnetic trap to store antiprotons and maximize their interaction with slow rare isotopes in order to trigger annihilations and measure the following radiations. The PUMA methodology is based on two steps. (i) The storage of antiprotons will be performed at the new AD/ELENA facility of CERN in collaboration with the GBAR collaboration. (ii) The PUMA physics program is to take place at CERN/ISOLDE and, on a later stage beyond the ERC grant period, at the new SPIRAL2 facility in Europe. PUMA will open new horizons for nuclear structure research.

2 548 298 €

Start date: 2018-01-01, End date: 2022-12-31

This project aims at developing theoretical and numerical methods to simulate space- and time-resolved ultrafast dynamics in novel hybrid molecular-metal nanoparticle systems. The excitation of collective electron dynamics inside the metallic nanoparticles induced by external light fields leads to strongly re-shaped electromagnetic near-fields with complex spatial and temporal profile. The interaction of these modified and enhanced near-fields with molecules located in close vicinity to the metallic nanoparticle is the origin of many astonishing physical and chemical phenomena, such as the formation of new quasi-particles, new mechanisms for chemical reactions or the ultra-high spatial resolution and selectivity in molecular detection.. Besides being of fundamental interest, this interplay between near-fields and molecules promises great potential on the application side, potentially enabling revolutionary breakthrough in new emerging technologies in a broad range of research fields, such as nanophotonics, energy and environmental research, biophotonics, light-harvesting energy sources, highly sensitive nano-sensors etc. This necessitates a solid theoretical understanding and simulation of these hybrid systems. The goal of project QUEM-CHEM is the development of new approaches and methods beyond the state of the art, aiming at a synergy of existing but independently applied methods: • Quantum chemistry (QU) in order to calculate the quantum nature of the molecule-metallic nanoparticle moiety, • Electro-dynamic simulations (EM) describing the complex evolution of the light fields and the near fields around nanostructures, as well as • Dynamical methods to incorporate the response of the molecule to the near-fields Thus, the possible outcome of this highly interdisciplinary project will provide new knowledge in both, physics and chemistry, and might have impact on a large variety of new arising critical technologies.

1 901 400 €

Start date: 2018-05-01, End date: 2023-04-30

The biggest challenge to using ultracold fermionic atoms to simulate strongly correlated phases is cooling the system to sufficiently low temperatures. The aim of QuStA is to tackle this challenge with a novel bottom-up approach and assemble many-body systems from individually prepared building blocks. This vision has come within reach through recent breakthroughs in our group in preparing and manipulating few-atom systems with unprecedented fidelity. Building on this experience, we will prepare multiple such few-atom systems and develop strategies to merge them adiabatically to form a many-body system. Initially, we will focus on studying the physics of the Hubbard model, which is prototypical of strongly-correlated systems. Starting from many independently prepared double-well systems, we will assemble a finite lattice system of up to 10 x 10 sites with extremely low entropy. Since our approach will allow us full control over the parameters of the system - such as tunneling, interactions, and doping - we will be in the unique position to investigate the low-temperature phase diagram of the Hubbard model. Our quantum state assembly approach will also allow us to go beyond the Hubbard model and investigate the emergence of correlations in other interesting systems. In particular, we will take an innovative approach of preparing and merging itinerant spin chains to explore bi-layered lattice systems and spin ladders. These experiments will have far-reaching implications beyond the field of ultracold atoms. Our systems will provide an ideal platform to benchmark theories on strongly correlated phenomena since it clearly surpasses the capabilities of modern classical computers. We envision that the insight gained from our experiments will lead to the understanding of exotic quantum phenomena, such as high-Tc superconductivity.

1 958 101 €

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

A fundamental property of optical photons is their extremely weak interactions, which can be ignored for all practical purposes and applications. This phenomena forms the basis for our understanding of light and is at the heart for the rich variety of tools available to manipulate and control optical beams. On the other hand, a controlled and strong interaction between individual photons would be ideal to generate non-classical states of light, prepare correlated quantum states of photons, and harvest quantum mechanics as a new resource for future technology. Rydberg slow light polaritons have recently emerged as a promising candidate towards this goal, and first experiments have demonstrated a strong interaction between individual photons. The aim of this project is to develop and advance the research field of Rydberg slow light polaritons with the ultimate goal to generate strongly interacting quantum many-body states with photons. The theoretical analysis is based on a microscopic description of the Rydberg polaritons in an atomic ensemble, and combines well established tools from condensed matter physics for solving quantum many-body systems, as well as the inclusion of dissipation in this non-equilibrium problem. The goals of the present project addresses questions on the optimal generation of non-classical states of light such as deterministic single photon sources and Schrödinger cat states of photons, as well as assess their potential for application in quantum information and quantum technology. In addition, we will shed light on the role of dissipation in this quantum many-body system, and analyze potential problems and fundamental limitations of Rydberg polaritons, as well as address questions on equilibration and non-equilibrium dynamics. A special focus will be on the generation of quantum many-body states of photons with topological properties, and explore novel applications of photonic states with topological properties.

1 505 750 €

Start date: 2016-06-01, End date: 2021-05-31

Correlations are central for our modern view on the foundations of quantum theory and applications like quantum information processing. So far, research concentrated on correlations between two or more particles. Indeed, for this situation it is well established that spatial quantum correlations are a useful resource for tasks like quantum cryptography and quantum metrology. There are, however, other types of correlations in quantum mechanics, which arise if a sequence of measurements on a single quantum system is made. These temporal quantum correlations have recently attracted attention, because they are central for the understanding of some differences between the quantum and the classical world. Moreover, due to experimental progress their observation has become feasible with trapped ions, polarized photons, or other quantum optical systems. This project aims at a full understanding and characterization of temporal quantum correlations. For that, we will derive criteria and measures for temporal quantum correlations and investigate their connection to information theory. Then, we will elucidate to which extent temporal correlations can be used to prove that a system is quantum and not classical. Finally, we consider implementations of temporal quantum correlations using continuous variable systems like nanomechanical oscillators and applications in quantum information processing.

1 673 875 €

Start date: 2016-05-01, End date: 2021-04-30

The discovery of a new particle, compatible with the Higgs boson, at the Large Hadron Collider, marked a major triumph of the Standard Model of particle physics. However, many fundamental questions remain and direct or indirect evidence of new physics can be probed with the large number of proton-proton collision data, collected in 2011 and 2012 at 7 and 8 TeV centre-of-mass energy. With this proposal we plan to exploit the large sample of top-quark pair events that is already recorded, and the sample that will be collected from 2015 onwards, at the ultimate energy of 14 TeV. In particular we plan to study the coupling of top quarks to neutral bosons, by measuring the production of associated tt̄γ, tt̄Z and tt̄H. Anomalous electromagnetic or weak couplings could be uncovered by studying kinematic properties of the resulting photon or Z-boson, once the signal is established. By studying the tt̄H production in detail the mechanism of Yukawa coupling of the Higgs boson to fermions will be tested, possibly providing important confidence in the characterisation of the new boson. In all measurements we plan to include the tt̄ dilepton channel, that, despite the smaller branching fraction has typically superior signal-to-noise ratios. An essential part of the programme will be the calibration of the b-tagging algorithms, where we plan to use tt̄ events. For associated Higgs production we will explore the decays H→ bb̄ and H→ γγ.

1 964 088 €

Start date: 2014-01-01, End date: 2018-12-31

We explore unconventional ways how ultracold fermions pair and form collective quantum phases exhibiting long-range order, such as superfluidity and magnetically order. Specifically, we plan to realize and study pairing with orbital angular momentum and pairing induced by long-range interaction. Besides the fundamental interest in unravelling unconventional pairing mechanisms and the interplay between superfluidity and quantum magnetism, our project will also lead to gaining experimental control over topologically protected quantum states. This will pave the way for future topological quantum computers, which are particularly robust to environmental decoherence. Our project addresses three different aspects: (1) We plan to realize p-wave superfluids in two dimensions. This quantum phase exhibits topological excitations (vortices) with anyonic statistics and an isomorphism to the fractional quantum-Hall effect. We will investigate the unusual properties of p-wave superfluids, such as Majorana fermions, i.e. quasiparticles being their own anti-particles, which are predicted to be localized at vortices. This will boost the long-standing efforts in the cold atoms and condensed matter communities to understand topological states of matter. (2) We aim to realize d-wave pairing in optical lattices using a novel experimental approach. d-wave pairing is closely related to high-Tc superconductivity in the cuprates and we are interested in exploring its interplay with magnetic order. Superfluidity and magnetic order are antagonistic phenomena from a conventional BCS-theory point-of-view and hence several fundamental questions will be answered. (3) We plan to induce long-range interactions using a high-finesse optical cavity leading to a light-induced pairing mechanism. We will search for Cooper pairing in spin-polarized Fermi gases mediated by the interaction of Fermions with a quantized light field. This provides access to a new class of combined light-matter quantum states.

1 925 525 €

Start date: 2014-10-01, End date: 2019-09-30