ERC FUNDED PROJECTS

One of the greatest challenges in exploiting the electron spin for information processing is that it is not a conserved quantity like the electron charge. In addition, spin lifetimes are rather short and correspondingly coherence is quickly lost. This challenge culminates in the coherent manipulation and detection of information from a single spin. Except in a few special systems, so far, single spins cannot be manipulated coherently on the atomic scale, while spin coherence times can only be measured on spin ensembles. A new concept is needed for coherence measurements on arbitrary single spins. Here, the principal investigator (PI) will combine a novel time- and spin-resolved low-temperature scanning tunneling microscope (STM) with the concept of pulsed electron paramagnetic resonance. With this unique and innovative setup, he will be able to address long-standing problems, such as relaxation and coherence times of arbitrary single spin systems on the atomic scale as well as individual spin interactions with the immediate surroundings. Spin readout will be realized through the detection of the absolute spin polarization in the tunneling current by a superconducting tip based on the Meservey-Tedrow-Fulde effect, which the PI has recently demonstrated for the first time in STM. For the coherent excitation, a specially designed pulsed GHz light source will be implemented. The goal is to better understand the spin dynamics and coherence times of single spin systems as well as the spin interactions involved in the decay mechanisms. This will have direct impact on the feasibility of quantum spin information processing with single spin systems on different decoupling surfaces and their scalability at the atomic level. A successful demonstration will enhance the detection limit of spins by several orders of magnitude and fill important missing links in the understanding of spin dynamics and quantum computing with single spins.

2 469 136 €

Start date: 2016-07-01, End date: 2021-06-30

Supra-molecular protein machineries control diverse cellular processes. Knowing their structural organization is crucial for understanding their function. As classical structural biology techniques are limited in studying such assemblies in their natural cellular environment, there is a critical methodological gap inhibiting a direct link between structure and function. Consequently, the structural intermediates underlying a full activity cycle of a large multi-protein complex have been impossible to visualize. Recent advances in fluorescence microscopy, in particular the development of groundbreaking superresolution microscopy (SRM) methods, can now help bridge this gap. With this interdisciplinary proposal, my group will develop unique and innovative optical, biological and computational imaging technologies to determine the structural organization of multi-protein assemblies in their functional cellular context. We will reach this goal by developing a method to robustly measure the precise 3D arrangements of proteins in supra-molecular assemblies in situ with nanometer isotropic resolution based on supercritical-angle detection and by measuring their absolute stoichiometries with engineered counting standards. We will also develop new data analysis tools to statistically analyze such data, taking into account the functional cellular context measured with correlative superresolution and electron microscopy, multi-color SRM and molecular biology tools. We will apply these new methods to address key questions on endocytosis, a fundamental membrane trafficking process. Our aim is to determine a time-resolved 3D superresolution localization map of the yeast endocytic proteins during the major functional transitions and to integrate these data into a mechanistic model of endocytosis. Importantly, the methods we develop here can be applied to many other large protein-based machines, and thus have the potential to have high impact in other key areas of cell biology.

1 686 469 €

Start date: 2017-06-01, End date: 2022-05-31

Our goal is to advance the field of DNA nanotechnology by achieving directed transport on the nanoscale using robustly functioning synthetic motor units. To do so, we propose to construct spatially periodic, diffusive mechanisms that have broken inversion symmetry and to subject these mechanisms to conditions away from thermal equilibrium. We will build on recent progress in creating complex DNA-based structures and construct various nanoscale rotary and translational Brownian ratchet mechanisms that have well- defined degrees of freedom for motion within periodic and asymmetric energy landscapes. The mechanisms will be self-assembled from DNA origami components. We will use cryo-Transmission Electron Microscopy (TEM) to evaluate and iteratively refine our structures. Conventional video-rate fluorescence microscopy, in addition to super-resolution microscopy, will be employed to study in solution and in real time the diffusive motion of the mechanisms on the single particle level. We will introduce various deterministic or stochastic thermal, mechanical, or chemical perturbations to drive the systems away from thermal equilibrium. We will use laser heating and cooling to experimentally test thermal and flashing ratcheting mechanisms; we will employ dissipative asymmetric fluxes arising in active matter as realized in high-density ATP-hydrolysing motility assays; and we will couple out-of-equilibrium chemical reactions to the motion of our mechanisms. The ultimate goal of our work is to take insights from these experiments and create robustly functioning nanoscale motor units that can drive directed motion against external load and perform at levels comparable to those of natural macromolecular motor proteins. Achieving this goal will create unprecedented technological opportunities, for example, to drive chemical synthesis, actively propel nanoscale drug- delivery vehicles, pump and separate molecules across barriers or package molecules into cargo components.

2 000 000 €

Start date: 2017-05-01, End date: 2022-04-30

Nano-spin-orbitronics is an emerging and fast growing field that aims at combining three degrees of freedom − spin, charge and spin-orbit interaction − to explore new nanotechnologies stemming from fundamental physics. New magnetic phases of matter are investigated using, in particular, atomic design to tailor beneficial physical properties down to the atomic level. Storage, transport and manipulation of magnetic information within a small set of atoms does not only require a fundamental understanding of their ground-state properties from the perspective of quantum mechanics, but crucially also their dynamical excited states. We propose to go beyond the state of the art by investigating from first-principles the dynamical properties of chiral spin textures in nanostructures from 2-dimensions to 0-dimension with these nanostructures being deposited on different substrates where spin-orbit interaction plays a major role. Understanding their response to external dynamical fields (electric/magnetic) or currents will impact on the burgeoning field of nano-spin-orbitronics. Indeed, to achieve efficient manipulation of nano-sized functional spin textures, it is imperative to exploit and understand their resonant motion, analogous to the role of ferromagnetic resonance in spintronics. A magnetic skyrmion is an example of a spin-swirling texture characterized by a topological number that will be explored. This spin state has huge potential in nanotechnologies thanks to the low spin currents needed to manipulate it. Based on time-dependent density functional theory and many-body perturbation theory, our innovative scheme will deliver a paradigm shift with respect to existing theoretical methodologies and will provide a fundamental understanding of: (i) the occurrence of chiral spin textures in reduced dimensions, (ii) their dynamical spin-excitation spectra and the coupling of the different excitation degrees of freedom and (iii) their impact on the electronic structure.

1 994 879 €

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