ERC FUNDED PROJECTS

Today, much interest in several fields of physics is devoted to the study of small, open quantum systems, whose properties are profoundly affected by the environment; i.e., the continuum of decay channels. In nuclear physics, these problems were originally studied in the context of nuclear reactions but their importance has been reestablished with the advent of radioactive-beam physics and the resulting interest in exotic nuclei. In particular, strong theory initiatives in this area of research will be instrumental for the success of the experimental program at the Facility for Antiproton and Ion Research (FAIR) in Germany. In addition, many of the aspects of open quantum systems are also being explored in the rapidly evolving research on ultracold atomic gases, quantum dots, and other nanodevices. A first-principles description of open quantum systems presents a substantial theoretical and computational challenge. However, the current availability of enormous computing power has allowed theorists to make spectacular progress on problems that were previously thought intractable. The importance of computational methods to study quantum many-body systems is stressed in this proposal. Our approach is based on the ab initio no-core shell model (NCSM), which is a well-established theoretical framework aimed originally at an exact description of nuclear structure starting from realistic inter-nucleon forces. A successful completion of this project requires extensions of the NCSM mathematical framework and the development of highly advanced computer codes. The '++' in the project title indicates the interdisciplinary aspects of the present research proposal and the ambition to make a significant impact on connected fields of many-body physics.

1 304 800 €

Start date: 2009-12-01, End date: 2014-11-30

We propose to investigate hybrid quantum systems composed of ultracold atoms and ions. The mutual interaction of the cold neutral atoms and the trapped ion offers a wealth of interesting new physical problems. They span from ultracold quantum chemistry over new concepts for quantum information processing to genuine quantum many-body physics. We plan to explore aspects of quantum chemistry with ultracold atoms and ions to obtain a full understanding of the interactions in this hybrid system. We will investigate the regime of low energy collisions and search for Feshbach resonances to tune the interaction strength between atoms and ions. Moreover, we will study collective effects in chemical reactions between a Bose-Einstein condensate and a single ion. Taking advantage of the extraordinary properties of the atom-ion mixture quantum information processing with hybrid systems will be performed. In particular, we plan to realize sympathetic ground state cooling of the ion with a Bose-Einstein condensate. When the ion is immersed into the ultracold neutral atom environment the nature of the decoherence will be tailored by tuning properties of the environment: A dissipative quantum phase transition is predicted when the ion is coupled to a one-dimensional Bose gas. Moreover, we plan to realize a scalable hybrid quantum processor composed of a single ion and an array of neutral atoms in an optical lattice. The third direction we will pursue is related to impurity effects in quantum many-body physics. We plan to study transport through a single impurity or atomic quantum dot with the goal of realizing a single atom transistor. A single atom transistor transfers the quantum state of the impurity coherently to a macroscopic neutral atom current. Finally, we plan to observe Anderson s orthogonality catastrophe in which the presence of a single impurity in a quantum gas orthogonalizes the quantum many-body function of a quantum state with respect to the unperturbed one.

1 405 000 €

Start date: 2009-10-01, End date: 2014-09-30

We envisage a new generation of dynamic holographic laser tweezers and stretching tools with unprecedented spatial control of gradient and scattering light forces, to unravel functional mysteries of cell biology and genetics: Based on our recently developed, highly successful and widely recognized amplitude and phase shaping techniques with cascaded spatial light modulators (SLM), we will create new holographic optical manipulators consisting of a line-shaped trap with balanced net scattering forces and controllable local phase-gradients. Combining these line stretchers with spiral phase contrast imaging or nonlinear optical microscopy will allow quantitative study of functional shape changes. The novel tool is hugely more versatile than standard optical tweezers, since direction and magnitude of the scattering force can be designed to precisely follow the structure. In combination with conventional multi-spot traps the line stretcher acts as a sensitive and adaptable local force sensor. In collaboration with local experts we want to tackle hot topics in Genetics, e.g. search for force profile signatures in regions with Copy Number Variations. Possibly the approach may shed light on basic physical characteristics such as, for example, chromosomal fragility in Fra(X) syndrome, the most common monogenic cause of mental retardation. The new design intrinsically offers enhanced microscopic resolution, as SLM-synthesized apertures and waveforms can enlarge the number of spatial frequencies forming the image. Ultimately, nonlinear holography can be implemented, sending phase shaped wavefronts to target samples. This can, e.g., be used to push the sensitivity of nonlinear chemical imaging, or for controlled photo-activation of targeted regions in neurons.

1 987 428 €

Start date: 2010-05-01, End date: 2015-04-30

The transition from quantum to classical is an essential issue in physics. At a practical level, quantum information thrives to build large quantum systems for tasks in communication or computing beyond the reach of classical devices. At the fundamental level, the question is whether there exists, in addition to environment-induced decoherence, another mechanism responsible for the disappearance of state superpositions at the macroscopic scale. Harmonic oscillators coupled to qubits are ideal to probe the limits of the quantum domain. Among various versions of this system, microwave Cavity Quantum Electrodynamics coupling Rydberg atoms to superconducting cavities has developed tools of un-matched sensitivity and precision. Building on these advances and on the development of deterministic atomic sources, DECLIC proposes to explore the dynamics of fields trapped in cavities and to study their decoherence under various perspectives. It will implement novel ways to generate non-classical states with large photon numbers stored in one cavity or non-locally split between two. DECLIC will record the gradual evolution of these states towards classicality and locality. Along this way, it will explore promising processes such as quantum random walks and collective photonic effects leading to non-classical interferometry breaking the standard quantum limit. Beyond witnessing decoherence, DECLIC will investigate ways to manipulate and control it, either by implementing feedback procedures steering the field towards targeted states, or by engineering artificial environments protecting against decoherence specific states of light. These experiments will provide invaluable clues for the understanding of other oscillator-qubit systems exploring the quantum to classical boundary.

2 500 000 €

Start date: 2010-02-01, End date: 2016-01-31