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Dispersionskräfte jenseits des Quantenvakuums: von Quantenpräzision zu Quantenkontrolle in der Nanotechnologie

Fachliche Zuordnung Optik, Quantenoptik und Physik der Atome, Moleküle und Plasmen
Förderung Förderung von 2013 bis 2021
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 239028562
 
Erstellungsjahr 2022

Zusammenfassung der Projektergebnisse

The project has increased our current understanding of dispersion forces with respect to I. the underlying microscopic processes and the impact of II. complex geometries and novel materials; III. continuous media; IV. non-trivial atomic, matter and field states; and V. quantum effects induced by motion. Dispersion forces between large bodies are ultimately due to interactions between their constituent atoms. Studying these in detail, we have found a surprising answer to the fundamental question whether the force between an excited and a ground state atom is oscillating or monotonous as a function of interatomic separation: it depends on the perspective. While the force on the groundstate atom is monotonous, that on the excited atom oscillates. The latter can be understood as a recoil force due to spontaneous emission. Similar photon recoil can lead to a lateral force on an atom near a surface. Recoil forces can be tailored and exploited in photonics. Photon exchange between atoms can be modified by surfaces, affecting interatomic Coulombic decay. In order to combine microscopic and macroscopic theories of dispersion forces, we have studied the optical properties of a polymer film by means of quantum chemistry and have then used the result to determine the Casimir–Lifshitz force between the film and a solid substrate. We have found that chemically inert and flexible polymers can lead to very strong adhesion forces, facilitating their potential use as a glue in nanofabrication. We have shown that the Casimir–Polder interaction of an atom with bodies of various shapes such as gratings, spheres and disks can give rise to complex potential landscapes. These in turn have an impact on matter-wave scattering by imprinting a position-dependent phase on the matter wave. For instance, the quantum signature of coherent matter-wave scattering at compact objects, the bright Poisson spot in the classical shadow region, is significantly enhanced due to the Casimir– Polder phase. Dispersion interactions can be used as probes of unusual atomic and surface properties according to the Curie dissymmetry principle, which can be paraphrased as “it takes a thief to catch a thief”. For instance, the impact of nonreciprocal media such as topological insulators can be detected with a circularly polarised atom which is also sensitive to the arrow of time; charge–parity violation in atoms can be probed using a similarly charge–parity asymmetric surface; and chiral metamaterials lead to force which are sensitive to the handedness of a chiral molecule. The latter allows for enantiomer separation schemes. In colloidal and biological systems, the dispersion force is modified by an intervening solvent medium, such as water. Its effect had been studied by two competing approaches via the Maxwell stress which has a unique microscopic basis in terms of the Lorentz force and the alternative Minkowski stress, with conflicting results. By comparing these with the microscopic forces between the colloidal particles and the solvent molecules, we have found to our surprise that only the Minkowski stress tensor leads to consistent results, in agreement with experimental data. The resulting force has been shown to have implications for carbon storage, ice condensation and gashydrate distribution on planetary oceans. We have studied the impact of quantum states of matter on the Casimir force between topological insulators. We have found that maximally attractive or repulsive forces can be achieved if the electromagnetic nature of the interacting substrates is most similar or opposite, respectively. By manipulating the substrates via external magnetic fields, one can tune the Casimir force in situ and induce a distinct Casimir torque. Quantum friction predicted for an atom moving with respect to a smooth surface is possibly the most hotly debated subject of the project. We have found that the predicted force significantly changes as a function of time, linking previous contradicting results. We propose to finally settle the controversy by measuring this elusive effect spectroscopically via vacuum Doppler shifts. We predict that in contrast to the paradigmatically studied parallel motion, the effect is significantly enhanced for atoms moving normal to the surface.

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