During the first 18 months of the ERC Synergy Grant, the project has established a robust foundation for planned research activities. The initial period focused primarily on technological achievements forming the basis for main research goals. Central activities included fabrication and testing of novel nanofibers suitable for integration with ultracold atom ensembles. Through close collaboration between UBER (Berlin) and UBO (Bonn), nanofibers with ~50% transmission at near-UV wavelengths for ~100-nm-diameter fibers were produced. Notably, the project achieved, to our knowledge for the first time, fabrication of nanofibers from photonic crystal fibers. These fibers were transferred to UBO for characterization of photodarkening susceptibility using a dedicated vacuum test setup constructed under Berlin's guidance.
The TU WIEN theoretical team developed approaches for describing both experimental setups. Simulation methods were implemented to study coupling between fiber-guided photons and superatom ensembles under realistic conditions, including various broadening effects and trapping geometries. A detailed numerical model describing the Berlin experiment accounted for lattice defects and quantum mechanical motion. The Bonn and Vienna teams implemented a thorough simulation of the proposed fiber-atom interface, providing essential input for finalizing experiment design and benchmarking results.
The experimental apparatus for producing ultracold Ytterbium atoms was constructed, with Rydberg excitation successfully demonstrated (without nanofiber integration). Optimization of this setup was published in a peer-reviewed article. At UBER, a novel magic-wavelength nanofiber-based two-color dipole trap was demonstrated, enabling trapping with deep sub-λ/2 spacing—a significant technological advancement creating prerequisites for selective radiance implementation.
The Vienna team achieved notable theoretical results. Effects of strong direct interactions between quantum emitters on cooperative radiance in regular arrays were studied, with findings published in Physical Review Letters. These calculations demonstrated that interactions can induce superradiance under conditions typically showing weak cooperative decay. Additionally, open many-body dynamics of laser-driven Rydberg atoms were investigated, revealing novel quantum time crystal phases in regular atom arrays, published in Nature Physics and on arXiv.
The project established a structured collaboration framework between UBER, UBO, and TU WIEN, with UBER leading nanofiber fabrication, UBO conducting characterization and experimental implementation, and TU WIEN providing theoretical support. Personnel mobility facilitated knowledge transfer, with UBO members trained in Berlin for handling fragile nanofibers. Regular virtual and occasional in-person interactions ensured close coordination. The consortium held two meetings to discuss progress and research directions. This collaborative approach enabled significant cross-fertilization between atomic physics, quantum optics, and fiber optics, leading to transformative outcomes not achievable through individual efforts.
