Cooperativity in Highly Excited Rydberg
Ensembles — Control and Entanglement
Research areas:
Research overview
Rydberg atoms are atoms with one or more electrons excited to very high lying quantum states. As a result of this excitation, Rydberg atoms aquire very exaggerated properties: for example, they can be extremely sensitive to external fields and they can interact with each other very strongly, even over macroscopic distances. In laser cooled atomic gases this gives rise to a rich spectrum of new many-body physics. In the ultracold regime, the interactions typically dominate over kinetic motion ("frozen" Rydberg gases) which results in an interaction-induced excitation blockade. Ultimately this could provide the basis for new single photon sources or as a platform for quantum information processing with neutral atoms. Experimental progress in producing ultra-cold Rydberg gases at high densities has already enabled studies of regimes where strong correlations between atoms dominate their behavior. This is accompanied by a number of theoretical efforts, aiming to develop a deeper understanding of physics in these strongly correlated regimes.

Research highlights
Highlights of the latest reseach into ultracold Rydberg atoms by COHERENCE network partners can be viewed on the following pages:
Scientific areas:
The scientific objectives of the COHERENCE network cover six interconnected Scientific Areas (SAs), as depicted schematically in the following diagram.

SA I — Many body phenomena and coherence. Situated at the interface between atomic-molecular-and-optical physics, condensed matter, and statistical physics, we aim to exploit the strong interactions between Rydberg atoms to create novel strongly correlated quantum systems. The formation of strongly-interacting Rydberg gases are being studied both experimentally and theoretically, for both homogeneous and periodic (optical lattice) environments.

SA II — Energy transport and charge transfer. The transfer of excitation or charge between sites in linear chains, e.g. the Förster process, is of fundamental significance in condensed matter, polymer physics and biological systems. We are investigating charge and energy transfer in cold Rydberg systems, which serves as an ideal model system for studying these processes. Ultracold Rydberg gases permit excellent control over the relevant time scales combined with a high spatial resolution needed to observe the dynamics. Resonant energy transfer in a structured mesoscopic Rydberg clouds can be used to realise a model for random walks and excitonic dynamics. In addition, energy diffusion between single Rydberg atoms are being explored.

SA III — Few-body phenomena and exotic molecules. The long range-interactions between Rydberg atoms can be exploted to form exotic Rydberg molecules. The goal is to explore more complex Rydberg structures involving many atoms and coherent control schemes to steer molecular dynamics. Such molecules will provide a test for theories of short-range but also long-range interactions that are of key importance in molecular physics.

SA IV — Quantum information and entanglement. The strong interactions of Rydberg atoms can be used to generate entangled states between many atoms and between photons for the realization of fast quantum gates and single photon non-linear optics. The unique properties of Rydberg atoms allow to simultaneously satisfy all the criteria for quantum computation such as quantum entanglement and single qubit addressability. We are exploring the implementation of quantum-information processing protocols with Rydberg atoms, both involving single atoms and mesoscopic ensembles. This SA draws on the topics explored in SA II-III (inter-particle interactions), SA V (Rydberg atom-surface interactions), and SA VI (sophisticated excitation schemes).

SA V — Rydberg interfaces and mechanical control. By controlling the response of Rydberg atoms to their environment it will be possible to develop sensitive new probes based on the special properties of Rydberg atoms. In particular, Rydberg atoms are ultra-sensitive to electric fields and may be used as local detectors for tiny field variations. In addition, the spectral absorption of Rydberg atoms is centred in the near-IR range, which makes them ideal detectors for thermal radiation. Our understanding Rydberg atom-surface interactions will be central to future applications of cold Rydberg gases in electrometry, quantum information, or surface probes on "atom chips". For this it will also be important to control both motional and internal degrees of freedom atom Rydberg atoms, for example, by using magnetic fields for atom trapping.

SA VI — Rydberg photonics and laser technology. In this intersectorial SA, the industrial partners TOPTICA and Photonics Technologies will work together with the academic teams to develop the next generation laser sources for efficient excitation and manipulation of Rydberg systems. Technological developements will include using new crystal materials, more robust oscillators and better controlled electronics. This may be combined with research on frequency comb generation based on mode-locked fibre lasers and optical phase locking of diode lasers. In parallel, the experimental groups are working on developing novel schemes for coherent manipulation of Rydberg states.