Title: Controlling interactions in cold atomic ensembles with light
Quantum simulations based on laser-cooled atomic gases have started to fulfill Feynman's vision of using well controlled quantum systems to obtain insight into problems which are hard to tackle on classical computers. Key to the success of ultracold atoms is the continuous development of novel methods to prepare, control and detect such systems. In this talk, I will focus on how long-range interactions can be added to the toolbox available in ultracold atomic quantum simulators.
Starting from an array of Rubidium-87 atoms trapped in an optical lattice, we realize long-range interacting spin models by laser coupling the atomic ground state to a Rydberg state. Combining single-atom sensitive local detection with interferometric techniques, we verified the presence of interactions and demonstrated their controllability. Tracking the collapse and revival dynamics of a coherent spin state, we could furthermore show that the coherence time of off-resonantly admixed interactions can be pushed towards the tunneling timescale in optical lattices, paving the way to engineering extended-range interactions in systems with motional dynamics in the future.
In a further experiment, we were able to observe a novel form of bound molecular state of two atoms simultaneously excited to their Rydberg states. Remarkably, the bond length of such "Rydberg macrodimers" reaches up to the micrometer scale and is hence accessible in a quantum gas microscope. The high spectral resolution of our measurement combined with microscopic readout enabled a precise characterization of the binding potential as well as the photoassociation pathway.
Finally, I will present our ongoing experimental efforts of using a high-finesse optical resonator to control the atom number in an ensemble. The real-time signal output of the cavity can be used for active feedback on an optical evaporation stage, allowing for the production of atomic ensembles with sub-Poissonian shot-to-shot atom number variation.