Studying strongly correlated systems EU-funded scientists used laser fields to generate quantum matter with novel, crystal-like properties. Industrial Technologies © Thinkstock Ultracold atomic gases are ideally suited for exploring the quantum physics of many-body systems and for investigating matter and exotic quantum phenomena. The EU-funded project 'Strongly correlated ultracold Rydberg gases' (CORYGAS) made use of the extraordinary properties of highly excited Rydberg atoms in dense atomic gases to explore the realm of strongly correlated many-body physics. To create Rydberg atoms, scientists used lasers to illuminate a dense ensemble of cold gas atoms. These ground-state atoms were excited in the Rydberg state and strongly interacted with each other, leading to spatial correlations. Scientists observed polaritons propagating through the excited ultracold atomic gas coupled via an electromagnetically induced transparency resonance. Strong long-range interactions between Rydberg excitations gave rise to polariton blockade, resulting in large optical nonlinearities, and modified polariton number statistics. By combining optical imaging and high-fidelity detection of the Rydberg polaritons, the team investigated this coupled atom-light system. The employed techniques greatly facilitated observation of energy transport. Full counting statistics provided valuable information on Rydberg interacting many-body systems. In particular, novel insight was obtained about the formation mechanism of correlations in such systems. Correlated systems comprising of few excitations (aggregates) were formed through sequential growth. These excitations interacted with each other to compensate for laser detuning. Furthermore, scientists observed a sudden and spontaneous evolution of an initially correlated gas of repulsively interacting Rydberg atoms to an ultracold plasma. Rydberg-Rydberg interactions were found to strongly affect the dynamics of plasma formation. CORYGAS showed that Rydberg interactions in ultracold gases are helping to study new strongly correlated many-body phases of matter and are shedding new light on self-ordering mechanisms. Ultimately, they are offering a fertile ground for investigating entangled states of atoms that should find many applications in quantum information systems. Keywords Correlated system, laser, ultracold atomic gas, many-body system, Rydberg atom, detuning, plasma
