Rydberg atoms are atoms in which the valence electron is excited to loosely bound state, which makes their properties highly sensitive to external electric fields, but also the presence of other Rydberg atoms nearby. This results in strong interactions between them, for example a blockade effect that prevents the excitation of more than one Rydberg atom over several micrometers. Thanks to their strong interaction, Rydberg atoms have found many applications, for example in quantum simulation and information processing.
Rydberg atoms also find applications in nonlinear quantum optics, that is to make individual photons, which would normally pass each other unnoticed, effectively interact with each other. To this end, photons are mapped into Rydberg polaritons, quasi-particles that carry the strong interactions of Rydberg atoms, as they travel through a gas of ultracold atoms. Alternatively, one can also use Rydberg superatoms, to effectively mediate interactions between photons. Rydberg superatoms are based on ensembles of many atoms that are saturated following the absorption of a single photon due to the blockade mechanism. They act like a single quantum emitter, but photons couple much more strongly to them compared to a single atom.
The objective of InterPol has been to study Rydberg polaritons and Rydberg superatoms in systems of increasing size in terms of both fundamental and application aspects and analyse the performance of such systems for future applications in optical quantum technology. For example, we show that a chain of Rydberg superatoms can remove photons from a light pulse one by one, but also identified effects that need to be mitigated to successfully scale systems to larger numbers of superatoms and polaritons.
