Signatures of strong interactions in Rydberg systems María M. Valado, Cristiano Simonelli, Stefano Scotto and Nicola Malossi Eur. Phys. J. Special Topics, 225 15-16 (2016) 3037-3060 Published online: 19 December 2016 DOI: 10.1140/epjst/e2016-60171-2