Abstract

Atoms in states of high principal quantum number, Rydberg atoms, are much studied due to their extremely large interaction energies. These interactions lead to phenomena such as a collective suppression of excitation, the “dipole blockade”, which in turn leads to highly entangled many-body states. Rydberg gases also spontaneously evolve into ultra-cold neutral plasmas, which are highly correlated many-body classical systems.

All previous cold Rydberg gas experiments use atoms with one valence electron. By using strontium, a divalent atom, we open up a whole new field of study. The second valence electron enables us to probe and control the Rydberg atoms in a previously impossible way. This includes, in our latest work, an elucidation of population transfer in a Rydberg gas at the cold-plasma formation threshold through excitation of both valence electrons.